Chemical PI preparation method for graphite heat-conducting film and application of chemical PI preparation method

Abstract

The invention relates to the technical field of high polymer materials, and particularly discloses a chemical method PI preparation method for a graphite heat-conducting film and application of the chemical method PI preparation method, and the chemical method PI preparation method comprises the following steps: adding an inorganic filler into a first solvent to obtain a filler dispersion liquid; adding a diamine monomer, a dianhydride monomer and the inorganic filler dispersion liquid into a first solvent, and carrying out condensation polymerization to obtain PAA resin; and defoaming the resin, adding a dehydrating agent and a catalyst, carrying out continuous coating, segmented drying and two-way stretching, and carrying out chemical imidization to obtain the polyimide film. According to the invention, the molecular linearity and ductility of the film are ensured by controlling the adding proportion and the block mode of the rigid monomer and the flexible monomer; 3-methylpyridine with a low boiling point is adopted as a catalyst, and a dehydrating agent AA and resin are added according to the ratio, so that the stable production of the ultra-thick PI film is ensured, and the thickness, molecular orientation and dry film quality stability control of the PI film is realized by adopting temperature zone setting of a film forming section and stretching ratio and tension adjustment of a stretching section.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a chemical method for preparing graphite thermal conductive films and its application. Background Technology

[0002] With the rapid development of technologies such as 5G, artificial intelligence (AI), high-performance computing (HPC), electric vehicles, and high-power LEDs, thick graphite thermal conductive films (typically over 100μm, even reaching 200μm) have become an ideal solution for solving high-power, high-heat-density heat dissipation problems due to their ultra-high in-plane thermal conductivity (>1500 W / mK) and greater heat capacity and heat flux handling capabilities. They are widely used for heat dissipation and heat conduction in key components such as server CPU / GPU heat dissipation modules, high-power power supply modules, and communication base station chips. Existing technologies for preparing thick PI precursor films based on thermal imidization or chemical imidization methods suffer from inherent defects that are difficult to overcome, such as poor foaming, excessive solvent residue, narrow process window, and high energy consumption. This results in low production yield, high cost, and unstable performance of thick, high-performance graphite thermal conductive films, becoming a major obstacle to the development of next-generation high-power heat dissipation technologies.

[0003] The method described in patent CN114956068A uses isoquinoline as a catalyst, resulting in high processing temperatures in the film-forming stage during the production of high-thickness PI films. The use of fully flexible segmental ODA-PMDA as the base formulation leads to over-foaming during the calcination of graphite films from high-thickness PI films. The method described in patent CN113788478A uses a three-layer co-extrusion coating process to prepare ultra-thick graphite thermal conductive films, but its production process is relatively complex and costly.

[0004] Therefore, in order to solve such problems, we propose a chemical method for preparing PI for graphite thermal conductive films and its application. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a chemical method for preparing graphite thermal conductive films and its application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A chemical method for preparing PI for graphite thermal conductive films includes the following preparation steps: 1) Preparation of inorganic filler dispersion: Inorganic filler is added to the first solvent and mixed and dispersed to obtain filler dispersion; 2) Resin preparation: Diamine monomer, dianhydride monomer and inorganic filler dispersion are added to the second solvent, and PAA resin is obtained by polycondensation reaction; 3) Film preparation: After degassing, PAA resin is added with a dehydrating agent and a catalyst, followed by continuous coating, segmented drying and biaxial stretching, and then chemical imidization to obtain a polyimide film.

[0007] Preferably, the first solvent and the second solvent are one of N,N-dimethylacetamide (DMAc) or N,N-dimethylformamide (DMF), with N,N-dimethylacetamide (DMAc) being the most preferred.

[0008] Preferably, the inorganic filler includes one or more of silicon dioxide, silicon carbide, boron nitride, calcium carbonate, and dicalcium phosphate, and the amount of inorganic filler added accounts for 0.08–0.32% of the total mass of the polyimide film. The inorganic filler is dicalcium phosphate, and the particle size of the dicalcium phosphate is 1–10 μm.

[0009] Preferably, the diamine monomer is a block copolymer of a rigid diamine monomer and a flexible diamine monomer, with a molar ratio of 0.30:0.70~0.05:0.95; the rigid diamine monomer is any one or a combination of p-phenylenediamine (p-PDA), 3,3'-dimethylbenzidine (DABP), 4,4'-diaminodiphenyl sulfone (DDS), and 4,4'-diaminobenzophenone (ABP); and the flexible diamine monomer is 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminodiphenylmethane (4,4'-MDA), or 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP). The dianhydride monomer is any one or more combinations of pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride (ODPA), and 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA).

[0010] Preferably, the total solids content of the diamine monomer and dianhydride monomer is set to 20-30%, and the molar ratio of diamine monomer to dianhydride monomer is 1:0.995 to 1:1.005. The viscosity of the resin is 180,000-250,000 centipoise (cps).

[0011] Preferably, the dehydrating agent is acetic anhydride (AA), and the catalyst is at least one of benzoic acid, triethylamine, and 3-methylpyridine (3MP), preferably 3-methylpyridine.

[0012] Preferably, the molar ratio of PAA to dehydrating agent resin is 1:2.0~3.0, and the molar ratio of PAA resin to catalyst is 1:0.8~2.5.

[0013] Preferably, the polyimide film is formed by continuous coating with a steel belt mirror and segmented drying, with the temperature range of the film-forming section set to 90-120°C.

[0014] Preferably, the polyimide film is stretched using biaxial stretching technology, with the stretching section having a first section at 180–280°C and a second section at 300–400°C, the tension in the MD direction controlled at 25–90N, preferably 60–90N, and the TD track ratio set to 0.6–1.4; the total thickness of the polyimide film is 75–175μm, preferably 100–150μm.

[0015] An application of chemically produced polyimide (PI) for graphite thermal conductive films, wherein the PI is prepared by the above-mentioned chemically produced PI for graphite thermal conductive films, and the PI is used to prepare graphite thermal conductive films; the polyimide film is sequentially carbonized and graphitized, and then calendered and cut to obtain the graphite thermal conductive film. The thermal conductivity of the graphite thermal conductive film is >1600W / (m·K).

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1: This invention forms a block linear polyamic acid (PAA) precursor by controlling the addition ratio of rigid monomers and flexible monomers. The flexible segments can improve the toughness and elongation of the film, while the rigid segments can improve the linearity of the film molecules and thermal orientation. This allows the gas generated during the foaming process inside the film to be discharged in an orderly manner without excessive foaming.

[0017] 2: This invention uses low-boiling-point 3-methylpyridine as a catalyst, which facilitates the escape of solvent during the production of ultra-thick PI films, reduces the processing temperature of each chamber in the film-forming section, and leaves sufficient room for adjustment of the film-forming process.

[0018] 3: This invention employs a film-forming section and a stretching section orientation system to achieve control over the thickness, molecular orientation, and dry film quality stability of the PI film. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the overall process of the present invention; Figure 2 This is a schematic diagram of the PAA block structure of the present invention; Figure 3This is the tension-to-track ratio adjustment curve of the tension section in this invention; Figure 4 This is a SEM cross-sectional view of the graphite film of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] Figure 1 The overall process flow diagram includes polymerization (resin synthesis), degassing, mixing (mixing and coating), film formation section (film formation), stretching section (biaxial stretching), and carbonization / graphitization.

[0023] Step 1: Resin Synthesis Section - This section is the core section for the polymerization of the triblock PI precursor. PAA removes microbubbles generated during polymerization under vacuum conditions.

[0024] Step 2: Thin Film Preparation Section - This section completes the mixing of PAA with catalyst and dehydrating agent, coating, drying, and biaxial stretching (MD and TD) to achieve the thickness, molecular orientation, and dry film quality stability of PI film.

[0025] Step 3: Graphitization Section - After film formation, the PI film undergoes carbonization / graphitization treatment to obtain a thermal diffusivity of over 1600 mm² / s and high thermal conductivity, which is the core of the thermal interface material.

[0026] Figure 2 : Schematic diagram of PAA block structure (showing the three-segment structure of PMDA, ODA, and PDA). This structure is a schematic diagram of the ODA-PDA-PMDA block molecular chain unit. ODA-PMDA forms a flexible segment (improving toughness and elongation); PDA-PMDA forms a rigid segment (improving molecular linearity and thermal conductivity orientation). The final segment structure exhibits good MD and TD orientation during thermal stretching in the stretching section, which is beneficial to improving the uniformity and thermal diffusivity of subsequent graphitization.

[0027] Figure 3 The tension of the stretching section and the track ratio adjustment curve are shown in the figure. The X-axis represents the unfolding ratio of the transverse track of the stretching section equipment, and the Y-axis represents the tension in the corresponding machine direction (MD). The solid line indicates that the tension in the main stretching direction increases with the increase of the stretching ratio; the dashed line shows the changing trend of the track unfolding on the tension feedback in the TD direction.

[0028] Figure 4: SEM cross-sectional image of graphite film (highly dense arrangement). This image shows the highly dense, parallel-oriented graphite layer structure formed after graphitization treatment of the graphite thermal conductive film under a scanning electron microscope (SEM). The graphite layers are uniformly arranged, indicating that the graphite crystals are highly oriented along the film surface; the heat conduction direction is clear: the heat diffusion along the parallel direction is fast (>1600 mm² / s).

[0029] Example 1: (1) Resin preparation: at 1.5m 3 86.16 kg of ODA powder was added to 775 kg of DMF in the reactor. After it was completely dissolved, 117.26 kg of PMDA powder was added in three portions. The mixture was stirred and reacted at 20°C for 1 hour. Then, 0.537 kg of dispersed CaHPO4 was added, followed by 11.63 kg of PDA powder. The viscosity reached 2250 poise. The resin was then degassed under vacuum and stored at 0°C for later use.

[0030] (2) PI film preparation: The resin prepared in step (1) is fed to the mixer at a resin flow rate of 128 kg / h. At the same time, 137.20 kg of acetic anhydride, 80.19 kg of 3-methylpyridine and 157.18 kg of DMF are mixed evenly and fed to the mixer at a flow rate of 47.93 kg / h. After being mixed evenly in the mixer, it is cast onto the steel belt of the film forming section. After being baked in three stages at 110℃ / 115℃ / 120℃, it enters the hot stretching section of the stretching section for high-temperature treatment. The unfolding ratio of the transverse track of the stretching section equipment is set to 1.2 and the tension in the MD direction is adjusted to 80N to obtain a polyimide film (PI film) with a thickness of 100 μm.

[0031] (3) Preparation of graphite thermal conductive film: PI film is placed in carbonization furnace and graphitization furnace for high temperature treatment, and then rolled to obtain high thermal conductivity graphite thermal conductive film.

[0032] Example 2 (1) Resin preparation: at 1.5m 3 98.85 kg of ODA powder was added to 775 kg of DMF in the reactor. After it was completely dissolved, 117.26 kg of PMDA powder was added in three portions. The mixture was stirred and reacted at 20°C for 1 hour. Then, 0.537 kg of dispersed CaHPO4 was added, followed by 2.81 kg of PDA powder. The viscosity reached 2137 poise. The resin was then degassed under vacuum and stored at 0°C for later use.

[0033] (2) PI film preparation: The resin prepared in step (1) is fed to the mixer at a resin flow rate of 128 kg / h. At the same time, 132.62 kg of acetic anhydride, 77.43 kg of 3-methylpyridine and 151.93 kg of DMF are mixed evenly and fed to the mixer at a flow rate of 46.33 kg / h. After being mixed evenly in the mixer, it is cast onto the steel belt of the film forming section. After being baked in three stages at 110℃ / 115℃ / 120℃, it enters the hot stretching section of the stretching section for high-temperature treatment. The unfolding ratio of the transverse track of the stretching section equipment is set to 1.2 and the tension in the MD direction is adjusted to 80N to obtain a polyimide film with a thickness of 100 μm.

[0034] (3) Preparation of graphite thermal conductive film: PI film is placed in carbonization furnace and graphitization furnace for high temperature treatment, and then rolled to obtain high thermal conductivity graphite thermal conductive film.

[0035] Example 3 (1) Resin preparation: at 1.5m 3 77.13 kg of ODA powder was added to 775 kg of DMF in the reactor. After it was completely dissolved, 117.26 kg of PMDA powder was added in three portions. The mixture was stirred and reacted at 20°C for 1 hour. Then, 17.85 kg of PDA powder was added. The viscosity reached 2459 poise. The resin was degassed under vacuum and stored at 0°C for later use.

[0036] (2) PI film preparation: The resin prepared in step (1) is fed to the mixer at a resin flow rate of 128 kg / h. At the same time, 140.44 kg of acetic anhydride, 81.99 kg of 3-methylpyridine and 160.88 kg of DMF are mixed evenly and fed to the mixer at a flow rate of 49.06 kg / h. After being mixed evenly in the mixer, it is cast onto the steel belt of the film forming section. After being baked in three stages at 110℃ / 115℃ / 120℃, it enters the hot stretching section of the stretching section for high-temperature treatment. The unfolding ratio of the transverse track of the stretching section equipment is set to 1.2 and the tension in the MD direction is adjusted to 80N to obtain a polyimide film with a thickness of 100 μm.

[0037] (3) Preparation of graphite thermal conductive film: PI film is placed in carbonization furnace and graphitization furnace for high temperature treatment, and then rolled to obtain high thermal conductivity graphite thermal conductive film.

[0038] Example 4 (1) Resin preparation: Same as step (1) in Example 1.

[0039] (2) PI film preparation: The resin prepared in step (1) is fed to the mixer at a resin flow rate of 128 kg / h. At the same time, 164.65 kg of acetic anhydride, 125.16 kg of 3-methylpyridine and 157.18 kg of DMF are mixed evenly and fed to the mixer at a flow rate of 57.21 kg / h. After being mixed evenly in the mixer, it is cast onto the steel belt of the film forming section. After being baked in three stages at 100℃ / 105℃ / 115℃, it enters the hot stretching section of the stretching section for high-temperature treatment. The unfolding ratio of the transverse track of the stretching section equipment is set to 1.2 and the tension in the MD direction is adjusted to 80N to obtain a polyimide film with a thickness of 100 μm.

[0040] (3) Preparation of graphite thermal conductive film: PI film is placed in carbonization furnace and graphitization furnace for high temperature treatment, and then rolled to obtain high thermal conductivity graphite thermal conductive film.

[0041] Example 5 (1) Resin preparation: Same as step (1) in Example 1.

[0042] (2) PI film preparation: The resin prepared in step (1) is fed to the mixer at a resin flow rate of 128 kg / h. At the same time, 109.76 kg of acetic anhydride, 40.05 kg of 3-methylpyridine and 157.18 kg of DMF are mixed evenly and fed to the mixer at a flow rate of 39.30 kg / h. After being mixed evenly in the mixer, it is cast onto the steel belt of the film forming section. After being baked in three stages at 120℃ / 125℃ / 130℃, it enters the hot stretching section of the stretching section for high-temperature treatment. The unfolding ratio of the transverse track of the stretching section equipment is set to 1.2 and the tension in the MD direction is adjusted to 80 N to obtain a polyimide film with a thickness of 100 μm.

[0043] (3) Preparation of graphite thermal conductive film: PI film is placed in carbonization furnace and graphitization furnace for high temperature treatment, and then rolled to obtain high thermal conductivity graphite thermal conductive film.

[0044] Example 6 (1) Resin preparation: Same as step (1) in Example 1.

[0045] (2) PI film preparation: Same as step (2) in Example 1, except that the unfolding ratio of the transverse track of the stretching section equipment is set to 0.6 and the tension in the MD direction is adjusted to 60N.

[0046] (3) Preparation of graphite thermal conductive film: PI film is placed in carbonization furnace and graphitization furnace for high temperature treatment, and then rolled to obtain high thermal conductivity graphite thermal conductive film.

[0047] Example 7 (1) Resin preparation: Same as step (1) in Example 1.

[0048] (2) Preparation of PI film: Same as step (2) in Example 1, except that the unfolding ratio of the transverse track of the stretching section equipment is set to 1.4 and the tension in the MD direction is adjusted to 90N to obtain a polyimide film with a thickness of 100μm.

[0049] (3) Preparation of graphite thermal conductive film: PI film is placed in carbonization furnace and graphitization furnace for high temperature treatment, and then rolled to obtain high thermal conductivity graphite thermal conductive film.

[0050] Comparative Example 1 (1) Resin preparation: at 1.5m 3 102.91 kg of ODA powder was added to 775 kg of DMF in the reactor. After it was completely dissolved, 107.61 kg of PMDA powder was added in batches. After stirring and reacting at 20°C for 1 hour, 0.537 kg of dispersed CaHPO4 was added, followed by 4.48 kg of PMDA powder. The viscosity reached 2167 poise. The resin was then degassed under vacuum and stored at 0°C for later use.

[0051] (2) Preparation of PI film: Same as step (2) in Example 1.

[0052] (3) Preparation of graphite thermal conductive film: PI film is placed in carbonization furnace and graphitization furnace for high temperature treatment, and then rolled to obtain high thermal conductivity graphite thermal conductive film.

[0053] Comparative Example 2 (1) Resin preparation: Same as step (1) in Example 1.

[0054] (2) PI film preparation: The resin prepared in step (1) is fed to the mixer at a resin flow rate of 128 kg / h. At the same time, 137.20 kg of acetic anhydride, 111.09 kg of isoquinoline and 157.18 kg of DMF are mixed evenly and fed to the mixer at a flow rate of 51.90 kg / h. After being mixed evenly in the mixer, it is cast onto the steel belt of the film forming section. After being baked in three stages at 130℃ / 135℃ / 140℃, it enters the hot stretching section for high-temperature treatment. The development ratio of the transverse track of the stretching section equipment is set to 1.2 and the tension in the MD direction is adjusted to 80 N to obtain a polyimide film with a thickness of 100 μm.

[0055] (3) Preparation of graphite thermal conductive film: PI film is placed in carbonization furnace and graphitization furnace for high temperature treatment, and then rolled to obtain high thermal conductivity graphite thermal conductive film.

[0056] Comparative Example 3 (1) Resin preparation: Resin preparation: at 1.5m 349.75 kg of ODA powder was added to 805 kg of DMF in the reactor. After it was completely dissolved, 108.38 kg of PMDA powder was added in three portions. The mixture was stirred and reacted at 20°C for 1 hour. Then, 0.537 kg of dispersed CaHPO4 was added, followed by 26.9 kg of PDA powder. The viscosity reached 2240 poise. The resin was then degassed under vacuum and stored at 0°C for later use.

[0057] (2) Preparation of PI film: Same as step (2) in Example 1.

[0058] (3) Preparation of graphite thermal conductive film: PI film is placed in carbonization furnace and graphitization furnace for high temperature treatment, and then rolled to obtain high thermal conductivity graphite thermal conductive film.

[0059] The properties of the polyimide films and graphite thermal conductive films prepared in Examples 1-7 and Comparative Examples 1-3 are shown in the table below.

[0060] In the table, the PI graphite film is a commercially available 100µm chemically produced PI graphite film from Shidai Huaxin. From the experimental process and the results in the table above, it can be analyzed that by controlling the molar ratio of rigid monomers to flexible monomers (Examples 1-3 and Comparative Examples 1 and 3 represent different ratios of rigid and flexible monomers), a block linear structure can be formed, effectively suppressing over-foaming and avoiding poor surface quality after calendering. For example, in Comparative Example 1, using 3-methylpyridine as a catalyst can effectively reduce the processing temperature of the film-forming section. Similarly, in Comparative Example 2, by adjusting the stretching ratio and tension of the stretching section, the molecular linearity and extensibility of the film can be guaranteed. The table shows that the molar ratio of rigid monomers to flexible monomers exists within a range. When the molar ratio is 0.30:0.70, the thermal conductivity of the calendered graphite thermal conductive film is 1680 W / (m·K), while when the molar ratio is 0.05:0.95, the thermal conductivity of the calendered graphite thermal conductive film is 1600 W / (m·K). Within the molar ratio range of the examples, the thermal conductivity of the graphite thermal conductive film is >1600 W / (m·K). Thermal conductivity is the same as thermal conductivity coefficient.

[0061] Note: Appearance quality of graphite thermal conductive film after calendering: The PI film is evaluated visually according to the following standards. Good (√): Uniform thickness, smooth and flat surface, no powdering, delamination, pinholes, bubbles, etc. Poor (×): Uneven thickness, rough surface, powdering, delamination, pinholes, bubbles, etc.

[0062] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A chemical PI preparation method for graphite heat-conducting film, characterized in that, The preparation method comprises the following steps: 1) adding inorganic filler into the first solvent, and mixing and dispersing to obtain an inorganic filler dispersion liquid; 2) adding diamine monomer, dianhydride monomer and the inorganic filler dispersion liquid into the second solvent, and performing polycondensation reaction to obtain PAA resin; 3) after defoaming, adding dehydrating agent and catalyst, and then performing continuous coating, segmented drying and bidirectional stretching, and then performing chemical imidization to obtain polyimide film.

2. The chemical PI preparation method for graphite heat-conducting film according to claim 1, characterized in that, The first solvent and the second solvent are one of N,N-dimethylacetamide or N,N-dimethylformamide.

3. The chemical PI preparation method for graphite heat-conducting film according to claim 1, characterized in that, The inorganic filler comprises one or a combination of two or more of silicon dioxide, silicon carbide, boron nitride, calcium carbonate and calcium hydrogen phosphate, and the inorganic filler accounts for 0.08-0.25% of the total mass of the polyimide film, and the inorganic filler is calcium hydrogen phosphate, and the particle size of the calcium hydrogen phosphate is 1-10 μm.

4. The chemical PI preparation method for graphite heat-conducting film according to claim 1, characterized in that, The diamine monomer is a block combination of rigid diamine monomer and flexible diamine monomer, and the molar ratio is 0.30:0.70-0.05:0.95, the rigid diamine monomer is any one or a combination of p-phenylenediamine, 3,3'-dimethylbenzidine, 4,4'-diaminodiphenyl sulfone and 4,4'-diaminobenzophenone, the flexible diamine monomer is any one or a combination of 4,4'-diamino diphenyl ether, 4,4'-diaminodiphenylmethane and 2,2-bis[4-(4-aminophenoxy)phenyl]propane, and the dianhydride monomer is any one or a combination of pyromellitic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

5. The chemical PI preparation method for graphite heat-conducting film according to claim 1, characterized in that, The total solid content of the diamine monomer and the dianhydride monomer is set to 20-30%, the molar ratio of the diamine monomer to the dianhydride monomer is 1:0.995-1:1.005, and the resin viscosity is 180,000-250,000 centipoise.

6. The chemical PI preparation method for graphite heat-conducting film according to claim 1, characterized in that, The dehydrating agent is acetic anhydride, and the catalyst is at least one of benzoic acid, triethylamine and 3-methylpyridine, and preferably 3-methylpyridine.

7. The chemical PI preparation method for graphite heat-conducting film according to claim 1, characterized in that, The PAA resin and the dehydrating agent resin are mixed in a molar ratio of 1:2.0-3.0, and the PAA resin and the catalyst are mixed in a molar ratio of 1:0.8-2.

5.

8. The chemical PI preparation method for graphite heat-conducting film according to claim 1, characterized in that, The polyimide film is formed by using a steel belt mirror surface continuous coating, segmented drying, and setting the film forming section temperature zone to 70-160°C.

9. The chemical PI preparation method for graphite heat-conducting film according to claim 1, characterized in that, The polyimide film is stretched by using a bidirectional stretching technology, the hot stretching zone of the stretching section is set to 180-280°C in the first section and 300-400°C in the second section, the MD direction tension is controlled to 25-90 N, preferably 60-90 N, and the T.D. track ratio is set to 0.6-1.4, and the total thickness of the polyimide film is 75-175 μm.

10. Use of a chemical PI for a graphite heat-conducting film, characterized in that, The PI is prepared by using the chemical PI preparation method for the graphite heat conducting film according to any one of claims 1-9, the PI is used to prepare the graphite heat conducting film, the polyimide film is sequentially carbonized and graphitized, and then calendered and cut to obtain the graphite heat conducting film. The graphite heat conducting film has a heat conductivity of >1600 W / (m·K).

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