Highly heat-conductive flexible graphite film and method for producing the same

Abstract

The application relates to the technical field of graphite heat-conducting materials, in particular to a preparation method of high-heat-conducting flexible graphite film. The preparation method comprises the following steps: uniformly mixing flaky graphite with different particle sizes and concentrated sulfuric acid, then adding hydrogen peroxide dropwise and mixing to obtain a mixture; allowing the mixture to stand and expand to obtain an expanded graphite accumulation body with different expansion volumes; performing low-temperature sulfur removal on the expanded graphite accumulation body; and pressing the expanded graphite accumulation body after the sulfur removal into a flexible graphite film. The preparation method does not need to add other substances, utilizes the volume difference in the puffing process of flaky graphite with different particle sizes, improves the orientation degree of graphite sheet arrangement in the vertical direction of the graphite film, and then improves the heat conductivity in the vertical direction of the graphite film while maintaining the in-plane heat conductivity of the flexible graphite film, and the density and thickness of the prepared flexible graphite film are controllable.

Description

Technical Field

[0001] This invention relates to the field of graphite thermal conductive materials technology, and in particular to a highly thermally conductive flexible graphite film and its preparation method. Background Technology

[0002] Graphite crystals are composed of hexagonal network layers formed by carbon atoms bonded by sp2 bonds. The thermal conductivity of these hexagonal carbon network layers is 3000 W / (m·K). The layers are connected by van der Waals forces. The thermal conductivity of graphite in the direction perpendicular to the layers is 6 W / (m·K), much lower than that in the interlayer direction, exhibiting significant anisotropy. The thermal conductivity in the interlayer direction further decreases after graphite expands. Currently, flexible graphite is used as a thermal management material mainly to utilize its high interlayer thermal conductivity for heat dissipation. However, many heat dissipation applications require even higher thermal conductivity in the vertical direction. Due to the high anisotropy of flexible graphite, it is difficult to achieve high vertical thermal conductivity using traditional methods. The thermal conductivity of currently prepared flexible graphite films in the interlayer direction is 150 W / (m·K) to 400 W / (m·K), and in the vertical direction it is typically below 5 W / (m·K). Summary of the Invention

[0003] This invention provides a high thermal conductivity flexible graphite film and its preparation method, which solves the problem of low vertical thermal conductivity of existing flexible graphite films.

[0004] According to a first aspect of the present invention, the present invention provides a method for preparing a highly thermally conductive flexible graphite film, comprising the following steps:

[0005] Step (1): After mixing flake graphite of different particle sizes with concentrated sulfuric acid evenly, hydrogen peroxide is added dropwise and mixed to obtain a mixture; the mixture is allowed to stand and expand to obtain expanded graphite aggregates with different expansion volumes;

[0006] Step (2): The expanded graphite aggregate is subjected to low-temperature desulfurization;

[0007] Step (3): Press the desulfurized expanded graphite deposit into a flexible graphite film.

[0008] In the aforementioned scheme, the applicant's long-term research has found that the reason for the low thermal conductivity of flexible graphite films in the vertical direction is the low orientation degree of graphite flakes along the vertical direction of the graphite film. The present invention provides a method for preparing a high thermal conductivity flexible graphite film without adding other substances. By utilizing the volume difference during the expansion process of flake graphite with different particle sizes, the orientation degree of graphite flakes along the vertical direction of the graphite film is improved. This, in turn, improves the thermal conductivity of the flexible graphite film in the vertical direction while maintaining the internal thermal conductivity of the flexible graphite film. Furthermore, the density and thickness of the prepared flexible graphite film are controllable.

[0009] Further, in step (1), the flake graphite includes a first flake graphite with a particle size greater than 0.15 mm and a second flake graphite with a particle size less than or equal to 0.15 mm; preferably, the particle size of the first flake graphite is greater than or equal to 0.3 mm.

[0010] In the above scheme, large flake graphite with a particle size greater than 0.15 mm and small flake graphite with a particle size less than or equal to 0.15 mm are selected to combine flake graphite of different particle sizes. Due to the volume difference during the expansion process of flake graphite of different particle sizes, the orientation degree of graphite flakes along the vertical direction of the graphite film can be more effectively improved, thereby more effectively improving the thermal conductivity of the flexible graphite film in the vertical direction.

[0011] Further, in step (1), the mass ratio of the first flake graphite to the second flake graphite is (1-200):1.

[0012] In the above scheme, by limiting the mass ratio of the first sheet graphite and the second sheet graphite to a reasonable range, sheet graphite of different particle sizes can be combined in a more reasonable and effective manner. While maintaining the thermal conductivity within the flexible graphite film layer, it is more conducive to improving the thermal conductivity of the flexible graphite film in the vertical direction.

[0013] Further, in step (1), the weight-to-volume ratio of the flake graphite and the concentrated sulfuric acid is 1 g: (3-15) mL.

[0014] In the above scheme, limiting the weight-to-volume ratio of flake graphite and concentrated sulfuric acid to a reasonable range is beneficial to the expansion of flake graphite.

[0015] Further, in step (1), the volume ratio of the concentrated sulfuric acid to the hydrogen peroxide is (3-20):1.

[0016] In the above scheme, limiting the volume ratio of concentrated sulfuric acid and hydrogen peroxide to a reasonable range is beneficial to the expansion of flake graphite.

[0017] Furthermore, the ambient temperature for the mixture to stand and expand is 15℃-100℃, and the standing time is 0.5h-6h.

[0018] In the above scheme, limiting the ambient temperature and standing time of the mixture to a reasonable range is beneficial to the full expansion of the flake graphite.

[0019] Furthermore, in step (2), water washing is performed before low-temperature desulfurization, and the water washing method is either vacuum filtration or dialysis; the heating temperature for low-temperature desulfurization is 330℃-400℃.

[0020] In the above scheme, by limiting the water washing method and the heating temperature for low-temperature desulfurization, excess sulfuric acid in expanded graphite can be removed more effectively, and the energy consumption of the preparation process can be reduced.

[0021] Furthermore, in step (3), the pressing method is roller pressing, and the pressing number is 1 to 6 times.

[0022] In the above scheme, by limiting the pressing method, it is beneficial to form a flexible graphite film with appropriate density and thickness.

[0023] Furthermore, in step (3), the density of the flexible graphite film is 1 g / cm³. 3 -2.1g / cm 3 The thickness ranges from 30μm to 2000μm.

[0024] In the above scheme, the density and thickness of the flexible graphite film meet reasonable ranges, which is more conducive to its application as an industrial material.

[0025] Furthermore, the flake graphite includes one or more of natural flake graphite, natural microcrystalline graphite, kish graphite, and nano graphite.

[0026] In the above scheme, limiting the type of flake graphite makes it more conducive to the expansion of graphite, so as to form a flexible graphite film with excellent performance.

[0027] According to a second aspect of the present invention, the present invention provides a highly thermally conductive flexible graphite film, which is prepared by the above-described preparation method.

[0028] The present invention provides a method for preparing a high thermal conductivity flexible graphite film without adding other substances. By utilizing the volume difference during the expansion process of sheet graphite with different particle sizes, the orientation degree of graphite sheet arrangement along the vertical direction of the graphite film is improved. Thus, while maintaining the thermal conductivity within the flexible graphite film layer, the thermal conductivity of the flexible graphite film in the vertical direction is improved. Furthermore, the density and thickness of the prepared flexible graphite film are controllable. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] Example 1

[0031] This embodiment provides a method for preparing a highly thermally conductive flexible graphite film, which specifically includes the following steps:

[0032] Step (1): At a reaction temperature of 5°C, 875 mg of 0.50 mm flake graphite and 125 mg of 0.10 mm flake graphite were mixed evenly in 10.5 mL of concentrated sulfuric acid, and 3.5 mL of hydrogen peroxide was gradually added. The mixture was left to stand at room temperature (25°C) for 3 h to expand on its own and obtain expanded graphite stacks with different expansion volumes.

[0033] Step (2): The obtained expanded graphite pile is vacuum filtered to wash away excess concentrated sulfuric acid, and then treated in a muffle furnace at 350°C to further remove the sulfuric acid that cannot be washed off between layers.

[0034] Step (3): Roll press the desulfurized expanded graphite aggregate to a density of 1.7 g / cm³. 3 A flexible graphite film with a thickness of 100 μm. The pressing process is repeated 4 times.

[0035] Example 2

[0036] This embodiment provides a method for preparing a flexible graphite film, which specifically includes the following steps:

[0037] (1) At a reaction temperature of 5°C, 875 mg of 1 mm flake graphite and 125 mg of microcrystalline graphite (less than 0.1 mm) were mixed evenly in 10.5 mL of concentrated sulfuric acid, and 3.5 mL of hydrogen peroxide was gradually added. The mixture was left to stand at room temperature (25°C) for 3 h and expanded on its own to obtain expanded graphite stacks with different expansion volumes.

[0038] (2) The obtained expanded graphite pile was vacuum filtered to wash away excess concentrated sulfuric acid, and then treated in a muffle furnace at 350°C to further remove the sulfuric acid that could not be washed off between layers.

[0039] (3) Roll-press the desulfurized expanded graphite aggregate to a density of 1.7 g / cm³. 3 A flexible graphite film with a thickness of 100 μm. The pressing process is repeated 4 times.

[0040] Example 3

[0041] This embodiment provides a method for preparing a flexible graphite film, which specifically includes the following steps:

[0042] (1) At a reaction temperature of 5°C, 750 mg of 0.30 mm flake graphite and 250 mg of 0.15 mm flake graphite were mixed evenly in 10.5 mL of concentrated sulfuric acid, and 3.5 mL of hydrogen peroxide was gradually added. The reaction product was left to stand at room temperature for 3 h and then expanded on its own to obtain expanded graphite stacks with different expansion volumes.

[0043] (2) The obtained expanded graphite pile was vacuum filtered to wash away excess concentrated sulfuric acid, and then treated in a muffle furnace at 350°C to further remove the sulfuric acid that could not be washed off between layers.

[0044] (3) Roll-press the desulfurized expanded graphite aggregate to a density of 1.7 g / cm³. 3 A flexible graphite film with a thickness of 100 μm. The pressing process is repeated 4 times.

[0045] Example 4

[0046] The difference between this embodiment and Embodiment 3 is that the amount of concentrated sulfuric acid used is 5 mL, the amount of hydrogen peroxide used is 2 mL, and the mixture is rolled to a density of 1.7 g / cm³. 3 A flexible graphite film with a thickness of 500μm.

[0047] Example 5

[0048] The difference between this embodiment and Embodiment 3 is that the roll pressing is 2g / cm 3 A flexible graphite film with a thickness of 50 μm. The pressing process is repeated 5 times.

[0049] Example 6

[0050] The difference between this embodiment and Embodiment 3 is that the amount of 0.30mm and 0.15mm flake graphite added is 500mg.

[0051] Example 7

[0052] The difference between this embodiment and Embodiment 3 is that the amount of 0.30mm and 0.15mm flake graphite added is 990mg and 10mg, respectively.

[0053] Example 8

[0054] The difference between this embodiment and Embodiment 3 is that the amount of 0.30mm and 0.15mm flake graphite added is 995mg and 5mg, respectively.

[0055] Example 9

[0056] The difference between this embodiment and Embodiment 3 is that the amount of concentrated sulfuric acid used is 10 mL, and the amount of hydrogen peroxide used is 0.5 mL.

[0057] Example 10

[0058] The difference between this embodiment and Embodiment 3 is that the amount of concentrated sulfuric acid used is 10 mL, and the amount of hydrogen peroxide used is 2 mL.

[0059] Example 11

[0060] The difference between this embodiment and Embodiment 3 is that the mixed graphite used is 950 mg of 0.3 mm flake graphite and 50 mg of nano graphite (50 nm).

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 3 is that the graphite used in both examples is 0.3mm flake graphite.

[0063] Comparative Example 2

[0064] This comparative example was prepared using a high-temperature film-forming method, and the specific steps are as follows:

[0065] (1) At a reaction temperature of 5°C, 750 mg of 0.30 mm flake graphite and 250 mg of 0.15 mm flake graphite were mixed evenly in 4 mL of concentrated sulfuric acid, and 0.1 mL of hydrogen peroxide was gradually added dropwise. The reaction product was allowed to stand at 40°C for 1 h.

[0066] (2) The reaction product after standing is washed with water and filtered to remove sulfuric acid, and then dried in an oven at 80°C to obtain expandable graphite.

[0067] (3) The dried expandable graphite was placed in a muffle furnace at 900℃ for high-temperature expansion for 10s to obtain expanded graphite.

[0068] (4) The prepared expanded graphite was pre-pressed and rolled to a density of 1.7 g / cm³. 3 A flexible graphite film with a thickness of 100 μm. The pressing process is repeated 4 times.

[0069] The flexible graphite films obtained in Examples 1-11 and Comparative Examples 1-2 were tested for their thermal conductivity in the layer direction and vertical direction. The test method was carried out in accordance with the national standard GB / T 22588. The test results are shown in Table 1 below.

[0070] Table 1

[0071]

[0072] As can be seen from the experimental data in Table 1, the flexible graphite film prepared by the preparation method of the present invention has high thermal conductivity in both the planar direction and the vertical direction.

[0073] As can be seen from the results of Example 3 and Comparative Example 1, by reasonably matching the particle size of the flake graphite, the thermal conductivity of the graphite film in the vertical direction can be improved while maintaining the high thermal conductivity within the flexible graphite film layer.

[0074] As can be seen from the results of Example 3 and Comparative Example 2, the self-expansion of mixed particle size flake graphite into expanded graphite aggregate at room temperature is beneficial to improving the uniformity of expanded graphite particle distribution, thereby simultaneously improving the thermal conductivity of the graphite film in both the surface direction and the vertical direction, and the thermal conductivity is higher than that of the flexible graphite film prepared by the high temperature expansion method.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a flexible graphite film with high thermal conductivity, characterized in that, Includes the following steps: Step (1): After mixing flake graphite of different particle sizes with concentrated sulfuric acid evenly, hydrogen peroxide is added dropwise and mixed to obtain a mixture; the mixture is allowed to stand and expand to obtain expanded graphite aggregates with different expansion volumes; Step (2): The expanded graphite deposit is subjected to low-temperature desulfurization; Step (3): Press the desulfurized expanded graphite deposit into a flexible graphite film; In step (1), the flake graphite includes a first flake graphite with a particle size greater than or equal to 0.3 mm and less than or equal to 1 mm and a second flake graphite with a particle size greater than or equal to 50 nm and less than or equal to 0.15 mm; the mass ratio of the first flake graphite to the second flake graphite is (1-200):

1. In step (3), the pressing method is roller pressing, and the pressing number is 4 to 6 times; the density of the flexible graphite film is 1 g / cm³. 3 -2.1g / cm 3 The thickness ranges from 30μm to 2000μm.

2. The preparation method according to claim 1, characterized in that, In step (1), the weight-to-volume ratio of the flake graphite to the concentrated sulfuric acid is 1 g: (3-15) mL.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the volume ratio of concentrated sulfuric acid to hydrogen peroxide is (3-20):

1.

4. The preparation method according to claim 1, characterized in that, The mixture is allowed to stand and expand at an ambient temperature of 15℃-100℃ for a standing time of 0.5h-6h.

5. The preparation method according to claim 1, characterized in that, In step (2), water washing is performed before low-temperature desulfurization. The water washing method is either vacuum filtration or dialysis. The heating temperature for low-temperature desulfurization is 330℃-400℃.

6. The preparation method according to claim 1, characterized in that, The flake graphite includes one or more of the following: natural flake graphite, natural microcrystalline graphite, kish graphite, and nano graphite.

7. A flexible graphite film with high thermal conductivity, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

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