Multilayer elastic carbon-based thermal interface material and preparation method thereof

Abstract

The invention discloses a multilayer elastic carbon-based thermal interface material and a preparation method thereof, a mixture of carbon tubes (CNTs) and a polymer and a mixture of graphene oxide and the polymer are stacked layer by layer, and a uniform film is formed through a centrifugal spin-coating technology. Through further treatment, the composite film is converted into the graphene aerogel with high porosity. The aerogel is cut into slices, and then the slices are subjected to plasma etching. In the process, the carbon tube layer on the surface of the material is selectively removed, and a complex multi-stage structure is created. The thermal interface material prepared by the method has relatively high elasticity, does not contain polymers, has relatively good weather resistance and cannot be stiff and aged after working for a long time, so that the performance of the material is greatly improved, and the service life of the material is greatly prolonged.

Description

Technical Field

[0001] The present invention belongs to the field of thermal interface materials, and particularly relates to a multi-layer elastic carbon-based thermal interface material and a preparation method thereof. Background Art

[0002] As an efficient heat-conducting medium, carbon-based thermal interface materials play a crucial role in high-power density applications such as electronic devices, LED lighting, photovoltaic systems, and power electronics modules. Their main function is to fill the tiny gaps between the heat-generating components and the heat sink, reduce the contact thermal resistance, and thus improve the heat transfer efficiency. Traditionally, these materials are composed of carbon materials such as graphite flakes, carbon nanotubes, or graphene, etc., compounded with a polymer matrix. The polymer endows the material with certain elasticity and mechanical processing properties, enabling the material to adapt to interfaces of different shapes and sizes and being easy to operate during installation.

[0003] However, there are significant limitations in the existing carbon-based thermal interface materials that rely on polymers to provide elasticity. Polymer materials generally have poor weather resistance, which is mainly reflected in the following aspects: Firstly, when exposed to high-temperature environments for a long time, the polymer molecular chains will crosslink or break, resulting in the hardening, embrittlement, and even cracking of the material. This aging phenomenon not only weakens the mechanical properties of the material but also reduces its thermal conductivity. Because as the polymer ages, it may lose its original softness, unable to effectively fill the newly generated gaps, increasing the thermal resistance and affecting long-term stable thermal management.

[0004] Secondly, moisture, oxygen, and other chemical substances in the environment will also accelerate the aging process of the polymer. Moisture can penetrate into the material and trigger hydrolysis reactions; oxygen may promote oxidative degradation. In addition, factors such as ultraviolet radiation and temperature cycling changes will also damage the polymer and shorten its service life.

[0005] Furthermore, for some special application scenarios, such as the electronic control unit in the engine compartment of an automobile or a photovoltaic inverter used outdoors, the working environment is often more severe, facing a wider temperature range, higher humidity levels, and stronger chemical corrosion risks. In this case, the traditional polymer-based carbon-based thermal interface materials are more vulnerable to the above factors and thus lose their due performance faster. Summary of the Invention

[0006] The present invention aims to solve the problem of easy aging caused by the dependence on polymers to achieve elasticity in existing graphene-based thermal interface materials. This thermal interface material does not require the use of polymers to provide elasticity, and its service life is extended by more than three times. By designing a unique core-shell architecture, the outer layer of the material has a lower density than the central region, and only the highly graphitized part is retained, ensuring that the material has excellent flexibility, lubricity, and filling ability, significantly reducing the contact thermal resistance. Among them, the carbon tube structure can provide a heat conduction path and elasticity; the highly graphitized graphene structure provides a high heat conduction path, not only maintaining an efficient heat conduction path but also showing excellent support, elasticity, and filling characteristics.

[0007] One of the technical solutions of the present invention is to provide a multi-layer elastic carbon-based thermal interface material, which is formed by alternately stacking graphene layers and carbon tube layers in the horizontal direction to form a main layer in the middle and skin layers on the upper and lower sides; wherein the graphene layer is composed of highly graphitized graphene sheets oriented vertically, and the carbon tube layer is composed of carbon nanotubes oriented vertically; and the skin layer is formed by extending a part of the highly graphitized graphene sheets of the main layer to the upper and lower sides; the high graphitization degree is >96%.

[0008] The highly oriented carbon tubes in this thermal interface material can provide elasticity for the building unit, and at the same time, the complete carbon tube structure can provide a heat conduction path; the highly graphitized graphene structure provides a high heat conduction path. After plasma etching, the carbon tubes on the surface of the sheet are removed, leaving only the highly graphitized graphene structure, which has good flexibility and tilts into an I-shaped structure under external force, changing the line contact between the thermal interface and the heat sink into a surface contact, which is very conducive to filling the thermal interface gap and reducing the interface thermal resistance.

[0009] Furthermore, the thickness of the multi-layer elastic carbon-based thermal interface material is 0.2 - 0.5 mm.

[0010] Furthermore, the thickness of the skin layer is 1 - 5 μm.

[0011] Another technical solution of the present invention is to provide a preparation method of a multi-layer elastic carbon-based thermal interface material, which has the following steps: (1) By means of drum centrifugal spin coating, the coating is dropped into a horizontally arranged centrifugal drum, and a first composite layer with a thickness of 5 - 10 nm and a second composite layer with a thickness of 20 - 80 nm are successively spin-coated on the inner wall of the centrifugal drum under the action of centrifugal force; the coating of the first composite layer is composed of a mixture of carbon tubes and polymers with a mass ratio of 7:3 - 10:0, and the coating of the second composite layer is composed of a mixture of graphene oxide and polymers with a mass ratio of 3:7 - 8:2; the polymer is one or more of polyacrylonitrile, polyimide, furan resin, phenolic resin, and lignin; the length of the carbon tubes is 0.2 - 0.5 mm; (2) Repeat step 1 multiple times to obtain a composite film composed of alternately stacked first composite layers - second composite layers. (3) Heat press the above composite film at 270 - 300 °C in a nitrogen environment under 1 - 5 MPa, and then perform heat treatment at 2700 - 3000 °C in an argon atmosphere under a confined space to obtain a graphene aerogel, with the density of the aerogel being 0.5 - 0.9 g / cm 3 ; at high temperatures, the polymer in the material completely decomposes; (4) Cut the above graphene aerogel perpendicular to the direction of the carbon nanotubes, with a thickness of 0.2 - 0.5 mm; (5) Treat the surface layer with plasma until a uniformly vertically oriented graphene structure is exposed; (6) Continue to etch with plasma to etch away the carbon nanotubes on the upper and lower surfaces of the slice to form a cortex with a thickness of 1 - 5 μm.

[0012] (7) Place the plasma-treated slice in an argon environment and sinter at a high temperature of 2000 - 3000 °C. The damage caused to the material during the plasma etching process is repaired through high-temperature sintering.

[0013] During the centrifugal coating process, the carbon nanotubes are highly oriented. During the high-temperature sintering process, the gaps between the carbon nanotubes serve as gas escape channels. At the same time, the structural units of the material are stratified at the interfaces of the carbon nanotubes, and the thickness of the structural units is regulated, thereby affecting the flexibility of the material. The highly oriented carbon nanotubes provide a heat conduction path on the one hand and elasticity on the other hand.

[0014] During the preparation process of the above thermal interface material, continuous spin coating means that after the first coating is sprayed, the second coating is immediately sprayed. Thus, the second layer of film is compounded while the first layer of film is not completely dry, and the two layers of film are effectively fused, which is beneficial to a continuous heat conduction channel.

[0015] Further, the slicing method is laser etching slicing or wire cutting slicing.

[0016] The beneficial effects of the present invention: (1) This material does not rely on polymers to achieve elasticity, significantly improving the stability of the material; the highly oriented carbon nanotubes in the material can provide elasticity for the building units, and at the same time, the complete carbon nanotube structure can provide a heat conduction path; (2) By adopting a core-shell structure design inside the structural unit and utilizing the thermal conductivity of the carbon nanotubes, on the premise of ensuring that the efficient heat conduction path is not affected, the density of the outer layer of the thermal interface is lower than that of the central region, and only the highly graphitized part is retained, endowing the material with excellent flexibility, lubricity and filling properties, and also significantly reducing the contact thermal resistance. Brief Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the preparation process of the present invention.

[0018] Figure 2It is a physical diagram of Example 1.

[0019] Figure 3 It is a schematic structural diagram of Example 1.

[0020] Figure 4 It is a cross-sectional view of Example 1.

[0021] Figure 5 It is the compressive strain after multiple compression cycles of Example 1. Detailed implementation manners

[0022] The following examples are used to further illustrate the present invention. Their purpose is to explain the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified below, all are in parts by weight and weight percentages.

[0023] The raw materials used in the present invention are all conventional commercially available products unless otherwise specified; the methods used in the present invention are all conventional methods in the art unless otherwise specified.

[0024] The contact thermal resistance described in the present invention is detected by a TIM-Tester thermal interface material testing system.

[0025] The following will further illustrate the embodiments of the present invention through multiple examples.

[0026] It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope protected by the present application.

[0027] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms of "a", "the" and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0028] Example 1 (1) Mix carbon nanotubes and polyacrylonitrile with a mass ratio of 7:3 evenly to obtain a first coating; mix graphene oxide and polyacrylonitrile with a mass ratio of 3:7 evenly to obtain a second coating; the length of the carbon nanotubes is 0.2 mm; (2) Continuously drop the first coating and the second coating into a horizontally arranged centrifugal drum in sequence, control the measurement of each injection, and form a first composite layer with a thickness of 10 nm and a second composite layer with a thickness of 20 nm on the inner wall of the centrifugal drum under the action of centrifugal force; (3) Repeat step 2 multiple times to obtain a composite film with a thickness of 2 cm; its structure is as Figure 3 shown; (4) The above composite film was hot-pressed in a nitrogen environment at 270 °C (pressure 1 MPa), and then heat-treated at 2700 °C in an argon atmosphere under a limited space to obtain a graphene aerogel with a thickness of 4 cm and a density of 0.5 g / cm 3 graphene aerogel; (5) The above graphene aerogel was sliced with a thickness of 0.2 mm; (6) The surface layer was treated with plasma until a uniformly vertically oriented graphene structure was exposed; (7) Plasma etching was continued to etch away 1 μm of the carbon nanotube layer on the upper and lower surfaces of the sheet; (8) The sliced specimen after plasma treatment was placed in an argon environment and sintered at 2000 °C. Its cross-section is as Figure 4 shown. As Figure 5 shown, after 100 cycles, this material still has good elasticity. After testing, the contact thermal resistance of this example is 0.09 K·cm2 / W. The service life can reach 31,000 hours.

[0029] Example 2 (1) Carbon nanotubes and polyimide with a mass ratio of 10:0 were mixed evenly to obtain the first coating; graphene oxide and furan resin with a mass ratio of 8:2 were mixed evenly to obtain the second coating; the length of the carbon nanotubes was 0.5 mm; (2) The first coating and the second coating were successively and continuously dropped into a horizontally arranged centrifugal drum, and the metering of each injection was controlled. Under the action of centrifugal force, a 5-nm first composite layer and an 80-nm second composite layer were successively formed on the inner wall of the centrifugal drum; (3) Step 2 was repeated multiple times to obtain a composite film with a thickness of 1 cm; (4) The above composite film was hot-pressed in a nitrogen environment at 300 °C (pressure 5 MPa), and then heat-treated at 3000 °C in an argon atmosphere under a limited space to obtain a graphene aerogel with a thickness of 3 cm and a density of 0.7 g / cm 3 ; (5) The above graphene aerogel was sliced with a thickness of 0.2 mm; (6) The surface layer was treated with plasma until a uniformly vertically oriented graphene structure was exposed; (7) Plasma etching was continued to etch away 5 μm of the carbon nanotube layer on the upper and lower surfaces of the sheet; (8) The sliced specimen after plasma treatment was placed in an argon environment and sintered at 2000 °C. After testing, the contact thermal resistance of this example is 0.04 K·cm2 / W. The service life exceeds 3000 hours.

[0030] Example 3 (1)Mix carbon nanotubes and phenolic resin with a mass ratio of 10:0 evenly to obtain the first coating; mix graphene oxide and lignin with a mass ratio of 8:2 evenly to obtain the second coating; the length of the carbon nanotubes is 0.5 mm; (2)Sequentially and continuously drop the first coating and the second coating into a horizontally arranged centrifugal drum, control the measurement of each injection, and form a 5-nm first composite layer and an 80-nm second composite layer on the inner wall of the centrifugal drum under the action of centrifugal force; (3)Repeat step 2 multiple times to obtain a composite film with a thickness of 1 cm; (4)Hot press the above composite film in a nitrogen environment at 300 °C (pressure 5 MPa), and then perform heat treatment at 3000 °C in an argon atmosphere under a limited space to obtain a graphene aerogel with a thickness of 3 cm and a density of 0.9 g / cm 3 ; (5)Slice the above graphene aerogel, with a thickness of 0.5 mm; (6)Treat the surface layer with plasma until a uniformly vertically oriented graphene structure is exposed; (7)Continue to etch with plasma to etch away 5 μm of the carbon nanotube layer on the upper and lower surfaces of the sheet; (8)Place the sliced ​​specimen after plasma treatment in an argon environment and sinter at a high temperature of 2000 °C. After testing, the contact thermal resistance of this example is 0.07 K·cm2 / W. The service life exceeds 3000 hours.

[0031] The above embodiments have detailed the structure, features and effects of the present invention. The above are only the preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modified into equivalent embodiments with equivalent changes, still within the scope covered by the specification, shall be within the protection scope of the present invention.

Claims

1. A multi-layer elastic carbon-based thermal interface material, characterized in that, The graphene layer and the carbon nanotube layer are alternately stacked in the horizontal direction to form a main layer in the middle and skin layers on the upper and lower sides; wherein the graphene layer is composed of highly graphitized graphene sheets oriented vertically, and the carbon nanotube layer is composed of carbon nanotubes oriented vertically; and the skin layer is formed by extending a part of the highly graphitized graphene sheets of the main layer to the upper and lower sides; the high graphitization means that the degree of graphitization > 96%.

2. The multi-layer elastic carbon-based thermal interface material according to claim 1, wherein The thickness of the multi-layer elastic carbon-based thermal interface material is 0.2 - 0.5 mm.

3. The multi-layer elastic carbon-based thermal interface material according to claim 1, characterized in that, The thickness of the skin layer is 1 - 5 μm.

4. The multi-layer elastic carbon-based thermal interface material according to claim 1, characterized in that The main body layer is an aerogel structure with a density of 0.5-0.9 g / cm 3 .

5. A preparation method of a multi-layer elastic carbon-based thermal interface material, characterized in that, It has the following steps: (1) By means of drum centrifugal spin coating, the coating is dropped into a horizontally arranged centrifugal drum, and a first composite layer with a thickness of 5 - 10 nm and a second composite layer with a thickness of 20 - 80 nm are successively spin-coated on the inner wall of the centrifugal drum under the action of centrifugal force; the coating of the first composite layer is mixed by carbon nanotubes and a polymer in a mass ratio of 7:3 - 10:0, and the coating of the second composite layer is composed of graphene oxide and a polymer in a mass ratio of 3:7 - 8:2; the polymer is one or more of polyacrylonitrile, polyimide, furan resin, phenolic resin, lignin; the length of the carbon nanotubes is 0.2 - 0.5 mm; (2) Step 1 is repeated multiple times to obtain a composite film composed of a first composite layer - a second composite layer; (3) Thermally press the above composite film in a nitrogen environment at 270 - 300 °C, and then perform heat treatment at 2700 - 3000 °C in an argon atmosphere under a confined space to obtain a graphene aerogel, and the density of the aerogel is 0.5 - 0.9 g / cm 3 ; (4) The above graphene aerogel is sliced perpendicular to the direction of the carbon nanotubes, with a thickness of 0.2 - 0.5 mm; (5) The surface layer is treated with plasma until a uniformly vertically oriented graphene structure is exposed; (6) Continue to etch with plasma to etch away the carbon nanotubes on the upper and lower surfaces of the slice to form a skin layer with a thickness of 1 - 5 μm; (7) The plasma-treated slice is placed in an argon environment and sintered at a high temperature of 2000 - 3000 °C.

6. The preparation method according to claim 5, characterized in that, The slicing method is laser etching slicing or wire cutting slicing.

7. The preparation method according to claim 5, characterized in that, The pressure of hot pressing is 1 - 5 MPa.

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