Graphene heat-conducting film and preparation method thereof

Abstract

The application provides a preparation method of a graphene heat-conducting film, which comprises the following steps: preparing an oxidized graphene dilute solution, slowly dropping the oxidized graphene dilute solution into flowing water, forming an oxidized graphene film on the surface of the water, and then pre-treating, carbonizing, graphitizing and calendering the oxidized graphene film to obtain the graphene heat-conducting film. In the application, the surface tension of water is used to reduce the generation of the wrinkled, twisted and folded state of the graphene film in the assembling process, and the water flow direction and flow rate are controlled to promote the directional assembly of the graphene film, so that the heat-conducting performance of the graphene heat-conducting film is improved.

Description

Technical Field

[0001] This invention relates to the field of new materials, specifically to a graphene thermal conductive film and its preparation method. Background Technology

[0002] Graphene is currently the material with the highest theoretical thermal conductivity. Its excellent intrinsic thermal conductivity (thermal conductivity 3500~5300W / mK) is far superior to traditional heat dissipation materials such as silver, copper, and graphite. This has made it a focus of attention in the field of thermal management applications. Graphene thermal conductive films prepared by the oxidation-reduction method are the object of research and development by major market players.

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

[0004] When preparing graphene thermal conductive films using the redox method, thoroughly homogenizing the graphene oxide slurry to reduce the solute particle size is one way to reduce wrinkles, entanglements, and folds, but this process often takes longer. 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 includes the following steps:

[0006] A dilute solution of graphene oxide was prepared and slowly dripped into flowing water to form a graphene oxide film on the surface of the water. The graphene oxide film was then retrieved and pretreated, carbonized, graphitized, and calendered to obtain a graphene thermal conductive film.

[0007] Graphene oxide exhibits a size effect in water (due to its amphiphilic nature, small graphene sheets sink, while larger sheets float). Utilizing surface tension and the driving force of water flow, larger graphene sheets can be laid flat, reducing wrinkles, entanglements, and folds. Simultaneously, the water flow allows these large graphene sheets to assemble into a film along the same direction, forming a highly ordered graphene film.

[0008] In some embodiments of the first aspect of this application, the D50 sheet diameter of the graphene oxide dilute solution ranges from 5 to 100 μm; preferably, the D50 sheet diameter ranges from 10 to 75 μm. Typical, but not limiting, D50 sheet diameters of the graphene oxide dilute solution are 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, and 100 μm.

[0009] If the sheet diameter is too small, the graphene oxide will sink in water; if the sheet diameter is too large, the force generated by the surface tension of water and the driving force of water flow is insufficient to spread the graphene oxide evenly.

[0010] In some embodiments of the first aspect of this application, the solid content of the graphene oxide dilute solution is 0.05-1%, preferably 0.1-0.8%. Typically, but not limited to, 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%, or 1%. If the solid content of the graphene oxide dilute solution is too low, the amount of graphene oxide in the solution is insufficient to assemble into a graphene oxide 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 forms a multi-layered stacked state on the water surface, which has a relatively small effect on improving the thermal conductivity of the graphene thermal conductive film.

[0011] In some embodiments of the first aspect of this application, the dilute graphene oxide solution is obtained by diluting flake graphite after intercalation oxidation. More specifically, the desired graphene oxide cake is obtained by intercalation oxidation and pressure filtration of flake graphite using a modified Hummer's method. Subsequently, the graphene oxide cake is thoroughly stirred and dispersed in water to prepare a dilute graphene oxide solution. The stirring and dispersion method is one or more of magnetic stirring, ultrasonic stirring, and mechanical stirring.

[0012] In some embodiments of the first aspect of this application, the mesh size of the flake graphite is selected to be 50-800 mesh, preferably 100-500 mesh. After intercalation and oxidation, flake graphite yields graphene oxide. The mesh size of the flake graphite plays a decisive role in the D50 diameter of the dilute graphene oxide solution. If the mesh size is too large, the resulting graphene oxide flakes will be too small and sink in water; if the mesh size is too small, the resulting graphene oxide flakes will be too large, and the surface tension of water and the driving force of water flow will be insufficient to spread the graphene oxide evenly.

[0013] In some embodiments of the first aspect of this application, a dilute solution of graphene oxide is dropped into flowing water at a flow rate of 0.1 to 1 cm / s. Typically, but not limitingly, the flow rate 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, or 1 cm / s.

[0014] The control of water flow velocity determines the degree to which the force of water flow affects the ordered assembly of graphene oxide. When the water flow velocity is too slow, the graphene oxide cannot align itself vertically along the flow direction. Furthermore, large-sized graphene oxide sheets may not be able to completely spread on the water surface. In other words, the resulting wrinkles cannot be eliminated after heat treatment and calendering, increasing the obstruction of in-plane heat transfer and thus resulting in a graphene thermally conductive film with low thermal conductivity. On the other hand, when the water flow velocity is too fast, the strong force of the water flow impacts the graphene oxide sheets, preventing them from assembling and thus preventing the formation of a complete graphene oxide film.

[0015] In some embodiments of the first aspect of this application, the pretreatment temperature is 170~360℃, and the maximum temperature holding time is 8~20h; the carbonization treatment temperature is 1000~1700℃, and the maximum temperature holding time is 3~8h; the graphitization treatment temperature is 2500~3200℃, and the maximum temperature holding time is 1~3h.

[0016] In some embodiments of the first aspect of this application, during the calendering step, the pressure is 100~300MPa, and the holding time is 30~200min. The calendering method can be sheet pressing, roll pressing, or a combination of both. Typically, but not limitingly, the pressure can be set to 100MPa, 180MPa, 200MPa, 260MPa, or 300MPa; the holding time can be set to 30min, 60min, 90min, 120min, 180min, 200min, 240min, 280min, or 300min.

[0017] In some embodiments of the first aspect of this application, the membrane material to be treated needs to be pressurized during the pretreatment, carbonization and graphitization processes. Specifically, during the heat treatment of the graphene oxide membrane, the removal of functional groups releases a large amount of gas, causing the membrane material to undergo a violent volume expansion. Without pressurization, the membrane material will expand several times in the height direction, and the expansion coefficient is uncontrollable, resulting in an uncontrollable thickness of the final graphene thermal conductive film.

[0018] As a second aspect of this application, a graphene thermal conductive film is provided, which is prepared by the method described in the first aspect of this application.

[0019] The beneficial effects of this application are as follows:

[0020] By slowly dripping a low concentration of graphene oxide slurry into water at a certain flow rate, the surface tension of the water can be used to reduce the formation of wrinkles, entanglements, and folds in the graphene oxide film during assembly. Furthermore, the direction and speed of the water flow can be controlled to promote directional assembly.

[0021] The solvent used in the directional assembly in this application is water, which is common, readily available, and environmentally friendly, making it suitable for industrial production. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The graph shows the particle size distribution of the dilute graphene oxide solution provided in Example 1.

[0024] Figure 2 The morphology of graphene oxide provided in Example 1 in a water meter;

[0025] Figure 3 The morphology of graphene oxide in the slurry provided in Comparative Example 5. Detailed Implementation

[0026] The following detailed description of exemplary embodiments of the invention refers to the accompanying drawings, which form part of the description, illustrating exemplary embodiments in which the invention may be practiced, wherein features of the invention are identified by reference numerals. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and not to limit the description of the features and characteristics of the invention, to suggest the best mode for carrying out the invention, and is sufficient to enable those skilled in the art to practice the invention. However, it should be understood that various modifications and variations can be made without departing from the scope of the invention as defined by the appended claims. The detailed description and drawings should be considered illustrative only and not restrictive, and any such modifications and variations will fall within the scope of the invention described herein. Furthermore, the background art is intended to illustrate the current state of research and development and significance of the technology, and is not intended to limit the invention or the application field of the invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0028] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0029] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments. Example 1

[0030] S1. 325-mesh flake graphite was selected and oxidized and intercalated with concentrated sulfuric acid and potassium permanganate. After washing and filtration, graphene oxide cake was prepared. This cake was then mechanically dispersed into a 0.50% concentration dilute graphene oxide solution. Laser particle size analyzer results are shown below. Figure 1 As shown, its D50 diameter is 24.101 μm;

[0031] S2. Slowly add 100 mL of this solution dropwise into pure water at a flow rate of 0.1 cm / s. The morphology of the graphene oxide nanosheets on the water surface is as follows: Figure 2 As shown, graphene oxide nanosheets gradually assemble on the water surface in a direction of flow velocity to form a graphene oxide film. The film is then slowly lifted out of the water using a PET film and dried under a UV lamp to obtain the original film.

[0032] S3. The original film is placed in a regular drying oven at 240℃ for 20 hours for preliminary deoxidation and impurity removal. Then, it is successively treated in a carbonization furnace at a maximum temperature of 1700℃ for 3 hours and in a graphitization furnace at a maximum temperature of 3000℃ for 1 hour. Finally, a low-expansion graphene pre-compressed film can be obtained. 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.

[0033] S4. Place the pre-compressed film inside the vacuum plate press and set the vacuum level in the calendering chamber to 1*10. -3 A pressure of 180 MPa was applied and maintained for 90 minutes to obtain a graphene thermal conductive film.

[0034] The thickness of the graphene thermally conductive film was tested to be 20 μm, and its density was 2.218 g / cm³. 3 The thermal conductivity was measured to be 1780.6 W / m·K using a Netzsch 467 thermal conductivity meter. Example 2

[0035] S1. Select 150-mesh flake graphite, perform oxidative intercalation with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and pressure filtration. Disperse it fully into a 0.75% concentration dilute graphene oxide solution by mechanical stirring, with a D50 sheet diameter of 72.409 μm.

[0036] S2. Take 100 mL of the solution and slowly drop it into pure water with a flow rate of 1 cm / s. As the graphene oxide nanosheets gradually assemble on the water surface in the direction of the flow rate, a graphene oxide film is formed. Use a PET film to slowly lift it out of the water and place it under a UV lamp to bake and dry to obtain the original film.

[0037] S3. The original film is placed in a 300℃ ordinary drying oven for 16 hours for preliminary deoxidation and impurity removal; then, it is successively treated in a carbonization furnace at a maximum temperature of 1300℃ for 2 hours and in a graphitization furnace at a maximum temperature of 3000℃ for 2 hours to finally obtain a low-expansion graphene pre-compressed film. 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.

[0038] S4. Place the pre-compressed film in the vacuum plate press and set the vacuum level in the calendering chamber to 1*10. -3 A pressure of 300 MPa was applied and maintained for 30 minutes to obtain a graphene thermal conductive film.

[0039] The thickness of the graphene thermally conductive film was measured to be 25 μm, and its density was 2.109 g / cm³. 3 The thermal conductivity was measured to be 1764.6 W / m·K using a Netzsch 467 thermal conductivity meter. Example 3

[0040] S1. Select 500-mesh flake graphite, perform oxidative intercalation with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and pressure filtration. Disperse it fully into a 0.12% concentration dilute graphene oxide solution by mechanical stirring. Its D50 sheet diameter is 13.276 μm.

[0041] S2. Take 100 mL of the solution and slowly drop it into pure water with a flow rate of 0.3 cm / s. As the graphene oxide nanosheets gradually assemble on the water surface in the direction of the flow rate, a graphene oxide film is formed. Use a PET film to slowly lift it out of the water and place it under a UV lamp to bake and dry to obtain the original film.

[0042] S3. The original film is placed in a regular drying oven at 170℃ for 20 hours for preliminary deoxidation and impurity removal. Then, it is successively treated in a carbonization furnace at a maximum temperature of 1000℃ for 6 hours and in a graphitization furnace at a maximum temperature of 2800℃ for 2 hours. Finally, a low-expansion graphene pre-compressed film can be obtained. 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.

[0043] S4. Place the pre-compressed film in the vacuum plate press and set the vacuum level in the calendering chamber to 1*10. -3 A pressure of 100 MPa was applied and maintained for 180 min to obtain a graphene thermal conductive film.

[0044] The thickness of the graphene thermally conductive film was measured to be 15 μm, and its density was 2.156 g / cm³. 3 The thermal conductivity was measured to be 1758.3 W / m·K using a Netzsch 467 thermal conductivity meter. Example 4

[0045] S1. Select 100-mesh flake graphite, oxidize and intercalate it with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and filtration. Disperse it into a 0.76% concentration dilute graphene oxide solution by mechanical stirring. Its D50 sheet diameter is 83.647 μm.

[0046] S2. Take 100 mL of the solution and slowly drop it into pure water with a flow rate of 1 cm / s. As the graphene oxide nanosheets gradually assemble on the water surface in the direction of the flow rate, a graphene oxide film is formed. Use a PET film to slowly lift it out of the water and place it under a UV lamp to bake and dry to obtain the original film.

[0047] S3. The original film is placed in a 360℃ ordinary drying oven for 16 hours for preliminary deoxidation and impurity removal; then, it is successively treated in a carbonization furnace at a maximum temperature of 1200℃ for 6 hours and in a graphitization furnace at a maximum temperature of 3000℃ for 1 hour to finally obtain a low-expansion graphene pre-compressed film. 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.

[0048] S4. Place the pre-compressed film in the vacuum plate press and set the vacuum level in the calendering chamber to 1*10. -3 A pressure of 300 MPa was applied and maintained for 45 minutes to obtain a graphene thermal conductive film.

[0049] The thickness of the graphene thermally conductive film was tested to be 30 μm, and its density was 2.067 g / cm³. 3 The thermal conductivity was measured to be 1706.6 W / m·K using a Netzsch 467 thermal conductivity meter. Comparative Example 1

[0050] S1. Select 1000-mesh flake graphite, perform oxidative intercalation with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and pressure filtration. Disperse it fully into a 0.50% concentration dilute graphene oxide solution by mechanical stirring, with a D50 sheet diameter of 3.213 μm.

[0051] S2. Take 100 mL of this solution and slowly drip it into pure water at a flow rate of 0.1 cm / s. Because the graphene oxide flakes in the dilute graphene oxide solution are too small, most of them sink into the water and cannot self-assemble into the original film on the water surface. Comparative Example 2

[0052] S1. Select 30-mesh flake graphite, oxidize and intercalate it with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and filtration. Disperse it into a 0.9% concentration dilute graphene oxide solution by mechanical stirring. Its D50 sheet diameter is 120.386μm.

[0053] S2-S4: These are the same as steps S2-S4 in Example 1.

[0054] A graphene thermally conductive film was obtained, with a tested thickness of 35 μm and a density of 2.206 g / cm³. 3 The thermal conductivity was measured to be 1207.5 W / m·K using a Netzsch 467 thermal conductivity meter.

[0055] Because the graphene oxide sheets are too large, the surface tension of water and the driving force of water flow are insufficient to spread the graphene oxide evenly. The graphene film on the water surface is still mostly wrinkled, entangled, or folded, and its thermal conductivity is far lower than that of Example 1. Comparative Example 3

[0056] The difference between this comparative example and Example 1 is that flowing water is not used in step S2, while the other steps are the same as in Example 1.

[0057] A graphene thermally conductive film was obtained, and its thickness was measured to be 26 μm with a density of 2.137 g / cm³. 3 Its thermal conductivity is 1392.8 W / m·K.

[0058] Because graphene oxide cannot be aligned in a high degree along the flow direction, large-sized graphene oxide may not be able to spread completely flat on the water surface. In other words, the wrinkles caused by the inability to spread completely flat will not be eliminated after heat treatment and calendering, which increases the obstruction of in-plane heat transfer, resulting in low thermal conductivity of the obtained graphene thermal conductive film. Comparative Example 4

[0059] S1. Select 325 mesh flake graphite, perform oxidative intercalation with concentrated sulfuric acid and potassium permanganate, and then prepare graphene oxide cake by washing and pressure filtration. Disperse it fully into a 0.50% concentration dilute graphene oxide solution by mechanical stirring. Its D50 sheet diameter is 25.104 μm.

[0060] S2. Take 100 mL of this solution and slowly drop it into pure water with a flow rate of 2 cm / s. Due to the excessively fast flow rate of the water, the strong force of the water flow impacts the graphene oxide sheets, causing them to be unable to assemble, thus making it impossible to obtain a complete graphene oxide film. Comparative Example 5

[0061] S1. 325-mesh flake graphite was selected and oxidized and intercalated with concentrated sulfuric acid and potassium permanganate. After washing and filtration, graphene oxide cake was prepared. The graphene oxide cake was then dispersed in a disperser to obtain a slurry with a solid content of 5%. The morphology of the graphene oxide in the slurry was observed as follows: Figure 3 As shown;

[0062] S2. Homogenize and defoam the slurry obtained in S1, then place it on a coating machine for coating, with the substrate positioned properly and the coating gap being 2-4 mm; then dry the coated graphene oxide film in an oven (50-70℃) to obtain the original film.

[0063] S3. The original film is placed in a regular drying oven at 240℃ for 20 hours for preliminary deoxidation and impurity removal. Then, it is successively treated in a carbonization furnace at a maximum temperature of 1700℃ for 3 hours and in a graphitization furnace at a maximum temperature of 3000℃ for 1 hour. Finally, a low-expansion graphene pre-compressed film can be obtained. 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.

[0064] S4. Place the pre-compressed film in the vacuum plate press and set the vacuum level in the calendering chamber to 1*10. -3 Apply a pressure of 180 MPa and maintain the pressure for 90 minutes.

[0065] A graphene thermally conductive film was obtained, and its thickness was measured to be 23 μm, its density to be 2.197 g / cm3, and its thermal conductivity to be 1532.8 W / m·K. Comparative Example 6

[0066] The difference between this comparative example and Example 1 is that, in step S3, the membrane material to be treated was not subjected to a load.

[0067] The thermal expansion of graphene oxide films during heat treatment is not limited, resulting in uneven thickness of the sintered graphene films.

[0068] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0069] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention 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 the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a graphene thermally conductive film, characterized in that, Includes the following steps: A dilute solution of graphene oxide with a D50 sheet diameter range of 5~100μm and a solid content of 0.05~1% was prepared. The dilute solution of graphene oxide was then slowly dripped into flowing water at a flow rate of 0.1~1cm / s to form a graphene oxide film on the surface of the water. After the graphene oxide film was retrieved, it was pretreated, carbonized, graphitized, and calendered to obtain a graphene thermal conductive film.

2. A method for preparing a graphene thermally conductive film as described in claim 1, characterized in that, The D50 sheet size range of the dilute graphene oxide solution is 10~75μm.

3. A method for preparing a graphene thermally conductive film as described in claim 1, characterized in that, The solid content of the graphene oxide dilute solution is 0.1~0.8%.

4. A method for preparing a graphene thermally conductive film as described in claim 1, characterized in that, The solute in 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 described in claim 4, characterized in that, The mesh size of the flake graphite is 50-800 mesh.

6. A method for preparing a graphene thermally conductive film as described in claim 5, characterized in that, The mesh size of the flake graphite is 100-500 mesh.

7. A method for preparing a graphene thermally conductive film as described in claim 1, characterized in that, The pretreatment temperature is 170~360℃, and the maximum temperature holding time is 8~20h; the carbonization treatment temperature is 1000~1700℃, and the maximum temperature holding time is 3~8h; the graphitization treatment temperature is 2800~3200℃, and the maximum temperature holding time is 1~3h.

8. A method for preparing a graphene thermally conductive film as described in claim 1, characterized in that, In the calendering step, the pressure is 100~300MPa and the holding time is 30~200min.

9. A method for preparing a graphene thermally conductive film as described in claim 1, characterized in that, During the pretreatment, carbonization, and graphitization processes, the membrane material to be treated is pressurized by applying a load.

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