High temperature vulcanized silicone rubber is a kind of polyorganosiloxane (i.e. raw rubber) with high molecular weight (molecular weight is generally 400000-800000) added with reinforcing filler and other additives. It uses organic peroxide as vulcanizing agent, and is pressurized (molded, extruded, calendered) or injection molded, and crosslinked into rubber at high temperature. This rubber is generally referred to as silicone rubber.






The vulcanization of high-temperature vulcanized silicone rubber is generally divided into two stages. The first stage is to mix raw silicone rubber, reinforcing agent, additive, vulcanizing agent and structural control agent, and then press and heat the mixture in a metal mold to form and vulcanize, with a pressure of 50 kg / cm2, a temperature of 120-130 ℃, a time of 10-30 minutes. The second stage is to remove silicone rubber from the mold After taking it out, put it into the oven and bake it at 200-250 ℃ for several hours to 24 hours. The rubber is further vulcanized and the organic peroxide is decomposed and volatilized.






The reinforcing filler of silicone rubber is various types of silica, which can increase the strength of vulcanizate ten times. Adding various additives is mainly to reduce the cost of rubber, improve the properties of rubber and give vulcanizate various special properties, such as flame retardant, conductive and so on. Crosslinking agents are various organic peroxides, such as benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dibenzyl peroxide, 2, 5-di-tert-butyl-peroxyhexane, etc. the structure control agent is added to prevent the compound from being placed for too long, resulting in "structure" which makes the compound hard and hard to process and mature. Methyl hydroxy silicone oil or diphenyl dihydroxydecane can be used as the structure control agent.






The side groups on the main chain of silicone rubber can be methyl, ethyl, vinyl, phenyl, trifluoropyl, etc. The most commonly used one is methyl group. Other groups can also be introduced to improve processability and other properties. Therefore, according to the different side groups and the formula of the compound, various kinds of silicone rubber can be obtained, which can be generally divided into the following types: general type (containing methyl and vinyl), high temperature and low temperature type (containing phenyl, methyl and vinyl), low compression permanent deformation (containing methyl and vinyl), low shrinkage (devolatilization) and solvent resistance (fluorosilicone rubber), etc. Here are some important types of silicone rubber.






1、 Methyl silicone rubber






Dimethylsilicone rubber is one of the earliest silicone rubber which has been put into commercial production. It can keep good elasticity in the range of - 60 ~ 200 ℃, has good aging resistance, excellent electrical insulation performance, moisture-proof, shockproof and physiological inertia.






Dimethylsilicone rubber is mainly used for coating strong materials, and also can be made into various extrusion and rolling products for Electromechanical, aviation, automobile and medical industries. However, due to the low vulcanization activity of dimethylsilicone rubber, it is difficult to vulcanize when it is used in the manufacture of thick products, the inner layer is easy to blister and the high temperature compression permanent deformation is large, so it has been replaced by methylvinyl silicone rubber.