Do you know high-temperature vulcanized silicone rubber?

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• 日期: 2014-01-18
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High temperature vulcanized silicone rubber is a high molecular weight (MW typically 40 to 80 million) of polyorganosiloxane (ie gum) added reinforcing fillers and other additives, using organic peroxide vulcanizing agent, by compression molding (molding, extrusion, calendering) or injection molding, and at high temperatures into the rubber cross-linking. This 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, reinforcing agents, additives, vulcanizing agent and control agent were kneaded material is then kneaded in a pressurized metal mold heating the molding and curing, a pressure of about 50 kg / cm2, a temperature of 120 ~ 130 ℃, for 10 to 30 minutes, after the second stage is removed from the mold of silicon rubber, people put in an oven at 200 to 250 ℃ drying for several hours at 24 hours to further cure the 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, rubber to improve performance and giving a variety of special properties of vulcanized rubber, such as flame retardant, conductive and so on. Cross-linking agents are various organic peroxides such as benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di t-butylperoxy hexane and the like. Control agent in order to avoid placing too long mix of materials, resulting in "structured" so hard rubber, hard working and aging with a party, may be 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 may also be introduced to improve the processing performance and other properties. Thus, depending on the side of the group and the compound formulation, you can get a variety of different uses of silicone rubber, and can be divided into the following categories: general purpose (including methyl and vinyl), high temperature and low temperature (including phenyl, methyl and vinyl), low compression set (containing methyl and vinyl), low shrinkage (to volatile parts) and solvent (fluorine silicone 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 physiological inertness. characteristics. Dimethyl silicone rubber is mainly used for fabric coating, it can also be made from a variety of extrusion and rolled products for the electronics, aerospace, automotive and medical industries. But because dimethyl silicone rubber vulcanization low activity, for the manufacture of thick products, vulcanization difficult inner foaming and high temperature compression large permanent deformation, it has now been replaced by methyl vinyl silicone rubber.


2
. Methyl vinyl silicone rubber
Since the molecular structure of the silicone rubber of vinyl introducing a small amount can greatly improve the processability of silicone rubber vulcanization, and therefore silicone rubber in the present application, most 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 introduces most of the unsaturated vinyl in the side chain, it's processing performance and mechanical properties are superior to two groups of silicone rubber. It is in addition to a dimethyl silicone rubber general characteristics, but also has a wide temperature range, it can maintain a good elasticity in the range of a 60 ~ 260 ℃, it is more than likely dimethyl silicone rubber vulcanization, has a smaller compression set deformation, good stability of the swelling solvent and high pressure steam and excellent cold resistance, etc., and also because the use of less active peroxide vulcanization, thereby reducing the stability of the air bubbles and the rubber during vulcanization poor weakness. It is generally treated with methyl vinyl silicone rubber products making greater thickness. Methyl vinyl silicone rubber silicone rubber is the most widely used varieties in recent years, emerging 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-curing silicone rubber, silicone rubber and medical heat conductive silicone rubber. Methyl vinyl silicone rubber in the aviation industry, widely used as a gasket, sealing materials and brittle layer of shock protection member; can be used in the electrical industry, electronic components and other advanced insulation materials, high temperature dynamic seal potentiometer, underground telecommunication equipment seals; in medicine, since the 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 of the methyl vinyl silicone rubber. On the introduction of phenyl silicone side groups, due to destruction of the regularity of dimethyl siloxane structure, greatly reduces the crystallization temperature of the polymer, expanding the scope of application of the low temperature of the polymer material. Thus, methyl phenyl vinyl silicone rubber in addition to having a methyl vinyl silicone rubber all compression permanent deformation, 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 to silicon atoms) in 5 to 10% When called low-phenyl silicone rubber, it has a unique cold resistance, in -70 ~ -100 ℃ remain flexible rubber, all rubber is the best kind of temperature performance, coupled with it 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%, it has excellent flame properties in case of fire can be self-extinguishing. Phenyl content, said in an 40 to 50% higher phenyl silicone rubber, which 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 silicone rubber gradually decreased with the increase of the content of the phenyl group to improve the flame resistance and resistance to radiation vulcanizate 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, pipes and rods and the like.

4. Fluorosilicone
Fluorosilicone rubber refers γ- trifluoropropyl methyl polysiloxane. Fluoro silicone rubber with 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 aircraft , rockets, missiles, space flight, petrochemical used as fuel and lubricants in contact with the hose, gaskets, seals, a fuel tank in the village, 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 strong polar groups, greatly increasing the force between the molecular chains and improve the oil resistance, solvent resistance. At the same time, the introduction of a certain amount of nitrile group, destroyed the regularity of the polymer structure, but also greatly improved the cold. The type and content of nitrile group, a significant impact on performance, such as nitrile containing 7.5 mol% γ- propyl silicone rubber, low temperature performance and low-phenyl silicone rubber like (having a glass transition temperature of -114.5 ℃), oil resistance is better than phenyl silicone rubber. With γ- propyl nitrile content increases to 33 to 50 mol%, cold reduced oil resistance improved. Instead of using β- cyanoethyl γ- nitrile propyl nitrile silicone rubber can improve heat resistance, anti-aging 250 ℃ hot air. The main advantages of nitrile silicone rubber 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. Nitrile silicone rubber can be an ordinary equipment for processing.

6. Benzene silicone rubber
The main features of benzene silicone rubber, has excellent resistance to radiation, the radiation resistance to the universal methyl vinyl silicone rubber is 10 to 15 times, 5 to 10 times higher phenyl silicone rubber, therefore, can be used in aerospace industry, nuclear industry and nuclear reactors as high energy radiation-resistant cable sheathing, gaskets and heat shrink tubes.

7. Ethyl silicone rubber
Introducing 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, better resistance to cold. However, reactive than methyl ethyl large, therefore, with greater ethyl content, the heat resistance decreases. As low use of ethyl silicone rubber, silicone containing diethyl links in the polymer was 8 mol% is appropriate. Ethyl silicone rubber temperature is generally -70 ~ 200 ℃.

8. Silicon nitride rubber
The main advantage of silicon nitride rubber having excellent thermal stability, does not decompose at 430 ~ 480 ℃, and some even above 500 ℃ high temperature capability. Highlight weaknesses silicon nitride rubber is poor hydrolytic stability, once considered no future development. Later found the ring disilazane of the polymer main chain introduced with good thermal stability. Arylene modified silicon-containing elastomer ring disilazane heated in air to 425 ℃ not weightless, 570 ℃ when the weight loss is only 10%, and has good hydrolytic stability.