There are many methods for classifying silicone rubber, usually by curing.
The former form is divided into solid silicone rubber and liquid silicone rubber; it is divided into room temperature vulcanized silicone rubber according to vulcanization temperature, high temperature vulcanized silicone rubber; according to different monomers used, it can be divided into methyl vinyl silicone rubber, methyl phenyl ethylene Silicone rubber, fluorosilicone, nitrile silicone rubber, etc.; can be divided into general-purpose, ultra-low-temperature resistant, ultra-high temperature resistant, high-strength, oil-resistant, medical, etc. depending on the performance and use. The following is a brief introduction to commonly used silicone rubber:
Dimethyl silicone rubber
Dimethyl silicone rubber referred to as methyl silicone rubber:
In order to prepare high-molecular-weight linear dimethylpolysiloxane rubber, high-purity raw materials must be used. In order to ensure the purity of the raw materials, the industry usually firstly purifies the dimethyl group with a content of 99.5% or more. Chlorosilane in ethanol-water medium,
Hydrolyzed and condensed by acid catalysis, and the bifunctional siloxane tetramer, octamethylcyclotetrasiloxane, is separated, and then the tetracyclic body is formed under the action of a catalyst to form a polymer linear dimethyl group. Silicone.
Dimethicone rubber is a colorless, transparent elastomer that is usually vulcanized with a more reactive organic peroxide. Vulcanized rubber
Used in the range of -60~+250 °C, dimethyl silicone rubber has low vulcanization activity, high temperature compression and permanent deformation, and is not suitable for thick products. It is difficult to vulcanize thick products, and the inner layer is also easy to foam. Since methyl vinyl silicone rubber containing a small amount of vinyl is superior in performance, dimethyl silicone rubber has been gradually replaced by methyl vinyl silicone rubber. Other types of silicone rubbers produced and used today, which contain, in addition to the dimethylsiloxane structural unit, structural units of more or less other difunctional siloxanes, but are prepared in a manner similar to that of dimethicone. There is no essential difference between the preparation methods of rubber, and the preparation method generally comprises hydrolytic condensation of a desired bifunctional silicon monomer under conditions favorable for ring formation, and then adding Bajia according to the required ratio. The base ring tetrasiloxane is obtained by co-reacting under the action of a catalyst.
Methyl vinyl silicone rubber
Methyl vinyl silicone rubber is abbreviated as vinyl silicone rubber.
Since this rubber contains a small amount of vinyl side chains, it is easier to vulcanize than methyl silicone rubber, so that a wider variety of peroxides can be used for vulcanization, and the amount of peroxide can be greatly reduced. Compared with dimethyl silicone rubber, silicone rubber containing a small amount of vinyl can achieve significant improvement in compression set resistance, and low compression deformation reflects its better support as a seal at high temperatures. It is one of the requirements that must be met for O-rings and gaskets. Methyl vinyl silicone rubber has good process performance and convenient operation. It can be made into thick products and the surface of extruded and calendered semi-finished products is smooth. It is a commonly used silicone rubber.
Methyl phenyl vinyl silicone rubber
Methyl phenyl vinyl silicone rubber is abbreviated as phenyl silicone rubber. Such a rubber is obtained by introducing a diphenyl siloxane chain or a methyl phenyl siloxane chain in a molecular chain of a vinyl silicone rubber.
Depending on the phenyl content (phenyl: silicon atom) in the silicone rubber, it can be classified into a low phenyl group, a medium phenyl group and a high phenyl silicone rubber. When the rubber crystallizes or approaches the glass transition point or the two cases overlap, the rubber will be stiff. The introduction of an appropriate amount of large-volume groups to destroy the regularity of the polymer chain can lower the crystallization temperature of the polymer, and the glass can also be changed due to the change of the interaction between the polymer molecules due to the introduction of large volume groups. Temperature. The low phenyl silicone rubber (C6H5/Si = 6 to 11%) has excellent low temperature resistance for the above reasons and is independent of the type of phenyl monomer used. The vulcanizate has a brittleness temperature of -120 ° C and is the best low temperature rubber available today. Low phenyl silicone rubber has the advantages of vinyl silicone rubber and is not expensive, so there is a tendency to replace vinyl silicone rubber. When the phenyl content is greatly increased, the rigidity of the molecular chain is increased, resulting in a decrease in cold resistance and elasticity, but the ablation and radiation resistance are improved, and the phenyl content is up to C6H5/Si=20-34. % is medium phenyl silicone rubber with ablation resistance, and high phenyl silicone rubber (C6H5/Si=35~50%) has excellent radiation resistance.
Nitrile silicone rubber
Fluorosilicone rubber is a type of silicone rubber in which a side chain introduces a fluoroalkyl group. A commonly used fluorosilicone rubber is a fluorosilicone rubber containing a methyl group, a trifluoropropyl group, and a vinyl group.
Fluorosilicone has good heat resistance and excellent oil and solvent resistance, such as aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, petroleum-based fuel oils, lubricating oils, hydraulic oils and certain synthetic oils at room temperature. The stability at high temperatures is good, these are beyond the reach of pure silicone rubber. Fluorosilicone rubber has good low temperature properties and is a great improvement for pure fluororubber. The temperature range in which the fluorosilicone rubber containing trifluoropropyl group maintains elasticity is generally -50 ° C to +200 ° C. The high and low temperature resistance is inferior to that of vinyl silicone rubber, and toxic gas is generated when heated above 300 ° C. It is much worse than vinyl silicone rubber in terms of electrical insulation properties. Adding appropriate amount of low-viscosity hydroxyfluorosilicone oil to the fluorosilicone rubber compound, heat treatment of the rubber compound, and adding a small amount of vinyl silicone rubber can significantly improve the process performance, which is beneficial to solve the problems of adhesive sticking and storage structure. Can extend the effective use period of the rubber compound. When a methylphenylsiloxane chain is introduced into the above fluorosilicone rubber, it contributes to improvement of low-temperature resistance and good processability.
Nitrile silicone rubber is a type of silicone rubber in which a side chain is introduced with a nitrile alkyl group (generally β-nitrile ethyl or γ-nitrile propyl). The introduction of a polar nitrile group improves the oil resistance and durability of the silicone rubber, but its heat resistance, electrical insulation and processability are reduced.
The type and content of nitrile alkyl have a great influence on the properties of nitrile silicone rubber. For example, silicone rubber containing 7.5% by mole of γ-nitrile propyl has similar cold resistance to low phenyl silicone rubber and lower oil resistance. The base silicone rubber is good. When the γ-nitrile propyl content is increased to 33 to 50% by mole, the cold resistance is remarkably lowered, the oil resistance is improved, and the heat resistance is 200 °C. When the β-nitrile group is used instead of the γ-nitrile propyl group, the heat resistance of the nitrile silicone rubber can be further improved.
Phenylene and phenyl ether silicone rubber
A phenylene silicone rubber is a type of silicone rubber in which a phenylene group is introduced into a polysiloxane main chain.
Due to the introduction of the phenylene group, the radiation resistance of the silicone rubber is greatly improved, and the rigidity of the molecular chain is increased due to the presence of the aromatic ring, the flexibility is lowered, the glass transition temperature is increased, the cold resistance is lowered, and the tensile strength is decreased. Increased. Benzene silicone rubber has excellent high temperature resistance, radiation resistance, high temperature resistance up to 250~300 °C, and good dielectric properties and moisture, mildew and water vapor resistance. In the raw rubber composition of phenylene silicone rubber, it is suitable when the phenylene content is 60%, the phenyl content is 30%, and the methyl content is 10% (vinyl content 0.6%). In this case, the vulcanizate Has a good overall performance.
The shortcomings of phenylene silicone rubber are poor low temperature performance and brittleness temperature of -25 °C, which affects its application in some aspects. The low temperature performance of phenylene ether silicone rubber is far better than that of phenylene silicone rubber. The temperature is -64~70 °C.
The phenylene ether silicone rubber is a polysiloxane in which a phenyl ether group and a phenylene group are introduced in a molecular main chain.
Phenylene ether siloxane rubber has good mechanical properties, and the tensile strength can reach 150-180 kg/cm 2 (ie, 14.7~17.7Mpa is much higher than the strength of vinyl silicone rubber, and it has excellent radiation resistance and is superior to benzene. Silicone rubber. It can withstand hot air aging for 250 °C for a long time, and still has high strength after aging. Although the low temperature performance of phenylene ether silicone rubber is worse than vinyl silicone rubber, it is much better than phenylene silicone rubber. Its dielectric properties are close to those of vinyl silicone rubber, but phenyl ether silicone rubber is poorly resistant to oil, and is neither resistant to non-polar petroleum base oils nor to polar synthetic oils (such as 4109 diester synthetic lubricants, The performance of phosphate ester hydraulic oil. In short, phenyl ether silicone rubber has higher strength and radiation resistance than vinyl silicone rubber, similar high temperature resistance and dielectric properties, poor low temperature performance, oil resistance and Elasticity. Phenylene ether siloxane rubber has good processing properties and can be used to manufacture molded articles and extruded products with special requirements.
Contact：Sharon Song(Sales manager)
Zhejiang Runhe Organosilicone New Material Co.,Ltd(Factory)
Zhejiang Runhe Chemical New Material Co.,Ltd(Exporter)
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