Silicone Rubber, referred to as silica gel for short, refers to a high molecular polymer material whose main chain is alternately composed of silicon atoms and oxygen atoms, and the molecular side chains are connected with organic groups such as methyl groups and phenyl groups. The entire molecular chain of the silica gel material has a special organic and inorganic structure. The combination of the two makes it have the dual advantages of organic and inorganic materials, and has excellent high and low temperature resistance, weather resistance, arc resistance, electrical insulation and physiological inertia.

According to its curing temperature, silica gel can be divided into high temperature curing silica gel (HTV) and room temperature curing silica gel (RTV); according to product form and mixing method, it can be divided into mixing type silica gel and liquid silica gel; It can be divided into condensation reaction type, addition reaction type and organic peroxide initiated type. Next, according to the type of reaction, we will briefly introduce the silica gel material.

1. Condensation reaction type silica gel

Condensation reaction type silica gel is generally based on hydroxyl-terminated polysiloxane as the base polymer, and multifunctional silane or siloxane as the crosslinking agent. 3D Network Elastomer.

Taking the dealcoholized room temperature curing glue as an example, the curing mechanism is: the hydroxyl-terminated silicone oil and the cross-linking agent are pre-polycondensed (to form an alkoxy-end-capped), and after the prepolymer contacts the moisture in the air, the active group is partially hydrolyzed. A silanol group is generated, which undergoes a condensation reaction with the base polymer that has not been hydrolyzed, removes low molecular substances, and achieves curing through chemical cross-linking between polymer chains. According to the types of by-products generated by the cross-linking reaction, condensation-type silica gel can be subdivided into six types: deacidification type, deketoxime type, dealcoholization type, deamination type, deacetone type, and deamidation type. Condensed silica gel is generally used as building sealant, sealing of lighting devices such as automobile lamps, and anti-fouling materials for electrical insulators.

2. Addition type silicone

Addition type silica gel is based on vinyl-containing polysiloxane, and polysiloxane containing Si-H chemical bond is used as cross-linking agent. Silicone Rubber. Addition type silica gel is mainly composed of base polymer, crosslinking agent, catalyst, reinforcing filler and functionalized additive. Because the addition type silicone has the advantages of low shrinkage rate, no release of small molecules during the cross-linking process, and excellent high and low temperature resistance, most of the current LED packaging adhesives are addition type silicone.

3. Peroxide-initiated silica gel

The peroxide-initiated silica gel uses peroxide as a curing agent, and undergoes a cross-linking reaction with a vinyl-containing base polymer to obtain a three-dimensional network structure. Peroxide-initiated silica gel has two obvious disadvantages: one is that expensive high-purity silane monomers and intermediates are used as raw materials; Inert gas protection is required during curing, so the production and use costs are high, which also limits its application range to a large extent.