Graphene composite thermal conductive film and preparation method thereof

Abstract

The present invention belongs to the technical field of graphene thermally conductive films and provides a method for preparing a graphene composite thermally conductive film, comprising at least the following steps: preparing a graphene thermally conductive film, forming a plurality of through-holes in the graphene thermally conductive film, wherein the through-holes are irregularly shaped holes with diameters that are not completely uniform across the thickness of the graphene thermally conductive film; filling the through-holes with a thermally conductive metal and graphene oxide slurry; performing a heat treatment to obtain a graphene thermally conductive film filled with the thermally conductive metal and graphene material; and subsequently performing a calendering process to obtain a graphene composite thermally conductive film. The present invention achieves a graphene composite thermally conductive film with high reliability and excellent longitudinal thermal conductivity by creating specific through-holes, filling the through-holes with a thermally conductive metal and graphene oxide slurry, and then performing a heat treatment and calendering process.

Description

Technical Field

[0001] The present invention relates to the field of thermal management technology, and in particular to a graphene composite thermally conductive film and a preparation method thereof. Background Art

[0002] As a unique two-dimensional nanomaterial, graphene material has the characteristics of high electron mobility, large specific surface area, good thermal stability and excellent mechanical properties. At present, the graphene thermal conductive film prepared with graphene as the main body has been widely used in various fields such as electronic devices, energy storage technology and catalysis. Although the thermal conductivity of the graphene thermal conductive film is good within the surface, the thermal conductivity in the longitudinal direction has always been a pain point in the industry. At present, the longitudinal thermal conductivity coefficient of the graphene thermal conductive film is difficult to exceed 8W / (m·K). Based on this background, technical personnel in the industry have tried to compound graphene with metal materials to construct a longitudinal heat conduction path, but it is difficult for metal materials to penetrate between the layers of the graphene film, so the thermal conductivity effect after compounding is still not ideal.

[0003] Based on this, Chinese patent publication number CN112770592A discloses a method and a heat sink for improving the vertical heat transfer performance of a heat sink. A carbon-containing heat dissipation film is taken and processed to form through holes or blind holes in the z-axis direction of the film. A thermal conductive material is filled into the through holes or blind holes, and then the film is calendered and shaped to improve the vertical heat transfer effect of the carbon-containing heat dissipation film.

[0004] However, when the applicant of this application attempted to use graphene film as a carbon-containing heat dissipation film material and carried out corresponding processing, it was discovered that after calendering and shaping, many small gaps remained between the thermal conductive material in the pores and the pore walls of the heat sink, which had not been filled. In addition, the bonding strength between the thermal conductive material in the pores and the pore walls was poor. Therefore, the improvement in thermal conductivity after the thermal conductive material and the heat dissipation film material were combined was limited and could not achieve the expected effect. In addition, due to the existence of gaps and the weak bonding strength between the thermal conductive material and the pore walls, the thermal conductive material easily separated from the pores, and the reliability of the heat sink could not meet the requirements of use. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing a graphene composite thermally conductive film. By manufacturing irregularly shaped holes, the inner wall of the through-hole has excellent properties such as pore diameter along the thickness direction of the graphene thermally conductive film, high specific surface area, and many active sites. Then, a thermally conductive metal and graphene oxide slurry are filled into the through-hole. Through heat treatment and in combination with the excellent properties of the inner wall of the through-hole, the graphene oxide self-assembles in the gap between the inner wall of the hole and the thermally conductive metal to obtain a three-dimensional graphene material. After calendering, the three-dimensional graphene material and the thermally conductive metal jointly construct a tightly bonded and substantially gapless thermally conductive network and tightly fill the through-hole. This reduces the gaps within the thermally conductive network (i.e., between the thermally conductive metal and the three-dimensional graphene material) and between the thermally conductive network and the inner wall of the through-hole, strengthens the bonding force within the thermally conductive network (i.e., between the thermally conductive metal and the three-dimensional graphene material) and between the thermally conductive network and the inner wall of the through-hole, and improves the reliability and longitudinal thermal conductivity of the graphene composite thermally conductive film.

[0006] The solution provided by the present invention comprises at least the following steps: preparing a graphene thermally conductive film, on which a plurality of through holes are prepared, wherein the through holes are irregularly shaped holes whose apertures are not completely uniform in the thickness direction of the graphene thermally conductive film; filling the through holes with a thermally conductive metal and a graphene oxide slurry; heat-treating the graphene thermally conductive film filled with the thermally conductive metal and the graphene oxide slurry to obtain a graphene thermally conductive film filled with the thermally conductive metal and the three-dimensional graphene material; and subsequently performing a calendering process to obtain a graphene composite thermally conductive film.

[0007] The present invention improves the reliability and longitudinal thermal conductivity of a graphene composite thermally conductive film by constructing irregularly shaped pores, filling them with a thermally conductive metal and graphene oxide slurry, and combining them with heat treatment and calendering. The irregularly shaped pores exhibit varying diameters along the thickness of the graphene film, while the inner pore walls possess a large specific surface area and numerous active sites. Furthermore, graphene oxide exhibits the ability to self-assemble along the surface. During the heat treatment process, the graphene oxide slurry spreads to the gap between the inner wall of the through-hole and the thermally conductive metal and undergoes a self-assembly reaction to form a three-dimensional graphene material. Due to the variable characteristics of the aperture of the irregularly shaped hole, the growth direction of the graphene oxide self-assembly near the through-hole wall is offset, forming mutually staggered growth directions. Compared with the design of straight holes, it is easier to self-assemble to form a three-dimensional network structure. At the same time, the graphene oxide has the characteristic of spreading during the self-assembly process, and will penetrate into various parts of the through-hole and climb to various parts of the through-hole in the form of branches, thereby tightly wrapping the thermally conductive metal and climbing to the inner wall of the through-hole of the graphene thermal conductive film, thereby anchoring to the thermally conductive metal and the inner wall of the through-hole in a similar physical form; and And because the inner wall of the through-hole has a large specific surface area and more active sites, it has more binding sites with the reduced three-dimensional graphene material, which can further improve the bonding strength between the three-dimensional graphene material and the inner wall of the through-hole; then after calendering treatment, the thermally conductive metal and the three-dimensional graphene material together form a tightly bonded and basically gapless thermal conductive network and are tightly filled in the through-hole, reducing the gap inside the thermal conductive network (i.e., between the thermally conductive metal and the three-dimensional graphene material) and between the thermal conductive network and the inner wall of the through-hole, strengthening the bonding strength between the thermally conductive network (i.e., between the thermally conductive metal and the three-dimensional graphene material) and between the thermal conductive network and the inner wall of the through-hole, and improving the reliability and longitudinal thermal conductivity effect of the graphene composite thermal conductive film.

[0008] In a further technical solution, the heat treatment temperature is ≥200°C, and the heat treatment time is 1-10 hours; and / or the heat treatment process is: heat treating the graphene thermal conductive film filled with thermal conductive metal and graphene oxide slurry, during which the graphene oxide self-assembles along the inner wall of the through hole and / or the edge of the thermal conductive metal to form a three-dimensional graphene material and covers the thermal conductive metal, thereby obtaining the graphene thermal conductive film filled with the thermal conductive metal and the three-dimensional graphene material.

[0009] In a further technical solution, the heat treatment temperature is ≥ 400°C, the heat treatment is performed in a vacuum environment, and the heat treatment time is 1-10 hours. Preferably, the heat treatment temperature is 400°C to 2200°C. For example, it can be typically but not limited to 400°C, 500°C, 800°C, 1200°C, 1600°C, 2000°C, or 2200°C. The heat treatment temperature is typically but not limited to 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, or 10 hours.

[0010] The edges of graphene thermal conductive film are mainly terminated by carbon-hydrogen, while the edges of graphene oxide are terminated by carbon-oxygen (hydroxyl, carboxyl), carbon-hydrogen (hydrogen), etc. At a lower heat treatment temperature (for example, 200-400°C), graphene oxide can self-assemble to form a three-dimensional graphene material. The graphene oxide has the characteristic of spreading during the self-assembly process, tightly wrapping the thermal conductive metal and clinging to the inner wall of the through hole of the graphene thermal conductive film, thereby anchoring the thermal conductive metal and the inner wall of the through hole in a similar physical form; the study found that at 400°C and Above the temperature, and under the catalytic action of the thermally conductive metal (transition metal), the carbon-oxygen bonds and carbon-hydrogen bonds at the edges of graphene and graphene oxide are broken to form carbon active sites, and then the active sites on both sides form carbon-carbon bonds, achieving the purpose of edge fusion. As a result, the three-dimensional graphene material tightly wraps the thermally conductive metal, and at the same time, the three-dimensional graphene material and the graphene material on the inner wall of the through-hole are chemically bonded in the form of carbon-carbon bonds, making the bond tighter, further improving the reliability and longitudinal thermal conductivity of the graphene composite thermally conductive film.

[0011] In a further technical solution, the thermally conductive metal is one or more transition metals; the heat treatment process is as follows: the graphene thermally conductive film filled with the thermally conductive metal and graphene oxide slurry is heat-treated at a temperature of ≥400°C for 1-10 hours in a vacuum environment. The graphene oxide self-assembles along the inner wall of the through-hole and / or the edge of the thermally conductive metal to form a three-dimensional graphene material, which then covers the thermally conductive metal. Then, under the catalytic action of the thermally conductive metal, the three-dimensional graphene material and the graphene material on the inner wall of the through-hole generate carbon active sites, so that the three-dimensional graphene material tightly covers the thermally conductive metal while the three-dimensional graphene material and the graphene material on the inner wall of the through-hole chemically bond in the form of carbon-carbon bonds, thus obtaining the graphene thermally conductive film filled with the thermally conductive metal and the three-dimensional graphene material. This chemical bonding can further enhance the bonding strength between the thermally conductive network and the inner wall of the through-hole, further improving the reliability and longitudinal thermal conductivity of the graphene composite thermally conductive film.

[0012] In a further technical solution, the melting point of the thermally conductive metal is no higher than the heat treatment temperature. The heat treatment process involves heat-treating the graphene thermally conductive film, filled with a thermally conductive metal and graphene oxide slurry, at a temperature of 400°C or higher in a vacuum environment. The thermally conductive metal within the through-holes melts, and the graphene oxide self-assembles along the inner walls of the through-holes and / or the edges of the thermally conductive metal to form a three-dimensional graphene material that coats the thermally conductive metal. Under the catalytic action of the thermally conductive metal, carbon active sites are generated in the three-dimensional graphene material and on the inner walls of the through-holes of the graphene thermally conductive film. The thermally conductive metal melts during the heat treatment and spreads, particularly to the edge junctions of the three-dimensional graphene material and the graphene thermally conductive film. This further enhances its catalytic properties and promotes chemical bonding in the form of carbon-carbon bonds between the three-dimensional graphene material and the graphene thermally conductive film. The resulting graphene composite thermally conductive film exhibits improved reliability and longitudinal thermal conductivity.

[0013] In a further technical solution, the thermally conductive metal is in powder form, and the specific steps of filling the thermally conductive metal and graphene oxide slurry are: thoroughly mixing the thermally conductive metal and graphene oxide slurry to obtain a mixed slurry, and then filling the mixed slurry into the through-hole; or filling the thermally conductive metal into the through-hole, and then filling the graphene oxide slurry into the through-hole. Both of the above methods can achieve filling of the thermally conductive metal and graphene oxide slurry.

[0014] Specifically, a mixed slurry can be applied to the surface of the graphene thermally conductive film, filling the gaps in the through-holes with the mixed slurry. After coating, the surface of the graphene thermally conductive film is cleaned. Alternatively, the through-holes can be filled with a thermally conductive metal. The metal-filled graphene thermally conductive film is then placed on a filter membrane and transferred to a vacuum filtration device, where the through-holes are vacuum-infused with the graphene oxide slurry.

[0015] Existing thermally conductive metals can be used in this application, such as copper, nickel, silver, gold, aluminum, iron, cobalt, manganese, tin, zinc, magnesium or composite materials of the above metals.

[0016] In a further technical solution, the thermally conductive metal is selected from one or more transition metals, such as copper, nickel, silver, gold, iron, cobalt, manganese, or composites thereof, preferably copper, nickel, silver, gold, or composites thereof. More preferably, the thermally conductive metal is copper. Furthermore, the heat treatment temperature is preferably ≥ 400°C, and the heat treatment is performed in a vacuum environment for a duration of 1-10 hours.

[0017] When the thermally conductive metal is a transition metal, such as copper, its catalytic ability is related to the filling of its d-orbital electrons. Its empty d-orbitals can effectively form coordination bonds to participate in reactions. It exhibits excellent catalytic performance in certain reactions, such as catalytic hydrogenation reactions and Ullmann-type carbon-carbon coupling reactions, and its cost is lower than that of precious metals. During heat treatment, when the temperature reaches 400°C or above, these transition metals exhibit excellent catalytic properties, catalyzing the generation of more carbon active sites in the three-dimensional graphene material and the inner walls of the through-holes of the graphene thermal conductive film. This promotes more carbon-carbon bonding in the three-dimensional graphene material and the graphene material on the inner walls of the through-holes, further improving the reliability and longitudinal thermal conductivity of the graphene composite thermal conductive film.

[0018] In a further technical solution, the viscosity of the graphene oxide is controlled between 1000 and 15000 cP. The viscosity of the graphene oxide is typically, but not limited to, 1000 cP, 1500 cP, 2400 cP, 3000 cP, 4000 cP, 5600 cP, 7800 cP, 8300 cP, 10000 cP, 12000 cP, 14500 cP, or 15000 cP. The solid content of the graphene oxide slurry is controlled between 0.1% and 10%, typically, but not limited to, 0.1%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. By adjusting the viscosity and solid content of the graphene oxide slurry, the flowability of the graphene oxide can be controlled.

[0019] In a further technical solution, the volume ratio V1 of the thermally conductive metal to the through-hole is ≥80%, and the volume ratio of the thermally conductive metal to the graphene oxide slurry is 5-9:1. The volume ratio V1 of the thermally conductive metal to the through-hole is typically but not limitedly set to 80%, 81%, 83.3%, 85%, 87.5%, 90%, 91%, 92%, 93%, 94%, 95% or 96%, and is further preferably 80%~90%. The volume ratio of the thermally conductive metal to the graphene oxide slurry is typically but not limitedly set to 5:1, 6:1, 7:1, 8:1, 9:1. By regulating the volume ratio of the thermally conductive metal to the graphene oxide slurry and the volume ratio of the thermally conductive metal to the through-hole, the dosage relationship of the thermally conductive metal and the three-dimensional graphene material in the thermally conductive network can be regulated, thereby further regulating the reliability of the thermally conductive network and the longitudinal thermal conductivity effect.

[0020] In a further technical solution, the graphene thermally conductive film and the through hole satisfy at least one of the following conditions:

[0021] (1) The aperture of the through hole ranges from 0.1 to 3 mm;

[0022] (2) The difference between the widest and narrowest diameters of the through hole is 0.2 to 2.9 mm, more preferably 0.5 to 2.9 mm;

[0023] (3) The distribution density of the through holes is 0.25~80 / cm 2 ;

[0024] (4) The thickness of the graphene thermal conductive film is 30~5000μm;

[0025] (5) Along the thickness direction of the graphene thermal conductive film, the aperture in the middle of the through hole is smaller than the aperture at both ends.

[0026] The thickness, pore density, pore size, etc. of the graphene thermal conductive film can be designed according to needs.

[0027] In addition, by adjusting the difference between the widest and narrowest apertures of the through-hole, as well as the direction of aperture change of the irregularly shaped holes, the degree of deviation in the growth direction during the self-assembly of graphene oxide can be controlled to adjust the degree of interlacing of the formed three-dimensional graphene material, thereby further adjusting the reliability and longitudinal thermal conductivity of the graphene composite thermal conductive film.

[0028] In a further technical solution, the method of preparing the special-shaped holes is any one or more of laser drilling, mechanical drilling, and manual drilling with a milling cutter.

[0029] Another object of the present invention is to provide a graphene composite thermally conductive film, which is prepared by the above method.

[0030] In a further technical solution, the longitudinal thermal conductivity of the graphene composite thermally conductive film is ≥20W / (mK).

[0031] Beneficial effects of the present invention:

[0032] The present invention manufactures irregularly shaped holes so that the inner wall of the through-hole has excellent properties such as variable pore size, high specific surface area, and multiple active sites. Then, a thermally conductive metal and graphene oxide slurry are filled into the through-hole. Through heat treatment and in combination with the excellent properties of the inner wall of the through-hole, the graphene oxide self-assembles in the gap between the inner wall of the hole and the thermally conductive metal to obtain a three-dimensional graphene material. After calendering, the three-dimensional graphene material and the thermally conductive metal jointly construct a tightly combined and substantially gapless thermally conductive network and tightly fill the through-hole, thereby reducing the gaps inside the thermally conductive network (i.e., between the thermally conductive metal and the three-dimensional graphene material) and between the thermally conductive network and the inner wall of the through-hole, strengthening the bonding force inside the thermally conductive network (i.e., between the thermally conductive metal and the three-dimensional graphene material) and between the thermally conductive network and the inner wall of the through-hole, and improving the reliability and longitudinal thermal conductivity of the graphene composite thermally conductive film.

[0033] The thermally conductive metal is selected from transition metals and combined with a specific heat treatment temperature, which can catalyze the generation of more carbon active sites on the inner walls of the through-holes of the three-dimensional graphene material and the graphene thermally conductive film, so that the thermal conductive network and the inner walls of the through-holes are more tightly chemically bonded, further improving the reliability and longitudinal thermal conductivity of the graphene composite thermally conductive film. In addition, the transition metal has the characteristic of spreading when heat-treated to the melting temperature, and spreads more to the edge junctions of the three-dimensional graphene material and the graphene thermally conductive film, which can further exert its catalytic properties and further promote the chemical bonding between the three-dimensional graphene material and the graphene material, so that the reliability and longitudinal thermal conductivity of the obtained graphene composite thermally conductive film are better. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 This is a macroscopic physical picture of the graphene composite thermal conductive film prepared in Example 1.

[0036] Figure 2 This is an SEM image of the graphene thermal conductive film in Example 1 after being infused with a mixed slurry of graphene oxide and copper powder.

[0037] Figure 3 This is an SEM image of the graphene composite thermally conductive film after heat treatment and calendering treatment in Example 1.

[0038] Figure 4 This is a schematic diagram of the structure of the irregular-shaped holes in the graphene thermal conductive film in Example 1.

[0039] Figure 5 Schematic diagram of the cross-sectional structure of the irregularly shaped holes in the graphene thermal conductive film in Example 1.

[0040] Figure 6 This is the test data of the longitudinal thermal diffusion coefficient of the graphene composite thermally conductive film obtained in Example 1. DETAILED DESCRIPTION

[0041] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0043] The main purpose of each embodiment of the present invention is to obtain a thermally conductive graphene composite film with high longitudinal thermal conductivity and high reliability by changing the structural design of the through-holes of the graphene thermally conductive film and filling the through-holes with thermally conductive metal and graphene oxide slurry. By heat treatment, the graphene oxide self-assembles to form a three-dimensional graphene material, thereby obtaining a thermally conductive network that is tightly bonded and essentially gapless, and can be tightly filled in the through-holes. This solves not only the problem of gaps and weak bonding within the thermally conductive network that may exist when a thermally conductive network is obtained by combining multiple materials, but also the problem of gaps and weak bonding between the thermally conductive network and the inner wall of the through-hole. The specific principle is that the narrower part of the irregular hole not only provides physical limitation for the thermally conductive network filled in the through-hole, but also has a larger specific area than the straight hole. The graphene oxide has more binding sites with the inner wall of the through-hole during the self-assembly process, which can improve the bonding strength between the graphene oxide slurry and the thermally conductive metal and the inner wall of the through-hole. The reason why this solution can achieve the technical effect of improving the bonding strength between the thermally conductive metal and the inner wall of the through-hole is not only because the design of the irregular holes provides physical limitations and bonding sites to improve the bonding strength, but also because in the process of graphene oxide self-assembling to form a three-dimensional network structure after heat treatment, the irregular holes are conducive to the assembly of graphene oxide into a three-dimensional network by adhering to the wall, causing the growth direction of graphene oxide near the hole wall to shift with the change of the hole diameter, forming mutually staggered growth directions, so that the formed three-dimensional graphene material tightly wraps the thermally conductive metal and clings to the inner wall of the through-hole, and is anchored to the thermally conductive metal and the inner wall of the through-hole in a similar physical form. Compared with the design of straight holes, the mutual cross-linking between the three-dimensional graphene material and the thermally conductive metal and the inner wall of the through-hole is tighter. The above methods complement each other, and finally a graphene composite thermal conductive film with stronger bonding strength between the thermally conductive metal and the graphene thermal conductive film is obtained.

[0044] Example 1

[0045] This embodiment provides a method for preparing a graphene composite thermally conductive film, comprising the following steps:

[0046] (1) Prepare a graphene thermal conductive film with a size of 10 cm in length, 4 cm in width, and 800 μm in thickness. Prepare several through holes on the graphene thermal conductive film. First, use a tapered milling cutter to machine a tapered blind hole on one side of the graphene thermal conductive film. Then turn the graphene thermal conductive film over and use a tapered milling cutter to drill holes on the other side of the graphene thermal conductive film corresponding to the blind hole to obtain a through hole that is narrow in the middle and wide at both ends. The aperture of the through hole gradually increases from the middle to the two ends, forming a funnel-shaped channel. The maximum aperture of the through hole is 2 mm, and the narrowest aperture near the middle is 0.5 mm. The through holes are arranged in a 15*6 array pattern, with a total of 90 holes. The structure of the special-shaped hole is as follows: Figure 4 and Figure 5 The structural diagram is shown in .

[0047] (2) Prepare a mixed slurry of a thermally conductive metal and a graphene oxide slurry; the thermally conductive metal is a metal powder, specifically copper powder (melting point 1083.4°C). The copper powder filling volume V1 accounts for approximately 87.5% of the total volume of the through hole (the volume of the thermally conductive metal is calculated based on its mass and density, thereby controlling the filling volume of the thermally conductive metal). In this embodiment, the volume ratio of the copper powder to the graphene oxide slurry is 7:1, the viscosity of the graphene oxide slurry is 12000 cP, and the solid content is 5%.

[0048] (3) A mixed slurry of graphene oxide slurry and copper powder is poured into the through hole by coating. First, the thermal conductive metal and graphene oxide slurry are fully mixed. The graphene thermal conductive film is placed on the coating machine, and the coating machine vacuum-positions the graphene thermal conductive film. At the same time, the mixed slurry is coated on the surface of the graphene thermal conductive film. The copper powder and graphene oxide slurry fill the pores of the through hole. After coating, the surface of the graphene thermal conductive film is cleaned.

[0049] The above sample was sent to a scanning tunneling microscope to observe the microscopic morphology inside the hole. The SEM image is as follows: Figure 2 As shown, the copper metal powder and the graphene slurry are blended together, and the pores are almost filled with the metal powder and the graphene slurry.

[0050] The graphene thermal conductive film after vacuum infusion is heat-treated. In this embodiment, the heat treatment is performed in a vacuum environment, the heat treatment temperature is set to 1200° C., and the heat treatment time is 5 hours.

[0051] During the heat treatment process, the graphene oxide slurry in the through-hole begins to self-assemble to form a three-dimensional network of graphene. The three-dimensional network of graphene grows along the hole wall of the through-hole. The three-dimensional network of graphene has good compatibility with the graphene thermal conductive film. The three-dimensional network of graphene penetrates into various parts of the special-shaped through-hole and climbs to various parts of the special-shaped hole in the form of branches. The thermal conductive metal copper also melts at this temperature and spreads more to the edge junction of the three-dimensional network of graphene and the graphene thermal conductive film. The three-dimensional graphene oxide cross-links with the molten copper and wraps the molten copper.

[0052] (4) The graphene thermal conductive film filled with thermal conductive metal is subjected to calendering treatment, with the calendering pressure set to 1 ton and the holding time to 30 seconds to obtain a graphene composite thermal conductive film.

[0053] The graphene composite thermal conductive film obtained in this embodiment has a macroscopic morphology as shown in FIG. Figure 1 As shown in the figure, its surface is similar to that of graphene thermal conductive film, which is a silver-grey shiny film with a smooth surface and black pores. It is preliminarily judged to be a mixture of three-dimensional graphene cross-linked material and copper powder. The above sample was sent to a scanning tunneling microscope to observe the microscopic morphology of its pores. The SEM image is shown in the figure below. Figure 3 As shown, the three-dimensional graphene material wraps the thermal conductive metal and almost fills the through hole. The filler in the hole is relatively flat. The bright spots in the figure are the copper metal exposed outside the three-dimensional graphene network structure.

[0054] Example 2

[0055] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference between this embodiment and Example 1 is that the type of thermally conductive metal is different. The thermally conductive metal in this embodiment is silver powder, and a mixed slurry of thermally conductive metal silver (melting point 961.0°C) and graphene oxide is prepared. The other steps and conditions are the same as those in Example 1.

[0056] Example 3

[0057] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from Example 1 is that the type of thermally conductive metal is different. The thermally conductive metal in this embodiment is nickel powder, and a mixed slurry of thermally conductive metal nickel (melting point 1453.0°C) and graphene oxide is prepared. The other steps and conditions are the same as those in Example 1.

[0058] In the preparation method of this embodiment, nickel does not melt during the heat treatment process due to its high melting point.

[0059] Example 4

[0060] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from Example 1 is that the thermally conductive metal is aluminum powder, and a mixed slurry of thermally conductive metal aluminum (melting point 660.0°C) and graphene oxide is prepared. The other steps and conditions are the same as those in Example 1.

[0061] Example 5

[0062] This embodiment provides a method for preparing a graphene composite thermally conductive film, which differs from Example 1 in that the heat treatment temperature is 2200° C., the heat treatment time is 1 hour, and the other steps and conditions are the same as those in Example 1.

[0063] Example 6

[0064] This embodiment provides a method for preparing a graphene composite thermally conductive film, which differs from Example 1 in that the heat treatment temperature is 400° C., and the other steps and conditions are the same as those in Example 1.

[0065] In the preparation method of this embodiment, during the heat treatment process, copper does not melt due to the low heat treatment temperature.

[0066] Example 7

[0067] This embodiment provides a method for preparing a graphene composite thermally conductive film, which differs from Example 1 in that the heat treatment temperature is 200° C., the heat treatment time is 10 hours, and the other steps and conditions are the same as those in Example 1.

[0068] In the preparation method of this embodiment, during the heat treatment process, copper does not melt due to the low heat treatment temperature.

[0069] Example 8

[0070] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from Example 1 is that the volume ratio V1 of the copper powder filling amount to the total volume of the through-hole is approximately 88.9%. In this embodiment, the volume ratio of copper powder to graphene oxide slurry is 8:1, and the other steps and conditions are the same as those in Example 1.

[0071] Example 9

[0072] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from Example 1 is that the volume ratio V1 of the filling amount of the metallic copper powder to the total volume of the through-hole is approximately 90.0%. In this embodiment, the volume ratio of the copper powder to the graphene oxide is 9:1. The other steps and conditions are the same as those in Example 1.

[0073] Example 10

[0074] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from Example 1 is that the volume ratio V1 of the filling amount of the metal copper powder to the total volume of the through-hole is approximately 83.3%, the volume ratio of the thermally conductive metal and the graphene oxide slurry is 5:1, and the other steps and conditions are the same as those in Example 1.

[0075] Example 11

[0076] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from Example 1 is that the diameter of the through hole of the graphene thermally conductive film is set to 3 mm at the widest point, and the aperture at the narrowest point is set to 0.1 mm. The difference between the aperture at the widest point and the aperture at the narrowest point of the through hole is 2.9 mm. The other steps and conditions are the same as those in Example 1.

[0077] Example 12

[0078] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from Example 1 is that the diameter of the through hole of the graphene thermally conductive film at the widest point is set to 1 mm, the aperture at the narrowest point is set to 0.5 mm, and the difference between the aperture at the widest point and the aperture at the narrowest point of the through hole is 0.5 mm. The other steps and conditions are the same as those in Example 1.

[0079] Example 13

[0080] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from Example 1 is that the diameter of the through hole of the graphene thermally conductive film is set to 0.8 mm at the widest point, and the aperture at the narrowest point is set to 0.6 mm. The difference between the aperture at the widest point and the aperture at the narrowest point of the through hole is 0.2 mm. The other steps and conditions are the same as those in Example 1.

[0081] Example 14

[0082] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from embodiment 1 is that the distribution density of the through holes in the graphene thermally conductive film is 0.25 per cm 2 The widest diameter of the through hole is 3 mm, and the narrowest diameter of the through hole is 1.5 mm, that is, the size is 10 cm long, 4 cm wide, and 5000 μm thick. 10 through holes are prepared on the graphene thermal conductive film, and the other steps and conditions are the same as those in Example 1.

[0083] Example 15

[0084] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from embodiment 1 is that the distribution density of the through holes of the graphene thermally conductive film is 80 / cm 2The widest aperture of the through hole is 0.6 mm, and the narrowest aperture of the through hole is 0.1 mm, that is, the size is 10 cm long, 4 cm wide, and 30 μm thick. 3200 through holes are prepared on the graphene thermal conductive film, and the other steps and conditions are consistent with Example 1.

[0085] Example 16

[0086] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from Example 1 is that the shape of the irregularly shaped hole is different. The cross-section of the irregularly shaped hole in the thickness direction of the graphene thermally conductive film is an "I" shape. The specific punching method is as follows: a milling cutter is used to process blind holes with a diameter of 2 mm and a height of 200 μm at corresponding positions on the upper and lower surfaces of the graphene thermally conductive film. Then, with the center of the blind hole as the center, a blind hole with a diameter of 0.5 mm and a height of 400 μm is milled out to obtain an "I"-shaped irregularly shaped hole. The other steps and conditions are the same as those in Example 1.

[0087] Example 17

[0088] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from Example 1 is that the shape of the irregularly shaped hole is different. The cross-section of the irregularly shaped hole in the thickness direction of the graphene thermally conductive film is shaved. The specific punching method is as follows: a tapered through hole is machined in the graphene thermally conductive film using a tapered milling cutter. The aperture of the through hole decreases linearly from top to bottom. The maximum aperture of the copper hole is 2 mm, and the narrowest aperture is 0.5 mm. The other steps and conditions are the same as those in Example 1.

[0089] Example 18

[0090] This embodiment provides a method for preparing a graphene composite thermally conductive film. The difference from embodiment 1 is that the processes of step (2) and step (3) are different, specifically:

[0091] (2) Prepare thermally conductive metal and graphene oxide slurry separately; the thermally conductive metal is metal powder, specifically copper powder (melting point 1083.4°C). The copper powder filling amount accounts for approximately 93% of the total volume of the through-hole (the volume of the thermally conductive metal is calculated based on its mass and density, thereby controlling the filling amount of the thermally conductive metal). In this embodiment, the volume ratio of the copper powder to the graphene oxide slurry is 7:1. The viscosity of the graphene oxide slurry is 12000 cP, and the solid content is 5%.

[0092] (3) Fill the irregular pores of the graphene thermal conductive film with thermal conductive metal, then place the graphene thermal conductive film filled with metal powder on the filter membrane and transfer the entire film to a vacuum filtration device, and vacuum-infuse the graphene oxide slurry prepared in the above step into the irregular pores.

[0093] The graphene thermal conductive film after vacuum infusion is heat-treated. In this embodiment, the heat treatment temperature is set to 1200° C. and the heat treatment time is 5 hours.

[0094] Other steps and conditions are consistent with those in Example 1. Other steps and conditions are consistent with those in Example 1.

[0095] Comparative Example 1

[0096] On a graphene thermal conductive film with a size of 10 cm in length, 4 cm in width and 800 μm in thickness, 90 through holes with a pore diameter of 2 mm and an array pattern of 15*6 were punched. Copper was filled into the graphene thermal conductive film with channels, and then dried at 100°C for 2 hours to obtain a composite film material. The composite film material was calendered to obtain a sample.

[0097] This comparative example provides a method for preparing a graphene composite thermally conductive film, which specifically comprises the following steps:

[0098] (1) Prepare a graphene thermal conductive film with a size of 10 cm in length, 4 cm in width, and 800 μm in thickness. Use laser drilling to prepare a number of through holes on the graphene thermal conductive film. The through holes are straight holes with a hole diameter of 2 mm. The through holes are arranged in a 15*6 array pattern, with a total of 90 holes.

[0099] (2) Prepare thermally conductive metal; the thermally conductive metal is copper powder.

[0100] (3) Use direct filling method to fill the through hole with copper powder.

[0101] (4) The graphene thermal conductive film filled with thermal conductive metal is subjected to calendering treatment, with the calendering pressure set to 1 ton and the holding time to 30 seconds to obtain a graphene composite thermal conductive film.

[0102] In the graphene composite thermally conductive film obtained in this comparative example, the copper powder forms a thermally conductive network and fills the through-holes. There are many gaps between the copper powders in the thermally conductive network, and there is a large gap between the thermally conductive network and the inner wall of the through-hole.

[0103] Comparative Example 2

[0104] This comparative example provides a method for preparing a graphene composite thermally conductive film, which specifically comprises the following steps:

[0105] (1) Prepare a graphene thermal conductive film with a size of 10 cm in length, 4 cm in width, and 800 μm in thickness. Use laser drilling to prepare a number of through holes on the graphene thermal conductive film. The through holes are straight holes with a hole diameter of 0.5 mm. The through holes are arranged in a 15*6 array pattern, with a total of 90 holes.

[0106] (2) The same as step (2) in Comparative Example 1;

[0107] (3) Use direct filling method to fill the through hole with copper powder.

[0108] (4) is consistent with step (4) in Comparative Example 1.

[0109] In the graphene composite thermally conductive film obtained in this comparative example, the copper powder forms a thermally conductive network and fills the through-holes. There are many gaps between the copper powders in the thermally conductive network, and there is a large gap between the thermally conductive network and the inner wall of the through-hole.

[0110] Comparative Example 3

[0111] This comparative example provides a method for preparing a graphene composite thermally conductive film. This method differs from Example 1 in that the through-hole design is different: the through-holes are straight holes with a diameter of 2 mm. The specific through-hole processing steps include: using laser drilling, 90 through-holes are drilled in a 15x6 array pattern with a diameter of 2 mm. Other steps and conditions are consistent with Example 1.

[0112] Comparative Example 4

[0113] This comparative example provides a method for preparing a graphene composite thermally conductive film, which differs from Example 1 in that, in step (2), a thermally conductive metal is prepared, and the thermally conductive metal is copper powder; in step (3), the process of filling the through hole with the thermally conductive metal is: directly filling the through hole with copper powder.

[0114] Other steps and conditions are consistent with those in Example 1.

[0115] In the graphene composite thermally conductive film obtained in this comparative example, the copper powder forms a thermally conductive network and fills the through-holes. There are many gaps between the copper powders in the thermally conductive network, and there is a large gap between the thermally conductive network and the inner wall of the through-hole.

[0116] Comparative Example 5

[0117] This comparative example provides a method for preparing a graphene composite thermally conductive film, which differs from Example 1 in that, in step (2), a graphene oxide slurry is prepared, and the viscosity of the graphene oxide slurry is 12000 cP and the solid content is 5%; in step (3), the process of coating the graphene oxide slurry into the through-hole is as follows: first, the graphene thermally conductive film is placed on a coating machine, and the coating machine vacuum-positions the graphene thermally conductive film, and at the same time, the graphene oxide slurry is coated on the surface of the graphene thermally conductive film, and the graphene oxide slurry fills the pores of the through-hole. After coating, the surface of the graphene thermally conductive film is cleaned, and the heat treatment steps and conditions are the same as those in Example 1. Other steps and conditions are the same as those in Example 1.

[0118] Performance testing:

[0119] Reliability testing was conducted on samples obtained from Examples 1 to 18 and Comparative Examples 1 to 5. The samples were placed in a vibration jig, with one side of the graphene composite thermally conductive film fixed. The jig was then clamped in a reciprocating motion. The filler (which varied depending on the example, including a composite of three-dimensional graphene and thermally conductive metal, thermally conductive metal, or three-dimensional graphene) filling the holes was observed for any dropouts. The test results are shown in Table 1 below (dropout ratio = number of dropped filler / total number of through-holes).

[0120] Table 1 Reliability test results

[0121] Example Shake 5000 times to get the filler drop rate (%) Shake 10,000 times to drop filler % Shake 20,000 times to drop filler % Example 1 0 0 0 Example 2 0 0 0 Example 3 0 0 2.2 Example 4 0 1.1 5.6 Example 5 0 0 0 Example 6 0 0 1.1 Example 7 0 1.1 4.4 Example 8 0 0 0 Example 9 0 0 0 Example 10 0 0 2.2 Example 11 0 0 1.1 Example 12 0 0 0 Example 13 0 5.6 13.3 Example 14 0 0 0 Example 15 0 0 0 Example 16 0 0 0 Example 17 0 1.1 3.3 Example 18 0 0 0 Comparative Example 1 8.9 13.3 22.2 Comparative Example 2 5.6 13.3 18.9 Comparative Example 3 3.3 8.9 17.8 Comparative Example 4 84.4 90.0 100.0 Comparative Example 5 0 1.1 4.4

[0122] From the above experimental results, it can be seen that the embodiments of the present invention effectively improve the reliability of the graphene composite thermally conductive film by constructing special-shaped holes and filling them with thermally conductive metal and graphene oxide slurry, and coordinating with heat treatment and calendering treatment. From Examples 1 and 2, it can be seen that the use of transition metals as thermally conductive metals and the melting of thermally conductive metals at higher heat treatment temperatures can better catalyze the three-dimensional graphene material and the graphene material on the inner wall of the through hole to generate carbon active sites and chemically bond in the form of carbon-carbon bonds, with very excellent reliability. From Examples 1 and 3, it can be seen that since a thermally conductive metal with a melting point higher than the heat treatment temperature is used in Example 3, the thermally conductive metal will not melt during the heat treatment process, so the catalytic effect of the thermally conductive metal is relatively weakened, and the chemical bonding and reliability are slightly reduced. The graphene composite thermally conductive film obtained in Example 3 did not fall off when shaken 10,000 times. It can be seen from Examples 1 and 4 that although the thermally conductive metals selected in Examples 1 and 4 can be melted during the heat treatment process, the non-transition metal with weaker catalytic effect selected as the thermally conductive metal in Example 4 cannot generate more carbon active sites in the three-dimensional graphene material and the graphene material on the inner wall of the through hole and chemically bond in the form of carbon-carbon bonds, resulting in relatively reduced reliability. The graphene composite thermally conductive film obtained in Example 4 did not fall off when shaken 5000 times. As can be seen from Examples 1 and 5, both Examples 1 and 5 utilize relatively high heat treatment temperatures and employ catalytic thermally conductive metals, resulting in excellent reliability. As can be seen from Examples 1 and 6, Example 6 utilizes a relatively low heat treatment temperature, allowing the formation of a three-dimensional graphene material during the heat treatment process. At this heat treatment temperature, the thermally conductive metal begins to act catalytically, resulting in carbon active sites in the three-dimensional graphene material and the graphene material on the inner walls of the through-holes forming chemical bonds in the form of carbon-carbon bonds. However, the thermally conductive metal does not melt, resulting in relatively reduced reliability. The graphene composite thermally conductive film obtained in Example 6 did not fall off after being shaken 10,000 times. As can be seen from Examples 1 and 7, the thermally conductive metal fails to catalyze at this temperature, resulting in the inability of the three-dimensional graphene material and the graphene material on the inner walls of the through-holes to form carbon active sites and chemically bond in the form of carbon-carbon bonds. This results in relatively reduced reliability. The graphene composite thermally conductive film obtained in Example 7 did not fall off after being shaken 5,000 times. It can be seen from Examples 1 and 8-10 that the reliability of the graphene composite thermally conductive film can be controlled by adjusting the volume ratio of the thermally conductive metal and the through-holes. When the volume ratio of the thermally conductive metal and the through-holes is controlled to be 80-90%, the reliability is excellent. If the volume ratio of the thermally conductive metal and the through-holes is reduced (for example, in Example 10), the reliability is slightly reduced. The graphene composite thermally conductive film obtained in Example 10 did not fall off when shaken 10,000 times.As can be seen from Example 1, Examples 11-13, and Examples 16-17, all kinds of designed irregular holes can effectively regulate the growth direction of graphene oxide during self-assembly, forming mutually staggered growth directions, and infiltrating into various parts of the through-hole, climbing to various parts of the through-hole in the form of branches, and then tightly coating the thermally conductive metal and clinging to the inner wall of the through-hole of the graphene thermally conductive film, thereby anchoring to the thermally conductive metal and the inner wall of the through-hole in a similar physical form, effectively improving reliability, and the difference between the widest and narrowest pore diameters is 0.5~2.9mm, which has more excellent reliability. As can be seen from Example 1 and Examples 14-15, under various graphene thickness and pore density conditions, reliability can be effectively improved. As can be seen from Example 18, various filling methods can achieve better filling of thermally conductive metal and graphene oxide slurry, and improve the reliability of the graphene composite thermally conductive film.

[0123] Comparative Examples 1 and 2 use existing methods to prepare graphene composite thermal conductive films. There are gaps between the thermal conductive network formed by a single thermal conductive metal and the inner wall of the through hole, and the bonding force is poor, resulting in poor reliability. The graphene composite thermal conductive films obtained by the two methods have a high rate of falling off when shaken 5,000 times.

[0124] Comparative Example 3 uses through holes of equal diameter. Graphene oxide grows directionally along the hole wall during the self-assembly process without deviation, and cannot tightly cover the thermally conductive metal. Its adhesion to the inner wall of the through hole of the graphene thermally conductive film is also weak, that is, the three-dimensional graphene material cannot be firmly anchored to the thermally conductive metal and the inner wall of the through hole in a similar physical form. On the one hand, there will be certain gaps in the thermal conductive network formed by the three-dimensional graphene material and the thermally conductive metal, and the bonding force is poor. On the other hand, the bonding force between the thermally conductive network and the inner wall of the through hole is also poor, which makes it impossible to effectively improve the reliability. The resulting graphene composite thermally conductive film still has a certain proportion of falling off when shaken 5000 times.

[0125] In Comparative Example 4, only thermally conductive metal is filled. Although it is a special-shaped hole design, the thermally conductive metal does not have the staggered growth characteristics of graphene oxide during self-assembly during the heat treatment process. The bonding force between the thermally conductive network obtained by the thermally conductive metal and the inner wall of the through hole is also poor, and the reliability is poor. A large proportion of the graphene composite thermally conductive film obtained therefrom falls off when shaken 5,000 times.

[0126] In Comparative Example 5, only graphene oxide is filled, which has an irregular pore design and graphene oxide grows in an interlaced manner during self-assembly to form a three-dimensional graphene network, which is anchored to the inner wall of the through hole in a similar physical form, which can effectively improve reliability. The resulting graphene composite thermally conductive film does not fall off when shaken 5,000 times. However, due to the lack of catalytic effect of the thermally conductive metal, the three-dimensional graphene material cannot be chemically combined with the pore wall of the irregular pore. Therefore, a certain proportion of the resulting graphene composite thermally conductive film falls off when shaken 10,000 times.

[0127] According to the standard GB / T 22588-2008 "Flash method for measuring thermal diffusion coefficient or thermal conductivity", longitudinal thermal conductivity tests were performed on the samples obtained from Examples 1-18 and Comparative Examples 1-5. The specific test method is: cut the above samples into discs with a diameter of about 12.7 mm, wherein the cut discs include at least one through hole, measure and record their thickness, place them in a 4samples round / 12.7mm holder, and place them in a Netsch 467 instrument for testing. The test environment temperature is set to 25-27°C, the temperature threshold (tolerance / stability threshold) is 0.3K, the number of flash points is 5, the voltage is 260V, the pulse width is 44μs, the main gain is adjusted to 6633, the sampling time is adjusted to 6ms, the detection area is 3.7mm, and the parameter optimization is turned on. After the test is completed, the average longitudinal thermal conductivity data of each group of samples is recorded. Thermal conductivity = thermal diffusion coefficient * density * 0.85. Appendix Figure 6 The longitudinal thermal diffusion coefficient test data of the graphene composite thermal conductive film of Example 1 is shown.

[0128] The formula for calculating the improvement rate of the longitudinal thermal conductivity is: (longitudinal thermal conductivity of the graphene composite thermal conductive film / longitudinal thermal conductivity of the graphene thermal conductive film-1)*100%. The graphene thermal conductive film used in the present invention is purchased from the GOF-B series of Yunnan Yuntian Mo Rui. The measured longitudinal thermal conductivity is 6.025 W / (mK). The relevant test results are shown in Table 2.

[0129] Table 2 Longitudinal thermal conductivity test results

[0130] Example Longitudinal thermal conductivity W / (mK) Longitudinal thermal conductivity improvement rate (100%) Example 1 104.335 1631.7% Example 2 106.238 1663.3% Example 3 30.446 405.3% Example 4 58.120 864.6% Example 5 101.343 1582.0% Example 6 86.312 1332.6% Example 7 77.335 1183.6% Example 8 100.274 1564.3% Example 9 102.367 1599.0% Example 10 79.365 1217.3% Example 11 103.925 1624.9% Example 12 100.436 1567.0% Example 13 96.325 1498.8% Example 14 20.236 235.9% Example 15 108.452 1700.0% Example 16 104.387 1632.6% Example 17 99.357 1549.1% Example 18 100.257 1564.0% Comparative Example 1 89.427 1384.3% Comparative Example 2 93.268 1448.0% Comparative Example 3 95.862 1491.1% Comparative Example 4 78.368 1200.7% Comparative Example 5 3.698 -38.6%

[0131] The experimental results of the thermal conductivity tests described above demonstrate that the longitudinal thermal conductivity of the graphene composite thermally conductive film can be improved by filling the through-holes with a thermally conductive metal and graphene oxide slurry and then performing heat treatment and calendering. Examples 1-4 demonstrate that the effect of improving the longitudinal thermal conductivity primarily depends on the thermal conductivity of the thermally conductive metal itself. Specifically, the higher the thermal conductivity of the thermally conductive metal filled in the irregularly shaped holes, the greater the improvement in the longitudinal thermal conductivity of the graphene composite thermally conductive film. Since the thermal conductivity of thermally conductive metals follows the following pattern: silver > copper > aluminum > nickel, the degree of improvement in the longitudinal thermal conductivity of the graphene composite thermally conductive films obtained by filling with silver (Example 2), copper (Example 1), aluminum (Example 4), and nickel (Example 3) follows this pattern. In addition to the influence of the thermal conductivity of the thermally conductive metal, the filling of the three-dimensional graphene material can eliminate air trapped in the gaps within the through-holes, thereby contributing to a certain improvement in the longitudinal thermal conductivity. Specifically, it can be seen from Examples 1 and 5-7 that at the heat treatment temperature of Example 5, the thermally conductive metal melts, the coating effect between the three-dimensional graphene material and the thermally conductive metal is good, and its improvement in longitudinal thermal conductivity is similar to that of Example 1; at the heat treatment temperature of Examples 6 and 7, the thermally conductive metal does not melt, and the coating effect between the three-dimensional graphene material and the thermally conductive metal is poor, so the overall longitudinal thermal conductivity is relatively worse than that of Example 1. From Examples 1 and 8-10, it can be seen that the through holes in Examples 8-9 are filled with a large volume of thermally conductive metal, and the improvement in longitudinal thermal conductivity is similar to that of Example 1. The amount of thermally conductive metal filled in Example 10 is relatively small, and the structure of the longitudinal thermal conductive path is relatively weak, so the improvement in longitudinal thermal conductivity is relatively weak. From Examples 1, 11-13, and 16-17, it can be seen that the graphene composite thermally conductive films obtained by filling thermally conductive metal and graphene oxide slurry into various designs of special-shaped holes and subsequent treatment all have good longitudinal thermal conductivity. As shown in Examples 1, 14, and 15, the total volume of through-holes (or the total volume of thermally conductive metal filling) in the graphene composite thermally conductive film significantly affects the improvement in longitudinal thermal conductivity. Even with a relatively small total through-hole volume, Example 14 demonstrates a significant improvement in longitudinal thermal conductivity, increasing it by 235.9% compared to the untreated graphene thermally conductive film, achieving a longitudinal thermal conductivity of no less than 20 W / (mK). When the total through-hole volume increases to a certain level, the improvement in longitudinal thermal conductivity gradually slows. Adjusting the through-hole density and pore size range can further control the through-hole volume and longitudinal thermal conductivity. As shown in Examples 1 and 18, filling processes with various thermally conductive metals and graphene oxide slurries can effectively improve longitudinal thermal conductivity.

[0132] Comparative Examples 1 and 2 use the existing method to prepare the graphene composite thermal conductive film. After the calendering treatment, there are many gaps inside the thermal conductive network formed by the single thermal conductive metal (i.e., between copper and copper) and between the thermal conductive network and the inner wall of the through hole. There is a lot of air in the gap that is not eliminated, and the improvement of the longitudinal thermal conductivity effect is not as good as that of Example 1.

[0133] Comparative Example 3 uses through holes of equal diameter. The graphene oxide grows directionally along the hole wall during the self-assembly process without deviation, and cannot tightly cover the thermally conductive metal. There is a small amount of gap inside the thermal conductive network formed by the three-dimensional graphene material and the thermally conductive metal, and between the thermal conductive network and the inner wall of the through hole. Compared with Example 1, the improvement in the longitudinal thermal conductivity effect is slightly weaker.

[0134] In Comparative Example 4, only thermally conductive metal is filled. After the calendering treatment, there are many gaps inside the thermally conductive network formed by the thermally conductive metal alone (i.e., between copper and copper) and between the thermally conductive network and the inner wall of the through hole. A large amount of air is not removed, and the improvement in the longitudinal thermal conductivity effect is relatively weak compared to Example 1.

[0135] In Comparative Example 5, only graphene oxide is filled. Although it is designed with irregular holes and graphene oxide grows in an interlaced manner during self-assembly to form a three-dimensional graphene network, the three-dimensional graphene network itself has a large number of cavities and lacks thermally conductive metal as an effective thermal conductive medium. The longitudinal thermal conductivity effect is even worse than that of ordinary graphene thermal conductive film.

[0136] From the above reliability test results and longitudinal thermal conductivity coefficient results, it can be seen that the graphene composite thermal conductive film prepared by the technical solution described in this application has both excellent longitudinal thermal conductivity and excellent product reliability. The reasons for this are:

[0137] ① Metal has isotropic thermal conductivity, and its introduction provides a basis for improving the longitudinal thermal conductivity of the graphene thermal conductive film. In a further solution, the thermal conductive metal is heat-treated to a molten state, and the molten metal flows and spreads to eliminate the residual air in the through-hole, further promoting the improvement of the longitudinal thermal conductivity effect;

[0138] ② The provision of irregularly shaped holes and the addition of graphene oxide slurry ensure the product reliability of the graphene composite thermally conductive film: by creating irregularly shaped holes, the inner wall of the through-hole has a pore size that is not completely consistent along the thickness direction of the graphene thermally conductive film, which has the excellent characteristics of high specific surface area and many active sites. Graphene oxide has the characteristic of spreading during the self-assembly process, tightly wrapping the thermally conductive metal and firmly clinging to the inner wall of the through-hole of the graphene thermally conductive film. In a further solution, the catalytic effect of transition metals is utilized to chemically bond the three-dimensional graphene material and the graphene material on the inner wall of the through-hole in the form of carbon-carbon bonds at above 400°C, further improving the product reliability of the graphene composite thermally conductive film. At the same time, the thermally conductive metal and the three-dimensional graphene material together form a tightly bonded and essentially gapless thermal conductive network and tightly fill the through-hole, reducing the gap within the thermal conductive network (i.e., between the thermally conductive metal and the three-dimensional graphene material) and between the thermal conductive network and the inner wall of the through-hole, further improving the longitudinal thermal conductivity effect.

[0139] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a graphene composite thermally conductive film, characterized in that: At least the following steps are included: A graphene thermally conductive film is prepared, wherein a plurality of through holes are prepared on the graphene thermally conductive film, wherein the through holes are irregularly shaped holes whose apertures are not completely uniform in the thickness direction of the graphene thermally conductive film; a thermally conductive metal and a graphene oxide slurry are filled into the through holes; and the graphene thermally conductive film filled with the thermally conductive metal and the graphene oxide slurry is heat-treated to obtain a graphene thermally conductive film filled with the thermally conductive metal and the three-dimensional graphene material; Then, a calendering process is performed to obtain a graphene composite thermal conductive film; The melting point of the heat-conducting metal is not higher than the temperature of the heat treatment.

2. The method for preparing a graphene composite thermally conductive film according to claim 1, wherein: The heat treatment temperature is ≥200°C, and the heat treatment time is 1-10 hours; and / or the heat treatment process is: heat treating the graphene thermally conductive film filled with thermally conductive metal and graphene oxide slurry, during which the graphene oxide self-assembles along the inner wall of the through hole and / or the edge of the thermally conductive metal to form a three-dimensional graphene material and covers the thermally conductive metal, thereby obtaining the graphene thermally conductive film filled with the thermally conductive metal and the three-dimensional graphene material.

3. The method for preparing a graphene composite thermally conductive film according to claim 1, wherein: The heat treatment temperature is ≥400° C., the heat treatment is performed in a vacuum environment, and the heat treatment time is 1-10 hours.

4. The method for preparing a graphene composite thermally conductive film according to claim 3, wherein: The thermally conductive metal is one or more transition metals; the heat treatment process is as follows: the graphene thermally conductive film filled with the thermally conductive metal and graphene oxide slurry is heat treated at a temperature of ≥400°C for 1-10 hours in a vacuum environment. During the heat treatment, the graphene oxide self-assembles along the inner wall of the through hole and / or the edge of the thermally conductive metal to form a three-dimensional graphene material and covers the thermally conductive metal. Then, under the catalytic action of the thermally conductive metal, the three-dimensional graphene material and the graphene material on the inner wall of the through hole generate carbon active sites, and the three-dimensional graphene material and the graphene material on the inner wall of the through hole are chemically bonded in the form of carbon-carbon bonds, thereby obtaining the graphene thermally conductive film filled with the thermally conductive metal and the three-dimensional graphene material.

5. The method for preparing a graphene composite thermally conductive film according to claim 4, wherein: The heat treatment process is as follows: the graphene thermally conductive film filled with a thermally conductive metal and a graphene oxide slurry is heat treated at a temperature of ≥400°C in a vacuum environment, the thermally conductive metal in the through-hole is melted, and the graphene oxide self-assembles along the inner wall of the through-hole and / or the edge of the thermally conductive metal to form a three-dimensional graphene material and covers the thermally conductive metal. Under the catalytic action of the thermally conductive metal, carbon active sites are generated in the three-dimensional graphene material and the inner wall of the through-hole of the graphene thermally conductive film, and the three-dimensional graphene material and the graphene material on the inner wall of the through-hole are chemically bonded in the form of carbon-carbon bonds, thereby obtaining the graphene thermally conductive film filled with the thermally conductive metal and the three-dimensional graphene material.

6. The method for preparing a graphene composite thermally conductive film according to claim 1, wherein: The thermally conductive metal is in powder form. The specific steps of filling the thermally conductive metal and graphene oxide slurry are: fully mixing the thermally conductive metal and graphene oxide slurry to obtain a mixed slurry, and filling the mixed slurry into the through hole; or filling the thermally conductive metal into the through hole, and then filling the through hole with graphene oxide slurry.

7. The method for preparing a graphene composite thermally conductive film according to any one of claims 1 to 6, characterized in that: The thermally conductive metal is selected from one or more transition metals.

8. The method for preparing a graphene composite thermally conductive film according to claim 1, wherein: The volume ratio V1 of the thermally conductive metal and the through hole is ≥80%, the volume ratio of the thermally conductive metal to the graphene oxide slurry is 5-9:1, the viscosity of the graphene oxide slurry is 1000-15000 cP, and the solid content is 0.1%-10%.

9. The method for preparing a graphene composite thermally conductive film according to claim 1, wherein: The graphene thermally conductive film and the through hole satisfy at least one of the following conditions: (1) The aperture of the through hole ranges from 0.1 to 3 mm; (2) The difference between the widest diameter and the narrowest diameter of the through hole is 0.2 to 2.9 mm; (3) The distribution density of the through holes is 0.25 to 80 per cm 2 ; (4) The thickness of the graphene thermal conductive film is 30 to 5000 μm; (5) Along the thickness direction of the graphene thermal conductive film, the aperture of the middle portion of the through hole is smaller than the apertures at both ends.

10. A graphene composite thermally conductive film, characterized in that: The graphene composite thermally conductive film is prepared by the method according to any one of claims 1 to 9.

Images