Analysis of the status quo of silica gel materials for LED packaging
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Analysis of the status quo of silica gel materials for LED packaging
one. Classification of silicone materials
Silicone Rubber, abbreviated as silica gel, 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 and phenyl groups. The entire molecular chain of 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. It has excellent high and low temperature resistance, weather resistance, arc resistance, electrical insulation and physiological inertness.
The chemical structure of silicone materials
According to its product form and curing mechanism, silicone materials can be divided into the following types:
According to its curing temperature, silicone can be divided into high temperature curing silicone (HTV) and room temperature curing silicone (RTV); according to the product form and mixing method, it can be divided into mixing type silicone and liquid silicone; according to its crosslinking reaction mechanism, and Can be divided into condensation reaction type, addition reaction type and organic peroxide initiation type. Next, based on the type of reaction, a brief introduction to silica gel materials.
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 is the crosslinking agent. Under the action of a catalyst, condensation reaction can occur when exposed to water vapor or mixing at room temperature to form Three-dimensional network elastomer. The basic composition and chemical functions of condensation reaction type silica gel are shown below.
Taking dealcoholized room temperature curing adhesive as an example, the curing mechanism is: hydroxy-terminated silicone oil is pre-condensed with a crosslinking agent (to form alkoxy-terminated). After the prepolymer is exposed to moisture in the air, the active groups are partially hydrolyzed A silanol group is formed, and the silanol group undergoes a condensation reaction with the base polymer that has not yet been hydrolyzed to remove low molecular weight substances and achieve curing through chemical cross-linking between polymer chains.
Condensation type silica gel production device
According to the types of by-products generated by the cross-linking reaction, the condensation type silica gel can be subdivided into six types: deacidification type, deketoxime type, dealcoholization type, deamination type, deacetone type, and deamidation type. The advantages and disadvantages of condensed silica gel are as follows.
Condensed silica gel is generally used as a sealant for building seals, automotive lamp and other lighting devices, and antifouling materials for electrical insulators.
2. Addition molding silicone
Addition type silica gel is based on vinyl-containing polysiloxane and Si-H chemical bond-containing polysiloxane as cross-linking agent. Under the action of platinum catalyst, the addition reaction is carried out to obtain a three-dimensional cross-linked structure. Silicone Rubber.
Schematic diagram of platinum-catalyzed hydrosilylation reaction
Addition type silica gel is mainly composed of base polymer, crosslinking agent, catalyst, reinforcing filler and functional additives. Because addition molding silica gel has the advantages of low shrinkage, no small molecules released during the cross-linking process, and excellent high and low temperature resistance, most of the current LED encapsulants are addition molding silica gels. The addition molding silica gel is described in detail later.
3. Peroxide-initiated silica gel
Peroxide-initiated silica gel uses peroxide as a curing agent to cross-link with a vinyl-containing base polymer to obtain a three-dimensional network structure. Peroxide-initiated silica gel has two obvious shortcomings: one is that it needs to use more expensive high-purity silane monomers and intermediates as raw materials; the other is that the presence of peroxide in the silica gel causes air to seriously affect the curing. Inert gas protection is required during curing, so the production and use costs are high, which also largely limits the scope of its application.
