(1) The ink is required to have good adhesion and mechanical properties
Since tinplate prints are eventually made into food cans, toys, metal frames and barrels and cans of chemical products, they need to be cut, bent and stretched, so the printing ink is required to have good adhesion to tinplate and corresponding mechanical properties. In order to improve ink adhesion, the tinplate is first primed in white before printing. White is the base color of all pictures and has high brightness. After adding other high-energy hues, the brightness of each hue can be improved to form color levels.
(2) Requirements for white ink
The surface of tinplate is silver white (or yellow), with metallic luster, before printing color graphics, the surface needs to be painted white or printed white, limited by the ability of ink coverage, 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, whiteness requires white ink to have good adhesion with the primer, and it will not yellowish after multiple high-temperature baking, and it will not fade after high-temperature steaming. Priming tinplate can increase adhesion to tinplate and have good adhesion to white ink. The commonly used primer is epoxyamine-based type, which has the characteristics of light color, no yellowing and non-aging after multiple baking, and good flexibility and impact resistance.
(3) Requirements for color ink
Color inks printed with tinplate, in addition to a certain degree of water resistance, also need to have their own special requirements. Since the surface of tinplate is impermeable to moisture and solvents, it needs to be baked and dried, so its ink should be heat-cured. High requirements for pigment tinting strength and durability. In addition to the basic performance of general offset printing ink, the printing iron 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 printing iron.
(4) Drying process of ink
In tinplate printing production, the drying of ink is a complex physicochemical reaction process. It is necessary to reasonably control the drying speed of ink and master the physical and chemical mechanism in ink drying, in order to effectively carry out rapid printing operations and ensure product quality. Ink drying too quickly will reduce the normal transmission performance of ink and affect the normal progress of production; Cause the imprint to be faint, the ink color is light, and the ink dry knot appears on the surface of the printing plate and ink roller, which hinders the lower ink in the transmission; Expand the graphic and text dry knot layer of the printing plate outward; The amount of desiccant is too large, resulting in increased ink adsorption, dirty blank parts and other phenomena. The ink drying is too slow, which can cause overprinting difficulties, adhesion, adhesion, etc., and reduced firmness; It is easy to cause scratches during transmission. Therefore, the drying speed of the ink should be appropriate, too fast and too slow is unfavorable.
(5) Special structure of printing equipment
Due to the different substrates, the auxiliary mechanism of the tinplate printing machine is also different from the printing paper offset printing machine. Tinplate is insoluble in water and does not adsorb solvents, so printing inks need to be baked at high temperature to make the solvent volatilize and solidify the conjunctiva. Therefore, the printing process device generally needs to be equipped with a drying room. The whole tinplate printing automatic line is generally about 50 meters long, with the characteristics of precision and largeness. In addition, the tinplate printing machine is controlled by using magnet sheets and double sheets, and the high hardness of the tinplate material also determines that the advanced continuous iron transmission structure cannot be used in the printing process, and the structure of the push, alignment and stacking parts is different from the offset printing machine of the printing paper.
