What are the main types of silicone rubber?

Release time:

2021-11-09 10:27

There are many ways to classify silicone rubber, usually divided into solid silicone rubber and liquid silicone rubber according to the shape before curing; According to the vulcanization temperature is divided into room temperature vulcanized silicone rubber, high temperature vulcanized silicone rubber;

There are many ways to classify silicone rubber, usually divided into solid silicone rubber and liquid silicone rubber according to the shape before curing; According to the vulcanization temperature is divided into room temperature vulcanized silicone rubber, high temperature vulcanized silicone rubber; According to the different monomer used, it can be divided into methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber, fluorosilicone, nitrile silicone rubber, etc. According to the different performance and use can be divided into general type, super low temperature resistance type, super high temperature resistance type, high strength type, oil resistance type, medical type and so on.

Dimethyl silicone rubber for short methyl silicone rubber:

Preparation of high molecular weight linear dimethyl polysiloxane rubber, must have high purity of raw materials, in order to ensure the purity of raw materials, industry is usually after distillation, content of more than 99.5% of dimethyl dichlorosilane in ethanol-water medium, under the acid catalysis of hydrolysis condensation, and separation of difunctional siloxane tetramer that is, octamethylcyclotetrasiloxane, Then the tetracyclic body under the action of catalyst, the formation of polymer linear dimethyl polysiloxane.

Dimethyl silicone rubber raw rubber for colorless transparent elastomer, usually with high activity of organic peroxide sulfide. vulcanize

In the range of -60~+250℃, dimethyl silicone rubber vulcanization activity is low, high temperature compression permanent deformation, not suitable for thick products, thick products vulcanization is more difficult, the inner layer is easy to bubble. Dimethyl-vinyl silicone rubber has been gradually replaced by methyl-vinyl silicone rubber because the performance of methyl-vinyl silicone rubber containing a small amount of vinyl is better than that of methyl-vinyl silicone rubber. Other types of silicone rubber produced and applied today, in addition to containing dimethylsiloxane structural units, they also contain more or less other difunctional siloxane structural units, but their preparation method is not intrinsically different from that of dimethylsilicone rubber, the preparation method is generally in the conditions conducive to the formation of rings, The required difunctional silicon monomer is hydrolyzed and condensed, and then the required ratio of octamethylcyclotetrasiloxane is added, and then the reaction is made under the action of catalyst.

Methyl vinyl silicone rubber

Methyl vinyl silicone rubber is referred to as vinyl silicone rubber.

This kind of rubber contains a small amount of vinyl side chain, so it is easier to vulcanize than methyl silicone rubber, so that there are more kinds of peroxides available for vulcanization, and can greatly reduce the amount of peroxide. The use of silicone rubber containing a small amount of vinyl compared to dimethyl silicone rubber can make a significant improvement in compression resistance to permanent deformation. The low compression deformation reflects its better support at high temperature as a seal, which is one of the requirements for O-rings and washers. Methyl vinyl silicone rubber process performance is better, easy to operate, can be made into thick products and pressed out, calendering semi-finished products smooth surface, is a commonly used silicone rubber.

Methyl phenyl vinyl silicone rubber

Methyl phenyl vinyl silicone rubber for short phenyl silicone rubber. This rubber is produced by introducing diphenyl silicoxy chain or methyl phenyl silicoxy chain link into the molecular chain of vinyl silicone rubber.

According to the content of phenyl in silicone rubber (phenyl: silicon atom), it can be divided into low phenyl, middle phenyl and high phenyl silicone rubber. When the rubber crystallizes or is close to the glass transition point, or the two conditions overlap, it will cause the rubber to appear stiff. The introduction of appropriate large volume groups to destroy the regularity of polymer chains can reduce the crystallization temperature of polymer. At the same time, because the introduction of large volume groups changes the intermolecular forces of polymer, it can also change the glass transition temperature. Low phenyl silicone rubber (C6H5/Si=6~11%) has excellent low temperature resistance because of the above reasons, and is independent of the type of phenyl monomer used. The brittle temperature of vulcanized rubber is -120℃, which is the best rubber with low temperature performance today. Low phenyl silicone rubber has the advantages of vinyl silicone rubber, and the cost is not very high, so there is a tendency to replace vinyl silicone rubber. When the content of phenyl is greatly increased, the rigidity of the molecular chain will increase, resulting in the reduction of cold resistance and elasticity, but the ablative resistance and radiation resistance will be improved, the content of phenyl C6H5/Si=20~34% is the characteristics of the ablative resistance of phenyl silicone rubber. High phenyl silicone rubber (C6H5/Si=35~50%) has excellent radiation resistance.

Nitrile silicone rubber

Fluorosilicone rubber is a kind of silicone rubber which introduces fluoroalkyl side chain. The commonly used fluorosilicone rubber contains methyl, trifluoropropyl and vinyl fluorosilicone rubber.

Fluorine silicone has good heat resistance and excellent oil resistance, solvent resistance, such as aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, petroleum-based fuel oil, lubricating oil, hydraulic oil and some synthetic oil at room temperature and high temperature stability are better, these are not as simple as silicone rubber. Fluorine silicone rubber has good low temperature performance, for simple fluorine rubber, is a great improvement. Fluorosilicone rubber containing trifluoropropyl to maintain the elastic temperature range is generally -50℃~+200℃, high and low temperature resistance than vinyl silicone rubber is poor, and heating to 300℃ above will produce toxic gas. The electrical insulation property is much worse than vinyl silicone rubber. Adding appropriate amount of low viscosity hydroxy fluorosilicone oil to the rubber compound, heat treatment of the rubber compound, and adding a small amount of vinyl silicone rubber can make the process performance significantly improved, which is conducive to solving the problems such as adhesive roll and serious storage structure of the rubber compound, and can extend the effective service life of the rubber compound. The introduction of methyl phenyl silicon oxygen chain into the fluoro-silicone rubber will help to improve the low temperature resistance, and the processing property is good.

Nitrile silicone rubber is a class of silicone rubber with side chain introduction of nitrile alkyl (generally β - nitrile ethyl or γ - nitrile propyl). The introduction of polar nitrile group improved the oil resistance and solvent durability of silicone rubber, but its heat resistance, electrical insulation and processability were reduced.

The type and content of nitrile alkyl has a greater impact on the performance of nitrile silicone rubber, such as containing 7.5% grams of γ - nitrile propyl silicone rubber, its cold resistance and low phenyl silicone rubber similar, oil resistance is lower phenyl silicone rubber is good, when the content of γ - nitrile propyl increased to 33~50% grams of molecules, cold resistance is significantly reduced, oil resistance, heat resistance is 200℃. If β - nitrile ethyl is used instead of γ - nitrile propyl, the heat resistance of nitrile silicone rubber can be further improved.

Phenylene and phenylene ether silicone rubber

Benzyl silicone rubber is a kind of silicone rubber in which benzyl groups are introduced into the main chain of polysiloxane.

Due to the introduction of benzene group, the radiation resistance of silicone rubber is greatly improved. At the same time, because of the existence of aromatic ring, the molecular chain rigidity increases, the flexibility decreases, the glass transition temperature increases, the cold resistance decreases, and the tensile strength increases. Benzene-silicone rubber has excellent high temperature resistance, radiation resistance, high temperature resistance up to 250~300℃, and has good dielectric properties, moisture, mildew and water vapor resistance characteristics. In the raw rubber composition of benzene silicone rubber, when the benzene content is 60%, benzene content 30%, methyl content 10%(vinyl content 0.6%) is suitable, in this case, vulcanized rubber has good comprehensive performance.

The disadvantage of benzene-silicone rubber is that its low temperature performance is poor. The brittle temperature is -25℃, which affects its application in some aspects. The low temperature performance of benzene-ether silicone rubber is far 2. Compared with benzene silicone rubber, the brittleness temperature is -64~70℃.

Phenyl etheric silicone rubber is a polysiloxane with phenyl etheric and phenyl groups introduced into the main chain of the molecule.

Phenyl ether silicone rubber has good mechanical properties, generally tensile strength up to 150~180 kg/cm2 (14.7~17.7Mpa is much higher than the strength of vinyl silicone rubber, and has excellent radiation resistance and better than phenyl silicone rubber. It can withstand the aging of 250℃ hot air for a long time, and still has a high strength after aging. Although the low temperature performance of phenylene silicone rubber is worse than that of vinyl silicone rubber, it is far better than phenylene silicone rubber. Its dielectric properties are close to vinyl silicone rubber, but the oil resistance of phenyl ether silicone rubber is poor, neither resistant to non-polar petroleum-based oil, nor resistant to polar synthetic oil (such as 4109 double ester synthetic lubricating oil, phosphate ester hydraulic oil performance. In short, compared with vinyl silicone rubber, benzene ether silicone rubber has higher strength and radiation resistance, similar high temperature resistance and dielectric properties, poor low temperature performance, oil resistance and elasticity. Phenylene ether silicone rubber has good processing properties and can be used to manufacture special requirements of the model products and extrusion products.