Silicone rubbers are rubber compounds with both organic and inorganic properties, as well as highly pure fumed silica as two main components. They possess many characteristics, which are not present in other organic rubbers and have important roles in numerous industries. These include electrical, automobiles, food, medical, household appliances and leisure products. Silicone is unlike conventional rubber in that the molecule structure of the polymer consists of long chains of alternating silicone and oxygen atoms. This polymer therefore has an organic and inorganic nature; the inorganic part makes the polymer very resistant to high temperature, good electrical insulting properties and chemical inertness while the organic components make it extremely flexible.
- Heat Resistance
- Cold Resistance
- Weathering Resistance
- Electrical Properties
- Electric Conductivity
- Thermal Conductivity
- Resistance to Steam
- Resistance to Oil Solvents and Chemicals
- Compression Set
- High Tensile and Tear Strength
- Gas Permeability
- Transparency and Coloring
- Non-stickiness Properties Non-corrosive
Silicone rubbers are extremely heat resistant as compared to normal organic rubbers. There is almost no change in properties at high Temperature andthey can be used permanently. For their excellent heat resistance, they are widely applied as material for rubber parts that are used at high temperature.
The brittle point of silicone rubbers is as low as 76F to 94F In contrast the brittle point of normal organic rubbers is about 68F to 86F .
Silicone rubbers have excellent weathering resistance, under the ozone ambiences that are produced due to corona discharge, normal organic rubbers deteriorate tremendously but silicone rubbers remain almost unaffected. Furthermore, even under long term exposure to ultraviolet and weathering, their properties remain almost unchanged.
Silicone rubbers are excellent in electrical insulating properties and stable under a wide range of both frequency and temperature. Furthermore, no significant deterioration in characteristics is observed when silicone rubbers are immersed in liquid. In particular, silicone rubbers extreme resistance to corona discharge or high voltage electricity.
The thermal conductivity of silicone rubber is about 0.5 e+3cal.cm.sec. C, this value shows excellent thermal conductivity for silicone rubbers, thus they are used as heat sink sheets and heating rollers.
Resistance to Steam
Silicone rubbers have low water absorption of about 1% even when they are immersed in water for a long duration. Mechanical tensile strength and electrical properties are almost unaffected. Generally, silicone rubbers do not deteriorate when they are in contact with steam, the influence becomes significant when the steam pressure in increased. Siloxane polymer breaks under high-pressure steam above 302F causes the deterioration in properties.
When silicone rubbers are used as rubber materials for packing which undergo compressive deformation under heating condition, the capability to recover is especially important. The compression set of silicone rubbers is table over wide range of temperature from 140F to 482F.
Generally silicone rubbers require post cure. Especially in the case of the manufacturing products with low compression set. Post cure is desired and the selection of optimum vulcanizing agents is necessary.
High Tensile and Tear Strength
In general, the tear strength of silicone rubbers is about 15kgf/cm. However, high tensile and tear strength products (30kgf/cm to 50kgf/cm) are also made available by improving the polymer as well as selection of fillers and cross-linking agents. These products are best utilized to manufacture complicated moldings, which require greater tear strength, mold cavities with reverse tapers and huge moldings.
Silicone rubbers do not burn easily even though they are drawn closely to the flame. However, once they catch fire, they burn continuously. With the incorporation of minute flame retardant, silicone rubbers can possibly acquire incombustibility and ability to extinguish. The combustibility classification standards of UL94 and UL94V-0 standard are being developed.
These products do not release any smoke or toxic gases when burn, as they do not consist of any organic halogen compounds which are present in organic rubbers. Therefore, they are of course, used in household electrical appliances and office machines as well as materials for the closed space in aircraft, subways and building interiors. They become the indispensable products in safety aspects.
The membranes of silicone rubbers have better permeability for gases and water vapors as well as better selectivity in comparison to organic rubber. Their applications as gas-water separating membranes for artificial heart-lung and oxygen enriching devices are being examined.
Transparency and Coloring
Normal organic rubbers are black due to the incorporation of carbon. As for silicone rubbers, it is possible to produce highly transparent rubbers by incorporating fine silica which does not deteriorate the original transparency of silicone.
Silicone rubbers with excellent transparency and tensile strength are also being developed and utilized as medical, food processing tubes and various products. Due to the excellent transparency, coloration by pigments is easy. Thus, colorful products are possible.
Non-stickiness Properties Non-corrosive
Silicone rubbers are chemically inert and possess excellent mold releasing property. As such, they do not corrode other substances. Due to this property, they are used as fixed rolls of photocopy machines, printing rolls, sheets and (lost-wax) etc.