A vertical arrangement of graphene heat-conducting film with high thermal conductivity and low interface thermal resistance and a preparation method thereof

Abstract

This invention belongs to the field of thermal control technology, specifically relating to a vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance, and its preparation method. The preparation method involves first preparing a graphene foam film with high in-plane thermal conductivity, then treating it with oxygen plasma, and finally bonding it layer by layer with TPU hot melt adhesive to form a stacked block. The finished product is then obtained by cutting along the vertical direction of the stacked layers. This invention results in vertically aligned graphene sheets with the thermal conductivity direction aligned with the heat dissipation path, combining high out-of-plane thermal conductivity with low interfacial thermal resistance. Furthermore, the product exhibits excellent flexibility, making it suitable for the thermal management needs of high-power devices, AI chips, and other applications.

Description

Technical Field

[0001] This invention belongs to the field of thermal control technology, specifically relating to a vertically aligned graphene thermal conductive film with high thermal conductivity and low interfacial thermal resistance and its preparation method. Background Technology

[0002] With the miniaturization and high-density integration of electronic devices, as well as the development of high-power devices, AI chips, and data centers, increasingly higher demands are being placed on thermally conductive materials. Insufficient heat dissipation capacity has become a key technological bottleneck restricting their performance and reliability. Interface materials are used to fill the space between the heat sink and the heat source to eliminate air and reduce contact thermal resistance. Traditional thermal greases, phase change materials, and thermal pads suffer from low thermal conductivity (typically <5 W / (m·K)). Graphene, due to its extremely high intrinsic thermal conductivity (approximately 5300 W / (m·K)), is considered an ideal thermally conductive material. However, since graphene nanosheets are self-assembled into graphene films using solution methods, the graphene sheets are typically arranged horizontally (parallel to the film plane). While heat conduction efficiency is high in the in-plane direction, when passing through the film thickness direction (i.e., the main path for device heat dissipation), it needs to cross a large number of interlayer interfaces, resulting in a significant decrease in the vertical thermal conductivity and high interfacial thermal resistance with the contact surface.

[0003] In existing technologies, although attempts have been made to improve vertical thermal conductivity by constructing three-dimensional structures, the process is often complex or it is difficult to achieve the directional arrangement of graphite sheets, resulting in limited improvement in thermal conductivity and unsatisfactory interfacial thermal resistance.

[0004] Patent CN103625085A discloses a graphene foam film prepared with added polymer fibers. Although graphitization was performed later, the non-graphene carbon in the final product significantly reduced the thermal conductivity of the graphene foam. Patent CN117486206A discloses a high vertical thermal conductivity graphene framework, composite material, and its preparation method. This method uses graphene oxide solution to bond graphene oxide film, which is then cut and subjected to high-temperature graphitization. Due to the long process, it is difficult to guarantee the performance stability of the final product. Patent CN113147115A discloses a thermally conductive pad and its preparation method. In order to improve the thermal conductivity of the adhesive used to bond the thermally conductive film, this patent adds graphene microflakes, carbon fibers, boron nitride, and other thermally conductive fillers during the preparation process. Although the addition of these thermally conductive fillers can improve the thermal conductivity of the adhesive to a certain extent, it also increases the thickness of the adhesive, affecting the out-of-plane thermal conductivity and thermal resistance of the final product.

[0005] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides an interfacial thermally conductive film with a vertically aligned graphene structure and its preparation method. This thermally conductive film has a high thermal conductivity in the thickness direction and low interfacial thermal resistance, providing a better option for thermal management of various electronic products, especially high-power devices.

[0007] The present invention provides a method for preparing a vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance, the preparation method comprising the following steps:

[0008] (I) Preparation of graphene foam film with high in-plane thermal conductivity (I-1) The graphene oxide slurry is coated and dried to form a film, thus obtaining a graphene oxide film; (I-2) The graphene oxide film is initially reduced and foamed to obtain a foamed graphene film; (I-3) The foamed graphene film is further reduced at high temperature to obtain a high in-plane thermal conductivity graphene foam film; (II) Preparation of high thermal conductivity graphene film stack (II-1) The high in-plane thermal conductivity graphene foam film is subjected to oxygen plasma treatment to obtain plasma-treated graphene foam film. (II-2) The plasma-treated graphene foam film is bonded layer by layer using a high-elasticity adhesive to form a high thermal conductivity graphene film stack. (III) Preparation of vertically aligned graphene thermal conductive films with high thermal conductivity and low interfacial thermal resistance The high thermal conductivity graphene film stack is cut into thin sheets along a direction perpendicular to its stacking layers to obtain the vertically arranged graphene thermal conductive film with high thermal conductivity and low interfacial thermal resistance.

[0009] Its preparation process flow diagram is as follows: Figure 1 As shown.

[0010] Preferably, in step (I-1): The concentration of the graphene oxide slurry is 1-2 wt%; And / or, the thickness of the film formed by the scraping and drying process is 5000-6000 μm.

[0011] Preferably, in step (I-2), the preliminary reduction foaming method is as follows: first, the graphene oxide film is immersed in a reducing agent, then taken out and naturally dried, and then heated at 150-250°C.

[0012] Preferably, the reducing agent is a hydrazine hydrate solution with a concentration of 1-2 wt%.

[0013] Preferably, in step (I-3), the method of continuing the reduction treatment at high temperature is as follows: first carbonize at 1700-1800℃ for 3-4 hours, and then carbonize at 3000-3200℃ for 1-2 hours.

[0014] Preferably, in step (II-1), the oxygen plasma treatment is performed with an energy of 80-100W, an oxygen flow rate of 50-60 sccm, and a time of 3-5 min.

[0015] Preferably, in step (II-2): The high-elasticity adhesive is TPU hot melt adhesive (YJU106 model hot melt adhesive film produced by Xingxia Polymer Products); it should be emphasized that TPU hot melt adhesive can be in various forms, such as "film" or "liquid".

[0016] And / or, the bonding method is as follows: TPU hot melt adhesive is laid flat between the two layers of plasma-treated graphene foam film, and treated at 170-180℃ for 30-40s to bond the two layers of plasma-treated graphene foam film together.

[0017] Preferably, in step (III): The cutting rate is 2-3 mm / min; And / or, the thickness of the sheet is 0.2-2 mm.

[0018] Based on the same technical concept, the present invention further provides a vertically aligned graphene thermal conductive film with high thermal conductivity and low interfacial thermal resistance obtained by the above preparation method.

[0019] The beneficial effects of this invention are as follows: The foamed graphene film prepared by this invention achieves an ordered arrangement of graphene sheets along the planar direction within its interior, and exhibits greater flexibility and deformability compared to compacted graphene films. The use of elastic adhesive in the lamination bonding process ensures strong adhesion between the graphene films while maintaining the final product's softness and elasticity. Cutting perpendicular to the lamination planes results in the graphene sheets in the final product sample being arranged perpendicular to the in-plane direction. This ensures that the direction of maximum thermal conductivity of the graphene film aligns with the direction of heat conduction required in the application, both being out-of-plane directions of the thermally conductive film. This guarantees high thermal conductivity in the product. The flexibility and elasticity of the foamed graphene film and adhesive ensure the flexibility and elasticity of the final product, guaranteeing good contact between the product surface and the heat transfer contact surface under low pressure, further reducing the product's contact thermal resistance. More specifically: 1. Compared to the prior art CN103625085A, the in-plane thermal diffusivity of the graphene foam prepared from pure graphene oxide used in this invention can reach 450-600 mm. 2This provides a foundation for the high out-of-plane thermal conductivity of the final product. Furthermore, it exhibits an out-of-plane thermal conductivity greater than 110 W / (m·K) and a thermal resistance less than 0.08 k·cm. 2 / W.

[0020] 2. Compared with the existing technology CN117486206A, the present invention first prepares a foamed graphene film with a high in-plane thermal diffusivity, and then uses TPU film or adhesive to bond and cut the foamed graphene film, which can ensure that the final product has a high out-of-plane thermal diffusivity and low thermal resistance.

[0021] 3. Compared with the existing technology CN113147115A, the present invention uses TPU film and TPU adhesive to ensure that the foam graphene sheets are firmly bonded while using as much adhesive as possible in a uniform and minimal amount. This ensures that the final product has high out-of-plane thermal conductivity and low thermal resistance. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the preparation process of the present invention.

[0024] Figure 2 This is a real photo of a graphene foam film with high in-plane thermal conductivity.

[0025] Figure 3 This is a photograph of the vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance prepared in Example 1 (approximately 0.3mm × 25.4mm × 25.4mm in size).

[0026] Figure 4 This is a cross-sectional photograph of the vertically arranged graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance prepared in Example 1 (sample thickness is approximately 0.3 mm). Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0028] Example 1 This embodiment provides a method for preparing a vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance. The preparation method includes the following steps: (I) Preparation of graphene foam film with high in-plane thermal conductivity (I-1) 1 wt% of graphene oxide slurry was coated onto the surface of PP filter cloth with a coating thickness of 5000 μm. The slurry was then air-dried in a ventilated place to obtain a dense graphene oxide film with graphene arranged in an orderly manner along the in-plane direction. (I-2) The graphene oxide film was immersed in a 2wt% hydrazine hydrate solution and then dried naturally. It was then reduced and foamed in an oven at 200℃ to obtain a preliminarily reduced foamed graphene film. (I-3) The foamed graphene film was sequentially carbonized at 1700℃ for 3 hours, and finally treated in a graphitization furnace at 3000℃ for 1 hour to obtain a high in-plane thermal conductivity graphene foam film (density approximately 0.15 g / cm³). 3 The in-plane thermal diffusivity reaches 450 mm. 2 / s or more); Actual photos as shown Figure 2 As shown; (II) Preparation of high thermal conductivity graphene film stack (II-1) The graphene foam film with high in-plane thermal conductivity is subjected to oxygen plasma treatment (energy of 80W, oxygen flow rate of 50sccm, time of 3min) to obtain plasma-treated graphene foam film. (II-2) Then, a 20μm thick TPU film (adhesive film form, the same below) is laid flat between two layers of plasma-treated graphene foam film. It is then ironed at 170℃ for 30 seconds to bond the two plasma-treated graphene foam films together. This ironing and bonding process is repeated until all four layers of plasma-treated graphene foam film are bonded together. A TPU film is then placed on the surface of the four bonded plasma-treated graphene foam films, and a PTFE film is then covered on top. Finally, it is ironed at 170℃ for 30 seconds to bond the TPU film to the four bonded plasma-treated graphene foam films. The graphene foam film was bonded together, cooled, and the surface PTFE film was removed. Then, the four layers of bonded graphene film were cut into 30mm × 30mm pieces using a die-cutting tool. These pieces were then placed sequentially into a square mold with a 30mm × 30mm cavity, accumulating 400 layers. The layers were then pressed at 56 psi for 10 minutes, followed by hot pressing at 200℃ for 1 hour to a controlled thickness of 32mm. After cooling, the sample was demolded to obtain a high thermal conductivity graphene film stack. The block sample had a thickness of 31.79mm, a mass of 25.68g, and a density of 0.897g / cm³. 3 ; (III) Preparation of vertically aligned graphene thermal conductive films with high thermal conductivity and low interfacial thermal resistance Use an internal circular cutter to cut the block into 0.3mm (0.3mm × 25.4mm × 25.4mm) pieces perpendicular to the stacking direction at a speed of 2mm / min. Figure 3 As shown; cross-sectional photographs are as follows Figure 4 As shown, a clearly vertically aligned graphene sheet (2.0 mm thick) is formed, resulting in the high thermal conductivity and low interfacial thermal resistance vertically aligned graphene thermal conductive film. The 0.3 mm thick sample exhibited a thermal resistance of only 0.064 K·cm under a pressure of 40 psi. 2 The out-of-plane thermal conductivity of a 2mm thick sample measured by laser method was as high as 140.8 W / (m·K).

[0029] Example 2 This embodiment provides a method for preparing a vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance. The preparation method includes the following steps: (I) Preparation of graphene foam film with high in-plane thermal conductivity Commercially available graphene foam film is used instead; this embodiment uses AX5 graphene foam from Angxing Company, with a thickness of 0.3 mm and a density of 0.15 g / cm³. 3 The in-plane thermal diffusivity can reach 600 mm. 2 / s, thermal conductivity is 62W / (m·K), sheet resistance is 0.07Ω / sq; (II) Preparation of high thermal conductivity graphene film stack (II-1) The purchased AX5 foam graphene from Angxing Company was subjected to oxygen plasma treatment (energy of 80W, oxygen flow rate of 50sccm, time of 3min) to obtain plasma-treated graphene foam film. (II-2) Then, lay a 20μm thick TPU film between the two layers of plasma-treated graphene foam film, and iron it with an electric iron at 170℃ for 30 seconds to bond the two plasma-treated graphene foam films together. Repeat the above ironing and bonding steps to bond the four layers of plasma-treated graphene foam film together. Then, place a TPU film on the surface of the four-layer plasma-treated graphene foam film bonded together, and then cover the surface with a PTFE film. Iron it with an electric iron at 170℃ for 30 seconds to bond the TPU film to the four-layer plasma-treated graphene foam film bonded together. Graphene foam films were bonded together, cooled, and the surface PTFE film was removed. Then, a die-cutting tool was used to cut the four bonded graphene films into 30mm × 30mm pieces, which were then placed sequentially into a square mold with a 30mm × 30mm cavity, accumulating 400 layers. The layers were then pressed at 56 psi for 10 minutes, followed by hot pressing at 200℃ for 1 hour to a controlled thickness of 32mm. After cooling, the sample was demolded to obtain a high thermal conductivity graphene film stack. The block sample had a thickness of 31.8mm, a mass of 25.85g, and a density of 0.89g / cm³.3 ; (III) Preparation of vertically aligned graphene thermal conductive films with high thermal conductivity and low interfacial thermal resistance The block was cut into thin sheets of 0.3 mm and 2.0 mm thickness along the direction perpendicular to the stacking using an internal circular cutter at a speed of 2 mm / min, thus obtaining the vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance. The 0.3 mm thick sample showed a thermal resistance of only 0.041 K·cm under a pressure of 40 psi. 2 The out-of-plane thermal conductivity of a 2mm thick sample measured by laser method was as high as 184W / (m·K).

[0030] Example 3 This embodiment provides a method for preparing a vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance. The preparation method includes the following steps: First, the purchased AX5 Angxing foam graphene film was cut into 30mm x 30mm pieces using a die-cutting tool. Then, it was immersed in a 10% TPU / tetrahydrofuran solution (TPU in liquid form), removed, and dried. Next, 400 pieces of the immersed graphene film were placed into a mold and pressed for 1 hour at 180℃ in a vacuum hot press, maintaining a thickness of 44mm. After demolding, the resulting block sample had a thickness of 44mm, a weight of 25.76g, and a density of 0.65g / cm³. 3 The block was cut into 0.3 mm and 2.0 mm thick slices perpendicular to the stacking direction using an internal circular cutter at a speed of 2 mm / min. The 0.3 mm thick sample showed a thermal resistance of only 0.039 K·cm under a pressure of 40 psi. 2 The out-of-plane thermal conductivity of a 2mm thick sample measured by laser method was as high as 113W / (m·K).

[0031] Comparative Example 1 This comparative example provides a preparation method, which includes the following steps: (I) Preparation of graphene foam film with high in-plane thermal conductivity Commercially available graphene foam film is used instead; this embodiment uses AX5 graphene foam from Angxing Company, with a thickness of 0.3 mm and a density of 0.15 g / cm³. 3 The in-plane thermal diffusivity can reach 600 mm. 2 / s, thermal conductivity is 62W / (m·K), sheet resistance is 0.07Ω / sq; (II) Preparation of graphene film stacked bulk (II-1) The purchased AX5 foam graphene from Angxing Company was subjected to oxygen plasma treatment (energy of 80W, oxygen flow rate of 50sccm, time of 3min) to obtain plasma-treated graphene foam film. (II-2) Then, a 50μm thick TPU film is laid flat between two layers of plasma-treated graphene film, and ironed at 170℃ for 30 seconds to bond the two plasma-treated graphene foam films together. This ironing and bonding process is repeated until all four layers of plasma-treated graphene foam film are bonded together. A TPU film is then placed on the surface of the bonded graphene film, followed by a PTFE film. The TPU film is then heated with an iron to bond with the graphene film. After cooling, the top PTFE film is removed. The sample is cut into 15mm × 15mm pieces and placed in a mold, accumulating 76 layers (single-layer AX5 foam graphene film). It is then pressed at 63psi for 10 minutes, followed by hot pressing at 16psi for 1 hour on a 200℃ rolling mill. After cooling, the sample is demolded and removed. The sample thickness is 10.4mm, weight is 1.822g, and density is 0.775g / cm³. 3 .

[0032] (III) Preparation of graphene thermal conductive film The bulk sample was cut into 0.3 mm and 2.0 mm thick slices along a direction perpendicular to the stacked plane using an internal circular cutter. The thermal resistance of the 0.3 mm thick sample was measured to be only 0.529 K·cm under a pressure of 40 psi. 2 The out-of-plane thermal conductivity of a 2mm thick sample was measured to be 55.4 W / (m·K) using a laser method.

[0033] Analysis example 1. Compared with Examples 1-2, Example 3 uses a TPU adhesive soaking method to replace the TPU hot melt adhesive film layer-by-layer bonding step, thereby making the product contain less TPU adhesive. Although the sample density and out-of-plane thermal conductivity are reduced due to the small bulk compression ratio, its thermal resistance is even lower.

[0034] 2. Compared with the Example 1, Comparative Example 1 used a thicker (50 μm) TPU hot melt adhesive film, resulting in a higher adhesive content in the sample. This significantly affected the out-of-plane thermal conductivity of the product, causing it to drop to 55.4 W / (m·K), and the thermal resistance of the sample also increased to 0.529 K·cm. 2 / W.

[0035] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance, characterized in that, The preparation method includes the following steps: (I) Preparation of graphene foam film with high in-plane thermal conductivity (I-1) The graphene oxide slurry is coated and dried to form a film, thus obtaining a graphene oxide film; (I-2) The graphene oxide film is initially reduced and foamed to obtain a foamed graphene film; (I-3) The foamed graphene film is further reduced at high temperature to obtain a high in-plane thermal conductivity graphene foam film; wherein: the method of further reduction at high temperature is: first carbonization treatment at 1700-1800℃ for 3-4h, and then carbonization treatment at 3000-3200℃ for 1-2h. The in-plane thermal diffusivity of the graphene foam film with high in-plane thermal conductivity is 450-600 mm. 2 / s; (II) Preparation of high thermal conductivity graphene film stack (II-1) The high in-plane thermal conductivity graphene foam film is subjected to oxygen plasma treatment to obtain plasma-treated graphene foam film; wherein: the oxygen plasma treatment method is: energy of 80-100W, oxygen flow rate of 50-60sccm, and time of 3-5min. (II-2) The plasma-treated graphene foam film is bonded layer by layer using a high-elasticity adhesive to form a high thermal conductivity graphene film stack; wherein: The high-elasticity adhesive is a TPU hot melt adhesive; And / or, the bonding method is as follows: TPU hot melt adhesive is laid flat between the two layers of plasma-treated graphene foam film, and treated at 170-180℃ for 30-40s to bond the two layers of plasma-treated graphene foam film. (III) Preparation of vertically aligned graphene thermal conductive films with high thermal conductivity and low interfacial thermal resistance The high thermal conductivity graphene film stack is cut into thin sheets along a direction perpendicular to its stacking surfaces to obtain the vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance; wherein: The vertically aligned graphene thermal conductive film, characterized by high thermal conductivity and low interfacial thermal resistance, has a thermal resistance of less than 0.08 K·cm. 2 / W.

2. The method for preparing a vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance according to claim 1, characterized in that, In step (I-1): The concentration of the graphene oxide slurry is 1-2 wt%; And / or, the thickness of the film formed by the scraping and drying process is 5000-6000 μm.

3. The method of claim 1, wherein the vertically aligned graphene film has a thermal conductivity of at least 1,000 W / mK and an interfacial thermal resistance of less than 10"8 m2K / W. In step (I-2), the preliminary reduction foaming method is as follows: first, the graphene oxide film is immersed in a reducing agent, then taken out and naturally dried, and then heated at 150-250℃.

4. The method of claim 3, wherein the vertically aligned graphene film has a thermal conductivity of at least 1,000 W / m-K and an interfacial thermal resistance of less than 10"8 m2-K / W. The reducing agent is a hydrazine hydrate solution with a concentration of 1-2 wt%.

5. The method of claim 1, wherein the vertically aligned graphene film has a thermal conductivity of at least 1,000 W / m-K and an interfacial thermal resistance of less than 10"8 m2-K / W. In step (III): The cutting rate is 2-3 mm / min; And / or, the thickness of the sheet is 0.2-2 mm.

6. A vertically aligned graphene thermally conductive film with high thermal conductivity and low interfacial thermal resistance obtained by the preparation method according to any one of claims 1-5.

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