Six Common Problems about Printing Resin Plate Making
Photosensitive resin plate is a letterpress plate with photosensitivity, which uses synthetic polymer materials as film forming agents and unsaturated organic compounds as photo crosslinking agents. Almost all photosensitive resin plates are irradiated by light (mainly ultraviolet light), and cross-linking reaction occurs between molecules, thus forming a relief image with certain insolubility. Photosensitive resin plate can be divided into solid type and liquid type in plate making process. Solid series prefabricated plates composed of saturated photosensitive resins have high cost, but good quality, which can be used to make commodity packaging, trademark plates and screen printing plates; Liquid series instant coating plates composed of unsaturated polyester resin (simply speaking, when using, they are prepared with photosensitive liquid to make the substrate, and then coated with resin, photosensitive and made) are relatively cheap, which is suitable for rough text and line plates.
The following problems often appear in the process of plate-making of solid photosensitive resin plate, which can be solved only by comprehensive analysis, differential treatment and finding out the root of the problems.
First, the resin version of the text, lines, patterns and lines are too thin and too small, the small print and independent points fall off, and the small lines bend In resin plate making, there are some common problems, such as thin lines bending, small words and independent points falling off.
L, resin plate exposure time is insufficient; 2. The contrast of the negative film is small, with fog and unclear; 3. Improper baking of resin plate and thermal curing; 4. When brushing the resin version, the water temperature is low, the washing time is long, the bristles are too hard, and the brush version is too deep; 5. Excessive pressure and improper adjustment during printing.
1. When making resin plate, when encountering small words, lines, patterns and independent points, it is necessary to master the correct exposure time. The exposure time of 3kw iodine gallium lamp is about 20min, which must be longer than that of the normal version, so that small lines, characters and independent points can stand and not fall off. Due to the long exposure time, the gradient of the produced resin plate is small (about 70), and the image and text base is firm.
2. When baking the resin plate, drying and heat curing, under normal circumstances, the oven temperature is controlled at 60-80℃, in order to evaporate the water on the plate; If the drying temperature is too high, the resin plate will easily bubble.
3. The operator is required to be skilled in darkroom, and the contrast of film processing should be as human as possible, without fog, and the words and lines should be smooth and bright, and there is no shortage of pens and broken strokes.
4. When making solid resin plates, whether the plates are automatically brushed by the plate-making machine or manually brushed, the water temperature should be controlled at 50-60℃ and washed until the base is exposed. Brush the resin version to rotate the brush, brush the version on one side, it is easy to brush the side and slope, causing the small lines to bend and fall off; When brushing the version, you should choose those brushes with soft and suitable hairs. If the bristles are hard, the small words will be brushed and damaged; Pay attention to mastering the brush depth when brushing the resin version. It is not necessary to flush the bottom base when brushing the resin version. If the brush depth is too deep, the characters, lines and patterns on the version will be easily brushed off. In addition, pay attention not to take too long to flush the version.
5. When the resin plate is printed on the machine, it is necessary to reduce the pressure between the inking roller and the resin plate, and between the resin plate and the impression cylinder. Adjusting the printing pressure of the resin plate is smaller than adjusting the pressure of copper-zinc plate and type printing. Avoid crushing the fine characters and lines of the resin plate by the inking roller and impression cylinder due to excessive pressure, which will affect its printing resistance.
Second, the text and line version are ambiguous when making the resin version Main reasons:
1. overexposure; 2. Vacuum adsorption is not true when drying; 3. Film contrast is small and unclear.
1. Master the exact exposure time of the resin version, especially the hollow characters and lines are the easiest to paste, and try to make the pictures and texts bold when designing.
2. The air intake of the printing machine should be firm. If the suction is not true, there will be a gap between the resin plate and the film, and ultraviolet rays will be injected from all around, resulting in a photosensitive paste plate.
3. Before printing, it is necessary to carefully check whether the apricot negative film is pasted, which is transparent, contrasting and clear, so as to meet the needs of plate-making quality.
Third, the resin version does not wash Main reasons:
L, the resin plate has exceeded the shelf life, or let the light leak in the process of production, storage and transportation, and the resin plate is photosensitive and hardened; 2. The water temperature is too low when flushing the brush; 3. Poor darkroom treatment of film, poor light shielding and low density of film.
1. The shelf life of the resin plate is about half a piece, so the printing manufacturer should purchase it according to the production capacity and dosage of the factory, and don’t buy too much blindly, otherwise it will cause overdue failure.
2. Resin plates are photosensitive materials, and they are most afraid of light leakage in production, storage and transportation. When saving the resin plate, the temporarily unused plate should be placed in a sealed box and sealed with a black plastic bag; The resin plate should be stored in a dry and moisture-proof place.
3. When printing, the water humidity should be controlled at about 60-70℃. If the water temperature is too low, it will affect the dissolution of the non-photosensitive resin film after meeting water; The higher the water temperature, the faster the dissolution.
Fourth, there are patterns or scars on the resin plate Main reasons:
1. During exposure, a small amount of talcum powder and corn starch were not smeared on the resin plate, which caused the contact between the negative film and the resin plate to be not tight and there were bubbles; 2. The vacuum pump of the printing machine sucks air incorrectly; 3. The temple with transparent film is not smooth and foggy.
1. Wipe a small amount of talcum powder and corn starch on the surface of the resin plate, the purpose is to prevent the resin on the layout from sticking to the negative film, resulting in false aspiration. This problem can be solved by attaching a small amount of fine particles to the resin plate.
2. After the printing machine has been used for a period of time, it should be overhauled in time, filled with vacuum oil, and cleaned up the dust and paper hairs in the suction rubber tube wall. The suction air volume of the vacuum pump is generally 30-40m3/h.
3. The transparency of the negative film is better. Pay attention to the exposure and development time, fix and wash thoroughly, so that the negative film is free of fog and yellowing.
V. Curl and crack of resin plate Main reasons:
1. The drying and thermal curing time is too long; 2. Excessive post exposure (fill light); 3. The plates are out of date or have quality problems.
1. The drying and thermal curing time of resin plate should not be too long. As long as the layout is dry and the curved lines are straight.
2. Post-exposure (finishing) shall be carried out after drying and thermal curing treatment, and excessive finishing shall not be allowed, otherwise the resin will become hard and brittle. You can see the layout change from green to light red and then to ancient yellow. If the plate is seriously curled, it can be soaked in water for 5-10min, and then dried again.
3. When using plates, we should recognize the production date. Expired and deteriorated plates are easy to curl and should not be used again.
Sixth, the printed pictures and texts are incomplete Main reasons:
1. The glass plate of the printing press is seriously dirty; 2. The picture and text part of the negative film is dirty when the negative plate is inked, and the red tear film fragments of the imposition fall into the negative film; 3. Excessive force and hard bristles during printing.
1, develop good working habits of civilized and safe production. Before printing, clean the dirt such as dust, oil stains, ink spots and paper scraps inside and outside the glass plate of printing machine with water or cotton wool dipped in alcohol.
2. Be careful when drawing ink on the negative film. Do not cover the pictures and texts. Only when the ink is dry can the printing be made. Cover the layout with the imposition red tear film to prevent the fragments from falling off and shading the pictures and texts, resulting in incomplete pictures and texts.
3. When brushing the resin version, the force should be uniform, first heavy and then light; The bristles should not be too hard. At the same time, it is necessary to prevent hard objects from scratching the layout and causing damage.