High temperature vulcanized silicone rubber is a kind of high molecular weight polysiloxane (i.e. raw rubber) with reinforcing fillers and other additives. Using organic peroxide as vulcanizing agent, rubber is crosslinked at high temperature by molding (molding, extrusion and calendering) or injection molding. This kind of rubber is generally referred to as silicone rubber for short.
The vulcanization of high temperature vulcanized silicone rubber is generally divided into two stages. In the first stage, raw silicone rubber, reinforcing agent, additive, vulcanizing agent and structure control agent are mixed, and then the mixed materials are pressurized, heated and vulcanized in a metal mold at a pressure of about 50kg/cm2, a temperature of 120 ~ 130℃ and a time of10 ~ 30min. Rubber is further vulcanized, while organic peroxide is decomposed and volatilized.
The reinforcing filler of silicone rubber is various types of white carbon black, which can improve the strength of vulcanized rubber ten times. The main purpose of adding various additives is to reduce the cost of rubber, improve the properties of rubber and give vulcanized rubber various special properties such as flame retardancy and electrical conductivity. The crosslinking agent is various organic peroxides, such as benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, diisopropylbenzene peroxide, 2,5-di-tert-butylperoxyhexane, etc. The structure control agent is added to prevent the rubber mixture from being left for too long, causing "structure" and making it difficult to process and cure. Methyl hydroxy silicone oil or diphenyl dihydroxy alkyl can be used as structure control agent.
The side groups on the main chain of silicone rubber can be methyl, ethyl, vinyl, phenyl, trifluoropropyl, etc. The most commonly used is methyl, and other groups can be introduced to improve processability and other properties. Therefore, according to the different side groups and rubber formulations, silicone rubber with different uses can be obtained, which can be generally divided into the following types: universal type (containing methyl and vinyl), high temperature and low temperature type (containing phenyl, methyl and vinyl), low compression set (containing methyl and vinyl), low shrinkage (volatilization) and solvent-resistant type (fluorosilicone rubber). Several important silicone rubbers are introduced below.
I methyl silicone rubber
Dimethyl silicone rubber is the earliest silicone rubber put into commercial production, which can maintain good elasticity in the range of -60 ~ 200℃, good aging resistance, excellent electrical insulation, moisture-proof, shock-proof and physiological inertia.
Dimethyl silicone rubber is mainly used for coating strong materials, and can also be made into various extruded calendered products, which are used in electromechanical, aviation, automobile, medical and other industries. However, dimethyl silicone rubber was replaced by methyl vinyl silicone rubber because of its low vulcanization activity, difficult vulcanization, easy foaming of the inner layer and large permanent deformation under high temperature compression.
Two. silicone gasket
Because the vulcanization performance of silicone rubber can be greatly improved by introducing a small amount of vinyl into the macromolecular structure of silicone rubber, most of the silicone rubber used at present contains vinyl. Methyl vinyl silicone rubber is the most common type of silicone rubber, which is currently dominant in the production of silicone rubber at home and abroad. Because it introduces partially unsaturated vinyl groups into the side chain, its processability and physical and mechanical properties are better than those of double-base silicone rubber. Besides the general characteristics of dimethyl silicone rubber, it also has a wide application temperature range and can maintain good elasticity in the range of 60-260℃. It is easier to vulcanize than dimethyl silicone rubber, and has small compression set, good solvent swelling resistance, high pressure steam stability and excellent cold resistance. Moreover, due to the use of peroxide with low activity for vulcanization, the shortcomings of bubble generation and poor rubber stability during vulcanization are reduced. Therefore, methyl vinyl silicone rubber can generally be used to make products with large thickness. Methyl vinyl silicone rubber is the most widely used silicone rubber. In recent years, various kinds of high-performance and special-purpose silicone rubber have emerged, mostly vinyl silicone rubber, such as high-strength silicone rubber, low-compression permanent deformation silicone rubber, post-vulcanized silicone rubber, heat-resistant conductive silicone rubber, medical silicone rubber and so on. Methyl vinyl silicone rubber is widely used as a protective layer for gaskets, sealing materials and fragile shock-proof parts in aviation industry. In the electrical industry, it can be used as advanced insulating materials such as electronic components, dynamic sealing rings of high-temperature potentiometers and sealing rings of underground long-distance communication equipment; In medicine, methyl vinyl silicone rubber is used in plastic surgery, artificial heart valves, blood vessels and so on. Because it has little physiological reaction to human body and is non-toxic.
3. Methyl phenyl vinyl silicone rubber
Methyl phenyl vinyl silicone rubber is a product obtained by introducing methyl phenyl siloxane chain or diphenyl siloxane chain into the molecular chain of methyl vinyl silicone rubber. The introduction of phenyl into the side group of polysiloxane destroyed the regularity of dimethylsiloxane structure, which greatly reduced the crystallization temperature of polymer and expanded the low-temperature application range of this polymer material. Therefore, methyl phenyl vinyl silicone rubber not only has all the properties of methyl vinyl silicone rubber, such as small compression set, wide temperature range, oxidation resistance, weather resistance, impact resistance, moisture resistance and good electrical insulation, but also has excellent low temperature resistance, ablation resistance and radiation resistance. These properties vary with the content of phenyl in the molecular chain. Generally speaking, when the phenyl content (the ratio of phenyl to silicon atom) is 5 ~ 10%, it is called low phenyl silicone rubber. It has unique cold resistance, and can still keep the elasticity of rubber at -70 ~- 100℃, which is the best one of all rubbers at low temperature. In addition, it also has the advantages of methyl vinyl silicone rubber. When the phenyl content is 20 ~ 40%, it is said that middle phenyl silicone rubber has the advantages of methyl vinyl silicone rubber, and the cost is not high, so it has a great trend to replace methyl vinyl silicone rubber. When the phenyl content is 20 ~ 40%, it is called middle phenyl silicone rubber, which has excellent flame retardancy and can extinguish itself once it catches fire. When the phenyl content is 40 ~ 50%, it is called high phenyl silicone rubber, which has excellent radiation resistance and gamma ray resistance of 1xI08 roentgen. Generally speaking, with the increase of phenyl content, the rigidity of silicone rubber molecular chain increases gradually, and the low temperature resistance of silicone rubber decreases gradually, but with the increase of phenyl content, the flame retardant and radiation resistance of vulcanized rubber improve. The content comes from the rubber garden.
Methyl phenyl vinyl silicone rubber is one of the important materials in aerospace industry, cutting-edge technology and other sectors of national economy. It can be used to manufacture all kinds of molded and extruded products of cold-resistant rubber in aviation industry, and sealing rings, pads, tubes and rods of ablation-resistant, heat-resistant and radiation-resistant parts.
Four. Fluorosilicone rubber
Fluorosilicone rubber refers to γ-trifluoropropyl methyl polysiloxane. Fluorosilicone rubber has excellent chemical resistance, solvent resistance and lubricating oil resistance. This silicone rubber has small expansion rate in nonpolar solvents, good cold resistance and thermal stability, and good flame retardancy. Therefore, it is used as rubber hose, gasket, sealing ring, oil tank village, etc. It can also be used to make corrosion-resistant clothes, gloves, paints and adhesives in aircraft, rockets, missiles, aerospace and petrochemical industries.
Verb (abbreviation of verb) nitrile silicone rubber
Because the side chain of polymer molecules contains strong polar groups of β -nitrile ethyl or γ -nitrile propyl, the intermolecular force is greatly increased, and the oil resistance and solvent resistance are improved. At the same time, due to the introduction of a certain amount of nitrile alkyl, the regularity of polymer structure was destroyed and the cold resistance was greatly improved. The type and content of nitrile alkyl have great influence on the properties. For example, the silicone rubber containing 7.5mol %γ- nitrile propyl has similar low-temperature performance to that of low-phenyl silicone rubber (its glass transition temperature is-1 14.5℃), and its oil resistance is better than that of phenyl silicone rubber. With the increase of γ -nitrile propyl content to 33 ~ 50 mol%, the cold resistance decreased and the oil resistance increased. Using β-nitrile ethyl instead of γ-nitrile propyl can improve the heat resistance of NBR silicone rubber and resist hot air aging at 250℃.
The main advantages of NBR silicone rubber are excellent oil resistance and bath resistance, which can keep elasticity in the range of -60 ~ 180℃. Therefore, it can be made into oil-resistant rubber products for aviation industry, automobile industry and petroleum industry. It can also be used as environmental sealant and fuel tank sealant for high-performance aircraft, and can keep sealing at -54℃ to above 200℃. Nitrile-butadiene silicone rubber can be processed by common equipment.
Intransitive verb phenylene silicone rubber
The main feature of styrene silicone rubber is its excellent radiation resistance, which is 10 ~ 15 times that of general methyl vinyl silicone rubber and 5 ~ 10 times that of high phenyl silicone rubber. Therefore, it can be used as cable, sheath, gasket and heat shrinkable tube with high energy radiation resistance in aerospace industry, atomic energy industry and nuclear reactor.
Seven. Ethyl silicone rubber
Diethyl silicone rubber prepared by introducing ethyl into polysiloxane side chain has excellent cold resistance, which is better than dimethyl silicone rubber and general methyl vinyl silicone rubber. The higher the ethyl content, the better the cold resistance. However, the reactivity of ethyl is greater than that of methyl, so the heat resistance decreases with the increase of ethyl content. As ethyl silicone rubber used at low temperature, it is recommended to contain 8 mol% diethyl siloxane chain in the polymer. The use temperature of ethyl silicone rubber is generally -70-200℃. The content comes from the rubber garden.
Eight. silazane rubber
The main advantage of silicon-nitrogen rubber is its excellent thermal stability, which does not decompose at 430 ~ 480℃, and some can even withstand high temperatures above 500℃. The outstanding weakness of silicone rubber is its poor hydrolysis stability, which was once considered to have no development prospect. Later, it was found that the polymer containing cyclodisilazane in the main chain had good thermal stability. The elastomer containing siloxane-modified cyclodisilazane does not lose weight when heated to 425℃ in air, and the weight loss at 570℃ is only 65438 00%, which has good hydrolytic stability. Rubber information network, xiangjiaoyuan.com silicone rubber product introduction II- room temperature vulcanized silicone rubber
Room temperature vulcanized silicone rubber (RTV) is a new type of silicone elastomer that came out in 1960s. The most remarkable feature of this kind of rubber is that it can be cured in situ at room temperature, without heating or pressurizing, and it is extremely convenient to use. So it became an important part of silicone products as soon as it came out. At present, room temperature vulcanized silicone rubber has been widely used as adhesives, sealants, protective coatings, potting and molding materials, and has its uses in all walks of life. Room temperature vulcanized silicone rubber is called liquid silicone rubber because of its small molecular weight. Its physical form is usually flowable fluid or viscous paste, and its viscosity is between 100 ~ 1000000 centistoke. According to the use requirements, the rubber mixture before vulcanization can be made into self-leveling castable or putty that does not flow but can be scraped. The filler used in room temperature vulcanized silicone rubber is similar to that used in high temperature vulcanized silicone rubber, and silica is used as reinforcement, so that the fracture strength of vulcanized rubber reaches 10 ~ 60 kg/cm2. Adding different additives can make the compound have different specific gravity, hardness, strength, fluidity and thixotropy, and make vulcanized rubber have various special properties such as flame retardant, electrical conductivity, thermal conductivity and ablation resistance.
Room temperature vulcanized silicone rubber can be divided into one-component and two-component room temperature vulcanized silicone rubber according to its packaging mode, and can be divided into condensation type and addition type according to vulcanization mechanism. Therefore, RTV silicone rubber can be divided into three types according to composition, vulcanization mechanism and application process, namely, one-component RTV silicone rubber, two-component condensed RTV silicone rubber and two-component addition RTV silicone rubber.
The raw rubber of one-component and two-component condensation type room temperature vulcanized silicone rubber is α, ω-dihydroxy polysiloxane; Addition room temperature vulcanized silicone rubber is a polysiloxane containing alkenyl and hydrogen side groups (or end groups). Because it can achieve good curing effect at a temperature slightly higher than room temperature (50 ~ 150℃), it is also called low temperature vulcanized silicone rubber (LTV).
These three series of RTV silicone rubber have their own advantages and disadvantages: one-component RTV silicone rubber has the advantage of convenient use, but the deep vulcanization speed is difficult; Two-component RTV silicone rubber has the advantages of no heat release, small shrinkage, no expansion and no internal stress during curing, and can be cured at the same time on the inner surface and deeply vulcanized; The curing time of addition room temperature vulcanized silicone rubber mainly depends on the temperature, so the curing speed can be controlled by adjusting the temperature.
One-component room temperature vulcanized silicone rubber
The vulcanization reaction of one-component room temperature vulcanized silicone rubber is initiated by moisture in the air. The commonly used crosslinking agent is methyl triacetoxysilane, whose Si-O-C bond is easy to hydrolyze, and the acetoxy group combines with the hydrogen group in water to form acetic acid, and the hydroxyl group in water moves to the original acetoxy position to form trihydroxymethyl silane. Trihydroxymethyl silane is extremely unstable, and it is easy to condense with linear silicone with hydroxyl group to form cross-linked structure. Usually, raw silicone rubber containing silanol end groups, fillers, catalysts, cross-linking agents and other compounding agents are put into a sealed hose, and when in use, they are extruded from the container, vulcanized into elastomers with the help of moisture in the air, and at the same time, low molecular weight substances are released. Besides methyltriacetoxy silane, the crosslinking agent can also be silane containing alkoxy group, oxime group, amine group, amide group and ketone group. The dealcoholized one-component RTV silicone rubber releases alcohol after crosslinking with alkoxy group, and generates oxime after crosslinking with oxime group, which is called deoximated RTV silicone rubber. Therefore, with different crosslinking agents, one-component RTV silicone rubber can be deacidified, deoximated, dealcoholized, deaminated, deamidated and ketonized, but deacidified silicone rubber is the most widely used one at present.
The curing time of one-component room temperature vulcanized silicone rubber depends on curing system, temperature, humidity and the thickness of silicone rubber layer. Increasing the temperature and humidity of the environment can accelerate the curing process. Under typical environmental conditions, after 15 ~ 30 minutes, the surface of silicone rubber will not stick, and the 0.3 cm thick adhesive layer can be cured within one day. The curing depth and strength will gradually increase in about three weeks.
One-component RTV silicone rubber has excellent electrical properties and chemical inertness, as well as heat resistance, natural aging resistance, flame retardancy, moisture resistance and air permeability. They can keep elasticity for a long time in the range of -60 ~ 200℃. It does not absorb heat or release heat during curing, and has small shrinkage after curing and good adhesion to materials. Therefore, it is mainly used as adhesive and sealant, and other applications include in-situ forming gasket, protective coating and caulking material. Many formulations of one-component silicone rubber adhesive show self-adhesion to many materials such as most metals, glasses, ceramics and coagulants. For example, bare aluminum, the shear strength can reach 200 lbs/? 2, the tear strength can reach 20 kg/? 2(0.35 Joule/cm2). When bonding is difficult, primer can be applied to the substrate to improve the bonding strength. Primers can be reactive silane monomers or resins, and when they are cured on the substrate, a modified surface suitable for siloxane bonding is produced. This article comes from Rubber Information Network.
One-component room temperature vulcanized silicone rubber is easy to use, but its vulcanization depends on the moisture in inert atmosphere, which limits the thickness of vulcanized rubber and can only be used in occasions with a thickness less than 6 mm
The vulcanization reaction of one-component room temperature vulcanized silicone rubber is gradually carried out from the surface to the inside, and the thicker the adhesive layer, the slower the curing. When the deep part needs rapid vulcanization, the method of layered pouring and gradual vulcanization can be adopted, and some mixed rubber can be added each time, and then the material can be replenished after vulcanization, so that the total vulcanization time can be reduced. Adding magnesium oxide can accelerate the vulcanization of deep glue.
Two-component RTV silicone rubber Two-component RTV silicone rubber can be divided into condensation type and addition type.
2. Two-component condensation room temperature vulcanized silicone rubber
Two-component condensation RTV silicone rubber is the most common RTV silicone rubber. Its raw rubber is usually hydroxyl-terminated polysiloxane, which combines with other complexing agents and catalysts to form a compound. The viscosity of this compound ranges from 100 CST to one million CST. The vulcanization reaction of two-component room temperature vulcanized silicone rubber is not initiated by moisture in the air, but by catalyst. Silicone rubber, filler and crosslinking agent are usually packaged as one component, and the catalyst is packaged as another component separately, or other combination methods are adopted, but the catalyst and crosslinking agent must be packaged separately. No matter what packaging method is adopted, curing only begins when the two components are completely mixed together. The commonly used crosslinking agent is ethyl orthosilicate, and the catalyst is dibutyltin dilaurate. And suitable fillers and additives are added according to the properties of the required final product. In recent years, dibutyltin dilaurate is a moderately toxic substance, which has been banned from being used in food bags and plasma bags in many countries, and has been basically replaced by octyl tin with lower toxicity. Xiangjiaoyuan.com rubber information network.
The curing time of two-component condensation room temperature vulcanized silicone rubber mainly depends on the type, dosage and temperature of catalyst. The more catalyst is used, the faster vulcanization and the shorter shelf life. At room temperature, storage time is usually several hours. If you want to prolong the storage time of the rubber mixture, you can use the cooling method. It takes about one day for the two-component condensation type room temperature silicon sulfide rafter to be completely cured at room temperature, but it only takes 1 hour at 150℃. Synergistic effect can significantly improve the curing speed of γ -aminopropyl triethoxysilane. Two-component room temperature vulcanized silicone rubber can keep elasticity for a long time in the temperature range of 65 ~ 250℃, and has excellent electrical properties and chemical stability, water resistance, ozone resistance and weather resistance. In addition, it is simple to use and has strong process applicability, so it is widely used as potting and molding materials. After all kinds of electronic and electrical components are coated and packaged with room temperature vulcanized silicone rubber, the purpose of moisture-proof (anti-corrosion, shock-proof) can be achieved. Performance and stable parameters can be improved. Two-component RTV silicone rubber is especially suitable for deep potting materials, and its curing time is faster than that of single-component RTV silicone rubber.
Two-component room temperature vulcanized silicone rubber has excellent anti-sticking performance after vulcanization, and the shrinkage rate during vulcanization is extremely small, so it is suitable for making soft molds and molds of epoxy resin, polyester resin, polystyrene, polyurethane, vinyl plastic, paraffin wax, low melting point alloy and so on. In addition, various exquisite patterns can be reproduced by using the high simulation performance of two-component room temperature vulcanized silicone rubber. For example, in the reproduction of cultural relics, it can be used to copy ancient bronzes, and in the production of artificial leather, it can be used to copy the dermatoglyphics of snakes, pythons, crocodiles, pangolins and other animals, which has the effect of confusing the real with the fake.
Several specific problems should be paid attention to when using two-component room temperature vulcanized silicone rubber: first, weigh the base material, crosslinking agent and catalyst respectively, and then mix them in proportion. Generally, the two components should be provided in different colors, so that the mixing of the two components can be observed intuitively, and the mixing process should be carefully operated to minimize the amount of entrained gas. After the rubber is mixed evenly (with uniform color), bubbles can be removed by standing or depressurizing (vacuum degree is 700 mm Hg). After all the bubbles are discharged, they can be vulcanized at room temperature or specified temperature for a certain period of time and then vulcanized into silicone rubber.
The side groups on the main chain of two-component RTV silicone rubber can be replaced by other groups besides methyl, such as phenyl, trifluoropropyl and cyanoethyl. To improve its low temperature resistance, heat resistance, radiation resistance or solvent resistance. At the same time, additives with heat resistance, flame retardancy, thermal conductivity and electrical conductivity can be added as needed to prepare silicone rubber with ablation resistance, flame retardancy, thermal conductivity and electrical conductivity.
1. methyl room temperature vulcanized silicone rubber
Methyl room temperature vulcanized silicone rubber is an old variety of general silicone rubber, which has the advantages of water resistance, ozone resistance, arc resistance, corona resistance and weather aging resistance. It can be used in the temperature range of 60 ~ 200℃. Therefore, it is widely used as a potting material for electronic and electrical components, and a moistureproof, shockproof and high and low temperature resistant potting material for instruments. It can also be used to make molds and cast polyester resin, epoxy resin and low melting point alloy parts. It can also be used as a dental impression material. Coating methyl room temperature vulcanized silicone rubber on cotton cloth and paper bags can be made into conveyor belts and packaging bags for conveying sticky articles.
2. Methyl diphenyl room temperature vulcanized silicone rubber
Methyl diphenyl RTV silicone rubber not only has excellent properties of methyl RTV silicone rubber, but also has a wider service temperature range (-100 ~ 250℃) than methyl RTV silicone rubber. Low-phenyl room-temperature vulcanized silicone rubber (108- 1) with 2.5-5% phenyl can keep elasticity at the low temperature of-120℃, and it is the best variety of silicone rubber at present. Room temperature adhesive (108-2) with phenyl content of 10 ~ 20% has good radiation resistance, ablation resistance and self-extinguishing. If a certain amount of heat-resistant additives such as Fe2O3 are added to it, the thermal aging performance can be improved, and it is suitable for use at a high temperature above 250℃ or as an ablative putty coating and packaging material.
Methyl phenyl room temperature adhesive, like other room temperature adhesives, can be used for impregnation, stamping and demoulding. If the adhesion with other materials is to be increased, the surface of the adhered material must be treated before use. The steps of surface treatment are as follows: clean the surface of the material with acetone solvent for 65,438+0 ~ 2 times, then treat it with surfactant for 65,438+0 ~ 2 times, and bake it in an oven at 60℃ for several minutes. At this time, a film with less sticky hands can be formed on the surface of the material, and then glued.
3. methyl block RTV silicone rubber
Methyl block RTV silicone rubber is a modified variety of methyl RTV silicone rubber, which is a polymer of hydroxyl-terminated polydimethylsiloxane (107 glue) and methyltriethoxysilane oligomer (molecular weight 3 ~ 5). Under the catalysis of dibutyltin dilaurate, hydroxyl groups in polydimethylsiloxane and ethoxy groups in polymethyltriethoxysilane condense to form polymers with three-dimensional structure. The vulcanized elastomer has higher mechanical strength and adhesion than methyl room temperature vulcanized silicone rubber, and can be used for a long time in the temperature range of 70 ~ 200℃.
Methyl block RTV silicone rubber is shockproof, moisture-proof, waterproof, breathable, ozone-resistant, weather-resistant, weak acid and alkali-resistant. It has good electrical insulation, good adhesion and low cost. Therefore, it can be widely used in potting, coating, stamping, demoulding, drug carrier release and other occasions. Electronic components encapsulated by methyl block room temperature adhesive have the functions of shock resistance, moisture resistance, sealing, insulation and stable parameters. If the methyl block room temperature adhesive is directly coated on the loudspeaker, the intermediate frequency point of the loudspeaker can be reduced and eliminated, and the resonance frequency performance of the loudspeaker after vulcanization can be reduced by about 20 Hz. After adding a certain amount of additives, methyl block room temperature adhesive can be used as paper release agent. After coating a thin layer of methyl block room temperature adhesive on candy and biscuit conveyor belts in food industry, the anti-sticking performance of canvas can be improved, thus improving the appearance of food and improving the utilization rate of raw materials. The content comes from the rubber garden.
Adding a proper amount of fumed silica into methyl block room temperature adhesive can be used to install the joints of window glass, curtain wall, window frame, prefabricated board and expansion joint of airport runway. In addition, it can also be used as an adhesive for magnetic cores and templates in electronic computer memories, as well as for conductive silicone rubber and non-conductive silicone rubber. Treating fabrics with methyl block room temperature vulcanized silicone rubber can improve the handle, softness and bending wear resistance of fabrics.
4. Room temperature vulcanized silicone rubber
Room temperature vulcanized NBR silicone rubber is poly-β-nitrile ethyl methyl siloxane. Room temperature vulcanized silicone rubber not only has the light resistance, ozone resistance, moisture resistance, high and low temperature resistance and excellent electrical insulation performance of silicone rubber, but also has good oil resistance to nonpolar solvents such as aliphatic and aromatic solvents, and the oil resistance is close to that of ordinary oil-resistant nitrile rubber, so it can be used as sealing and potting material for oil-contaminated parts and oil-resistant electronic components.
5. Room temperature vulcanized fluorosilicone rubber
Room temperature vulcanized fluorosilicone rubber is poly-γ-trifluoropropyl methyl siloxane. Its main characteristics are fuel resistance, solvent resistance, high temperature degradation resistance and good extrusion performance. Mainly used for sealing and caulking the integral fuel tank of supersonic aircraft, bonding and fixing fluorosilicone rubber gaskets and washers; Adhesion of silicone rubber and fluorosilicone rubber, and fuel resistance in chemical engineering and general industry; Adhesion of solvent-resistant parts.
6. Room temperature vulcanized styrene silicone rubber
Room temperature vulcanized phenylene silicone rubber is a kind of silylene (biphenyl) siloxane polymer, and its outstanding advantage is its excellent high-energy radiation resistance. Experiments show that rubber can still keep its elasticity after being irradiated by 1x 109 roentgen gamma rays or 1x 10 18 neutrons /cm2, which is larger than room temperature vulcanized methyl silicone rubber 10 ~ 15.
Room temperature vulcanized styrene silicone rubber can be used as high temperature and radiation resistant adhesive sealing material and insulating protective layer for motors in atomic energy industry, nuclear power plants and aerospace fields.
3. Addition molding room temperature vulcanized silicone rubber
Two-component addition room temperature vulcanized silicone rubber can be divided into elastic silicone rubber and silicone rubber, the former has lower strength and the latter has higher strength. Their vulcanization mechanism is based on the addition reaction (hydrosilylation reaction) between the vinyl group (or propylene group) on the end group of raw silicone rubber and the hydrosilylation group on the cross-linking agent molecule.
In this reaction, polysiloxane containing hydride functional groups is used as crosslinking agent (vulcanizing agent), and chloroplatinic acid or other soluble platinum compounds are used as catalysts. The vulcanization reaction is carried out at room temperature. No by-products are released. Because low molecular weight substances are not released during crosslinking, the addition room temperature vulcanized silicone rubber does not shrink during vulcanization. This vulcanized rubber has the advantages of non-toxicity, high mechanical strength, excellent hydrolysis resistance (even under high pressure steam), good low compression deformation, low flammability, deep vulcanization, controllable temperature and so on. It is a kind of silicone rubber developed vigorously at home and abroad.
The packaging method of addition-type room temperature vulcanized silicone rubber is generally divided into m and n components: catalyst and silicone polymer containing vinyl functional groups as one component; A hydrogen-containing polysiloxane crosslinking agent is used as another component.
High-strength addition room temperature vulcanized silicone rubber is an excellent molding material because of its low linear shrinkage and no release of low molecules during vulcanization. In machinery industry, it is widely used for casting epoxy resin, polyester resin, polyurethane, polystyrene, vinyl plastic, paraffin wax, low melting point alloy, coagulant and so on. Addition-molding stuffy temperature vulcanized silicone rubber is suitable for the reproduction of cultural relics and artistic crafts because of its high fidelity, non-corrosion, simple molding process and easy demoulding. Please remember our website: Rubber Garden.
Introduction of Silicone Rubber Products (III)-Silicone Rubber
The addition room temperature vulcanized silicone rubber is colorless or yellowish transparent oily liquid, which becomes soft and transparent silicone rubber after vulcanization. This kind of gel can keep elasticity for a long time in the temperature range of -65 ~ 200℃. It has excellent electrical and chemical stability, water resistance, ozone resistance, weather resistance, hydrophobicity, moisture resistance, impact resistance and non-corrosiveness, and has the advantages of physiological inertia, non-toxicity, tasteless, easy pouring, deep vulcanization, low linear shrinkage and simple operation. Silicone gel is widely used as moisture-proof agent for electronic components in electronic industry. If the electronic components are encapsulated with transparent gel, it can not only play the role of shock prevention and waterproof protection, but also see the components, and use the probe to detect the faults of the components and replace them. Damaged silica gel can be encapsulated and repaired again.
Silica gel is an ideal internal coating material for transistors and integrated circuits because of its high purity, convenient use and certain elasticity, which can improve the qualification rate and reliability of semiconductor devices. Silicone gel can also be used as an elastic adhesive for optical instruments.
In medicine, silica gel can be used to implant human organs, such as artificial breasts, and to repair damaged organs.
Foamed silicone rubber. Foamed silicone rubber is a kind of sponge-like elastomer with holes, which is based on condensed hydroxyl-terminated silicone rubber, hydroxyl-containing silicone oil as foaming agent, vinyl platinum complex as catalyst (dibutyltin dilaurate as heating catalyst). In order to improve the quality of foam, some other components, such as silicone oil, should be added to make the vulcanization process produce more gas. Improve hand feeling and reduce foam density. The addition of diphenyl silicone glycol can not only control the foam structure, but also control the viscosity increase of the rubber compound during storage, but the dosage should not be too much, otherwise it will affect the electrical properties of the foam. In order to improve the physical and mechanical properties of the foam, transparent silicone rubber can also be added. The amount of vinyl complex of chloroplatinic acid as catalyst should not be too much, which is based on convenient operation, otherwise the viscosity will increase, which is not conducive to operation; When the amount of catalyst is insufficient, the vulcanization is incomplete, the foam surface is sticky, the elasticity is not good, it is soft and plastic, and the strength is poor. Copyright rubber information network
Foamed silicone rubber is liquid before vulcanization and is suitable for potting. Vulcanized foam can be used for a long time at -60~ 159℃. After aging at 150℃ for 72 hours or alternating hot and cold at -60 ~ 170℃ for ten times, the foam still maintained its original properties. Foamed silicone rubber has high thermal stability, good heat insulation, moisture resistance and impact resistance, especially at high frequency, and is an ideal lightweight packaging material. Used for "three defenses" protection. In addition, it can also be used as a filling material for thermal insulation interlayer, a floating material in salt fog environment and a sealing material. Foamed silicone rubber can also be used as filling, repairing and prosthetic materials in plastic surgery. In order to meet the fire protection requirements of transmission lines, Corning Company of the United States developed flame retardant room temperature vulcanized foamed silicone rubber DC3-6548. This kind of foam silicone rubber is mainly used for fireproof sealing where wires and cables pass (such as roofs, walls, holes in buildings, etc.). ), and its flame retardant performance is very good. Its limiting oxygen index reaches 39 (the limiting oxygen index of most plastics is only 20) and its service life is as long as 50 years. At present, this kind of flame retardant room temperature vulcanized foam silicone rubber has been widely used in nuclear power plants, computer centers, offshore oil production devices and other fields with harsh environmental conditions or particularly high fire protection requirements.