| Thermoconductive polymer materials have excellent mechanical properties,corrosion resistance and reworkability,combined with light weight and low price,and are widely used in thermal management technology fields such as communication equipment,lighting fixtures,and household appliances.Because of their poor thermal conductivity,most polymers cannot achieve efficient heat transfer in devices.How to effectively improve the thermal conductivity of polymers is an important problem.Adding fillers with high thermal conductivity to the polymer matrix is an effective way to improve the thermal conductivity of thermoconductive materials,and it has the characteristics of low price,simple operation,and easy industrial production.Commonly used thermoconductive fillers for thermoconductive polymer materials include metals,ceramics,carbon materials and so on.In order to expand the application of thermoconductive polymer materials in the field of electronic heat transfer,a preparation method of large-scale production of graphite modified boron nitride-based insulating thermoconductive material was developed in this paper.The main research contents include:Chapter 1:We reviewed the preparation methods,thermoconductive mechanism,and the current research status of conductive and insulating thermoconductive materials.According to components of insulating thermoconductive materials,the physical and chemical preparation methods of them are outlined.Finally,the basis and research content of this article are proposed.Chapter 2:Boron nitride microsheets(BNMS)was used to prepare insulating thermoconductive material,and a good transport network was constructed,which effectively improved the thermal conductivity of the resin.First,the filling rate of BNMS and the properties of thermoconductive materials were investigated.It was found that the properties of insulating thermoconductive grease obtained by filling epoxy resin with 50 wt.%BNMS was up to 4.6 W/mK.Under the temperature of 25～250℃,the insulating thermoconductive grease has great thermal stability,and its thermal weight loss rate is less than 0.5%.Secondly,the insulating thermoconductive grease prepared by different methods such as ultrasonic,liquid phase ball milling and high speed homogenization was investigated,among which the high speed homogenization method had the best effect.Moreover,the thermal conductivity of the insulating thermoconductive grease was verified.The junction temperature of the LED lamp could be reduced by 9.7℃,15.1℃ and 15.5℃ respectively by using ultrasonic,ball milling and high speed homogenizing method.Among them,the maximum thermal conductivity of insulating thermoconductive grease prepared by high-speed homogenization method is 9.5 W/mK.Finally,the insulating thermoconductive adhesive was prepared on this basis,and the best curing temperature and time were 80℃and 3 h when the ratio of resin to curing agent was 1/1.It was explored that the process route of large-scale green production of thermoconductive materials.Chapter 3:Graphite microplates(GMP)was introduced into BNMS-based insulating thermoconductive material,which enhanced the effective phonon transport and further improved the thermal conductivity of resin.By adjusting the ratio of GMP to BNMS in the thermoconductive resin film,the volume resistivity of 0.2 mm graphite film coated with the thermoconductive resin film was tested to increase with the increase of this ratio.When the boron nitride micron sheet/graphite ratio is 9/1,the volume resistivity is as high as 2.10×107 Ω·m,which meets the resistivity requirements of insulating materials used in electronic devices(>107 Ω·m).The thermal conductivity is measured to be 69.4 W/mK,which is 74.5%higher than that of 40 W/mK BNMSbased thermoconductive waterborne polyurethane resin film.In addition,when the filling rate of GMP and BNMS is 30%,the maximum thermal conductivity of GMPBNMS-based thermoconductive epoxy resin grease is 11.3 W/mK,which is 27.7%higher than that of BNMS-based thermoconductive epoxy resin grease.Moreover,the thermal conductivity of GMP-BNMS-based thermoconductive epoxy resin adhesive is 19.3 W/mK,which is 24.9%higher than that of BNMS-based thermoconductive epoxy resin adhesive.Chapter 4:Graphene nanoplats(GNP)was introduced into boron nitride nanosheets(BNNS)-based insulating thermoconductive material to construct the phonon transport network of nanometer scale,which greatly improved the thermal conductivity of the resin.By systematically analyzing the chemical structures and preparation methods of BNNS and GNP,the optimized process route of tanic acid(TA)assisted ball milling to obtain BNNS from BNMS was proposed.Considering the yield,reagent cost and environmental protection,water was selected as the solvent of TA.The size of BNNS prepared by this method is about 1.5 μm and the height is about 1.5 nm.This method is green and simple,and can be used to prepare BNNS on a large scale.The thermal conductivity of the prepared BNMS-based thermoconductive grease was tested.The result shows that TA can be adsorbed on BNNS in the form of C-O-N bond,which affects the effective phonon transport between BNNS and greatly reduces the thermal conductivity of BNNS.In order to remove TA,TA-BNNS were treated at high temperature to obtain BNNS,and it was proved that the removal of TA from TA-BNS could effectively enhance the thermal conductivity of BNNS.Similarly,GNP were prepared by ball milling assisted by aqueous solution of TA,but GNP could be obtained only by repeated cleaning of 1 mol/L NaOH solution.Finally,it was that the thermal conductivity of BNNS and GNP as composite fillers for the preparation of insulating thermoconductive grease,adhesive and film.And the thermal conductivity of those with thermal conductivity of 12.5 W/mK,26.2 W/mK and 84.8 W/mK were obtained,respectively.Chapter 5:Summarize the research work of this paper,and put forward the challenges and solutions for the practical application of boron nitride-based insulating thermoconductive materials in the future. |
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