A preparation method of a longitudinal heat conduction enhanced graphene TIM film

Abstract

The application provides a preparation method of a longitudinal heat conduction enhanced graphene TIM film, comprising the following steps: 1) preparing a graphene oxide film, and opening a plurality of through holes in the thickness direction of the graphene oxide film; 2) soaking the graphene oxide film provided with the through holes into a foaming agent, taking out and drying after reaction, and obtaining a graphene foaming film; 3) taking the graphene foaming film as filter cloth, and filling a carbon fiber mixed slurry into the through holes of the graphene foaming film in a vacuum suction filtration mode until the through holes are completely blocked by the carbon fiber mixed slurry; and 4) performing thermal reduction treatment on the graphene foaming film, and obtaining a longitudinal heat conduction enhanced graphene TIM film. Through the synergistic design of "arrayed punching-directional filling-graphitization", a "carbon fiber-GO" composite heat conduction path distributed along the Z direction (thickness direction) is constructed in the foaming film, and the longitudinal heat conduction performance of the graphene TIM film is improved.

Description

Technical Field

[0001] This invention relates to the field of graphene materials technology, and in particular to a method for preparing a longitudinally thermally enhanced graphene TIM film. Background Technology

[0002] Graphene is a widely studied two-dimensional carbon material, consisting of a unique honeycomb lattice of parallel conjugated atomic layers. Graphene possesses low atomic mass, strong bond energy, a single-crystal structure, and low anharmonic vibrations, with a theoretical thermal conductivity as high as 5300 W / (m·K). Simultaneously, graphene's unique single-layer structure endows it with extremely high flexibility. These unique properties make graphene a promising candidate for a thermally conductive material with both ultra-high thermal conductivity and ultra-flexibility. Graphene thermal conductive films and graphene TIM films are currently among the more mature applications of graphene materials in the field of thermal management.

[0003] In existing technologies, carbon fibers are added during the preparation of graphene TIM films to improve their thermal conductivity. Theoretically, the aim is to utilize the one-dimensional structure of carbon fibers as a "bridge" between graphene sheets, constructing a three-dimensional thermally conductive network of "graphene sheets - carbon fibers" to improve axial and radial thermal conductivity. However, in actual production, this leads to multiple negative impacts, which are essentially related to structural compatibility, interfacial interactions, and process adaptability. Specific problems include: 1. The micron-sized and high aspect ratio of carbon fibers make them prone to fiber entanglement and agglomeration in graphene slurry, and uniform dispersion cannot be achieved through conventional ultrasonication or dispersants. Agglomerated carbon fibers form a "macroscopic thermal barrier" within the film, not only blocking in-plane heat flow transfer between graphene sheets but also further amplifying thermal resistance due to air between fibers (air's thermal conductivity is only 0.026 W / (m・K)). 2. The high thermal conductivity of graphene thermal films relies on the preferred in-plane orientation of the sheets (achieved through coating and calendering to form tight stacking). Carbon fibers, being micron-sized rigid long fibers, embed themselves between graphene sheets in an "interlacing and bridging" manner, completely blocking the directional alignment and tight adhesion of the sheets, resulting in large-area breaks in the in-plane thermal conductivity pathways. Simultaneously, the axial thermal conductivity advantage of carbon fibers is difficult to utilize, and large-sized fibers cannot form a continuous axial thermal conductivity network. 3. The entanglement of carbon fibers causes an exponential increase in the viscosity of the graphene slurry, leading to coating process failures. Defects such as uneven film thickness, surface streaks, and pinholes are prone to occur during coating, and may even clog the coating die, interrupting the production line. Summary of the Invention

[0004] To address the technical problem mentioned above that adding carbon fibers during the current preparation of graphene TIM films fails to improve thermal conductivity, this invention provides a method for preparing a longitudinally thermally enhanced graphene TIM film. This method involves compounding carbon fibers and graphene oxide slurry into a carbon fiber mixture slurry, which is then filled into the pores of the graphene TIM film using vacuum filtration. During vacuum filtration, the carbon fibers are oriented longitudinally under the influence of gravity and the external force of the vacuum pump, thus forming longitudinal thermally conductive channels in conjunction with the graphene oxide slurry. The specific preparation method includes the following steps: A graphene oxide film is prepared by forming several through holes along the thickness direction of the graphene oxide film; The graphene oxide film with through holes is immersed in a foaming agent. After the reaction is completed, it is taken out and dried to obtain a graphene foamed film. Using the graphene foamed membrane as a filter cloth, carbon fiber mixed slurry is filled into the through-pores of the graphene foamed membrane by vacuum filtration until the through-pores are completely blocked by the carbon fiber mixed slurry. The graphene foamed film is subjected to thermal reduction treatment to obtain a graphene TIM film with enhanced longitudinal thermal conductivity.

[0005] In a further technical solution, the method for preparing the carbon fiber mixed slurry involves taking a graphene oxide slurry with a solid content of 5 wt%, adding carbon fibers to the graphene oxide slurry, and mixing them uniformly. The carbon fibers and graphene oxide are compounded at a mass ratio of 0.6–0.8:1. The length of the carbon fibers is 100–200 μm, and the diameter is 5–10 μm. The mass ratio of carbon fibers to graphene oxide is typically, but not limited to, 0.6:1, 0.7:1, and 0.8:1. The length of the carbon fibers is typically, but not limited to, 100 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, and 200 μm. The diameter of the carbon fibers is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm.

[0006] In a further technical solution, in step 1, the diameter of the through hole is set to 0.05mm-0.3mm, and the spacing between adjacent through holes is 1mm-2mm. The diameter of the through hole is typically, but not limited to, 0.05mm, 0.1mm, 0.15mm, 0.2mm, 0.25mm, and 0.3mm. The spacing between the through holes is typically, but not limited to, 1mm, 1.5mm, and 2mm.

[0007] In a further technical solution, in step 2, the foaming agent is a hydrazine hydrate solution with a concentration of 3-10 wt%, the foaming temperature is 25-60℃, and the foaming time is 60-90 s. The concentration of the hydrazine hydrate solution is typically, but not limited to, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, and 10 wt%. The foaming temperature is typically, but not limited to, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, and 60℃. The foaming time is, but not limited to, 63 s, 65 s, 68 s, 70 s, 75 s, 80 s, 83 s, 85 s, 88 s, and 90 s. Because the graphene foamed membrane needs to be used as a filter cloth, it will generate strong adsorption force during the vacuum filtration process. Only a thick membrane with a high degree of foaming can remain flat during the vacuum filtration process. In addition, carbon fibers need to be implanted inside the through holes. Only when the graphene foamed membrane is thick enough can there be enough space inside the through holes for the carbon fibers to build a longitudinal heat conduction network.

[0008] In a further technical solution, in step 3, during the vacuum filtration process, the graphene foamed membrane is laid flat on the filter plate of the Buchner funnel as a filter cloth to ensure that the surface of the graphene foamed membrane is wrinkle-free. The carbon fiber mixed slurry is slowly poured into the Buchner funnel, and the vacuum pump is started for filtration until the through holes opened along the thickness direction of the graphene foamed membrane are completely blocked. After cleaning the mixed slurry on the surface of the graphene foamed membrane, it is dried.

[0009] In a further technical solution, during the vacuum filtration process, the vacuum degree of the vacuum pump is set to 0.09 MPa.

[0010] In a further technical solution, the vacuum filtration process takes at least 5 minutes. The vacuum filtration time is typically, but not limited to, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, and 10 minutes.

[0011] In a further technical solution, when drying the graphene foamed membrane after vacuum filtration, the drying temperature is set to 40-80℃, and the drying time is set to 40-80 min. The drying temperature is typically, but not limited to, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, and 80℃. The drying time is typically, but not limited to, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, and 80 min.

[0012] In a further technical solution, step 4, the thermal reduction treatment includes pretreatment, carbonization treatment, and graphitization treatment.

[0013] In a further technical solution, in the pretreatment step, the foamed film is placed in an oven at 120-150℃ for 1-2 hours; in the carbonization step, the pretreated film is placed in a high-temperature furnace and heated to 1100-1250℃ in a nitrogen atmosphere at a heating rate of 10-15℃ / min, and then carbonized for 1-2 hours after reaching the target temperature; in the graphitization step, argon protection is switched, and the temperature is raised to 2800-3200℃ at a rate of 5-15℃ / min, and then graphitized for 1-3 hours after reaching the target temperature, and then slowly cooled to obtain a longitudinally thermally enhanced graphene TIM film. During the pretreatment process, the oven temperature is typically, but not limited to, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, and 150°C, and the pretreatment time is typically, but not limited to, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, and 120 min. In the carbonization step, the heating rate is typically, but not limited to, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, and 15°C / min, the target carbonization temperature is typically, but not limited to, 110°C, 1150°C, 1200°C, and 1250°C, and the carbonization time after reaching the target temperature is typically, but not limited to, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, and 120 min. Beneficial effects

[0014] Through a synergistic design of "arrayed perforation-directional filling-graphitization," a "carbon fiber-GO" composite thermal conductivity pathway distributed along the Z-axis (thickness direction) was constructed in the foamed film. The precise arrangement of the arrayed perforations provides directional channels for the thermally conductive medium, while the carbon fibers are oriented along the pore axis to form a highly thermally conductive framework. The GO sheets and the graphitized carbon matrix form a dense interface, significantly reducing the Z-axis thermal resistance. Compared to conventional graphene TIM films that do not employ this approach, the Z-axis thermal conductivity is improved by over 400%, reaching 15-20 W / (m·K). This effectively addresses the industry pain point of traditional graphene TIM films—"excellent in-plane thermal conductivity but weak Z-axis thermal conductivity"—and meets the core requirement of high-power electronic devices for efficient Z-axis heat dissipation. Meanwhile, the porous foamed membrane forms a three-dimensional porous matrix after being treated with hydrazine hydrate. Its pore structure forms a mechanical interlock with the carbon fiber / GO mixed slurry. Combined with the structural densification during the carbonization and graphitization process, a strong chemical bond and physical bond are formed between the filler phase (carbon fiber-GO) and the matrix carbon, avoiding the problem of heat transfer medium falling off and migrating during use. This ensures that the TIM membrane maintains stable heat dissipation performance during long-term service. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 It is a longitudinally thermally enhanced graphene TIM film prepared by the method in Example 1.

[0017] Figure 2 This is a SEM image of the longitudinally thermally enhanced graphene TIM film prepared by the method in Example 1. Specific Implementation To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. The components of the embodiments of this invention can be arranged and designed in various different configurations. Example 1

[0019] A method for preparing a longitudinally thermally enhanced graphene (TIM) film includes the following steps: 1) Prepare a graphene oxide film by mechanically drilling several through holes along the thickness direction of the graphene oxide film. The diameter of the through holes is set to 2 μm, and the spacing between adjacent through holes is set to 2 mm.

[0020] 2) The graphene oxide membrane with through holes is immersed in a 10wt% hydrazine hydrate solution at 25°C for 90 seconds. After the foaming reaction is completed, the membrane is removed and drained, and then dried in an oven at 60°C for 30 minutes to obtain a graphene foamed membrane. 3) Using the graphene foamed membrane as a filter cloth, lay it flat on the filter plate of the Buchner funnel, ensuring that the side of the membrane containing the through holes faces upward and is wrinkle-free; slowly pour the carbon fiber mixed slurry into the Buchner funnel, start the vacuum pump (vacuum degree 0.09MPa) for filtration for 5 minutes, at which time the array pores of the foamed membrane are completely filled and sealed by the carbon fiber / GO mixed slurry; clean off the mixed slurry on the surface of the graphene foamed membrane, remove the membrane material, and dry it at 45°C for 1 hour.

[0021] The carbon fiber slurry is prepared in advance. Specifically, the preparation method is to take a graphene oxide slurry with a solid content of 5 wt%, add carbon fiber to the graphene oxide slurry and mix it evenly. The carbon fiber and graphene oxide are compounded in a mass ratio of 0.8:1. The length of the carbon fiber is 100-200 μm and the diameter is 5-10 μm.

[0022] 4) The graphene foamed film is subjected to thermal reduction treatment, which includes pretreatment, carbonization, and graphitization. In the pretreatment step, the foamed film is placed in an oven at 150°C for 2 hours. In the carbonization step, the pretreated film is placed in a high-temperature furnace and heated to 1200°C at a rate of 15°C / min under a nitrogen atmosphere. After reaching the target temperature, it is carbonized for 2 hours. In the graphitization step, argon protection is switched, and the temperature is increased to 2800°C at a rate of 5°C / min. After reaching the target temperature, it is graphitized for 1.5 hours. After slow cooling, a longitudinally thermally enhanced graphene TIM film is obtained. Figure 1 As shown.

[0023] SEM observation of the longitudinally thermally enhanced graphene TIM film, microstructure as follows: Figure 2 As shown, at the hole location, the carbon fibers are oriented along the axial direction (Z direction) of the hole, and the GO sheets are uniformly wrapped around the surface of the carbon fibers, forming a "carbon fiber-GO" composite filling structure.

[0024] The Z-direction thermal conductivity was measured using a Netzsch 467 thermal conductivity meter, and the thermal conductivity reached 15.4 W / m·K, which is 400% higher than the Z-direction thermal conductivity (3 W / m·K) of the graphene TIM film obtained without perforation and filtration treatment. Example 2

[0025] Compared with Example 1, the foaming time in this embodiment was adjusted to 60 seconds to investigate the effect of the change in foaming time on the filling effect of carbon fiber mixed slurry.

[0026] 1) Prepare a graphene oxide film by mechanically drilling several through holes along the thickness direction of the graphene oxide film. The diameter of the through holes is set to 2 μm, and the spacing between adjacent through holes is set to 2 mm.

[0027] 2) The graphene oxide membrane with through holes is immersed in a 10wt% hydrazine hydrate solution at 25°C for 60 seconds. After the foaming reaction is completed, the membrane is removed and drained, and then dried in an oven at 60°C for 30 minutes to obtain a graphene foamed membrane. 3) Using the graphene foamed membrane as a filter cloth, lay it flat on the filter plate of the Buchner funnel, ensuring that the side of the membrane containing the through holes faces upward and is wrinkle-free; slowly pour the carbon fiber mixed slurry into the Buchner funnel, start the vacuum pump (vacuum degree 0.09MPa) for filtration for 5 minutes, at which time the array pores of the foamed membrane are completely filled and sealed by the carbon fiber / GO mixed slurry; clean off the mixed slurry on the surface of the graphene foamed membrane, remove the membrane material, and dry it at 45°C for 1 hour.

[0028] The carbon fiber slurry is prepared in advance. Specifically, the preparation method is to take a graphene oxide slurry with a solid content of 5 wt%, add carbon fiber to the graphene oxide slurry and mix it evenly. The carbon fiber and graphene oxide are compounded in a mass ratio of 0.8:1. The length of the carbon fiber is 100-200 μm and the diameter is 5-10 μm.

[0029] 4) The graphene foamed film is subjected to thermal reduction treatment, which includes pretreatment, carbonization treatment and graphitization treatment. In the pretreatment step, the foamed film is placed in an oven at 150°C for 2 hours. In the carbonization treatment step, the pretreated film is placed in a high-temperature furnace and heated to 1200°C in a nitrogen atmosphere at a heating rate of 15°C / min. After reaching the target temperature, it is carbonized for 2 hours. In the graphitization treatment step, argon protection is switched and the temperature is raised to 2800°C at 5°C / min. After reaching the target temperature, it is graphitized for 1.5 hours. After slow cooling, a longitudinally thermally enhanced graphene TIM film is obtained. Example 3

[0030] Compared with Example 1, the foaming time in this embodiment was adjusted to 80 seconds to investigate the effect of the change in foaming time on the filling effect of the carbon fiber mixed slurry. The other steps are the same as in Example 1, and will not be repeated here. Example 4

[0031] Compared with Example 1, in this embodiment, the carbon fiber and graphene oxide are compounded in a mass ratio of 0.6:1 during the preparation of the carbon fiber mixed slurry, and the effect of changing the component ratio of the carbon fiber mixed slurry on the filling effect is investigated.

[0032] 1) Prepare a graphene oxide film by mechanically drilling several through holes along the thickness direction of the graphene oxide film. The diameter of the through holes is set to 2 μm, and the spacing between adjacent through holes is set to 2 mm.

[0033] 2) The graphene oxide membrane with through holes is immersed in a 10wt% hydrazine hydrate solution at 25°C for 60 seconds. After the foaming reaction is completed, the membrane is removed and drained, and then dried in an oven at 60°C for 30 minutes to obtain a graphene foamed membrane. 3) Using the graphene foamed membrane as a filter cloth, lay it flat on the filter plate of the Buchner funnel, ensuring that the side of the membrane containing the through holes faces upward and is wrinkle-free; slowly pour the carbon fiber mixed slurry into the Buchner funnel, start the vacuum pump (vacuum degree 0.09MPa) for filtration for 5 minutes, at which time the array pores of the foamed membrane are completely filled and sealed by the carbon fiber / GO mixed slurry; clean off the mixed slurry on the surface of the graphene foamed membrane, remove the membrane material, and dry it at 45°C for 1 hour.

[0034] The carbon fiber slurry is prepared in advance. Specifically, the preparation method is to take a graphene oxide slurry with a solid content of 5 wt%, add carbon fiber to the graphene oxide slurry and mix it evenly. The carbon fiber and graphene oxide are compounded in a mass ratio of 0.6:1. The length of the carbon fiber is 100-200 μm and the diameter is 5-10 μm.

[0035] 4) The graphene foamed film is subjected to thermal reduction treatment, which includes pretreatment, carbonization treatment and graphitization treatment. In the pretreatment step, the foamed film is placed in an oven at 150°C for 2 hours. In the carbonization treatment step, the pretreated film is placed in a high-temperature furnace and heated to 1200°C in a nitrogen atmosphere at a heating rate of 15°C / min. After reaching the target temperature, it is carbonized for 2 hours. In the graphitization treatment step, argon protection is switched and the temperature is raised to 2800°C at 5°C / min. After reaching the target temperature, it is graphitized for 1.5 hours. After slow cooling, a longitudinally thermally enhanced graphene TIM film is obtained.

[0036] Comparative Example 1 In Comparative Example 1, the foaming time was adjusted to 30 seconds. Other steps were the same as in Example 1 and will not be repeated here. The graphene TIM membrane obtained in Comparative Example 1 was tested for its Z-direction thermal conductivity using a Netzsch 467 thermal conductivity meter. The thermal conductivity was 8.2 W / m·K. The improvement in thermal conductivity was not as good as in Example 1. Analysis suggests that the insufficient foaming time was due to the inability to achieve a sufficient thickness. This would result in strong adsorption during vacuum filtration when used as a filter cloth. Only a thick membrane with a high degree of foaming can remain flat during vacuum filtration. In the comparative example, the insufficient foaming degree and the inadequate placement of the pores prevented the carbon fibers from forming vertical thermal conduction pathways, thus resulting in a lower improvement in longitudinal thermal conductivity compared to Example 1.

[0037] Comparative Example 2 In Comparative Example 2, the carbon fiber slurry was replaced with a graphene oxide slurry with a solid content of 5 wt%.

[0038] 1) Prepare a graphene oxide film by mechanically drilling several through holes along the thickness direction of the graphene oxide film. The diameter of the through holes is set to 2 μm, and the spacing between adjacent through holes is set to 2 mm.

[0039] 2) The graphene oxide membrane with through holes is immersed in a 10wt% hydrazine hydrate solution at 25°C for 90 seconds. After the foaming reaction is completed, the membrane is removed and drained, and then dried in an oven at 60°C for 30 minutes to obtain a graphene foamed membrane. 3) Using the graphene foamed membrane as filter cloth, lay it flat on the filter plate of the Buchner funnel, ensuring that the side of the membrane with through holes faces upward and is wrinkle-free; slowly pour the graphene oxide slurry with a solid content of 5wt% into the Buchner funnel, start the vacuum pump (vacuum degree 0.09MPa) for filtration for 5min; clean off the slurry on the surface of the graphene foamed membrane, remove the membrane material, and dry it at 45℃ for 1h.

[0040] 4) The graphene foamed film is subjected to thermal reduction treatment, which includes pretreatment, carbonization treatment and graphitization treatment. In the pretreatment step, the foamed film is placed in an oven at 150°C for 2 hours. In the carbonization treatment step, the pretreated film is placed in a high-temperature furnace and heated to 1200°C in a nitrogen atmosphere at a heating rate of 15°C / min. After reaching the target temperature, it is carbonized for 2 hours. In the graphitization treatment step, argon protection is switched and the temperature is raised to 2800°C at 5°C / min. After reaching the target temperature, it is graphitized for 1.5 hours. After slow cooling, a longitudinally thermally enhanced graphene TIM film is obtained.

[0041] The Z-direction thermal conductivity of the graphene TIM film obtained in Comparative Example 1 was tested using a Netzsch 467 thermal conductivity meter, and the thermal conductivity was 3.2 W / m·K. Analysis suggests that because the filling slurry used graphene oxide slurry, it failed to form an effective longitudinal thermal conduction path in the through-holes, and therefore the thermal conductivity was not improved.

[0042] 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 or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a longitudinally thermally enhanced graphene TIM film, characterized in that, Includes the following steps: A graphene oxide film is prepared by forming several through holes along the thickness direction of the graphene oxide film; The graphene oxide film with through holes is immersed in a foaming agent. After the reaction is completed, it is taken out and dried to obtain a graphene foamed film. Using the graphene foamed membrane as a filter cloth, carbon fiber mixed slurry is filled into the through-pores of the graphene foamed membrane by vacuum filtration until the through-pores are completely blocked by the carbon fiber mixed slurry. The graphene foamed film is subjected to thermal reduction treatment to obtain a graphene TIM film with enhanced longitudinal thermal conductivity.

2. The method for preparing a longitudinally thermally enhanced graphene TIM film according to claim 1, characterized in that: The method for preparing the carbon fiber mixed slurry is as follows: take a graphene oxide slurry with a solid content of 5 wt%, add carbon fiber to the graphene oxide slurry and mix evenly, wherein the carbon fiber and graphene oxide are compounded in a mass ratio of 0.6-0.8:1, and the carbon fiber has a length of 100-200 μm and a diameter of 5-10 μm.

3. The method for preparing a longitudinally thermally enhanced graphene TIM film according to claim 1, characterized in that: In step 1, the diameter of the through hole is set to 0.05mm-0.3mm, and the spacing between adjacent through holes is 1mm-2mm.

4. The method for preparing a longitudinally thermally enhanced graphene TIM film according to claim 1, characterized in that: In step 2, the foaming agent is a 3-10 wt% hydrazine hydrate solution, the foaming temperature is 25-60℃, and the foaming time is 60-90s.

5. The method for preparing a longitudinally thermally enhanced graphene TIM film according to claim 1, characterized in that: In step 3, during the vacuum filtration process, the graphene foamed membrane is laid flat on the filter plate of the Buchner funnel as a filter cloth, ensuring that the surface of the graphene foamed membrane is wrinkle-free. The carbon fiber mixed slurry is slowly poured into the Buchner funnel, and the vacuum pump is started for filtration until the through holes opened along the thickness direction of the graphene foamed membrane are completely blocked. After cleaning the mixed slurry on the surface of the graphene foamed membrane, it is dried.

6. The method for preparing a longitudinally thermally enhanced graphene TIM film according to claim 5, characterized in that: During the vacuum filtration process, the vacuum level of the vacuum pump is set to 0.09 MPa.

7. The method for preparing a longitudinally thermally enhanced graphene TIM film according to claim 5, characterized in that: During vacuum filtration, the vacuum filtration time is greater than or equal to 5 minutes.

8. The method for preparing a longitudinally thermally enhanced graphene TIM film according to claim 5, characterized in that: After vacuum filtration, the graphene foamed membrane is dried at a temperature of 40-80°C for 40-80 minutes.

9. The method for preparing a longitudinally thermally enhanced graphene TIM film according to claim 1, characterized in that: In step 4, the thermal reduction treatment includes pretreatment, carbonization treatment, and graphitization treatment.

10. The method for preparing a longitudinally thermally enhanced graphene TIM film according to claim 9, characterized in that: In the pretreatment step, the foamed film is placed in an oven at 120-150℃ for 1-2 hours; in the carbonization step, the pretreated film is placed in a high-temperature furnace and heated to 1100-1250℃ in a nitrogen atmosphere at a heating rate of 10-15℃ / min. After reaching the target temperature, it is carbonized for 1-2 hours; in the graphitization step, argon protection is switched and the temperature is raised to 2800-3200℃ at a rate of 5-15℃ / min. After reaching the target temperature, it is graphitized for 1-3 hours. After slow cooling, a longitudinally thermally enhanced graphene TIM film is obtained.

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