Coating type and suitability
Epoxy-phenolic resin coating:
The coating is the most widely used. It has good corrosion resistance for acidic foods, and its epoxy resin component gives it good adhesion and flexibility. Its baking temperature is about 200～210°C/15min.
It is mainly used for food cans such as soups, meats, fish, fruits and fruit juices. It can also be used for coating inner and outer surfaces of crown caps and other kinds of caps. The content ratio of the two resins can vary within a wide range. Although the adjusted formula can play a role in resistance to phosphate, it will reduce the adhesion of phenolic resin. For foods with high sulfur content, zinc oxide and aluminum powder fillers may be added: to prevent the occurrence of vulcanization spots on the inner wall of the tank. Coatings containing zinc oxide are not suitable for acidic foods and cause discoloration of individual green vegetables.
To obtain a good coating quality, in addition to the paint itself has sulfur and acid resistance, drying conditions in the drying room have a close relationship with the formation of the coating structure.
Baking temperature and baking time depend on the curing conditions required for the coating of the paint. Therefore, the operator must fully understand the relationship between the temperature in the drying room and the surface temperature of the tinplate in the production, so as to ensure that the coating on the surface of the tinplate can be cured at the required temperature and time, thereby obtaining a high-quality coating.
In general, the temperature of the drying room differs from the temperature of the tinplate surface by 20°C. The temperature difference has a close relationship with the heat capacity of the drying room, the specification of the tinplate, and the printing speed, and must be determined according to actual conditions.
The commonly used test method is to select five fixed points on the surface of tinplate, attach a temperature measurement paper on the surface, and then apply the iron sheet attached with the temperature measurement paper through the hot drying room, and require that the maximum temperature difference between the five test points is 10 Within °C. From the temperature measuring paper, the temperature and heat distribution of the drying room can be judged to know whether the coating is heated evenly.