Silicone resin, scientific name polysiloxane resin; English name: SilicONe resin, one of the four major SilicONe materials, has both the dual properties of organic resin and inorganic material, with high temperature resistance, weather resistance and chemical resistance that is difficult to achieve in general organic resin. In recent years, the research on silicone resins has made rapid progress and some achievements have been applied in industry.
Silicone is highly crosslinked network structure of organic siloxane, usually with methyl trichlorosilane, dimethyl dichlorosilane, phenyl trichlorosilane, diphenyl dichlorosilane or various mixture of methyl phenyl dichlorosilane, in the presence of organic solvents such as toluene, hydrolytic decomposition under low temperature, acid hydrolysate. The initial products of hydrolysis are a mixture of circular, linear, and crosslinked polymers, often containing considerable hydroxyl groups. The hydrolysate is washed to remove the acid, and the neutral primary polycondensation polymer is thermally oxidized in air or further polycondensation in the presence of catalyst, finally forming a highly cross-linked three-dimensional network structure.
Curing of silicone resins is usually achieved by condensation of silicon alcohol to form silicon oxygen links. When the condensation reaction is in progress, the reaction rate decreases due to the gradual reduction of the concentration of silanol, increasing steric resistance and poor fluidity. Therefore, to cure the resin completely, the reaction must be accelerated by heating and adding catalysts. Many substances catalyze the condensation of siliconols, including acids and bases, soluble organic salts of lead, cobalt, tin, iron and other metals, organic compounds such as tin dibutyl dilaurate or N, N, N', N' tetramethylguanidine salts, etc.
The properties of the finished product of silicone depend on the number of organic groups (the ratio of R to Si). The ratio of R to Si in the molecular composition of general practical silicone resins is between 1.2 and 1.6. As a general rule, the smaller the R: Si value is, the better the cured silicone resin will be at lower temperatures. The higher the R: Si value is, the cured silicone resin needs to be baked for a long time at 200-250 ℃. The hardness of the paint film is poor, but the thermal elasticity is much better than the former.
In addition, the ratio of methyl to phenyl groups in organic groups also has a great influence on the properties of silicone resins. The lower the content of phenyl in the organic group, the softer the film, the faster the condensation, the higher the content of phenyl, the harder the film, the more thermoplastic. Phenyl content between 20 ~ 60%, the best bending resistance and heat resistance of the film. In addition, the introduction of phenyl can improve the compatibility of silicone resin with pigments, and also improve the compatibility of silicone resin with other silicone resins and silicone adhesion to various substrates.
Silicone resin is mainly used for preparation of silicone insulating paint, silicone coatings, silicone adhesives and silicone plastics. High-grade building exterior wall coating and other high-performance coatings are the main market of silicone resin, the main varieties are modified polyester and modified acrylic resin. In addition, in recent years, the consumption of silicone resins in the electronic/electrical industry has grown rapidly, which is also an important driving force for the development of global silicone resins in the future, and the market prospect is very broad.
1. Plastic: mainly used in heat resistance, insulation, natural, anti-arc silicone plastic, semiconductor components shell sealing plastic, foam plastic.
2. Coating: silicone resin has excellent heat resistance, cold resistance, weather resistance, water resistance and other characteristics, and can obtain colorless transparent and good adhesion and wear resistance of the coating anti-adhesion film removal coating and moisture-proof hydrophobic coating.
3. Adhesives: as adhesives, polysiloxane has two kinds of silicone type and silicone type, which are different in structure and crosslinking density. Resin type adhesive and pure silicone type and modified resin respectively.
4. Electrical insulating paint: the volume, quality and service life of motor appliances have a great relationship with the performance of electrical insulating materials. Therefore, a variety of electrical insulating paints are required in industry, including coil impregnation paint, glass cloth impregnation paint, mica bonded insulating paint and silicon paint for electronic and electrical protection.
5. Powder and trapezoidal polymer: compared with inorganic filler, silicon resin powder has low relative density, and has the characteristics of heat resistance, weather resistance, lubricity and hydrophobicity. Trapezoidal silicone resin has higher heat resistance, electrical insulation and flame resistance than the general network three-dimensional structure of silicone resin
Reprinted from eEPW Encyclopedia