Graphene heat-conducting film as well as preparation method and application thereof

Abstract

The invention provides a graphene heat-conducting film and a preparation method and application thereof, and relates to the technical field of graphene materials, the preparation method of the graphene heat-conducting film comprises the following steps: mixing graphene microsphere powder and first graphene oxide slurry, and then preparing a film to obtain the graphene heat-conducting film; wherein the graphene microsphere powder is prepared by the following steps: sequentially carrying out drying and heat treatment on second graphene oxide slurry, so as to obtain the graphene microsphere powder. The graphene heat-conducting film prepared from the graphene microsphere powder and the graphene oxide slurry with the stretching characteristic is low in Young modulus and better in ductility.

Description

Technical Field

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

[0002] Graphene thermal conductive film has excellent thermal conductivity and heat dissipation performance, and is widely used in the fields of thermal conductivity and heat dissipation of 5G chips and thin and light electronic products. In pursuit of higher thermal conductivity, graphene thermal conductive film often needs to undergo one or more graphitization treatments at 2800℃-3500℃. Graphene thermal conductive film after high-temperature graphitization is often brittle and has a high Young's modulus, making it difficult to adapt to bending, twisting, folding or stress application scenarios, which greatly limits the application and promotion of graphene thermal conductive film. At present, scientific researchers' research on graphene thermal conductive film mainly focuses on how to obtain higher thermal diffusion coefficients and planar thermal conductivity coefficients. There are few reports on the improvement of the physical parameters of the basic materials of graphene thermal conductive film. Young's modulus is an important physical parameter of the material. Low Young's modulus materials have relatively excellent elastic deformation and ductility, and are widely used in application scenarios that require close attachment and certain stress. In order to obtain higher thermal conductivity parameters, graphene thermal conductive films often pursue the ultimate flat arrangement of graphene sheets and dense interlayer stacking. After self-assembly reaction and rearrangement of graphitized carbon atoms, the graphene sheets in the graphene thermal conductive film no longer have the characteristics of planar stretching and translation, making the graphene thermal conductive film brittle and resulting in a high Young's modulus, which is difficult to adapt to the use of non-planar loads that need to be closely attached or in certain stress scenarios.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] One of the purposes of the present invention is to provide a method for preparing a graphene thermally conductive film, so as to at least solve one of the technical problems existing in the prior art. The method for preparing the graphene thermally conductive film comprises the following steps: mixing graphene microsphere powder and a first graphene oxide slurry to form a film to prepare a graphene thermally conductive film; wherein the graphene microsphere powder is prepared by the following steps: sequentially drying and heat treating the second graphene oxide slurry to obtain the graphene microsphere powder. The graphene thermally conductive film prepared by the present invention using graphene microsphere powder with stretch characteristics and graphene oxide slurry has a low Young's modulus and better ductility.

[0005] The second object of the present invention is to provide a graphene thermal conductive film. The graphene thermal conductive film is prepared by using a graphene thermal conductive film preparation method.

[0006] The third object of the present invention is to provide an application of the graphene thermally conductive film prepared by the graphene thermally conductive film preparation method in electronic products, aerospace vehicles and sensors.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0008] In a first aspect, the present invention provides a method for preparing a graphene thermally conductive film, the method for preparing a graphene thermally conductive film comprising the following steps:

[0009] The graphene microsphere powder and the first graphene oxide slurry are mixed to form a film to prepare a graphene thermal conductive film;

[0010] Wherein, the graphene microsphere powder is prepared by the following steps:

[0011] The second graphene oxide slurry is dried and heat-treated in sequence to obtain the graphene microsphere powder.

[0012] Further, the heat treatment includes microwave heat treatment or thermal reduction treatment;

[0013] Preferably, the microwave heat treatment comprises: performing microwave heat treatment on the dried second graphene oxide slurry under an inert gas atmosphere;

[0014] Preferably, the temperature of microwave heat treatment is 200-450°C and the treatment time is 1-5 min;

[0015] Preferably, the temperature of the thermal reduction treatment is 200-400° C., and the treatment time is 20-40 min.

[0016] Furthermore, the median particle size of the second graphene oxide slurry is greater than 0 and less than or equal to 5 μm;

[0017] Preferably, homogenization is used to adjust the particle size of the second graphene oxide slurry;

[0018] Preferably, the pressure of the homogenization treatment is 600-1200 bar and / or the number of the homogenization treatment is 3-10 times.

[0019] Furthermore, the second graphene oxide slurry is prepared by mixing graphene oxide cake and water, and the content of the graphene oxide slurry is greater than 0 and less than or equal to 2%.

[0020] Furthermore, the first graphene oxide slurry is prepared by mixing graphene oxide cake and water, and has a solid content of 3-6%;

[0021] Preferably, after mixing the graphene oxide cake and water, pH adjustment and sand grinding are sequentially performed;

[0022] Preferably, the pH of the first graphene oxide slurry is 5-7;

[0023] Preferably, the first graphene oxide slurry is sand-milled 2-8 times with a sand mill at a rotation speed of 1500-2000 r / min.

[0024] Furthermore, the film preparation further comprises: mixing the graphene microsphere powder and the first graphene oxide slurry, and sequentially coating and drying the composite slurry to obtain a graphene oxide composite film;

[0025] Preferably, the added mass of the graphene microsphere powder is 1-10% of the mass of the graphene oxide cake used to prepare the first graphene oxide slurry;

[0026] Preferably, the mixing time is 3-12h;

[0027] Preferably, the drying temperature is 40-80°C, preferably 70°C.

[0028] Furthermore, the method for preparing the graphene thermal conductive film further comprises: sequentially performing heat treatment, carbonization treatment and graphitization treatment on the graphene oxide composite film;

[0029] Preferably, the heat treatment comprises: sandwiching the graphene oxide composite film between a stainless steel sheet and an artificial graphite film, and then performing heat treatment in a nitrogen atmosphere to obtain a treated film;

[0030] Preferably, the heat treatment temperature is 200-280°C, the heat treatment time is 2-5h, and the heating rate is 0.5-2°C / min;

[0031] Preferably, the carbonization treatment comprises: sandwiching the treated film between an artificial graphite film and a graphite plate, and then performing a carbonization treatment under a nitrogen atmosphere to obtain a carbonized film;

[0032] Preferably, the temperature of the carbonization treatment is 1000-1500°C, the treatment time is 1-4h, and the heating rate is 0.5-2°C / min;

[0033] Preferably, the graphitization treatment comprises: sandwiching the carbonized film between an artificial graphite film and a graphite plate, and then performing a graphitization treatment under an argon atmosphere to obtain a graphitized sample;

[0034] Preferably, the temperature of the graphitization treatment is 2800° C.-3500° C., and the treatment time is 0.5-2 h.

[0035] Furthermore, the graphitized sample is subjected to calendering treatment to prepare a graphene thermal conductive film;

[0036] Preferably, the calendering process uses a flat calender.

[0037] Furthermore, the drying temperature is 150-200°C.

[0038] In a second aspect, the present invention provides a graphene thermally conductive film prepared by the graphene thermally conductive film preparation method.

[0039] In a third aspect, the present invention provides an application of a graphene thermally conductive film prepared by the graphene thermally conductive film preparation method in aerospace vehicles and sensor electronic products.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The method for preparing a graphene thermally conductive film provided by the present invention adopts a graphene microsphere powder with stretching characteristics and a graphene oxide slurry to prepare a graphene thermally conductive film with low Young's modulus, and utilizes the stretchable and slippable characteristics of the graphene microspheres to enhance the recoverable deformation of the graphene thermally conductive film in the force direction. In the process of preparing the graphene microsphere powder, heat treatment is used to achieve partial deoxidation, which can effectively remove part of the -CO type oxygen-containing groups in the graphene oxide slurry, such as hydroxyl groups, while retaining most of the -C=O type oxygen-containing groups, such as carboxyl functional groups, to ensure that the graphene microspheres can participate in the self-assembly reaction, and can construct a hollow supporting skeleton structure of the graphene microspheres, so as to reduce the Young's modulus of the graphene thermally conductive film by the wrinkle rebound and slippable characteristics.

[0042] The graphene thermal conductive film provided by the present invention has a lower Young's modulus and relatively good ductility than the graphene thermal conductive film prepared by the traditional process, and is more suitable for non-planar close attachment or use in certain stress scenarios than the graphene thermal conductive film prepared by the traditional process. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0044] Figure 1 is the SEM image of graphene oxide microspheres in Example 3;

[0045] Figure 2 This is a test graph of Young's modulus of the graphene thermal conductive film obtained in Example 3;

[0046] Figure 3 This is a test graph of Young's modulus of the graphene thermal conductive film obtained in Example 10;

[0047] Figure 4 This is a test graph of Young's modulus of the graphene thermal conductive film obtained in Comparative Example 3;

[0048] Figure 5 This is the Young's modulus test spectrum of the graphene thermal conductive film obtained in Comparative Example 2. DETAILED DESCRIPTION

[0049] Unless otherwise defined herein, scientific and technical terms used in conjunction with the present invention shall have the meanings commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear, however, in the case of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, unless otherwise stated, the use of "or" means "and / or". In addition, the use of the term "including" and other forms is non-limiting.

[0050] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] A first aspect of the present invention provides a method for preparing a graphene thermally conductive film, the method comprising the following steps:

[0052] The graphene microsphere powder and the first graphene oxide slurry are mixed to form a film to prepare a graphene thermal conductive film;

[0053] Wherein, the graphene microsphere powder is prepared by the following steps:

[0054] The second graphene oxide slurry is dried and heat-treated in sequence to obtain the graphene microsphere powder.

[0055] In the present invention, a composite slurry is prepared by using graphene microsphere powder with stretching properties and graphene oxide, and then a low Young's modulus graphene thermal conductive film is prepared by using the composite slurry, and the stretchable and slippable properties of the graphene microspheres are used to enhance the recoverable deformation of the graphene thermal conductive film in the force direction. In the process of preparing the graphene microsphere powder, heat treatment is used to achieve partial deoxidation, which can effectively remove some -CO type oxygen-containing groups in the graphene oxide slurry, such as hydroxyl groups, while retaining most of the -C=O type oxygen-containing groups, such as carboxyl functional groups, to ensure that the graphene microspheres can participate in the self-assembly reaction, and a hollow supporting skeleton structure of the graphene microspheres can be constructed, so as to reduce the Young's modulus of the graphene thermal conductive film by using the wrinkle rebound and slippable properties.

[0056] Further, the heat treatment includes microwave heat treatment or thermal reduction treatment;

[0057] Preferably, the microwave heat treatment comprises: performing microwave heat treatment on the dried second graphene oxide slurry under an inert gas atmosphere;

[0058] Preferably, the temperature of the microwave heat treatment is 200-450°C, for example, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, etc., and the treatment time is 1-5min, for example, 1min, 2min, 3min, 4min, 5min, etc.;

[0059] Preferably, the temperature of the thermal reduction treatment is 200-400°C, for example, it can be 200°C, 250°C, 300°C, 350°C, 400°C, etc.

[0060] In the present invention, the graphene oxide slurry is spray-dried to obtain graphene oxide microsphere powder, and then the graphene oxide microsphere powder is subjected to microwave heat treatment or thermal reduction treatment to achieve partial deoxygenation treatment. The present invention adopts specific treatment parameters to achieve at least three effects: 1. The primary purpose of microwave heat treatment or thermal reduction treatment is to remove part of the -CO type oxygen-containing groups, such as hydroxyl groups. Since the graphene microsphere powder will be subsequently configured with the graphene oxide slurry to prepare a graphene thermal conductive film, it is avoided that the oxygen-containing groups in the graphene microsphere structure are removed during the subsequent heat treatment stage to produce gas, thereby generating large air pockets and large bubble structures (the reason why the graphene microspheres will produce large air pockets when defunctionalizing is that their structure is spherical, which is different from the two-dimensional sheet-like graphene oxide). Only the upper and lower surfaces produce gas, while the surrounding areas produce gas more violently, thereby tearing the internal structure of the graphene film to produce large air pockets), which destroys the flat orderliness of the graphene sheets and causes tearing damage and cracking, which is not conducive to heat conduction; 2. The second purpose of microwave heat treatment or thermal reduction treatment is to retain most of the -C=O type oxygen-containing groups to ensure that the graphene microspheres can participate in the self-assembly reaction during the self-assembly stage of the graphene oxide coating film. Only by participating in the self-assembly reaction to form chemical bonds can a heat conduction channel be formed to ensure that the thermal conductivity of the graphene thermal conductive film is not sacrificed; 3. The third purpose of microwave heat treatment or thermal reduction treatment under specific conditions is to construct a hollow supporting skeleton structure of graphene microspheres, so as to reduce the Young's modulus of the graphene thermal conductive film with wrinkle rebound and slip characteristics.

[0061] In the present invention, when the heat treatment temperature is too high and the time is too long, the thermal conductivity of the product becomes poor and the Young's modulus value is too large. When the heat treatment temperature is too low, the thermal conductivity of the product becomes poor.

[0062] Further, the median particle size of the second graphene oxide slurry is greater than 0 and less than or equal to 5 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.;

[0063] In the present invention, before spraying, the graphene oxide slurry is subjected to a particle size control treatment to be processed into a graphene oxide slurry with a small flake size. The definition of the small flake size is that the particle size of the graphene oxide is controlled to D50≤5μm before spraying. When the particle size D50>5μm, the addition has almost no improvement on the Young's modulus of the graphene thermal conductive film, and its thermal conductivity will decrease (exponentially decrease) relative to the graphene thermal conductive film without addition. This is mainly attributed to the fact that the large particle size of the graphene microspheres will seriously block the self-assembly of the graphene oxide sheets and affect the long-range order of the graphene film.

[0064] Preferably, homogenization is used to adjust the particle size of the second graphene oxide slurry;

[0065] Preferably, the pressure of the homogenization treatment is 600-1500 bar and / or the number of homogenization treatments is 3-10 times; specifically, the pressure of the homogenization treatment is 600-1200 bar, for example, it can be 600 bar, 700 bar, 800 bar, 900 bar, 1000 bar, 1100 bar, 1200 bar, etc.; the number of homogenization treatments is 3-10 times, for example, it can be 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, etc.

[0066] In the present invention, the homogenization pressure affects the particle size of the graphene oxide microsphere powder. If the particle size is too small, it is difficult to form a spherical structure, and the improvement effect on the Young's modulus is poor. If the particle size is large, it is not conducive to self-assembly, the microspheres are unevenly dispersed, the thermal conductivity becomes poor, and the improvement of the Young's modulus is not obvious.

[0067] Furthermore, the second graphene oxide slurry is prepared by mixing graphene oxide cake and water, and the content of the graphene oxide slurry is greater than 0 and less than or equal to 2%, for example, it can be 0.5%, 1%, 1.5%, 2%, etc.

[0068] Preferably, after the second graphene oxide slurry is subjected to the particle size control treatment and before being dried, the second graphene oxide slurry is diluted;

[0069] In the present invention, the second graphene oxide slurry is initially prepared by mixing graphene oxide cake and water, with an initial solid content of 1-6%, and then homogenization treatment is performed to adjust the particle size, and then the second graphene oxide slurry after the particle size adjustment is diluted to a solid content greater than 0 and less than or equal to 2%. The purpose of dilution is to allow the second graphene oxide slurry to exist in the form of a monodisperse after spray drying. If the solid content is greater than 2%, the viscosity of the second graphene oxide slurry is too high, and it is difficult to draw the material during the spray drying process, and the nozzle is easily blocked. At the same time, the graphene oxide is easy to appear in the form of aggregates and cannot be evenly dispersed. The obtained graphene microsphere powder will agglomerate after microwave puffing and drying.

[0070] Furthermore, the drying temperature is 150-200°C, for example, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc.

[0071] Further, the first graphene oxide slurry is prepared by mixing graphene oxide cake and water, and has a solid content of 3-6%, for example, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, etc.;

[0072] Preferably, after mixing the graphene oxide cake and water, pH adjustment and sand grinding are sequentially performed;

[0073] Preferably, the pH of the first graphene oxide slurry is 5-7, for example, 5, 5.5, 6, 6.5, 7, etc.;

[0074] Preferably, the first graphene oxide slurry is sand milled 2-8 times, for example, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, etc., and the rotation speed is 1500-2000r / min, for example, 1500r / min, 1600r / min, 1700r / min, 1800r / min, 1900r / min, 2000r / min, etc.

[0075] In the present invention, after the first graphene oxide slurry is sand-milled by a sand mill, the slurry is visually uniform in color without color difference or stripes.

[0076] Furthermore, the film preparation further comprises: mixing the graphene microsphere powder and the first graphene oxide slurry, coating and drying the obtained composite slurry in sequence to obtain a graphene oxide composite film;

[0077] Preferably, the added mass of the graphene microsphere powder is 1-10% of the mass of the graphene oxide cake used to prepare the first graphene oxide slurry, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.;

[0078] Preferably, the stirring time is 3-12 hours, for example, it can be 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, etc.;

[0079] Preferably, the drying temperature is 40-80°C, for example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc.

[0080] In the present invention, a specific range of drying temperatures is used. If the temperature is too high, the film will dry too quickly and cracks will occur in the film.

[0081] Furthermore, the method for preparing the graphene thermal conductive film further comprises: sequentially performing heat treatment, carbonization treatment and graphitization treatment on the graphene oxide composite film;

[0082] Preferably, the heat treatment comprises: sandwiching the graphene oxide composite film between a stainless steel sheet and an artificial graphite film, and then performing heat treatment in a nitrogen atmosphere to obtain a treated film;

[0083] Preferably, the heat treatment temperature is 200-280°C, for example, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, etc., the heat treatment time is 2-5h, for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, etc., and the heating rate is 0.5-2°C / min, for example, 0.5°C / min, 1°C / min, 1.5°C / min, 2°C / min, etc.;

[0084] Preferably, the carbonization treatment comprises: sandwiching the treated film between an artificial graphite film and a graphite plate, and then performing a carbonization treatment under a nitrogen atmosphere to obtain a carbonized film;

[0085] Preferably, the temperature of the carbonization treatment is 1000-1500°C, for example, it can be 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, etc., the treatment time is 1-4h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, etc., and the heating rate is 0.5-2°C / min, for example, it can be 0.5°C / min, 1°C / min, 1.5°C / min, 2°C / min, etc.;

[0086] Preferably, the graphitization treatment comprises: sandwiching the carbonized film between an artificial graphite film and a graphite plate, and then performing a graphitization treatment under an argon atmosphere to obtain a graphitized sample;

[0087] Preferably, the temperature of the graphitization treatment is 2800°C-3500°C, for example, it can be 2800°C, 2900°C, 3000°C, 3100°C, 3200°C, 3300°C, 3400°C, 3500°C, etc., and the treatment time is 0.5-2h, for example, it can be 0.5h, 1h, 1.5h, 2h, etc.

[0088] Furthermore, the graphitized sample is subjected to calendering treatment to prepare a graphene thermal conductive film;

[0089] Preferably, the calendering process uses a flat calender.

[0090] A second aspect of the present invention provides a graphene thermally conductive film prepared by the graphene thermally conductive film preparation method.

[0091] A third aspect of the present invention provides an application of a graphene thermally conductive film prepared by the graphene thermally conductive film preparation method in electronic products, aerospace vehicles and sensors.

[0092] The graphene thermal conductive film of the present invention is mainly used in folding screen mobile phones and is applicable to non-static scenes such as certain force bending, curved surfaces, torsion, etc.

[0093] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.

[0094] Figure 3 The graphene thermal conductive film obtained in Example 4; Figure 4 The graphene thermal conductive film obtained in Example 6; Figure 5 This is the graphene thermal conductive film obtained in Comparative Example 2.

[0095] Example 1

[0096] This embodiment provides a method for preparing a graphene thermal conductive film, comprising the following steps:

[0097] S1. Preparation of graphene microsphere powder: using conventional graphene oxide cake purchased from Yuntian Mo Rui as raw material, the graphene oxide cake and deionized water are configured into a 1% solid graphene oxide slurry; the configured graphene oxide slurry is homogenized 10 times under 600 bar conditions to adjust the flake diameter, and a low-diameter graphene oxide slurry (0<D50≤5μm) is obtained; the graphene oxide slurry after the flake diameter is adjusted is diluted to 0.5% solid content using deionized water to obtain a dilute graphene oxide slurry; the small-diameter graphene oxide slurry is spray-dried at 150°C using a spray dryer to obtain graphene oxide microsphere powder; a microwave heat treatment is performed in an inert gas atmosphere at 450°C for 1 min using a microwave puffing furnace, the purpose of which is to partially deoxidize the graphene oxide microsphere powder, and the graphene microsphere powder is obtained after passing through a 200-mesh sieve;

[0098] S2, using graphene oxide cake and deionized water to prepare graphene oxide slurry with a solid content of 3%, using ammonia water to adjust the pH value of the slurry to 5 range, using a planetary mixer to stir and disperse to obtain an initial graphene oxide slurry; using a turbine sand mill to sand grind 8 times at a speed of 1500r / min to obtain a graphene oxide slurry; adding the graphene microsphere powder obtained in step S1 to the graphene oxide slurry according to 10% of the mass of the graphene oxide cake in S2, using a planetary mixer to stir at high speed for 3h, and then vacuum degassing for 3h under a low pressure condition of -95kpa to obtain a uniformly stirred composite slurry; using a coating machine to coat the composite slurry on a substrate to form a film with a coating thickness of 5mm, and drying in a blast oven at 40°C to obtain a graphene oxide composite film after drying;

[0099] S3, using 304 stainless steel sheets and artificial graphite films to sandwich the graphene oxide composite film obtained in step S2, and heat-treating it at 200°C for 5 hours in a nitrogen atmosphere with a heating rate of 2°C / min to obtain a low-temperature treated film; transferring the obtained low-temperature treated film to a carbonization furnace by sandwiching it with an artificial graphite film and a graphite plate, and carbonizing it at 1000°C for 4 hours in a nitrogen atmosphere with a heating rate of 2°C / min. After naturally cooling to room temperature, removing the aluminum foil substrate to obtain a carbonized film;

[0100] S4. Use an artificial graphite film and a graphite plate to sandwich the carbonized film sample obtained in step S3, transfer it to a high-temperature graphitization furnace, and perform high-temperature graphitization treatment at 2800°C for 2 hours under the protection of a high-purity argon atmosphere to obtain a graphitized sample; and perform calendering treatment on the obtained graphitized sample under a flat plate calender to obtain a graphene thermal conductive film with low Young's modulus.

[0101] Example 2

[0102] This embodiment provides a method for preparing a graphene thermal conductive film, comprising the following steps:

[0103] S1. Preparation of graphene microsphere powder: using conventional graphene oxide cake purchased from Yuntian Mo Rui as raw material, the graphene oxide cake and deionized water are configured into a 6% solid graphene oxide slurry; the configured graphene oxide slurry is homogenized 3 times under 1200 bar to adjust the flake diameter, and a low-diameter graphene oxide slurry (0<D50≤5μm) is obtained; the graphene oxide slurry after the flake diameter is adjusted is diluted to 2% solid content using deionized water to obtain a dilute graphene oxide slurry; the small-diameter graphene oxide slurry is spray-dried at 200°C using a spray dryer to obtain graphene oxide microsphere powder; a microwave heat treatment is performed in an inert gas atmosphere at 200°C for 5 minutes using a microwave puffing furnace, the purpose of which is to partially deoxidize the graphene oxide microsphere powder, and the graphene microsphere powder is obtained after passing through a 200-mesh sieve;

[0104] S2, using graphene oxide cake and deionized water to prepare graphene oxide slurry with a solid content of 6%, using ammonia water to adjust the pH value of the slurry to 7 range, using a planetary mixer to stir and disperse to obtain an initial graphene oxide slurry; using a turbine sand mill to sand grind twice at a speed of 2000r / min to obtain a graphene oxide slurry; adding the graphene microsphere powder obtained in step S1 to the graphene oxide slurry according to 1% of the mass of the graphene oxide cake in S2, using a planetary mixer to stir at high speed for 12h, and then vacuum degassing for 3h under a low pressure condition of -95kpa to obtain a uniformly stirred composite slurry; using a coating machine to coat the composite slurry on a substrate to form a film with a coating thickness of 5mm, and drying in a blast oven at 80°C to obtain a graphene oxide composite film after drying;

[0105] S3, using 304 stainless steel sheets and artificial graphite films to sandwich the graphene oxide composite film obtained in step S2, and heat-treating it at 280°C for 2 hours in a nitrogen atmosphere at a heating rate of 0.5°C / min to obtain a low-temperature treated film; transferring the obtained low-temperature treated film to a carbonization furnace by sandwiching it with an artificial graphite film and a graphite plate, and carbonizing it at 1500°C for 1 hour in a nitrogen atmosphere at a heating rate of 0.5°C / min. After naturally cooling to room temperature, removing the aluminum foil substrate to obtain a carbonized film;

[0106] S4. Use an artificial graphite film and a graphite plate to sandwich the carbonized film samples obtained in step S3, transfer them to a high-temperature graphitization furnace, and perform high-temperature graphitization treatment at 3500°C for 0.5 under the protection of a high-purity argon atmosphere to obtain a graphitized sample; and perform calendering treatment on the obtained graphitized sample under a flat plate calender to obtain a graphene thermal conductive film with a low Young's modulus.

[0107] Example 3

[0108] This embodiment provides a method for preparing a graphene thermal conductive film, comprising the following steps:

[0109] S1. Preparation of graphene microsphere powder: using conventional graphene oxide cake purchased from Yuntian Mo Rui as raw material, the graphene oxide cake and deionized water are configured into a graphene oxide slurry with a solid content of 4.5%; the configured graphene oxide slurry is homogenized 6 times under 1000 bar conditions to adjust the flake diameter, and a low-diameter graphene oxide slurry (0<D50≤5μm) is obtained; the graphene oxide slurry after the flake diameter is adjusted is diluted to a solid content of 0.8% using deionized water to obtain a dilute graphene oxide slurry; the small-diameter graphene oxide slurry is spray-dried at 200°C using a spray dryer to obtain graphene oxide microsphere powder; a microwave heat treatment is performed in an inert gas atmosphere at 400°C for 4 minutes using a microwave puffing furnace, the purpose of which is to partially deoxidize the graphene oxide microsphere powder, and the graphene microsphere powder is obtained after passing through a 200-mesh sieve;

[0110] S2, using graphene oxide cake and deionized water to prepare graphene oxide slurry with a solid content of 4.5%, using ammonia water to adjust the pH value of the slurry to 6, using a planetary mixer to stir and disperse to obtain an initial graphene oxide slurry; using a turbine sand mill to sand grind 5 times at a speed of 1800r / min to obtain a graphene oxide slurry; adding the graphene microsphere powder obtained in step S1 to the graphene oxide slurry according to 5% of the mass of the graphene oxide cake in S2, using a planetary mixer to stir at high speed for 4h, and then vacuum degassing for 3h under a low pressure of -95kpa to obtain a uniformly stirred composite slurry; using a coating machine to coat the composite slurry on a substrate to form a film with a coating thickness of 5mm, and drying in a blast oven at 70°C to obtain a graphene oxide composite film after drying;

[0111] S3, using 304 stainless steel sheets and artificial graphite films to sandwich the graphene oxide composite film obtained in step S2, and heat-treating it at 260°C for 3 hours in a nitrogen atmosphere at a heating rate of 1°C / min to obtain a low-temperature treated film; transferring the obtained low-temperature treated film to a carbonization furnace by sandwiching it with an artificial graphite film and a graphite plate, and carbonizing it at 1300°C for 2 hours in a nitrogen atmosphere at a heating rate of 1°C / min. After naturally cooling to room temperature, removing the aluminum foil substrate to obtain a carbonized film;

[0112] S4. Use an artificial graphite film and a graphite plate to sandwich the carbonized film samples obtained in step S3, transfer them to a high-temperature graphitization furnace, and perform high-temperature graphitization treatment at 2950°C for 2 hours under the protection of a high-purity argon atmosphere to obtain a graphitized sample; and perform calendering treatment on the obtained graphitized sample under a flat plate calender to obtain a graphene thermal conductive film with low Young's modulus.

[0113] in, Figure 1 is the SEM image of graphene oxide microspheres in Example 3; Figure 2This is the Young's modulus test spectrum of the graphene thermal conductive film obtained in Example 3.

[0114] Example 4

[0115] This embodiment provides a method for preparing a graphene thermally conductive film, which differs from Embodiment 3 in that the homogenization pressure in step S1 is 550 bar, and the purpose is to explore the influence of the homogenization pressure on the performance of the graphene thermally conductive film.

[0116] Example 5

[0117] This embodiment provides a method for preparing a graphene thermally conductive film, which differs from Embodiment 3 in that the homogenization pressure in step S1 is 1500 bar.

[0118] Example 6

[0119] This embodiment provides a method for preparing a graphene thermal conductive film. The difference from Embodiment 3 is that the processing time of the microwave constant temperature deoxidation stage in step S1 is 30 seconds, and its purpose is to explore the influence of the microwave constant temperature deoxidation time of graphene oxide microspheres on the performance of the graphene thermal conductive film.

[0120] Example 7

[0121] This embodiment provides a method for preparing a graphene thermally conductive film, which is different from Embodiment 3 in that the processing time of the microwave constant temperature deoxidation stage in step S1 is 6 minutes.

[0122] Example 8

[0123] This embodiment provides a method for preparing a graphene thermal conductive film, which differs from Embodiment 3 in that the deoxidation treatment adopts a thermal reduction method, and an industrial nitrogen-filled oven equipment is used to partially deoxidize the graphene oxide microsphere powder. The thermal reduction treatment temperature is 200° C. and the time is 40 minutes.

[0124] Example 9

[0125] This embodiment provides a method for preparing a graphene thermal conductive film, which differs from Embodiment 8 in that the thermal reduction treatment temperature is 400° C. and the time is 20 min.

[0126] Example 10

[0127] This embodiment provides a method for preparing a graphene thermal conductive film, which is different from Embodiment 8 in that the thermal reduction treatment temperature is 300° C. and the time is 30 min.

[0128] in, Figure 3 This is a test graph of Young's modulus of the graphene thermal conductive film obtained in Example 10.

[0129] Embodiment 11

[0130] This embodiment provides a method for preparing a graphene thermal conductive film, which differs from Embodiment 10 in that the thermal reduction treatment temperature is 450°C.

[0131] Example 12

[0132] This embodiment provides a method for preparing a graphene thermal conductive film, which differs from Embodiment 10 in that the thermal reduction treatment temperature is 150°C.

[0133] Embodiment 13

[0134] This embodiment provides a method for preparing a graphene thermal conductive film, which differs from Embodiment 10 in that the thermal reduction treatment time is 50 minutes.

[0135] Embodiment 14

[0136] This embodiment provides a method for preparing a graphene thermal conductive film, which differs from Embodiment 10 in that the thermal reduction treatment time is 10 minutes.

[0137] Comparative Example 1

[0138] This comparative example provides a method for preparing a graphene thermally conductive film, which differs from Example 3 in that step S1 is not performed, that is, graphene microsphere powder is not used for compounding and slurrying, and pure graphene oxide slurry is used as the coating slurry to prepare the graphene thermally conductive film, the purpose of which is to explore the influence of graphene microspheres on the Young's modulus value of the graphene thermally conductive film.

[0139] Comparative Example 2

[0140] This comparative example provides a method for preparing a graphene thermal conductive film. The difference from Example 3 is that conventional graphene powder that has been conventionally expanded and carbonized at 1350°C for 2 hours is used instead of graphene microsphere powder as a compound material, and its microscopic morphology is an expanded graphene flake structure. The purpose is to explore the influence of the morphology of the compounded graphene material on the performance of the graphene thermal conductive film.

[0141] in, Figure 5 This is the graphene thermal conductive film obtained in Comparative Example 2.

[0142] Comparative Example 3

[0143] This embodiment provides a method for preparing a graphene thermally conductive film. The difference from Embodiment 3 is that the microwave constant temperature deoxidation stage of step S1 is carried out under an inert atmosphere at 900° C., and its purpose is to explore the influence of the microwave constant temperature deoxidation temperature of graphene oxide microspheres on the performance of the graphene thermally conductive film.

[0144] in, Figure 4 This is the graphene thermal conductive film obtained in Comparative Example 3.

[0145] Comparative Example 4

[0146] This embodiment provides a method for preparing a graphene thermally conductive film, which differs from Embodiment 3 in that the microwave constant temperature deoxidation stage in step S1 is carried out under an inert atmosphere at 150°C.

[0147] Test Case

[0148] Test sample: graphene thermal conductive film prepared by Examples 1-14 and Comparative Examples 1-4.

[0149] Test method: Conduct Young's modulus and thermal conductivity characterization tests on the test samples.

[0150] The test results are shown in Table 1.

[0151] Table 1

[0152]

[0153]

[0154] It can be seen from the data in Table 1 that the Young's modulus of Examples 1 to 3 is greatly improved compared to the thermally conductive film prepared by the conventional method in Comparative Example 1, and the thermal conductivity is also at a high level. The Young's modulus of Example 4 is higher than that of Example 3, which is attributed to the fact that the diameter of the graphene microspheres is larger due to the regulation of the precursor, resulting in a larger size of the graphene microspheres (D50>5μm), which is not conducive to the self-assembly reaction of the graphene oxide composite coating film, and is prone to introducing edge defects, uneven dispersion of the microspheres, poor thermal conductivity, and no obvious improvement in the Young's modulus; compared with Example 3, the Young's modulus of Example 5 is higher than that of Example 3, which is attributed to the fact that the homogenization pressure is too high, it is difficult to form the morphology of the microspheres, and the improvement effect on the Young's modulus is poor; compared with Example 3, the microwave heating treatment time in Example 6 is too short, and the functional If the removal of the group is not sufficient, the phenomenon of gas production around will still occur, which will destroy the orderliness of the flattening of the graphene sheet and cause tearing damage and cracking, which is not conducive to heat conduction; compared with Example 3, the heat treatment time of Example 7 is longer, but since the reaction temperature of the self-assembly group is not reached, the effect on thermal conductivity and Young's modulus is not large; the difference between Example 8-10 and Example 3 is that a heat treatment method of thermal reduction is adopted. Combined with the test data, the thermal conductivity and Young's modulus of Examples 8-10 are not much different from those of Example 3, proving that the heat treatment process of thermal reduction can also achieve the purpose of removing the target functional group in Example 3. Example 9 increases the heat treatment temperature compared to Example 8, but the heat treatment temperature is still within the removal range of the target group and will not affect the self-assembly group. Therefore, the thermal conductivity and Young's modulus of Example 9 are similar to those of Example 8. Compared with Example 8, Example 10 further increases the heat treatment temperature, and the heat treatment temperature is still within the removal range of the target group, which will not cause the self-assembly group to fall off.Compared with Example 10, the processing temperature of Example 11 is too high, the effective groups of the microspheres fall off, and cannot participate in the self-assembly of the film-forming process, the Young's modulus is too large, and the thermal conductivity is also poor; compared with Example 10, the processing temperature of Example 12 is low, the secondary gas production is large, the air pockets are too large, which affects the orderliness of the film formation and the thermal conductivity is poor, but has little effect on the Young's modulus; compared with Example 10, the reaction time of Example 13 is long, but because the reaction temperature of the self-assembly group is not reached, the effect on the thermal conductivity and Young's modulus is not large; compared with Example 10, the reaction time of Example 14 is short, the secondary degassed microspheres produce gas to form large air pockets, which destroys the orderliness of the graphene film and the thermal conductivity is poor; the Young's modulus of Comparative Example 3 is higher than that of Example 3, which can be attributed to the graphene oxide microsphere powder The temperature is high in the microwave constant temperature deoxidation stage, resulting in the release of most of the oxygen-containing groups. In the self-assembly stage of the graphene oxide coating film, due to the lack of groups on the surface of the graphene microspheres, they cannot participate in the self-assembly reaction well, resulting in the presence of more phonon scattering points inside the graphene thermal conductive film, which is not conducive to the improvement of the thermal conductivity. The graphene microspheres that do not participate in the self-assembly reaction have limited stress stretching and sliding effects under stress. The thermal conductivity of Comparative Example 4 is lower than that of Example 3, which can be attributed to the fact that the heat treatment temperature of Comparative Example 4 is too low to achieve the purpose of removing some -CO type oxygen-containing groups (such as hydroxyl groups). In the subsequent carbonization and graphitization stage, the gas production around is more intense, thereby tearing the internal structure of the graphene film to produce large air pockets, thereby destroying the flattening orderliness of the graphene sheets and causing tearing damage and cracking, which is not conducive to thermal conductivity. The Young's modulus of Comparative Example 1 is significantly higher than that of Example 3. Compared with Example 3, the graphene thermal conductive film obtained in Comparative Example 1 is more rigid and brittle, and obvious creases will appear when bent, which can be attributed to the fact that there are no microspheres or wrinkled structures with stretchable and sliding properties inside the graphene thermal conductive film. After the self-assembly reaction and high-temperature graphitization of the graphene thermal conductive film, the graphene sheet loses the plane translation property, so the graphene thermal conductive film pattern modulus increases. The thermal conductivity of Comparative Example 2 is poor, and the Young's modulus is not improved. This can be attributed to the fact that the carbonized graphene cannot participate in the self-assembly reaction, so a large number of defects are introduced into the graphene thermal conductive film, resulting in a decrease in the thermal conductivity of the graphene thermal conductive film. Since the graphene powder cannot participate in the self-assembly reaction, its plane sliding effect under stress is poor.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a graphene thermally conductive film, characterized in that: The method for preparing the graphene thermal conductive film comprises the following steps: The graphene microsphere powder and the first graphene oxide slurry are mixed to form a film to prepare a graphene thermal conductive film; Wherein, the graphene microsphere powder is prepared by the following steps: The second graphene oxide slurry is dried and heat-treated in sequence to obtain the graphene microsphere powder.

2. The method for preparing a graphene thermally conductive film according to claim 1, characterized in that: The heat treatment includes microwave heat treatment or thermal reduction treatment; Preferably, the microwave heat treatment comprises: performing microwave heat treatment on the dried second graphene oxide slurry under an inert gas atmosphere; Preferably, the temperature of microwave heat treatment is 200-450°C and the treatment time is 1-5 min; Preferably, the temperature of the thermal reduction treatment is 200-400° C., and the treatment time is 20-40 min.

3. The method for preparing a graphene thermally conductive film according to claim 1, characterized in that: The median particle size of the second graphene oxide slurry is greater than 0 and less than or equal to 5 μm; Preferably, homogenization is used to adjust the particle size of the second graphene oxide slurry; Preferably, the pressure of the homogenization treatment is 600-1200 bar and / or the number of the homogenization treatment is 3-10 times.

4. The method for preparing a graphene thermally conductive film according to claim 3, characterized in that: The second graphene oxide slurry is prepared by mixing graphene oxide cake and water, and the content of the graphene oxide slurry is greater than 0 and less than or equal to 2%.

5. The method for preparing a graphene thermally conductive film according to claim 1, characterized in that: The first graphene oxide slurry is prepared by mixing graphene oxide cake and water, with a solid content of 3-6%; Preferably, after mixing the graphene oxide cake and water, pH adjustment and sand grinding are sequentially performed; Preferably, the pH of the first graphene oxide slurry is 5-7; Preferably, the first graphene oxide slurry is sand-milled 2-8 times with a sand mill at a rotation speed of 1500-2000 r / min.

6. The method for preparing a graphene thermally conductive film according to claim 1, characterized in that: The film preparation comprises: coating and drying a composite slurry obtained by mixing graphene microsphere powder and a first graphene oxide slurry in sequence to obtain a graphene oxide composite film; Preferably, the added mass of the graphene microsphere powder is 1-10% of the mass of the graphene oxide cake used to prepare the first graphene oxide slurry; Preferably, the mixing time is 3-12h; Preferably, the drying temperature is 40-80°C, preferably 70°C.

7. The method for preparing a graphene thermally conductive film according to claim 6, characterized in that: The method for preparing the graphene thermal conductive film further comprises: sequentially performing heat treatment, carbonization treatment and graphitization treatment on the graphene oxide composite film; Preferably, the heat treatment comprises: sandwiching the graphene oxide composite film between a stainless steel sheet and an artificial graphite film, and then performing heat treatment in a nitrogen atmosphere to obtain a treated film; Preferably, the heat treatment temperature is 200-280°C, the heat treatment time is 2-5h, and the heating rate is 0.5-2°C / min; Preferably, the carbonization treatment comprises: sandwiching the treated film between an artificial graphite film and a graphite plate, and then performing a carbonization treatment under a nitrogen atmosphere to obtain a carbonized film; Preferably, the temperature of the carbonization treatment is 1000-1500°C, the treatment time is 1-4h, and the heating rate is 0.5-2°C / min; Preferably, the graphitization treatment comprises: sandwiching the carbonized film between an artificial graphite film and a graphite plate, and then performing a graphitization treatment under an argon atmosphere to obtain a graphitized sample; Preferably, the temperature of the graphitization treatment is 2800°C-3500°C, and the treatment time is 0.5-2h; Preferably, the graphitized sample is subjected to calendering treatment to prepare a graphene thermal conductive film; Preferably, the calendering process uses a flat calender.

8. The method for preparing a graphene thermally conductive film according to claim 1, characterized in that: The drying temperature is 150-200°C.

9. A graphene thermally conductive film prepared by the method for preparing a graphene thermally conductive film according to any one of claims 1 to 8.

10. Application of the graphene thermally conductive film prepared by the method for preparing a graphene thermally conductive film according to any one of claims 1 to 8 in electronic products, aerospace vehicles and sensors.

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