Related knowledge of tinplate packaging material printing

Tinplate printing principle:

Tinplate printing also uses the physical properties of water and ink to repel each other. With the help of printing pressure, the printing plate graphics are transferred to the tinplate through the blanket, which belongs to the principle of lithographic offset printing. Due to the special physical and chemical properties of tinplate and the reprocessing properties of printed matter, its printing process is quite different from ordinary offset printing.

Tinplate printing has special requirements for ink:

(1) The ink is required to have good adhesion and mechanical properties

Since tinplate prints are ultimately made into food cans, toys, metal photo 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 the corresponding machinery. performance. In order to improve the adhesion of the ink, the tinplate needs to be whitened first 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 a gradation.

(2) Requirements for white ink

The surface of tinplate is silvery white (or yellow) with metallic luster. Before printing color graphics, the surface needs to be whitened or printed. Due to the limitation of ink coverage, monochrome machines often need to be printed twice, and its whiteness up to 75%. Whiteness is an important indicator of the quality of tinplate printing products. It is required that the white ink has a good bonding force with the primer, and will not yellow after repeated high temperature baking, and will not lose color after high temperature steaming. Primer on tinplate can increase the adhesion with tinplate and has good bonding force to white ink. The commonly used primer is epoxy amine type, which has the characteristics of light color, no yellowing and no aging after repeated baking, and good flexibility and impact resistance.

(3) Requirements for color ink

In addition to a certain degree of water resistance, the color ink printed on tinplate also needs to have its special requirements. Since the surface of tinplate is impermeable to moisture and solvent, it needs to be baked and dried, so its ink should be heat-curable. The tinting strength and durability of the pigment are required to be high. In addition to the basic properties of general offset printing 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 tinplate printing, the drying of ink is a complex physical and chemical reaction process. It is necessary to reasonably control the drying speed of ink and master the physical and chemical mechanism of ink drying, so as to effectively carry out fast printing operations and ensure product quality. If the ink dries too fast, it will reduce the normal transfer performance of the ink and affect the normal production; it will cause the imprint to become vacant, the ink color will become pale, the ink will dry on the surface of the printing plate and the ink roller, which will block the ink in the transfer; The layer expands outward; the excessive amount of desiccant causes the ink adsorption to increase, and the blank part becomes dirty. If the ink dries too slowly, it can cause difficulty in overprinting, sticking, adhesion, etc., and reduce the firmness; it is easy to cause scratches during the transmission process. Therefore, the drying speed of the ink should be appropriate, too fast or too slow is unfavorable.

(5) Special structure of printing equipment

Due to the different substrates, the auxiliary mechanism of the tinplate printing press is also different from that of the printing paper offset press. Tinplate is insoluble in water and does not absorb solvents, so the printing ink needs 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 entire tinplate printing automatic line is generally more than 50 meters long, and has the characteristics of precision and bulk. In addition, the tinplate printing machine is controlled by magnets for splitting and double sheeting. The high hardness of the tinplate material also determines that the advanced continuous iron conveying structure cannot be used in the printing process. paper offset press