| With high electrical insulation performance and ageing resistance,epoxy resins are widely used for the insulation of electrical equipment and the encapsulation of electronic devices.As electrical equipment evolves towards high power and large capacity,the heat generated inside increases significantly.The traditional epoxy resin can not meet the heat dissipation demand of the equipment.The development of epoxy resin composite with high thermal conductivity and insulation properties has therefore been receiving lots of attention.In this paper,a new method of building a thermally conductive network using the polyimide to improve the orientation and distribution of boron nitride in the epoxy resin is proposed.Epoxy resin composites with good thermal conductivity,heat resistance,and insulation properties have been produced.The thermal conductivity,mechanical and electrical properties of the epoxy resin composite were studied.The main contents of the paper include:(1)The influence of orientation of boron nitride on the thermal conductivity of epoxy resin composite was studied.A finite element model with different dispersion patterns of boron nitride in the epoxy resin matrix was established,and its equivalent thermal conductivity was simulated and analyzed.Results showed that the orientation of the thermally conductive fillers showed more significant effect on the improvement of thermal conductivity of the composites under the same filling amount.The orientation angle of the thermally conductive filler in the matrix facilitated the mutual contact and the reduction in the contact thermal resistance between the fillers.(2)The thermal network of the orientated polyimide/nano-scale boron nitride and the preparation of epoxy resin composite were presented.The freezing platform of three-dimensional BNNSs heat transfer network was built,and polyimide/nano-boron nitride aerogels with different nano-scale boron nitride contents were prepared.Results showed that the aerogels were three-dimensionally continuous and porous structures.The addition of PI effectively improved the molding effect of nano-scale boron nitride aerogels and the dispersibility of nano-BN in the matrix.The mechanical properties and thermal stability of the epoxy resin composite were improved.The influence of polyimide/nano-scale boron nitride on the thermal conductivity of epoxy resin composite was investigated.Results showed that the epoxy resin composite had an out-of-plane thermal conductivity of 0.823 W/(m·K),4.1 times higher than that of the standard epoxy resin.The thermal effect of the epoxy resin composite on the enclosed bus was examined by simulation.Results showed that the operating temperature of the bus was decreased by 7.28 °C under the rated current of 5000 A.(3)The thermal network of polyimide/nano-sized boron nitride was inspected for its effect on the electrical insulation and breakdown performance of the epoxy resin composite.Results showed that the volume resistivity and power-frequency breakdown voltage of the epoxy resin composite can be increased through the addition of orientated polyimide/boron nitride.The surface flashover voltage is similar to that of the randomly dispersed boron nitride/epoxy resin composite.The above studies show that the polyimide/nano boron nitride/epoxy resin composite has excellent electrical insulation performance. |
