Specification of printing, development and quality control of printing plate (medium)

To make a qualified plate, the key is to standardize the development of the exposed PS plate.

â– 1. Developer

The PS version of the developer is an alkaline solution consisting of a developer, a protective agent, a wetting agent, and a solvent. The PS version of the developer marketed on the market is mostly concentrated, that is, it can be used by simply diluting the developer stock solution with water in a certain proportion.

1) Developer

The developer is used to dissolve the exposed photosensitive layer of the positive PS plate. Commonly used alkaline substances, such as sodium hydroxide, potassium hydroxide, sodium silicate and so on. China generally uses sodium hydroxide (caustic soda).

Sodium silicate is a salt formed by strong alkali and weak acid. It has strong alkalinity and stable performance. Because sodium silicate is easy to be hydrolyzed, hydroxide ions are generated during hydrolysis to continuously supplement the consumption of hydroxide ions in the developer during the development process. Keep the pH of the developer within a certain range.

Each PS version of the kit specializing in the production of commonly used sodium hydroxide and sodium silicate in the appropriate proportion of preparation, the two can be used to make up.

2) Protective agent

The protective agent, also known as an inhibitor, can stabilize the performance of the developer, at the same time, it can reduce the erosion of the developer during the development process of the developer, and can also protect the photosensitive layer of the graphic part from the immersion of the developer. The commonly used protective agents are sodium phosphate and potassium chloride.

Sodium phosphate has a buffering effect that stabilizes the pH and development of the developer. Phosphoric acid produced by hydrolysis also has a builder function, which facilitates the rapid removal of processing fluid left on the plate after development. Potassium chloride forms chloride ions in the developer and has the effect of suppressing the swelling of the unexposed photosensitive layer during the development process, and it also contributes to water washing.

3) Wetting agent

The role of the wetting agent is to reduce the surface tension of the developer so that the developer can quickly and evenly wet the plate. The commonly used wetting agents are sodium dodecyl benzene sulfonate, TX-10 and other surfactants, all of which are viscous liquids that can only be added to the developer and cannot be added to the developer powder. Obviously not as concentrated developer.

4) Solvent

The developer uses water as the solvent, and the water quality will affect the quality and effect of the developer, especially the machine development processing. If the water used for preparing the developer is too hard, the calcium and magnesium ions in the water can easily foul and clog the nozzle; the water is too soft and easy to produce foam and affect the development. Therefore, deionized water or distilled water is preferably used when formulating the developer and diluting the developer. If tap water is used, it is best to add a small amount of complexing agent such as EDTA and Sodium to prevent the precipitation of metal ions such as calcium and magnesium in the water. If the water quality is too soft, it is best to add a few drops of defoamer to the developer.

If bubbles are generated during development, only a few drops of antifoaming agent may be added to the developing solution, for example, a mixture of ethanol, n-butanol = 1:1, or the use of commercially available brands such as Anchor. Foam.


â–  2. Development

PS version of the development of processing manual and machine development.

Hand-developing is usually carried out in polyvinyl chloride shallow trough, the exposed PS plate is placed in the developing tank, the developing working fluid is completely immersed in the plate surface, and then the soft nylon brush is used for scrubbing, and the photosensitive layer of the visible light part is completely dissolved and detached. Remove the plate, rinse the residue on the plate with water, and then perform the other steps of PS plate processing.

Developing with a developing machine can eliminate the influence of human factors. The printed plate produced has good uniformity and stable quality. A conditional printer or plate making factory should still use the developing machine to process the exposed PS plate.

After the positive PS plate was made into a printing plate, the photosensitive layer was directly used as the graphic basis of the lipophilicity during printing, and the coating thickness was only about 2 μm. In the case of normal printing conditions, slight changes in conditions during development or improper control can have a negative effect on the photosensitive film layer of the printing plate.

(to be continued)