Lithographic printing plate is different from relief printing and intaglio printing plate, and the printed part and blank part of lithographic printing plate are almost on the same plane. The printed part on the lithographic printing plate is lipophilic, which can repel water and absorb ink, while the blank part has good hydrophilicity, which can repel ink after absorbing water.
When printing, wet the printing plate with water to make the blank part absorb water, and then ink it. Because the blank part has absorbed water, it can no longer absorb ink, but the printing part absorbs ink, and the printing part on the printing plate can be printed after it has ink. Therefore, protecting the wettability of lithography blank is an important measure to ensure lithography quality. ?
The following are some measures to protect the wettability of lithography blank parts:
Plate surface treatment: Plate surface treatment is to make the printing part have a good foundation and expand the specific surface of the layout. The adsorption capacity is enhanced, but for the blank part, it is beneficial to store water and reduce surface tension. The surface treatment of plate is to establish sand net, and the methods of establishing sand net are: mechanical method, electrolytic method, sandblasting method and corrosion method, and mechanical grinding method is usually used.
Mechanical grinding method is to grind the sheet in a grinding machine to form a sand net. The depth and thickness of the sand net are related to the size and specific gravity of the grinding ball, the hardness and fineness of the grinding ball, the water quantity, the stroke of the grinding machine and the grinding time. ?
Film removal on the layout: the film removal work is relatively simple. When the acidic stripping solution is poured on the layout, the adhesive layer will gradually turn white and fall off from the layout. Then rinse it with water and brush it with a brush. The glue layer on the page should be removed, otherwise it will get dirty when printing. After post-etching and gluing, a stable blank part is established. ?
Multilayer metal lithography: Multilayer metal lithography is a lithographic printing plate composed of two or three layers of different metals. The printed part and the blank part are made of different metals, and the printed part is made of lipophilic metals, such as copper. The blank part is made of hydrophilic metals such as chromium and nickel. Multilayer metal plates can be divided into two layers and three layers according to the number of metal layers.
The printed part of the multilayer metal plate is copper, which has good oleophilicity, and the blank part is chromium, which has good hydrophilicity and high wear resistance, reduces the transmission of moisture and temperature during printing, and makes the ink layer printed on paper appear thick and shiny.