阅读说明：本技术 一种细菌纤维素/氮化硼复合高导热柔性薄膜材料及制备方法 (Bacterial cellulose/boron nitride composite high-thermal-conductivity flexible film material and preparation method thereof ) 是由 李石琨 刘斌 淮秀兰 贾潇 邓亚民 杜军 徐翠 于 2021-09-16 设计创作，主要内容包括：本发明公开了一种细菌纤维素/氮化硼复合高导热柔性薄膜材料及其制备方法,属于导热材料技术领域。本发明通过改性剂对氮化硼填料进行表面改性处理,并在细菌纤维素分散液中均匀分散、交联键合,进一步抽滤得到薄膜；经热压处理后,将细菌纤维素碳化,使其导热性能大幅度提升,同时消除薄膜空隙,在氮化硼和碳化细菌纤维素之间构筑导热通路,获得具备高导热性能的薄膜；将经有机溶剂稀释的环氧树脂均匀喷涂在导热薄膜的表面,经热压处理,环氧树脂与氮化硼、碳化细菌纤维素表面的不饱和基团反应交联,提升了导热薄膜表面的韧性和力学性能,从而得到细菌纤维素/氮化硼复合高导热柔性薄膜材料。(The invention discloses a bacterial cellulose/boron nitride composite high-thermal-conductivity flexible film material and a preparation method thereof, and belongs to the technical field of thermal conductive materials. According to the invention, the boron nitride filler is subjected to surface modification treatment by a modifier, and is uniformly dispersed and cross-linked in a bacterial cellulose dispersion liquid, and a film is obtained by further suction filtration; after hot pressing treatment, carbonizing the bacterial cellulose to greatly improve the heat-conducting property of the bacterial cellulose, eliminating film gaps, and constructing a heat-conducting passage between boron nitride and the carbonized bacterial cellulose to obtain a film with high heat-conducting property; the epoxy resin diluted by the organic solvent is uniformly sprayed on the surface of the heat-conducting film, and the epoxy resin reacts with unsaturated groups on the surfaces of the boron nitride and the carbonized bacterial cellulose for crosslinking through hot pressing treatment, so that the toughness and the mechanical property of the surface of the heat-conducting film are improved, and the bacterial cellulose/boron nitride composite high-heat-conductivity flexible film material is obtained.)

1. The bacterial cellulose/boron nitride composite high-thermal-conductivity flexible film material is characterized in that: the raw materials comprise the following components in percentage by weight: 30-60% of boron nitride, 10-50% of bacterial cellulose, 2-10% of a modifier, 3-10% of epoxy resin and 1-5% of a curing agent, wherein the sum of the weight percentages of all the raw materials is 100%;

the modifier is selected from one or more of dopamine, 3-aminopropyltrimethoxysilane, gamma-glycidoxypropyltrimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-beta- (aminoethyl) gamma-aminopropyltrimethoxysilane, 3-aminopropylmethyldimethoxysilane or N-beta- (aminoethyl) gamma-aminopropylmethyldiethoxysilane;

the epoxy resin is selected from one or more of organic silicon epoxy resin, acrylate epoxy resin and dimer acid epoxy resin;

the curing agent is selected from one or more of ethylenediamine, triethylamine, triethanolamine and diethylenetriamine.

2. The preparation method of the bacterial cellulose/boron nitride composite high-thermal-conductivity flexible film material as claimed in claim 1, is characterized in that: the method comprises the following steps:

s01, heating and drying the boron nitride powder in a vacuum environment to obtain dry powder;

s02, adding a modifier into the dispersion liquid, adding the dried powder obtained in the step S01 after uniformly mixing, washing and filtering the mixture by using a mixed solution of deionized water and absolute ethyl alcohol after ultrasonic treatment and high-speed stirring, and finally freeze-drying the mixture to obtain modified boron nitride powder;

s03, blending the modified boron nitride powder obtained in the step S02 with deionized water dispersion liquid of bacterial cellulose, placing the mixture in a vacuum stirrer to be uniformly stirred to obtain a mixed solution of boron nitride and bacterial cellulose, and then performing solid-liquid separation in a vacuum filtration device to obtain a film structure;

s04, carrying out flat plate hot pressing on the film to obtain a high-performance heat-conducting film;

s05, spraying a mixture of low-viscosity epoxy resin diluted by an organic solvent and a curing agent on the surface of the film, and carrying out hot pressing to obtain the high-thermal-conductivity flexible heat-conducting composite material.

3. The method of claim 2, wherein: in step S01, the boron nitride powder is placed in a vacuum drying oven, and the heating temperature range is 50-300 DEG C^oC, treating for 6-12 h to obtain dry powder; the particle size of the boron nitride powder filler is 0.5-30 μm.

4. The method of claim 2, wherein: in step S02, the dispersion is selected from one or more of deionized water, absolute ethyl alcohol, isopropyl alcohol, or acetone; the mass concentration of the modifier solution is 2-10%, and the pH value is 7-10.

5. The method of claim 2, wherein: in the step S02, the ultrasonic treatment time is 0.5-2 h, the stirring time is 6-48 h, and the ultrasonic temperature is 20-40^oC, stirring at the temperature of 20-80 DEG C^oAnd C, the freeze drying time is 24-48 h.

6. The method of claim 2, wherein: in step S03, the bacterial cellulose has a diameter of 50-300 nm and a length of 20-100 μm.

7. The method of claim 2, wherein: in step S03, the rotation speed of the vacuum stirrer is 1800-2500 rpm, and the stirring time is 5-10 min.

8. The method of claim 2, wherein: the pumping filtration membrane of the vacuum filtration device is a nylon membrane with the aperture of 0.5-15 mu m, and the pumping filtration time is 3-6 h.

9. The method of claim 2, wherein: in step S04, the pressure of the flat plate hot pressing is 3-5 MPa, and the temperature is 150-250 MPa^oC, the time is 0.5-5 h.

10. The method of claim 2, wherein: in step S05, the concentration of resin in the low viscosity epoxy resin diluted by the organic solvent is 5-25%, the spraying thickness is 10-100 μm, the hot pressing pressure is 1-3 MPa, and the hot pressing temperature is 100-200^oC, the time is 0.5-6 h.

Technical Field

The invention belongs to the technical field of heat conduction materials, and particularly relates to a bacterial cellulose/boron nitride composite high-heat-conduction flexible film material and a preparation method thereof.

Background

With the development of miniaturization, light weight and high integration of electronic devices, the number of billions of transistors in the core area of the electronic devices means that more heat is generated by electronic components in the packaged circuit board, and if the heat cannot be conducted in time, the heat is rapidly accumulated, so that the internal temperature of the devices is rapidly increased, and dangerous accidents such as thermal failure and even explosion occur. The thermal interface material can be used for filling a gap between a heat source and a radiator and conducting heat out in time, so that the thermal management requirement is met. The interface material with high thermal conductivity has the defects of low tensile strength, brittleness, bending intolerance and the like due to the fact that the cross-linking density between organic matrixes is reduced due to the increase of the filling volume of the filler. In order to meet the urgent need of heat management generated in the foldable electronic equipment, the development of the composite flexible film thermal interface material with excellent heat conductivity and good mechanical strength has important significance.

The Bacterial Cellulose (BC) is a natural material with ultrahigh length-diameter ratio, uniform size and obdurability, has an ultralong crystal region structure, has mechanical strength far exceeding that of common plant fibers, is an ideal reinforcing material, and is widely applied to the fields of medical treatment, cosmetics, special paper and the like. Meanwhile, the fiber surface is rich in functional groups such as hydroxyl, carboxyl and the like, and cross-linking bonding between the filler and the matrix is facilitated, so that the high-efficiency utilization of the bacterial cellulose becomes a research hotspot. However, the bacterial cellulose belongs to a biopolymer, the self thermal conductivity is low, the application of the bacterial cellulose in the aspect of heat conduction materials is limited, how to perform cross-linking compounding between the bacterial cellulose and the high heat conduction filler is performed, the strength and the heat conduction capability of the material are improved, and the research direction is towards preparing the heat conduction composite material with excellent heat conduction performance and stable mechanical strength.

Boron Nitride (BN) is a two-dimensional ceramic material with an in-plane thermal conductivity approaching 300 W.m^-1·K^-1And for electrical insulation, methods such as suction filtration, calendering, spinning, coating and hot pressing are generally adopted to prepare BN/polymer composite materials to realize the arrangement of fillers so as to improve the in-plane thermal conductivity, for example, patents CN112552681A and CN110258170A, but the obtained boron nitride is only arranged in a horizontal direction, and there is a large interface thermal resistance between the boron nitride and the matrix material, and the obtained composite materials have poor toughness and low mechanical strength.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a bacterial cellulose/boron nitride composite high-thermal-conductivity flexible film material and a preparation method thereof. The boron nitride and bacterial cellulose film is obtained by a vacuum filtration method, cellulose is carbonized by a hot pressing method, a heat conduction network in the film is constructed, and the compactness and the heat conduction performance of the film are further improved. And spraying the epoxy resin diluted by the organic solvent on the surface of the film, and finally performing hot-pressing curing and crosslinking to further improve the toughness and the surface strength of the film material to obtain the high-thermal-conductivity flexible composite material.

In order to achieve the purpose, the invention adopts the following technical scheme:

a bacterial cellulose/boron nitride composite high-thermal-conductivity flexible film material comprises the following raw materials in percentage by weight: 30-60% of boron nitride, 10-50% of bacterial cellulose, 2-10% of a modifier, 3-10% of epoxy resin and 1-5% of a curing agent, wherein the sum of the weight percentages of all the raw materials is 100%;

the modifier is selected from one or more of dopamine, 3-aminopropyltrimethoxysilane, gamma-glycidoxypropyltrimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-beta- (aminoethyl) gamma-aminopropyltrimethoxysilane, 3-aminopropylmethyldimethoxysilane or N-beta- (aminoethyl) gamma-aminopropylmethyldiethoxysilane;

the epoxy resin is selected from one or more of organic silicon epoxy resin, acrylate epoxy resin and dimer acid epoxy resin;

the curing agent is selected from one or more of ethylenediamine, triethylamine, triethanolamine and diethylenetriamine.

A preparation method of a bacterial cellulose/boron nitride composite high-thermal-conductivity flexible film material comprises the following steps:

s01, heating and drying the boron nitride powder in a vacuum environment to obtain dry powder;

s02, adding a modifier into the dispersion liquid, adding the dried powder obtained in the step S01 after uniformly mixing, washing and filtering the mixture by using a mixed solution of deionized water and absolute ethyl alcohol after ultrasonic treatment and high-speed stirring, and finally freeze-drying the mixture to obtain modified boron nitride powder, wherein unsaturated groups on the surface of the modified boron nitride powder can be subjected to crosslinking reaction with bacterial cellulose and epoxy resin;

s03, blending the modified boron nitride powder obtained in the step S02 with deionized water dispersion liquid of bacterial cellulose, placing the mixture in a vacuum stirrer to be uniformly stirred to obtain a mixed solution of boron nitride and bacterial cellulose, and then performing solid-liquid separation in a vacuum filtration device to obtain a film structure;

s04, carrying out flat plate hot pressing on the film, carbonizing the bacterial cellulose at high temperature, greatly improving the heat conduction performance, simultaneously extruding redundant gas and eliminating gaps under the action of pressure, and constructing a heat conduction passage between boron nitride and the cellulose to obtain a high-performance heat conduction film;

s05, spraying a mixture of low-viscosity epoxy resin diluted by an organic solvent and a curing agent on the surface of the film, curing and crosslinking unsaturated groups on the heat-conducting surface of the boron nitride and the carbonized bacterial fiber and the epoxy resin after hot pressing, and improving the toughness of the heat-conducting film to obtain the high-heat-conductivity flexible heat-conducting composite material.

Further, in step S01, the boron nitride powder is placed in a vacuum drying oven, heated at 50-300 ℃ for 6-12 hours, and dried powder is obtained.

Further, in step S01, the particle size of the boron nitride powder filler is 0.5 to 30 μm. When the particle size of the filler is lower than the optimal value, the quantity of the filler in the same scale in the heat transfer path of the film is more, the formed two-phase interface is more, so that phonon scattering is serious, the heat-conducting property of the film is rapidly reduced, and meanwhile, the filler is difficult to fix in a three-dimensional network constructed by bacterial cellulose due to the over-small particle size, and the phenomenon of falling off is easy to generate; when the particle size of the filler is larger than the optimal value, the filler is easy to bend and fold in the stirring and dispersing process, and the film forming and heat conducting properties are affected.

Further, in step S02, the dispersion liquid is selected from one or more of deionized water, absolute ethyl alcohol, isopropyl alcohol, or acetone.

Further, in step S02, the modifier solution has a mass concentration of 2-10% and a pH of 7-10.

Further, in the step S02, the ultrasonic treatment time is 0.5-2 hours, the stirring time is 6-48 hours, the ultrasonic temperature is 20-40 ℃, the stirring temperature is 20-80 ℃, and the freeze drying time is 24-48 hours.

Further, in step S03, the bacterial cellulose has a diameter of 50-300 nm and a length of 20-100 μm. When the diameter of the bacterial cellulose is lower than the optimal value, the specific surface area is rapidly increased, the formed stereo network framework structure has serious phonon scattering, the heat conduction performance is obviously reduced, the mechanical strength is poor, and the prepared film is easy to generate defects such as fracture and the like. When the diameter of the bacterial cellulose is higher than the optimal value, winding and bending are easy to occur, and the heat-conducting property and the mechanical strength of the membrane are influenced.

Further, in step S03, the rotation speed of the vacuum mixer is 1800-2500 rpm, and the mixing time is 5-10 min.

Further, in step S03, the suction filtration membrane of the vacuum filtration device is a nylon membrane with a pore diameter of 0.5-15 μm, and the suction filtration time is 3-6 hours until the membrane completely removes the solution. When the aperture of the filter membrane is lower than the optimal value, the filtration rate is obviously reduced, the removal time of the prepared membrane solution is prolonged, and the center of the membrane is wet, the periphery of the membrane is dry and membrane wrinkles are caused; when the aperture of the filter membrane is higher than the optimal value, the aperture of the filter membrane is too large, although the filtration rate is obviously improved, the situation of losing boron nitride and cellulose solids exists, the bottom surface of the prepared membrane is uneven, and the defects are obvious.

Further, in step S04, the pressure of the flat plate hot pressing is 3-5 MPa, the temperature is 150-250 ℃, and the time is 0.5-5 h. When the pressure is lower than the optimal value, the gap is difficult to eliminate, the compactness of the film is influenced, and the heat conduction performance is obviously reduced; when the pressure is higher than the preferable value, the fiber structure is easily damaged, resulting in a decrease in thermal conductivity and mechanical strength. When the temperature is lower than the optimal value, the carbonization degree of the bacterial cellulose is not enough, and the heat conduction performance is influenced; when the temperature is higher than the preferred value, the boron nitride surface treating agent is easy to be pyrolyzed, so that the binding force between the epoxy resin sprayed in the subsequent step S05 and the boron nitride filler is poor, and the toughness of the film is influenced.

Further, in the step S05, the resin concentration of the low-viscosity epoxy resin diluted by the organic solvent is 5-25%, the spraying thickness is 10-100 μm, the hot pressing pressure is 1-3 MPa, the hot pressing temperature is 100-200 ℃, and the time is 0.5-6 h. When the concentration of the epoxy resin is lower than the optimal value, the surface spraying thickness fluctuation is easily caused, and the toughness of the heat-conducting film is greatly changed among different batches; when the concentration of the epoxy resin is higher than the optimal value, the viscosity is too high, so that the sprayed surface is uneven, and the surface of the heat-conducting film has mechanical defects.

Compared with the prior art, the bacterial cellulose/boron nitride composite high-thermal-conductivity flexible film material provided by the invention has the advantages that the boron nitride filler is subjected to surface modification treatment through the modifier, is uniformly dispersed and cross-linked in the bacterial cellulose dispersion liquid, and is further subjected to suction filtration to obtain a film; after hot pressing treatment, carbonizing the bacterial cellulose to greatly improve the heat-conducting property of the bacterial cellulose, eliminating film gaps, and constructing a heat-conducting passage between boron nitride and the carbonized bacterial cellulose to obtain a film with high heat-conducting property; the epoxy resin diluted by the organic solvent is uniformly sprayed on the surface of the heat-conducting film, and the epoxy resin reacts with unsaturated groups on the surfaces of the boron nitride and the carbonized bacterial cellulose for crosslinking through hot pressing treatment, so that the toughness and the mechanical property of the surface of the heat-conducting film are improved, and the bacterial cellulose/boron nitride composite high-heat-conductivity flexible film material is obtained.

Drawings

Fig. 1 is a schematic diagram of a preparation process of the bacterial cellulose/boron nitride composite high thermal conductive flexible film material of the invention, wherein: 1 is boron nitride, 2 is modified boron nitride, 3 is bacterial cellulose, 4 is carbonized bacterial cellulose, and 5 is epoxy resin.

FIG. 2 is a sectional SEM photograph of a sample of example 4.

Detailed Description

The invention provides a bacterial cellulose/boron nitride composite high-thermal-conductivity flexible film material and a preparation method thereof, and the following describes the specific embodiment of the invention in detail with reference to the attached drawings.

Example 1

S01, taking 100g of Boron Nitride (BN), wherein the average grain diameter is 10 mu m, and placing the Boron Nitride (BN) in a vacuum drying oven at 100 ℃ for drying for 12 hours;

s02, dissolving 0.484g of tris (hydroxymethyl) aminomethane buffer solution in a mixed solvent of 500mL of deionized water and 2.5g of absolute ethyl alcohol, adjusting the pH to 8.5, then adding 1.2g of dopamine hydrochloride, after uniform mixing, adding 3g of dried boron nitride, carrying out ultrasonic treatment for 1h, magnetically stirring for 24h at room temperature to promote the self-polymerization of dopamine molecules in the solution, carrying out suction filtration and deionized water washing for 3 times after the reaction is finished, and finally carrying out freeze drying for 12h to obtain modified boron nitride powder (BN @ PDA powder);

s03, preparing 25mL and 1mg/mL of Bacterial Cellulose (BC) deionized water solution, weighing 12.5mg of BN @ PDA powder, blending, stirring at 2000rpm for 5min in a vacuum stirrer to obtain uniform BN @ PDA/BC suspension, and performing vacuum filtration on a nylon membrane with the particle size of 5 microns for 3h to obtain a composite film material, wherein the average diameter of BC is 100nm, and the length of BC is 75 microns;

and S04, carrying out hot pressing treatment on the film in a double-sided heating flat plate hot press at the temperature of 200 ℃, the pressure of 5MPa and the hot pressing time of 10 min.

S05, uniformly spraying a mixture of low-viscosity organosilicon epoxy resin diluted by acetone and ethylenediamine on the surface of the film, wherein the ratio of the organosilicon epoxy resin to the ethylenediamine is 3:1, the concentration of the organosilicon epoxy resin is 8%, the spraying thickness is 20 micrometers, transferring the film into a hot press, the hot pressing pressure is 2MPa, the hot pressing temperature is 150 ℃, the time is 1h, and after the hot pressing is finished, taking out the film material by using a scraper and removing redundant resin to obtain the film material BN @ PDA/BC/EP.

In the BN @ PDA/BC/EP heat-conducting film material prepared in the embodiment, the mass of the BN @ PDA is 30% of the total mass of the heat-conducting film.

Example 2

S01, the method is the same as the embodiment 1;

s02, the method is the same as the embodiment 1;

s03, preparing 25mL and 1mg/mL BC deionized water solution, wherein the average diameter of BC is 100nm, the length of BC is 75 micrometers, weighing 25mg BN @ PDA powder, blending, stirring at 2000rpm for 5min in a vacuum stirrer to obtain uniform BN @ PDA/BC suspension, and performing vacuum filtration on a nylon membrane with the particle size of 5 micrometers for 3 hours to obtain a composite film material;

s04, the method is the same as the embodiment 1;

s05, the method is the same as the embodiment 1.

In the BN @ PDA/BC/EP heat-conducting film material prepared in the embodiment, the mass of the BN @ PDA is 40% of the total mass of the heat-conducting film.

Example 3

S01, the method is the same as the embodiment 1;

s02, the method is the same as the embodiment 1;

s03, preparing 25mL and 1mg/mL BC deionized water solution, wherein the average diameter of BC is 100nm, the length of BC is 75 micrometers, weighing 37.5mg BN @ PDA powder, blending, stirring in a vacuum stirrer at 2000rpm for 5min to obtain uniform BN @ PDA/BC suspension, and performing vacuum filtration on a nylon membrane with the particle size of 5 micrometers for 3h to obtain a composite film material;

s04, the method is the same as the embodiment 1;

s05, the method is the same as the embodiment 1.

In the BN @ PDA/BC/EP heat-conducting film material prepared in the embodiment, the mass of the BN @ PDA is 50% of the total mass of the heat-conducting film.

Example 4

S01, the method is the same as the embodiment 1;

s02, the method is the same as the embodiment 1;

s03, preparing 25mL and 1mg/mL BC deionized water solution, weighing 50mg BN @ PDA powder, blending, stirring at 2000rpm for 5min in a vacuum stirrer to obtain uniform BN @ PDA/BC suspension, and performing vacuum filtration on a nylon membrane with the particle size of 5 microns for 3h to obtain a composite film material, wherein the average diameter of BC is 100nm and the length of BC is 75 microns;

s04, the method is the same as the embodiment 1;

s05, the method is the same as the embodiment 1.

In the BN @ PDA/BC/EP heat-conducting film material prepared in the embodiment, the mass of the BN @ PDA is 60% of the total mass of the heat-conducting film.

FIG. 2 is a SEM image of a cross-section of a sample of example 4; as can be seen from fig. 2: the cross-linking effect of unmodified boron nitride and bacterial cellulose is poor, obvious gaps and boron nitride aggregates exist in the interior of the composite material, the boron nitride modified by dopamine is in a layer-by-layer regular arrangement structure in the in-plane direction of the composite material, and a tightly stacked heat conduction network is constructed by the boron nitride and the bacterial cellulose.

Comparative example 1

S01, placing 100g of boron nitride with the average grain diameter of 10 microns in a vacuum drying oven at 100 ℃ for drying for 12 hours;

s02, preparing 25mL and 1mg/mL BC deionized water solution, wherein the average diameter of BC is 100nm, the length of BC is 75 microns, weighing 12.5mg BN powder, blending, stirring in a vacuum stirrer at 2000rpm for 5min to obtain BN/BC suspension, and performing vacuum filtration on a nylon membrane with the particle size of 5 microns for 3h to obtain a composite film material;

s03, carrying out hot pressing treatment on the film at the temperature of 200 ℃ and under the pressure of 5MPa for 10 min;

s04, uniformly spraying a mixture of low-viscosity organic silicon epoxy resin diluted by acetone and ethylenediamine on the surface of the thin film, wherein the ratio of the organic silicon epoxy resin to the ethylenediamine is 3:1, the spraying thickness is 20 mu m, the hot pressing pressure is 1.5MPa, the hot pressing temperature is 150 ℃, the time is 3 hours, and after the hot pressing is finished, taking out the thin film material by using a scraper and removing redundant resin.

In the BN/BC/EP heat-conducting film material prepared by the comparative example, the mass of BN is 30 percent of the total mass of the heat-conducting film.

Comparative example 2

S01, the same as the comparative example 1;

s02, preparing 25mL and 1mg/mL BC deionized water solution, wherein the average diameter of BC is 100nm, the length of BC is 75 microns, weighing 25mg BN powder, blending, stirring in a vacuum stirrer at 2000rpm for 5min to obtain BN/BC suspension, and performing vacuum filtration on a nylon membrane with the particle size of 5 microns for 3h to obtain a composite film material;

s03, the method is the same as the comparative example 1;

s04. the same as in comparative example 1.

In the BN/BC/EP heat-conducting film material prepared by the embodiment, the mass of BN is 40 percent of the total mass of the heat-conducting film.

Comparative example 3

S01, the same as the comparative example 1;

s02, preparing 25mL and 1mg/mL BC deionized water solution, wherein the average diameter of BC is 100nm, the length of BC is 75 microns, weighing 37.5mg BN powder, blending, stirring in a vacuum stirrer at 2000rpm for 5min to obtain BN/BC suspension, and performing vacuum filtration on a nylon membrane with the particle size of 5 microns for 3h to obtain a composite film material;

s03, the method is the same as the comparative example 1;

s04. the same as in comparative example 1.

In the BN/BC/EP heat-conducting film material prepared by the embodiment, the mass of BN is 50 percent of the total mass of the heat-conducting film.

Comparative example 4

S01, the same as the comparative example 1;

s02, preparing 25mL and 1mg/mL BC deionized water solution, wherein the average diameter of BC is 100nm, the length of BC is 75 microns, weighing 50mg BN powder, blending, stirring in a vacuum stirrer at 2000rpm for 5min to obtain BN/BC suspension, and performing vacuum filtration on a nylon membrane with the particle size of 5 microns for 3h to obtain a composite film material;

s03, the method is the same as the comparative example 1;

s04. the same as in comparative example 1.

In the BN/BC/EP heat-conducting film material prepared by the embodiment, the mass of BN is 60 percent of the total mass of the heat-conducting film.

Comparative example 5

S01, placing 100g of boron nitride with the average grain diameter of 0.5 mu m in a vacuum drying oven at 100 ℃ for drying for 12 h;

s02, the method is the same as the embodiment 1;

s03, preparing 25mL and 1mg/mL BC deionized water solution, weighing 50mg BN @ PDA powder, blending, stirring at 2000rpm for 5min in a vacuum stirrer to obtain BN @ PDA/BC suspension, and performing vacuum filtration on a nylon membrane with the particle size of 1 micron for 3h to obtain a composite film material, wherein the average diameter of BC is 100nm and the length of BC is 75 microns;

s04, the method is the same as the embodiment 1;

s05, the method is the same as the embodiment 1.

In the BN @ PDA/BC/EP heat-conducting film material prepared in the embodiment, the mass of the BN @ PDA is 60% of the total mass of the heat-conducting film.

Comparative example 6

S01, placing 100g of boron nitride with the average grain diameter of 15 microns in a vacuum drying oven at 100 ℃ for drying for 12 hours;

s02, the method is the same as the embodiment 1;

s03, the method is the same as the embodiment 4;

s04, the method is the same as the embodiment 1;

s05, the method is the same as the embodiment 1.

In the BN @ PDA/BC/EP heat-conducting film material prepared in the embodiment, the mass of the BN @ PDA is 60% of the total mass of the heat-conducting film.

Comparative example 7

S01, placing 100g of boron nitride with the average grain diameter of 30 microns in a vacuum drying oven at 100 ℃ for drying for 12 hours;

s02, the method is the same as the embodiment 1;

s03, preparing 25mL and 1mg/mL BC deionized water solution, weighing 50mg BN @ PDA powder, blending, stirring at 2000rpm for 5min in a vacuum stirrer to obtain BN @ PDA/BC suspension, and performing vacuum filtration on a nylon membrane with the particle size of 15 microns for 4h to obtain a composite film material, wherein the average diameter of BC is 100nm and the length of BC is 75 microns;

s04, the method is the same as the embodiment 1;

s05, the method is the same as the embodiment 1.

In the BN @ PDA/BC/EP heat-conducting film material prepared in the embodiment, the mass of the BN @ PDA is 60% of the total mass of the heat-conducting film.

Comparative example 8

S01, the method is the same as the embodiment 1;

s02, dissolving 7g of 3-aminopropyltrimethoxysilane (KH-550) in 500mL of a solution of deionized water and ethanol 4:1, adding 15g of dried boron nitride powder, uniformly mixing, performing ultrasonic treatment for 1h, magnetically stirring for 6h at the temperature of 80 ℃, performing suction filtration and deionized water washing for 3 times after the reaction is finished, and finally performing freeze drying for 12h to obtain BN @ KH-550 powder;

s03, the method is the same as the embodiment 4;

s04, the method is the same as the embodiment 1;

s05, the method is the same as the embodiment 1.

In the heat-conducting film material prepared by the embodiment, the mass of BN @ KH-550/BC/EP is 60% of the total mass of the heat-conducting film.

Comparative example 9

S01, the method is the same as the embodiment 1;

s02, dissolving 5g of gamma-glycidoxypropyltrimethoxysilane (KH-560) in 500mL of deionized water, adding 15g of dried boron nitride powder, uniformly mixing, performing ultrasonic treatment for 1h, magnetically stirring for 8h at 70 ℃, performing suction filtration and deionized water washing for 3 times after reaction is finished, and finally performing freeze drying for 12h to obtain BN @ KH-560 powder;

s03, the method is the same as the embodiment 4;

s04, the method is the same as the embodiment 1;

s05, the method is the same as the embodiment 1.

In the BN @ KH560/BC/EP heat-conducting film material prepared in the embodiment, the mass of the BN @ KH-560 is 60 percent of the total mass of the heat-conducting film.

Comparative example 10

S01, the method is the same as the embodiment 1;

s02, dissolving 5g of gamma-mercaptopropyl-trimethoxysilane (KH-590) in 500mL of deionized water, adding 15g of dry boron nitride powder, uniformly mixing, performing ultrasonic treatment for 1h, magnetically stirring for 5h at 70 ℃, performing suction filtration and deionized water washing for 3 times after reaction is finished, and finally performing freeze drying for 12h to obtain BN @ KH-590 powder;

s03, the method is the same as the embodiment 4;

s04, the method is the same as the embodiment 1;

s05, the method is the same as the embodiment 1.

In the heat-conducting film material prepared by the embodiment, the mass of BN @ KH-590/BC/EP is 60 percent of the total mass of the heat-conducting film.

The thermal diffusivity alpha of the film was measured at 25 ℃ using a relaxation-resistant laser thermal conductivity meter (LFA467) and the in-plane thermal conductivity k ═ α × ρ × C was calculated_pWhere ρ is the density of the film, C_pIs the specific heat capacity of the film; and testing the corresponding tensile property of the film under different preparation conditions by using a tensile tester (BOS-200 NS).

The test results of the high thermal conductivity flexible film material prepared by the invention are shown in table 1.

Compared with the comparative examples 1 to 4, the modified BN @ PDA/BC/EP heat-conducting films in the examples 1 to 4 have higher heat conductivity and tensile strength. When the filling mass fraction is 60%, the thermal conductivity of the modified BN @ PDA is improved from 16.6W/m/K to 26.8W/m/K and the tensile strength is improved from 4.4MPa to 12.6MPa relative to the original BN composite material. The main reason is that dopamine is firstly self-polymerized into polydopamine, an aromatic structure of the polydopamine is interacted with BN through pi-pi bonds and van der Waals force to form a non-covalent bond combination with an internal structure of the BN, the compatibility between the BN and a BC solution is effectively improved, and simultaneously, the polydopamine and a functional group such as hydroxyl, carboxyl, amino and the like on the surface of the BC undergo dehydration condensation reaction to further weaken the thermal resistance of an interface and form a more efficient heat conduction path, and unsaturated groups on the surfaces of the BN and the BC further strengthen the curing crosslinking with epoxy resin, so that the thermal and mechanical properties of the composite material are remarkably improved. In addition, with the increase of the filling quality, the amplitude of the increase of the thermal conductivity is steadily increased, and the tensile strength is gradually reduced, mainly because the content of BN accumulated in the plane is a main factor determining the thermal conductivity of the film, and the proportion of BC influences the mechanical property of the composite material.

Example 4 compares with comparative examples 5-7 to find that, with the increase of the particle size of BN, the thermal conductivity and tensile strength of the composite material increase first and then decrease, when nano-grade BN is used, compared with BN with the particle size of 10 μm, the quantity of the filler in the heat transfer path of the film is increased, the number of formed two-phase interfaces is increased, so that phonon scattering is serious, the heat conductivity of the film is reduced rapidly, but the tensile strength is increased relatively, because the cross-linking between BC and BN is increased relatively, so that the mechanical property of the film is enhanced; when the particle size is increased to 30 μm, although the high length-diameter ratio filler is beneficial to forming a heat conduction network, the thermal resistance of the corresponding two-phase interface between large particles is increased, even obvious gaps are formed, interface defects are caused, and therefore the heat conduction performance and the mechanical performance of the film material are reduced.

Compared with the comparative examples 8-10, the embodiment 4 shows that, relatively speaking, the modification effect of dopamine is significantly higher than that of silane coupling agents, and the corresponding composite material has higher thermal conductivity and tensile strength, which are mainly attributed to the super-strong mussel adhesion characteristic of dopamine, and meanwhile, the dopamine is rich in a large amount of unsaturated groups, so that the interfacial bonding force of BN with BC and EP can be significantly improved, while the silane coupling agent generally has high requirements on reaction bonding conditions, and the organic functional group is only one of vinyl, epoxy or amino, is difficult to be fully crosslinked with BC, and has significantly lower interfacial bonding force than dopamine.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.