Classification And Characteristics Of Silicone Rubber

1, heat resistance

The heat resistance of silicone rubber in air is much better than that of organic rubber. Its physical and mechanical properties are basically unchanged at 150 ° C. It can be used semi-permanently. It can be used for more than 1000 hours at 200 ° C. It can be used for a short time at 380 ° C. Silicone rubber is therefore widely used as a rubber component for use in high temperature applications.

2, weather resistance

There is no unsaturated bond in the silicone rubber main chain, and the Si-O-Si bond is very stable to oxygen, ozone and ultraviolet rays, so it does not require any additives, that is, it has excellent weather resistance. When corona discharge occurs in ozone, the organic rubber is very Fast aging, but the impact on silicone rubber is not serious. Long-term exposure to ultraviolet light and wind and rain, its physical and mechanical properties change little, after several decades of outdoor exposure test, no aging phenomenon such as cracks or degradation and tackiness.

3, electrical characteristics

Silicone rubber has excellent electrical insulation properties, its volume resistance is up to 1×(1014～1016)·cm, anti-creepage is 10～30min (special grade can reach 3.5kv/6h), arc resistance is 80～100s (special Grade can reach 420s); surface resistance is (1~10)?×1012?.cm; conductive grade can reach 1×(10-3～107)?.cm; dielectric loss tangent (tgδ) is less than 10-3 , dielectric constant 2.7 ~ 3.3 (50Hz / 25 ° C), dielectric strength 18 ~ 36KV / mm, and not much change in a wide range of temperature and frequency. Even after immersion in water, electrical properties are rarely reduced, very It is suitable for use as an electrical insulating material. Silicone rubber has excellent damping effect on corona discharge and arc under high pressure.

4, compression permanent deformation

Compressive permanent deformation is an important performance when silicone rubber is used as a gasket under high and low temperature conditions. Dimethyl silicone rubber has poor compression set, and the deformation value is as high as 60% after compression at 150 ° C for 22 hours. The base vinyl silicone rubber, especially the product vulcanized with alkyl series peroxide, has excellent compression set and its deformation value can be below 20%. The two-stage vulcanization condition also has a great influence on the compression set value. That is, the higher the second-stage vulcanization temperature, the lower the compression set value. In order to improve the compression set of the vulcanized rubber product, oxidized mercury, cadmium oxide, zinc oxide and bismuth compounds may be added to the rubber compound.

5, oil and chemical resistance

General purpose silicone rubber has medium oil resistance and solvent resistance. The performance depends mainly on the type of silicone rubber, the type and amount of filler, the type of additives and the crosslinking density. Silicone rubber invades polar organic solvents. The volume will increase by 10% to 15%. It can be swelled by 10% and 45% at 150 °C in ASTM? No. 1 oil and No. 3 oil, and will expand by 150% in non-polar solvents and fuels. 200%

6, radiation resistance

Methyl vinyl silicone rubber has moderate durability and can absorb radiation dose (4.0~5.0)×1013Gy. It is obviously improved after the introduction of phenyl group, and can withstand the dose of 9.0×103Gy. When phenylene is introduced into the main chain After the base, the effect becomes outstanding.

7, water vapor resistance

Silicone rubber has a very good performance of durable low pressure water vapor (less than 130 ° C). It is immersed in warm water and boiling water for a long time, the volume increase is less than 1%, and its mechanical properties and electrical properties are rarely affected. However, water exceeding 140 ° C The vapor easily causes the Si-O-Si main chain to break, which rapidly reduces the physical and mechanical properties of the silicone rubber. The water vapor resistance of silicone rubber is related to the type and amount of filler used, the crosslinking density, and the type of vulcanizing agent.

8, thermal expansion, thermal conductivity, specific heat capacity and flame retardancy

The coefficient of thermal expansion of silicone rubber is larger than that of ordinary organic rubber, and mainly depends on the amount of filler, that is, the greater the relative density of silicone rubber, the smaller the expansion ratio. The shrinkage of silicone rubber generally varies between (2 ~ 4) 10-4 / K, equivalent to 2.0 ~ 2.5 times of organic rubber, or 20 times that of steel. The thermal conductivity of silicone rubber is 0.20 ~ 0.30W / ( mK), which is equivalent to twice the amount of organic rubber, and the special grade can exceed 1.2W/mK. Due to the large thermal conductivity of the silicone rubber, the internal heating rate of the rubber during vulcanization is fast, so that the vulcanization rate can be accelerated or the vulcanization time can be reduced. When a thermal conductive filler such as AI2O3, BN, MgO, Ag or the like is added to the silicone rubber, the thermal conductivity can be increased to 2.0 to 14 W/(m.K).