Investigation On The Preparation And Properties Of Epoxy Resin/Boron Nitride Composites With High-Thermal Conductivity

Electrical and electronic equipments are gradually developing towards high frequency,high power density and lightweight.Especially the chips and equipments used in 5G cormunication are in urgent need of dielectric materials with low dielectric constant,low dielectric loss,high thermal conductivity and excellent insulation.Epoxy resin has excellent electrical properties,heat resistance and mechanical properties,and is widely used in electrical and electronic equipment,devices,substrate insulation and packaging.Compared with other thermal insulating inorganic particles,boron nitride(BN)has the lowest dielectric constant and dielectric loss,besides its high breakdown field strength and thermal conductivity.The thermal conductivity and electrical aging resistance of epoxy resin can be greatly improved by a large amount of boron nitride filling modification.However,due to its surface inertia,unmodified boron nitride is difficult to be filled in large quantities in epoxy resin,and it is difficult to disperse uniformly,which limits its performance.Ii this dissertation,the surface of boron nitride powder is modified by surface chemical modification,physical modification and mechanochemical effect modification.Composite materials with excellent properties are prepared.The effects of surface modification methods on the viscosity,thermal conductivity and electrical properties of composite materials are studied.The research on chemical modification reveals:the surface chemical modification of boron nitride by silane coupling agent can reduce the viscosity of the composites.The viscosity of composites filled with 30wt%BN modified by KH550,KH560 and KH570 are 151602,682830 and 245392mPa s,respectively,which are 83.7%,26.4%and 73.5%lower than that of the composite filled with unmodified BN.The viscosity reduction effect of KH560 modification is relatively best.Direct modification with coupling agent has no effect on improving thermal conductivity.The thermal conductivity of the composites can be improved by using sodium hydroxide alkali solution to activate the surface of boron nitride powder and then chemical modification with silane coupling agent.When the boron nitride content is 30wt%and 40wt%,the thermal conductivity of the composites is 1.16 and 1.71W/m·K,which is 6.4 and 9.5 times higher than that of pure epoxy resin,and the viscosity of the composites prepared by this method can be further reduced.The viscosity of the composites is 126978mPa s at 30wt%filling,which is 86.3%lower than that of the unmodified composites.The results of physical modification show that the viscosity of the composites can be greatly reduced by physical action.The lowest viscosity of the composites filled with 30wt%physically modified boron nitride is 3656 mPa s,which is 1/254 before modification.Physical modification can reduce the viscosity of epoxy resin/boron nitride system and increase the maximum filling amount and thermal conductivity.The maximum filling amount can reach 50wt%,and the thermal conductivity is 1.82W/m K,which is 10.1 times higher than that of pure epoxy resin.The results of mechanochemical effect modification show that the modification of boron nitride by mechanochemical effect can reduce the viscosity of composites and improve their thermal conductivity.The process of adding coupling agent before mechanochemical effect modification has the best effect.The viscosities of composites filed wite30wt%BN modified by KH550?KH560 and KH570 and then modified by mechanochemical effect for 5 hours are 12475,5287 and 8017mPa s,which is 1/33,1/79 and 1/52 before modification.The modification effect of KH560 is the best.The thermal conductivity of composites filled with 50wt%BN modified by KH550,KH560 and KH570 and then modified by mechanochemical effect for 5 hours are 1.54,1.63 and 1.67W/m K,respectively,which is 8.6,9.1 and 9.3 times higher than that of pure epoxy resin.The longer the modification time of mechanochemical effect is in the range of 2.5-10h,the smaller the viscosity of the composite is,but the thermal conductivity decreases slightly.The modification time can be determined according to the actual demand.The viscosity of composites filled with 50wt%BN modified by mechanochemical effect for 2.5h is 12344mPa·s,which is 1/34 before modification,and the thermal conductivity is 2.05W/m·K,which is 11.4 times higher than that of pure epoxy resin.Adding hydrogen peroxide solution,then modifying by mechanochemical effect,and finally adding coupling agent,can promote the modification effect of silane coupling agent The viscosity of the composite modified by this process is 2973 mPa s-which is 1/140 before modification.For the hexagonal boron nitride at 50,10 and 2μm,the viscosity of composites decreases with the increase of particle size,and the thermal conductivity increases with the increase of particle size.The viscosity and thermal conductivity of the three particle size mixtures are inferior to a single 50μm.The research on electrical insulation performance reveals:the composite material with 30wt%boron nitride has excellent insulation properties and belongs to the material with high breakdown field strength,high resistivity,low dielectric constant ripeness and dielectric loss.It meets the requirements of electrical and electronic equipment.The insulation properties of the composites can be optimized by ball milling modification.