Dimethyl silicone rubber does not contain vinyl in its molecule and is a saturated rubber. Generally, highly reactive peroxides are used as vulcanizing agents. The peroxide radicals take hydrogen from the methyl groups of the silicone rubber to form macromolecular radicals. Macromolecular free radicals are recombined to form a cross-linking bond, such as dibenzoyl peroxide as a vulcanizing agent.

From the above reaction, it can be seen that the silicone rubber containing vinyl can regenerate free radicals that can continue the reaction after vulcanization, so the introduction of a small amount of vinyl in the silicone rubber can greatly improve the vulcanization activity and improve The crosslinking efficiency of the vulcanizing agent reduces the amount of peroxide and improves the performance of the product. Since the initial free radicals that initiate the cross-linking reaction are derived from the decomposition of peroxides, increasing the amount of peroxides within a certain range can significantly increase the degree of crosslinking of silicone rubber vulcanizates, which will lead to an increase in the tensile strength of the rubber compound. , And can improve dynamic performance and compression deformation, but the tear resistance has decreased.

According to the level of peroxide curing activity, the commonly used peroxides are divided into two types: general-purpose and vinyl-specific. Universal type with high activity and can cure all kinds of silicone rubber, such as dibenzoyl peroxide (BP), 2? 4-dichlorodibenzoyl peroxide (DCBP), tert-butyl peroxide Esters (TBPB) belong to this type. Vinyl special type has low activity and can only vulcanize silicone rubber containing vinyl, such as di-tert-butyl peroxide (DTBP), dicumyl peroxide (DCP and odorless DCP), 2.5? Methyl-2? 5-di-tert-butyl hexane peroxide (DBPMH) and so on belong to this type. Dibenzoyl peroxide is often made into silicone greases with an active ingredient of 50% to ensure production safety and improve its dispersibility in rubber compounds. The decomposition products are benzene, benzoic acid and carbon dioxide. They are volatile and must be pressurized during a period of vulcanization. Because the decomposition products contain acidic substances, the amount of the decomposition products should not be excessive to avoid reducing the heat resistance of the product. Thick-walled model products. Generally, 100 parts of dimethyl silicone rubber is used with 4-6 parts of dibenzoyl peroxide paste, and the amount of vinyl silicone rubber is 0.5-2 parts.

2.4—Compared with dibenzoyl peroxide, dichlorodibenzoyl peroxide has a lower decomposition temperature than dibenzoyl peroxide and a higher decomposition rate. Because of the low decomposition temperature, the scorch performance is not as good. OK, so the amount of this substance should be as small as possible. Its decomposition products are 2.4-dichlorobenzoic acid and 2.4-dichlorobenzene, which are less volatile, so air bubbles can be avoided without vulcanization during vulcanization, which is especially suitable for continuous vulcanization of hot air at normal pressure for extruding products. The amount is similar to that of dibenzoyl peroxide.

Dibenzoyl peroxide, 2.4-dichlorodibenzoyl peroxide is an aroyl peroxide and cannot be used in carbon black compounds because carbon black interferes with the vulcanization of peroxides. Light-colored compounds have a strong tendency to scorch, and the acidic substances in their decomposition products will damage the heat resistance of the silicone rubber products of the sealing system.

Di-tert-butyl peroxide is effective for vinyl-containing silicone rubber, it is not easy to scorch, the vulcanizate has less compression deformation, and good physical and mechanical properties. The disadvantage is that the vapor pressure is high, so the volatilization is also high, and it is very volatile during the rubber storage process. This product can be used in model products. And can be used for molding thick products and carbon black compounds. Dosage is generally 0.5-1 serving.

Dicumyl peroxide DCP and odorless DCP, and 2.5-dimethyl-2.5-di-t-butylperoxyhexane are not easy to volatilize, easy to use, low compression deformation of the vulcanizate, and do not decompose products with carboxyl groups Therefore, it is particularly stable in the vulcanizate of sealing products. They are suitable for molded thick products, metal-bonded products and injection products, as well as carbon black-containing compounds, which have a wide range of applications. When 2.5-dimethyl-2.5-di-tert-butyl hexane peroxide is used, the vulcanizate has higher elongation. When using dicumyl peroxide, the decomposition product has an odor. This odor is stored in the product for a long time. When 2.5-dimethyl-2.5-di-tert-butyl hexane peroxide is used, it can be avoided. Such disadvantages. These two peroxides have lower tear strength. The dosage is generally 0.5—1.

The amount of peroxide should not be too large. When it exceeds the appropriate amount, the elongation and tear strength of the vulcanizate will be reduced. This downward trend is particularly the case with 2.4-dichlorodibenzoyl peroxide and dibenzoyl peroxide.