Study On Improving The Refractive Index Of Epoxy Resin For LED Packaging

With the increasing of the power of Light Emitting Diode (LED) and the brightness of the device, the traditional packaging materials can not meet the needs of production. At present, the research of LED packaging materials mainly focus on improving the refractive index, transmittance, the thermodynamic properties of the packaging materials and the ability to bear the ultraviolet ray. High refractive index of the materials can not only increase the optical output of the device, but also reduce the heat of the light conversion in the packaging material and improve the service life of the equipment which is fairly important to the improvement of LED technology. Therefore, the research of the high refractive index LED packaging material with moderate cost and high comprehensive performance has broad application prospects.In this paper, the refractive index of LED is mainly improved by the introduction of high refractive index groups in epoxy resin packaging materials. The main results and conclusions of this thesis are listed as follows:Firstly, The trifunctional epoxy resin (TEP) was synthesized using tri(4-hydroxyphenyl)ethane(THPE) and epichlorohydrin as materials. The refractive indices of TEP was 1.6002.1,2-Benzenebis(methanethiol) (OBDMT) was synthesized using 1,2-Bis(chloromethyl)- benzene and thiocarbamide. The OBDMT was an aliphatic thiols curing agent and it had an benzene group. The molecular structure of TEP and OBDMT were character-ized by 1H-NMR and FT-IR.Secondly, The OBDMT and common polythiol curing agent (PCA), the traditional curing agent methylhexahydrophthalic anhydride(MHHPA) were used to cure TEP. Then the optical properties, heat resistance and mechanical properties were analyzed by Abel refraction instrument, ultraviolet and visible spectrophotometer, DSC, TGA, universal testing machine and impact testing machine. The results showed that the sulfur atoms and benzene group in epoxy resin contributed to the obvious increasing of their refractive indices. The refractive indices of TEP/OBDMT cured resin was up to 1.6420, and the cured resin not only had good light transmittance(90%) and the ability to absorb ultraviolet light, but also had excellent thermal stability (Tg=160℃, thermal decomposition temperature=285℃) and bending strength is more than 120MPa, which indicates TEP/OBDMT cured resin can be applied to LED packaging field.Thirdly, The TP-THPE Copolymerization epoxy prepolymer was synthesized using 4,4’-Thiobis-phenol(TP) and tri(4-hydroxyphenyl)ethane and epichlorohydrin as materials. Four factors such as the mole ratio of TP and THPE, etherification temperature, etherification time, closed loop time and closed loop temperature. The molecular structure of TP-THPE was character-ized by 1H-NMR and FT-IR.The OBDMT and MHHPA were used to cure TP-THPE Copolymerization epoxy prepolymer. Then the optical properties, heat resistance and mechanical properties were analyzed. The refractive index of TP-THPE/TP cured product reached 1.6480, Significantly higher than MHHPA/TP-THPE. The transmittance of the two is more than 85%, the decomposition temperature is 260℃ and bending strength is more than 120MPa.Fourthly, The curing temperature of TEP/MHHPA and TP-THPE/MHHPA was determined by non-isothermal DSC method. The apparent activation energy Ea and the reaction series N of two kinds of curing systems were calculated by Kissinger-Akahira-Sunose(KAS) and Flynn-Wall-Ozawa(FWO). The results show that the reaction order of the two is not an integer, the curing process is a complex reaction.