In the offset printing work, it is often encountered that the PS plate, especially the regenerated PS plate plate, is not smooth enough and has a horseshoe-shaped convex-concave impression, which seriously affects the quality of the offset printing plate. In places with horseshoe markings. Because the PS version of the photosensitive film and sulfuric acid paper or film text, lines, dot film can not be close to pull together, while there is a certain gap, it is easy to cause text, lines, dots made false virtual, PS version can not be printed on the machine The phenomenon.

1, the cause of horseshoe prints and solutions

Our common PS plates in offset printing platemaking work can be roughly divided into two types: one is the printing of high-grade fine packaging and decoration, trademark, and the original PS plate used for four-color overprint color covers. This plate is of high price and quality. Well, the surface is relatively flat; the second is used to print low-grade books, forms, miscellaneous pieces of recycled PS version. This type of plate is low in price, unstable in quality, and the surface of the recycled PS plate is not smooth enough and has more horseshoe prints.

Due to the regeneration of the PS plate after several times the original PS plate regeneration. In the process of regeneration, various processes such as disassembly, cleaning, grinding, electrolytic corrosion, coating and recoating of the PS plate, drying, etc., the PS plate is only about 0.4mm thick, for example, the format of the PS plate is large, and the plate is again Thin, PS plate in the regeneration process is often due to repeated multiple regeneration, operation is likely to cause regeneration PS version has a horseshoe print. The PS version is best stored upright like a glass transporter during transportation. Careful loading and unloading can reduce horseshoe markings.

In addition, in the sun PS version of the operator must be responsible and careful work attitude, take out the PS version from the packing box gently, when found on the PS version of the surface horseshoe imprint, you can use a small bamboo board from the PS The back of the version is poked up. If possible, press it on the platform to make the PS version as flat as possible.

2, adjust the selenium machine vacuum pump

When we encounter in the actual work of the PS version layout with uneven horseshoe prints, the pressure of the vacuum pump must be readjusted before the printing to increase the pressure during vacuuming. Extend the inspiratory time before the exposure of the PS plate, let the vacuum pumping suction suck enough so that the PS version of the photosensitive film surface and sulfuric acid paper or film on the text, network, lines can fit closely, the sun out of the PS version of the network is clear Bright and clean, the idea is not strong, to achieve the quality requirements of offset printing.

Reprinted from: Graphic Arts Forum