Preparation And Properties Of Silicone Resins For LED Encapsulation

Light emitting diode(LED)has become a new generation of light source because of the advantages of long life,energy conservation,environmental protection and so on.The selection of packaging materials is the key problem in the practical application of LED.The appearance,brightness and lifetime of LED rely heavily on the performance of packaging materials.With the popularization of high-power LED,traditional epoxy resin encapsulation materials have difficulty inmeeting the performance requirements because of the weaknesses of large internal stress,aging yellowing and unsatisfactory thermal stability.Thus,there is a growing demand for high-performance packaging materials such as silicone and silicone modified epoxy resins.In this paper,two kinds of encapsulating silicone materials were prepared through hydrosilylation and epoxy anhydride curing respectively,and their properties were characterized and discussed.Details are as follow:(1)Vinyl silicone resins as basic polymer,and several low-viscosity hydrogen containing silicone resins as diluent and crosslinking agents,were synthesized by sol-gel method.The two kinds of resins cured to be packaging materials through hydrosilylation with Pt catalyst.Synthesis experiment conditions were discussed and the suitable one chosen is: 1.4wt% HCl as the catalyst,n(H2O)/n(alkoxy)=1.2,n(ethanol)/n(monomer)=1.0,stirring for 6 hours at 65?.The prepared vinyl silicone resin is colorless with suitable viscosity.The hydrogen containing silicone resin,of which the R/Si value is 1.2,was adopted as crosslinker.The influence of the molecular structure of hydropolysiloxane curing agents on curing behavior and properties of the cured resins were investigated.The results show that compared to linear hydropolysiloxane,hydrogen containing silicone resins curing system have higher curing activity,crystallinity,mechanical strength,better dielectric property and thermal stability.However,the toughness and transparency are relatively low.(2)Transparent silicone resins containing epoxy and phenyl groups(EPSR)were synthesized by hydrolysis and condensation of 3-glycidoxypropyl trimethoxysilane,phenyl and methyl alkoxysilane.The influence of preparation methods and concentration of hydrochloric acid on properties of the prepolymer was studied.The results show that when using 1.2wt% HCl as catalyst,or adopting dewater method without adding catalyst,the prepolymer have suitable viscosity and high epoxy value.While the resins prepared with HCl catalyst have better storage stability.EPSR and epoxy resin E51 were blending according to various mass ratio,and cured with methylhexahydrophthalic anhydride accelerated by aluminum 2,4-pentanedionate to obtain transparent organic-inorganic hybrid materials.The influence of EPSR/E51 ratio on curing behavior,optical and thermal properties,fire and water resistance,and adhesive property of the cured resins were studied.The results show that the introduction of EPSR is conducive to lowering the curing temperature of the blending hybrids,improving the flexibility,transmittance,flame retardant and waterproof of the cured resins.While a small amount of epoxy resin can significantly improve adhesive property and reduce costs.When the EPSR/E51 ratio ranges from 60/40 to 80/20,the cured products have better comprehensive properties,expecting to be used for LED encapsulation.