Classification of silicone materials

Organosilicon materials can be divided into silane coupling agent (organosilicon chemical reagent), silicone oil (silicone grease, silicone lotion, silicone surfactant), high-temperature vulcanized silicone rubber, liquid silicone rubber, silicone resin, composite, etc. according to their different forms. Silane coupling agents

There are generally three methods for the application of silane coupling agents:

First, it is used as a surface treatment agent for skeleton materials; Second, it is added to the adhesive, and third, it is directly added to the polymer material. From the perspective of giving full play to its effectiveness and reducing costs, the first two methods are better.

The application of silane coupling agent can be summarized into three aspects:

1. The surface treatment of glass fiber can improve the adhesion between glass fiber and resin, and greatly improve the strength, electrical, water resistance, weather resistance and other properties of glass fiber reinforced composites. Even in the wet state, it can significantly improve the mechanical properties of composites. The use of silane coupling agents in glass fibers has been quite common. The silane coupling agents used in this field account for about 50% of the total consumption, among which vinyl silane, amino silane, methacryloyloxy silane, etc. are widely used.

2. Used for filling plastics with inorganic fillers. The filler can be surface treated in advance or directly added into the resin. It can improve the dispersion and adhesion of filler in the resin, improve the process performance, and improve the mechanical, electrical and weather resistance of filler plastics (including rubber).

3. As a tackifier for sealants, adhesives and coatings, it can improve their adhesive strength, water resistance, weather resistance and other properties. Silane coupling agent can often solve the problem that some materials cannot be bonded for a long time. Bioactive silicone

Organic silicon that can be fully absorbed by organisms widely exists in plants, such as wheat, oats and other cereals. So far, scientists have found that the highest content is Equisetum arvense. Up to now, the organic silicon extraction technology that can be absorbed and utilized by high-purity liquid biology is only mastered by France and other developed countries. silicone oil

Silicone oil is a kind of polyorganosiloxane with chain structure of different polymerization degree. The most commonly used silicone oil is methyl silicone oil. Silicone oil is generally colorless (or light yellow), tasteless, non-toxic, and nonvolatile liquid. Silicone oil is insoluble in water, methanol, glycol and - ethoxyethanol. It is miscible with benzene, dimethyl ether, methyl ethyl ketone, carbon tetrachloride or kerosene, and slightly soluble in acetone, dioxane, ethanol and alcohol. It has very low vapor pressure, high flash point and ignition point, and low freezing point. With the different number of chain segments n, the molecular weight increases, and the viscosity also increases. This silicone oil can have different viscosities. Silicon oil can be divided into methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, methyl chlorophenyl silicone oil, methyl ethoxy silicone oil, methyl trifluoropropyl silicone oil, methyl vinyl silicone oil, methyl hydroxy silicone oil, ethyl hydrogen silicone oil, hydroxy hydrogen silicone oil, cyanide silicone oil, etc. according to chemical structure;

In terms of application, there are damping silicone oil, diffusion pump silicone oil, hydraulic oil, insulating oil, heat transfer oil, brake oil, etc. Silicone oil has excellent heat resistance, electrical insulation, weather resistance, hydrophobicity, physiological inertia and small surface tension. In addition, it has low viscosity temperature coefficient and high compression resistance. Some varieties also have radiation resistance.

Silicone lotion (a form of silicone oil) mainly includes silicone oil fabric softener; Silicone oil lotion defoamer: it is a defoamer with the most extensive use and the largest amount among silicone defoamers. silicon rubber

1. Room temperature vulcanized silicone rubber

Room temperature vulcanized silicone rubber (RTV) is a new type of silicone elastomer, which came out in the 1960s. The most prominent feature of this rubber is that it can be cured in place at room temperature without heating, such as pressing, and it is extremely convenient to use. Therefore, as soon as it came out, it quickly became an important part of the entire silicone product. RTV silicone rubber has been widely used as adhesives, sealants, protective coatings, potting and molding materials in all walks of life.

classification

Room temperature vulcanized silicone rubber can be divided into single component and two-component room temperature vulcanized silicone rubber according to its packaging mode, and can also be divided into condensation type and addition type according to the vulcanization mechanism. Therefore, RTV silicone rubber can be divided into three types according to its composition, curing mechanism and application process, namely, one component RTV silicone rubber, two component condensation RTV silicone rubber and two component addition RTV silicone rubber. The three series of RTV silicone rubber have their own characteristics: one component RTV silicone rubber has the advantage of convenient use, but it is difficult to cure in deep; The advantages of two-component RTV silicone rubber are that it does not release heat, has small shrinkage, does not expand, and has no internal stress during curing. The curing can be carried out inside and on the surface at the same time, and can be deep vulcanized; The curing time of addition RTV silicone rubber is mainly determined by temperature. Therefore, the curing speed can be controlled by adjusting the temperature.

One component RTV silicone rubber

The vulcanization reaction of one component room temperature vulcanized silicone rubber is to vulcanize into elastomer by reacting with water in the air. With different chain agents, one component RTV silicone rubber can be deacidification, deaximation, dealcoholization, deamination, deamidation, deacetylation and many other varieties. The curing time of one component RTV silicone rubber depends on the 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, the surface of silicone rubber can be free of viscosity after 15-30 minutes, and the adhesive layer with a thickness of 0.3cm 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, chemical inertness, heat resistance, natural aging resistance, flame resistance, moisture resistance, air permeability and other properties. They can remain elastic for a long time in the range of - 60~200 ℃. It does not absorb or release heat during curing, has small shrinkage after curing, and has good adhesion to materials. Therefore, it is mainly used as adhesive and sealant. Other applications include in situ formed gaskets, protective coatings and caulking materials. Many single component silicone rubber adhesive formulations exhibit automatic adhesion properties to a variety of materials such as most metals, glass, ceramics and aggregates. When the bonding is difficult, a primer can be applied on the substrate to improve the bonding strength. The primer can be a reactive silane monomer or resin. When they are cured on the substrate, a modified surface suitable for silicone bonding is generated. Although one component room temperature vulcanized silicone rubber is convenient to use, its vulcanization is based on the moisture in the lazy atmosphere, which limits the thickness of the vulcanizate, and can only be used in situations where the thickness is less than 6mm. The vulcanization reaction of one component RTV silicone rubber proceeds gradually from the surface to the depth. The thicker the rubber layer, the slower the curing. When the deep part also needs to be cured quickly, layered pouring and gradual vulcanization method can be used. Some rubber can be added each time, and then added after vulcanization, which can reduce the total vulcanization time. The addition of magnesium oxide can accelerate the vulcanization of deep rubber.

Two component condensation RTV silicone rubber

The curing reaction of two-component RTV silicone rubber is not initiated by the moisture in the air, but by the catalyst. The rubber and catalyst are usually packaged as one component. Curing occurs only when the two components are completely mixed together. The curing time of two-component condensation RTV silicone rubber mainly depends on the type, amount and temperature of catalyst. The more catalyst is used, the faster the vulcanization is, and the shorter the shelving time is. At room temperature, the shelving time is usually several hours. If you want to extend the shelving time of the rubber, you can use the cooling method. It takes about one day for the two-component condensation RTV silicone rubber to fully cure at room temperature, but only one hour at 150 ℃. The curing speed can be significantly improved by using accelerants for synergistic effect.

The two-component room temperature vulcanized silicone rubber can maintain elasticity during the synthesis principle period of the long modified styrene acrylic lotion in the temperature range of 65~250 ℃, and has excellent electrical performance and chemical stability. It can resist water, ozone and weather aging. In addition, it is simple in use and has strong process applicability. Therefore, it is widely used as potting and molding materials. After various electronic and electrical components are coated and sealed with RTV silicone rubber, It can prevent moisture (Anticorrosion, shockproof and other protective effects. It can improve performance and stability parameters. Two component RTV silicone rubber is particularly suitable for deep potting materials and has a fast curing time, which is superior to single component RTV silicone rubber. Two component RTV silicone rubber has excellent adhesion resistance after curing. In addition, it has very small shrinkage during curing. Therefore, it is suitable for making soft molds, casting epoxy resin Polyester resin, polystyrene, polyurethane, vinyl plastic, paraffin, low melting point alloy, etc. In addition, the high simulation performance of two-component RTV silicone rubber can be used to replicate various exquisite patterns on cultural relics. Attention shall be paid to the use of two-component RTV silicone rubber: first, weigh the rubber and catalyst separately, and then mix them in proportion. The mixing process shall be carefully operated to minimize the amount of entrained air. After the rubber is mixed evenly (with uniform color), the bubbles can be removed by standing or depressurizing (vacuum degree 700 mm Hg). After all the bubbles are discharged, the silicone rubber can be vulcanized at room temperature or at the specified temperature for a certain time.

Two component addition molding RTV silicone rubber

Two component addition RTV silicone rubber can be divided into elastic silicone gel and silicone rubber. The former has lower strength, while the latter has higher strength. Their vulcanization mechanism is based on the addition reaction (hydrosilylation) of vinyl (or propylene group) on the end group of silicone raw rubber and hydrosilylation group on the cross-linking agent molecule. In this reaction, no by-products are released. As low molecular weight compounds are not released during the cross-linking process, the addition RTV silicone rubber will not shrink during the curing process. This type of vulcanizate has the advantages of non-toxic, high mechanical strength, excellent hydrolytic stability (even under high pressure steam), good low pressure shrinkage deformation, low flammability, deep vulcanization, and the vulcanization speed can be controlled by temperature. Therefore, it is a type of silicone rubber that has been vigorously developed at home and abroad.

Addition type RTV silicone rubber

The packaging method is generally divided into two components: A and B: the catalyst is taken as one component; The cross-linking agent is another component. High strength addition RTV silicone rubber is an excellent material for molding because of its low linear shrinkage and low molecular weight during vulcanization. In the machinery industry, it has been widely used for molding to cast epoxy resin, polyester resin, polyurethane, polystyrene, vinyl plastic, paraffin, low melting point alloy, and coagulation. Vulcanization by addition molding at room temperature

2. High temperature vulcanized silicone rubber

High temperature vulcanized silicone rubber is a kind of polyorganosiloxane (i.e. raw rubber) with high molecular weight (generally 400000-800000) added with reinforcing filler and other additives, which is formed by pressure molding (molding, extrusion, calendering) or injection molding with organic peroxide as the curing agent and cross-linked at high temperature. This rubber is generally referred to as silicone rubber.

The reinforcing filler of silicone rubber is various types of white carbon black, which can increase the strength of vulcanizate by ten times. Adding various additives is mainly to reduce the cost of rubber, improve the properties of rubber compound and endow various special properties of vulcanizate, such as flame retardancy and conductivity.

3. Silicon gel

After vulcanization, this kind of rubber becomes a soft and transparent organic silicon gel, which can maintain elasticity for a long time in the temperature range of - 65~200 ℃. It has excellent electrical and chemical stability, water resistance, ozone resistance, weather aging resistance, hydrophobicity, moisture resistance, shock resistance, non corrosion, and is physiologically inert, non-toxic, tasteless, easy to pour, deep vulcanization, low linear shrinkage, simple operation, etc, Organosilicon gel is widely used in the electronic industry as a moisture-proof, insulating coating and potting material for electronic components, and plays the role of dust-proof, moisture-proof, shockproof and insulation protection for electronic components and assemblies. If transparent gel is used to encapsulate electronic components, it can not only play the role of shockproof and waterproof protection, but also can see the components and use the probe to detect the failure of the components and replace them. Damaged silicon gel can be filled and repaired again. Organic silicon gel is an ideal internal coating material for transistors and integrated circuits due to its high purity, convenient use and certain elasticity, which can improve the qualification rate and reliability of semiconductor devices; Organic silicon gel can also be used as elastic adhesive for optical instruments. In medical treatment, silicone gel can be used as an organ implanted in the body, such as artificial breast, and used to repair damaged organs

4. Foam silicone rubber

Foam silicone rubber is liquid before vulcanization, suitable for potting material. Foam silicone rubber is an ideal lightweight packaging material because of its high thermal stability, good thermal insulation, insulation, moisture resistance, seismic resistance, especially at high frequencies.

Dow Corning developed flame retardant room temperature vulcanized foam silicone rubber DC3-6548. This foam silicone rubber is mainly used for fire sealing at the places where wires and cables pass through (such as holes in roofs, walls, buildings, etc.). It has very good flame retardancy. Its limiting oxygen index reaches 39 (the limiting oxygen index of most plastics is only 20), and its service life is up to 50 years. This flame retardant room temperature vulcanized foam silicone rubber has been widely used in nuclear power plants, computer centers, offshore oil production devices and other places with harsh environmental conditions or high fire protection requirements. silicone

Silicone resin is a highly cross-linked polyorganosiloxane with network structure. It is usually a mixture of methyl trichlorosilane, dimethyl dichlorosilane, phenyl trichlorosilane, diphenyl dichlorosilane or methyl phenyl dichlorosilane. In the presence of organic solvent such as toluene, it is decomposed with water at a lower temperature to obtain acidic hydrolysate. The initial product of hydrolysis is a mixture of cyclic, linear and cross-linked polymers, usually containing considerable hydroxyl groups. The hydrolysate is washed to remove the acid, and the neutral initial polycondensate is thermally oxidized in air or further polycondensated in the presence of catalyst, finally forming a highly cross-linked three-dimensional network structure.

Silicone is a thermosetting plastic. One of its most outstanding properties is its excellent thermal oxidation stability. After heating at 250 ℃ for 24 hours, the weight loss of silicone resin is only 2~8%. Another outstanding performance of silicone resin is its excellent electrical insulation performance, which can maintain its good insulation performance in a wide range of temperatures and frequencies.

In view of the above characteristics, the silicone resin is mainly used as insulating varnish (including varnish, enamel, varnish, impregnating varnish, etc.) to impregnate H-class motor and transformer coils, and to impregnate glass cloth, glass cloth wire and asbestos cloth to make motor bushings, electrical insulation windings, etc. Large area mica sheet insulation material can be made by bonding mica with silicone insulating paint, which can be used as the main insulation of high-voltage motor. In addition, silicone resin can also be used as heat-resistant and weather resistant anti-corrosion coatings, metal protective coatings, waterproof and moisture-proof coatings for building projects, mold release agents, adhesives, and secondary processing into silicone plastics for electronic, electrical and national defense industries, as semiconductor packaging materials and insulating materials for electronic and electrical components.

Silicone resin can be roughly divided into silicone insulating paint, silicone coating, silicone plastic and silicone adhesive according to its main use and crosslinking mode.