From the perspective of the development of lithography, the following plates have been widely used:
Lithography, to this day, lithography is still widely used in the reproduction of ancient paintings, printing of New Year paintings, etc., in order to achieve special effects;
The Collo version is a transliteration of English collotype. Colrotype printing belongs to the field of lithography. It is one of the earliest photolithography. Because it uses thick glass as the base, it is also called "glass printing". The Loro plate is coated on a thick frosted glass plate with chromium gel photosensitive solution, and exposed to light with the negative film and the photosensitive film layer, and then a photochemical reaction occurs to cause the gel layer to harden to form an image. The density of the image density is not composed of dots of different sizes, but is caused by the difference in the amount of light received by the adhesive film, which makes the adhesive film harder. The degree of hardening determines the difference in the expansion of the film. Different degrees of expansion form fine wrinkles with different density and density. The greater the amount of light received, the greater the degree of hardening, the smaller the swelling, the more wrinkles, less moisture absorption, more ink adhesion, and the darker the color tone after printing. Luoban printing is direct printing, so the pictures on the printing plate should be the reverse image. Collotype is a direct printing, which is most suitable for reflecting the traditional Chinese calligraphy and painting works
Photosensitive protein plate, also known as negative plate or planographic plate, the base is aluminum or zinc plate. The lipophilic and hydrophobic film in the graphic part is a hardened protein film with a high publishing base plane of about 3 to 5 μm, and the hydrophilic and oleophobic film layer in the blank part is an inorganic salt layer. The operation process of protein plate making is simple, the cost of raw materials used is low, but the printing resistance is low, generally 5000 ~ 10000 printing. Due to the fact that the photosensitive resin foundation is not strong, the platemaking quality is unstable, and the defects such as low print resistance cause almost no use now.
Flat gravure, flat gravure, also known as positive plate, the base is zinc plate. For the positive plate of the gravure printing plate, the uncured and hardened film is dissolved and removed by the developing solution to expose the metal in the graphic part. The metal is slightly corroded with an etching solution to make the metal in the graphic part lower than the plate surface by 5-8 μm Then apply the oleophilic base paint, and the oleophilic and hydrophobic graphic part will be formed. Although the printing capacity and printing quality have been improved compared with the protein version, but the gravure is also difficult to see now.
Multi-layer metal plate. Multi-layer metal plate uses two metals with opposite hydrophilicity and lipophilicity as printing plates. There are two-layer metal plate and three-layer metal plate. According to the concave and convex shape of the text, it is divided into flat intaglio and flat relief. At present, two-layer planogravure and three-layer planogravure are the most used. Chromium plating on the copper skin makes a two-layer planogravure; copper plating on the iron plate and then chromium or nickel plating makes a three-layer planogravure. Multi-layer metal plate printing process. The lipophilic part of the multi-layer metal plate is the metallic copper with the best lipophilicity, and is treated with potassium ethylxanthate to absorb the ink directly. At this time, the printing capacity has reached a very high stage, but the multi-layer metal plate has a poor dot reduction ability, and the plate making cycle is too long, the process is complicated, and it is no longer visible.
Pre-coated photosensitive plate (PS plate), PS plate is the abbreviation of pre-coated plate. Due to stable quality, printing capacity, simple process, suitable for large-scale printing, PS plate has now become the only version of lithographic offset printing materials.
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