Graphene heat-conducting film and preparation method thereof

Abstract

The invention provides a preparation method of a graphene heat-conducting film, which comprises the following steps: preparing a graphene oxide dilute solution, slowly dripping the graphene oxide dilute solution into flowing water, forming a graphene oxide film on the surface of the water, fishing out the graphene oxide film, and carrying out pretreatment, carbonization, graphitization and calendering to obtain the graphene heat-conducting film. The generation of wrinkling, winding and folding states of the graphene oxide film in the assembly process is reduced by utilizing the effect of surface tension of water, and directional assembly of the graphene oxide film and the graphene oxide film can be promoted by controlling the flow direction and the flow speed of water, so that the heat-conducting property of the graphene heat-conducting film is improved.

Description

Technical Field

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

[0002] Graphene is currently the material with the highest theoretical thermal conductivity. Its outstanding intrinsic thermal conductivity (thermal conductivity 3500~5300W / mK) is much higher than traditional heat dissipation materials such as silver, copper, and graphite. This has attracted great attention in the field of thermal management applications. The graphene thermal conductive film prepared by the redox method is the object of research and development by major market players.

[0003] In the process of preparing graphene thermal conductive film by redox method, the self-assembly degree of graphene oxide is one of the key factors affecting the thermal conductivity of graphene thermal conductive film. Graphene oxide usually takes three forms in the slurry: flat, wrinkled, entangled, and folded. However, the latter three forms are not conducive to the macroscopic self-assembly of graphene oxide film because they are easy to form microcapsule structures and void structures. The larger the particle size of graphene oxide, the easier it is to cause the formation of these three forms.

[0004] When preparing graphene thermal conductive film by redox method, fully homogenizing the graphene oxide slurry to reduce the solute particle size is one of the methods to reduce wrinkles, entanglements and folding morphologies, but this process often takes longer time. Summary of the invention

[0005] Based on the above reasons, the first aspect of the present invention provides a method for preparing a graphene thermally conductive film, which comprises the following steps: A graphene oxide dilute solution is prepared and slowly dripped into flowing water to form a graphene oxide film on the surface of the water. The graphene oxide film is scooped up and then pretreated, carbonized, graphitized, and rolled to obtain a graphene thermal conductive film.

[0006] Graphene oxide will show a size effect in water (due to the amphiphilic properties of graphene oxide and water, when the diameter of graphene oxide is too small, it will sink into the water; when the size is large, it can float on the surface of the water). Relying on the surface tension of water and the driving force brought by the flow of water, graphene oxide with a larger diameter can be spread out, thereby reducing the wrinkles, entanglements, and folding of graphene oxide. At the same time, the driving force brought by the flow of water can make these large-sized graphene oxides assemble into a film in the same direction, thereby forming a highly ordered graphene oxide original film.

[0007] In some embodiments of the first aspect of the present application, the D50 flake diameter of the graphene oxide dilute solution is in the range of 5 to 100 μm; preferably, the D50 flake diameter of the graphene oxide dilute solution is in the range of 10 to 75 μm. Typically but not limiting, the D50 flake diameter of the graphene oxide dilute solution is 10 μm, 13.276 μm, 20 μm, 24.101 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 72.409 μm, 80 μm, 83.647 μm, 90 μm, 100 μm.

[0008] If the diameter of the flake is small, the graphene oxide will sink into the water; if the diameter of the flake is too large, the force brought by the surface tension of the water and the driving force of the water flow will not be enough to spread the graphene oxide flat.

[0009] In some embodiments of the first aspect of the present application, the solid content of the graphene oxide dilute solution is 0.05-1%, preferably, the solid content of the graphene oxide dilute solution is 0.1-0.8%. Typically, but restrictively, the solid content of the graphene oxide dilute solution is 0.05%, 0.1%, 0.12%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.75%, 0.8%, 0.9%, 0.96%, 1%. If the solid content of the graphene oxide dilute solution is too low, the graphene oxide contained in the solution is too little to be assembled into a graphene oxide original film on the water surface; if the solid content is too high, the graphene oxide agglomerates in the slurry, and after being dropped into water, it is in a multi-layer stacked state on the water surface, which has little effect on improving the thermal conductivity of the graphene thermal conductive film.

[0010] In some embodiments of the first aspect of the present application, the graphene oxide dilute solution is obtained by diluting the flake graphite after intercalation oxidation. More specifically, the flake graphite is intercalated and oxidized by an improved Hummer's method and filtered to obtain the desired graphene oxide cake, and then the graphene oxide cake is fully stirred and dispersed in water to uniformly configure into the graphene oxide dilute solution, wherein the stirring and dispersing method is a combination of one or more of magnetic stirring, ultrasonic stirring and dispersing, and mechanical stirring.

[0011] In some embodiments of the first aspect of the present application, the mesh number of the flake graphite is selected to be 50-800 meshes, preferably, the mesh number of the flake graphite is 100-500 meshes. After intercalation oxidation of flake graphite, graphene oxide is obtained, and the mesh number of flake graphite plays a decisive role in the D50 sheet diameter of the dilute graphene oxide solution. If the mesh number is too large, the diameter of the obtained graphene oxide sheet is too small and it will sink in the water; if the mesh number is too small, the diameter of the obtained graphene oxide sheet is too large, and the force brought by the surface tension of water and the driving force of the water flow is not enough to lay the graphene oxide flat.

[0012] In some embodiments of the first aspect of the present application, the graphene oxide dilute solution is dripped into flowing water, and the flow rate of the water is 0.1-1 cm / s. Typically but not limiting, the flow rate of the water is 0.1 cm / s, 0.2 cm / s, 0.3 cm / s, 0.4 cm / s, 0.5 cm / s, 0.6 cm / s, 0.7 cm / s, 0.8 cm / s, 0.9 cm / s, 1 cm / s.

[0013] The control of flow rate determines the degree of influence of water flow force on the orderly assembly of graphene oxide. That is, when the water flow rate is too slow, graphene oxide cannot be highly arranged along the flow direction, and large-sized graphene oxide may not be completely spread on the water surface. In other words, the wrinkle problem caused by the inability to be completely spread will cause the wrinkles of this film material to be unable to be eliminated after heat treatment and calendering, increasing the obstacles to heat transfer within the surface, so that the thermal conductivity of the obtained graphene thermal conductive film is low. On the other hand, when the water flow rate is too fast, the strong water flow force impacts the graphene oxide sheets, making it impossible for them to assemble, and thus it is impossible to obtain a complete graphene oxide original film.

[0014] In some embodiments of the first aspect of the present application, the pretreatment temperature is 170~360°C, and the maximum temperature insulation time is 8~20h; the carbonization treatment temperature is 1000~1700°C, and the maximum temperature insulation time is 3~8h; the graphitization treatment temperature is 2500~3200°C, and the maximum temperature insulation time is 1~3h.

[0015] In some embodiments of the first aspect of the present application, in the calendering step, the pressure is 100-300 MPa, and the holding time is 30-200 min, wherein the calendering method can be one of plate pressing and roller pressing or a combination of the two. Typically but not limiting, the pressure can be set to 100 MPa, 180 MPa, 200 MPa, 260 MPa, 300 MPa; the holding time can be set to 30 min, 60 min, 90 min, 120 min, 180 min, 200 min, 240 min, 280 min, 300 min.

[0016] In some embodiments of the first aspect of the present application, the film material to be treated needs to be pressurized during the pretreatment, carbonization and graphitization processes. Specifically, during the heat treatment of the graphene oxide film on the film material to be treated, a large amount of gas is released due to the removal of functional groups, causing the film material to undergo a drastic volume expansion. In the absence of pressurization, the film material will expand several times in the height direction, and the expansion coefficient is uncontrollable, resulting in uncontrollable thickness of the final finished graphene thermal conductive film.

[0017] As a second aspect of the present application, a graphene thermally conductive film is provided. The graphene thermally conductive film is prepared by the method described in the first aspect of the present application.

[0018] The beneficial effects of this application are: By slowly dripping a low-concentration graphene oxide slurry into water at a certain flow rate, the effect of water surface tension can be used to reduce the formation of wrinkles, entanglements, and folding of the graphene oxide film during the assembly process. The direction and flow rate of water can also be controlled to promote their directional assembly.

[0019] The solvent used for the directed assembly in the present application is water, which is common and readily available in daily life, environmentally friendly, and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0021] Figure 1 This is a test chart of the particle size results of the graphene oxide dilute solution provided in Example 1; Figure 2 The morphology of the graphene oxide provided in Example 1 on the water surface; Figure 3 This is the morphology of graphene oxide in the slurry provided in Comparative Example 5. DETAILED DESCRIPTION

[0022] The following detailed description of exemplary embodiments of the present invention refers to the accompanying drawings, which form a part of the description, in which exemplary embodiments of the present invention are shown as examples, wherein the features of the present invention are identified by reference numerals. The following more detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but is merely for illustration and does not limit the description of the features and characteristics of the present invention, in order to propose the best way to perform the present invention, and is sufficient to enable those skilled in the art to implement the present invention. However, it should be understood that various modifications and variations may be made without departing from the scope of the present invention as defined by the appended claims. The detailed description and the accompanying drawings should be considered only as illustrative, not restrictive, and if there are any such modifications and variations, they will all fall within the scope of the present invention described herein. In addition, the background technology is intended to illustrate the current status and significance of the research and development of the present technology, and is not intended to limit the present invention or the application field of the present application and the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which the present invention belongs; the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the term "and / or" used herein includes any and all combinations of one or more related listed items.

[0024] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0025] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments. Example 1

[0026] S1. Select 325 mesh flake graphite, oxidize and intercalate with concentrated sulfuric acid and potassium permanganate, then wash and filter to prepare graphene oxide cake, and fully disperse it into a 0.50% graphene oxide dilute solution by mechanical stirring. The laser particle size analyzer test results are as follows: Figure 1 As shown, its D50 sheet diameter is 24.101 μm; S2. Pipette 100 mL of the solution and slowly drip it into pure water with a flow rate of 0.1 cm / s. The morphology of graphene oxide nanosheets on the water surface is as follows: Figure 2 As shown, the graphene oxide nanosheets gradually assemble on the water surface in a directional manner along the flow direction to form a graphene oxide film, which is slowly scooped out of the water with a PET film and placed under a UV lamp for baking and drying to obtain the original film; S3, placing the original film in a common drying oven at 240°C for 20 hours for preliminary deoxidation and impurity removal; then, treating it in a carbonization furnace with a maximum temperature of 1700°C for 3 hours and in a graphitization furnace with a maximum temperature of 3000°C for 1 hour, and finally obtaining a low-expansion graphene pre-pressed film, wherein during the pretreatment, carbonization and graphitization processes, the film to be treated at each stage is subjected to a load of 30Kg, 25Kg and 10Kg respectively; S4, place the pre-pressed film in a vacuum plate press, and set the vacuum degree in the calendering chamber to 1*10 -3 Pa, apply a pressure of 180 MPa and maintain the pressure for 90 min to obtain a graphene thermal conductive film.

[0027] The thickness of the tested graphene thermal conductive film is 20μm and the density is 2.218g / cm 3 The thermal conductivity tested by NETZSCH 467 thermal conductivity meter is 1780.6 W / m·K. Example 2

[0028] S1. Select 150 mesh flake graphite, perform oxidation intercalation with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and filter pressing. Then, disperse it into a 0.75% graphene oxide dilute solution by mechanical stirring, and its D50 flake diameter is 72.409 μm; S2, 100 mL of the solution was slowly dripped into pure water with a flow rate of 1 cm / s, and the graphene oxide nanosheets were gradually assembled on the water surface in a directional manner along the flow direction to form a layer of graphene oxide film, which was slowly picked up from the water with a PET film, and placed under a UV lamp for baking and drying to obtain the original film; S3, placing the original film in a common drying oven at 300°C for 16 hours for preliminary deoxidation and impurity removal; then, treating it in a carbonization furnace with a maximum temperature of 1300°C for 2 hours and in a graphitization furnace with a maximum temperature of 3000°C for 2 hours, and finally obtaining a low-expansion graphene pre-pressed film, wherein during the pretreatment, carbonization and graphitization processes, the film to be treated at each stage is subjected to a load of 30Kg, 25Kg and 10Kg respectively; S4, place the pre-pressed film in a vacuum plate press, and set the vacuum degree in the calendering chamber to 1*10 -3 Pa, apply a pressure of 300 MPa and maintain the pressure for 30 min to obtain a graphene thermal conductive film.

[0029] The graphene thermal conductive film tested has a thickness of 25 μm and a density of 2.109 g / cm 3 The thermal conductivity tested by NETZSCH 467 thermal conductivity meter is 1764.6 W / m·K. Example 3

[0030] S1. Select 500 mesh flake graphite, perform oxidation intercalation with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and filter pressing, and fully disperse it into a 0.12% graphene oxide dilute solution by mechanical stirring, and its D50 flake diameter is 13.276 μm; S2, 100 mL of the solution was slowly dripped into pure water with a flow rate of 0.3 cm / s, and the graphene oxide nanosheets were gradually assembled on the water surface in a directional manner along the flow direction to form a layer of graphene oxide film, which was slowly picked up from the water with a PET film, and placed under a UV lamp for baking and drying to obtain the original film; S3, placing the original film in a common drying oven at 170°C for 20 hours for preliminary deoxidation and impurity removal; then, treating it in a carbonization furnace with a maximum temperature of 1000°C for 6 hours and in a graphitization furnace with a maximum temperature of 2800°C for 2 hours, and finally obtaining a low-expansion graphene pre-pressed film, wherein during the pretreatment, carbonization and graphitization processes, the film to be treated at each stage is subjected to a load of 30Kg, 25Kg and 10Kg respectively; S4, place the pre-pressed film in a vacuum plate press, and set the vacuum degree in the calendering chamber to 1*10 -3 Pa, apply a pressure of 100 MPa and maintain the pressure for 180 min to obtain a graphene thermal conductive film.

[0031] The thickness of the tested graphene thermal conductive film is 15μm and the density is 2.156g / cm 3 The thermal conductivity tested by NETZSCH 467 thermal conductivity meter is 1758.3 W / m·K. Example 4

[0032] S1. Select 100 mesh flake graphite, oxidize and intercalate with concentrated sulfuric acid and potassium permanganate, then wash and filter to prepare graphene oxide cake, and fully disperse it into a 0.76% graphene oxide dilute solution by mechanical stirring, and its D50 flake diameter is 83.647 μm; S2, 100 mL of the solution was slowly dripped into pure water with a flow rate of 1 cm / s, and the graphene oxide nanosheets were gradually assembled on the water surface in a directional manner along the flow direction to form a layer of graphene oxide film, which was slowly picked up from the water with a PET film, and placed under a UV lamp for baking and drying to obtain the original film; S3, placing the original film in a common drying oven at 360°C for 16 hours for preliminary deoxidation and impurity removal; then, treating it in a carbonization furnace with a maximum temperature of 1200°C for 6 hours and in a graphitization furnace with a maximum temperature of 3000°C for 1 hour, and finally obtaining a low-expansion graphene pre-pressed film, wherein during the pretreatment, carbonization and graphitization processes, the film to be treated at each stage is subjected to a load of 30Kg, 25Kg and 10Kg respectively; S4, place the pre-pressed film in a vacuum plate press, and set the vacuum degree in the calendering chamber to 1*10 -3 Pa, apply a pressure of 300 MPa and maintain the pressure for 45 min to obtain a graphene thermal conductive film.

[0033] The thickness of the tested graphene thermal conductive film is 30μm and the density is 2.067g / cm 3 The thermal conductivity tested by NETZSCH 467 thermal conductivity meter is 1706.6 W / m·K. Comparative Example 1

[0034] S1. Select 1000 mesh flake graphite, perform oxidation intercalation with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and filter pressing, and fully disperse it into a 0.50% graphene oxide dilute solution by mechanical stirring, and its D50 flake diameter is 3.213 μm; S2. 100 mL of the solution was slowly dripped into pure water at a flow rate of 0.1 cm / s. Since the diameter of the graphene oxide sheets in the dilute graphene oxide solution was too small, most of them sank into the water and could not self-assemble into the original film on the water surface. Comparative Example 2

[0035] S1. Select 30 mesh flake graphite, perform oxidation intercalation with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and filter pressing. Then, disperse it into a 0.9% graphene oxide dilute solution by mechanical stirring, and the D50 flake diameter is 120.386 μm. S2-S4: are the same as steps S2-S4 in Example 1.

[0036] The graphene thermal conductive film was obtained, with a test thickness of 35 μm and a density of 2.206 g / cm 3 The thermal conductivity tested by NETZSCH 467 thermal conductivity meter is 1207.5 W / m·K.

[0037] Since the diameter of the graphene oxide sheet is too large, the force brought by the surface tension of water and the driving force of the water flow is not enough to spread the graphene oxide flat, and the graphene film on the water surface is still mostly wrinkled, entangled, or folded, and its thermal conductivity is much lower than that of Example 1. Comparative Example 3

[0038] The difference between this comparative example and Example 1 is that in step S2, flowing water is not used, and the remaining steps are the same as those in Example 1.

[0039] The graphene thermal conductive film was obtained. The test showed that the thickness of the graphene thermal conductive film was 26 μm and the density was 2.137 g / cm 3 , the thermal conductivity is 1392.8W / m·K.

[0040] Since graphene oxide cannot be highly arranged along the flow direction, large-sized graphene oxide may not be completely spread out on the water surface. In other words, the wrinkle problem caused by the inability to spread out completely will make it impossible to eliminate the wrinkles of this film material after heat treatment and calendering, increasing the obstacles to in-plane heat transfer, resulting in low thermal conductivity of the obtained graphene thermal conductive film. Comparative Example 4

[0041] S1. Select 325 mesh flake graphite, perform oxidation intercalation with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and filter pressing. Then, disperse it into a 0.50% graphene oxide dilute solution by mechanical stirring, and its D50 flake diameter is 25.104 μm; S2. 100 mL of the solution is slowly dripped into pure water at a flow rate of 2 cm / s. Since the water flow rate is too fast, the strong water flow force impacts the graphene oxide sheets, making it impossible for them to assemble, and thus it is impossible to obtain a complete graphene oxide original film. Comparative Example 5

[0042] S1. Select 325 mesh flake graphite, perform oxidation intercalation with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and filter pressing. Add the graphene oxide cake into a disperser for dispersion, and then obtain a slurry with a solid content of 5%. The morphology of the graphene oxide in the slurry is observed as follows: Figure 3 As shown; S2, homogenizing and defoaming the slurry obtained in S1, and then placing it on a coating machine for coating, placing the substrate, and the coating gap is 2-4 mm; then drying the coated graphene oxide film in an oven (50-70° C.) to obtain an original film; S3, placing the original film in a common drying oven at 240°C for 20 hours for preliminary deoxidation and impurity removal; then, treating it in a carbonization furnace with a maximum temperature of 1700°C for 3 hours and in a graphitization furnace with a maximum temperature of 3000°C for 1 hour, and finally obtaining a low-expansion graphene pre-pressed film, wherein during the pretreatment, carbonization and graphitization processes, the film to be treated at each stage is subjected to a load of 30Kg, 25Kg and 10Kg respectively; S4, place the pre-pressed film in a vacuum plate press, and set the vacuum degree in the calendering chamber to 1*10 -3 Pa, apply a pressure of 180MPa and maintain the pressure for 90min.

[0043] A graphene thermal conductive film was obtained, and the thickness of the graphene thermal conductive film was measured to be 23 μm, the density was 2.197 g / cm3, and the thermal conductivity was 1532.8 W / m·K. Comparative Example 6

[0044] The difference between this comparative example and Example 1 is that in step S3, no weight is applied to the film material to be processed.

[0045] The thermal expansion of the graphene oxide film during the heat treatment process cannot be restricted, and the thickness of the sintered graphene film is uneven.

[0046] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0047] The above is a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing a graphene thermally conductive film, characterized in that: The following steps are involved: A graphene oxide dilute solution is prepared and slowly dripped into flowing water to form a graphene oxide film on the surface of the water. The graphene oxide film is scooped up and then pretreated, carbonized, graphitized, and rolled to obtain a graphene thermal conductive film.

2. A method for preparing the graphene thermally conductive film according to claim 1, characterized in that: The D50 flake diameter of the graphene oxide dilute solution is in the range of 5 to 100 μm; preferably, the D50 flake diameter of the graphene oxide dilute solution is in the range of 10 to 75 μm.

3. A method for preparing the graphene thermal conductive film according to claim 1, characterized in that: The solid content of the graphene oxide dilute solution is 0.05-1%; preferably, the solid content of the graphene oxide dilute solution is 0.1-0.8%.

4. A method for preparing the graphene thermally conductive film according to claim 1, characterized in that: The solute of the graphene oxide dilute solution is obtained by diluting flake graphite after intercalation oxidation.

5. A method for preparing a graphene thermally conductive film as claimed in claim 4, characterized in that: The mesh number of the flake graphite is 50-800 meshes, and preferably, the mesh number of the flake graphite is 100-500 meshes.

6. A method for preparing the graphene thermal conductive film according to claim 1, characterized in that: The graphene oxide dilute solution is slowly dripped into flowing water, and the flow rate of the water is 0.1-1 cm / s.

7. A method for preparing the graphene thermally conductive film according to claim 1, characterized in that: The pretreatment temperature is 170-360°C, and the maximum temperature insulation time is 8-20h; the carbonization treatment temperature is 1000-1700°C, and the maximum temperature insulation time is 3-8h; the graphitization treatment temperature is 2800-3200°C, and the maximum temperature insulation time is 1-3h.

8. A method for preparing the graphene thermally conductive film according to claim 1, characterized in that: In the calendering step, the pressure is 100-300 MPa and the holding time is 30-200 min.

9. A method for preparing a graphene thermally conductive film according to claim 1, characterized in that: The membrane material to be treated is pressurized during the pretreatment, carbonization treatment and graphitization treatment.

10. A graphene thermally conductive film prepared by the preparation method according to any one of claims 1 to 9.

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