POD-based graphite film with interface affinity and preparation method thereof

Abstract

The present application relates to the technical field of heat management materials, and particularly relates to a POD-based graphite film with interface affinity and a preparation method thereof, the preparation method being as follows: a modified POD polymer solution is prepared by polycondensation and copolymerization reaction of terephthalic acid, isophthalic acid, hydrazine salt and a functional monomer in a fuming sulfuric acid system, the functional monomer containing at least one of a carboxyl group and a hydroxyl group; after the modified POD polymer solution is scraped into a film, the film is formed through a coagulation bath, dried, and then subjected to oxygen plasma treatment to obtain a POD precursor film; after the POD precursor film is subjected to carbonization treatment and graphitization treatment, the POD-based graphite film is obtained, wherein a borate or an aqueous ferric nitrate solution is sprayed on the surface of the carbonized film before graphitization treatment. Through a synergistic modification strategy of molecular design-surface activation-interface optimization, the present application solves the problem of poor interface bonding force of traditional graphite films and is suitable for heat dissipation applications in various fields.

Description

Technical Field

[0001] This invention relates to a POD-based graphite film with interfacial affinity and its preparation method, belonging to the field of thermal management materials technology. Background Technology

[0002] With the rapid development of technologies such as 5G communication and high-power electronic devices, the demand for efficient heat dissipation materials is becoming increasingly urgent. Graphite films, due to their excellent in-plane thermal conductivity (typically >1000 W / (m·K)), have become ideal thermal management materials. In recent years, graphite films prepared using aromatic polyoxadiazole (POD) as a precursor have shown significant advantages: compared with traditional polyimide (PI)-based graphite films, POD-based graphite films have higher carbonization yields and more ordered graphitized structures, with thermal conductivity reaching over 1500 W / (m·K) and better thickness controllability (50-200 μm), showing broad application prospects in ultra-thin heat spreaders and high-power chip heat dissipation. However, in practical applications, POD-based graphite films usually need to be used in combination with materials such as copper foil, aluminum, or epoxy resin, and their inherent interfacial bonding defects severely restrict their performance.

[0003] The interface problems of POD-based graphite films mainly stem from their intrinsic properties: First, the POD molecular chain contains rigid aromatic rings and oxadiazole heterocyclic structures, which, while imparting excellent thermal stability, also lead to surface chemical inertness and weak chemical bonding with metal / ceramic substrates, with measured peel strength generally below 0.5 N / cm. Second, during graphitization, the POD molecular chain transforms into a highly oriented sp² carbon layer. While this crystal structure is beneficial for in-plane thermal conductivity, it exhibits poor phonon vibrational spectrum matching with heterogeneous materials (such as copper and epoxy resin). These problems make it difficult for graphite films to achieve efficient heat transfer in practical heat dissipation systems, and may even lead to device failure due to interface peeling.

[0004] Existing technologies have explored some methods for modifying the interface of graphite films, but all have significant limitations. For example, patent application CN118086990A proposes to introduce hexagonal defects on the graphite film surface through high-temperature air etching (500-700℃) to increase the specific surface area, followed by copper electroplating to enhance adhesion. While this method can increase the peel strength to 1.5 N / cm, the high-temperature etching will destroy the integrity of the graphite lattice, resulting in a decrease in tensile strength of more than 30%. Furthermore, strict acid and alkali cleaning (such as KOH alkaline washing to remove oxides and HCl acid washing to activate the surface) is required before electroplating, making the process complex and prone to introducing ion contamination. Another patent application CN117777958A uses parylene vapor deposition to form an ultrathin insulating layer (<15 μm) on the graphite film surface. While this method can improve interfacial wettability, it faces challenges in thickness control: when the deposited layer is <0.5 μm, the scratch resistance is insufficient, and when it is >10 μm, the overall thermal conductivity decreases by more than 20%. Furthermore, these methods only address the post-processing of finished graphite films and fail to achieve synergistic optimization from a global perspective encompassing molecular design, preparation process, and structural evolution.

[0005] The core bottleneck of current technology lies in the fact that existing modification schemes are mostly "local repair" strategies, focusing only on surface morphology control (such as etching and coating) or optimizing a single performance (such as conductivity and insulation), lacking a systematic and synergistic approach to the molecular structure design of POD precursors, interface construction during film formation, and graphitization behavior regulation. This fragmented improvement mode results in limited performance enhancement and is often accompanied by significant side effects (such as mechanical damage and thermal conductivity decay). Therefore, there is an urgent need to develop a synergistic modification strategy that spans the entire process of POD precursor preparation, film formation, and graphitization. This strategy should introduce active functional groups at the molecular level to enhance chemical bonding capabilities, construct multi-level rough structures at the mesoscopic level to improve mechanical interlocking effects, and optimize thermal stress distribution at the macroscopic level through gradient interface design. Ultimately, this will achieve a synergistic improvement in interface affinity and intrinsic thermal / mechanical properties, promoting the large-scale application of POD-based graphite films in high-end heat dissipation fields. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a POD-based graphite film with interfacial affinity and its preparation method. It is an effective strategy to improve the bonding performance of graphite films with other heat dissipation media at the molecular level. By introducing specific functional groups or constructing gradient interface structures in the POD precursor film, the interfacial bonding performance of POD-based graphite films can be significantly improved.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing a POD-based graphite film with interfacial affinity, wherein the preparation method is as follows:

[0008] S1. A modified POD polymer solution is prepared by condensation copolymerization reaction of terephthalic acid, isophthalic acid, hydrazine salt and functional monomer in a fuming sulfuric acid system, wherein the functional monomer contains at least one group selected from carboxyl and hydroxyl groups.

[0009] S2. After the modified POD polymer solution is scraped into a film, it is formed in a coagulation bath, dried, and then treated with oxygen plasma to obtain a POD precursor film.

[0010] S3. After carbonizing and graphitizing the POD precursor film, the POD-based graphite film is obtained, wherein boric acid or ferric nitrate aqueous solution is sprayed onto the surface of the carbonized film before graphitization.

[0011] Furthermore, the functional monomer is selected from at least one of 5-hydroxyisophthalic acid, 3,5-dicarboxybenzoic acid, and 4-hydroxybenzoic acid;

[0012] The hydrazine salt is selected from at least one of hydrazine sulfate or hydrazine hydrochloride.

[0013] Furthermore, in step S1, the molar ratio of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomer is (5-8):(0.5-1.2):(1-2):(0.1-0.5).

[0014] Further, the specific operation in step S1 is as follows: terephthalic acid, isophthalic acid, hydrazine salt and functional monomer are added to fuming sulfuric acid and dispersed evenly. The mixture is then heated to 70-90℃ and stirred for 1-2 hours. The temperature is then further increased to 120-140℃ and stirred for 2-4 hours. Benzoic acid is added as a capping agent. The temperature is then increased to 140-170℃ and stirred for 0.5-2 hours. After degassing, a modified POD polymer solution is obtained.

[0015] Furthermore, the molar ratio of benzoic acid to the total molar ratio of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomers is (0.01-0.03):1;

[0016] The total mass ratio of the terephthalic acid, isophthalic acid, hydrazine salt, and functional monomer to the fuming sulfuric acid is (0.05~0.15):(0.85~0.95).

[0017] Furthermore, in step S2, after the film is scraped, it undergoes a three-stage coagulation bath to form a film, with the temperature of each coagulation bath being 20-40℃.

[0018] First-stage coagulation bath: sulfuric acid aqueous solution with a mass concentration of 40%-60%, time 5-10 min;

[0019] Second-stage coagulation bath: sulfuric acid aqueous solution with a mass concentration of 20%-30%, time 10-20 min;

[0020] The third stage of coagulation bath: sulfuric acid aqueous solution with a mass concentration of 5%-15% for 10-20 minutes.

[0021] Furthermore, in step S2, the conditions for oxygen plasma treatment are: power 50-100W, treatment time 30-60s.

[0022] Furthermore, in step S3, the carbonization process is as follows:

[0023] Pre-oxidize at 200-300℃ for 1-3 hours by heating at a rate of 3-10℃ / min.

[0024] Heating at a rate of 2-5℃ / min to 500-600℃ for low-temperature decomposition for 1-3 hours;

[0025] Heat to 1200-1500℃ at a heating rate of 2-5℃ / min and carbonize for 1-3 hours.

[0026] Furthermore, in step S3, a 1%-5% boric acid or ferric nitrate aqueous solution is sprayed onto the surface of the carbonized film.

[0027] The graphitization process is as follows:

[0028] Heat to 2000-2200℃ at a heating rate of 3-10℃ / min, and hold for 1-3 hours;

[0029] Heat to 2400-2500℃ at a heating rate of 2-5℃ / min, and hold for 1-3 hours;

[0030] Heat to 2600-3000℃ at a heating rate of 2-5℃ / min, and hold for 1-3 hours.

[0031] A POD-based graphite film with interfacial affinity, wherein the POD-based graphite film is prepared according to the preparation method described in this invention.

[0032] The beneficial effects of this invention are:

[0033] In the method for preparing POD-based graphite films with interfacial affinity described in this invention, carboxyl / hydroxyl functional groups are introduced into the molecular chain of the POD precursor film. Combined with plasma surface activation and catalytic graphitization techniques, this significantly improves the interfacial affinity of the graphite film while maintaining high thermal conductivity. This performance improvement stems primarily from multiple effects: firstly, the introduction of carboxyl / hydroxyl functional groups enhances the chemical bonding ability between the graphite film and the metal / ceramic substrate; secondly, plasma treatment enriches the surface with oxygen-containing functional groups, increasing surface energy; and thirdly, the sp²-sp³ gradient interface formed by catalytic graphitization optimizes the phonon transport path.

[0034] The method for preparing a POD-based graphite film with interfacial affinity described in this invention employs a synergistic modification strategy of molecular design, surface activation, and interface optimization: functional groups at the molecular level are introduced through copolymerization, resulting in strong and uniform bonding; surface activation is achieved through plasma treatment, allowing precise control of the surface functional group content; and interface optimization is achieved through catalytic graphitization, constructing a gradient transition structure. Simultaneously, this invention strictly controls the functional group content and process parameters to avoid excessive modification affecting the intrinsic thermal conductivity of the graphite film. The graphite film of this invention achieves a good balance between high thermal conductivity and interfacial affinity, possessing significant application value. Detailed Implementation

[0035] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0037] A method for preparing a POD-based graphite film with interfacial affinity, the method comprising:

[0038] S1. A modified POD polymer solution is prepared by condensation copolymerization reaction of terephthalic acid, isophthalic acid, hydrazine salt and functional monomer in a fuming sulfuric acid system, wherein the functional monomer contains at least one group selected from carboxyl and hydroxyl groups.

[0039] S2. After the modified POD polymer solution is scraped into a film, it is formed in a coagulation bath, dried, and then treated with oxygen plasma to obtain a POD precursor film.

[0040] S3. After carbonizing and graphitizing the POD precursor film, the POD-based graphite film is obtained, wherein boric acid or ferric nitrate aqueous solution is sprayed onto the surface of the carbonized film before graphitization.

[0041] Specifically, the functional monomer is selected from at least one of 5-hydroxyisophthalic acid, 3,5-dicarboxybenzoic acid, and 4-hydroxybenzoic acid;

[0042] The hydrazine salt is selected from at least one of hydrazine sulfate or hydrazine hydrochloride.

[0043] More specifically, in this embodiment of the invention, the concentration of fuming sulfuric acid is 115% (based on sulfur trioxide content).

[0044] Specifically, in step S1, the molar ratio of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomer is (5-8):(0.5-1.2):(1-2):(0.1-0.5).

[0045] More specifically, in the modified POD polymer solution, the polymer has the following structural formula:

[0046] ;

[0047] Where x:y:z = (0.8~0.5):(0.2~0.5):(0.2~0.1).

[0048] Specifically, the operation in step S1 is as follows: terephthalic acid, isophthalic acid, hydrazine salt and functional monomer are added to fuming sulfuric acid and dispersed evenly. The mixture is then heated to 70-90℃ and stirred for 1-2 hours. The temperature is then further increased to 120-140℃ and stirred for 2-4 hours. Benzoic acid is added as a capping agent. The temperature is then increased to 140-170℃ and stirred for 0.5-2 hours. Finally, vacuum degassing is performed at 80℃ to obtain the modified POD polymer solution.

[0049] Specifically, the molar ratio of benzoic acid to the total molar ratio of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomers is (0.01-0.03):1;

[0050] The total mass ratio of the terephthalic acid, isophthalic acid, hydrazine salt, and functional monomer to the fuming sulfuric acid is (0.05~0.15):(0.85~0.95).

[0051] More specifically, in step S2, the modified POD polymer solution prepared in step S1 is poured onto a heated glass plate at 80°C and coated with a film to a thickness of 1000 mm. The coated wet film and the glass plate are then placed in a coagulation bath to solidify.

[0052] Specifically, in step S2, after the film is scraped, it is formed through a three-stage coagulation bath, with the temperature of each coagulation bath being 20-40℃.

[0053] First-stage coagulation bath: sulfuric acid aqueous solution with a mass concentration of 40%-60%, time 5-10 min;

[0054] Second-stage coagulation bath: sulfuric acid aqueous solution with a mass concentration of 20%-30%, time 10-20 min;

[0055] The third stage of coagulation bath: sulfuric acid aqueous solution with a mass concentration of 5%-15% for 10-20 minutes.

[0056] Specifically, in step S2, the conditions for oxygen plasma treatment are: power 50-100W and treatment time 30-60s.

[0057] Specifically, in step S3, the carbonization process is as follows:

[0058] Pre-oxidize at 200-300℃ for 1-3 hours by heating at a rate of 3-10℃ / min.

[0059] Heating at a rate of 2-5℃ / min to 500-600℃ for low-temperature decomposition for 1-3 hours;

[0060] Heat to 1200-1500℃ at a heating rate of 2-5℃ / min and carbonize for 1-3 hours.

[0061] Specifically, in step S3, a 1%-5% boric acid or ferric nitrate aqueous solution is sprayed onto the surface of the carbonized film.

[0062] The graphitization process is as follows:

[0063] Heat to 2000-2200℃ at a heating rate of 3-10℃ / min, and hold for 1-3 hours;

[0064] Heat to 2400-2500℃ at a heating rate of 2-5℃ / min, and hold for 1-3 hours;

[0065] Heat to 2600-3000℃ at a heating rate of 2-5℃ / min, and hold for 1-3 hours.

[0066] A POD-based graphite film with interfacial affinity, wherein the POD-based graphite film is prepared according to the preparation method described in this invention.

[0067] Example 1

[0068] The preparation method of a POD-based graphite film with interfacial affinity is as follows:

[0069] S1. Preparation of modified POD polymer solution:

[0070] Terephthalic acid, isophthalic acid, hydrazine sulfate and 5-hydroxyisophthalic acid were dispersed and dissolved in fuming sulfuric acid with an effective concentration of 115%. After each monomer was dissolved, the temperature was raised to 80°C and stirred for 1 hour. Then the temperature was raised to 120°C and stirred for 2 hours. Benzoic acid was added as a capping agent. The temperature was then raised to 150°C and stirred for 1 hour. Finally, the temperature was lowered to 80°C and vacuum degassing was performed for 2 hours to obtain a modified POD polymer solution.

[0071] The molar ratio of terephthalic acid, isophthalic acid, hydrazine sulfate, and 5-hydroxyisophthalic acid is 7.8:1:1:0.2; the ratio of the total moles of terephthalic acid, isophthalic acid, hydrazine sulfate, and 5-hydroxyisophthalic acid to the moles of benzoic acid is 1:0.01; and the ratio of the total mass of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomer to the mass of fuming sulfuric acid is 0.10:0.90.

[0072] Preparation of S2 and POD precursor films:

[0073] The modified POD polymer solution prepared in step S1 was poured onto a heated glass plate at 80°C and coated with a film to a thickness of 1 mm. The coated wet film and the glass plate were placed in the first coagulation bath (45% sulfuric acid aqueous solution, 25°C) for 8 min to solidify. The wet film was peeled off from the glass plate and placed in the second coagulation bath (25% sulfuric acid aqueous solution, 25°C) for 15 min. The wet film was then placed in the third coagulation bath (10% sulfuric acid aqueous solution, 25°C) for 10 min. The completely solidified wet film was washed with deionized water for more than 8 h, dried at 100°C for 40 min, and then subjected to oxygen plasma treatment to obtain the POD precursor film. The treatment power was 60 W and the treatment time was 35 s.

[0074] S3. Preparation of POD-based graphite film:

[0075] The POD precursor film prepared in step S2 is used to prepare a graphite film through carbonization and graphitization processes.

[0076] The carbonization process is as follows: Under argon protection, the POD precursor film is placed in a carbonization furnace and pre-oxidized by heating from room temperature to 300℃ at a heating rate of 6℃ / min and holding for 2 hours; then it is heated to 600℃ at a heating rate of 3℃ / min for low-temperature decomposition and held for 2 hours; then it is heated to 1500℃ at a heating rate of 3℃ / min for carbonization and held for 2 hours to obtain the POD carbonized film.

[0077] The graphitization process is as follows: Under argon protection, a 5% boric acid aqueous solution (10% of the mass of the POD carbonized film) is sprayed onto the surface of the POD carbonized film. The POD carbonized film is heated to 2200℃ at a heating rate of 10℃ / min and held for 3 hours. Then, it is heated to 2500℃ at a heating rate of 5℃ / min and held for 3 hours. Next, it is heated to 3000℃ at a heating rate of 5℃ / min and held for 3 hours. Finally, it is slowly cooled to room temperature at a cooling rate of 10℃ / min to obtain the POD-based graphite film.

[0078] Example 2

[0079] The preparation method is the same as in Example 1, except that the proportions of some monomers are changed in the preparation stage of the POD solution, and the ingredients are prepared according to the recalculated mass of each monomer. In this Example 2, the molar ratio of terephthalic acid, isophthalic acid, hydrazine sulfate, and 5-hydroxyisophthalic acid is 7.0:0.9:1.5:0.4, the ratio of the total moles of terephthalic acid, isophthalic acid, hydrazine sulfate, and 5-hydroxyisophthalic acid to the moles of benzoic acid is 1:0.015, and the mass ratio of the total mass of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomers to the mass of fuming sulfuric acid is 0.15:0.95.

[0080] Example 3

[0081] The preparation method is the same as in Example 1, except that the proportions of some monomers are changed in the preparation stage of the POD solution, and the ingredients are prepared according to the recalculated mass of each monomer. In this Example 3, the molar ratio of terephthalic acid, isophthalic acid, hydrazine sulfate, and 5-hydroxyisophthalic acid is 6.5:0.8:1:0.4, the ratio of the total moles of terephthalic acid, isophthalic acid, hydrazine sulfate, and 5-hydroxyisophthalic acid to the moles of benzoic acid is 1:0.012, and the mass ratio of the total mass of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomers to the mass of fuming sulfuric acid is 0.10:0.90.

[0082] Example 4

[0083] The preparation method is the same as in Example 1, except that in the preparation stage of the POD solution, 5-hydroxyisophthalic acid is replaced with 3,5-dicarboxybenzoic acid, and the ingredients are prepared according to the recalculated mass of each monomer. The molar ratio of terephthalic acid, isophthalic acid, hydrazine sulfate, and 3,5-dicarboxybenzoic acid is 7.5:1:1:0.5; the ratio of the total moles of terephthalic acid, isophthalic acid, hydrazine sulfate, and 3,5-dicarboxybenzoic acid to the moles of benzoic acid is 1:0.01; and the mass ratio of the total mass of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomers to fuming sulfuric acid is 0.10:0.90.

[0084] Example 5

[0085] The preparation method of a POD-based graphite film with interfacial affinity is as follows:

[0086] S1. The preparation method is the same as in Example 1.

[0087] Preparation of S2 and POD precursor films:

[0088] The modified POD polymer solution prepared in step S1 was poured onto a heated glass plate at 80°C and coated with a film to a thickness of 1 mm. The coated wet film and the glass plate were placed in the first coagulation bath (45% sulfuric acid aqueous solution, 25°C) for 8 min to solidify. The wet film was peeled off from the glass plate and placed in the second coagulation bath (25% sulfuric acid aqueous solution, 25°C) for 15 min. The wet film was then placed in the third coagulation bath (10% sulfuric acid aqueous solution, 25°C) for 10 min. The completely solidified wet film was washed with deionized water for more than 8 h, dried at 120°C for 35 min, and then subjected to oxygen plasma treatment to obtain the POD precursor film. The treatment power was 80 W and the treatment time was 35 s.

[0089] S3: The preparation method is the same as in Example 1.

[0090] Example 6

[0091] The preparation method of a POD-based graphite film with interfacial affinity is as follows:

[0092] S1. The preparation method is the same as in Example 1.

[0093] Preparation of S2 and POD precursor films:

[0094] The modified POD polymer solution prepared in step S1 was poured onto a heated glass plate at 80°C and coated with a film to a thickness of 1 mm. The coated wet film and glass plate were placed in the first coagulation bath (45% sulfuric acid aqueous solution, 20°C) for 8 min to solidify. The wet film was peeled off from the glass plate and placed in the second coagulation bath (25% sulfuric acid aqueous solution, 20°C) for 15 min. The wet film was then placed in the third coagulation bath (10% sulfuric acid aqueous solution, 20°C) for 10 min. The completely solidified wet film was washed with deionized water for more than 8 h, dried at 120°C for 35 min, and then subjected to oxygen plasma treatment to obtain the POD precursor film. The treatment power was 60 W and the treatment time was 60 s.

[0095] S3. The preparation method is the same as in Example 1.

[0096] Example 7

[0097] The preparation method of a POD-based graphite film with interfacial affinity is as follows:

[0098] S1. The preparation method is the same as in Example 1.

[0099] S2, the preparation method is the same as in Example 1.

[0100] S3. The POD precursor film prepared in step S2 is processed by carbonization and graphitization to obtain a graphite film.

[0101] The carbonization process is as follows: the preparation method is the same as in Example 1.

[0102] The graphitization process is as follows: Under argon protection, a 2% boric acid aqueous solution (10% of the mass of the POD carbonized film) is sprayed onto the surface of the POD carbonized film. The POD carbonized film is heated to 2200℃ at a heating rate of 10℃ / min and held for 3 hours. Then, it is heated to 2500℃ at a heating rate of 5℃ / min and held for 3 hours. Next, it is heated to 3000℃ at a heating rate of 5℃ / min and held for 3 hours. Finally, it is slowly cooled to room temperature at a cooling rate of 10℃ / min to obtain the POD-based graphite film.

[0103] Example 8

[0104] The preparation method of a POD-based graphite film with interfacial affinity is as follows:

[0105] S1. Preparation of modified POD polymer solution:

[0106] Terephthalic acid, isophthalic acid, hydrazine sulfate and 4-hydroxybenzoic acid were dispersed and dissolved in fuming sulfuric acid with an effective concentration of 115%. After each monomer was dissolved, the temperature was raised to 70°C and stirred for 2 hours. Then the temperature was raised to 120°C and stirred for 2 hours. Benzoic acid was added as a capping agent. The temperature was then raised to 140°C and stirred for 2 hours. Finally, the temperature was lowered to 80°C and vacuum degassing was performed for 2 hours to obtain a modified POD polymer solution.

[0107] The molar ratio of terephthalic acid, isophthalic acid, hydrazine sulfate, and 4-hydroxybenzoic acid is 5:0.5:1:0.1; the ratio of the total moles of terephthalic acid, isophthalic acid, hydrazine sulfate, and 4-hydroxybenzoic acid to the moles of benzoic acid is 1:0.03; and the ratio of the total mass of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomer to the mass of fuming sulfuric acid is 0.05:0.95.

[0108] Preparation of S2 and POD precursor films:

[0109] The modified POD polymer solution prepared in step S1 was poured onto a heated glass plate at 80°C and coated with a film to a thickness of 1 mm. The coated wet film and the glass plate were placed in the first coagulation bath (40% sulfuric acid aqueous solution, 25°C) for 5 min to solidify. The wet film was peeled off from the glass plate and placed in the second coagulation bath (20% sulfuric acid aqueous solution, 25°C) for 10 min. The wet film was then placed in the third coagulation bath (5% sulfuric acid aqueous solution, 25°C) for 10 min. The completely solidified wet film was washed with deionized water for more than 8 h, dried at 100°C for 40 min, and then subjected to oxygen plasma treatment to obtain the POD precursor film. The treatment power was 50 W and the treatment time was 60 s.

[0110] S3. Preparation of POD-based graphite film:

[0111] The POD precursor film prepared in step S2 is used to prepare a graphite film through carbonization and graphitization processes.

[0112] The carbonization process is as follows: Under argon protection, the POD precursor film is placed in a carbonization furnace and heated from room temperature to 200℃ at a heating rate of 3℃ / min for pre-oxidation treatment, and held at this temperature for 3 hours; then heated to 600℃ at a heating rate of 5℃ / min for low-temperature decomposition treatment, and held at this temperature for 1 hour; then heated to 1200℃ at a heating rate of 2℃ / min for carbonization, and held at this temperature for 3 hours to obtain the POD carbonized film.

[0113] The graphitization process is as follows: Under argon protection, a 1% ferric nitrate aqueous solution (10% of the mass of the POD carbonized film) is sprayed onto the surface of the POD carbonized film. The POD carbonized film is heated to 2000℃ at a heating rate of 3℃ / min and held for 1 hour. Then, it is heated to 2400℃ at a heating rate of 2℃ / min and held for 3 hours. Next, it is heated to 2600℃ at a heating rate of 2℃ / min and held for 1 hour. Finally, it is slowly cooled to room temperature at a cooling rate of 10℃ / min to obtain the POD-based graphite film.

[0114] Example 9

[0115] The preparation method of a POD-based graphite film with interfacial affinity is as follows:

[0116] S1. Preparation of modified POD polymer solution:

[0117] Terephthalic acid, isophthalic acid, hydrazine sulfate and 5-hydroxyisophthalic acid were dispersed and dissolved in fuming sulfuric acid with an effective concentration of 115%. After each monomer was dissolved, the temperature was raised to 90°C and stirred for 1 hour. Then the temperature was raised to 140°C and stirred for 1 hour. Benzoic acid was added as a capping agent. The temperature was then raised to 170°C and stirred for 0.5 hours. Finally, the temperature was lowered to 80°C and vacuum degassing was performed for 2 hours to obtain a modified POD polymer solution.

[0118] The molar ratio of terephthalic acid, isophthalic acid, hydrazine sulfate, and 5-hydroxyisophthalic acid is 8:1.2:2:0.4; the ratio of the total moles of terephthalic acid, isophthalic acid, hydrazine sulfate, and 5-hydroxyisophthalic acid to the moles of benzoic acid is 1:0.02; and the ratio of the total mass of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomer to the mass of fuming sulfuric acid is 0.15:0.85.

[0119] Preparation of S2 and POD precursor films:

[0120] The modified POD polymer solution prepared in step S1 was poured onto a heated glass plate at 80°C and coated with a film to a thickness of 1 mm. The coated wet film and the glass plate were placed in the first coagulation bath (60% sulfuric acid aqueous solution, 30°C) for 10 min to solidify. The wet film was peeled off from the glass plate and placed in the second coagulation bath (30% sulfuric acid aqueous solution, 30°C) for 20 min. The wet film was then placed in the third coagulation bath (15% sulfuric acid aqueous solution, 30°C) for 20 min. The completely solidified wet film was washed with deionized water for more than 8 h, dried at 100°C for 40 min, and then subjected to oxygen plasma treatment to obtain the POD precursor film. The treatment power was 100 W and the treatment time was 30 s.

[0121] S3. Preparation of POD-based graphite film:

[0122] The POD precursor film prepared in step S2 is used to prepare a graphite film through carbonization and graphitization processes.

[0123] The carbonization process is as follows: Under argon protection, the POD precursor film is placed in a carbonization furnace and heated from room temperature to 300℃ at a heating rate of 10℃ / min for pre-oxidation treatment and held for 1 hour; then heated to 500℃ at a heating rate of 2℃ / min for low-temperature decomposition treatment and held for 3 hours; then heated to 1500℃ at a heating rate of 5℃ / min for carbonization and held for 1 hour to obtain the POD carbonized film.

[0124] The graphitization process is as follows: Under argon protection, a 3% boric acid aqueous solution (10% of the mass of the POD carbonized film) is sprayed onto the surface of the POD carbonized film. The POD carbonized film is heated to 2200℃ at a heating rate of 10℃ / min and held for 3 hours. Then, it is heated to 2500℃ at a heating rate of 5℃ / min and held for 1 hour. Next, it is heated to 2800℃ at a heating rate of 4℃ / min and held for 2 hours. Finally, it is slowly cooled to room temperature at a cooling rate of 10℃ / min to obtain the POD-based graphite film.

[0125] Comparative Example 1

[0126] The preparation method of a POD-based graphite film is as follows:

[0127] S1. The preparation method is the same as in Example 1, except that 5-hydroxyisophthalic acid is not added, and the quality of other raw materials remains unchanged.

[0128] S2. The preparation method is the same as in Example 1, except that oxygen plasma treatment is not performed.

[0129] S3. The preparation method is the same as in Example 1, except that boric acid treatment was not performed before graphitization.

[0130] Comparative Example 2

[0131] The preparation method of a POD-based graphite film is as follows:

[0132] S1. The preparation method is the same as in Example 1, except that 5-hydroxyisophthalic acid is not added, and the quality of other raw materials remains unchanged.

[0133] S2. The preparation method is the same as in Example 1, except that oxygen plasma treatment is not performed.

[0134] S3. The preparation method is the same as in Example 1.

[0135] Comparative Example 3

[0136] The preparation method of a POD-based graphite film is as follows:

[0137] S1. The preparation method is the same as in Example 1, except that 5-hydroxyisophthalic acid is not added, and the quality of other raw materials remains unchanged.

[0138] S2, the preparation method is the same as in Example 1.

[0139] S3. The preparation method is the same as in Example 1.

[0140] Comparative Example 4

[0141] The preparation method of a POD-based graphite film is as follows:

[0142] S1. The preparation method is the same as in Example 1.

[0143] S2. The preparation method is the same as in Example 1, except that oxygen plasma treatment is not performed.

[0144] S3. The preparation method is the same as in Example 1.

[0145] Comparative Example 5

[0146] The preparation method of a POD-based graphite film is as follows:

[0147] S1. The preparation method is the same as in Example 1.

[0148] S2, the preparation method is the same as in Example 1.

[0149] S3. The preparation method is the same as in Example 1, except that boric acid treatment was not performed before graphitization.

[0150] Comparative Example 6

[0151] The preparation method of a POD-based graphite film is as follows:

[0152] S1. The preparation method is the same as in Example 1, except that the proportion of 5-hydroxyisophthalic acid is increased. In this Comparative Example 6, the molar ratio of terephthalic acid, isophthalic acid, hydrazine sulfate, and 5-hydroxyisophthalic acid is 7.8:1:1:1.

[0153] S2, the preparation method is the same as in Example 1.

[0154] S3. The preparation method is the same as in Example 1.

[0155] Comparative Example 7

[0156] The preparation method of a POD-based graphite film is as follows:

[0157] S1. The preparation method is the same as in Example 1.

[0158] S2. The preparation method is the same as in Example 1, except that only a first-stage coagulation bath was used in the molding process. The coagulation bath conditions used in Comparative Example 7 were: 40% sulfuric acid aqueous solution, temperature of 25°C, and coagulation bath treatment time of 33 min.

[0159] S3. The preparation method is the same as in Example 1.

[0160] The POD-based graphite films prepared in the above embodiments and comparative examples were subjected to performance tests, and the specific test results are shown in Table 1 below. The test methods involved include:

[0161] (1) Thermal conductivity test: The thermal conductivity and thermal diffusivity of each sample were tested using the stable plate method.

[0162] (2) Peel strength test: After the graphite film is bonded to the copper substrate (a thermally conductive acrylic pressure-sensitive adhesive with a thickness of 30 micrometers is used for bonding), the peel strength is tested using a tensile testing machine (refer to ASTM D903 standard).

[0163] Table 1 Performance test results of POD-based graphite film

[0164]

[0165] As can be seen from the data in the table above, the POD-based graphite films prepared using the method described in Examples 1-9 of this invention exhibit improved interfacial bonding and thermal conductivity through molecular structure design and process optimization. This results in POD-based graphite films possessing high thermal conductivity and excellent thermal diffusivity, while also exhibiting good mechanical strength and interfacial stability. Furthermore, by employing suitable three-stage gradient coagulation bath conditions, the POD-based graphite films achieve excellent surface integrity while maintaining a dense and uniform internal structure free of defects.

[0166] The comparison of the experimental results of Comparative Example 1 and Example 1 shows that when no modification measures are introduced during the preparation of POD-based graphite film, the thermal conductivity is lower than that of Example 1, and the peel strength (0.8 N / mm) is only 30.8% of that of Example 1 (2.6 N / mm), which proves that the modification method of the present invention plays a decisive role in improving performance.

[0167] The comparison of the experimental results of Comparative Example 2, Comparative Example 3 and Example 1 shows that when only partial modification measures are used, the thermal conductivity and peel strength of Comparative Example 2 are significantly lower than those of Example 1, and the peel strength of Comparative Example 3 (without plasma treatment) is only 57.7% of that of Example 1. This indicates that molecular modification and surface treatment must be carried out simultaneously to obtain the best performance.

[0168] A comparison of the experimental results from Comparative Example 4 and Example 1 shows that if oxygen plasma treatment is not performed in step S2, the peel strength and thermal conductivity decrease significantly. This indicates that oxygen plasma activation plays a crucial role in enhancing the surface energy of the film and improving the bonding efficiency of subsequent impregnation treatments, and is an important step in achieving high interfacial adhesion and high thermal conductivity.

[0169] A comparison of the experimental results of Comparative Example 5 and Example 1 shows that if boric acid treatment is not performed before graphitization in step S3, the thermal conductivity is significantly lower than that of Example 1, and the thermal diffusivity also shows a significant decreasing trend. This indicates that the introduction of boric acid can promote the degree of ordering within the carbon atom plane and reduce the generation of defects in the graphitization process, thereby making a significant contribution to improving the thermal conductivity of the film.

[0170] A comparison of the experimental results of Comparative Example 6 and Example 1 shows that if the proportion of functional monomers is too high, the density, thermal conductivity, and mechanical peel strength of the resulting film are all inferior to those of Example 1. This indicates that an excessively high proportion of hydroxyl-containing monomers will disrupt the rigid balance of the POD backbone, reduce the regularity of the system, and lead to an increase in defects in the layered structure after carbonization. This is not conducive to the construction of a high thermal conductivity network, nor is it conducive to obtaining stable interface properties.

[0171] A comparison of the experimental results from Comparative Example 7 and Example 1 shows that if only a single-stage coagulation bath is used, the thermal diffusivity and peel strength are significantly lower than those of Example 1. A single coagulation bath results in uneven coagulation rates inside and outside the film during film formation, leading to an increase in micropores, defects, and residual stress within the film, which in turn affects the overall density and interface stability of the graphitized structure. This demonstrates the necessity of a three-stage gradient coagulation bath for achieving uniform molding, reducing internal stress, and improving performance.

[0172] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0173] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing a POD-based graphite film with interfacial affinity, characterized in that, The preparation method is as follows: S1. A modified POD polymer solution is prepared by condensation copolymerization reaction of terephthalic acid, isophthalic acid, hydrazine salt and functional monomer in a fuming sulfuric acid system, wherein the functional monomer contains at least one group selected from carboxyl and hydroxyl groups. S2. After the modified POD polymer solution is scraped into a film, it is formed in a coagulation bath, dried, and then treated with oxygen plasma to obtain a POD precursor film. S3. After carbonizing and graphitizing the POD precursor film, the POD-based graphite film is obtained, wherein boric acid or ferric nitrate aqueous solution is sprayed onto the surface of the carbonized film before graphitization. In step S1, the molar ratio of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomer is (5-8):(0.5-1.2):(1-2):(0.1-0.5); In step S2, after the film is scraped, it is formed through a three-stage coagulation bath, with the temperature of each coagulation bath being 20-40℃. First-stage coagulation bath: sulfuric acid aqueous solution with a mass concentration of 40%-60%, time 5-10 min; Second-stage coagulation bath: sulfuric acid aqueous solution with a mass concentration of 20%-30%, time 10-20 min; The third stage of coagulation bath: sulfuric acid aqueous solution with a mass concentration of 5%-15% for 10-20 minutes.

2. The method for preparing a POD-based graphite film with interfacial affinity according to claim 1, characterized in that, The functional monomer is selected from at least one of 5-hydroxyisophthalic acid, 3,5-dicarboxybenzoic acid, and 4-hydroxybenzoic acid; The hydrazine salt is selected from at least one of hydrazine sulfate or hydrazine hydrochloride.

3. The method for preparing a POD-based graphite film with interfacial affinity according to claim 1, characterized in that, The specific operation in step S1 is as follows: terephthalic acid, isophthalic acid, hydrazine salt and functional monomer are added to fuming sulfuric acid and dispersed evenly. The mixture is then heated to 70-90℃ and stirred for 1-2 hours. The temperature is then further increased to 120-140℃ and stirred for 2-4 hours. Benzoic acid is added as a capping agent. The temperature is then increased to 140-170℃ and stirred for 0.5-2 hours. After degassing, a modified POD polymer solution is obtained.

4. The method for preparing a POD-based graphite film with interfacial affinity according to claim 3, characterized in that, The molar ratio of benzoic acid to the total molar ratio of terephthalic acid, isophthalic acid, hydrazine salt, and functional monomers is (0.01-0.03):1; The total mass ratio of the terephthalic acid, isophthalic acid, hydrazine salt, and functional monomer to the fuming sulfuric acid is (0.05~0.15):(0.85~0.95).

5. The method for preparing a POD-based graphite film with interfacial affinity according to claim 1, characterized in that, In step S2, the conditions for oxygen plasma treatment are: power 50-100W, treatment time 30-60s.

6. The method for preparing a POD-based graphite film with interfacial affinity according to claim 1, characterized in that, In step S3, the carbonization process is as follows: Pre-oxidize at 200-300℃ for 1-3 hours by heating at a rate of 3-10℃ / min. Heating at a rate of 2-5℃ / min to 500-600℃ for low-temperature decomposition for 1-3 hours; Heat to 1200-1500℃ at a heating rate of 2-5℃ / min and carbonize for 1-3 hours.

7. The method for preparing a POD-based graphite film with interfacial affinity according to claim 1, characterized in that, In step S3, a 1%-5% (w / w) aqueous solution of boric acid or ferric nitrate is sprayed onto the surface of the carbonized film. The graphitization process is as follows: Heat to 2000-2200℃ at a heating rate of 3-10℃ / min, and hold for 1-3 hours; Heat to 2400-2500℃ at a heating rate of 2-5℃ / min, and hold for 1-3 hours; Heat to 2600-3000℃ at a heating rate of 2-5℃ / min, and hold for 1-3 hours.

8. A POD-based graphite film with interfacial affinity, characterized in that, The POD-based graphite film is prepared according to the preparation method described in any one of claims 1-7.

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