Tinplate printing is also the use of the physical properties of water and ink repulsion. With the help of printing pressure, the printing plate graphic is transferred onto the tinplate by a blanket, which belongs to the principle of lithographic offset printing. Due to the special physicochemical properties of tinplate and the reworkability of printed materials, the printing process is quite different from ordinary offset printing.
Tinplate printing has special requirements for inks:
1. Requires ink with good adhesion and mechanical properties
As tinplate prints are ultimately to be made into food cans, beverage cans, toys, aerosol cans, chemical barrels, miscellaneous cans of various shapes, etc., they need to be cut, bent, and stretched, thus requiring printing inks to be better for tinplate. Adhesion and corresponding mechanical properties. In order to improve the adhesion of the ink, the tinplate first needs to be painted white or primed before the printing. White is the basic color of all pictures, and has a high degree of brightness. After adding other high-energy hue, it can increase the brightness and form the color gradation.
2. Requirements for white ink
The surface of the tinplate is a silvery metallic luster. Before printing color images, it is necessary to coat the surface with white or white ink, which is limited by the ability of ink coverage. For example, printing with a monochrome machine often requires 2 times of white printing, and its whiteness can be Up to 75%. Whiteness, as an important indicator of the quality of tinplate printing products, requires white ink to have good adhesion with the primer. After many times of high-temperature baking, it does not yellowen, and high-temperature cooking does not take away color. Priming tinplate makes it have strong adhesion with tinplate and good adhesion to white ink. Commonly used primers are epoxy amine type, with light color, no yellowing after many times of baking, no aging, and good flexibility and impact resistance.
3. Requirements for color ink
In addition to having a certain degree of water resistance, tinplate printed color inks also require special requirements. Since tinplate surface does not penetrate moisture and solvents, it needs to be baked and dried, so its ink should be heat-cured. The coloring power and durability of the pigment are more demanding. In addition to the basic properties of offset printing inks, iron printing inks should also have characteristics such as heat resistance, strong ink film adhesion, impact resistance, good rigidity, resistance to cooking and light resistance, etc., according to the characteristics of the printed iron.
4. Ink drying process
In the production of tinplate printing, the drying of the ink is a complicated physical and chemical reaction process. It is necessary to reasonably control the drying speed of ink and master the physicochemical mechanism in ink drying in order to effectively perform fast printing operations and ensure product quality. Ink drying too fast will reduce the normal ink transfer performance, affect the normal production; caused by the imprinted ink, pale ink, printing plate, ink roller surface appears dry ink, so that the transfer of the ink is blocked; make the plate graphic dry knot The layer expands outwards; so that the amount of desiccant is too large and the ink absorption increases, and the blank part becomes dirty. The ink drying is too slow and can cause difficulties in overprinting, adhesion, poor adhesion, and reduced firmness, which can easily cause scratches in the transport process. Therefore, the drying speed of the ink should be suitable, too fast and too slow are unfavorable.
