Generally, printed tinplate sheet is coated with bright oil after printing to protect the image and text and enhance the decorative effect. After the tinplate is printed, printed tinplate sheet is coated with wrinkle oil (Crystal Clear Varnish), and it is wrinkled and shaped after being baked by a special process, which is crystal-transparent scale.
The reflection of light makes the finely printed pictures and texts on the electrolytic tinplate sheet printed have a three-dimensional effect. The technological process of coating wrinkle oil is as follows: Coating wrinkle oil on printed tinplate sheet---insulation baking wrinkling---high temperature drying and forming, Coating wrinkle oil on printed tinplate sheet is a four-roller coating machine, and a roller coating method is used to coat a tinplate printing with a thin and even layer of wrinkle oil.
The operating viscosity of wrinkle oil is 25~30s, the usage amount is about 15g/m² on electrolytic tinplate sheet printed, and the dry film thickness is about 10pm. The characteristics of the wrinkle oil itself directly determine the quality of the printed tinplate sheet product, and the thickness of the coating cannot be ignored, too thick or too thin can not get the desired effect on tinplate printing .
If the film is too thick, only large cracks will appear without wrinkling; if the film is too thin, the pattern is unclear or the surface is smooth. In general, the color of the printing ink does not have much effect on wrinkle oil wrinkling. However, some darker colors do not wrinkle very well, and applying wrinkle oil on gold or silver (tinplate) works best.
Low temperature baking and wrinkling is the most critical process, and the quality of the product is mainly determined by the control of baking temperature and time. Baking should use a special oven, such as a tunnel oven, to ensure uniform temperature distribution in the oven. Generally, it is dried by burning liquefied petroleum gas or kerosene, blowing hot air, and transferring heat through air convection.
The system now uses more advanced automatic ignition and thermostatic control technology. The baking process used is not only related to the structure of the oven, but also related to the tinplate printing speed of the offset press. At present, most of the printing tinplate use medium and low speed offset presses, and the rotation speed is 30~70rpm. The high speed of the offset press, the short drying time, the higher the drying temperature, and vice versa. Because the drying time and temperature have a compensatory relationship within a certain range. If the baking temperature is too high, there will be no wrinkles at all, and the effect is the same as applying bright oil; if the baking temperature is too low, although wrinkles will appear, it is easy to damage the film layer, and it is difficult to automatically feed the material when it is dried at high temperature.
After low-temperature baking and wrinkling on electrolytic tinplate sheet printed , the product has been basically formed, but it is only dry to the touch, and it needs to be dried at a high temperature of 140 to 145 ° C for 10 to 15 minutes to make it completely dry. Only then can it have excellent physical and chemical properties for stamping and forming.