Applications liquid silicone rubber

Silicone rubber has both excellent low temperature and high temperature properties. It can withstand temperatures up to 315°C and workable at -65°C. Poor performance with low tear strength and abrasion resistance limit their use in most applications. Liquid silicone compounds LTV which are room temperature vulcanizable are useful for small repairs and sealing application and have been used for poured-in-place gaskets. 

Extrusion Coating - The use of liquid silicone rubber in coating application requires less energy than conventional dispersion coating processes. Solventless material, rapid cure time, absence of by-products and the elimination of multiple passes all contribute to the reduced energy demand of the liquid polymer system. 

Liquid silicone rubbers have also been used in some extruded applications. Vulcanization of the extruded material may be carried out by using infrared heaters or circulated hot air. The process has been applied to wire coating, ignition cables, optical fibers, various tapes, and braided glass-fiber sleeving, as well as for covering delicate products. 

For many applications, especially in the automotive industry, precision parts can only be mass-produced competitively and cost-effectively by using liquid silicone rubber. Successful applications include seals, 0-rings, membranes including central locking membranes, switch... 

Applications requiring low adhesion take advantage of the surface properties of the methyl groups (see Mould adhesion and fouling). They include liquid silicone rubber (LSR) used in moulding applications, silicone Release coatings to dispense organic Pressure-sensitive adhesives (PSA) and silicone PSAs. 

Nonetheless, LSR is not a material which can be processed entirely without problems. Liquid silicone rubber is a modem high performance material that must be thoroughly managed in practical applications. An entire series of process factors must be observed in order to produce LSR moulded parts with quality and high value. Each process factor in the cyclical flow shown in Figure 7.18 must be mastered preeisely in order to work successfully with liquid silicone mbber. 

Liquid silicone rubber can also be combined with some thermoplastics and is an area of much commercial interest, one current application is in the automotive industry. General Motors produce a thermoplastic/LSR multi-shot air intake manifold on the Northstar model [3]. Other potential applications include shower heads and water resistant mobile phones. 

However, conductive elastomers have only ca <10-3 of the conductivity of solid metals. Also, the contact resistance of elastomers changes with time when they are compressed. Therefore, elastomers are not used where significant currents must be carried or when low or stable resistance is required. Typical applications, which require a high density of contacts and easy disassembly for servicing, include connection between liquid crystal display panels (see Liquid CRYSTALS) and between printed circuit boards in watches. Another type of elastomeric contact has a nonconducting silicone rubber core around which is wrapped metalized contacts that are separated from each other by insulating areas (25). A newer material has closely spaced strings of small spherical metal particles in contact, or fine solid wires, which are oriented in the elastomer so that electrical conduction occurs only in the Z direction (26). 

There is a separate Council of Europe Resolution, APRes (2004), on silicone materials for food contact. The resolution defines the silicone product group being comprised of silicone rubbers, silicone liquids, silicone pastes and silicone resins. Blends of silicone rubber with organic polymers are covered by the resolution where the silicone monomer units are the predominant species by weight. Silicones that are used as food additives or processing aids (e.g. as defoamers in the manufacture of substances such as wine) are not covered by this resolution, but polysiloxanes used as emulsifiers are. The resolution gives an overall migration limit of 10 mg/dm of the surface area of the product or material, or 60 mg/kg of food. There are restrictions on the types of monomers that can be used to produce the silicone polymers and there is an inventory list Technical document No. 1 - List of substances used in the manufacture of silicone used for food contact applications . 

A detail of a state-of-the-art 5-roll application system is shown in Fig. 3. The liquid silicone bath is situated between the first two rolls. The liquid silicone is subsequently transferred to the next steel and rubber roll, and the latter transfers the silicone on the substrate. The steel backing roller presses the paper against the rubber applicator roller. 

In Chapter 18, we described solvent extraction and solid-phase extraction sample preparation methods, which are applicable to GC analyses as well as others. A convenient way of sampling volatile samples for GC analysis is the technique of head-space analysis. A sample in a sealed vial is equilibrated at a fixed temperature, for example, for 10 min, and the vapor in equilibrium above the sample is sampled and injected into the gas chromatograph. A typical 20-mL glass vial is capped with a silicone rubber septum lined with polytetrafluoroethylene (PTFE). A syringe needle can be inserted to withdraw a 1-mL portion. Or the pressurized vapor is allowed to expand into a 1-mL sample loop at atmospheric pressure, and then an auxiliary carrier gas carries the loop contents to the GC loop injector. Volatile compounds in solid or liquid samples can be determined at parts per million or less. Pharmaceutical tablets can be dissolved in a water-sodium sulfate solution... 

Hydrophilic and hydrophobic fumed silicas are mainly used to improve the mechanical strength of RTV-, HTV-or liquid silicone mbber. Fumed silicas with higher surface area usually lead to higher transparency of the silicone rubber which is important for special applications... 

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