(1) The ink is required to have good adhesion and mechanical properties
Because tinplate prints are ultimately made into food cans, toys, metal phase frames and chemical products, barrels, cans, need to be cut, bending and stretching processes, so the printing ink is required to have better adhesion to the tinplate and the corresponding mechanical properties. In order to improve ink adhesion, it is first necessary to white the tinplate before printing. White is the primary color of all the pictures, with high brightness. After adding other high-energy hue, it can improve the brightness of each color and form color level.
(2) Requirements for white ink
The surface of tinplate is silver (or yellow), there is a metallic luster, before printing color graphics, the surface needs to be painted white or printed white, limited by the ink coverage ability, the monochrome machine often needs to be printed white twice, its whiteness can reach 75%. As an important indicator of the quality of tinplate printing products, the white ink is required to have a good bonding force with the primer, and the color will not go out after many high temperature baking and high temperature steaming. The primer of tinplate can increase the adhesion with tinplate and has a good binding force for white ink. The commonly used primer is epoxy amine type, which has the characteristics of light color, no yellowing after repeated baking, no aging, and good flexibility and impact resistance.
(3) Requirements for color ink
Tinplate printing color ink, in addition to a certain degree of water resistance, but also need to have its special requirements. Because the surface of the tinplate is impervious to moisture and solvents, it needs to be baked and dried, so its ink should be thermoset. High requirements on the coloring power and durability of pigments. In addition to the basic properties of the general offset printing ink, according to the characteristics of the iron printing ink should also have heat resistance, ink film adhesion, impact resistance, good hardness, cooking resistance and light resistance.
(4) Ink drying process
In the production of tinplate printing, ink drying is a complex physicochemical reaction process. It is necessary to reasonably control the drying speed of ink and master the physical and chemical mechanism of ink drying in order to effectively carry out rapid printing operations and ensure product quality. Ink drying too fast will reduce the normal transfer performance of ink, affect the normal progress of production; Resulting in imprinting is weak, the ink color is pale, the ink is dry on the surface of the plate and the ink roller, so that the ink in the transfer is blocked; Make the printing plate graphic dry layer to expand outward; The amount of desiccant is too large, resulting in increased ink adsorption, and the blank part is dirty. The ink drying too slow can cause overprinting difficulties, adhesion, adhesion, etc., the firmness is reduced; It is easy to cause scratches in the transmission process. Therefore, the drying speed of the ink should be appropriate, too fast and too slow are unfavorable.
(5) Special structure of printing equipment
Due to the difference in substrate, the auxiliary mechanism of the tinplate press is also different from that of the printed paper offset press. The tinplate is insoluble in water and does not adsorb solvents, so the printing ink needs to be baked at high temperature to make the solvent volatilize the conjunctiva cure. Therefore, the printing process equipment is generally equipped with a drying room. The entire tinplate printing automatic line is generally more than 50 meters in length, with the characteristics of precision and huge. In addition, the tinplate printing machine is controlled by magnet distribution and double sheet, and the high hardness of tinplate material also determines that advanced continuous iron transmission structure cannot be used in the printing process, and the structure of the push section, level and pile part is different from that of the printing paper offset press.