High-thermal-conductivity graphite film and preparation method thereof

Abstract

The invention discloses a high-thermal-conductivity graphite film and a preparation method thereof. The high-thermal-conductivity graphite film creatively integrates three core technologies of high-temperature physical expansion, stepped graphitization reconstruction and composite fiber reinforcement. Through a multi-section high-temperature quenching process, directional regulation and control of a graphite crystal structure are realized, and uniformly expanded interlayer channels are constructed on a molecular level; according to the gradient graphitization process, lattice distortion is eliminated step by step by accurately controlling the heating rate and heat preservation nodes, and self-assembly of a three-dimensional ordered structure is promoted; the nano-crystalline cellulose and the special fibers are cooperatively introduced, so that a continuous heat conduction network penetrating through the interior of the material is formed, lamellar slippage is inhibited through a mechanical interlocking effect, and the mechanical integrity and the heat conduction efficiency of the material are remarkably improved. The heat conductivity coefficient of the obtained high-heat-conductivity graphite film reaches 900-1300 W / m.K.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of graphite film preparation, and particularly relates to a high-thermal-conductivity graphite film and a preparation method thereof. BACKGROUND

[0002] Under the background of rapid evolution of the electronic information industry towards high integration and high power density, the contradiction between the heat dissipation rate and the heat dissipation efficiency of electronic devices has become a key scientific problem restricting the performance improvement and reliability of equipment. As a kind of intrinsic planar thermal conductivity anisotropic carbon-based functional material, the high-thermal-conductivity graphite film, with the characteristics of light weight, flexibility, high thermal diffusion coefficient and the like, plays an irreplaceable role in microelectronic chip micro-area heat diffusion, new energy battery pack heat gradient balance, 5G base station power amplifier module heat dissipation and AI server cluster heat management, and has become the core material of the heat management system of high-end electronic equipment.

[0003] The current mainstream high-thermal-conductivity graphite film preparation technology mainly includes polyimide (PI) film pyrolysis method and graphene oxide (GO) slurry film forming method, but both processes have significant technical limitations. The PI pyrolysis method uses polyamide acid (PAA) formed by polycondensation of aromatic dianhydride and diamine monomers as a precursor, and graphite film is prepared by imidization and high-temperature graphitization. However, the high molecular precursor in the pyrolysis process is limited by the synergistic effect of molecular chain segment migration dynamics and graphitization crystallization thermodynamics, and the thickness and graphitization degree are significantly negatively correlated, which is difficult to break through the preparation threshold of ultra-thin below 5 μm or ultra-thick above 200 μm, greatly limiting its application in extreme size demand scenarios.

[0004] The GO slurry film forming method is based on the solution self-assembly characteristics of graphene oxide layers, and graphite film is prepared by intercalation exfoliation-dispersion film forming-reduction graphitization process. However, the intercalation reaction system of this process is highly sensitive to reaction conditions (such as acid concentration, temperature, time), and fluctuations in pH value or deviations in reaction time can cause changes in exfoliation efficiency, directly affecting the lateral size and defect density of GO layers, and then causing differences in thermal conductivity between batches; in addition, GO layers are prone to form disordered stacking structures due to π-π stacking and van der Waals forces during the film forming process, and crystal repair is required by high-temperature graphitization above 2800℃, resulting in a production cycle of a single batch of more than 72 h, which seriously restricts the industrial production efficiency. SUMMARY

[0005] In view of the defects of the prior art, the application provides a high-thermal-conductivity graphite film and a preparation method thereof, which integratively combines high-temperature physical puffing, stepwise graphitization reconstruction and composite fiber reinforcement three core technologies. Through a multi-stage high-temperature rapid cooling process, the directional regulation of the graphite crystal structure is realized, and the uniformly expanded interlayer channel is constructed at the molecular level; the gradient graphitization process eliminates the lattice distortion step by step by precisely controlling the heating rate and the holding node, and promotes the self-assembly of the three-dimensional ordered structure; and the synergistic introduction of nanocellulose and special fibers not only forms a continuous thermal conduction network throughout the material, but also inhibits the lamella slip through the mechanical interlocking effect, and significantly improves the mechanical integrity and thermal conduction efficiency of the material. The high-thermal-conductivity graphite film obtained has a thermal conductivity of 900-1300 W / m·K.

[0006] The application provides a preparation method of a high-thermal-conductivity graphite film, which has the following steps: (1) Put large flake graphite into a vacuum arc furnace, heat to 700-900 DEG C, keep warm for 30-50 min, cool to 300-400 DEG C, immerse in 10-40 DEG C water, take out and dry, heat to 2400-2600 DEG C, keep warm for 10-30 min, cool to 300-400 DEG C, immerse in 10-40 DEG C water, take out and dry, heat to 2600-3000 DEG C, keep warm for 5-15 min, cool to 300-400 DEG C, immerse in 10-40 DEG C water, dry, to obtain raw material A, graphite powder. The first stage (700-900 DEG C): through the medium-temperature pre-puffing, the gas (such as H2O, CO2) adsorbed between the graphite layers is caused to escape, initial micropores (pore diameter ≈1-3 nm) are formed, and channels are provided for the subsequent intercalation agent to penetrate.

[0007] (2) The raw material A-graphite powder is slowly added into a mixed solution of concentrated sulfuric acid and potassium permanganate, and the mass ratio of the graphite powder, the concentrated sulfuric acid and the potassium permanganate is usually (1-5):(20-50):(3-10). The stirring speed is 100-900 revolutions per minute, and the reaction time is 1-3 hours. The material B-oxidized graphite with a mass fraction of 1-20% is obtained by alternately washing with a large amount of deionized water and a dilute hydrochloric acid solution (HCl, mass fraction 1-5%) until the pH value of the filtrate approaches neutral. The process significantly reduces the oxidation depth by limiting the amount of potassium permanganate (only 3-10 times), retains more sp 2Carbon structure. Instead of strong acid / strong base repeated treatment, using dilute hydrochloric acid (1-5%) and deionized water alternately washing, reducing the structure damage caused by ion exchange between graphite oxide interlayer; (3) Adding nanocellulose or polyvinyl alcohol in material B-oxidized graphite, accounting for 0.5-5% of the mass percentage of oxidized graphite, and adding superfine acrylic short fibers, the diameter is 0.1-10 μm, the aspect ratio (10-15):1, accounting for 0.2-3% of the mass percentage of oxidized graphite, after beating, homogenizing dispersion, and flat plate grinding, material C-mixed pulp is obtained; nanocellulose has high aspect ratio (>100:1) bridging graphite sheet, and the surface hydroxyl group forms hydrogen bond with graphite π bond. Superfine acrylic short fibers pyrolysis carbonization forms graphitized fiber skeleton, and then mechanical interlocking inhibits interlayer slip.

[0008] (4) Material C-mixed pulp is laid flat on the continuous filter screen track through the flow box, 3-8 stages of vacuum are carried out under the filter screen, free water is quickly removed to prevent sheet layer agglomeration, and infrared heating is carried out at the same time, the temperature is controlled at 80-120℃, and after drying, roll material D is obtained; (5) Roll material D is placed in a vacuum furnace and heated, the temperature rising speed is 1℃ / min in the interval of 500-800℃, and the temperature is kept at a certain temperature point of 600-700℃ for 30-60 min, and then the temperature is raised to 1000-1200℃ for 10-30 min, to obtain material E. 1℃ / min rising rate matches the relaxation time (τ≈60s) of van der Waals force between graphite layers, so that the stress of interlayer slip is fully released.

[0009] (6) Material E is placed in a vacuum arc furnace and heated to 3000-3400℃ and kept for 30-60 min. After cooling, high thermal conductivity graphite film is obtained through multi-stage calendering, and the thermal conductivity reaches 900-1300 W / m·K.

[0010] The advantages of the present application are: through three-stage high temperature treatment (700-900℃→2400-2600℃→2600-3000℃), the graphite sheet is peeled, then nanocellulose or polyvinyl alcohol (0.5-5wt%) and superfine acrylic short fibers (aspect ratio 10-15:1) are added to form a three-dimensional heat conduction network, vacuum filtration combined with infrared heating is used to realize the directional arrangement of the sheet layer, in addition, 1℃ / min slow heating in a specific temperature interval (500-800℃) eliminates the residual stress between the layers, and finally high thermal conductivity graphite film with thermal conductivity of 900-1300 W / m·K is obtained. DETAILED DESCRIPTION

[0011] The following examples are used to further illustrate the present application, and the purpose is to illustrate the present application, and should not be interpreted as limiting the scope of the present application. The following uses weight parts and weight percentage unless otherwise specified.

[0012] The raw materials used in the present application are all conventional commercially available products unless otherwise specified; the methods used in the present application are all conventional methods in the art unless otherwise specified.

[0013] The embodiments of the present application are further described in the following examples.

[0014] It should be understood that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0015] The terms used in the embodiments of the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0016] Example 1 (1) Put large flake graphite into a vacuum arc furnace, heat to 700℃, keep for 30 min, cool to 300℃, immerse in 10℃ water; take out and dry, heat to 2400℃, keep for 10 min, cool to 300℃, immerse in 10℃ water; take out and dry, heat to 2600℃, keep for 5 min, cool to 300℃, immerse in 10-℃ water, dry, to get raw material A; (2) Slowly add raw material A to the mixed solution of concentrated sulfuric acid and potassium permanganate, wherein the mass ratio of graphite powder, concentrated sulfuric acid and potassium permanganate is 1:20:3. Stir constantly during the addition process to ensure uniform dispersion of the graphite powder in the solution. The stirring speed is 100 revolutions per minute, and the reaction time is 3 hours. Wash alternately with a large amount of deionized water and dilute hydrochloric acid solution (HCl, mass fraction of 1%) until the pH value of the filtrate approaches neutral, to obtain material B with a mass fraction of 1%; (3) Add nano-cellulose to material B, accounting for 0.5% of the mass percentage of graphite oxide, and add superfine acrylic short fibers with a diameter of 0.1 μm and an aspect ratio of 10:1, accounting for 0.2% of the mass percentage of graphite oxide. After beating, homogenizing dispersion and flat plate grinding, material C is obtained; (4) Lay material C on the continuous filter screen track through the flow box, vacuumize under the filter screen to quickly remove free water and prevent sheet layer aggregation, and perform infrared heating with the temperature controlled at 80℃, to obtain roll material D after drying; (5) Put the material D into a vacuum furnace and heat it, with a temperature rising speed of 1 ℃ / min in the range of 500-800 ℃, and keep it at 600 ℃ for 30 min, and then raise the temperature to 1000 ℃ for 10 min, to obtain material E.

[0017] (6) Put the material E into a vacuum arc furnace and heat it to 3000 ℃ for 30 min. After cooling, it is subjected to multi-stage calendering to obtain a high-thermal-conductivity graphite film, with a thermal conductivity of 900 W / m·K.

[0018] Example 2 (1) Put large flake graphite into a vacuum arc furnace and heat it to 900 ℃ for 50 min, then lower the temperature to 400 ℃, and immerse it in 40 ℃ water. After taking it out and drying, raise the temperature to 2600 ℃ for 30 min, lower the temperature to 400 ℃, and immerse it in 40 ℃ water. After taking it out and drying, raise the temperature to 3000 ℃ for 15 min, lower the temperature to 400 ℃, and immerse it in 40 ℃ water. After drying, the raw material A is obtained. (2) Slowly add the raw material A into a mixed solution of concentrated sulfuric acid and potassium permanganate, with a mass ratio of graphite powder, concentrated sulfuric acid and potassium permanganate being 5:50:10. Stir constantly during the adding process to ensure that the graphite powder is uniformly dispersed in the solution. The stirring speed is 900 revolutions per minute, and the reaction time is 3 hours. Wash it alternately with a large amount of deionized water and dilute hydrochloric acid solution (HCl, mass fraction of 5%) until the pH value of the filtrate approaches neutral, to obtain material B with a mass fraction of 20%; (3) Add polyvinyl alcohol to material B, with a mass percentage of 5% of the oxidized graphite, and add superfine acrylic short fibers, with a diameter of 10 μm and an aspect ratio of 15:1, with a mass percentage of 3% of the oxidized graphite. After beating, uniform dispersion and flat plate grinding, material C is obtained. (4) Lay material C on a continuous filter screen belt through a flow box, and perform vacuum pumping under the filter screen to quickly remove free water and prevent sheet aggregation. At the same time, infrared heating is performed, with a temperature controlled at 120 ℃. After drying, roll material D is obtained. (5) Put the material D into a vacuum furnace and heat it, with a temperature rising speed of 1 ℃ / min in the range of 500-800 ℃, and keep it at 700 ℃ for 60 min, and then raise the temperature to 1200 ℃ for 30 min, to obtain material E.

[0019] (6) Put the material E into a vacuum arc furnace and heat it to 3400 ℃ for 60 min. After cooling, it is subjected to multi-stage calendering to obtain a high-thermal-conductivity graphite film, with a thermal conductivity of 1300 W / m·K.

[0020] Example 3 (1) Put large flake graphite into a vacuum arc furnace, heat to 800℃, keep for 30 min, cool to 300℃, immerse in 25℃ water, take out and dry, heat to 2500℃, keep for 20 min, cool to 300℃, immerse in 25℃ water, take out and dry, heat to 2800℃, keep for 10 min, cool to 3000℃, immerse in 25℃ water, dry, to obtain raw material A.

[0021] (2) Slowly add raw material A into a mixed solution of concentrated sulfuric acid and potassium permanganate, wherein the mass ratio of graphite powder, concentrated sulfuric acid and potassium permanganate is 2:30:5. The stirring speed is 600 rpm during the adding process, and the reaction time is 2 hours. Wash alternately with a large amount of deionized water and dilute hydrochloric acid solution (HCl, mass fraction of 2%) until the pH value of the filtrate approaches neutral, to obtain material B with a mass fraction of 10%; (3) Add polyvinyl alcohol to material B, accounting for 3% of the mass percentage of graphite oxide, and add superfine acrylic short fibers with a diameter of 5 μm and an aspect ratio of 15:1, accounting for 1% of the mass percentage of graphite oxide, after beating, uniform dispersion and flat plate grinding, to obtain material C; (4) Lay material C on a continuous filter screen belt through a flow box, vacuumize under the filter screen, quickly remove free water, and carry out infrared heating at a temperature of 100℃, to obtain roll material D after drying; (5) Put material D into a vacuum furnace, heat at a temperature rising speed of 1℃ / min in the range of 500-800℃, keep at 600℃ for 40 min, and then heat to 1000℃ for 20 min, to obtain material E.

[0022] (6) Put material E into a vacuum arc furnace, heat to 3200℃, keep for 30 min. After cooling, carry out multi-stage calendering, to obtain high thermal conductivity graphite film with a thermal conductivity of 1000 W / m·K.

[0023] The above examples illustrate the structure, features and effects of the present application. The above description is only the preferred embodiment of the present application, any changes or modifications made in accordance with the idea of the present application, or equivalent embodiments with equivalent changes, shall be within the scope of the present application.

Claims

1. A method for preparing a high thermal conductivity graphite film, characterized in that: Flake graphite is subjected to three heating-cooling cycles under vacuum conditions to exfoliate the graphite; graphite oxide is prepared using the exfoliated flake graphite as the material, and then nanocellulose or polyvinyl alcohol is added to the graphite oxide, and acrylic staple fibers are added. After uniform dispersion, water is removed; the temperature is then increased in three stages in a vacuum furnace, and finally cooled and rolled to obtain a high thermal conductivity graphite film.

2. The method according to claim 1, characterized in that The three heating-cooling cycle treatments are as follows: first heating to 700-900°C, keeping warm for 30-50 minutes, cooling to 300-400°C, and immersing in water at 10-40°C; taking out and drying, heating to 2400-2600°C, keeping warm for 10-30 minutes, cooling to 300-400°C, and immersing in water at 10-40°C; taking out and drying, heating to 2600-3000°C, keeping warm for 5-15 minutes, cooling to 300-400°C, and immersing in water at 10-40°C.

3. The method according to claim 1, characterized in that The method for preparing graphite oxide comprises: adding graphite powder to a mixed solution of concentrated sulfuric acid and potassium permanganate, stirring uniformly, wherein the mass ratio of graphite powder, concentrated sulfuric acid and potassium permanganate is (1-5):(20-50):(3-10), and the reaction time is 1-3 hours; and washing alternately with deionized water and a 1-5wt% dilute hydrochloric acid solution until the pH value of the filtrate is neutral.

4. The method according to claim 3, characterized in that The stirring speed is 100-900 rpm.

5. The method according to claim 1, wherein The acrylic staple fiber has a diameter of 0.1-10 μm and an aspect ratio of (10-15):

1.

6. The method according to claim 1, characterized in that The mass percentage of the nanocellulose or polyvinyl alcohol to the graphite oxide is 0.5-5%, and the mass percentage of the acrylic staple fiber to the graphite oxide is 0.2-3%.

7. The method according to claim 1, characterized in that The mass fraction of the graphite oxide is 1-20%.

8. The method according to claim 1, characterized in that The dewatering method comprises the following steps: spreading a mixture of graphite oxide, nanocellulose or polyvinyl alcohol, and acrylic staple fibers on a continuous filter screen crawler through a headbox, performing 3-8 levels of vacuuming under the filter screen, and simultaneously performing infrared heating to control the temperature at 80-120°C.

9. The method according to claim 1, characterized in that The three-stage heating is as follows: heating to 600-700°C and keeping warm for 30-60 minutes, then heating to 1000-1200°C and keeping warm for 10-30 minutes, and finally heating to 3000-3400°C and keeping warm for 30-60 minutes; wherein, the heating rate in the range of 500-800°C is 1°C / min.

10. A high thermal conductivity graphite film prepared by the method according to claim 1.