Tinplate printing special requirements for ink

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 to the tinplate by the blanket, which belongs to the principle of lithographic offset printing. Due to the special physicochemical properties of tinplate and the reworkability of printed matter, the printing process is quite different from ordinary offset printing.

Tinplate printing has special requirements for inks:

(1) Requires ink to have better adhesion and mechanical properties

As tinplate prints are eventually made into cans and cans for food cans, toys, metal photo frames, and chemical products, they need to be cut, bent, and stretched. Therefore, printing inks are required to have good adhesion to tinplate and corresponding mechanical properties. performance. In order to improve the adhesion of the ink, it is necessary to first perform white coloring on the tin before printing. White is the basic color of all pictures and has a high degree of brightness. After adding other high-energy hue, the color contrast can be increased to form a color gradation.

(2) Requirements for white ink

The surface of tinplate is silvery (or yellow) and has a metallic luster. Before the printing of color images, the surface needs to be painted white or printed. Due to the limitation of ink coverage, the monochrome machine often needs to be printed twice, its whiteness. Up to 75%. Whiteness, as an important indicator of the quality of tinplate printing products, requires white ink to have a good bond with the primer. After many times of high-temperature baking, it is not yellowed, and high-temperature steaming does not remove the color. Priming tinplate can increase the adhesion with tinplate and have 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 ordinary 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) Drying process of ink

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 result in difficulties in overprinting, adhesion, adhesion, etc., and the reduction in firmness; it 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.

(5) Special structure of printing equipment

Due to different substrates, the auxiliary mechanism of tinplate printing presses is also different from offset printing presses. Tinplate is insoluble in water and does not absorb solvents. Therefore, the printing ink needs to be baked at a high temperature to cure the solvent volatilization conjunctiva. Therefore, a printing room is generally equipped with a drying room. The entire length of the tinplate printing automatic line is generally more than 50 meters in length, and has the characteristics of precision and largeness. In addition, the tinplate press is controlled by magnet sorting and double sheeting. The high hardness of the tinplate material also determines that the advanced continuous iron feeding structure cannot be used in the printing process, and is different from the structure of the pusher, level and stacking part. Offset printing paper machine.

Reprinted from: Chen Yi