Why use Silicone Rubber?

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 such as electrical, electronics, automobiles, food, medical, household appliances and leisure products. Silicone rubber is uniquely different from 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 with good electrical insulating properties and chemical inertness while the organic component makes it extremely flexible.

Characteristics
  • Heat Resistance
  • Cold Resistance
  • Weathering Resistance
  • Electrical Properties
  • Electric Conductivity
  • Thermal Conductivity
  • Resistance to Radioactive Rays
  • Resistance to Steam
  • Resistance to Oil Solvents and Chemicals
  • Compression Sets
  • High Tensile and Tear Strength
  • Flame Retardancy
  • Gas Permeability
  • Physiological Inertness
  • Transparency and Colouring
  • Non Stickiness
  • Non Corrosive
Heat Resistance

Silicone rubbers are extremely heat resistant as compared to normal organic rubbers. At 150˚C there are virtually no changes in the physical properties and can be used at this temperature almost indefinitely. 200˚C is the normal maximum operating temperature for General Purpose silicones but there are grades which operate up to 315˚C. Return to Top

Cold Resistance

Silicone rubbers are extremely cold resistant. The brittle point of normal organic rubbers is about –20°C to –30°C. In contrast, the brittle point of silicone rubbers is as low as –60°C to –70°C. Return to Top

Weathering Resistance

Silicone Rubbers have excellent weathering resistance. Unlike normal organic rubbers, Silicone Rubber substantially resists the deteriorating effects of sunlight, ozone, rain water and atmospheric gases. Very dry conditions, coupled with harsh sunlight will not dry out or have any effect on Silicone Rubber. Return to Top

Electrical Properties

Silicone Rubbers have excellent electrical properties and are stable under a wide range of frequency and temperature. There is no significant deterioration in characteristics when immersed in a liquid. Electrical failure occurs when the environment destroys the physical properties of an elastomer but Silicone Rubber , with its excellent resistance to severe environmental conditions, provides constant electrical insulation properties for much longer than other elastomeric materials. The dielectric breakdown for Silicone Rubber is between 400 and 700 volts/mil, depending upon the compound. Return to Top

Electric Conductivity

Electric conductive silicone rubbers are rubber compounds with electric conductive materials such as carbon being incorporated. Various products with electric resistance ranging from a few ohms-cm to e+3 ohms-cm are available. Moreover, other properties are also comparable to those of normal silicone rubbers. Therefore, they are widely used as contact points of keyboards, around heaters and sealing materials for anti-static components and high voltage cables. In general, electric conductive silicone rubbers available in the market are mostly those with volume electric resistivity ranging 1 to e+3 ohms-cm. Return to Top

Thermal Conductivity

The thermal conductivity of silicone rubber is about 0.5 e+3 cal.cm.sec. C, this value shows excellent thermal conductivity for silicone rubbers, thus they are used as heat sink sheets and heating rollers. Return to Top

Resistance to Radioactive Rays

Normal silicone rubbers (dimenthyl silicone rubbers) do not show excellent resistance to radioactive rays in particular as compared to other organic rubbers. However, methyl phenyl silicone rubbers, with the phenyl radical being incorporated into the polymer, possess good resistance to radioactive rays. They are utilised as cables and connectors in nuclear power stations. Return to Top

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 is increased. Siloxane polymer breaks under high-pressure steam above 150°C, causing the deterioration in properties. This problem can be rectified by silicone rubber formulation, selection of vulcanising agents and post cure. Return to Top

Resistance to Oil Solvents and Chemicals

Silicone rubbers have good oil resistance at high temperature, slightly inferior at temperatures below 100°C but offering superior resistance to oil above 100°C. In addition, resistance to solvents and chemicals are also excellent. Return to Top

Compression Set

Silicone Rubber is superior to other elastomers in its resistance to compression set (deformation). It shows a marked superiority at both high and low temperatures. This is particularly important when a silicone rubber part is used as a diaphragm, impact absorber, bellows or in other applications where the component is placed under pressure or is flexed. Return to Top

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 utilised to manufacture complicated mouldings, which require greater tear strength, mould cavities with reverse tapers and large mouldings. Return to Top

Flame Retardancy

To some extent, silicone rubber is inherently flame retardant and many grades will pass UL94 HB. However, there are grades which pass the stringent UL94 and UL94V-0 and are low smoke/low toxicity. These do not contain any of the organic halogen compounds which are present in organic rubbers. Flame retardant silicone rubbers are commonly used in household electrical appliances, office machines, aircraft, building interiors and specifically for seals and gaskets used in mass transportation. Return to Top

Gas Permeability

The membranes of silicone rubbers have better permeability for gases and water vapour 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. Return to Top

Physiological Inertness

Silicone rubbers are generally inert to physiology. An interesting property is that they do not easily cause the coagulation of blood. Therefore, they are being utilised as catheters, hollow fibres and artificial heart-lung, vaccines, medical rubber stoppers and lenses for ultrasonic diagnosis. Return to Top

Transparency and Colouring

Normal organic rubbers are black due to the incorporation of carbon. With silicone rubber it is possible to produce highly transparent material by incorporating fine silica which do not deteriorate the original transparency of silicone. Silicone rubbers with excellent transparency and tensile strength are also being developed and utilised as medical, food processing tubes and various products. Due to the excellent transparency, coloration by pigments is easy and colourful products are possible. Return to Top

Non-stick Properties Non-corrosive

Silicone rubbers are chemically inert and possess excellent mould 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. Return to Top