Heat-conducting composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of heat-conducting composite materials, and discloses a heat-conducting composite material which is a quartz fiber felt matrix reinforced epoxy resin composite material. The epoxy resin composite material is prepared from the following components in parts by mass: 100 parts of epoxy resin, 20 to 80 parts of epoxy group grafted aluminum oxide microspheres, 10 to 50 parts of hydroxyl-rich boron nitride nanosheets, 4 to 10 parts of a curing agent and 0.3 to 1 part of an accelerant. The surface modifier with an epoxy functional group is adopted to eliminate the interface thermal resistance of an inorganic micro-nano composite structure (spherical and lamellar) material, the interface strength and fusion of the filler and a resin matrix are improved, the heat conductivity coefficient of the composite material can be efficiently improved, and the composite material shows high insulating property and mechanical property.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of heat-conducting composite materials, and particularly relates to a heat-conducting composite material and a preparation method and application thereof. BACKGROUND

[0002] The statements herein are provided only to complement the background of the present application and are not necessarily indicative of the prior art.

[0003] The heat-conducting performance is one of the most important basic properties of solid materials, and the amorphous material has unique and high-value applications in the fields of flexible electronics, wearable devices, artificial intelligence chips, etc. compared with the crystal material.

[0004] As a typical representative of amorphous materials, the polymer and its composite material have been widely used in the thermal management field such as chip packaging due to its self-adaptive filling characteristics. However, the thermal conductivity of the polymer is generally low (less than 0.2 W / mK), which is far from the properties that the thermal interface material should have, and therefore, it is often necessary to add fillers, i.e. to introduce external heat-conducting factors (including alumina, aluminum nitride, boron nitride, silicon carbide, etc. micro-nano powder) to improve its own heat-conducting performance. However, due to the introduction of the heat-conducting factor, a new organic-inorganic interface is formed in the material, and if the filler cannot form a long-distance heat-conducting channel in the material, the improvement of the heat-conducting performance of the material is very limited, i.e. if a small amount of fillers are added, the thermal conductivity is generally not high, less than 0.4 W / mK; and a large amount of fillers will change the intrinsic properties of the polymer, i.e. the flexibility disappears, which cannot achieve the purpose of effective filling.

[0005] In addition, the specific gravity of the micro-nano filler is quite different from that of the polymer matrix, and it is difficult for the micro-nano filler to achieve uniform dispersion in the polymer. Moreover, the aluminum nitride is easily decomposed when it contacts moisture in the air, and its heat-conducting performance decreases rapidly; the boron nitride has a typical two-dimensional structure, i.e. a graphite-like structure, which leads to a low heat-conducting performance in the vertical direction, and its outstanding advantage is mainly reflected in the in-plane direction, and in the blending addition, its improvement of the heat-conducting performance of the composite material is very limited. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application aims to provide a heat-conducting composite material and a preparation method and application thereof.

[0007] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme: In a first aspect, the present application provides a heat-conducting composite material, which is a quartz fiber felt matrix reinforced epoxy resin composite material. The epoxy resin composite material comprises the following components in parts by mass: 100 parts of epoxy resin, 20-80 parts of epoxy group grafted alumina microspheres, 10-50 parts of boron nitride nanosheet rich in hydroxyl groups, 4-10 parts of curing agent, and 0.3-1 part of accelerator.

[0008] In a second aspect, the application provides a preparation method of the heat-conducting composite material, comprising the following steps: taking a quartz fiber felt as a base material, coating the upper and lower surfaces of the base material with the epoxy resin composite material to obtain a prepreg; The prepreg is laminated and then hot-pressed to obtain the heat-conducting composite material.

[0009] In a third aspect, the application provides an application of the heat-conducting composite material in the preparation of a flexible electronic device, a wearable device, or an artificial intelligence chip.

[0010] The application achieves the following beneficial effects through one or more embodiments: The application provides a preparation method of a quartz fiber reinforced epoxy resin composite material with high heat conductivity and high insulation, and an inorganic micro-nano composite structure (spherical, lamellar) material is modified with a surface modifier with an epoxy functional group to eliminate interface thermal resistance, improve the interface strength and fusion of the filler and the resin matrix, efficiently improve the thermal conductivity of the composite material, and exhibit high insulation performance and mechanical performance; compared with a comparative example with the same addition, the composite material exhibits more excellent performance, especially in the improvement of thermal conductivity; in addition, the bridge structure formed by the spherical filler and the two-dimensional lamellar structure filler has a positive effect on inhibiting the spread of electrical treeing and positively affects the construction of the heat conduction path. BRIEF DESCRIPTION OF DRAWINGS

[0011] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application, and are incorporated in and constitute a part of this application. The embodiments of these drawings illustrate the application and serve to explain the principles of the application. They should not be considered in a limiting sense.

[0012] Figure 1 is a stress-strain curve of the sample; Figure 2 is an XRD curve of alumina and boron nitride. DETAILED DESCRIPTION

[0013] It should be noted that the following detailed description is illustrative only and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0014] To solve the technical problems proposed in the background art, the application provides a heat-conducting composite material, which is a quartz fiber felt matrix reinforced epoxy resin composite material. The epoxy resin composite comprises the following components in parts by mass: 100 parts of epoxy resin, 20-80 parts of epoxy group grafted alumina microspheres, 10-50 parts of hydroxyl-rich boron nitride nanosheets, 4-10 parts of curing agent, and 0.3-1 part of accelerator.

[0015] The quartz fiber felt matrix serves as the framework of the composite material, provides excellent mechanical strength, avoids the brittleness of the polymer caused by the addition of a large amount of fillers, ensures the self-adaptive filling characteristics of the material, and can effectively reduce the thermal expansion coefficient of the composite material.

[0016] The spherical structure of the epoxy group grafted alumina microspheres is easy to form a continuous heat conduction path, and alumina itself has high thermal conductivity. The compatibility of the filler with the epoxy resin matrix is significantly improved by epoxy group grafting modification, reducing the thermal resistance loss of the organic-inorganic interface. The spherical structure reduces the porosity of the material, and the modified interface bonding improves the insulation performance of the material.

[0017] The sheet structure of the hydroxyl-rich boron nitride nanosheet can fill the gap between the spherical alumina microspheres, constructing a multi-dimensional heat conduction network of "spherical framework + sheet bridging", and making up for the defect of insufficient vertical heat conduction of boron nitride. Hydroxyl modification (hydrogen peroxide wetting + ball milling preparation) enhances the hydrogen bonding with the epoxy resin, improves the dispersion uniformity, and further reduces the interface thermal resistance. In addition, the sheet structure of the nanosheet can inhibit the spread of electrical trees, and cooperate with the porosity control of the spherical alumina to significantly improve the insulation stability of the material.

[0018] The spherical alumina microspheres serve as the macroscopic heat conduction framework, and the sheet-like boron nitride nanosheets fill the gaps and bridge adjacent microspheres, forming a continuous and multi-dimensional heat conduction path, greatly improving the thermal conductivity. The epoxy group grafted alumina and the hydroxyl-rich boron nitride interact through functional groups, further strengthening the interface bonding between fillers and between fillers and the resin matrix, and eliminating multiple interface thermal resistances.

[0019] The mass ratio of the quartz fiber felt matrix to the epoxy resin is 1-10:2-3, and further can be 2-8:2-3, and further can be 3-7:2-3.

[0020] In some embodiments, the diameter of the quartz fiber in the quartz fiber felt is 13-16 μm.

[0021] In some embodiments, the epoxy resin is selected from at least two of bisphenol A epoxy resin, epoxy resin, bisphenol F epoxy resin, alicyclic glycidyl ester type epoxy resin, or aliphatic glycidyl ether epoxy resin.

[0022] Preferably, the epoxy resin is a mixture of bisphenol A epoxy resin, epoxy resin, bisphenol F epoxy resin, alicyclic glycidyl ester type epoxy resin, and aliphatic glycidyl ether epoxy resin, and the mass ratio of bisphenol A epoxy resin, epoxy resin, bisphenol F epoxy resin, alicyclic glycidyl ester type epoxy resin, and aliphatic glycidyl ether epoxy resin is 40-60:10-30:10-20:5-15:2-10.

[0023] The viscosities of different types of epoxy resins differ significantly (for example, the viscosity of aliphatic glycidyl ether epoxy resin is low, and the viscosity of bisphenol A epoxy resin is moderate), and after mixing, the processing viscosity can be adjusted to an appropriate value, which promotes the uniform dispersion of the epoxy group grafted alumina microspheres and the hydroxyl-rich boron nitride nanosheets, reduces the agglomeration of the fillers, and lays the foundation for the construction of continuous thermal conduction channels.

[0024] The bisphenol A epoxy resin provides a high-strength foundation to ensure the structural support capability of the composite material; the bisphenol F epoxy resin and the aliphatic glycidyl ether epoxy resin enhance the flexibility of the system, avoiding the defect of excessive brittleness of a single resin; and in combination with the quartz fiber felt skeleton, the self-adaptive filling properties of the material are further maintained, preventing the reduction of flexibility caused by the addition of a large amount of fillers.

[0025] The alicyclic glycidyl ester type epoxy resin has high heat resistance and low shrinkage, and after mixing, the glass transition temperature of the composite material can be increased.

[0026] The mixed resin contains various functional groups (epoxy groups, hydroxyl groups, etc.), which can form chemical bonds or hydrogen bonds with the fillers after surface modification. The alicyclic glycidyl ester type epoxy resin has excellent electrical insulation, and after mixing, the voltage resistance and insulation stability of the composite material can be improved.

[0027] In some embodiments, the diameter of the epoxy group grafted alumina microspheres is 30-150 µm, preferably 50-100 µm. If the diameter is less than 30 µm, the microspheres are prone to agglomeration due to excessive surface energy, which destroys the continuity of the thermal conduction channel, resulting in limited improvement in the thermal conductivity. If the diameter is greater than 150 µm, the microspheres are difficult to disperse uniformly in the epoxy resin matrix, and are prone to sedimentation or porosity, reducing the thermal efficiency and insulation performance.

[0028] In some embodiments, the hydroxyl-rich boron nitride nanosheet has a particle size of at least one of 50-100 nm, 300-500 nm, or 100-200 µm.

[0029] In some embodiments, the curing agent is dicyandiamide, O-tolylbiguanide, alpha, omega-diphenylbiguanide, succinic acid dihydrazide, or p-hydroxybenzyl hydrazide.

[0030] Dicyandiamide has very low reactivity with epoxy resin system at room temperature, which can keep the prepreg stable for long-term storage and avoid premature curing failure. This feature solves the problem of short storage period of ordinary amine curing agent at room temperature.

[0031] Dicyandiamide needs to be used with organic urea accelerators to significantly reduce the curing temperature and shorten the curing time. This synergistic effect not only ensures the flowability of the resin system during processing (which is beneficial for filler dispersion and fiber infiltration), but also quickly crosslinks and forms during hot pressing, balancing processability and production efficiency.

[0032] The epoxy resin system cured by dicyandiamide has a high-density crosslinked structure, which can effectively increase the glass transition temperature of the composite material, making it suitable for high-temperature application scenarios such as chip packaging. It is also beneficial to the improvement of the voltage resistance and dielectric loss of the composite material.

[0033] In some embodiments, the accelerator is organic urea, which can be UR300 or UR500.

[0034] During the heating process of hot pressing, the urea group (-NH-CO-NH-) in the molecular structure of organic urea is activated, releasing active groups, which react with the cyano group (-CN) of dicyandiamide to generate highly active guanidine intermediates; the intermediates further attack the epoxy group of the epoxy resin, opening the three-membered ring and promoting the addition reaction between the epoxy group and the amino group of dicyandiamide to form a three-dimensional crosslinked network.

[0035] In a second aspect, the present application provides a preparation method of the heat-conducting composite material, comprising the following steps: uniformly mixing the components in the epoxy resin composite material in proportion to obtain an epoxy resin composite material; Using the epoxy resin composite material, a prepreg is obtained by coating the upper and lower surfaces of a quartz fiber felt substrate with the epoxy resin composite material; The prepreg is stacked and then hot-pressed to obtain a heat-conducting composite material.

[0036] In some embodiments, the preparation method of the epoxy resin composite material is: after uniformly mixing the components in proportion, adding dicyandiamide to the mixture and continuing to disperse; Then, add epoxy group grafted alumina microspheres and hydroxyl-rich boron nitride nanosheets in portions, disperse uniformly, and finally add organic urea and mix uniformly to obtain the epoxy resin composite material.

[0037] Different types of epoxy resins (such as bisphenol A, bisphenol F, and alicyclic) have different viscosities and functional group distributions. First, uniformly mix the components in proportion to form a stable resin matrix, which can prevent local viscosity unevenness from causing subsequent filler dispersion difficulties.

[0038] Dicyandiamide is a latent curing agent, which has very low reactivity with epoxy resin at room temperature. Adding dicyandiamide first and dispersing it can make it uniformly distributed in the resin matrix, and because no accelerator is added, it will not trigger the curing reaction, ensuring the stability of the prepreg. If dicyandiamide is added later, it is easy to cause incomplete curing in some areas due to uneven dispersion, affecting the performance of the material.

[0039] Finally, adding the accelerator can avoid its premature activation of dicyandiamide, ensuring that the resin system remains fluid during the coating (heated roller 85℃) and lamination processes, and only triggers the curing reaction during hot pressing (160℃), balancing processability and curing efficiency.

[0040] In some embodiments, the preparation method of the epoxy group grafted alumina microspheres is as follows: the isopropanol dispersion solution of alumina microspheres is mixed with a mixed solution of KH550, water, sodium hydroxide and isopropanol, and then heated to 80-90℃ for 2-5h to obtain first-grafted alumina microspheres; The first-grafted alumina microspheres are added to tetrahydrofuran, and dimethylchlorosilane is added thereto, mixed, and kept below 20℃ for 10-15h to obtain second-grafted alumina microspheres; The second-grafted alumina microspheres and allyl glycidyl ether are added to toluene, and stirred at 90-110℃ for 5-7h to obtain epoxy group grafted alumina microspheres.

[0041] KH550 (γ-aminopropyltriethoxysilane) molecular structure contains ethoxy (-OC2H5) and amino (-NH2). In the presence of water and sodium hydroxide (alkaline catalyst), ethoxy undergoes hydrolysis reaction to generate silicon hydroxyl (-SiOH), and the alkaline condition (NaOH) accelerates the hydrolysis rate of ethoxy, ensuring efficient generation of silicon hydroxyl. A large number of hydroxyl (Al-OH) groups naturally exist on the surface of alumina microspheres, and the reactivity of these hydroxyl groups is further improved in alkaline environment, making them more easily chemically bonded with silicon hydroxyl. The hydrolysis generated silicon hydroxyl (-SiOH) and the Al-OH on the surface of alumina undergo dehydration condensation to form Si-O-Al covalent bond, thereby stably grafting KH550 molecules to the surface of alumina microspheres.

[0042] The second grafting is to react the amino group on the surface of the first-grafted alumina microspheres with dimethylchlorosilane to introduce silane-containing groups on the surface, providing reaction sites for the third grafting (reaction with allyl glycidyl ether), and finally realizing the grafting of epoxy groups.

[0043] Dimethylchlorosilane is highly active and prone to self-polymerization or over-reaction at high temperature, so the reaction temperature needs to be below 20℃.

[0044] Preferably, the mass ratio of the alumina microspheres, the KH550, the water and the sodium hydroxide in the first grafting is 40-50:30-40:2-5:3-5.

[0045] In some embodiments, the mass ratio of the first-grafted alumina microspheres and the dimethylchlorosilane in the second grafting is 25-35:10-15.

[0046] In some embodiments, the mass ratio of the second-grafted alumina microspheres and the allyl glycidyl ether is 30-40:15-25.

[0047] In some embodiments, the method for preparing the boron nitride nanosheet rich in hydroxyl groups comprises the following steps: wetting the boron nitride with hydrogen peroxide, and then performing ball milling.

[0048] Preferably, the power of the ball milling is 3-4 kW, and the ball milling time is 1-3 h.

[0049] In some embodiments, the temperature of the heating roller used in the process of coating the surface of the quartz fiber felt is 80-90℃.

[0050] In some embodiments, the obtained prepreg is cooled before being subjected to the lamination and hot pressing.

[0051] In some embodiments, the lamination structure is preheated to 120-140℃ when hot pressing, the initial pressure is 1-4 MPa, the pressure is increased at 3-5 MPa / 10℃, the temperature is increased to 160-180℃, and the temperature is maintained for 5-15 min.

[0052] Preferably, after the hot pressing, cold pressing is performed to shape the heat-conducting composite material.

[0053] In a third aspect, the application provides the use of the heat-conducting composite material in the preparation of a flexible electronic device, a wearable device or an artificial intelligence chip.

[0054] The application will be further described below with reference to the embodiments.

[0055] Embodiment 1 A method for preparing a heat-conducting composite material, comprising the following steps: (1) surface modification of alumina microspheres: 46 parts of alumina microspheres are dispersed in 200 parts of isopropanol by vigorous stirring (600 r / min) to obtain a first dispersion liquid, and the diameter of the alumina is 50-100 µm; 33 parts of KH550, 3 parts of deionized water and 4 parts of sodium hydroxide are dissolved in 100 parts of isopropanol to obtain a second dispersion liquid; After mixing the above first dispersion liquid and second dispersion liquid, the mixed solution is heated to 85°C and kept for 4h, then cooled to room temperature, and after filtration and drying, the first grafted alumina microspheres (named M1) are obtained; The first grafted alumina microspheres 30 parts are added into 200 parts of tetrahydrofuran, and dimethylchlorosilane 12 parts is added in several times, stirring, and keeping the solution temperature not more than 20°C for 12h, after the reaction is completed, after filtration and drying, the second grafted alumina microspheres (M2) are obtained; 33 parts of second grafted alumina microspheres (M2) and 20 parts of allyl glycidyl ether are added into 200 parts of toluene, the reaction kettle is nitrogen sealed, heated to 100°C for 6h, after cooling, filtration and drying, the epoxy grafted alumina microspheres (M3) are obtained; (2) Preparation and functionalization of boron nitride nanosheets: The commercially available boron nitride is in a stacked structure, in order to improve its dispersibility and functional characteristics of two-dimensional structure, the purchased boron nitride needs to be exfoliated and functionalized. The purchased boron nitride 1kg is placed in a planetary ball mill, adding hydrogen peroxide (30%) 500mL for wetting, and then starting the ball mill, the power is set to 3.5kW, after ball milling for 2h, the sample is taken out, washed with water, filtered and dried, to obtain the exfoliated boron nitride nanosheets (N1) rich in hydroxyl functional groups, with a vertical size of (10-30) nm.

[0056] (3) Preparation of resin system: Bisphenol A epoxy resin (E51) 50 parts, epoxy resin (E20) 20 parts, bisphenol F type epoxy resin (BPF 170) 15 parts, alicyclic glycidyl ester epoxy resin (S-28) 10 parts, aliphatic glycidyl ether epoxy resin (S-27) 5 parts are added into a star-shaped disperser in turn, fully stirred (stirring speed 300r / min) and mixed uniformly, then dicyandiamide (3000 mesh) 5.2 parts is added, and continues to be dispersed for 30min; Then add alumina microspheres (M3) 52 parts (volume fraction 13vol%) and boron nitride nanosheets (N1) 30 parts (13.6vol%) in several times, continue to disperse for 2h; Then, add organic urea (UR300) 0.5 parts, continue to stir for 30min to obtain the epoxy resin composite system.

[0057] (4) Preparation of the thermal conductive composite material: a three-roll film machine was used to prepare the adhesive film, wherein the heating roller temperature was 75°C, the resin supply speed was 2 kg / min, the vehicle speed was 15 m / min, the adhesive film was controlled to have a gram weight of 25±1 g / m^2 by using an X-ray gram weight online detection device, and the effective width of the adhesive film was 1200 mm; a quartz fiber felt with a surface density of 130 g / m^2 was selected as the substrate (quartz fiber felt with a surface density of 100 g / m^2 or 200 g / m^2 can be selected according to the needs), and a laminating machine was used for upper and lower film lamination, wherein the vehicle speed was 7 m / min, the heating roller temperature was set to 85°C, and after cooling by a cooling plate, a prepreg was obtained, which was wound and transferred to a cold storage for use, and the cold storage temperature was 4°C.

[0058] (5) Preparation of the composite material: after the prepreg was cut and the film was torn, it was stacked according to 5 layers of 1 mm, and then placed in a molding machine for hot pressing, wherein the preheating temperature was 130°C, the initial pressure was 2 MPa, the pressure was increased according to 5 MPa / 10°C, the temperature was increased to 160°C and the pressure was increased to 15 MPa, and after 10 min of heat preservation, the mold was removed and the product was ejected, and then placed in a cold press for cold pressing and shaping for 30 min to obtain the thermal conductive composite material.

[0059] Example 2 M3 and N1 were used as the reinforcing phase, wherein the amount of M3 was 28 parts (7 vol%), the amount of N1 was 15.4 parts (7 vol%), and the other steps were the same as in Example 1.

[0060] Example 3 M3 and N1 were used as the reinforcing phase, wherein the amount of M3 was 76 parts (volume fraction of about 19 vol%), the amount of N1 was 38 parts (volume fraction of about 19 vol%), and the other steps were the same as in Example 1.

[0061] Comparative Example 1 Pure resin (resin system in Example 1) was used to prepare the composite material, and the steps were the same.

[0062] Comparative Example 2 Unmodified alumina microspheres and boron nitride were used to prepare the composite material, and the addition amount was the same as in Example 1. Comparative Example 3 Modified alumina microspheres M3 were used to prepare the composite material, and the addition amount was 52 parts (volume fraction of about 13 vol%), and the boron nitride nanosheet was not modified, and the other steps were the same as in Example 1. Comparative Example 4 Modified boron nitride nanosheet N1 was used to prepare the composite material, and the addition amount was 30 parts (volume fraction of about 13 vol%), and the alumina microspheres were not modified, and the other steps were the same as in Example 1.

[0063] Table 1

[0064] From the test results, it can be seen that the embodiment 1 achieves the best effect, and in the comparative examples 2, 3 and 4 in which the micro-nano composite filler is not surface modified, no significant improvement in the thermal conductivity is observed, which shows that surface modification of the micro-nano composite filler (spherical alumina and boron nitride nanosheet with a sheet structure) can significantly eliminate the interface thermal resistance, and the bridge structure constructed by alumina and boron nitride can efficiently improve the thermal conductivity of the composite material; at the same time, due to the addition of the micro-nano composite structure material, the spread of the electric tree can be inhibited, thereby improving the overall insulation performance of the material; in addition, the appropriate addition amount has a positive effect on the strength improvement of the material, and shows good toughening effect.

[0065] The preferred embodiments of the application have been described above, but the application is not limited to the above. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A thermally conductive composite material, characterized by: The application discloses a quartz fiber felt matrix reinforced epoxy resin composite material. The epoxy resin composite material comprises the following components in parts by mass: 100 parts of epoxy resin, 20-80 parts of epoxy group grafted alumina microspheres, 10-50 parts of hydroxyl-rich boron nitride nanosheets, 4-10 parts of a curing agent, and 0.3-1 part of an accelerator.

2. The thermally conductive composite of claim 1, wherein: The diameter of the quartz fiber in the quartz fiber felt is 13-16 microns. Preferably, the epoxy resin is selected from at least two of bisphenol A epoxy resin, epoxy resin, bisphenol F epoxy resin, alicyclic glycidyl ester type epoxy resin or aliphatic glycidyl ether epoxy resin. Preferably, the epoxy resin is a mixture of bisphenol A epoxy resin, epoxy resin, bisphenol F epoxy resin, alicyclic glycidyl ester type epoxy resin and aliphatic glycidyl ether epoxy resin, and the mass ratio of bisphenol A epoxy resin, epoxy resin, bisphenol F epoxy resin, alicyclic glycidyl ester type epoxy resin and aliphatic glycidyl ether epoxy resin is 40-60:10-30:10-20:5-15:2-10.

3. The thermally conductive composite of claim 1, wherein: The diameter of the epoxy group grafted alumina microspheres is 30-150 microns, preferably 50-100 microns. Preferably, the hydroxyl-rich boron nitride nanosheets have at least one of a particle size of 50-100 nanometers, 300-500 nanometers or 100-200 microns.

4. The thermally conductive composite of claim 1, wherein: The curing agent is dicyandiamide, O-tolylbiguanide, alpha, omega-diphenylbiguanide, succinic acid dihydrazide or p-hydroxybenzyl hydrazide. Preferably, the accelerator is organic urea, which can be UR300 or UR500.

5. A method of producing the thermally conductive composite material according to any one of claims 1 to 4, characterized by: The method comprises the following steps: uniformly mixing the components in the epoxy resin composite material in proportion to obtain the epoxy resin composite material. The quartz fiber felt is used as a substrate, and the epoxy resin composite material is coated on the upper and lower surfaces of the quartz fiber felt to obtain a prepreg. The prepreg is laminated and then hot-pressed to obtain a heat-conducting composite material.

6. The method of claim 5, wherein: The preparation method of the epoxy resin composite material is as follows: the components of the epoxy resin are uniformly mixed in proportion, dicyandiamide is added, and then the epoxy group grafted alumina microspheres and the hydroxyl-rich boron nitride nanosheets are added in batches, and finally, the organic urea is added and uniformly mixed to obtain the epoxy resin composite material. The preparation method of the epoxy group grafted alumina microspheres is as follows: the isopropyl alcohol dispersion solution of the alumina microspheres is uniformly mixed with a mixed solution of KH550, water, sodium hydroxide and isopropyl alcohol, heated to 80-90 DEG C and kept for 2-5 hours to obtain the first grafted alumina microspheres.

7. The method of claim 5, wherein: The first grafted alumina microspheres are added into tetrahydrofuran, dimethylchlorosilane is added, mixed, kept below 20 DEG C and reacted for 10-15 hours to obtain the second grafted alumina microspheres. The second grafted alumina microspheres and allyl glycidyl ether are added into toluene, stirred and reacted at 90-110 DEG C for 5-7 hours to obtain the epoxy group grafted alumina microspheres. Preferably, the mass ratio of the alumina microspheres, KH550, water and sodium hydroxide in the first grafting is 40-50:30-40:2-5:3-5. ​ Preferably, the mass ratio of the primary grafted alumina microspheres and dimethyl chlorosilane in the secondary grafting is 25-35:10-15; Preferably, the mass ratio of the primary grafted alumina microspheres and dimethyl chlorosilane in the secondary grafting is 25-35:10-15; 8. The method of claim 5, wherein: The preparation method of the boron nitride nanosheet rich in hydroxyl groups comprises the following steps: wetting boron nitride with hydrogen peroxide, and then performing ball milling, so as to obtain the boron nitride nanosheet rich in hydroxyl groups. Preferably, the power of the ball milling is 3-4 kW, and the ball milling time is 1-3 h.

9. The method of claim 5, wherein: In the process of coating on the surface of the quartz fiber felt, the temperature of the heating roller used is 80-90 DEG C; Preferably, in the hot pressing, the laminated structure is preheated to 120-140 DEG C, the initial pressure is 1-4 MPa, the pressure is increased at 3-5 MPa / 10 DEG C, the temperature is increased to 160-180 DEG C, and the temperature is kept for 5-15 min. Preferably, after the hot pressing, cold pressing is performed to obtain the heat-conducting composite material. 10.The heat-conducting composite material of any one of claims 1-4, or the heat-conducting composite material prepared by the preparation method of any one of claims 5-9 is applied to the preparation of a flexible electronic device, a wearable device or an artificial intelligence chip.

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