Room temperature vulcanized silicone rubber (RTV) is a new type of silicone elastomer that was introduced in the 1960s. The most remarkable feature of this rubber is that it can be cured in situ without heating or pressing at room temperature, and it is extremely convenient to use. Therefore, it has become an important part of the entire silicone product. At room temperature, vulcanized silicone rubber has been widely used as an adhesive, sealant, protective coating, potting and molding material, and has its use in various industries. Room temperature vulcanized silicone rubber is known as liquid silicone rubber because of its low molecular weight. Its physical form is usually a flowable fluid or a viscous paste with a viscosity of between 100 and 1,000,000 centistokes. Depending on the requirements of use, the pre-vulcanized compound can be formulated as an automatic leveling infusion or a non-rogue but scratchable putty. The filler used in the room temperature vulcanized silicone rubber is similar to the high temperature vulcanized silicone rubber, and is reinforced with white carbon black to give the vulcanized rubber a tear strength of 10 to 60 kg/cm 2 . Adding different additives can make the rubber compound have different specific gravity, hardness, strength, fluidity and thixotropic properties, and make the vulcanized rubber have various special properties such as flame retardant, conductive, heat conduction 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 method. According to the vulcanization mechanism, it can be divided into condensation type and addition molding. Therefore, room temperature vulcanized silicone rubber can be divided into three types according to composition, vulcanization mechanism and use process, namely, one-component room temperature vulcanized silicone rubber, two-component condensation type room temperature vulcanized silicone rubber and two-component addition type room temperature vulcanized silicone rubber. .


The raw rubber of the one-component and two-component condensation type room temperature vulcanized silicone rubbers are all α,ω-dihydroxypolysiloxane; the addition of room temperature vulcanized silicone rubber is an alkenyl group and a hydrogen containing side group (or terminal group). Polysiloxane is also known as low-temperature vulcanized silicone rubber (LTV) because it can obtain a good ripening effect at a temperature slightly higher than room temperature (50 to 150 ° C) during aging.


These three series of room temperature vulcanized silicone rubbers have their own advantages and disadvantages:
single-component room temperature vulcanized silicone rubber has the advantages of convenient use, but deep curing speed is difficult; the advantage of two-component room temperature vulcanized silicone rubber is that it does not exotherm during curing. , shrinkage rate is small, no expansion, no internal stress, curing can be carried out at the same time inside and on the surface, can be deep vulcanized; the vulcanization time of the addition room temperature vulcanized silicone rubber is mainly determined by the temperature, therefore, the temperature can be controlled to control its vulcanization. speed.

1. One-component room temperature vulcanized silicone rubber
The vulcanization of one-component room temperature vulcanized silicone rubber is initiated by moisture in the air. The commonly used cross-linking agent is methyltriacetoxysilane, whose Si-OC bond is easily hydrolyzed, and the acetoxy group combines with the hydrogen group in water to form acetic acid, and the hydroxyl group in water is transferred to the original acetoxy group. Positionally, it becomes trishydroxymethylsilane. Trishydroxymethylsilane is extremely unstable and easily condenses with a linear organosilicon having a terminal hydroxyl group to form a crosslinked structure. Usually, the silicone raw rubber containing silanol end groups and fillers, catalysts, cross-linking agents and other compounding agents are put into a sealed hose, which is extruded from the container during use and vulcanized by means of moisture in the air. Elastomers, while releasing low molecular weight. The crosslinking agent may be a silane containing an alkoxy group, a thiol group, an amine group, an amide group or a ketone group in addition to the methyltriacetoxysilane. When alcohol is exchanged with an alkoxy group, it is called a dealcoholized one-component room temperature vulcanized silicone rubber. When it is crosslinked with a sulfhydryl group, it is called a deuterium type room temperature vulcanized silicone rubber. Therefore, with the cross-linking Different components, single-component room temperature vulcanized silicone rubber can be many types such as deacidification type, depurination type, dealcoholization type, deamination type, deamidation type and deketone type, but the deacidification type is currently the most widely used. One.


The vulcanization time of the one-component room temperature vulcanized silicone rubber depends on the vulcanization system, temperature, humidity, and thickness of the silicone rubber layer. Increasing the temperature and humidity of the environment can accelerate the vulcanization process. Under typical environmental conditions, after 15 to 30 minutes, the surface of the silicone rubber may be non-tacky, and a layer of 0.3 cm thick may be cured in one day. The depth and strength of curing will gradually increase in about three weeks.


The 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, and gas permeability. They maintain flexibility for a long period of time in the range of -60 to 200 °C. It does not absorb heat when it is cured, does not release heat, has a 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 molded gaskets, protective coatings and caulking materials. Many single-component silicone rubber adhesive formulations exhibit automatic bonding properties on a variety of materials such as most metals, glass, ceramics and coagulations, such as bare aluminum, with shear strengths up to 200 lbs/ft. 2, tear strength up to 20 pounds · 呎 / 吋 2 (0.35 joules / cm 2). When the bonding is difficult, the primer may be applied to the substrate to improve the bonding strength. The primer may be a reactive silane monomer or resin, and when they are cured on the substrate, a modified layer is formed. On the surface of silicone bonding.


Although the one-component room temperature vulcanized silicone rubber is convenient to use, since the vulcanization is based on the moisture in the lazy atmosphere, the thickness of the vulcanized rubber is limited, and it can only be used in applications requiring a thickness of 6 mm or less.


The vulcanization reaction of the one-component room temperature vulcanized silicone rubber is carried out gradually from the surface to the depth, and the thicker the rubber layer, the slower the curing. When the deep part is also to be solidified quickly, the layered watering stepwise vulcanization method can be used, and some rubber can be added each time, and then the vulcanization is added, which can reduce the total vulcanization time. The addition of magnesium oxide accelerates the vulcanization of the deep glue.


Two-component room temperature vulcanized silicone rubber two-component room temperature vulcanized silicone rubber can be further divided into condensation type and addition molding.

2, two-component condensation type room temperature vulcanized silicone rubber
Two-component condensation type room temperature vulcanized silicone rubber is the most common type of room temperature vulcanized silicone rubber. The raw rubber is usually a hydroxyl terminated polysiloxane, which is combined with other compounding agents and catalysts to form a rubber compound. The viscosity can range from 100 centistokes to one million centistokes. The vulcanization reaction of the two-component room temperature vulcanized silicone rubber is not caused by the moisture in the air, but by the catalyst. The silicone rubber, filler, and cross-linking agent are usually packaged as one component, the catalyst is packaged as another component, or in other combinations, but the catalyst and the cross-linking agent must be separately packaged. Regardless of the packaging method, curing begins only when the two components are completely mixed together. A commonly used crosslinking agent is ethyl orthosilicate, and the catalyst is dibutyltin dilaurate. Appropriate fillers and additives are added depending on the nature of the desired end product. In recent years, in many countries, because dibutyltin dilaurate is a moderately toxic grade, the addition of dibutyltin in food bags and plasma bags has been largely replaced by low toxicity octyltin.


The vulcanization time of the two-component condensation type room temperature vulcanized silicone rubber mainly depends on the type, amount and temperature of the catalyst. The more the amount of catalyst used, the faster the vulcanization, and the shorter the shelf life. At room temperature, the shelf life is usually a few hours. To extend the shelf life of the compound, a cooling method can be used. The two-component condensation type room temperature vulcanized silicone rubber requires a day or so to reach full curing at room temperature, but it takes only one hour at a temperature of 150 °C. The curing speed can be significantly improved by using the synergistic effect of the accelerator γ-aminopropyltriethoxysilane. Two-component room temperature vulcanized silicone rubber can maintain elasticity for a long time in a temperature range of 65-250 ° C, and has excellent electrical properties and chemical stability, water, ozone and weathering resistance, combined with simple usage and high process applicability Therefore, it is widely used as potting and molding materials. After coating and potting with room temperature vulcanized silicone rubber, various electronic and electrical components can protect against moisture (anti-corrosion, anti-vibration, etc.) and can improve performance and stability parameters. Two-component room temperature vulcanized silicone rubber is especially suitable for deep irrigation. The sealing material has a faster curing time, which is superior to the one-component room temperature vulcanized silicone rubber.


The two-component room temperature vulcanized silicone rubber has excellent anti-sticking properties after vulcanization, and has a small shrinkage rate during vulcanization. Therefore, it is suitable for use in the manufacture of soft molds for casting epoxy resin, polyester resin, polystyrene, Molds of polyurethane, vinyl, paraffin, low melting point alloys, etc. In addition, the high simulation performance of the two-component room temperature vulcanized silicone rubber can be used to replicate a variety of delicate patterns. For example, in the reproduction of cultural relics can be used to copy ancient bronzes, in the production of artificial leather can be used to copy the skin of snakes, crickets, crocodiles and pangolins, to play the role of false real.


Two-component room temperature vulcanized silicone rubber should pay attention to several specific problems when it is used: first, the base material, the crosslinking agent and the catalyst are separately weighed and then mixed in proportion. Usually the two components should be provided in different colors so that the mixing of the two components can be visually observed and the mixing process should be handled carefully to minimize the amount of gas entrained. After the rubber compound is mixed (even color), the bubbles can be removed by standing or decompressing (vacuum degree 700 mmHg). After the bubbles are completely discharged, they are vulcanized into silicon at room temperature or at a predetermined temperature for a certain period of time. Rubber.


The side group on the main component of the two-component room temperature vulcanized silicone rubber siloxane may be substituted with other groups such as phenyl, trifluoropropyl, cyanoethyl or the like in addition to the methyl group to improve its resistance to low temperature and heat. , radiation resistance or solvent resistance. At the same time, heat-resistant, flame-retardant, heat-conductive, and conductive additives may be added as needed to obtain a silicone rubber having ablation resistance, flame retardancy, heat conduction, and electrical conductivity.

1. Methyl room temperature vulcanized silicone rubber
Methyl room temperature vulcanized silicone rubber is an old variety of general-purpose silicone rubber, which has the advantages of water resistance, ozone resistance, arc resistance, corona resistance and weathering resistance. It can be used in a temperature range of 60 to 200 °C. Therefore, it is widely used as a filling and sealing material for electronic and electrical components, and as a moisture-proof, shock-proof, high-low temperature resistant perfusion and sealing material for instrumentation. It can also be used to make molds for casting polyester resins, epoxy resins and low melting point alloy parts. It can also be used as an impression material for dental products. It is coated on cotton cloth and paper bag with methyl room temperature vulcanized silicone rubber to form a conveyor belt and a packaging bag for conveying viscous articles.


2. Methyl bisphenyl room temperature vulcanized silicone rubber
Methyl bisphenyl room temperature vulcanized silicone rubber has a wider operating temperature range (-100 to 250 ° C) than methyl room temperature vulcanized silicone rubber, in addition to the excellent properties of methyl room temperature vulcanized silicone rubber. The low phenyl room temperature vulcanized silicone rubber (108-1) with a phenyl content of 2.5 to 5% can maintain elasticity at a low temperature of -120 ° C, which is the best low temperature performance of silicone rubber; the phenyl content is 10 ~20% of room temperature glue (108-2) has good resistance to radiation, ablation and self-extinguishing. If a certain amount of heat-resistant additives such as Fe2O3 are added to it, it can improve heat aging performance. Use at high temperatures above °C or as a resistive putty coating and encapsulating material.


Methyl phenyl room temperature glue can be used for dipping, stamping and stripping, just like other room temperature glues. In order to increase the adhesion to other materials, the material to be adhered must be surface treated before using the material. The surface treatment steps are as follows: the surface of the material is washed 1 or 2 times with acetone solvent, and then treated with a surface agent. ~2 times, baked in an oven at 60 ° C for a few minutes, at this time on the surface of the material to form a layer of less sticky film, you can glue.


3. Methyl block room temperature vulcanized silicone rubber
The methyl block room temperature vulcanization silicone rubber is a modified version of methyl room temperature vulcanized silicone rubber, which is a polydimethylsiloxane (107 gum) and a methyltriethoxysilane oligomer which are blocked by a hydroxyl group ( A copolymer having a molecular weight of 3 to 5). Under the catalysis of dibutyltin dilaurate, the hydroxyl group in the polydimethylsiloxane and the ethoxy group in the polymethyltriethoxysilane condense to form a three-directional polymer, the vulcanized bomb The body has higher mechanical strength and adhesion than methyl room temperature vulcanized silicone rubber, and can be used for a long time in a temperature range of 70 to 200 °C.


Methyl block room temperature vulcanized silicone rubber has anti-vibration, moisture-proof, waterproof, breathable, ozone-resistant, weather-resistant, weak acid and weak base properties. It has good electrical insulation properties, good adhesion and low cost. Therefore, it can be widely used for potting, coating, stamping, demoulding, releasing drug carriers and the like. The electronic components potted with methyl block room temperature glue have the functions of shockproof, moisture proof, sealing, insulation and stability. By directly coating the methyl block room temperature glue on the speaker, the intermediate frequency of the speaker can be reduced and eliminated, and the resonant frequency performance of the speaker after vulcanization can be reduced by about 20 Hz. It can be used as a paper release agent after blending a certain amount of additives into the methyl block room temperature gel. After coating a thin layer of methyl block room temperature glue on the confectionery and biscuit conveyor belt of the food industry, the anti-stick property of the canvas can be improved, thereby improving the appearance of the food and improving the utilization rate of the raw material.


Add appropriate amount of fumed silica to the methyl block room temperature gel for installation of window glass, curtain walls, window frames, joints for prefabricated panels, and expansion joints for airport runways. In addition, it can also be used as an adhesive for magnetic cores and stencils in electronic computer memory, and as an adhesive for conductive silicone rubber and non-conductive silicone rubber. Treatment of the fabric with methyl block room temperature vulcanized silicone rubber improves the hand, softness and resistance to sharpening of the fabric.


4. Room temperature vulcanized silicone rubber
Room temperature vulcanized silicone rubber is poly-β-nitrile ethyl methyl siloxane. The room temperature vulcanization silicone rubber has the characteristics of light resistance, ozone resistance, moisture resistance, high and low temperature resistance and excellent electrical insulation properties. The solvent is excellent in resistance to aliphatic and aromatic solvents, and its oil resistance is similar to that of ordinary oil-resistant nitrile rubber. It can be used as a sealed injection material for oil-contaminated parts and oil-resistant electronic components.


5. Room temperature vulcanized fluorosilicone rubber
The room temperature vulcanized fluorosilicone rubber is poly γ-trifluoropropyl methyl siloxane, which is mainly characterized by fuel oil resistance, solvent resistance and high temperature resistance to degradation, and also has good extrusion properties. Mainly used for sealing and caulking of supersonic aircraft integral fuel tank, fluorosilicone rubber gasket, gasket bonding; silicone rubber and fluorosilicone rubber bonding, chemical engineering and general industrial fuel oil resistance; solvent resistant parts Bonding.


6. Room temperature vulcanization of phenylene silicone rubber
The room temperature vulcanized phenylene silicone rubber is a silicon benzene (biphenyl) siloxane polymer, which has the outstanding advantage of having excellent high energy ray resistance. Tests have shown that after being subjected to 1x109 roentgen γ-ray or 1xl018 neutron/cm 2 neutron irradiation, the rubber elasticity can be maintained, which is 10-15 times larger than room temperature vulcanized methyl silicone rubber and 5~ larger than room temperature vulcanized phenyl silicone rubber. 10 times.


Room temperature vulcanized phenylene silicone rubber can be used as a high temperature resistant and radiation resistant adhesive sealing material and an insulating protective layer for motors in atomic energy industry, nuclear power plant and space flight.

3, the addition of room temperature vulcanized silicone rubber
The two-component addition molding room temperature vulcanized silicone rubber has the characteristics of elastic silicone gel and silicone rubber, and the former has lower strength and the latter has higher strength. Their vulcanization mechanism is based on the addition reaction (hydrosilylation reaction) of the vinyl (or propylene group) on the silicone gum end group and the hydrosilyl group on the chain extender molecule.


In this reaction, a hydride-functional polysiloxane is used as a crosslinking agent (vulcanizing agent) chloroplatinic acid or other soluble platinum compound as a catalyst. The sulfurization reaction is carried out at room temperature. Do not release by-products. Since the low molecular weight is not released during the interlacing process, the addition of the room temperature vulcanized silicone rubber does not cause shrinkage during the vulcanization process. This type of vulcanizate is non-toxic, has high mechanical strength, excellent hydrolysis stability (even under high pressure steam), good low compression set, low flammability, deep vulcanization, and vulcanization rate can be controlled by temperature. The advantage is therefore a kind of silicone rubber which is vigorously developed at home and abroad.


The addition of room temperature vulcanized silicone rubber is generally packaged in two parts, M and N: a catalyst and a vinyl polymer having a vinyl group as a component; a hydrogen-containing polysiloxane The chain agent is used as another component.


The high-strength addition-molding room temperature vulcanized silicone rubber is an excellent material for molding because of its low line shrinkage rate and low molecular weight during vulcanization. It has been widely used in the mechanical industry to mold epoxy resin, polyester resin, polyurethane, polystyrene, vinyl, paraffin, low melting point alloy, coagulation and the like. The high-simulation, non-corrosive, simple molding process and easy demoulding of the vulcanized silicone rubber are suitable for the reproduction of cultural relics and the reproduction of fine arts and crafts.