Graphene film, composite heating diaphragm, heating equipment and preparation method thereof

Abstract

The embodiment of the invention provides a graphene film, a composite heating diaphragm, heating equipment and a preparation method thereof. The preparation method of the graphene film, provided by the embodiment of the invention, comprises the following steps: S1, obtaining a small-sheet-diameter graphene oxide dispersion liquid, coating a substrate with the graphene oxide dispersion liquid, and drying to obtain a graphene oxide film; s2, performing low-temperature and high-vacuum treatment on the graphene oxide film obtained in the step S1 to obtain a pre-reduced graphene film; and S3, carrying out high-temperature graphitization treatment on the graphene film pre-reduced in S2 under an inert condition to obtain a graphene layer, and calendering the graphene layer to obtain the graphene film. Therefore, the preparation method of the graphene film provided by the embodiment of the invention has good controllability and stability, and can effectively ensure that the prepared graphene film has expected performance.

Description

Technical Field

[0001] This invention relates to the field of heating technology, specifically to a graphene film, a composite heating film having the graphene film, a heating device, and a method for preparing the same. Background Technology

[0002] Traditional metal wires or carbon fibers may have their electrical and mechanical properties significantly affected after bending or cutting, and may even break. Moreover, conventional heating wires generate concentrated heat, requiring long windings. The heat is emitted linearly, resulting in poor heat uniformity, long heating times, low energy efficiency, and low heat conversion efficiency, which can easily lead to localized burning or undercooking of bread.

[0003] To meet the core requirements of rapid heating, uniform heating, high temperature resistance, insulation safety, and long-term stable operation, graphene films are used for heating. However, the performance of graphene films is highly dependent on the processing technology. In related technologies, mainstream methods often employ the assembly of large-size graphene oxide sheets. The stacking of these sheets easily leads to interface defects, obstructing heat transport paths. Furthermore, gases generated from the decomposition of residual oxygen-containing functional groups during high-temperature processing cannot be effectively expelled, causing internal wrinkles and increased porosity, significantly reducing structural stability. Inadequate processing results in low crystallinity and high porosity in the graphene films, hindering the achievement of high electrical and thermal conductivity. This, in turn, leads to low heating efficiency and limited lifespan of graphene films in practical applications. Summary of the Invention

[0004] In view of this, the present invention aims to provide a graphene film, a composite heating film, a heating device and a method for preparing the same, so as to solve the problem of poor performance of graphene films in the prior art due to unreasonable processes.

[0005] This invention provides a graphene film. The graphene film has the following characteristics: The electrical conductivity of the graphene film is 10. 2 S / m ~ 1.2 × 10 6 S / m; The in-plane thermal conductivity of the graphene film is 80 W / mK to 1850 W / mK; The tensile strength of the graphene film is 15MPa~50MPa; The density of the graphene film is 1.2 g / cm³. 3 ~2.2 g / cm 3 ; The thickness of the graphene film is 2μm~500μm; The porosity of the graphene film is 0.5% to 5%.

[0006] This invention provides a method for preparing a graphene film.

[0007] One aspect of this invention is a composite heating film.

[0008] This invention provides a method for preparing a composite heating film.

[0009] One aspect of this invention is a heating device.

[0010] The method for preparing the graphene film according to embodiments of the present invention includes the following steps: S1 Obtain a graphene oxide dispersion with a sheet diameter of 0.1μm~2μm, and coat the graphene oxide dispersion onto a substrate. After drying, obtain a graphene oxide film. S2 involves subjecting the graphene oxide film obtained in S1 to low-temperature, high-vacuum treatment to obtain a pre-reduced graphene film; S3 involves subjecting the pre-reduced graphene film from S2 to high-temperature graphitization under inert conditions to obtain a graphene layer, followed by calendering of the graphene layer to obtain the graphene film as described in claim 1.

[0011] The graphene film preparation method of this invention ensures film uniformity and density by precisely controlling the graphene oxide sheet size and dispersion concentration. Low-temperature pre-reduction under high vacuum effectively removes oxygen-containing functional groups and suppresses structural defect formation. High-temperature graphitization promotes lattice reconstruction, improving electrical and thermal conductivity. The calendering process further enhances interlayer bonding and orientation, optimizing the mechanical and electrothermal properties of the final film. These steps work synergistically to achieve controllable adjustment of material properties, meeting the needs of large-scale production.

[0012] Specifically, by oriented graphene oxide films with small flakes, a continuous and dense microstructure of conductive / thermal conductive networks can be formed, significantly reducing interfacial thermal resistance and electron scattering probability. Combining ultra-low vacuum cryogenic treatment and graphitization processes improves the efficiency of gas emission within the film and suppresses defect formation, thereby obtaining a highly oriented graphene film with low grain boundary resistance. The small-flake graphene oxide film reduces the diffusion resistance of gas molecules at high temperatures, while the ultra-low vacuum environment effectively removes residual solvents and decomposition products, ensuring film densification and lattice continuity.

[0013] When pre-reduced graphene films undergo high-temperature graphitization, the process must be carried out under the protection of an inert gas to prevent oxidation of the film layer at high temperatures. Simultaneously, the high-temperature graphitization process promotes the reconstruction of the graphene lattice, allowing carbon atoms to rearrange at high temperatures to form a more regular sp² hybrid structure, significantly improving the film's electrical and thermal conductivity. This process can lead to a more perfect lattice structure in the graphene film, thereby enhancing its electrical and thermal properties. Furthermore, by controlling the interlayer stacking density and surface flatness of the graphene film through calendering, its adaptability in flexible electronic devices can be further improved.

[0014] Furthermore, by combining the synergistic effect of low-temperature high-vacuum and high-temperature graphitization processes, the structural collapse and crack propagation problems commonly encountered in traditional reduction processes are effectively avoided, ensuring that the membrane material maintains excellent electrothermal response stability even after being bent thousands of times.

[0015] Moreover, the preparation method is highly reproducible, suitable for large-scale, continuous production, and does not rely on harsh chemical reagents or complex equipment, thus showing good prospects for industrial application.

[0016] Therefore, the graphene film preparation method of the present invention has good controllability and stability, and can effectively ensure that the prepared graphene film has the expected performance.

[0017] In one embodiment, in step S1, the graphene oxide filter cake is dispersed in a solvent by high-pressure homogenization to obtain the graphene oxide dispersion, wherein the high-pressure homogenization pressure of the graphene oxide filter cake is 800 bar to 1500 bar, and the homogenization time is 0.5 h to 6 h.

[0018] In one embodiment, the viscosity of the graphene oxide dispersion is 1500 mpa·s to 20000 mpa·s.

[0019] In one embodiment, in step S1, the carbon-to-oxygen ratio of the graphene oxide filter cake is 2:1 to 6:1.

[0020] In one embodiment, in step S1, the solvent is pure water or deionized water.

[0021] In one embodiment, in step S1, the graphene oxide dispersion is coated onto the substrate by a coating method.

[0022] In one embodiment, in step S1, the substrate comprises at least one of copper, aluminum, stainless steel, polyethylene terephthalate, polyimide, polyethylene, glass, polyester, nonwoven fabric, carbon cloth, and cotton fiber.

[0023] In one embodiment, in step S1, the graphene oxide dispersion coated on the substrate is dried at 25°C to 90°C for 12 h to 96 h.

[0024] In one embodiment, the thickness of the obtained graphene oxide film in step S1 is less than 500 μm.

[0025] In one embodiment, in step S2, the graphene oxide film obtained in S1 is subjected to a vacuum of 10... -2 ~10 -5 The pre-reduced graphene film was prepared under controlled temperature conditions of 250℃~600℃.

[0026] In one embodiment, in step S2, the heating rate of the pre-reduced graphene film is less than 3 °C / min.

[0027] In one embodiment, in step S2, the weight loss ratio during the process of preparing the pre-reduced graphene film from the graphene oxide film is 30% to 40%.

[0028] In one embodiment, in step S3, the high-temperature graphitization temperature is 2200℃~3000℃, and the processing time is 1.5h~2.5h.

[0029] In one embodiment, the gas used for the inert conditions is at least one of argon, nitrogen, and helium.

[0030] In one embodiment, in step S3, the thickness of the graphene film obtained after calendering is 0.01 mm to 5 mm.

[0031] In one embodiment, in step S3, the graphene layer is calendered sequentially by roll pressing and flat static pressing, and the stress during calendering is controlled to be ≤200 MPa.

[0032] The composite heating film of this invention includes a first encapsulation layer, a second encapsulation layer, and a graphene film according to any one of the above. The graphene film layer has a heating element and a connecting electrode. The first encapsulation layer, the graphene film layer, and the second encapsulation layer are stacked sequentially. The heating element is sealed between the first encapsulation layer and the second encapsulation layer, and the connecting electrode extends beyond the first encapsulation layer and the second encapsulation layer.

[0033] The method for preparing the composite heating film according to embodiments of the present invention includes the following steps: The graphene film described in any one of the above-mentioned methods is rolled onto the substrate layer, and then the graphene film is engraved into a preset pattern by laser engraving to form the heating body and connecting electrodes; the engraved graphene film and the substrate layer are placed between the first encapsulation layer and the second encapsulation layer for hot pressing encapsulation, so that the heating body is completely sealed in the two layers of mica sheets.

[0034] The heating device of this invention includes the composite heating film according to the above. Attached Figure Description

[0035] Figure 1 A scanning electron microscope for graphene oxide nanosheets; Figure 2 This is a histogram showing the size distribution of graphene oxide nanosheets. Figure 3 This is a scanning electron microscope image of the graphene film surface. Figure 4 This is a scanning electron microscope image of a cross-section of a graphene film. Figure 5 Graphite film is used as the electrode pattern, and graphene film is used as the electrode pattern. Figure 6 The structural diagram obtained by the composite packaging process is: one layer of mica sheet + one layer of graphene heating film + one layer of mica sheet; Figure 7 The images show a comparison of the toasting effects of a toaster assembled using the composite material of this invention and a toaster of the prior art. The left side shows the toasting effect of the graphene heating element, and the right side shows the toasting effect of the comparative example of the metallic mica sheet. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0037] The following is for reference. Figures 1-7 The following describes, by way of example, the graphene film, composite heating film, heating device, and their preparation methods or effects according to embodiments of the present invention.

[0038] The graphene film of this invention has the following characteristics: the electrical conductivity of the graphene film is 10⁻⁶. 2 S / m ~ 1.2 × 10 6 The graphene film has a thermal conductivity of 80 W / mK to 1850 W / mK; a tensile strength of 15 MPa to 50 MPa; and a density of 1.2 g / cm³. 3 ~2.2 g / cm 3The thickness of the graphene film is 2μm to 500μm; the porosity of the graphene film is 0.5% to 5%.

[0039] The graphene film of this invention exhibits excellent electrical, thermal, and mechanical properties by defining the following performance characteristics of graphene. This graphene film possesses a highly ordered layered structure, effectively reducing interfacial thermal resistance and electron scattering, and significantly improving carrier mobility and thermal conductivity.

[0040] By limiting the range of electrical conductivity, not only is insufficient heating efficiency due to excessively low conductivity avoided, but excessively high conductivity also prevents localized overheating caused by excessive current density. Simultaneously, limiting the in-plane thermal conductivity ensures rapid and uniform heat dissipation, reducing hotspot accumulation and improving safety and energy efficiency. The appropriate match between tensile strength and density endows the material with excellent mechanical stability, adapting to long-term use requirements under complex working conditions and ensuring high thermal conductivity even under frequent bending or vibration. Specific thickness and porosity ranges further optimize thermal response speed and heat dissipation balance, ensuring structural integrity and efficient heat output in flexible applications.

[0041] Meanwhile, by controlling the porosity within the range of 0.5%-5%, the material's density and flexibility are effectively balanced, preventing performance degradation caused by the propagation of microcracks. On the one hand, this avoids the problem of loose structure and reduced strength caused by excessively high porosity; on the other hand, it prevents the defects of increased brittleness and weakened bending durability caused by excessively low porosity, ensuring that the graphene film can maintain stable electrothermal performance under repeated bending or dynamic loads.

[0042] Graphene, with its unique two-dimensional honeycomb lattice structure, exhibits excellent electrical and thermal conductivity, making it an ideal choice for next-generation electrothermal materials. Compared to traditional electrothermal materials such as metal wires (nickel-chromium alloys) or carbon fibers, graphene electrothermal films directly convert electrical energy into heat energy.

[0043] By synergistically controlling the above parameters, this invention achieves a balance between material functionality and reliability, meets the usage requirements of complex application environments such as high temperature, high humidity, and high stress, and expands its application prospects in smart wearables, flexible electronics, and high-efficiency heating equipment.

[0044] Therefore, the graphene film of the present invention has excellent electrothermal conversion performance and long-term working stability.

[0045] Optionally, the graphene film has an electrical conductivity of 10. 2 S / m, 10 3 S / m, 10 4 S / m, 10 5 S / m, 2×10 5 S / m, 3×10 5S / m, 4×10 5 S / m, 5×10 5 S / m, 6×10 5 S / m, 7×10 5 S / m, 8×10 5 S / m, 9×10 5 S / m, 1.2×10 6 Different values ​​such as S / m can be selected and adjusted according to different application scenarios and requirements. Preferably, the conductivity of the graphene film is... ~ .

[0046] Optionally, the in-plane thermal conductivity of the graphene film is 80 W / mK, 100 W / mK, 150 W / mK, 200 W / mK, 250 W / mK, 300 W / mK, 400 W / mK, 500 W / mK, 600 W / mK, 800 W / mK, 1000 W / mK, 1200 W / mK, 1400 W / mK, 1600 W / mK, 1800 W / mK, and 1850 W / mK. Preferably, the in-plane thermal conductivity of the graphene film is 1000 W / mK to 1600 W / mK.

[0047] Optionally, the tensile strength of the graphene film is 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, or 50 MPa. Preferably, the tensile strength of the graphene film is 40 to 50 MPa.

[0048] Optionally, the density of the graphene film is 1.2 g / cm³. 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3 2.1g / cm 3 and 2.2 g / cm 3 Preferably, the density of the graphene film is 1.8~2.2 g / cm³. 3 .

[0049] Optionally, the thickness of the graphene film can be 2μm, 10μm, 50μm, 100μm, 150μm, 200μm, 300μm or 500μm, preferably, the thickness of the graphene film is 50~300 μm.

[0050] Optionally, the porosity of the graphene film is 0.5%, 1%, 2%, 3%, 4% or 5%, preferably, the porosity of the graphene film is 0.5% to 3%.

[0051] The method for preparing the graphene film according to embodiments of the present invention includes the following steps: S1 Obtain a graphene oxide dispersion with a sheet diameter of 0.1μm~2μm, and coat the graphene oxide dispersion onto a substrate. After drying, obtain a graphene oxide film. S2 involves subjecting the graphene oxide film obtained in S1 to low-temperature, high-vacuum treatment to obtain a pre-reduced graphene film; S3 involves subjecting the pre-reduced graphene film from S2 to high-temperature graphitization under inert conditions to obtain a graphene layer, followed by calendering of the graphene layer to obtain the graphene film as described in claim 1.

[0052] The graphene film preparation method of this invention ensures film uniformity and density by precisely controlling the graphene oxide sheet size and dispersion concentration. Low-temperature pre-reduction under high vacuum effectively removes oxygen-containing functional groups and suppresses structural defect formation. High-temperature graphitization promotes lattice reconstruction, improving electrical and thermal conductivity. The calendering process further enhances interlayer bonding and orientation, optimizing the mechanical and electrothermal properties of the final film. These steps work synergistically to achieve controllable adjustment of material properties, meeting the needs of large-scale production.

[0053] Specifically, by oriented graphene oxide films with small flakes, a continuous and dense microstructure of conductive / thermal conductive networks can be formed, significantly reducing interfacial thermal resistance and electron scattering probability. Combining ultra-low vacuum cryogenic treatment and graphitization processes improves the efficiency of gas emission within the film and suppresses defect formation, thereby obtaining a highly oriented graphene film with low grain boundary resistance. The small-flake graphene oxide film reduces the diffusion resistance of gas molecules at high temperatures, while the ultra-low vacuum environment effectively removes residual solvents and decomposition products, ensuring film densification and lattice continuity.

[0054] When pre-reduced graphene films undergo high-temperature graphitization, the process must be carried out under the protection of an inert gas to prevent oxidation of the film layer at high temperatures. Simultaneously, the high-temperature graphitization process promotes the reconstruction of the graphene lattice, allowing carbon atoms to rearrange at high temperatures to form a more regular sp² hybrid structure, significantly improving the film's electrical and thermal conductivity. This process can lead to a more perfect lattice structure in the graphene film, thereby enhancing its electrical and thermal properties. Furthermore, by controlling the interlayer stacking density and surface flatness of the graphene film through calendering, its adaptability in flexible electronic devices can be further improved.

[0055] Furthermore, by combining the synergistic effect of low-temperature high-vacuum and high-temperature graphitization processes, the structural collapse and crack propagation problems commonly encountered in traditional reduction processes are effectively avoided, ensuring that the membrane material maintains excellent electrothermal response stability even after being bent thousands of times.

[0056] Moreover, the preparation method is highly reproducible, suitable for large-scale, continuous production, and does not rely on harsh chemical reagents or complex equipment, thus showing good prospects for industrial application.

[0057] Therefore, the graphene film preparation method of the present invention has good controllability and stability, and can effectively ensure that the prepared graphene film has the expected performance.

[0058] Optionally, the graphene oxide in the graphene oxide dispersion may have different sheet diameters, such as 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm, 1.5 μm, 1.7 μm, 1.9 μm, and 2 μm. These specific sheet diameter values ​​can be flexibly selected according to the needs of the actual preparation process. In practice, smaller sheet diameters make it easier for graphene oxide to form a uniform film during the coating process, which is beneficial to improving the compactness and continuity of the film; while larger sheet diameters may improve the mechanical properties of the film to some extent.

[0059] Preferably, the graphene oxide in the graphene oxide dispersion has a sheet diameter of 0.1 μm to 1.3 μm.

[0060] Specifically, the sheet diameter refers to the maximum lateral dimension of a graphene oxide sheet in a two-dimensional plane (usually measured in micrometers, μm), which can be understood as the "diameter" or "equivalent particle size" of the sheet-like particles, even if their shape is irregular. Since graphene oxide sheets are usually irregular polygonal, near-circular, or fragmented, the statistical average of multiple sheet diameter measurements (such as D50) is used.

[0061] In step S1, the graphene oxide filter cake is dispersed in a solvent by high-pressure homogenization to obtain the graphene oxide dispersion, wherein the high-pressure homogenization pressure of the graphene oxide filter cake is 800~1500 bar.

[0062] The graphene membrane preparation method of this invention effectively exfoliates graphene oxide agglomerates through high-pressure homogenization, obtaining a stable and uniform dispersion to ensure the quality of subsequent film formation. High-pressure homogenization enables the graphene oxide filter cake to be uniformly dispersed in the solvent, avoiding sheet agglomeration and stacking, thus laying the foundation for the subsequent preparation of high-quality graphene membranes.

[0063] This also avoids excessive homogenization pressure, which could lead to excessive fragmentation of the graphene film, significantly reducing its size and increasing structural defects, resulting in a marked decrease in the conductivity and mechanical strength of the reduced graphene film. Conversely, insufficient homogenization pressure could lead to incomplete dissociation of agglomerates, resulting in a large number of multilayer GO stacks or flocculent aggregates in the dispersion, causing an excessively high proportion of multilayer sheets and insufficient film density after formation.

[0064] The viscosity of the graphene oxide dispersion is 1500 mpa·s to 20000 mpa·s.

[0065] The graphene film preparation method of this invention effectively controls the rheological behavior during the coating and film formation process by limiting the viscosity range of the graphene oxide dispersion, ensuring uniform wet film thickness and no edge accumulation. Too low a viscosity can easily lead to coating breakage or increased porosity, while too high a viscosity affects degassing and spreading, increasing the defect density within the film.

[0066] Optionally, the viscosity of the graphene oxide dispersion can be different values ​​such as 1500 mPa·s, 1600 mPa·s, 1800 mPa·s, 2000 mPa·s, 3000 mPa·s, 4000 mPa·s, 5000 mPa·s, 6000 mPa·s, 7000 mPa·s, 8000 mPa·s, 9000 mPa·s, 10000 mPa·s, 12000 mPa·s, 15000 mPa·s, 18000 mPa·s, and 20000 mPa·s. These specific viscosity values ​​can be selected and adjusted according to different coating processes and equipment. Preferably, the viscosity of the graphene oxide dispersion is 5000 mPa·s to 15000 mPa·s.

[0067] In step S1, the carbon-to-oxygen ratio of the graphene oxide filter cake is 2:1 to 6:1.

[0068] In the method for preparing graphene films according to embodiments of the present invention, the carbon-oxygen ratio range is beneficial to provide sufficient oxygen-containing functional groups to enhance its dispersibility in solvents while maintaining the integrity of the sheet structure.

[0069] Too low a carbon-to-oxygen ratio leads to excessive hydrophilicity and decreased thermal stability, while too high a ratio hinders exfoliation and dispersion. Precise control of the carbon-to-oxygen ratio also affects the removal kinetics of oxygen-containing groups during low-temperature pre-reduction, preventing sheet shrinkage caused by localized over-reduction. This carbon-to-oxygen ratio range facilitates gradient deoxidation during subsequent thermal reduction, avoiding structural distortion and stress accumulation caused by rapid deoxidation, thereby maintaining the continuity and integrity of the graphene sheets. It also improves the conductivity and mechanical properties of the final graphene film.

[0070] Optionally, the carbon-to-oxygen ratio of the graphene oxide filter cake can be different values ​​such as 2:1, 1:1, 3:1, 4:1, 5:1, and 6:1. These specific carbon-to-oxygen ratio values ​​can be flexibly determined according to actual preparation needs and requirements for the performance of graphene oxide. Preferably, the carbon-to-oxygen ratio of the graphene oxide filter cake is 2:1 to 4:1. This range ensures good dispersibility while taking into account structural stability during the thermal reduction process and efficient construction of the conductive network.

[0071] Furthermore, controlling the homogenization pressure and the synergistic effect of the carbon-oxygen ratio further optimizes the rheological properties and stability of the dispersion, ensuring the repeatability of shear thinning behavior during coating. This process parameter window also helps reduce energy consumption, improve production efficiency, and balance the integrity of the material structure with the feasibility of large-scale preparation.

[0072] In step S1, during the high-pressure homogenization stage, the solvent is pure water or deionized water. Using pure water or deionized water as the solvent not only facilitates the uniform dispersion of graphene oxide sheets but also effectively avoids the adverse effects of introducing impurity ions on subsequent conductivity. Its high polarity helps stabilize oxygen-containing functional groups, enhancing the long-term storage stability of the dispersion. Simultaneously, the hydrogen bonding between water molecules and the sheets can moderately regulate rheological behavior, improving the uniformity and adhesion of the coating film. This enhances dispersion stability, inhibits the aggregation of recombinant functional groups, and promotes uniform arrangement between sheets, thereby improving the rheological properties and film quality of the graphene oxide dispersion.

[0073] In step S1, the graphene oxide dispersion is coated onto the substrate by a coating method.

[0074] The method for preparing the graphene film according to embodiments of the present invention involves coating the graphene oxide dispersion onto a substrate using a coating method. The coating process allows for precise control of the thickness and uniformity of the graphene oxide film, ensuring the consistency and stability of the film layer.

[0075] In step S1, the substrate includes at least one of copper, aluminum, stainless steel, polyethylene terephthalate, polyimide, polyethylene, glass, polyester, nonwoven fabric, carbon cloth, and cotton fiber.

[0076] The graphene film preparation method of this invention, by selecting the above-mentioned substrate material, can meet the requirements of different application scenarios for flexibility, conductivity, high temperature resistance and mechanical strength.

[0077] In step S1, the graphene oxide dispersion coated on the substrate is dried at 25°C to 90°C.

[0078] The method for preparing graphene film in this invention limits the temperature range of drying after coating to 25°C to 90°C, which can effectively remove solvent and prevent the film from cracking or blistering due to excessively fast drying. At the same time, it prevents the early aggregation or structural distortion of graphene oxide sheets caused by excessively high temperature.

[0079] The graphene oxide dispersion coated on the substrate was dried at different temperatures, including 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C. Preferably, the drying temperature was 60°C to 80°C.

[0080] These mild drying conditions help maintain the rheological stability of the dispersion during film formation, promote orderly stacking of layers, and improve film density. The drying time is optimized based on film thickness and substrate type, typically controlled between 1 and 6 hours to ensure sufficient moisture evaporation and reasonable energy consumption. The wet gel-state film formed at this stage provides a structurally uniform precursor for subsequent reduction processes, ensuring the consistency of the final graphene film's conductivity and mechanical properties.

[0081] In step S1, the thickness of the obtained graphene oxide film is less than 500 μm.

[0082] This thickness range helps to maintain good conductivity while also ensuring the film's flexibility and light transmittance, making it suitable for applications in flexible electronics, transparent conductive films, and sensor devices. Excessively thick films not only increase brittleness but may also lead to increased risks of crack propagation and interface delamination; while excessively thin films make it difficult to form a continuous conductive network.

[0083] By optimizing the coating parameters and dispersion concentration, the film thickness can be precisely controlled within the range of 100–500 μm, ensuring batch stability and process repeatability. The dried graphene oxide film can be directly used in the subsequent reduction process, or it can be multi-layered according to process requirements to control the final film thickness and conductivity.

[0084] In step S2, the graphene oxide film obtained in S1 is subjected to a vacuum of 10... -2 ~10 -5 The pre-reduced graphene film was prepared under controlled temperature conditions of 250℃~600℃. Thermal reduction treatment was then performed under these conditions to effectively remove oxygen-containing functional groups, promote the recovery of the sp² carbon network, and improve conductivity and thermal stability. A vacuum environment suppressed the disordered pyrolysis of the graphene oxide sheets, reduced defect formation, and ensured the uniformity of the reduction process.

[0085] For example, temperature control within the range of 400℃ to 600℃ balances deoxidation efficiency and substrate tolerance, making it particularly suitable for polymer substrate-compatible processes. This stage can achieve resistivity as low as 10⁻⁶.-3 The film achieves a strength on the order of Ω·cm while maintaining film integrity and adhesion. The reduced film can be used in flexible supercapacitors, electromagnetic shielding coatings, and wearable sensing units.

[0086] The low-temperature treatment involves a heating rate of less than 3 °C / min. Slow heating helps release residual stress within the film, preventing microcracks or interlayer delamination caused by thermal shock, while simultaneously promoting the gradient decomposition of oxygen-containing groups to form a uniform porous structure. These process parameters are particularly suitable for continuous production of large-area films, significantly improving batch-to-batch consistency and yield.

[0087] In step S2, the weight loss ratio during the process of preparing the pre-reduced graphene film from the graphene oxide film is 30%~40%.

[0088] This weight loss ratio corresponds to the balance range between the controllable removal of oxygen-containing functional groups and the reconstruction of the carbon framework. If it is too low, the reduction will be insufficient, while if it is too high, it will easily lead to layer breakage and void aggregation. By controlling the heating program and vacuum level, the mass loss can be concentrated in the dehydration, decarboxylation, and deepoxidation stages, achieving structural densification while retaining necessary interlayer connection sites. Furthermore, the precise control of the weight loss ratio further ensures the structural stability of the film during subsequent high-temperature annealing or chemical doping processes, enabling synergistic optimization of ordered carbon layer stacking and defect repair.

[0089] In step S3, the high-temperature graphitization temperature is 2200℃~3000℃, and the processing time is 1.5h~2.5h. Preferably, the processing time is 2h.

[0090] The graphene film preparation method of this invention, by setting the high-temperature graphitization temperature within the range of 2200℃ to 3000℃, can further improve the graphene lattice and significantly enhance its crystallinity. Precise control of the processing time can be adjusted according to different application requirements and film material characteristics to achieve optimal electrical and thermal properties.

[0091] The inert conditions are achieved using at least one of argon, nitrogen, and helium. These gases not only possess excellent thermal stability and chemical inertness, but also effectively isolate external active substances, preventing side reactions between carbon atoms and impurities at high temperatures.

[0092] In step S3, the thickness of the graphene film obtained after calendering is 0.01 mm to 5 mm. This thickness range can meet diverse needs, from ultra-thin flexible electronic devices to high-density thermal management materials. By adjusting the gap between the calendering rolls and the temperature gradient, the interlayer shear force and plastic flow are synergistically controlled, promoting the orientation and alignment of graphite microcrystals and significantly improving the in-plane thermal conductivity and mechanical strength of the film material.

[0093] In step S3, the graphene layer is calendered by rolling and static pressing in sequence, and the stress during calendering is controlled to be ≤200 MPa.

[0094] This stress control window effectively promotes interlayer bonding while preventing microcracks and structural distortions caused by localized stress concentration. The rolling stage enhances the in-plane orientation of the graphene sheets through continuous shearing, while the planar static pressing further eliminates interlayer voids, achieving densification and reconstruction. The temporal coupling of these two processes significantly reduces interfacial thermal resistance while maintaining film integrity.

[0095] The composite heating film of this invention includes a first encapsulation layer and a second encapsulation layer, and a graphene film according to any one of the above. The graphene film layer has a heating body and a connecting electrode. The first encapsulation layer, the graphene film layer and the second encapsulation layer are stacked sequentially. The heating body is sealed between the first encapsulation layer and the second encapsulation layer, and the connecting electrode extends beyond the first encapsulation layer and the second encapsulation layer.

[0096] Therefore, the composite heating film of this invention effectively improves the safety and environmental tolerance of the heating film through the high insulation and thermal stability of the encapsulation layer, while limiting the deformation of the graphene film during thermal expansion and ensuring the reliability of long-term operation.

[0097] For example, the encapsulation layer can be a mica sheet, which can be muscovite, biotite, phlogopite, lithium mica, lithium iron phosphate mica, pearl mica, as well as artificial synthetic mica or natural mica.

[0098] Furthermore, by using mica sheet encapsulation technology, the high heat resistance and insulation properties of mica sheets can protect the graphene film from mechanical deformation and chemical corrosion, while enhancing the interfacial thermal resistance matching to achieve efficient heat conduction.

[0099] Optionally, the graphene film is used as the heating unit, employing a combination of four sheets with a power of 385W+370W+370W+385W, where the 385W sheet is the edge sheet and the 370W sheet is the middle sheet. The mica sheets have thicknesses of 0.3mm and 0.15mm. The thinner mica sheet faces the bread, and the two middle heating sheets are bonded to the 0.3mm mica sheet with silicone adhesive, separated by aluminum foil to insulate heat and reflect infrared rays.

[0100] The method for preparing the composite heating film according to embodiments of the present invention includes the following steps: The graphene film described in any of the above is rolled onto the substrate layer, and then the graphene film is engraved into a preset pattern by laser engraving to form the heating body and the connecting electrode; the engraved graphene film and the substrate layer are placed between the first encapsulation layer and the second encapsulation layer for hot pressing and encapsulation, so that the heating body is completely sealed in the two encapsulation layers, while the connecting electrode is left exposed outside the encapsulation structure to realize external circuit connection.

[0101] The method for preparing the composite heating film in this invention ensures a strong interface bond between the encapsulation layer and the graphene film layer by precisely controlling the hot-pressing temperature and pressure gradient, with no residual bubbles, while also preventing lattice distortion of the graphene structure at high temperatures.

[0102] Optionally, the laser engraving parameters can be optimized to achieve a linewidth accuracy of ±5μm, ensuring the geometric consistency of the heating pattern and the uniformity of current conduction. The substrate layer is made of a high-temperature resistant polymer material, which allows for non-destructive separation in the subsequent peeling process, ultimately resulting in a self-supporting composite heating film.

[0103] Optionally, the preset pattern is one of a snake, a U-shape, and a linear shape, and the base layer is a PET base layer.

[0104] The substrate layer and the graphene film with the preset pattern are adhered to a first mica sheet. After removing the substrate layer by low-temperature hot pressing, a second mica sheet is placed on top of the first mica sheet and hot-pressed at 500℃-600℃ for at least 8 hours to obtain the composite heating film. After 1000 hours of continuous operation, the composite heating film exhibits a thermal resistance change rate of less than 3% and a surface temperature distribution uniformity deviation of no more than ±1.5℃, demonstrating excellent thermal stability and electrical durability.

[0105] The heating device of this invention includes the composite heating film described above. The heating device embeds the composite heating film within a heat-resistant insulating shell, and the outer layer is coated with an infrared reflective coating, effectively improving heat radiation efficiency and reducing heat loss.

[0106] The heating device in this invention can be a toaster, griddle, oven, air fryer, kettle, heating cup, heated lunch box, warming plate, heated table, or heater. In other embodiments, the heating device can also be a heated glove, knee pad, hot compress therapy device, moxibustion auxiliary device, flexible heating pad, wall heating decorative panel, desktop heater, pipe heat tracing, equipment insulation and preheating mold.

[0107] For example, the application of composite heating films in toasters (traditional toasters typically use iron-chromium-aluminum or nickel-chromium alloy (Ni-Cr) heating wires as heating elements) enables even toasting of bread with consistent color and allows for rapid start-up without preheating. In air fryers, their efficient heat radiation characteristics help shorten cooking time while reducing energy consumption. When used in heated tables or heaters, combined with an infrared reflective coating, they can direct heat in a directional manner, improving comfort.

[0108] Example of effect Example 1 (1) 200 g of graphene oxide filter cake with a solid content of 5 wt% was placed into 200 mL of ultrapure water and homogenized under high pressure of 1200 bar to obtain graphene oxide dispersion.

[0109] (2) The uniformly dispersed graphene oxide dispersion was coated onto polyethylene terephthalate by coating method, and dried in air at 60 °C to remove the solvent water, so as to obtain a graphene oxide film with uniform thickness.

[0110] (3) The prepared graphene oxide film was placed in a vacuum of 10 -5 In a vacuum sintering furnace, the temperature is raised to 300 °C at a heating rate of 1 °C / min.

[0111] (4) The low-temperature treated graphene oxide film is placed in a high-temperature graphitization furnace and heated to 3000 °C in an inert gas atmosphere. The prepared porous graphene film is then rolled into a dense graphene film at 200 MPa by a plate static pressing method.

[0112] Example 2 The difference between this embodiment and Embodiment 1 is that the mass of the graphene oxide filter cake in step 1 is 100 g, while the rest of the preparation method is the same as in Embodiment 1.

[0113] Example 3 The difference between this embodiment and Embodiment 1 is that the mass of the graphene oxide filter cake in step 1 is 300 g, while the rest of the preparation method is the same as in Embodiment 1.

[0114] Example 4 The difference between this embodiment and Embodiment 1 is that the high-pressure homogenization in step 1 is 800 bar, while the rest of the preparation methods are the same as in Embodiment 1.

[0115] Example 5 The difference between this embodiment and Embodiment 1 is that the high-pressure homogenization in step 1 is 1500 bar, while the rest of the preparation methods are the same as in Embodiment 1.

[0116] Example 6 The difference between this embodiment and embodiment 1 is that the substrate in step 2 is a copper foil, while the rest of the preparation method is the same as in embodiment 1.

[0117] Example 7 The difference between this embodiment and Embodiment 1 is that the substrate in step 2 is polyethylene, while the rest of the preparation method is the same as in Embodiment 1.

[0118] Example 8 The difference between this embodiment and embodiment 1 is that the substrate in step 2 is a non-woven fabric, while the rest of the preparation method is the same as in embodiment 1.

[0119] Example 9 The difference between this embodiment and Embodiment 1 is that the drying temperature in step 2 is 25 ℃, while the rest of the preparation method is the same as in Embodiment 1.

[0120] Example 10 The difference between this embodiment and Embodiment 1 is that the drying temperature in step 2 is 80 ℃, while the rest of the preparation method is the same as in Embodiment 1.

[0121] Example 11 The difference between this embodiment and Embodiment 1 is that the vacuum degree in step 3 is 10⁻³ Pa, while the rest of the preparation method is the same as in Embodiment 1.

[0122] Example 12 The difference between this embodiment and Embodiment 1 is that the heating rate in step 3 is 3 °C / min, while the rest of the preparation method is the same as in Embodiment 1.

[0123] Example 13 The difference between this embodiment and Embodiment 1 is that the heating temperature in step 3 is 200 ℃, while the rest of the preparation method is the same as in Embodiment 1.

[0124] Example 14 The difference between this embodiment and Embodiment 1 is that the heating temperature in step 3 is 600 ℃, while the rest of the preparation method is the same as in Embodiment 1.

[0125] Example 15 The difference between this embodiment and Embodiment 1 is that the graphitization temperature in step 4 is 2500 ℃, while the rest of the preparation method is the same as in Embodiment 1.

[0126] Example 16 The difference between this embodiment and Embodiment 1 is that the calendering pressure in step 4 is 100 MPa, while the rest of the preparation method remains the same as in Embodiment 1.

[0127] Comparative Example 1 The difference between this comparative example and Example 1 is that the high-pressure homogenization in step 1 is 500 bar, while the rest of the preparation methods are the same as in Example 1.

[0128] Comparative Example 2 The difference between this comparative example and Example 1 is that the high-pressure homogenization in step 1 is 2000 bar, while the rest of the preparation methods are the same as in Example 1.

[0129] Comparative Example 3 The difference between this comparative example and Example 1 is that the drying temperature in step 2 is 100 °C, while the rest of the preparation method is the same as in Example 1.

[0130] Comparative Example 4 The difference between this comparative example and Example 1 is that the vacuum degree in step 3 is 10. -1 The remaining preparation methods are consistent with those in Example 1.

[0131] Comparative Example 5 The difference between this comparative example and Example 1 is that the vacuum level described in step 3 is at atmospheric pressure, while the rest of the preparation method is the same as in Example 1.

[0132] Comparative Example 6 The difference between this comparative example and Example 1 is that the heating rate in step 3 is 10 °C / min, while the rest of the preparation method is the same as in Example 1.

[0133] Comparative Example 7 The difference between this comparative example and Example 1 is that the high-temperature graphitization temperature in step 4 is 1800 °C, while the rest of the preparation method is the same as in Example 1.

[0134] As can be seen from Examples 1 and 2-3, if the concentration of graphene oxide slurry is too low, its viscosity will be too low, resulting in greater fluidity of graphene oxide during the coating process and poor sheet orientation; if the concentration of graphene oxide is too high, its viscosity will be too high, making it difficult for graphene oxide to flow during the coating process, resulting in poor uniformity of the coating dispersion thickness, which in turn reduces its electrical conductivity and thermal properties.

[0135] As can be seen from Examples 1 and 4-5 and Comparative Examples 1-2, if the high-pressure homogenization pressure is too low, it is difficult for graphene oxide to be exfoliated into a single layer of graphene oxide, and some particles will agglomerate during the film formation process. If the high-pressure homogenization pressure is too high, the sheet size of graphene oxide will be too small, resulting in a low viscosity of graphene oxide, and ultimately a poor film-forming property of graphene oxide film.

[0136] As can be seen from Examples 1 and 6-8, different substrate choices will affect the electrical and thermal properties of graphene films. The smoother the substrate surface, the smaller the surface wrinkles and roughness of the resulting graphene film, which is more conducive to the transmission of electrons and phonons.

[0137] As can be seen from Examples 1 and 9-10, if the drying temperature of the graphene oxide film is too low, it will result in more interlayer bound water. The more interlayer bound water will cause more water molecules to be released during the low-temperature treatment stage, thereby destroying the orderliness of the graphene film. If the drying temperature of the graphene oxide film is too high, it will increase the capillary force between the sheets during the drying process, increase the wrinkles and orientation of the graphene film, and reduce its electrical conductivity and thermal conductivity.

[0138] As can be seen from Examples 1 and 11 and Comparative Examples 4-5, if the vacuum level during the low-temperature treatment is too low, it will be difficult for the gas to escape effectively from the inside of the film, thereby generating high pressure inside the graphene film and damaging the orientation and crystallinity of the graphene film.

[0139] As can be seen from Examples 1 and 12, if the heating rate of the low-temperature treatment is too fast, it will cause the oxygen-containing functional groups and interlayer bound water in the precursor to release a large amount of gas rapidly, resulting in high pressure inside the membrane.

[0140] As can be seen from Examples 1 and 13-14, if the low-temperature treatment temperature is too low, too many oxygen-containing functional groups will remain, and the residual oxygen-containing groups will further damage the orientation of the graphene film during the subsequent graphitization process; if the low-temperature treatment temperature is too high, some of the reduced graphene oxide will be partially oxidized in the air due to the high temperature, thus affecting the next graphitization process.

[0141] As can be seen from Examples 1 and 15, if the high-temperature graphitization temperature is too low, the crystallinity of the graphene film will be poor, thereby affecting the electrical conductivity and thermal conductivity of the graphene film.

[0142] As can be seen from Examples 1 and 16, if the rolling pressure is low, the pores of the graphene film will be large. Excessive porosity will affect the transmission of electrons and phonons in the graphene film, thereby affecting the thermal conversion efficiency and thermal response time of the graphene film.

[0143] As can be seen from Example 1 and Comparative Example 3, if the low-temperature drying temperature is too high, the moisture in the precursor will be lost too quickly, causing the graphene oxide to curl and crack, resulting in poor thickness uniformity and affecting its subsequent low-temperature carbonization and graphitization.

[0144] As can be seen from Example 1 and Comparative Example 6, if the low-temperature processing speed is too fast, it will cause a surge in the gas release of the graphene oxide film in the precursor, resulting in excessive internal pressure and collapse of the film.

[0145] As can be seen from Example 1 and Comparative Example 7, if the high-temperature graphitization temperature is too low, carbon atoms are difficult to arrange to form an ordered sp2 hybrid structure, resulting in more internal defects and poor crystallinity, which leads to lower electrical and thermal conductivity.

[0146] First, the graphene film is pressed onto a PET substrate using a roller press, and then the graphene film is engraved into shape using a laser engraving machine. The designed serpentine, U-shaped, and linear patterns are used to attach the cut graphene film pattern to the mica sheet using high-temperature adhesive. After hot pressing at a low temperature of 50~80℃ for 10 minutes, the PET substrate is removed, copper electrodes are fixed at both ends of the graphene film pattern, and finally a layer of mica sheet is covered on the other side. After hot pressing at 500-600℃ for 8 hours, the mica sheet-encapsulated graphene heating film is obtained.

[0147] Prepared into a toast oven: The graphene heating layer uses pure graphene heating film, which is designed and cut into corresponding graphene heating wires according to voltage, power parameters and size requirements. The thickness is generally 0.01mm-0.5mm. It has the advantages of high thermal conductivity, high electrical conductivity, high thermal radiation and stable performance, and can heat up quickly and evenly.

[0148] Mica insulation layer: High-purity mica or synthetic mica sheets are selected with a thickness of 0.1mm-0.5mm. It has high temperature resistance (>600℃), high insulation (breakdown voltage >5kV / mm) and excellent thermal conductivity to ensure uniform heat dissipation and isolate the circuit.

[0149] Example: like Figure 6 As shown, the graphene heating element uses a four-piece combination of 385W+370W+370W+385W, with the 385W piece being the edge piece and the 370W piece being the middle piece. The mica thicknesses are 300 micrometers and 150 micrometers, with the thinner mica piece facing the bread. The two middle heating elements have two thicker 300-micrometer mica pieces bonded together with silicone, separated by aluminum foil to insulate heat and reflect infrared rays.

[0150] The comparative sample metal wire (iron-chromium-aluminum) heating element uses a three-piece combination of 300W + 400W + 300W, where the 300W piece is the edge piece and the 400W piece is the middle piece. The mica sheet is 300 micrometers thick and is used for structural support and to facilitate the winding of the metal heating wire. The metal wire of the edge piece is wound on one side, with the wire facing the bread. The metal wire of the middle piece is wound on both sides.

[0151] The experimental bread slices were 10cm × 10cm × 2cm in size, and two slices were used. The experimental results are shown in the appendix. Figure 7The left side shows the baking effect of the graphene heating element, and the right side shows the baking effect of the comparative metal mica sheet. The comparison shows that the baking efficiency of the graphene heating element is improved by 40-55%.

[0152] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0153] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0154] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0155] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0156] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0157] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0158] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A graphene film, characterized in that, The graphene film has the following properties: The electrical conductivity of the graphene film is 10. 2 S / m ~ 1.2 × 10 6 S / m; The in-plane thermal conductivity of the graphene film is 80 W / mK to 1850 W / mK; The tensile strength of the graphene film is 15MPa~50MPa; The density of the graphene film is 1.2 g / cm³. 3 ~2.2 g / cm 3 ; The thickness of the graphene film is 2μm~500μm; The porosity of the graphene film is 0.5% to 5%.

2. A method for preparing a graphene film, characterized in that, Includes the following steps: S1 Obtain a graphene oxide dispersion with a sheet diameter of 0.1μm~2μm, and coat the graphene oxide dispersion onto a substrate. After drying, obtain a graphene oxide film. S2 involves subjecting the graphene oxide film obtained in S1 to low-temperature, high-vacuum treatment to obtain a pre-reduced graphene film; S3 involves subjecting the pre-reduced graphene film from S2 to high-temperature graphitization under inert conditions to obtain a graphene layer, followed by calendering of the graphene layer to obtain the graphene film as described in claim 1.

3. The method for preparing the graphene film according to claim 2, characterized in that, In step S1, the graphene oxide filter cake is dispersed in a solvent by high-pressure homogenization to obtain the graphene oxide dispersion, wherein the high-pressure homogenization pressure of the graphene oxide filter cake is 800 bar to 1500 bar, and the homogenization time is 0.5 h to 6 h. And / or, the viscosity of the graphene oxide dispersion is 1500 mpa·s to 20000 mpa·s.

4. The method for preparing the graphene film according to claim 3, characterized in that, In step S1, the carbon-to-oxygen ratio of the graphene oxide filter cake is 2:1 to 6:1; And / or, in step S1, the solvent is pure water or deionized water.

5. The method for preparing the graphene film according to claim 2, characterized in that, In step S1, the graphene oxide dispersion is coated onto the substrate by a coating method; And / or, in step S1, the substrate comprises at least one of copper, aluminum, stainless steel, polyethylene terephthalate, polyimide, polyethylene, glass, polyester, nonwoven fabric, carbon cloth, and cotton fiber. And / or, in step S1, the graphene oxide dispersion coated on the substrate is dried at 25°C to 90°C for 12 to 96 hours. And / or, in step S1, the thickness of the obtained graphene oxide film is less than 500 μm.

6. The method for preparing the graphene film according to claim 3, characterized in that, In step S2, the graphene oxide film obtained in S1 is subjected to a vacuum of 10... -2 ~10 -5 Pa, and the pre-reduced graphene film under controlled temperature conditions of 250℃~600℃; And / or, in step S2, the heating rate of the pre-reduced graphene film is less than 3 °C / min; And / or, in step S2, the weight loss ratio during the preparation of the pre-reduced graphene film from the graphene oxide film is 30%-40%.

7. The method for preparing the graphene film according to claim 3, characterized in that, In step S3, the temperature for high-temperature graphitization is 2200℃~3000℃, and the processing time is 1.5h~2.5h; And / or, in step S3, the gas used for the inert conditions is at least one of argon, nitrogen and helium; And / or, in step S3, the thickness of the graphene film obtained after calendering is 0.01 mm to 5 mm; And / or, in step S3, the graphene layer is calendered by rolling and static pressing in sequence, and the stress during calendering is controlled to be ≤200 MPa.

8. A composite heating diaphragm, characterized in that, include The graphene film according to any one of claims 2-7, wherein the graphene film layer has a heating body and a connecting electrode; A first encapsulation layer and a second encapsulation layer are stacked sequentially, the first encapsulation layer, the graphene film layer and the second encapsulation layer are sealed between the first encapsulation layer and the second encapsulation layer, and the connecting electrode extends beyond the first encapsulation layer and the second encapsulation layer.

9. A method for preparing a composite heating film, characterized in that, Includes the following steps: The graphene film of any one of claims 2-7 is rolled onto the substrate layer, and then the graphene film is engraved into a preset pattern by laser engraving to form a heating body and connecting electrodes; the engraved graphene film and the substrate layer are placed between the first encapsulation layer and the second encapsulation layer for hot-press encapsulation, so that the heating body is completely sealed in the two layers of mica sheets.

10. A heating device, characterized in that, Includes the composite heating film according to claim 9.

Images