Metals include ferrous metals (such as steel) and non-ferrous metals (such as aluminum alloys). In order to prevent rust, they must have surface treatment. There are many surface treatment methods, and cathodic protection surface treatment is a commonly used method. In the cathodic protection process, a zinc-rich epoxy primer is used.
Zinc powder is a chemically active raw material. The electrode potential of zinc is 0.7628V, and the electrode potential of iron is 0.409V. In the paint film, the zinc powder contacts each other and contacts with steel to conduct electricity. Therefore, when the steel structure coated with zinc-rich epoxy primer is corroded, because the electrode potential of metallic zinc is negative in a wide temperature range, zinc is the anode and is corroded, and iron has the cathodic protection and plays the cathodic protection of sacrificial anode. At the same time, the product of zinc powder corrosion can fill the pores of the coating film, seal the damaged part of the coating film, and play a role of shielding the corrosive medium. Therefore, although the coating of zinc-rich paint is relatively thin, it still has a good anti-rust effect and a long service life.
Organic resins, such as epoxy resin, chlorinated rubber, vinyl resin and polyurethane, are often used as the film-forming base of zinc-rich epoxy primer. As early as 1962, it was discovered that a zinc-rich epoxy primer formulated using a partial hydrolysate of alkoxysilane (such as ethyl orthosilicate) or a mixture of alkali metal silicate and zinc powder can provide a good effect on iron substrates. The cathodic protection performance is better than the organic resin-based zinc-rich epoxy primer. However, the disadvantage of this technology is the short shelf life of the paint and the short valid period during use. After 12 years, it was discovered that the stability and overall performance of the zinc-rich epoxy primer obtained by transesterifying silicate and organic polyols (such as ethylene glycol or glycerol) were greatly improved. This innovation was one of the most widely cited silicone inventions from 1964 to 1985. Because the zinc-rich epoxy primer introduces Si-O bond polymer, it has good corrosion resistance and adhesion, excellent weather resistance and heat resistance.