Analysis on the problems often encountered in screen printing and their solutions
The result of the cross influence of various reasons. This is what the operator should pay special attention to when judging the cause of failure and taking corresponding countermeasures.
Section 1 Requirements of Screen Printing for Screen Printing Screen printing plate making and printing process have the following basic requirements for the performance of screen:
1. high tension resistance. Tensile strength refers to the ability of resisting damage (fracture) when the screen is under tension. In addition, the strength change of the silk screen after moisture absorption Should be small.
2. The elongation at break is small. Elongation refers to the ratio of elongation to original length of silk screen when it breaks under a certain tension, expressed as a percentage. Great elongation, The plane stability is poor, but the silk screen also needs to have enough elasticity under a certain tension (about 3%).
3. Good resilience. Resilience refers to the length recovery ability of silk screen when it is stretched for a certain length (such as after 3% elongation) and external force is released, which is called elongation back Redundancy, the greater the value, the better. After springback, the edge after printing is clear.
4. Good stability against temperature and humidity changes.
5. The ink has good passing performance.
6. Good resistance to chemicals.
7. See the engineering bill for specific items.
In the second quarter, net frame and tension net I. Selection of materials for net frame LY12, LF2 and other cemented carbide aluminum square tube profiles are generally selected, with dimensions of 20mm wide and 20mm thick, and the four corners are processed by argon arc welding or riveting. The metal frame has high precision and stable size.
II. Selection of screen materials At present, nylon mesh and polyester mesh are widely used. Nylon screen has poor heat resistance, and it is easy to produce thermoplastic deformation after being heated, which makes the tension uneven and affects the screen printing quality. Bonding mesh or screen template should not be baked at high temperature. Polyester mesh has good heat resistance, stable size, and the pattern does not change greatly due to the change of temperature and humidity. In order to ensure the accuracy of screen printing, it is best to choose monofilament polyester screen. At the same time, the screen with high mesh number, fine wire diameter and small mesh should be selected, and the color of the screen should be yellow or brownish yellow, so as to prevent vignetting.
III. Stretching the net It is best to use pneumatic net stretching machine, and the quality requirements of net stretching are as follows:
1. the tension of tension net is appropriate and uniform (1) when using pneumatic tension net, it must stand for 3-6 hours before stretching the net glue; (2) The stretched net should be placed for at least 24 hours, especially for large goods or machine printed nets, so as to ensure equal stress at each point and prevent deformation. Network The higher the mesh, the longer the screen should be placed, generally 2-3 days is appropriate. After placement, the tension of the screen plate is stable, and the stress of the famous points is equal to ensure the screen The version is not deformed and is not easy to be damaged.
2. Keep the warp and weft yarns vertical 3. Prevent relaxation IV. Screen stencil making process At present, the most widely used method is to make silk screen template. In this manufacturing process, attention should be paid to the proper thickness of sizing coating, and strict control of drying, exposure and development, so as to obtain high-quality silk screen template.
Section 3 Requirements of Screen Printing for Photosensitive Materials 1. Requirements of photosensitive materials for screen plate making: good plate making performance, easy coating, proper photosensitive spectrum range, generally 340~440μm, Sensitive wavelength, plate making operation and plate storage need strict darkroom conditions; If the wavelength is too short, the choice of light source and the protection of personnel will become more difficult Difficult; High sensitivity, can achieve the purpose of energy saving and rapid plate making; Good developing performance, high resolution, good stability, easy storage and less sensation Waste.
2. Requirements of screen printing for photosensitive materials: The film formed by photosensitive materials should meet the performance requirements of different types of inks and have considerable printing resistance Force, can bear a considerable number of scraping ink pressure; Good binding ability with silk screen, no film release failure during printing; Easy to peel, not easy to produce ghosts Shadow, conducive to the recycling of screen printing plate.
For non-drying ink, it is required that the photosensitive film reach a certain thickness of 10~40μm on the printing surface, which is about the thickness of 1~2 copies of 80g paper.
The fourth section printing light source and equipment 1. Selection of light source for printing.
Printing is an extremely important process in the process of screen making by photosensitive method. It is of great significance to improve the quality of screen printing plate, effectively save energy, simplify operation, maintain the health of operators and reduce costs if the light source of printing plate is selected and used correctly. Because of the different kinds of photosensitive materials, it is necessary to choose and use light sources that meet the needs of various photosensitive materials.
At present, the color sensitivity of all kinds of screen photosensitive materials used by us is mostly distributed between 250 and 510 μ m. Therefore, in theory, any light source with the peak wavelength of 250~510μm on the energy distribution curve of the emission spectrum can be used for screen printing. In addition, when printing the plate, we should fully study the size of the plate, the output power of the light source, the distance between the plate and the light source, and pay special attention to the function of the light reflector.
2. Matters needing attention when choosing light source 1. The emission spectrum of the light source should match the absorption characteristics and color sensitivity of the photosensitive material. The energy of light varies with the frequency of wavelength. The shorter the wavelength, the higher the frequency and the greater the photon energy. When light is absorbed by matter in the process of radiation, photons have certain energy, which will cause physical and chemical changes in matter. The chemical reaction caused by light energy is called photochemical reaction. Photochemical matching means that the spectral output distribution of the selected light source should be matched with the spectral sensitivity of the photosensitive material. That is to say, the wavelength range in which the photosensitive material absorbs light and undergoes photochemical reaction is just the output range of the light source emission spectrum, and the maximum absorption peak of the photosensitive material is just at the output peak of the light source. In this way, the light energy of the light source is absorbed by the photosensitive material to the maximum extent and photochemical reaction occurs.
2. High luminous efficiency and high intensity. With other conditions unchanged, the greater the power and luminous efficiency of the light source, the greater its luminous intensity or brightness, and the higher the illumination of the exposed surface, the shorter the time required for the photosensitive material to obtain the same exposure.
3. Light source has little heat radiation. On the premise of ensuring that the light source has enough luminous intensity or bright light, the thermal radiation of the light source should be as small as possible. When using a high-power and strong light source, measures such as forced cooling (air cooling and water cooling) must be taken for the lamp tube, and other measures should be taken to control the exposure temperature of the photosensitive material below 32℃.
4. Uniform luminous intensity. The luminous intensity of the illumination surface of the light source should be as uniform as possible. The exposure device shall be designed to ensure that the illumination difference of each point on the exposure surface of the photosensitive material does not exceed 15%. Light source has strong adaptability to environment. The light source should have strong environmental adaptability, and can work normally under various temperature, airflow and voltage changes. Of course, in actual production, it is unrealistic to choose a light source that can fully meet the above requirements. The purpose of the above-mentioned selection principle is only to hope that the plate-making operators should consider the influence of the light source on the exposure quality of photosensitive materials when choosing to use the plate-making light source.
3. Printing equipment. Printing machine is the main printing equipment, which is the exposure equipment of photosensitive materials. Compared with simple printing device, it has great advantages. If simple printing equipment is used instead of vacuum printing machine, the precision of pattern restoration will be affected to a certain extent.
Section 5 Selection of Photosensitive Materials The requirement of screen printing for screen printing is its reproducibility of images. An important factor that determines reproducibility is to choose a good photosensitive material. Reproducibility of screen printing plate refers to the ability of screen printing plate to reproduce original image. It is manifested in the accuracy, clarity and resolution of the screen printing plate.
1. Accuracy of screen printing plate.
The accuracy of screen printing plate refers to the position and size accuracy of images, characters, symbols, etc. It is related to the materials and methods of plate making, such as manual sealing and cutting, and the accuracy of plate making is often lower than that of photosensitive plate making; The precision of indirect plate making is higher than that of direct plate making.
Second, the clarity of the screen printing plate.
In photography, sharpness refers to the degree of change of image edge density on soft plate, and in screen printing plate, it refers to the uniformity of image edge in both horizontal and vertical directions. It includes three elements: shoulder sharpness, bridging and flatness.
1. Shoulder sharpness. It refers to the square degree of the shoulder of the film image. Square shoulder (90 degrees) has good three-dimensional imprint; Shoulder collapse, uneven ink thickness at the edge of the print and enlarged print.
2. Bridging. It refers to the performance of keeping the shape of the original image when the edge of the film image crosses the screen. The bridging property is good, and the image edge reproducibility is good. The image edge crossing the net will be deformed. The degree of deformation is related to the film material, the manufacturing method and the positional relationship between the image edge and the mesh, and its imprint is zigzag.
3. Flatness. Refers to the flatness of the printing surface of the plate film (the surface in contact with the substrate). Flatness determines the degree of close contact between printing film and printing surface. The flatness is good, the two sides are closely connected when printing, the ink flow will not cross the border, and the imprint is smooth; When the flatness is poor, the surface of the printing film fluctuates with the silk and holes of the screen, and the ink flow will flow into the unsealed part, resulting in sawtooth on the edge of the print, and a sawtooth appears every two meshes, and the beginning and size of the teeth are close to the unsealed range. The roughness meter can be used to measure the fluctuation difference of the film surface. If the difference is large, the flatness is poor; The difference is between 3~7μm, and the prints with good clarity can be obtained on various printing surfaces.
4. Thickness of printing mask. The film thickness on the printing surface of the screen printing plate affects the thickness and clarity of the ink layer of the imprint, especially the fine image, and even changes the halftone value and color of the dot. When the product requires thick ink layer and thick lines, the film should be thicker accordingly. Therefore, the role of the film should meet the thickness requirements.
5. Printing resistance of screen printing plate. Printing resistance refers to the ability of a printing plate to withstand the number of printing times. There are many factors that affect the printing resistance. From the point of view of plate making, it mainly depends on the mechanical and chemical strength of the printing plate itself and the fastness of its combination with silk screen. The printing resistance of printing plates should be adapted to the screen printing task, some of which can only bear dozens of copies, and some of which exceed 100,000 copies.
6. The release property of screen printing plate. The release property refers to the difficulty of removing the printing plate film from the silk screen of the printing plate. The standard of plate-making quality is not that the higher the better, but that the more economical the better, on the premise of meeting the task needs.
In order to meet the above requirements and produce a more qualified printing plate, it is necessary to select sensitive materials with good quality and print fine photo effects. As far as KFG ink is concerned, the sensitive paste we require is oily and thick film sensitive paste (preferably imported).
Section 6 photosensitive plate making method When the equipment and other conditions required for plate making are available, we will make plate making. Photosensitive plate-making methods are divided into three types: direct method, indirect method and direct method. In essence, the technical indexes of the above three plate-making methods are the same, but the process methods of coating photosensitive adhesive or film are different. Here we are talking about direct method.
Coat the master several times Clean the screen, dry, coat the photoresist, dry, print, expose, develop, dry and revise.
Prepare photosensitive adhesive and rinse with pressurized water II. Specific methods:
1. Pre-processing. In order to prevent shrinkage, sand holes and broken images of photosensitive film caused by dirt, dust, grease, etc., it is necessary to fully wash the screen with detergent before coating photosensitive liquid. At this time, the detergent used is generally neutral or weakly alkaline washing powder for domestic use. However, the wire mesh detergent sold in the market, such as 20% caustic soda water solution, has good degreasing effect, can improve the wettability of the photosensitive liquid to the wire mesh, and can form a very uniform coating film. Therefore, the effect of using this wire mesh detergent is very good. There are various ways of cleaning from manual operation to automatic cleaning machine (spray gun is the most commonly used, and ultrasonic cleaning is also available). No matter what method, whether it is a new network or an old network, it must be degreased with cleaning solution, washed with water, dehydrated and dried. Other pretreatment, there are physical methods to rub on the surface of the screen for coarsening, in order to improve the adhesion of the screen to the photosensitive film. In addition, in order to prevent the degradation of image primary reproducibility caused by random reflection of light on the screen surface, there are screens that are also industrially dyed with dyes such as yellow, red and orange on the screen surface.
2. Coating of photosensitive liquid. There are many methods for coating photosensitive liquid on the Internet, among which scraping bucket method and rotating method are the most commonly used.
(1) Rotary coating is a method in which the plate is fixed on the coater to pass back, the photosensitive liquid is poured into the center of the plate, and the fallen liquid is uniformly coated around to form a film due to centrifugal force. Compared with coating with a scraper, a highly uniform film can be obtained. If the viscosity, rotating speed, mesh and other conditions of the photosensitive liquid are unchanged, anyone can carry out the coating with fixed quality, but it is only suitable for the coating of small plates (generally no more than 50×50).
(2) Scraper coating includes manual coating method and machine coating method. The length of glue hopper is selected according to the size of coating surface. If the sheet area =a×b(a is short side, B is long side), the glue scraping area = (A+4 cm) × (B+6 cm) is suitable. The length of the scraper is a+cm.
(3) The edge of the scraping bucket in contact with the wire mesh must ensure high flatness, and there must be no marks of bruise. If the flatness is low or bruised, streaks or uneven film thickness will appear on the coated film, resulting in burrs, uneven ink thickness and uneven color brilliance on the printed lines.
(4) Coating sequence of scraper bucket: a. Put the net frame stretched with net vertically at an inclination angle of 80~90 degrees, pour photosensitive liquid with a capacity of 6 ~ 70% into the bucket, and press the front end of the bucket onto the net. B, tilt the front end of the bucket so that the liquid surface contacts the wire mesh. C, coating is carried out while keeping the inclination angle unchanged. At this time, if the coating speed is too fast, it is easy to generate bubbles and cause pinholes. D, when the coating is 1~2cm away from the edge of the net frame, restore the inclination angle of the bucket to be close to the level, and coat until there is no excess liquid left. After all the photosensitive adhesive is coated in this way, the frame is turned upside down and then coated again, and then dried. The first drying should be sufficient. If drying with hot air, the proper temperature should be mastered. If the temperature is too high, it is possible to produce hot ash, which must be paid attention to. After drying, coat it 2~3 times according to the same essentials until it appears luster. The strength of the scraper contacting the net varies with the coating speed. If the scraper goes back and forth once, the thickness of the photosensitive film coated once is 1.2~1.6μm in a completely dry state. Therefore, the film thickness of 10μm can be obtained after 7~8 passes. Usually, the coated screen surface is the surface in contact with the substrate. In order to improve its printing resistance, it can be counted as a stroke for the scraper to go back and forth on the Internet once or twice. This kind of coating bucket can be mastered only by a little practice. If the number of strokes is fixed, the corresponding film thickness can usually be obtained. However, when the film thickness is quite strict, it must be measured by a film thickness meter. Calculation of gluing times: Generally, the method of “wet coating and drying” is adopted, that is, coating and drying are alternately carried out, and each alternation is called once. Generally, the film layer needs to be coated for 2~4 times, 2~3 times each time.
3. Drying of photosensitive film It is safest to coat and dry photosensitive film under yellow lamp. As mentioned earlier, it is most important to pay attention to the temperature when drying the photosensitive film with hot air. The sensitivity of emulsion in liquid phase is low, and the sensitivity increases with the drying of coating film, and can reach the specified sensitivity only after it is completely dried, so it should be fully dried before printing, and printing should be completed in a short time after drying. If dust falls on the membrane surface during drying, pinholes will also occur, so care must be taken not to have dust during the operation time of membrane surface drying.
4. Print The photosensitive film should be printed as soon as possible after it is completely dried, and the film surface of the negative plate should be closely attached to the photosensitive film surface for exposure.
(1) before exposure, the master should be further inspected. For the blank part of the master, the higher the transparency, the better. The higher the transparency, the greater the luminous flux. The photosensitive adhesive is cured completely. The developed image is clear and the edges are neat.
(2) Exposure should be carried out in a special screen printer. Printing machine is the main equipment for drying high-quality screen printing plates. When printing a pattern composed of fine lines or dots, a special screen printing machine with a vacuum tightening device and a selected halogen light source must be used.
(3) The most important step in exposure is to make the screen frame and the master closely attached. If the contact between the screen and the master plate is not real, the exposed drawings will inevitably become weak, and will be completely discarded in serious cases.
(4) To harden the photosensitive film, the most ideal light source is a light source that can emit wavelengths from ultraviolet to violet.
(5) Before printing, it is necessary to determine the bottom and back of the positive film, and first check whether there is dirt or dust on the positive film, the screen photosensitive film surface and the glass surface of the printing frame. Then put the positive film and the frame film into the drying frame for sealing, and check it again from the glass surface. If the positive film image is placed in the correct position of the frame, it may be electrically exposed.
(6) Exposure. The quality of plate making often depends on factors such as light source, distance between photoreceptor surface and light source and exposure time. Exposure conditions should be determined according to the type of emulsion, the thickness of coated photoresist, the type of light source, the distance from light source to film surface, exposure time, etc. To this end, we should try to get the appropriate data in advance, and carry out the actual operation according to the data. A, the distance between the light source and the photosensitive surface: it is an important condition for printing, and factors such as the intensity of the light source should be considered when determining the distance. In general, if the distance between the light source and the photoreceptor surface is very small, it will cause overexposure in the middle part of the layout and uneven exposure between the center and edge of the layout. On the contrary, if the distance between the light source and the photoreceptor surface is too large, it will result in underexposure or vignetting. If the positive figure is square or rectangular, take the diagonal as d, if it is round, take the diameter as d, and when the distance between the light source and the exposure surface is f, place the light source at least one and a half times the distance of the original diagonal or diameter. B, light source, the relationship between exposure time and distance. The distance between the light source and the photosensitive film and the exposure time should be determined according to the requirements of photosensitive materials and the requirements of the light source used by the printing press. Under normal circumstances, if the light source is placed at a distance of s, the exposure time is t, and if the distance is 2S, the exposure time should be 3T. In addition, when the distance between light source and photoreceptor surface is fixed, the exposure time will be shorter with the higher light source irradiation intensity, and the longer exposure time will be when the light source irradiation intensity is fixed, otherwise, the shorter exposure time will be. C, irradiation method of light source. The light should be parallel lines perpendicular to the photosensitive surface. Under the permitted conditions, it is advisable to keep the distance of the light source far, in order to get as much direct light as possible.
Suggested exposure time table:
Mesh Light source 30—60 70—100 120—280 200—275 305—350 1000 watt quartz lamp 6 minutes 5 minutes 4.5 minutes 4 minutes 3.5 minutes 1000 watt mercury lamp 5 minutes 4 minutes 3.5 minutes 3 minutes 2.5 minutes 5000 watt halogen lamp 75 seconds 60 seconds 45 seconds 40 seconds 35 seconds Pay special attention to:
(1) When drying high-mesh fine dots, the exposure time is reduced by 5% on the basis of the above table. After washing, do another post-exposure (without film) to ensure the printing resistance of the printing plate. The exposure time is 2~3 times of the normal exposure time.
(2) If the photosensitive paste is a thick film photosensitive paste, the exposure time should be prolonged, for example, the exposure time should be prolonged by 50% when it is 40 microns thick and 120 meshes, and so on.
(3) If you want to make high-quality printing, please use the EXPOSNRE CALCULATOR to calculate the accurate exposure time.
5. Developing. Immerse the exposed printing plate in water for one or two minutes, shake the screen plate and other insensitive parts to absorb moisture and swell, and then rinse with water to develop. Development should be done with a high-pressure spray gun, but in any case, it must be completed in a short time as far as possible by completely dissolving the insensitive part. When the pattern is fine, use a magnifying glass of 8~10 times to check whether the subtle part is completely transparent, which must be completely transparent. After development, quickly remove water with a clean large white newspaper, sponge or hair dryer for drying. Control principle, on the premise of getting wet, the shorter the time, the better. If the time is too long, the wet expansion of the film will severely affect the clarity of the image; If the time is too short and the development is not complete, it will leave the blinding, block the mesh, and cause the waste plate. Montmorillonoid is a very thin residual film of photoresist, which is easy to appear in the image details, highly transparent, difficult to distinguish from water film, and often mistaken for transparent.
6. Drying. The developed screen plate should be placed in a dust-free drying cabinet and dried with warm air. The drying temperature of the screen plate drying box can generally be controlled at about 40 degrees. When drying, the moisture on the screen surface should be blown off in advance, so as to avoid the residual glue and cloudiness caused by the moisture flowing down the screen surface during drying, which will affect the clarity of the line edge and the lack of small network points.
7. Strengthening and revising the plate film. In order to strengthen the film, improve the water resistance and solvent resistance, coating hardener can be adopted.
8. Inspection. Screen printing inspection is the last process of the whole plate-making work, and it is also an extremely important process. The minor defects exposed after development can be corrected by revision. If major defects occur, the plate must be re-made. In the quality inspection of screen printing, at least the following problems should be paid attention to: (1) Whether the exposure time is accurate. In addition to using density ladder to check the degree of film hardening, you can also look at the reproduction degree of fine parts of the bottom plate on the screen, and observe whether the lines are complete, whether the edges are clear, whether the sawtooth shape is serious, and the transparency of small dots. (2) Whether the mesh is completely transparent. Check the quality of the screen printing plate, including whether all the pictures and texts are developed, whether there are burrs, defects, broken pens and closed lines in the picture and text outlets and lines, etc. If the above conditions are found, various methods should be taken in time to make up for them, so as to ensure the printing quality. (3) Test the adaptability of various photosensitive materials. Check whether there are bubbles and sand holes in the omentum, and remedy them in time. Seal the four-sided silk screen. Check whether the printing positioning marks meet the printing requirements.
Section 7 Faults and Causes of Direct Plate Making Method 1. The loss of photosensitive film during development can’t make a plate. (1) under exposure. (2) The dose of sensitizer is insufficient or ineffective, and the sensitivity decreases.
2. The whole image produces light gray. (1) The workplace in the process of coating and drying photosensitive liquid is too bright. (2) Insufficient exposure time and insufficient development. (3) Excessive heating during coating and drying of some photosensitive liquids. (4) Exposure time is too long.
3. The subtle part of the image is not developed. (1) the exposure time is too long. (2) The positive film is upside down, and the positive film does not fit well with the photosensitive film. (3) Inadequate pretreatment of silk screen. (4) The photosensitive film is too thick, the type of photosensitive adhesive is not properly selected, or the photosensitive adhesive fails.
4. There are a lot of bubbles in the coated screen plate. (1) silk screen degreasing treatment is insufficient. (2) Clean the screen before coating the photosensitive adhesive. (3) In the coating process, the temperature difference between screen drying and photosensitive adhesive is large. (4) The storage temperature of the photoresist is too high. (5) The photoresist and coating layer are too thin. (6) Uneven coating speed.
5. There are too many pinholes in the layout. (1) Dust is the main cause. (2) The advance is caused by the foaming of the photosensitive liquid itself. (3) When using the coating scraper bucket, the coating scraper bucket moves too fast and bubbles easily to produce pinholes. (4) Adding too much sensitizer will also produce pinholes. (5) Dust is easy to fall on the coating surface, so the workplace must be kept clean, for example, the printing glass surface, the positive soft surface and the photosensitive liquid coating surface must be kept completely clean. (6) A small amount of octanol can be added to the photosensitive liquid as defoamer.
6. After the screen printing plate is developed, obvious pores appear. (1) Whether high-temperature drying has been carried out after the shadow. (2) Whether a sensitizer with a long shelf life is used. (4) Whether dust falls into the photoresist. (5) Whether the sensitizer and emulsion should be fully stirred when mixing, and whether they should be used after the bubbles disappear. (6) Master whether the exposure time is appropriate.
7. The graphic resolution is not high after printing. (1) Whether the development is sufficient or not, and whether to use clean water for pressurized flushing after development. (2) Whether the secondary screen has been cleaned before use. (3) Whether the screen is dry in horizontal position. (4) Whether to choose and use the sensitive adhesive with high resolution.
Section 8 Problems and Countermeasures Related to Precision in the Process of Plate Making First, the reasons that affect the accuracy of plate making are various and roughly summarized as the following 15 points:
1. Screen, including the type of screen used, the number of screens, the fineness of wire diameter, the size of screen opening area, the size of screen expansion ratio, the weaving method of screen and the color of screen, etc.
2. Net frame, including its material, size and strength, etc.
3. The magnitude of tension.
4. Choose the angle of tension net.
5. Bonding method of net frame and silk screen.
6. Pretreatment of silk screen.
7. Scraper material, scraper width, hardness, scraping angle, cutting edge state, net distance and scraping pressure are all very important, so polyester rubber should be used to make scraper. The hardness of the scraper is mostly in the range of Shore A60-80, the scraping angle is 20-30 degrees, and the cutting edge must always be flat and sharp. The screen distance is generally 2-4mm, and the screen plate is parallel to the table top, so it is advisable to print clear graphics by scraping pressure.
8. Photosensitive materials, including sensitivity, resolution, cohesiveness, expansion ratio, thickness, hardness, water resistance, solvent resistance, friction resistance and printing resistance.
9. The blending time of the sensitizer, and the standing time after blending.
10. Drying methods and conditions, including drying temperature, humidity and drying time.
11. In printing, the type of light source used, the length of exposure time, the distance of light source, etc.
12. The density of the negative film obtained by photographic plate making.
13. Development, including development methods: water development, warm water development, and drug development; Developing conditions: temperature, soaking time, type and use of sprinkler, etc.
14. Drying temperature and time after development.
15. Selection of secondary exposure time and revision.
Two, the representative problems and solutions in the process of plate making.
1. The image resolution is low, and the level is lost.
Causes of occurrence:
(1) During printing, the contact between the base plate and the adhesive film is not true.
(2) The bottom plate (positive picture) is of poor quality.
(3) The quality of the photoresist itself is poor and the resolution is low.
(4) Improper selection of light source.
(5) The screen mesh is too low.
(6) Improper development and washing.
(1) make them in close contact by vacuum adsorption or other means.
(2) Check the density and image quality of the base plate.
(3) Choose high quality photosensitive adhesive.
(4) Use a light source matching the spectral wavelength of the photoresist.
(5) Improve the mesh number of silk screen.
(6) Check the developing and flushing procedures and adjust the water pressure and temperature.
2. Poor definition of image edges.
Causes of occurrence:
(1) During printing, the contact between the base plate and the adhesive film is not true.
(2) Insufficient development and flushing.
(3) Light scattering during exposure.
(4) uneven coating of photosensitive adhesive film.
(5) The screen mesh number is too low for image selection.
(1) using vacuum adsorption or other means to make it close.
(2) Rinse the image from both sides until it is clean and clear.
(3) Use colored silk screen.
(4) Check the coating process and increase the screen tension.
(5) Improve the mesh number of silk screen.
3. Image thin lines and small dots disappear.
Causes of occurrence:
(1) When printing, the bottom plate and the silk screen adhesive film are not attached correctly.
(2) The density of the base plate is insufficient.
(3) The exposure time is not long.
(4) Uneven illumination by light source.
(5) Insufficient development.
(6) The residual liquid of photosensitive pulp is opened into a transparent impervious layer, which blocks the screen. Images can be seen on the screen but patterns cannot be printed, which is more common in small dots with high mesh number and the edges of lines and patterns.
(1) Improve the vacuum degree of the vacuum printing machine.
(2) The film with high density is selected to make the photographic graphic background.
(3) Reduce the exposure time or increase the distance between the light source and the exposed object.
(4) Select point light source with black box.
(5) Fully develop.
(6) Pay attention to the details when developing the printing plate, and absorb the residual liquid quickly after printing plate. If conditions permit, the mesh can be blown through by high-pressure air pump.
4. The printing plate produces bubbles.
Causes of occurrence:
(1) The photosensitive adhesive is mixed unevenly before use, or there are bubbles in the photosensitive adhesive itself.
(2) There is more dust in the plate-making environment, and dust falls on the screen film.
(3) The coating speed of the photoresist is uneven or too fast (gas remains in the photoresist).
(4) When printing, dust falls on the plate-making film.
(1) Before coating the photosensitive adhesive, fully stir the photosensitive adhesive with a glass rod or a wooden rod, or add an appropriate defoamer.
(2) Pay attention to the degree of dust in the air of plate-making environment, minimize dust and prevent dust from falling into it.
(3) When coating, the coating speed should be kept uniform, and on the other hand, the coating speed should not be too fast.
(4) The screen plate used in printing should be clean and dust-free, which is also an important aspect to avoid bubbles.
5. The sawtooth phenomenon of printed image lines.
Causes of occurrence:
(1) Improper selection of screen mesh.
(3) The film thickness is not enough.
(4) Diffraction of light during exposure.
(5) Uneven tension of tension net.
(6) Excessive water pressure and long time during development.
(1) according to the graphics to replace the appropriate screen.
(2) Carry out exposure test and increase exposure time.
(3) Uniform coating to increase the thickness of adhesive layer.
(4) Use colored silk screen.
(5) Improve tension and uniformity of tension net.
(6) Reduce flushing pressure and time.
6. The printing plate is difficult to develop.
Causes of occurrence:
(1) the exposure time is too long.
(2) After scraping, it is stored for too long.
(3) High drying temperature causes thermal crosslinking.
(4) The photoresist has been exposed.
(5) When printing, the contact between the bottom plate and the adhesive film is false.
(6) The photosensitive adhesive fails.
(7) Diffraction of light during exposure.
(1) carry out exposure test and adjust exposure time.
(2) Shorten the storage time.
(3) Control the drying temperature according to the instructions.
(4) Check the lights in the operation room.
(5) Vacuum adsorption or other methods are adopted to make the negative film closely contact with the photosensitive film.
(6) Replace with new photosensitive adhesive.
(7) Use colored silk screen.
7. Bottom film residue Causes of occurrence:
(1) The interval between preparation and use of photographic emulsion is too long.
(2) Uneven coating.
(3) High drying temperature causes thermal crosslinking.
(4) Improper selection of exposure lamp source.
(5) Underexposure or overexposure.
(6) When printing, the contact between the bottom plate and the adhesive film is false.
(7) When printing, the contact between the bottom plate and the adhesive film is false. The black and white contrast of the master itself is small.
(8) Insufficient development time.
(9) The time, method and intensity of printing are not mastered correctly.
(1) shorten the use interval.
(2) Increase the tension of the screen, and apply glue evenly with the screen sizing device.
(3) Control the drying temperature according to the instructions of photosensitive adhesive.
(4) Choose the lamp source reasonably, and it is advisable to use strong ultraviolet light (halogen lamp).
(5) Carry out exposure test and adjust exposure time.
(6) vacuum adsorption or other methods are adopted to make them tightly jointed.
(7) Check the transparency and blackness of the master.
(8) Increase the development time to show the pictures and texts.
(9) Please refer to the relevant chapters of this manual for correct control of printing time, method and intensity.
8. The screen plate has pinholes Causes of occurrence:
(1) Poor degreasing of silk screen and unclean descaling.
(2) The bottom plate is unclean, and there is dirt on the printing plate after work.
(3) The gluing speed is too fast.
(4) There are bubbles or dirt in the emulsion.
(5) There is water on the silk screen fiber, which causes poor drying.
(6) Sizing scratches are insufficient.
(7) The photosensitive adhesive fails.
(1) clean the screen with a good cleaning agent.
(2) Remove dust and dirt from the positive picture and vacuum frame.
(3) coating at a slow and uniform speed.
(4) stirring and standing for a period of time.
(5) Dry the screen thoroughly at the specified temperature.
(6) Increase the number of gluing scrapes (2-3 times) (7) Replace with new photosensitive adhesive 9. The bonding between the photosensitive adhesive film and the screen is not good.
Causes of occurrence:
(1) Poor degreasing of silk screen and unclean descaling.
(2) The drying time is not enough.
(3) Inappropriate flushing.
(4) Under-exposure, undissolved parts will be decomposed gently during development.
(5) Uneven coating.
(6) The mixture of colloid and sensitizer is uneven, and the emulsion stays for too long.
(1) clean the screen with a good cleaning agent.
(2) Dry the screen thoroughly at the specified temperature.
(3) Check the flushing temperature according to the instructions of photosensitive adhesive.
(4) Increase exposure time and conduct exposure test.
(5) Increase the tension of the screen, and apply glue evenly with the screen sizing device.
(6) Stir and mix evenly, check the ratio and the storage period specified by the manufacturer.
10. The photosensitive film is used for a short time or the screen is damaged.
Causes of occurrence:
(1) the degreasing and descaling of the silk screen are not clean and the drying is not complete.
(2) The wooden net frame is deformed.
(3) Unbalanced shrinkage occurs on the photosensitive film surface of screen tension relaxation.
(4) The drying temperature is too high to deform the screen.
(5) The film thickness is not enough.
(6) Ink fineness is not enough or there are foreign bodies.
(7) Mechanical friction.
(8) improper solvent reacts with photosensitive adhesive.
(10) The ink quality is poor, it dries quickly on the screen, and the printing plate is washed too much.
(11) The scraping pressure is too high during printing.
(1) Clean and dry the screen with a good cleaning agent and put it in a clean and dust-free place to prevent secondary pollution.
(2) Replace with aluminum mesh frame.
(3) Increase the tension of the stretched screen, and put it for a period of time before printing the screen glue. The stretched screen should be put for 2-3 days before being used for printing.
(4) Use a constant temperature controller to ensure that the temperature is below 40℃ (or refer to the operating instructions of photosensitive paste).
(5) Uniform coating to increase the thickness of adhesive layer.
(6) Continue to grind the ink, remove foreign matter and filter it for use.
(7) Softer items should be scrubbed when washing plates.
(8) Pay attention to the matching of solvent and photosensitive adhesive.
(9) Conduct exposure test, increase exposure time and conduct secondary exposure.
(10) Improve the ink quality, avoid drying too fast, and reduce the number of plate wiping.
(11) Reduce the pressure of scraping plate, and grind the scraping edge.
1. What are the causes and solutions of the paste version?
Paste plate, also known as blocking plate, refers to the phenomenon that the printing ink can not be transferred to the substrate in the printing of the graphic through hole of the screen printing plate. This phenomenon will affect the printing quality, and even can’t print normally when it is serious.
The causes of pasting phenomenon in the process of screen printing are complicated. The reasons for pasting can be analyzed from the following aspects.
(1) the reason of substrate. There are many kinds of substrates for screen printing, and the texture characteristics of the substrates are also a factor that produces the phenomenon of pasting. For example: paper, wood board. Fabrics and other substrates have low surface smoothness and poor surface strength, which are easy to produce the phenomenon of powder falling and hair falling in the printing process, thus causing paste plate.
② Due to the workshop temperature, humidity and ink properties, the screen printing workshop requires a certain temperature and relative humidity. If the temperature is high and the relative humidity is low, the volatile solvent in the ink will evaporate quickly, and the viscosity of the ink will become high, thus blocking the mesh. Another point to note is that if the downtime is too long, it will also produce the phenomenon of pasting, and the longer the time, the more serious the pasting will be. Secondly, if the ambient temperature is low, the poor fluidity of the ink will easily lead to paste plate.
③ the reason of screen printing. The prepared screen printing plate can be used only after being rinsed with water and dried before use. If the plate is left for too long and not printed in time, dust will adhere to it more or less during the preservation process, and if it is not cleaned during printing, it will cause paste plate.
④ Reasons of printing pressure. Excessive imprinting force in the printing process will cause the scraper to bend, and the scraper is not in line contact with the screen printing plate and the substrate, but in surface contact, so that the ink can not be scraped off every time, leaving residual ink, which will cause the conjunctival paste plate after a certain time.
⑤ Reasons for improper gap between screen printing plate and substrate. The gap between the screen printing plate and the substrate should not be too small. If the gap is too small, the screen printing plate cannot be separated from the substrate after scratch printing. When the screen printing plate is lifted, a certain amount of ink adheres to the bottom of the printing plate, which is easy to cause pasting.
⑥ The reason of ink. When the particles of pigments and other solid materials in screen printing ink are large, it is easy to block the mesh. In addition, the mesh number and through hole area of the selected screen are smaller than the granularity of the ink, which makes it difficult for the coarse-grained ink to pass through the mesh, resulting in screen sealing. For the paste plate caused by larger ink particles, it can be solved by manufacturing ink, and the main method is to strictly control the fineness of ink.
Ink dries too fast in the printing process, which is easy to cause paste plate failure. Especially, this phenomenon is more prominent when using volatile drying ink, so it is necessary to select appropriate solvent to control the drying speed when printing. The influence of climate should be considered when choosing ink. Generally, quick-drying ink should be used in winter, and late-drying agent should be added to ink in summer. If the late-drying agent is used, it is necessary to switch to other types of ink.
Using oxidative drying ink, the phenomenon of pasting is not very common, but if excessive use of desiccant occurs in summer, the phenomenon of pasting will also occur. Generally, the use of desiccant should be controlled in summer.
When using two-liquid reactive ink, the printing ink itself is slow to dry, so there is almost no pasting phenomenon, but occasionally there is a pasting phenomenon.
In the printing process, the increase of ink viscosity leads to paste printing plate, which is mainly due to the evaporation of ink solvent on the plate, which leads to the increase of ink viscosity and the phenomenon of net sealing. If the printed graphic area is relatively large, the ink consumption on the screen printing plate will be more, and the paste phenomenon will be less. If the graphic area is small and the ink consumption on the screen printing plate is small, it is easy to cause paste printing plate, and the countermeasures are often changed to new ink. The poor fluidity of the ink will make the ink paste when it does not pass through the screen. This situation can be solved by reducing the viscosity of the ink and improving the fluidity of the ink.
After the paste plate failure occurs, it can be scrubbed with proper solvent according to the nature of the ink on the plate. The main point of scrubbing is to start from the printing surface and wipe gently from the middle to the periphery. Check the printing plate after wiping. If there is any defect, repair it in time. After repair, start printing again. It should be noted that every time the film plate is scrubbed, it will become thinner. If the film plate is seriously damaged during scrubbing, it will have to be printed with a new version.
2. What are the reasons and solutions for the unstable fixation of ink on the substrate?
① When printing the printing material, it is very important to carry out strict degreasing and pretreatment inspection on the printing material before printing. When grease, binder, dust and other substances are attached to the substrate surface, it will cause poor adhesion between ink and substrate. Inadequate surface treatment of plastic products before printing will also cause the failure of ink fixation.
② As a printing material, polyethylene stock must be treated with surface flame in order to improve the adhesion with ink during printing. If it is a metal material, it must be degreased and dusted before printing. After printing, it should be dried at the temperature required by the ink. If the drying is improper, the ink film will peel off. In addition, in order to make textiles waterproof in textile printing, it is generally necessary to carry out silicon processing treatment, so that the phenomenon of poor ink adhesion is not easy to occur during printing.
(3) Articles such as glass and ceramics should be sintered at high temperature after printing, so as long as the temperature treatment is appropriate, the adhesion will be good. A simple method to test the fixation fastness of ink film: when the printed object is paper, the printing surface can be bent repeatedly to see if the ink at the crease is peeled off. If the ink is peeled off, its adhesive strength will be weak.
In addition, exposing the printed matter to rain and dew to see if the ink is easy to peel off is also a method to check the fixation fastness of the ink film.
(4) The adhesive force of the ink itself is not enough, which causes the ink film to be firmly fixed, so it is best to replace other kinds of ink for printing. Inappropriate selection of dilution solvent will also lead to the phenomenon of weak ink fixation. When choosing happy solvent, the properties of ink should be considered to avoid the phenomenon of weak adhesion between ink and substrate.
3. Causes and solutions of edge defects of ink film In screen printing products, a common problem is the jagged gross margin (including incomplete or broken lines) at the edge of printing ink film. There are many reasons for burr, but the main reason lies in the quality of screen printing plate itself.
① The resolution of photosensitive adhesive is not high, resulting in broken or incomplete fine lines.
② When the exposure time is insufficient or too long, and the development is insufficient, the edges of the screen printed pictures and texts will be irregular and jagged. For a good screen printing plate, the edges of pictures and texts should be smooth and tidy.
③ The surface of screen printing is uneven. When printing, there is still a gap between the screen printing and the printing house. Because the ink is suspended and infiltrated, burrs appear on the edge of the printed ink.
④ In the printing process, because the printing film expands after contacting with solvent, and the degree of expansion is different in warp and weft directions, the surface of the printing film is uneven. When printing, the contact surface between the screen printing plate and the substrate appears locally: the gap, the ink is suspended and penetrated, and the ink film will appear burrs.
In order to prevent the occurrence of jagged haircuts, the following solutions can be considered:
(1) using high mesh screen to make plate; ② Selecting photosensitive materials with high resolution for plate making; (3) Making a screen printing plate with a certain film thickness to reduce expansion deformation; (4) as far as possible, the diagonal tension method is adopted, and the best angle is 22.5; ⑤ For fine line printing, try to use the indirect plate making method, because there may be fewer burrs in the indirect plate making method; ⑥ In the process of plate making and printing, try to control the temperature expansion factor and use photosensitive materials with small expansion coefficient; ⑦ Improve the plate-making quality, ensure that the surface of the screen printing plate is flat and smooth, and the edges of the screen lines should be neat; ⑧ Spray the screen printing plate with water spray gun to improve the developing effect; ⑨ The distance between screen plate and substrate, scraper angle and printing pressure should be appropriate.
4. What are the causes and solutions of uneven inking?
There are various reasons for the uneven thickness of the ink film. As far as the ink is concerned, the ink is poorly prepared, or the normally prepared ink is mixed with the ink skin. When printing, due to the expansion and softening of the solvent, the mesh that should penetrate the ink is blocked, which plays the role of a printing film and prevents the ink from passing through.
In order to prevent this failure, the prepared ink (especially the old ink) should be filtered once before use. When reusing the used printing plate, the old ink attached to the plate frame must be completely removed. When keeping the printing plate after printing, wash it thoroughly (including the scraper). If we do it according to the above requirements, it will not happen.
If the tip of the front end of the blade is damaged, there will be traces along the moving direction of the scraper. Especially when printing transparent objects, there will be obvious uneven inking. Therefore, the front end of the board must be well protected from damage. If it is damaged, it must be carefully ground with a grinder.
The unevenness of the printing table will also affect the ink uniformity. The ink layer is thin in convex part and thick in concave part, which is also called uneven inking. In addition, if dust is stuck on the back of the substrate or on the printing table, the above faults will also occur.
5. What is the treatment method of pinhole phenomenon?
Pinhole phenomenon is the biggest headache for screen printing workers. If it is printing opaque objects such as billboards and thick paper, it is not easy to observe small holes, which is generally not a problem. However, pinholes are not allowed when precise printing is carried out on aluminum plate, glass plate and acrylic plate, which needs post-processing and corrosion processing. In addition, there are many reasons for pinholes, many of which can not be explained at present, and some of which are quality management problems. Pinhole is one of the most important inspection items in printing product inspection.
① Dust and foreign matter attached to the plate. When making plate, there will be some sol mixed in when washing and developing. In addition, when the emulsion is coated, dust is mixed in, which will cause pinholes when it adheres to the screen. When these are tested, they can be found and repaired in time if they are checked carefully. If dust and foreign matter adhere to the screen, blocking the opening of the screen will also cause pinhole phenomenon. Before formal printing, the dust can be removed from the plate by printing several sheets of paper with strong ink absorption.
② Cleaning the substrate surface. Aluminum plates, glass plates, acrylic plates, etc. should be printed immediately after pretreatment before printing. In multi-color printing, the method of rubbing with alcohol before printing is generally adopted. In addition, semi-automatic and fully automatic ultrasonic cleaning machines can also be used. After pretreatment, dirt such as grease can be removed, and dust attached to the surface can also be removed.
The detergent of cleaning machine is often mixed with broken fiber, which is dissolved in alcohol. When cleaning the substrate surface, a thin surfactant film is often formed, and pinholes will occur when printing ink on the film. Therefore, special attention should be paid when using cleaning agents and alcohol. When the substrate is transported by hand, the fingerprint of the hand will also adhere to the printing surface, and pinhole will be formed during printing.
6. What causes bubbles?
Bubbles sometimes appear on the ink after printing, and the main reasons for the bubbles are as follows:
Poor prepress treatment of substrate. Dust and oil stains are attached to the surface of the substrate.
Bubbles in ink. In order to adjust the ink, when adding solvents and additives for stirring, some bubbles will be mixed in the ink. If left unattended, the ink with low viscosity will naturally defoam, while the ink with high viscosity will not naturally defoam. Some of these bubbles are naturally eliminated due to the transfer of ink in printing, while others become larger and larger. In order to remove these bubbles, defoamers should be used, and the addition amount of defoamers in ink is generally about 1 ~ 1%. If the amount exceeds the specified amount, it will play a foaming role.
Even if the ink is foamed after transfer, as long as the substrate is wet and the ink fluidity is good, the bubbles on the surface of the printing ink film will be gradually eliminated, and the ink will form a flat printing ink film. If the ink bubbles are not eliminated, the ink film will form an annular uneven film surface. Generally, bubbles in ink can be defoamed by the screen when passing through the screen. In addition, using hot water or boiling water when mixing and stirring the ink will have a better defoaming effect.
For transparent inks such as red, blue and green, the binder of these inks is easy to foam because of the small proportion of organic pigments in microparticles. If the corresponding diluent, tackifier or release agent is added, the ink can also be converted into stable ink with good printability.
Excessive printing speed or uneven printing speed. Reduce the printing speed appropriately and keep the uniformity of printing speed.
If the above measures can’t eliminate the bubbles in the printed matter, consider using other types of inks.
7. What are the measures to prevent net marks?
Screen marks sometimes appear on the ink film surface of screen printed products, and the main reason for the screen marks is poor fluidity of ink. In the process of screen printing, when the printing plate is lifted, the ink transferred to the substrate fills the net trace by its own flow, so that the ink film surface is smooth and flat. If the ink fluidity is poor, when the screen printing plate is lifted, the ink flow is relatively small, and the screen trace cannot be filled up, so that the ink film with smooth and flat surface cannot be obtained. In order to prevent screen marks on printed matter, the following methods can be adopted.
(1) printing with ink with high fluidity.
② It may be considered to use ink with slow drying speed to print, and increase the flow time of ink to gradually spread and solidify the ink.
③ When making plate, try to use monofilament screen with thinner silk.
8. What are the precautions for inaccurate printing position?
Even if there are no problems in screen size, printing press and so on, the inconsistent shapes of printing materials will cause inaccurate printing position. For example, in paper overprint printing, after one color printing, it is dried, and the change of temperature causes its size to change. As a result, in the second and third printing, there will be a fault of inaccurate overprint. When the printing materials are plastic products, the change of temperature and humidity in the printing place can cause the change of its size, which affects the printing accuracy. Moreover, the shape of plastic products and the conditions (such as temperature and time) during molding are not completely consistent, which must be considered when printing, and corresponding measures should be taken to make corrections in advance as much as possible.
9. What are the main applications of screen printing?
Screen printing is widely used. Except water and air (including other liquids and gases), any kind of object can be used as a substrate. When someone commented on screen printing, they once said: If you want to find an ideal printing method on the earth and achieve the purpose of printing, it is probably screen printing.
Specifically, screen printing is mainly used in the following aspects:
① Paper printing Fine arts printing–advertisements, pictorial magazines, calendars, lantern papers, etc.
label printing Transfer printing Packaging printing Printing of building materials-wallpaper, etc.
② Plastic printing Plastic film–vinyl toys, schoolbags, plastic bags, etc.
Plastic standard plates-fake metal composite materials and various standard plates.
Production parts–instrument parts.
③ wood products printing Arts and crafts–lacquerware, wooden arts and crafts, toys.
Processing semi-finished products–sporting goods, wooden boards, ceilings, road signs, signboards, fake metal plates, billboards, etc.
④ Printing of metal products Metal cylinder, metal vessel, metal product.
⑤ Printing of glass and ceramic products Glass–mirrors, glass plates, cups, bottles, etc.
Ceramics–utensils and handicrafts.
6 sign plate Text description board, dial, line items.
⑦ circuit board printing Printed circuit board, civil or industrial substrate, thick film integrated circuit board.
⑧ Printing and dyeing Printing and dyeing–flags, cloth, towels, handkerchiefs, shirts, backs, knitwear, etc.
Other printing–pockets, shoes, number cloth and various bags, backpacks, bags, schoolbags, etc.
Pet-name ruby leather products printing 10. How to solve the image distortion?
When printing, the printing pressure applied to the printing plate by the scraper can make the line contact between the printing plate and the object to be printed, and do not exceed. If the pressure is too high, the printing plate will contact with the substrate, which will make the screen expand and contract, resulting in deformation of the printed image. Screen printing is the smallest printing among all printing methods. If we forget this, we can’t print a good print.
If you can’t print without increasing the pressure, you should reduce the gap between the layout and the substrate surface, so that the pressure of the scraper can be reduced.
11. What is a tensiometer?
Tension meter is an instrument for measuring the mutual traction force between the contact bodies of the fixed wire mesh when the wire mesh is subjected to tension. There are two kinds of tensiometers: mechanical and electronic, and the unit of tension measurement is Newton/centimeter. Tension can also be expressed by relative values. Cm tensiometer is a kind of tension expressed by relative value, which is calculated by the depth (mm) of wire mesh sinking caused by its own weight. The tension value can be obtained directly from the indicator panel or indirectly from the control panel. There are two kinds of tensioners: manual operation and mechanical operation. Tension meter is an important testing instrument for testing the quality of screen printing plate. In order to ensure the tension required by plate making, a tensiometer should be used to measure the tension during or after net stretching.
12. What is a mesh ruler? What is its purpose?
Mesh ruler is called longitude and latitude densitometer. It is mainly used to measure the mesh number of various screens. There are two kinds of mesh ruler: glass plate and plastic plate. The measuring method is as follows: when measuring, first make the screen in a transparent state or put it on the reading table, put the mesh scale on the screen, and then move it slowly in the screen row so that the vertical lines on the screen scale are parallel to the warp or weft of the screen. At this time, due to the overlapping effect between the warp and weft of the screen and the vertical lines on the screen scale, a diamond pattern is formed on the screen scale, and the corresponding scale numbers on the screen scale indicated by the horizontal diagonal of the pattern are the number of tested screens.
Mesh ruler is a common tool for measuring mesh number. Generally, it is necessary to keep the precision of measuring instruments and the accuracy of measuring data. It is necessary to keep the mesh ruler clean to prevent scratches and bruises on the mesh ruler. After use, the instrument should be wiped clean and properly kept.
13. What is a densitometer? What is the purpose of densitometer?
Densitometer’s original manuscript measuring instrument commonly used in printing houses. It is a photoelectric measuring instrument for measuring gray value of black-and-white manuscript and continuous tone or dot value. There are two types of densitometers: transmission densitometer and reflection densitometer. Transmission densitometer is suitable for measuring transparent manuscript, and reflection densitometer is suitable for measuring field manuscript. The measuring range of densitometer is 0-2.5. The larger the number, the higher the blackness. The basic principle of measurement is to measure the blackening degree of photosensitive materials after exposure and development. In plate making, the silver bromide on the photosensitive material is irradiated by light and reduced to metallic silver after development, forming a certain degree of opacity. High in blackness and density: Low in blackness and density. The meter with filter can also measure the color density of color original. Its measuring principle is similar to the above basic principle.
14 What is a colorimeter? What is its purpose?
Colorimeter has a weighing colorimeter. It is an instrument for measuring the color characteristics of materials. The main purpose of colorimeter is to measure and analyze the color, hue and color value of measured materials. If the colorimeter is connected with the computer, the ability of analyzing and processing colors can be improved, and users can search and call up various data from the color storage of the microcomputer for color matching according to their needs.
15. What is a hardness tester? What is its purpose?
Hardness tester is an instrument for measuring the hardness of objects, which can be divided into simple hardness tester and complex hardness tester according to the degree of simplification. Hardness tester is widely used in rubber industry. In the process of screen printing, hardness tester is mainly used to detect the hardness of scraping materials.
What is the purpose of 16 scraping pressure gauge?
Scraping pressure gauge is a display instrument that measures the friction between scraping plate and screen according to scraping pressure. The unit of measurement is kg/cm. The test method is: put the test strip between the stencil and the screen, and use the pressure gauge to carry out the pull test. When measuring, according to the number indicated on the dial, get the friction value.
17. What is the purpose and coating method of scraper bucket?
Scraper is a tool for coating photosensitive agent on silk screen, also known as screen sizing device. The scraper bucket is usually made of stainless steel, which is light in weight, light in use, strong in corrosion resistance, not easy to rust, and convenient to manufacture.
Scraper can be used for two purposes, one is coating photosensitive adhesive, and the other is for sealing net. When coating photosensitive adhesive, first pour the photosensitive emulsion into the scraper bucket, generally the amount of which should not exceed 1/2 of the capacity of the scraper bucket. When in use, tilt the net frame of the stretched net by about 70 degrees, lean against the fixed bracket, horizontally lean against the lower end of the net frame, and then tilt the scraper slightly upwards to make the sensitizer contact with the net. And then move smoothly from bottom to top. In order to firmly combine the photosensitive film with the screen. Coating is blade coating on the inner and outer sides of the net frame. The times of coating on the outside of the frame are more than those on the outside. Specifically, the operation method is as follows: blade coating once and dry coating once. In order to ensure the uniformity of the coating film thickness, the position of the net frame is changed up and down once after each scraping coating, and the operation method is repeated until the required film thickness is reached.
18. What are the main technical specifications and requirements of scraper bucket?
It can be seen from the foregoing that the scraper is an important tool for coating photosensitive adhesive, and the quality of scraper directly affects the quality of screen printing plate. Attention should be paid to the following aspects: firstly, the edge of the scraper that contacts with the wire mesh must ensure high flatness, and there should be no marks of bruise. If the flatness is low or bruised, streaks or uneven film thickness will appear on the coated film, resulting in burrs and uneven ink thickness on the printed lines. Secondly, the edge of cutting edge is required to be smooth. If this point is ignored, the wire mesh will be damaged during coating. Thirdly, because the stretched silk screen has certain purchasing elasticity, it is easy to have uneven film thickness during scraping, that is, the film thickness in the middle part is thin while the film thickness on the four sides is thin. In order to avoid this kind of problem, usually when making scraper, the side contacting the screen is slightly arc-shaped, which can avoid the uneven film thickness caused by the elasticity of the screen. Fourthly, stainless steel with no embroidering, corrosion resistance and light weight should be selected as far as possible when making scraper.
19. What material is the net frame made of? What are its characteristics?
The materials used to make the net frame mainly include wood, hollow aluminum profile, cast aluminum molding frame, steel and other materials. The most commonly used net frame is made of aluminum profiles. However, all kinds of net frames have their own characteristics. When selecting, we can select net frames of different materials according to different situations, which are introduced in turn below.
Wooden net frame has the characteristics of simple manufacture, light weight, convenient operation, low price, simple net stretching method, etc. This kind of screen frame is suitable for manual printing. However, the screen frame made of this kind of wooden material has poor solvent resistance and water resistance, and it is easy to deform after being soaked in water, which will affect the printing accuracy. This kind of net frame was widely used in the past, but now it is rarely used.
Hollow aluminum profile mesh frame and cast aluminum molding mesh frame have the characteristics of easy operation, high strength, firmness, no deformation, strong solvent resistance and water resistance, and beautiful appearance. Suitable for mechanical printing and manual printing.
Steel mesh frame has the characteristics of firmness, high strength, good solvent resistance and water resistance, but it is a little bulky and inconvenient to operate, so its application range is very small.
20. What are the conditions for choosing a net frame?
The screen frame is one of the important materials for making screen printing plates. Whether the screen frame is suitable or not has a direct impact on the plate making quality and printing quality. In order to ensure plate making, printing quality and other requirements, the screen frame can be selected according to the following conditions.
(1) the net frame must have a certain strength. Because when the net is stretched, the silk screen produces a certain tension and pressure on the net frame. This requires that the net frame withstand voltage, can’t produce deformation, and keep the size of the net frame accurate.
(2) Under the condition of ensuring strength, try to choose light weight for easy operation and use.
③ The bonding surface between the mesh frame and the wire mesh should be rough to strengthen the bonding force between the wire mesh and the mesh frame.
③ the firmness of the net frame. In use, the net frame should always come into contact with water, solvent and be affected by temperature changes, which requires that the net frame should not be skewed, which can reduce waste and cost.
⑤ Net frames of different specifications should be configured in production. When using, the appropriate net frames should be determined according to the printing size, which can reduce waste and facilitate operation.
21 What are the main specifications of aluminum mesh frame?
From the foregoing, it can be seen that the screen frame made of hollow aluminum profiles has the characteristics of light weight, stable size, beautiful appearance and convenient operation.
22. What are the physical performance indexes of common net frame materials?
The most common screen frame used in screen printing is aluminum screen frame, followed by wooden screen frame and steel screen frame. The main physical performance indexes of these frames are as follows:
① Elastic coefficient, in Newton/cm. The elastic coefficient of wood material is 0.12×107 Newton/cm, and that of aluminum material The material is 0.75×107 Newton/cm, and the elastic coefficient of steel material is 2.1×107 Newton/cm.
② moment of inertia, expressed in cm4. When the cross-sectional shape of the mesh frame material is hollow rectangle (the outer frame size is 5×4 cm and the wall thickness is 2.5 mm), the inertia moments of aluminum and steel materials are 15.088cm4, and the cross-sectional shape of wooden mesh frame is 41.667cm4.
③ Density, expressed in g/cm3 (g/cm3). Wood density is 0.9g/cm3, steel density is 7.8g/cm3, and aluminum density is 2.7g/cm3.
④ coefficient of thermal expansion (105/oC). The thermal expansion coefficients of aluminum, steel and wood are 2.4×105/oC, 1.2×105/oC and 3.0×105/oC respectively.
23. What are the main characteristic indexes of screen material?
Silk screens commonly used in screen printing include silk screen, nylon screen, polyester screen and stainless steel screen. The main characteristic indexes of various screens are as follows.
① tensile strength [g/d (g/diameter)]: 3.7-4.1g/d for silk mesh, 4.5-5.8g/d for nylon mesh, 4.3-5.5g/d for polyester mesh and 1.5g/d for stainless steel mesh.
② The wet-dry strength ratio (%) is 92 ~ 100% for silk mesh, 89 ~ 90% for nylon mesh, 100% for polyester mesh and 100% for stainless steel mesh.
③ Nodule strength [g/d] is 2.9g/d for silk mesh, 4.5-5.4g/d for nylon mesh and 3.4-4.4g/d for polyester mesh.
④ Tensile elongation (%): 8-22% of silk mesh, 26-32% of nylon mesh, 16-30% of polyester mesh and 38% of stainless steel mesh.
⑤ The dry-wet elongation ratio (%) is 120 ~ 134% for silk mesh, 115 ~ 122% for nylon mesh, 100% for polyester mesh and 100% for stainless steel mesh.
⑥ Stretching recovery rate (%,calculated at 3% stretching) is 80 for silk mesh, 15.088cm4 for inertia moment of aluminum material and steel material, and 41.667cm4 for solid rectangle (5× 4cm) for wooden mesh frame.
⑦ Density, expressed in g/cm3. Wood density is 0.9g/cm3, steel density is 7.8g/cm3, and aluminum density is 2.7g/cm3.
⑧ coefficient of thermal expansion (10l/oC). The thermal expansion coefficients of aluminum, steel and wood are 2.4 10l/oC, 1.2 10l/oC and 3.1 10l/oC respectively.
24. What are the nylon nets for screen printing?
Nylon mesh is made of chemical synthetic fibers and belongs to polyamide system. Nylon mesh has high strength, good wear resistance, chemical resistance, water resistance and elasticity. Because of its uniform diameter and smooth surface, the ink has excellent passability. The disadvantage is that the tensile property of nylon mesh is larger. In a period of time after stretching the screen, the tension of the screen is reduced, which makes the screen printing plate relax and the accuracy decreases. Therefore, it is not suitable for printing circuit boards with high dimensional accuracy.
25. What are the characteristics of polyester screen for screen printing?
Polyester mesh is also made of chemical synthetic fibers and belongs to polyester system. Polyester mesh has the advantages of solvent resistance, high temperature resistance, water resistance and chemical resistance. Polyester mesh has stable physical properties and small stretchability when it is subjected to greater external pressure. Its disadvantage is that it has poor wear resistance compared with nylon mesh. Besides the advantages of nylon screen printing, polyester screen is also suitable for printing printed circuit boards with high dimensional accuracy.
26. What are the characteristics of stainless steel screen for screen printing?
Stainless steel wire mesh is made of stainless steel material. Stainless steel wire mesh is characterized by good wear resistance, high strength and small technical elongation; Due to the fine wire diameter, the passing performance and dimensional accuracy of the ink are stable. Its disadvantages are good flexibility and high price. After stretching, the screen cannot be restored to its original state. Stainless steel screen is suitable for high-precision printing such as circuit boards and integrated circuits.
27. How to choose silk screen?
Screen is the basis of screen printing. Choosing the appropriate screen is an indispensable link. Because of the wide application range of screen printing, there are many factors related to it. When selecting screens, different screens should be selected according to specific conditions and printing requirements. Usually, when selecting screens, the following different angles can be considered.
(1) according to the type of substrate screen. When selecting, it can be used according to fiber 3 fabrics, paper products, glass, ceramics, metals, plastics, wood products, electronic products, etc.
② Different inks have different adaptive characteristics according to the properties of the inks. Therefore, the drying time and color clarity of ink, the ink absorption capacity of the substrate and other factors should be considered when selecting the screen.
③ According to the material and performance of the screen, the material and physical performance of the screen should be considered when selecting the screen, and the corresponding screen should be selected according to different suitability.
(4) according to the printing standard, select the screen, and check the printing speed, printing pressure, printing resistance of the printing plate and the absorption capacity of the substrate.
28. What problems should be paid attention to when selecting silk screen?
Several way of selecting that screen have been describe above. However, choosing silk screen is not a simple problem. Besides silk screen, we should also consider the cost of printing ink and substrate, etc. Mastering the selection method and paying attention to the related problems, choosing the appropriate screen can be handy. The following problems should be paid attention to when selecting screen.
(1) first consider the difficulty of ink passing through the screen, and generally consider this aspect when choosing. The ink for halftone uses ink with high transparency. The pigment particles are fine, and the ratio of pigment carrier is more. The ink has good passability, and this ink can pass well when using high mesh screen; Generally, plastic ink has good passability; Special-purpose inks, inks with high pigment concentration, are relatively poor in passability even though they are fine particles.
② If the surface of the substrate is rough, the screen with lower mesh number is generally used.
Such as leather, canvas, foam sheets, wood and other materials. Because the surface of the substrate is rough and the ink absorption is strong, the screen with lower mesh number should be used to ensure enough ink to pass through.
③ Select the screen according to the fineness of the graphic lines of the manuscript. Contrary to the above situation, high mesh screen should be selected for fine lines in general.
④ The cost should also be considered when selecting silk screen. On the premise of meeting the printing requirements, try to choose silk screen with lower price.
29 How to choose the screen according to the substrate?
There are many kinds of substrates in screen printing, and the substrate materials also have their own characteristics. Usually, the screen can be selected according to the substrate material.
(1) Fiber fabric printing, when the substrate material is fiber fabric, such as clothes, scarves, ties, schoolbags, etc., it can be made of silk mesh, nylon mesh or polyester mesh.
② Paper printing When the substrate material is paper, such as printing: advertising pictures, famous letters, wallpapers, calendars, etc., thin silk net, thick silk net, nylon net, thin polyester net, multi-filament polyester net and monofilament polyester net can be selected.
③ Printing of plastics, glass, ceramics, metal products and wood products When the substrate materials are glassware, metal containers, wood, ceramics, plastic products, toys, etc., thick silk mesh, monofilament nylon mesh, thin polyester mesh, thin silk mesh and stainless steel wire mesh can be selected.
(4) Electronic device printing When the substrate material is a circuit board, such as integrated circuits, semiconductor components, insulating cloth, television components, etc. Thick silk mesh, monofilament nylon mesh or multifilament polyester mesh can be selected.
How are the old and new models of screen at home and abroad expressed?
According to the specification table of nylon and silk screen promulgated by national standard GB2014-80, the expression method of screen model is as follows:
JF: means nylon (JIN) (or nylon) FANG flat group.
JP: indicates nylon flat weave.
JQ: refers to the whole twisted yarn structure of nylon yarn.
JCQ19: indicates the whole (QUAN) skein structure of nylon and silk mixed weaving.
CQ: indicates the structure of silk twisted yarn.
CB: indicates silk semi-twisted yarn structure.
CP: indicates the plain weave of silk.
The old model of JF screen is denoted by SP.
The old model of JP screen is denoted by NX.
The model of JCQ screen 110 is denoted by GG.
J: stands for JIN nylon (commonly called nylon).
C: represents silkworm silk.
Q: indicates the whole (QUAN) skein structure.
B； Means a BAN skein weave.
P: indicates the flat twisted tissue.
F: FANG flat tissue.
Representation method of Swiss screen specifications and models; S: indicates “s” shaped screen. The wire diameter is thin, but the mesh is large. It is suitable for reproduction of artworks and photographic screen making.
T: stands for “t”-shaped screen. The wire diameter is thicker than S type, and the mesh size is smaller than S type. It is suitable for making screen printing plates of images or characters composed of color blocks or lines.
HD: indicates “HD” screen. The wire diameter is the thickest, the mesh is the smallest, and the screen is the thickest, which is suitable for making the pattern screen printing plate composed of thick lines.
Example: 77 T, which means 77 mesh T-shaped screen.
90 HD means 90 mesh HD screen.
Representation method of Japanese screen specifications and models:
NP, SSP, SP and (GG.) respectively represent silk products, which are plain woven and multifilament.
NO 66-NO 66-S refers to plain woven and twill woven monofilaments of nylon products.
No, NoS, TPM, TNP, TP represent polyester products, which are plain woven, No, NoS, TPM are monofilaments, TNP and TP are multifilaments, and TP represents monofilaments in warp and multifilaments in weft.
No stands for stainless steel wire mesh, including plain weave and twill weave (single thread).
31. What are the commonly used solvents for screen printing?
Solvents are mainly used in screen printing to adjust the viscosity and drying speed of ink, and to clean screen printing plates and printing scrapers after printing. Commonly used solvents mainly include aliphatic hydrocarbons, aromatic hydrocarbons, ketene, ester, ethanol, glycol ether and other six categories. And the solvents in each category can be divided into several categories.
What are the coating methods of 32 photosensitive liquid?
According to the operation methods, the coating methods of photosensitive liquid can be divided into manual coating and mechanical coating. Each category can be subdivided into several sub-categories, which are detailed as follows:
Manual coating can be divided into the following methods due to the different tools used.
(1) brush with lint-free brush.
② Scraping coating with thin plastic plate.
③ Scrape coating with stainless steel scraper.
(4) The tape casting coating method is also a kind of manual coating plate making. Its special feature is that it is not directly coated with tools, but semi-sensitive glue is put in a container, and the sensitive glue is directly and continuously poured on the vertically erected screen frame plate, so that the sensitive glue automatically flows down to form a plate film on the screen. This plate making method is suitable for making screen printing plates with special effects.
The above ①, ② and ③ kinds of manual coating are more suitable for screen printing plates with small size and are easy to operate.
Mechanical coating mainly refers to the coating of photosensitive liquid by mechanical action. Mechanical coating can be divided into semi-automatic coating and full-automatic coating (semi-automatic coating requires manual assistance in addition to mechanical coating. Fully automatic coating is done automatically by machinery). Mechanical coating is suitable for large-area screen coating.
33. What is the significance of secondary exposure? How to master its time?
In order to further improve the water resistance of the screen printing plate made after printing; Friction resistance, solvent resistance, strength, fastness and printing resistance of screen printing plates are usually hardened by secondary exposure (besides secondary exposure, drugs are also used to harden screen printing plates). The secondary exposure time is usually determined according to the actual situation of the screen, including the selected screen, coating thickness and many other factors. Generally, the second exposure time is about 1-3 times of the first exposure time.
Hardening of screen printing plates is suitable for mass printing and disposable screen printing plates. Under what circumstances can the screen printing plate not be hardened? Firstly, the hardening treatment of the screen printing plate can be avoided in small batch printing. Secondly, after the screen printing plate is printed, it is ready to release the film. If the screen printing plate is reused, the secondary exposure hardening treatment cannot be carried out, otherwise it will cause the air crash of releasing the film.
34. What are the basic conditions for selecting light sources for screen printing plates?
When making screen printing plates, the basic conditions for selecting light sources mainly include the following; (1) intensity of light source The light source used must have a certain intensity, and any kind of manuscript should be able to meet the needs of exposure in a short time.
(2) Stability requires that the intensity of the light source used must remain stable during the exposure process, and cannot be changed from strong to weak.
(3) uniformity of light source illumination The illumination intensity of the light source used on the manuscript must be consistent. That is to say, the position around the original must be under the same light intensity.
④ The light source with high efficiency should be exposed in a short time, and the exposure effect can be achieved.
⑤ Simple operation and maintenance The selected light source equipment should be easy to operate and easy to maintain.
35. How to calculate the thinnest width of fine lines reproduced by screen?
In screen printing, the printing accuracy of reproductions is closely related to the screen, and the screen mesh has an important influence on reproducing the fine lines of the original. Therefore, to carefully select the screen, it is necessary to make the screen mesh correspond to the printed fine lines. Make the selected screen specifications have the performance of reproducing the fine lines of the original, so as to ensure the printing effect.
Screen printing fine lines generally refers to the line width between 0.1-0.2 mm.
The thinnest width of fine lines reproduced by screen means that in screen printing, what is the width value of the selected screen that can reproduce the thinnest lines? This is usually directly related to the width of wire mesh and mesh. The following formula can be used as a basis for the calculation of screen selection. Calculation formula of thinnest line width value:
In K=2S+R formula, k represents the width of the thinnest line, s represents the wire diameter width of the screen, and r represents the width of the mesh.
Calculation example: If 200 mesh/inch nylon mesh is selected, what is the thinnest width of its reproduction line?
Looking at the NM200-inch screen, the wire diameter (s) is 0.05 mm, and the mesh width (r) is 0.077 mm. By substituting the above formula, it is found that K=2×50+77=177=0.177 mm, and the thinnest width of the reproduced line of NM200 mesh/inch screen is 0.177 mm.
36. What is the influence of screen color on plate making?
Screen has white, yellow, amber, red, etc. The color of screen has great influence on the quality of plate making. Colored screens, such as yellow, red and amber screens, can prevent light diffusion when printing, while using white screens will cause obvious diffusion. This is because the photosensitive material has a large absorption peak in the ultraviolet region, and because the white screen reflects white light when illuminated by the light source, it affects the photosensitive material. Irradiation light reaches the emulsion coating through the transparent part of the positive film, and the phenomena of reflection, buckling-reflection and diffuse reflection occur when the irradiation light contacts the white screen, which makes the printing plate appear floating phenomenon, that is, halo. If colored screen is used, this phenomenon will be prevented because colored screen can absorb part of the irradiation light, thus reducing the reflection intensity of irradiation light, and colored screen reflects colored light, which is inactive light, so it will not affect sensitive materials, especially when fine printed products are printed, the screen is 37. What is the relationship between screen mesh and dot?
The mesh number of screen and the dot only form a certain relationship when copying the continuously adjusted manuscript. Using screen printing technology to copy the original with continuous tone color, if the screen printing plate is directly made with continuous tone photographic negative and printed, the copy with the same continuous tone as the original cannot be obtained. Because the screen printing plate only shows two states, that is, the mesh of the picture and text part is open, and the mesh of the non-picture and text part is closed. It is not because the mesh size and arrangement rules of one kind of screen mesh are uniform, so the printing ink passing through the screen mesh is basically equal. So that it can’t show the hierarchical changes of the original text. In order to fully reflect the changes of the original pattern on the screen printing plate, it is necessary to make the continuously adjusted original into dot negative. That is to say, the change of depth and level of the manuscript is represented by dots with different sizes and uniform density. On the screen printing plate, the dots with the highest density have a large area, while the dots with low density have a small area. The dots with the same density have the same area, and the center distance between them is equal, and they are regularly arranged at a certain angle. A continuous tone copy can be obtained by drying and printing a screen printing plate with this dot negative. The density of dot arrangement is usually expressed by the number of screening lines. The unit expression is: line/inch or line/cm, which means the number of dots arranged in a unit length.
38. What is the technological process of stretching the net?
Stretching screen is the first process of making screen printing plate. The quality of web stretching has a direct relationship with the quality of plate making. Therefore, it is necessary to do a good job of preparing and stretching the net carefully.
First, select the corresponding mesh frame according to the printing size, and clean the bonding side between the mesh frame and the screen. If it is used for the first time, it is necessary to rub it lightly with fine sandpaper to make the surface of the mesh frame rough, which is easy to improve the bonding force between the mesh frame and the screen. If it is used, it should also be rubbed clean with sandpaper to remove residual glue and other substances. Before stretching the net, the cleaned net frame should be pre-coated with adhesive and dried. When stretching the net, stretch the net manually or mechanically. After the wire mesh is tightened, make the wire mesh and the net frame stick together, and make contact between the wire mesh and the net frame. Coat some parts with adhesive, and then blow dry. Pay attention to that the adhesive should not be coated too thick or too thin. When blowing dry, use rubber plate or soft cloth to wipe the bonded parts while applying a certain pressure, so as to make the bonding between the screen and the frame stronger. After the adhesive is dried, release the external tension, cut the silk screen around the outside of the screen frame, and then attach it to the bonding position between the silk screen and the screen frame with a single-sided self-adhesive paper tape, which can protect the silk screen and the screen frame, and prevent the solvent or water from dissolving the adhesive during printing to ensure the effective use of the screen printing plate. Finally, rinse the screen with clear water or cleaning agent, and after the screen is dried, it can be used for photosensitive adhesive coating (plate making).
39. How many methods are there to stretch the net? What are their characteristics?
Stretching screen is an essential process for making screen printing plate. Stretching the net is to firmly fix the silk screen on the net frame under a certain tension. And make the stretched screen have a certain tension to meet the requirements of sensitizer coating and other plate making. The tension of screen and the quality of stretched screen have a direct impact on printing quality. In color printing, it is required that the tension of each color plate of the screen printing plate must be basically the same, so as to ensure the accuracy of overprinting. Only by stretching the net can the quality of plate making and printing plate be guaranteed. There are two main methods of net stretching: manual net stretching and mechanical net stretching. Hand stretching net is a simple and traditional method. Generally applicable to wooden net frames. In this method, the silk screen is fixed on the wooden frame by manual use of nails, wood strips, adhesives and other materials. The tension of manual net stretching can generally meet the requirements, but it is troublesome and time-consuming because of uneven tension, and the quality of net stretching is not easy to guarantee. This method is mostly used in occasions where a small amount of printing is required and printing accuracy is not high.
Mechanical mesh stretching is the use of mechanical force to make the mesh taut, and firmly adhere it to the mesh frame with adhesive. After the adhesive is dried, take off the net frame and seal the edge with polyester film single-sided pressure-sensitive adhesive tape. To prevent the adhesive from dissolving and make the screen printing plate look neat. Mesh frames of various materials can be stretched mechanically. Mechanical net stretching has the characteristics of uniform tension and short net stretching time. Easy to master the required tension. Suitable for plate making with high precision.
40. How to choose the angle of tension net?
Stretching angle refers to the angle between the warp and weft (silk) of the screen and the edge of the screen frame.
There are two forms of tension net, one is positive tension net, the other is diagonal tension net. These two methods of stretching nets are described below.
A positive tension net is one in which the warp and weft of the screen are parallel and perpendicular to the four sides of the net frame. That is, the warp and weft are at 90 degrees with the edge of the net frame.
Oblique tension net means that the warp and weft of the screen make a certain angle with the four sides of the frame. It is convenient to operate by stretching the net in the form of positive stretching net, and because of making full use of the net, the scraps of the net can be saved. Reduce screen waste. However, in the process of process printing, it is easy to have tortoises by using this form of stretched screen, so the process of process printing generally does not use stretched screen. It is beneficial to improve the printing quality and to increase the ink leakage by using diagonal tension screen. The disadvantage is that the silk screen is wasted greatly. In color printing, where the printing accuracy is high, the selection of the stretching angle has a direct impact on the printing quality. If the stretching angle is not suitable, the moire will appear. Therefore, in the printing of half copies, the commonly used stretching angle is 20-35 degrees. When printing high-resolution circuit boards, it is more suitable to choose 45 degrees because of the high screen mesh. In practice, in order to reduce the waste of screen, positive screen stretching is usually used for copying printed matter.
41. How to determine the tension of wire mesh?
The accuracy of screen printing is related to the accuracy of screen printing plate, and screen tension is one of the important factors affecting the quality of screen printing plate. The tension of the screen is related to the material and strength of the screen frame, the tree quality of the screen, the temperature, humidity and the method of stretching the screen. Usually, in the case of manual mesh stretching and no tensiometer, the determination of tension is mainly determined by experience. When stretching the mesh, you can press the mesh with your fingers, and generally press the mesh with your fingers to feel that the mesh has certain elasticity.
Tension meter is generally used to test the tension of screen when using the screen stretching machine and the large screen frame.
When using the net-stretching machine to stretch the net, because the movement (tightness adjustment) of the net-stretching chuck is controlled by the air pressure gauge, the air pressure value of the net-stretching is different for different quality screens. Generally, the air pressure of silk net is 7-9kg/cm2, nylon net 8-10kg/cm2 and polyester net 8-10 kg/cm2. The air pressure of stainless steel wire mesh is 10-13kg/cm2.
The above are the air pressure reference values of several kinds of screens when stretching, which can be used for stretching according to the actual situation to obtain ideal stretching tension.
42. What kinds of adhesives are commonly used for mesh stretching?
The screen and frame are firmly bonded together by the action of adhesive used for stretching the screen. There are many kinds of adhesives used for bonding nets. When selecting, different adhesives should be selected according to the material of the net frame and the type of wire mesh. The main adhesives used in web stretching are polyvinyl acetal glue (Peifu glue), vinyl perchloride adhesive, rubber adhesive, phenolic-neoprene, nitrile rubber, etc.
43. How is the vignetting produced?
A common phenomenon in screen printing of vignetting. The main manifestation is that the screen holes at the edges of the graphic parts on the screen printing plate after printing are not all through holes after development, some meshes are still blocked by photosensitive glue, the edges of graphic parts are uneven, some fine lines of graphic parts are lost, and the size of graphic parts also changes. Thereby reducing the printing quality. There are two main reasons for vignetting. When direct plate making is used, white silk screen is used. The white silk screen has reflection and scattering effects on the light source of printing, which makes the photosensitive material at the edge of the picture and text uneven, resulting in vignetting: the plate-making negative film is not tightly attached to the screen printing during printing, which makes the photosensitive material at the edge of the picture and text uneven, resulting in vignetting.
44. How to prevent vignetting?
In order to prevent vignetting and improve the quality of plate making and printing, the following measures can be taken to control it.
(1) Use colored silk screens instead of white silk screens, and use red, yellow, orange and other colored silk screens to make plate. The color of the silk screen itself absorbs the light of the light source of printing plate, reducing the reflection and scattering of the silk screen light during printing plate, and achieving the purpose of preventing vignetting.
(2) Pre-coating vignetting prevention solution is a solution prepared by mixing ethanol, cresol and ethanol soluble red dye according to a certain ratio. Before coating this solution, the screen must be cleaned and dried, then coated with vignetting prevention solution and then dried. After drying, the photosensitive adhesive can be coated and printed, which can prevent vignetting.
③ During printing, pay attention to sticking the plate-making negative film and screen printing plate to ensure that the photosensitive material receives light evenly and achieve the plate-making effect of preventing vignetting.
45. Why is the silk screen pretreated? What are the methods?
In the process of manufacturing, transportation, storage and use, dust, oil and other things will adhere to the surface of the screen, which will seriously affect the combination of the screen and the photosensitive adhesive, resulting in a decline in the quality of the screen printing plate. In order to ensure the close combination of the screen and the photosensitive adhesive, the screen should be pretreated before coating the photosensitive adhesive. Pre-treatment of silk screen is an important process of making silk screen printing plate. There are usually two methods for pretreatment of silk screen. Namely physical treatment and chemical treatment.
Physical treatment: The purpose of this method is to polarize the surface of the screen to facilitate the combination of the screen and the photosensitive adhesive.
In this method, pumice and silicone carbide are ground into powder, and the surface of the screen is treated mechanically. Or the silk screen is treated with silicone carbide powder, and the powder particles are below 20 microns. After treatment, the screen is cleaned and dried with water, and then can be used for plate making.
Chemical treatment: usually, before plate making, phenol, cresol and phosphoric acid corrosives are used to treat the surface of synthetic fiber screen, so as to make the screen surface rough and achieve the purpose of close combination with photosensitive adhesive. However, the use of phenol, cresol and phosphoric acid corrosives is easy to damage the screen, so full attention should be paid to chemical treatment.
In addition to polarization treatment on the screen surface, the screen can also be degreased and cleaned by caustic alkali and cleaning agent. The degreasing cleaning method can effectively remove the oil stains and dust on the screen surface, and make the screen firmly bonded with photosensitive adhesive. After washing with the above solvent, rinse with clear water, and dry it, and then it can be used for plate making.
46. What is the imaging principle of screen printing plate?
It can be seen from the foregoing that the silk screen is woven from a certain material, and its longitude and latitude intersect to form a mesh. During plate making, a certain thickness of photosensitive adhesive is coated on the screen and dried to form a photosensitive film on the screen, and then the negative film for making positive pictures and texts is attached to the coated screen and put into a printing machine for exposure. In this way, the graphic part of the silk screen is not cured because it is not exposed to light, while the non-graphic part is photo-cured. After developing and washing, the uncured photosensitive material of the graphic part is washed away, so that the screen hole is a through hole. Photosensitive materials in non-graphic parts are solidified to block the mesh. When printing, the screen holes of the graphic part leak ink, while the non-graphic part does not leak ink, thus obtaining printing ink. This is the imaging principle of screen printing plate.
47. How to develop and fix the screen printing plate?
The production process of screen printing plate is relatively simple, which is more prominent with the emergence of new photosensitive materials. The screen printing plate is made of modern photosensitive materials, and the negative film of the photographic printing plate is attached to the screen frame coated with photosensitive materials for printing. After printing, the screen frame is soaked in clear water, warm water or medicinal water for about 10 minutes, and the pictures and texts are displayed (the development time of different photosensitive materials is also different). Then gently scrub the screen plate with sponge in water, so that the meshes of the picture and text parts basically become through holes. Then pressurize and spray water to remove all the screen holes in the graphic and text parts, and finally wipe off the water marks and dry them to make the screen printing plate.
48. How to determine the thickness of the screen printing plate?
The thickness of the screen printing plate refers to the thickness of the screen coated with photosensitive adhesive. That is, the thickness of the screen printing plate is equal to that of the screen, which has a close relationship with the thickness of the screen printing plate. In general, when the screen printing plate is thick, the ink layer after printing is higher, and if the screen printing plate is thin, the ink layer after printing is lower. Under special circumstances, it is required to use a screen printing plate made of thick film photosensitive material, with a thickness of up to 1mm. For example, the thickness of Braille screen printing plate is generally between 0.1-0.250 mm.
When using the direct plate making method, the thickness of the screen printing plate is obtained by coating the photosensitive adhesive several times. The required thickness of the screen printing plate can be obtained by coating once, drying once and circulating in turn.
When using indirect plate making method or direct plate making method, the thickness of screen printing plate is obtained by selecting photosensitive diaphragm with different thickness according to printing requirements.
49. What factors are related to plate-making accuracy?
When making screen printing plates, the plate-making accuracy is mainly related to the following factors.
① Screen, including the type of screen used, the mesh number, the diameter, the opening area, the expansion ratio, the weaving method and the color of the screen, etc.
② Net frame, including its material, size and strength, etc.
③ the magnitude of tension ④ Selection of tension angle.
⑤ Bonding method of mesh frame and silk screen.
⑥ Pretreatment of silk screen.
⑦ Photosensitive materials, including sensitivity, resolution, adhesion, expansion ratio, thickness, hardness, water resistance, solvent resistance, abrasion resistance and printing resistance.
⑧ The blending time of the sensitizer, and the standing time after blending.
Pet-name ruby coating method of sensitizer.
Attending drying methods and conditions, including drying temperature, humidity and drying time.
11. Printing, including the type of light source used, the length of exposure time, the distance between the substrate and the light source during exposure, etc.
⒓. Density of photographic master.
⒔ Development, including: development methods: water development, warm water development, drug development: development conditions: temperature, soaking time, type and use of sprinkler, etc.
⒕ Drying temperature and time after development.
⒖ Selection of secondary exposure time.
50. What should I do when the screen printing plate is finished?
After the screen printing plate is produced, it is necessary to conduct comprehensive inspection and post-processing. Treatment methods are mainly carried out from the following aspects.
① Check the quality of the screen printing plate, including whether all the pictures and texts are developed, whether there are burrs, defects, broken pens and blocked meshes in the picture and text outlets, etc. If the above conditions are found, various methods should be taken to remedy them in time. If it can’t be remedied, you can consider making a new plate to ensure the printing quality in the future.
② Check whether there are bubbles and sand holes in the mesh membrane and the four edges near the mesh frame are sealed: the bubbles and sand holes should be remedied in time. Seal the four-sided screen to avoid ink leakage during printing.
(3) Check whether the printing positioning mark meets the requirements of printing sheet.
(4) Stick the bonding part between the screen and the frame with adhesive tape to improve the bonding firmness between the screen and the frame. 、 ⑤ Paste the plate label, and paste the plate label on the unified frame position, indicating the following items: print name, color category, color number, screen mesh number, plate line number, photosensitive material model, plate making date and plate maker.
⑥ Transfer the complete set of plates to the printing process. 、 51. How to keep the screen printing plate?
The screen frame with stretched net, the screen printing plate made in the sun and the screen printing plate to be preserved after printing shall be properly kept. If the preservation is not good and the screen is damaged, it cannot be used continuously, resulting in scrapping.
Screen frames or screen printing plates are usually stored by plate racks, which can be stored horizontally or vertically. Horizontal screen printing plates of the same specification are placed in the first layer of the plate frame, which can be overlapped. Erect the screen printing plate in the plate slot on the plate frame. It is best to store the larger screen plate vertically to prevent the screen printing plate from sagging. Finally, it should be mentioned that no matter which form is used to store the printing plate, the dustproof of the screen plate cannot be ignored.
52. What are the main technical requirements of screen printing for plate making?
The main technical requirements of screen printing for plate making are as follows.
① Photosensitive materials should have good photosensitivity and fast photosensitivity.
② Photosensitive materials should have good preservation.
③ Screen printing plates should have good operability and be easy to operate.
④ The screen printing plate has high printing resistance and good abrasion resistance.
⑤ The screen printing plate must keep certain precision.
⑥ The screen printing plate should have high water resistance and solvent resistance.
⑦ Photosensitive materials should have strong film-forming power and high resolution, and do not need special temperature and film liquid development.
53. What are the main technical requirements for scraping?
In screen printing, the moving stencil of ink passes through the screen printing plate under a certain pressure and is transferred to the substrate to form pictures and texts. Therefore, all kinds of indicators of the stencil have an impact on the printing effect. Because the substrate materials are various and have different conditions, they can be roughly divided into two types: plane and curved surface (including spherical surface). Therefore, the following factors should be considered when choosing the stencil according to different substrates and substrate surface shapes.
(1) Scraper hardness The ink transfer amount and the reproducibility of graphics and text are related to the scraper hardness. Generally, when printing on hard printed materials, a soft scraper can be used, so that the layout and printed materials can be fully contacted by the pressure exerted during scraping, so as to improve the printing effect. On the contrary, when printing soft substrate, it is necessary to use hard scraper to make good contact between the layout and the substrate, which is the same. Because there are many kinds of substrates, and the textures of substrates are different, the smoother substrates are generally selected with a harder scraper, otherwise, the printing effect with a softer scraper will be more ideal. When the scraper is applied with a certain pressure, the scraper will bend to a certain extent. Therefore, when using the scraper, the bending fatigue and mechanical strength of the scraper should be considered, and the scraper is required to have certain elasticity. Scraper will generate heat due to friction while scraping, which makes its hardness change when its temperature rises. When choosing scraper materials, it should pay attention to selecting materials that are not easily deformed by heat. Generally, the hardness of scraper materials should be 60 to 90 degrees Shore hardness.
(2) Wear resistance of scrapers Because the scrapers are in direct contact with the screen printing plate, there is friction every time when scraping and printing (in screen printing, the number of prints can reach tens of thousands). Therefore, it is required that the scraper has good wear resistance, lubricity and certain mechanical strength, so that friction can be reduced as much as possible during scraping and printing to ensure the service life of the scraper.
③ Solvent Resistance of Scrapers Scrapers should be exposed to various inks and solvents, such as ethanol and gasoline. All kinds of rubber materials have different affinities to solvents. Scrapers change in varying degrees after contacting with ink or solvent, and the hardness of scrapers often changes, and the volume expands and deforms after contacting with solvent. If the scraper expands, the edge precision of the scraper will be reduced, and the printing quality will be affected by uneven ink leakage during printing. It is generally believed that rubber with high hardness has high crosslinking density, and the molecules of ink and solvent are difficult to immerse in the molecules of rubber, so the expansion coefficient is small. When choosing scrapers, it can be considered to meet the printing requirements as much as possible. In order to minimize the deformation, rubber scrapers with higher hardness can be selected.
53. What are the main materials used for scraper?
Because the scraper comes into contact with various inks and solvents in printing, it requires high wear resistance and certain hardness. In order to meet the requirements of screen printing, the materials used to make scrapers are generally natural rubber and synthetic rubber. Scrapers used in printing and dyeing industry are mostly made of natural rubber, and scrapers made of natural rubber, synthetic rubber and polyurethane rubber are mostly used in manual printing.
54. What are the common specifications of scraper?
Scraper specifications of screen printing generally refer to product specifications sold in the market. In use, the length of scraping board should be determined according to the use requirements. There are two kinds of scrapers sold in the market. One is the scrapers with handles or fixtures installed. This kind of scrapers can be directly used for printing by selecting appropriate lengths according to their use. The other is the scraper rubber strip, which can be used only after the rubber strip is purchased.
56. What is the function of ink scraper?
Screen printing machines, such as novamec s-type screen printing machines, have two scrapers, one scraper is a scraping scraper and the other scraper is an ink feeding scraper. Scratch-printing scraper and ink-feeding scraper move back and forth alternately when the printing machine works. When printing, the scraper squeezes ink for printing. After the return trip, the scraper starts to work and contacts with the screen printing plate to send ink back. The working procedures of the scraper and ink-feeding scraper are as follows: scraping ink from one end (beginning end) to the other end (end) of the screen printing plate. In order to make the screen printing plate, Therefore, the screen printing machine must be equipped with an ink scraper to return the ink in addition to the scraping scraper, so as to scrape back the ink scraped to the end of the screen printing plate. In addition to ink feeding, the scraping plate also plays the role of blocking the mesh of the picture and text with ink, so as to prevent the ink in the mesh from drying and affecting the next printing. Most of the ink feeding scrapers are aluminum products or metal products.
When scraping by hand, only one scraper is used, which is used for printing and ink return.
57. What preparations should be made before printing?
Preparing well before printing is an essential work to ensure the smooth progress of printing. The following basic preparations should be made before printing production.
(1) clean up the printing site, ensure that there is a certain operating space around the printing table or printing machine, and avoid other objects interfering with the work. Keep the site clean to avoid dust and other influences on printing quality.
② Pay attention to adjusting the humidity and temperature of the printing workshop to meet the printing requirements.
(3) Prepare suitable scrapers, and check whether the scrapers are bruised. If there are bruises, grind them to prevent the printing plate from being scratched and affecting the printing quality.
④ Check whether the screen printing plate is in good condition, correct any problems found in time, ensure that the screen printing plate is closed around the graphics and text, and avoid ink leakage in the non-graphics and text parts. Wipe the layout lightly with a damp cloth to remove dust from the layout.
⑤ according to the characteristics of the substrate, adjust the appropriate gap between the screen printing plate and the substrate.
⑥ Check whether the color and viscosity of the ink used meet the requirements.
⑦ Determine the position of the substrate on the printing table according to its size. Fix the rules of printing auxiliary equipment.
⑧ Do a good job in drying machines such as paper drying racks, and adjust the drying temperature in advance. Make preparations for the above inspection, and then start printing.
In addition, according to the actual needs, pay attention to other related preparations.
58. What problems should be paid attention to before printing?
In addition to making preparations before screen printing, attention should also be paid to other related issues. Attention should be paid to the following aspects before printing.
① Clean screen printing in printing places With the continuous improvement of printing accuracy requirements, high-precision printing, especially printed circuit boards and electrical components, also puts forward higher requirements for the environment. Generally, the printing workshop and plate-making workshop must be clean and there is no dust in the air, otherwise the printing quality will be affected. If necessary, air purification equipment should be installed in the workshops with high requirements for printing accuracy to keep the printing and plate-making workshops clean.
② Temperature and Humidity The temperature and humidity change greatly in spring, summer, autumn and winter, which have a great influence on printing accuracy, especially in multi-color overprinting. Therefore, indoor humidity and temperature should be relatively stable, and the indoor temperature and humidity should be adjusted appropriately according to seasonal changes to ensure printing dimensional accuracy.
③ Fully understand the nature of the substrate. Because of the wide application range of screen printing, there are many kinds of printing materials, and the shapes of the substrates are also different. Before printing, we should choose appropriate inks, solvents and scrapers according to different requirements.
59. Screen printing ink usually do what is the test?
Due to the wide application range of screen printing, the requirements for screen printing ink are also strict. Therefore, in order to meet the different requirements of printing products for ink, the screen printing ink should be tested in the following aspects.
(1) Adhesion The adhesion degree of ink on different materials is determined by experiments.
(2) Flexibility Test the adhesion firmness between the ink and the substrate material through the Flexibility Test.
(3) Rubbing resistance Rubbing resistance mainly tests the printing surface of cloth, paper, film and other materials to test the adhesion and firmness of ink to the printing material.
④ After the printed surface of abrasion-resistant cotton cloth is exposed to sunlight, rub the cotton cloth for a certain number of times to check the pollution degree of the cotton cloth.
⑤ weather resistance weather resistance also includes light resistance. Weather resistance is usually to put the printed matter outdoors and carry out tests such as wind, sun, rain, etc. to check the discoloration and fading degree of the pigment of the printed matter and the decomposition and discoloration degree of the printing ink film, etc.
⑥ Heat resistance and cold resistance Because some printed materials should be used at different temperatures. Therefore, some printed materials need to be processed at high temperature after printing, and some printed materials need to be processed at low temperature after printing. Through the experiments of heat resistance and cold resistance, the change degree of ink at different temperatures was tested.
⑦ Hot water resistance test Usually, a certain amount of warm water is added to the printing surface per unit area and stirred for a certain time to check the pollution degree of water. Especially, observe the degree of pigment dissolved in water to determine whether the ink is suitable for printing edible utensils and toys.
⑧ Oil resistance Oil resistance refers to the adaptability to grease and machine oil, which is different from solvent resistance.
60. What are the characteristics of color screen printing?
Compared with gravure printing and offset printing, color screen printing has the following characteristics besides the characteristics of screen printing itself.
(1) has the expressive force of wanting very much, bright colors and strong stereoscopic impression.
② It has strong light resistance, drug resistance and durability, and can be used for a long time without fading, especially for screen printing on plastic substrates.
③ The cost is relatively low.
In addition to the above advantages, color screen printing is also not ideal, that is, when making plate by color screen printing, it is difficult to make plate because of factors such as matching of screen mesh and screen mesh, screening angle and so on.
61. How is the color sequence of color screen printing arranged?
The color sequence of color screen printing is generally yellow, cyan, magenta and black. Considering the process requirements, some color sequences are arranged as cyan, magenta, yellow and black. Foreign countries also use black, yellow, magenta and cyan as the printing color sequence. Because of the different shapes of substrates (plane and curved surface) and different properties of substrate materials in screen printing, the color sequence should be black, yellow, cyan and magenta. The arrangement of color sequence has an important restriction on reflecting the original color. How to ensure that the color of the copy is not distorted, besides mastering the use of ink, it also needs long-term work practice and accumulated experience to constantly explore and summarize. There are two factors to be considered in determining the color sequence of screen printing, one of which is the transparency of printing ink on the substrate, which is the main factor of the two factors. Because in screen printing, new color inks are produced by mixing or superimposing inks of different colors, if the transparency of printing ink on the substrate is poor, the first color ink will be covered when printing the second color, but it cannot be combined with the second color to produce a new color. The second factor is that people’s eyes have different abilities to feel various colors. Generally speaking, human eyes are most sensitive to magenta, followed by cyan and least sensitive to yellow. Because people have different sensitivity to color, it often leads to the enlargement or reduction of yellow dot, the loss and the change of ink quantity are indistinguishable, thus affecting the printing quality.
The correct degree and requirements of screen printing process are as follows: firstly, printing with cyan, and then contrast check of tone reproduction with ladder scale and color scale. The second color is printed with yellow plate, so that the two colors are overlapped into green, and then the printing quality is checked against the ladder scale and color code by using the characteristic that people’s eyes have strong ability to recognize the green tone. The third color products are printed in red, and finally in black. The black version enhances the outline and dark tone level. After printing the four-color plate, you get the same color copy as the original.
62. What problems should be paid attention to in color screen printing?
Several problems should be paid attention to in color screen printing, which are described as follows.
(1) in the color screen printing to use strong, no deformation of the metal frame. This is because if a weak screen frame or a wooden frame is used for plate making, skew or deformation will easily occur in printing, and the quality of the screen printing plate will be reduced, and the accuracy is difficult to guarantee. When the deformation is serious, the screen printing plate cannot be used. Thereby affecting the printing quality. Therefore, a strong metal mesh frame must be used. The frame size of a set of color screen printing plates should be the same. The main purpose is to use uniform positioning rules when printing, and to facilitate overprinting. The mesh number and material of a set of color screen printing plates should be the same, and the tension of tension and thickness of screen printing plates should be consistent. The main purpose is to ensure the uniform ink layer and the same effect after printing with various printing plates, and perfectly reproduce the original color and graphics.
② The hardness of the scraper used is generally 70 Shore hardness. Scraper cutting edge precision should be high. Due to the moderate hardness, it is beneficial to meet the printing requirements, improve the printing accuracy and ensure the printing quality.
③ Screen printing ink with high viscosity should be used as much as possible. The ink with higher viscosity will not cause the problem that the picture and text lines become thicker and bigger due to oil leakage and diffusion, which is beneficial to improve the fineness and clarity of the picture and text lines.
④ The number of screen lines (lines/inch) in photographic screen making is generally between 55 and 120 lines. This can reduce or avoid the occurrence of moire.
Generally, the proportional relationship between the number of screening lines and the number of screen meshes is: screen mesh: 4.2× the number of screening lines.
63. Why should there be a certain gap between the screen printing plate and the substrate?
It is determined by the characteristics of screen printing that a certain gap should be kept between screen printing plate and printed matter. Screen printing plate is based on screen, which is stretched on the frame. When the screen is in a horizontal state, it will have a certain sag. Especially in the process of scratch printing, the sag value will increase. In order to ensure the printing quality, the lowest part of the screen printing plate must leave the substrate. In screen printing, the scraper and the screen printing plate are in movable line contact, and the screen printing plate and scraper cannot contact with the substrate before and after scraping, especially the screen printing plate leaves the substrate with the scraper moving. If the screen printing plate never leaves the graphic part before printing, the ink will continue to permeate and diffuse, resulting in the expansion of graphic and text lines, which will reduce the printing dimensional accuracy and distort the substrate.
There must be a certain gap between the screen printing plate and the substrate, which is also closely related to the movement form of the substrate. When the substrate is printed, especially when the curved surface of the formed object (such as container, etc.) is printed, the substrate must move in a circle at the same time. There is a certain gap, which will not cause blurring or line deformation of the substrate.
64. How to determine the gap between the screen printing plate and the substrate?
It has been mentioned above why there must be a certain purchase gap between the screen printing plate and the substrate when printing, but the size of the gap can not be arbitrary. If the gap between the screen printing plate and the substrate is too small, it is easy to cause infiltration and plate sticking along the moving direction of the scraper. If the gap is too large, the screen printing plate will not recover after stamping, and it will relax and sag, making the printed screen size smaller than that of the screen printing plate. Serious will also make the screen printing plate damaged and unable to print. If the stainless steel screen with small elasticity is used, the layout will not contact the surface of the substrate, so that printing cannot be carried out. .
The main basis for determining the gap between screen printing and substrate is:
① Size of screen printing plate.
(2) the size of the tension.
③ Center sag of screen printing plate.
④ the shape of the substrate.
⑤ The nature of the substrate.
⑥ Surface morphology of substrate.
⑦ Ink viscosity, etc.
The gap between screen printing plate and substrate has different values due to different printing conditions. Generally, objects with hard substrate surface, such as ceramics, glass, metal surface and hard plastic, which have low ink absorption, have higher requirements for printing gap value. However, the requirements of printing gap value for objects with soft surface, such as cloth, paper and soft plastics, which have strong ink absorption, are not so strict. Usually, the gap value between 1-3 mm is required when printing printed products with high precision. The gap can be 2-6 mm for ordinary printed matter. The gap value is smaller in curved printing, while the gap value is larger in flat printing.
65. What is the reason for the screen printing plate to seal the screen? How to solve it?
In screen printing, screen sealing is also an important aspect that affects printing quality. There are many reasons for the screen printing plate to seal the screen in the printing process. The main reasons are as follows: ① The particles in printing ink are larger. (2) The ink will become conjunctival after drying on the screen printing plate. (3) Excessive viscosity of ink affects printing omission (4) Poor fluidity of ink at lower temperature.
The above four reasons can lead to the occurrence of net closure. Problems encountered in daily production should be analyzed in detail and the correct way should be chosen to solve them. Now several solutions are introduced as follows, which can be used for reference.
First of all, from the ink manufacturing and use methods to talk about the solution to seal the net. To seal the net caused by larger ink particles, we can start to solve the problem when making ink. The main method is to strictly control the ink granularity. From the perspective of modern ink manufacturing technology, it is not difficult to solve the problem of larger ink particles.
In the printing process, the viscosity of ink increases due to solvent volatilization, and instantaneous drying is formed at the mesh to block the mesh (conjunctiva after drying), resulting in net closure. Especially, this phenomenon is more prominent when using evaporative drying ink. Evaporative drying ink is dried by using solvent, so it is necessary to select appropriate solvent to control the drying speed during printing, and pay attention to ventilation, temperature and humidity in production workshop. The influence of climate should be considered when choosing ink. Generally, quick-drying ink is used in winter, late-drying ink is used in summer, and ink with dryness between the above two is used in spring and autumn. Another point is that a late drying agent can be used in fine line printing. If the screen is blocked when using the late drying agent, it is necessary to switch to other types of inks. Using oxidation drying ink, the net sealing phenomenon does not occur very much, but if excessive use of desiccant occurs in summer, the net sealing phenomenon will also occur, and it is generally necessary to control the use of desiccant in summer.
When using two-liquid reactive ink, due to the slow drying speed of the ink itself, the net sealing phenomenon hardly occurs, but occasionally the net sealing phenomenon occurs because the viscosity of the ink increases after the solvent evaporates, resulting in net sealing. In this case, an appropriate amount of late drying agent can be added to the ink for dilution to prevent the net sealing phenomenon.
In the printing process, the viscosity of ink increases, resulting in net sealing. The main reason is that the ink on the screen printing plate evaporates due to solvent, which leads to the increase of ink viscosity, resulting in net sealing. If the area of printed graphics and text is relatively large, the ink consumption on the dead screen printing plate will be more, and the screen sealing phenomenon will be less. If the graphic area is small, the ink consumption on the screen printing plate is small, and the ink has a long round trip time on the screen printing plate. With the ink moving on the screen printing plate for many times, the viscosity increases gradually, which is easy to cause screen sealing. In this case, it is necessary to switch to new ink frequently, which can prevent the occurrence of net sealing.
The poor fluidity of ink will make the ink seal when it does not pass through the screen. This situation can be solved by reducing ink viscosity and improving ink fluidity.
In addition, the mesh number and opening area of the selected screen are smaller than the granularity of the ink, which makes it difficult for the ink with more particles to pass through the mesh, and the screen sealing phenomenon is also one of the reasons.
66. What are the reasons and prevention measures for the smudging of screen printed products?
After printing, screen printing products sometimes get dirty, which is mainly caused by insufficient drying of ink. Usually, when printing with oxidation-drying ink, there are many smudging phenomena. This is because the ink layer of screen printing is thick, while the surface drying speed of oxidation-drying ink is fast and the internal drying is slow. When printed matter comes into contact with printed matter or printed matter comes into contact with other objects, smudging will occur. Generally, adding cobalt desiccant or lead desiccant to the ink can improve the drying speed of the ink and play a role in preventing smudging. In addition, when the printed matter is stacked, it should not be overlapped and stacked too much (because of the excessive backlog of printed matter, it is easy to get dirty), and the printed matter must be fully dried before stacking. Using evaporative drying ink can reduce the dirt rubbing phenomenon. It is also an important measure to avoid smudging by strictly observing the technological requirements and operating in strict accordance with the technological operation rules during printing.
67. Why do bubbles appear on the surface of finished ink? How to avoid it?
Bubbles sometimes appear on the ink after printing, and the main reasons for the bubbles are as follows.
① Dust and oil stains are attached to the substrate surface.
② The ink itself has bubbles or uneven viscosity during printing.
③ The printing speed is too fast or uneven.
The internal factors of bubble generation are: due to the high viscosity and high surface tension of the ink, the gasoline in the ink is difficult to escape from the ink film and stay in the ink layer. If the ink viscosity is low and the ink surface tension is small, the bubbles will disappear by themselves, so there will be no bubble in the ink of printed matter.
Generally, the following measures can be taken to prevent the ink layer from generating bubbles.
(1) try to use hydrophobic solvent.
② When bubbles are generated in the ink itself, a proper amount of defoamer can be added to the ink. If the ink flow is poor, when the screen printing plate is lifted, the ink flow is relatively small, and the screen trace can not be filled up, so that a smooth and flat grinding layer can not be obtained.
To prevent screen marks after printing, the following methods can be adopted.
(1) printing with ink with higher fluidity.
② It may be considered to use ink with slow drying speed for printing, and increase the flow time of ink to make the ink gradually solidify.
③ When making plate, try to use single diameter screen with smaller diameter.
68. Why is the surface of finished ink layer cracked? How to prevent it?
The main reason for the cracking of the ink layer on the surface of the substrate after screen printing is caused by the action of solvent and the great change of temperature. Generally, weak solvents such as alcohol and petroleum-based solvents will also crack in styrene products. Some substrate materials will also cause cracks due to their own factors. In order to prevent cracking, the properties of ink and solvent resistance of substrate should be considered when choosing solvent. Materials with strong solvent resistance and oil resistance can be selected as the printing material. Pay attention to keep the workshop temperature balanced. In multi-color overprinting, each color should be fully dried after printing, and the drying temperature should be strictly controlled. Generally speaking, paying attention to the above aspects can effectively control the cracking phenomenon of the wear layer.
69. After printing, the printing plate can be treated as follows according to the actual situation.
(1) after the first printing, if the screen printing plate needs to be printed for the second time, the residual ink on the screen printing plate must be cleaned to ensure that the mesh of the graphic and text parts is not blocked by the ink, and then properly stored after being fully dried. For next use.
② If the screen is no longer used after printing, and the screen is intended to be scrapped, the ink around the screen frame can be cleaned and the screen can be removed, or the screen can be directly removed first, and then the screen frame can be cleaned and used for the next screen stretching.
③ After screen printing, under the condition of preparing for secondary plate making, the residual ink can be cleaned first, then the photosensitive film on the screen plate can be removed with a release agent, cleaned with clear water, dried and stored for the next plate making.
70. When printing plates are reused, what are the reasons and methods of stripping treatment?
Stripping means that after the screen printing plate is printed, the plate is no longer used, and it is planned to make a new plate. In order to reduce the waste of the screen and reduce the cost, the cured photosensitive material on the screen printing plate can be peeled off from the screen and used again after cleaning and drying. The process of peeling off the screen printing plate with photosensitive material is called stripping.
Generally, the release agent is used. The main components of the release agent are bleaching powder, hypochlorite, hydrogen dioxide, caustic alkali, ammonia water, potassium permanganate, oxalic acid, etc.
The stripping process is as follows: when stripping, clean the ink on the screen printing plate first, then wipe both sides of the screen printing plate with a stripping agent or soak in the stripping agent. After soaking for about 5-10 minutes, the plate film turns white, which can be washed with water (or scrubbed with sponge). After removing the plate film, the screen can be washed with water and dried, and then it can be used for coating plate making again.
71. How are screen printing inks classified?
There are many kinds of screen printing inks, and their classification methods are also various. But the main classification methods are as follows.
(1) According to the characteristics of ink, it can be classified into fluorescent ink, bright ink, fast fixing ink, magnetic ink, conductive ink, fragrance ink, ultraviolet drying ink, sublimation ink, transfer printing ink, etc.
② Classification according to the state of ink A. colloidal ink: water-based ink, oily ink, resin ink, resin ink, starch paste, etc.
B solid ink: toner for electrostatic screen printing.
③ Classification according to printability A. paper inks: oily inks, water-based inks, high-gloss inks, semi-gloss inks, evaporation-drying inks, natural drying inks, coated paper inks, plastic synthetic paper inks, and paperboard carton inks.
B. Ink for fabrics: water-based ink, oil-based ink, emulsion ink, etc.
C. wood ink: water-based ink and oil-based ink.
D metal inks: special inks for different metals such as aluminum, iron, copper, stainless steel, etc., including evaporation drying type, oxidation polymerization type and two-liquid reaction type inks, etc.
E. ink for leather.
F. Ink for glass: ink for glass instruments and glass crafts.
G. printing ink for plastics; PVC ink, styrene ink, polyethylene ink and propylene ink; Ink for polypropylene, acetic acid, celluloid and poly-brewed resin.
H printing inks for printed circuit boards: conductive inks, corrosion-resistant inks, electroplating-resistant, fluorine-resistant and alkali-resistant inks.
1. Ink for ceramic glassware.
④ Classification according to ink drying form A. volatile dry ink (including water-based ink).
B. oxidative polymerization ink.
C. two-liquid reactive ink.
And d, heating the curing ink.
E. ultraviolet curing ink.
F. electron beam radiation drying ink.
72. What are the components of screen printing ink?
Screen printing ink is composed of colorant, binder, filler and adjuvant. These compositions are blended and ground into ink.
All the materials mentioned above are composed of various substances and have different types, which are introduced as follows:
(1) coloring A. pigments, which are divided into various organic pigments, natural inorganic pigments and artificial inorganic pigments.
B dyes, which are divided into water-soluble dyes, solvents and oil dyes.
② connecting materials A. natural resins, including rosin, shellac, rubber, gum Arabic, etc.
B. Synthetic resins, including rosin modified series, phenolic modified series, synthetic rubber, polyamide, etc., and solid resins such as petroleum system and epoxy system; Alkyd, epoxy, acrylic liquid resin.
C. vegetable oil, including tung oil, stillingia oil, linseed oil, etc.
D solvents, including alcohol series, fat series, fat series, petroleum series solvents, etc.
③ filler A. natural filler, including terrazzo powder.
B. Artificial fillers, including barium sulfate, calcium carbonate, colloidal calcium, magnesium carbonate, etc.
④ adjuvant Adjuvants include drier, drier, plasticizer, defoamer, emulsifier, stabilizer, anti-settling agent, curing agent and leveling agent.
73. What is a two-liquid reactive ink? What are its characteristics?
Ink with mixed resin and curing agent in printing is called two-liquid reactive ink. This kind of ink mostly uses epoxy resin, and the curing agent uses more ammonia. The advantages are: very small solvent components, good adhesion to various materials, hard and tough ink film, strong oil resistance, solvent resistance, heat resistance, etc. Disadvantages: since the two solutions start to react after mixing, the viscosity of the ink gradually increases during printing, and the mixed ink cannot be preserved.
74. What is a heat-curable ink? What are its characteristics?
The resin and curing agent are mixed in advance, and then heated to react with the resin after printing to form an ink film. This kind of ink is called heating curing ink. The resin of this kind of ink is a single-liquid epoxy resin, which has almost no difference in film characteristics with two-liquid ink, but its film flexibility is quite different. Because the ink hardly reacts at room temperature, it is easier to print than two-liquid ink. However, it is difficult to keep the ink for a long time because it must be barbecued at a high temperature above 150℃.
75. What is UV curable ink? What are its characteristics?
In the drying process, the resin is polymerized by ultraviolet radiation to form an ink film, which is called ultraviolet curable ink (i.e., UV ink). Ultraviolet ink is composed of pigment, prepolymer, crosslinking agent, photoinitiator, assistant, etc. This kind of ink mainly uses photopolymerizable photosensitive resin of modified acrylic prepolymer, and mixes photosensitive monomer, photopolymerization initiator, pigment and assistant together to make the photosensitive resin form ink skin and film according to photopolymerization principle. Advantages: UV ink does not use any solvent, does not generate solvent volatilization in the printing process, is beneficial to environmental protection and personal health of workers, has good stability in the printing process, fast drying speed, saves heat energy, has glossy film, has better reproducibility of color density than ordinary ink, and has excellent wear resistance, water resistance, oil resistance and solvent resistance, etc. Ultraviolet ink has a high flash point (above 100℃), which is not suitable for burning and is safe to use. Disadvantages: the part not illuminated by ultraviolet rays is not cured, the black part absorbing light and the self-part reflecting light are cured slowly, not all kinds of materials can be bonded, and the ink cost is high.
76. What are the characteristics of water-based ink?
Ink with water as solvent is called water-based ink. This kind of ink uses the evaporation of water in the ink in the drying process to solidify the dissolved auxiliary resin and form a film. This kind of ink is also called water-based ink. Water-based ink is prepared by blending water-based resin, pigment, auxiliary agent and water-based system additive. The advantages of water-based ink are: because most of the solvent is water, less pollution is beneficial to environmental protection, and the ink has good passability and reproducibility to screen. Its disadvantages are: poor ink gloss, low precision and poor adhesion, so it is necessary to use a watermark-resistant version. When printing paper, it is easy to cause the paper to turn over and bend, which affects the overprint quality. In addition, the evaporation rate of water in ink is slow, so the drying time is longer.
77. What is the foaming ink made of? What are its characteristics?
Foaming ink is prepared by blending water-based resin, water solvent with water as main body, microsphere foam and other additives. Because the foaming ink uses water-based binder, it is easy to use and pollution-free, and the ink has good permeability and reproducibility to silk screen. The ink layer has good solvent resistance, drug resistance, wear resistance and no deformation under heavy load.
Emulsions used in foaming inks are generally cross-linked synthetic resin emulsions, cross-linked propylene emulsions, cross-linked reactive propylene emulsions or bad oxygen emulsions and urethane emulsions.
The microsphere foam in foaming ink is a thermoplastic polymer particle, which is hollow, and is generally polymerized by polyvinylidene chloride and acrylonitrile, or methyl acrylate and acrylonitrile. The hollow part contains volatile expanding agent, which is mostly carbon compounds such as ethane, propane and butane. The diameter of microspheres is generally between 5 and 150 microns. The content of microsphere foam in ink is generally 5-50%, and the content of microsphere foam is low and the foaming effect is not good. If the content is too high, the fluidity of ink will decrease and the ink layer will be uneven.
The ink uses various dyes, pigments and colorants to adjust the ink to obtain the desired color.
Other auxiliaries used in ink include stabilizers, tackifiers, defoamers, oxidation inhibitors, ultraviolet absorbers, etc. The formula for making foaming ink is introduced as follows.
Cross-linked epoxy emulsion 50% Epoxy ethylene glycol 8% 25% of microsphere foam 0.2% defoamer 1.8% of water dispersible pigment Crosslinking agent 10% Water 5% 78. What is fluorescent ink? What should we pay attention to in use?
Fluorescent ink for screen printing is an ink made of fluorescent pigment as coloring material. Fluorescent pigment is prepared from fluorescent dye and synthetic resin. The ink particle size is between 5 and 15 particles.
Fluorescent ink for screen printing is suitable for printing paper and vinyl film. There are two kinds of paper fluorescent inks: oxidation drying type and evaporation drying type. Fluorescent ink for ethylene film is evaporative drying type.
Pay attention to the following points when using fluorescent ink.
① Fluorescent ink is not suitable for long-term outdoor use because of its poor light resistance. Therefore, fluorescent ink should not be used for screen printing products used outdoors.
② Fluorescent ink is suitable for screens below 200 meshes.
③ After printing, the amount of ink is 50-60g/m2, and its color development and light resistance are ideal.
④ When the substrate is transparent, white ink should be printed once before printing fluorescent ink, which can improve the fluorescent effect. Generally, fluorescent ink is easily confused with luminous ink, which can be distinguished by comparing the characteristics of the two inks.
79. What are the drying methods of ink?
Drying methods of ink can be divided into natural drying, heating drying, ultraviolet drying, electron beam irradiation drying, infrared drying, microwave drying and other forms.
In addition to the above drying methods, it can be divided into physical drying and chemical drying according to the different ink resins contained in the ink. Secondly, according to the different properties of ink, it can be divided into osmotic drying, oxidative conjunctival drying and volatile drying.
The drying forms of inks with special properties include photopolymerization drying and ultraviolet drying. Most inks usually only use one drying method, but some inks are mainly dried in a certain drying form, and at the same time, they are dried together with other auxiliary drying forms. The drying type of ink is shown on the previous page.
Generally, volatile drying ink, water-based ink, oxidative polymerization ink and two-liquid reaction ink are dried by natural drying, cold and hot air drying or infrared radiation drying. Heating curing ink is dried by infrared radiation. Ultraviolet curing ink is dried by ultraviolet irradiation.
In actual printing production, which drying method should be adopted should be selected according to the actual conditions of ink used, drying equipment and site.
80. What are the drying methods of glass after printing?
The drying method of glass products after printing is different from other substrates, and there are two methods, namely natural drying and forced drying.
Natural drying is to put printed glass products in a proper place and let them dry naturally. Due to the difference of air temperature and air circulation, the drying speed is different. Sometimes, in order to speed up the drying speed, it can also be dried by cold air and hot air. Glass products should be fully dried after printing before firing. When firing, the temperature should not exceed 120℃. And the firing temperature should be gradually increased from low to high. This must be paid attention to.
Forced drying is often used when printing large quantities of multicolor glass products. The most commonly used is electric heating drying. In multi-color printing, one color should be dried once for each printing, and firing can only be carried out after four-color printing, and the firing temperature should not exceed 120℃.
81. In screen printing plate making, which kind of lamp source is ideal?
Ultraviolet electro luminescent is an ideal light source. If there is a strong ultraviolet electro luminescent, the effect is better. In China, there are mainly five kinds of 20W/A, 30W/A, 40W/A, 80W/A and 80W/ a, followed by high-pressure mercury lamps and high-pressure office lamps, which are not ordinary small solar lamps but special lamps for plate making.
When making plate with these two lamps, pay attention to the temperature of the glass surface in the high temperature season, and if necessary, add a fan for cooling to prevent overheating and crosslinking of the photosensitive adhesive.
And it can’t be started continuously, that is, after the lights are turned off, it can be started again at least 5 minutes later.
82. How long does it take to print with UV electro luminescent exposure? What are the high-pressure mercury lamps and high-pressure pickaxe lamps?
The printing time of ultraviolet electro luminescent is generally controlled between 3-6 minutes (referring to 1000 W mercury lamp or dysprosium lamp), with thick glue layer, longer time, thinner glue layer, shorter time, longer winter and shorter summer. For high-pressure mercury lamp and high-pressure dysprosium lamp, the grid voltage is high, the light is strong, and the printing time can be shorter, and vice versa The exact time can be calculated 83. What are the advantages of outside electro luminescent?
Ultraviolet electro luminescent, which adopts electric ballast, is not affected by the power grid voltage, and can be started with only 130 volts. The range of light it emits is exactly what photosensitive materials need. This kind of lamp can run continuously and start continuously, and has low calorific value and less one-time investment. It is the most ideal light source for screen printing.
84. The distance between several main printing lamps.
Ultraviolet electro luminescent. Generally, the distance between lamp tube and glass should be controlled between 7-10CM, and the distance between lamp 1 and glass should be controlled between 50-70CM for high-pressure mercury lamp and high-pressure dysprosium lamp. The design height of lamp distance should consider the relationship between lamp distance and light intensity, the uniformity of lamp distance and light, and the calorific value of lamp.
85. Why can’t you use fluorescent lamps for printing?
Ordinary fluorescent lamp is the least ideal light source, because the light between 3800A-4300A is very weak, which is only about one twentieth of ultraviolet luminescence. It takes a long time to print, has poor photo-crosslinking effect, low grid voltage and weaker light intensity, which can only make a small part of photosensitive adhesive produce chemical reaction, and the adhesive film will automatically fall off when developing, which will also cause a large number of transparent residual adhesive, and most or part of the ink will not leak during printing 86. What should I pay attention to when using electric ballast?
The biggest feature of electric ballast is its low starting voltage, which can be started at 130 volts, and the power grid voltage is generally around 200 volts, so there is no obvious difference between strong and weak light. The emitted light is stable, and there is almost no flash.
The disadvantage is that electric ballast is afraid of heat and humidity. When installing electric ballast, consider ventilation and place it in a dry place. Do not run continuously for a long time in high temperature weather.
87. How long is the service life of UV electro luminescent?
Generally speaking, the service life of ultraviolet cold light tubes is 1000 hours, and the accumulated working time exceeds 1000 hours or approaches 1000 hours, so the tubes should be replaced. Usually, when the accumulated working time reaches about 750 hours, new tubes should be replaced to ensure the printing quality. (depending on the light source, it needs to be replaced if it turns white) 88. How to use the exposure slide rule?
Exposure slide rule is a way to choose the best exposure time by comparing five exposure effects at one time. It consists of five sets of definition standard plates and numbers.
There is no color filter behind the first group, and the exposure factor is 1. There is a neutral gray filter behind the other four groups, with coefficients of 0.7, 0.5, 0.33 and 0.25 respectively. At the same time, five kinds of exposure time can be compared.
If the best time at that time is measured on a printing machine, and the exposure slide rule is printed for a certain time, such as 4 minutes, which group has the best effect, if 0.7 is the best group, it is best to multiply it by 0.7 and equal to 2.8 minutes, that is, the actual exposure time is multiplied by the best coefficient to get the best printing time.
89. What’s the harm of the screen being stretched too tightly?
The tension is too high, it is laborious to scrape the ink, and it is easy to tear the screen. (master the correct tension) 90. What’s the harm of the silk screen being stretched too loosely?
The tension is too small, and the resilience in printing is too small, which can not achieve the rebound effect, and it is easy to rub dots and thin lines.
91. How to measure tension?
For small screen frames, only one point needs to be measured in the center of the screen, and for medium screen, it is best to measure five points, and for large screen, measure six points.
92. Which angle is the most effective and the worst?
The screen is at 5-10 degrees with the frame edge, and the plate-making effect is the worst.
93. Which kind of tension angle saves the wire mesh most?
90-degree screen stretching is the most economical, so it is not necessary to use 45-degree and 22.5-degree screen stretching for products with low screen printing accuracy.
94. How to dissolve the stripping powder?
The dissolving speed of demoulding powder in water is very slow, so it can’t be dissolved once. The correct dissolving method should be to dissolve some water for many times, and then pour it out after adding fresh water to stir and dissolve, so that it can be dissolved completely after 4-5 times.
95. Dissolve the demoulding powder. Do you have any helpless solvent to speed up the dissolution?
When dissolving the demoulding powder, a small amount of acid can be added, and 1-2ML per kilogram of water can effectively accelerate the dissolution speed.
96. Is photosensitive latex poisoned? Where’s the photosensitive powder?
Latex is a basically non-toxic colloid, and photosensitive powder is also non-toxic, but it cannot be imported.
97. Is it better to coat photoresist quickly or slowly?
The speed of coating photosensitive adhesive should not be too slow, and the adhesive solution is easy to penetrate into the ink surface, and it is easy to cause uneven coating. If the speed is too fast, pinhole is easy to occur. The photosensitive adhesive should be coated at an appropriate coating speed. Generally, medium uniform coating is adopted.
98. Can you brush the photoresist with a brush?
Brush can’t be used to brush photosensitive adhesive. First, the coating is uneven. Second, the surface of the adhesive layer is uneven. It can only be coated with hard, preferably stainless steel gluer.
99. How to coat the screen below 100 mesh?
Coating coarse mesh screen, such as 30 mesh and 50 mesh screen, often has many pinholes. To make up for the fact that coarse mesh screen is difficult to coat, first, the photosensitive adhesive should be thicker. The printing surface should be scraped back and forth several times to fully wet the screen, and then the ink surface should be scraped flat. After drying, the printing surface should be continuously scraped for 2-3 times at a slightly faster speed.
100. How many lines can be screened in screen printing?
Generally, it can reach 80 lines, up to 100 lines. From the perspective of printing clarity, 80 lines and 65 lines have better visual effect, high number of lines, and easy to paste.
101. How to control the screen stretching angle when making screen printing stencil?
If making red, blue, yellow, black and four-color screen printing plates, the screen stretching angles can be 0 degrees, 4 degrees, 0 degrees and 12 degrees.
102. Screen printing, how to prevent the generation of tortoise shells?
First of all, we should choose to weave evenly with silk screens. Some silk screens with uneven measurement cannot be used for screening and plate making. In addition, the screen is stretched at an angle to make plate making, which generally does not produce tortoise shells.
103. What is the corresponding mesh number after the screening line number is decided?
Generally, the mesh number of silk screen is more than 3.5 times, not more than 6 times. If the number of threads is 80, the minimum number of threads is 80*3.5=280 meshes.
The line thickness of the same photo negative is too different. How to choose the printing time?
Under the condition of great disparity in thread thickness, the printing time should be mainly selected with thin thread.
105. When the screen printing ink surface is sticky and has paste-like substances, how is it produced? How to overcome it?
The sticky substance is uncrosslinked adhesive film, which dissolves in water and becomes sticky. The adhesive layer on the ink surface should not be coated too much, and the printing time should be extended appropriately.
106. What is the reason why the adhesive layer on the printing surface falls off when developing?
Let’s talk about film paper first. If it is exposed and falls off on polyester silk net, it may be that the screen is not well grinded, that is, the screen coarsening treatment is not good enough, and the adhesion fastness is poor and it falls off. Another possibility is that the printing time is too short, and the film will fall off after swelling. One is to increase the screen grinding time, and the other is to increase the printing time. If the photoresist film falls off when developing, it may be caused by short printing time, so long as the printing time is increased, the problem of stripping can be solved.
107. When visualization, rub the rubber surface with your finger on the adhesive film machine several times and cause pinholes. What is the reason?
Similar to this situation, it is caused by insufficient printing time (under other conditions unchanged).
108. When displaying, the central image of the screen is very good, and the glue film is very firm, but what is the reason that the glue film is easy to fall off at the edge of the image?
This shows that the printing time is moderate, and the edge is partially peeled off. There are three possibilities: first, the light at the edge is weak, and the printing plate is insufficient; second, the glue at the edge is too thick; third, it is not dried locally. Generally, the distribution of printing lamps is larger than the film surface of the screen printing plate. So that the whole screen printing plate can be evenly exposed to light.
109. Can the prepared screen be heated and cured or printed twice (solvent-resistant photosensitive adhesive), and does it have any effect on stripping?
Screen printing plate made of solvent-resistant photosensitive adhesive generally adopts secondary printing plate instead of heating curing. Otherwise, it is difficult to release the film.
110. Why is it difficult to strip the edges of image lines?
Around the image, the adhesive layer is often too thin, resulting in excessive printing, and it is difficult to release the film. The edge of the line often comes into contact with the ink, and the ink on the edge cannot be cleaned every time the printing is completed. Some components in the ink will cause chronic hardening of the adhesive film, and the longer the time, the more difficult it will be to release the film. Therefore, the ink must be thoroughly cleaned with an opening agent (ink cleaner) every time the printing is completed.
111. After degumming, few parts can’t be removed. How should they be removed?
If there is a small amount of residual film that cannot be removed, it can be wiped with dimethyl amide. Be careful not to rinse with water after drying. It can only be dried and wiped clean with a dry towel and cotton yarn.
112. Why is the yellow screen better than the white screen?
Yellow screen printing has poor reflection, strong absorption of light energy and sufficient photo-crosslinking, while white screen printing has strong reflection and relatively poor photo-crosslinking, so it is difficult to release the film.
113. How did the turtle shadow on the online version come into being and how was it removed?
Turtle shadow is mainly formed by dyeing the colorant in the glue layer and the color in the ink on the screen. It can be soaked with turtle shadow cleaner for about 10 minutes, and then washed with tap water.
114. Does turtle shadow have any influence on secondary plate making?
Strictly speaking, it should have an impact, which makes it difficult to locate the printing plate, and the line of sight is blurred, so it needs to be cleaned and reproduced.
115. Can the screen be coated with photoresist and film paper without drying?
The wet screen printing plate can’t be coated with sensitive adhesive immediately, and can’t be sensitized immediately. The reason is that there is water on the wet screen surface. When coating sensitive adhesive, latex and floating water on the surface can’t be well dissolved and uniform, which will cause serious uneven coating, and even can’t be coated. When sensitizing the film, the floating water on the surface will reduce the sensitization effect, so it must be coated or pasted after drying.
116. Can photosensitive powder be poured into latex and stirred again after a while?
When the photosensitive powder is poured into latex, it should be stirred evenly immediately. Otherwise, the photosensitive Lou accumulated on the surface of latex will absorb moisture, solidify and agglomerate, and can’t stir evenly when stirring.
117. Can the diazo sensitive adhesive just stirred be coated immediately?
The newly prepared photosensitive adhesive cannot be coated immediately, because bubbles are generated during the stirring process, so it is best to wait two hours before coating after the bubbles disappear.
118. When coating photosensitive adhesive, from the second coating after drying, only the printing surface is coated, not the ink surface!
119. How to use photosensitive powder correctly when preparing glue?
When preparing glue, it is best to use a small amount of distilled water, about 50 ml, to dissolve the photosensitive powder into solution, and then add it into the emulsion, so that it is easy to mix evenly, and the photosensitive powder will not coagulate and agglomerate due to uneven stirring.
120. Why is a yellow mark scratched on the silk screen?
When coating photosensitive adhesive, it is only applied on the printing surface, but not on the ink surface, and the yellow or yellow-green marks are scraped on the screen plate, which are caused by the incomplete mixing and dissolution of photosensitive powder. In fact, it is the photosensitive powder that absorbs moisture and condenses into a group. It should be stirred for a while to make the photosensitive powder dissolve completely.
121. Photosensitive powder and dichromate can be dissolved in hot water?
Photosensitive powder can’t be dissolved in hot water, but should be dissolved in cold water. The temperature is high, which makes the photosensitive material change easily.
122. Does the screen printing of unwashed ink have any effect on stripping?
The ink was not cleaned, and the film surface was hydrophobic.
123. whether the stripping solution can be applied on the wet adhesive film will have an impact?
Generally, it should be painted on the film without floating water. Otherwise, it will reduce the solubility of the stripping solution and the stripping effect.
124. How to eliminate electrostatic fault?
Electrostatic current is generally very small, but the potential difference is very large, and phenomena such as attraction, repulsion, conduction and discharge may occur. These phenomena will lead to product deterioration, performance decline, flame, electrification and other adverse consequences.
(1) adverse effects on screen printing. When printing the silk screen, the rubber part and the silk screen are charged due to the pressurization of the scraping rubber. The screen itself is charged, which will affect the normal inking, resulting in blocking fault: it will be sucked by the screen at the moment when the substrate is output.
A. synthetic resin inks are easily charged.
B. Even if the substrate is as absorbent as paper, static electricity will be generated when the air is dry. Plastic substrates have good insulation, are not affected by temperature, and are easy to generate static electricity.
C. the printing area is large, and the electrification is large, which is easy to produce adverse effects.
D because spark discharge can cause flame, be very careful when using flammable solvents.
E. electric shock caused by static electricity is caused by contact with charged objects or spark discharge when static electricity is grounded before accumulation. Although the current generated by electric shock is very small and will not cause danger, frequent electric shock will bring adverse effects to the psychology of operators.
②. Methods to prevent static electricity. The methods to prevent static electricity are as follows: adjust the ambient temperature and increase the air humidity. The appropriate temperature is generally about 20oC and the relative temperature is about 60%; Put a small amount of antistatic agent into alcohol for scrubbing printing materials; Reduce friction pressure and speed; Reduce the friction, pressure and impact of the substrate as much as possible; Install general grounding device; Using the ionization of flame, infrared ray and ultraviolet ray; Ionization of corona discharge using high voltage current.
125. What is the solution to poor overprint?
Touching the ink film again is called overprinting. In multi-printing, the ink of the next printing cannot be printed clearly on the ink film of the previous printing. This phenomenon is easy to occur and difficult to occur due to different types of inks. For example, the oxidative polymerization ink has too much desiccant to promote drying, and when the ink film is oxidized and hardened excessively, the two colors of ink will repel each other. In addition, if the volatile ink is excessive, the defoamer will form a thin film on the surface of the film strand, which will prevent overprinting. The remedy is to use ink with good overprinting performance, reduce the viscosity of the ink, add additives in the ink, and reduce the drying speed of the ink.
126. What’s the solution for the size expansion of finished film stocks?
After screen printing, sometimes the printing size is enlarged. The main reason for the expansion of printing size is that the ink viscosity is relatively low and the fluidity is too large; Screen printing expands in size during production, which is also the reason for the expansion of printing size.
In order to avoid printing ink overflowing around after printing due to excessive fluidity, a certain amount of thickener can be added to the ink with excessive fluidity to reduce the fluidity of the ink, and quick-drying ink can be used to accelerate the drying speed of the ink after printing and reduce the flow of the ink. When making the screen printing plate, we should strictly guarantee the quality of the screen printing plate.
127. What is the solution to ink film cracking?
The cracking of membrane strand is caused by the action of solvent and the great change of temperature. The factors of the substrate material itself will also lead to the phenomenon of ink film cracking.
In order to prevent the ink film from cracking, the properties of ink and the solvent resistance of the substrate should be considered when choosing solvents. Choose the material with strong solvent resistance and ink resistance as the printing material, and pay attention to keep the workshop temperature balanced. In multi-color overprinting, every color printing should be fully dried and strictly controlled at the drying temperature, which can effectively prevent the occurrence of ink film cracking.
128. What’s the solution to the problem?
Ink spreading refers to the phenomenon that ink overflows on the outside of printed lines. When printing a line, ink overflows on one side of the moving direction of the scraper, which affects the neatness of the line. This phenomenon is called inking. Refining ink can be solved by adjusting the relationship between printing plate and ink, and the relationship between scraping plate operation and screen stretching angle. The shape of the through hole of the screen printing plate is different due to different plate making methods (indirect method, direct method and direct method). The ideal through hole should be close to the substrate surface during scratch printing. The printing plate with ideal through hole shape prints fresh and sharp ink film, which is neat and accurate in size, and does not spread ink. In order to prevent inking, the film should have proper thickness, elasticity and smoothness, so soft nylon screen and polyester screen with high dimensional accuracy can be used for plate making. In order to prevent ink spreading, it is best to use oblique method to stretch the net in plate making.
129. How to solve the dirty back?
Dirty back refers to the phenomenon that the ink on the lower printed matter sticks to the back of the upper printed matter when printed products are piled up. If this phenomenon is not controlled, it will lead to page sticking and affect the printing of the other side of double-sided printed matter. Poor drying of ink is the main cause of dirty back.
The way to solve the problem is to adjust the ink viscosity, use quick-drying ink, add drier to the ink, spray powder on the surface of semi-finished products, or add lining paper.
130. How to solve sticky pages?
During the stacking process of screen printing products, there will be adhesion fault between printed pages, which is also called adhesion fault. Adhesion will cause quality problems and even discard printed matter. The main reasons for sticking are as follows:
(1) After printing, the printing ink is not dry enough. When the ink is not dry, the printed matter will be stacked and piled up, resulting in sticky dirt and adhesion.
② Improper selection of composition materials of screen printing ink is also the cause of adhesion between printed products. When the softening point of synthetic resin film in ink is relatively low or the volatility of ink is not good, adhesion will occur. Generally, the evaporation-drying ink uses thermoplastic resin, which has poor thermal property. If the solvent remains on the ink film after printing, the ink film will soften, resulting in adhesion of printed matter. Especially in summer, because of the high temperature, it is easy to cause adhesion between printed materials.
③ The printing ink can dissolve the substrate to a certain extent, which will also cause adhesion between printing. Among the solvents used in printing, some solvents have great solubility to the substrate. After printing, the ink dissolves the surface of the substrate to a certain extent. At this time, although the surface of the ink has dried, the contact part between the ink and the substrate has not dried completely, and the phenomenon of sticking will occur under the action of overlapping gravity. When the substrate is soft vinyl material, some plasticizers in the vinyl material transfer to the ink film after printing, which causes the ink film to soften and also leads to adhesion.
(4) In order to prevent adhesion, the ink and solvent suitable for printing materials should be selected first. Secondly, choose ink with faster drying speed and pay attention to full drying. Operate in strict accordance with process requirements. General gloss ink is easy to cause adhesion, so pay attention to it.
⑤ The rubber strip of scraper is worn, and the blade part is round, which leads to thickening of the scraped ink film, or excessive printing pressure and thickening of the ink film will also cause adhesion failure.
131. How to solve the printing plate ink leakage?
Part of the plate film leaks ink, which is called ink leakage fault. The reasons are as follows: part of the scraper is injured; the pressure of scraping ink is high; the gap between the plate and the substrate is too large; the plate frame is deformed greatly, and the local printing pressure is not enough; the viscosity of the ink is too high; the ink is uneven; the screen is too thin; the printing speed is too fast, etc.
If the substrate and ink are mixed with dust and then printed without treatment, the printing film will be damaged due to the pressure of the scraper. When making plate, the exposure of the wooden foot will produce pinholes, which will cause the printing film to leak ink. At this time, adhesive tape can be applied from the back of the plate for emergency treatment. If this operation is not very fast, the printing ink of the layout will be dry, and the whole plate will have to be wiped with solvent. Wiping the plate is also the cause of film peeling, so it is best to avoid it. Ink leakage often occurs in the part where ink stays, so it is best to strengthen this part when making plate.
In the process of manual printing, when inserting metal plates and hard plastic plates into the printing table, it is easy for sharp corners to puncture the plate film, so be very careful. Generally, it is best to check and reinforce before printing. To prevent ink leakage. Before printing, the printing plate should be inspected or repaired: the pinhole of the plate film should be repaired, and the periphery of the printing plate should be fully strengthened before printing.
132. How to solve flying ink?
Ink flying is the phenomenon of ink drawing. The causes are: uneven ink grinding; slow release of the scraper during printing; less white around the printed image; static electricity, which leads to too small angle of ink drawing scraper.
133. How to solve the ink?
Ink-nourishing refers to the appearance of speckled marks in the graphic and dark parts of the substrate, which impairs the printing effect. Especially, it is easy to produce this phenomenon by using transparent ink. The reasons are as follows: the printing speed and ink drying are too slow; the ink layer is too thin; the ink thixotropy is large; the influence of static electricity: the pigment in the ink is poorly dispersed; because of the polarity of the pigment particles, the particles agglutinate with each other, resulting in color spots.
The improvement methods are: improving the fluidity of ink; using quick-drying solvent; printing with ink with high viscosity as much as possible; using ink made of pigment with small oil absorption as much as possible; minimizing the influence of static electricity.