The difference between metal box printing ink and carton printing ink

Reasonable selection of paint and varnish is the key to affecting the printing quality of metal boxes. Reasonable selection of paint and varnish is a prerequisite to ensure that the metal box printing has good firmness, color, whiteness, gloss and processing suitability. According to different uses, metal printing coatings can be divided into primer coatings, white coatings, varnishes, inner wall coatings, edge coatings and so on. Side seam coatings can be divided into inner side seam coatings and outer side seam coatings. After the inner side seam coatings are dried, they are required to meet the food hygiene requirements.

Metal box printing ink is a special ink printed on tinplate and other metal sheets. It is mainly composed of pigments, binders, fillers and auxiliary agents.

In addition to the printability of general offset printing inks, metal box printing inks should also have the following characteristics

(1) Impact resistance and strong adhesion. In the post-printing process, metal materials such as tinplate must go through canning processes such as cutting, bending, impact, and seaming. Therefore, the ink layer should have sufficient adhesion to make the printed tinplate withstand the stamping of the mold. And has excellent machining properties (including flexibility, surface hardness and impact strength, etc.). At the same time, the ink layer is required to have good lipophilicity, so that it can be well combined with the varnish to ensure a certain adhesion between the tinplate and the ink layer and the varnish.

(2) Firm and hard. In the process of can making, the tinplate prints after printing and polishing will inevitably collide with each other, and the cut tinplate is very sharp, it is easy to damage the pattern on the metal surface and cause the ink layer to fall off, so the ink layer is required Firm and hard.

(3) Heat resistance. In the drying process, the printed parts have to go through a certain temperature and time heating and drying process. Therefore, pigments and binders with strong heat resistance should be selected to prevent the ink from yellowing after heating.

(4) Solvent resistance. In order to make the appearance of metal prints beautiful, increase the hardness, and prevent damage caused by friction, glazing treatment is required. The glazing oil contains a large amount of strong solvents, and it is required that the dried ink layer does not change color, swell, or shrink.

(5) Light resistance. Metal containers are required to change the color of the pattern under sunlight and light.

(6) Retort resistance. Some metal cans need to be boiled for sterilization or heated before drinking. Therefore, it is required that the ink layer does not change color, stain, generate bubbles, and lose gloss after being steamed.

Since the surface of the metal printing material cannot penetrate, it is easy to cause dots to increase. Compared with carton printing inks, metal box printing and offset printing should use high-viscosity inks. The metal surface is a non-absorbent surface. Excessive wetting water on the plate is prone to emulsification of the ink. Therefore, the water and ink balance on the plate should be achieved by controlling the thickness of the water film on the plate and the amount of ink.

In metal box printing, in order to improve the adaptability of post-press processing and to make the surface of the printed part have a certain degree of gloss, the glazing treatment (post-press coating) should be carried out before the printing ink is completely dried to form a uniform and smooth Coating film to avoid bleeding. At the same time, the metal printing ink should have a certain degree of hardness and toughness, and its properties cannot be changed when heated repeatedly. The base color coating and varnish should have good adhesion.