Graphene heat conduction film and preparation method thereof, and graphene foam and preparation method thereof

Abstract

According to the preparation method of the graphene heat conduction film or the graphene foam, in the preparation process of the graphene heat conduction film or the graphene foam, a porous graphene oxide film with a surface structure in a fluctuating shape is used as a substrate, graphene oxide slurry is used for immersing the substrate, and then the substrate is flatly coated and integrally dried, so that the graphene heat conduction film or the graphene foam is obtained. And then carrying out heat treatment to prepare the graphene heat-conducting film or graphene foam. The arrangement direction of graphene oxide sheets in the porous graphene oxide film is consistent with the direction of the fluctuating surface structure, and after heat treatment, the porous graphene oxide film has a good in-plane heat conductivity coefficient in the surface direction; graphene sheet layer arrangement orientation consistent with the surface direction of the fluctuating morphology of the porous graphene oxide film is reserved in the finally prepared graphene heat conduction film or graphene foam, and a good longitudinal heat conduction channel is provided for the graphene heat conduction film.

Description

Technical Field

[0001] The present application relates to the technical field of graphene preparation, and more specifically, to a graphene thermal conductive film and a preparation method thereof, and a graphene foam and a preparation method thereof. Background Art

[0002] Graphene thermal conductive film and its derivatives have important application value in the fields of electronic device heat dissipation, chip heat dissipation, and flexible device heat dissipation due to their high thermal conductivity, light weight and flexibility.

[0003] Graphene thermally conductive film has significant anisotropic thermal conductivity properties. Specifically, its thermal conductivity in the in-plane direction (parallel to the plane of the graphene sheet) is high. The in-plane thermal conductivity of commercially available graphene thermally conductive film is usually ≥1000W / (m·K), and heat can be quickly and evenly spread in a two-dimensional plane. However, its thermal conductivity in the out-of-plane direction (perpendicular to the plane of the graphene sheet, that is, the thickness direction) is low, usually ≤5W / (m·K), making it difficult for heat to pass through the film itself efficiently.

[0004] Graphene thermally conductive film and its derivatives can quickly and evenly diffuse the heat generated by local hot spots (such as CPU and GPU chips, batteries, and camera modules) to a larger area covered by the entire film. Although the heat is diffused within the surface, it ultimately needs to be transferred from the film to external heat dissipation components (such as the metal middle frame, heat dissipation fins, etc.). Its low out-of-plane thermal conductivity coefficient becomes a bottleneck for further heat dissipation. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing a graphene thermally conductive film and a graphene thermally conductive film prepared by the method, wherein the graphene thermally conductive film has good longitudinal thermal conductivity.

[0006] A first aspect of the present application provides a method for preparing a graphene thermally conductive film, the specific preparation method comprising the following steps: A porous substrate is immersed in a first graphene oxide slurry, the first graphene oxide slurry is evenly coated and dried as a whole, and then heat-treated to prepare a graphene thermal conductive film, wherein the porous substrate is a porous graphene oxide membrane, and the porous graphene oxide membrane has a surface structure with an undulating morphology.

[0007] A first graphene oxide slurry is immersed in the porous graphene oxide membrane, applied evenly, and dried to form a monolithic structure with the porous graphene membrane. Subsequently, a heat treatment is performed to remove most of the oxygen-containing functional groups, forming a monolithic graphene thermally conductive membrane. The graphene oxide sheets within the porous graphene oxide membrane are aligned with the undulating surface structure, resulting in excellent in-plane thermal conductivity along the surface after heat treatment. After heat treatment, the porous graphene oxide membrane serves as a component of the overall graphene thermally conductive membrane, with the graphene sheets aligned along the undulating structure, providing excellent longitudinal heat conduction pathways for the membrane.

[0008] As some embodiments of the first aspect of the present application, the porous graphene oxide membrane is prepared by punching the graphene oxide membrane, and the punching method is mechanical punching or laser punching, and the pore size is 0.5-1.0 mm.

[0009] The perforated porous graphene film facilitates the first graphene oxide slurry to penetrate between the holes to achieve better anchoring, so that the graphene thermal conductive film has stronger interlayer bonding force.

[0010] As some embodiments of the first aspect of the present application, the graphene oxide film is obtained by coating or filtering the second graphene oxide slurry.

[0011] As some embodiments of the first aspect of the present application, the method for preparing the graphene thermally conductive film further includes the following steps: S1. Providing an upper mold and a lower mold, wherein the upper mold and the lower mold each have a recessed portion and a raised portion, wherein the recessed portion of the upper mold corresponds to the raised portion of the lower mold to form a complementary meshing structure; S2, placing the graphene oxide film or the porous graphene oxide film between the upper mold and the lower mold; S3. The upper mold and the lower mold are closed, and the porous graphene oxide membrane is plastically deformed by the complementary meshing structure of the upper mold and the lower mold to form a surface structure with an undulating morphology.

[0012] As some embodiments of the first aspect of the present application, the method for preparing the graphene thermally conductive film further includes the following steps: S1. providing an elastic matrix in a stretched state; S2. coating a second graphene oxide slurry on the provided elastic substrate to form a graphene oxide film on the elastic substrate; S3. Shrinking the elastic substrate to obtain a graphene oxide film having an undulating surface structure.

[0013] As the elastic matrix shrinks, the graphene oxide film formed on the elastic matrix also deforms and wrinkles, thereby forming a graphene oxide film with an undulating surface structure.

[0014] As some embodiments of the first aspect of the present application, the elastic matrix is ​​silicone rubber.

[0015] As some embodiments of the first aspect of the present application, the heat treatment includes pretreatment, carbonization treatment and graphitization treatment; Among them, the maximum temperature of pretreatment is 240~360℃; Among them, the highest temperature of carbonization treatment is 900~1400℃; Among them, the highest temperature of graphitization treatment is 2800~3200℃.

[0016] Graphene oxide membranes are composed of multiple layers of graphene oxide stacked together. During the heat treatment process, oxygen-containing functional groups will fall off and release a large amount of gas. If the heat treatment is too intense, a large amount of gas will be instantly generated to break through the membrane material, causing irreversible structural damage to the membrane material. Therefore, a segmented heat treatment method is used to slow down the gas production efficiency of the graphene oxide membrane.

[0017] As some embodiments of the first aspect of the present application, after the heat treatment, a calendering step is also included to ensure that the graphene thermal conductive film has a target thickness and a target density.

[0018] The second aspect of the present application provides a graphene thermally conductive film, which is prepared using the preparation method provided by the first aspect of the present application.

[0019] The third aspect of the present application provides a method for preparing graphene foam, which not only uses the preparation method provided in the first aspect of the present application, but also includes the following preparation steps: before the heat treatment after overall drying, the overall dried structure is infiltrated with a chemical foaming agent. Specifically, the chemical foaming agent includes at least one of hydrazine hydrate, sodium hydrogen borate, dimethylhydrazine, and thiourea, and the concentration of the chemical foaming agent is 0.5~50%.

[0020] Chemical reduction foaming is an important step in preparing graphene foam. Through the action of the foaming agent, a stable three-dimensional pore structure similar to a honeycomb is formed inside the graphene oxide membrane. When subjected to external compressive stress, the three-dimensional pore structure can quickly disperse the stress and be compressed without destroying the membrane structure. When no longer subjected to external forces, the membrane rebounds. The graphene foam prepared using the technical solution provided in this application not only has good in-plane and out-of-plane thermal conductivity, but also has good compression rebound properties. It can be applied to technical fields that require heat conduction, cushioning and shock absorption, and caulking.

[0021] The fourth aspect of the present application provides a graphene foam, which is prepared using the preparation method provided in the third aspect of the present application.

[0022] The beneficial effects of this application are: In the preparation process of a graphene thermally conductive film or graphene foam, a porous graphene oxide film with an undulating surface structure is used as a substrate. The substrate is then impregnated with a graphene oxide slurry, coated evenly, and dried. The film or foam is then heat-treated to produce the graphene thermally conductive film or foam. The orientation of the graphene oxide sheets within the porous graphene oxide film is aligned with the orientation of its undulating surface structure. After heat treatment, the film or foam exhibits good in-plane thermal conductivity along the surface. The resulting graphene thermally conductive film or foam retains the graphene sheet orientation aligned with the undulating surface of the porous graphene oxide film, providing a good longitudinal heat conduction path for the film.

[0023] The longitudinal thermal conductivity of the graphene thermal conductive film and graphene foam provided in the present application is superior to that of conventional graphene thermal conductive films and graphene foams obtained by coating, drying, and heat treating a graphene oxide slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0025] Figure 1 This is an SEM image of a conventional graphene thermal conductive film; Figure 2 This is the SEM image of conventional graphene foam; Figure 3 Schematic diagram of the sheet orientation of a graphene oxide film with an undulating surface structure; Figure 4 Schematic diagram of the preparation process of steps S2 to S6 of the preparation method provided in Example 1; Figure 5 This is a schematic diagram of the preparation process of steps S2 to S6 of the preparation method provided in Example 4. DETAILED DESCRIPTION

[0026] The following detailed description of exemplary embodiments of the present application refers to the accompanying drawings, which form a part of the description, and in which exemplary embodiments that can be implemented by the present application are shown as examples. The following more detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but is merely for illustration and does not limit the description of the characteristics and features of the present application, so as to propose the best way to perform the application and be sufficient to enable those skilled in the art to implement the application. However, it should be understood that various modifications and variations can be made without departing from the scope of the present application as defined by the appended claims. The detailed description and drawings should be considered only as illustrative, not restrictive, and if any such modifications and variations exist, they will fall within the scope of the application described herein. In addition, the background technology is intended to illustrate the current status and significance of the research and development of the technology and is not intended to limit the application and the field of application of the application.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the term "and / or" used herein includes any and all combinations of one or more of the relevant listed items.

[0028] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0029] In order to facilitate understanding of the technical solution of the present application, the technical problem of the present application is first described below.

[0030] Generally speaking, graphene thermal conductive film or graphene foam has excellent in-plane thermal conductivity, but its out-of-plane thermal conductivity is relatively poor. The underlying reasons are as follows: Figure 1 、 Figure 2 As shown in the figure, SEM images of conventional graphene thermal conductive film and graphene foam are respectively shown. The graphene sheets are highly oriented in the plane of the film, and the lattice directions of the graphene sheets are basically consistent, which makes the thermal conductivity of the graphene thermal conductive film and graphene foam higher in the plane.

[0031] The high in-plane thermal conductivity of graphene thermal conductive film or graphene foam can quickly and evenly diffuse the heat generated by local hot spots (such as GPU and CPU chips, batteries, and camera modules) to the entire area covered by the film. Although the heat is diffused in the surface, in order to conduct the heat from the inside of the film to the external heat dissipation components, it is urgent to improve the longitudinal thermal conductivity of the graphene thermal conductive film or graphene foam.

[0032] A first aspect of the present application provides a method for preparing a graphene thermally conductive film, the specific preparation method comprising the following steps: A porous substrate is immersed in a first graphene oxide slurry, the first graphene oxide slurry is evenly coated and dried as a whole, and then heat-treated to prepare a graphene thermal conductive film, wherein the porous substrate is a porous graphene oxide membrane, and the porous graphene oxide membrane has a surface structure with an undulating morphology.

[0033] like Figure 3 As shown, the graphene oxide sheets in the porous graphene oxide membrane 1 have a planar orientation structure. When it has an undulating surface structure through certain means, the arrangement direction of the graphene oxide sheets in the porous graphene oxide membrane 1 is consistent with the direction of its undulating surface structure. After the substrate with the undulating surface structure is immersed in the first graphene oxide slurry 2, the first graphene oxide slurry is coated flat and dried as a whole, and then heat-treated to prepare a graphene thermal conductive film. During the heat treatment, the orientation arrangement direction of the graphene oxide sheets in the original porous graphene oxide membrane remains unchanged, providing a good longitudinal heat conduction channel for the graphene thermal conductive film.

[0034] As some embodiments of the first aspect of the present application, the porous graphene oxide membrane is prepared by punching the graphene oxide membrane, and the punching method is mechanical punching or laser punching, and the pore size is 0.5-1.0 mm.

[0035] In some embodiments of the present application, the mechanical punching method includes one or more of drilling, punching, milling, turning / boring; the laser punching includes one or more of single pulse punching, impact punching / perforation, circular cutting punching / trepanning punching; typically but not limitatively, the aperture size is 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm.

[0036] By drilling holes in the graphene oxide film, the first graphene oxide slurry can penetrate between the holes to achieve better anchoring between the porous graphene film and the first graphene oxide slurry, so that the prepared graphene thermal conductive film has better interlayer bonding strength.

[0037] In some embodiments of the present application, the graphene oxide membrane is obtained by coating or filtering a second graphene oxide slurry: typically but not limitatively, the steps for preparing the graphene oxide membrane obtained by the coating method are as follows: prepare a second graphene oxide slurry with a solid content of 3% to 8%, coat it on a substrate to a target thickness and dry it to obtain a target graphene oxide membrane. The thickness of the graphene oxide membrane obtained by the coating method can reach 10μm to 1000μm; typically but not limitatively, the steps for preparing the graphene oxide membrane obtained by the filtration method are as follows: prepare a second graphene oxide slurry with a solid content of 0.1% to 3%, filter it onto a porous substrate, and obtain the target graphene oxide membrane after drying. The thickness of the graphene oxide membrane obtained by the filtration method can be ≤20μm.

[0038] In some embodiments of the present application, the undulating surface structure of the graphene oxide film can be obtained by the following preparation method: S1. Providing an upper mold and a lower mold, wherein each of the upper mold and the lower mold has a recessed portion and a raised portion, wherein the recessed portion of the upper mold corresponds to the raised portion of the lower mold in position to form a complementary meshing structure; S2, placing the graphene oxide film or the porous graphene oxide film obtained by punching the graphene oxide film between the upper mold and the lower mold; S3. The upper mold and the lower mold are closed, and the graphene oxide film or the porous graphene oxide film is plastically deformed by the complementary meshing structure of the upper mold and the lower mold to form a surface structure with an undulating morphology.

[0039] In some embodiments of the present application, the graphene oxide membrane or the porous graphene oxide membrane is subjected to a wetting treatment before being clamped by the upper and lower molds. The wetting treatment includes but is not limited to immersion treatment, water vapor contact treatment, and spraying treatment. The wetting treatment is beneficial to the plastic deformation of the graphene oxide membrane or the porous graphene oxide membrane.

[0040] In some embodiments of the present application, the undulating surface structure of the graphene oxide film can be obtained by the following preparation method: S1. providing an elastic matrix in a stretched state; S2. coating a second graphene oxide slurry on the provided elastic substrate to form a graphene oxide film on the elastic substrate; S3. Shrinking the elastic substrate to obtain a graphene oxide film having an undulating surface structure.

[0041] As the elastic substrate shrinks, the graphene oxide film formed on the elastic substrate also deforms and wrinkles, thereby forming a graphene oxide film with an undulating surface structure; the drilling of the graphene oxide film can be performed before the elastic substrate shrinks, or it can be performed on the formed graphene oxide film with an undulating surface structure after the elastic substrate shrinks, and the specific order is not limited.

[0042] In some embodiments of the present application, the elastic matrix is ​​silicone rubber.

[0043] In some embodiments of the present application, the heat treatment includes pretreatment, carbonization, and graphitization. The maximum temperature for pretreatment is 240-360°C; the maximum temperature for carbonization is 900-1400°C; and the maximum temperature for graphitization is 2800-3200°C. Because the graphene oxide film is composed of multiple layers of graphene oxide, oxygen-containing functional groups will shed during the heat treatment, releasing a large amount of gas. If the heat treatment is too intense, a large amount of gas will be generated instantaneously. The gas release will break through the film material and cause irreversible structural damage. Therefore, the use of a staged heat treatment scheme can slow down the gas production efficiency of the graphene oxide film, thereby achieving gentle gas release.

[0044] In some embodiments of the present application, after the heat treatment, a calendering step is further included to ensure that the graphene thermally conductive film has a target thickness and a target density.

[0045] Some embodiments of the present application provide a graphene thermally conductive film, which is prepared using the preparation method provided in the first aspect of the present application.

[0046] Some embodiments of the present application provide a method for preparing graphene foam, which not only uses the preparation method provided in the first aspect of the present application, but also includes the following preparation steps: before performing the heat treatment after overall drying, the overall dried structure is infiltrated with a chemical foaming agent. Specifically, the chemical foaming agent includes at least one of hydrazine hydrate, sodium hydrogen borate, dimethylhydrazine, and thiourea, and the concentration of the chemical foaming agent is 0.5~50%.

[0047] Chemical reduction foaming is an important step in preparing graphene foam. Through the action of the foaming agent, a stable three-dimensional pore structure similar to a honeycomb is formed inside the graphene oxide membrane. When subjected to external compressive stress, the three-dimensional pore structure can quickly disperse the stress and be compressed without destroying the membrane structure. When no longer subjected to external forces, the membrane rebounds. The graphene foam prepared using the technical solution provided in this application not only has good in-plane and out-of-plane thermal conductivity, but also has good compression rebound properties. It can be applied to technical fields that require heat conduction, cushioning and shock absorption, and caulking.

[0048] Typically, but not limiting, the concentration of the blowing agent is 1%, 5%, 10%, 30%, 50%.

[0049] Some embodiments of the present application provide a graphene foam, which is prepared using the preparation method of graphene oxide foam provided in the present application.

[0050] Some embodiments and comparative examples are described in detail below.

[0051] The test methods involved in this application are as follows: The out-of-plane (longitudinal) thermal conductivity test method involves cutting samples into 12.7mm diameter discs, measuring and recording their thickness, placing them in a 4-sample round / 12.7mm holder, and testing them in a NETZSCH 467 instrument. The test environment temperature was set at 25-27°C, the temperature threshold (tolerance / stability threshold) was 0.3K, the number of flash points was 5, the voltage was 260V, the pulse width was 44μs, the main gain was adjusted to 6633, the sampling time was adjusted to 6ms, the detection area was 3.7mm, and parameter optimization was enabled. After testing, the average longitudinal thermal conductivity of each sample group was recorded. Thermal conductivity = thermal diffusivity × density × specific heat capacity; where density = mass / volume, and the specific heat capacity is taken as 0.85. Example 1

[0052] S1. Weigh a certain mass of graphene oxide cake (solid content of 50.94%, oxygen content of 36.77%), use water as solvent, add ammonia water, adjust the pH of the solution to 6, prepare a second graphene oxide slurry with a solid content of 5% and a viscosity of 15000cp, and coat the second graphene oxide slurry on a PP substrate to form a graphene oxide film, and let it dry; S2. Use a needle tip puncher to punch holes in the graphene oxide film with a hole size of 0.5 mm.

[0053] S3. Providing an upper mold and a lower mold, wherein each of the upper mold and the lower mold has a recessed portion and a raised portion, wherein the recessed portion of the upper mold corresponds to the raised portion of the lower mold in position to form a complementary meshing structure; S4, wetting the porous graphene oxide membrane obtained after punching and placing it between the upper mold and the lower mold; S5, closing the upper mold and the lower mold, and plastically deforming the graphene oxide film or the porous graphene oxide film through the complementary meshing structure of the upper mold and the lower mold to form a surface structure with an undulating morphology; S6. Immerse the porous graphene oxide membrane having an undulating surface structure obtained in step S5 with a first graphene oxide slurry, apply the first graphene oxide slurry evenly, and dry the entire membrane. In this embodiment, the first graphene oxide slurry is the same as the second graphene oxide slurry. S7. The entire dried film material is pretreated at 320° C., carbonized at 1300° C., and graphitized at 3000° C., and then rolled using a flat press to obtain a target graphene thermal conductive film.

[0054] The preparation process diagram of steps S2 to S6 in this embodiment is as follows Figure 4 shown.

[0055] It is worth mentioning that in the present embodiment, the first graphene oxide slurry is the same as the second graphene oxide slurry; in other embodiments, different graphene oxide cakes can be used to separately configure a first graphene oxide slurry with a solid content of 3% to 8%; in the present embodiment, a needle tip puncher is used to mechanically punch the porous graphene membrane, and in other embodiments, laser pulse punching can be used; in the present application, the punching aperture is 0.5 mm, and in other embodiments, the aperture size can be 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, or 1.0 mm; in the present embodiment, the maximum pretreatment temperature is 320°C, the maximum carbonization temperature is 1300°C, and the maximum graphitization temperature is 3000°C. In other embodiments, the maximum pretreatment temperature can be 240°C or 360°C, the maximum carbonization temperature can be 900°C or 1400°C, and the maximum graphitization temperature can be 2800°C or 3150°C.

[0056] The graphene thermal conductive film obtained in step S7 was tested for longitudinal thermal conductivity, and the test showed that the thermal conductivity thereof was 9.6 W / (m·K). Example 2

[0057] This embodiment differs from Example 1 in that, in step S1, the graphene oxide membrane is prepared by a filtration method, specifically: a certain mass of graphene oxide cake (solid content of 50.94%, oxygen content of 36.77%) is weighed, water is used as a solvent, ammonia water is added, the pH of the solution is adjusted to 6, a second graphene oxide slurry with a solid content of 0.5% and a viscosity of 450cp is prepared, and the second graphene oxide slurry is poured into a Buchner funnel and filtered under a vacuum of 0.1 MPa, and dried at room temperature to obtain the graphene oxide membrane.

[0058] The other steps in this embodiment are consistent with those in Example 1.

[0059] The longitudinal thermal conductivity coefficient of the graphene thermal conductive film obtained in this embodiment was tested, and the test showed that the thermal conductivity coefficient was 8.9 W / (m·K). Example 3

[0060] This embodiment differs from embodiment 1 in that it further includes a chemical reduction foaming step to prepare graphene foam, and the specific steps are as follows: S1. Weigh a certain mass of graphene oxide cake (solid content of 50.94%, oxygen content of 36.77%), use water as solvent, add ammonia water, adjust the pH of the solution to 6, prepare a second graphene oxide slurry with a solid content of 5% and a viscosity of 15000cp, and coat the second graphene oxide slurry on a PP substrate to form a graphene oxide film; S2. Use a needle tip puncher to punch holes in the graphene oxide film with a hole size of 0.5 mm.

[0061] S3. Providing an upper mold and a lower mold, wherein each of the upper mold and the lower mold has a recessed portion and a raised portion, wherein the recessed portion of the upper mold corresponds to the raised portion of the lower mold in position to form a complementary meshing structure; S4, placing the porous graphene oxide membrane obtained after punching between the upper mold and the lower mold; S5, closing the upper mold and the lower mold, and plastically deforming the graphene oxide film or the porous graphene oxide film through the complementary meshing structure of the upper mold and the lower mold to form a surface structure with an undulating morphology; S6. Immerse the porous graphene oxide membrane having an undulating surface structure obtained in step S5 with a first graphene oxide slurry, apply the first graphene oxide slurry evenly, and dry the entire membrane. In this embodiment, the first graphene oxide slurry is the same as the second graphene oxide slurry. S7, using a 30% hydrazine hydrate solution to soak the sample obtained in step S6 for 3S, and then drying it again; S8. The entire dried film material is pretreated at 320° C., carbonized at 1400° C., and graphitized at 3000° C. to obtain the target graphene foam.

[0062] It is worth mentioning that in this embodiment, the chemical foaming agent used is hydrazine hydrate, and in other embodiments, the chemical foaming agent may also use sodium hydrogen borate, dimethylhydrazine, and thiourea; in this embodiment, the concentration of the chemical foaming agent is 30%, and in other embodiments, its concentration may be 1%, 10%, 30%, and 50%; in this embodiment, the graphene foam is not calendered, and in other embodiments, the graphene foam may be calendered to obtain the target thickness.

[0063] The graphene foam obtained in step S8 was tested for longitudinal thermal conductivity, and the test showed that the thermal conductivity was 8.3 W / (m·K). Example 4

[0064] This embodiment differs from the first embodiment in that another method is used to form a surface structure with an undulating morphology on the surface of the graphene oxide film, which is specifically: S1. Weigh a certain mass of graphene oxide cake (solid content of 50.94%, oxygen content of 36.77%), use water as solvent, add ammonia water, adjust the pH of the solution to 6, and prepare a second graphene oxide slurry with a solid content of 5% and a viscosity of 15000cp; S2, providing silicone rubber in a stretched state; S3, coating a second graphene oxide slurry on the provided elastic substrate to form a graphene oxide film on the elastic substrate; S4. Shrinking the elastic substrate to obtain a graphene oxide film having an undulating surface structure.

[0065] The preparation process diagram of steps S2 to S4 in this embodiment is as follows Figure 5 shown.

[0066] S5, using a needle tip puncher to punch holes in the graphene oxide film with an undulating surface structure, with a hole size of 0.5 mm; S6. Immerse the porous graphene oxide membrane having an undulating surface structure obtained in step S5 with a first graphene oxide slurry, apply the first graphene oxide slurry evenly, and dry the entire membrane. In this embodiment, the first graphene oxide slurry is the same as the second graphene oxide slurry. S7. The dried film material is pretreated at 320° C., carbonized at 1400° C., and graphitized at 3000° C. to obtain a target graphene thermal conductive film.

[0067] The graphene thermal conductive film obtained in step S7 was tested for longitudinal thermal conductivity, and the test showed that the thermal conductivity thereof was 9.3 W / (m·K). Comparative Example 1

[0068] S1. Weigh a certain mass of graphene oxide cake (solid content of 50.94%, oxygen content of 36.77%), use water as solvent, add ammonia water, adjust the pH of the solution to 6, prepare a first graphene oxide slurry with a solid content of 5% and a viscosity of 15000 cp, and coat the first graphene oxide slurry on a PP substrate to form a graphene oxide film; S2. After drying the graphene oxide film prepared in step S1, perform a pretreatment at 320° C., a carbonization treatment at 1400° C., and a graphitization treatment at 3000° C. to obtain a graphene thermally conductive film.

[0069] The graphene thermal conductive film obtained in step S2 was tested for longitudinal thermal conductivity, and the test showed that the thermal conductivity was 4.3 W / (m·K). Comparative Example 2

[0070] S1. Weigh a certain mass of graphene oxide cake (solid content of 50.94%, oxygen content of 36.77%), use water as solvent, add ammonia water, adjust the pH of the solution to 6, prepare a second graphene oxide slurry with a solid content of 5% and a viscosity of 15000cp, and coat the second graphene oxide slurry on a PP substrate to form a graphene oxide film, and let it dry; S2, using a 30% hydrazine hydrate solution to soak the sample obtained in step S2 for 3s, and then drying it again; S3. After drying the graphene oxide film prepared in step S2, perform a pretreatment at 320° C., a carbonization treatment at 1400° C., and a graphitization treatment at 3000° C. to obtain a graphene thermally conductive film.

[0071] The graphene thermal conductive film obtained in step S3 was tested for longitudinal thermal conductivity, and the test showed that the thermal conductivity thereof was 2.5 W / (m·K).

[0072] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0073] The above description is a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and such modifications or substitutions should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A method for preparing a graphene thermally conductive film, characterized in that: The following steps are involved: A porous substrate is immersed in a first graphene oxide slurry, the first graphene oxide slurry is evenly coated and dried as a whole, and then heat-treated to prepare a graphene thermal conductive film. The porous substrate is a porous graphene oxide film, and the porous graphene oxide film has a surface structure with an undulating morphology.

2. The method for preparing the graphene thermally conductive film according to claim 1, wherein: The porous graphene oxide membrane is prepared by punching the graphene oxide membrane, the punching method is mechanical punching or laser punching, and the pore size is 0.5-1.0 mm.

3. The method for preparing the graphene thermally conductive film according to claim 2, wherein: The graphene oxide film is obtained by coating or filtering the second graphene oxide slurry.

4. The method for preparing the graphene thermally conductive film according to claim 3, wherein: The following steps are also included: S1. Providing an upper mold and a lower mold, wherein each of the upper mold and the lower mold has a recessed portion and a raised portion, wherein the recessed portion of the upper mold corresponds to the raised portion of the lower mold in position to form a complementary meshing structure; S2, placing the graphene oxide film or the porous graphene oxide film between the upper mold and the lower mold; S3. The upper mold and the lower mold are closed, and the graphene oxide film or the porous graphene oxide film is plastically deformed by the complementary meshing structure of the upper mold and the lower mold to form a surface structure with an undulating morphology.

5. The method for preparing the graphene thermally conductive film according to claim 3, wherein: The following steps are also included: S1. providing an elastic matrix in a stretched state; S2, coating a second graphene oxide slurry on the elastic substrate to form a graphene oxide film on the elastic substrate; S3. Shrinking the elastic matrix to obtain a graphene oxide film having an undulating surface structure.

6. The method for preparing the graphene thermally conductive film according to claim 1, wherein: The heat treatment includes pretreatment, carbonization treatment and graphitization treatment; The maximum temperature of the pretreatment is 240-360°C; The maximum temperature of the carbonization treatment is 900-1400°C; The maximum temperature of the graphitization treatment is 2800-3200°C.

7. The method for preparing the graphene thermally conductive film according to claim 1, wherein: After the heat treatment, a calendering step is further included.

8. A method for preparing graphene foam, comprising the preparation method according to any one of claims 1 to 7, characterized in that: After overall drying and before the heat treatment, the method further includes a chemical foaming agent infiltration step. Specifically, the chemical foaming agent includes at least one of hydrazine hydrate, sodium hydrogen borate, dimethylhydrazine, and thiourea, and the concentration of the chemical foaming agent is 0.5-50%.

9. A graphene thermally conductive film, characterized in that: It is prepared using the preparation method according to any one of claims 1 to 7.

10. A graphene foam, characterized in that: It is prepared using the preparation method described in claim 8.

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