Preparation method of graphite film with ultrahigh thermal conductivity

Abstract

The invention discloses a preparation method of an ultrahigh heat-conducting graphite film, which comprises the following steps: S1, putting a polyimide film into a high-temperature furnace, and pre-carbonizing to obtain a carbonized film; s2, carrying out heating and cooling circulation treatment on the pre-carbonized film under the protection of inert gas, then carrying out carbonization treatment, and naturally cooling to room temperature to obtain a carbonized film; s3, spraying a graphene oxide nanosheet and hexagonal boron nitride nanosheet dispersion liquid on the surface of the carbonized film, and drying to obtain the carbonized film sprayed with the graphene oxide nanosheet and the hexagonal boron nitride nanosheet; s4, carrying out gradient heating graphitization treatment on the carbonized film sprayed with the graphene oxide nanosheets and the hexagonal boron nitride nanosheets under the protection of inert gas, and cooling to obtain a carbon foam film; and S5, calendering the carbon foam film by a calender to obtain the ultrahigh heat conduction graphite film. According to the overall process scheme, the thermophysical performance of the graphite film is improved, the method is suitable for continuous industrial production, and the product stability and reliability are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat-conducting materials, and particularly to a preparation method of an ultra-high heat-conducting graphite film. Background Art

[0002] With the continuous improvement of the integration degree of electronic devices, especially in the fields of high-performance computing, 5G communication, aerospace and LED chips, the power consumption and heat flux density of electronic devices have increased sharply, resulting in a significant increase in heat dissipation requirements. Effective thermal management has become a key factor determining the performance, stability and service life of electronic devices. Therefore, developing high heat-conducting materials to improve the heat dissipation efficiency has become an important research direction in the current material field.

[0003] Graphite has become one of the ideal heat-conducting materials due to its excellent thermal conductivity, chemical stability and light weight. Artificial graphite films, especially ultra-thin graphite films prepared by the polyimide (PI) film carbonization-graphitization process, have become hot materials in the field of electronic device heat dissipation due to their superior in-plane thermal conductivity. The conventional process usually adopts vacuum carbonization treatment at 1200-1300 °C and then high-temperature graphitization treatment at 2800-3200 °C 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, when the PI film is subjected to high-temperature heat treatment, due to uneven heating of different layers, internal stress is easily generated, causing the film layer to bend, warp or break, affecting the quality of the final product; with the increase of the thickness of the PI film, the heat conduction is uneven during the carbonization and graphitization processes, resulting in different degrees of graphitization of the inner and outer layers and affecting the thermal conductivity. In addition, the thermal conductivity of the graphite film is greatly affected by the orientation degree and crystallinity of the graphite sheet layer, and it is difficult to accurately control the arrangement of the graphite sheet layer along the plane direction by the traditional process, resulting in limited heat conduction ability.

[0004] Therefore, it is urgent to optimize the preparation method of the PI film graphite film, overcome the above problems, improve the structural uniformity, thermal conductivity and mechanical stability of the 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 art, the present invention provides a preparation method of an ultra-high heat-conducting graphite film, which significantly improves the thermal conductivity, thermal stability and mechanical strength of the graphite film through the process synergy effect, and at the same time ensures the uniformity and reliability of the product, making it have a wide application prospect in the fields of electronic heat dissipation, flexible heat-conducting interface materials and high-power device thermal management.

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

[0007] A preparation method of an ultra-high heat-conducting graphite film, comprising the following steps:

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

[0009] S2. Carry out a heating and cooling cycle treatment on the pre-carbonized film under the protection of an inert gas, then continue to heat it at a rate of 3 - 5 °C / min to 1300 - 1500 °C, keep it at this temperature for 2 - 3 h for carbonization treatment, and naturally cool it to room temperature to obtain a carbonized film;

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

[0011] S4. Under the protection of an inert gas, heat the carbonized film sprayed with graphene oxide nanosheets and hexagonal boron nitride nanosheets at a rate of 5 - 8 °C / min to 800 - 900 °C, and keep it at this temperature for 0.5 h; then heat it at a rate of 3 - 5 °C / min to 1500 - 1600 °C, and keep it at this temperature for 0.5 - 1 h; then heat it at a rate of 1 - 2 °C / min to 2000 - 2200 °C, and keep it at this temperature for 0.5 - 1 h; finally, heat it at a rate of 4 - 6 °C / min to 2800 °C, and keep it at this temperature for 1 - 3 h; naturally cool it to obtain a carbon foam film;

[0012] S5. Roll the carbon foam film through a rolling mill to obtain an ultra-high thermal conductivity graphite film.

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

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

[0015] Further, the heating and cooling cycle treatment in step S2 is specifically as follows: Heat the pre-carbonized film at a rate of 2 - 3 °C / min to 540 - 550 °C, keep it for 5 - 10 min, then cool it at a rate of 3 - 5 °C / min to 450 - 500 °C, and keep it for 20 - 30 min; the number of cycles is 2 - 5 times.

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

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

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

[0019] Furthermore, the graphene oxide nanosheet and hexagonal boron nitride nanosheet dispersion 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, a pressure of 1 - 2 MPa is applied during the continuous gradient heating process in step S4.

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

[0022] Advantages of the present invention:

[0023] 1. By adopting the heating and cooling cycle, spraying of the auxiliary heat conduction layer, and continuous gradient heating graphitization treatment, the present invention significantly improves the heat conduction uniformity of the PI film during the carbonization and graphitization processes, making the graphitization degree inside and outside the film tend to be consistent, thereby achieving ultra-high uniformity and high thermal conductivity in the final product. At the same time, the heating and cooling cycle and air pressure regulation effectively release the thermal stress inside the material, reduce the generation of microcracks, the introduction of auxiliary nanosheets further constructs an efficient heat conduction bridge, and the applied pressure also densifies the carbon foam structure. The overall process scheme not only improves the thermophysical properties of the graphite film but also is suitable for continuous industrial production, improving the product stability and reliability.

[0024] 2. The heating and cooling cycle treatment in step S2 of the present invention realizes the uniform fracture and rearrangement of the polyimide molecular chain, promotes the regular formation of the carbon hexacyclic structure; the alternating pressure change of maintaining 100 - 120 kPa air pressure during the heating stage and 70 - 90 kPa air pressure during the cooling stage enhances the molecular migration ability inside the film and significantly reduces the stress concentration at the microscale; the precise correspondence between the number of cycles and the raw material thickness ensures consistent internal structure uniformity for products of different thicknesses.

[0025] 3. In step S3 of the present invention, the spraying of the graphene oxide nanosheet and hexagonal boron nitride nanosheet dispersion further improves the uniformity and thermal conductivity of the graphite film through synergy. 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, greatly reducing the porosity of the graphite film. At the same time, the oxygen-containing functional groups of the graphene oxide bond with the active sites of the carbonized film to repair microcracks and improve the mechanical properties of the graphite film. The unique two-dimensional honeycomb crystal structure of the hexagonal boron nitride nanosheet is very similar to that of graphite and is called "white graphite". However, the in-plane thermal conductivity of the hexagonal boron nitride nanoplane is as high as 2000 W / m·K. This excellent thermal conductivity stems from its rigid lattice structure formed by strong covalent B-N bonds and low phonon scattering characteristics. The hexagonal boron nitride nanosheets sprayed on the surface of the carbonized film can fill the microscopic defects and pores in the graphite structure, reducing the interfacial thermal resistance on the heat conduction path. The thermal expansion coefficient of the hexagonal boron nitride nanos is similar to that of graphite, and it can maintain a stable structure during the graphitization process, reducing the accumulation of thermal stress and improving the uniformity of the film. When working synergistically with the graphene oxide nanosheets, van der Waals forces and dipole-dipole interactions can form between the hexagonal boron nitride and the graphene oxide, promoting the rearrangement of carbon atoms during the high-temperature treatment process and increasing the degree of graphitization. Description of the Drawings

[0026] The drawings are used to provide further explanation of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. 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 Appearance image of the ultra-high thermal conductivity graphite film prepared in Example 1;

[0031] Figure 5 Appearance image of the graphite film prepared in Comparative Example 1;

[0032] Figure 6 Appearance image of the graphite film prepared in Comparative Example 2. Detailed Description of the Embodiments

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

[0034] Example 1

[0035] A preparation method of an ultra-high thermal conductivity graphite film, comprising the following steps:

[0036] S1. Place a polyimide film with a thickness of 225 μm into a high-temperature furnace, evacuate to keep the pressure in the high-temperature furnace below 15 Pa, heat it at 3 °C / min to 500 °C, and keep it warm for 0.5 h to obtain a pre-carbonized film;

[0037] S2. Carry out a heating and cooling cycle treatment on the pre-carbonized film under argon protection, that is, heat it at 2 °C / min to 550 °C, keep it for 10 min, then cool it at 5 °C / min to 480 °C, and keep it for 30 min; maintain the furnace pressure at 120 kPa during the heating stage; maintain the furnace pressure at 80 kPa during the cooling stage; the number of cycles is 5 times; then continue to heat it at 5 °C / min to 1500 °C, keep it warm for 2.5 h, carry out carbonization treatment, and naturally cool to room temperature to obtain a carbonized film;

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

[0039] Among them, 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 is sodium dodecyl sulfate, and the concentration is 0.15 wt%; the concentration of the silane coupling agent is 0.1 wt%.

[0040] S4. Under argon protection, heat the carbonized film sprayed with graphene oxide nanosheets and hexagonal boron nitride nanosheets at 6 °C / min to 900 °C, keep it warm for 0.5 h; heat it at 5 °C / min to 1600 °C, keep it warm for 0.5 h; heat it at 2 °C / min to 2200 °C, keep it warm for 0.5 h; finally heat it at 5 °C / min to 2800 °C, keep it warm for 2 h; apply a pressure of 1.5 MPa during the continuous gradient heating process; naturally cool down to obtain a carbon foam film;

[0041] S5. Roll the carbon foam film with a rolling machine, and the pressure of the rolling machine is 4 MPa, then the ultra-high thermal conductivity graphite film is obtained.

[0042] Example 2

[0043] A preparation method of an ultra-high thermal conductivity graphite film, comprising the following steps:

[0044] S1. Place a polyimide film with a thickness of 225 μm into a high-temperature furnace, evacuate to keep the pressure in the high-temperature furnace below 15 Pa, heat it at 3 °C / min to 500 °C, and keep it warm for 0.5 h to obtain a pre-carbonized film;

[0045] S2. The pre-carbonized film is subjected to a heating and cooling cycle treatment under argon protection, that is, it is heated to 550 °C at a rate of 2 °C / min, held for 10 min, then cooled to 500 °C at a rate of 4 °C / min, and held for 20 min; the pressure inside the furnace is maintained at 100 kPa during the heating stage; the pressure inside the furnace is maintained at 80 kPa during the cooling stage; the number of cycles is 5; then it is continuously heated to 1500 °C at a rate of 5 °C / min, held for 2.5 h for carbonization treatment, and naturally cooled to room temperature to obtain a carbonized film;

[0046] S4. A dispersion liquid of graphene oxide nanosheets and hexagonal boron nitride nanosheets is sprayed on the surface of the carbonized film and dried to obtain a carbonized film sprayed with graphene oxide nanosheets and hexagonal boron nitride nanosheets;

[0047] Among them, the solvent in the dispersion liquid 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 is 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 sprayed with graphene oxide nanosheets and hexagonal boron nitride nanosheets is heated to 900 °C at a rate of 6 °C / min under argon protection and held for 0.5 h; heated to 1600 °C at a rate of 5 °C / min and held for 0.5 h; heated to 2200 °C at a rate of 2 °C / min and held for 0.5 h; finally heated to 2800 °C at a rate of 5 °C / min and held for 2 h; a pressure of 1.5 MPa is applied during the continuous gradient heating process; it is naturally cooled to obtain a carbon foam film;

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

[0050] Example 3

[0051] S1. A polyimide film with a thickness of 225 μm is placed in a high-temperature furnace, and the pressure inside the high-temperature furnace is evacuated to be lower than 15 Pa, and it is heated to 500 °C at a rate of 3 °C / min and held for 0.5 h to obtain a pre-carbonized film;

[0052] S2. The pre-carbonized film is subjected to a heating and cooling cycle treatment under argon protection, that is, it is heated to 550 °C at a rate of 2 °C / min, held for 10 min, then cooled to 480 °C at a rate of 5 °C / min, and held for 30 min; the pressure inside the furnace is maintained at 120 kPa during the heating stage; the pressure inside the furnace is maintained at 80 kPa during the cooling stage; the number of cycles is 5; then it is continuously heated to 1500 °C at a rate of 5 °C / min, held for 2.5 h for carbonization treatment, and naturally cooled to room temperature to obtain a carbonized film;

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

[0054] Among them, 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 is sodium dodecyl sulfate with a concentration of 0.1 wt%; the concentration of the silane coupling agent is 0.1 wt%.

[0055] S4. Under the protection of argon, heat the carbonized film sprayed with graphene oxide nanosheets and hexagonal boron nitride nanosheets to 900 °C at a rate of 6 °C / min, and hold for 0.5 h; heat to 1600 °C at a rate of 5 °C / min and hold for 0.5 h; heat to 2200 °C at a rate of 2 °C / min and hold for 0.5 h; finally, heat to 2800 °C at a rate of 5 °C / min and hold for 2 h; apply a pressure of 1.5 MPa during the continuous gradient heating process; cool naturally to obtain a carbon foam film;

[0056] S5. Roll the carbon foam film with a rolling mill 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, comprising the following steps:

[0059] S1. Place a polyimide film with a thickness of 200 μm into a high-temperature furnace, evacuate to keep the pressure in the high-temperature furnace below 15 Pa, heat to 500 °C at a rate of 3 °C / min, and hold for 0.5 h to obtain a pre-carbonized film;

[0060] S2. Carry out a heating and cooling cycle treatment on the pre-carbonized film under the protection of argon, that is, heat to 550 °C at a rate of 2 °C / min, hold for 10 min, then cool to 480 °C at a rate of 5 °C / min and hold for 30 min; maintain the furnace pressure at 120 kPa during the heating stage; maintain the furnace pressure at 80 kPa during the cooling stage; the number of cycles is 4 times; then continue to heat to 1500 °C at a rate of 5 °C / min and hold for 2.5 h for carbonization treatment, and naturally cool to room temperature to obtain a carbonized film;

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

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

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

[0064] S5. The carbon foam film is rolled by a rolling mill with a pressure of 4 MPa to obtain an ultra-high thermal conductivity graphite film.

[0065] Based on Examples 1-4, further, when obtaining the pre-carbonized film in S1, image monitoring and analysis are also carried out on the inside of the high-temperature furnace, including:

[0066] Obtain the internal monitoring image of the high-temperature furnace, identify the polyimide film according to the internal monitoring image of the high-temperature furnace, lock the image of the polyimide film to obtain the polyimide film detection image;

[0067] Analyze the shape of the polyimide film according to the polyimide film detection image to obtain the real-time shape information of the polyimide film;

[0068] Analyze the deformation of the polyimide film according to the real-time shape information of the polyimide film, and judge whether the deformation of the polyimide film is size shrinkage to obtain the deformation analysis result;

[0069] When the deformation analysis result shows that the deformation of the polyimide film is not size shrinkage, further analyze the aggregation situation of the polyimide film to obtain the aggregation characteristics of the polyimide film;

[0070] Analyze whether the deformation of the polyimide film needs to be intervened and adjusted in combination with the aggregation characteristics of the polyimide film. When intervention and adjustment are required, perform stretching treatment on the polyimide film according to the aggregation characteristics of the polyimide film.

[0071] The above visualization of the inside of the high-temperature furnace through image monitoring and analysis enables the polyimide film to obtain a better pre-carbonized film during pre-carbonization in the high-temperature furnace, avoiding the aggregation of the polyimide film due to thermal deformation, which affects the pre-carbonization of the internal polyimide film, ensuring that all the polyimide film can be pre-carbonized, optimizing the structure and performance of the polyimide film, and ensuring 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 and forming module, and a second detection module. When the carbon foam film is calendered by the calender, 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 conducts a material characteristic analysis on the ultra-high thermal conductivity graphite film to determine the glass transition temperature and melting temperature of the ultra-high thermal conductivity graphite film; 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, determines the first control information of the calender based on the target calendering temperature, obtains the material information of the carbon foam film, and conducts a calendering roller speed analysis in combination with the target thickness of the ultra-high thermal conductivity graphite film to determine the target speed ratio of the calender, and then determines the second control information of the calender based on the target speed ratio of the calender, obtains the target pressure of the calender, and determines the third control information of the calender based on the target pressure; the first detection module respectively acquires images of the carbon foam film and the calendering roller to obtain a first acquisition image and a second acquisition image, conducts image recognition and analysis based on the first acquisition image to determine whether there are impurities in the carbon foam film, obtaining a first analysis result, and then when the first analysis result is that there are impurities in the carbon foam film, removes the impurities in the carbon foam film, and when the first analysis result is that there are no impurities in the carbon foam film, obtains a first detection pass signal, and at the same time conducts image recognition and analysis based on the second acquisition image to determine whether the surface of the calendering roller is smooth, obtaining a second analysis result, and then when the second analysis result is that the surface of the calendering roller is not smooth, conducts surface treatment on the calendering roller, and when the second analysis result is that the surface of the calendering roller is smooth, obtains a second detection pass signal; after obtaining the first detection pass signal and the second detection pass signal, the calendering and forming module respectively regulates the surface temperature and speed ratio of the calendering roller according to the first control information and the second control information of the calender, so that the surface temperature of the calendering roller reaches the target calendering temperature, and at the same time the speed ratio of the calendering roller reaches the target speed ratio, and then regulates the pressure of the calendering roller according to the third control information of the calender, so that the pressure of the calendering roller reaches the target pressure, and then drives the calendering roller to calender the carbon foam film to initially obtain the ultra-high thermal conductivity graphite film; the second detection module conducts a surface quality detection on the initially obtained ultra-high thermal conductivity graphite film, analyzes 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, locates the defects, and then gives a detection result prompt based on the positioning result, and 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 above-mentioned calendering forming of the carbon foam film by the calender enables the production of an ultra-high thermal conductivity graphite film that meets the requirements. The analysis of the target product is realized through the first analysis module, enabling the calendering forming module to obtain a target product that meets the requirements based on the material characteristics and requirements of the target product. The control analysis of the calendering forming module is realized through the second analysis module, realizing the control conversion of the target parameters, enabling the determination of control information based on the target calendering temperature, target speed ratio, and target pressure respectively, and obtaining the first control information of the calender, the second control information of the calender, and the third control information of the calender. The detection of the material to be calendered and the calender roller is realized through the first detection module, avoiding impurities in the carbon foam film of the material to be calendered from affecting the purity of the ultra-high thermal conductivity graphite film, ensuring the performance of the ultra-high thermal conductivity graphite film, and at the same time avoiding scratches or defects on the ultra-high thermal conductivity graphite film caused by the uneven surface of the calender roller, ensuring the quality of the ultra-high thermal conductivity graphite film. After the first detection pass signal and the second detection pass signal, the calendering forming module performs the first control information of the calender, the second control information of the calender, and the third control information of the calender, ensuring that there are no impurities in the carbon foam film and the surface of the calender roller is smooth when the calender roller is calendering. Moreover, since the regulation of the surface temperature and speed ratio of the calender roller takes a long time, the regulation is preferentially carried out according to the first control information of the calender and the second control information of the calender. When the surface temperature of the calender roller reaches the target calendering temperature and the speed ratio of the calender roller reaches the target speed ratio, the pressure regulation of the calender roller is carried out according to the third control information of the calender, reducing the effective time for accurate calendering regulation, reducing energy consumption, reducing resource waste, and softening the carbon foam film through the target calendering temperature when the calender roller calenders the carbon foam film, avoiding secondary damage to the carbon foam film. The target speed ratio ensures that the calender roller evenly calenders the carbon foam film during the calendering process, making the thickness of the target product obtained by calendering forming uniform. At the same time, the target pressure realizes the control of the thickness and density of the target product obtained by calendering forming, making the thickness and density of the ultra-high thermal conductivity graphite film after calendering meet the target thickness. In addition, the surface quality of the preliminarily obtained ultra-high thermal conductivity graphite film is detected through the second detection module, avoiding defects in the ultra-high thermal conductivity graphite film from affecting its use, thereby achieving ultra-high uniformity and high thermal conductivity in the final product.

[0074] Comparative Example 1

[0075] A preparation method of a thermal conductive graphite film, comprising the following steps:

[0076] S1. Place a polyimide film with a thickness of 225 μm into a high-temperature furnace, evacuate to keep the pressure in the high-temperature furnace below 15 Pa, heat up to 500 °C at a rate of 3 °C / min, and keep it warm for 0.5 h to obtain a pre-carbonized film;

[0077] S2. The pre-carbonized film is subjected to a heating and cooling cycle treatment under argon protection, that is, it is heated to 550 °C at a rate of 2 °C / min, held for 10 min, and then cooled to 480 °C at a rate of 5 °C / min and held for 30 min; the pressure inside the furnace is maintained at 120 kPa during the heating stage; the pressure inside the furnace is maintained at 80 kPa during the cooling stage; the number of cycles is 5; then it is continuously heated to 1500 °C at a rate of 5 °C / min and kept warm for 2.5 h for carbonization treatment to obtain a carbonized film;

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

[0079] S4. The carbon foam film is calendered by a calender, and the pressure of the calender is 4 MPa to obtain a thermally conductive graphite film.

[0080] Comparative Example 2

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

[0082] S1. A polyimide film with a thickness of 225 μm is placed in a high-temperature furnace, and the pressure inside the high-temperature furnace is kept below 15 Pa by vacuum pumping, heated to 500 °C at a rate of 3 °C / min, and held for 0.5 h to obtain a pre-carbonized film;

[0083] S2. Under argon protection, the pre-carbonized film is continuously heated to 1500 °C at a rate of 5 °C / min, held for 3 h for carbonization treatment, and naturally cooled to room temperature to obtain a carbonized film;

[0084] S3. A dispersion liquid of graphene oxide nanosheets and hexagonal boron nitride nanosheets is sprayed on the surface of the carbonized film and dried to obtain a carbonized film sprayed with graphene oxide nanosheets and hexagonal boron nitride nanosheets;

[0085] Among them, the solvent in the dispersion liquid 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 is sodium dodecyl sulfate with a concentration of 0.15 wt%; the concentration of the silane coupling agent is 0.1 wt%.

[0086] S4. Under the protection of argon, heat the carbonized film sprayed with graphene oxide nanosheets and hexagonal boron nitride nanosheets to 900 °C at a rate of 6 °C / min, hold for 0.5 h; heat to 1600 °C at a rate of 5 °C / min, hold for 0.5 h; heat to 2200 °C at a rate of 2 °C / min, hold for 0.5 h; finally heat to 2800 °C at a rate of 5 °C / min, hold for 2 h; apply a pressure of 1.5 MPa during the continuous gradient heating process; cool naturally to obtain a carbon foam film;

[0087] S5. Roll the carbon foam film with a rolling mill under a pressure of 4 MPa to obtain a thermally conductive graphite film.

[0088] Test Example

[0089] Perform performance tests on the graphite films prepared in Examples 1-4 and Comparative Examples 1-2.

[0090] Thermal conductivity test: Use Netzsch LFA467 to test the thermal diffusivity of the graphite film. The test temperature is set at room temperature (25 °C), the voltage is 260 v, the sampling time is 30 ms, the detection area is 14 mm, and the test sample size is a disc with a diameter of 2.54 cm.

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

[0092] Table 1

[0093]

[0094]

[0095] It can be seen from the results in Table 1 that 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 reflects the influence of process parameters on the performance of the final graphite film, especially the significant contribution of the nanosheet coating and the heating and cooling cycle treatment to improving the thermal diffusivity. In the present invention, the heating and 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 the rearrangement of carbon atoms 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 are missing, the porosity of the graphite film is high, the heat conduction path is broken, and the defects are not repaired during the direct graphitization after carbonization treatment. The performance of the graphite film is significantly inferior to that in the examples.

[0097] In Comparative Example 2, there is no heating and cooling cycle treatment, and the stress release process is missing. The existence of internal stress results in a large number of defects and disordered regions in the final graphitization structure, resulting in the thermal conductivity and density of the graphite film being lower than those in the examples.

[0098] Finally, it should be noted that the above-described embodiments merely represent several implementation manners of the present invention and are not intended to limit the present invention. For those of ordinary skill in the art, any modifications, equivalent replacements, improvements, etc. made without departing from the concept of the present invention shall be included within the protection scope of the present invention. Therefore, the protection scope of this invention patent shall be subject to the appended claims.

Claims

1. A method for preparing a super-high thermal conductivity graphite film, characterized in that It includes the following steps: S1. Put the polyimide film into a high-temperature furnace, heat it up to 450 - 500 °C at a rate of 2 - 3 °C / min under vacuum conditions, keep it warm for 0.5 - 1 h to obtain a pre-carbonized film; S2. Carry out a heating and cooling cycle treatment on the pre-carbonized film under the protection of inert gas, then continue to heat it up to 1300 - 1500 °C at a rate of 3 - 5 °C / min, keep it warm for 2 - 3 h for carbonization treatment, and naturally cool it to room temperature to obtain a carbonized film; S3. Spray a dispersion liquid of graphene oxide nanosheets and hexagonal boron nitride nanosheets on the surface of the carbonized film, and dry it to obtain a carbonized film sprayed with graphene oxide nanosheets and hexagonal boron nitride nanosheets; S4. Under the protection of inert gas, heat the carbonized film sprayed with graphene oxide nanosheets and hexagonal boron nitride nanosheets to 800 - 900 °C at a rate of 5 - 8 °C / min, keep it warm for 0.5 h; heat it up to 1500 - 1600 °C at a rate of 3 - 5 °C / min, keep it warm for 0.5 - 1 h; heat it up to 2000 - 2200 °C at a rate of 1 - 2 °C / min, keep it warm for 0.5 - 1 h; finally, heat it up to 2800 °C at a rate of 4 - 6 °C / min, keep it warm for 1 - 3 h; naturally cool it to obtain a carbon foam film; S5. Roll the carbon foam film through a rolling mill to obtain an ultra-high thermal conductivity graphite film.

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

3. The preparation method of the ultra-high thermal conductivity graphite film according to claim 1, characterized in that In step S1, the vacuum condition is to keep the pressure in the high-temperature furnace lower than 15 Pa.

4. The preparation method of the ultra-high thermal conductivity graphite film according to claim 1, characterized in that, In step S2, the heating and cooling cycle treatment is specifically: heat the pre-carbonized film to 540 - 550 °C at a rate of 2 - 3 °C / min, keep it for 5 - 10 min, then cool it to 450 - 500 °C at a rate of 3 - 5 °C / min, keep it for 20 - 30 min; the number of cycles is 2 - 5 times.

5. The preparation method of the ultra-high thermal conductivity graphite film according to claim 4, characterized in that, Maintain the air pressure in the furnace at 100 - 120 kPa during the heating stage; maintain the air pressure in the furnace at 70 - 90 kPa during the cooling stage.

6. The method for preparing the ultra-high thermal conductivity graphite film according to claim 4, wherein, The number of cycles is related to the thickness of the polyimide film. When the thickness of the polyimide film is 38 - 50 μm, cycle 2 times; when the thickness of the polyimide film is 51 - 120 μm, cycle 3 times; when the thickness of the polyimide film is 121 - 220 μm, cycle 4 times; when the thickness of the polyimide film is 221 - 300 μm, cycle 5 times.

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

8. The method for preparing the ultra-high thermal conductivity graphite film according to claim 7, characterized in that, The dispersion liquid of graphene oxide nanosheets and hexagonal boron nitride nanosheets also includes a dispersant and a silane coupling agent. The dispersant is sodium dodecyl sulfate, and the concentration is 0.1 - 0.2 wt%; the concentration of the silane coupling agent is 0.05 - 0.1 wt%.

9. The preparation method of the ultra-high thermal conductivity graphite film according to claim 1, characterized in that, Apply a pressure of 1 - 2 MPa during the continuous gradient heating process in step S4.

10. The preparation method of the ultra-high thermal conductivity graphite film according to claim 1, wherein, The pressure of the rolling mill in step S5 is 3 - 5 MPa.

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