Preparation method of ultrahigh thermal conductivity graphite film

Abstract

The application discloses a preparation method of super-high thermal conductive graphite film, which comprises the following steps: S1, polyimide film is placed in a high-temperature furnace for pre-carbonization to obtain a carbonized film; S2, the pre-carbonized film is subjected to temperature rising and falling cycle treatment under inert gas protection, and then is subjected to carbonization treatment, and is naturally cooled to room temperature to obtain a carbonized film; S3, graphene oxide nanosheet and hexagonal boron nitride nanosheet dispersion liquid are sprayed on the surface of the carbonized film, and the carbonized film is dried to obtain a carbonized film sprayed with graphene oxide nanosheet and hexagonal boron nitride nanosheet; S4, the carbonized film sprayed with graphene oxide nanosheet and hexagonal boron nitride nanosheet is subjected to gradient temperature rising graphitization treatment under inert gas protection, and is cooled to obtain a carbon foam film; and S5, the carbon foam film is subjected to calendering by a calendering machine to obtain the super-high thermal conductive graphite film. The whole process scheme improves the thermophysical properties of the graphite film, is suitable for continuous industrial production, and improves the product stability and reliability.

Description

Technical Field

[0001] This invention relates to the field of thermal conductive materials technology, and specifically to a method for preparing an ultra-high thermal conductivity graphite film. Background Technology

[0002] With the increasing integration of electronic devices, especially in high-performance computing, 5G communication, aerospace, and LED chip fields, the power consumption and heat flux density of electronic devices are rising sharply, leading to a significant increase in heat dissipation requirements. Effective thermal management has become a key factor determining the performance, stability, and lifespan of electronic devices. Therefore, developing high thermal conductivity materials to improve heat dissipation efficiency has become an important research direction in the field of materials science.

[0003] Graphite, due to its excellent thermal conductivity, chemical stability, and lightweight properties, has become one of the ideal thermal conductive materials. Artificial graphite films, especially ultrathin graphite films prepared through a polyimide (PI) film carbonization-graphitization process, have become a hot material in the field of heat dissipation for electronic devices due to their superior in-plane thermal conductivity. Conventional processes typically involve vacuum carbonization at 1200–1300℃, followed by high-temperature graphitization at 2800–3200℃ to form a highly crystalline graphite film. This method has the advantages of relatively simple process, short cycle, and low cost. However, in actual preparation, during high-temperature heat treatment, uneven heating of different layers of the PI film can easily generate internal stress, causing the film layers to bend, warp, or break, affecting the quality of the final product. Furthermore, as the thickness of the PI film increases, uneven heat conduction during carbonization and graphitization leads to different degrees of graphitization between the inner and outer layers, affecting thermal conductivity. In addition, the thermal conductivity of graphite films is greatly affected by the orientation and crystallinity of the graphite sheets. Traditional processes make it difficult to precisely control the arrangement of graphite sheets along the surface direction, which limits the thermal conductivity.

[0004] Therefore, it is urgent to optimize the preparation method of PI film and graphite film, overcome the above problems, and improve the structural uniformity, thermal conductivity and mechanical stability of graphite film, so as to meet the heat dissipation requirements of high-performance electronic devices. Summary of the Invention

[0005] Based on the problems existing in the background technology, the present invention provides a method for preparing ultra-high thermal conductivity graphite film. Through the process synergy effect, the thermal conductivity, thermal stability and mechanical strength of graphite film are significantly improved, while ensuring the uniformity and reliability of the product, making it have broad application prospects in the fields of electronic heat dissipation, flexible thermal interface materials and thermal management of high power devices.

[0006] This invention is implemented through the following technical solutions:

[0007] A method for preparing an ultra-high thermal conductivity graphite film includes the following steps:

[0008] S1. Place the polyimide film in a high-temperature furnace, heat it to 450-500℃ under vacuum conditions at a rate of 2-3℃ / min, and hold it at that temperature for 0.5-1h to obtain a pre-carbonized film.

[0009] S2. The pre-carbonized film is subjected to a heating and cooling cycle under inert gas protection, and then the temperature is further increased to 1300-1500℃ at 3-5℃ / min, held for 2-3 hours, and carbonized. The film is then naturally cooled to room temperature to obtain the carbonized film.

[0010] S3. Spray a dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets onto the surface of the carbonized film, and dry it to obtain a carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets.

[0011] S4. The carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets is heated to 800-900℃ at 5-8℃ / min and held for 0.5h under inert gas protection; then heated to 1500-1600℃ at 3-5℃ / min and held for 0.5-1h; then heated to 2000-2200℃ at 1-2℃ / min and held for 0.5-1h; finally heated to 2800℃ at 4-6℃ / min and held for 1-3h; and then cooled naturally to obtain a carbon foam film.

[0012] S5. The carbon foam film is calendered by a calender to obtain an ultra-high thermal conductivity graphite film.

[0013] Furthermore, the thickness of the polyimide film in step S1 is 38-300 μm.

[0014] Furthermore, in step S1, the vacuum condition is to maintain the pressure inside the high-temperature furnace below 15 Pa.

[0015] Furthermore, the heating and cooling cycle treatment in step S2 is as follows: the pre-carbonized film is heated to 540-550℃ at a rate of 2-3℃ / min and held for 5-10 min, and then cooled to 450-500℃ at a rate of 3-5℃ / min and held for 20-30 min; the cycle is repeated 2-5 times.

[0016] Furthermore, during the heating phase, the furnace pressure is maintained at 100-120 kPa; during the cooling phase, the furnace pressure is maintained at 70-90 kPa.

[0017] Furthermore, the number of cycles is related to the thickness of the polyimide film: 2 cycles when the thickness of the polyimide film is 38-50 μm; 3 cycles when the thickness of the polyimide film is 51-120 μm; 4 cycles when the thickness of the polyimide film is 121-220 μm; and 5 cycles when the thickness of the polyimide film is 221-300 μm.

[0018] Furthermore, the solvent in the dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets is isopropanol or ethanol; the concentration of graphene oxide nanosheets is 0.5-1.0 mg / mL; and the concentration of hexagonal boron nitride nanosheets is 0.3-0.8 mg / mL.

[0019] Furthermore, the dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets also includes a dispersant and a silane coupling agent. The dispersant is sodium dodecyl sulfate with a concentration of 0.1-0.2 wt%; the concentration of the silane coupling agent is 0.05-0.1 wt%.

[0020] Furthermore, in step S4, a pressure of 1-2 MPa is applied during the continuous gradient heating process.

[0021] Furthermore, in step S5, the pressure of the calender is 3-5 MPa.

[0022] The beneficial effects of this invention are:

[0023] 1. This invention significantly improves the uniformity of thermal conductivity of PI films during carbonization and graphitization by employing heating and cooling cycles, auxiliary thermal conductive layer spraying, and continuous gradient heating graphitization treatment. This makes the degree of graphitization inside and outside the film more consistent, thereby achieving ultra-high uniformity and high thermal conductivity in the final product. At the same time, heating and cooling cycles and air pressure control effectively release the thermal stress in the material and reduce the generation of microcracks. The introduction of auxiliary nanosheets further constructs efficient thermal bridges, and the applied pressure also densifies the carbon foam structure. The overall process not only improves the thermophysical properties of the graphite film, but is also suitable for continuous industrial production, improving product stability and reliability.

[0024] 2. The heating and cooling cycle treatment in step S2 of this invention achieves uniform breakage and rearrangement of polyimide molecular chains, promoting the regular formation of the C6 ring structure; the alternating pressure change of maintaining a gas pressure of 100-120 kPa during the heating stage and maintaining a gas pressure of 70-90 kPa during the cooling stage enhances the molecular migration ability inside the film and significantly reduces microscale stress concentration; the precise correspondence between the number of cycles and the thickness of the raw material ensures that products of different thicknesses can obtain consistent internal structural uniformity.

[0025] 3. In step S3 of this invention, the spraying of graphene oxide nanosheets and hexagonal boron nitride nanosheet dispersions synergistically enhances the uniformity and thermal conductivity of the graphite film. After spraying, the graphene oxide nanosheets penetrate into the pores of the carbonized film and are reduced to continuous graphene sheets during the subsequent graphitization process, significantly reducing the porosity of the graphite film. Simultaneously, the oxygen-containing functional groups of graphene oxide bond with the active sites of the carbonized film, repairing microcracks and improving the mechanical properties of the graphite film. Hexagonal boron nitride nanosheets possess a unique two-dimensional honeycomb crystal structure very similar to graphite, earning them the nickname "white graphite." However, the in-plane thermal conductivity of hexagonal boron nitride nanosheets reaches as high as 2000 W / m·K. This superior thermal conductivity stems from the rigid lattice structure formed by its strong covalent BN bonds and its low phonon scattering characteristics. Hexagonal boron nitride nanosheets sprayed onto the surface of carbonized films can fill the microscopic defects and pores in the graphite structure, reducing interfacial thermal resistance along the heat conduction path. The thermal expansion coefficient of hexagonal boron nitride nanosheets is similar to that of graphite, enabling them to maintain structural stability during graphitization, reducing thermal stress accumulation, and improving film uniformity. When working synergistically with graphene oxide nanosheets, van der Waals forces and dipole-dipole interactions can form between hexagonal boron nitride and graphene oxide, promoting carbon atom rearrangement and increasing the degree of graphitization during high-temperature processing. Attached Figure Description

[0026] The accompanying drawings are provided to further explain the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0027] Figure 1 SEM image of the ultra-high thermal conductivity graphite film prepared in Example 1;

[0028] Figure 2 SEM image of the graphite film prepared in Comparative Example 1;

[0029] Figure 3 SEM image of the graphite film prepared in Comparative Example 2;

[0030] Figure 4 The image shows the appearance of the ultra-high thermal conductivity graphite film prepared in Example 1.

[0031] Figure 5 The image shows the appearance of the graphite film prepared in Comparative Example 1.

[0032] Figure 6 The image shows the appearance of the graphite film prepared in Comparative Example 2. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0034] Example 1

[0035] A method for preparing an ultra-high thermal conductivity graphite film includes the following steps:

[0036] S1. Place a 225μm thick polyimide film into a high-temperature furnace, evacuate to keep the pressure inside the furnace below 15Pa, raise the temperature to 500℃ at 3℃ / min, and hold for 0.5h to obtain a pre-carbonized film.

[0037] S2. The pre-carbonized film is subjected to a heating and cooling cycle under argon protection, i.e., the temperature is increased to 550℃ at 2℃ / min and held for 10min, then decreased to 480℃ at 5℃ / min and held for 30min; the furnace pressure is maintained at 120kPa during the heating phase and 80kPa during the cooling phase; the cycle is repeated 5 times; then the temperature is increased to 1500℃ at 5℃ / min and held for 2.5h for carbonization treatment, and then naturally cooled to room temperature to obtain the carbonized film.

[0038] S3. Spray a dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets onto the surface of the carbonized film, and dry it to obtain a carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets.

[0039] The solvent in the dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets is ethanol; the concentration of graphene oxide nanosheets is 1.0 mg / mL; the concentration of hexagonal boron nitride nanosheets is 0.6 mg / mL; it also includes a dispersant and a silane coupling agent, the dispersant being sodium dodecyl sulfate with a concentration of 0.15 wt%; the concentration of the silane coupling agent is 0.1 wt%.

[0040] S4. The carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets was heated to 900℃ at 6℃ / min and held for 0.5h under argon protection; then heated to 1600℃ at 5℃ / min and held for 0.5h; then heated to 2200℃ at 2℃ / min and held for 0.5h; finally heated to 2800℃ at 5℃ / min and held for 2h; a pressure of 1.5MPa was applied during the continuous gradient heating process; and the film was cooled naturally to obtain a carbon foam film.

[0041] S5. The carbon foam film is calendered in a calender at a pressure of 4 MPa to obtain an ultra-high thermal conductivity graphite film.

[0042] Example 2

[0043] A method for preparing an ultra-high thermal conductivity graphite film includes the following steps:

[0044] S1. Place a 225μm thick polyimide film into a high-temperature furnace, evacuate to keep the pressure inside the furnace below 15Pa, raise the temperature to 500℃ at 3℃ / min, and hold for 0.5h to obtain a pre-carbonized film.

[0045] S2. The pre-carbonized film is subjected to a heating and cooling cycle under argon protection, i.e., the temperature is increased to 550℃ at 2℃ / min and held for 10min, then decreased to 500℃ at 4℃ / min and held for 20min; the furnace pressure is maintained at 100kPa during the heating phase and at 80kPa during the cooling phase; the cycle is repeated 5 times; then the temperature is increased to 1500℃ at 5℃ / min and held for 2.5h for carbonization treatment, and then naturally cooled to room temperature to obtain the carbonized film;

[0046] S3. Spray a dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets onto the surface of the carbonized film, and dry it to obtain a carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets.

[0047] The solvent in the dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets is ethanol; the concentration of graphene oxide nanosheets is 1.0 mg / mL; the concentration of hexagonal boron nitride nanosheets is 0.6 mg / mL; it also includes a dispersant and a silane coupling agent, the dispersant being sodium dodecyl sulfate with a concentration of 0.15 wt%; the concentration of the silane coupling agent is 0.1 wt%.

[0048] S4. The carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets was heated to 900℃ at 6℃ / min and held for 0.5h under argon protection; then heated to 1600℃ at 5℃ / min and held for 0.5h; then heated to 2200℃ at 2℃ / min and held for 0.5h; finally heated to 2800℃ at 5℃ / min and held for 2h; a pressure of 1.5MPa was applied during the continuous gradient heating process; and the film was cooled naturally to obtain a carbon foam film.

[0049] S5. The carbon foam film is calendered in a calender at a pressure of 4 MPa to obtain an ultra-high thermal conductivity graphite film.

[0050] Example 3

[0051] S1. Place a 225μm thick polyimide film into a high-temperature furnace, evacuate to keep the pressure inside the furnace below 15Pa, raise the temperature to 500℃ at 3℃ / min, and hold for 0.5h to obtain a pre-carbonized film.

[0052] S2. The pre-carbonized film is subjected to a heating and cooling cycle under argon protection, i.e., the temperature is increased to 550℃ at 2℃ / min and held for 10min, then decreased to 480℃ at 5℃ / min and held for 30min; the furnace pressure is maintained at 120kPa during the heating phase and 80kPa during the cooling phase; the cycle is repeated 5 times; then the temperature is increased to 1500℃ at 5℃ / min and held for 2.5h for carbonization treatment, and then naturally cooled to room temperature to obtain the carbonized film.

[0053] S3. Spray a dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets onto the surface of the carbonized film, and dry it to obtain a carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets.

[0054] The solvent in the dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets is ethanol; the concentration of graphene oxide nanosheets is 0.8 mg / mL; the concentration of hexagonal boron nitride nanosheets is 0.8 mg / mL; it also includes a dispersant and a silane coupling agent, the dispersant being sodium dodecyl sulfate with a concentration of 0.1 wt%; the concentration of the silane coupling agent is 0.1 wt%.

[0055] S4. The carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets was heated to 900℃ at 6℃ / min and held for 0.5h under argon protection; then heated to 1600℃ at 5℃ / min and held for 0.5h; then heated to 2200℃ at 2℃ / min and held for 0.5h; finally heated to 2800℃ at 5℃ / min and held for 2h; a pressure of 1.5MPa was applied during the continuous gradient heating process; and the film was cooled naturally to obtain a carbon foam film.

[0056] S5. The carbon foam film is calendered in a calender at a pressure of 4 MPa to obtain an ultra-high thermal conductivity graphite film.

[0057] Example 4

[0058] A method for preparing an ultra-high thermal conductivity graphite film includes the following steps:

[0059] S1. Place a 200μm thick polyimide film into a high-temperature furnace, evacuate to keep the pressure inside the furnace below 15Pa, raise the temperature to 500℃ at 3℃ / min, and hold for 0.5h to obtain a pre-carbonized film.

[0060] S2. The pre-carbonized film is subjected to a heating and cooling cycle under argon protection, i.e., the temperature is increased to 550℃ at 2℃ / min and held for 10min, then decreased to 480℃ at 5℃ / min and held for 30min; the furnace pressure is maintained at 120kPa during the heating phase and at 80kPa during the cooling phase; the cycle is repeated 4 times; then the temperature is increased to 1500℃ at 5℃ / min and held for 2.5h for carbonization treatment, and then naturally cooled to room temperature to obtain the carbonized film;

[0061] S3. Spray a dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets onto the surface of the carbonized film, and dry it to obtain a carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets.

[0062] The solvent in the dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets is ethanol; the concentration of graphene oxide nanosheets is 1.0 mg / mL; the concentration of hexagonal boron nitride nanosheets is 0.6 mg / mL; it also includes a dispersant and a silane coupling agent, the dispersant being sodium dodecyl sulfate with a concentration of 0.15 wt%; the concentration of the silane coupling agent is 0.1 wt%.

[0063] S4. The carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets was heated to 900℃ at 6℃ / min and held for 0.5h under argon protection; then heated to 1600℃ at 5℃ / min and held for 0.5h; then heated to 2200℃ at 2℃ / min and held for 0.5h; finally heated to 2800℃ at 5℃ / min and held for 2h; a pressure of 1.5MPa was applied during the continuous gradient heating process; and the film was cooled naturally to obtain a carbon foam film.

[0064] S5. The carbon foam film is calendered in a calender at a pressure of 4 MPa to obtain an ultra-high thermal conductivity graphite film.

[0065] Based on Examples 1-4, further, in step S1, when acquiring the pre-carbonized film, image monitoring and analysis are performed on the interior of the high-temperature furnace, including:

[0066] Acquire monitoring images of the interior of a high-temperature furnace, identify the polyimide film based on the monitoring images, lock the image of the polyimide film, and obtain the polyimide film detection image;

[0067] The shape of the polyimide film is analyzed based on the detected images to obtain real-time shape information of the polyimide film.

[0068] The deformation of the polyimide film is analyzed based on the real-time shape information of the polyimide film to determine whether the deformation of the polyimide film is due to dimensional shrinkage, and the deformation analysis results are obtained.

[0069] When the deformation analysis results indicate that the deformation of the polyimide film is not a dimensional shrinkage, further analysis of the aggregation of the polyimide film is conducted to obtain the aggregation characteristics of the polyimide film.

[0070] Based on the aggregation characteristics of the polyimide film, it is determined whether the deformation of the polyimide film needs to be adjusted. If adjustment is required, the polyimide film is stretched according to its aggregation characteristics.

[0071] The above-mentioned visualization of the interior of the high-temperature furnace through image monitoring and analysis enables the polyimide film to be better pre-carbonized during pre-carbonization in the high-temperature furnace. This avoids the polyimide film from agglomerating due to thermal deformation, which affects the internal pre-carbonization of the polyimide film and ensures that the polyimide film can be fully pre-carbonized. This optimizes the structure and performance of the polyimide film and guarantees the carbonization effect of the pre-carbonized film.

[0072] Furthermore, the calender includes: a first analysis module, a first detection module, a second analysis module, a calendering module, and a second detection module. When the carbon foam film is calendered, the first analysis module analyzes the target product to determine the thickness of the ultra-high thermal conductivity graphite film, obtaining the target thickness of the ultra-high thermal conductivity graphite film, and performs material characteristic analysis on the ultra-high thermal conductivity graphite film to determine its glass transition temperature and melting temperature. The second analysis module determines the target calendering temperature based on the glass transition temperature and melting temperature of the ultra-high thermal conductivity graphite film, and determines the first control information of the calender based on the target calendering temperature to obtain the material information of the carbon foam film. The target speed of the calendering drum is analyzed based on the target thickness of the ultra-high thermal conductivity graphite film to determine the target speed ratio of the calender. Then, based on the target speed ratio, the second control information of the calender is determined, the target pressure of the calender is acquired, and the third control information of the calender is determined based on the target pressure. The first detection module acquires images of the carbon foam film and the calendering drum, obtaining a first acquired image and a second acquired image. Based on the first acquired image, image recognition and analysis are performed to determine whether impurities exist in the carbon foam film, obtaining a first analysis result. Then, if the first analysis result indicates the presence of impurities in the carbon foam film, the impurities are removed. When there are no impurities in the foam film, a first detection pass signal is obtained. Simultaneously, image recognition and analysis are performed based on the second acquired image to determine whether the calendering roller surface is smooth, resulting in a second analysis result. If the second analysis result indicates that the calendering roller surface is not smooth, surface treatment is performed on the calendering roller. If the second analysis result indicates that the calendering roller surface is smooth, a second detection pass signal is obtained. After receiving the first and second detection pass signals, the calendering module adjusts the calendering roller surface temperature and speed ratio according to the calender's first and second control information, respectively, to ensure that the calendering roller surface temperature reaches the target calendering temperature. The calendering roller reaches the target speed ratio, and then the pressure of the calendering roller is adjusted according to the third control information of the calendering machine to achieve the target pressure. Then, the calendering roller is driven to calender the carbon foam film to initially obtain an ultra-high thermal conductivity graphite film. The second detection module performs surface quality detection on the initially obtained ultra-high thermal conductivity graphite film, analyzing whether there are defects such as scratches, bubbles or wrinkles on the surface of the initially obtained ultra-high thermal conductivity graphite film. If there are defects on the surface, the defects are located, and the detection result is indicated based on the location result. If there are no defects on the surface, the initially obtained ultra-high thermal conductivity graphite film is the ultra-high thermal conductivity graphite film that meets the requirements.

[0073] The aforementioned calendering process achieves the calendering and forming of carbon foam film, resulting in an ultra-high thermal conductivity graphite film that meets the required specifications. The first analysis module analyzes the target product, enabling the calendering module to obtain a product that meets the required specifications based on the material properties and specifications. The second analysis module controls and analyzes the calendering module, enabling the conversion of target parameters. Based on the target calendering temperature, target speed ratio, and target pressure, control information is determined, resulting in first, second, and third control information for the calender. The first detection module inspects the calendered material and the calendering rollers, preventing impurities in the carbon foam film from affecting the purity of the ultra-high thermal conductivity graphite film and ensuring its performance. It also prevents scratches or defects on the ultra-high thermal conductivity graphite film caused by an uneven calendering roller surface, ensuring the quality of the ultra-high thermal conductivity graphite film. The calendering module, based on the first and second pass signals, then processes the first, second, and third control information of the calender. This ensures that the carbon foam film is free of impurities and that the calender roller surface is smooth during calendering. Furthermore, since adjusting the calender roller surface temperature and speed ratio takes a considerable amount of time, the first and second control information of the calender roller are prioritized for adjustment. This ensures that the calender roller surface temperature and speed ratio reach the target calendering temperature and speed ratio before the third control information is used. The control information system regulates the pressure of the calendering rollers, reducing the effective time for accurate calendering control, minimizing energy consumption and resource waste. Furthermore, the target calendering temperature allows the calendering rollers to gently calender the carbon foam film, preventing secondary damage. The target speed ratio ensures even calendering of the carbon foam film during the calendering process, resulting in a uniform thickness of the calendered product. Simultaneously, the target pressure controls the thickness and density of the calendered product, ensuring that the thickness and density of the calendered ultra-high thermal conductivity graphite film meet the target requirements. In addition, a second detection module performs surface quality inspection on the initially obtained ultra-high thermal conductivity graphite film, preventing defects from affecting its use, thus achieving ultra-high uniformity and high thermal conductivity in the final product.

[0074] Comparative Example 1

[0075] A method for preparing a thermally conductive graphite film includes the following steps:

[0076] S1. Place a 225μm thick polyimide film into a high-temperature furnace, evacuate to keep the pressure inside the furnace below 15Pa, raise the temperature to 500℃ at 3℃ / min, and hold for 0.5h to obtain a pre-carbonized film.

[0077] S2. The pre-carbonized film is subjected to a heating and cooling cycle under argon protection, i.e., the temperature is increased to 550℃ at 2℃ / min and held for 10min, then decreased to 480℃ at 5℃ / min and held for 30min; the furnace pressure is maintained at 120kPa during the heating phase and 80kPa during the cooling phase; the cycle is repeated 5 times; then the temperature is increased to 1500℃ at 5℃ / min and held for 2.5h to perform carbonization treatment, thus obtaining the carbonized film;

[0078] S3. Under argon protection, the carbonized film is heated to 2000-2200℃ at 1-2℃ / min and held for 0.5-1h; finally, it is heated to 2800℃ at 4-6℃ / min and held for 1-3h; a pressure of 1.5MPa is applied during the heating process; and the film is cooled naturally to obtain a carbon foam film.

[0079] S4. The carbon foam film is calendered in a calender at a pressure of 4 MPa to obtain a thermally conductive graphite film.

[0080] Comparative Example 2

[0081] A method for preparing a thermally conductive graphite film includes the following steps:

[0082] S1. Place a 225μm thick polyimide film into a high-temperature furnace, evacuate to keep the pressure inside the furnace below 15Pa, raise the temperature to 500℃ at 3℃ / min, and hold for 0.5h to obtain a pre-carbonized film.

[0083] S2. The pre-carbonized film is heated to 1500℃ at 5℃ / min under argon protection, held at this temperature for 3h, and then naturally cooled to room temperature to obtain the carbonized film.

[0084] S3. Spray a dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets onto the surface of the carbonized film, and dry it to obtain a carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets.

[0085] The solvent in the dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets is ethanol; the concentration of graphene oxide nanosheets is 1.0 mg / mL; the concentration of hexagonal boron nitride nanosheets is 0.6 mg / mL; it also includes a dispersant and a silane coupling agent, the dispersant being sodium dodecyl sulfate with a concentration of 0.15 wt%; the concentration of the silane coupling agent is 0.1 wt%.

[0086] S4. The carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets was heated to 900℃ at 6℃ / min and held for 0.5h under argon protection; then heated to 1600℃ at 5℃ / min and held for 0.5h; then heated to 2200℃ at 2℃ / min and held for 0.5h; finally heated to 2800℃ at 5℃ / min and held for 2h; a pressure of 1.5MPa was applied during the continuous gradient heating process; and the film was cooled naturally to obtain a carbon foam film.

[0087] S5. The carbon foam film is calendered in a calender at a pressure of 4 MPa to obtain a thermally conductive graphite film.

[0088] Test case

[0089] The graphite films prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to performance tests.

[0090] Thermal conductivity test: The thermal diffusivity of the graphite film was tested using Netzsch LFA467. The test temperature was set at room temperature (25℃), the voltage was 260V, the sampling time was 30ms, the detection area was 14mm, and the test sample size was a circular piece with a diameter of 2.54cm.

[0091] The test results are shown in Table 1.

[0092] Table 1

[0093]

[0094]

[0095] As shown in Table 1, the thermal diffusivity of the graphite films prepared in Examples 1-4 is significantly higher than that in Comparative Examples 1-2. The data in Table 1 reflect the influence of process parameters on the final graphite film performance, especially the significant contributions of the nanosheet coating and the heating-cooling cycle treatment to improving the thermal diffusivity. In this invention, the heating-cooling cycle treatment is crucial for releasing stress and improving the uniformity of the graphite film. Stress management directly affects the final graphitization quality and orientation consistency. Van der Waals forces and dipole-dipole interactions can be formed between hexagonal boron nitride and graphene oxide, promoting carbon atom rearrangement and improving the degree of graphitization during high-temperature treatment.

[0096] In Comparative Example 1, the graphene oxide and hexagonal boron nitride nanosheet reinforcement layers were missing, resulting in high porosity of the graphite film, broken thermal conduction paths, and direct graphitization after carbonization without repairing defects. Consequently, the performance of the graphite film was significantly inferior to that in the examples.

[0097] In Comparative Example 2, there was no heating and cooling cycle treatment, and the stress release process was lacking. The presence of internal stress resulted in a large number of defects and disordered regions in the final graphitized structure, causing the thermal conductivity and density of the graphite film to be lower than those in the example.

[0098] Finally, it should be noted that the above embodiments are merely illustrative of several implementations of the present invention and are not intended to limit the scope of the invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made without departing from the concept of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing an ultra-high thermal conductivity graphite film, characterized in that, Includes the following steps: S1. Place the polyimide film in a high-temperature furnace, heat it to 450-500℃ under vacuum conditions at a rate of 2-3℃ / min, and hold it at that temperature for 0.5-1h to obtain a pre-carbonized film. S2. The pre-carbonized film is subjected to a heating and cooling cycle under inert gas protection, and then the temperature is further increased to 1300-1500℃ at 3-5℃ / min, held for 2-3 hours, and carbonized. The film is then naturally cooled to room temperature to obtain the carbonized film. S3. Spray a dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets onto the surface of the carbonized film, and dry it to obtain a carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets. S4. The carbonized film coated with graphene oxide nanosheets and hexagonal boron nitride nanosheets is heated to 800-900℃ at 5-8℃ / min and held for 0.5h under inert gas protection; then heated to 1500-1600℃ at 3-5℃ / min and held for 0.5-1h; then heated to 2000-2200℃ at 1-2℃ / min and held for 0.5-1h; finally heated to 2800℃ at 4-6℃ / min and held for 1-3h; and then cooled naturally to obtain a carbon foam film. S5. The carbon foam film is calendered by a calender to obtain an ultra-high thermal conductivity graphite film; The specific heating and cooling cycle in step S2 is as follows: the pre-carbonized film is heated to 540-550℃ at a rate of 2-3℃ / min and held for 5-10 min, then cooled to 450-500℃ at a rate of 3-5℃ / min and held for 20-30 min; the cycle is repeated 2-5 times; the furnace pressure is maintained at 100-120 kPa during the heating phase; and the furnace pressure is maintained at 70-90 kPa during the cooling phase.

2. The method for preparing the ultra-high thermal conductivity graphite film according to claim 1, characterized in that, The thickness of the polyimide film in step S1 is 38-300 μm.

3. The method for preparing the ultra-high thermal conductivity graphite film according to claim 1, characterized in that, In step S1, the vacuum condition is to maintain the pressure inside the high-temperature furnace below 15 Pa.

4. The method for preparing the ultra-high thermal conductivity graphite film according to claim 1, characterized in that, The number of cycles is related to the thickness of the polyimide film: 2 cycles when the thickness of the polyimide film is 38-50 μm; 3 cycles when the thickness of the polyimide film is 51-120 μm; 4 cycles when the thickness of the polyimide film is 121-220 μm; and 5 cycles when the thickness of the polyimide film is 221-300 μm.

5. The method for preparing an ultra-high thermal conductivity graphite film according to claim 1, characterized in that, The solvent in the dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets is isopropanol or ethanol; the concentration of graphene oxide nanosheets is 0.5-1.0 mg / mL; and the concentration of hexagonal boron nitride nanosheets is 0.3-0.8 mg / mL.

6. The method for preparing an ultra-high thermal conductivity graphite film according to claim 1, characterized in that, The dispersion of graphene oxide nanosheets and hexagonal boron nitride nanosheets also includes a dispersant and a silane coupling agent. The dispersant is sodium dodecyl sulfate with a concentration of 0.1-0.2 wt%; the concentration of the silane coupling agent is 0.05-0.1 wt%.

7. The method for preparing an ultra-high thermal conductivity graphite film according to claim 1, characterized in that, In step S4, a pressure of 1-2 MPa is applied during the continuous gradient heating process.

8. The method for preparing an ultra-high thermal conductivity graphite film according to claim 1, characterized in that, The pressure of the calender in step S5 is 3-5 MPa.

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