An ultra-thick polyimide graphite film, a preparation method and application thereof

Abstract

The present application relates to the technical field of polyimide film, in particular to a kind of super-thick polyimide graphite film, preparation method and application;The preparation method is: S1, foaming agent is added to solvent and stirred uniformly to obtain mixed solution;S2, aromatic diamine monomer is added to mixed solution, and stirred uniformly to obtain diamine solution;S3, aromatic dianhydride is added to diamine solution in batches to carry out polycondensation reaction, and polyamide acid resin solution is obtained;S4, polyamide acid resin solution is coated on substrate, and first layer polyimide layer is formed;S5, polyaromatic oxadiazole fiber paper is laid in first layer polyamide acid resin, then a layer of polyamide acid resin is coated, and three-layer structure is formed;S6, the polyamide acid resin of three-layer structure is heat-treated to form gel film;S7, gel film is imidized, and super-thick polyimide base film is obtained;S8, super-thick polyimide base film is sequentially carbonized and graphitized, and super-thick polyimide graphite film is obtained.

Description

Technical Field

[0001] This invention relates to the field of polyimide film technology, specifically to an ultra-thick polyimide graphite film, its preparation method, and its application. Background Technology

[0002] As electronic products become increasingly functional and complex, their internal power density increases, leading to greater heat generation on device surfaces. Sustained high temperatures can cause a gradual deterioration in the performance and reliability of electronic products, making heat dissipation a pressing issue. High thermal conductivity polyimide-graphite film is a novel two-dimensional thermally conductive material, crucial for overcoming the heat dissipation challenge in 5G electronic devices. Ultra-thick or multi-layered composite polyimide-graphite films leverage the high thermal conductivity of graphite films, increasing thickness or designing multi-layered structures to enhance overall or local thickness, significantly increasing heat flux in the direction of heat transfer and providing highly efficient heat dissipation to meet the heat dissipation requirements of electronic products in complex environments. However, the adhesives used in multi-layered graphite films generate thermal resistance, greatly reducing the thermal diffusion capacity of the thermally conductive film. Therefore, fabricating ultra-thick polyimide-graphite thermally conductive films is key to solving the heat dissipation problem of 5G electronic devices.

[0003] However, due to the increased thickness of the polyimide film (>70µm), severe dimensional shrinkage occurs during the carbonization and graphitization process. Uneven internal stress leads to insufficient foaming within the film, resulting in decreased thermal conductivity and surface defects such as wrinkles and pits, severely impacting the performance and downstream applications of the graphite film. Therefore, the market is extremely concerned about how to prepare ultra-thick graphite thermally conductive films with stable performance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes an ultra-thick polyimide graphite film, its preparation method, and its applications.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for preparing an ultrathick polyimide graphite film, the method comprising the following steps:

[0007] S1. Add the foaming agent to the organic solvent and stir until a mixed solution is obtained;

[0008] S2. Add the aromatic diamine monomer to the mixed solution and stir until homogeneous to obtain a diamine solution;

[0009] S3. Under nitrogen protection, aromatic dianhydrides are added to the diamine solution in batches, and then a polycondensation reaction is carried out to obtain a polyamic acid resin solution.

[0010] S4. Coat the substrate with a polyamic acid resin solution to form the first polyimide layer;

[0011] S5. Lay the polyaryloxadiazole fiber paper flat on the first layer of polyamic acid resin, and then coat the polyaryloxadiazole fiber paper with another layer of polyamic acid resin to form a three-layer structure.

[0012] S6. Heat-treat the above three-layer polyamic acid resin to form a gel film;

[0013] S7. The gel membrane is subjected to imidization treatment to obtain an ultra-thick polyimide-based membrane with a three-layer structure.

[0014] S8. The ultra-thick polyimide-based film with a three-layer structure is subjected to carbonization and graphitization treatment in sequence to obtain an ultra-thick polyimide-graphite film.

[0015] Preferably, the foaming agent is at least one of silicon carbide, boron nitride, silicon nitride, or a metal salt, the particle size of the foaming agent is 1-3 μm, and the amount used accounts for 0.1-1% of the total mass of the aromatic diamine monomer and the aromatic dianhydride monomer; the organic solvent is at least one of N,N'-dimethylacetamide or N,N'-dimethylformamide.

[0016] Preferably, the aromatic diamine monomer is at least one of p-phenylenediamine or 4,4'-diaminodiphenyl ether; the aromatic dianhydride monomer is at least one of pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0017] Preferably, in step S3, the molar ratio of aromatic diamine monomer to aromatic dianhydride monomer is 1:0.98-1, the reaction temperature of the polycondensation reaction is 10-30°C, the reaction time is 6-24 h, the solid content of the polyamic acid resin solution is 10-20%, and the rotational viscosity is 100000-150000 mPa·s.

[0018] Preferably, in step S6, the heat treatment involves raising the temperature to 80-110°C at a rate of 2-10°C / min and holding the temperature for 25-40 minutes.

[0019] Preferably, in step S7, the imidization process is as follows: the three-layer polyamic acid gel film is peeled off from the substrate, fixed on a needle plate, placed in a forced-air drying oven, heated to 150-200°C at 2-10°C / min and held for 30 min, then heated to 200-250°C at 2-10°C / min and held for 30 min for imidization treatment; then heated to 300-340°C at 2-10°C / min and held for 30 min for annealing treatment.

[0020] Preferably, in step S8, the carbonization process involves stacking polyimide films and graphite sheets, placing them in a carbonization furnace, evacuating the furnace, heating the furnace at 2–4 °C / min to 900–1200 °C, and holding the temperature for 2–3 hours. The graphitization process involves placing the carbonized polyimide film in a graphitization furnace, heating it to 2000 °C at 1–10 °C / min under an argon atmosphere, then heating it to 3000 °C at 1–5 °C / min, and holding it at 2000 °C, 2400 °C, 2800 °C, and 3000 °C for 0.5–1 hours each, and finally cooling it to room temperature at 10 °C / min.

[0021] An ultra-thick polyimide graphite film is prepared by the preparation method described above.

[0022] Preferably, the total thickness of the ultra-thick polyimide-based film is 100-300 μm, and from top to bottom are a polyimide layer, a polyaryloxadiazole fiber paper layer, and a polyimide layer, with a thickness ratio of 1:(1-4):1 for each layer.

[0023] The above-described ultra-thick polyimide graphite film is used in electronic products.

[0024] The beneficial effects of this invention are:

[0025] 1. The polyimide-based film prepared in this invention is composed of three layers: polyimide on both sides and polyarylene oxadiazole fiber paper in the middle. Both polyarylene oxadiazole and polyimide are polymer-based materials, and the main chain of polyarylene oxadiazole is composed of alternating benzene rings and oxadiazole rings, with a molecular structure similar to that of polyimide, resulting in better compatibility between the two. At the same time, the polyarylene oxadiazole fiber paper has tiny pores, allowing the polyimide on both sides to permeate into the pores. The polyimide on both sides connects the three layers of the polyimide-based film through the pores, forming a whole and avoiding the problems of delamination and cracking that occur after the polyimide-based film is carbonized and graphitized.

[0026] 2. The polyarylene oxadiazole fiber paper used in this invention is composed of polyarylene oxadiazole fibers, which are interwoven and arranged in a multi-layered network structure. During the graphitization process of the ultra-thick polyimide-based film, the multi-layered network structure of the polyarylene oxadiazole fibers can support the ultra-thick graphite film, avoiding problems such as breakage and cracking caused by excessive thickness of the graphite film.

[0027] 3. The polyaryl oxadiazole main chain in this invention contains a large number of oxadiazole rings and has a high nitrogen content, making it easy to foam during the carbonization and graphitization process. This solves the problem of traditional polyimide thick films not foaming and having low thermal conductivity due to the thickness of the film during the graphite film firing process.

[0028] 4. The ultra-thick graphite film prepared by this invention has a thickness of 100-300 μm, a thermal conductivity of >1500 W / (m·K), and a uniform and delicate film surface. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] A method for preparing an ultrathick polyimide graphite film includes the following steps:

[0032] S1: Take 0.188 g of silicon nitride, place it in 200 mL of N,N'-dimethylacetamide (DMAc), and sonicate for 2 h to disperse it evenly to obtain a mixed solution;

[0033] S2: Add 3.934 g of p-phenylenediamine (36 mmol) and 17.0 g of 4,4'-diaminodiphenyl ether (85 mmol) to the mixed solution, and stir mechanically at room temperature for 3 h to completely dissolve p-phenylenediamine and 4,4'-diaminodiphenyl ether to obtain a diamine solution;

[0034] S3: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to a silicon nitride diamine solution and reacted at room temperature for 8 h to obtain a polyamic acid solution with a solid content of 20%, a viscosity of 120000 (mPa·s) and a silicon nitride content of 4‰.

[0035] S4: Use a coating machine to coat the polyamic acid solution onto the glass substrate, with a coating thickness of 30μm;

[0036] S5: Lay a 100µm thick polyaryloxadiazole fiber paper on the first layer of polyamic acid resin, and then coat the polyaryloxadiazole fiber paper with a 30µm thick polyamic acid solution to form a polyimide / polyaryloxadiazole fiber paper / polyimide three-layer structure.

[0037] S6: Place the three-layer polyimide film in an oven and heat it to 100°C at a rate of 4°C / min, and keep it at that temperature for 30 min to obtain a gel film;

[0038] S7: Fix the gel membrane onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 30 min, then heat it to 240℃ at 4℃ / min and hold for 30 min for imidization treatment; finally heat it to 340℃ at 4℃ / min and hold for 30 min for annealing treatment, thus preparing the ultra-thick polyimide-based membrane.

[0039] S8: Cut the ultra-thick polyimide-based film into 10cm×10cm sizes, place it between two layers of graphite sheets, put it in a carbonization furnace, and evacuate it. Heat it to 1200℃ at a heating rate of 3℃ / min, hold it for 3 hours, and cool it to room temperature to remove the carbonized film. Place the carbonized sample in a graphitization furnace, maintain an argon atmosphere throughout the graphitization process, heat it to 2000℃ at a rate of 2℃ / min, then heat it to 3000℃ at a rate of 2℃ / min, and hold it at 2000℃, 2400℃, 2800℃, and 3000℃ for 1 hour each. Finally, cool it to room temperature at a cooling rate of 10℃ / min to obtain the ultra-thick polyimide graphite film.

[0040] Example 2

[0041] A method for preparing an ultrathick polyimide graphite film includes the following steps:

[0042] S1: Take 0.235g of silicon nitride, place it in 200mL of N,N'-dimethylacetamide (DMAc), and sonicate for 2h to disperse it evenly to obtain a mixed solution;

[0043] S2: Add 3.934 g of p-phenylenediamine (36 mmol) and 17.0 g of 4,4'-diaminodiphenyl ether (85 mmol) to the mixed solution, and stir mechanically at room temperature for 3 h to completely dissolve p-phenylenediamine and 4,4'-diaminodiphenyl ether to obtain a diamine solution;

[0044] S3: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a polyamic acid solution with a solid content of 20%, a viscosity of 120000 (mPa·s) and a silicon nitride content of 5‰.

[0045] S4: Use a coating machine to coat the polyamic acid solution onto the glass substrate, with a coating thickness of 40μm;

[0046] S5: A 100µm thick polyarylene diazole fiber paper is laid flat on the first layer of polyamic acid resin, and a 40µm thick polyamic acid solution is coated on the polyarylene diazole fiber paper to form a three-layer structure of polyimide / polyarylene diazole fiber paper / polyimide.

[0047] S6: Place the three-layer polyimide film in an oven and heat it to 100°C at a rate of 4°C / min, and keep it at that temperature for 30 min to obtain a gel film;

[0048] S7: Fix the gel membrane onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 30 min, then heat it to 240℃ at 4℃ / min and hold for 30 min for imidization treatment; finally heat it to 340℃ at 4℃ / min and hold for 30 min for annealing treatment, thus preparing the ultra-thick polyimide-based membrane.

[0049] S8: Cut the ultra-thick polyimide-based film into 10cm×10cm sizes, place it between two layers of graphite sheets, put it in a carbonization furnace, and evacuate it. Heat it to 1200℃ at a heating rate of 3℃ / min, hold it for 3 hours, and cool it to room temperature to remove the carbonized film. Place the carbonized sample in a graphitization furnace, maintain an argon atmosphere throughout the graphitization process, heat it to 2000℃ at a rate of 2℃ / min, then heat it to 3000℃ at a rate of 2℃ / min, and hold it at 2000℃, 2400℃, 2800℃, and 3000℃ for 1 hour each. Finally, cool it to room temperature at a cooling rate of 10℃ / min to obtain the ultra-thick polyimide graphite film.

[0050] Example 3

[0051] A method for preparing an ultrathick polyimide graphite film includes the following steps:

[0052] S1: Take 0.283g of silicon nitride, place it in 200mL of N,N'-dimethylacetamide (DMAc), and sonicate for 2h to disperse it evenly to obtain a mixed solution;

[0053] S2: Add 3.934 g of p-phenylenediamine (36 mmol) and 17.0 g of 4,4'-diaminodiphenyl ether (85 mmol) to a silicon nitride solution, and stir mechanically at room temperature for 3 h to completely dissolve p-phenylenediamine and 4,4'-diaminodiphenyl ether to obtain a diamine solution;

[0054] S3: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a polyamic acid solution with a solid content of 20%, a viscosity of 120000 (mPa·s) and a silicon nitride content of 6‰.

[0055] S4: Use a coating machine to coat the polyamic acid solution onto the glass substrate, with a coating thickness of 50μm;

[0056] S5: A 100µm thick polyaryloxadiazole fiber paper is laid flat on the first layer of polyamic acid resin, and a 50µm thick polyamic acid solution is coated on the polyaryloxadiazole fiber paper to form a three-layer structure of polyimide / polyaryloxadiazole fiber paper / polyimide.

[0057] S6: Place the three-layer polyimide film in an oven and heat it to 100°C at a rate of 4°C / min, and keep it at that temperature for 30 min to obtain a gel film;

[0058] S7: Fix the gel membrane onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 30 min, then heat it to 240℃ at 4℃ / min and hold for 30 min for imidization treatment; finally heat it to 340℃ at 4℃ / min and hold for 30 min for annealing treatment, thus preparing the ultra-thick polyimide-based membrane.

[0059] S8: Cut the ultra-thick polyimide-based film into 10cm×10cm sizes, place it between two layers of graphite sheets, put it in a carbonization furnace, and evacuate it. Heat it to 1200℃ at a heating rate of 3℃ / min, hold it for 3 hours, and cool it to room temperature to remove the carbonized film. Place the carbonized sample in a graphitization furnace, maintain an argon atmosphere throughout the graphitization process, heat it to 2000℃ at a rate of 2℃ / min, then heat it to 3000℃ at a rate of 2℃ / min, and hold it at 2000℃, 2400℃, 2800℃, and 3000℃ for 1 hour each. Finally, cool it to room temperature at a cooling rate of 10℃ / min to obtain the ultra-thick polyimide graphite film.

[0060] Example 4

[0061] A method for preparing an ultrathick polyimide graphite film includes the following steps:

[0062] S1: Take 0.330 g of silicon nitride, place it in 200 mL of N,N'-dimethylacetamide (DMAc), and sonicate for 2 h to disperse it evenly to obtain a mixed solution;

[0063] S2: Add 3.934 g of p-phenylenediamine (36 mmol) and 17.0 g of 4,4'-diaminodiphenyl ether (85 mmol) to the mixed solution, and stir mechanically at room temperature for 3 h to completely dissolve p-phenylenediamine and 4,4'-diaminodiphenyl ether to obtain a diamine solution;

[0064] S3: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a polyamic acid solution with a solid content of 20%, a viscosity of 120000 (mPa·s) and a silicon nitride content of 7‰.

[0065] S4: Use a coating machine to coat the polyamic acid solution onto the glass substrate, with a coating thickness of 50μm;

[0066] S5: A 150µm thick polyaryloxadiazole fiber paper is laid flat on the first layer of polyamic acid resin, and a 50µm thick polyamic acid solution is coated on the polyaryloxadiazole fiber paper to form a three-layer structure of polyimide / polyaryloxadiazole fiber paper / polyimide.

[0067] S6: Place the three-layer polyimide film in an oven and heat it to 100°C at a rate of 4°C / min, and keep it at that temperature for 30 min to obtain a gel film;

[0068] S7: Fix the gel membrane onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 30 min, then heat it to 240℃ at 4℃ / min and hold for 30 min for imidization treatment; finally heat it to 340℃ at 4℃ / min and hold for 30 min for annealing treatment, thus preparing the ultra-thick polyimide-based membrane.

[0069] S8: Cut the ultra-thick polyimide-based film into 10cm×10cm sizes, place it between two layers of graphite sheets, put it in a carbonization furnace, and evacuate it. Heat it to 1200℃ at a heating rate of 3℃ / min, hold it for 3 hours, and cool it to room temperature to remove the carbonized film. Place the carbonized sample in a graphitization furnace, maintain an argon atmosphere throughout the graphitization process, heat it to 2000℃ at a rate of 2℃ / min, then heat it to 3000℃ at a rate of 2℃ / min, and hold it at 2000℃, 2400℃, 2800℃, and 3000℃ for 1 hour each. Finally, cool it to room temperature at a cooling rate of 10℃ / min to obtain the ultra-thick polyimide graphite film.

[0070] Comparative Example 1

[0071] A method for preparing an ultrathick polyimide graphite film includes the following steps:

[0072] S1: Take 0.330 g of silicon nitride, place it in 200 mL of N,N'-dimethylacetamide (DMAc), and sonicate for 2 h to disperse it evenly to obtain a mixed solution;

[0073] S2: Add 3.934 g of p-phenylenediamine (36 mmol) and 17.0 g of 4,4'-diaminodiphenyl ether (85 mmol) to a silicon nitride solution, and stir mechanically at room temperature for 3 h to completely dissolve p-phenylenediamine and 4,4'-diaminodiphenyl ether to obtain a diamine solution;

[0074] S3: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a polyamic acid solution with a solid content of 20%, a viscosity of 120000 (mPa·s) and a silicon nitride content of 7‰.

[0075] S4: The polyamic acid solution was coated onto the glass substrate using a coating machine to a thickness of 150 μm. The substrate was then placed in an oven and heated to 100 °C at a rate of 4 °C / min, and kept at that temperature for 30 min to obtain a gel film.

[0076] S5: Fix the gel membrane onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 30 min, then heat it to 240℃ at 4℃ / min and hold for 30 min for imidization treatment; finally heat it to 340℃ at 4℃ / min and hold for 30 min for annealing treatment, thus preparing the ultra-thick polyimide-based membrane.

[0077] S6: Cut the ultra-thick polyimide-based film into 10cm×10cm pieces, place them between two graphite sheets, and put them in a carbonization furnace. Evacuate the furnace and heat the film to 1200℃ at a rate of 3℃ / min. Hold the temperature for 3 hours and cool it to room temperature before removing the carbonized film. Place the carbonized sample in a graphitization furnace and maintain an argon atmosphere throughout the graphitization process. Heat the film to 2000℃ at a rate of 2℃ / min, then to 3000℃ at a rate of 2℃ / min. Hold the film at 2000℃, 2400℃, 2800℃, and 3000℃ for 1 hour each. Finally, cool the film to room temperature at a rate of 10℃ / min to obtain the ultra-thick polyimide graphite film.

[0078] Comparative Example 2

[0079] A method for preparing an ultrathick polyimide graphite film includes the following steps:

[0080] S1: Take 0.235g of silicon nitride, place it in 200mL of N,N'-dimethylacetamide (DMAc), and sonicate for 2h to disperse it evenly to obtain a mixed solution;

[0081] S2: Add 3.934 g of p-phenylenediamine (36 mmol) and 17.0 g of 4,4'-diaminodiphenyl ether (85 mmol) to a silicon nitride solution, and stir mechanically at room temperature for 3 h to completely dissolve p-phenylenediamine and 4,4'-diaminodiphenyl ether to obtain a diamine solution;

[0082] S3: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a polyamic acid solution with a solid content of 20%, a viscosity of 120000 (mPa·s) and a silicon nitride content of 5‰.

[0083] S4: Use a coating machine to coat the polyamic acid solution onto the glass substrate, with a coating thickness of 50μm;

[0084] S5: Lay 100um thick polyarylene diazole fiber paper flat on polyamic acid resin to form a polyimide / polyarylene diazole fiber paper two-layer structure.

[0085] S6: Place the two-layer polyimide film in an oven and heat it to 100°C at a rate of 4°C / min, and keep it at that temperature for 30 min to obtain a gel film;

[0086] S7: Fix the gel membrane onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 30 min, then heat it to 240℃ at 4℃ / min and hold for 30 min for imidization treatment; finally heat it to 340℃ at 4℃ / min and hold for 30 min for annealing treatment, thus preparing the ultra-thick polyimide-based membrane.

[0087] S8: Cut the ultra-thick polyimide-based film into 10cm×10cm sizes, place it between two layers of graphite sheets, put it in a carbonization furnace, and evacuate it. Heat it to 1200℃ at a heating rate of 3℃ / min, hold it for 3 hours, and cool it to room temperature to remove the carbonized film. Place the carbonized sample in a graphitization furnace, maintain an argon atmosphere throughout the graphitization process, heat it to 2000℃ at a rate of 2℃ / min, then heat it to 3000℃ at a rate of 2℃ / min, and hold it at 2000℃, 2400℃, 2800℃, and 3000℃ for 1 hour each. Finally, cool it to room temperature at a cooling rate of 10℃ / min to obtain the ultra-thick polyimide graphite film.

[0088] Comparative Example 3

[0089] A method for preparing a polyarylene oxadiazole graphite film includes the following steps:

[0090] S1: Cut a 150µm thick polyarylene diazole fiber paper into 10cm×10cm pieces, place them between two graphite sheets, and put them in a carbonization furnace. Evacuate the furnace and heat the sample to 1200℃ at a rate of 3℃ / min. Hold the temperature for 3 hours and cool to room temperature to remove the carbonized film. Place the carbonized sample in a graphitization furnace and maintain an argon atmosphere throughout the graphitization process. Heat the sample to 2000℃ at a rate of 2℃ / min, then to 3000℃ at a rate of 2℃ / min. Hold the sample at 2000℃, 2400℃, 2800℃, and 3000℃ for 1 hour each. Finally, cool the sample to room temperature at a rate of 10℃ / min to obtain the polyarylene diazole graphite film.

[0091] The performance of the polyimide graphite films obtained in the embodiments and comparative examples of the present invention was tested, and the test results are shown in Table 1.

[0092] Table 1. Performance test results of polyimide graphite film

[0093]

[0094]

[0095] As shown in Table 1, in Comparative Example 1, the polyimide film was not fully foamed due to its excessive thickness, resulting in low thermal conductivity and severe wrinkles on the graphite film surface, rendering it unusable. Compared to Comparative Example 1, the addition of polyarylene diazole fiber paper in Examples 1-4 ensured sufficient foaming of the thick polyimide film. After calendering, the ultra-thick graphite film surface was smooth and flat, without cracks or delamination, and its thermal conductivity was significantly improved, reaching over 1500 W / (m·K). Compared to Comparative Example 2, in Examples 1-4, the polyimide-based film with a two-layer structure of polyimide / polyarylene diazole fiber paper experienced severe powder shedding and cracks after graphitization, resulting in low thermal conductivity. The three-layer structure ultra-thick graphite film exhibited better appearance and thermal conductivity than the two-layer structure ultra-thick graphite film. Compared to Comparative Example 3, in Examples 1-4, the polyarylene diazole fiber paper, when used alone and graphitized, resulted in severe powder shedding and numerous cracks on the film surface. The combination of polyaryloxadiazole fiber paper and two layers of polyimide avoids the problem of insufficient foaming of ultra-thick polyimide-based films. At the same time, the thermal conductivity of ultra-thick graphite films is greatly improved, and the appearance performance of the films is better.

[0096] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0097] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing an ultra-thick polyimide graphite film, characterized in that, The preparation method includes the following steps: S1. Add the foaming agent to the organic solvent and stir until a mixed solution is obtained; S2. Add the aromatic diamine monomer to the mixed solution and stir until homogeneous to obtain a diamine solution; S3. Under nitrogen protection, aromatic dianhydrides are added to the diamine solution in batches, and then a polycondensation reaction is carried out to obtain a polyamic acid resin solution. S4. Coat the polyamic acid resin solution onto the substrate to form the first polyamic acid resin layer; S5. Lay the polyaryloxadiazole fiber paper flat on the first layer of polyamic acid resin, and then coat the polyaryloxadiazole fiber paper with another layer of polyamic acid resin to form a three-layer structure; the polyaryloxadiazole fiber paper is composed of polyaryloxadiazole fibers, which are interwoven and arranged in a multi-layered mesh structure. S6. Heat-treat the above three-layer polyamic acid resin to form a gel film; S7. The gel membrane is subjected to imidization treatment to obtain an ultra-thick polyimide-based membrane with a three-layer structure; wherein, there are tiny pores on the polyaryloxadiazole fiber paper, and the polyimide on both sides permeates into the pores, and the three-layer ultra-thick polyimide-based membrane is formed into a whole through the connection of the pores. S8. The ultra-thick polyimide-based film with a three-layer structure is subjected to carbonization and graphitization treatment in sequence to obtain an ultra-thick polyimide-graphite film.

2. The method for preparing an ultra-thick polyimide graphite film according to claim 1, characterized in that, The foaming agent is at least one of silicon carbide, boron nitride, silicon nitride, or a metal salt, and the particle size of the foaming agent is 1-3 μm, with an amount accounting for 0.1-1% of the total mass of the aromatic diamine monomer and the aromatic dianhydride monomer; the organic solvent is at least one of N,N'-dimethylacetamide or N,N'-dimethylformamide.

3. The method for preparing an ultra-thick polyimide graphite film according to claim 1, characterized in that, The aromatic diamine monomer is at least one of p-phenylenediamine or 4,4'-diaminodiphenyl ether; the aromatic dianhydride monomer is at least one of pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride.

4. The method for preparing an ultra-thick polyimide graphite film according to claim 1, characterized in that, In step S3, the molar ratio of aromatic diamine monomer to aromatic dianhydride monomer is 1:0.98-1, the reaction temperature of the polycondensation reaction is 10-30℃, the reaction time is 6-24h, the solid content of the polyamic acid resin solution is 10-20%, and the rotational viscosity is 100000-150000mPa·s.

5. The method for preparing an ultra-thick polyimide graphite film according to claim 1, characterized in that, In step S6, the heat treatment involves raising the temperature to 80-110°C at a rate of 2-10°C / min and holding it at that temperature for 25-40 minutes.

6. The method for preparing an ultra-thick polyimide graphite film according to claim 1, characterized in that, In step S7, the imidization process is as follows: the three-layer polyamic acid gel film is peeled off from the substrate, fixed on a needle plate, placed in a forced-air drying oven, heated to 150-200℃ at 2-10℃ / min and held for 30 min, then heated to 200-250℃ at 2-10℃ / min and held for 30 min for imidization treatment; then heated to 300-340℃ at 2-10℃ / min and held for 30 min for annealing treatment.

7. The method for preparing an ultra-thick polyimide graphite film according to claim 1, characterized in that, In step S8, the carbonization process involves stacking polyimide films and graphite sheets, placing them in a carbonization furnace, evacuating the furnace, and heating the furnace at 2–4 °C / min to 900–1200 °C, holding the temperature for 2–3 hours. The graphitization process involves placing the carbonized polyimide film in a graphitization furnace, heating it to 2000 °C at 1–10 °C / min under an argon atmosphere, then heating it to 3000 °C at 1–5 °C / min, and holding it at 2000 °C, 2400 °C, 2800 °C, and 3000 °C for 0.5–1 hours each, and finally cooling it to room temperature at 10 °C / min.

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