Silicone rubbers consist of long-chain polysiloxanes and various fillers, such as pyrogenic silica. They can be converted into silicone elastomers by vulcanization. They are classified according to the curing method, the viscosity of the base polymer, and whether they cure at high or room temperature:
- Solid silicone rubber (HTV)
- Liquid silicones (LSR)
- 2-part silicone rubber (RTV-2)
- Silicone rubber (RTV-1)
- Silicone gels
- Solid Silicone Rubber
- Liquid Silicone Rubber
- RTV-2 Silicone Rubber
- RTV-1 Silicone Rubber
- Silicone Gels
Solid silicone rubber (HTV) – High-Temperature Vulcanizing Silicone Rubbers
Solid silicone rubbers are cured at elevated temperature, either by means of organic peroxides or with platinum catalyst. The cured rubber is compounded with reinforcing fillers to give it its mechanical strength. The preferred fillers are pyrogenic silicas with BET surface areas >100 m2/g. It is also possible to add precipitated silicas, inactive fillers (quartz, diatomaceous earths) or specific carbon black grades. Thanks to their outstanding properties, HTV silicone rubbers have a whole host of applications. This includes a wide range of service temperatures (-50 to +200°C, or even -90 to +300°C for special formulations), no known physical or physiological harmful effects, and excellent aging resistance.
High-temperature vulcanizing silicone rubbers are suitable for a wide variety of application areas – in the automotive industry, electrical and electronics applications, the transmission and distribution industry, the construction sector, mechanical and process engineering, and in the fields of food, health care and the medical sector.
Liquid silicone rubber (LSR) – High-temperature-vulcanizing silicone rubbers
Liquid silicone rubbers are also members of the group of high-temperature-vulcanizing rubbers. Their consistency and curing mechanism imbue them with outstanding processing advantages. Liquid silicone rubbers are characterized by a low viscosity compared to solid silicone rubbers (HTV). Liquid silicone rubbers are pumpable two-part compounds that are delivered ready to use. They are vulcanized by addition curing. Component A contains a Pt catalyst and component B a SiH-functional polysiloxane as curing agent. Compared to peroxide curing, liquid silicone rubbers do not release any curing byproducts.
Liquid silicone rubbers offer a wide range of applications, from the automotive industry, mechanical and process engineering, through electrical applications, the transmission and distribution industry, through to construction, foods, health care and the medical sector. For automotive applications, in particular, we offer fluorinated liquid silicone rubbers that are characterized by particularly high stability towards gasoline and engine and gear oils.
2-Part Silicone Rubber (RTV-2)
RTV-2 silicone rubbers are two-part pourable, spreadable or kneadable compositions that vulcanize when the curing agent component is added and form highly elastic silicone rubber. They are cured at room temperature (RTV = room-temperature vulcanizing). There are two ways of vulcanizing them: In condensation-curing, an organotin catalyst is usually used; alcohol is produced as a byproduct. Addition curing, on the other hand, uses a platinum catalyst and does not produce byproducts. Special silicone rubber grades can be flash vulcanized using UV light. The vulcanization time can be controlled by adjusting the UV intensity and exposure time. Most cured RTV-2 sillcone rubbers retain their full elasticity up to 200°C. Some products can even be briefly heated to 300°C. At low temperatures, they retain their flexibility down to -50°C, or even to -100°C in the case of special grades.
By choosing particularly slow-acting Pt catalysts, WACKER also offers you a range of premixed one-part systems with a long shelf life, which only vulcanize at elevated temperature. Based on the polymer structure, which is analogous to addition-curing RTV-2 silicone rubber grades, this group, too, is classified as RTV-2. The thermal conductivity of RTV-2 silicone rubber generally allows them to be used for insulating electrical power equipment without causing overheating. The most useful electrical properties are the insulation resistance, breakdown resistance and dissipation factor. The gas permeability of RTV-2 silicone rubbers is around ten times higher than that of natural rubber at room temperature. Another feature that is advantageous in many applications is the excellent release property of the cured rubber surfaces towards organic and inorganic materials.
The extensive portfolio of RTV-2 silicone rubber products allows cured rubbers to be produced with extremely versatile, highly specialized properties. This results in a versatile, successful solution portfolio for individual problems in diverse industrial areas, such as moldmaking, electronics and optoelectronics, household appliances, mechanical engineering and industrial process engineering, health care applications and solar/photovoltaics.
Silicone Rubber (RTV-1)
RTV-1 silicone rubbers are one-part, ready-to-use RTV systems. They consist of polydimethylsiloxane, curing agent, fillers and additives. After application, they are crosslinked by contact with atmospheric moisture releasing byproducts in the process. Crosslinking starts with the formation of a skin on the surface of the applied silicone rubber and gradually progresses into the interior of the compound. Depending on the nature of the crosslinker, a small amount of an amine, acetic acid or a neutral compound, such as alcohol, is released during vulcanization. Thanks to their outstanding properties, RTV-1 silicone rubbers solve a wide variety of sealing, bonding and coating problems. Their outstanding weathering and aging resistance is the result of their special chemical properties.
RTV-1 silicone rubbers are ideal for almost all sealing, bonding and coating applications. This material has a similarly wide range of applications in different industries, such as automotive, construction, household appliances, electrical and electronics, health care, medical and textile.
Silicone gels are a special group of RTV-2 silicone rubbers that are characterized by particularly low crosslinking density. They produce very soft vulcanizates below the Shore A hardness range. Silicone gels are often used as damping materials in medical applications or as encapsulation compound in electrical and electronic applications. Their benefit is that, under temperature fluctuations, they exert only minimal stress on the encapsulated components. Silicone gels are always addition-curing silicone rubber grades.
Silicone gels are suitable for various industrial applications, such as in the automotive field, in the transmission and distribution industry and in health care and medicine. For the automotive industry, in particular, we offer low-temperature gels and fluorinated materials.