Highly oriented graphene heat conducting film and method of making same

Abstract

The application provides a highly-oriented graphene heat-conducting film and a preparation method thereof, and belongs to the field of graphene materials. The method comprises the following steps: in the process of drying, an elastic base material coated with graphene oxide slurry is gradually stretched along the length direction of the elastic base material, drying treatment is performed in a stretched state, carbonization and graphitization treatment are performed after the elastic base material is separated, a graphene foam film is obtained, and the graphene foam film is subjected to calendering treatment to obtain the graphene heat-conducting film. The application is characterized in that the graphene oxide film is stretched during the drying process. At this time, the graphene oxide can still be moved in a small range in the solvent, the graphene oxide sheet can be unfolded by external force when being crumpled, the graphene oxide sheet is fixed after the drying is completed, and horizontal high-oriented graphene is obtained after carbonization and graphitization treatment. The method is simple, efficient and convenient for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of graphene materials, and particularly relates to a highly oriented graphene thermally conductive film and its preparation method. Background Technology

[0002] Graphene thermal conductive films, characterized by high horizontal thermal conductivity and good mechanical properties, are widely used in electronic products. With the increasing prevalence of 5G, devices operate at higher speeds, generating more heat, necessitating heat dissipation products with even better thermal conductivity and heat dissipation performance. Graphene thermal conductive films possess the potential for high thermal conductivity; however, currently conventionally prepared graphene thermal conductive films suffer from insufficient internal graphene orientation, resulting in relatively low thermal conductivity. Further improving high thermal performance is a pressing issue that needs to be addressed for graphene thermal conductive films.

[0003] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0004] To address the technical problems of poor orientation and poor horizontal thermal conductivity of graphene materials in existing technologies, a highly oriented graphene thermally conductive film and its preparation method are provided.

[0005] The first aspect of this invention provides a method for preparing a highly oriented graphene thermal conductive film, wherein the highly flexible graphene thermal conductive film is used for heat dissipation in 3C electronic products, comprising: gradually stretching an elastic substrate coated with graphene oxide slurry along the length direction of the elastic substrate during the drying process, performing a drying treatment while maintaining the stretch, separating it from the elastic substrate and then performing carbonization and graphitization treatment to obtain a graphene foam film, and performing a calendering treatment on the graphene foam film to obtain the graphene thermal conductive film.

[0006] In some embodiments, the method for preparing the graphene oxide slurry includes: dispersing graphene oxide at high speed in a solvent, and obtaining the graphene oxide slurry after filtration and defoaming treatment.

[0007] In some embodiments, the solvent is selected from one or more of water, DMF, NMP, ethanol, and isopropanol.

[0008] In some embodiments, the solid content of the graphene slurry is 1%-10%; preferably, the solid content of the graphene slurry is 3%-8%.

[0009] If the solid content is higher than 8%, the horizontal thermal conductivity will be worse under the same thickness and density, because the graphene sheets are more densely arranged in a unit volume after the solid content is higher, and it is difficult to stretch them out after stretching. If the solid content is lower than 3%, it is more difficult to coat to the same thickness, and the drying time is longer, which reduces production efficiency.

[0010] In some embodiments, the substrate is selected from one of PU film, silicone film, and rubber film;

[0011] And / or, the coating thickness is 2000-10000 μm.

[0012] In some embodiments, the stretching displacement speed is 0.01-0.1 mm / min, the stretching behavior is sufficient to produce an orientation effect, and the stretching displacement time is 1-60 seconds.

[0013] In some embodiments, the drying temperature is 20-80°C, and the drying time is not required, as long as the product is completely dried, preferably 1-24 hours.

[0014] In some embodiments, the carbonization temperature is 1000-2000℃, the holding time is 1-2h, and the carbonization heating rate is 1-5℃ / min.

[0015] In some embodiments, the graphitization temperature is 2000-3200℃, the holding time is 4-20h, and the heating rate is 0.5-1℃ / min.

[0016] In some embodiments, the calendering pressure is 10-200 MPa, preferably 100-200 MPa, and more preferably 200 MPa.

[0017] In some embodiments, a method for preparing a highly oriented graphene thermally conductive film includes:

[0018] 1) Preparation of graphene oxide slurry: Graphene oxide is formulated into a slurry with a solid content of 1-10%, and the solvent is one or more of the following: water, DMF, NMP, ethanol, and isopropanol. The slurry is then subjected to high-speed dispersion, filtration, and defoaming treatment to obtain a uniform graphene oxide slurry. The preferred solid content of the graphene oxide slurry is 3-8%.

[0019] 2) The above-mentioned graphene oxide slurry is coated onto a substrate using a doctor blade. The substrate is elastic, such as a PU film, silicone film, or rubber film. The coating thickness is 2000-10000 μm. The substrate is then dried. During the drying process, the substrate is gradually stretched at a displacement speed of 0.01-0.1 mm / min for 1-60 seconds. After drying, the solvent evaporates completely. Due to the poor compatibility between graphene oxide and the substrate, the graphene oxide film separates well from the substrate, resulting in a dried graphene oxide film.

[0020] The drying process is essentially the process of orienting graphene oxide sheets. As the solvent decreases, the graphene oxide sheets gradually become fixed. Stretching at this point allows the graphene oxide to still move within a small area in the solvent, enabling external force to help unfold the wrinkles when possible. Once drying is complete, the graphene oxide sheets are fixed, thus enhancing their high orientation. Stretching before drying is not feasible, mainly because before stretching, the graphene oxide has relatively large space to move in the solvent. While stretching can assist orientation to some extent, the large space still means the orientation can be disrupted. During drying, stretching, with the solvent decreasing gradually, allows the wrinkled graphene sheets to be stretched and flattened. The space for movement of the oriented graphene oxide sheets is continuously compressed. Once the wrinkles are flattened with external force, the obstructed space makes it difficult for them to wrinkle again.

[0021] 3) The dried graphene oxide film obtained in 2) above is subjected to carbonization and graphitization heat treatment to obtain a graphene foam film; the carbonization temperature is 1000-2000℃, the holding time is 1-2h, and the heating rate is 1-5℃ / min; the graphitization temperature is 2000-3200℃, the holding time is 4-20h, and the heating rate is 0.5-1℃ / min.

[0022] 4) The above graphene foam film is calendered at a pressure of 10-200 MPa to obtain a graphene thermal conductive film.

[0023] A second aspect of this invention provides a highly oriented graphene thermally conductive film with a horizontal thermal conductivity of 1500-2000 W / mK;

[0024] The highly oriented graphene thermally conductive film was prepared by the above-described preparation method.

[0025] The highly flexible graphene thermal conductive film is used for heat dissipation in 3C electronic products.

[0026] Compared with existing technologies, the technical effects achieved by this invention are as follows:

[0027] The drying process involves the orientation and alignment of graphene sheets. During drying, the substrate is stretched, and as the solvent decreases, the graphene oxide sheets gradually become fixed. This application cleverly chooses to stretch the sheets during drying, allowing the graphene oxide to still move slightly within the solvent. This enables the folds in the graphene oxide sheets to be unfolded with external force when possible. Once drying is complete and the graphene oxide sheets are fixed, carbonization and graphitization treatments yield horizontally highly oriented graphene. The method is simple, efficient, and suitable for large-scale production. The horizontal thermal conductivity of the graphene thermal conductive film obtained in this application can stably reach 1500 W / mK, with a maximum of 2000 W / mK. Attached Figure Description

[0028] Figure 1 This is a SEM image of the highly oriented graphene thermally conductive film prepared in Example 1 of the present invention;

[0029] Figure 2 SEM image of conventional graphene thermal conductive film in the prior art. Detailed Implementation

[0030] The technical solution of the present invention will be described below with reference to the accompanying drawings and specific embodiments. It should be understood that the one or more steps mentioned in the present invention do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or limiting the scope of the present invention. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of the present invention.

[0031] The raw materials and instruments used in the examples are not subject to any specific restrictions on their source. They can be purchased from the market or prepared using conventional methods known to those skilled in the art. The graphene material was purchased from Yuntian Morui Technology Co., Ltd., a professional manufacturer of graphene thermal conductive films.

[0032] Example 1: A method for preparing a highly oriented graphene thermally conductive film

[0033] (1) Preparation of graphene oxide slurry: Graphene oxide is mixed with water and stirred at high speed until uniform. After filtration (to remove large graphene oxide particles) and vacuum defoaming treatment, a graphene oxide slurry with a solid content of 8% is obtained.

[0034] (2) The above graphene oxide slurry was coated onto the PU film substrate by a doctor blade to a coating thickness of 8000 μm and then dried at a temperature of 80°C. During the drying process, the substrate was gradually stretched at a displacement speed of 0.01 mm / min for 30 s to obtain a dried graphene oxide film.

[0035] (3) The dried graphene oxide film obtained in (2) above is subjected to carbonization and graphitization heat treatment to obtain graphene foam film; the carbonization temperature is 2000℃, the holding time is 2h, and the heating rate is 5℃ / min; the graphitization temperature is 3200℃, the holding time is 20h, and the heating rate is 1℃ / min.

[0036] (4) The graphene foam film is calendered at a pressure of 200 MPa to obtain a graphene thermal conductive film.

[0037] SEM scan of the prepared graphene thermally conductive film is shown below. Figure 1 As shown, it is evident that the graphene thermal conductive film prepared in this embodiment has a high degree of orientation in the horizontal direction, rather than being wrinkled. Testing revealed that the density of the graphene thermal conductive film prepared in this embodiment is 2.25 g / cm³. 3 The horizontal thermal conductivity is 1700 W / mK.

[0038] Example 2: A method for preparing a highly oriented graphene thermally conductive film

[0039] The difference between this embodiment and Embodiment 1 is that the solid content of the graphene oxide slurry is 5%, and the stretching displacement time is set to 20s. The rest is the same as in Embodiment 1.

[0040] The density of the graphene thermally conductive film prepared in this embodiment was tested to be 2.25 g / cm³. 3 The horizontal thermal conductivity is 1820 W / mK, and the structure is consistent with the graphene thermal conductive film obtained in Example 1.

[0041] Example 3: A method for preparing a highly oriented graphene thermally conductive film

[0042] The difference between this embodiment and Embodiment 1 is that the solid content of the graphene oxide slurry is 3%, and the stretching displacement time is set to 15s. The rest is the same as in Embodiment 1.

[0043] The density of the graphene thermally conductive film prepared in this embodiment was tested to be 2.28 g / cm³. 3 The horizontal thermal conductivity is 1980 W / mK, and the structure is consistent with the graphene thermal conductive film obtained in Example 1.

[0044] Example 4: A method for preparing a highly oriented graphene thermally conductive film

[0045] The difference between this embodiment and Embodiment 1 is that the solid content of the graphene oxide slurry is 10%, and the stretching displacement time is set to 60s. The rest is the same as in Embodiment 1.

[0046] The density of the graphene thermally conductive film prepared in this embodiment was tested to be 2.21 g / cm³. 3 The horizontal thermal conductivity is 1500 W / mK, and the structure is consistent with the graphene thermal conductive film obtained in Example 1.

[0047] Comparative Example 1

[0048] (1) Preparation of graphene oxide slurry: Graphene oxide and DMF are mixed and stirred at high speed until uniform. After filtration (to remove large graphene oxide particles) and vacuum defoaming treatment, a graphene oxide slurry with a solid content of 8% is obtained.

[0049] (2) The above graphene oxide slurry was coated onto a conventional PET substrate that does not have tensile resilience by means of a doctor blade. The coating thickness was 8000 μm, and then dried at a temperature of 80°C to obtain a dried graphene oxide film.

[0050] (3) The dried graphene oxide film obtained in (2) above is subjected to carbonization and graphitization heat treatment to obtain graphene foam film; the carbonization temperature is 2000℃, the holding time is 2h, and the heating rate is 5℃ / min; the graphitization temperature is 3200℃, the holding time is 20h, and the heating rate is 1℃ / min.

[0051] (4) The graphene foam film is calendered at a pressure of 200 MPa to obtain a graphene thermal conductive film.

[0052] The density of the graphene thermally conductive film prepared in this comparative example was tested to be 2.21 g / cm³. 3 The horizontal thermal conductivity is 1403 W / mK. Figure 2 This is a graphene thermal conductive film prepared by conventional methods. Because the graphene thermal conductive film is formed by overlapping multiple graphene sheets at the microscopic level, Figure 2 The layers in the graphene thermal conductive film are not perfectly parallel, resulting in a small contact area between them, which affects heat conduction. Due to the inconsistent overlap between the layers, the macroscopic properties of the film exhibit varying thermal conductivity across different locations.

[0053] Examples 1-4 are thermally conductive films that have undergone stretching treatment, such as... Figure 1As shown in the SEM image of Example 1, the graphene sheets are almost completely parallel and partially overlap. Experiments by the inventors revealed that the stretching speed and stretching time affect the thermal conductivity of the thermally conductive film. The optimal performance was achieved with a stretching displacement speed of 0.01 mm / min and a stretching displacement time of 15 seconds. Analysis suggests that the closer the graphene sheets are to being parallel and the more they overlap, the better the thermal conductivity. Therefore, a stretching process in the fabrication process results in a better thermal conductivity for the graphene thermally conductive film. However, excessive stretching time worsens the overlap between the graphene sheets, leading to a decrease in thermal conductivity after 15 seconds.

[0054] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a highly oriented graphene thermally conductive film, characterized in that, include: An elastic substrate coated with graphene oxide slurry is gradually stretched along its length during the drying process. The stretching displacement speed is 0.01-0.1 mm / min, and the stretching displacement time is 1-60 seconds. The substrate is dried while being stretched. After separation from the elastic substrate, the substrate is carbonized and graphitized to obtain a graphene foam film. The graphene foam film is then subjected to calendering to obtain the graphene thermal conductive film.

2. The preparation method according to claim 1, characterized in that, The preparation method of the graphene oxide slurry includes: dispersing graphene oxide in a solvent at high speed, and obtaining the graphene oxide slurry after filtration and defoaming treatment.

3. The preparation method according to claim 2, characterized in that, The solvent is selected from one or more of water, DMF, NMP, ethanol, and isopropanol.

4. The preparation method according to claim 1, characterized in that, The solid content of the graphene slurry is 1%-10%.

5. The preparation method according to claim 4, characterized in that, The solid content of the graphene slurry is 3%-8%.

6. The preparation method according to claim 1, characterized in that, The elastic substrate is selected from one of PU film, silicone film, and rubber film; And / or, the coating thickness is 2000-10000 μm.

7. The preparation method according to claim 1, characterized in that, The carbonization temperature is 1000-2000℃, the holding time is 1-2h, and the heating rate of the carbonization is 1-5℃ / min.

8. The preparation method according to claim 1, characterized in that, The graphitization temperature is 2000-3200℃, the holding time is 4-20h, and the heating rate is 0.5-1℃ / min.

9. The preparation method according to claim 1, characterized in that, The pressure of the calendering process is 10-200 MPa.

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