Can silica fiberglass cloth be combined with other materials?

Can silica fiberglass cloth be combined with other materials?

This is determined by the properties of the silica fiberglass cloth. You can put the cloth inside the silica gel directly and cure, and then cut. Or you can use a surface treatment agent and primer, preferably processing at the same time to make it most durable. Silica gel is sticky at low temperature. If it is not achieve the molding temperature, the raw material will be sticky. And if adding the molding glue, it means that the plastic and mold are isolated, so it is not sticky anymore. Silica fiberglass cloth is the polymer elastomer with excellent heat and aging resistance and high insulating properties.

Silica fiberglass cloth is a high-temperature inorganic fiber. Its silica (SiO2) content is more than 96%, and softening point is close to 1700 ℃. It can be used for a long time under 900 ℃;it is able to work for 10 minutes under 1450 ℃;it can remain intact for 15 seconds at 1600℃. Because of its chemical stability, high temperature resistance, corrosion resistance and other characteristics, its products are widely used in many industrial fields like aerospace, metallurgy, chemical, building materials, fire and so on.

Silica fiberglass cloth is a new composite material with high performance and versatility, which is composed of glass fiber. And it has been widely used in aerospace, chemical, large-scale power generation equipment, machinery, metal non-metallic expansion joints (compensator) etc.

Features of silica fiberglass cloth

The products, glass fiber coated with silica, have its unique high temperature resistance, air permeability, excellent weathering resistance, and have the characteristics of soft and toughness. So that it is superior to ordinary coated fabrics.

How about the pressure resistance of silica fiberglass cloth?

Learn about the types and applications of silica fiberglass cloth

Silica fiberglass cloth has two forms, single side and double sides. It can be used in high temperature. The long-term operating temperature is under 250 ℃,and the working pressure should be 300kpa. The short-term (16 hours) can withstand 280 ℃.So it has the very good weathering resistance. Single-sided silica fiberglass cloth is mainly used in flexible fabric compensator, and double-sided can be used for sealing layer. Silica fiberglass rubber can be made of flame-retardant products for fire-fighting requirements. But we should note that the silica fiberglass rubber cloth cannot be used in the case of flue gas and steam containing SO2.

The products, glass fiber coated with silica, have its unique high temperature resistance, air permeability, excellent weathering resistance, and have the characteristics of soft and toughness. So that it is superior to ordinary coated fabrics.

Silica fiberglass cloth can be used as a flexible connection device. It can prevent the damage of the pipeline for expanding with heat and contracting with cold. Silica fiberglass cloth has high temperature resistance, corrosion resistance, anti-aging properties and flexibility, so it can be widely used in petroleum, chemical, cement, Energy and other fields.

Silica fiberglass cloth can be used as the internal and external anticorrosion layer of the pipeline. Because of excellent corrosion resistance and high strength, it is an ideal anti-corrosion material.

Silica fiberglass cloth can be used as the fireproof curtain that has good fire retardant effect, a tight structure and high temperature resistance. So it can protect the object from the thermal point and spark zone, and completely prevent burning or isolate combustion. When the fire control center sends out a fire alarm or receives a “smoke” signal, the fireproof curtain hanging above the ceiling will quickly drop to a setting height to form a smoke zone separation. Smoke exhaust fan to discharge high-temperature flue gas outdoors. Smoke exhaust fan will discharge high-temperature flue gas outdoors, which saves the time for the fire rescue and evacuation.

Silica glass fiber cloth can be used for the production of industrial removable insulation sleeve. Its products are soft and resilient, and can be arbitrarily bent and cut. They are free of asbestos and any other harmful substances, so that they are completely harmless to people and environment. Their appearances are beautiful and can be scrubbed.

How to make the silica fiberglass cloth more durable?

Silicone cloth

Silica fiberglass cloth uses the high-temperature and high-strength glass fiber. It is a kind of glass fiber fabric after special treatment. Silica fiberglass cloth has a tight structure and high temperature resistance, its base cloth are high-strength, anti-tearing, anti-oil, anti-fire, waterproof and anticorrosive. It also has long service life. To prolong the use of silica fiberglass cloth, we need to understand its characteristics. We should pay attention to the usage requirements, do not use the sharp thing thorn to scrap it. Use it in a reasonable temperature, and its long-term using temperature is 230℃-300℃.

How long is the service life of silica fiberglass cloth?
As we all know, silica fiberglass cloth generally doesn’t have warranty period, it can be stored for a long term. However, if it is used for a high-temperature soft connection, its service life will be different depending on the operating environment. Some can be used for 1 year, some can be for 2 years, and some can be used for more than 5 years, which is based on the different conditions. We should choose the most suitable silica fiberglass cloth based on the specific environment, temperature, etc.

Features of silica fiberglass cloth

1. Excellent resistance to high temperature or low temperature. ( -70 ℃~260 ℃);
2. Silica fiberglass cloth is high-strength, soft and toughness, and also can be cut;
3. Good chemical resistance, anti-oil and waterproof [scrub];
4. It can resistant heat, aging and weather, as well as ozone, oxygen, light and so on. Service life can reach 10 years.
5. Used in acid gas absorption device on the inlet and outlet.
6. High insulation performance, dielectric constant 3-3.2, breakdown voltage 20-50KVMM.

Application Range:

1. Non-metallic compensator: Silica fiberglass cloth can be used as a flexible connection device. Glass fiber coated with silicone rubber as a flexible expansion joint of the substrate, it can prevent the damage of the pipeline for expanding with heat and contracting with cold. Silica fiberglass cloth has high temperature resistance, corrosion resistance, anti-aging properties and flexibility, so it can be widely used in petroleum, chemical, cement, Energy and other fields.

2. Silica fiberglass cloth can be used as the internal and external anticorrosion layer of the pipeline. Because of excellent corrosion resistance and high strength, it is an ideal anti-corrosion material.

Is silica fiberglass cloth easily torn?

Fireproof silicone cloth

The silica fiberglass cloth of Core-Tex is a high-performance, multi-purpose composite material products, which uses high strength, high temperature resistant glass fiber cloth, and then is rolled or impregnated by organic silica gel. My company’s high-strength fabric has good mechanical properties, chemical corrosion resistance (strong acid, alkali,etc.),high insulation properties, anti-ultraviolet and anti-static. Mei Run silica fiberglass cloth is soft and not easy to be torn, and it is anti-aging, has strong adhesion and smooth surface. It does not drop glue when it is sewing.

Silica fiberglass cloth produced by Shenzhen Core-Tex Corp, New Material Corp can be used to make equipment insulation sets, power plant skin, non-metallic expansion joint skin, fan soft connection, fireproof curtain and so on. It is widely used, low capacity weight, thermal shock resistant, chemical resistant, and easy to be processed, so it can be widely applied to heat insulation, insulation, sealing, fire protection, energy saving, labor insurance, electronics, aerospace and other fields.

1.Non-metallic compensator: Silica fiberglass cloth can be used as a flexible connection device. It can prevent the damage of the pipeline for expanding with heat and contracting with cold. Silica fiberglass cloth has high temperature resistance, corrosion resistance, anti-aging properties and flexibility, so it can be widely used in petroleum, chemical, cement, Energy and other fields.

2.Anti-corrosion aspect: Glass fiber coated with silicone rubber can be used as the internal and external anticorrosion layer of the pipeline. Because of excellent corrosion resistance and high strength, it is an ideal anti-corrosion material.

3. Thermal insulation aspect: Non-metallic soft-connected temperature-resistant and flame- retardant materials.

Is silica fiberglass cloth easily torn?

The silica fiberglass cloth of Core-Tex is a high-performance, multi-purpose composite material products, which uses high strength, high temperature resistant glass fiber cloth, and then is rolled or impregnated by organic silica gel. My company’s high-strength fabric has good mechanical properties, chemical corrosion resistance (strong acid, alkali,etc.),high insulation properties, anti-ultraviolet and anti-static. Mei Run silica fiberglass cloth is soft and not easy to be torn, and it is anti-aging, has strong adhesion and smooth surface. It does not drop glue when it is sewing.

Silica fiberglass cloth produced by Shenzhen Core-Tex Corp, New Material Corp can be used to make equipment insulation sets, power plant skin, non-metallic expansion joint skin, fan soft connection, fireproof curtain and so on. It is widely used, low capacity weight, thermal shock resistant, chemical resistant, and easy to be processed, so it can be widely applied to heat insulation, insulation, sealing, fire protection, energy saving, labor insurance, electronics, aerospace and other fields.

1.Non-metallic compensator: Silica fiberglass cloth can be used as a flexible connection device. It can prevent the damage of the pipeline for expanding with heat and contracting with cold. Silica fiberglass cloth has high temperature resistance, corrosion resistance, anti-aging properties and flexibility, so it can be widely used in petroleum, chemical, cement, Energy and other fields.

2.Anti-corrosion aspect: Glass fiber coated with silicone rubber can be used as the internal and external anticorrosion layer of the pipeline. Because of excellent corrosion resistance and high strength, it is an ideal anti-corrosion material.

3. Thermal insulation aspect: Non-metallic soft-connected temperature-resistant and flame- retardant materials.

Silicone cloth

Silicone cloth

The introduction of silicone cloth

Silicone cloth, the silicone rubber vulcanized to acid and alkali resistant, wear resistant, high temperature resistant, corrosion resistant composite fabric. Silicone cloth is widely used into silicone pipe of chemical plants, refineries, ports, industrial hot water and steam transportation, automotive, medical, diving, food, and other industries.

The appllication of silicone cloth

1. Electrical insulation: the electrical insulation level of silicone cloth his high, which can withstand high voltage load, and can be made into insulation cloth, sleeving and other products.

2. Fabric expansion joint: Silicone cloth can be used as a flexible connecting for pipes. Silicone rubber coated glass fiber membrane structural material is used as the base material of flexible expansion joints. It can solve the damage of pipes caused by thermal expansion and contraction. Silicone cloth has high temperature resistance and corrosion resistance, anti-aging performance, good flexibility, which can be widely used in petroleum, chemical, cement, energy and other fields.

3. Anti-corrosion: silicone rubber coated glass fiber cloth, can be used as a pipe, internal and external anti-corrosion layer, excellent anti-corrosion performance, high strength. It is an ideal anti-corrosion material.

Other fields: silicone rubber coated glass fiber membrane structural materials can be applied to building sealing materials, high temperature anti-corrosion conveyor belts, packaging materials and other fields.

The silicone cloth is also divided into a single-sided silicone cloth and a double-sided silicone cloth, what’s more, high-temperature curing silicone cloth and room temperature curing silicone cloth.

The regular color of the silicone cloth is red, blue gray, black, white, and other colors can also be customized.

Fireproof standard for fireproof cloth

US CA117 fireproof standard

US CA117 is a widely used one-time fireproof standard in the United States. It does not require post-washing testing and is suitable for most textiles exported to the United States. The new CA117 standard is compared with the old CA117 standard, but new standard hasn’t been published yet.

(1) The standard has been in use for 30 years. Because the standard has great practical value.

(2) This standard is formulated from the actual situation after fully studying the cause of the fire, so it is more scientific. The test of fire source is a cigarette smoldering (smoldering) test, a simulated match igniting test, and a simulation of newspaper igniting test, which matches the actual bubble fire scene.

(3) The test index is more intuitive, the instrument investment is not large, and the operation is convenient. The enterprise can carry out inspection and testing at the time of production and at the factory.

(4) In the grading, the old California CA117 standard is recommended for occasions with lower requirements, and the California new standard is recommended for higher requirements. The new standard improves the vertical burning index and increases the imitation amount. The newspaper ignited the butane gas burning test).

(5) At present, most Chinese manufacturers are familiar with the CA117 standard in California. With the increase in the export volume of products, the adoption of this standard can avoid technical trade barriers caused by different technical regulations.

British BS5852 fire protection standard

Application: Upholstered furniture background knowledge: BS5852 can be divided into two parts according to the release time – the first part released in 1979 is mainly defined by the test standards of No. 0 fire source and No. 1 fire source. At the same time, a 30-minute water?immersion test must be performed before testing. – The flame retardant standard supplemented in 1990 defines the test criteria for sources 2 to 7.

Focus on the research, development and application of flame retardant fibers and their products

In recent years, the ignition or combustion of textiles has brought huge losses to people’s lives and property safety, and has become a serious social problem. A lot of research work has been done on flame retardant fibers and their textiles around the world to learn about the research, development and application of flame retardant fibers and their products.

* Classification of flame retardant fibers

Flame retardant fibers mainly include intrinsic flame retardant fibers and modified flame retardant fibers.

Intrinsic flame retardant fibers are mainly inorganic fibers and organic high performance fibers, The inorganic fibers include basalt fiber, glass fiber, quartz fiber, boron fiber, ceramic fiber, etc.; Organic high-performance fibers include aramid, polyimide fiber, polyphenylene sulfide fiber, polysulfonamide and polytetrafluoroethylene fiber.

Modified flame retardant fiber mainly refers to fibers with good flame retardant properties obtained by physical or chemical modification, such as flame retardant polyester, nylon, vinylon and cellulose fibers. The main preparation methods include copolymerized section spinning method, blend spinning method, composite spinning method, and coating method etc..

Due to its unique properties, flame retardant fibers have broad application prospects in civil, military and industrial applications. It can be used not only for flame retardant textiles for automobiles, trains and airplanes, but also for aerospace flame-retardant composite materials, decorative textiles for public places such as hotels, restaurants, hospitals, military, forest fire-fighting protective clothing and home textile products.

* Development status of flame retardant fibers

1.Flame retardant polyester fibers

Flame-retardant polyesters were industrialized as early as the 1980s. In the mid-1990s, phosphorus-based flame retardant monomers developed by Celanese were successfully used in traditional textiles. DuPont, Hearst, Torobo and other companies use organic and inorganic flame retardants and compound flame retardant systems to achieve flame retardant polyester fiber industrialization by copolymerization and blending. Toray Fiber Research Institute (China) Co., Ltd. has obtained cationic dyeable flame retardant polyester fiber by copolymerization and blending. The flame retardant polyester obtained by the BASF company in Germany by copolymerization can be used to produce fibers. Italian Ital Match Chemicals, DSM in the Netherlands and ADEKA in Japan all have patent reports on flame retardant polyester fibers.

In recent years, China’s flame retardant polyester fiber has developed rapidly. Sichuan University, Qingdao University, Beijing Institute of Clothing Technology and Donghua University have research reports or patents for flame retardant polyester fiber. For example, Jiangsu Shenghong Group, Shanghai Petrochemical, Yihua Limited, Shanghai Defulun’s flame retardant polyester filament or short fiber have achieved large-scale production, and achieved export earnings, including the flame retardant polyester industrial yarn produced by Shanghai Petrochemical. The strength reaches 6.0 cN/dtex. However, the performance of the flame retardant polyester fiber against melt drop and smoke suppression still needs to be further improved.

2. Flame retardant polyamide fibers

Research on flame retardant polyamides is mostly concentrated in the field of resins, and is mainly based on blending flame retardant. BASF, Rhodia, DSM and other companies are representative of flame retardant plastic products. However, the flame retardant polyamide fiber is difficult to prepare, and only EMS of Switzerland has announced the development of copolymerized flame retardant polyamide fiber, but there is no commercial product.

China’s research on copolymerized flame-retardant polyamide fibers is mainly concentrated in universities and research institutes, and has not yet been industrialized. Donghua University and Guangdong Xinhui Meida Co., Ltd. have jointly developed flame-retardant polyamide 6 fiber, but the long-lasting water-resistant resistance is limited. Shenma’s B890UN grade and a few other flame retardant polyamide products from other companies are added to phosphorus or other halogen-free flame retardants by mechanical blending, and their flame retardant properties can reach UL94 V-0. Shanghai ANTU Flame Retardant Fiber Co., Ltd. also reported on sheath-core flame retardant polyamide 6 fiber. The bio-based polyamide 56 fiber developed by Shanghai Cathay Industrial Biotech has intrinsic flame retardant properties, a limiting oxygen index of more than 32, and a fiber strength of ≥ 4.5 cN/dtex, which is widely used in the field of flame retardant clothing and decoration. The FR4 CCL produced by Shenzhen Core-Tex Composite Materials Co.,Ltd. has intrinsic flame retardant properties.

3. Flame retardant regenerated cellulose fibers

The research on flame retardant cellulose fiber and its products abroad is ahead of the domestic market and has already achieved industrialization. Companies such as Lenzing in Austria, Kemira in Finland, and Asahi Kasei in Japan have realized the industrialization of flame retardant regenerated cellulose fibers by blending. The fibers have been widely used in protective clothing, knitted fabrics and home textiles.

Domestic Qingdao University, Tianjin Polytechnic University and CHTC Helon Co., Ltd. have independently developed silicon-based, phosphorus-based and phosphorus-nitrogen flame retardants to prepare flame retardant viscose fibers with good performance; Tangshan Sanyou Group Xingda Chemical Fibre Co., Ltd. and Jilin Chemical Fiber Group Co., Ltd. developed phosphorus-based flame retardant viscose fiber using phosphorus-based flame retardant; SOL Flame-Retardant Fiber Co., Ltd. has developed a new generation of environmentally friendly silicon-nitrogen flame retardant viscose fiber. However, the strength and flame retardant durability of the flame retardant viscose fiber are still to be further improved.

4. Flame retardant vinylon

At present, only China, Japan and North Korea have industrialized production of Vinylon, but neither Japan nor North Korea has flame retardant vinylon products.

China’s flame retardant vinylon was developed by Sichuan University in the 1980s in cooperation with Sichuan Vinylon Works, At the beginning of this century, the former General Military Reserve began to organize Sichuan University and Sichuan Vinylon Plant to develop high-strength vinylon, On this basis, the Military Reserve Institute continued to organize Sichuan University and Shanghai Quan Yu Biotechnology Co., Ltd. to independently develop a high-efficiency halogen-free, low-smoke, non-toxic flame retardant that integrates acid source, carbon source and gas source, and developed a complete set of process technology for the production of flame retardant vinylon, successfully produced a high-strength flame-retardant vinylon with limiting oxygen index of 29, fiber strength of ≥ 7.5 cN/dtex, and dyeability. Flame-retardant vinylon and other flame-retardant fiber blended fabrics have been used in the Armed Police Snow Leopard Commando, Falcon Commando, Armed Police Air Combat Brigade, Armed Police Rescue Force, Rocket Army Battle Suit, and PLA Peacekeeping Force.

* Trend of flame retardant fiber development

With the increasing awareness of human safety and the continuous improvement of flame retardant regulations, the development of flame retardant textiles will continue to increase, especially permanent flame retardant textiles will become a new hot spot in the market. The research on flame retardant modified polymer fibers may show the following development trend.

1. Long-lasting environment-friendly high-quality flame retardant fibers

Long-lasting environmental protection and high-quality flame-retardant fiber is the future development trend. Such as the long-acting flame-retardant, anti-melt, anti-smoke integrated melt-spun fiber, high-strength environmentally friendly long-lasting flame-retardant wet-spun fiber. Flame retardant polymer processability, flame retardancy, resistance to droplets, smoke suppression and the balance of mechanical properties are the future research and development direction of flame retardant fiber.

2. Functional composite flame retardant fibers

Flame-retardant, stain repellent, water-repellent, antibacterial and other composite functional fibers are the future development trend.

3. Green and environment-friendly flame retardant fibers

The development of high-efficiency, non-toxic, halogen-free, smoke-free, and droplet-free flame retardant fibers is a future development trend.

4. Comfortable flame retardant fibers

In the case of comfortable flame retardant fibers, it should have both flame retardancy, heat and moisture comfort, and good processability.

5. High-tech flame retardant fibers

High-tech flame-retardant fiber has unique molecular structure, no need to add flame retardant or modification, and it has high temperature and flame retardant performance, and has high added value and good economic benefit. It is the future development direction of flame retardant fibers.

Research Progress of Heat Resistance of Silicone Rubber

Silicone rubber is a special synthetic rubber, places an important position in the rubber family. Because of its special structure, it has excellent performance, such as high resistance, low temperature, high voltage resistance, ozone resistance, radiation resistance, weather resistance, physiological inertia and high air permeability, as well as lubricants and other media show excellent chemistry inert, its application is very extensive.

Although the silicone rubber has excellent heat resistance, with the rapid development of science and technology, it has been unable to meet the requirements of harsh conditions, therefore, how to improve the heat resistance of silicone rubber, that the research is the current hot topic.

Thermal aging of silicone rubber
Thermal aging is the most important form of silicone rubber aging. The using environment of silicone rubber is in high temperature air, due to the combination of two factors of heat and oxygen to cause thermal aging. In the process of thermal oxygen aging, heat promotes the oxidation of silicone rubber, and oxygen promotes the thermal degradation of silicone rubber.

The structural changes of silicone rubber in the process of thermal oxygen aging can be divided into two categories: one is the degradation of the molecular chain of thermal oxygen aging reaction; the another one is the molecular chain of cross-linking between the thermal aging reaction. The molecular chain breakage-based rubber was sticky after aging; the main cross-linked rubber was hardening and crisp after aging, both will make the mechanical properties of rubber decreased or lost, and will be useless. The vulcanized silicone rubber are crosslinked when the air heats up, and the rate of elongation at break is much greater than the reduction in tensile strength. Methyl vinyl silicone rubber as the based vulcanized rubber, the cross-linking was reduced at 350℃, there is no change at 30℃, increased at 205℃, the cross-linking is independent of temperature after the continued aging.

Factors and Mechanism of Silicone Rubber Aging
Silicone rubber molecular chain structure and composition are to determine the level of heat resistance of the main factors. silicone rubber main chain has Si-O atoms only, because of its flexibility, easy to curl, some trace impurities (such as water, silicon hydroxyl or residual catalyst) can quickly lead to degradation of the main chain. The difficulty in degradation not only depends on the structure of the silicone rubber, but also on the nature and content of the impurities. The high polarity of the Si-O bond also determines that it is susceptible to polar attack and rapidly causes thermal rearrangement degradation of the backbone.
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In addition to the thermal rearrangement degradation of the above main chain, there is also the oxidation of the pendant groups to make the reaction more complicated.

Oxygen can only interact directly with organic groups of silicon atoms. Obviously, the chain structure around the main chain has a great impact on the thermal stability, alkyl groups of side chain increased, the thermal stability of silicone rubber decreased. For example, dimethyl silicone rubber oxidize at 20℃, diethyl silicone rubber at 138℃, butyl silicone rubber was significantly oxidized at 120℃. Substituting methyl groups with vinyl also slightly reduces the thermal stability of the silicone rubber.

The end of silicone rubber will be with -OH during the synthesis, which is to promote the cross-linking use of silicone rubber in the using process, increase the molecular weight, and causing aging.
2

White carbon black is almost used in silicone rubber processing to strengthen, and there is a certain amount of active silicon hydroxyl groups on the surface of white carbon black, while the surface residual adsorbed water and water produced by the base condensation, so that the heat resistance of silicone rubber decreased.
3

The greater the amount of white carbon black used in the silicone rubber, the more active hydroxyl, the more adverse heat resistance will be.
4

In most cases, there will be catalyst left inevitably during the silicone rubber synthesis process. Both the acidic or alkaline catalyst impact the thermal stability of silicone rubber. The vinyl silicone rubber prepared by the acidic catalyst was heated at 305℃ for 2 h in vacuum and 25% of loss weight; while the same weight loss was achieved at 256℃ prepared with basic catalyst. Examples of catalytic synthesis of silicone rubber by KOH:
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Therefore, avoiding residual monomers and catalysts helps to improve the thermal aging resistance of silicone rubber.

The way to improve the aging resistance of silicone rubber
For the silicone rubber vulcanized thermal aging mechanism, there are several ways to to improve its heat aging performance as following: ① Change the structure of silicone rubber side chain groups, such as the introduction of phenyl, etc., to prevent the silicone rubber due to the decomposition of side chain groups caused by molecular chain crosslinking or degradation. This is because the phenyl itself is not easy to oxidation, forming steric hindrance in the silicon chain, so that the silicone chain is more difficult to ring degradation. And because of its conjugate effect, the block effect is greater, so the thermal decomposition temperature is higher. (2) The thermal stability of the crosslinked bonds of vulcanized rubber was improved by introducing large volume segments, such as carbon decaboryl, phenylene, phenylene ether and cyclodiilazinyl groups in the molecular chain of silicone rubber. ③Add heat-resistant additives to the compound To prevent side chain oxidation crosslinking and backbone cyclization degradation., such as ferric oxide, dioxane, hexaphenyl cyclotrisilane, etc.

As ①, ② two methods need to be achieved in the process of synthesis of silicone rubber, the process is difficult, the cost is high. The most commonly used method is ③ at present, which is effective, low cost, easier to achieve. This article is briefly introducing several commonly used measures of the method ③.

Add metal oxide antioxidant
From the the aging mechanism of silicone rubber, silicone bond oxidation is mainly caused by the free radical scavenging reaction of pendant groups. If this chain reaction is destroyed, the oxidation process will be prevented. Fe2O3 is the most commonly used antioxidant, the amount is generally 3 to 5.

Relevant studies have reported that the composite metal oxide prepared by liquid phase coprecipitation method can significantly improve the heat resistance of silicone rubber. The study suggests that the iron-tin composite metal oxide is more effective than the single iron oxide and tin oxide in improving the heat resistance of silicone rubber. This is because the prepared composite metal oxide crystal structure has changed, they will play a role in addition to their own, there is synergistic effect.
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There is inhibit oxidation, and improve the heat resistance of silicone rubber.

Add silazane
The addition of silazane to silicone rubber can significantly improve the heat resistance of silicone rubber, the principle is: silazane can effectively inhibit the end of the main chain of the deduction degradation, the elimination of silicone rubber in the trace moisture and silicon light , so that the temperature resistance of silicone rubber up to 350℃.
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And the hydrolytic apparent activation energy of silazane, the higher the hydrolytic stability, the better thermal stability of silicone rubber will be. Commonly used silazanes are: hexamethyldisilazane, hexamethylcyclotrisilazane and so on.

Add silicone resin
Silicone is highly crosslinked reticular structure of polyorganosiloxane, which is a kind of thermosetting resin. Its skeleton consists of siloxane bonds having the same structure as quartz and glass, and one of the most prominent properties is excellent thermal oxidation stability. After heating at 205℃ for 42h, the lose weight of silicone resin is only 2% to 8% of weight, and after heating at 350℃ for 24 hours, the weight loss of silicone was less than 20%.

Direction of development
With the development of high-tech, the use of silicone rubber will be further expanded, the performance requirements of silicone rubber will be higher and higher, silicone rubber heat resistance research will also enter a new stage. At present, the main filler material of silicon rubber is fumed white carbon black, because of its complex preparation process, the cost is very high, especially it has a negative impact on the heat resistance of silicone rubber, so looking for a suitable filler to reinforce the silicon rubber, which will be the main direction of future development. It is reported that by changing the surface energy of mineral fillers, that is expected to achieve mineral filler on the silicone rubber reinforcement. With mineral filler for silicone rubber filler, not only can reduce the cost of silicone rubber products, what’ more, the heat resistance of silicone rubber has no negative impact, and even some mineral filler contributes to the heat resistance of silicone rubber. With the improvement of heat resistance of silicone rubber and the development of new filler, it will be hot topic of silicone rubber research in the field.

At present, there is a lot of research on the heat resistance of silicone rubber, and the use of special treatment of high-fine mineral filler instead of white carbon black, which developed a high hardness of silicone rubber (Soher A 58), not only with heat resistance and excellent mechanical properties, and greatly improve the thermal conductivity, mainly used for hot stamping with silicone version, the production of silicone roller.

If you want to know more about the product information, please fell free to contact us system@corefrp.com, we have a dedicated technical engineers to answer your questions, and we provide free sample service.

pdfResearch Progress of Heat Resistance of Silicone Rubber.pdf

The research progress of silicone rubber

Silicone rubber is a linear, high Mr (relative molecular mass) polysiloxane, its Mr generally more than 1.5×105, the molecular backbone consists of silicon atoms and oxygen atoms alternately (-Si-O-Si-), the bond energy of the Si-O bond (422 kJ/mol) is higher than the C-C bond (240 kJ / mol). Silicone rubber is non-toxic and tasteless, and has a good resistance to high and low temperature (without losing the original strength and elasticity at temperature of 300℃ and -90℃), electrical insulation, light aging resistance, aging resistance, mildew resistance and chemical stability, and thus in the aerospace industry and agriculture, medical and health and electrical and electronic industries and other fields are widely used.

Silicone rubber can be divided into heat vulcanized (HTV) type silicone rubber and room temperature vulcanization (RTV) type silicone rubber according to its vulcanization characteristics. The vulcanizing agent can crosslink the linear silicone rubber into a three-dimensional network structure (reduced plasticity, elasticity). Besides of some thermoplastic silicone without vulcanization, the natural rubber and a variety of synthetic rubber are usually required to use vulcanizing agent vulcanization (After the vulcanization of silicone has a value, its mechanical properties greatly improved.). To meet the special needs, special properties of silicone rubber should be used, such as conductive silicone rubber, thermal silicone rubber, heat-resistant silicone rubber, oil-resistant silicone rubber, shielding silicone rubber, flame-retardant silicone rubber, damping silicone rubber, silicone rubber insulation and sponge silicone rubber.

With the rapid development of high-tech, people has put forward higher requirements on the use of silicone rubber performance, such as good mechanical properties, heat resistance, anti-radiation performance, adhesive properties and weathering resistance, etc., so the modification of silicone rubber (physical modification, chemical modification, etc.) is imperative.

Classification of silicone rubber
HTV silicone rubber
HTV silicone rubber (high temperature vulcanized silicone rubber) with large output, and it is widely used, the Mr (4.0~6.0)×105. HTV silicone rubber can be divided into methyl silicone rubber, dimethyl vinyl silicone rubber, methyl vinyl phenyl silicone rubber, nitrile silicone rubber and fluorinated silicone rubber. Adding reinforcing filler, curing agent and other additives into the HTV silicone rubber, after mixing that can be used for molded products, extruded products. For HTV silicone rubber, organic peroxide is used for curing, and dibenzoyl peroxide (BPO) is widely used as organic peroxides. HTV silicone rubber has excellent resistance to high and low temperature performance, physiological inertia, electrical insulation properties, ozone resistance, weather resistance, hydrophobicity and moisture resistance.

Dimethyl silicone rubber
Dimethyl silicone rubber referred to as methyl silicone rubber, silicone rubber is the oldest type, it can maintain good flexibility at the temperature of -60 ~ 250℃. The raw rubber is a colorless transparent elastomer, usually with high activity of organic peroxide vulcanization. Dimethyl silicone rubber vulcanization activity is low, there will be permanent deformation under high temperature compression. It ‘s not suitable for the preparation of thick products (this is because the curing is more difficult for thicker product , bubble will appear inside). The methyl vinyl silicone rubber obtained after the introduction of vinyl is easy to crosslink, the mechanical properties of the prepared product are good, so the dimethyl silicone rubber has been gradually replaced by methyl vinyl silicone rubber.

Methyl vinyl silicone rubber
Methyl vinyl silicone rubber (referred to as vinyl silicone rubber), that is a mixture of dimethylsiloxane and a small amount of vinyl siloxane. This kind of rubber contains a small amount of vinyl side chain, so it is easier to vulcanize than dimethyl silicone rubber, and there are more types of peroxide for its vulcanization, which can greatly reduce the dosage of peroxide. To compare with dimethyl silicone rubber, silicone rubber with a small amount of vinyl can effectively improve the anti-compression and permanent deformation of the product (low compression deformation endow good high temperature support for sealing elements , which is the performance of O-ring and washers, etc.). Methyl vinyl silicone rubber process performance is good, easy to operate, can be made of thick products, the surface of semi-finished product by calender is smooth, meanwhile, methyl vinyl silicone rubber coated fiberglass fabric, with high strength, anti-aging, long service life , it’s currently commonly used silicone rubber.

RTV silicone rubber
RTV silicone rubber is a terminal hydroxyl or acetoxy silicone rubber, its Mr is lower, and it is viscous fluid, which can be vulcanized at room temperature. The vulcanizing agent is ethyl orthosilicate. This type of rubber by adding the appropriate amount of reinforcing agent, vulcanizing agent and catalyst (or impacted by the moisture in the air), which vulcanize at room temperature to form an elastomer. Fully vulcanized products have good heat resistance, cold resistance and dielectric properties, but the mechanical strength is low, which can be used for casting and coating compounds.

Single component RTV silicone rubber
One-component RTV silicone rubber consists of end-based silicone-containing silicone rubber, reinforcing agent and other additives; it is necessary to add a catalyst without using a single-component RTV-type silicone rubber, you can get the elastomer (this is because it can be associated with moisture in the air cross-linking reaction). This silicone rubber has good adhesive properties on the metal, glass and plastic and so on, the drawback is that the process of vulcanization with acetic acid generation [acetic acid can spread from the vulcanized rubber, but it has corrosive effect on the contacting objects (especially metal) ] One-component RTV silicone rubber is easy to use, especially for sealing, caulking and other materials.

Two-component RTV silicone rubber
Two-component RTV silicone rubber consists of hydroxyl-containing silicone rubber, reinforcing agent and vulcanization agent and other preparation, the use of additional catalyst. Commonly used vulcanization agent is organic tin salts, the condensation reaction takes place between the silicone rubber containing the hydroxyl group and the vulcanizing agent when vulcanizing, and form crosslinked structure. By changing the vulcanizing agent and catalyst content, the rate of vulcanization can be adjusted (the alcohol produced during the vulcanization process gradually escapes from the vulcanizedrubber).

Silicone rubber modification
Silicone rubber modification method is physical modification and chemical modification: the former is modified by blending or modified by filling, the latter through chemical grafting, copolymerization and other methods to achieve the purpose of modification. Blending modification is helpful to compensate for the deficiency of single component. Filling modification can improve the mechanical properties of the polymer, reduce the cost of raw materials or endow new function to the material. The blending modification and filling modification which is simple and flexible.

Blending modification
Blending with polyurethane rubber (PUR)
PUR has high strength and good elasticity, with excellent wear resistance, but its molecular structure contains a large number of -NCO, hydroxyl, urea groups and other strong polar groups, resulting in relatively large surface material, high friction factor and poor heat resistance, so the working life of PUR is short. PUR and silicone rubber blends, can significantly improve the heat resistance. In addition, due to the large difference between the two material, the blending system is poor, if the two material interpenetrated to network structure, can significantly improve the compatibility of the system.

Blending with fluorous rubber
FPM has good oil resistance, solvent resistance, chemical resistance, strong oxidizing agent resistance, high temperature resistance and flame resistance and many other advantages, but its flexibility, low temperature resistance and processing performance are poor, the silicone rubber and FPM can improve the system of cold resistance and processing performance after blending. The polarity of FPM and silicone rubber is different, the two material is incompatible system, it’s technical difficulties to improve the compatibility of the two material.
The co-vulcanization of rubber blends has a great effect on its properties. Silicone rubber is used as a vulcanizing agent, and a number of FPMs with peroxide as vulcanizing agents have been developed so that peroxide can be used as co-vulcanizing agent. When V(FPM): V(silicone rubber) = 80:20, the brittle temperature of the system is about 10℃lower than FPM, the low temperature performance is obviously improved and the cost is reduced.

The blending modification of silicone rubber is an effective way to improve the performance of the single material and has made significant progress, but how to make the phases of the blend achieve synchronic crosslinking, or co-crosslinking a reasonable distribution aid, and how to choose the right compatibilizer, there are still many problems.

Filling modification
Nano filling modification
Nanoparticles have quantum size effect, small size effect, surface effect and macroscopic quantum tunneling effect, which show many special properties. It has a good prospect in the fields of catalysis, light absorption, magnetic media and new materials, and also has great development space for the modification of polymer materials.

Nano-TiO2 can improve the anti-radiation properties of silicone rubber, which is due to the nano-TiO2 has the nano-ion properties, and it can effectively increase the physical or chemical crosslinking point of silicone rubber, so that can effectively improve the cross-linking density of silicone rubber. When the system is subjected to external force, due to the interaction of the stress field, the micro-deformation zone in the matrix can absorb part of the energy, so the anti-radiation ability of the system is good.

With the rapid development of nano technology, more and more new nano-materials will have huge impact on the silicone rubber industry. Nano-materials is used for the modification of the silicone rubber, so that the properties is been developed. Therefore, it’s significant to develop new nano materials to modify traditional silicone rubber products, improve its development space and market competitiveness.

Fill modification of white carbon
Fumed white carbon black is high purity amorphous silica, the particle size is 4 ~ 10nm (most is 10 ~ 30nm), the density is very small, it’s light blue transparent particles when in the very thin layer, and it is mainly used In the reinforced HTV silicone rubber.

Some researchers have investigated the effect of silica fillers on the properties of silicone rubber CKTB-6 (Ukrainian production). The results show that the strength and hardness of the vulcanized rubber is improved and the elasticity decreases with the increasing content of the silica in the compound. Adding a certain amount of titanium dioxide during introducing the fumed white carbon black, which can effectively improve the strength and elasticity of vulcanized rubber.

At present, fumed white carbon black as the main reinforcing agent, which endow silicone rubber good mechanical properties. However, the large amount of hydroxyl groups contained on the surface of the gas-phase silica can react with the end groups of the silicone rubber molecules and are susceptible to structural effects, resulting in hardening of the compounds, difficulty in processing and expensive price.

Modification of mineral powder
Many mineral fillers are rich in Lewis, Bronsted acid point and other active sites, due to these characteristics of mineral powder, through a series of physical or chemical methods, so that it has the ability to combine with silicone rubber, which can effectively enhance the silicone rubber mold quantity, improve the mechanical properties of products. Mineral powder was used to take place of fumed white carbon black as silicone rubber enhancer, that can reduce the cost of products, but also increase the added value of mineral powder.

The modification of mineral powder filler can not only reduce the processing cost of rubber industrial products, but also improve the performance of rubber products, but there are few reports in this area. In order to better play the role of mineral materials, and improve the comprehensive utilization of mineral resources, it is necessary to increase the research in this area.

Conductive modification
The composite conductive material prepared by adding the conductive filler with silicone rubber as the base material, which has good resistance to high and low temperature resistance, aging resistance, molding processability and electrical conductivity. Therefore, it has been widely used in anti-static materials, electromagnetic shielding materials, and its application areas have been all over the aerospace, electrical and electronic, computer, construction, medical and food and other industries.

The development of conductive silicone rubber is mainly focused on the development of anti-static materials and electromagnetic shielding products, the development trend is mainly to improve the conductivity, reduce the filler filling, improve the processing performance and mechanical properties. Therefore, the development of new conductive varieties, the development of multi-functional conductive silicone rubber, is also one of the important areas of the research.

The application of silicone rubber
Medical
Medical equipment
Over the past 20 years, silicone rubber with its excellent performance (good biocompatibility, stability and comfort, etc.), it has become one of the development trend of medical materials. According to the different contact time, medical silicone rubber can be divided into long-term implantation and short-term contact type. Which implanted in the body more than 29d of the device called long-term implantation, otherwise known as short-term contact type.

Drug release system
Prolong the efficacy of drugs, improve the specificity and safety of drugs, which is an important issue in pharmaceutical research. The method of silicone rubber to control the release of drugs are mainly encapsulation and particle dispersion.

Silicone rubber film has a good permeability of O2 and CO2, and its moisture permeability and human skin moisture evaporation is similar, while its non-toxic to the human body, harmless, no allergies, easy to cause foreign body reaction or rejection and so on. In addition, silicone rubber film with nylon, polyester fiber reinforced, can be used as artificial film.

Auto industry
Silicone rubber has good resistance to flexibility, high temperature resistance and aging resistance, since the 1950s, it has been used in many important rubber seal products, the rapid development of the automotive industry , and the demand of silicone rubber is significantly increased. Automotive engine with silicone rubber sealing products can meet the requirement of service life of more than 10a and 150000km. In recent years, the heat resistance temperature of the silicone rubber without secondary vulcanization is increased by 50℃, the adhesive property and the mechanical strength are improved.
Silicone rubber is widely used for the sealing products. The main sealing products are automotive engine crankshaft seals, fuel pump seals, air conditioning compressor seals, potentiometer insulation bushings and potting materials.

Market expectation
In 2006, the total market volume of silicone rubber in the developed countries and areas was about 328kt (in terms of polysiloxane). The US market was about 156,000 t, the European market was about 138,000 t and the Japanese market was about 34,000 t.
With the rapid development of the world economy, the future demand for silicone rubber materials will be greatly increased. With deep research of silicone rubber, and modification, a variety of modified silicone rubber is bound to the new, high-performance, diversification and multi-functional direction.

If you want to know more about the product information, please fell free to contact us system@corefrp.com, we have a dedicated technical engineers to answer your questions, and we provide free sample service.

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The progress of high temperature vulcanization addition reaction silicone rubber

Silicone rubber has many unique and excellent features, such as high and low temperature resistance, UV resistance, radiation resistance, weather resistance, electrical insulation, high permeability, physiological inertia. Silicone rubber has been widely used in aviation, aerospace, electrical, electronics, chemical, instrumentation, automobile, machinery and other industries as well as medical and health, daily life in various fields, which has become indispensable new materials in modern chemical industry. Silicone rubber can not only do mold products, but also can composite with fabric, such as silicone coated fiberglass cloth, which widely used in the production of modern industry. Therefore, the development and application of silicone rubber and organic silicone, and promote the transformation and development of many technical fields.

There are many types of silicone rubber, it can be divided into single-component and two-component type according to its packaging ; it can be divided into solid and liquid silicone rubber according to its material form; it can be divided into high temperature, Low temperature (room temperature) silicone rubber according to the vulcanization temperature ; it can be divided into peroxide-induced, condensation reaction and addition reaction type silicone rubber according to the vulcanization mechanism . High temperature vulcanization silicone rubber mainly refers to no extra high investment injection molding, using the peroxide high temperature vulcanized silicone rubber molding equipment and molding process, the silicone rubber can be produced directly. In recent years, with the increasing researches of silicone rubber, high temperature vulcanization silicone rubber research has become a hot topic in the rubber industry.

Features of high temperature vulcanization addition reaction silicone rubber
The addition reaction silicone rubber has many excellent features: There is no small molecule in the vulcanization process, the vulcanization process itself does not produce any by-products; the dosage of catalyst is less, and the vulcanized product is safe to the human body; Vulcanization process without the participation of extra ingredients, it can be done in depth vulcanization; can be vulcanization under atmospheric pressure (hot air); Vulcanized rubber with high transparency, flame retardant, excellent physical and mechanical properties; The linear shrinkage and compression set of the addition silicone rubber vulcanized products are the lowest in the three vulcanized silicone.

At present, for the research and application of room temperature vulcanization addition reaction silicone rubber, because the catalyst activity is too high, generally use two-component A / B packaging, this form is not only inconvenient during use, there is still the existence of residual residue of the waste and processing problems. Compared with room temperature vulcanization addition reaction silicone rubber, the advantages of high temperature vulcanization silicone rubber is stable at room temperature or low temperature storage, vulcanize under high temperature, it can effectively avoid the disadvantages of room temperature vulcanized silicone rubber .
At present, the research focus of high temperature vulcanization addition reaction silicone rubber is mainly focused on the research of catalyst / inhibitor system, the key is the activity of inhibitor catalyst, especially the storage stability of catalyst.

At present, several manufacturers of have been formed series of mature products of high-temperature vulcanization addition silicone rubber, such as ELASTOSILplusR series of high temperature vulcanization addition silicone rubber from Wacker Company , which has developed high strength, impact, self-adhesive, single Component extrusion, fire retardant and other different products.

Progress of basic polymer and compounding agents
Basic polymer
The basic polymer of the addition silicone rubber is polymethyl vinyl siloxane, referred to as vinyl silicone rubber. The study found that silicone rubber molecules as long as they contain two or more vinyl, whether it is vinyl silicone rubber, phenyl silicone rubber, fluorosilicone rubber can be treated with addition vulcanization. At present, the research on vinyl silicone rubber mainly focused on the study of structure, the purpose is to produce high strength, especially high resistance addition silicone rubber.

Crosslinking agent
Polysiloxanes containing more than two Si-H groups in the molecule which can be used as the crosslinking component of the silicon-hydrogen-addition vulcanized silicone rubber. The structure and dosage of the crosslinking agent have a significant effect on the properties of the addition silicone rubber. After the addition reaction of vinyltrimethoxysilane with 1,3,5,7-tetramethylcyclotetrasiloxane, and reacted with 1,1,3,3-tetramethyldisiloxane in the presence of an acid catalyst to produce Si-H group-containing diblock siloxane as a crosslinking agent, the vulcanization activity and the performance of the vulcanized silicone rubber can be improved.

Reinforcing filler
Fumed silica is the most important reinforcing agent for silicone rubber. In order to achieve better reinforcement effect and processing performance, the need for silica treatment, there should be some treatment for fumed silica. Using the surface with a vinyl siloxane oligomer or vinyl siloxane-containing high specific surface area of fumed silica as a reinforcing filler, the tensile strength and tear strength of addition reaction silicone rubber has improved. It has been reported that in the process of on-site treatment of white carbon black, the anti-tear properties of silicone rubber can be improved after dilution heat treatment process

Tackifier
Silicone Hydrogenated vulcanized silicone rubber is substantially unbonded to the substrate. In the case of bonding with a contact substrate, the substrate is previously subjected to a primer treatment or adding the tackifier in the compound. Phenyl-containing hydrosiloxane copolymer and methyl hydrogen cyclosiloxane and used as cross-linking and thickening ingredients, which can be dubbed on the plastic and metal, and have a good adhesion. An alkoxysilane containing an addition functional group, a siloxane oligomer containing an addition functional group-containing alkoxy group, a cyanuric acid ester containing an addition functional group and an alkoxy group as tackifier, which has good adhesion for plastic (PC, PPS, etc.), metal, glass, etc. , and rubber storage stability is good, the color of product does not change at high temperatures.
The reaction products of Silane coupling agent and titanate for the preparation of the adhesive agent have good adhesion on the plastic (PPS, PBT, etc.), metal (copper, aluminum, steel, etc.). Silane coupling agent can be selected from Methacryloxypropyltrimethoxysilane, glycidoxypropyltrimethoxysilane , titanate can be selected from butyl titanate, isopropyl titanate, diisopropoxide (Ethyl acetoacetate) titanium, etc. .Silane coupling agent and titanate mix at a mass ratio of 1: 1 and reacted at 50 to 80℃ for 50 to 100 hours to hydrolyze a part of the alkoxy ester exchanger to form an oligomer.

Other additives
The catalytic efficiency of platinum catalyst is high , but there is a fatal drawback of the platinum catalyst, that is, when the system containing N, P, S organic compounds, or containing Sn, Pb, Hg, Bi, As and other heavy metal ion compounds, and organic compound containing unsaturated bond such as an alkynyl group, the platinum catalyst is liable to be poisoned and loose the catalytic activity..
In the presence of Si-Vi and platinum catalyst, Si-H will produce side reactions to produce hydrogen, there will be bubbles, which affect the mechanical properties of silicone rubber and dimensional stability. In order to eliminate the influence of such side effects, adding hydrogen absorbing agent into the material.

The research progress of Catalyst / inhibitor system
Common catalyst
The vulcanization mechanism of the addition silicone rubber is hydrosilylation reaction, the catalyst for the hydrosilylation reaction can be used in principle. Till now, almost all of the transition metals such as Pt, Pd, Rh, Ru, Ni, Co and the like are suitable for the hydrosilylation catalyst.
The earliest use of the hydrosilylation catalyst is chloroplatinic acid (H2PtCl6 6H2O). Chloroplatinic acid solution catalytic system belongs to the inorganic chloride ion ligand, when used in chloroplatinic acid dissolved in solvent (such as isopropyl alcohol), can be directly used for catalytic hydrogen hydride addition reaction. The advantage is that the catalyst has a good compatibility with the reactant matrix and can be homogeneous, so that the activity and selectivity of the metal active center can be adjusted by changing the ligand to modify the stereoselective or electronic environment of the metal active center. It was found that the catalytic activity of platinum in the low valence state was higher than that in the high valence state. For the chloroplatinic acid-divinyltetramethylsiloxane catalyst, when the platinum is reduced to zero, the activity of the catalyst is high. For the chloroplatinic acid-isopropanol catalyst, the valence of platinum is higher, the catalytic activity relatively low. Meanwhile, Chloroplatinic acid and divinyltetramethylsiloxane complex catalyst in the reaction system, which is in the better dispersion, high activity, and with better catalytic effect.
At present, the most commonly used catalyst is high activity, soluble in organic polysiloxane chloride complex, such as platinum – vinyl siloxane complex and so on. There are two kinds of preparation of platinum-vinylsiloxane complexes: one is the reaction of chloroplatinic acid with vinylsiloxane, and then the Willing method of acid washing; the another method is chloroplatinic acid and vinyl siloxane alkane in an alcoholic solution, followed by acid removal with sodium bicarbonate. The former is also referred to as chloroplatinic acid vinyl siloxane complex; the latter called Karstedt catalyst, because the complex of chlorine has been basically removed, platinum in the zero-valence state, and catalytic activity is high.

The type of inhibitor
The vinyl silicone rubber, the crosslinking agent and the catalyst are mixed and reacted at room temperature. Therefore, in order to adjust the vulcanization rate and prolong the use time, it is necessary to use a reaction inhibitor to suppress the hydrosilation reaction of vulcanization. When the inhibitor is added to the compound, it can form a certain form of complex with the catalyst, so that the catalyst can not catalyze the crosslinking reaction at room temperature, so that the compound can be placed at room temperature for a long time, only heated to a certain temperature to vulcanize. It should be noted that the inhibition of the catalyst activity does not permanently deactivate the catalyst, and when the rubber is vulcanized, the inhibited activity must be completely released. Some of the organic matter containing S, N, Sn and other elements, which make the catalyst activity lower. However, when the temperature rises, the vulcanization can be carried out, but even at a relatively high temperature, the vulcanization rate becomes very slow, and even the vulcanized product is wrinkled. This type of inhibitor is undesirable.
Inhibitors are generally divided into two types: one is added as a additive in the compound, with platinum action to block its activity; the other is prepared in advance which contain the inhibitory ligand complex catalyst, thereby inhibiting the catalytic activity. Till now, has been found that there are six types of the inhibitor which can be reacted with platinum.
(1) Unsaturated compound inhibitors. Mainly containing alkynyl and polyvinyl compounds, at present, there are a variety of common alkyne compounds (mainly acetyl alcohol), containing vinylsiloxane, maleic acid and its derivatives, fumaric acid and its derivatives. Thus, many people consider to use acetylene and hydrogen-containing silicone oil in the platinum complex catalyzed reaction to form a new unsaturated alcohol, the above defects are eliminated by alcohol, and also have a better inhibitory effect on the platinum catalyst at a certain temperature.

(2) Sulfur-containing compounds inhibitors. Such as sulfoxides, including organic sulfoxides and silicone sulfoxides, the inhibitors can make the stock to be stored for 3 months at room temperature .

(3) Peroxide inhibitors. This inhibitor makes the active period of one-component addition vulcanized silicone compound from six months to one year, so that active period of the two-component is several weeks, so that there is sufficient safe operating time for high-temperature addition silicone rubber. For high temperature addition rubber, when the temperature below the curing temperature, the peroxide inhibits the reaction, When the temperature above the curing temperature, it can accelerate the addition reaction.

(4) Metal salt inhibitor. The metal ions in these metal salts are Sn2 +, Hg2 +, Bi2 +, Cu2 + and Cu +, among which Sn2 + salt is used more. The dosage of metal salt is twice of platinum, which can make rubber curing cycle extended to more than 3 months.

(5) Nitrogen compound inhibitor. This is the most species of inhibitor, and it’s widely used to medium and high temperature vulcanized silicone rubber. Including acrylonitrile, tetramethylguanidine carboxylate, hydrazine, aminosilicon, silamines.

(6) Phosphorus compound inhibitor. There are triphenylphosphine compound, divalent platinum – phosphorus compound and zero-valent platinum-phosphorus compound. The platinum-phosphorus compound is a kind of composite catalyst, when the temperature is lower than the vulcanization temperature, the ligand compound has an inhibitory effect on the activity of platinum in the central atom. When the temperature is higher than the vulcanization temperature, the ligand dissociates, platinum restore the catalytic activity, addition reaction is going on, and the rubber will vulcanize. The main drawback of the divalent platinum-phosphorus compound is that it can not be subjected to closed heating vulcanization.

New catalyst / inhibitor system
Improvement of platinum catalyst
Although there are many kinds of inhibitor compounds, the inhibitory effect is not satisfactory. In order to achieve a reduction in the activity of the catalyst without inactivation, it can be achieved by improving the platinum catalyst. The method of improving the platinum catalyst is mainly to further complex the catalyst to limit its activity, such as using Carbene to complex the common platinum catalyst. Karstedt catalyst or maleate complex catalyst and carbene complexation of the catalyst, the gel time at room temperature greatly increased. The drawback of this method is that the production of Carbene is more troublesome, requiring very low temperatures in very dry conditions, it’s difficult to achieve the conditions for conventional laboratories.

Microencapsulated platinum catalyst
Microencapsulated platinum catalyst refers to using thermoplastic resin or thermoplastic siloxane (softening point of 50 ~ 200℃) encapsulation of platinum complexes, made into microcapsules, as a hydrogen hydride catalyst. Using microencapsulated platinum catalyst prepared by the rubber material in the resin or silicone softening point below, the storage is stable, when the temperature rose to above softening point of the resin or silicone, the resin or silicone soft (melt), release Platinum catalyst, and then with addition reaction, cross-linked into elastomers. Preparation of microencapsulated platinum catalyst methods are spray drying, hot melt and water dispersion method, can be used for the packaging of many materials, such as polyvinyl alcohol, polyacrylate, polystyrene, silicone and so on. This is the best way to inhibit the activity of the catalyst, which can significantly increase the shelf life of the compound, and some even up to 1 year. There are prominent problems while using microencapsulated platinum catalyst, the most critical issue is the dispersion. The catalyst capsule must be in a phase-separated state with the silicone rubber system, and its dispersion must be uniform. Otherwise the vulcanization of the catalyst distribution is uneven, will inevitably lead to uneven vulcanization, get unqualified products. In addition, the storage time is too long, the catalyst capsule is liable to precipitate. Therefore, how to solve the dispersion of capsules, the particles should be small enough, ans the size is uniform, which is the key to this method. At present, this research has not made significant progress.

Preparation of platinum-inhibitor complexes
Using commonly used inhibitors and catalysts to form compounds to produce ready-made catalytic/inhibitory mixtures, which is also one of the most promising methods to inhibit platinum catalyst activity. The compound that have been reported are complexes of platinum and alkynes, complexes of cycloaliphatic platinum and alkynes, complexes of triorganophosphine and alkynyl compounds, and so on. The complexed silicone rubber formulated with platinum halide and alkynol catalyzed by alkali catalysis, that has the characteristics of long operation time and good anti-toxicity. The cyclopentadienyl platinum and alkynyl alcohol are catalyzed by alkali catalyst under the reaction of the formation of complex catalyst, the composition of the additive silicone rubber has a long storage life, high catalytic activity when heated. However, the conditions of preparation of platinum-inhibitor complexes is difficult, and it’s also difficult to achieve the conditions for conventional laboratories.
Other methods
In addition to the above from the catalyst/inhibitor system to solve the catalyst activity inhibition and achieve high temperature addition vulcanization, currently it has been proposed another solution ideas. That is starting from improving the structure of silicone rubber. A large group is introduced into the main chain (especially the silyl group and the silyl group) to produce a steric hindrance to prevent the progress of the hydrosilylation reaction.

As high temperature vulcanization addition reaction silicone rubber has easy storage and transportation, easy to use, excellent performance and other characteristics, so that the addition silicone rubber is gradually to the direction of high temperature vulcanized silicone rubber development. Meanwhile, the catalyst / inhibitor system for high temperature vulcanization addition silicone rubber plays a vital role, which showing a good research and development prospects. The development of a higher activity, high selectivity, and easy control of the catalyst inhibitor system will promote the renewal and development of high temperature vulcanization addition silicone rubber.

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Liquid Silicone Rubber

Silicone rubber is a kind of linear polymer, which is different from other rubber in that its molecular backbone is not composed of interconnected carbon atoms, but by the silicon atoms and oxygen atoms between the composition. Silicone rubber has high thermal stability due to the high bond strength of Si-O, and it has excellent resistance to ozone aging, electrical properties and bioavailability (physiological inertness).

Silicone rubber can be divided into three categories according to its curing mechanism: organic peroxide initiated free radical crosslinking (referred to as heat vulcanization), polycondensation reaction type (referred to as room temperature vulcanization) and addition reaction type.

Heat vulcanized silicone rubber refers to the high molecular weight (40 to 70 thousand) of silicone rubber. Using the organic peroxides as a curing agent, after heating to decompose organic peroxides to produce free radicals, and it is crosslinked with the organic pendant side of the rubber to obtain vulcanized rubber. The cure mechanism is shown in pic 1:
Pic1
Pic1, Peroxidation mechanism of silicone rubber
Room temperature vulcanization (condensation vulcanized) silicone rubber generally referred to as RTV, which can vulcanize silicone rubber without heating Its molecular structure is characterized by the molecular chain at both ends containing hydroxyl or acyloxy and other active functional groups, under certain conditions, through these functional groups condensation reaction, the formation of cross-linked structure can be elastomer. According to its curing mechanism and processing methods, it can be divided into single-component room temperature vulcanized silicone rubber and two-component room temperature vulcanized silicone rubber. The vulcanization mechanism shown in Pic 2, Pic 3.
Pic 2
Pic 2 The vulcanization mechanism of one – component room temperature vulcanized silicone rubber

Pic 3
Pic 3 Vulcanization mechanism of two – component room temperature vulcanized silicone rubber

Addition vulcanized silicone rubber means that the vinyl group-containing polydimethylsiloxane with a functionality of 2 is catalyzed by a platinum compound, and polyfunctional hydrogen-containing siloxanes adduction reaction, resulting in chain growth and chain crosslinking of a silicone rubber (shown in Pic 4). Due to the processing and many other reasons, the raw rubber is liquid, polymerization is more than 1000, so usually called liquid silicone rubber (LSR). Addition silicone rubber has solid type, such as the USA DowCorning company Q747 series and Germany WACKER company 400 series.
Pic 4
Pic 4 The Vulcanization mechanism of addition vulcanized silicone rubber

The characteristics of liquid silicone rubber
Development
Liquid silicone rubber injection molding technology research began in the 1970s, the initial purpose is to shape some of the complex shape of the product, such as aerospace seal accessories. To the 1980’s, liquid silicone rubber is paid attention by many countries, the demand is rising rapidly. Because liquid silicone rubber injection molding not only has the advantages of low cost, low energy consumption, high production efficiency, can be automated production, and the adaptability of temperature is also very good, it can maintain good flexibility in the larger temperature range .

There are several companies that produce the liquid silicone rubber , a number of manufacturers, such as: the USA Dow Corning , GE, Toshiba silicone company, Germany WACKER , Rhodia silicone company.
For GE company, its production of liquid silicone rubber with universal grade, fast curing / high tear, low compression permanent deformation, oil proof, low viscosity, high elastic life and many other types .

According to the SRI research report [2], the sales volume of liquid silicone rubber is only 90,000 tons, but the average annual growth rate is more than 10% to 2003.

Characteristics
Liquid silicone rubber without vulcanization by-products, no pollution to the environment;
Two-component mixture can be stored at room temperature for a long time;
The compound is supplied in two components and mixed with 1: 1.
Easy to mix, fast curing, easy to operate;
Easy to color, good flexibility for product ; very short and efficient production cycle;
Less flash by controlling the mold;
Good elasticity, excellent resistance to ultraviolet light and ozone;
Low moisture resistance and good solvent resistance;
Good dielectric properties in large temperature range ;
Can not contact with N, P, S and other elements of organic matter;
Can not contact ionic compounds containing heavy metals such as Sn, Pb, Hg, Bi, As and the like;
Can not contact with alkynyl and other unsaturated bonds of organic compounds.

The basic composition of liquid silicone rubber
There are two components A and B of liquid silicone rubber , as shown in Table 1.
Table 1 Composition of liquid silicone rubber
Table 1

The comparison of liquid silicone rubber with heat vulcanized silicone rubber
The comparison of performance.
The composition, performance, processing technology and other aspects of comparison of liquid silicone rubber (LSR) and heat vulcanized silicone rubber (HTV) shown in Table 2.

As shown in Table 3, the performance of liquid silicone rubber and heat vulcanized silicone rubber at room temperature is not very different, the oil resistance of liquid silicone rubber is also quite good (for the same heat vulcanized silicone rubber). Due to the advantages of liquid silicone rubber, it is determined that liquid silicone rubber will have a tendency to gradually replace heat vulcanized silicone rubber.

Table 2 The comparison of liquid silicone rubber with heat vulcanized silicone rubber
Table 2

Table 3 Physical properties of liquid silicone rubber
Table 3

Comparison of process performance
Liquid silicone rubber, A, B two components after mixing injection molding by the feed pump, this type of processing reduces the production cycle from a few minutes to a few seconds, which can achieve lower production costs and simplify the purpose of the operation process. And the product’s surface smooth, there is no need for trimming this follow-up process.

The vulcanized silicone rubber is pre-machined and is manually molded by the operator. The automatic production of this process is relatively low, the production cycle is long and the mold releaseability is relatively poor. The molded product needs to be repaired.after molding process. Of course, hot vulcanized silicone rubber can also be processed by rubber injection molding vulcanizing machine, but this method requires a higher production equipment, the need for a dedicated injection system.

Therefore, for the molding process of liquid silicone rubber, there are many advantages of the molding process, following operation, application.

Application

Liquid silicone rubber is now widely used in injection mold, fabric coating, immersion or extrusion coating, food and other rubber products. Because viscosity of liquid silicone rubber is relatively low, So it has the characteristics of fast dispersion and non-stickiness to glass and other substrates. Although the liquid silicone rubber raw materials prices is slightly higher than ordinary silicone rubber, but the cost is lower than ordinary silicone rubber, for small product, the superiority is more obvious.

Liquid silicone rubber products of high purity, good transparency, volatile matter content is low, oil proof, chemical resistance, the choice of a wide range of colors, anti-aging, light resistance, insulation, insulation is particularly prominent. Due to the advantages of the liquid silicone rubber, it is widely used in automotive, construction, electronic power, health care, mechanical engineering and other fields.

Power products
Liquid silicone rubber is widely used in powder field. Such as insulators, cable joints, arrester and so on. The following application is introducing the application of insulators, cable joints.

Post composite insulator
Post composite insulator are suitable for power station facilities. It has good hydrophobic, anti-aging, anti-trapping and erosion resistance, with high tensile strength, bending strength, and high mechanical strength, impact resistance, shock and anti-fracture performance, Light weight, easy installation.( Pic 5).
Pic 5
(Pic 5 Post composite insulator)

The product has been previously made of ceramic, hot vulcanized silicone rubber. However, the ceramic products fragile, heavy weight, the installation of inconvenience are fund during using, etc. Heat vulcanized silicone rubber products, with the higher cost, longer production cycle, the molding process is relatively complex and so on. The liquid silicone rubber products, with short production cycle, the molding process is relatively simple, low production costs, without post-processing, so liquid silicone rubber products will replace ceramic products and heat vulcanized silicone rubber products.

Composite insulator
This product is a new type of wall bushing, using the new insulation materials for internal insulation, using high-performance high-temperature vulcanized silicone rubber for external insulation, with excellent resistance to pollution and explosion-proof performance, that conform to the power sector without oil and development trend, it is new generation of high-pressure products ( Pic 6).
Pic 6
Composite insulator

Composite suspension insulator
This product is particularly suitable for polluting areas, high mechanical tensile load, large span and compact line. With light weight, small size, not easily broken, bending, high torsional strength, strong explosion-proof. The product diagram shown in Pic 7.
Pic 7
Pic 7 Composite suspension insulator

Other industries
As well known, heat vulcanized silicone rubber is a linear rise in the application in the automotive industry is a linear rise in the application, heat vulcanized silicone rubber is made of various types of seals due to good heat resistance and ease of handling. However, due to the high cost, low production efficiency, vulcanization byproducts and other shortcomings of these products, it is being gradually replaced by liquid silicone rubber products At the same time, in the mechanical engineering, health care and other industries, the traditional hot vulcanized silicone rubber products are also replaced by liquid silicone rubber.

Liquid silicone rubber has good market, there is a gradual replacement trends of heat vulcanized silicone rubber, owing to the advantages of liquid silicone rubber, so that the prospects for liquid silicone rubber will be very good.

If you want to know more about the product information, please fell free to contact us system@corefrp.com, we have a dedicated technical engineers to answer your questions, and we provide free sample service.

pdfLiquid Silicone Rubber.pdf