Silica gel is a high performance, multi-purpose composite new product with high temperature resistance, anti-corrosion, high strength glass fiber cloth and organic silicone rubber. So what kind of material is silicon rubber, and why does it have excellent properties after coating? So let's do that. Silicon rubber according to its vulcanization characteristics can be divided into hot vulcanized silicone rubber and room temperature vulcanized silicone rubber. According to the different performance and purpose, it can be divided into general type, ultra-low temperature resistance, ultra-high temperature resistance, high strength type, oil resistant type, medical type and so on. According to the different monomers, it can be divided into methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber, fluorine silicon rubber, and so on.
1. Dimethyl silicone rubber (methyl silicone rubber) :
Preparation of high molecular weight linear dimethyl polysiloxane rubber, there must be high purity of raw materials, to ensure the purity of raw materials, industrial is usually after a first rectified purification, content is more than 99.5% of dimethyl dichlorosilane in ethanol - water medium, under the acid catalytic hydrolysis condensation, and isolated bifunctional degrees of four polymers namely eight methyl siloxane ring four siloxane, and then make the fourth body under the effect of catalyst, the formation of polymer linear dimethyl polysiloxane.
Dimethyl silicone rubber is a colorless and transparent elastomer, usually vulcanized with high activity organic peroxide. Vulcanizates can be used to 60 ~ + 250 ℃, dimethyl silicone rubber vulcanization activity is low, the high temperature compression permanent deformation is big, should not be in the thick products, thick products vulcanization is difficult, the inner is also easy to blister. The dimethyl silicone rubber has been replaced by methyl vinyl silicone rubber because of the performance of a small amount of vinyl silicone rubber.
2. Methyl vinyl silicone rubber (vinyl silicone rubber) :
Due to the rubber contains a small amount of vinyl side chain, so easier than methyl silicone rubber vulcanization, so use are available in a wide variety of peroxide vulcanizing, and can greatly reduce the dosage of peroxide. Containing a small amount of vinyl silicone rubber with dimethyl silicone rubber, compression permanent deformation resistance can get significant improvement, low compression deformation shows it as a seal at high temperature has better support, it is type O ring and gasket and so on must have one of the requirements. The process of methyl vinyl silicone rubber is good and easy to operate. It can be made into thick products and the surface of the semi-finished product is smooth. It is a kind of silicon rubber commonly used at present.
3. Methyl phenyl vinyl silicone rubber (abbreviated phenyl silicone rubber) :
This rubber is introduced in the molecular chain of vinyl silicone rubber, which is introduced into a diphenyl silicate chain or methyl phenyl silicate chain.
According to the difference of phenyl content (phenyl: silicon) in silicone rubber, it can be divided into low phenyl, medium phenyl and high phenyl silicone rubber. When the rubber happens to crystallize or close to the glass transition point or the two conditions overlap, the rubber will become rigid. Introducing the right amount of mass groups in the regularity of the polymer chain is damaged, can reduce the crystallization temperature of polymer, due to the introduction of mass groups at the same time change the force between the polymer molecules, so it can change the glass transition temperature. Low phenyl silicone rubber (C6H5 /Si=6~ 11%) is superior to low temperature due to the above reasons, and has nothing to do with the type of phenyl monomer. Analysis of the brittleness temperature to - 120 ℃, is now the best rubber performance at low temperature.
4. Fluorine silicon and nitrile silicone rubber:
Fluorosilicone rubber is a kind of silicon rubber which is introduced into fluoroalkyl by side chain. The commonly used fluorosilicone rubber is fluorinated silicone rubber containing methyl, trifluoropropyl and vinyl.
Fluorine silica gel has good heat resistance and good oil resistance, solvent resistance, such as the fat hydrocarbon, aromatic hydrocarbon, chlorinated hydrocarbons and petroleum base, fuel oil, lubricating oil, hydraulic oil, and some synthetic oil at normal temperature and high temperature stability are good, these are beyond pure silicone rubber. Fluorosilicone rubber has good low temperature performance, which is a great improvement for pure fluoro rubber.
5. Phenylene and phenyl ether support silicone rubber:
Phenylene silicone rubber is a kind of silicone rubber that is introduced into the main chain of polysiloxane.
Because the introduction of phenylene base, therefore make the radiation resistant properties of the silicone rubber is greatly increased, at the same time because of the existence of aromatic ring increased molecular chain rigidity, flexibility is reduced, the glass transition temperature, cold resistant performance degradation, while tensile strength increase significantly. Phenylene silicone rubber has excellent high temperature resistance, radiation resistance, high temperature can reach 250 ~ 300 ℃, and with good dielectric properties and moisture mildew water vapor resistance and other properties. In of phenylene silicone rubber, when the phenylene content is 60%, 30%, methyl phenyl content when the content of 10% (vinyl content 0.6%) is appropriate, in this case, the vulcanizates with good comprehensive performance.
Phenylene silicone rubber disadvantage is that the poor performance at low temperature brittleness temperature is 25 ℃, affect the application of it in some ways, benzene ether through low temperature performance of silicone rubber is far more phenylene silicone rubber as well, brittleness temperature is 64 ~ 70 ℃.
Polysiloxane, which is the main chain of benzene ether and benzene, is introduced by the polymer.
Phenyl ether through silicone rubber with good mechanical properties, general tensile strength can reach 150 ~ 180 kg/cm, it can be long time 250 ℃ hot air aging resistance, still has the high strength after aging. The low temperature performance of phenylethylene silicone rubber is worse than that of vinyl silicone, but it is far better than the benzene silicone rubber. Its dielectric properties are close to the vinyl silicone rubber, but the oil resistance of phenylethylene silicone rubber is not resistant to the non-polar oil base oil and the non-polar synthesis oil. Anyhow, benzene ether through silicone rubber compared with vinyl silicone rubber with high strength and resistance to radiation performance, similar to that of high temperature resistant performance and dielectric properties, poor performance at low temperature, oil resistance and flexibility. Phenylene ether silicone rubber has good machining properties and can be used to make the special requirements of model products and extruded products.
6. Room temperature vulcanized silicone rubber:
Room temperature vulcanized silicone rubber (RTV) refers to a class of silicone rubber that is not heated at room temperature. Room temperature vulcanized silicone rubber is a kind of silicone rubber with hydroxyl (or acetyl), which is low in molecular weight and usually is a viscous fluid. This type of rubber can be vulcanized at room temperature after adding a proper amount of filler, vulcanizing agent and catalyst (or moisture in the air). After vulcanization is completely, it is very good in heat resistance, cold resistance, dielectric property and so on, but its mechanical strength is lower, it can be used for casting and coating. Room temperature vulcanized silicone rubber can be divided into two types: single and double.
Type one-component RTV silicone rubber, is by the end of the base containing acetoxyl group with silicone rubber and reinforcing filler and other additives, and does not need to add the catalyst when using, from the seal packing with moisture in the air after the role can be vulcanized elastomer. This kind of silicone rubber to metal, glass and plastic, etc. Have good adhesive force, its shortcomings is accompanied by acetic acid in the process of sulfide generated, although can spread to escape from the vulcanizates, but the contact objects, especially in metal corrosion effects. Single unit type function is convenient, especially suitable for sealing, sealing, etc.
7. Liquid silicone rubber:
According to the molecular structure contains functional groups (junction) position, often think of liquid rubber with functional groups are divided into two categories: one is at the ends of the molecular structure of functional group in a type called telechelic liquid rubber; The other group is the active functional group in the main chain, which is unregulated distribution, which is called a non-teleclawed liquid rubber in the molecular structure of the functional group. Of course, there is also the intermediate functional group with the terminal group, the focus is on the remote claw type liquid rubber. For liquid rubber, a chain growth agent or crosslinking agent with the appropriate functional group should be selected according to the active functional energy base.
Liquid silicone rubber can be used for coating, impregnation and perfusion. For example, coating a glass fiber cloth to form a silicone cloth. Such as viscosity of 0.07 ~ 50 mpa seconds / 25 ℃ hydroxy end capping of poly dimethyl siloxane, using methyl vinyl pyrrolidone silane for the chain extension agent, organic peroxides, such as two benzoyl peroxide, 25 - dimethyl base 5-2 tertiary butyl peroxide hexane as vulcanizing agent, this kind of rubber good liquidity, low viscosity, in the vulcanization process of chain growth reaction at the same time, it can obtain high molecular weight of the elastomer, has the good physical and mechanical properties.
Chain extension agent methyl vinyl pyrrolidone silane, can be composed with methyl vinyl pyrrolidone dichloride silane reaction and, in the presence of triethylamine between product easy to hydrolysis, therefore, should be stored in dry sealed container, the compound of pyrrolidone base at room temperature with polydimethylsiloxane hydroxyl-terminated slow reaction, the reaction rate increases with temperature and speed up.
Theoretically, this reaction can be carried out continuously until an infinite molecular weight is obtained. The vinyl of methyl vinyl pyrrolidone silane can also be used as the activation point of the sulfide reaction, which can cause the polydimethyl siloxane crosslinking to produce the elastic body of the high molecular weight.
Because pyrrolidone and hydroxy reaction at room temperature is very slow, so after joining components by mixing rubber has a long shelf life, within an hour of rubber viscosity basically remain unchanged, but still keep a good liquidity, but into tiny pore in. After mixing the rubber when heated to 150 ℃ for 10 minutes sulfide into elastomer.
Application of silica gel products
1. Silica gel products are indispensable components for making photocopiers, keyboards, electronic dictionaries, remote controls, toys, and silicone keys.
2. Can be used for durable shape gasket, electronic accessories packaging materials, automotive electronic accessories maintenance materials.
3. It can be used to make electronic components, molding high pressure edge.
4. It can be used to make conductive silica gel, medical silicone, foam silicone, molding silica gel, etc.
5. Construction and repair of houses, sealing of high-speed km joints and sealing of Bridges, etc.
6. It can be used for baby products, maternal and baby products, baby bottles and bottle protection covers.
7. It can be used in the production of kitchen products, cooking utensils and related auxiliary cooking utensils.
8. It can be used in medical devices and accessories, and it is widely used in medical industry due to its colorless, odorless and non-toxic properties. 9. Anti-corrosion: silicone rubber coated glass fiber cloth can be used as the pipe, the internal and external corrosion protection of the deposit, good corrosion resistance, high strength, is an ideal anticorrosive material. 10. Electrical insulation: the silicone cloth has a high electrical insulation level and can withstand high voltage load, which can be made into insulating cloth, casing and other products.