Effectively Using Platinum Silicone Rubber

Two-part Platinum cure silicones, also called Poly-addition silicones, are ideal silicone casting rubbers. They are excellent for moulding with a fully enclosed mould, as they cure at room temperature conditions. (You will notice that RTV is used a lot in the product codes with silicones, it stands for Room Temperature Vulcanisation).

Platinum silicones are very stable. They have very low, or no shrinkage, we supply them in a wide range of hardnesses (Shore A) and they have very high tear strength, excellent mould and library life.

Many platinum silicones are translucent and are used for a variety of applications such as prosthetics. In mould making, using a translucent silicone means that you can see the master or model inside. This makes the cutting of the mould to release the master model much easier.

Many mould makers use polyester fibreglass support cases and pour the silicone in, to produce a skin mould of their master model. Platinum silicones are the preferred silicones to use, but like a thoroughbred race horse, they can be a bit temperamental and can suffer from cure inhibition (Non-curing). They can be affected by the chemicals in polyester resins, such as the curing catalysts MEKP and the styrene.

To reduce the effects of the polyester fibreglass case chemistry on the platinum silicone, spray the inside of the case with clear acrylic — our ‘2k Clear Acrylic Lacquer’ is ideal. It will act as a barrier and will not affect the platinum silicone. To further ensure that the silicone cures properly, use additive ‘PA39’ with the platinum silicone which will also reduce cure time.

The more reliable method for curing a platinum silicone skin is to replace the fibreglass support case with a polyurethane gelcoat, such as ‘Shell Shock’ — fast or slow setting, and then use ‘Plasti-Paste’, instead of the fibre matting and laminating resin. These materials do not affect the platinum silicone and are quicker and less messy than the gelcoat, fibre matt and laminating resin method.

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