Preparation method of high-thermal-conductivity polyimide-based graphite film

Abstract

The invention belongs to the technical field of heat-conducting materials, and provides a preparation method of a high-heat-conductivity polyimide-based graphite film. The preparation method comprises the following steps: (1) mixing aminated diamond and nickel-doped aminated graphene to obtain a difunctional composite filler; (2) adding a difunctional composite filler into the polyamide acid solution, and dispersing and defoaming to obtain a polyamide acid composite solution; (3) carrying out film casting on the polyamide acid composite solution, and then carrying out gradient imidization to obtain a polyimide composite film; (4) performing segmented gradient carbonization on the polyimide composite film, and then performing catalytic graphitization; and (5) performing interface densification, and cutting to obtain a finished product. The preparation method is high in repeatability, special customized equipment is not needed, and the obtained high-thermal-conductivity polyimide-based graphite film has excellent flexibility, high temperature resistance and insulation safety, can be widely applied to multiple fields of 5G base stations, power batteries, aerospace electronic equipment and the like, and is huge in industrialization potential.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive materials technology, specifically, it relates to a method for preparing a high thermal conductivity polyimide-based graphite film. Background Technology

[0002] With the rapid development of 5G communication, new energy vehicles, vehicle power batteries, and high-end electronic equipment, the power density of devices continues to increase, leading to a sharp increase in heat generation. This places more stringent demands on the thermal conductivity, thickness adaptability, structural stability, and energy consumption of heat dissipation materials. High thermal conductivity polyimide-based graphite films, with their excellent heat resistance, flexibility, and thermal conductivity, have become a core candidate material for high-end heat dissipation applications. The expansion of their application scenarios is increasingly driving the need to improve the overall performance of these materials. Polyimide-based graphite films are typically prepared from polyimide films through carbonization and graphitization processes. Their thermal conductivity primarily depends on the ordered graphite crystal structure and the interconnected thermal conduction pathways formed after graphitization. However, existing preparation techniques still face numerous challenges in practical applications, severely hindering their industrialization and performance upgrades. For example, in terms of thermal conductivity, existing graphite films generally suffer from low interlayer thermal conductivity. In traditional fabrication methods, the filler is unevenly dispersed and often forms a two-dimensional thermally conductive network, resulting in a significant difference between in-plane and vertical thermal conductivity. This makes it difficult for heat to be transferred quickly between layers, easily forming local hot spots and affecting the uniformity of heat dissipation and the lifespan of the device. At the same time, in pursuit of high in-plane thermal conductivity, existing technologies often sacrifice vertical thermal conductivity, thus failing to meet the requirements of high-end devices for three-dimensional heat dissipation. Furthermore, in existing technologies, the single filler system used cannot simultaneously achieve both thermal path construction and structural stability, and the synergistic effect of composite fillers is not fully utilized.

[0003] For example, in terms of thickness adaptability and structural stability, existing processes for preparing graphite films are mostly limited to thin specifications. When attempting to prepare films thicker than 100μm, problems such as cracking, delamination, and loose structure easily occur. This is mainly because during the carbonization and graphitization process of thick films, the internal stress distribution is uneven, the molecular chain orientation and crystal growth are poorly consistent, and the interlayer bonding force is weak, resulting in a low yield of thick films and making them unsuitable for the demand for thick heat dissipation materials in power batteries, large base station equipment, and other applications. For example, in terms of energy consumption during preparation, existing graphitization processes require extremely high temperatures to transform amorphous carbon into an ordered graphite structure, typically exceeding 2800℃. This not only consumes a large amount of energy and increases production costs but also places extremely high demands on the high-temperature resistance of equipment, limiting the large-scale application of the process. Furthermore, high-temperature treatment exacerbates the brittleness of the membrane material, reducing its flexibility and structural integrity, further impacting the material's practical application. In summary, developing a preparation method that can simultaneously address the issues of low interlayer thermal conductivity, easy cracking of thick films, and high energy consumption in graphitization, while reducing preparation energy consumption and achieving stable preparation and comprehensive performance improvement of thick-sized graphite films, has become a pressing technical challenge in the field of high thermal conductivity polyimide-based graphite films. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a method for preparing a high thermal conductivity polyimide-based graphite film. This preparation method exhibits high repeatability, requires no specially customized equipment, and yields a high thermal conductivity polyimide-based graphite film that combines excellent flexibility, high-temperature resistance, and insulation safety. It can be widely applied in various fields such as 5G base stations, power batteries, and aerospace electronic equipment, demonstrating significant industrialization potential.

[0005] To achieve the above objectives, the solution adopted by the present invention is as follows: A method for preparing a high thermal conductivity polyimide-based graphite film includes: (1) preparation of bifunctional composite filler: preparing nickel-doped aminated graphene; mixing aminated diamond and nickel-doped aminated graphene at a mass ratio of 1:3-1:5, ultrasonically dispersing and drying to obtain bifunctional composite filler; (2) synthesis of polyamic acid composite solution: adding 1.5-3% of the mass of bifunctional composite filler to polyamic acid solution, dispersing and degassing to obtain polyamic acid composite solution; (3) casting polyamic acid composite solution into a film and then gradient imidizing to obtain polyimide composite film; (4) performing segmented gradient carbonization on polyimide composite film and then catalytic graphitization; (5) then performing interface densification and cutting to obtain finished product.

[0006] Further, in a preferred embodiment of the present invention, step (1) includes: ultrasonically dispersing graphene oxide in deionized water to obtain an aqueous solution of graphene oxide, adding a water-soluble nickel salt and an aminosilane coupling agent to react, and filtering and drying to obtain nickel-doped amino graphene.

[0007] Further, in a preferred embodiment of the present invention, in step (1), the carbon-to-oxygen ratio of the graphene oxide is 1.9-2.2, the sheet diameter is 50-80 μm, and the concentration of the aqueous solution of the graphene oxide is 2-5 mg / mL; the water-soluble nickel salt is nickel nitrate with a concentration of 0.05-0.1 mol / L, and the aminosilane coupling agent is KH550, with an amount of 5-8% of the mass of the graphene oxide; the reaction is stirred at 60-80°C for 2-3 h; and the reaction is vacuum dried at 80°C for 2 h.

[0008] Furthermore, in a preferred embodiment of the present invention, in step (1), the particle size of the amination diamond is 5-10 μm, the degree of amination is ≥90%, the dispersion medium during mixing is anhydrous ethanol, and the ultrasonic dispersion time is 20 min.

[0009] Further, in a preferred embodiment of the present invention, step (3) includes: casting the polyamic acid composite solution into a film by a doctor blade, then pre-drying it at 80°C for 1 hour, at 120°C for 1.5 hours, and at 150°C for 1 hour to remove the solvent, followed by segmented gradient thermal imidization under a nitrogen atmosphere, and then obtaining a polyimide composite film after cooling.

[0010] Further, in a preferred embodiment of the present invention, step (4) includes gradient carbonization under an argon atmosphere, heating from 1500°C to 2000°C at a heating rate of 5°C / min and holding for 30 min, and then heating to 2400-2600°C at a heating rate of 5°C / min and holding for 45-60 min to perform catalytic graphitization.

[0011] Further, in a preferred embodiment of the present invention, step (5) includes: after hot pressing densification, after oxygen plasma treatment at a power of 80W for 5 minutes, a SiO2 insulating layer with a thickness of 1-2μm is coated, and then the finished product is cut.

[0012] Furthermore, in a preferred embodiment of the present invention, in step (5), hot pressing densification is carried out at 200-250°C, 8-12 MPa, a reduction rate of 15-20%, and a holding time of 30 min.

[0013] Further, in a preferred embodiment of the present invention, step (2) includes: dissolving 4,4'-diaminodiphenyl ether in N,N-dimethylacetamide under nitrogen gas at a flow rate of 3-5 L / min, stirring until completely clear, and controlling the solid content to 10-12%; then adding pyromellitic dianhydride in batches at 0-5°C according to a molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride of 1:1.02, stirring and reacting for 3-4 h to obtain a polyamic acid solution with a viscosity of 60000-70000 mPa·s.

[0014] Further, in a preferred embodiment of the present invention, step (2) includes: ultrasonically dispersing the polyamic acid solution and the bifunctional composite filler for 40 min, mechanically stirring at a speed of 300 r / min for 2 h, and vacuum degassing at -0.09 MPa for 30 min to obtain the polyamic acid composite solution.

[0015] The beneficial effects of the method for preparing a high thermal conductivity polyimide-based graphite film provided by this invention are: (1) The preparation method of the high thermal conductivity polyimide-based graphite film provided by the present invention can construct a three-dimensional thermal conductivity path by using a bifunctional composite filler of nickel-doped aminated graphene and aminated diamond. At the same time, nickel can catalyze and optimize the crystal structure. Under the specific technical conditions mentioned above in this application, the in-plane thermal conductivity and vertical thermal conductivity of the finished product are significantly improved, and the thermal conductivity can be fully optimized.

[0016] (2) The preparation method of the high thermal conductivity polyimide-based graphite film provided by the present invention adopts gradient imidization and segmented gradient carbonization process, which can accurately control the heating rate and holding time, significantly reduce the internal stress of the film layer, and combine with interface densification hot pressing treatment, can stably prepare a 100-500μm thick film. The finished product has no cracking or delamination, and the porosity is ≤8%, which can solve the problems of performance degradation and structural instability of existing thick films.

[0017] (3) The preparation method of the high thermal conductivity polyimide-based graphite film provided by the present invention utilizes the nickel element to catalyze graphitization, reducing the graphitization temperature from the traditional 2600-3000℃ to 2400-2600℃, greatly reducing energy consumption. At the same time, the catalytic effect can also promote the orderly arrangement of carbon atoms, and the mechanical properties and thermal stability are improved simultaneously. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] The following is a detailed description of a method for preparing a high thermal conductivity polyimide-based graphite film according to an embodiment of the present invention.

[0020] A method for preparing a high thermal conductivity polyimide-based graphite film, comprising: (1) Preparation of bifunctional composite filler: Graphene oxide with a carbon-to-oxygen ratio of 1.9-2.2 and a sheet diameter of 50-80 μm was ultrasonically dispersed in deionized water to obtain an aqueous solution of graphene oxide with a concentration of 2-5 mg / mL; under these conditions, it is possible to obtain uniformly dispersed graphene oxide. Then, nickel nitrate with a concentration of 0.05-0.1 mol / L (this concentration is calculated based on the volume of the aqueous solution of graphene oxide) and KH550 with an amount of 5-8% of the mass of graphene oxide were added, and the mixture was stirred and reacted at 60-80℃ for 2-3 h; after filtration, it was vacuum dried at 80℃ for 2 h to obtain nickel-doped aminated graphene; under these conditions, nickel ions were loaded on the surface of graphene oxide and formed catalytic active sites, and KH550 achieved aminated modification of graphene oxide, thereby improving the interfacial bonding force with the polyamic acid matrix and diamond.

[0021] Next, ammoniated diamond with a particle size of 5-10 μm and an amination degree of ≥90% was mixed with nickel-doped ammoniated graphene at a mass ratio of 1:3-1:5, ultrasonically dispersed in anhydrous ethanol for 20 min, and dried to obtain a bifunctional composite filler. Under these conditions, the two fillers were uniformly composited and dried to obtain a bifunctional composite filler. Among them, ammoniated diamond can optimize in-plane thermal conductivity, and nickel-doped ammoniated graphene can construct interlayer thermal conductivity pathways and play a catalytic role in graphitization, thereby synergistically improving thermal conductivity.

[0022] (2) Synthesis of polyamic acid composite solution: Under nitrogen gas at a flow rate of 3-5 L / min, 4,4'-diaminodiphenyl ether is dissolved in N,N-dimethylacetamide and stirred until completely clear, controlling the solid content to 10-12%. Then, at 0-5℃, pyromellitic dianhydride is added in batches at a molar ratio of 1:1.02 of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride, and the reaction is stirred for 3-4 hours to obtain a polyamic acid solution with a viscosity of 60,000-70,000 mPa·s. Under these conditions, low temperature and batch feeding can avoid local overheating that could lead to gelation, thereby precisely controlling the viscosity of the polyamic acid solution to ensure its film-forming properties.

[0023] Next, 1.5-3% (by weight) of bifunctional composite filler was added to the polyamic acid solution. After ultrasonic dispersion for 40 min, the solution was mechanically stirred at 300 r / min for 2 h, and then vacuum degassed at -0.09 MPa for 30 min to obtain the polyamic acid composite solution. Under these conditions, a uniform polyamic acid composite solution can be obtained, avoiding filler agglomeration and air bubbles that could affect the membrane density.

[0024] (3) The polyamic acid composite solution is cast into a film by a doctor blade: the doctor blade gap is 200-500μm, the casting speed is 0.8-1.2m / min, the substrate is a stainless steel plate, and a wet film is obtained by standing at room temperature for 1h. Under these conditions, the casting parameters can be controlled to ensure the uniformity of the film thickness. Then, the film is pre-dried in a gradient manner by holding at 80℃ for 1h, 120℃ for 1.5h, and 150℃ for 1h, and the solvent is removed by hot air circulation. Under these conditions, the rapid evaporation of the solvent can be avoided to prevent the film layer from becoming porous, and a self-supporting gel film is obtained. Then, the film is subjected to segmented gradient thermal imidization in a nitrogen atmosphere, and after cooling, a polyimide composite film is obtained.

[0025] The gradient thermal imidization process includes: holding at 150°C for 1 hour in a nitrogen atmosphere, then raising the temperature from 150°C to 250°C at a rate of 2°C / min and holding for 1 hour, then raising the temperature to 350°C at a rate of 3°C / min and holding for 1.5 hours, and finally raising the temperature to 400°C at a rate of 2°C / min and holding for 30 minutes to complete the imidization reaction. Under these conditions, internal stress can be reduced, film cracking can be avoided, and a polyimide composite film is obtained after cooling.

[0026] (4) After segmented gradient carbonization of the polyimide composite film, catalytic graphitization is carried out: under an argon atmosphere with a pressure of 0.15-0.2 MPa, the temperature is increased from room temperature to 500℃ at a heating rate of 0.15℃ / min and held for 1.5h, then increased to 1000℃ at a heating rate of 0.1℃ / min and held for 2h, then increased to 1500℃ at a heating rate of 0.1℃ / min and held for 3h. At this time, N, O and other heteroatoms can be slowly removed to form an ordered carbon structure. The low heating rate and segmented holding can reduce thermal stress. Next, under an argon atmosphere with a pressure of 0.8-1.0 MPa, the temperature was increased from 1500℃ to 2000℃ at a heating rate of 5℃ / min and held for 30 min. Then, the temperature was increased to 2400-2600℃ at a heating rate of 5℃ / min and held for 45-60 min. Under these conditions, nickel can catalyze the rearrangement of carbon atoms, reducing the graphitization temperature. At the same time, the amylating groups promote the fusion of the filler and the carbon matrix interface, reducing the interfacial thermal resistance, and finally obtaining an excellent crystalline structure.

[0027] (5) After interface densification, the finished product is cut: hot pressing densification is carried out at 200-250℃, 8-12MPa, and a reduction rate of 15-20% for 30 minutes. Under these conditions, the pores of the film layer can be eliminated and the density can be increased, thereby optimizing the thermal conductivity and mechanical properties. After hot pressing densification, oxygen plasma is used at 80W for 5 minutes and then a SiO2 insulating layer with a thickness of 1-2μm is coated. The above plasma modification can balance conductivity and insulation, avoid the risk of short circuit in application, and the finished product is cut.

[0028] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0029] Example 1 This embodiment provides a method for preparing a high thermal conductivity polyimide-based graphite film, including: (1) Preparation of bifunctional composite filler: Graphene oxide with a carbon-oxygen ratio of 2.0 and a sheet diameter of 60 μm was ultrasonically dispersed in deionized water to obtain an aqueous solution of graphene oxide with a concentration of 4 mg / mL; then nickel nitrate with a concentration of 0.08 mol / L and KH550 with an amount of 6% of the mass of graphene oxide were added, and the mixture was stirred at 70 °C for 2.5 h; after filtration, it was vacuum dried at 80 °C for 2 h to obtain nickel-doped aminated graphene; then aminated diamond with a particle size of 5-10 μm and an amination degree of ≥90% was mixed with nickel-doped aminated graphene at a mass ratio of 1:4, ultrasonically dispersed in anhydrous ethanol for 20 min, and dried to obtain bifunctional composite filler.

[0030] (2) Synthesis of polyamic acid composite solution: Under nitrogen gas with a flow rate of 4 L / min, 4,4'-diaminodiphenyl ether was dissolved in N,N-dimethylacetamide and stirred until completely clear, with the solid content controlled at 10-12%; then, at 2℃, pyromellitic dianhydride was added in batches at a molar ratio of 1:1.02 between 4,4'-diaminodiphenyl ether and pyromellitic dianhydride, and the reaction was stirred for 3.5 h to obtain a polyamic acid solution; then, 2% by mass of bifunctional composite filler was added to the polyamic acid solution, ultrasonically dispersed for 40 min, mechanically stirred at a speed of 300 r / min for 2 h, and vacuum degassed at -0.09 MPa for 30 min to obtain a polyamic acid composite solution.

[0031] (3) The polyamic acid composite solution was cast into a film by a doctor blade: the doctor blade gap was 300 μm, the casting speed was 1 m / min, the substrate was a stainless steel plate, and the film was left to stand at room temperature for 1 h to obtain a wet film; the doctor blade gap was 300 μm, the casting speed was 1 m / min, the substrate was a stainless steel plate, and the film was left to stand at room temperature for 1 h to obtain a wet film; then the film was subjected to segmented gradient thermal imidization under a nitrogen atmosphere, and the film was kept at 150 °C for 1 h under a nitrogen atmosphere, then the temperature was increased from 150 °C to 250 °C at a heating rate of 2 °C / min and kept for 1 h, then the temperature was increased to 350 °C at a heating rate of 3 °C / min and kept for 1.5 h, then the temperature was increased to 400 °C at a heating rate of 2 °C / min and kept for 30 min to complete the imidization reaction; after cooling, a polyimide composite film was obtained.

[0032] (4) After the polyimide composite film is subjected to segmented gradient carbonization, it is catalytically graphitized: In an argon atmosphere with a pressure of 0.18 MPa, the temperature is increased from room temperature to 500℃ at a heating rate of 0.15℃ / min and held for 1.5h, then increased to 1000℃ at a heating rate of 0.1℃ / min and held for 2h, then increased to 1500℃ at a heating rate of 0.1℃ / min and held for 3h; then in an argon atmosphere with a pressure of 0.9 MPa, the temperature is increased from 1500℃ to 2500℃ at a heating rate of 5℃ / min and held for 50min.

[0033] (5) Hot pressing densification was carried out at 220℃, 10MPa, and 18% reduction rate for 30 minutes. After hot pressing densification, the finished product was cut.

[0034] Example 2 This embodiment provides a method for preparing a high thermal conductivity polyimide-based graphite film. The difference from Embodiment 1 is that step (1) includes: preparation of bifunctional composite filler: graphene oxide with a carbon-to-oxygen ratio of 1.9 and a sheet diameter of 80 μm is ultrasonically dispersed in deionized water to obtain an aqueous solution of graphene oxide with a concentration of 2 mg / mL; then nickel nitrate with a concentration of 0.05 mol / L and KH550 with an amount of 5% of the mass of graphene oxide are added, and the mixture is stirred at 60°C for 3 h; filtered and vacuum dried at 80°C for 2 h to obtain nickel-doped aminated graphene; then aminated diamond with a particle size of 5-10 μm and an amination degree ≥90% is mixed with nickel-doped aminated graphene at a mass ratio of 1:3, ultrasonically dispersed in anhydrous ethanol for 20 min, and dried to obtain bifunctional composite filler.

[0035] Example 3 This embodiment provides a method for preparing a high thermal conductivity polyimide-based graphite film. The difference from Embodiment 1 is that step (1) includes: preparation of bifunctional composite filler: graphene oxide with a carbon-to-oxygen ratio of 2.2 and a sheet diameter of 50 μm is ultrasonically dispersed in deionized water to obtain an aqueous solution of graphene oxide with a concentration of 5 mg / mL; then nickel nitrate with a concentration of 0.1 mol / L and KH550 with an amount of 8% of the mass of graphene oxide are added, and the mixture is stirred and reacted at 80°C for 2 h; filtered and vacuum dried at 80°C for 2 h to obtain nickel-doped aminated graphene; then aminated diamond with a particle size of 5-10 μm and an amination degree ≥90% is mixed with nickel-doped aminated graphene at a mass ratio of 1:5, ultrasonically dispersed in anhydrous ethanol for 20 min, and dried to obtain bifunctional composite filler.

[0036] Example 4 This embodiment provides a method for preparing a high thermal conductivity polyimide-based graphite film. The difference from Embodiment 1 is that step (3) includes: casting a polyamic acid composite solution into a film by a doctor blade: the doctor blade gap is 200-500 μm, the casting speed is 0.8-1.2 m / min, the substrate is a stainless steel plate, and the film is left to stand at room temperature for 1 h to obtain a wet film; the doctor blade gap is 200-500 μm, the casting speed is 0.8-1.2 m / min, the substrate is a stainless steel plate, and the film is left to stand at room temperature for 1 h to obtain a wet film; Then, it was pre-dried in a gradient manner by holding at 80℃ for 1 hour, 120℃ for 1.5 hours, and 150℃ for 1 hour, and the solvent was removed by hot air circulation. Next, a segmented gradient thermal imidization was performed under a nitrogen atmosphere. The temperature was held at 150°C for 1 hour under a nitrogen atmosphere, then increased from 150°C to 250°C at a heating rate of 2°C / min and held for 1 hour, then increased to 350°C at a heating rate of 3°C / min and held for 1.5 hours, and finally increased to 400°C at a heating rate of 2°C / min and held for 30 minutes to complete the imidization reaction. After cooling, a polyimide composite film was obtained.

[0037] Example 5 This embodiment provides a method for preparing a high thermal conductivity polyimide-based graphite film. The difference from Embodiment 4 is that step (4) includes: performing segmented gradient carbonization of the polyimide composite film followed by catalytic graphitization: in an argon atmosphere at a pressure of 0.18 MPa, the temperature is increased from room temperature to 500°C at a heating rate of 0.15°C / min and held for 1.5 h, then increased to 1000°C at a heating rate of 0.1°C / min and held for 2 h, then increased to 1500°C at a heating rate of 0.1°C / min and held for 3 h; then in an argon atmosphere at a pressure of 0.9 MPa, the temperature is increased from 1500°C to 2000°C at a heating rate of 5°C / min and held for 30 min, then increased to 2400°C at a heating rate of 5°C / min and held for 60 min.

[0038] Example 6 This embodiment provides a method for preparing a high thermal conductivity polyimide-based graphite film. The difference from embodiment 5 is that step (5) includes: hot pressing densification at 220°C, 10MPa, 18% reduction rate, and holding for 30 minutes. After hot pressing densification, an oxygen plasma treatment at 80W for 5 minutes is applied, followed by coating with a SiO2 insulating layer with a thickness of 1-2μm, and then cutting to obtain the finished product.

[0039] Comparative Example 1 This comparative example provides a method for preparing a high thermal conductivity polyimide-based graphite film. The difference from Example 1 is that step (1) includes: preparation of filler: graphene oxide with a carbon-to-oxygen ratio of 2.0 and a sheet diameter of 60 μm is ultrasonically dispersed in deionized water to obtain an aqueous solution of graphene oxide with a concentration of 4 mg / mL; then nickel nitrate with a concentration of 0.08 mol / L and KH550 with an amount of 6% of the mass of graphene oxide are added, and the mixture is stirred and reacted at 70°C for 2.5 h; filtered and vacuum dried at 80°C for 2 h to obtain nickel-doped amino graphene.

[0040] (2) Synthesis of polyamic acid composite solution: Under nitrogen gas with a flow rate of 4 L / min, 4,4'-diaminodiphenyl ether was dissolved in N,N-dimethylacetamide and stirred until completely clear, with the solid content controlled at 10-12%; then, at 2℃, pyromellitic dianhydride was added in batches at a molar ratio of 1:1.02 of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride, and the reaction was stirred for 3.5 h to obtain a polyamic acid solution; then, 2% of the filler by mass was added to the polyamic acid solution, ultrasonically dispersed for 40 min, mechanically stirred at a speed of 300 r / min for 2 h, and vacuum degassed at -0.09 MPa for 30 min to obtain a polyamic acid composite solution.

[0041] Comparative Example 2 This comparative example provides a method for preparing a high thermal conductivity polyimide-based graphite film. The difference from Example 1 is that step (1) includes: preparation of filler: using aminated diamond with a particle size of 5-10 μm and an amination degree ≥90% as filler; (2) synthesis of polyamic acid composite solution: under nitrogen gas with a flow rate of 4 L / min, 4,4'-diaminodiphenyl ether is dissolved in N,N-dimethylacetamide and stirred until completely clear, controlling the solid content to 10-12%; then at 2°C, pyromellitic dianhydride is added in batches according to the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride of 1:1.02, and stirred for 3.5 h to obtain a polyamic acid solution; then 2% of the filler by mass is added to the polyamic acid solution, ultrasonically dispersed for 40 min, mechanically stirred at a speed of 300 r / min for 2 h, and vacuum degassed at -0.09 MPa for 30 min to obtain a polyamic acid composite solution.

[0042] Comparative Example 3 This comparative example provides a method for preparing a high thermal conductivity polyimide-based graphite film. The difference from Example 1 is that in step (1): graphene oxide with a carbon-to-oxygen ratio of 2.0 and a sheet diameter of 60 μm is ultrasonically dispersed in deionized water to obtain an aqueous solution of graphene oxide with a concentration of 4 mg / mL; then nickel nitrate with a concentration of 0.08 mol / L and KH550 with an amount of 6% of the mass of graphene oxide are added, and the mixture is stirred at 70°C for 2.5 h; filtered and vacuum dried at 80°C for 2 h to obtain nickel-doped aminated graphene; then aminated diamond with a particle size of 5-10 μm and an amination degree ≥90% is mixed with nickel-doped aminated graphene at a mass ratio of 1:1, ultrasonically dispersed in anhydrous ethanol for 20 min, and dried to obtain a bifunctional composite filler.

[0043] Comparative Example 4 This comparative example provides a method for preparing a high thermal conductivity polyimide-based graphite film. The difference from Example 1 is that in step (2), the polyamic acid composite solution is synthesized as follows: under nitrogen gas at a flow rate of 4 L / min, 4,4'-diaminodiphenyl ether is dissolved in N,N-dimethylacetamide and stirred until completely clear, controlling the solid content to 10-12%; then, at 2°C, pyromellitic dianhydride is added in batches at a molar ratio of 1:1.02 of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride, and the mixture is stirred for 3.5 h to obtain a polyamic acid solution; then, 5% of the mass of the bifunctional composite filler is added to the polyamic acid solution, ultrasonically dispersed for 40 min, mechanically stirred at a speed of 300 r / min for 2 h, and vacuum degassed at -0.09 MPa for 30 min to obtain the polyamic acid composite solution.

[0044] Experimental Example 1 The high thermal conductivity polyimide-based graphite films prepared using the methods provided in Examples 1-6 and Comparative Examples 1-4 were subjected to the following performance tests: In-plane thermal conductivity and perpendicular thermal conductivity: measured in accordance with the relevant standards of GB / T 22588-2008; Finished product thickness: Measured according to the relevant standard GB / T 13542.2-2009; Porosity: Liquid wetting method test: Dry the sample to constant weight (mass m1), vacuum immerse it in anhydrous ethanol for 2 hours, remove it, wipe the surface dry, weigh the saturated mass m2, and calculate the porosity according to the formula porosity = (m2-m1) / [ρethanol×sample volume]. Appearance; Tensile strength: determined in accordance with the relevant standard of ISO 527:2012; Damage assessment after 2000 bends: Using a 5mm diameter cylindrical shaft, the sample was repeatedly bent 180°, with each bend held for 10 seconds. After a total of 2000 bends, the sample was observed for cracking.

[0045] The results of tests for in-plane thermal conductivity, vertical thermal conductivity, finished product thickness, porosity, and appearance are shown in Table 1; the results of tests for tensile strength and the degree of breakage after 2000 bending cycles are shown in Table 2.

[0046] Table 1 Table 2 As shown in Tables 1 and 2, the preparation method provided in this application, by using a bifunctional composite filler formed by aminated diamond and nickel-doped aminated graphene, and then combining it with a polyamic acid solution under specific technical conditions, followed by gradient imidization, segmented carbonization, and interface densification under specific conditions, can greatly exert a synergistic effect, constructing an in-plane and interlayer heat conduction path. Combined with the catalytic graphitization effect of nickel, this significantly improves the thermal conductivity and mechanical properties of the product, achieving a simultaneous improvement in high thermal conductivity, excellent mechanical properties, and a regular appearance. It has broad industrialization prospects in consumer electronics, new energy, aerospace, and other fields.

[0047] In summary, the preparation method of the high thermal conductivity polyimide-based graphite film provided by this invention offers excellent reproducibility, requires no special customized equipment, and yields a high thermal conductivity polyimide-based graphite film that combines excellent flexibility, high temperature resistance, and insulation safety. This allows for wide application in various fields such as 5G base stations, power batteries, and aerospace electronic equipment, demonstrating significant industrialization potential.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high thermal conductivity polyimide-based graphite film, characterized in that: include: (1) Preparation of bifunctional composite filler: Nickel-doped aminated graphene was prepared; aminated diamond and nickel-doped aminated graphene were mixed at a mass ratio of 1:3-1:5, ultrasonically dispersed and dried to obtain bifunctional composite filler; (2) Synthesis of polyamic acid composite solution: Add 1.5-3% of the bifunctional composite filler by mass to the polyamic acid solution, and obtain the polyamic acid composite solution after dispersion and degassing; (3) After casting the polyamic acid composite solution into a film, it is subjected to gradient imidization to obtain a polyimide composite film; (4) The polyimide composite film is subjected to segmented gradient carbonization and then catalytic graphitization; (5) Next, after the interface is densified, the finished product is cut.

2. The method for preparing a high thermal conductivity polyimide-based graphite film according to claim 1, characterized in that: Step (1) includes: ultrasonically dispersing graphene oxide in deionized water to obtain an aqueous solution of graphene oxide, adding water-soluble nickel salt and aminosilane coupling agent to react, filtering and drying to obtain nickel-doped amino graphene.

3. The method for preparing a high thermal conductivity polyimide-based graphite film according to claim 2, characterized in that: In step (1), the carbon-to-oxygen ratio of the graphene oxide is 1.9-2.2, the sheet diameter is 50-80 μm, and the concentration of the graphene oxide aqueous solution is 2-5 mg / mL; the water-soluble nickel salt is nickel nitrate with a concentration of 0.05-0.1 mol / L, and the aminosilane coupling agent is KH550, with an amount of 5-8% of the mass of the graphene oxide; the reaction is stirred at 60-80℃ for 2-3 h; and then vacuum dried at 80℃ for 2 h.

4. The method for preparing a high thermal conductivity polyimide-based graphite film according to claim 2, characterized in that: In step (1), the particle size of the amination diamond is 5-10 μm, the degree of amination is ≥90%, the dispersion medium during mixing is anhydrous ethanol, and the ultrasonic dispersion time is 20 min.

5. The method for preparing a high thermal conductivity polyimide-based graphite film according to claim 1, characterized in that: Step (3) includes: casting the polyamic acid composite solution into a film by a doctor blade, then pre-drying it at 80°C for 1 hour, 120°C for 1.5 hours, and 150°C for 1 hour to remove the solvent, followed by segmented gradient thermal imidization under a nitrogen atmosphere, and finally obtaining a polyimide composite film after cooling.

6. The method for preparing a high thermal conductivity polyimide-based graphite film according to claim 1, characterized in that: Step (4) includes gradient carbonization under an argon atmosphere, heating from 1500℃ to 2000℃ at a heating rate of 5℃ / min and holding for 30min, and then heating to 2400-2600℃ at a heating rate of 5℃ / min and holding for 45-60min to perform catalytic graphitization.

7. The method for preparing the high thermal conductivity polyimide-based graphite film according to claim 1, characterized in that: Step (5) includes: after hot pressing densification, oxygen plasma treatment at 80W for 5 minutes is applied to coat a SiO2 insulating layer with a thickness of 1-2μm, and then the finished product is cut.

8. The method for preparing a high thermal conductivity polyimide-based graphite film according to claim 4, characterized in that: In step (5), hot pressing densification is carried out at 200-250℃, 8-12MPa, with a reduction rate of 15-20%, and held for 30 minutes.

9. The method for preparing a high thermal conductivity polyimide-based graphite film according to claim 1, characterized in that: Step (2) includes: dissolving 4,4'-diaminodiphenyl ether in N,N-dimethylacetamide under nitrogen gas at a flow rate of 3-5 L / min, stirring until completely clear, and controlling the solid content to 10-12%; then adding the pyromellitic dianhydride in batches at 0-5℃ according to the molar ratio of the 4,4'-diaminodiphenyl ether to pyromellitic dianhydride of 1:1.02, stirring for 3-4 h to obtain the polyamic acid solution with a viscosity of 60000-70000 mPa·s.

10. The method for preparing a high thermal conductivity polyimide-based graphite film according to claim 9, characterized in that: Step (2) includes: ultrasonically dispersing the polyamic acid solution and the bifunctional composite filler for 40 min, mechanically stirring at a speed of 300 r / min for 2 h, and vacuum degassing at -0.09 MPa for 30 min to obtain the polyamic acid composite solution.

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