Interpretation of the importance of developer for printing plate making

1. Developer concentration

The concentration of the developer refers to the relative content of the developer, that is, the total content of NaOH and Na2SiO3. Most of the developing solutions sold on the market are concentrated liquids, and they need to be diluted in proportion when they are used. The concentration of the developing solution is usually expressed by the dilution ratio of the developing solution. On the premise that other conditions remain unchanged, the development speed is directly proportional to the concentration of the developer, that is, the greater the concentration of the developer, the faster the development speed.

When the temperature is 22 ℃ and the development time is 60 seconds, the effect of the concentration of the PD-type developer on the performance of the PS plate is shown in Table 1 (omitted). From the data in the table, it can be seen that with the exposure level of 3 levels of cleanness, the concentration of the PD type developer is 1: 6.

When the concentration of the developer is too large, the development operation is often difficult to control due to the excessive development speed; in particular, its corrosiveness to the graphic foundation is enhanced, which is easy to cause dot shrinkage, damage, bright adjustment, small dot loss and thin coating , Resulting in the disadvantages of reduced printing resistance; at the same time, the oxide film and sealing layer of the blank part will also be corroded and destroyed, and the whitening phenomenon occurs on the plate surface, which makes the hydrophilicity and wear resistance of the printing plate worse. The developer concentration is large, and crystals are easily precipitated.

When the concentration of the developing solution is low, the alkalinity is weak, the developing speed is slow, and the phenomenon of unclean development, soiling of the plate surface, and white spots in the dark tone are apt to appear.

The normal concentration of the developer can pass the dot ladder test; when developing under normal exposure conditions for 30 to 100 seconds, if there are more small black spots lost, it means that the developer concentration is too large; if there are more small white spots, it means that development The liquid concentration is low. Therefore, it is best to use the developer within the concentration range specified by the manufacturer.

2. Developing temperature

When the developing temperature is high, the thermal motion of the molecules in the developing solution is violent, and the solubility of the resin in the coating is large; the temperature is low, the thermal motion of the molecules is weakened, and the solubility of the resin is less; The development time required for different temperatures is also different.

When the developing temperature is low, the negative impact on the quality of the plate is usually greater than when the temperature is high, so the user must adjust the temperature of the developer to the specified range in winter, so that the plate making can get satisfactory results.

Under other conditions unchanged, the development speed of the PS plate is directly proportional to the development temperature, that is, the higher the development temperature, the faster the development speed.

3. Development time

The development time of the PS plate is mainly determined by the conditions such as the type of PS plate, the exposure time, the concentration of the developer, and the development temperature. When the above conditions are determined, the development degree of the PS plate is directly proportional to the development time, that is, the longer the development time, the more thorough the development. However, if the development time is too long, the phenomenon of dot shrinkage will occur.

4. Circulating stirring of developer

Development is accomplished by contact and dissolution between the developer and the photosensitive layer of the PS plate, so power development is often used. If manual development requires shaking of the development tray, during mechanical development, circulation pumps and brush roller devices are used to speed up the flow and circulation of the developer, so that the development speed and development uniformity are improved. Contrary to the static development method, the developer cannot effectively flow and circulate, the development speed will be significantly reduced, and the development uniformity is also poor.

5. Fatigue decline and supplement of developer

During the development process, the developing solution will gradually fatigue and decline as the development progresses and due to the absorption of carbon dioxide in the air or the reaction with the calcium and magnesium ions in the water, the development performance becomes poor, and the development ability is weakened.

Generally speaking, when developing the printing plate, the development effect can be observed with the blank steps of the gray ladder ruled out under the same exposure conditions. If the development effect is not good, the developer must be replaced in time.

With the increasing amount of processing and the continuous dissolution of CO2 in the air, the OH-concentration in the developing solution will decrease, the pH value will become lower and lower, and the development time should slowly become longer, and finally under normal exposure conditions The PS version cannot be developed. This is the phenomenon of fatigue deterioration of the developer. However, as the pH value of the developing solution decreases, the erosion force of the alkali solution to the oxide layer and the coating resin decreases, and the dot reproducibility and printing resistance of the plate material are better than that of the newly prepared developing solution. But we must pay attention to two points, one is that the amount of processing must be controlled within the allowable range of the developer; the second is that the used developer must be sealed and preserved from the air, because even the developer that has not shown a version is exposed to the air After a week, the development performance will be significantly reduced.

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