Graphene heat-conducting film and preparation method thereof

Abstract

The preparation method comprises the following steps: before coating, adding a carbon material into graphene oxide slurry, and uniformly stirring and mixing to obtain mixed slurry; the carbon material and the graphene oxide slurry are compounded according to the mass ratio of (10-25): 500; the carbon material comprises carbon nanotubes, carbon fibers, expanded graphite, homogeneous graphene, graphene oxide coating film leftover materials and graphene heat-conducting film leftover materials which are compounded according to the mass ratio of (1-5): (1-5): (0.5-3): (1-10): (1-20): (1-20). The longitudinal heat conductivity coefficient of the graphene heat conduction film is 9-20 W / m.K. The graphene micro-nano cavity superconducting film is prepared by compounding the GO slurry and various carbon materials and combining foaming and heat treatment processes, and the graphene micro-nano cavity superconducting film has remarkable beneficial effects in the aspect of improving the Z-direction heat conduction coefficient and the comprehensive performance.

Description

Technical Field

[0001] This invention belongs to the field of graphene new material technology, and specifically relates to a graphene thermal conductive film and a method for preparing the graphene thermal conductive film to improve the longitudinal thermal conductivity. Background Technology

[0002] Graphene, a two-dimensional carbon nanomaterial, has attracted much attention in the field of efficient thermal management due to its ultra-high in-plane thermal conductivity (theoretically reaching 5000 W / m·K). Its excellent in-plane thermal conductivity makes it show great application potential in areas such as heat dissipation films and flexible electronic devices. However, the weak interlayer van der Waals forces in graphene significantly limit its longitudinal (out-of-plane) thermal conductivity, typically less than 10 W / m·K, far lower than the in-plane value. This strong anisotropy in thermal conductivity severely restricts its application in scenarios requiring vertical heat dissipation, such as three-dimensional integrated chips and high-power electronic devices.

[0003] Currently, strategies to improve longitudinal thermal conductivity mainly include interlayer covalent bond bridging, intercalation doping, and three-dimensional structure reconstruction. However, these methods often involve increased process complexity, in-plane thermal conductivity loss, or decreased mechanical properties. In the current industrial production of graphene thermal conductive films, most improvements are achieved through interlayer covalent bond bridging, such as adding carbon nanotubes to construct thermally conductive channels between graphene layers, thus enhancing longitudinal thermal conductivity. However, this approach introduces new problems: strong interlayer coupling may compromise the intrinsic high mobility of graphene, and poor self-assembly can lead to surface cracking in the graphene thermal conductive film. Therefore, effectively improving the longitudinal thermal conductivity of graphene while maintaining its high in-plane thermal conductivity and mitigating surface cracking has become a key challenge in overcoming the technological bottlenecks of next-generation thermal management materials. Summary of the Invention

[0004] Based on the aforementioned technical problems, the purpose of this invention is to provide a method for preparing a graphene thermally conductive film that can improve the longitudinal thermal conductivity while avoiding surface cracking. Specifically, it includes the following steps: A graphene oxide slurry was prepared. Ammonia solution with a mass concentration of 25%-28% was added dropwise to deionized water under a stirring speed of 60-100 rpm. Graphene oxide cakes were then added to the system, and the mixture was dispersed in a planetary mixer at 800-1000 rpm for 0.5-2 hours. After dispersion, the mixture was transferred to a high-pressure homogenizer and homogenized 2-4 times at a pressure of 600-1000 bar and a temperature of 13-20°C to ensure thorough exfoliation of the graphene oxide sheets. The slurry viscosity was controlled at approximately 2500 mPa·s-3800 mPa·s, yielding a graphene oxide slurry with a solid content of 2%-9%. Typical, but not limited, solid contents of the graphene oxide slurry were set to 2%, 3.5%, 4%, 5%, 6%, 8%, and 9%.

[0005] Carbon materials are added to the graphene oxide slurry and stirred until homogeneous to obtain a mixed slurry. The carbon materials and the graphene oxide slurry are compounded at a mass ratio of 10-25g:500g. The carbon materials include carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded at a mass ratio of 1-2:1-2:0.5:1-2:8-10:5-10. The mass ratio of the carbon materials to the graphene oxide slurry is typically, but not limited to, 10g:500g, 15g:500g, and 25g:500g. The mass ratio of the carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps is typically, but not limited to, 1:1:0.5:1:8:5 and 2:2:0.5:2:10:10.

[0006] After adding the carbon material, mix in a high-powered stirrer at a speed of 40 r / min to 80 r / min for 40 min to 80 min, and then degas in a centrifugal degassing machine at a vacuum degree of less than 0.05 MPa and a speed of 600 r / min to 1000 r / min for 10 min to 30 min to obtain a uniformly mixed slurry.

[0007] 2) The mixed slurry is coated onto a substrate and dried to obtain a graphene oxide film. The substrate is a polyimide fabric substrate with a thickness of 0.3-1 mm, preferably 0.5 mm. A blade coating method is used, with a coating thickness of 3 mm-10 mm, preferably 5 mm. The drying process after coating is carried out in a forced-air drying oven at a temperature of 60-70°C for 3-5 hours.

[0008] 3) The graphene oxide film is immersed in a reducing agent for foaming treatment, and then dried to obtain a graphene foamed film.

[0009] In the foaming process, a hydrazine hydrate solution with a mass concentration of 8-12% is used as a reducing agent. The graphene oxide film is immersed in the reducing agent at an ambient temperature of 20-30°C for 40-80 seconds. Preferably, the mass concentration of hydrazine hydrate is 10%, the ambient temperature during the immersion process is set to 25°C, and the immersion time is 60 seconds.

[0010] The membrane after soaking is dried in a forced-air drying oven at 50-65℃ for 20-40 minutes to obtain a graphene foamed membrane; preferably, the drying temperature of the forced-air drying oven is 60℃ and the drying time is set to 30 minutes.

[0011] The graphene foamed film is subjected to thermal reduction treatment to obtain a graphene thermally conductive film. Specifically, the graphene foamed films are stacked, with a sheet of graphite paper placed between each film, and adjacent films are spaced apart. The films are then pretreated in an oven at 150°C for 2 hours. Afterward, the pretreated films are placed in a high-temperature furnace, first heated to 1200°C at a nitrogen atmosphere at a rate of 15°C / min for carbonization for 2 hours, then heated to 2800°C at a rate of 5°C / min for graphitization for 1.5 hours. Finally, the films are slowly cooled to obtain the graphene thermally conductive film.

[0012] Another object of the present invention is to provide a graphene thermal conductive film prepared by the above method, wherein the longitudinal thermal conductivity of the graphene thermal conductive film is 9-20 W / m·K.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: This patent prepares graphene micro-nano cavity superconducting films by compounding GO slurry with various carbon materials and combining foaming and heat treatment processes, which has significant beneficial effects on improving the Z-thermal conductivity and overall performance.

[0014] In terms of material blending, carbon materials include three types: carbon nanotubes, expanded graphite, and carbon fibers. Carbon nanotubes, with their excellent one-dimensional structure and high aspect ratio, can form efficient thermal conduction pathways in graphene oxide slurry, running through the superconducting film and bridging heat conduction along the Z-axis.

[0015] Expanded graphite, after expansion, exhibits a loose and porous structure. When combined with graphene oxide, it can synergistically construct more continuous thermally conductive channels during the foaming process, promoting heat transfer. The high strength and high modulus properties of carbon fiber enhance the stability of the membrane structure, reduce structural losses during heat conduction, and ensure the continuity of Z-direction thermal conduction.

[0016] Homogeneous graphene and graphene oxide have similar structures and can be well integrated. Compared with graphene oxide, homogeneous graphene lacks oxygen-containing functional groups and does not participate in the self-assembly process of graphene oxide into a film. However, it will physically attach between the layers of graphene oxide film to form a stable carbon network and optimize the Z-direction heat conduction path.

[0017] The addition of broken GO coating film scraps and thermal conductive film scraps not only enables resource reuse but also forms a good thermal conductivity path in the superconducting film, replenishes the carbon source, and further improves the network structure of the carbon material in the film, making the Z-direction heat conduction smoother. The foaming and heat treatment processes further amplify the advantages of material blending. During foaming, numerous micron- and nano-sized pores are formed within the material, constructing a unique micro / nano cavity structure. These pores act as "high-speed channels" for heat conduction, significantly improving Z-axis heat conduction efficiency. Subsequent heat treatment promotes the rearrangement of the carbon material structure, forming a highly ordered graphitized structure, reducing thermal resistance, and greatly enhancing Z-axis thermal conductivity. Furthermore, the superconducting film prepared by this process also possesses excellent mechanical properties, chemical stability, and lightweight advantages, showing broad application prospects in fields such as electronic heat dissipation and aerospace. Attached Figure Description

[0018] Figure 1 It is the graphene thermal conductive film prepared in Example 2.

[0019] Figure 2 This is the thermal conductivity test result of Example 2. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field, and there are no specific restrictions on their sources; they can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0021] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0022] The technical solution of the present invention is illustrated below through specific embodiments. It should be understood that the one or more steps mentioned in the present invention do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or limiting the scope of the present invention. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of the present invention. Example

[0023] A graphene oxide slurry with a solid content of 5% was prepared. 100g of GO cake, 10g of ammonia, and 890g of deionized water were placed in a planetary mixer and run at a stirring speed of 80r / min and a dispersion speed of 1000r / min for 1 hour to obtain a graphene oxide slurry with a solid content of 5%. The graphene oxide slurry was then transferred to a high-pressure homogenizer and homogenized twice at a pressure of 600-1000 bar and a temperature of 15℃ to ensure sufficient exfoliation of the graphene oxide sheets, and the slurry viscosity was controlled at approximately 3000 mPa·s.

[0024] Carbon materials are added to the graphene oxide slurry and stirred until homogeneous to obtain a mixed slurry. The carbon materials and the graphene oxide slurry are compounded at a mass ratio of 15:500. The carbon materials include carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded at a mass ratio of 2:2:0.5:2:10:10. After adding the above carbon materials, the mixture is stirred in a high-powered stirrer at 60 r / min for 60 min, and then degassed in a centrifuge at a vacuum of 0.03 MPa and a speed of 800 r / min for 20 min.

[0025] The mixed slurry was coated onto a substrate and dried to obtain a graphene oxide film. Alternatively, a blade coating method was used to coat the mixed slurry onto a 0.5 mm thick polyimide fabric substrate, with a coating thickness of 5 mm. The coating was then dried in a 65°C forced-air drying oven for 4 hours to obtain the coated film.

[0026] The graphene oxide film was immersed in a reducing agent for foaming treatment, and then dried to obtain a graphene foamed film. The coated film was foamed by immersing it in a 10% hydrazine hydrate solution at 25°C for 60 seconds, then removed and dried in a forced-air drying oven at 60°C for 30 minutes to obtain the graphene foamed film.

[0027] The graphene foamed film was subjected to thermal reduction treatment to obtain a graphene thermally conductive film. The specific operation of the thermal reduction treatment involved placing graphite paper between each graphene foamed film and pre-treating it in an oven at 150°C for 2 hours. Subsequently, the pre-treated films were placed in a high-temperature furnace, first carbonized at 1200°C for 2 hours under a nitrogen atmosphere at a heating rate of 15°C / min, then switched to argon protection and graphitized at 2800°C for 1.5 hours at a heating rate of 5°C / min. After slow cooling, the final product was obtained. Example

[0028] Compared with Example 1, the difference in this example is that the carbon material and the graphene oxide slurry are compounded in a mass ratio of 10:500.

[0029] A graphene oxide slurry with a solid content of 3.5% was prepared. 70g of GO cake, 7g of ammonia, and 923g of deionized water were placed in a planetary mixer and run at a stirring speed of 80r / min and a dispersion speed of 1000r / min for 1 hour to obtain a graphene oxide slurry with a solid content of 3.5%. The graphene oxide slurry was then transferred to a high-pressure homogenizer and homogenized twice at a pressure of 600-1000 bar and a temperature of 15℃ to ensure sufficient exfoliation of the graphene oxide sheets, and the slurry viscosity was controlled at approximately 3000 mPa·s.

[0030] Carbon materials are added to the graphene oxide slurry and stirred until homogeneous to obtain a mixed slurry. The carbon materials and the graphene oxide slurry are compounded at a mass ratio of 1:500. The carbon materials include carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded at a mass ratio of 2:2:0.5:2:10:10. After adding the above carbon materials, the mixture is stirred in a high-powered stirrer at 60 r / min for 60 min, and then degassed in a centrifuge at a vacuum of 0.03 MPa and a speed of 800 r / min for 20 min.

[0031] The mixed slurry was coated onto a substrate and dried to obtain a graphene oxide film. Alternatively, a blade coating method was used to coat the mixed slurry onto a 0.5 mm thick polyimide fabric substrate, with a coating thickness of 5 mm. The coating was then dried in a 65°C forced-air drying oven for 4 hours to obtain the coated film.

[0032] The graphene oxide film was immersed in a reducing agent for foaming treatment, and then dried to obtain a graphene foamed film. The coated film was foamed by immersing it in a 10% hydrazine hydrate solution at 25°C for 60 seconds, then removed and dried in a forced-air drying oven at 60°C for 30 minutes to obtain the graphene foamed film.

[0033] The graphene foamed film was subjected to thermal reduction treatment to obtain a graphene thermally conductive film. The specific operation of the thermal reduction treatment involved placing graphite paper between each graphene foamed film and pre-treating it in an oven at 150°C for 2 hours. Subsequently, the pre-treated films were placed in a high-temperature furnace, first carbonized at 1200°C for 2 hours under a nitrogen atmosphere at a heating rate of 15°C / min, then switched to argon protection and graphitized at 2800°C for 1.5 hours at a heating rate of 5°C / min. After slow cooling, the final product was obtained. Example

[0034] Compared with Example 1, the difference in this example is that the carbon material and the graphene oxide slurry are compounded in a mass ratio of 25:500.

[0035] A graphene oxide slurry with a solid content of 8% was prepared. 160g of GO cake, 16g of ammonia, and 824g of deionized water were placed in a planetary mixer and run at a stirring speed of 80r / min and a dispersion speed of 1000r / min for 1 hour to obtain a graphene oxide slurry with a solid content of 8%. The graphene oxide slurry was then transferred to a high-pressure homogenizer and homogenized twice at a pressure of 600-1000 bar and a temperature of 15℃ to ensure sufficient exfoliation of the graphene oxide sheets, and the slurry viscosity was controlled at approximately 3000 mPa·s.

[0036] Carbon materials are added to the graphene oxide slurry and stirred until homogeneous to obtain a mixed slurry. The carbon materials and the graphene oxide slurry are compounded at a mass ratio of 25:500. The carbon materials include carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded at a mass ratio of 2:2:0.5:2:10:10. After adding the above carbon materials, the mixture is stirred in a high-powered stirrer at 60 r / min for 60 min, and then degassed in a centrifuge at a vacuum of 0.03 MPa and a speed of 800 r / min for 20 min.

[0037] The mixed slurry was coated onto a substrate and dried to obtain a graphene oxide film. Alternatively, a blade coating method was used to coat the mixed slurry onto a 0.5 mm thick polyimide fabric substrate, with a coating thickness of 5 mm. The coating was then dried in a 65°C forced-air drying oven for 4 hours to obtain the coated film.

[0038] The graphene oxide film was immersed in a reducing agent for foaming treatment, and then dried to obtain a graphene foamed film. The coated film was foamed by immersing it in a 10% hydrazine hydrate solution at 25°C for 60 seconds, then removed and dried in a forced-air drying oven at 60°C for 30 minutes to obtain the graphene foamed film.

[0039] The graphene foamed film was subjected to thermal reduction treatment to obtain a graphene thermally conductive film. The specific operation of the thermal reduction treatment involved placing graphite paper between each graphene foamed film and pre-treating it in an oven at 150°C for 2 hours. Subsequently, the pre-treated films were placed in a high-temperature furnace, first carbonized at 1200°C for 2 hours under a nitrogen atmosphere at a heating rate of 15°C / min, then switched to argon protection and graphitized at 2800°C for 1.5 hours at a heating rate of 5°C / min. After slow cooling, the final product was obtained. Example

[0040] Compared with Example 1, the carbon material includes carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded in a mass ratio of 1:1:0.5:1:8:5.

[0041] A graphene oxide slurry with a solid content of 4% was prepared. 80g of GO cake, 80g of ammonia water, and 912g of deionized water were placed in a planetary mixer and run at a stirring speed of 80r / min and a dispersion speed of 1000r / min for 1 hour to obtain a graphene oxide slurry with a solid content of 4%. The graphene oxide slurry was then transferred to a high-pressure homogenizer and homogenized twice at a pressure of 600-1000 bar and a temperature of 15℃ to ensure sufficient exfoliation of the graphene oxide sheets. The slurry viscosity was controlled at approximately 3000 mPa·s.

[0042] Carbon materials are added to the graphene oxide slurry and stirred until homogeneous to obtain a mixed slurry. The carbon materials and the graphene oxide slurry are compounded at a mass ratio of 15:500. The carbon materials include carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded at a mass ratio of 1:1:0.5:1:8:5. After adding the above carbon materials, the mixture is stirred in a high-powered stirrer at 60 r / min for 60 min, and then degassed in a centrifuge at a vacuum of 0.03 MPa and a speed of 800 r / min for 20 min.

[0043] The mixed slurry was coated onto a substrate and dried to obtain a graphene oxide film. Alternatively, a blade coating method was used to coat the mixed slurry onto a 0.5 mm thick polyimide fabric substrate, with a coating thickness of 5 mm. The coating was then dried in a 65°C forced-air drying oven for 4 hours to obtain the coated film.

[0044] The graphene oxide film was immersed in a reducing agent for foaming treatment, and then dried to obtain a graphene foamed film. The coated film was foamed by immersing it in a 10% hydrazine hydrate solution at 25°C for 60 seconds, then removed and dried in a forced-air drying oven at 60°C for 30 minutes to obtain the graphene foamed film.

[0045] The graphene foamed film was subjected to thermal reduction treatment to obtain a graphene thermally conductive film. The specific operation of the thermal reduction treatment involved placing graphite paper between each graphene foamed film and pre-treating it in an oven at 150°C for 2 hours. Subsequently, the pre-treated films were placed in a high-temperature furnace, first carbonized at 1200°C for 2 hours under a nitrogen atmosphere at a heating rate of 15°C / min, then switched to argon protection and graphitized at 2800°C for 1.5 hours at a heating rate of 5°C / min. After slow cooling, the final product was obtained.

[0046] A graphene oxide slurry with a solid content of 5% was prepared. 100g of GO cake, 10g of ammonia, and 890g of deionized water were placed in a planetary mixer and run at a stirring speed of 80r / min and a dispersion speed of 1000r / min for 1 hour to obtain a graphene oxide slurry with a solid content of 5%. The graphene oxide slurry was then transferred to a high-pressure homogenizer and homogenized twice at a pressure of 600-1000 bar and a temperature of 15℃ to ensure sufficient exfoliation of the graphene oxide sheets and control the slurry viscosity to approximately 3000 mPa·s. Subsequently, the slurry was degassed for 20 minutes in a centrifugal degassing machine at a vacuum degree of 0.03 MPa and a rotation speed of 800r / min.

[0047] Graphene oxide slurry was coated onto a substrate and dried to obtain a graphene oxide film. Using a blade coating method, graphene oxide slurry was coated onto a 0.5 mm thick polyimide fabric substrate, with a coating thickness of 5 mm. The coating was then dried in a 65°C forced-air drying oven for 4 hours to obtain the coated film.

[0048] The graphene oxide film was immersed in a reducing agent for foaming treatment, and then dried to obtain a graphene foamed film. The coated film was foamed by immersing it in a 10% hydrazine hydrate solution at 25°C for 60 seconds, then removed and dried in a forced-air drying oven at 60°C for 30 minutes to obtain the graphene foamed film.

[0049] The graphene foamed film was subjected to thermal reduction treatment to obtain a graphene thermally conductive film. The specific operation of the thermal reduction treatment involved placing graphite paper between each graphene foamed film and pre-treating it in an oven at 150°C for 2 hours. Subsequently, the pre-treated films were placed in a high-temperature furnace, first carbonized at 1200°C for 2 hours under a nitrogen atmosphere at a heating rate of 15°C / min, then switched to argon protection and graphitized at 2800°C for 1.5 hours at a heating rate of 5°C / min. After slow cooling, the final product was obtained.

[0050] Compared with Example 1, the carbon materials in this comparative example include carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded in a mass ratio of 5:5:0:0:0:0.

[0051] A graphene oxide slurry with a solid content of 5% was prepared. 100g of GO cake, 10g of ammonia, and 890g of deionized water were placed in a planetary mixer and run at a stirring speed of 80r / min and a dispersion speed of 1000r / min for 1 hour to obtain a graphene oxide slurry with a solid content of 5%. The graphene oxide slurry was then transferred to a high-pressure homogenizer and homogenized twice at a pressure of 600-1000 bar and a temperature of 15℃ to ensure sufficient exfoliation of the graphene oxide sheets, and the slurry viscosity was controlled at approximately 3000 mPa·s.

[0052] Carbon materials are added to the graphene oxide slurry and stirred until homogeneous to obtain a mixed slurry. The carbon materials and the graphene oxide slurry are compounded at a mass ratio of 15:500. The carbon materials include carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded at a mass ratio of 5:5:0:0:0:0. After adding the above carbon materials, the mixture is stirred in a high-powered stirrer at 60 r / min for 60 min, and then degassed in a centrifuge at a vacuum of 0.03 MPa and a speed of 800 r / min for 20 min.

[0053] The mixed slurry was coated onto a substrate and dried to obtain a graphene oxide film. Alternatively, a blade coating method was used to coat the mixed slurry onto a 0.5 mm thick polyimide fabric substrate, with a coating thickness of 5 mm. The coating was then dried in a 65°C forced-air drying oven for 4 hours to obtain the coated film.

[0054] The graphene oxide film was immersed in a reducing agent for foaming treatment, and then dried to obtain a graphene foamed film. The coated film was foamed by immersing it in a 10% hydrazine hydrate solution at 25°C for 60 seconds, then removed and dried in a forced-air drying oven at 60°C for 30 minutes to obtain the graphene foamed film.

[0055] The graphene foamed film was subjected to thermal reduction treatment to obtain a graphene thermally conductive film. The specific operation of the thermal reduction treatment involved placing graphite paper between each graphene foamed film and pre-treating it in an oven at 150°C for 2 hours. Subsequently, the pre-treated films were placed in a high-temperature furnace, first carbonized at 1200°C for 2 hours under a nitrogen atmosphere at a heating rate of 15°C / min, then switched to argon protection and graphitized at 2800°C for 1.5 hours at a heating rate of 5°C / min. After slow cooling, the final product was obtained.

[0056] Compared with Example 1, the difference in this comparative example is that the carbon material and the graphene oxide slurry are compounded in a mass ratio of 5:500. The carbon material includes carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded in a mass ratio of 0:0:0:0:20:20.

[0057] A graphene oxide slurry with a solid content of 6% was prepared. 100g of GO cake, 10g of ammonia, and 890g of deionized water were placed in a planetary mixer and run at a stirring speed of 80r / min and a dispersion speed of 1000r / min for 1 hour to obtain a graphene oxide slurry with a solid content of 6%. The graphene oxide slurry was then transferred to a high-pressure homogenizer and homogenized twice at a pressure of 600-1000 bar and a temperature of 15℃ to ensure sufficient exfoliation of the graphene oxide sheets. The viscosity of the slurry was controlled at approximately 3000 mPa·s.

[0058] Carbon materials are added to the graphene oxide slurry and stirred until homogeneous to obtain a mixed slurry. The carbon materials and the graphene oxide slurry are compounded at a mass ratio of 5:500. The carbon materials include carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded at a mass ratio of 0:0:0:0:20:20. After adding the above carbon materials, the mixture is stirred in a high-powered stirrer at 60 r / min for 60 min, and then degassed in a centrifuge at a vacuum of 0.03 MPa and a speed of 800 r / min for 20 min.

[0059] The mixed slurry was coated onto a substrate and dried to obtain a graphene oxide film. Alternatively, a blade coating method was used to coat the mixed slurry onto a 0.5 mm thick polyimide fabric substrate, with a coating thickness of 5 mm. The coating was then dried in a 65°C forced-air drying oven for 4 hours to obtain the coated film.

[0060] The graphene oxide film was immersed in a reducing agent for foaming treatment, and then dried to obtain a graphene foamed film. The coated film was foamed by immersing it in a 10% hydrazine hydrate solution at 25°C for 60 seconds, then removed and dried in a forced-air drying oven at 60°C for 30 minutes to obtain the graphene foamed film.

[0061] The graphene foamed film was subjected to thermal reduction treatment to obtain a graphene thermally conductive film. The specific operation of the thermal reduction treatment involved placing graphite paper between each graphene foamed film and pre-treating it in an oven at 150°C for 2 hours. Subsequently, the pre-treated films were placed in a high-temperature furnace, first carbonized at 1200°C for 2 hours under a nitrogen atmosphere at a heating rate of 15°C / min, then switched to argon protection and graphitized at 2800°C for 1.5 hours at a heating rate of 5°C / min. After slow cooling, the final product was obtained.

[0062] The graphene thermally conductive films obtained in Examples 1-4 and Comparative Examples 1-3 were used for thermal conductivity testing using the laser flash method, according to ASTM-E1461 2013. Samples were cut into 12.7 mm diameter circular pieces, their thickness was measured and recorded, and they were placed in a 4-sample round / 12.7 mm holder and tested using a Netzsch 467 instrument. The test environment temperature was set to 25-27℃, the temperature threshold (tolerance / stability threshold) to 0.3 K, the number of flash points to 5, the voltage to 260 V, the pulse width to 44 μs, the main gain to 6633, the sampling time to 6 ms, the detection area to 3.7 mm², and parameter optimization enabled. After the test, the average longitudinal thermal conductivity of each group of samples was recorded. Thermal conductivity = thermal diffusivity × density × specific heat capacity. The test results are shown in the table below:

[0063] Analysis of the experimental results revealed that, in Example 1, carbon material was added at a mass ratio of 15:500. The graphene thermal conductive film prepared in this example had a longitudinal thermal conductivity of 15 W / mK, which is 5 times that of the ordinary graphene thermal conductive film in Comparative Example 1 without added carbon material. In Example 2, carbon material was added at a mass ratio of 10:500. The thermal conductive film prepared in this example had a longitudinal thermal conductivity of 9 W / mK, which is 3 times that of the conventional graphene thermal conductive film in Comparative Example 1. In Example 3, carbon material was added at a mass ratio of 25:500. The graphene thermal conductive film prepared in this example had a longitudinal thermal conductivity of 18 W / mK, which is 6 times that of the conventional graphene thermal conductive film in Comparative Example 1. The test results from Examples 1-3 show that adding carbon materials containing carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene film scraps to the graphene oxide slurry can improve the longitudinal thermal conductivity of the graphene thermal conductive film. In Example 4, the proportions of carbon nanotubes, carbon fibers, homogenized graphene, and scraps were slightly reduced, but the improvement in thermal conductivity was not significantly different from the examples, and it was four times the longitudinal thermal conductivity of the conventional graphene thermal conductive film in Comparative Example 1. In Comparative Example 2, only carbon nanotubes and carbon fibers were added to the carbon material, and the improvement in longitudinal thermal conductivity was not as good as in Examples 1-4. Analysis suggests that without the role of expanded graphite, graphene oxide cannot obtain enough space to embed carbon nanotubes and carbon fibers during self-assembly, and cannot synergistically form a highly efficient longitudinal thermal conductive pathway. In Comparative Example 3, only scraps of graphene oxide coating film and graphene thermal conductive film were added to the carbon material, and the thermal conductivity was not improved at all. This is because the addition of scraps can only improve the utilization rate of raw materials. Graphene oxide cannot be aligned along the orientation direction during self-assembly, so it does not help improve longitudinal thermal conductivity.

[0064] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0065] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a graphene thermally conductive film, comprising the following steps: 1) Prepare graphene oxide slurry with a solid content of 3.5%-8.5%; 2) The slurry is coated onto the substrate and dried to obtain a graphene oxide film; 3) The graphene oxide film is immersed in a reducing agent for foaming treatment, and then dried to obtain a graphene foamed film; 4) The graphene foamed film is subjected to thermal reduction treatment to obtain a graphene thermally conductive film; The feature is that: before coating, carbon material is added to the graphene oxide slurry and stirred to mix evenly to obtain a mixed slurry; the carbon material and the graphene oxide slurry are compounded in a mass ratio of 10-25:500; the carbon material includes carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded in a mass ratio of 1-5:1-5:0.5-3:1-10:1-20:1-20.

2. The method for preparing a graphene thermally conductive film according to claim 1, characterized in that: The carbon materials include carbon nanotubes, carbon fibers, expanded graphite, homogenized graphene, graphene oxide coating film scraps, and graphene thermal conductive film scraps compounded in a mass ratio of 1-2:1-2:0.5:1-2:8-10:5-10.

3. The method for preparing a graphene thermally conductive film according to claim 2, characterized in that: After adding the carbon material, mix in a high-powered stirrer at a speed of 40 r / min to 80 r / min for 40 min to 80 min, and then degas in a centrifugal degassing machine at a vacuum degree of less than 0.05 MPa and a speed of 600 r / min to 1000 r / min for 10 min to 30 min to obtain a uniformly mixed slurry.

4. The method for preparing a graphene thermally conductive film according to claim 3, characterized in that: After adding the carbon material, the mixture is stirred for 60 minutes in a high-powered stirrer at 60 r / min, and then degassed for 20 minutes in a centrifugal degassing machine at 0.03 MPa and 800 r / min to obtain a uniformly mixed slurry.

5. The method for preparing a graphene thermally conductive film according to claim 1, characterized in that: In step 2), the substrate is selected as a polyimide fabric substrate with a thickness of 0.3-1mm, preferably, the thickness of the polyimide fabric substrate is 0.5mm.

6. The method for preparing a graphene thermally conductive film according to claim 5, characterized in that: In step 2), the coating thickness is set to 3mm-10mm, preferably 5mm.

7. The method for preparing a graphene thermally conductive film according to claim 1, characterized in that: In step 3), a hydrazine hydrate solution with a mass concentration of 8-12% is selected as a reducing agent. The graphene oxide film is immersed in the reducing agent at an ambient temperature of 20-30°C for 40-80 seconds. Preferably, the mass concentration of hydrazine hydrate is 10%, the ambient temperature during the immersion process is set to 25°C, and the immersion time is 60 seconds.

8. The method for preparing a graphene thermally conductive film according to claim 1, characterized in that: In step 3), the membrane after soaking is dried in a forced-air drying oven at 50-65°C for 20-40 minutes to obtain a graphene foamed membrane; preferably, the drying temperature of the forced-air drying oven is 60°C and the drying time is set to 30 minutes.

9. The method for preparing a graphene thermally conductive film according to claim 1, characterized in that: In step 4), the graphene foamed film is stacked and placed in an oven at 150°C for 2 hours for pretreatment. Then, the pretreated film is placed in a high-temperature furnace and heated to 1200°C in a nitrogen atmosphere at a heating rate of 15°C / min for carbonization treatment for 2 hours. Then, argon protection is switched and the temperature is increased to 2800°C at a heating rate of 5°C / min for graphitization treatment for 1.5 hours. After slow cooling, a graphene thermal conductive film is obtained.

10. A graphene thermally conductive film, characterized in that: The graphene thermal conductive film is prepared using the method described in claims 1-9, and has a longitudinal thermal conductivity of 9-20 W / m·K.

Images