In 1935, the first application of silicon-based (SBT) technology appeared. American scholar Hyde and Soviet scholar Andrianov developed the industrial application of silicone, and obtained silicone polymers through hydrolysis reaction, giving birth to the first generation of silicone products - silicone resin; in 1941, GE successfully carried out industrial production of methylchlorosilane synthesized by direct method; in 1943, silicone resin was industrialized using silicone monomer synthesized by direct method and used as high-temperature resistant insulating coating. After decades of development, the silicone materials used in coatings are no longer limited to silicone resins. With the development of the electronics industry, coatings and inks based on silicone rubber have also developed rapidly. In order to improve the performance of coatings, various silicone oils and their secondary processed products are also widely used as functional additives for coatings. In a broad sense, fabric finishing agents, leather finishing agents and paper release agents are also silicone coatings on the surface of fabrics, leather and paper, but the coating industry does not currently include them.
Application of silicone in coatings
Insulating materials
The first application technology of silicone resin as coating is silicone resin impregnated glass fiber cloth tape, which is used as the insulation protective layer of wires on US Navy submarines. my country developed silicone resin in the 1950s. In the initial stage, it was mainly used for insulation impregnation of H-class motor coils, impregnation of glass fiber cloth for H-class motor wire and slot insulation, impregnation of glass fiber insulation sleeves, mica tape for insulation, etc.
Primer
The bonding force between the coating and the substrate includes mechanical bonding force, chemical bonding force, diffusion force and dipole force. The size of the bonding force directly affects the adhesion of the coating.
The main methods to improve the adhesion between the coating and the substrate are: substrate grinding, sandblasting, reducing the construction viscosity of the coating, increasing the construction temperature, improving the wettability of the substrate (using solvent wiping, corona, flame burning, oxidant treatment, etc.), and related to silicone is the use of adhesion promoters, that is, the use of primers. The silicone materials used for primers are mainly silanes. Alkoxysilane can improve the adhesion, fluidity, leveling, wear resistance, dispersion of pigments and fillers, water resistance and salt spray resistance of coatings and substrates, and has been widely used in primer formulations for various metals and silicon-containing materials.
Heat-resistant coatings
Since the main chain of silicone polymer is a SI-O-SI-O bond and the side group is an organic group, it has the characteristics of both inorganic and organic substances, and its high temperature resistance is better than most organic resins.
The heat resistance of resins used for coatings decreases in the following order: pure silicone resin> organic resin modified silicone resin> silicone modified organic resin> styrene-free acrylic resin/polycarboxylic acid resin> polyester/isocyanuric acid triglycidyl ester> epoxy/carboxyl polyester> acrylic acid/isocyanate> polyester/isocyanate> epoxy/phenolic acid> epoxy/dicyandiamide> epoxy/amine, so silicone resin is the main film-forming substance for heat-resistant coatings.
Industrial maintenance coatings
Industrial maintenance coatings are mainly used in industrial anti-corrosion, home appliances, ship water parts, furniture and coiled materials. In the early years, considering the high cost of silicone, industrial maintenance coatings mostly used organic resin coatings. In recent years, due to the continuous rise in oil prices, the development trend of the coating market is to reduce volatile organic compound (VOC) emissions and reduce costs. Extending the service life of coatings is one of the ways to reduce VOC emissions and reduce costs. Introducing silicone in organic resins is a good way to extend the life of coatings.
Sanitary coatings
Food hygiene is essential to human health. Coatings that meet sanitation standards are required in health care and food processing equipment. The way to achieve sanitation standards is either frequent cleaning or active sterilization of the coating surface. The selection of new bactericides is subject to multiple reviews, and the commercialization of new sterilizers requires expensive testing costs and cumbersome approval documents; on the contrary, prevention of microbial contamination can be achieved through easy-to-clean coatings, which can reduce many troubles. The most commonly used disinfection method is ultraviolet irradiation; however, ultraviolet irradiation will reduce the adhesion and wear resistance of organic resin coatings, and cleaning with detergents with abrasives and chemical disinfectants will destroy the protective properties of the coating. If silicone is introduced into the coating, it can give the coating excellent UV resistance, hydrophobicity, low surface energy (20-22 mN/m), non-stickiness and resistance to chemical detergents, extending the service life of the coating.