Silicone rubber is a large product with large output and wide application in silicone products. Silicone rubber after vulcanization has excellent resistance to high, low temperature, weather resistance, water repellent, electrical insulation, physiological inertia and other characteristics, in the national defense military industry, medical and health care, industrial and agricultural production and people's daily life has been widely used. This paper gives a brief introduction to the main characteristics and future development direction of silicone rubber.
1. Introduction to characteristics and applications of silicone rubber
Silicone rubber polymer molecule is a chain structure connected by Si-O (silicon-oxygen) bond, the main component of which is high molar mass linear polysiloxane. Because the Si-O-Si key is the basic bond type, the silicon atom mainly connects the methyl, the side chain introduces a very small number of unsaturated groups, the molecular force is small, the molecule is helical structure, the methyl is arranged outward and can rotate freely, so that silicone rubber has better heat resistance, electrical insulation, chemical stability and so on than other ordinary rubber. Typical silicone rubber is poly-formaldehyde siloxane, with a spiral molecular configuration, its intermolecular force is small, so it has a good resilience, while pointing to the spiral outside the formaldehyde base can be freely rotated, so that silicone rubber has a unique surface properties, such as hydrophobicity and surface anti-stickiness. The following table lists the main features and uses of silicone rubber.
Heat resistance: Silicone rubber has much better heat resistance than ordinary rubber, can be used almost forever at 150 degrees without change in performance, can be used continuously at 200 degrees for 10,000 hours, and may be used for a period of time at 350 degrees. Widely used in demanding heat-resistant situations: Thermos bottle sealing ring pressure cooker ring heat-resistant handle
Cold resistance: ordinary rubber late for-20 degrees ~-30 degree, that is, silicone rubber in-60 degrees ~-70 degree still has a good elasticity, some special formula of silicone rubber can also withstand very low temperature. Low Temperature sealing ring
Weather resistance: Ordinary rubber degrades rapidly under the action of ozone produced by corona discharge, while silicone rubber is not affected by ozone. And for a long time in ultraviolet and other climatic conditions, its physical property has only minor changes. Sealing materials for outdoor use
Electrical properties: Silicone rubber has a high resistivity and maintains a stable resistance value over a wide temperature and frequency range. At the same time, silicone rubber has good resistance to high voltage corona discharge and arc discharge. High Voltage insulator TV high pressure cap electrical parts Other
Conductivity: When conductive fillers (such as carbon black) are added, silicone rubber has a keyboard conductive contact point
Thermal conductivity: When adding some heat conduction filler, silicone rubber will have thermal conductivity heat sink thermal gasket copier, fax machine heat conduction roller
Radiant: The radiation resistance of silicone rubber containing benzene greatly improves the connectors for electric insulated cable nuclear power plants, etc.
Flame Retardant: Silicone rubber itself combustible, but when adding a small amount of anti-combustion agent, it has flame retardancy and self-extinguishing, and because silicone rubber does not contain organic halides, so burning without smoke or release of poison gas. A variety of strictly fireproof occasions
Breathability: Silicone rubber film has better breathability than ordinary rubber and plastic wax film. Another feature is that it has a strong selectivity to different breathability rates. Gas exchange membrane medical supplies artificial organs
2. The main properties and applications of silicone rubber: silicone rubber According to its vulcanization temperature, can be divided into high temperature (heating) vulcanization type and room temperature vulcanization type two categories, high-temperature adhesive is mainly used in the manufacture of a variety of silicone rubber products, while room temperature glue is mainly used as adhesives, sealing materials or molds.
(1) Thermal vulcanized silicone Rubber (HTV) Thermal vulcanized Silicone Rubber (HTV) is an important category of silicone products, methyl vinyl silicone rubber (VMQ) is the main variety of HTV *, commonly known as high temperature glue. Methyl vinyl Silicone rubber (raw rubber) is colorless, odorless, non-toxic, no mechanical impurities of the glue, raw rubber according to the need to add appropriate reinforcement agent, structural Control agent, vulcanizing agent and other additives mixed together, and then heating molding or extrusion molding, and then through two sections of vulcanization into a variety of products. Its products have excellent electrical insulation, anti-arc, Corona, EDM ability, waterproof, moisture-proof, impact resistance, good earthquake resistance, with physiological inertia, breathability and other properties. Mainly used in aviation, instrumentation, electrical and electronic appliances, navigation, metallurgy, machinery, automotive, medical and health departments, can do a variety of shapes of seals, gaskets, tubes, cables, can also do ****, blood vessels, breathable film and rubber molds, precision casting mold release agent.
(2) room temperature vulcanized Silicone Rubber (RTV) room temperature vulcanized silicone rubber generally includes condensation type and addition molding two categories. The molded room temperature adhesive is based on the vinyl linear polysiloxane as the base adhesive, with hydrogen siloxane as crosslinking agent, in the presence of the catalyst at room temperature to medium temperature cross-linked reaction and become elastomer. It has good heat resistance, hydrophobicity, electrical insulation, at the same time, due to the introduction of active end base, so that it has excellent physical and mechanical properties, especially in tensile strength, relative elongation and tear strength has been significantly improved. It is suitable for a variety of vulcanization methods, such as radiation vulcanization, peroxide vulcanization and molding vulcanization, widely used in heat resistance, moisture-proof, electrical insulation, high-strength silicone rubber products. Condensation type room temperature vulcanized silicone rubber is characterized by the condensation reaction between silicon hydroxyl group and other active substances, at room temperature can be crosslinked into elastomer silicone rubber, the product is divided into single-part packaging and double-part packaging two forms. Single component room temperature vulcanized silicone rubber (referred to as RTV-1 gum) is one of the main products in condensed liquid silicone rubber. It is usually prepared from basic polymers, crosslinking agents, catalysts, fillers and additives. Product packaging in the sealed hose, when used extrusion, contact with the air can be self-vulcanized into elastomers, the use of extremely convenient. Vulcanized adhesive can be used in the (–60~+200℃) temperature range for a long time, with excellent electrical insulation properties and chemical stability, water resistance, ozone, resistance to climate aging, a variety of metal and non-metallic materials have good adhesion. Mainly used as a variety of electronic components and electrical equipment Shang, sealing materials from insulation, moisture-proof, shockproof effect, as a semiconductor device surface protection materials, can also be used as sealing filler and elastic adhesives. Two-component room temperature vulcanized silicone rubber (referred to as RTV-2 gum) is not easy to use RTV-1 glue, but the proportion of its components are rich in change, a variety can get a variety of specifications of the performance of sulfide products, but also deep vulcanization, so it is widely used in electronic appliances, automobiles, machinery, construction, textiles, chemicals, light industry, Printing and other industries for insulation, packaging, seam, sealing, moisture-proof, seismic and production of roller materials. In addition, due to the excellent demoulding nature of RTV-2, it is widely used as a soft mold material for the reproduction and manufacture of cultural relics, handicrafts, toys, electronic appliances, mechanical parts, etc. One of the typical applications of silicone sealants is the glass curtain wall. The glass and aluminum alloy frame is bonded with silicone structure adhesive as the external wall material, and the expansion joint is used as waterproof seal with silicone weathering adhesive. Other applications include the surrounding seals for aluminum alloy doors and windows and plastic steel doors and windows, the stitching of glass mounting and moving grooves, the sealing of rivets and fixing screws: kitchens, bathrooms, sanitary ware in toilets and waterproof seals between countertops, walls and furniture, and seals for aquariums, canopies, metal caps, windows, counters, wall panels and colored steel plates , And is used for waterproof seam sealing between plate of high grade highway. In addition to building sealants, RTV also includes sealing materials for aerospace, nuclear power plants, electronics, machinery, automobiles and other industries, silicone sealing materials for the sealing of electronic components, silicone mold adhesives for soft mold materials, etc. The demand for these varieties is relatively small, but in many cases it is indispensable.