| Illuminating instruments have developed from incandescent lamp to fluorescent lamp. Nowadays, with the rapid progress in semiconductor luminescent technology, the solid-state light source based on LED (Light emiting diode) might developed as the fourth generateon light source for human being and it was regarded as one of the most promising fields in 21st century. As a new type of light source, the main obstacle need to be overcome was focus on how to improve the extraction efficiency for Power LED. Therefore, encapsulant materials with excellent performance should be developed. Silicone material exhibits superior heat resistance, lower temprature resistance and better radiation resistance, which made it suitable for encapsulant of Power LED where large amount of heat was generated during luminance. Unfortunately, most saled encapsulant materials were relyed on import, which is not good for research and development of our national semiconductor lighting project. Power LED package material could be divided into two types, viz., silicone gel and silicone resin. As it was known by all that silicone materials exhibt poor mechanical properties if they were not reinforcened by fillers. As the most widely used fillers, although silica can greatly improve the mechanical properties of silicone materials, but it still can not reach the optic properties required by LED encapsulant due to the difference in refractive index between silica and the matrix. Therefore, it is quite interesting to investigate the modification of common MQ resin and its application in optical silicone rubber with high refractive index and transmittance. in this thesis, on the basis of the preparation of transparent, high refractive index addition silicone gel and modification of MQ resin, the modified MQ resin will be functioned as the reinforcing fillers, the optical and mechanic properties of thus obtained liquid silicone rubber will be studied in detail. This paper can be divided into four parts.(1). The progress and present situation of LED and also present the future development of encapsulate materials were briefly reviewed. The components of addittion silicone rubber and various influencing factors on its properties were discussed in detail. The preparing methods of MQ resin,a kind of novel reinforcement fillers, and its application were systematically summerized. The research goal and technical route for this thesis were subsequently presented.(2). A series of transparent vinyldimethylsiloxyl terminated poly(dimethyl-methylphenyl-methylvinyl) siloxane copolymers were prepared by ring-opening copolymerization method. Various factors, such as the catalysts, suitable amount, reaction time and so on, were carefully investigated. The result indicated that transparent copolymers with the highest refractive index (1.5247) could be obtained when the balance polymerization was conducted at 100℃for 5 h and catalyzed by tetramethylammonium hydroxide silanolate.(3). The synthesis of transparent addition silicone gel was investigated. The silicone gel was composed of three parts, viz.,matrix, crosslink agent and catalyst. The matrix was composed of vinyldimethylsiloxyl terminated polysiloxane and polysiloxane containing active Si-H bond in either backbone or end-capping position could be served as crosslinking agent for matrix. The most common catalyst used for vulcanization of addition silicone rubber or silicone gel was platinum and its complexes. It was found that the vulcanization process of addition silicone rubber and gel was greatly influenced by many factors such as the vinyl content in matrix, the amount of crosslinking agent and curing temperature, etc. Besides, the influence of catalysts and the difference in refractive index between matrix and crosslinking agent on transmittance of vulcanized products were thorouly investigated. A kind of gel-type LED encapsulant with highest refractive index (1.5247) and transmittance higher than 90% at wavelength of 800 nm or higher than 80% at wavelength of 400 nm was prepared, which is suitable for encapsulant of LED.(4). Various functionalized MQ resins were synthesized and used as the fillers in polymer system to improve its mechanical properties. In order to accurately determine the ratio between M and Q segment in MQ resin, a kind of characterization method was presented based on element analysis or'H-NMR spectrum. Phenyl containing MQ resin terminated by either methyldiphenylethoxysilane or dimethylphenylethoxysilane were prepared and the result were discussed in detail. MQ resins with refractive index ranged from 1.4231 to 1.4990 were obtained by cohydrolysis of sodium silicate and end-caping agents composed of dimethylphenylethoxy-silane and hexamethyldisiloxane in presence of acid. Subsequently, the MQ resin reinforced silicone rubber was studied in detail. The transmittance of silicone rubber reinforced by MQ resin was tested. Meanwhile, the influence of addition of MQ resin on viscosity of pre-cured mixtures was investigated and the effect of vinyl content in MQ resin and the amount of MQ resin on mechanical properties of cured silicone rubber were also discussed. The reinforcing effect of MQ resin on silicone rubber with different content of MePhSiO segment was further investigated. It was found that whether methylvinyl MQ resin or methylphenylvinyl MQ resin had little influence on viscosity of silicone rubber. In general, silicone rubber with MePhSiO segement less than 10 mol% can be reinforced by MQ resin. When MQ resin with vinyl content of 1.89 wt% was used in an amount of 20 wt%, silicone rubber free with MePhSiO segement exhibited optimal results: tensile strength was 2.38 MPa, hardness(Type A) was 31.7, elongation(%) at break was 70% and. transmittance at wavelength of 400 nm was 91%, and it is also suitable for encapsulant of LED. |
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