1 characteristics of silicone materials

The silicone polymer has a Si—O bond as the main chain and an organic group on the silicon atom, and may have R 3 SiO 1 /2 ( M) , R 3 SiO 2 /2 ( D) , R 3 SiO 3 /2 ( T ) , R 3 SiO 2 ( Q) The chain links are combined according to a certain ratio; the Si-O bond can be higher, which makes it have better high temperature resistance or radiation performance, and the Si-O bond angle is larger, which makes the molecular chain of the material soft. . Silicone materials have excellent properties in terms of heat resistance and yellowing resistance. The silicone material is easily modified, and functional groups having an increased refractive index such as sulfur, benzene, phenol, and epoxy groups can be introduced into the side chain to increase the refractive index of the packaging material and improve the luminous efficiency of the LED.

2 Synthesis of silicone resin

According to its refractive index, it can be divided into two types: low refractive index (1.4) and high refractive index (1.5). The refractive index of 1.4 is mainly methyl type silicone material, and the refractive index of 1.53 is mainly phenyl type silicone material. Since the refractive index of the silicone material is larger, the light extraction efficiency is higher, so the refractive index of the silicone material should be increased as much as possible.

The silicone resin is generally obtained by using an organosilane as a raw material and hydrolyzing and polycondensing in the presence of a solvent. The raw materials synthesized are generally chlorosilanes or alkoxysilanes. The specific process is as follows: one is that silane is hydrolyzed to silanol under certain conditions, the other is that silanol itself undergoes polycondensation reaction, and the third is neutralized by water washing, and concentrated to remove small molecules to obtain a silicone resin. For example, Xu Xiaoqiu first hydrolyzed methylphenyldiethoxysilane, pyrolyzed it into a methylphenyl ring, and then synthesized it by anionic ring-opening polymerization to synthesize a phenyl vinyl silicone oil with a colorless transparency of 1.5 or more. Wu Tao et al. Preparation of vinyl-terminated methylbenzene under the action of a basic catalyst from an anionic ring-opening polymerization method using a cyclic methylphenylsiloxane containing a dimethylsiloxane chain and a vinyl double head. Base silicone oil. Wu Chuan et al. used acid catalysis, octamethylcyclotetrasiloxane (D4), or mixed 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) with methylphenyl in toluene Polymerization in a solvent to prepare a cross-linking silicone hydrosilylation oil. The ratio of the amount of Ph to Si is 0.30 to 0.60, the mass fraction of active hydrogen is 0 to 0.5%, the refractive index is 1.39 to 1.51 (25 ° C), and the dynamic viscosity is 100 to 550 mPa·s. Wang Xiaotong et al. synthesized phenylvinyl transparent silicone resin by solvent-free method; vinyl trimethoxysilane, hydroxyl terminated polydimethylsiloxane, diphenyldimethoxysilane and phenyltrimethoxysilane were selected. The raw material and the aqueous hydrochloric acid solution are used as a catalyst to carry out a hydrolysis condensation reaction to synthesize a high refractive index transparent silicone resin having fluidity at room temperature. In order to reduce the surface tension of the LED encapsulant, Yang Xiongfa and others made it easy to vacuum defoaming, and prepared a transparent vinyl silicone oil containing a methyl trifluoropropyl silicon oxy-chain and a methylphenyl siloxane. Huang Ronghua et al. used methyl vinyl chlorosilane phenyl chlorosilane, methyl chlorosilane and phenyl chlorosilane as raw materials, and blocked with methyl heading agent and vinyl heading agent to synthesize phenyl vinyl silicone resin. Then, filtration with a membrane having a pore diameter of 0.55 μm can effectively remove residual small particles of hydrochloric acid, improve product transparency, and obtain a colorless transparent vinyl phenyl silicone resin.

3 Silicone resin in LED packaging materials

At present, there are many patents on LED packaging materials, and phenyl encapsulating materials are the most studied. Zhang Wei et al. used tetraphenylcyclotetrasiloxane and vinyl double head as raw materials, and polymerized at 80-100 ° C for 6-8 hours in the presence of a base catalyst to synthesize vinyl phenyl silicone oil; Silane and hydrogen-containing double head are used as raw materials, reacted at 70-80 ° C for 3 h in the presence of hydrochloric acid, and then washed with water to obtain hydrogen-containing phenyl resin. Vinyl phenyl silicone oil and hydrogen-containing resin are cured for LED packaging materials. It has high refractive index (>1.54), high light transmittance, good heat resistance and thermal shock stability. Yang Huan, Yang Gang, Gao Qun use hydrolytic condensation to obtain phenyl silicone resin: phenyltrimethoxysilane, diphenyldimethoxysilane, vinyltrimethoxysilane as raw material, aqueous hydrochloric acid as catalyst, temperature rise The hydrolysis condensation reaction was carried out for 6 hours, and finally distilled under reduced pressure at 120 ° C for 3 hours. After obtaining a transparent silicone resin at room temperature, a certain amount of hydrogen-containing silicone oil and a Pt catalyst were added to carry out a hydrosilylation curing reaction. Ding Xiaowei et al. obtained a phenyl-containing hydrogen-based silicone resin by first hydrolyzing an alkoxysilane into a prepolymer and then polycondensing it with a hydrogen-containing alkoxysilane. The process is simple, controllable and environmentally friendly, with a refractive index of up to 1.531. The inorganic ultrafine particle composite type silicone LED encapsulant prepared by introducing the modification of the inorganic oxide fine particles having a high refractive index has the advantages of high refractive index and strong anti-ultraviolet radiation. Zhang Wenfei et al. modified nano zinc oxide with N-(trimethoxysilylpropyl)-4-azido-2,3,5,6-tetrafluorobenzamide and grafted it onto the silicone polymer chain. The grafting reaction changes the refractive index of the nanocomposite and makes the refractive index of the ZnO nanoparticle and the silicone matrix more matching, which improves the refractive index of the silicone polymer, and has great prospects for LED packaging materials. Zhan Xibing and others used a non-hydrolyzed sol-gel to prepare a series of transparent titanium hybrid silicone resin. The refractive index of the resin is as high as 1.62, and the obtained product has good light transmittance and thermal stability. We use phenyltrimethoxysilane, methylphenyldiethoxysilane, methylvinyldimethoxysilane as raw materials, organic acid as catalyst, synthetic vinyl phenyl silicone resin, vinyl obtained. The phenyl silicone resin and the hydrogen-containing silicone resin are cured, the Shore D hardness is 55-75 D, the refractive index is > 1. 53. The light transmittance is more than 99%, and is preferably used for the LED packaging material.

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