Silicone Classification Silicone is a cross-linked semi-inorganic polymer in which silicon-oxygen-silicon is the main chain and an organic group is bonded to the silicon atom. It is a direct process for the production of silicone monomer silicone resin with outstanding weather resistance, which is unmatched by any kind of organic resin. Even under strong ultraviolet light, silicone resin is resistant to yellowing. Silicone Adhesives Silicone adhesives can be classified into silicone based adhesives and silicone rubber based adhesives. The former is mainly used for bonding metals and heat resistant silicones to iron, aluminum and tin. The metal bonding performance is good, and it is easy to bond to glass and ceramics, but the adhesion to copper is poor. A silicone adhesive based on pure silicone.
Silicone coatings have many disadvantages: poor film forming performance, including high curing temperature, long time, inconvenient construction in large areas, and poor adhesion of the coating film to the bottom layer. The modification with fluorination mainly increases the solvent resistance, oil repellency (anti-stickiness) and surface energy of the silicone resin. Silicone resins have a lower critical surface tension than other resins but higher than fluororesins.
Silicone is a thermoset plastic and one of its most outstanding properties is its excellent thermal oxidative stability. After heating at 250 ° C for 24 hours, the silicone weight loss is only 2 to 8%. Another outstanding property of silicone is its excellent electrical insulation properties, which maintain its good insulation properties over a wide temperature and frequency range.
The amount of silicone-containing organic groups, ie, R/Si value, is one of the main indicators for controlling the quality of silicone resin. The curability of silicone resin, film flexibility, hardness, heat resistance and thermal crack resistance are all related to R. /Si related. Generally, the R/Si of the linear silicone oil is slightly larger than 2, the R/Si of the silicone rubber is close to 2, and the R/Si of the silicone resin is about 1.0. The smaller the R/Si value, the better the curing property of the silicone resin, the smaller the thermal weight loss, the harder the paint film, but the lower the flexibility, the more brittle the paint film and the lower the impact strength; the larger the R/Si value, the more the silicone resin It needs to be baked at a high temperature (200-250 ° C) for a long time or by means of a drier, so that the flexibility is good, the hardness of the paint film is poor, and the impact strength is good.
In addition, the properties of the silicone resin are also closely related to the type of the organic group R. When the organic group is -CH3, the silicone resin can be imparted with thermal stability, water repellency, mold release property, and arc resistance; when the organic group is -C6H5 When the silicone resin is imparted with oxidative stability, the thermal stability of the resin can be improved; when the organic group is -CH=CH2, the curing property of the silicone resin can be improved and the coupling property can be imparted; when the organic group is a phenyl group or an ethyl group, It can improve the blending property of silicone resin and organic matter; when the organic group is -NH2(CH2), it can improve the water solubility of the polymer while giving coupling property; when the organic group is a long-chain alkyl group, silicon can be improved. Water repellency of the resin. Therefore, a silicone resin having a different group can be selected according to specific performance requirements to prepare a silicone resin.
Characteristics
(1) Silicone resin has good bonding performance to metals such as iron, aluminum and tin, and is easy to bond to glass and ceramics, but has poor adhesion to copper;
(2) Silicone resin based on pure silicone resin, based on silicone resin, mixed with inorganic filler and solvent, and emits small molecules during curing, which requires heating and pressurization;
(3) Silicone resin-based adhesive curing temperature is too high, and application is limited;
(4) adding a small amount of ethyl orthosilicate, potassium acetate and silicate glass, the curing temperature is lowered to 220 ~ 200 ° C, the high temperature strength is still 392-4 90MPa;
(5) Pure silicone resin has low mechanical strength and can be obtained by copolymerization modification with organic resins such as polyester, epoxy or phenolic to obtain high temperature resistance and excellent mechanical properties, and is used for high temperature resistant structural adhesive.