The graphic and blank parts of the lithographic printing are almost on the same plane, but the two parts have completely opposite properties for the intimate relationship between water and oil. The graphic part is lipophilic and hydrophobic, while the blank part is hydrophilic and oleophobic. Therefore, in the printing process, the graphic part absorbs the ink and repels the fountain solution; while the blank part of the printing plate absorbs the fountain solution and repels the ink. During the printing process, the blank portion is first wetted by the fountain solution, and then the graphic portion is coated with the ink, and then the graphic portion of the ink is transferred onto the paper. Therefore, lithography is based on the principle of oil, water immiscibility, the transfer of graphics on the plate above the substrate.
Modern lithographic printing generally uses indirect printing, which means that the ink on the graphic part of the printing plate is transferred to the surface of the substrate by means of intermediate carrier transfer. Therefore, lithographic printing is also called lithographic offset printing, that is, according to indirect Printing principle, the printing plate transfers the graphic through the blanket transfer roller to the substrate for printing.
The basic principle of the general lithography printing department.
The printing plate on the plate cylinder 2 first applies water on the plate surface with water roller 9 (ink is blank and resists ink) before the ink is applied on the plate cylinder 2, and then the ink is applied to the plate by the ink roller 1 (image 3 is inked). Reject the principle of printing. Therefore, in addition to an ink inking device, a water supply device is also provided. The ink on the upper part of the printing plate is not directly transferred to the surface of the printing material, but is first transferred onto the blanket and then transferred onto the paper by the blanket. Therefore, the blanket cylinder 4 is specially provided. When the paper passes between the blanket cylinder and the impression cylinder, printing is performed under the effect of the printing pressure to complete the printing.
Plates for typographic plates are generally chosen to have moderate levels of metal aluminum and zinc, both hydrophilic and lipophilic. In order to improve the hydrophilicity of the printing plate made of this plate material, on the surface of the aluminum printing plate or the zinc printing plate, a hydrophilic metallic flower film of a stable metal inorganic salt or metal oxide is formed by chemical treatment or Chromizing the printing plate; In order to make the surface of the printing plate absorb enough water, the surface of the printing plate has a certain degree of roughness by grinding to increase the surface area of ​​the plate and increase the water storage capacity; in order to improve the oleophilicity of the printing plate, The plate is coated with various non-polar layers in the graphic part or copper plated in the graphic part. Through the mechanical or chemical treatment of the printing plate surface, the oleophilic graphic part of the printing plate is selective for the adsorption of water and ink, that is, it only adsorbs ink, not only water. Through grinding, the roughness of the printing plate is increased, so that the blank portion of the printing plate is only adsorbed to the ink. The hydrophilic blank portion of the printing plate has no selectivity for the adsorption of water and ink, that is, it adsorbs both water and ink. In short, the adsorption of water and ink, the oleophilic graphic part of the printing plate is selective, and the hydrophilic blank part of the printing plate does not have such selectivity. In the printing process, if the ink is applied first, the oleophilic graphic portion on the printing plate and the hydrophilic blank portion are adsorbed simultaneously, and the printing process cannot be performed.
In actual printing, water must be supplied to the printing plate. The water is adsorbed by the hydrophilic blank and cannot be absorbed by the oleophilic graphic part. Then the plate is inked, and the ink is oleophilic. When adsorbed, the blank portion wetted by the fountain solution is not substantially adsorbed. This will ensure the normal printing process.
Modern lithographic printing generally uses indirect printing, which means that the ink on the graphic part of the printing plate is transferred to the surface of the substrate by means of intermediate carrier transfer. Therefore, lithographic printing is also called lithographic offset printing, that is, according to indirect Printing principle, the printing plate transfers the graphic through the blanket transfer roller to the substrate for printing.
The basic principle of the general lithography printing department.
The printing plate on the plate cylinder 2 first applies water on the plate surface with water roller 9 (ink is blank and resists ink) before the ink is applied on the plate cylinder 2, and then the ink is applied to the plate by the ink roller 1 (image 3 is inked). Reject the principle of printing. Therefore, in addition to an ink inking device, a water supply device is also provided. The ink on the upper part of the printing plate is not directly transferred to the surface of the printing material, but is first transferred onto the blanket and then transferred onto the paper by the blanket. Therefore, the blanket cylinder 4 is specially provided. When the paper passes between the blanket cylinder and the impression cylinder, printing is performed under the effect of the printing pressure to complete the printing.
Plates for typographic plates are generally chosen to have moderate levels of metal aluminum and zinc, both hydrophilic and lipophilic. In order to improve the hydrophilicity of the printing plate made of this plate material, on the surface of the aluminum printing plate or the zinc printing plate, a hydrophilic metallic flower film of a stable metal inorganic salt or metal oxide is formed by chemical treatment or Chromizing the printing plate; In order to make the surface of the printing plate absorb enough water, the surface of the printing plate has a certain degree of roughness by grinding to increase the surface area of ​​the plate and increase the water storage capacity; in order to improve the oleophilicity of the printing plate, The plate is coated with various non-polar layers in the graphic part or copper plated in the graphic part. Through the mechanical or chemical treatment of the printing plate surface, the oleophilic graphic part of the printing plate is selective for the adsorption of water and ink, that is, it only adsorbs ink, not only water. Through grinding, the roughness of the printing plate is increased, so that the blank portion of the printing plate is only adsorbed to the ink. The hydrophilic blank portion of the printing plate has no selectivity for the adsorption of water and ink, that is, it adsorbs both water and ink. In short, the adsorption of water and ink, the oleophilic graphic part of the printing plate is selective, and the hydrophilic blank part of the printing plate does not have such selectivity. In the printing process, if the ink is applied first, the oleophilic graphic portion on the printing plate and the hydrophilic blank portion are adsorbed simultaneously, and the printing process cannot be performed.
In actual printing, water must be supplied to the printing plate. The water is adsorbed by the hydrophilic blank and cannot be absorbed by the oleophilic graphic part. Then the plate is inked, and the ink is oleophilic. When adsorbed, the blank portion wetted by the fountain solution is not substantially adsorbed. This will ensure the normal printing process.
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