On the Importance of Developing Solution for Printing Plate Making
1. developer concentration The concentration of developer refers to the relative content of developer, that is, the total content of NaOH and Na2SiO3. Most of the developing solutions sold in the market are concentrated liquids, which need to be diluted proportionally when used. The concentration of developing solutions is expressed by the dilution ratio of developing solutions. On the premise that other conditions are unchanged, the developing speed is directly proportional to the developer concentration, that is, the higher the developer concentration, the faster the developing speed.
When the temperature is 22℃ and the developing time is 60 seconds, the influence of PD developer concentration on the performance of PS plate is shown in Table 1 (omitted). It can be seen from the data in the table that the exposure amount is based on Grade 3 cleanness, and the concentration of PD developer is 1∶6 as the best.
When the concentration of developing solution is too high, it is often difficult to control the developing operation because the developing speed is too fast; In particular, its corrosiveness to graphic and text foundation is enhanced, which is easy to cause dot reduction, damage, loss of bright and small dot and thinning of coating, resulting in the decline of printing resistance; At the same time, the oxide film and sealing layer in the blank parts will also be corroded and destroyed, and the layout will appear white, which will make the hydrophilicity and wear resistance of the printing plate worse. The concentration of developing solution is high, and crystallization is easy to separate out.
When the concentration of developing solution is low, the alkalinity is weak, the developing speed is slow, and it is easy to appear such phenomena as dirty development, dirty layout, and dark white spots.
The normal concentration of developer can pass the dot ladder test; When developing for 30 ~ 100 seconds under normal exposure conditions, if there are more small black spots lost, it means that the concentration of developing solution is too large; If there are more white spots, the developer concentration is low. Therefore, it is best to use the developer in the concentration range specified by the manufacturer.
2. Development temperature When the developing temperature is high, the molecular thermal movement in the developing solution is intense, and the dissolving power of the resin in the coating is great; When the temperature is low, the molecular thermal motion is weakened, and the solubility of resin is poor; Therefore, under the same exposure conditions, the development time required by different temperatures is also different.
The negative impact of low developing temperature on plate quality is usually greater than that of high temperature, so users must adjust the temperature of developing solution to the specified range in winter, so that plate-making can get satisfactory results.
Under other conditions unchanged, the developing speed of PS plate is proportional to the developing temperature, that is, the higher the developing temperature, the faster the developing speed.
3. Development time The development time of PS plate is mainly determined by the type of PS plate, exposure time, developer concentration, development temperature and other conditions. When the above conditions are determined, the development degree of PS plate is proportional to the development time, that is, the longer the development time, the more thorough the development. However, too long developing time will lead to the phenomenon of dot reduction.
4. Circulating stirring of developing solution Development is accomplished by the contact and dissolution between the developing solution and the photosensitive layer of PS plate, so dynamic development is often used. For example, when developing manually, the developing disk should be shaken, and when developing mechanically, the circulating pump and brush roller device should be used to speed up the flow and circulation of developing solution, so as to improve the developing speed and uniformity. On the contrary, using static developing method, the developing solution can not flow and circulate effectively, and the developing speed will be obviously reduced and the developing uniformity will be poor.
5. Fatigue recession and supplement of developer In the developing process, the developing solution will gradually fatigue and decline with the development and because it absorbs carbon dioxide in the air or reacts with calcium and magnesium plasma in water, resulting in poor developing performance and weak developing ability.
Generally speaking, when developing a printing plate, the development effect can be observed by comparing with the gray scale blank series exposed under the same exposure conditions. If the development effect is not good, the developer should be replaced in time.
With the increasing amount of printing plate and the continuous dissolution of CO2 in the air, the concentration of OH- in the developer will decrease, the pH value will become lower and lower, and the development time should be lengthened slowly. Finally, the PS plate cannot be developed under normal exposure conditions, which is the phenomenon of fatigue decline of the developer. However, with the decrease of pH value of developing solution, the corrosion of alkali solution to oxide layer and coating resin decreases, and the dot reproducibility and printing resistance of plate are better than those of newly prepared developing solution. However, we must pay attention to two points. First, the amount of printing must be controlled within the allowable range of developing solution; Second, after use, the developer must be sealed and kept isolated from the air, because even if the developer that has never been displayed before is exposed to the air, the developing performance will obviously decrease after one week.