| Light-emitting diodes (LED) are expected to be the fourth generation lighting source because of their low energy consumption and High Brightness. In order to improve the light efficiency and avoid the water vapor and chemical in the atmosphere erosion LED chips, encapsulation materials that can guarantee the credibility and working life of LEDs are essential. Epoxy resins as traditional encapsulation materials, have many excellent properties such as high transmittance, good adhesion etc. But they have weaknesses such as strong curing internal stress, bad thermal aging resistance. Silicone resins as excellent candidates for LED encapsulation owing to their high thermal stability, molecular structural design flexibility and good thermal aging resistance. However, they have relatively poor adhesive property.In order to overcome the shortcomings mentioned above, a series of transparent epoxy-modified silicone resins for LED package were prepared in this thesis. The relationship between structure and properties were studied in detail and their performance in the LED packaging is also investigated.Firstly, transparent epoxy-modified silicone resins were produced through an easy control sol-gel method with y-(2,3-epoxypropoxy)propytrimethoxysilane and dimethyldiethoxylsilane. Theeffectives of reaction conditions and preparation technology on the structures and performances of the products were investigated. Subsequently, series of epoxy-modified silicone resin materials for LED encapsulation were prepared as following:(1) The epoxy-modified silicone resins were cured with MHHPAN accelerated by N-Benzyldimethylamine. The epoxy-modified silicone resins with R/Si=1.6 cured at 80? for 1 h,120? for 1 h,150? for 1 h have high transmittance (At the wavelength of 450nm.transmittance around this wavelength is up to 95%), high thermal stability, an adjustable hardness between 10-80 Shore D.(2) Moderate-temperature curing agent PEAs were selected to be cure agents for the epoxy-modified silicone resins prepared. The effective of various molecular weight of PEAs, different r value(the molar ratio of active hydrogen to epoxy group) on the cured epoxy-modified silicone resins were investigated. It shows that the materials can cured at room temperature with suitable hardness of 50±5 Shore A. The cured materials exhibits fairly high thermal stability (Td5%=368?) when r=l and R/Si=1.6.(3) Furthermore, the epoxy-modified silicone resins can be cured with UV by initiator 1176. The influence of the content of light initiator and curing time were conducted and it shows when the content of light initiator to 3wt%, the resin can almost be cured totally after 10s (the cured ration is 87.4%), and the cured materials are with pencil hardness of 5H, the volume shrinkage rate of 0.84%, cohesional strength of 1 grade.Subsequently, Methyl phenyl silicone resins containing hydrogen (HMPH) have been successfully synthesized by a sol-gel condensation process of dimethyldiethoxylsilane,Phenyltrimethoxysilane,dimethoxymethylphenylsilane andl,1,3,3-Tetramethyldisiloxane. Then the LED encapsulation materials are prepared by hydrosilylation of HMPH resin and allyl glycidyl ether (AGE),the materials obtained exhibit good properties such as high refractive index (as high as 1.525), good transparency, good adhesion, adjustable hardness in the rage of 40?60 Shore A. It exhibits that the materials produced can be a good candidate for UV cured LED encapsulation materials. |
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