Preparation And Properties Of LED Halogen-free Flame Retardant High Refractive Index Packaging Resin

Light-emitting diode(LED)is a new type of solid light source in the 21st century.LED packaging materials can provide enough protection for the chip to prevent the chip from failure due to chemical erosion or mechanical damage.Due to the large difference in refractive index between the chip and the encapsulation resin material,the photoelectric removal efficiency is less than 20%,and the rest is converted into heat energy,which not only causes a large amount of waste of light energy,but also lays a great fire hazard.Therefore,if the packaging resin material can be endowed with better refractive index and flame retarding properties,not only can increase the light removal efficiency,reduce heat release,but also can effectively reduce the probability of fire.In this study,the packaging resin with both halogen-free flame retardant and high refractive index was prepared from improving the refraction index and flame retarding properties of packaging resin.In this paper,DOPO-a green halogen-free phosphorous flame retardant,was selected to react with Acrylamide(AM),Thiourea(THU)and the Urea to synthesize flame retardant curing agent for encapsulated resin.Sulfur was introduced directly or indirectly to improve the refractive index of encapsulated resin.On the one hand,flame retardants containing sulfur and those without sulfur were synthesized,and the effects of sulfur on flame retardant performance and refractive index of the resin system were directly compared.In addition,the effects of different valence states of sulfur on flame retardant performance and refractive index of the resin system were investigated by introducing sulfur elements with different valence states in the way of equivalent substitution.Through vertical burning test and limit oxygen index test measured the flame retardant properties of the resin system,and through the scanning electron microscope(SEM)to observe the residual carbon surface morphology after further speculated that combustion situation,using the abbe refractometer and spectrophotometer measured refractive index and light transmittance parameters.DOPO-Urea and DOPO-THU were prepared with DOPO,Urea and THU as raw materials.The structure of the product was analyzed by FTIR and NMR.DSC and TGA analyzed the thermal stability of the resin system,and the results showed that the introduction of sulfur increased the T_g of the flame retardant resin,promoted the carbonization,and greatly increased the refractive index.The flame retardant test results showed that the samples containing sulfur would partially weaken the flame retardant effect.When the phosphorus content was 1.5%and the sulfur content was 1.548%,the DOPO-THU epoxy curing material reached V-0 level,the oxygen index(LOI)reached 29.12%,and the sample curing index reached 1.5980 and the highest transmittance reached 82%,with excellent transparency and flame retardancy.The sample refractive index and light transmittance were also greatly improved to complete the preparation of halogen-free flame retardant epoxy resin with high refractive index.DOPO and Acrylamide(AM)were as raw material,synthetic DOPO based flame retardant DOPO-AM,and indirectly by means of partial replacement of DGEBA introduction and DGEBA structure similar but different valence state of sulfur:Diglycidyl ether of thiobis-phenol(DGETP),Diglycidyleher of bisphenol-S(DGEBS)and Sodium N-cyclohexylsulfamate(SNC),flame retardant epoxy curing,to explore the different valence state of sulfur elements on the properties of epoxy curing effect.When the phosphorus content was only 0.75%,the dopo-am cured substance could pass through the flame retardant V-0grade,LOI was as high as 34.55%,the refraction index of the resin sample introduced with-2DGETP could reach 1.5869,and the light transmittance could also reach 81%.And the epoxy resin with good refraction index and flame retardant performance can be prepared.DOPO-GMA was synthesized from DOPO and Glycidyl methacrylate(GMA).When the phosphorus content is 6%,the LOI of acrylate resin reaches 27.7%,and through the flame retardant V-0 level,its refractive index also reaches 1.5749,light transmittance reaches87.18%.the acrylate resin with good transparency and flame retardant can be prepared.