Composite graphene heat-conducting film and preparation process thereof

Abstract

According to the composite graphene heat-conducting film and the preparation process, firstly, boron nitride is modified through dopamine, the dispersing performance of the boron nitride in a polyimide film is improved, meanwhile, amino in the modified boron nitride and pyromellitic dianhydride are subjected to a chemical reaction, and the thermal conductivity of the composite graphene heat-conducting film is improved; the loading stability of the boron nitride in the polyimide film is improved, and the boron nitride is not easy to fall off, so that the heat-conducting property of the composite graphene heat-conducting film is improved; then the surface of a polyimide film is coated with zinc-loaded graphene to obtain a composite film, the composite film is soaked in an epichlorohydrin aqueous solution, under the action of a cross-linking agent epichlorohydrin, active groups such as hydroxyl and carboxyl in graphene can be subjected to a cross-linking reaction with amino in modified boron nitride, the bonding strength is improved, and the corrosion resistance is improved. After multiple times of bending, the prepared composite graphene heat-conducting film still has excellent heat-conducting property and flame-retardant property.

Description

Technical Field

[0001] The present invention relates to the technical field of heat-conducting film materials, and particularly to a composite graphene heat-conducting film and a preparation process thereof. Background Art

[0002] With the development of electronic devices towards miniaturization, integration and high performance, the heat dissipation problem has become a key factor restricting the improvement of their performance. As an efficient heat management material, the heat-conducting film can effectively conduct heat from the heat source to the external environment, which is of great significance for ensuring the stable operation of electronic devices.

[0003] Pure polymer materials usually have a low thermal conductivity, making it extremely difficult for electronic devices to dissipate heat. Currently, the methods for improving the thermal conductivity of polymer materials mainly include the following aspects: 1. Modification of the polymer matrix: By chemical synthesis, polymers with an ordered structure are prepared to increase the crystallinity of the polymer and reduce phonon scattering, thereby improving the thermal conductivity of the polymer matrix; 2. Filling with high-thermal-conductivity fillers: Using high-thermal-conductivity inorganic fillers such as metal oxides, nitrides, carbides, etc., to improve the thermal conductivity of the material by constructing a heat-conducting channel in the polymer matrix; Compared with the modification of the polymer matrix, adding heat-conducting fillers with better thermal conductivity, such as carbon nanotubes, to ordinary polymer materials and uniformly mixing the two through a certain process to obtain a filled heat-conducting polymer material is a simpler process and can better meet the actual production requirements, which is the main method for preparing heat-conducting polymer composites at present; However, the addition of a large amount of heat-conducting fillers requires solving a series of problems such as the dispersibility, compatibility, and interfacial properties of the heat-conducting fillers in the polymer matrix. In addition, the random distribution of heat-conducting fillers in the polymer matrix usually forms a discontinuous heat-conducting network, greatly increasing the interfacial thermal resistance between the fillers, which limits the improvement of the thermal conductivity to a certain extent. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a composite graphene heat-conducting film and a preparation process thereof.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A preparation process of a composite graphene heat-conducting film includes the following steps:

[0007] S1. Dissolve pyromellitic dianhydride and modified boron nitride in an organic solvent, then add 4,4-diaminobenzophenone thereto, and stir at room temperature for 4 - 8 h to obtain a polyamic acid mixed solution;

[0008] S2. Cast the polyamic acid mixed solution into a film on a substrate, then carry out a heat preservation reaction in an inert atmosphere. After the reaction ends, peel off the substrate to obtain a polyimide film;

[0009] S3. Add the pretreated graphene into the zinc salt solution, shake and adsorb for 2 - 3 h, then filter, wash and dry to obtain the zinc-loaded graphene;

[0010] S4. Disperse the zinc-loaded graphene in absolute ethanol to obtain a dispersion, then coat the dispersion on the surface of the polyimide film and dry to obtain a composite film;

[0011] S5. Immerse the composite film in an aqueous solution of epichlorohydrin for 30 - 60 min, then take it out and dry it in a vacuum drying oven to obtain the composite graphene thermal conductive film.

[0012] Preferably, in step S1, the preparation method of the modified boron nitride is as follows: Add dopamine hydrochloride into the Tris-HCl buffer solution, adjust the pH to 8 - 10, then add hexagonal boron nitride and soak for 16 - 24 h. After soaking, take it out, wash it with water and dry it in vacuum to obtain the modified boron nitride.

[0013] Preferably, in step S1, the mass ratio of pyromellitic dianhydride, modified boron nitride and 4,4-diaminobenzophenone is 10 - 15:0.5 - 1:10.

[0014] Preferably, in step S2, the temperature for the heat preservation reaction is 200 - 210 °C and the heat preservation time is 4 - 8 h.

[0015] Preferably, in step S3, the preparation method of the pretreated graphene is as follows: Add graphene into concentrated sulfuric acid, stir at 80 - 90 °C for 2 - 4 h, then wash the obtained product until it is neutral and dry to obtain the pretreated graphene.

[0016] Preferably, in step S3, the mass ratio of the pretreated graphene to the zinc salt solution is 8 - 10:100, and the mass fraction of the zinc salt solution is 1 - 3%.

[0017] Preferably, in step S4, the mass ratio of the zinc-loaded graphene to absolute ethanol is 5 - 10:100.

[0018] Preferably, in step S4, the coating amount is 5 - 10 g / cm 2 .

[0019] Preferably, in step S5, the mass fraction of the aqueous solution of epichlorohydrin is 2 - 4%.

[0020] The present invention also provides a composite graphene thermal conductive film prepared by the above preparation process.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) In the present invention, boron nitride is first modified with dopamine to deposit a layer of polydopamine on the surface of boron nitride. After the boron nitride is modified with polydopamine, amino active functional groups are introduced, improving the dispersion performance of boron nitride in the polyimide film. At the same time, the amino groups in the modified boron nitride chemically react with pyromellitic dianhydride, enhancing the loading stability of boron nitride in the polyimide film and making it not easy to fall off, thereby improving the thermal conductivity of the composite graphene thermal conductive film. In addition, polydopamine has excellent flame retardant properties, and introducing it into the composite graphene thermal conductive film improves the flame retardant performance of the composite graphene thermal conductive film.

[0023] (2) In the present invention, graphene is first added to concentrated sulfuric acid for weak oxidation treatment to increase the number of active groups such as hydroxyl and carboxyl groups on the surface of graphene. Then, through the chelation of hydroxyl and carboxyl groups with metal ions, zinc ions are loaded in the graphene. The addition of zinc can reduce the combustion rate of the material and promote the formation of a stable carbon layer when the material is heated. Acting together with polydopamine, it further improves the flame retardant performance of the composite graphene thermal conductive film. Subsequently, the zinc-loaded graphene is coated on the surface of the polyimide film to obtain a composite film. Then, the composite film is immersed in an aqueous solution of epichlorohydrin. Under the action of the cross-linking agent epichlorohydrin, the active groups such as hydroxyl and carboxyl groups in the graphene can cross-link with the amino groups in the modified boron nitride, improving the bonding strength. After being bent multiple times, the prepared composite graphene thermal conductive film still has excellent thermal conductivity and flame retardant performance. Specific embodiments

[0024] The present invention is further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0025] It should be noted that, unless otherwise specified, the chemical reagents involved in the present invention are all purchased through commercial channels.

[0026] A preparation process of a composite graphene thermal conductive film includes the following steps:

[0027] S1. Prepare a polyamic acid mixture

[0028] Disperse pyromellitic dianhydride and modified boron nitride in an organic solvent, and then add 4,4-diaminobenzophenone thereto, and stir at room temperature for 4 - 8 h to obtain a polyamic acid mixture.

[0029] In this step, the preparation method of the modified boron nitride is as follows: Add hydrochloric acid dopamine to Tris-HCl buffer solution, adjust the pH to 8 - 10, then add hexagonal boron nitride and soak for 16 - 24 h. After the soaking is completed, take it out, wash it with water, and then dry it under vacuum to obtain modified boron nitride.

[0030] Specifically, the dosage ratio of dopamine hydrochloride, Tris-HCl buffer solution and hexagonal boron nitride is 1-3 g:50 mL:1-3 g, and further preferably 2 g:50 mL:2 g.

[0031] In this step, the mass ratio of pyromellitic dianhydride, modified boron nitride and 4,4-diaminobenzophenone is 10-15:0.5-1:10. In some embodiments of the present invention, for example, it can be selected as 10:0.5:10, 10:0.8:10, 10:1:10, 12:0.5:10, 12:0.8:10, 15:0.5:10, 15:1:10, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0032] S2. Preparation of polyimide film

[0033] Cast the polyamic acid mixture into a film on a substrate, then carry out a heat preservation reaction in an inert atmosphere. After the reaction is completed, peel off the substrate to obtain the polyimide film.

[0034] In this step, the wet film thickness of the casting film is 1-3 mm. For example, it can be selected as 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0035] The temperature of the heat preservation reaction is 200-210 °C. For example, it can be selected as 200 °C, 202 °C, 204 °C, 206 °C, 208 °C, 210 °C; the heat preservation time is 4-8 h. For example, it can be selected as 4 h, 5 h, 6 h, 7 h, 8 h; but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0036] In this step, during the heating process of the polyamic acid, by losing one molecule of water, its amide acid group (-COOH) undergoes a condensation reaction to form an imide group (-NH-), thereby transforming into polyimide.

[0037] S3. Graphene loaded with zinc

[0038] Add the pretreated graphene to the zinc salt solution, oscillate and adsorb for 2-3 h, and then filter, wash and dry to obtain the graphene loaded with zinc.

[0039] In this step, the preparation method of the pretreated graphene is as follows: add graphene to concentrated sulfuric acid, stir at 80-90 °C for 2-4 h, and then wash the obtained product to neutrality and dry to obtain the pretreated graphene.

[0040] In this step, the mass ratio of the pretreated graphene to the zinc salt solution is 8 - 10:100. For example, 8:100, 9:100, 10:100 can be selected; the mass fraction of the zinc salt solution is 1 - 3%. For example, 1%, 2%, 3% can be selected, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0041] In this step, the selected zinc salt is a soluble zinc salt, such as zinc sulfate, zinc nitrate or zinc chloride.

[0042] S4. Preparation of the composite film

[0043] Disperse the zinc-loaded graphene in absolute ethanol to obtain a dispersion, and then coat the dispersion on the surface of the polyimide film and dry it to obtain the composite film.

[0044] In this step, the mass ratio of the zinc-loaded graphene to the absolute ethanol is 5 - 10:100. For example, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100 can be selected, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0045] In this step, the coating is a single-sided coating, and the coating amount is 5 - 10 g / cm 2 , for example, 5 g / cm 2 , 6 g / cm 2 , 7 g / cm 2 , 8 g / cm 2 , 9 g / cm 2 , 10 g / cm 2 , but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0046] S5. Preparation of the composite graphene thermal conductive film

[0047] Immerse the composite film in an aqueous solution of epichlorohydrin for 30 - 60 min, then take it out and put it in a vacuum drying oven for drying to obtain the composite graphene thermal conductive film.

[0048] In this step, the mass fraction of the aqueous solution of epichlorohydrin is 2 - 4%. For example, 2%, 3%, 4% can be selected, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0049] In this step, the drying temperature in the vacuum drying oven is 60 - 80 °C.

[0050] The following further illustrates the present invention through specific examples. The boron nitride selected in the present invention is hexagonal boron nitride with a mesh number of 2000; the graphene is from Wuhan Institute of Low-Dimensional Materials Co., Ltd., CAS: 7440 - 44 - 0.

[0051] Example 1

[0052] A preparation process of a composite graphene thermal conductive film includes the following steps:

[0053] S1. Disperse 10 g of pyromellitic dianhydride and 0.5 g of modified boron nitride in 250 mL of an organic solvent DMF, then add 10 g of 4,4-diaminobenzophenone thereto, and stir at room temperature for 6 h to obtain a polyamic acid mixed solution;

[0054] Among them, the preparation method of the modified boron nitride is as follows: Add 2 g of hydrochloric acid dopamine to 50 mL of Tris-HCl buffer solution, adjust the pH to 9, then add 2 g of hexagonal boron nitride and soak for 18 h. After the soaking is completed, take it out, wash it with water and dry it under vacuum to obtain the modified boron nitride;

[0055] S2. Cast the polyamic acid mixed solution into a film on a glass substrate, and the thickness of the wet film is 2 mm. Then, keep it at 200 °C in an inert atmosphere for 6 h. After the reaction is completed, peel off the substrate to obtain a polyimide film;

[0056] S3. Add 8 g of pretreated graphene to 100 g of a 1 wt% zinc nitrate solution, oscillate and adsorb for 3 h, then filter, wash and dry to obtain zinc-loaded graphene;

[0057] The preparation method of the pretreated graphene is as follows: Add 8 g of graphene to 50 mL of concentrated sulfuric acid, stir at 80 °C for 3 h, then wash the obtained product to neutrality and dry it to obtain the pretreated graphene;

[0058] S4. Disperse 5 g of zinc-loaded graphene in 100 g of absolute ethanol to obtain a dispersion liquid. Then, coat the dispersion liquid on the surface of the polyimide film, coat it on one side, and the coating amount is 8 g / cm 2 , dry to obtain a composite film;

[0059] S5. Immerse the composite film in a 3 wt% aqueous solution of epichlorohydrin, where the mass-volume ratio of the composite film to the epichlorohydrin aqueous solution is 1 g:15 mL, soak for 30 min, then take it out and put it in a vacuum drying oven to dry, and obtain the composite graphene thermal conductive film.

[0060] Example 2

[0061] A preparation process of a composite graphene thermal conductive film includes the following steps:

[0062] S1. Disperse 12 g of pyromellitic dianhydride and 0.8 g of modified boron nitride in 250 mL of organic solvent DMF, then add 10 g of 4,4-diaminobenzophenone thereto, and stir at room temperature for 8 h to obtain a polyamic acid mixture;

[0063] Among them, the preparation method of the modified boron nitride is as follows: Add 2 g of hydrochloric acid dopamine to 50 mL of Tris-HCl buffer solution, adjust the pH to 10, then add 2 g of hexagonal boron nitride and soak for 18 h. After soaking, take it out, wash it with water and dry it under vacuum to obtain modified boron nitride;

[0064] S2. Cast the polyamic acid mixture into a film on a glass substrate, with the thickness of the wet film being 2.5 mm, then carry out a heat preservation reaction at 200 °C in an inert atmosphere for 6 h. After the reaction is completed, peel off the substrate to obtain a polyimide film;

[0065] S3. Add 10 g of pretreated graphene to 100 g of a 3 wt% zinc nitrate solution, oscillate and adsorb for 3 h, then filter, wash and dry to obtain zinc-loaded graphene;

[0066] The preparation method of the pretreated graphene is as follows: Add 8 g of graphene to 50 mL of concentrated sulfuric acid, stir at 80 °C for 3 h, then wash the obtained product to neutrality and dry it to obtain pretreated graphene;

[0067] S4. Disperse 8 g of zinc-loaded graphene in 100 g of absolute ethanol to obtain a dispersion liquid, then coat the dispersion liquid on the surface of the polyimide film, coat it on one side, and the coating amount is 5 g / cm 2 , and dry it to obtain a composite film;

[0068] S5. Immerse the composite film in a 1 wt% aqueous solution of epichlorohydrin, where the mass-volume ratio of the composite film to the epichlorohydrin aqueous solution is 1 g:15 mL, soak for 30 min, then take it out and dry it in a vacuum drying oven to obtain a composite graphene thermal conductive film.

[0069] Example 3

[0070] A preparation process of a composite graphene thermal conductive film, comprising the following steps:

[0071] S1. Disperse 15 g of pyromellitic dianhydride and 1 g of modified boron nitride in 250 mL of organic solvent DMF, then add 10 g of 4,4-diaminobenzophenone thereto, and stir at room temperature for 8 h to obtain a polyamic acid mixture;

[0072] Among them, the preparation method of the modified boron nitride is as follows: Add 2 g of hydrochloric acid dopamine into 50 mL of Tris-HCl buffer solution, adjust the pH to 10, then add 2 g of hexagonal boron nitride and soak for 18 h. After the soaking is completed, take it out, wash it with water and dry it under vacuum to obtain the modified boron nitride;

[0073] S2. Cast the polyamic acid mixture into a film on a glass substrate. The thickness of the wet film is 3 mm, and then keep it reacting at 200 °C in an inert atmosphere for 6 h. After the reaction is completed, peel off the substrate to obtain the polyimide film;

[0074] S3. Add 10 g of pretreated graphene into 100 g of 2 wt% zinc nitrate solution, oscillate and adsorb for 3 h, then filter, wash and dry to obtain the zinc-loaded graphene;

[0075] The preparation method of the pretreated graphene is as follows: Add 8 g of graphene into 50 mL of concentrated sulfuric acid, stir at 80 °C for 3 h, then wash the obtained product to neutrality and dry it to obtain the pretreated graphene;

[0076] S4. Disperse 8 g of zinc-loaded graphene in 100 g of absolute ethanol to obtain a dispersion liquid, and then coat the dispersion liquid on the surface of the polyimide film, coat it on one side, and the coating amount is 10 g / cm 2 , dry to obtain the composite film;

[0077] S5. Immerse the composite film in a 2 wt% aqueous solution of epichlorohydrin, where the mass-volume ratio of the composite film to the epichlorohydrin aqueous solution is 1 g:15 mL, soak for 60 min, then take it out and dry it in a vacuum drying oven to obtain the composite graphene thermal conductive film.

[0078] Example 4

[0079] A preparation process of a composite graphene thermal conductive film includes the following steps:

[0080] S1. Disperse 12 g of pyromellitic dianhydride and 0.6 g of modified boron nitride in 250 mL of organic solvent DMF, then add 10 g of 4,4-diaminobenzophenone to it, and stir at room temperature for 8 h to obtain a polyamic acid mixture;

[0081] Among them, the preparation method of the modified boron nitride is as follows: Add 2 g of hydrochloric acid dopamine into 50 mL of Tris-HCl buffer solution, adjust the pH to 10, then add 2 g of hexagonal boron nitride and soak for 18 h. After the soaking is completed, take it out, wash it with water and dry it under vacuum to obtain the modified boron nitride;

[0082] S2. Cast the polyamic acid mixture into a film on a glass substrate. The thickness of the wet film is 1.5 mm. Then, carry out a heat preservation reaction at 200 °C in an inert atmosphere for 6 h. After the reaction ends, peel off the substrate to obtain a polyimide film;

[0083] S3. Add 10 g of pretreated graphene to 100 g of a 3 wt% zinc nitrate solution, oscillate and adsorb for 3 h, and then filter, wash, and dry to obtain zinc-loaded graphene;

[0084] The preparation method of the pretreated graphene is as follows: Add 8 g of graphene to 50 mL of concentrated sulfuric acid, stir at 80 °C for 3 h, and then wash the obtained product to neutrality and dry to obtain the pretreated graphene;

[0085] S4. Disperse 8 g of zinc-loaded graphene in 100 g of absolute ethanol to obtain a dispersion liquid. Then, coat the dispersion liquid on the surface of the polyimide film, coat on one side, and the coating amount is 6 g / cm 2 , and dry to obtain a composite film;

[0086] S5. Immerse the composite film in a 2 wt% aqueous epichlorohydrin solution, where the mass-volume ratio of the composite film to the aqueous epichlorohydrin solution is 1 g:15 mL, soak for 60 min, then take it out and dry it in a vacuum drying oven to obtain a composite graphene thermal conductive film.

[0087] Comparative Example 1

[0088] A preparation process of a composite graphene thermal conductive film includes the following steps:

[0089] S1. Disperse 10 g of pyromellitic dianhydride and 0.5 g of boron nitride in 250 mL of an organic solvent DMF, and then add 10 g of 4,4-diaminobenzophenone thereto, and stir at room temperature for 6 h to obtain a polyamic acid mixture;

[0090] S2. Cast the polyamic acid mixture into a film on a glass substrate. The thickness of the wet film is 2 mm. Then, carry out a heat preservation reaction at 200 °C in an inert atmosphere for 6 h. After the reaction ends, peel off the substrate to obtain a polyimide film;

[0091] S3. Add 8 g of pretreated graphene to 100 g of a 1 wt% zinc nitrate solution, oscillate and adsorb for 3 h, and then filter, wash, and dry to obtain zinc-loaded graphene;

[0092] The preparation method of the pretreated graphene is as follows: Add 8 g of graphene to 50 mL of concentrated sulfuric acid, stir at 80 °C for 3 h, and then wash the obtained product to neutrality and dry to obtain the pretreated graphene;

[0093] S4. Disperse 5 g of zinc-loaded graphene in 100 g of absolute ethanol to obtain a dispersion, and then coat the dispersion on the surface of a polyimide film, with single-sided coating and a coating amount of 8 g / cm 2 , and dry to obtain a composite film;

[0094] S5. Immerse the composite film in an aqueous solution of 3 wt% epichlorohydrin, where the mass-volume ratio of the composite film to the epichlorohydrin aqueous solution is 1 g:15 mL, soak for 30 min, then take it out and dry it in a vacuum drying oven to obtain the composite graphene thermal conductive film.

[0095] Comparative Example 1 was not subjected to modification treatment on boron nitride compared with Example 1.

[0096] Comparative Example 2

[0097] A preparation process of a composite graphene thermal conductive film includes the following steps:

[0098] S1. Disperse 10 g of pyromellitic dianhydride and 0.5 g of modified boron nitride in 250 mL of an organic solvent DMF, then add 10 g of 4,4-diaminobenzophenone thereto, and stir at room temperature for 6 h to obtain a polyamic acid mixture;

[0099] Among them, the preparation method of the modified boron nitride is as follows: Add 2 g of dopamine hydrochloride to 50 mL of Tris-HCl buffer solution, adjust the pH to 9, then add 2 g of hexagonal boron nitride and soak for 18 h. After soaking, take it out, wash it with water and dry it in vacuum to obtain the modified boron nitride;

[0100] S2. Cast the polyamic acid mixture into a film on a glass substrate, with the thickness of the wet film being 2 mm, then carry out a heat preservation reaction at 200 °C in an inert atmosphere for 6 h. After the reaction is completed, peel off the substrate to obtain a polyimide film;

[0101] S3. Disperse 5 g of pretreated graphene in 100 g of absolute ethanol to obtain a dispersion, and then coat the dispersion on the surface of the polyimide film, with single-sided coating and a coating amount of 8 g / cm 2 , and dry to obtain a composite film;

[0102] The preparation method of the pretreated graphene is as follows: Add 8 g of graphene to 50 mL of concentrated sulfuric acid, stir at 80 °C for 3 h, then wash the obtained product to neutrality and dry it to obtain the pretreated graphene;

[0103] S4. Immerse the composite film in an aqueous solution of 3 wt% epichlorohydrin, where the mass-volume ratio of the composite film to the epichlorohydrin aqueous solution is 1 g:15 mL, soak for 30 min, then take it out and dry it in a vacuum drying oven to obtain the composite graphene thermal conductive film.

[0104] Comparative Example 2 was not subjected to zinc loading treatment on the pretreated graphene as compared with Example 1.

[0105] Comparative Example 3

[0106] A preparation process of a composite graphene thermal conductive film comprises the following steps:

[0107] S1. Dissolve 10 g of pyromellitic dianhydride and 0.5 g of modified boron nitride in 250 mL of an organic solvent DMF, then add 10 g of 4,4-diaminobenzophenone thereto, and stir at room temperature for 6 h to obtain a polyamic acid mixed solution;

[0108] Among them, the preparation method of the modified boron nitride is as follows: Add 2 g of dopamine hydrochloride to 50 mL of Tris-HCl buffer solution, adjust the pH to 9, then add 2 g of hexagonal boron nitride and soak for 18 h. After the soaking is completed, take it out, wash it with water and dry it under vacuum to obtain the modified boron nitride;

[0109] S2. Cast the polyamic acid mixed solution into a film on a glass substrate, the thickness of the wet film is 2 mm, then carry out a heat preservation reaction at 200 °C in an inert atmosphere for 6 h. After the reaction is completed, peel off the substrate to obtain a polyimide film;

[0110] S3. Add 8 g of pretreated graphene to 100 g of a 1 wt% zinc nitrate solution, oscillate and adsorb for 3 h, then filter, wash and dry to obtain zinc-loaded graphene;

[0111] The preparation method of the pretreated graphene is as follows: Add 8 g of graphene to 50 mL of concentrated sulfuric acid, stir at 80 °C for 3 h, then wash the obtained product to neutrality and dry it to obtain the pretreated graphene;

[0112] S4. Disperse 5 g of zinc-loaded graphene in 100 g of absolute ethanol to obtain a dispersion liquid, then coat the dispersion liquid on the surface of the polyimide film, coat it on one side, and the coating amount is 8 g / cm 2 , dry it to obtain the composite graphene thermal conductive film.

[0113] Comparative Example 3 was not subjected to cross-linking treatment with epichlorohydrin as compared with Example 1.

[0114] Perform performance tests on the composite graphene thermal conductive films prepared in Examples 1-4 and Comparative Examples 1-3:

[0115] Among them, the test method of the thermal conductivity is carried out according to the standard of GB / T 10295-2008;

[0116] Limiting oxygen index: Tested in accordance with GB / T 2406.2-2009, the test specimens were made into type I splines, and the ignition method was A; tested 3 times, and the test results were averaged.

[0117] The test results are shown in Table 1:

[0118] Table 1

[0119] Thermal conductivity (W / (m·k)) Limiting oxygen index (%) Example 1 2.67 34.1 Example 2 2.62 33.6 Example 3 2.71 34.3 Example 4 2.65 33.8 Comparative Example 1 1.39 29.2 Comparative Example 2 2.64 31.7 Comparative Example 3 2.58 33.9

[0120] The thermal conductive films prepared in Example 1 and Comparative Example 3 were bent 100 times, and then their thermal conductivity and limiting oxygen index were tested. The test results are shown in Table 2:

[0121] Table 2

[0122] Thermal conductivity (W / (m·k)) Limiting oxygen index (%) Example 1 2.53 32.8 Comparative Example 3 1.36 28.0

[0123] In Comparative Example 3, since crosslinking agent epichlorohydrin was not used for crosslinking, after multiple bends, the graphene loaded with zinc peeled off, resulting in a decrease in the thermal conductivity and limiting oxygen index of the composite film.

[0124] Finally, it should be noted that the above embodiments do not limit the present invention in any form. For those skilled in the art, based on the present invention, some modifications and improvements can be made. Therefore, any modification or improvement made without departing from the spirit of the present invention falls within the scope of protection required by the present invention.

Claims

1. A preparation process of a composite graphene thermal conductive film, characterized in that, It includes the following steps: S1. Dissolve pyromellitic dianhydride and modified boron nitride in an organic solvent, then add 4,4-diaminobenzophenone thereto, and stir at room temperature for 4 - 8 h to obtain a polyamic acid mixture; S2. Cast the polyamic acid mixture into a film on a substrate, then carry out a heat preservation reaction under an inert atmosphere. After the reaction ends, peel off the substrate to obtain a polyimide film; S3. Add pretreated graphene to a zinc salt solution, oscillate and adsorb for 2 - 3 h, then filter, wash, and dry to obtain zinc-loaded graphene; S4. Disperse the zinc-loaded graphene in absolute ethanol to obtain a dispersion, then coat the dispersion on the surface of the polyimide film and dry to obtain a composite film; S5. Immerse the composite film in an aqueous solution of epichlorohydrin for 30 - 60 min, then take it out and dry it in a vacuum drying oven to obtain a composite graphene thermal conductive film.

2. The preparation process according to claim 1, characterized in that, In step S1, the preparation method of the modified boron nitride is as follows: Add dopamine hydrochloride to a Tris-HCl buffer solution, adjust the pH to 8 - 10, then add hexagonal boron nitride and soak for 16 - 24 h. After the soaking ends, take it out, wash it with water, and dry it under vacuum to obtain the modified boron nitride.

3. The preparation process according to claim 1, characterized in that, In step S1, the mass ratio of pyromellitic dianhydride, modified boron nitride, and 4,4-diaminobenzophenone is 10 - 15:0.5 - 1:

10.

4. The preparation process according to claim 1, wherein In step S2, the temperature of the heat preservation reaction is 200 - 210 °C, and the heat preservation time is 4 - 8 h.

5. The preparation process according to claim 1, characterized in that, In step S3, the preparation method of the pretreated graphene is as follows: Add graphene to concentrated sulfuric acid, stir at 80 - 90 °C for 2 - 4 h, then wash the obtained product until it is neutral and dry it to obtain the pretreated graphene.

6. The preparation process according to claim 1, characterized in that, In step S3, the mass ratio of the pretreated graphene to the zinc salt solution is 8 - 10:100, and the mass fraction of the zinc salt solution is 1 - 3%.

7. The preparation process according to claim 1, wherein In step S4, the mass ratio of the zinc-loaded graphene to absolute ethanol is 5 - 10:

100.

8. The preparation process according to claim 1, characterized in that, In step S4, the coating amount is 5-10 g / cm 2 .

9. The preparation process according to claim 1, characterized in that, In step S5, the mass fraction of the aqueous solution of epichlorohydrin is 2 - 4%.

10. A composite graphene thermal conductive film prepared by the preparation process according to any one of claims 1 - 9.