High-impedance graphene heat-conducting film and preparation method thereof

Abstract

The invention discloses a high-impedance graphene heat-conducting film and a preparation method thereof, the high-impedance graphene heat-conducting film contains high-temperature-resistant insulating particles, and the melting point of the high-temperature-resistant insulating particles is greater than or equal to 1500 DEG C; and the particle size distribution of the high-temperature-resistant insulating particles meets the condition that D95 is less than or equal to 3 microns. The preparation method comprises the following steps that dry graphene oxide powder and desalted water are mixed to prepare graphene oxide slurry with the carbon-oxygen ratio smaller than 2.9, the graphene oxide slurry and high-temperature-resistant insulating particles are evenly mixed and then coated, and the high-resistance graphene oxide heat conduction film is obtained. The high-impedance graphene oxide heat-conducting film is sequentially subjected to low-temperature heat treatment, medium-temperature heat treatment, high-temperature heat treatment and calendering treatment, and then the high-impedance graphene heat-conducting film is obtained. According to the method, industrial large-scale preparation of the high-impedance graphene heat-conducting film is realized, and application of the graphene heat-conducting film to a heating device is facilitated.

Description

Technical Field

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

[0002] Graphene is a two-dimensional carbon nanomaterial composed of carbon atoms in a hexagonal honeycomb lattice with sp² hybrid orbitals. This structure allows electrons to move at high speed without obstacles on a two-dimensional plane, greatly improving electrical conductivity. The electrons and holes (carriers) in graphene have very high mobility, up to ~200,000 cm² / Vs, which means that electrons can move quickly under the action of an electric field, which is conducive to the rapid transmission of current, making graphene have good electrical conductivity. At the same time, the carbon atoms in graphene form a conjugated system through strong π-π interactions, which is not only conducive to electron transmission, but also allows phonons (quanta of thermal energy) in the lattice to be efficiently transmitted, resulting in extremely high thermal conductivity.

[0003] Based on the good electrical conductivity and extremely high thermal conductivity of graphene, some products on the market currently use graphene films for graphic design and manufacture them into heating modules, such as the Chinese utility model patent with announcement number CN211982154U. Based on the high electrical-thermal radiation conversion efficiency, the pure graphene heating element is superior to traditional metal heating wires in terms of heating speed and uniformity, and the heating area is larger. However, in the actual pattern design process, due to the relatively low resistivity of the graphene heating element itself, designing according to the customer's predetermined size will result in too much power, with the risk of overload and short circuit, especially in scenarios with high voltage, this problem is more prominent.

[0004] At present, there are mainly the following methods for regulating the resistance of graphene heating elements: 1. Introducing defects: Introducing defects in the graphene structure by physical or chemical methods, such as single atomic vacancies, Stone-Wales defects, etc., can interfere with the transmission path of electrons, thereby increasing resistance and possibly affecting the efficiency of heat conduction. 2. Constructing composite materials: Mixing or stacking graphene with other high-resistance materials to form composite materials. This structure can reduce the overall thermal conductivity through methods such as interface scattering, and may change the resistance characteristics. 3. Regulating the number of layers and orientation: The thermal conductivity of graphene film is related to its number of layers and stacking method. A specific number of layers and non-coplanar arrangement can reduce the transfer efficiency of heat flow and indirectly affect the resistance properties. 4. Chemical functionalization: Grafting molecules or groups on the surface of graphene by chemical methods can change the electronic structure, thereby affecting its electrical and thermal properties, but this usually also reduces the conductivity.

[0005] However, the above methods are all based on atomic-level structural construction, which is difficult to achieve in the actual industrial large-scale production process, and has a great impact on the thermal conductivity of the graphene heating element itself. Therefore, how to achieve the resistance adjustment of the graphene heating element has become one of the problems that technicians in this field need to solve urgently. Summary of the invention

[0006] The object of the present invention is to provide a high-impedance graphene thermal conductive film, wherein the high-impedance graphene thermal conductive film contains high-temperature resistant insulating particles, the melting point of the high-temperature resistant insulating particles is greater than or equal to 1500°C; the particle size distribution of the high-temperature resistant insulating particles satisfies: D95≤3μm.

[0007] In a further technical solution, the resistivity of the high-impedance graphene thermal conductive film is greater than 1.0×10 -6 (Ω.cm). High temperature resistant insulating particles are added during the preparation of graphene oxide slurry. During the film formation process, the high temperature resistant insulating particles will combine with the carbon atoms of graphene to form lattice defects or replace the position of carbon atoms, breaking the original two-dimensional crystal structure of graphene and further adjusting its electrical properties. High impedance insulating particles are mixed into the graphene thermal conductive film. These metal ions will affect the charge transfer characteristics of graphene, increase the scattering effect, and increase the resistance, thereby achieving the effect of adjusting the resistance.

[0008] In a further technical solution, the thermal conductivity of the high-impedance graphene thermally conductive film is greater than or equal to 400 W / (mK).

[0009] In a further technical solution, the high temperature resistant insulating particles include ZrO 2 , HfO 2 、Al 2 O 3 、TiO 2 、SiO 2 , BN, Y 2 O 3 The melting points of the above-mentioned metal oxides are all above 1500°C, they will not be lost during the medium-temperature treatment, and they can partially participate in the reconstruction of carbon-carbon bonds during the high-temperature treatment, thereby playing a role in adjusting the resistance.

[0010] In a further technical solution, the graphene oxide powder used to prepare the high-impedance graphene thermal conductive film has a carbon-oxygen ratio of less than 2.9.

[0011] In a further technical solution, the flake diameter of the graphene oxide in the graphene oxide powder is ≥1 μm. The relationship between the flake diameter of the graphene oxide and the particle size of the high temperature resistant insulating particles has an impact on the subsequent film formation and the appearance of the film. When the ratio of the two is unbalanced, the cohesion of the film will not be achieved, resulting in cracking problems.

[0012] Another object of the present invention is to provide a method for preparing a high-impedance graphene thermally conductive film, comprising the following steps: mixing dry graphene oxide powder and desalted water to prepare a graphene oxide slurry with a carbon-oxygen ratio of less than 2.9, uniformly mixing the graphene oxide slurry with high-temperature resistant insulating particles and then coating them to obtain a high-impedance graphene oxide thermally conductive film, wherein the high-impedance graphene oxide thermally conductive film is sequentially subjected to low-temperature heat treatment, medium-temperature heat treatment, high-temperature heat treatment and calendering treatment to obtain a high-impedance graphene oxide thermally conductive film; after the medium-temperature heat treatment step, the residual mass of the high-impedance graphene oxide thermally conductive film is greater than 100%.

[0013] In a further technical solution, the high temperature resistant insulating particles are selected to have a flake diameter smaller than that of graphene oxide. When the high temperature resistant insulating particles are amphoteric oxides, the graphene oxide powder and the high temperature resistant insulating particles are mixed in a ratio of 1:0.025~0.1; when the high temperature resistant insulating particles are selected from neutral or alkaline substances, the graphene oxide powder and the high temperature resistant insulating particles are mixed in a ratio of 1:0.1~1.

[0014] In a further technical solution, in the heat treatment step, the heat treatment temperature is 1500-2500° C., and the heat treatment time is 1-60 min.

[0015] In a further technical solution, in the calendering step, the calendering pressure is set to 30 ~ 80MPa.

[0016] Compared with the prior art, the technical effects achieved by the present invention are as follows: The present invention adds high temperature resistant insulating particles in the preparation stage of graphene oxide slurry. During the film forming process, the high temperature resistant insulating particles will combine with the carbon atoms of graphene to form lattice defects or replace the position of carbon atoms, breaking the original two-dimensional crystal structure of graphene and further adjusting its electrical properties. High impedance insulating particles are mixed into the graphene thermal conductive film. These metal ions will affect the charge transfer characteristics of graphene, increase the scattering effect, and thus increase the resistance, thereby achieving the effect of adjusting the resistance. At the same time, by regulating the relationship between the high temperature resistant insulating particles and the diameter of the graphene oxide sheets during the preparation process, the effect of resistance adjustment and self-assembly film formation is ensured, avoiding the problem of insufficient cohesion of the graphene thermal conductive film due to the presence of high temperature resistant insulating particles, and ensuring that cracking does not occur during the heat treatment process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 These are sample images of Examples 1-4.

[0018] Figure 2 These are sample images of Examples 1-7.

[0019] Figure 3This is a sample picture of Example 1-1.

[0020] Figure 4 This is the thermogravimetric analysis chart of Example 2-1.

[0021] Figure 5 This is the thermogravimetric analysis diagram of a conventional thermal conductive film. DETAILED DESCRIPTION

[0022] The content of the present invention is further described below in conjunction with specific examples, but it should not be construed as limiting the present invention. If not specifically indicated, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art, and there is no specific restriction on their sources, and they can be purchased in the market or prepared according to conventional methods well known to those skilled in the art.

[0023] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising”, etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0024] The technical solution of the present invention is described below by specific embodiments. It should be understood that one or more steps mentioned in the present invention do not exclude the existence of other methods and steps before and after the combination step, or other methods and steps can be inserted between these explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Unless otherwise specified, the numbering of each method step is only for the purpose of identifying each method step, and does not limit the order of arrangement of each method or limit the scope of implementation of the present invention. The change or adjustment of the relative relationship thereof can also be regarded as the scope of implementation of the present invention without substantial changes in the technical content.

[0025] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

[0026] According to an embodiment of the present invention, a method for preparing a high-impedance graphene thermal conductive film is provided, comprising the following steps: Prepare graphene oxide slurry, purchase graphene oxide powder (water content less than 1%) from Yuntian Mo Rui, add desalted water into the reactor loaded with graphene oxide cake, and prepare graphene oxide slurry.

[0027] Add high temperature resistant insulating particles into the reaction kettle and mix and stir evenly. After compounding, a composite slurry with a solid content of 3% to 5% is obtained.

[0028] The composite slurry is coated on a mesh substrate, the mesh substrate can be made of PET, PP, PE, PTFE or PI, etc., and is dried in a drying oven at a speed of 0.5m / min to 1.0m / min for 40 to 90min to obtain a high-impedance graphene oxide thermal conductive film, wherein the thickness of the high-impedance graphene oxide thermal conductive film is 1 to 5mm.

[0029] The high-impedance graphene oxide thermal conductive film is placed in an industrial oven and subjected to low-temperature heat treatment at a temperature not higher than 300° C. The low-temperature heat treatment time is less than 60 minutes to remove impurities.

[0030] The high-impedance graphene oxide thermal conductive film after low-temperature treatment is subjected to medium-temperature heat treatment, the temperature of the medium-temperature heat treatment is not higher than 1300°C, and after reaching the highest temperature, the temperature is kept constant for 20-40 minutes to further remove impurities.

[0031] Finally, a high-temperature heat treatment is performed at a temperature below 2500°C to further remove impurities while reorganizing the structure of carbon atoms in the high-impedance graphene oxide thermal conductive film and repairing defects in the film. After reaching the highest temperature, it is maintained for 20-40 minutes to obtain a high-impedance, low-density graphene thermal conductive film.

[0032] The high-impedance, low-density graphene thermal conductive film obtained in step 6 is placed in the calendering chamber of the flat press, and the air pressure in the calendering chamber is pumped to no more than 1*10 -3 After 30-80MPa pressure is applied to the film, a high-impedance graphene thermal conductive film is obtained.

[0033] Test standard: The resistivity test standard is based on "GB / T 30544.13-2018 Nanotechnology Nanomaterials Part 13: Test Methods for Electrical Properties of Graphene Materials". The four-probe method in the standard is used to test the resistivity of graphene thermal conductive film samples. Four equally spaced probes are placed on the sample, two outer probes apply current, and two inner probes measure the voltage drop to calculate the resistivity. Example 1

[0034] Graphene oxide powder was purchased from Yunnan Yuntian Mo Rui, model MPGO-4210, and high temperature resistant insulation particles were selected from Al 2 O3 , high temperature resistant insulating particles; the solid content of the composite slurry is 4.85%; the drying speed is 0.8m / min, and the drying time is 40min; the thickness of the high impedance graphene oxide thermal conductive film is 3mm; the low temperature heat treatment temperature is 250℃, and the low temperature heat treatment time is less than 30min; the medium temperature heat treatment reaches the highest temperature and maintains for 30min; the high temperature heat treatment temperature is set to 2400℃, and maintains for 30min after reaching the highest temperature; the pressure applied by the flat press in the calendering step is 70MPa. Observe the appearance and resistivity changes of the high impedance graphene thermal conductive film, and the test results are as follows:

[0035]

[0036] First, the resistivity of conventional industrial mass-produced graphene thermal conductive film is 1.3*10 -6 In Examples 1-1 to 3, the mass ratio of graphene oxide powder to high temperature resistant insulating particles is between 0.025 and 1, the average flake diameter of graphene oxide powder is larger than the average particle diameter of high temperature resistant insulating particles, and the resistivity is greatly improved compared with conventional graphene thermal conductive films. Within the range, as the content of high temperature resistant insulating particles increases, the resistivity also slowly increases.

[0037] The amount of high temperature resistant insulating particles added in Examples 1-4 exceeds the preset range, such as Figure 1 As shown, serious cracking problems occurred during the drying stage after coating. The amount of high-temperature insulating particles added in Example 1-5 is lower than the lower limit of the range. In this addition amount scheme, the resistivity of the film is hardly improved. In Example 1-6, the flake diameter of graphene oxide is the same as the particle size of high-temperature resistant insulating particles, and no film is formed after coating. When the flake diameter is the same, the high-temperature insulating particles affect the self-assembly reaction of graphene oxide, resulting in a poor film-forming effect. Although the resistivity of Example 1-7 has increased, appearance cracks appear when the medium-temperature treatment temperature is higher than 1200°C, as shown in FIG. Figure 2 In Example 1-8, the medium temperature treatment temperature was too low, and cracking occurred during the calendering process. After analysis, it was believed that due to the addition of high-temperature insulating particles, the medium temperature heat treatment temperature was too low, which would lead to poor cohesion and easy cracking. If the medium temperature treatment temperature was too high, the reaction would be too intense and cracking would occur. Example 2 Graphene oxide powder was purchased from Yunnan Yuntian Mo Rui, model MPGO-4210, and high temperature resistant insulation particles were selected from ZrO 2, high temperature resistant insulating particles; the solid content of the composite slurry is 4.50%; the drying speed is 0.8m / min, and the drying time is 40min; the thickness of the high impedance graphene oxide thermal conductive film is 3mm; the low temperature heat treatment temperature is 250℃, and the low temperature heat treatment time is less than 30min; the medium temperature heat treatment reaches the highest temperature and maintains for 30min; the high temperature heat treatment temperature is set to 2400℃, and maintains for 30min after reaching the highest temperature; the pressure applied by the flat press in the calendering process is 70MPa. Observe the appearance and resistivity changes of the high impedance graphene thermal conductive film, and the test results are as follows:

[0038] The difference between this embodiment and embodiment 1 is that the high temperature insulating particles are neutral or alkaline materials, specifically ZrO 2 In Examples 2-1 to 2-3, the mass ratio of graphene oxide powder to high temperature resistant insulating particles is between 0.1 and 1, the average flake diameter of graphene oxide powder is larger than the average particle diameter of high temperature resistant insulating particles, and the resistivity is greatly improved compared with conventional graphene thermal conductive films. Within the range, as the content of high temperature resistant insulating particles increases, the resistivity also slowly increases. The same rule as in Example 1.

[0039] In Example 2-4, the amount of high temperature resistant insulating particles added exceeded the preset range, and serious cracking problems also occurred during the drying stage. The amount of Example 2-5 added was lower than the preset range, and the resistivity improvement was not obvious. Example 2-6 also showed the same rule, and the relationship between the sheet diameters would affect the self-assembly effect. The results of Example 2-7 and Example 2-8 were consistent with those of Example 11-7 and Example 1-8. It is proved that the above rules will not change due to changes in materials.

[0040] According to GB / T 27761-2011 Test method for weight loss and residual amount of thermogravimetric analyzer, thermogravimetric analysis was performed on Example 2-1, Example 2-2 and Example 2-3. The TG curve and DTG curve are as follows: Figure 4 As shown in the figure, when the temperature reaches 600°C, the residual mass begins to increase gradually, and finally reaches 103% when the temperature reaches 800°C. Figure 5 It is a conventional graphene thermal conductive film, and the residual mass after 600℃ is 98%. After analysis, it is believed that when the high impedance film is successfully prepared, the high impedance film contains ZrO 2 The high temperature resistant insulating particles are all metal oxides, mainly zirconium oxide in this embodiment. Zirconium oxide reacts with an inert protective gas (specifically nitrogen). When the temperature reaches a certain level, the nitrogen molecules obtain enough energy to overcome the reaction barrier and react with the oxygen atoms in zirconium oxide to form nitrogen oxides (such as ZrN x O y). At the same time, the reaction process is accompanied by the change of particle size, combining with the carbon atoms of graphene to form lattice defects or replace the position of carbon atoms, affecting the original electrical properties. In addition, the presence of high-impedance particles will affect the charge transfer characteristics of graphene, increase the scattering effect, and thus increase the resistance. Therefore, it can be seen from the results of thermogravimetric analysis that ZrO still exists in the high-impedance film. 2 .

[0041] 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.

[0042] The above is a specific implementation of the present application, but the protection scope of the present application 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 in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A high-impedance graphene thermally conductive film, characterized in that: The high-impedance graphene thermal conductive film contains high-temperature resistant insulating particles, the melting point of the high-temperature resistant insulating particles is greater than or equal to 1500° C.; the particle size distribution of the high-temperature resistant insulating particles satisfies: D95≤3μm.

2. A high-impedance graphene thermal conductive film according to claim 1, characterized in that: The resistivity of the high-impedance graphene thermal conductive film is greater than 1.0×10 -6 (Ω.cm).

3. The high-impedance graphene thermal conductive film according to claim 1, characterized in that: The thermal conductivity of the high-impedance graphene thermally conductive film is greater than or equal to 400 W / (mK).

4. The high-impedance graphene thermal conductive film according to claim 1, characterized in that: The high temperature resistant insulating particles include one or more of ZrO2, HfO2, Al2O3, TiO2, SiO2, BN, and Y2O3.

5. The high-impedance graphene thermal conductive film according to claim 1, characterized in that: The graphene oxide powder used to prepare the high-impedance graphene thermal conductive film has a carbon-oxygen ratio of less than 2.

9.

6. The high-impedance graphene thermal conductive film according to claim 5, characterized in that: The average particle size of the high temperature resistant insulating particles is smaller than the average flake size of the graphene oxide powder.

7. A method for preparing a high-impedance graphene thermally conductive film, characterized in that: The method comprises the following steps: mixing dry graphene oxide powder and desalted water to prepare graphene oxide slurry with a carbon-oxygen ratio of less than 2.9, uniformly mixing the graphene oxide slurry with high temperature resistant insulating particles and then coating them to obtain a high impedance graphene oxide thermal conductive film, wherein the high impedance graphene oxide thermal conductive film is sequentially subjected to low temperature heat treatment, medium temperature heat treatment, high temperature heat treatment and calendering treatment to obtain a high impedance graphene thermal conductive film; After the medium-temperature heat treatment step, the residual mass of the high-impedance graphene oxide thermal conductive film is greater than 100%.

8. The method for preparing a high-impedance graphene thermally conductive film according to claim 7, characterized in that: The average particle size of the high temperature resistant insulating particles is smaller than the average flake size of the graphene oxide powder, and the average flake size of the graphene oxide powder is ≥3μm. When the high temperature resistant insulating particles are amphoteric oxides, the graphene oxide powder and the high temperature resistant insulating particles are mixed in a ratio of 1:0.025~0.1; when the high temperature resistant insulating particles are selected from neutral or alkaline substances, the graphene oxide powder and the high temperature resistant insulating particles are mixed in a ratio of 1:0.1~1.

9. The method for preparing a high-impedance graphene thermally conductive film according to claim 7, characterized in that: In the heat treatment step, the temperature of the medium-temperature heat treatment is 1000-1200°C, the temperature of the high-temperature heat treatment is 1500-2500°C, and the holding time after the high-temperature heat treatment reaches the highest temperature is 20-60 minutes.

10. The method for preparing a high-impedance graphene thermal conductive film according to claim 7, characterized in that: In the calendering step, the calendering pressure is set to 30 ~ 80MPa.

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