Silicone rubber is mainly divided into RTV silicone rubber and high temperature vulcanized silicone rubber. Therefore, by component RTV silicone rubber, curing mechanism and the use of technology can be divided into three types, namely RTV-1 silicone rubber, two-component RTV silicone rubber and two component addition type room temperature vulcanized silicone rubber. Room temperature vulcanized silicone rubber the three series have their own characteristics: RTV-1 silicone rubber has the advantages of convenient use, but deep curing speed is difficult; RTV silicone rubber has the advantages of no heat curing, the shrinkage rate is very small, no swelling, no internal stress, can be cured at the same time in the interior and surface, can deep vulcanization; curing time and room temperature vulcanizing silicone rubber mainly depends on the temperature.
Silicone rubber can be divided into two types of heat vulcanized silicone rubber and RTV silicone rubber according to its vulcanization characteristics. According to the performance and use of different, can be divided into general type, ultra low temperature, super high temperature resistant, high strength type, oil resistant, medical type, and so on. Depending on the monomer used, it can be divided into methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber, fluorine silicon, nitrile silicone rubber and so on.
1, two methyl silicone rubber
(referred to as methyl silicone rubber):
Type two methyl silicone rubber was prepared with high molecular weight, must have high purity raw materials, to ensure the raw material purity, the industry usually is the first after distillation purification, the content of two methyl chlorosilane two above 99.5% in ethanol water medium was hydrolyzed by acid catalyzed condensation, and isolated difunctional siloxane poly four methyl siloxane ring four is eight, then the ring body under the action of catalyst, the formation of polymer type two methyl polysiloxane.
Two methyl silicone rubber elastomer is colorless and transparent, usually with high activity of organic peroxide vulcanization. Vulcanizate
When used in the range of -60~+250 DEG C, the two methyl silicone rubber has low sulfidation activity, high temperature compression and permanent deformation. It is not suitable for making thick products, it is difficult to cure thick products, and the inner layer is easy to blister. Since the properties of methyl vinyl silicone rubber containing a small amount of vinyl are superior, the two methyl silicone rubber has been gradually replaced by methyl vinyl silicone rubber. The production and application of other types of silicone rubber, which contains two methyl siloxane structural units, but also structural units containing other difunctional siloxane more or less, but its preparation method and two methyl silicone rubber preparation method is not essentially different, the preparation method is generally in favor of the formation of the ring body under the condition that some required difunctionality monomer hydrolysis and condensation of silicon, and then according to the required proportion of adding eight methyl siloxane ring four, then the reaction in the catalyst prepared.
2, methyl vinyl silicone rubber
(referred to as vinyl silicone rubber):
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This kind of rubber has a small amount of vinyl side chain, so it is easier to be vulcanized than methyl silicone rubber, so that more kinds of peroxide can be used for vulcanization, and the dosage of peroxide can be greatly reduced. With a small amount of vinyl silicone rubber and silicone rubber in two, the anti compression permanent deformation properties obtained significant improvement, low compression deformation reflects it as seals at high temperature with better support, this is one of the necessary O rings and washers and other requirements. Methyl vinyl silicone rubber has better technological performance, easy operation, and can be made into thick products and extruded and rolled. The surface of semi-finished products is smooth. It is a kind of common silicone rubber.
3, methyl phenyl vinyl silicone rubber
(referred to as phenyl silicone rubber):
This rubber is obtained in the molecular chain of vinyl silicone rubber by introducing two phenyl silica links or methyl phenyl silicone links.
According to the phenyl content of silicone (phenyl: silicon atoms), it can be divided into low phenyl, middle phenyl and high phenyl silicone rubber. When the rubber is crystallized or near the glass transition point, or the two cases overlap, the rubber will become rigid. The introduction of large volume moderate groups make damage regularity of the polymer chain, can reduce the crystallization temperature of the polymer at the same time, due to the introduction of large volume groups changed the force of the polymer molecules, it can also change the glass transition temperature. Low phenyl silicone rubber (C6H5/Si=6~11%), which has excellent low-temperature resistance due to the above reasons, is independent of the type of phenyl monomer used. The brittleness temperature of vulcanizate is -120 DEG C, which is the best rubber at low temperature. Low phenyl silicone rubber has the advantage of vinyl silicone rubber and is not very expensive. Therefore, it has a tendency to replace vinyl silicone rubber. In greatly improve the phenyl content when you make the rigidity of the molecular chain increases, which leads to the decrease of cold resistance and elastic, but ablation resistance and radiation resistance will be increased, content of C6H5/Si=20~34% in phenyl phenyl silicone rubber has the characteristics of ablation resistant, high phenyl silicone rubber (C6H5/Si=35~50%) has excellent radiation resistance.
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