Thermal expansion microsphere / graphene composite film with intelligent heat conduction and heat insulation switching function and preparation method of thermal expansion microsphere / graphene composite film

Abstract

The invention discloses an intelligent heat conduction and heat insulation switching thermal expansion microsphere / graphene composite film and a preparation method thereof.The preparation method comprises the steps that thermal expansion microspheres are prepared, the thermal expansion microspheres comprise a core material and a polymer shell, and the core material is selected from low-boiling-point alkane or a mixture of water-based liquid and a flame retardant; preparing a water-based polymer solution, adding the prepared thermal expansion microspheres and graphene powder into the water-based polymer solution, and performing ultrasonic dispersion to form a composite membrane solution; coating the composite film solution in a mold, controlling the thickness of the coating, removing bubbles through vacuum filtration, and then carrying out hot pressing treatment; and drying the hot-pressed composite film to obtain the thermal expansion microsphere / graphene composite film. The heat dissipation device has the functions of high-efficiency heat dissipation and heat disaster isolation. When the equipment operates normally, the heat-conducting property is presented; when the equipment breaks down and generates heat disasters, the equipment can be quickly switched to a heat insulation state. Meanwhile, the fabric has a certain flame-retardant function.

Description

Technical Field

[0001] The present invention belongs to the field of intelligent thermal conductive materials, and relates to a thermal expansion microsphere / graphene composite film with intelligent thermal conduction and heat insulation switching and a preparation method thereof. Background Art

[0002] As a new type of two-dimensional carbon nanomaterial, graphene has attracted much attention in the field of thermal management due to its unique layered structure and excellent thermal conductivity. The in-plane thermal conductivity of graphene is extremely high (up to 1000 - 5000 W / (m·K)), while the interlayer thermal conductivity is relatively low. This significant thermal conductivity anisotropy makes it have broad application potential in heat dissipation materials. However, a single graphene material cannot effectively block the diffusion of heat under thermal runaway conditions, so it needs to be combined with other functional materials to achieve intelligent thermal management. Thermal expansion microspheres are polymer microspheres with a core-shell structure, whose core is a low-boiling alkane or water, and the shell is a thermoplastic polymer. When the temperature rises to the expansion temperature of the microspheres, the volume of the microspheres expands rapidly, increasing the volume of the microspheres to several times to dozens of times the original volume.

[0003] At present, the technologies in the field of thermal management mainly focus on improving the thermal conductivity of materials. Common thermal conductive materials include thermal conductive silicone grease, thermal conductive paste, heat dissipation film, etc. These materials construct a thermal conductive network by filling high-thermal-conductivity fillers (such as graphene, boron nitride, etc.) to improve the thermal conductivity of the materials. In addition, three-dimensional interconnected filler structures (such as graphene aerogel) are also widely used in polymer-based composite materials to reduce the interfacial thermal resistance and improve the phonon transfer efficiency.

[0004] Although the existing thermal management technologies have made certain progress in improving the thermal conductivity of materials, there are still some significant problems. First, traditional thermal conductive materials cannot effectively block the diffusion of heat under thermal runaway conditions, but may instead conduct heat to the surrounding areas, exacerbating the spread of fire accidents. Second, most of the existing thermal management materials only have a single thermal conductive function and lack an intelligent switching mechanism, and cannot achieve efficient heat dissipation and heat insulation adaptive switching under normal working conditions and thermal runaway conditions. In addition, the dispersion of high-thermal-conductivity fillers and the interfacial thermal resistance problem also limit the improvement of the thermal conductivity of materials. Especially under high filler loading, the processability and mechanical properties of materials often decrease significantly. Therefore, there is an urgent need to develop a new type of thermal management material that can achieve intelligent switching between high thermal conductivity and high heat insulation under different conditions to meet the thermal management requirements of power equipment under extreme working conditions. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a thermal expansion microsphere / graphene composite film with intelligent thermal conduction and heat insulation switching and a preparation method thereof. The thermal expansion microsphere / graphene composite film has the functions of efficient heat dissipation and heat disaster isolation.

[0006] The technical solution provided by the present invention is as follows:

[0007] The present invention provides a method for preparing a thermally expandable microsphere / graphene composite film with intelligent thermal conduction and insulation switching, comprising the following steps: Prepare thermally expandable microspheres, wherein the thermally expandable microspheres comprise a core material and a polymer shell, and the core material is selected from low-boiling alkanes or a mixture of an aqueous liquid and a flame retardant; Prepare an aqueous polymer solution, add the prepared thermally expandable microspheres and graphene powder to the aqueous polymer solution, and ultrasonically disperse to form a composite film solution; Coat the composite film solution in a mold and control the coating thickness, and perform hot pressing treatment after removing bubbles by vacuum filtration; Dry the hot-pressed composite film to obtain the thermally expandable microsphere / graphene composite film.

[0008] Further, the method for preparing the thermally expandable microspheres comprises the following steps: Mix acrylic monomers, initiators with the following components to form an oil phase: Low-boiling alkanes and a flame retardant; or Span 80 and Tween 80; Mix the following components to form an aqueous phase: Sodium dodecyl sulfate and deionized water; or an aqueous liquid and a flame retardant; Mix the oil phase and the aqueous phase, transfer to a reaction vessel after high-speed stirring and emulsification, react at 50-90 °C for 3-12 hours under nitrogen protection, and prepare thermally expandable microspheres through centrifugal washing; Wherein, when the oil phase uses low-boiling alkanes and a flame retardant, the aqueous phase correspondingly uses sodium dodecyl sulfate and deionized water; when the oil phase uses Span 80 and Tween 80, the aqueous phase correspondingly uses an aqueous liquid and a flame retardant.

[0009] Further, the acrylic monomers include methyl methacrylate and methacrylic acid; the low-boiling alkanes are selected from any one or more of n-octane, n-nonane, and n-decane; the aqueous liquids are selected from any one or more of water, methanol, ethanol, acetone, n-butanol, and ethyl acetate; the flame retardants are selected from any one or more of trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and tris(xylene) phosphate.

[0010] Further, when the nuclear material is a mixture of an aqueous liquid and a flame retardant, the mass ratio of the acrylic monomer, initiator, Span 80, Tween 80, aqueous liquid, and flame retardant is (20 - 40):(0.1 - 0.2):(1 - 3):1:(10 - 15):(2 - 4). When the nuclear material is a mixture of a low-boiling alkane and a flame retardant, the mass ratio of the acrylic monomer, initiator, sodium dodecyl sulfate, deionized water, low-boiling alkane, and flame retardant is (20 - 40):(0.1 - 0.2):(1 - 4):100:(10 - 15):(2 - 4).

[0011] Further, during the preparation of the aqueous polymer solution, the mass ratio of deionized water to the aqueous polymer is 200:(5 - 7).

[0012] Further, the aqueous polymer is selected from any one or more of acrylic acid, vinyl acrylic acid, styrene acrylic acid, vinyl acetate, vinyl acetate-ethylene copolymer, and polyvinyl alcohol.

[0013] Further, the mass ratio of the aqueous polymer, thermally expandable microspheres, and graphene powder is 10:(1 - 10):400.

[0014] Further, the coating thickness is 10 - 50 μm, and the vacuum filtration time is 3 - 10 min.

[0015] Further, the temperature of the hot pressing treatment is 75 - 85°C, the pressure is 5 - 6 MPa, and the time is 5 - 15 min.

[0016] The present invention also provides a thermally expandable microsphere / graphene composite film with intelligent heat conduction and heat insulation switching, which is prepared according to the above-mentioned preparation method.

[0017] Beneficial effects

[0018] The present invention first uniformly disperses thermally expandable microspheres with a core of a low-boiling alkane or water and a flame retardant compounded and graphene powder in an aqueous polymer solution, then uniformly coats the mixed solution obtained by ultrasonic dispersion in a mold, and finally removes air bubbles by vacuum filtration to ensure the uniform distribution of the microspheres, and performs hot pressing molding to closely combine the thermally expandable microspheres and graphene at an appropriate temperature and pressure to form a composite film with the function of intelligent heat dissipation and heat insulation switching. By combining the high thermal conductivity of graphene with the intelligent response characteristics of thermally expandable microspheres, this composite film realizes the efficient heat dissipation of the material under normal working conditions and the rapid heat insulation switching under thermal runaway conditions. At normal temperatures, the thermal conduction network in the graphene composite film provides good heat dissipation ability; when the temperature reaches the level that causes heat disasters, the expandable microspheres in the composite film rapidly expand at high temperatures to form a heat insulation gas layer, which can effectively block the diffusion of heat, significantly reduce the risk of heat spread caused by thermal runaway, and improve the safety of electrical equipment. At the same time, the present invention has a certain flame retardant function. Description of the Drawings

[0019] Figure 1 Scanning electron microscope images of the thermally expandable microsphere / graphene composite film before and after expansion in Example 1 of the present invention;

[0020] Figure 2 Schematic diagram of the thermally expandable microsphere / graphene composite film in an embodiment of the present invention;

[0021] Figure 3 Schematic structural diagram of the heat conduction and heat insulation switching of the thermally expandable microsphere / graphene composite film in an embodiment of the present invention;

[0022] Figure 4 Thermal conductivity coefficient diagrams of the heat conduction and heat insulation modes of the thermally expandable microsphere / graphene composite films prepared in Examples 1, 2, 3, and 4;

[0023] Figure 5 Thermal switch ratio diagrams of the thermally expandable microsphere / graphene composite films prepared in Examples 1, 2, 3, and 4. Detailed Description of the Embodiments

[0024] The following further describes the present invention in detail with reference to the drawings:

[0025] The experimental methods used in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0026] The reagent materials used in this example can be purchased conventionally. For the quantitative experiments involved in the embodiments, at least three repeated experiments are set, and the results are averaged.

[0027] Example 1

[0028] An embodiment of the present invention provides a method for preparing a thermally expandable microsphere / graphene composite film with intelligent thermal conductivity and heat insulation switching. The specific process is as follows:

[0029] (1)Weigh 7 g of methyl methacrylate, 5 g of methacrylic acid, 6 g of n-octane, 1.2 g of trioctyl phosphate, and 0.12 g of azobisisobutyronitrile and mix them evenly as the oil phase; weigh 2 g of sodium dodecyl sulfate and dissolve it in 60 mL of deionized water and mix evenly as the water phase; use a high-speed stirrer to stir at a speed of 6000 revolutions per minute for 10 minutes to mix the oil phase and the water phase, then transfer the mixture to a three-necked flask, continuously stir at a speed of 300 revolutions per minute under a nitrogen atmosphere, and react at 65 °C for 16 hours to obtain thermally expandable microspheres with low-boiling alkanes and trioctyl phosphate as the core.

[0030] (2)Weigh 0.6 g of polyvinyl alcohol powder, add it to 20 g of deionized water, heat to 90 °C and continuously stir until the PVA is completely dissolved to form a uniform PVA solution. Subsequently, add 0.067 g of thermally expandable microspheres with low-boiling alkanes and trioctyl phosphate as the core and 24 g of graphene powder to the PVA solution, and disperse them with an ultrasonic disperser for 20 minutes to ensure that the expandable microspheres and graphene powder are evenly dispersed in the solution.

[0031] (3)Next, pour the mixed solution into a mold, and use a scraper to control the coating thickness within the range of 10 - 50 microns. Put the coated mold into a vacuum filtration device, filter for 5 minutes to remove air bubbles and ensure that the microspheres are evenly distributed. Then transfer the mold to a hot press, hot press at a temperature of 82 °C and a pressure of 5 MPa for 10 minutes, and dry the hot-pressed composite film in an oven at 60 °C for 1 hour to remove residual moisture, thus obtaining the thermally expandable microsphere / graphene composite film.

[0032] Example 2

[0033] An embodiment of the present invention provides a method for preparing a thermally expandable microsphere / graphene composite film with intelligent thermal conductivity and heat insulation switching. The specific process is as follows:

[0034] (1)Weigh 7 g of methyl methacrylate, 5 g of methacrylic acid, 6 g of n-nonane, 1.2 g of trioctyl phosphate, and 0.12 g of azobisisobutyronitrile and mix them evenly as the oil phase; weigh 2 g of sodium dodecyl sulfate and dissolve it in 60 mL of deionized water and mix evenly as the water phase; use a high-speed stirrer to stir at a speed of 6000 revolutions per minute for 10 minutes to mix the oil phase and the water phase, then transfer the mixture to a three-necked flask, continuously stir at a speed of 300 revolutions per minute under a nitrogen atmosphere, and react at 65 °C for 16 hours to obtain thermally expandable microspheres with low-boiling alkanes and trioctyl phosphate as the core.

[0035] (2) Weigh 0.6 g of styrene acrylic acid powder, add it to 20 g of deionized water, heat it to 90 °C and continuously stir until the styrene acrylic acid is completely dissolved to form a uniform styrene acrylic acid solution. Subsequently, add 0.26 g of thermally expandable microspheres with low-boiling alkanes and trioctyl phosphate as the core and 24 g of graphene powder to the styrene acrylic acid solution, and disperse them with an ultrasonic disperser for 20 minutes to ensure that the expandable microspheres and graphene powder are evenly dispersed in the solution.

[0036] (3) Next, pour the mixed solution into a mold, and use a scraper to control the coating thickness within the range of 10 - 50 microns. Put the coated mold into a vacuum filtration device, filter for 5 minutes to remove air bubbles and ensure the uniform distribution of microspheres. Then transfer the mold to a hot press, hot press at 82 °C and 5 MPa for 10 minutes, and dry the hot-pressed composite film in an oven at 60 °C for 1 hour to remove residual moisture, thus obtaining a thermally expandable microsphere / graphene composite film.

[0037] Example 3

[0038] The embodiment of the present invention provides a method for preparing a thermally expandable microsphere / graphene composite film with intelligent heat conduction and heat insulation switching, and the specific process is as follows:

[0039] (1) Weigh 7 g of methyl methacrylate, 5 g of methacrylic acid, 6 g of n-decane, 1.2 g of trioctyl phosphate and 0.12 g of azobisisobutyronitrile and mix them evenly as the oil phase; weigh 2 g of sodium dodecyl sulfate and dissolve it in 60 mL of deionized water and mix evenly as the water phase; after mixing the oil phase and water phase with a high-speed stirrer at a speed of 6000 revolutions per minute for 10 minutes, transfer the mixture to a three-necked flask, continuously stir at a speed of 300 revolutions per minute under a nitrogen atmosphere, and react at 65 °C for 16 hours to obtain thermally expandable microspheres with low-boiling alkanes and trioctyl phosphate as the core.

[0040] (2) Weigh 0.6 g of vinyl acrylic acid powder, add it to 20 g of deionized water, heat it to 90 °C and continuously stir until the vinyl acrylic acid is completely dissolved to form a uniform vinyl acrylic acid solution. Subsequently, add 0.6 g of thermally expandable microspheres with low-boiling alkanes and trioctyl phosphate as the core and 24 g of graphene powder to the vinyl acrylic acid solution, and disperse them with an ultrasonic disperser for 20 minutes to ensure that the expandable microspheres and graphene powder are evenly dispersed in the solution.

[0041] (3) Next, pour the mixed solution into a mold, and use a scraper to control the coating thickness within the range of 10 - 50 microns. Place the coated mold into a vacuum filtration device and filter for 5 minutes to remove air bubbles and ensure uniform distribution of the microspheres. Then transfer the mold to a hot press and hot press at a temperature of 82 °C and a pressure of 5 MPa for 10 minutes. Dry the hot-pressed composite film in an oven at 60 °C for 1 hour to remove residual moisture, and obtain a thermally expandable microsphere / graphene composite film.

[0042] Example 4

[0043] An embodiment of the present invention provides a method for preparing a thermally expandable microsphere / graphene composite film with intelligent thermal conduction and heat insulation switching, and the specific process is as follows:

[0044] (1) Weigh 7 g of methyl methacrylate, 5 g of methacrylic acid, 1.2 g of Span 80, 0.6 g of Tween 80, and 0.12 g of azobisisobutyronitrile and mix them evenly as the oil phase; weigh 9 g of water and 1.2 g of trimethyl phosphate as the water phase; use a high-speed stirrer to stir at a speed of 6000 revolutions per minute for 10 minutes to mix the oil phase and the water phase, then transfer the mixture to a three-necked flask, continuously stir at a speed of 300 revolutions per minute under a nitrogen atmosphere, and react at 65 °C for 16 hours to obtain thermally expandable microspheres with water and trimethyl phosphate as the core.

[0045] (2) Weigh 0.6 g of polyvinyl alcohol powder, add it to 20 g of deionized water, heat to 90 °C and continuously stir until the PVA is completely dissolved to form a uniform PVA solution. Subsequently, add 0.067 g of thermally expandable microspheres with water and trimethyl phosphate as the core and 24 g of graphene powder to the PVA solution, and use an ultrasonic disperser to disperse for 20 minutes to ensure that the expandable microspheres and graphene powder are evenly dispersed in the solution.

[0046] (3) Next, pour the mixed solution into a mold, and use a scraper to control the coating thickness within the range of 10 - 50 microns. Place the coated mold into a vacuum filtration device and filter for 5 minutes to remove air bubbles and ensure uniform distribution of the microspheres. Then transfer the mold to a hot press and hot press at a temperature of 82 °C and a pressure of 5 MPa for 10 minutes. Dry the hot-pressed composite film in an oven at 60 °C for 1 hour to remove residual moisture, and obtain a thermally expandable microsphere / graphene composite film.

[0047] Comparative Example 1

[0048] The preparation method of the graphene composite film without thermally expandable microspheres in the comparative example of the present invention is as follows:

[0049] (1) Weigh 0.6 g of acrylic acid powder, add it to 20 g of deionized water, heat it to 90 °C and continuously stir until the acrylic acid is completely dissolved to form a uniform acrylic acid solution. Subsequently, add 24 g of graphene powder to the acrylic acid solution and disperse it with an ultrasonic disperser for 20 minutes to ensure that the graphene powder is uniformly dispersed in the solution.

[0050] (2) Next, pour the mixed solution into a mold and use a scraper to control the coating thickness within the range of 10 - 50 microns. Place the coated mold into a vacuum filtration device and filter for 5 minutes to remove air bubbles. Then transfer the mold to a hot press and hot press it at a temperature of 82 °C and a pressure of 5 MPa for 10 minutes. Dry the hot-pressed composite film in an oven at 60 °C for 1 hour to remove residual moisture, thus obtaining a graphene composite film without thermal expansion microspheres.

[0051] Related performance tests

[0052] Detect the materials obtained in Examples 1 - 4 and Comparative Example 1. The thermal conductivity of the materials is tested by the Netzsch Laser Thermal Conductivity Tester 467. The relevant data is shown in Table 1.

[0053] Table 1

[0054]

[0055] Table 1 shows the thermal conductivities of the graphene composite films prepared in Examples 1, 2, 3, 4 and Comparative Example 1. Among them, the thermal conductivity of the graphene composite film without thermal expansion microspheres (Comparative Example 1) is 1192.067 W·m-1K-1, which is higher than that of the graphene composite films with thermal expansion microspheres (Examples 1, 2, 3). This is because the main component of the thermal expansion microspheres is polymer, and its thermal conductivity is low. After being compounded with graphene, the thermal conductivity of the composite film is significantly reduced.

[0056] Figure 1 It is the scanning electron microscope image of the thermal expansion microsphere / graphene composite film before and after expansion in Example 1. It can be seen from the figure that the thickness of the composite film increases significantly after expansion, which is the effect of the volume expansion of the thermal expansion microspheres. Therefore, after expansion, the graphene thermal conduction network is damaged, and the thermal conductivity of the thermal expansion microspheres is low (0.2 - 0.5 W / mK), thus realizing the transformation of the composite film from a high thermal conductivity state to a low thermal conductivity state or even an insulating state.

[0057] Figure 2 It is a schematic diagram of the thermal expansion microsphere / graphene composite film. Figure 3It is a schematic structural diagram of the heat conduction and heat insulation switching of the thermally expandable microsphere / graphene composite film. In the figure, 1 is a schematic diagram of an electrical device, 2 is the prepared graphene composite film, and 3 is the thermally expandable microsphere. At normal temperature, the graphene composite film is in close contact with the electrical device, and the heat conduction effect is good; when the temperature reaches the temperature at which a heat disaster occurs, the volume of the microsphere expands rapidly to several to dozens of times its original volume, forming a heat insulation gas layer, effectively blocking the diffusion of heat.

[0058] Figure 4 It can be seen that compared with the in-plane thermal conductivity coefficient of the thermally expandable microsphere / graphene composite film at normal temperature, the thermal conductivity coefficient of the composite film generally decreases at high temperature because the thermally expandable microsphere expands at high temperature to form a polymer layer. By comparing Examples 1, 2, and 3, it is found that the composite film in Example 1 has the best thermal conductivity performance, and the composite film in Example 3 has the best heat insulation performance after expansion. This is because as the mass fraction of the thermally expandable microsphere continuously increases, the influence of the polymer component on the graphene composite film becomes greater. By comparing Example 1 and Example 4, it is found that the composite film prepared with the thermally expandable microsphere with water as the core is lower in thermal conductivity and heat insulation performance than the composite film prepared with the thermally expandable microsphere with alkane as the core. It shows that the experimental scheme using the thermally expandable microsphere with alkane as the core is better.

[0059] To explore the comprehensive performance of the prepared graphene composite film, Figure 5 calculate the heat switch ratio r, and the heat switch ratio of Example 2 is the highest. Under this formulation, the graphene composite film not only has good thermal conductivity and heat insulation performance, but its intelligent performance of heat conduction and heat insulation switching is particularly prominent.

[0060] The above are only the preferred embodiments of the present invention, and are not intended to limit the invention in other forms. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of a thermal expansion microsphere / graphene composite film with intelligent thermal conduction and heat insulation switching, characterized in that, The method includes the following steps: Prepare thermally expandable microspheres, which comprise a core material and a polymer shell, and the core material is selected from low-boiling alkanes or a mixture of an aqueous liquid and a flame retardant; Prepare an aqueous polymer solution, add the prepared thermally expandable microspheres and graphene powder to the aqueous polymer solution, and ultrasonically disperse to form a composite film solution; Coat the composite film solution in a mold and control the coating thickness, and perform hot pressing after removing air bubbles by vacuum filtration; Dry the hot-pressed composite film to obtain the thermally expandable microsphere / graphene composite film.

2. The preparation method of the thermally expandable microsphere / graphene composite film with intelligent heat conduction and heat insulation switching according to claim 1, characterized in that, The method for preparing the thermally expandable microspheres includes the following steps: Mix acrylic monomers, initiators with the following components to form an oil phase: Low-boiling alkanes and a flame retardant; or Span 80 and Tween 80; Mix the following components to form an aqueous phase: Sodium dodecyl sulfate and deionized water; or an aqueous liquid and a flame retardant; Mix the oil phase and the aqueous phase, transfer to a reaction vessel after high-speed stirring and emulsification, react at 50-90 °C for 3-12 hours under nitrogen protection, and obtain thermally expandable microspheres after centrifugal washing; Wherein, when the oil phase uses low-boiling alkanes and a flame retardant, the aqueous phase correspondingly uses sodium dodecyl sulfate and deionized water; when the oil phase uses Span 80 and Tween 80, the aqueous phase correspondingly uses an aqueous liquid and a flame retardant.

3. The preparation method of the thermal expansion microsphere / graphene composite film according to claim 2, characterized in that, The acrylic monomers include methyl methacrylate and methacrylic acid; the low-boiling alkanes are selected from any one or more of n-octane, n-nonane, and n-decane; the aqueous liquids are selected from any one or more of water, methanol, ethanol, acetone, n-butanol, and ethyl acetate; the flame retardants are selected from any one or more of trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and tris(xylene) phosphate.

4. The preparation method of the thermal expansion microsphere / graphene composite film according to claim 2, wherein, When the core material is a mixture of an aqueous liquid and a flame retardant, the mass ratio of acrylic monomers, initiators, Span 80, Tween 80, aqueous liquid and flame retardant is (20-40):(0.1-0.2):(1-3):1:(10-15):(2-4), and when the core material is a mixture of low-boiling alkanes and a flame retardant, the mass ratio of acrylic monomers, initiators, sodium dodecyl sulfate, deionized water, low-boiling alkanes and flame retardant is (20-40):(0.1-0.2):(1-4):100:(10-15):(2-4).

5. The preparation method of the thermally expandable microsphere / graphene composite film with intelligent heat conduction and heat insulation switching according to claim 1, characterized in that During the preparation of the aqueous polymer solution, the mass ratio of deionized water to the aqueous polymer is 200:(5-7).

6. The preparation method of the thermally expandable microsphere / graphene composite film with intelligent heat conduction and heat insulation switching according to claim 5, characterized in that, The aqueous polymer is selected from any one or more of acrylic acid, vinyl acrylic acid, styrene acrylic acid, vinyl acetate, vinyl acetate-ethylene copolymer, and polyvinyl alcohol.

7. The preparation method of the thermally expandable microsphere / graphene composite film with intelligent heat conduction and heat insulation switching according to claim 5, characterized in that, The mass ratio of the aqueous polymer, thermally expandable microspheres and graphene powder is 10:(1-10):

400.

8. The preparation method of the thermally expandable microsphere / graphene composite film with intelligent heat conduction and heat insulation switching according to claim 1, characterized in that, The coating thickness is 10-50 μm, and the vacuum filtration time is 3-10 min.

9. The preparation method of the intelligent heat conduction and heat insulation switching thermal expansion microsphere / graphene composite film according to claim 1, characterized in that, The temperature of the hot pressing treatment is 75-85 °C, the pressure is 5-6 MPa, and the time is 5-15 min.

10. A thermally expandable microsphere / graphene composite film with intelligent heat conduction and heat insulation switching, characterized in that, Prepared according to the method described in claims 1-9.

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