Introduction of process performance of polyamide coatings, perchloroethylene coatings and organic fluorine coatings

As the scope of food safety definitions continues to expand, countries are increasingly demanding food and agricultural product packaging. In the international market, many foods and agricultural products are packed in steel drums. The hygienic requirements for the paint on the inner wall have attracted wide attention from all countries. In order to meet the needs of the international market, China also makes health requirements for the paint on the inner wall of export food and agricultural product packaging barrels. Specific regulations have been issued. According to the regulations, the food grade coatings allowed on the inner wall of the drum are: polyamide coating, perchloroethylene coating and organic fluorine coating.

Polyamide epoxy resin coatings are epoxy resin coatings, and epoxy resin coatings are also curing film forming coatings. The epoxy resin is generally formed by polymerizing bisphenol A (diphenol propane) and epichlorohydrin. Depending on the degree of polymerization, the molecular weight of the epoxy resin is also different. From a hygienic point of view, the larger the molecular weight (ie, the smaller the epoxy value), the more stable, and the less likely the harmful substances are dissolved to migrate into the food, so the safety is higher. As a curing agent for polyamide epoxy resin coatings, polyamide itself is a high molecular compound, and no toxicity has been reported. The quality of the polyamide epoxy resin (the epoxy value of the epoxy resin) is closely related to the ratio of the curing agent and the degree of curing. The curing agent ratio is appropriate, and the higher the degree of curing, the less uncured material migrates into the food in the epoxy resin coating. According to GB9686-88 "Sanitary Standard for Polyamide Epoxy Resin Coatings on Inner Walls of Food Containers", the evaporation residue of polyamide epoxy resin coatings in various solvents should be controlled below 30 mg/L.

The perchloroethylene coating is made of perchloroethylene resin. With plasticizer, it is naturally dried to form a film after being coated and sprayed on the inner wall of the drum. Perchloroethylene coatings are generally classified into primers and topcoats. The perchloroethylene resin contains a perchloroethylene monomer, which is a carcinogenic toxic compound. The perchloroethylene coating after film formation may still contain residual vinyl chloride. The vinyl chloride monomer residue in the perchloroethylene coating after film formation according to GB7105-86 "Sanitary Standard for Perchloroethylene Vinyl Interior Coatings for Food Containers" shall be controlled at 1 Mg/kg or less. Additives such as plasticizers and solvents used in perchloroethylene coatings must comply with the relevant provisions of GB9685-94 "Sanitary Standards for the Use of Auxiliaries for Food Containers and Packaging Materials". Do not use toxic or highly toxic additives. The coating film is required to be uniform, free from bubbles, spots, wrinkles and shedding.

Organic fluorine coatings include polyvinyl fluoride, polytetrafluoroethylene and polyhexafluoropropylene coatings. These coatings are polymerized with vinyl fluoride, tetrafluoroethylene and hexafluoropropylene as the main raw materials, and are coated with certain additives in the packaging drum. The inner wall surface. Organic fluorine coatings have the characteristics of anti-adhesion and corrosion resistance, but their acid resistance is poor, so it is widely used in steel drums containing inner coating drums for honey. In terms of application, the organic fluorine coating on the steel barrel of the inner coated honey packaging barrel is polytetrafluoroethylene, referred to as PVF coating. It is a kind of polymer compound, chemically stable, and generally does not have monomer residue. It is a safer inner wall coating for food packaging barrels. However, when cleaning the inner wall of the steel drum of the packaging drum, most of the current barrel manufacturing enterprises use the spray cleaning and drying line for cleaning. The cleaning agent is usually chromate, which may cause the chromium salt to remain on the surface of the container and then be mixed into the inner wall coating.

Therefore, in the production of inner wall honey packaging barrel steel drum, the inner wall honey packaging barrel steel drum should be inspected according to GB1167-89 "Sanitary Standard for Polytetrafluoroethylene Coating on the Inner Wall of Food Containers". The standard stipulates that the appropriate amount of chromium and fluorine should be controlled between 0.01 mg / liter and 0.2 mg / liter, respectively. In addition, when PTFE is baked, if the temperature reaches 280 ° C, it will fission and produce highly volatile toxic fluoride. Therefore, when using PTFE inner wall honey packaging barrel steel drum, it is generally baked. The baking temperature must not exceed 250 °C.

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