Metal printing is printing on a metal plate, so it is also called printing, metal printing. It is usually printed on the surface of tinned iron or aluminum plate.
The products printed on the metal sheet are mainly used for manufacturing food packaging boxes, stationery boxes, children's toys and interior decoration products.
Metal printing uses hard metal substrates, which are very easy to wear plates, so lithographic printing is used, and graphics are transferred through rubber cylinders. Therefore, the structure of the printing machine is basically the same as that of ordinary printing paper. The metal plate cannot be bent like a paper and attached to the impression cylinder, and can only pass horizontally between the rubber cylinder and the impression cylinder. In addition, the iron offset printing machine must be equipped with a drying system.
The process of metal printing is:
Sheet metal processing → printing → drying
1. Iron sheet treatment
Before printing, use a dilute alkaline solution or alcohol to wipe off the dust and oil on the surface of the metal plate.
2. Printing
The surface of the metal plate is smooth and non-absorbent. Therefore, the ink printed on the metal sheet must have good adhesion, and must have good heat resistance, light resistance, solvent resistance, cooking resistance and mechanical impact resistance.
On the metal plate, it is usually printed multiple times, the first time the bottom varnish is printed to protect the metal from corrosion. The second time, the bottom layer was printed with white ink to cover the color of the metal, and then the graphics were printed in order according to the printing color sequence. Finally, varnish is printed to protect printed graphics.
3. Dry
The metal surface is not absorbent, so every time you print, you need to dry the ink. Drying method can use steam, infrared, electric heating and so on. The printed matter enters from one end of the drying tunnel and finishes drying when the other end comes out. The humidity of the drying tunnel depends on the printing ink, generally between 150-200 ℃. The temperature of the bottom varnish is 200 ° C, and the drying temperature of the gloss oil is about 150 ° C. If the temperature is too low, the drying is not thorough, and if the temperature is too high, the ink discolors and the mechanical properties decrease.
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