Study On Synthesis Of Nano SiO₂-epoxy Hybrid Resin In Ultrasonic Field And Its Blending With EPIB

Currently, LED encapsulates are mainly made of cycloaliphatic epoxy resin or silicone resin. Cycloaliphatic epoxy encapsulate possesses high moisture absorption and high modulus; while silicone encapsulate possesses low strength, high moisture permeability, poor adhesion and sealing. The two encapsulates both cannot meet the requirements for LED packaging. Low molecular weight polyisobutylene(LMWPIB) possesses ultrahigh purity, excellent transparency, outstanding UV resistance and very low moisture permeability. These features match with the requirements for LED encapsulate and make LMWPIB a potential LED potting. However, LMWPIB has only one end double bond, epoxidized polyisobutylene(EPIB) is not easy to solidify. In this thesis, a nano silica-epoxy hybrid resin compatible with EPIB was synthesized and added to EPIB as cross linking agent. The effect of the hybrid resin on the transparency and aging performance of EPIB encapsulate were studied.In ultrasonic field, the aggregates of fumed silica were broken and the primary partials were grafted with epoxy siloxane through the condensation of silicon hydroxyls. The synthesized nano silica-epoxy hybrid resin was added to EPIB rein and cured with MHHPA together at high temperature. Laser particle size analyzer, perchloric acid titration method, infrared spectrometer, thermal gravimetric analyzer were used to analyze the hybrid resin and the effect of reaction conditions on grafting efficiency. Differential scanning calorimeter was used to compare the reactivity of hybrid resin. Dynamic mechanical analyzer was used to determine the cross linking density of cured samples; UV-visible spectrometer was used to measured the transparency and aging performance.In alkaline alcohol/water medium, ultrasound could break the aggregates of fumed silica and promote the grafting of silica with epoxy siloxane. Nano silica-epoxy hybrid resin could be synthesized conveniently. At 70 oC and siloxane content below 8 %, the grafting efficiency increased with increasing siloxane concentration, ultrasonic reaction time and pH value, but decreased with increasing the length of alkoxy chain and the amount of silioxane groups. At epoxy siloxane concentration 8 %, ultrasonic time 20 min, pH value 9.0, the grafting efficiency of 2-(3, 4-cyclohexyl) epoxy silane could be 72 %; the epoxy value of synthesized hybrid resin was 0.021 mol/100 g; the average amount of epoxy groups on a silica primary particle were 8 x 103 and the grafted rate of hydroxyls on silica primary particles was 17.5%.The reactivity of the hybrid resin is similar to that of cycloalicyclic epoxy resin CY179, but higher than that of EPIB. At a heating rate of 5 ℃/min, the exotherm of hybrid resin with MHHPA started from ~ 100℃ and peaked at 150 ℃. The hybrid resin is compatible with EPIB. A colorless transparent potting could be prepared by solution mixing. With MHHPA curing agent, the hybrid resin could work as cross-linking agent for EPIB and bought EPIB chains to a macromolecular network. After added 5 and 15 phr hybrid resin, the Tg of cured EPIB increased from- 33 ℃ to-22 and-26℃, respectively. The storage modulus increased from 0.4 MPa to 0.7 and 0.9 MPa and crosslinking density increased from 57 mol/cm3 to 99 and 120 mol/cm3.The transmittances of cured EPIB with 3 and 5 phr hybrid resin were 99.8 % and 98.4 %, respectively. The transmittance decreased with increasing hybrid resin content. The cured EPIB exhibited excellent UV resistance. Irradiated with 334 nm xenon lamp for 168 hr at 50 oC, the yellowing index of cured EPIB with 3 and 5 phr hybrid resin were 0.82% and 0.72%. The yellowing index decreased with increasing hybrid resin content. As thermal aging in oven, the hydroxyls of hybrid resin could condense further; the surface of specimens became rough, consequently, the transmittance decreased.