Synthetic editing


Usually, various mixtures of methyltrichlorosilane, dimethyldichlorosilane, Phenyltrichlorosilane, Diphenyldichlorosilane or methylphenyldichlorosilane are used. In the presence of organic solvent such as toluene, water is added to decompose at a lower temperature to obtain acid hydrolysate. The initial product of hydrolysis is a mixture of ring-shaped, linear and cross-linked polymers, usually containing quite a lot of hydroxyl groups. The hydrolysate was washed to remove acid, and the neutral prepolymer was oxidized in air or further polycondensated in the presence of catalyst.


Features and performance editing


Characteristic


The classification of silicones silicones are semi inorganic polymers with silicon oxygen silicon as the main chain and organic groups on the silicon atom. It has outstanding weather resistance with the direct production of silicone monomer silicone resin, which is beyond the reach of any kind of organic resin. Even under the strong UV irradiation, silicone resin is also resistant to yellowing. According to the source of raw materials, silicone adhesive can be divided into two types: one is based on silicone resin and the other is based on silicone rubber. The former is mainly used for bonding metal and heat-resistant silicone resin with good bonding performance to metal such as iron, aluminum and tin. It is also easy to bond to glass and ceramics, but it has poor adhesion to copper. Organic silica gel adhesive based on pure silicone resin.


Silicone coating has many disadvantages: poor film-forming performance, including high curing temperature, long time, inconvenient construction in large area, and poor adhesion of the coating to the bottom layer. Fluorination is mainly used to improve the solvent resistance, oil repellency and reduce surface energy of silicone resin. The critical surface tension of silicone resin is lower than that of other resins, but higher than that of fluorine resin.


Silicone is a kind of thermosetting plastics. One of its outstanding properties is its excellent thermal oxidation stability. After heating at 250 ℃ for 24 hours, the weight loss of silicone is only 2-8%. Another outstanding performance of silicone is its excellent electrical insulation performance, which can maintain its good insulation performance in a wide range of temperature and frequency.


The R / Si value, which is the number of organic groups in silicone resin, is one of the main indexes to control the quality of silicone resin. The curing, film flexibility, hardness, heat resistance and cracking resistance of silicone resin are all related to R / Si. Generally, the R / Si of linear silicone oil is slightly larger than 2, that of silicone rubber is close to 2, and that of silicone resin is about 1.0. The smaller the R / Si value is, the better the curing performance of the silicone resin is. The smaller the thermal weight loss is, the harder the paint film is, but the lower the flexibility, the embrittlement of the paint film and the lower the impact strength. The larger the R / Si value is, the silicone resin needs to be baked at high temperature (200-250 ℃) for a long time or cured with the help of the drier, so that the flexibility is better, the hardness of the paint film is poor, and the impact strength is better.


In addition, the performance of silicone is closely related to the type of organic group R. when the organic group is - CH3, it can give the silicone thermal stability, hydrophobicity, demoulding and arc resistance; when the organic group is - C6H5, it can give the silicone oxidation stability, which can improve the thermal stability of the resin; when the organic group is - CH = CH2, it can improve the curing performance of the silicone and give the coupling property; when there is When the organic group is phenyl or ethyl, it can improve the blending property of silicone and organic compounds; when the organic group is - NH2 (CH2), it can improve the water solubility of polymer and give coupling property; when the organic group is long chain alkyl, it can improve the hydrophobicity of silicone. Therefore, siloxane monomers with different groups can be selected to prepare silicone resin according to specific performance requirements.


Characteristic


(1) Silicon resin has good bonding performance to metals such as iron, aluminum and tin, and it is easy to bond to glass and ceramics, but it has poor adhesion to copper;


(2) Organic silica gel adhesive with pure silicone resin as the base material, silicone resin as the base material, adding inorganic filler and solvent to mix. When curing, small molecules are released, which need to be heated and pressurized;


(3) The curing temperature of silicone based adhesive is too high, so its application is limited;


(4) Adding a small amount of ethyl orthosilicate, potassium acetate and silicate glass, the curing temperature dropped to 220-200 ℃, and the high temperature strength was still 392-490mpa;


(5) The pure silicone resin has low mechanical strength. When it is copolymerized with polyester, epoxy or phenolic resin, it can obtain high temperature resistance and excellent mechanical properties, which can be used in high temperature resistant structural adhesive.