The third problem of the most popular printing dry

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The third problem of printing drying board (Part 1)

1. what causes may cause the image to be sunken?

as long as the negative film is not closely connected with the photosensitive coating of PS version, the image will be sunken. This is for solid and thicker lines. Text has little impact, but it will have a serious impact on points, thin lines and small text. The common causes of sunning deficiency are as follows:

① insufficient power of the vacuum pump of the plate printer, unsealed plate frame, blocked pores or improper setting of the air extraction time lead to poor air extraction; The pressure drop in the frame is not enough, and the photographic coating of the negative and the PS version is not "left" and can be closely connected

② when placing the negative film, light blocking paper or printing plate, some of them were exposed outside the printing machine, affecting the sealing of the printing frame, resulting in insufficient decompression

③ there are sand particles or other impurities between the negative film and the printing plate; The edges of the manually spliced negatives are not cut neatly; The edges of the adhesive tape paper or two negatives overlap, resulting in that the negatives at local positions are not closely connected with the photosensitive coating of the PS version

④ due to the smooth surface, the PS plate may be attached to the original plate because the surrounding air is first drawn out, while the middle air is left inside because the surrounding air is sealed, resulting in the middle negative film is not closely connected with the photosensitive layer of the printing plate, resulting in sunning. The solution is to adopt the secondary air extraction method, which divides the air extraction into two steps. During the first air extraction, if the air extraction is uneven and interference patterns can be seen, the air extraction should be stopped. When the records queried are not deleted between the negative and the printing plate, the extracted air diffuses around due to high pressure, which destroys the sealing state around. After the interference patterns disappear, the second air extraction should be carried out immediately. After two times of air pumping, the phenomenon of deficiency caused by uneven air pumping can generally be eliminated. Some printing plates strive to promote the development of new material market utilization. The power machine is automatically pumped twice

2. what effect does the concentration of the developer have on the development quality?

the higher the concentration of the developer, the faster the development speed. However, when the concentration is too high, the developer can also dissolve the photosensitive layer without light in the image and text part, resulting in poor inking of the printing plate, smaller dots and lower printing resistance

the lower the developer concentration, the slower the development speed. If it is too low, the development will be incomplete, the blank part will have a blue background, and the full version will be dirty during printing. In this case, the printing plate with low requirements can be developed again after adding new developer

3. what are the factors that affect the developer concentration in production

① the amount of main agent added when preparing the developer

② number of developed plates. The process of development is the reaction between the main agent and the plate photosensitive layer. With the increase of the number of developed plates, the remaining main agent will be less and less

③ time of developer in air. When the developer is exposed to the air, the main developer alkali will adsorb carbon dioxide in the air to neutralize, making the developer ineffective. Therefore, the thin layer of developer accumulated into an average should be sealed and stored as far as possible

4. what effect does the temperature of the developer have on the development quality?

the higher the temperature of the developer is, the faster the development speed is. However, if the temperature is too high, the developer will dissolve the photosensitive layer of the graphic part and the alumina of the blank part, which will also lead to poor inking of the printing plate. Failure such as decrease of printing resistance. When the temperature is too low, the development speed is too slow, or even at a standstill. The suitable developing temperature is ℃

5. what should be paid attention to in manual development

① pay attention to control the temperature of the developer

② the developer shall be placed in a covered tank to reduce the effect of the developer's failure due to adsorption of carbon dioxide

③ after the development, pay attention to clean the residual developer on the printing plate. If the developer is prepared with strong alkali, use 1%-3% dilute phosphoric acid to neutralize the residual developer, and then clean it with water

6. what should be paid attention to when using the automatic developer

① the developer should be preheated to reach the set temperature before use

② there shall be no dry sand on the rubber roller of the developer to avoid scratching the plate surface. Always clean all kinds of rubber rollers in the developing tank, especially the rubber coated ones, to avoid drying of the rubber rollers and damage to the drive motor. (to be continued)

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