China is the world's largest LED application market, but the development of high-end LED and other fields is relatively lagging behind, and the production capacity is insufficient, which is far from meeting the needs of the market. Corti, Philips, Osram , Kyocera, Sumitomo Electric, Nichia and other foreign brands have long-term Has occupied the domestic high-end market. In addition, the core technology of high-end LED materials is basically in the hands of European and American enterprises. Most domestic enterprises are at the low end of the industry, and it is difficult to gain the upper hand in competition with foreign companies. Moreover, the trend of homogenization competition in some areas began to appear, and the phenomenon of disrupting market order by sub-filling and malicious price reduction further weakened the market competitiveness of domestic enterprises, thus limiting the rapid development of the domestic LED material industry.
The continuous development of LED packaging materials has led to the continuous improvement of the corresponding packaging technology. The packaging material has an important influence on the function of the LED chip . The poor heat dissipation or low light extraction rate will cause the function of the chip to fail. Therefore, the packaging material must have high thermal conductivity, high transmittance, good heat resistance and UV resistance. (UV light) shields good features. With the rapid development of white LEDs, the outer packaging materials must maintain high transparency in the visible range and have good absorption of ultraviolet and visible light (to prevent ultraviolet and visible radiation).
The traditional epoxy resin (EP) has the disadvantages of easy yellowing, large internal stress and poor thermal stability, so it cannot meet the packaging requirements of white LEDs, and is replaced by a silicone material with excellent performance. Silicone encapsulants have excellent thermal stability, water resistance and light transmissibility due to their organic and inorganic groups. They have become the focus of research on LED packaging materials at home and abroad; however, organic Silicon still has some disadvantages (such as poor UV aging resistance, low thermal conductivity, etc.). In recent years, researchers at home and abroad have used nanotechnology to modify silicones and have received extensive attention.
1. POSS modified EP packaging material
EP refers to a polymer compound containing two or more reactive epoxy groups in the molecule, which can be crosslinked with an amine, an acid anhydride, and a PF (phenolic resin) to form an insoluble polymer having a three-dimensional network crosslinked structure. Object. Therefore, EP has advantages such as excellent adhesion, good sealing properties, and low cost, and is a main material for packaging such as LEDs and integrated circuits. However, with the rapid development of technology, the performance requirements of packaging materials are getting higher and higher. Traditional EP packaging materials have the disadvantages of fast aging rate, easy discoloration and brittle materials, so the modified EP packaging materials are bound to be Row.
POSS is a compound composed of an inorganic core composed of silicon and oxygen and an organic peripheral group, and has a three-dimensional structure and a machine-inorganic hybrid nanocage structure. Compared with traditional inorganic nanoparticles, POSS has good heat resistance, structural stability and thermodynamic properties due to its special molecular structure, and the POSS molecular structure can be "cut" and "assembled" as needed. Therefore, the use of POSS modified EP can overcome the shortcomings of traditional EP packaging materials.
Xiao et al first synthesized (3-oxidized glycidyl propyl) dimethylsiloxy POSS and vinyl epoxy cyclohexane dimethylsiloxy POSS, followed by 4,4'-diphenylmethane and tetra After mixing the methyl phthalic acid, a corresponding hybrid material is prepared. The results show that with the increasing assimilation temperature, the hardness of POSS modified EP decreases gradually. Although the thermal expansion coefficient of composites is higher than that of bisphenol A type EP (DGEBA) at low temperature, the dependence of expansion coefficient on temperature is higher. It is small and its coefficient of thermal expansion is still low, so that it can effectively improve light stability and heat resistance.
Fu et al. use POSS modified EP containing propylidene. Studies have shown that although the Tg (glass transition temperature) of the modified EP is significantly reduced, the high temperature light stability, heat resistance and UV aging resistance of EP are significantly improved.
Based on g-(2,3-epoxypropoxy)propyltrimethoxysilane, Zhou Lijun and other preparations of epoxy silsesquioxane (SSQ-EP) with good compatibility with DGEBA were prepared by hydrolysis polycondensation. Then, the hybridization of SSQ-EP and DGEBA improves the disadvantages of poor heat resistance and yellowing of DGEBA, and enables DGEBA/SSQ-EP hybrid materials to maintain high light transmittance. The research shows that when m(DGEBA):m(SSQ-EP)=1:1, the comprehensive performance of hybrid materials is relatively optimal (the refractive index is 1.51, the transmittance is 92.07% and the heat aging resistance is excellent). .
Li Xueming et al. cross-linked and hybridized EP with POSS containing epoxy groups to prepare epoxy polyorganosilsesquioxane (EP/POSS) hybrid materials. Studies have shown that POSS and EP form a hybrid material after rapid in-situ hybridization in the UV curing process, and the obtained epoxy polyorganosil silsesquioxane hybrid material has high light transmittance, small thermal expansion coefficient and UV resistance. The advantages of good aging, overcome the shortcomings of poor flexibility of EP materials for LEDs, high temperature curing of silicone modified EP, etc., and are suitable for LED packaging.
2, silicone packaging materials
Although POSS can improve the heat resistance, thermal stability and light stability of EP, since EP itself contains epoxy groups, it is easily oxidized at high temperatures, and yellowing occurs after long-term use. Meet the requirements of high performance LED packaging materials. Compared with EP, silicone materials have good transparency, high temperature resistance, weather resistance and hydrophobicity. Currently widely studied silicone packaging materials are mainly two types of addition silicone resin and addition silicone rubber. This is because it does not produce by-products after vulcanization crosslinking and the size of the sulfide is relatively stable.
The addition molding silicone encapsulating material is a vinyl-containing silicone resin as a base polymer, a Si-H-containing silicone resin or a hydrogen-containing silicone oil as a crosslinking agent, and is subjected to crosslinking at room temperature or under heating in the presence of a platinum catalyst. Co-cured.
Kim et al. prepared a hydrogen-containing oligomeric resin (mixed with phenyl and vinyl-containing oligosiloxanes) by sol-gel condensation using vinyltrimethoxysilane and diphenyldihydroxysilane as raw materials. . Studies have shown that the purified phenyl silicone resin exhibits low shrinkage and high transparency in the curing reaction, and maintains good thermal stability and high refractive index at around 440 ° C, and is suitable as a silicone encapsulant for LEDs.
Zhang Wei et al. mixed vinyl phenyl silicone oil, hydrogen-containing silicone resin and vinyl silicone resin in proportion, and then solidified under the action of a platinum catalyst to form a silicone resin material for LED packaging. The research shows that the material has the characteristics of high refractive index (more than 1.54), good transparency, excellent heat resistance and thermal shock stability, and is suitable for silicone resin materials for LED packaging.
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