Talk about the food packaging coating of 622 epoxy coating applied to steel drum
Shanghai Xugong Coating Technology Co., Ltd. Xu Guoxing
Epoxy coating is one of the best coatings for metal. It is the earliest and most common internal coating used in the domestic steel drum industry. It is also one of the coatings commonly used in foreign steel drum industry.
One of the main film formers of epoxy coatings. It is epoxy resin. The epoxy resin used in the X-622 steel drum inner coating is a bisphenol A diglycidyl ether type resin obtained by polymerizing epichlorohydrin and bisphenol A in the presence of sodium hydroxide.
Since both epichlorohydrin and bisphenol A are difunctional compounds, such epoxy resins are linear in structure. This epoxy resin contains a hydroxyl group, an ether group and a very reactive epoxy group. Among them, the hydroxyl group and the ether group have a strong polarity, so that the epoxy resin generates a strong force with the adjacent interface. Therefore, the paint used in the X-622 steel drum has a strong adhesion to the surface of the steel drum. The active epoxy group gives the coating and the surface of the steel barrel a high strength bonding force.
The molecular chain of the bisphenol A diglycidyl ether type epoxy resin used in the X-622 steel drum inner coating is carbon-carbon bond and ether bond structure, and the chemical property is very stable. Therefore, its chemical resistance and acid and alkali resistance are very good. In addition, the epoxy group of this epoxy resin has a small internal rotation resistance at both ends of the molecule, and the epoxy resin used in the coating of the X-622 steel drum is softened by low viscosity. Processing, so it is more flexible. This is very suitable for the inner coating process of the steel drum industry (coating of the barrel and the bottom of the bucket, top coating, baking and curing, and then re-winding).
The X-622 steel drum inner coating utilizes the reactive epoxy group in the epoxy resin structure to crosslink and solidify with various organic compounds to form a strong three-dimensional network structure film, and the butanol etherified phenolic resin. Crosslinking at high temperatures further enhances the mechanical and chemical resistance of the coatings used in X-622 steel drums. The cross-linking curing reaction at this high temperature only releases three parts of water, no other by-products are released during the process, and the shrinkage is small, and the cross-linking curing has a very strong and dense network structure film, thereby further enhancing Adhesion, mechanical properties, corrosion resistance and chemical resistance of the coating.
The "6009 Epoxy Resin and Curing Agent Coating Toxicity Test Report" of the Shanghai Health and Epidemic Prevention Station Toxicology Room (1989) said: The gold-cured epoxy resin product is generally considered to be practically non-toxic or substantially non-toxic. The high molecular weight epoxy resin and the phenolic or amino resin cured coating film can be above 15000mg/KG in an oral test of rats, and it is negative by AmeS test, which proves that there is no teratogenicity, no cell mutation, and no carcinogenicity. Can be used for the coating of the inner wall of food cans. (6009 epoxy resin is bisphenol A diglycidyl ether epoxy resin)
Edited by Qu Guilin and published by Chemical Industry Press, "Epoxy Resin and Epoxy Coatings" also records: Shanghai Coatings Research Institute uses epoxy resin to develop and produce food can coatings; Japan Kansai Coatings Co., Ltd. uses bisphenol A epoxy resin 1. Developed canned interior coatings; Dainippon Ink Company developed a food canned enamel coating with excellent food preservation properties based on bisphenol A epoxy resin.
In addition, there are many reports about non-toxic epoxy resins and foods in foreign countries:
For example, bisphenol A epoxy resin and phenolic epoxy resin rats can be orally administered with LD50>2000mg/Kg.
(Hine, C., RoWe.VK, darmer, KI, "Epoxy Compounds"
Clayton, GD, Clayton, FE, (eds), "pate'ys Industrial Hygiene and Toxicology" vol. 2A, 2141~2258 John Wiley & Sone, Inc., New York, 1981.)
Another example: the experimental animals were placed in a saturated steam of low-concentration epoxy resin for 50 days, 7 hours a day, no obvious toxicity. The dominant lethal mutation index (Ames) test proved to be non-carcinogenic, teratogenic, and non-cell-mutating, and safe to use.
(Holland, JM, Gosslee, DG, Williams, Cancer Researce, 39, 1718~1725 (1979));
(Holland, JM Gibson, LC, Whitaker, Eisenhowen et al., "Chronic Dermal Toxicity of epoxy Resins I, Skin Cocinogcnic Potency and General Toxicity", report ORNL5762 Prepared for the US DOE by Oak Ridge National Laboratory Oak Ridge, Tenn, 1981. )
Therefore, the epoxy resin cured by the butanol etherified phenolic resin is substantially non-toxic, so that such a coating can be completely applied to the inner wall of a food steel drum. In fact, epoxy resins and phenolic resins have a long history as coatings in contact with food at home and abroad.
In fact, according to the requirements of GB4805 food canned inner wall epoxy phenolic coating hygiene standards for testing:
1. Soak the paint in free phenol (water) at 95 Â° C for half an hour. The standard requires that the amount of leaching be less than 0.1 mg per liter, while the 622 coating does not exist at all.
2. Soak the paint in free formaldehyde (water) at 95 degrees Celsius for half an hour. The standard requires that the amount of leaching be less than 0.1 mg per liter, and the 622 coating is not tested at all;
3, other tests such as: 60 degrees Celsius 4% acetic acid; 60 degrees Celsius 20% ethanol; 37 degrees Celsius n-hexane; 95 degrees Celsius water, 622 paint detection value is only about one-third of the standard allowable value, while 622 paint 95 Celsius consumption of potassium permanganate is only about one-fifth of the standard allowable value.
622 coatings have been tested by SGS and are considered to meet the requirements of the US FDA for packaging coatings for food and medicine.
But here is the finished gold-cured coating. If it is not finished with gold, it is of course toxic, and all the properties of the coating are not reflected. Conversely, if the curing temperature is too high, in addition to the coking of the coating, the original performance is destroyed, and other toxic gases such as propylene and methyl chloride are produced. Therefore, such coatings are preferably baked at a temperature of approximately 185 degrees Celsius for 45 minutes. For the drying tunnel which can not form 40 minutes, it can also be cured according to different baking conditions and baking methods with reference to 220 Â° C for 20 minutes.
The model number of 622 paint is named after the trial production of the paint and the date of commencement of production. It has been nearly half a century since the official mass production began in February of the year. Due to its excellent performance, once the paint is used on steel drums, many barrel factories come to buy them. However, due to the nature of the state-owned barrel factory (the paint shop inside the barrel factory, the paint is not in the business scope), it cannot be sold. It was not until the reform and opening up that it made great strides toward the market. The industries involved have been used in various industries such as chemical industry, light industry, pharmaceuticals, food, etc., especially in the export packaging steel drums of honey, juice, edible oil and chemical. In recent years, 622 coatings have been exported to the Middle East, Southeast Asia, Russia and other foreign barrel factories, and have received wide acclaim.
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