1. Temperature characteristics
Organic silicone products are silicone-oxygen (Si-O) bond as the main chain structure, C-C bond bonding energy of 82.6 kcal/g molecule, the bonding energy of the Si-O bond in the organosilicon products, the bonding energy of the Si-O bond in the organosilicon products, the bonding energy of the Si-O bond in the organosilicon products. C-C bond bond energy of 82.6 kcal/g molecule, Si - O bond energy in the silicone for 121 kcal/g molecule, so the thermal stability of silicone products is high, high temperature (or radiation irradiation) molecules of the chemical bond does not break, do not decompose. Silicone can not only high temperature resistance, but also low temperature resistance, can be used in a wide temperature range. Whether it is chemical properties or physical and mechanical properties, with the temperature change is very small.
2. Weathering
Organic silicon products, the main chain for -Si-O-, no double bond exists, so it is not easy to be decomposed by ultraviolet light and ozone. Organic silicon has better thermal stability than other polymer materials, as well as irradiation and weathering resistance. The service life of silicone in the natural environment can be up to several decades.
3. Electrical insulation
Silicone products have good electrical insulation properties, its dielectric loss, voltage resistance, arc resistance, corona resistance, volume resistance coefficient and surface resistance coefficient, etc. are among the best in insulating materials, and their electrical properties by the temperature and frequency is very small. Therefore, they are a stable electrical insulating material and are widely used in the electronic and electrical industries. Silicone in addition to excellent heat resistance, but also has excellent water repellency, which is the use of electrical equipment in wet conditions with high reliability of the guarantee.
4. Physiological inertness
Polysiloxane compounds are known to be one of the most inactive compounds. They are very resistant to biological aging, no rejection with the animal body, and have good anticoagulant properties.
5. Low surface tension and low surface energy
Silicone main chain is very smooth, its intermolecular forces are much weaker than hydrocarbons, therefore, than the same molecular weight of hydrocarbons with low viscosity, weak surface tension, surface energy is small, strong film-forming ability. This low surface tension and low surface energy is the main reason why it has been used in many ways: hydrophobic, defoaming, foam stabilization, anti-sticking, lubrication, varnish and other excellent properties.
Second, the use of silicone
Because silicone has these excellent properties, so it has a very wide range of applications. It is not only as aviation, cutting-edge technology, military technology sector of the use of special materials, but also used in various sectors of the national economy, the scope of its application has been expanded to: construction, electrical and electronic, textile, automotive, machinery, leather and paper, chemical and light industry, metal and paint, medicine and health care.
Third, the classification of silicone
Silicone is mainly divided into silicone rubber, silicone resin, silicone oil three categories.
Room temperature vulcanized silicone rubber and its classification
Room temperature vulcanized silicone rubber (RTV) is a new type of silicone elastomers introduced in the sixties, the most notable feature of this rubber is that it can be cured without heating at room temperature, such as pressure, and it is extremely convenient to use. Therefore, as soon as it was introduced, it quickly became an important part of the entire silicone products. Now room temperature vulcanized silicone rubber has been widely used as adhesives, sealants, protective coatings, potting and molding materials, in all walks of life have its uses.
Room temperature vulcanized silicone rubber according to its packaging can be divided into single-component and two-component room temperature vulcanized silicone rubber, according to the vulcanization mechanism can be divided into condensation type and addition molding. Therefore, room temperature vulcanized silicone rubber according to the composition, vulcanization mechanism and the use of different processes can be divided into three major types, namely, single-component room temperature vulcanized silicone rubber, two-component condensation room temperature vulcanized silicone rubber and two-component addition molding room temperature vulcanized silicone rubber. These three series of room temperature vulcanization of silicone rubber has its own characteristics: one-component room temperature vulcanization of silicone rubber has the advantage of ease of use, but the deep curing speed is more difficult; two-component room temperature vulcanization of silicone rubber has the advantage of curing is not exothermic, shrinkage is very small, does not expand, no internal stress, curing can be carried out at the same time in the interior and the surface, can be deep vulcanization; add molding room temperature vulcanization of silicone rubber vulcanization time is determined mainly by the temperature, so the use of temperature regulation can control the room temperature vulcanization. Therefore, the use of temperature regulation can control the speed of vulcanization.
In many synthetic rubbers, silicone rubber is the best among them. It is odorless and non-toxic, not afraid of high temperatures and cold characteristics, in three hundred degrees Celsius and minus ninety degrees when "calm and easy", "the face does not change color", still do not lose the original strength and elasticity. Silicone rubber also has good electrical insulation, oxygen aging resistance, light aging resistance and mildew resistance, chemical stability. As a result of these excellent properties, making silicone rubber in modern medicine has gained a very wide range of important uses. In recent years, by the hospital, research units and factories **** with the collaboration, the trial production of a variety of successful silicone rubber medical supplies.
Silicone rubber anti-noise earplugs: comfortable to wear, can be a good barrier to noise, protect the eardrum.
Silicone rubber fetal head suction: easy to operate, safe to use, can be deformed according to the size of the fetal head, suction when the fetal scalp will not be sucked up to avoid scalp hematoma and intracranial injuries and other maladies, can greatly reduce the pain of difficult-to-deliver pregnant women in labor.
Silicone rubber artificial blood vessels: has a special physiological function, can do with the human body "intimate", the human organism does not exclude it, after a certain period of time, it will be completely with the human body tissue instances up the stability of the very good.
Silicone rubber tympanic membrane repair sheet: the sheet is thin and soft, smoothness and toughness are good. It is the ideal material for repairing the eardrum, and it is easy to operate, and the effect is quite good.
In addition, there are silicone rubber artificial trachea, artificial lungs, artificial bone, silicone rubber duodenal tube, etc., the efficacy is very ideal.
With the progress and development of modern science and technology, the use of silicone rubber in medicine will have broader prospects.
Foam silicone rubber is a condensed hydroxyl sealing end of the silicone rubber as the base material, hydroxyl hydrogenated silicone oil as a blowing agent, vinyl platinum complex for the catalyst (heating
type catalyst for the dibutyldimonolaurate tin), foaming at room temperature vulcanized into a spongy spongy elastomers with holes. In order to improve the quality of the foam body should also add some other components, such as containing silicone oil, so that the vulcanization process produces more gas; improve the feel of the foam body and reduce the density. The addition of diphenylsilanediol can not only control the structure of the foam body, but also control the viscosity of the rubber material in the storage process, but its dosage can not be too much, otherwise it will affect the electrical properties of the foam body. In order to improve the physical and mechanical properties of the foam body, transparent silicone rubber can also be added. Catalyst chloroplatinic acid vinyl complex of the dosage can not be too much, to the ease of operation shall prevail, otherwise it will make the viscosity increase is not conducive to the operation; when the catalyst dosage is insufficient, the vulcanization is incomplete, the foam body surface viscous, elasticity is not good, soft and with plasticity, poor strength.
Silicone rubber foam is liquid before vulcanization, suitable for potting materials. After vulcanization of the foam body can be used in -60 ~ 159 ℃ for a long time, by 150 ℃, 72 hours old, or a 60 ~ 70 ℃ ten times the use of hot and cold alternation, the foam body still maintains the original performance.
Foam silicone rubber due to high thermal stability, good thermal insulation, insulation, moisture resistance, shock resistance, especially in the high-frequency shock resistance, so it is an ideal lightweight encapsulation material. Used for a variety of electronic components, instruments, meters, flying body instrument wheel, etc. can play a "moisture-proof, shock-proof, corrosion-proof," the "three" protection. In addition, it can also be used as filler material for adiabatic interlayer and floating material in salt spray atmosphere and sealing material. Foam silicone rubber in medicine can also be used as orthopedic filling, repair and clothing materials.
The U.S. anti-Corning company in order to apply the fire protection requirements of the transmission line, developed into a flame-retardant room-temperature vulcanization of foam silicone rubber DC3-6548. This foam silicone rubber is mainly used for wires and cables through the place (for example, roofs, walls, buildings, etc. at the holes) of the fire sealing, fire retardant performance is very good, the limit of the oxygen index of 39 (the limit of the majority of the plastics oxygen index of 20), the service life of up to 50 years. The service life is up to 50 years. At present, this kind of flame retardant room temperature vulcanization foam silicone rubber has been widely used in nuclear power plants, computer centers, offshore oil recovery devices and other harsh environmental conditions, or fire requirements of particularly high places.
Two-component condensation type room temperature vulcanization silicone rubber introduction2007-05-24 09:09Two-component condensation type room temperature vulcanization silicone rubber is the most common type of room temperature vulcanization of silicone rubber, its raw rubber is usually hydroxyl-sealed polysiloxane, and then with other agents, catalysts, combined with the composition of the compound, the viscosity of this compound can be from the range of 100 centistokes to one million centistokes between.
The vulcanization of two-component, room-temperature vulcanized silicone rubber is initiated not by moisture in the air, but by a catalyst. Usually the silicone rubber, filler, crosslinker as a component package, the catalyst alone as another component package, or other combinations, but must be separated from the catalyst and crosslinker packaging. Regardless of the packaging method, only when the two components are completely mixed together, curing will begin to occur. The commonly used crosslinker is ethyl orthosilicate and the catalyst is dibutyltin dilaurate. Appropriate fillers and additives are also added depending on the nature of the desired end product. In recent years, many countries have banned the addition of dibutyltin in food bags and plasma bags due to the fact that dibutyltin dilaurate belongs to the moderately toxic class of substances, and it has basically been replaced by octyltin, which is low in toxicity.
The vulcanization time of two-component condensation type room temperature vulcanized silicone rubber mainly depends on the type of catalyst, the amount of catalyst and temperature. The more catalyst used, the faster the vulcanization, and the shorter the shelf time. At room temperature, the shelf time is generally a few hours, if you want to extend the shelf time of the rubber, available cooling method. Two-component condensation type room temperature vulcanization silicone rafter adhesive at room temperature to achieve full curing needs about a day's time, but in the temperature of 150 ℃ only 1 hour. The rate of cure can be significantly increased by using the accelerator γ-aminopropyltriethoxysilane for synergistic effects.
Two-component room temperature vulcanized silicone rubber can be in a 65 ~ 250 ℃ temperature range of long-term elasticity, and has excellent electrical properties and chemical stability, water resistance, ozone resistance, weather aging, coupled with simple usage, process applicability, therefore, widely used as a potting and mold making materials. Various electronic and electrical components with room temperature vulcanized silicone rubber coating, potting, can play a moisture (corrosion, shock and other protective effects.). Can improve performance and stabilize parameters. Two-component room temperature vulcanized silicone rubber is particularly suitable for deep potting materials and has a faster vulcanization time, which is better than one-component room temperature vulcanized silicone rubber.
I. One-component room temperature vulcanized silicone rubber
One-component room temperature vulcanized silicone rubber vulcanization reaction is to rely on the role of moisture in the air and vulcanized into elastomers. With the different chain agent, one-component room temperature vulcanized silicone rubber can be deacidified, deoxime, dehydrogenated, deaminated, deamidated and deketonized and many other varieties. The vulcanization time of one-component room temperature vulcanized silicone rubber depends on the vulcanization system, temperature, humidity and the thickness of the silicone rubber layer. Increasing the ambient temperature and humidity can speed up the vulcanization process. Under typical environmental conditions, generally after 15 to 30 minutes, the surface of the silicone rubber can be free of adhesion, and the thickness of the rubber layer of 0.3 cm can be cured within a day. The depth and strength of cure is gradually enhanced in about three weeks.
One-component room temperature vulcanized silicone rubber has excellent electrical properties and chemical inertness, as well as heat resistance, natural aging resistance, flame resistance, moisture resistance, air permeability and other properties. They can maintain elasticity for a long time in the range of -60~200℃. It does not absorb heat or exotherm when curing, has small shrinkage after curing, and has good adhesion to materials. Therefore, it is mainly used as an adhesive and sealant, and other applications include in-situ molding gaskets, protective coatings and inlay materials. Many one-component silicone rubber adhesive formulations exhibit self-bonding properties to a wide range of materials such as most metals, glass, ceramics and coagulation. When bonding difficulties, the substrate can be into the primer to improve bond strength, the primer can be reactive silane monomers or resins, when they are cured on the substrate to produce a layer of modified suitable for silicone bonding surface. One-component room temperature vulcanized silicone rubber, although easy to use, but because of its vulcanization is dependent on the moisture in the lazy atmosphere, so that the thickness of the vulcanized rubber is limited, can only be used for occasions that require a thickness of less than 6 mm. One-component room temperature vulcanized silicone rubber vulcanization reaction is gradually from the surface to the depth, the thicker the rubber layer, the slower the curing. When the deep also want to fast curing, can be used in layers of pouring step-by-step vulcanization method, each time you can add some rubber, such as vulcanization and then add material, which can reduce the total vulcanization time. Adding magnesium oxide can accelerate the vulcanization of the deep glue.
II. Two-component condensation type room temperature vulcanization of silicone rubber
Two-component room temperature vulcanization of silicone rubber vulcanization reaction is not relying on the moisture in the air, but by the catalyst to initiate. Usually the rubber and catalyst are packaged separately as a component. Only when the two components are completely mixed together will curing begin to occur. The curing time of two-component condensed room temperature vulcanized silicone rubber depends mainly on the type and amount of catalyst and the temperature. The higher the amount of catalyst, the faster the vulcanization and the shorter the resting time. At room temperature, the shelf time is generally a few hours, if you want to extend the shelf time of the rubber, can be used to cool the method. Two-component condensation type room temperature vulcanization silicone rafter adhesive at room temperature to achieve full curing needs about a day, but in the temperature of 150 ℃ only 1 hour. The rate of cure can be significantly increased by using accelerators for synergistic effects.
Two-component room temperature vulcanized silicone rubber can be in a 65 ~ 250 ℃ temperature range for a long time to maintain the elasticity, and has excellent electrical properties and chemical stability, can be resistant to water, ozone, climate aging, coupled with simple usage, process applicability, therefore, widely used as a potting and mold making materials. Various electronic and electrical components with room temperature vulcanized silicone rubber coating, potting, can play a moisture-proof (anti-corrosion, shock and other protective effects.). Can improve performance and stabilize parameters. Two-component room temperature vulcanized silicone rubber is particularly suitable for deep potting materials and has a faster vulcanization time, which is better than one-component room temperature vulcanized silicone rubber. Two-component room temperature vulcanized silicone rubber vulcanization has excellent anti-adhesive properties, coupled with the vulcanization of the shrinkage rate is very small, so it is suitable for use in the manufacture of soft molds for casting epoxy resins, polyester resins, polystyrene, polyurethane, vinyl plastics, paraffin waxes, low melting point alloys and other molds. In addition, the use of two-component room temperature vulcanized silicone rubber's high simulation performance can be reproduced on the cultural relics of a variety of exquisite patterns. Two-component room temperature vulcanization silicone rubber should be noted when using: first of all, the rubber and catalyst are weighed separately, and then mixed in proportion. The mixing process should be carefully operated to minimize the amount of entrapped gas. After mixing the rubber (color uniformity), can be removed through the static or decompression (vacuum 700 mm Hg) to remove air bubbles, to be fully discharged bubbles, at room temperature or at the specified temperature for a certain period of time that is vulcanized into silicone rubber.
III. Two-component plus molding room temperature vulcanization of silicone rubber
Two-component plus molding room temperature vulcanization of silicone rubber has elastic silicone gel and silicone rubber points, the former lower strength, the latter higher strength. Their vulcanization mechanism is based on the silicone raw rubber end group on the vinyl (or propylene-based) and crosslinking agent molecules on the silicone hydrogen-based addition reaction (hydrosilylation reaction) to complete. In this reaction, no by-products are released. Since no low molecules are released during the crosslinking process, additively molded room temperature vulcanized silicone rubber does not shrink during vulcanization. This class of vulcanized rubber is non-toxic, high mechanical strength, excellent hydrolysis resistance stability (even under high pressure steam), good low compression deformation, low combustibility, can be deep vulcanization, as well as the speed of vulcanization can be controlled by the temperature and so on, so it is a class of domestic and foreign vigorously development of silicone rubber. Two-component room temperature vulcanized silicone rubber can be in a 65 ~ 250 ℃ temperature range to maintain long-term elasticity, and has excellent electrical properties and chemical stability, can be resistant to water, ozone, climate aging, coupled with simple usage, process applicability, therefore, widely used as a potting and mold making materials. Various electronic and electrical components with room temperature vulcanized silicone rubber coating, potting, can play a moisture (corrosion, shock and other protective effects.). Can improve performance and stabilize parameters. Two-component room temperature vulcanized silicone rubber is particularly suitable for deep potting materials and has a faster vulcanization time, which is better than one-component room temperature vulcanized silicone rubber.
Two-component room temperature vulcanized silicone rubber vulcanization has excellent anti-adhesive properties, coupled with the vulcanization of the shrinkage rate is very small, so it is suitable for use in the manufacture of soft molds for casting epoxy resins, polyester resins, polystyrene, polyurethanes, vinyl plastics, paraffin waxes, low-melting-point alloys and other molds. In addition, the use of two-component room temperature vulcanized silicone rubber's high simulation performance can be reproduced a variety of exquisite patterns. For example, in the cultural relics reproduction can be used to copy the ancient bronze, in the production of artificial leather can be used to copy the snake, python, crocodile and pangolin and other animal skin pattern, to play the effect of fake to real.
Two-component room temperature vulcanized silicone rubber should pay attention to a few specific issues in use: first of all, the base material, crosslinking agent and catalyst were weighed, and then mixed in proportion. Usually two components should be provided in different colors to use, so that the mixing of the two components can be observed intuitively, the mixing process should be carefully operated in order to minimize the amount of entrapped gas. After mixing the rubber (uniform color), can be removed by standing or decompression (vacuum 700 mm Hg) to remove air bubbles, to be all the air bubbles out, at room temperature or at the specified temperature for a certain period of time that is vulcanized into a silicone rubber.
Two-component room temperature vulcanized silicone rubber silicone rubber main chain of the side groups in addition to methyl, can be replaced with other groups such as phenyl, trifluoropropyl, cyanoethyl, etc., in order to improve its resistance to low temperatures, heat, radiation, or solvent resistance and other properties. At the same time, heat-resistant, flame-retardant, thermally conductive and electrically conductive additives can also be added as needed to produce silicone rubber with ablative, flame-retardant, thermally conductive and electrically conductive properties.
(A) methyl room temperature vulcanized silicone rubber
Methyl room temperature vulcanized silicone rubber for the old varieties of general-purpose silicone rubber, with water resistance, ozone resistance, arc resistance, corona resistance and weather aging and other advantages. It can be a 60 ~ 200 ℃ temperature range. Therefore, it is widely used as filling and sealing materials for electronic and electrical components, moisture-proof, shock-proof, high and low temperature resistant filling and sealing materials for instruments and meters. It can also be used to make molds for casting polyester resin, epoxy resin and low melting point alloy parts. It can also be used as dental impression material. Methyl room temperature vulcanized silicone rubber coated in cotton cloth, paper bags, can be made for conveying sticky goods conveyor belts and bags.
(B) Methyl biphenyl room temperature vulcanized silicone rubber
Methyl biphenyl room temperature vulcanized silicone rubber in addition to methyl room temperature vulcanized silicone rubber has excellent performance, than the methyl room temperature vulcanized silicone rubber has a wider range of use temperature (-100 ~ 250 ℃). Phenyl content of 2.5-5% of low-phenyl room temperature vulcanized silicone rubber (108-1) can be -120 ℃ at low temperatures to maintain the elasticity of the current silicone rubber in the low-temperature performance of one of the best varieties; phenyl content of 10-20% of the room-temperature rubber (108-2) has a very good resistance to irradiation, ablation and self-extinguishing, if you add a certain amount of heat-resistant additives, such as Fe2O3, and so on, can improve the heat aging performance, suitable for 250 to 250 ℃. Heat aging performance, suitable for use at high temperatures above 250 ℃ or do ablative putty coating and encapsulation materials.
Methyl phenyl room temperature adhesive and other room temperature adhesive, can be used for impregnation, molding and film removal. If you want to increase the adhesion with other materials, you must use the material before the material, the material to be adhered to the surface treatment, surface treatment steps are as follows: acetone solvent on the surface of the material to clean 1 ~ 2 times, and then with the surface agent treatment 1 ~ 2 times in the 60 ℃ oven for a few minutes, this time in the formation of a layer of the surface of the material is less sticky film, can be on the glue.
(C) methyl block room temperature vulcanized silicone rubber
Methyl block room temperature vulcanized silicone rubber is a modified variety of methyl room temperature vulcanized silicone rubber, it is by the hydroxyl head of polydimethylsiloxane (107 rubber) and methyltriethoxysilane oligomer (molecular weight of 3 to 5) **** polymer. Catalyzed by dibutyl tin dilaurate, polydimethylsiloxane in the hydroxyl and polymethyltriethoxysilane in the ethoxy condensation to generate a three-way structure of the polymer, after vulcanization of the elastic to the body than the methyl room-temperature vulcanization of the silicone rubber has a high mechanical strength and adhesive force, can be used for a long period of time in a temperature range of 70 ~ 200 ℃.
Methyl-segmented room temperature vulcanized silicone rubber has shockproof, moisture-proof, waterproof, breathable, ozone-resistant, weather-resistant aging, weak acid and alkali resistance. It has good electrical insulation properties, also has good adhesion, and low cost. Therefore, it can be widely used for potting, coating, molding, stripping, releasing drug carriers and other occasions. Methyl segmented room temperature adhesive potting of electronic components with shockproof, moisture, sealing, insulation, stabilization of various parameters and other functions. Methyl embedded room temperature adhesive directly coated to the speaker, can reduce and eliminate the mid-frequency points of the speaker, after vulcanization of the speaker resonance frequency performance can be reduced by about 20 Hz. In the methyl segmented room temperature adhesive with a certain amount of additives can be used as paper anti-adhesive. In the food industry, candy, cookie conveyor belt coated with a thin layer of methyl blocking room temperature adhesive, can improve the anti-adhesive properties of canvas, thus improving the appearance of food, improve the utilization of raw materials.
Adding appropriate amount of fumed silica to the methyl segmented room temperature adhesive can be used to install window glass, curtain walls, window frames, prefabricated panels, joints, and expansion joints of airport runways. In addition, it can also be used as an adhesive for magnetic cores and templates in electronic computer memory, and as an adhesive for conductive silicone rubber and non-conductive silicone rubber. Methyl segmented room temperature vulcanized silicone rubber treatment of fabrics can improve the feel of the fabric, softness and resistance to curved abrasion.
(D) room temperature vulcanization eyed silicone rubber.
Room temperature vulcanization nitrile silicone rubber is a poly β- nitrile ethyl methyl silicone, room temperature vulcanization guess silicone rubber in addition to silicone rubber light, ozone, moisture, high and low temperature resistance and excellent electrical insulation properties, the main feature is the resistance to non-polar solvents, such as aliphatic, aromatic solvents, good performance, and its oil resistance and ordinary oil nitrile rubber is close to the oil-resistant, can be used as oil contaminated parts and oil-resistant electronic components. It can be used as sealing material for oil contaminated parts and oil resistant electronic components.
(E) room temperature vulcanization of fluorosilicone rubber
Room temperature vulcanization of fluorosilicone rubber is a poly γ-trifluoropropyl methyl silicone, its main feature is fuel oil resistance, solvent resistance and high temperature degradation resistance, but also has a good performance of extrusion. Mainly used for supersonic aircraft overall tank sealing, embedded seams, fluorosilicone rubber gaskets, gasket bonding fixed; silicone rubber and fluorosilicone rubber bonding, as well as chemical engineering and general industry fuel oil resistant; solvent resistant parts of the bond.
(F) room temperature vulcanization of benzene-supported silicone rubber
Room temperature vulcanization of benzene-supported silicone rubber is silicone benzene (biphenyl) pro silicone polymer, its outstanding advantage is that it has excellent resistance to high-energy ray performance. Tests have proved that after 1x109 roentgen γ-rays or 1xl018 neutrons / cm2 neutron irradiation, can still maintain the elasticity of the rubber, than the room temperature vulcanization of methyl silicone rubber is 10 to 15 times greater than the room temperature vulcanization of phenyl silicone rubber is 5 to 10 times greater than the room temperature vulcanization of phenyl silicone rubber.
Room temperature vulcanized phenyl silicone rubber can be applied to the atomic energy industry, nuclear power devices and space flight as high temperature, radiation-resistant adhesive sealing materials and motor insulation layer.
Room Temperature Vulcanized Silicone Rubber (RTV) is a new type of silicone elastomer introduced in the sixties, the most notable feature of this rubber is that it can be cured in place at room temperature without heating, such as pressure, and is extremely convenient to use. Therefore, as soon as it was introduced, it quickly became an important part of the entire silicone products. Now room temperature vulcanized silicone rubber has been widely used as adhesives, sealants, protective coatings, potting and mold making materials, in all walks of life have its uses.
Room temperature vulcanized silicone rubber is known as liquid silicone rubber because of its low molecular weight, and its physical form is usually a flowable fluid or a viscous paste, with a viscosity of 100 to 1,000,000 centistokes. According to the requirements of use, can be vulcanized before the rubber material with automatic leveling of the filling material or not flow but can be coated with putty. Room temperature vulcanized silicone rubber filler used with high temperature vulcanized silicone rubber similar to the use of silica reinforcement, so that the vulcanized rubber has 10 to 60 kg / cm2 tensile strength. Fill with different additives can make the rubber has a different specific gravity, hardness, strength, mobility and thixotropy, as well as make the vulcanized rubber has a flame retardant, electrical conductivity, thermal conductivity, ablative resistance and other special properties.
Room temperature vulcanized silicone rubber according to its packaging can be divided into single-component and two-component room temperature vulcanized silicone rubber, according to the vulcanization mechanism can be divided into condensation type and addition molding. Therefore, room temperature vulcanized silicone rubber according to the composition, vulcanization mechanism and the use of different processes can be divided into three major types, namely, single-component room temperature vulcanized silicone rubber, two-component condensation room temperature vulcanized silicone rubber and two-component molding room temperature vulcanized silicone rubber.
One-component and two-component condensation room temperature vulcanization of silicone rubber raw rubber are α,ω-dihydroxy polysiloxane; molding room temperature vulcanization of silicone rubber is containing alkenyl and hydrogen side group (or end group) of polysiloxane, because in the ripening, often slightly higher than the room temperature of the case (50 ~ 150 ℃) can achieve good ripening results, so, also known as low-temperature vulcanization of silicone rubber (LTV).
The three series of room temperature vulcanized silicone rubber has its own advantages and disadvantages: one-component room temperature vulcanized silicone rubber has the advantage of ease of use, but the deep curing speed is more difficult; two-component room temperature vulcanized silicone rubber has the advantage of curing is not exothermic, shrinkage is very small, no expansion, no internal stress, curing can be carried out at the same time in the interior and the surface, can be deep vulcanization; plus molding room temperature vulcanized silicone rubber vulcanization time The vulcanization time of room temperature vulcanized silicone rubber is mainly determined by the temperature, therefore, the use of temperature adjustment can control the speed of vulcanization.
One-component room temperature vulcanized silicone rubber One-component room temperature vulcanized silicone rubber vulcanization reaction is to rely on the moisture in the air to trigger. Commonly used cross-chaining agent is methyl triacetoxysilane, its Si-O-C bond is easily hydrolyzed, acetoxy and hydrogen in the water combined into acetic acid, and the hydroxyl group in the water to move to the original position of the acetoxy, to become three hydroxymethylsilane. Trihydroxymethylsilane is extremely unstable, and it is easy to condense with the linear silicone whose end group is hydroxyl to become a cross-chain structure. Normally, the silicone rubber containing silanol end groups and fillers, catalysts, crosslinking agents and other agents are packed into a sealed hose, which is extruded from the container when in use, and vulcanized into an elastomer with the help of moisture in the air, and at the same time, low molecular weights are released.
In addition to methyltriacetoxysilane, the cross-linking agent can be a silane containing an alkoxy group, an oxime group, an amine group, an amide group, or a ketone group. When cross-linked with alkoxy alcohol released, known as dehydrogenated one-component room temperature vulcanization silicone rubber, when cross-linked with oxime group to generate oxime, known as deoxime room temperature vulcanization silicone rubber, therefore, with the different cross-linking agent, one-component room temperature vulcanization silicone rubber can be deacidified, deoxime, dehydrogenated, deaminated, deamidated and ketone dehydrogenated and so on, but deacidified is one of the most widely used at present.
The vulcanization time of one-component room temperature vulcanized silicone rubber depends on the vulcanization system, temperature, humidity, and the thickness of the silicone rubber layer, and increasing the ambient temperature and humidity can speed up the vulcanization process. In typical environmental conditions, generally 15 to 30 minutes after the surface of the silicone rubber can be no sticky, thickness of 0.3 cm layer can be cured within a day. The depth and strength of cure is gradually enhanced in about three weeks.
One-component room-temperature vulcanized silicone rubber has excellent electrical properties and chemical inertness, as well as heat resistance, natural aging resistance, flame resistance, moisture resistance, breathability and other properties. They can maintain elasticity for a long time in the range of -60 to 200℃. It does not absorb heat or exotherm when curing, has small shrinkage after curing, and has good adhesion to materials. Therefore, it is mainly used as an adhesive and sealant, and other applications include in-situ molding gaskets, protective coatings and inlay materials. Many one-component silicone rubber adhesive formulations exhibit automatic bonding properties to a wide range of materials such as most metals, glass, ceramics, and coagulation, for example, to bare aluminum, shear strength of up to 200 lb/in2, and tear strength of up to 20 lb - ft/in2 (0.35 Joule/cm2). When bonding is difficult, the bond strength can be improved by priming the substrate, which can be reactive silane monomers or resins that, when cured on the substrate, produce a modified surface suitable for silicone bonding.
Single-component room-temperature vulcanized silicone rubber is easy to use, but because of its vulcanization is dependent on the moisture in the lazy atmosphere, so that the thickness of the vulcanized rubber is limited, can only be used for the need for less than 6 mm thickness of the occasion.
One-component room temperature vulcanized silicone rubber vulcanization reaction is gradually from the surface to the depth of the rubber layer, the thicker, the slower the curing. When the deep also want to fast curing, can be used in layers of pouring step by step vulcanization method, each time you can add some rubber, such as vulcanization and then add material, so you can reduce the total vulcanization time. Adding magnesium oxide can accelerate the vulcanization of the deep glue.
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Silicone rubber, silicone, fine pore silicone, inorganic silicone, silicone desiccant