Study On Preparation And Characterization Of Transparent Silicone-based Composites For Power LED Encapsulant

Light-emitting diodes (LED) have been called as “green solid-state lighting” thatare proposed for specially lighting applications due to its superior characteristics suchas high energy efficiency, reliability and environmental-friendly property. As thedevelopment of LED manufacturing technology, it is used as lighting and expected toenter the ordinary families. To meet the requirements of packaging material forhigh-power white LED, it should not only possess a high thermal stability and thermalconductivity to prevent heat accumulating, but also should maintain a high UV-lightshielding, visible-light transparency and UV-irradiation resistance. However,Traditional epoxy resins (EP) have many disadvantages which make it hard to meetthe requirements of packaging for high-power white LED. Therefore, the reliability ofthose is becoming an urgent issue for the emerging illumination applications.With vinyl-polysiloxane and hydrogen-polysiloxane as main raw materials, atwo-component silicone rubber was synthesized by platinum catalysis(Pt) under hightemperature, mixed with vinyl-MQ silicone resins, diluents, tackifier and silanecoupling agent. The influences of some factors (such R=（Si-H）/n（Si-Vi）, catalysis and MQresins) on the silicone rubber properties were discussed. The results showed that thesilicone rubber had both a transmittance＞95%at700nm and good thermalresistance, and the mechanical properties of materials were shown outstanding whenR=1.25、w(catalysis)=0.2%and w(MQ resins)=15%.Based on the previous research, a novel fluorine/silicone composites wereprepared with DMFA-12via chemical modification method. The result showed thatthe composites displayed good corrosion resistance and mechanical properties. Thecomposites had both a high transmittance＞85%at700nm and good hydrophobicperformance (contact angle up to101°) when it was mixed with4wt%DMFA-12,and the initial decomposition temperature was tremendously higher than pure silicone(increased by63℃).In order to further improve the comprehensive performance of silicone rubber,the paper reported that the homemade nano-ZnO particles were grafted to themolecular chain of poly(methylhydrosiloxane)(PMHS) by chemical modificationmethod, and the transparent silicone/nano-ZnO composites was synthesized undercatalytic action of Pt and with the graft polymer ZnO–PMHS and vinyl polysiloxaneas reactants. The effect of content and size of ZnO on mechanical and optical propertyof the composites was researched. It was found that the ZnO nano-grains wereconnected to molecular chain of polymer by chemical grafting, and the refraction ofcomposites was changed by grafting reaction of ZnO nano-grains. When the contentof nano-ZnO is0.06wt%, the transmittance of composites at640nm is up to80%,and the shielding efficiency for ultraviolet below300nm reaches90%. Compared with the composites without nano-ZnO, ultraviolet resistance of organic siliconenano-ZnO composites is increased by5times, the initial heat decompositiontemperature improved by25%and residue quality of thermal decompositionenhanced by15%. The nano-ZnO/organic silicone composites present an excellentthermal resistance and ultraviolet aging resistance, meeting the packaging requirementfor LED.