Silicone rubber refers to the rubber whose main chain is composed of silicon and oxygen atoms alternately, and the silicon atoms are usually connected with two organic groups.Common silicone rubber mainly consists ofmethylAnd a small amountVinylIt is composed of silicon oxygen chain links.phenylThe introduction of can improve the high and low temperature resistance of silicone rubberCyano groupThe heat resistance and oil resistance of silicone rubber can be improved by introducing.Silicone rubber has good low temperature resistance and can work at - 55 ℃ generally.introducephenylAfter that, it can reach - 73 ℃.The heat resistance of silicone rubber is also very outstanding. It can work for a long time at 180 ℃, and can withstand a few weeks or longer with elasticity even slightly higher than 200 ℃. It can withstand a high temperature of more than 300 ℃ instantaneously.Silicone rubberAir permeabilityOkay,oxygenThe transmissivity is the highest in synthetic polymers.In addition, silicone rubber is also physiologically inert and will not causeCoagulationTherefore, it is widely used in the medical field.[1]
Silicone rubber partial heat vulcanization type（high temperaturevulcanizationsilica gelHTV）、Room temperature vulcanization (RTV), in which RTV is divided into polycondensation reaction type and addition reaction type.High temperature silicone rubberIt is mainly used to manufacture various silicone rubber products, while room temperature silicone rubber is mainly used as adhesivePottingMaterial ormoulduse.The amount of hot vulcanization type is the largest, and the hot vulcanization type is divided intomethylsiliconrubber(MQ), methylVinylSilicone rubber (VMQ, the most amount and product brand), methyl vinyl phenyl silicone rubber PVMQ (low temperature resistance and radiation resistance), and other silicone rubberFluorosilicone rubberEtc.
Chinese name
silicon rubber[3]
Foreign name
Silicone rubber[3]
Performance characteristics
Tasteless and non-toxic, not afraid of high temperature and cold
Silicone rubber was first developed by the United StatesFerric trichlorideIt is synthesized by catalyst.In 1945, silicone rubber products came out.In 1948, silicone rubber reinforced by fumed silica with high specific surface area was successfully developed, which made the performance of silicone rubber leap to the practical stage and laid the foundation of modern silicone rubber production technology.The United States is the country that started to produce silicone rubber from the synthesis of dimethyldichlorosilane.Russia, Germany, Japan, South Korea and China.The industrialization research of silicone rubber in China began in 1957, and many research institutes and enterprises have successively developed various silicone rubber.By the end of 2003, China's silicone rubber production capacity was 135 thousand tons, including 100 thousand tons of high-temperature rubber.[1]
classification
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The manufacturer of silicone rubber generally has dozens or even hundreds of varieties and brands, most of which are numbered according to commodity characteristics and uses, and also according tovulcanizationClassified by means and chemical structure.according toVulcanization temperatureSilicone rubber can be divided into high-temperature vulcanized silicone rubber and room temperature vulcanized silicone rubber.From the packaging form, it can be divided into single component and two-component RTV silicone rubber.according toDegree of polymerizationSilicone rubber can also be divided into mixed silicone rubber and liquid silicone rubber.[1]
The classification of silicone rubber series products is shown in the figure.[1]
Classification of silicone rubber series products
High temperature vulcanized silicone rubber
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High temperature vulcanized silicone rubber means that the process of polysiloxane becoming elastomer is vulcanized at high temperature (110-170 ℃).It is mainly highmolecular weightPolymethylvinylsiloxane offiller、Vulcanizing agentAnd vulcanized under heating and pressureelastomer。Silicone rubber is mainly reinforced by various types of white carbon black, which can increase the strength of vulcanizate dozens of times.Sometimes, in order to reduce costs or improve the properties of the compound and give the vulcanizate various special properties, corresponding additives are also added.Vulcanizing agents are various organic peroxides or addition reaction catalysts.[1]
Type and preparation of raw rubber
Raw rubberThe main types are methyl silicone rubber, methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber and fluorosilicone rubber, as shown in the figure.In addition, phenylene groups can also be introduced into the main chain.The largest amount is methyl vinyl silicone raw rubber.Due to the introduction of vinyl, the active group for crosslinking, the crosslinking efficiency of peroxide crosslinking for raw silicone rubber has been greatly improved.Almost all commercial silicone rubber contains a certain amount of vinyl.[1]
Type and structure of raw rubber
In industry, silicone rubber is mainly produced by alkali catalytic polymerization and acid catalytic polymerization.KOH and temporary catalyst [(CHthree)fourNOH、(n-CfourHnine)fourPOH]。[1]
Processing and forming
machiningThe forming method is shown in the figure.The purpose of primary vulcanization is to carry out cross-linking reaction of polymer chain;The purpose of secondary vulcanization is to supplement cross linking, eliminate decomposition products of vulcanizing agent and other volatile compounds to stabilize various properties of vulcanizate.The common equipment includes open rubber mixer, kneader and vacuum mixer.[1]
Processing and molding method of silicone rubber
main performance
(1) High temperature performance.The remarkable feature of silicone rubber is its high temperature stability. Although the strength of silicone rubber at room temperature is only half of that of natural rubber or some synthetic rubber, it can still maintain a certain flexibility, resilience and surface hardness under the high temperature environment above 200 ℃, and its mechanical properties have no obvious change.(2) The glass transition temperature of low temperature performance silicone rubber is generally - 70~- 50 ℃, and the special formula can reach - 100 ℃, indicating its excellent low temperature performance.This is of great significance to the aviation and aerospace industries.(3) Weathering resistance The Si-O-Si bond in silicone rubber is very stable to oxygen, ozone and ultraviolet rays. Without any additives, it has excellent weather resistance.(4) Electrical performance.Silicone rubber has excellent insulation performance, corona resistance and arc resistance.(5) Physical and mechanical properties.The physical and mechanical properties of silicone rubber at room temperature are worse than those of general rubber, but at 150 ℃ and - 50 ℃, its physical and mechanical properties are better than those of general rubber.(6) Oil resistance and chemical reagent resistance.Common silicone rubber has medium oil resistance and solvent resistance.(7) Gas permeability.The permeability of silicone rubber to air, nitrogen, oxygen, carbon dioxide and other gases at room temperature is 30-50 times higher than that of natural rubber.(8) Physiological inertia.Silicone rubber is non-toxic, tasteless, odorless, does not adhere to human tissues, has anticoagulant effect, and has very little reactivity to body tissues.It is especially suitable for medical materials.[1]
Room temperature vulcanized silicone rubber
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room temperatureThe difference between vulcanized silicone rubber and high-temperature vulcanized silicone rubber is that it is based on polysiloxane with small molecular weight, and can be vulcanized into elastomer with room temperature or a little heating under the action of cross-linking agent and catalyst.RTV silicone rubber consists of base rubber, crosslinking agent, catalyst, filler, etc.From the packaging form, it can be divided into single component and double component.[1]
Basic adhesive
The base adhesive is preferably hydroxy terminatedPolydimethylsiloxaneFor special purposes, polymethylsiloxane containing alkoxy group or other active groups can be selected.α. ω - dihydroxy polysiloxane is the basic adhesive of two-component and one component condensation silicone rubber, which is usually called 107 adhesive in the market.[1]
One component RTV silicone rubber
One component RTV silicone rubber is one of the main products of condensation silicone rubber.It is composed of basic adhesive, filler, cross-linking agent, catalyst, plasticizer, pigment, etc.The base adhesive is α, ω - dihydroxy polysiloxane.The filler plays the role of reinforcement, compatibilization and special performance.There are many kinds of crosslinking agents, catalysts and other fillers, depending on market demand and product performance.The typical formula is shown in the figure.[1]
One component RTV silicone rubber
Two component RTV silicone rubber
The two-component RTV silicone rubber has the same ingredients as the single component except for the crosslinking agent.Two component RTV silicone rubber usually uses tetraethyl orthosilicate or polysilicate as crosslinking agent, and the latter has high crosslinking speed.The vulcanization reaction is shown in the figure.[1]
Two component RTV silicone rubber
Application of RTV silicone rubber
(1) Construction industry.It is used for bonding glass and metal curtain wall, roof sealing, door and window sealing, and bonding and sealing of various pools and tiles.
(2) Electronics industry.The packaging and pouring materials used for electronic and electrical components can be damp proof, shock resistant, shock resistant, temperature shock resistant and chemical corrosion resistant.
(3) Mold.Silicone rubber is widely used in soft mold industry due to its excellent simulation and good demoulding performance.
(4) Automobile, ship and aviation.It can be used as local forming gasket, window seal, electronic and electrical connector anti corona, etc.[1]
Additive liquid silicone rubber
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The addition liquid silicone rubber is mainly made of polydimethylsiloxane containing vinyl end group as the base rubber, polymethylsiloxane containing dimethyl chain link and methyl hydrogen chain link as the crosslinking agent, and platinum complex as the crosslinking catalyst.The silicone rubber with network structure can be obtained by addition reaction of rubber with room temperature or heating under the action of catalyst.[1]
Main varieties
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Silicone rubber products
There are many ways to classify silicone rubber, which is generally divided into solid silicone rubber andLiquid silicone rubber；Divided intoRoom temperature vulcanized silicone rubber，High temperature vulcanized silicone rubber；According to the different monomers used, it can be divided intomethylVinyl silicone rubber, methyl phenyl vinyl silicone rubber, fluorosilicone,Nitrile silicone rubberEtc;According to the different performance and use, it can be divided into general type, super low temperature resistant type, super high temperature resistant type, high strength type, oil resistant type, medical type, etc.The common silicone rubber is briefly introduced as follows:
Preparation of high molecular weight linearDimethylpolysiloxaneRubber must have high purity raw materials. In order to ensure the purity of raw materials, in industry, it is usually first to refine and purify the dimethyldichlorosilane with the content of more than 99.5% in the ethanol water medium, hydrolyze and condense under the acid catalysis, and separate the tetramer of bifunctional siloxane, namelyOctamethylcyclotetrasiloxane, and then make the quadricyclecatalyzerUnder the action, macromolecular linear dimethyl polysiloxane is formed.
When used in the range of - 60~+250 ℃, dimethyl silicone rubber has low vulcanization activity, large high temperature compression permanent deformation, and is not suitable for making thick products. Thick products are difficult to vulcanize, and the inner layer is also easy to blister.Due to the superior performance of methyl vinyl silicone rubber containing a small amount of vinyl, dimethyl silicone rubber has gradually been replaced by methyl vinyl silicone rubber.Other types of silicone rubber produced and applied today, except forDimethylsiloxaneIn addition to the structural unit, there are more or less other structural units containing bifunctional siloxanes, but the preparation method is not fundamentally different from that of dimethyl silicone rubber. The preparation method is generally to hydrolyze and condense a certain bifunctional silicon monomer under the conditions conducive to the formation of the ring, and then add it according to the required proportionOctamethylcyclotetrasiloxaneAnd then it is prepared by co reaction under the action of catalyst.
Methyl vinyl silicone rubber
Methyl vinyl silicone rubber is called vinyl silicone rubber for short.
This kind of rubber contains a small amount of vinyl side chain, so it is better thanMethyl silicone rubberIt is easy to vulcanize, so that more kinds of peroxides can be used for vulcanization, and the amount of peroxides can be greatly reduced.Silicone rubber with a small amount of vinyl andDimethyl silicone rubberIn comparison, the compression set resistance can be significantly improved, and the low compression set reflects that it can be used as aSealing elementIt has better support at high temperature, which is O-ring andWasherOne of the requirements that must be met.Methyl vinyl silicone rubber is a kind of common silicone rubber with good process performance and easy operation, which can be made into thick products, and the surface of semi-finished products pressed and calendered is smooth.
Methylphenyl vinyl silicone rubber
Methylphenyl vinyl silicone rubber is called phenyl silicone rubber for short.This rubber is made of vinyl silicone rubberMolecular chainIt is obtained by introducing diphenyl siloxane chain link or methyl phenyl siloxane chain link.
According to the difference of phenyl content (phenyl: silicon atom) in silicone rubber, it can be divided into low phenyl, medium phenyl and high phenyl silicone rubber.WhenrubberCrystallization occurs or is close toGlass transitionThe point or the overlap of these two conditions will cause the rubber to appear rigid.The introduction of an appropriate amount of large volume groups can destroy the regularity of the polymer chain, which can reduce the crystallization temperature of the polymer. At the same time, the introduction of large volume groups can also change the force between polymer moleculesGlass transition temperature。Low phenyl silicone rubber (CsixHfive/Si=6~11%), that is, due to the above reasons, it has excellent low temperature resistance and is independent of the type of phenyl monomer used.The brittleness temperature of vulcanizate is - 120 ℃, which is the best rubber with low temperature performance nowadays.Low phenyl silicone rubber has the advantages of vinyl silicone rubber, and the cost is not very high, so it has the tendency to replace vinyl silicone rubber.When the phenyl content is greatly increased, the rigidity of the molecular chain will increase, which will lead to the reduction of cold resistance and elasticity, but the ablation resistance and radiation resistance will be improved. When the phenyl content reaches C6H5/Si=20~34%, the medium phenyl silicone rubber has the characteristics of ablation resistance. High phenyl silicone rubber (CsixHfive/Si=35~50%) has excellent radiation resistance.
Nitrile silicone rubber
Fluorosilicone rubber is a kind of silicone rubber with side chain introduced fluoroalkyl.The commonly used fluorosilicone rubber is the fluorosilicone rubber containing methyl, trifluoropropyl and vinyl groups.
fluorinesilica gelIt has good heat resistance, excellent oil resistance and solvent resistance, such as good stability of aliphatic hydrocarbon, aromatic hydrocarbon, chlorinated hydrocarbon, petroleum based fuel oil, lubricating oil, hydraulic oil and some synthetic oil at room temperature and high temperature, which is beyond the pure silicone rubber.Fluorosilicone rubber has good low-temperature performanceFluororubberIt is a great improvement.The temperature range of keeping elasticity of fluorosilicone rubber containing trifluoropropyl group is generally - 50 ℃~+200 ℃. Its high and low temperature resistance is worse than that of vinyl silicone rubber, and it will produce toxic gas when heated to more than 300 ℃.The electrical insulation performance is much worse than that of vinyl silicone rubber.Adding an appropriate amount of low viscosity hydroxy fluorosilicone oil to the fluorosilicone rubber compound, heat treating the compound, and adding a small amount of vinyl silicone rubber can significantly improve the process performance, help solve the problems of roller sticking and serious storage structure of the compound, and extend the effective service life of the compound.When the methyl phenyl siloxane chain link is introduced into the fluorosilicone rubber, the low-temperature resistance will be improved, and the processing property will be good.
Nitrile silicone rubberIt is a kind of silicone rubber with side chain introduced with nitrile alkyl (generally β - nitrile ethyl or γ - nitrile propyl).The introduction of polar nitrile group improved the oil resistance and durable solvent performance of silicone rubber, but its heat resistance, electrical insulation and processability decreased.
The type and content of nitrile alkyl group have a great impact on the properties of nitrile silicone rubber. For example, the silicone rubber containing 7.5% mole of γ - nitrile propyl group has similar cold resistance to low phenyl silicone rubber, and the oil resistance is better than low phenyl silicone rubber. When the content of γ - nitrile propyl group increases to 33~50% mole, the cold resistance is significantly reduced, the oil resistance is improved, and the heat resistance is 200 ℃.If β - cyanoethyl is used instead of γ - cyanopropyl, the heat resistance of nitrile silicone rubber can be further improved.
Phenylene and Phenyletherene Silicone Rubber
Phenylene silicone rubber is a kind of silicone rubber in which the phenylene group is introduced into the main chain of polysiloxane.
Due to the introduction of phenylene group, the radiation resistance of silicone rubber is greatly improved. At the same time, because of the existence of aromatic ring, the rigidity of molecular chain is increased, the flexibility is reduced, the glass transition temperature is increased, the cold resistance is decreased, and the tensile strength is increased.Phenylene silicone rubber has excellent high temperature resistance and radiation resistance, which can withstand high temperature up to 250~300 ℃, and has goodDielectric propertiesAnd moisture-proof, mildew proof, water vapor resistant, etc.In the raw rubber composition of phenylene silicone rubber, when the benzene content is 60%, the phenyl content is 30%, and the methyl content is 10% (vinyl content is 0.6%), it is appropriate. In this case, the vulcanizate has good comprehensive properties.
The disadvantage of phenylene silicone rubber is its poor low-temperature performance. The brittleness temperature is - 25 ℃, which affects its application in some aspects. The low-temperature performance of phenylene ether silicone rubber is far better than that of phenylene silicone rubber. The brittleness temperature is - 64~70 ℃.
Phenyl ether supported silicone rubber is a polysiloxane whose molecular main chain is introduced into the phenyl ether and phenylene groups.
Phenyletherylene silicone rubber has good mechanical properties, and its general tensile strength can reach 150~180kg/cm2 (that is, 14.7~17.7Mpa is much higher than the strength of vinyl silicone rubber, while it has excellent radiation resistance and is superior to phenylene silicone rubber. It can withstand prolonged hot air aging at 250 ℃, and still has high strength after aging.Although the low temperature performance of phenyl ether silicone rubber is worse than that of vinyl silicone rubber, it is far better than that of phenylene silicone rubber.Its dielectric property is similar to that of vinyl silicone rubber, but the oil resistance of phenyl ether supported silicone rubber is poor. It is not resistant to either non-polar petroleum based oil or polar synthetic oil (such as 4109 diester synthetic lubricant and phosphate hydraulic oil).In a word, compared with vinyl silicone rubber, phenyl ether supported silicone rubber has higher strength and radiation resistance, similar high temperature resistance and dielectric properties, and poor low temperature performance, oil resistance and elasticity.Phenyletherylene silicone rubber has good processing properties and can be used to manufacture model products and extrusion products with special requirements.
Medical field
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In manysynthetic rubberAmong them, silicone rubber is the best.It is tasteless, non-toxic and fearlesshigh temperatureAnd the ability to resist severe cold. At 300 degrees Celsius and minus 90 degrees Celsius, the original strength and elasticity remain unchanged.Silicone rubber also has good electrical insulation, oxygen resistance, aging resistance, light resistance, aging resistance and mildew resistancechemical stabilityEtc.Because of these excellent properties, silicone rubber has played an important role in modern medicine.With the cooperation of hospitals, scientific research institutions and factories, a variety of silicone rubber medical supplies have been successfully trial produced.
silicon rubberNoise prevention earplug: Comfortable to wear, can well block noise and protect eardrum.
Silicone rubber tire headAspirator: It is easy to operate and safe to use. It can deform according to the size of the fetal head, and the fetal scalp will not be sucked up when being sucked. It can avoid scalp hematoma, intracranial injury and other ills, and can greatly reduce the pain of dystocia pregnant women during delivery.
Silicone rubber artificial blood vessel: with special physiological function, it can be "intimate" with the human body, and the human body does not reject it. After a certain period of time, it will be completely combined with the human tissue with excellent stability.
Silicone rubber tympanic membrane patch: The patch is thin and soft, with good smoothness and toughness.It is an ideal material for repairing eardrum, and is easy to operate with good effect.
In addition, there are silicone rubber artificial trachea, artificial lung, artificial bone, silicone rubber duodenal tube, etc., all of which are very effective.
Amount of silicone rubber
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According to the statistics of China Association of Automobile Manufacturers, in 2012, the production and sales of automobiles respectively reached 19.2718 million and 19.3064 million, with year-on-year growth of 4.63% and 4.33%silicon rubberThe dosage of is about 20000 tons.According to the latest research of Guanyantianxia, increasing the amount of silicone materials used in auto parts can significantly improve the safety performance of automobiles. Therefore, the increase of automobile production and single vehicle consumption will promote the increase of demand for silicone rubber in the automobile industry.The state encourages the development of self owned brands of automobiles, and key auto parts are self owned. The 2012 Catalogue of Models Selected for Official Use by Party and Government Organs (Draft for Comments) provides a guarantee for self owned brands to expand their market share in government procurement, and to change the current situation of domestic government procurement dominated by joint brand products.Promote the development of independent brands, and the prosperity of the domestic automobile industry will provide a strong guarantee for the application of automobile adhesive.It is predicted that in the next three years, China's RTV silicone rubber will grow by 20% annually in the automotive industry.
In addition, silicone rubber is the most important non petroleum based synthetic rubber, accounting for about 98% of the consumption of non petroleum based synthetic rubber.However, due to the sharp rise in oil prices, and China's breakthrough in the production technology of silicone monomer, the key raw material of silicone rubber, the production technology of silicone monomer was monopolized by several multinational companies before 2005, but now China has developed into the first largest country of silicone monomer in the world,For these two reasons, the price of silicone rubber has been lower than that of petroleum based synthetic rubber since 2011, only about 80%~90% of the bulk petroleum based rubber, becoming the cheapest synthetic rubber and starting to replace petroleum based synthetic rubber on a large scale.This will greatly expand the market space of the silicone industry and drive the consumption of silicone oil, silane coupling agent, silicone resin and other silicone products.
Development of silicone rubber
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The silicone rubber industry has made remarkable achievements.With the leap forward growth of consumption, the silicone rubber industry has begun to transform from high-performance special rubber to mass synthetic rubber, becoming one of the largest rubber varieties.It is reported that according to the type of rubber consumed, natural rubber accounts for 41.8%, styrene butadiene rubber and cis-1,4% in total, while silicone rubber is usually only used in a few non tire fields such as building sealant and conductive keys, accounting for 6.4% of the total rubber consumption.Therefore, as silicone rubber replaces other types of rubber in some non tire segments, its consumption will be doubled and the market space will be further opened.In this regard, industry insiders also agree with the above views.It is estimated that by 2015, silicone rubber will account for 10% to 15% of the total domestic rubber consumption, that is, silicone rubber consumption is expected to reach 1 million to 1.5 million tons, and by 2020, silicone rubber is expected to account for 20% to 33% of the total rubber consumption, that is, silicone rubber consumption is expected to reach 3 million to 5 million tons.In other words, the development potential and long-term development of silicone rubber industry are very attractive, and its rapid development will also have a far-reaching impact on upstream and downstream industries.In fact, the upstream and downstream industrial linkage effect of silicone rubber industry has begun to appear gradually.Some experts pointed out that the biggest highlight of the development of silicone rubber industry is that it can significantly improve the domestic self-sufficiency rate of rubber.According to statistics, if the proportion of silicone rubber in China's rubber consumption increases from 6.5% to 33% by 2020, the overall domestic self-sufficiency rate of China's rubber can increase from about 50% to more than 80%, thus greatly easing the tight supply of rubber and reducing the production cost of the rubber processing industry.It can be seen that the development of silicone rubber industry is not only the single development of a single industry, but also involves the common development of multiple industries. It has far-reaching significance for enhancing the profitability of the rubber processing industry and improving the quality of rubber products.[2]
