High temperature vulcanized silicone rubber is a high molecular weight (usually 40 to 80 million molecular weight) of polyorganosiloxane (ie raw rubber) by adding reinforcing filler and other additives, the use of organic peroxide as a vulcanizing agent, by compression molding (Molded, extruded, calendered) or injection molded and crossed into rubber at high temperatures. This rubber is generally referred to as silicone rubber.
The vulcanization of the high temperature vulcanized silicone rubber is generally carried out in two stages. The first stage is the mixing of the silica gel, the reinforcing agent, the additive, the vulcanizing agent and the structural control agent, and then pressing the kneaded material in the metal mold Heating and molding, the pressure of 50 kg / cm2 or so, the temperature is 120 ~ 130 ℃, the time is 10 to 30 minutes, the second stage is the silicone rubber removed from the mold, put the oven, in the 200 ~ 250 Drying for several hours to 24 hours, so that the rubber further vulcanization, while the decomposition of organic peroxide volatile. Silicone rubber reinforced filler is a variety of types of silica, it can increase the strength of vulcanized rubber ten times. Add a variety of additives is mainly to reduce the cost of plastic to improve the performance of rubber and vulcanized to give a variety of special properties such as flame retardant, conductive and so on. Crosslinking agents are various organic peroxides such as benzoyl peroxide, benzoyl 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di Tert-butyl peroxyhexane and the like. The structure control agent is used to avoid the mixing of the compound for too long, resulting in "structural" to make the compound harder, difficult to process and curing to join, can be used methyl hydroxyl silicone oil or diphenyl dihydroxy silane as a structural control agent The
The pendant groups on the silicone rubber backbone may be methyl, ethyl, vinyl, phenyl, trifluoropropyl and the like. The most commonly used methyl groups can also introduce other groups to improve processability and other properties. Therefore, according to the different side-based groups and rubber formulations, you can get a variety of different uses of silicone rubber, generally can be divided into the following types: General (with methyl and vinyl), high temperature and low temperature (including Phenyl, methyl and vinyl), low compression and permanent deformation (including methyl and vinyl), low shrinkage (volatile) and solvent resistance (fluorosilicone). Here are some important types of silicone rubber.
1. Dimethyl silicone rubber
Dimethyl silicone rubber is the first commercial production of silicone rubber, can be in the range of -60 ~ 200 ℃ to maintain good flexibility, good aging resistance, excellent electrical insulation properties and moisture, shock and physiological inertia, etc. characteristic. Dimethyl silicone rubber is mainly used for fabric coating, can also be made into a variety of extrusion and rolling products for the mechanical and electrical, aviation, automotive and medical industries. However, due to the low activity of dimethyl silicone rubber vulcanization, for the manufacture of thick products, the vulcanization is difficult, the inner layer is easy to foam and high temperature compression permanent deformation, it has been replaced by methyl vinyl silicone rubber.
2. Methyl vinyl silicone rubber
As the introduction of a small amount of silicone rubber macromolecule vinyl can greatly improve the vulcanization of silicone rubber processing performance, so in the current application of silicone rubber, mostly containing vinyl. Methyl vinyl silicone rubber is the most common kind of silicone rubber, silicone rubber production at home and abroad in the current dominant. Because of its introduction in the side chain part of the unsaturated vinyl, so that its processing performance and physical and mechanical properties are better than two silicon rubber. In addition to the general characteristics of dimethyl silicone rubber, it also has a wide temperature range, can be in a range of 60 ~ 260 ℃ to maintain good flexibility, it is easier than the dimethyl silicone rubber vulcanization, with a small compression permanent Deformation, good resistance to solvent expansion and high pressure steam stability and excellent cold resistance, etc., but also because of the use of low activity of peroxide vulcanization, thereby reducing the vulcanization of the bubble and rubber stability weakness. It is generally made with methyl vinyl silicone rubber can produce larger thickness of the product. Methyl vinyl silicone rubber is the most widely used variety of silicone rubber, in recent years continue to emerge a variety of high performance and special purpose silicone rubber, mostly vinyl silicone rubber-based glue, such as high-strength silicone rubber, low Compression of permanent deformation of silicone rubber, without post-vulcanized silicone rubber, heat-resistant conductive silicone rubber and medical silicone rubber. Methyl vinyl silicone rubber in the aviation industry, widely used as washers, sealing materials and fragile, shockproof parts of the protective layer; in the electrical industry can be used for electronic components such as high-level insulation materials, high temperature potentiometer dynamic seals, Underground long-distance communications equipment, sealing ring; in medicine, due to methyl vinyl silicone rubber on the human body physiological response is small, non-toxic, it is used for surgical plastic surgery, artificial heart valves, blood vessels.
3. Methylphenyl vinyl silicone rubber
Methylphenylvinyl silicone rubber is a product in which a methylphenylsiloxane chain or a diphenylsiloxane chain is introduced into the molecular chain of methylvinyl silicone rubber. The introduction of phenyl groups on the pendant groups of polysiloxanes greatly reduces the crystallization temperature of the polymer due to the destruction of the regularity of the structure of the dimethylsiloxane, thus expanding the low temperature range of the polymer material. Therefore, methylphenyl vinyl silicone rubber in addition to methyl vinyl silicone rubber with all the compression set is small, the use of a wide temperature range, anti-oxidation, weather, shock, moisture and good electrical insulation properties, but also has excellent Low temperature resistance, ablation resistance and radiation resistance, etc. These properties vary with the phenyl content in the molecular chain. Generally speaking, the phenyl content (ratio of phenyl group to silicon atom) is in the range of 5 to 10% Known as low-phenyl silicone rubber, it has a unique cold performance, in -70 ~ -100 ℃ can still maintain the flexibility of rubber, rubber is the best of all the low-temperature performance, combined with both methyl vinyl silicon The advantages of rubber and the cost is not high, so much to replace the methyl vinyl silicone rubber trend. Phenyl content of 20 to 40%, said the phenyl silicone rubber, it has excellent flame resistance, once the fire can be self-extinguishing. Phenyl content of 40 ~ 50%, said high phenyl silicone rubber, it has excellent resistance to radiation, resistance to γ-ray 1xI08 Lunqin. In general, with the increase of phenyl content, the rigidity of silicone rubber molecular chain gradually increased, the silicone rubber low temperature performance gradually decreased, but with the increase in the content of phenyl, vulcanized rubber to improve the resistance and radiation Illuminate. Methylphenyl vinyl silicone rubber is the aerospace industry, cutting-edge technology and other departments of the national economy, one of the important materials for the production of various molded and extruded products used as the aviation industry, cold-resistant rubber and for ablation, Heat-resistant or resistant parts of the radiation ring, pad, pipe and bar and so on.
4. Fluorosilicone rubber
Fluorosilicone rubber refers to γ-trifluoropropylmethylpolysiloxane. Fluorosilicone rubber has excellent resistance to chemical substances, solvent resistance and resistance to lubricating oil, such silicone rubber in non-polar solvent in the expansion rate of small, cold and thermal stability, resistance to fire also, so the aircraft , Rocket, missile, space flight, petrochemical used as contact with fuel oil and lubricants hose, gaskets, seals, fuel tank village, etc., can also be used to manufacture corrosion-resistant clothing, gloves and coatings, adhesives, etc. The
5. Nitrile silicone rubber
As the polymer side chain contains β-nitrile ethyl or γ-nitrile carbon strong polar groups, greatly increased the interaction between the molecular chain, improved oil resistance, solvent resistance. At the same time, due to the introduction of a certain amount of nitrile alkyl, destruction of the polymer structure of the regularity, but also greatly improved the cold resistance. The nitrile alkyl type and its content have great influence on the performance, such as silicone rubber containing 7.5 mol% γ-nitrile carbon, and the low temperature performance is similar to that of low phenyl silicone rubber (the glass transition temperature is -114.5 ℃) Oil resistance is better than phenyl silicone rubber. With γ-nitrile propyl content increased to 33 to 50 mole%, cold resistance, oil resistance improved. With β-nitrile ethyl instead of γ-nitrile propyl can improve the heat resistance of nitrile rubber, resistant to 250 ℃ hot air aging. The main advantage of nitrile silicone rubber is excellent resistance to oil and bath resistance, can be in the range of -60 ~ 180 ℃ to maintain flexibility, therefore, can be made of oil-resistant rubber products for the aviation industry, the automotive industry and the oil industry; Can be used as high-performance aircraft environmental sealant and tank sealant, in -54 ℃ to 200 ℃ above to keep the seal. Nitrile silicone rubber can be processed by ordinary equipment.
6. Benzene silicone rubber
Benzene silicone rubber is characterized by excellent resistance to radiation, the radiation resistance of the general methyl vinyl silicone rubber 10 to 15 times the high phenyl silicone rubber 5 to 10 times, therefore, can be used for aerospace Industry, atomic energy industry and nuclear reactors as high-energy radiation-resistant cables, sheaths, washers and heat shrink tubes.
7. Ethyl silicone rubber
In the polysiloxane side chain introduced ethyl ethyl diethyl rubber, its outstanding performance is particularly good cold resistance, cold resistance is better than dimethyl silicone rubber and general methyl vinyl silicone rubber. The higher the ethyl content, the better the cold resistance. But the ethyl reactivity is greater than the methyl group, therefore, with the ethyl content of the larger, heat resistance decreases. As the ethyl silicone rubber used for low temperature, it is preferable that the content of the diethylsiloxane chain is 8 mol% in the polymer. The use temperature of ethyl silicone rubber is generally -70 to 200 ° C.
8. Silicone rubber
The main advantage of silicon-nitrogen rubber is excellent thermal stability, not in the 430 ~ 480 ℃ decomposition, and some even more than 500 ℃ high temperature. The prominent weakness of silicon-nitrogen rubber is poor stability of hydrolysis, was once considered no development prospects. It was later found that the introduction of cyclodisilazane in the main chain of the polymer has good thermal stability. The silazolane-containing elastomer modified with silicon fulvum was heated to 425 ° C in air without weight loss and only 10% at 570 ° C and had better hydrolytic stability.