Silicone Rubber Changes Our Lives

Introduction: Silicone rubber is a large category of silicone products with the largest output and the most extensive application. After vulcanization, silicone rubber has excellent high and low temperature resistance, weather resistance, hydrophobicity, electrical insulation, physiological inertness and other characteristics. It has been widely used in national defense, military industry, medical and health care, industrial and agricultural production and people's daily life. This article introduces the main characteristics and future development direction of silicone rubber.

1. Introduction to the characteristics and uses of silicone rubber

Silicone rubber polymer molecules are chain structures connected by Si-O (silicon-oxygen) bonds, and their main components are high molar mass linear polysiloxanes. Since Si-O-Si bonds are the basic bond type of its composition, silicon atoms are mainly connected to methyl groups, and a very small amount of unsaturated groups are introduced on the side chains. The intermolecular force is small, the molecule has a helical structure, and the methyl groups are arranged outward and can rotate freely, which makes silicone rubber have better heat resistance, electrical insulation, chemical stability, etc. than other ordinary rubbers. Typical silicone rubber is polydimethylsiloxane, which has a helical molecular configuration with small intermolecular forces, thus having good resilience. At the same time, the formaldehyde group pointing outside the helix can rotate freely, thus giving silicone rubber unique surface properties, such as hydrophobicity and surface anti-stickiness. The following table lists the main characteristics and uses of silicone rubber.

Heat resistance: Silicone rubber has much better heat resistance than ordinary rubber. It can be used almost forever at 150 degrees without performance changes; it can be used continuously for 10,000 hours at 200 degrees; it can also be used for a period of time at 350 degrees. Widely used in occasions requiring heat resistance: thermos seal ring, pressure cooker ring, heat-resistant handle.

Cold resistance: Ordinary rubber has a temperature of -20 degrees to -30 degrees, that is, silicone rubber still has good elasticity at -60 degrees to -70 degrees, and some specially formulated silicone rubber can withstand extremely low temperatures. Low temperature seal ring.

Weather resistance: Ordinary rubber degrades rapidly under the action of ozone generated by corona discharge, while silicone rubber is not affected by ozone. And its physical properties change only slightly under ultraviolet and other climatic conditions for a long time. Sealing materials for outdoor use.

Electrical properties: Silicone rubber has a high resistivity and its resistance remains stable over a wide range of temperature and frequency. At the same time, silicone rubber has good resistance to high-voltage corona discharge and arc discharge. Like High-voltage insulators, TV high-voltage caps, Electrical components, Others.

Conductivity: When conductive fillers (such as carbon black) are added, silicone rubber has Keyboard conductive contact points.

Thermal conductivity: When certain thermally conductive fillers are added, silicone rubber has thermal conductivity. Like Heat sink, Thermal conductive sealing pads, Copier, fax machine thermal conductive rollers.

Radiation: The radiation resistance of silicone rubber containing phenyl is greatly improved. Like Electrical insulation cables Connectors for nuclear power plants, etc.

Flame retardancy: Silicone rubber itself is flammable, but when a small amount of flame retardant is added, it has flame retardancy and self-extinguishing properties; and because silicone rubber does not contain organic halides, it does not smoke or emit toxic gases when burned. Various occasions with strict fire protection.

Breathing property: Silicone rubber film has better breathing property than ordinary rubber and plastic wax film. Another characteristic is that it has strong selectivity for different breathing rates. Like Gas exchange membrane medical products and Artificial organs.

2. Main properties and applications of silicone rubber: Silicone rubber can be divided into two categories according to its vulcanization temperature: high temperature (heating) vulcanization type and room temperature vulcanization type. High temperature rubber is mainly used to manufacture various silicone rubber products, while room temperature rubber is mainly used as adhesive, potting material or mold.

(1) Hot vulcanized silicone rubber (HTV) Hot vulcanized silicone rubber (HTV) is the most important type of silicone product. Methyl vinyl silicone rubber (VMQ) is the most important type of HTV, commonly known as high temperature rubber. Methyl vinyl silicone rubber (raw rubber) is a colorless, odorless, non-toxic, and mechanical impurity-free gel. Raw rubber is mixed with appropriate reinforcing agents, structure control agents, vulcanizing agents and other additives as needed, and then heated for compression molding or extrusion molding, and then subjected to two-stage vulcanization to make various products. Its products have excellent electrical insulation, strong resistance to arc, corona and electric spark, good waterproof, moisture-proof, impact resistance and shock resistance, and have physiological inertness and air permeability. It is mainly used in aviation, instrumentation, electronic appliances, navigation, metallurgy, machinery, automobile, medical and health departments. It can be made into various shapes of sealing rings, gaskets, pipes, cables, human organs, blood vessels, breathable membranes and rubber molds, precision casting release agents, etc.

(2) Room temperature vulcanized silicone rubber (RTV) Room temperature vulcanized silicone rubber generally includes two categories: condensation type and addition type. Addition type room temperature rubber is based on linear polysiloxane with vinyl as the base rubber and hydrogen-containing siloxane as the crosslinking agent. It undergoes crosslinking reaction at room temperature to medium temperature in the presence of a catalyst to become an elastomer. It has good heat resistance, hydrophobicity and electrical insulation. At the same time, due to the introduction of active end groups, it has excellent physical and mechanical properties, especially in tensile strength, relative elongation and tear strength. It is suitable for a variety of vulcanization methods, such as radiation vulcanization, peroxide vulcanization and addition vulcanization, and is widely used in heat-resistant, moisture-proof, electrical insulation, high-strength silicone rubber products, etc. Condensation-type room temperature vulcanized silicone rubber is characterized by the condensation reaction between silanol and other active substances. It can be cross-linked to become an elastomer at room temperature. The product is divided into two forms: single-component packaging and two-component packaging. Single-component room temperature vulcanized silicone rubber (RTV-1 glue for short) is one of the main products of condensation-type liquid silicone rubber. It is usually formulated with base polymers, crosslinking agents, catalysts, fillers and additives. The product is packaged in a sealed hose, extruded when used, and can be vulcanized into an elastomer by itself after contacting the air, which is extremely convenient to use. The vulcanized rubber can be used for a long time in the temperature range of (-60~+200℃), has excellent electrical insulation properties and chemical stability, is resistant to water, ozone, and weather aging, and has good adhesion to a variety of metal and non-metal materials. It is mainly used as coating and encapsulation materials for various electronic components and electrical equipment to play the role of insulation, moisture-proof and shock-proof; as surface protection material for semiconductor devices; it can also be used as sealing filler and elastic adhesive. Two-component room temperature vulcanized silicone rubber (RTV-2 glue for short) is not as convenient as RTV-1 glue in use, but its component ratio is rich in variation. One variety can produce vulcanized products with various specifications and performances, and it can also be deeply vulcanized. Therefore, it is widely used in electronics, automobiles, machinery, construction, textiles, chemicals, light industry, printing and other industries as insulation, packaging, caulking, sealing, moisture-proof, shock-proof and roller making materials. In addition, because RTV-2 has excellent demoulding properties, it is widely used as a soft mold material for the replication and manufacture of cultural relics, handicrafts, toys, electronic appliances, mechanical parts, etc. One of the typical applications of silicone sealant is glass curtain wall. Glass and aluminum alloy frames are bonded with silicone structural adhesive as exterior wall materials, and expansion joints are waterproofed and sealed with silicone weather-resistant adhesive. Other applications include the peripheral sealing of aluminum alloy doors and windows and plastic steel doors and windows, the sealing of the joints, rivets and fixing screws of glass installation and moving grooves: the waterproof sealing between sanitary ware and countertops, walls and furniture in kitchens, bathrooms and toilets; the sealing of aquariums, ceilings, metal roofs, display windows, counters, wainscots and color steel plates; the waterproof caulking sealing between high-grade highway slabs, etc. In addition to sealants for construction, RTV also includes sealing materials for aerospace, nuclear power plants, electronics, machinery, automobiles and other industries, silicone potting materials for electronic component potting, silicone mold glue used as soft mold materials, etc. The demand for these varieties is relatively small, but they are indispensable in many occasions.

3. Current status of the development of my country's silicone rubber industry Since Dow Corning (DC) of the United States first realized the industrial production of organochlorosilane in 1943, after more than 50 years of development, a new situation has been formed in the current international silicone market with DC, GE, R-P, Wacker and Shin-Etsu as the top five companies. There are more than ten large-scale silicone professional companies in the world. The production scale of methylchlorosilane is getting bigger and bigger. Various silicone oils and secondary processed products, silicone rubber, silicone resin, silane coupling agents, silane surfactants, etc. are widely used in various industrial sectors. There are more than 5,000 varieties and specifications of silicone products, and the output and sales are increasing day by day. In the past 30 years, the growth rate of silicone industrial products has remained at 8%~15%, far exceeding the growth rate of the national economy of general countries. At present, silicone is widely used in my country, with continuous growth in quantity and variety, and the application field is constantly expanding. my country has become the most potential market for silicone products.