A method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity

Abstract

The present invention relates to a method for preparing a graphene thermal conductive film with high in-plane and inter-plane thermal conductivity, which mainly comprises the following steps: S1: mixing a graphene oxide aqueous solution, a dispersing aid and a functional compound, uniformly dispersing by ultrasonication, and then degassing to obtain a graphene oxide slurry; S2: coating the slurry on a substrate, drying, and obtaining a graphene oxide film; S3: subjecting the graphene oxide film to a high-temperature heat treatment under a protective atmosphere to obtain a fluffy graphene thermal conductive film; S4: subjecting the fluffy graphene thermal conductive film to a mechanical pressing treatment to obtain a graphene thermal conductive film with high in-plane and inter-plane thermal conductivity. The method provided by the present invention is simple and convenient, has low cost, and the obtained graphene thermal conductive film has good high in-plane and inter-plane thermal conductivity.

Description

Technical Field

[0001] The invention relates to the field of thermally conductive films, and in particular to a method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity. Background Art

[0002] Traditional thermal interface materials mainly include materials such as alumina and copper, which not only have low thermal conductivity, but also low system portability. In addition, the mismatch in thermal expansion coefficients between these materials and electronic devices may lead to stress failure, further affecting the thermal conductivity of the materials. Therefore, it is of great significance to develop lightweight and efficient thermal interface materials.

[0003] At present, compared with traditional thermal conductive materials (graphite, aluminum, copper, etc.), graphene thermal conductive film has high thermal conductivity and light weight, and is one of the ideal thermal conductive materials. It is mainly prepared by high-temperature reduction or chemical reduction method using graphene oxide as a precursor. However, in the process of removing oxygen-containing functional groups, it is difficult to ensure good connection between graphene microsheets, resulting in strong phonon scattering at the boundary; at the same time, in the interlayer direction, due to the weak van der Waals force, the thermal conductivity is very low. And the expansion caused by high temperature or chemical reduction process further damages the heat conduction path between layers, which leads to the graphene thermal conductive film having strong anisotropic thermal conductivity, that is, the through-plane thermal conductivity is significantly lower than the in-plane thermal conductivity by three to four orders of magnitude. Although high in-plane thermal conductivity is beneficial to prevent the formation of local hot spots in electronic devices, high in-plane thermal conductivity is essential for transferring heat from electronic devices to heat sinks. Therefore, the strong anisotropic thermal properties of graphene films limit their application as thermal interface materials.

[0004] In order to improve the through-plane thermal conductivity of graphene films, the commonly used method is to introduce nano-scale fillers to establish through-plane thermal conduction paths. Nano-fillers cause more phonon scattering at the boundaries of graphene microsheets, greatly reducing the in-plane thermal conductivity of graphene films. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem that when nanofillers are used in the prior art to prepare a high inter-plane graphene thermal conductive film, an interfacial thermal resistance is generated in the in-plane heat conduction direction of the graphene thermal conductive film, thereby affecting the in-plane thermal conductivity, and the contradiction between the in-plane and inter-plane thermal conductivity of the graphene film. The present invention provides a method for preparing a graphene thermal conductive film with high in-plane and inter-plane thermal conductivity, so that the preparation method provided by the present invention can significantly improve the inter-plane thermal conductivity of the graphene thermal conductive film while ensuring the high in-plane thermal conductivity of the graphene thermal conductive film.

[0006] The specific plan is as follows:

[0007] A method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity comprises the following steps:

[0008] S1: mixing a graphene oxide aqueous solution, a dispersing aid and a functional compound, uniformly dispersing them by ultrasonication, and then degassing the mixture to obtain a graphene oxide slurry; the functional compound is melamine;

[0009] S2: coating the slurry on a substrate and drying it to obtain a graphene oxide film;

[0010] S3: Under a protective atmosphere, subjecting the graphene oxide film to a high-temperature heat treatment to obtain a fluffy graphene thermally conductive film;

[0011] S4: Mechanically pressing the fluffy graphene thermally conductive film to obtain a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity.

[0012] Further, in step S1, the dispersing aid is one of ethanolamine and ammonia water;

[0013] Optionally, the ultrasonic dispersion time is 30 to 60 minutes.

[0014] Further, in step S1, the mass percentage of graphene oxide in the graphene oxide aqueous solution is 1-5wt%;

[0015] Optionally, the mass ratio of the dispersing aid to the graphene oxide in the graphene oxide slurry is (5-20):100;

[0016] Optionally, the mass ratio of the functional compound to the graphene oxide in the graphene oxide slurry is (1-10):100.

[0017] Further, in step S2, the coating is performed by scraping;

[0018] Optionally, the substrate is one of a polyimide substrate or a polyethylene terephthalate substrate;

[0019] Optionally, the coating has a thickness of 3-8 mm;

[0020] Preferably, the coating thickness is 5 mm;

[0021] Optionally, the drying temperature is 45-80°C.

[0022] Furthermore, in step S3, the protective atmosphere is one of nitrogen or argon.

[0023] Further, in step S3, the high temperature heat treatment includes treatment at a temperature of 1300-1500° C. for 1-5 hours, and treatment at a temperature of 2800-3100° C. for 3-5 hours;

[0024] Optionally, the heating rate during the 1300-1500°C high temperature heat treatment is 1-2°C / s;

[0025] Optionally, the heating rate during the 2800-3100° C. high temperature heat treatment is 5-10° C. / min.

[0026] Furthermore, in step S3, the pressure of the mechanical pressing treatment is 50-100 MPa, and the pressure holding time is 60-240 min.

[0027] The present invention also protects a graphene thermal conductive film with high in-plane and inter-plane thermal conductivity prepared by the above-described method, the specific contents of which are as follows:

[0028] Furthermore, the thickness of the graphene thermally conductive film with high in-plane and inter-plane thermal conductivity is 30-70 μm;

[0029] Optionally, the graphene thermally conductive film has an in-plane thermal conductivity of ≥1300 W / (m·K) and an inter-plane thermal conductivity of ≥5 W / (m·K).

[0030] On the other hand, the present invention also protects the application of the graphene thermal conductive film with high in-plane and inter-plane thermal conductivity in the field of thermal conduction.

[0031] Beneficial effects:

[0032] In the present invention, the dispersing aid can reduce the viscosity of the slurry and improve the solubility of the functional compound; the functional compound can construct a heat conduction path between the layers of the graphene oxide microsheet, inhibit the reduction of the interlayer heat conduction path during the heat treatment process, and as a nitrogen doping source, make up for the defects (such as vacancies) in the graphene microsheet, which can effectively improve the in-plane and inter-plane thermal conductivity of the final product graphene thermal conductive film. At the same time, the use of dispersing aids containing hydroxyl and amine groups such as ethanolamine and ammonia is conducive to the formation of hydrogen bonds and other structures in the aqueous solution, which can effectively reduce the viscosity of the aqueous solution; and dispersing aids such as ethanolamine and ammonia can effectively enhance the dispersion of the functional compounds used, which is convenient for better interaction with graphene oxide.

[0033] Furthermore, the viscosity is controlled to ensure good fluidity of the aqueous solution during the coating process, so that the surface of the film after drying can be smoother.

[0034] Furthermore, the more graphene oxide there is during the heat treatment, the more expansion it will produce, which will affect the film structure. Therefore, during the preparation process, the mass ratio of graphene oxide in the graphene oxide aqueous solution needs to be controlled to 1-5wt% to avoid excessive expansion and stabilize the film structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings will be briefly introduced below. Obviously, the accompanying drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

[0036] Figure 1 It is a flow chart of a method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity provided by an embodiment of the present invention;

[0037] Figure 2 This is a cross-sectional SEM image of a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity provided by an embodiment of the present invention, magnified 1000 times; DETAILED DESCRIPTION

[0038] The following are definitions of some terms used in the present invention. Other terms not mentioned here have definitions and meanings known in the art:

[0039] In-plane: The heat transfer direction parallel to the upper and lower surfaces of the film is defined as the in-plane heat transfer direction of the film.

[0040] Inter-plane: The heat transfer direction between the surfaces of the film is defined as the heat transfer direction perpendicular to the upper and lower surfaces of the film, that is, heat is transferred from one surface to another.

[0041] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. In the embodiments, if specific techniques or conditions are not indicated, the techniques or conditions described in the literature in this area or the product specifications are carried out. The reagents used or the instruments that are not indicated by the manufacturer are all conventional products that can be obtained commercially. In the following embodiments, if not specifically stated, "%" refers to weight percentage, and parts refer to weight parts.

[0042] The test methods used below include:

[0043] Thermal conductivity determination method: Differential scanning calorimeter was used to measure the specific heat capacity (C p ), the thermal diffusion coefficient (α) of the film is measured by a laser flash meter, and the density (ρ) of the film is measured by the water displacement method. The thermal conductivity (κ) of the film is calculated by formula (1):

[0044] κ=α×C p ×ρ, (1)

[0045] Example 1

[0046] like Figure 1 As shown, a method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity specifically comprises the following steps:

[0047] S1: 50 g of graphene oxide aqueous solution (the mass proportion of graphene oxide is 3 wt%), 0.15 g of ethanolamine and 75 mg of melamine were ultrasonically dispersed at a power of 720 W for 30 min, and then homogenized and degassed to obtain graphene oxide slurry;

[0048] S2: The graphene oxide slurry was coated on the PET substrate by blade coating with a thickness of 5 mm, and then placed in an oven and dried at 45° C. for 10 h to obtain a graphene oxide film.

[0049] S3: The graphene oxide film is heat treated under a protective atmosphere (nitrogen), firstly, the temperature is raised from room temperature to 1500°C at a rate of 1°C / s and kept at that temperature for 4 hours. After cooling down, the temperature is raised from room temperature to 3000°C at a rate of 5°C / min and kept at that temperature for 5 hours.

[0050] S4: The obtained fluffy graphene thermal conductive film is subjected to mechanical pressing treatment at a pressure of 80 MPa, and the pressure is maintained for 120 min to obtain a final graphene thermal conductive film having a thickness of 30 μm. Figure 2 shown.

[0051] The results show that the in-plane thermal conductivity of the obtained graphene thermal conductive film is 1320W / (m·K), while the inter-plane thermal conductivity is 5.09W / (m·K).

[0052] Example 2

[0053] A method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity specifically comprises the following steps:

[0054] S1: 50 g of graphene oxide aqueous solution (the mass proportion of graphene oxide is 5 wt%), 0.25 g of ethanolamine and 125 mg of melamine are ultrasonically dispersed at a power of 720 W for 60 min, and then homogenized and degassed to obtain graphene oxide slurry;

[0055] S2: The graphene oxide slurry was coated on the PI substrate by blade coating with a thickness of 5 mm, and then placed in an oven and dried at 60° C. for 10 h to obtain a graphene oxide film.

[0056] S3: The graphene oxide film is heat treated under a protective atmosphere (nitrogen), firstly, the temperature is increased from room temperature to 1500°C at a rate of 2°C / s and kept at that temperature for 4 hours; after cooling, the temperature is increased from room temperature to 3000°C at a rate of 2°C / min and kept at that temperature for 5 hours.

[0057] S4: The obtained fluffy graphene thermal conductive film is subjected to mechanical pressing treatment at a pressure of 50 MPa, and the pressure is maintained for 180 minutes to obtain a final graphene thermal conductive film having a thickness of 70 μm.

[0058] The obtained graphene thermal conductive film has an in-plane thermal conductivity of more than 1300 W / (m·K), and a surface thermal conductivity of more than 5 W / (m·K).

[0059] Example 3

[0060] A method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity specifically comprises the following steps:

[0061] S1: 30 g of graphene oxide aqueous solution (the mass proportion of graphene oxide is 5 wt%), 0.15 g of ethanolamine and 75 mg of melamine were ultrasonically dispersed at a power of 720 W for 30 min, and then homogenized and degassed to obtain graphene oxide slurry;

[0062] S2: The graphene oxide slurry was coated on the PET substrate by blade coating with a thickness of 5 mm, and then placed in an oven and dried at 80° C. for 10 h to obtain a graphene oxide film.

[0063] S3: The graphene oxide film is heat treated under a protective atmosphere (nitrogen), firstly, the temperature is increased from room temperature to 1500°C at a rate of 2°C / s and kept at that temperature for 4 hours. After cooling down, the temperature is increased from room temperature to 3000°C at a rate of 8°C / min and kept at that temperature for 5 hours.

[0064] S4: The obtained fluffy graphene thermal conductive film is subjected to mechanical pressing treatment at a pressure of 100 MPa, and the pressure is maintained for 60 minutes to obtain a final graphene thermal conductive film having a thickness of 50 μm.

[0065] The results show that the in-plane thermal conductivity of the obtained graphene thermal conductive film is above 1300 W / (m·K), while the inter-plane thermal conductivity is above 5 W / (m·K).

[0066] Example 4

[0067] The specific preparation method of reference embodiment 1 is different only in that the mass ratio of the dispersing aid to graphene oxide in step S1 of this embodiment is 5:100.

[0068] Example 5

[0069] The specific preparation method of reference embodiment 1 is different only in that the mass ratio of the dispersing aid to graphene oxide in step S1 of this embodiment is 20:100.

[0070] Example 6

[0071] The specific preparation method of reference Example 1 is different only in that the mass ratio of the functional compound to graphene oxide in step S1 of this embodiment is 3:100.

[0072] Example 7

[0073] The specific preparation method of reference embodiment 1 is different only in that the mass ratio of the functional compound to graphene oxide in step S1 of this embodiment is 10:100.

[0074] Example 8

[0075] The specific preparation method of reference embodiment 1 is different only in that in step S1 of this embodiment, 30 g of graphene oxide aqueous solution (the mass proportion of graphene oxide is 1 wt%) is used.

[0076] Example 9

[0077] The specific preparation method of reference embodiment 1 is different only in that ammonia water is used as the dispersant in step S1 of this embodiment.

[0078] Comparative Example 1: Other conventional dispersing aids

[0079] The specific preparation method of reference Example 1 is different only in that no dispersing aid is added in step 1 of this embodiment;

[0080] The specific contents are as follows:

[0081] S1: 50 g of graphene oxide aqueous solution (the mass proportion of graphene oxide is 3 wt%), 0.15 g of polyethylene glycol and 75 mg of melamine were ultrasonically dispersed at a power of 720 W for 30 min, and then homogenized and degassed to obtain graphene oxide slurry.

[0082] Comparative Example 2: No functional compound added

[0083] The specific preparation method of reference Example 1 is different only in that no functional compound is added in step 1 of this embodiment;

[0084] The specific contents are as follows:

[0085] S1: 50 g of graphene oxide aqueous solution (the mass proportion of graphene oxide is 3 wt%) and 0.15 g of ethanolamine were ultrasonically dispersed at a power of 720 W for 30 min, and then homogenized and degassed to obtain graphene oxide slurry.

[0086] Comparative Example 3

[0087] The specific preparation method of reference embodiment 1 is different only in that the mass ratio of the dispersing aid to graphene oxide in step S1 of this embodiment is 25:100.

[0088] Comparative Example 4

[0089] The specific preparation method of reference Example 1 is different only in that the mass ratio of the functional compound to graphene oxide in step S1 of this embodiment is 15:100.

[0090] As can be seen from Comparative Example 1, the commonly used dispersing aid polyethylene glycol is selected for preparation, which cannot enhance the dispersibility of the functional compound and cannot achieve the full effect between the functional compound and graphene; as can be seen from Comparative Example 2, if the functional compound is not added for mixed preparation, the thermal conductivity path between the graphene oxide microsheet layers cannot be constructed, which will lead to the reduction of the interlayer thermal conductivity path during the heat treatment process, and the defects in the graphene microsheets cannot be compensated, and the thermal conductivity between the surfaces and within the surface is finally reduced. As can be seen from Comparative Examples 3-4, when the dispersant is added in excess, the viscosity of the graphene oxide aqueous solution will be too low, so that it cannot be formed into a film during the drying film forming process, and the thickness of the obtained film is greatly reduced, which cannot meet the actual application requirements of the thermal conductive film; and when the functional compound is added in excess, it will cause the functional compound to form excessive accumulation between the graphene oxide layers, destroying the complete interlayer stacking structure of the graphene oxide, and the thermal conductivity within the surface and between the surfaces will be greatly reduced.

[0091] Comparative Example 5

[0092] The specific preparation method of reference Example 1 is different only in that in step S1 of this comparative example, 30 g of graphene oxide aqueous solution (the mass proportion of graphene oxide is 10 wt%) is used.

[0093] The results show that when the mass of graphene oxide accounts for a large proportion, the viscosity of the graphene oxide aqueous solution will be too high, the surface flatness of the obtained film will decrease after drying, and the thickness will increase significantly, which will affect the thermal properties of the film. In addition, it will produce a more obvious expansion during the heat treatment process, destroying the thermal conduction path between graphene layers.

[0094] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0095] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0096] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity, characterized in that: The following steps are involved: S1: mixing a graphene oxide aqueous solution, a dispersing agent and a functional compound, uniformly dispersing them by ultrasonication, and then degassing the mixture to obtain a graphene oxide slurry; the functional compound is melamine; the dispersing agent is ethanolamine or ammonia; S2: coating the slurry on a substrate and drying it to obtain a graphene oxide film; S3: Under a protective atmosphere, subjecting the graphene oxide film to a high-temperature heat treatment to obtain a fluffy graphene thermally conductive film; S4: Mechanically pressing the fluffy graphene thermally conductive film to obtain a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity.

2. The method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity according to claim 1, characterized in that: In step S1, optionally, the ultrasonic dispersion time is 30 to 60 minutes.

3. The method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity according to claim 1, characterized in that: In step S1, the mass percentage of graphene oxide in the graphene oxide aqueous solution is 1-5wt%; Optionally, the mass ratio of the dispersing aid to the graphene oxide in the graphene oxide slurry is (5-20):100; Optionally, the mass ratio of the functional compound to the graphene oxide in the graphene oxide slurry is (1-10):

100.

4. The method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity according to claim 1, characterized in that: In step S2, the coating is performed by scraping; Optionally, the substrate is one of a polyimide substrate or a polyethylene terephthalate substrate; Optionally, the coating has a thickness of 3-8 mm; Optionally, the drying temperature is 45-80°C.

5. The method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity according to claim 4, characterized in that: The coating thickness is 5 mm.

6. The method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity according to claim 1, characterized in that: In step S3, the protective atmosphere is one of nitrogen or argon.

7. The method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity according to claim 1, characterized in that: In step S3, the high temperature heat treatment includes treatment at a temperature of 1300-1500° C. for 1-5 hours, and treatment at a temperature of 2800-3100° C. for 3-5 hours; Optionally, the heating rate during the 1300-1500°C high temperature heat treatment is 1-2°C / s; Optionally, the heating rate during the 2800-3100° C. high temperature heat treatment is 5-10° C. / min.

8. The method for preparing a graphene thermally conductive film with high in-plane and inter-plane thermal conductivity according to claim 1, characterized in that: In step S3, the pressure of the mechanical pressing treatment is 50-100 MPa, and the pressure holding time is 60-240 min.

9. A graphene thermally conductive film with high in-plane and inter-plane thermal conductivity prepared by the method according to any one of claims 1 to 8.

10. The graphene thermally conductive film with high in-plane and inter-plane thermal conductivity according to claim 9, characterized in that: The thickness of the graphene thermal conductive film with high in-plane and inter-plane thermal conductivity is 30-70 μm; Optionally, the graphene thermally conductive film has an in-plane thermal conductivity of ≥1300 W / (m·K) and an inter-plane thermal conductivity of ≥5 W / (m·K).

11. The use of the graphene thermally conductive film with high in-plane and inter-plane thermal conductivity according to claim 10, characterized in that: The graphene thermally conductive film with high in-plane and inter-plane thermal conductivity is applied in the field of thermal conduction.

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