Silicone rubbers mould release agents

Any substance used to prevent rubber sticking to itself or to the surface of a mould. The lubricant may be a dry powder such as soapstone or a liquid such as silicone emulsion. See Dusting Agent and Mould Release Agent. 

Many rubber compounds have a tendency to stick in the mould cavity after vulcanisation and require some type of mould release agent. The substances used are surface-active materials such as detergents, soaps, wetting agents, silicone emulsions, aqueous dispersions of talc, mica and fatty acids, applied by spray or brush. Alternatively, dry types based on polytetrafluoroethylene or polyethylene, usually carried in a solvent, can be aerosol applied. An alternative is the addition of an incompatible material to the rubber compound which will bleed to the rubber surface during vulcanisation. 

Axel claims that its latest external mould release agent XTEND 19MDR can increase the lifetime of the room temperature vulcanised silicone rubber moulds used in polyurethane and... 

A general (diagrammatic) cross-sectional view of the mould is presented in Fig. 2, from which it may be seen that the mould consists of three essential parts, viz., (1) an aluminium alloy split female mould, (2) an intermediate silicone rubber male core, and (3) a tapered central aluminium alloy plug. Important features to note are the spacer inserted between the split halves of the outer mould, the available space below the central plug, and the channels moulded into the silicone rubber (top and bottom) to form a reservoir for the resin. Prior to use with epoxide resins, the mould surfaces are treated with a silicone release agent (Tego 290 -Ambersil Ltd.) and cured for 3 hours at 230 C. 

It must be remembered that although silicone elastomer is selfreleasing from epoxy resins and from clean metal surfaces, it will bond to silicone release agents. It is therefore essential to mould the rubber prior to treating any parts of the mould with release agent. 

Self-adbesive silicone rubbers for injection moulding are restricted to LR mainly. The most peculiar property of these rubbers is the fact that the mould does not have to be treated with a special release agent (which is expensive and complicated to use) when working with these silicone rubbers. 

Most recently self-adhesive HTVs have been developed. However, they require special release agents or a specially structured mould suface. They are mainly intended for bonding silicone rubber to steel. 

Silicones confer anti-stick properties on surfaces. Moulds for rubbers, as in tyre manufacture, or for plastics are usually silicone treated to give easy release. Silicones are also useful surfactants and anti-foam agents. 

---