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- 日期: 2014-01-18
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High temperature vulcanized silicone rubber is a high molecular weight (molecular weight generally from 40 to 800,000) polyorganosiloxane (i.e., raw rubber) was added to the reinforcing fillers and other additives, using an organic peroxide as vulcanizing agent, by press molding (molding, extrusion, calendering), or injection molding, and cross-linking at high temperature into a rubber. This rubber is generally referred to as silicone rubber.
High temperature vulcanized silicone rubber vulcanization is generally divided into two stages, the first stage is silicone rubber, a reinforcing agent, additives, vulcanizing agent and control agent are kneaded, the kneaded material and then pressurized in a metal mold heating the molding and curing, a pressure of 50 kg / cm2, a temperature of 120 ~ 130 ℃, for 10 to 30 minutes, the second stage after the silicon rubber is removed from the mold, were put in an oven at 200 to 250 ℃ bake at a few hours to 24 hours, so that further vulcanized rubber, while the organic peroxide decomposes volatile. Reinforcing fillers are various types of silicone rubber silica, it can increase tenfold the strength of vulcanized rubber. Various additives mainly to reduce the cost of plastic and rubber materials to improve performance and giving a variety of special properties of vulcanized rubber, such as fire, electrical conductivity, etc. Cross-linking agents are various organic peroxides such as benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di t-butyl peroxide, such as hexane. Control agent is to avoid placing material mix for too long, have a "structured" to make rubber hardens, it is difficult to join the aging process, can be used hydroxy methyl silicone oil or diphenyl hydroxysilane as a control agent .
Pendant on the main chain of the silicone rubber may be methyl, ethyl, vinyl, phenyl, trifluoropropyl. The most commonly used is methyl, other groups can also be introduced to improve the processability and other properties. Therefore, depending on the side groups and rubber formula, you can get a variety of different uses of silicone rubber, and can be divided into the following types: general-purpose (including methyl and vinyl), high temperature and low temperature (including phenyl, methyl and vinyl), low compression set (including methyl and vinyl), low shrinkage (volatiles parts), and solvent (fluorosilicone rubber) and the like. Here are several important types of silicone rubber.
1. Dimethyl silicone rubber
Dimethyl silicone rubber is put into commercial production of one of the first silicone rubber, can maintain good flexibility in the range of -60 ~ 200 ℃, anti-aging properties, has excellent electrical insulation properties and moisture, shock and physical inertia, etc. characteristics. Dimethyl silicone rubber is mainly used for fabric coating, can also be made from a variety of extrusion and rolled products for electrical, aerospace, automotive and medical industries. However, due to dimethyl silicone rubber vulcanization active low for the manufacture of thick products, curing difficult inner foaming and high temperature compression large permanent deformation, it has now been replaced by methyl vinyl silicone rubber.
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. Methyl vinyl silicone rubber
Because the silicone rubber introducing a small amount of vinyl macromer structure can greatly improve the processability of silicone rubber vulcanization, and therefore the current application of the silicone rubber, most of them contain a vinyl group. Methyl vinyl silicone rubber is the most common kind of silicone rubber, currently dominated by domestic and foreign production of silicone rubber. Because it is part of an unsaturated vinyl groups introduced in the side chain, so that its processing properties and mechanical properties are superior to the two groups of silicone rubber. It is in addition to a dimethyl silicone rubber general characteristics, but also has a wide temperature range, good flexibility can be maintained within the range of a 60 ~ 260 ℃, it is easier than dimethyl silicone rubber vulcanization, has a smaller compression set deformation, better stability and resistance to solvent swelling pressure steam as well as excellent cold resistance, etc., and also because the use of less active peroxide vulcanization, thereby reducing the generation of bubbles and the stability of the time of vulcanization of rubber poor weakness. It is generally with methyl vinyl silicone rubber products making greater thickness. Methyl vinyl silicone rubber silicone rubber is the most widely used species, emerging in recent years, a variety of high performance and special-purpose silicone rubber, mostly based on vinyl silicone rubber-based adhesive, such as high-strength silicone rubber, low compression set of silicone rubber, without post-vulcanized silicone rubber, heat-conductive silicone rubber and medical silicone rubber and the like. Methyl vinyl silicone rubber in the aviation industry, widely used as a gasket, sealing materials and fragile, shockproof protective layer components; can be used in the electrical industry, electronic components and other advanced insulation materials, high temperature potentiometer dynamic seals, underground telecommunication equipment seals; in medicine, due to methyl vinyl silicone rubber on human physiological reactions, non-toxic, it is used as a plastic surgery, artificial heart valves and blood vessels.
3. Methyl phenyl vinyl silicone rubber
Methyl phenyl vinyl silicone rubber is introduced methylphenyl silicone chain link or links diphenyl silicone products obtained in the molecular chain methyl vinyl silicone rubber. Introducing phenyl polysiloxane side groups, due to destruction of the regularity of dimethyl siloxane structure, greatly reduces the crystallization temperature of the polymer, the application of the low temperature range expanded polymeric material. Therefore, methyl phenyl vinyl silicone rubber addition of methyl vinyl silicone rubber compression set all small, wide temperature range, anti-oxidation, weathering, vibration, moisture and good electrical insulation properties, but also has excellent low temperature resistance, ablation and radiation-resistant properties. These properties with different molecular chain phenyl content varies, in general, phenyl content (ratio of phenyl silicon atoms) in the 5 to 10% When called low-phenyl silicone rubber, which has a unique cold can, at -70 ~ -100 ℃ remain flexible rubber, rubber is the best kind of all low-temperature performance, combined it with both methyl vinyl silicone Advantages of rubber and the cost is not high, so much to replace methyl vinyl silicone rubber trend. Phenyl, said phenyl content silicone rubber in 20 to 40%, having excellent flame characteristics, can be self-extinguishing when on fire. Phenyl content, said in an 40 to 50 percent of high phenyl silicone rubber, it has excellent resistance to radiation resistance, γ- 1xI08 Roentgen rays. In general, with the increase of the content of a phenyl group, a silicone rubber molecular chain increases the rigidity, low temperature properties of the silicone rubber gradually decreased with the increase of the content of a phenyl group to improve the flame resistance and resistance to radiation vulcanizates according to sex. Methyl phenyl vinyl silicone rubber is an important material in the aerospace industry, technology, and other sectors of the national economy, for making a variety of molded and extruded rubber products used for cold and for the aviation industry ablative, heat aging resistance to radiation or parts of seals, pads, tubes and bars and so on.
4. Fluorosilicone
Fluorosilicone rubbers are γ- trifluoropropyl methyl polysiloxane. Fluorosilicone rubber has excellent resistance to chemicals, solvents and oil resistance, this small silicone rubber in a non-polar solvent swelling, cold resistance and good thermal stability, resistance to fire resistance or, as it is in the plane , rockets, missiles, space flight, petrochemicals and lubricants for use as fuel in contact with hoses, gaskets, seals, fuel tank in the village, etc., can also be used to make corrosion-resistant clothing, gloves and coatings, adhesives, etc. .
5. Nitrile silicone rubber
Since the side chains of the polymer molecules contain β- or γ- nitrile nitrile ethyl propyl strongly polar groups, greatly increasing the force between the molecular chains and improve the oil resistance, solvent resistance. Meanwhile, due to the introduction of a certain amount of the nitrile group, destroyed the regularity of the polymer structure, but also greatly improved resistance to cold. The type and content of a nitrile group, a great impact on performance, such as nitrile containing 7.5 mol% γ- propyl silicone rubber, low temperature performance and low similarity phenyl silicone rubber (having a glass transition temperature of -114.5 ℃), good oil resistance than phenyl silicone rubber. With γ- propyl nitrile content was increased to 33 to 50 mol%, cold reduced, oil resistance is improved. With β- cyanoethyl instead γ- nitrile propyl nitrile silicone rubber can improve heat resistance, resistance to aging 250 ℃ hot air. The main advantages of silicone rubber nitrile is excellent performance and resistance to oil bath agent can maintain flexibility in the range of -60 ~ 180 ℃, therefore, can be made into oil and rubber products for the aerospace industry, automotive and oil industries; also can be used as a high-performance aircraft fuel tank sealant environmental sealing agent, at least -54 ℃ to 200 ℃ can remain sealed. Silicone rubber nitrile ordinary equipment available for processing.
6. Benzene silicone rubber
The main features of benzene silicone rubber has excellent resistance to radiation, the radiation resistance for universal methyl vinyl silicone rubber is 10 to 15 times, 5 to 10 times higher phenyl silicone rubber, therefore, can be used for aerospace industry, nuclear industry and nuclear reactors as a high-energy radiation resistant cable sheathing, gaskets and heat shrink tubes.
7. Ethyl silicone rubber
Introduction of ethyl side chains on the polysiloxane obtained diethyl silicone rubber, its outstanding performance is particularly good resistance to cold, cold better than dimethyl silicone rubber and general methyl vinyl silicone rubber. Ethyl content is higher, cold better. However, the reactivity ratio of methyl ethyl large, therefore, with the greater the content of ethyl, heat resistance decreased. As low ethyl silicone rubber used to contain diethyl siloxane chain links in the polymer was 8 mol% is appropriate. Ethyl silicone rubber use temperature is generally -70 ~ 200 ℃.
8. Silicon nitride rubber
The main advantage is that silicon nitride rubber has excellent thermal stability, does not decompose at 430 ~ 480 ℃, and some even withstand temperatures above 500 ℃. Highlighting the weaknesses of the silicon nitride rubber is poor hydrolytic stability, once considered no future development. Later found the ring disilazane introduced polymer main chain has good thermal stability. Arylene modified silicon-containing elastomer ring disilazane, and heated in air to 425 ℃ not weightless, 570 ℃ when the weight loss of only 10%, and has good hydrolytic stability.