At present, tinplate cans on the market usually have to be coated with a certain kind of paint on their inner surface. The purpose is to prevent the chemical interaction between the filling and the wall of the can and the contamination of the filling with trace elements , which protects the filling. The quality of the material. The packaged product can be stored, transported and sold for a long time without affecting its value in use.
- coating process
The reason why tinplate cans have become the best packaging materials for food cans is their effectiveness should be attributed to the important protective effect of the inner coating to a large extent. The performance of the coating should not only have corrosion resistance but also have good adhesion , Flexible, non-toxic and tasteless. The coating must be able to withstand high-temperature heating without losing its performance. In addition, the type of coating and the thickness of the coating must be selected according to the contents of the can.
The coating thickness of the coating is generally required to be controlled between 3.5-6.0g/m2. Within this thickness range, the coating has a certain porosity, and the liquid containing the contents penetrates the surface of the tin layer through these gaps, slowly fusing the tin to form tin ions, so as to achieve the purpose of extending the shelf life of the iron can.
- Coating principle
The coating process is before the tinplate cutting and punching, and after the printing. The paint using the roller coaster is transferred to the rubber cylinder through the homogenizing roller. Under the blanket cylinder, there is an impression cylinder with a gripper device inside. Promote the passage of tinplate to complete the painting operation. Due to the spacing between the tinplates, a small amount of paint will be taken away by the impression cylinder. Use a scraper to scrape off the impression cylinder, and the scraped paint will flow into the receiving tray, after being collected, flow back to the storage bucket through the conduit and be recycled.
In order to obtain a good coating quality, in addition to the performance of the coating itself, reasonable control of the baking conditions has a close relationship with the formation of the coating structure. The baking temperature and baking time depend on the fixed conditions required by the paint coating. Therefore, the operator must fully understand the relationship between the temperature of the baking environment and the surface temperature of the tinplate during production and ensure that the coating printed on the surface of the tinplate can be cured at the required temperature and time to obtain a high-quality coating. Under normal circumstances, the temperature of the drying room and the temperature of the surface of the tinplate differ by 20°C. The temperature difference is closely related to the heat capacity of the drying room, the specifications of the tinplate, and the printing speed, and must be measured according to the actual situation.
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