Silicone rubber, referred to as silicone rubber, refers to a polymer material whose main chain is composed of silicon atoms and oxygen atoms alternately, and the molecular side chain is connected with methyl, phenyl and other organic groups. The whole molecular chain of silicone rubber material has a special structure of organic and inorganic materials. The combination of the two makes it have the dual advantages of organic and inorganic materials, and has excellent characteristics of high and low temperature resistance, weather resistance, arc resistance, electrical insulation and physiological inertia.

Silicone rubber can be divided into high-temperature curing silicone rubber (HTV) and room temperature curing silicone rubber (RTV) according to its curing temperature; According to product form and mixing method, it can be divided into mixed silicone rubber and liquid silicone rubber; According to the crosslinking reaction mechanism, it can be divided into condensation reaction type, addition reaction type and organic peroxide type. Next, we will briefly introduce silicone rubber materials according to the reaction type.

1. Condensation reactive silicone rubber
Condensation reactive silicone rubber is generally based on hydroxyl terminated polysiloxane as the basic polymer, and multifunctional silane or siloxane as the cross-linking agent. Under the action of catalyst, condensation reaction can occur at room temperature when meeting water vapor or mixing evenly, forming three-dimensional network elastomer. Condensed silicone rubber is generally used as building sealant, sealing of lamps and lanterns such as automobile lamps, and antifouling material for electrical insulators.

2. Addition silicone
Addition silicone rubber is a silicone rubber with three-dimensional cross-linking structure, which is based on the vinyl containing polysiloxane as the basic polymer, and the Si-H chemical bond containing polysiloxane as the cross-linking agent. Addition silicone rubber is mainly composed of basic polymer, cross-linking agent, catalyst, reinforcing filler and functional additive. Because of the advantages of addition silicone, such as low shrinkage, no small molecule release in the crosslinking process, and excellent resistance to high and low temperatures, the vast majority of LED packaging adhesives are addition silicone.

3. Peroxide induced silicone rubber
Peroxide induced silicone rubber is a three-dimensional network solid structure obtained by crosslinking reaction between peroxide and basic polymer containing vinyl group with peroxide as curing agent. Peroxide induced silicone rubber has two obvious disadvantages: first, it needs to use expensive high-purity silane monomers and intermediates as raw materials; second, because of the presence of peroxide in silicone rubber, air will seriously affect the curing, and inert gas protection is required during curing, so the production and use costs are high, which also limits its application scope to a large extent.

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