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Platinum cure silicone is silicone vulcanized by platinum, a precious metal, as catalyst. This process is also called addition curing.
When platinum is added to silicone raw material, hydrogen in silicone oil reacts with vinyl double bond, creating an ethyl bridge between them. The bridge connects and cures the raw silicone, enhancing strength and durability. But at the same time, platinum curing process doesn’t generate any by-products, which increase the purity and safety of silicone.
From the appearance, platinum cured silicone looks clearer than peroxide cured silicone.
Peroxide curing is the process of polycondensation reaction in which organic polymer compounds are forms, but small molecules, like benzoic acid generates at the same time. These peroxide residues will rise to silicone surface and form white powdery substance, which is also known as “blooming” . The blooming contains some volatile organic acids. To remove the peroxide residues and increase silicone strength, post curing is required. That’s why food silicone parts need the additional post curing process.
In rubber elastomer industry, there are three curing system, peroxide curing system, sulfur curing system and platinum curing system, while platinum curing and peroxide curing are most commonly used in curing silicone. This article will focus on the differences between platinum cured silicone and peroxide cured silicone.
Platinum curing silicone is safer than peroxide curing silicone. Platinum silicone is odourless, clear, and can be food grade and bio-compatible grade.
Platinum curing will not create any residues or hazardous substance to final part, which make it stand out from curing silicone and turn out to be the safest cured silicone. Especially in platinum liquid silicone curing, the production environment is clean and material feeding is in closed injection system which avoid the external contamination to the final silicone parts. No catalyst residues can make cured silicone more transparent. No curing residues also means no fouling to the mold. So platinum cured silicone is widely used in medical bio-compatible parts, food-contact products, beverage products.
Such as：Platinum-Cure Silicone Mask, Nasal, Tubing, Diaphram & Membrane Check Valve, Baby Nipple & Pacifier etc.
Platinum curing is the process of addition polymerization reaction in which organic polymer compounds are synthesized, but without forming any small molecules that will affect properties of silicone rubber. The crosslinking is very strong. Therefore, platinum cured silicone performs better in tear strength, elongation, tensile strength and resilience.
Curing silicone by platinum can be 120°C that is much lower than peroxide curing temperature. In addition, it significantly shortens the curing time and expedite the production.
Silicone parts by platinum curing have steady sizes because of the small shrinkage rate. Purity, security and better strength property improve the quality of final silicone parts.
Since platinum cured silicone is low temperature curing silicone, it is applied to silicone to plastic overmolding, silicone to electronics overmolding, and other substrate overmolding that can not resist too high temperature.
Platinum Cure Silicone Disadvantages
Though platinum cured has so many advantages, platinum catalyst is very expensive. And it is easily contaminated by subjects containing heavy metals or N, P, S atoms which will prohibit its curing ability. Silicone raw material with platinum should be used in 4-8 hours at temperature not over 25°C. So we need to take cares to the storage environment.
Peroxide catalyst can not totally cure silicone, even secondary vulcanization. Peroxide curing generate some by-products, or called peroxide residues. These residues sometimes make the silicone surface greasy. If silicone curing time is not enough or curing temperature is too low, peroxide residues will rise to surface and form the blooming with time going by, and silicon mechanical properties and safety are reduced. Post curing can efficiently remove the residues inside peroxide silicone, and strengthen the crossl ink.
Peroxide cured silicone also has its advantages. It is very cost-effective and easy to operate silicone rubber mixing with peroxide. Storage time can be longer. Silicone rubber raw material with peroxide catalyst can be kept about 1 month. With post curing, peroxide cured silicone can be food contact safe grade as well.
Generally, tooling cost for peroxide-cured silicone is also cheap, especially, for new products development, small quantity orders or lower quality requiremnt.That is the main reason peroxide-cured silicone rubber still exists to this day.