According to their different forms, silicone materials can be divided into: silane coupling agent (organosilicon chemical reagent), silicone oil (silicone grease, silicone emulsion, silicone surfactant), high temperature vulcanized silicone rubber, liquid silicone rubber, silicone resin, Complex etc.

Silane coupling agent

 

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

 

       One is as a surface treatment agent for framework materials; the second is added to adhesives, and the third is directly added to polymer materials. 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 roughly summarized into three aspects:

 

       1. Used in the surface treatment of glass fiber, it can improve the bonding performance of glass fiber and resin, and greatly improve the strength, electrical, water resistance, weather resistance and other properties of glass fiber reinforced composite materials. The improvement of the mechanical properties of the material is also very effective. The use of silane coupling agents in glass fibers is quite common. The silane coupling agents used in this area account for about 50% of the total consumption. Among them, the most used varieties are vinyl silane, amino silane, and methyl. Acryloyloxysilane, etc.

 

       2. Used to fill plastic with inorganic fillers. The filler can be surface treated in advance, or directly added to the resin. It can improve the dispersion and adhesion of the filler in the resin, improve the process performance and enhance the mechanical, electrical and weather resistance properties of the filled plastic (including rubber).

 

       3. Used as a sealant, adhesive and coating tackifier, which can improve their bonding strength, water resistance, weather resistance and other properties. Silane coupling agents can often solve the problem that certain materials cannot be bonded for a long time.

 

Silicone oil

 

       Silicone oil is a kind of polyorganosiloxane with chain structure with different polymerization degrees. The most commonly used silicone oil is methyl silicone oil. Silicone oil is generally colorless (or light yellow), odorless, non-toxic, and non-volatile 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. It is slightly soluble in acetone, dioxane, ethanol and alcohol. . It has a small vapor pressure, a higher flash point and ignition point, and a lower freezing point. As the number of segments n is different, the molecular weight increases and the viscosity also increases. The solid silicone oil can have various viscosities. According to the chemical structure, silicone oil is 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 trifluoropropane Base silicone oil, methyl vinyl silicone oil, methyl hydroxy silicone oil, ethyl hydrogen silicone oil, hydroxy hydrogen silicone oil, cyanogen-containing silicone oil, etc.;

 

       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 inertness and small surface tension. In addition, it also has a low viscosity-temperature coefficient and high compression resistance) Some varieties also have radiation resistance Performance. Silicone emulsion (a form of silicone oil) mainly includes silicone oil fabric softening finishing agent; silicone oil emulsion type defoamer: it is the most widely used and the largest amount of silicone defoamers.

Silicone Rubber

 

1. Room temperature vulcanized silicone rubber

 

      Room temperature vulcanized silicone rubber (RTV) is a new type of silicone elastomer that came out in the 1960s. The most notable feature of this rubber is that it can be cured on-site without heating or pressing at room temperature, 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. 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.

 

classification

 

      Room temperature vulcanized silicone rubber can be divided into single-component and two-component room temperature vulcanized silicone rubber according to its packaging method, and can be divided into condensation type and addition molding according to the vulcanization mechanism. Therefore, room temperature vulcanization silicone rubber can be divided into three types according to the composition, vulcanization mechanism and use process, namely, one-component room temperature vulcanization silicone rubber, two-component condensation type room temperature vulcanization silicone rubber and two-component addition type room temperature vulcanization silicone rubber . These three series of room temperature vulcanization silicone rubbers have their own characteristics: the advantage of single-component room temperature vulcanization silicone rubber is convenient to use, but the deep curing speed is more difficult; the advantage of two-component room temperature vulcanization silicone rubber is that it does not emit heat during curing. The shrinkage rate is small, no expansion, no internal stress, curing can be carried out at the same time inside and on the surface, and deep vulcanization is possible; the vulcanization time of addition-molded room temperature vulcanization silicone rubber is mainly determined by the temperature, so the vulcanization 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 vulcanized into an elastomer by reacting with moisture in the air. With the difference of chain agents, single-component room temperature vulcanized silicone rubber can be of many varieties, such as deacidification type, deoxime type, dealcoholization type, deamination type, deamidation type and deketone type. The vulcanization time of 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 speed up the vulcanization process. Under typical environmental conditions, generally after 15 to 30 minutes, the surface of the silicone rubber may not be sticky, and the 0.3 cm thick adhesive layer can be cured within a day. The depth and strength of curing will gradually increase 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, and air permeability. They can maintain elasticity for a long time in the range of -60～200℃. It does not absorb or emit heat during curing, has a small shrinkage rate after curing, and has good adhesion to materials. Therefore, it is mainly used as an adhesive and sealant. Other applications include in-situ gaskets, protective coatings and caulking materials. Many formulations of one-component silicone rubber adhesives exhibit automatic bonding properties to a variety of materials such as most metals, glass, ceramics and concrete. When bonding is difficult, a primer can be applied to 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 layer suitable for Silicone bonded surface.

 

       Although the single-component room temperature vulcanized silicone rubber is easy to use, its vulcanization is dependent on the moisture in the atmosphere, so the thickness of the vulcanized rubber is limited, and can only be used in occasions where the thickness is less than 6 mm. The vulcanization reaction of one-component room temperature vulcanized silicone rubber is gradually carried out from the surface to the depth. The thicker the rubber layer, the slower the curing. When the deep part needs to be cured quickly, the layered pouring and gradual vulcanization method can be used, and some rubber materials can be added each time, and the materials can be added after vulcanization, which can reduce the total vulcanization time. Adding magnesium oxide can accelerate the vulcanization of the deep layer glue.

 

       Two-component condensation type room temperature vulcanized silicone rubber: The vulcanization reaction of two-component room temperature vulcanized silicone rubber is not triggered by moisture in the air, but by a catalyst. Usually the rubber and catalyst are packaged as one component separately. Only when the two components are completely mixed together does curing begin to occur. The vulcanization time of 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, the faster the sulfurization, 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, you can use the cooling method. It takes about one day for two-component condensation type room temperature vulcanized silicon rafters to fully cure at room temperature, but it only takes 1 hour at a temperature of 150°C. The synergistic effect through the use of accelerators can significantly increase the curing speed.

 

       Two-component room temperature vulcanized silicone rubber can maintain long-term elasticity within a temperature range of 65-250°C, and has excellent electrical properties and chemical stability. It is resistant to water, ozone, and weathering. In addition, it is simple to use and has strong process applicability. Therefore, it is widely used as potting and molding materials. Various electronic and electrical components are coated and potted with room temperature vulcanized silicone rubber, which can protect against moisture (anti-corrosion, shock resistance, etc.). It can improve performance and stabilize parameters. Two-component room temperature vulcanized silicone rubber is particularly suitable for deep filling The sealing material also has a faster vulcanization time, which is superior to single-component room temperature vulcanized silicone rubber.

 

       Two-component room temperature vulcanized silicone rubber has excellent anti-sticking performance after vulcanization, and the shrinkage rate is very small during vulcanization. Therefore, it is suitable for making soft molds for casting epoxy resin, polyester resin, polystyrene, Molds for polyurethane, vinyl, paraffin, low melting point alloys, etc. In addition, the high simulation performance of two-component room temperature vulcanized silicone rubber can replicate various exquisite patterns on cultural relics. Pay attention to the use of two-component room temperature vulcanized silicone rubber: first weigh the rubber and catalyst separately, and then mix them in proportion. The mixing process should be carefully operated to minimize the amount of entrapped gas. After the rubber material is uniformly mixed (uniform color), the bubbles can be removed by standing or decompression (vacuum 700 mmHg). After all the bubbles are discharged, put it at room temperature or at a specified temperature for a certain period of time to vulcanize into silicon rubber.

       Two-component addition molding room temperature vulcanization silicone rubber: Two-component addition molding room temperature vulcanization silicone rubber is divided into elastic silicone gel and silicone rubber. The former has lower strength and the latter has higher strength. Their vulcanization mechanism is based on the addition reaction (hydrosilation reaction) between the vinyl groups (or propylene groups) on the end groups of the silicone rubber and the silanyl groups on the cross-linking agent molecules. In this reaction, no by-product is emitted. Since low molecular substances are not released during the cross-linking process, the addition-molded RTV silicone rubber does not shrink during the vulcanization process. This type of vulcanizates are non-toxic, high mechanical strength, excellent hydrolytic stability (even under high pressure steam), good low compression set, low flammability, deep vulcanization, and vulcanization speed can be controlled by temperature, etc. Advantages, so it is a type of silicone rubber that has been vigorously developed at home and abroad.

 

       Addition molding room temperature vulcanization silicone rubber packaging is generally divided into two components: A and B: the catalyst is used as one component; the cross-linking agent is used as the other component. High-strength addition-molding room temperature vulcanized silicone rubber is an excellent material for molding due to its low linear shrinkage and no release of low molecules during vulcanization. In the machinery industry, it has been widely used to make molds to cast epoxy resin, polyester resin, polyurethane, polystyrene, vinyl plastic, paraffin, low melting point alloy, and coagulation. Use addition molding room temperature vulcanization.

 

2. High temperature vulcanized silicone rubber

 

       High-temperature vulcanized silicone rubber is a high molecular weight (molecular weight is generally 400-800,000) polyorganosiloxane (ie raw rubber) added with reinforcing fillers and other various additives, using organic peroxide as the vulcanizing agent, and molded under pressure (Molding, extrusion, calendering) or injection molding, and cross-linked into rubber at high temperature. This rubber is generally referred to as silicone rubber for short.

 

The reinforcing filler of silicone rubber is various types of white carbon black, which can increase the strength of vulcanized rubber ten times. The main purpose of adding various additives is to reduce the cost of the rubber, improve the properties of the rubber, and give the vulcanized rubber various special properties such as flame retardant and electrical conductivity.

 

3. Silicone gel

 

       After vulcanization, this glue becomes a soft and transparent silicone gel, which can maintain elasticity for a long time in the temperature range of -65～200℃. It has excellent electrical properties and chemical stability, water resistance, ozone resistance, weathering resistance, and water repellency. , Moisture-proof, shock-proof, non-corrosive, and has the advantages of physiological inertness, non-toxic, odorless, easy to infuse, deep vulcanization, low linear shrinkage, simple operation, etc., silicone gel is widely used in the electronics industry as electronic components Moisture-proof and insulating coating and potting materials can protect electronic components and assemblies from dust, moisture, shock and insulation. If you use transparent gel to encapsulate electronic components, not only can it play a role of shockproof and waterproof protection, but you can also see the components and use the probe to detect component failures and replace them. The damaged silicone gel can be potted again repair. Due to its high purity, easy use, and certain flexibility, silicone gel is an ideal internal coating material for transistors and integrated circuits, which can improve the qualification rate and reliability of semiconductor devices; silicone gel can also be used Used as an elastic adhesive for optical instruments. In medical treatment, silicone gel can be used to implant organs in the human body, such as artificial breasts, and to repair damaged organs.

 

4. Foam silicone rubber

 

       The foamed silicone rubber is liquid before vulcanization and is suitable for potting materials. Foamed silicone rubber has high thermal stability, good thermal insulation, insulation, moisture resistance, shock resistance, especially good shock resistance at high frequencies, so it is an ideal lightweight packaging material.

 

Silicone

 

       Silicone resin is a highly cross-linked polyorganosiloxane with a network structure, usually using methyltrichlorosilane, dimethyldichlorosilane, phenyltrichlorosilane, diphenyldichlorosilane or methylphenyl Various mixtures of dichlorosilane, in the presence of organic solvents such as toluene, are hydrolyzed at lower temperatures to obtain acid hydrolysates. The initial product of the hydrolysis is a mixture of cyclic, linear and cross-linked polymers, usually containing a considerable number of hydroxyl groups. The hydrolyzate is washed with water to remove the acid, and the neutral primary polycondensate is thermally oxidized in the air or further polycondensed in the presence of a catalyst, and finally forms a highly cross-linked three-dimensional network structure.

 

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

 

       In view of the above characteristics, silicone resin is mainly used as insulating paint (including varnish, enamel, colored paint, impregnating paint, etc.) to impregnate H-class motors and transformer coils, and to impregnate glass cloth, glass cloth silk and asbestos cloth to make motor covers Tubes, electrical insulation windings, etc. Using organic silicon insulating varnish to bond mica can make a large area of ​​mica sheet insulating material, which can be used as the main insulation of high-voltage motors. In addition, silicone resin can also be used as heat-resistant, weather-resistant anti-corrosion coatings, metal protective coatings, waterproof and moisture-proof coatings for construction projects, release agents, adhesives, and secondary processing into silicone plastics for electronics, electrical and defense industries Above, as semiconductor packaging materials and insulating materials for electronic and electrical parts.

 

      Silicone resins can be roughly divided into organic silicon insulating varnishes, organic silicon coatings, organic silicon plastics and organic silicon adhesives according to their main uses and cross-linking methods.