Metal printing is a method of printing on metal plates, usually with graphic images printed on materials such as tin-plated iron or aluminum.
The printing method of metal printing press uses flat plate offset printing. The structure of the plate making and printing press is basically the same as that of ordinary paper printing. Because the metal plate to be printed cannot be bent and tightly attached to the printing roller like paper, the metal plate can only pass horizontally between the rubber roller and the printing pressure roller, so the arrangement between the three rollers of the printing part and the output part is different from that of ordinary offset printing.
Metal printing has multiple coating compositions due to the characteristics of metal raw materials.
Before printing, the metal plate is cleaned and then printed using offset printing. First, print a layer of bottom varnish, then print a white bottom layer, and then print graphics and text in order, and finally print gloss oil. Because metal does not have absorbency, it must be dried by baking after each color is printed, so the metal printing press is equipped with a drying device. The purpose of baking is to accelerate the oxidation and film drying of volatile ink and prevent it from affecting the overprinting of the next color.
Drying methods such as steam, infrared, and electric heating can be used. The plate drying oven is long-shaped. When the printed product enters from one end and comes out from the other end, it has already been dried. The oven temperature is between 150 and 2000℃. The temperature when printing the bottom varnish needs to be 200℃, and when printing the overprinting and gloss oil, the oven temperature is about 150℃.
Metal prints are prone to wear printing plates, so indirect printing is used, and the print is transferred through the metal printing press rubber cloth, with a hard-soft-hard contact form to meet the printing transfer performance.
The ink used in metal printing has special requirements. Because the substrate is metal, it is more difficult for the ink to adhere to the metal surface. Therefore, the ink should meet the following requirements: heat resistance, after baking at 150℃, the ink color should still be bright, the color ink should not be dim, and white should not turn yellow; firmness, that is, strong adhesion, so that the graphics and texts printed are not detached during mechanical stamping after can making; resistance to pressure steam, the ink layer can withstand the influence of steam after food cans are sterilized and disinfected, without changing or expanding; resistant to solvent corrosion, as well as light resistance, weather resistance, etc., which can withstand sunlight and various climates without changing color or changing color slightly.
Metal printing press is commonly used in the manufacture of candy and biscuit boxes, food cans, stationery boxes, beer cans, children's toys, and beautiful decorations.