Polyimide core-shell microspheres prepared based on pickering emulsion method and application thereof

Abstract

The present application relates to a kind of based on Pickering emulsion method preparation heat-conducting filler-polyimide core-shell microspheres method, the method includes the following steps: aromatic diamine monomer is added with aromatic dianhydride monomer and organic polar solvent into reaction vessel and is reacted;Deposition in water, crush, wash and dry, to obtain polyamide acid salt precursor powder;Then with triethylamine and water stirring reaction, to obtain aqueous phase;Heat-conducting filler and hydrophobic polymer are dispersed in solvent to obtain oil phase;Oil phase and aqueous phase are mixed and emulsified, to obtain water-in-oil Pickering emulsion;Demulsification in precipitator, dry, to obtain heat-conducting filler-polyimide core-shell structure microspheres.The present application also provides the heat-conducting filler-polyimide core-shell microspheres prepared by the method, the method for preparing polyimide-based heat-conducting composite material using the core-shell microspheres and the composite material obtained therefrom.The present application method can efficiently prepare three-dimensional heat-conducting composite material with high thermal conductivity in horizontal and vertical directions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer-based composite materials, and specifically relates to a thermally conductive filler-polyimide core-shell microsphere prepared by using a water-in-oil type Pickering emulsion and application of the thermally conductive filler-polyimide core-shell microsphere in a thermally conductive composite material. BACKGROUND

[0002] In recent years, with the rapid progress of electronic integration technology, electronic devices gradually develop towards small size, high power and high integration, which brings convenience to people's work and life, but at the same time, it also puts forward higher requirements for the heat dissipation performance of materials. Insufficient heat dissipation and other factors such as heat accumulation are not conducive to maintaining the original power of electronic devices, deteriorating their use efficiency, and seriously affecting the service life of electronic devices.

[0003] In view of this problem, it is necessary to develop reasonable thermally conductive materials to solve the problem of heat accumulation, and effectively dissipate heat and regulate the temperature of the device, which plays a crucial role in maintaining the performance stability of electronic devices for a long time, prolonging the service life and enhancing the reliability of the device.

[0004] Polymers have good application prospects in thermally conductive materials due to their light weight, low density, low cost, high strength, corrosion resistance and easy processing. However, most polymers have low intrinsic thermal conductivity (0.2-0.5 W / m·K), which makes it difficult to directly apply them. Therefore, in order to broaden the application of thermally conductive polymers and their thermally conductive composites in the electronic field, it is necessary to improve their thermal conductivity.

[0005] In order to prepare polyimide-based thermally conductive composites with good thermal conductivity, many researchers have carried out in-depth research. At present, the most common method is to use high-thermal-conductivity thermally conductive fillers to blend modify common polymers. Although this method can improve the thermal conductivity of the composite material to a certain extent, simple physical blending is not conducive to the lapping of thermally conductive fillers to form a thermally conductive path, which in turn affects the efficiency of the thermally conductive fillers for the material. The introduction of low content of thermally conductive fillers will promote the composite material to exhibit a similar "island phase structure", at this time the thermally conductive carrier with high thermal conductivity will be covered by the polymer with low thermal conductivity, which is not conducive to the improvement of the overall performance of the material. Therefore, how to maintain high thermal conductivity at low filler content is an important issue.

[0006] CN117487334A discloses a boron nitride / polyethylene heat-conducting composite film and a specific preparation method thereof. The specific operation method is as follows: polyethylene material is chemically crosslinked, and the boron nitride is obtained by melt blending with the polyethylene material to obtain a polymer heat-conducting composite material. When the content of boron nitride nanosheet in the composite material is 30wt%, the thermal conductivity reaches 1.97W / m·K. Compared with the composite material prepared without chemical crosslinking (1.51W / m·K), the thermal conductivity has been improved to a certain extent.

[0007] CN117987957A discloses a heat-conducting polyimide film and a preparation method thereof. In the method, boron nitride and polyamide acid solution are prepared into a fiber film by electrospinning, and the fiber film is immersed in a PAA (polyamide acid) glue solution to obtain a heat-conducting film after immersion. The thermal conductivity of the heat-conducting film is 1.15W / m·K when the content of boron nitride is 15wt%.

[0008] At present, although some patents have realized the improvement of the heat-conducting performance of the material, most of the methods are still physical blending methods, and the improvement of the thermal conductivity of the material is limited.

[0009] In summary, a new technical solution is needed to obtain a high-thermal-conductivity composite material. Polyimide is a special engineering plastic with excellent high-temperature resistance, and the preparation of a polyimide composite material with certain heat-conducting capacity has great research space and application prospect in the heat dissipation field of electronic equipment. The preparation of core-shell microspheres with polyimide as the core and heat-conducting fillers as the shell is the best solution to improve the heat-conducting performance of the material. However, polyimide is usually dissolved in polar solvents such as N,N-dimethylformamide, and it is difficult to implement the preparation of core-shell microspheres through conventional solutions. In order to overcome the above-mentioned shortcomings, a new technical solution is needed. SUMMARY

[0010] In view of the problems existing in the prior art, the present application provides a heat-conducting filler-polyimide core-shell microsphere prepared based on a Pickering emulsion method and the application thereof in a heat-conducting composite material. Specifically, a water-in-oil Pickering emulsion is prepared to prepare emulsion droplets of heat-conducting fillers coated with a polymer, and the heat-conducting filler-polyimide core-shell microsphere with high thermal conductivity can be obtained after demulsification. Then, the core-shell microsphere is subjected to hot die pressing to obtain a polyimide-based heat-conducting composite material with a three-dimensional network.

[0011] In a first aspect, the present application provides a method for preparing a heat-conducting filler-polyimide core-shell microsphere based on a Pickering emulsion method, wherein the method comprises the following steps:

[0012] (1) adding aromatic diamine monomers and aromatic dianhydride monomers and an organic polar solvent into a reaction container to react, to obtain a polyamic acid solution;

[0013] (2) depositing the polyamic acid solution in water to obtain a precipitate, and then crushing, washing and drying the precipitate to obtain a polyamic acid salt precursor powder;

[0014] (3) adding the polyamic acid salt precursor powder, triethylamine and water into a reaction container to react, to obtain an aqueous polyamic acid salt solution as an aqueous phase;

[0015] (4) dispersing a thermally conductive filler and a hydrophobic polymer in a non-aqueous organic solvent to obtain an oil phase;

[0016] (5) mixing and emulsifying the oil phase and the aqueous phase to obtain a water-in-oil Pickering emulsion;

[0017] (6) transferring the water-in-oil Pickering emulsion into a precipitant to perform demulsification, to obtain a mixture powder;

[0018] (7) drying the mixture powder to obtain thermally conductive filler-polyimide core-shell structure microspheres.

[0019] The application provides in a second aspect a thermally conductive filler-polyimide core-shell microsphere prepared by the method according to the first aspect of the application.

[0020] The application provides in a third aspect a method for preparing a polyimide-based thermally conductive composite material with a three-dimensional network structure, which uses the thermally conductive filler-polyimide core-shell microsphere according to the second aspect of the application.

[0021] The application provides in a fourth aspect a polyimide-based thermally conductive composite material prepared by the method according to the third aspect of the application. The polyimide-based thermally conductive composite material has a 3D thermally conductive skeleton after hot die pressing, wherein the particle size of the core-shell microspheres is about 24 μm; the vertical thermal conductivity at room temperature is about 4.37 W / m·K; and the horizontal thermal conductivity is about 6.08 W / m·K.

[0022] Compared with the prior art, the application has the following advantages:

[0023] The application uses a water-in-oil Pickering emulsion method to prepare a thermally conductive filler-coated polyimide core-shell structure, which is more comprehensive, direct and efficient compared with a chemical plating layer or a chemical vapor deposition method.

[0024] The present application uses a polyamide acid salt solution as the water phase and an organic dispersion liquid containing large-particle-size heat-conductive fillers (the fillers with a size below 1 micron are generally used in the prior art) as the oil phase. The lipophilicity of the heat-conductive fillers is improved by adding a hydrophobic polymer, and the water-oil two-phase interface of the emulsion is improved by a high-speed emulsifier, so as to prepare a water-in-oil Pickering emulsion.

[0025] The method of the present application does not need to add any surfactant, and the water-oil two-phase balance is realized by modification of the particles, and the heat-conductive fillers can be wrapped on the surface of the aqueous droplets to form a water-in-oil structure.

[0026] The method of the present application can form a three-dimensional heat-conductive structure of the composite material by hot-pressing the core-shell microspheres, and the composite material exhibits excellent heat-conductive capacity in the vertical and horizontal directions of the material. The connection network of the heat-conductive fillers is promoted by the emulsion method to realize self-assembly, and the heat transfer in the material is better realized. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The droplet morphology of the Pickering emulsion obtained by observing under a polarizing microscope for Example 1.

[0028] Figure 2 The scanning electron microscope (SEM) image of the graphene-polyimide core-shell microspheres after demulsification for Example 1.

[0029] Figure 3 The scanning electron microscope (SEM) image of the cross section of the graphene / polyimide composite material after hot-pressing for Example 1. DETAILED DESCRIPTION

[0030] The detailed description set forth below will be better understood in conjunction with the appended drawings as follows:

[0031] The present application provides, in a first aspect, a method for preparing heat-conductive filler-polyimide core-shell microspheres based on a Pickering emulsion method, wherein the method comprises the following steps:

[0032] (1) aromatic diamine monomers and aromatic dianhydride monomers are added to a reaction container to react with an organic polar solvent to obtain a polyamide acid solution;

[0033] (2) the polyamide acid solution is deposited in water to obtain a precipitate, and then the precipitate is crushed, washed and dried to obtain a polyamide acid salt precursor powder;

[0034] (3) the polyamide acid salt precursor powder, triethylamine and water are added to a reaction container to react to obtain a water-based polyamide acid salt solution as the water phase;

[0035] (4) dispersing the thermally conductive filler and the hydrophobic polymer in a non-aqueous organic solvent to obtain an oil phase;

[0036] (5) mixing the oil phase and the water phase, and emulsifying to obtain a water-in-oil Pickering emulsion;

[0037] (6) transferring the water-in-oil Pickering emulsion into a precipitant to break the emulsion to obtain a mixture powder;

[0038] (7) drying the mixture powder to obtain the thermally conductive filler-polyimide core-shell structure microspheres.

[0039] In step (1), the aromatic diamine monomer can be dissolved in the organic polar solvent and the aromatic dianhydride monomer is added into the reaction vessel for reaction under stirring to obtain a polyamic acid solution.

[0040] In step (2), the polyamic acid solution can be poured into water (such as deionized water) to deposit a white filamentous object, which is crushed, washed, and dried to obtain a polyamic acid salt precursor powder.

[0041] In step (3), the polyamic acid salt precursor powder, triethylamine, and deionized water can be added into a reaction vessel and stirred uniformly to obtain an aqueous polyamic acid salt solution (as a water phase).

[0042] In step (4), the thermally conductive filler and the hydrophobic polymer can be dispersed in the water-insoluble organic solvent (i.e. non-aqueous organic solvent) to obtain an oil phase.

[0043] In step (5), the oil phase and the water phase can be mixed and emulsified by, for example, a high-speed emulsifier to obtain a water-in-oil (W / O) Pickering emulsion.

[0044] In some preferred embodiments, the aromatic diamine is selected from one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, and a mixture of water-soluble aromatic diamines, and more preferably is 4,4'-diaminodiphenyl ether. It is additionally preferred that the water-soluble aromatic diamine is selected from one or more of p-phenylenediamine, m-phenylenediamine, and o-phenylenediamine.

[0045] Some specific examples of the aromatic diamine have the following structural formulae:

[0046]

[0047] In the case where the aromatic diamine is a water-soluble aromatic diamine, the above steps (1) to (3) can also be performed by adding water to a reactor, then directly dissolving a water-soluble aromatic diamine monomer in the water in the reactor, and then adding an aromatic dianhydride monomer and triethylamine to the reaction vessel to continue the reaction, to obtain a water-based polyamic acid salt solution (as an aqueous phase). Preferably, the mass ratio of the water-soluble aromatic diamine to triethylamine is 1:1 to 3:1, more preferably 2:1 to 3:1. It is further preferable to control the solid content of the water-based polyamic acid solution to be 5 to 20 wt%, as described below.

[0048] In other preferred embodiments, the aromatic dianhydride is selected from a mixture of one or more of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, pyromellitic dianhydride, and hydrogenated pyromellitic dianhydride, more preferably 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride.

[0049] Some specific examples of the aromatic diamine have the structural formula shown below:

[0050]

[0051] In other preferred embodiments, the organic polar solvent is selected from a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0052] In other preferred embodiments, the thermally conductive filler is selected from a mixture of one or more of graphite, graphite nanoplatelets (GNP), multi-walled carbon nanotubes (MWCNTs), graphene oxide (GO), hexagonal boron nitride (hBN), aluminum oxide (AI2O3), silicon carbide (SiC), and a metallic thermally conductive filler.

[0053] Preferably, the metallic thermally conductive filler is a metallic nanoparticle and / or a low-melting-point alloy. More preferably, the metallic nanoparticle is selected from a mixture of one or more of silver nanoparticles, copper nanoparticles, nickel nanoparticles, and iron nanoparticles, and / or the low-melting-point alloy is a tin-bismuth alloy and / or a liquid metal having a melting point of 20-50°C.

[0054] More preferably, the graphite or boron nitride (e.g., hexagonal boron nitride) has a plate diameter of 0.5 to 10 pm.

[0055] Further more preferably, the graphite nanoplatelet has a plate diameter of 2 pm to 10 pm and a thickness of 1 nm to 5 nm.

[0056] Further more preferably, the graphene oxide has a plate diameter of 2 pm to 20 pm;

[0057] It is further preferred that the multi-walled carbon nanotube or silicon carbide has a size of 2 μm to 10 μm and a diameter of 10-50 nm; and the alumina (e.g. spherical alumina) has a diameter of 0.5-10 μm.

[0058] In some preferred embodiments, the hydrophobic polymer is selected from a mixture of one or more of decaglycerol, dodecanol, hexadecanol, undecanoic acid, dodecylamine, hexadecylamine, and octadecylamine, preferably hexadecylamine or octadecylamine.

[0059] In some preferred embodiments, the non-aqueous organic solvent is selected from a mixture of one or more of n-hexane, cyclohexane, toluene, xylene, dichloromethane, and trichloromethane, preferably xylene.

[0060] In some preferred embodiments, the precipitant is (1) a mixture of triethylamine, acetic anhydride, and ethanol; (b) a mixture of pyridine, acetic anhydride, and ethanol; or (c) a mixture of pyridine, acetic anhydride, and glacial acetic acid. Preferably, the mass ratio of the mixture is 1:2:(20-50) in the order of the components as above.

[0061] Preferably, in step (1), the solid content of the polyamic acid solution is controlled to be 5 wt% to 20 wt%.

[0062] More preferably, in step (2), the washing uses a washing solution selected from a mixture of one or more of water, ethanol, and isopropanol.

[0063] More preferably, in step (2), the drying temperature is 40°C to 70°C, and the drying time is 6 h to 48 h.

[0064] More preferably, in step (3), the mass ratio of the polyamic acid salt precursor powder to triethylamine is 1:1 to 3:1, and further preferably 2:1 to 3:1.

[0065] More preferably, in step (3), the mass ratio of water to the precursor powder is 100:1 to 5:1, and more preferably 20:1 to 5:1.

[0066] More preferably, in step (3), the stirring speed is 500-1500 rpm, the stirring time is 6 h to 24 h, and the reaction temperature is room temperature.

[0067] More preferably, in step (4), the addition concentration of the hydrophobic polymer in the oil phase is 10 mM to 26 mM, and more preferably 16 mM to 22 mM.

[0068] More preferably, in step (4), the content of the thermally conductive filler is 5wt% to 50wt% of the total amount of the thermally conductive filler and the hydrophobic polymer.

[0069] More preferably, in step (5), the volume ratio of the oil phase to the water phase is 1.5:1-20:1, more preferably 1.5:1-3:1.

[0070] More preferably, in step (5), the emulsification is carried out in an emulsifier, preferably at a speed of 10000rpm to 20000rpm, more preferably at a speed of 12000rpm to 18000rpm.

[0071] More preferably, in step (7), the temperature of the drying is 60℃ to 100℃, preferably 60℃ to 80℃, and the drying time of the drying is 2h to 30h.

[0072] The present application uses a polyamide acid salt aqueous solution as the water phase in the emulsion and forms a core structure, uses a thermally conductive filler as the oil phase in the emulsion and forms a shell structure, adds a hydrophobic polymer for interface adjustment, mixes the oil phase and the water phase, emulsifies them in a homogenizer, obtains a Pickering emulsion, and then uses the Pickering emulsion to obtain the thermally conductive filler-polyimide core-shell microspheres through demulsification.

[0073] However, in step (3), the method of the present application is not only limited to water-based polyimide salts, but is also applicable to other water-soluble polymers. The water-soluble polymers include but are not limited to polyvinyl alcohol, polyvinylpyrrolidone, water-based epoxy resin, water-based polyurethane, water-based acrylic resin, cellulose nanofiber, and other polymers. The preparation of these polymers is also applicable to the method of the present application.

[0074] The present application provides, in a second aspect, a thermally conductive filler-polyimide core-shell microsphere prepared by the method according to the first aspect of the present application.

[0075] The present application provides, in a third aspect, a method for preparing a polyimide-based thermally conductive composite material with a three-dimensional network structure, which uses the thermally conductive filler-polyimide core-shell microsphere according to the second aspect of the present application.

[0076] In some preferred embodiments, the method is carried out by placing the thermally conductive filler-polyimide core-shell microsphere in a vacuum hot press for hot molding to obtain the polyimide-based thermally conductive composite material with a three-dimensional network structure.

[0077] In some more preferred embodiments, the hot die pressing is performed by preheating for 15 min, then adjusting the oil jack to pressurize to 0.5 MPa to 20 MPa, and maintaining the pressure for 15 min to 25 min (e.g., 20 min).

[0078] In some preferred embodiments, the hot pressing temperature of the hot die pressing is 300℃ to 380℃; and / or the pressure in the vacuum chamber of the vacuum hot pressing machine is less than 10 Pa.

[0079] Alternatively, when the water-based polyimide salt is replaced by other water-soluble polymers (such as polyvinyl alcohol, polyvinylpyrrolidone, water-based epoxy resin, water-based polyurethane, water-based acrylic resin, cellulose nanofiber), the hot pressing temperature is 150℃-250℃.

[0080] In a fourth aspect, the present application provides a polyimide-based thermal conductive composite material prepared by the method according to the third aspect of the present application. The polyimide-based thermal conductive composite material has a 3D thermal conductive skeleton after hot die pressing, wherein the particle size of the core-shell microspheres can reach about 24 μm; the vertical thermal conductivity at room temperature can reach about 4.37 W / m·K; and the horizontal thermal conductivity can reach about 6.08 W / m·K.

[0081] Examples

[0082] In order to better understand the present application, the following examples further illustrate the content of the present application, but the content of the present application is not limited only to the following examples.

[0083] Example 1: Preparation of graphene-polyimide core-shell microspheres and thermal conductive composite material with a mass fraction of about 30wt%

[0084] 20.023g (100mmol) of 4,4'-diamino diphenyl ether (ODA) and 455.805g of N,N-dimethylacetamide (DMAc) were weighed into a 1L three-necked flask, the three-necked flask was connected to a nitrogen inlet, and stirring was continued at a stirring speed of 1000r / min for 30min until the added 4,4'-diamino diphenyl ether was completely dissolved. Then 31.022g (100mmol) of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA) was added to the solution, the stirring speed was the same as above, and the reaction temperature was controlled at 20℃, and stirring was continued for 12h to ensure complete reaction of ODA and ODPA, obtaining a polyamic acid solution with a solid content of 10wt%. The polyamic acid solution was deposited in deionized water, and white filaments were precipitated, which were crushed by a solid crusher at a speed of 10000r for 2min to obtain a solid powder. The solid powder was washed with 2L deionized water and 2L ethanol in turn, and then dried in a hot air oven at 50℃ for 24h to obtain a polyamic acid salt precursor powder.

[0085] Take 1 g of polyamide acid salt precursor powder and 0.476 g of triethylamine dissolved in 10 g of deionized water to prepare a polyamide acid salt solution as the water phase in the emulsion. Take 0.40 g of graphene (average particle size 8.2 μm) and 0.057 g (16 mM) of hexadecylamine dispersed in 15 ml of dimethylbenzene as the oil phase in the emulsion. Add the oil phase to the water phase and homogenize in a high-speed homogenizer at 13000 rpm for 2 minutes to obtain a water-in-oil Pickering emulsion (as shown in Figure 1 Add 0.5 g of pyridine, 1 g of acetic anhydride and 10 g of ethanol to the Pickering emulsion to induce chemical imidization of the polyamide acid salt, and after washing and suction filtration of the deposited solid filler, graphene-polyimide core-shell microspheres with a particle size of about 24 μm are obtained (as shown in Figure 2

[0086] Take the graphene-polyimide core-shell microspheres described above and place them in a hot mold, and place the hot mold on a vacuum hot press, set the temperature to 320°C, control the internal pressure of the vacuum chamber to be less than 10 Pa, preheat for 15 min, adjust the oil pressure jack to pressurize the material to 2 MPa, and after holding for 20 min, cool to room temperature, and take out to obtain graphene / polyimide thermal conductive composite material 1.27 g (as shown in Figure 3

[0087] The vertical thermal conductivity and horizontal thermal conductivity of the composite material are 4.37 and 6.08 W / m·K, respectively, when the graphene content is 31.5 wt%.

[0088] Example 2: Preparation of graphene-polyimide core-shell microspheres and thermal conductive composite material with a mass fraction of about 10 wt%

[0089] The same method as in Example 1 is used, except that the graphene content is about 10 wt%. Specifically, in this embodiment, other conditions remain unchanged, and only the amount of graphene (average particle size 8.2 μm) added is changed to 0.09 g, and the final mass of the composite material is 0.91 g. The vertical thermal conductivity and horizontal thermal conductivity of the composite material are 0.97 and 1.35 W / m·K, respectively, when the graphene content is 9.89 wt%.

[0090] Example 3: Preparation of graphene-polyimide core-shell microspheres and thermal conductive composite material with a mass fraction of about 20 wt%

[0091] ​​The same method as in Example 1 was used, except that the graphene content was about 20 wt%. Specifically, the graphene (average particle size 8.2 pm) was added in an amount of 0.2 g, and the final mass of the composite material was 1.02 g. The vertical thermal conductivity and the horizontal thermal conductivity of the composite material were 2.44 and 3.39 W / m-K, respectively, when the graphene content was 19.6 wt%.

[0092] Example 4: Preparation of Alumina / Polyimide Core-Shell Microspheres and Thermally Conductive Composite Material

[0093] An amount of 20.023 g (100 mmol) of 3,4'-diaminophenyl ether and 444.996 g of N,N-dimethylacetamide (DMAc) were added to a 1 L three-necked flask, the three-necked flask was connected to a nitrogen inlet, and stirring was continued at a speed of 1000 r / min for 30 min until the added 3,4'-diaminophenyl ether was completely dissolved. Then, 29.421 g (100 mmol) of 3,3',4,4'-biphenyl tetracarboxylic dianhydride (s-BPDA) was added to the solution, the stirring speed was the same as above, the reaction temperature was controlled at 20°C, and stirring was continued for 12 h to make the 3,4'-diaminophenyl ether and s-BPDA react completely, obtaining a polyamic acid solution with a solid content of 10 wt%. The polyamic acid solution was deposited in deionized water to precipitate white filaments, which were crushed by a solid crusher at a speed of 10000 r for 2 min to obtain a solid powder. The solid powder was sequentially washed with 2 L of deionized water and 2 L of ethanol, and then dried in a hot air oven at 50°C for 24 h to obtain a polyamic acid salt precursor powder.

[0094] An amount of 1 g of the polyamic acid salt precursor powder and 0.476 g of triethylamine were dissolved in 10 g of deionized water to prepare a polyamic acid salt solution as the aqueous phase in the emulsion. An amount of 0.40 g of alumina (average size 2.5 pm) and 0.028 g (10 mM) of dodecanol were dispersed in 15 ml of xylene to prepare an oil phase in the emulsion. The oil phase was added to the aqueous phase, and homogenized in a high-speed homogenizer at 13000 rpm for 2 min to obtain a water-in-oil Pickering emulsion. To the Pickering emulsion, 0.5 g of pyridine and 1 g of acetic anhydride and 10 g of ethanol were added to cause chemical imidization of the polyamic acid salt, and the precipitated solid filler was washed with water and alcohol, and then suction filtered to obtain alumina / polyimide core-shell microspheres.

[0095] The above alumina / polyimide core-shell microspheres were placed in a hot mold, and the hot mold was placed on a vacuum hot press, the temperature was set to 320°C, the internal pressure of the vacuum chamber was controlled to be less than 10 Pa, after preheating for 15 min, the oil pressure jack was adjusted, and the material was pressurized to 2 MPa, and after holding for 20 min, it was cooled to room temperature, and then 1.26 g of alumina / polyimide thermal conductive composite material was obtained.

[0096] The composite material has a vertical thermal conductivity of 2.44 W / m·K and a horizontal thermal conductivity of 2.92 W / m·K when the content of alumina is 31.7 wt%.

[0097] Example 5: Preparation of boron nitride / polyimide core-shell microspheres and thermal conductive composite material

[0098] 20.023 g (100 mmol) of 4,4'-diamino diphenyl ether and 376.515 g of N,N-dimethylacetamide (DMAc) were weighed into a 1 L three-necked flask, the three-necked flask was connected to a nitrogen inlet, and the stirring speed was 1000 r / min. The stirring was continued for 30 min until the 4,4'-diamino diphenyl ether was completely dissolved. Then 21.812 g (100 mmol) of pyromellitic anhydride (PMDA) was added to the solution, the stirring speed was the same as above, and the reaction temperature was controlled at 20°C. The stirring was continued for 12 h to ensure the completion of the reaction, and a polyamide acid solution with a solid content of 10 wt% was obtained. The polyamide acid solution was deposited in deionized water for a period of time, and white filaments were precipitated. After being crushed by a solid crusher at 10000 r / min for 2 min, a solid powder was obtained. The solid powder was washed with 2 L of deionized water and 2 L of ethanol, respectively, and then dried in a hot air oven at 50°C for 24 h to obtain a polyamide acid salt precursor powder.

[0099] 1 g of polyamide acid salt precursor powder and 0.476 g of triethylamine were dissolved in 10 g of deionized water to prepare a polyamide acid salt solution as the aqueous phase in the emulsion. 0.2 g of boron nitride (average particle size 3.4 μm) and 0.068 g (10 mM) of decaglycerol were dispersed in 15 ml of cyclohexane to prepare an oil phase in the emulsion. The oil phase was added to the aqueous phase, and homogenized in a high-speed homogenizer at 13000 rpm for 2 min to obtain a water-in-oil Pickering emulsion. To the Pickering emulsion, 0.5 g of pyridine and 1 g of acetic anhydride were added to promote the chemical imidization of the polyamide acid salt, and 10 g of ethanol was added to obtain boron nitride / polyimide core-shell microspheres.

[0100] The above boron nitride / polyimide core-shell microspheres were placed in a hot mold, and the hot mold was placed on a vacuum hot press, the temperature was set to 400°C, the internal pressure of the vacuum chamber was controlled to be less than 10 Pa, after preheating for 15 min, the oil pressure jack was adjusted, and the material was pressurized to 2 MPa, and after holding for 20 min, it was cooled to room temperature, and then 1.04 g of boron nitride / polyimide thermal conductive composite material was obtained.

[0101] The composite material has a vertical thermal conductivity of 1.78 W / m·K and a horizontal thermal conductivity of 2.67 W / m·K when the content of boron nitride is 19.2 wt%.

[0102] Example 6: Preparation of multi-walled carbon nanotube / polyimide core-shell microspheres and thermal conductive composite material

[0103] 20.023 g (100 mmol) of 4,4'-diamino diphenyl ether and 455.805 g of N,N-dimethylacetamide (DMAc) were weighed into a 1 L three-necked flask, the three-necked flask was connected to a nitrogen inlet, and stirring was continued at a speed of 1000 r / min for 30 min until the added 4,4'-diamino diphenyl ether was completely dissolved. Then 31.022 g (100 mmol) of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA) was added to the solution, the stirring speed was the same as above, and the reaction temperature was controlled at 20°C, and the stirring was continued for 12 h to ensure the completion of the reaction, and a polyamide acid solution with a solid content of 10 wt% was obtained. The polyamide acid solution was deposited in deionized water for a period of time, and white filaments were precipitated, which were ground into a solid powder after 10000 r / min for 2 min by a solid grinder. The solid powder was washed with 2 L of deionized water and 2 L of ethanol in turn, and then dried in a hot air oven at 50°C for 24 h to obtain a polyamide acid salt precursor powder.

[0104] 1 g of polyamide acid salt precursor powder and 0.476 g of triethylamine were dissolved in 10 g of deionized water to prepare a polyamide acid salt solution as the aqueous phase in the emulsion. 0.2 g of multi-walled carbon nanotubes (average size 7.4 μm) and 0.068 g (10 mM) of decaglycerol were dispersed in 15 ml of cyclohexane to serve as the oil phase in the emulsion. The oil phase was added to the aqueous phase, and homogenized in a high-speed homogenizer at 13000 rpm for 2 min to obtain a water-in-oil Pickering emulsion. To the Pickering emulsion, 0.5 g of pyridine and 1 g of acetic anhydride were added to promote the chemical imidization of the polyamide acid salt, and 10 g of ethanol was added to obtain multi-walled carbon nanotube / polyimide core-shell microspheres after water washing, alcohol washing and suction filtration of the deposited solid filler.

[0105] Take the multi-walled carbon nanotube / polyimide core-shell microspheres into the hot mold, and place the hot mold on the vacuum hot press, set the temperature to 340℃, control the internal pressure of the vacuum chamber to be less than 10Pa, preheat for 15min, adjust the oil jack, pressurize the material to 2MPa, keep the temperature and pressure for 20min, and then cool to room temperature. Take out the boron nitride / polyimide thermal conductive composite 1.02g.

[0106] The vertical thermal conductivity and horizontal thermal conductivity of the composite are 2.72 and 3.80 W / m·K respectively when the content of multi-walled carbon nanotubes is 19.6wt%.

[0107] Example 7: Preparation of silicon carbide / polyimide core-shell microspheres and thermal conductive composite

[0108] The same method as in Example 1 is basically adopted, except that the thermal conductive filler is silicon carbide (average particle size 6.7μm); in this example, other conditions remain unchanged, only the thermal conductive filler is changed to silicon carbide, and finally the mass of the composite material is 1.26g. The vertical thermal conductivity and horizontal thermal conductivity of the composite are 2.93 and 3.51 W / m·K respectively when the content of silicon carbide is 31.7wt%.

[0109] Example 8: Preparation of graphene-polyimide core-shell microspheres and thermal conductive composite

[0110] The same method as in Example 1 is basically adopted, except that the hydrophobic polymer is octadecylamine; in this example, other conditions remain unchanged, only the hydrophobic polymer is changed to 0.064g (16mM) octadecylamine, and finally the mass of the composite material is 1.29g. The vertical thermal conductivity and horizontal thermal conductivity of the composite are 4.26 and 5.72 W / m·K respectively when the content of graphene is 31.0wt%.

[0111] Example 9: Preparation of graphene-polyimide core-shell microspheres and thermal conductive composite

[0112] The same method as in Example 1 is basically adopted, except that the hydrophobic polymer is undecylic acid; in this example, other conditions remain unchanged, only the hydrophobic polymer is changed to add 0.047g (16mM) undecylic acid, and finally the mass of the composite material is 1.30g. The vertical thermal conductivity and horizontal thermal conductivity of the composite are 4.21 and 5.47 W / m·K respectively when the content of graphene is 30.7wt%.

[0113] Example 10: Preparation of graphene-polyimide core-shell microspheres and thermal conductive composite

[0114] The same method as in Example 1 was used, except that the concentration of the hydrophobic polymer was changed to 10 mM; and the mass of the final composite material was 1.29 g. The vertical and horizontal thermal conductivities of the composite material were 3.25 and 4.55 W / m-K, respectively, when the content of graphene was 31.0 wt%.

[0115] Example 11: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0116] The same method as in Example 1 was used, except that the concentration of the hydrophobic polymer was changed to 12 mM; and the mass of the final composite material was 1.32 g. The vertical and horizontal thermal conductivities of the composite material were 3.58 and 5.01 W / m-K, respectively, when the content of graphene was 30.3 wt%.

[0117] Example 12: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0118] The same method as in Example 1 was used, except that the concentration of the hydrophobic polymer was changed to 30 mM; and the mass of the final composite material was 1.31 g. The vertical and horizontal thermal conductivities of the composite material were 3.53 and 5.08 W / m-K, respectively, when the content of graphene was 30.5 wt%.

[0119] Example 13: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0120] The same method as in Example 1 was used, except that the concentration of the hydrophobic polymer was changed to 40 mM; and the mass of the final composite material was 1.34 g. The vertical and horizontal thermal conductivities of the composite material were 3.13 and 4.51 W / m-K, respectively, when the content of graphene was 29.8 wt%.

[0121] Example 14: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0122] The same method as in Example 1 was used, except that the concentration of the hydrophobic polymer was changed to 50 mM; and the mass of the final composite material was 1.37 g. The vertical and horizontal thermal conductivities of the composite material were 2.77 and 3.88 W / m-K, respectively, when the content of graphene was 29.1 wt%.

[0123] Example 15: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0124] The same method as in Example 1 was used, except that the ratio of oil phase to water phase was controlled to be 2:1; only the solvent in the oil phase was changed to 20 ml, and other conditions were unchanged; finally, the mass of the composite material was 1.31 g. The vertical thermal conductivity and horizontal thermal conductivity of the composite material were 3.87 and 5.41 W / m·K, respectively, when the content of graphene was 30.5 wt%.

[0125] Example 16: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0126] The same method as in Example 1 was used, except that the ratio of oil phase to water phase was controlled to be 4:1; only the solvent in the oil phase was changed to 40 ml, and other conditions were unchanged; finally, the mass of the composite material was 1.35 g. The vertical thermal conductivity and horizontal thermal conductivity of the composite material were 3.25 and 4.62 W / m·K, respectively, when the content of graphene was 29.6 wt%.

[0127] Example 17: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0128] The same method as in Example 1 was used, except that the ratio of oil phase to water phase was controlled to be 6:1; only the solvent in the oil phase was changed to 60 ml, and other conditions were unchanged; finally, the mass of the composite material was 1.32 g. The vertical thermal conductivity and horizontal thermal conductivity of the composite material were 2.75 and 3.91 W / m·K, respectively, when the content of graphene was 30.3 wt%.

[0129] Example 18: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0130] The same method as in Example 1 was used, except that the ratio of oil phase to water phase was controlled to be 8:1; only the solvent in the oil phase was changed to 80 ml, and other conditions were unchanged; finally, the mass of the composite material was 1.34 g. The vertical thermal conductivity and horizontal thermal conductivity of the composite material were 2.41 and 3.42 W / m·K, respectively, when the content of graphene was 29.8 wt%.

[0131] Example 19: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0132] The same method as in Example 1 was used, except that the ratio of oil phase to water phase was controlled to be 9:1; only the solvent in the oil phase was changed to 90 ml, and other conditions were unchanged; finally, the mass of the composite material was 1.37 g. The vertical thermal conductivity and horizontal thermal conductivity of the composite material were 2.04 and 2.86 W / m·K, respectively, when the content of graphene was 29.1 wt%.

[0133] Example 20: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0134] The same method as in Example 1 was used, except that the ratio of the oil phase to the water phase was controlled to be 10:1; only the solvent in the oil phase was changed to 100 ml, and other conditions were unchanged; and finally the mass of the composite material was 1.39 g. When the content of graphene in the composite material was 28.7 wt%, the vertical thermal conductivity and the horizontal thermal conductivity were 1.88 and 2.67 W / m·K, respectively.

[0135] Comparative Example 1: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0136] 20.023 g (100 mmol) of 4,4'-diamino diphenyl ether and 455.805 g of N,N-dimethylacetamide (DMAc) were weighed into a 1 L three-necked flask, the three-necked flask was connected to a nitrogen inlet, and stirring was continued at a speed of 1000 r / min for 30 min until the 4,4'-diamino diphenyl ether was completely dissolved. Then 31.022 g (100 mmol) of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA) was added to the solution, the stirring speed was the same as above, and the reaction temperature was controlled at 20°C, and stirring was continued for 12 h to allow the two to react fully, obtaining a polyamic acid solution with a solid content of 10 wt%. The polyamic acid solution was deposited in deionized water, and white filaments were precipitated, which were crushed by a solid crusher at a speed of 10000 r for 2 min to obtain a solid powder. The solid powder was washed with 2 L of deionized water and 2 L of ethanol in turn, and then dried in a hot air oven at 50°C for 24 h to obtain a polyamic acid salt precursor powder.

[0137] 1 g of the polyamic acid salt precursor powder was taken and mixed with 0.40 g of graphene in 500 ml of ethanol for 30 min to obtain a liquid mixture. The liquid mixture was filtered, washed with water and alcohol to obtain a graphene / polyamic acid salt mixed powder.

[0138] The mixed powder was placed in a hot mold, and the hot mold was placed on a vacuum hot press, the temperature was set to 320°C, the internal pressure of the vacuum chamber was controlled to be less than 10 Pa, preheating was performed for 15 min, then the oil pressure jack was adjusted to pressurize the material to 2 MPa, and after 20 min of heat preservation and pressure, it was cooled to room temperature, and then taken out to obtain a graphene / polyimide thermally conductive composite material 1.23 g.

[0139] When the content of graphene in the composite material was 32.5 wt%, the vertical thermal conductivity and the horizontal thermal conductivity were 1.62 and 2.17 W / m·K, respectively.

[0140] Comparative Example 2

[0141] The same method as in Comparative Example 1 was used, except that the content of graphene in the composite material was about 10%. The results of the determination are shown in Table 1.

[0142] Comparative Example 3

[0143] The same method as in Comparative Example 1 was used, except that the content of graphene in the composite material was about 20%. The results of the determination are shown in Table 1.

[0144] The present inventors compared the amount of thermally conductive filler (graphene) and the vertical and horizontal thermal conductivities in Examples 1 to 3 and Comparative Examples 1 to 3, and the results are shown in Table 2.

[0145] Comparative Example 4: Preparation of graphene-polyimide core-shell microspheres and thermally conductive composite material

[0146] 20.023 g (100 mmol) of 4,4'-diamino diphenyl ether, 455.805 g of N,N-dimethylacetamide (DMAc) were weighed into a 1 L three-necked flask, the three-necked flask was connected to a nitrogen inlet, and stirring was continued at 1000 r / min for 30 min until the added 4,4'-diamino diphenyl ether was completely dissolved. Then 31.022 g (100 mmol) of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA) was added to the solution, the stirring speed was the same as above, and the reaction temperature was controlled at 20°C, and stirring was continued for 12 h to make the ODA and ODPA react completely, to obtain a polyamic acid solution with a solid content of 10 wt%. The polyamic acid solution was deposited in deionized water, and white filaments were precipitated, which were crushed by a solid crusher at a speed of 10000 r for 2 min to obtain a solid powder. The solid powder was washed with 2 L of deionized water and 2 L of ethanol in turn, and then dried in a hot air oven at 50°C for 24 h to obtain a polyamic acid salt precursor powder.

[0147] 1 g of polyamic acid salt precursor powder and 0.476 g of triethylamine were dissolved in 10 g of deionized water to prepare a polyamic acid salt solution as the aqueous phase in the emulsion. 0.40 g of graphene (average size 800 nm) and 0.057 g (16 mM) of hexadecylamine were dispersed in 15 ml of dimethylbenzene to prepare an oil phase in the emulsion. The oil phase was added to the aqueous phase, and homogenized in a high-speed homogenizer at 13000 rpm for 2 min to obtain a water-in-oil Pickering emulsion. 0.5 g of pyridine, 1 g of acetic anhydride and 10 g of ethanol were added to the Pickering emulsion to cause chemical imidization of the polyamic acid salt, and the deposited solid filler was washed with water and alcohol, and then suction filtered to obtain graphene-polyimide core-shell microspheres.

[0148] The graphene-polyimide core-shell microspheres described above were placed in a hot mold, and the hot mold was placed on a vacuum hot press, the temperature was set to 320℃, the internal pressure of the vacuum chamber was controlled to be less than 10Pa, after preheating for 15min, the oil pressure jack was adjusted, and the material was pressurized to 2MPa, after holding for 20min, it was cooled to room temperature, and then graphene / polyimide thermal conductive composite material 1.29g was obtained.

[0149] The vertical thermal conductivity and horizontal thermal conductivity of the composite material were 1.78 and 2.56W / m·K respectively when the content of graphene was 31.0wt%.

[0150] Preparation of graphene-polyimide core-shell microspheres and thermal conductive composite material

[0151] The same method as in Comparative Example 4 was used, except that the content of graphene was about 10wt%; specifically, in this comparative example, other conditions were unchanged, only the amount of graphene added was changed to 0.09g, and finally the mass of the composite material was 0.90g. The vertical thermal conductivity and horizontal thermal conductivity of the composite material were 1.37 and 1.78W / m·K respectively when the content of graphene was 10.0wt%.

[0152] Preparation of graphene-polyimide core-shell microspheres and thermal conductive composite material

[0153] The same method as in Comparative Example 4 was used, except that the content of graphene was about 20wt%; specifically, in this comparative example, other conditions were unchanged, only the amount of graphene added was changed to 0.2g, and finally the mass of the composite material was 1.02g. The vertical thermal conductivity and horizontal thermal conductivity of the composite material were 0.77 and 0.92W / m·K respectively when the content of graphene was 19.6wt%.

[0154]

[0155]

[0156]

[0157] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing thermally conductive filler-coated polyimide core-shell microspheres based on the Pickering emulsion method, characterized in that, The method includes the following steps: (1) Add aromatic diamine monomer and aromatic dianhydride monomer to an organic polar solvent and react them in a reaction vessel to obtain a polyamic acid solution; (2) The polyamic acid solution is deposited in water to obtain a precipitate, and then the precipitate is crushed, washed and dried to obtain a polyamic acid salt precursor powder; (3) The polyamic acid salt precursor powder, triethylamine and water are added to the reaction vessel to react and obtain an aqueous polyamic acid salt solution as the aqueous phase; (4) Disperse the thermally conductive filler and the hydrophobic polymer in a non-aqueous organic solvent to obtain an oil phase, wherein the hydrophobic polymer is selected from one or more of decaethylene glycol, dodecanol, hexadecyl alcohol, undecanoic acid, dodecanamine, hexadecamine, and octadecylamine, and the concentration of the hydrophobic polymer added to the oil phase is 10 mM-50 mM. (5) The oil phase and the water phase are mixed and emulsified to obtain a water-in-oil Pickering emulsion, wherein the volume ratio of the oil phase to the water phase is 1.5:1-20:1; (6) The water-in-oil Pickering emulsion is transferred to a precipitant for demulsification to obtain a mixture powder; (7) The mixture powder is dried to obtain thermally conductive filler-polyimide core-shell structured microspheres.

2. The method according to claim 1, characterized in that: The hydrophobic polymer is hexadecylamine or octadecylamine.

3. The method according to claim 1, characterized in that: The aromatic diamine is selected from one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether and water-soluble aromatic diamines; The aromatic dianhydride is selected from one or more mixtures of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, and hydrogenated pyromellitic dianhydride; and / or The organic polar solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide, or a mixture thereof.

4. The method according to claim 3, characterized in that: The aromatic diamine is 4,4'-diaminodiphenyl ether.

5. The method according to claim 3, characterized in that: The water-soluble aromatic diamine is selected from one or a mixture of several of p-phenylenediamine, m-phenylenediamine, and o-phenylenediamine.

6. The method according to claim 3, characterized in that: The aromatic dianhydride is 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride.

7. The method according to any one of claims 1 to 6, characterized in that: The thermally conductive filler is selected from one or more of graphite, graphite nanosheets, multi-walled carbon nanotubes, graphene oxide, hexagonal boron nitride, alumina, silicon carbide and metal thermally conductive fillers; The hydrophobic polymer is hexadecylamine or octadecylamine; and / or The non-aqueous organic solvent is selected from one or more of n-hexane, cyclohexane, toluene, xylene, dichloromethane, and chloroform.

8. The method according to claim 7, characterized in that: The thermally conductive metal filler is metal nanoparticles and / or a low-melting-point alloy.

9. The method according to claim 8, characterized in that: The metal nanoparticles are selected from one or more of silver nanoparticles, copper nanoparticles, nickel nanoparticles, and iron nanoparticles, and / or mixtures thereof. The low-melting-point alloy is a tin-bismuth alloy and / or a liquid metal with a melting point of 20°C to 50°C.

10. The method according to claim 7, characterized in that: The non-aqueous organic solvent is xylene.

11. The method according to claim 7, characterized in that: The diameter of the graphite or hexagonal boron nitride flakes is 0.5 to 10 μm; The graphite nanosheets have a diameter of 2 μm to 10 μm and a thickness of 1 nm to 5 nm. The graphene oxide sheets have a diameter of 2 μm to 20 μm; The multi-walled carbon nanotubes or silicon carbide have a size of 2 μm to 10 μm and a diameter of 10-50 nm. The diameter of the alumina is 0.5-10 μm.

12. The method according to any one of claims 1 to 6, characterized in that: The precipitant is: (1) a mixture of triethylamine, acetic anhydride and ethanol; (b) a mixture of pyridine, acetic anhydride and ethanol; or (c) a mixture of pyridine, acetic anhydride and glacial acetic acid.

13. The method according to claim 12, characterized in that: The mixture is prepared in a mass ratio of 1:2:(20~50) according to the above component order.

14. The method according to any one of claims 1 to 6, characterized in that: In step (1), the solid content of the polyamic acid solution is controlled to be 5wt%-20wt%; In step (3), the mass ratio of the polyamic acid salt precursor powder to triethylamine is 1:1 to 3:1; In step (3), the mass ratio of water to the precursor powder is 100:1-5:1; In step (4), the concentration of the hydrophobic polymer added to the oil phase is 16 mM to 22 mM; In step (4), the content of the thermally conductive filler is 5 wt% to 50 wt% of the total amount of the thermally conductive filler and the hydrophobic polymer; and / or In step (5), the volume ratio of the oil phase to the water phase is 1.5:1-3:

1.

15. The method according to claim 14, characterized in that: In step (3), the mass ratio of the polyamic acid salt precursor powder to triethylamine is 2:1 to 3:

1.

16. Thermally conductive filler-coated polyimide core-shell microspheres prepared by the method according to any one of claims 1 to 15.

17. A method for preparing a polyimide-based thermally conductive composite material with a three-dimensional network structure, characterized in that, The method uses the thermally conductive filler described in claim 16 to coat polyimide core-shell microspheres.

18. The method according to claim 17, characterized in that: The method is carried out as follows: the thermally conductive filler-coated polyimide core-shell microspheres are placed in a vacuum hot press for hot molding to obtain the polyimide-based thermally conductive composite material with a three-dimensional network structure.

19. The method according to claim 18, characterized in that: The hot pressing temperature of the hot molding is 300°C to 380°C; and / or The pressure inside the vacuum chamber of the vacuum hot press is less than 10 Pa.

20. The method according to claim 18, characterized in that: The hot molding process is carried out as follows: first, preheat for 15 minutes, then adjust the hydraulic jack to pressurize to 0.5 MPa to 20 MPa, and maintain the temperature and pressure for 15 to 25 minutes.

21. The method according to claim 20, characterized in that: The hot molding process is carried out as follows: first, preheat for 15 minutes, then adjust the hydraulic jack to pressurize to 0.5 MPa to 20 MPa, and maintain the temperature and pressure for 20 minutes.

22. A polyimide-based thermally conductive composite material having a three-dimensional network structure prepared by the method according to any one of claims 17 to 21.

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