1) The ink has good adhesion and mechanical properties
Because the tinplate printing materials need to be cut, bent and stretched to be made into cans of food, toys, metal photo frames and barrels and cans of chemical products, the printing ink is required to have good adhesion and corresponding mechanical properties to the tinplate. In order to improve the ink adhesion, the white backing of the sheet is required before printing. White is the basic color of all pictures, with high lightness. After adding other high-energy hues, the brightness of each hue can be improved to form a color scale.
(2) Requirements for white ink
The surface of tinplate is silver white (or yellow) with metallic luster. Before printing color pictures and texts, the surface needs to be painted white or printed white. Due to the limitation of ink coverage, monochrome machines often need to be printed white twice, and its whiteness can reach 75%. Whiteness, as an important indicator of the quality of tinplate printing products, requires that the white ink has good adhesion with the primer, and does not turn yellow after repeated high-temperature baking and high-temperature steaming.
(3) Requirements for color ink
The color ink printed on tinplate should not only have a certain degree of water resistance, but also have its special requirements. Since the surface of the sheet is impervious to moisture and solvent and needs to be baked and dried, the ink should be heat cured. The requirements for coloring power and durability of pigments are high. In addition to the basic properties of general offset ink, iron printing ink should also have the characteristics of heat resistance, strong ink film adhesion, impact resistance, good hardness, cooking resistance and light resistance according to the characteristics of iron printing.
(4) Drying process of ink
In the production of sheet printing, ink drying is a complex physical and chemical reaction process. Only by reasonably controlling the drying speed of ink and mastering the physical and chemical mechanism of ink drying can we effectively carry out rapid printing operation and ensure product quality. Ink drying too fast will reduce the normal transmission performance of ink and affect the normal progress of production; It causes the blotting to be weak, the ink color to be weak, and the ink on the surface of the printing plate and ink roller is dry, which hinders the ink dropping in the transmission; Make the dry layer of printing plate expand outward; The excessive amount of desiccant causes the increase of ink adsorption and the dirty blank part. The ink drying too slowly can cause overprint difficulty, adhesion, adhesion and firmness reduction; It is easy to cause scratches during transmission. Therefore, the drying speed of ink should be appropriate. Too fast and too slow are unfavorable.