Research overview of silicone high temperature resistant anticorrosive coatings

Organic high temperature anti-corrosion coatings include: organic silicon, organic fluorine, organic titanium and other categories, but the most widely used, the most superior performance is mainly organic silicon high temperature anti-corrosion coatings.

In recent years, organosilicon polymer has become the first choice for the research and application of high temperature resistant coatings due to its excellent sealing, heat resistance and weather resistance. In 1937, J.F. Hyde, an American, first made silicone resin impregnated with glass cloth for electrical insulation. In 1943, D-Coming completed the construction of a methyl phenyl silicone intermediate pilot plant, and in 1945, industrial production was realized. The industrial production of silicone resin usually takes methyl trichlorosilane, phenyltrichlorosilane and so on as the main raw materials. In order to reduce the brittleness and hardness of resin and improve the adhesion of resin, dimethyl dichlorosilane, methylphenyl dichlorosilane and other two functional monomers can be added. The monomer was hydrolyzed and polycondensation in the solvent, and the by-product hydrogen chloride was washed away to obtain the resin liquid containing a small amount of silicon hydroxyl group. When used, a small amount of catalyst such as cobalt naphthenate should be added to make the resin further polycondensation complete, to get crosslinked three-dimensional network curing resin.

The main research direction of silicone resin is pure silicone resin and modified silicone resin. - step in terms of pure organic silicon, as to improve the heat resistance and aging resistance of the resin, often in the introduction of B - Si - O - structure, Ti, Al other elements such as organic siloxane elements, or organic base silane steering trapezoid organic silicon polymer, pure silicone ability at higher temperature, but need high temperature drying (150 ~ 250 ° C), curing time is long, Poor adhesion, hot and cold alternating environment, a certain time after the corrosion coating cracks, or even off. The coatings with good properties can be obtained by using resin modified organosilicon. Many scholars at home and abroad have done a lot of research on polyurethane, acrylic acid, alkyd and epoxy modified silicone resins, and epoxy modified is the most successful.

Epoxy modified silicone resin has the advantages of both epoxy resin and polysiloxane, good adhesion, medium resistance, water resistance and atmospheric aging resistance, and can be cured with amine curing agent, greatly reducing the curing temperature of silicone resin, even can be cured at room temperature, under 200°C can be used for a long time. However, the common epoxy modified organic silicon has low temperature tolerance and can not be used for a long time at 500-600℃. Measures must be taken to increase the temperature tolerance of epoxy modified organic silicon before it can be used in higher coating systems.

Silicone resin has excellent high temperature resistance and outstanding dielectric property. It has excellent corona resistance, arc resistance, dielectric loss Angle tangent value is low, these are not other synthetic resin. Silicone resin can be made of 180℃ resistant motor insulation materials, such as glass cloth, glass cloth laminate, mica tape, impregnation paint, enamel, etc. After the addition of aluminum powder, the latter two can be combined into high temperature coatings with long-term resistance of 500°C and instantaneous resistance of 1000°C, which are used to paint jet engine tail nozzle and metal chimney, etc. Made of glass fiber or asbestos, it can be used as a material to manufacture arc resistant switches with strong current and high voltage.

Silicone resin made of methyltrialkoxy silane (commonly known as silicone glass resin) can be used to treat the surface of paper, plastic and metal, so that it has good brightness and wear resistance. Silicone resin modified (such as alkyd resin) can be used as outdoor coatings with good weather resistance. Since the bond energy of silicon oxygen bond is as high as 443.1KJ·mol-1, it has high temperature resistance as a coating.

Simple silicone resin heat resistance up to 250℃, but there are problems such as mechanical strength, adhesion and solvent resistance is poor, especially the curing film temperature is too high, generally above 200°C baking, thus limiting its application. The modified epoxy resin with good mechanical properties and strong adhesion can greatly improve the high temperature resistance and durability of the coating, and realize the curing at room temperature. The addition of suitable pigments and fillers can greatly improve the heat resistance of the coating. The properties of the final processed silicone products depend on the number of organic groups contained (i.e., the ratio of R to Si). In addition, silicone is a thermosetting plastic, and one of its most outstanding properties is its excellent thermal oxidation stability. After heating at 250°C for 24 hours, the weight loss of the silicone resin was only 2 to 8%.

Another outstanding property of silicone is its excellent electrical insulation performance, which can be maintained over a wide range of temperatures and frequencies. Generally, the electrical breakdown strength of silicone resin is 50 kV/mm, the volume resistivity is 1013 ~ 1015 ohms/cm, the dielectric constant is 3, and the tangent value of dielectric loss Angle is about 10 ~ 30. In addition, silicone resin also has excellent moisture resistance, waterproof, rust resistance, cold resistance, ozone resistance and weather resistance, the corrosion resistance of the vast majority of water-containing chemical reagents such as dilute mineral acid is good, but the solvent resistance is poor.

In view of the above characteristics, silicone resin is mainly used as insulating paint (including varnish, enamel, color paint, impregnating paint, etc.) to impregnate H-class motor and transformer coil, and used to impregnate glass cloth, glass cloth and asbestos cloth to make motor bushing, electrical insulation winding, etc. A large area mica sheet insulation material can be prepared by bonding mica with silicone insulating paint, which can be used as the main insulation of high voltage motor. In addition, silicone resin can also be used as heat-resistant and weather-resistant anti-corrosion coating, metal protective coating, waterproof and moisture-proof coating for building engineering, release agent, adhesive and secondary processing into silicone plastic, used in the electronics, electrical and defense industry, as semiconductor packaging materials and electronic, electrical parts of the insulation material.