Addition or platinum cured silicone rubber offers an increasingly popular alternative to conventional peroxide cure silicone products – especially for healthcare applications which require the utmost purity and cleanliness of materials. The name “addition cure” derives from the vulcanization reaction which consists of a multi-functional silicon hydride cross-linker, which in the presence of a precious metal catalyst such as platinum, cures with a longer cross-link chain for added tensile strength and flexing capability over peroxide cured silicones.
Conventional peroxide cure silicones – dimethyl polysiloxane and methylvinyl polysiloxane – comprise majority of the gum base molded and rotocured silicone rubber sheet on the commercial market. A by-product of the heat curing process can be a white crystalline powder diffusing to the surface known as bloom. To prevent future reversion of the rubber and meet general healthcare requirements, post-baking for 2 to 4 hours in a hot air circulating oven from 400°F to 480°F is recommended. Our preferred silicone sheet manufacturers post bake the roto-cured sheets of silicone as a standard practice. The post baking or post curing process will generally improve the compression set performance of peroxide cured silicone rubber. Silicone sheets without a post-cure will often have a sweet, distinctive odor – which may be dichlorobenzoyl peroxide. A post bake will drive off this odor.
The liquid silicone rubber (LSR) compounds we injection mold are Platinum Cure Silicones. They are provided to us in pails or drums of Part A and Part B. The Part A contains the catalyst and the Part B contains the cross-linker. Unmixed – these syrupy materials will not cure. However, when mixed in a 1 to 1 ratio and heated to 350°F – liquid silicone compounds will cure in less than one minute. There are no by-products as found in the conventional peroxide cure silicones – therefore there is generally no need for a post-cure of molded LSR components.
Generally, platinum cure silicones will have better tensile strength and elongation properties than peroxide cure silicones. However, peroxide cure silicones usually have better compression set properties for gaskets requiring critical long term sealing at extended temperatures. Therefore – both of these silicone product families have their benefits.