Thermal interface material with high compression resilience and preparation method thereof

Abstract

According to the high-compression-resilience thermal interface material and the preparation method thereof, high-thermal-conductivity fibers and elastic macromolecules are introduced between graphene sheets which are arranged in an oriented mode, and the graphene sheets form a bent structure on the surfaces of the fibers under the action of pressure; graphene and high-heat-conduction fibers are firmly combined through elastic macromolecules, the compression resilience capacity is improved, physical crosslinking is formed between bent graphene sheets through pi-pi conjugation, and therefore the material with a heat conduction framework and an elastic microstructure is constructed. And then cutting along the direction perpendicular to the graphene sheets to obtain the interface material containing the bent graphene sheets and the high-thermal-conductivity fibers, so that the material has high vertical thermal conductivity, high horizontal thermal conductivity and high compression ratio.

Description

Technical Field

[0001] The invention relates to the field of graphene materials, in particular to a high compression rebound thermal interface material and a preparation method thereof. Background Art

[0002] As the heat flux density of high-power electronic devices exceeds 200 W / cm², higher requirements are placed on traditional thermal interface materials. At present, high-performance thermal interface materials must simultaneously meet the requirements of vertical thermal conductivity>15 W / mK and equivalent thermal impedance<0.1 Kcm 2 / W and compression rate>35% at 50psi and other stringent requirements. Conventional thermal conductive silicone pads and thermal conductive silicone grease are difficult to meet the above requirements.

[0003] Graphene materials have extremely high theoretical thermal conductivity and have been widely used in the field of high-performance heat dissipation materials. For example, graphene heat dissipation films have been used in many new mobile phone products. The addition of graphene has effectively improved the thermal conductivity of conventional polymer materials. However, in thermal interface materials, existing technologies have two major shortcomings: first, the traditional composite process makes the graphene sheets arranged in a straight line, which leads to too low compression rate due to excessive rigidity, and poor deformation ability on the interface leads to excessive interface thermal resistance; second, by introducing three-dimensional structures such as holes and wrinkles into the horizontally oriented graphene film, although the thermal conductivity in the vertical direction is improved to a certain extent, it is still maintained below 10 W / mK, limiting its application.

[0004] Therefore, it is urgent to develop a new structural control strategy based on the vertically oriented graphene structure to achieve the precise construction of the curved morphology of graphene sheets at the mesoscopic scale (1~100μm) and simultaneously optimize the thermal conductivity path and mechanical rebound properties. Summary of the invention

[0005] In view of the problem that the current traditional graphene material preparation process is difficult to take into account both high thermal conductivity and high rebound, the present invention provides a high compression rebound thermal interface material and a preparation method thereof, by introducing high thermal conductivity fibers between oriented graphene sheets, so that the graphene sheets form a wavy curved structure on the fiber surface, and after high temperature treatment, conjugate cross-linking occurs at the tangent part of the curved surface to form a three-dimensional heat conduction channel. After vertical cutting, a thermal interface material with high vertical thermal conductivity and high compressibility can be obtained.

[0006] Specifically, the present invention adopts the following technical solution, comprising the following steps: (1) Preparation of graphene raw materials: The graphene oxide film is foamed by a plasticizing foaming process, and then a graphene foam film with a thickness of 50 to 500 μm is obtained by high-temperature reduction treatment at 2700 to 3200 °C; (2) Fiber array construction: A high thermal conductivity fiber array coated with an elastic polymer precursor is laid on the surface of the graphene foam film in the same direction and meets the following requirements: a. Fiber diameter d = 2 ~ 30 μm; b. The distance between adjacent fibers is s≥4μm and satisfies s / d≥0.5; (3) Multilayer composite: alternately stack fiber layers and graphene foam membranes to control the total thickness of the final laminated material to be no less than 4 cm; the fiber angle between adjacent fiber layers is no more than 3°; the highly oriented fiber layer can ensure the deformation of the rGO membrane between fibers to form a wavy structure.

[0007] (4) Hot pressing: Apply a pressure of 5 to 40 MPa to the laminated material obtained in step (3), with the pressure direction perpendicular to the surface of the graphene film, and treat it at 20 to 100°C for 1 to 6 hours to obtain a composite block; due to the fiber steric hindrance, the graphene sheets are ππ stacked to form physical crosslinks.

[0008] (5) Directional slicing: Slice the composite block obtained in step (3), with the cutting direction perpendicular to the graphene film surface and parallel to the axis of the high thermal conductivity fiber. The cutting thickness is 0.2~1mm. Remove the sheet containing fibers on the surface to obtain a thermal interface material with high compression rebound.

[0009] Furthermore, the average diameter of the graphene oxide sheets in the graphene oxide film in step (1) is not less than 2 μm. The graphene oxide sheet diameter is controlled within a reasonable range in order to effectively form a wavy curved structure and to form a heat conduction channel through the upper and lower surfaces of the thermal interface. If the graphene oxide sheet is too small and the number of edges is too high, the heat conduction channel will be interrupted and the vertical thermal conductivity will decrease.

[0010] Furthermore, the high thermal conductivity fiber array in step (2) is a mixture of one or more of an asphalt-based carbon fiber array, a graphene fiber array, a boron nitride fiber array, and a carbon nanotube fiber array, and the thermal conductivity along the fiber direction is not less than 400W / mK. The high thermal conductivity fiber array, on the one hand, assists the deformation of the graphene film, and on the other hand, has its own thermal conductivity, which helps heat transfer in the horizontal direction. Compared with the traditional single vertical heat dissipation interface material, it is more conducive to the uniform distribution of heat and avoids heat accumulation.

[0011] Furthermore, the elastic polymer precursor in step (2) is one of uncured silicone and polyurethane. Silicone and polyurethane are common elastic polymer materials that can be cured in low-temperature hot pressing under the action of a catalyst to provide good elasticity.

[0012] Furthermore, the diameter of the high thermal conductivity fibers in the high thermal conductivity fiber array in step (2) is 5-15 μm.

[0013] Furthermore, the slicing method in step (5) is one of wire cutting, ultrasonic knife cutting or laser cutting.

[0014] By rationally regulating the thickness of the reduced graphene oxide film and the diameter and spacing of the high thermal conductivity fiber, the alternating laminated material is densified under pressure. Due to its high flexibility, the wrinkled graphene sheets in the graphene foam film bend and deform on the fiber surface to form a wavy structure. The wavy structure can bring a spring-like mechanical effect, making the thermal interface material have high compression performance in the vertical direction. In addition, the curved graphene sheets produce conjugated physical cross-links on the fiber surface due to extrusion, further improving the compressibility and resilience. Furthermore, the elastic polymer not only plays a bonding role, but also significantly improves the compression resilience, which is beneficial to improving the overall mechanical performance of the material.

[0015] The present invention also provides a high compression and resilience thermal interface material prepared by the above method, which is composed of wavy graphene sheets, high thermal conductivity fibers and elastic polymers, wherein the wavy graphene sheets are arranged vertically as a whole, the high thermal conductivity fibers are arranged horizontally, the elastic polymers are distributed between the graphene sheets and the high thermal conductivity fibers and play a connecting role, and the wavy graphene sheets produce local physical cross-linking at the positions on both sides of the fibers. The graphene sheets are arranged vertically to provide a heat conduction channel; the high thermal conductivity fibers are arranged horizontally to provide horizontal heat conduction; the elastic polymer combines the fibers and graphene to improve horizontal strength and vertical elasticity.

[0016] Furthermore, the high thermal conductivity fiber is a mixture of one or more of asphalt-based carbon fiber, graphene fiber, boron nitride fiber, and carbon nanotube fiber, and the thermal conductivity along the fiber direction is not less than 400 W / mK.

[0017] The thermal interface material has a compression rebound rate of not less than 90% under 50% strain, and a thermal impedance of not more than 0.1 Kcm under 50% strain. 2 / W.

[0018] Beneficial effects of the present invention: (1) Improving the compression resilience of thermal interface materials in two dimensions: structurally, by introducing high thermal conductivity fibers and forming a curved structure, a wavy structure is spontaneously formed on the cross section of the material. Different from the traditional simple stacking, firstly, it avoids the excessive rigidity caused by the vertical sheet structure; secondly, the wavy graphene sheets will produce a spring rebound effect after being compressed in the plane, showing a higher rebound rate; thirdly, the graphene sheets are squeezed on the outside of the fiber to form conjugated cross-links, further improving the heat dissipation capacity and lateral strength between the sheets. In terms of materials, after the introduction of elastic polymers, the bonding effect not only increases the force of graphene and high thermal conductivity fibers, significantly optimizing the horizontal tensile strength of the material, but also provides additional elasticity for the compression rebound of the material, comprehensively improving the vertical compression and rebound properties of the material.

[0019] (2) Construction of three-dimensional thermal conduction channels: The two-dimensional characteristics of graphene determine that its thermal conductivity is high in the plane but low in the vertical direction. After the introduction of high thermal conductivity fibers, heat can be quickly transmitted along the fibers in the horizontal direction. At the same time, after inducing the graphene sheets to form a wavy structure, local cross-linking is produced, which also significantly improves the thermal conductivity in the horizontal direction. At the same time, the vertically arranged graphene sheets construct a rich thermal conduction channel, so that the material can achieve both horizontal and vertical thermal conductivity.

[0020] (3) The method is simple and easy to scale up: Based on the conventional graphene material molding method, the introduction of high thermal conductivity fibers can easily realize batch preparation, with low requirements for equipment, materials and personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a flow chart of the preparation method.

[0022] Figure 2 This is a cross-sectional scanning electron microscope image of the thermal interface material obtained in Example 1.

[0023] Figure 3 This is a cross-sectional scanning electron microscope image of the thermal interface material obtained in Example 2.

[0024] Figure 4 This is the compression-rebound curve of Example 1.

[0025] Figure 5 This is the compression-rebound curve of Comparative Example 1. DETAILED DESCRIPTION

[0026] The following examples are used to further illustrate the present invention, and their purpose is to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified, all parts by weight and weight percentages are used below.

[0027] The raw materials used in the present invention, unless otherwise specified, are conventional commercially available products; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.

[0028] The embodiments of the present invention are further described below with reference to a plurality of embodiments.

[0029] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0030] 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 "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0031] As is common knowledge in this field, thermal impedance is the sum of the thermal resistance of the material itself and the thermal resistance between the contact surface. It is tested using the ASTM D 5470 method, and the equipment is the LW-9389MD interface material thermal resistance and thermal conductivity coefficient meter. The compression rebound test is tested using a universal test tensile machine, where the compression strength is the stress under compression to the required strain. The compression rebound rate test method is: the initial thickness of the test sample is T1, the sample is compressed to 50% deformation, and then held for 1 minute. After releasing the external force, wait for 10 minutes to measure the thickness T2, and the rebound rate = T2 / T1*100%.

[0032] Example 1 (1) Preparation of graphene raw materials: The graphene oxide film is foamed by plasticizing and foaming process, and then reduced by high temperature treatment at 3200°C to obtain a graphene foam film with a thickness of 200 μm, wherein the diameter of the graphene oxide flakes is 5-10 μm; (2) Fiber array construction: A graphene fiber array (thermal conductivity ≥ 1000 W / mK) coated with a mixture of silica gel AB components is laid on the surface of the graphene foam film in the same direction and meets the following requirements: a. Fiber diameter d = 5~8μm; b. The distance between adjacent fibers is s=4μm; (3) Multilayer composite: alternately stack fiber layers and graphene foam films, control the total thickness of the final laminated material to 8 cm, and make the fibers between adjacent fiber layers parallel to each other; (4) Hot pressing: applying a pressure of 20 MPa to the laminated material obtained in step (3), with the pressure direction perpendicular to the surface of the graphene film, and treating at 80° C. for 4 h to obtain a composite block; (5) Directional slicing: The composite block obtained in step (4) is sliced ​​using wire cutting, with the cutting direction being perpendicular to the graphene film surface and parallel to the axis of the high thermal conductivity fiber. The cutting thickness is 0.3 mm, and the sheet containing fibers on the surface is removed to obtain a thermal interface material with high compression rebound.

[0033] like Figure 2As shown in the figure, the thermal interface material is composed of wavy graphene sheets, graphene fibers and silica gel, wherein the wavy graphene sheets are arranged vertically as a whole, the graphene fibers are arranged horizontally, the silica gel is distributed between the graphene sheets and the graphene fibers and plays a connecting role, and the wavy graphene sheets produce local physical cross-linking at both sides of the fibers. The compression rebound rate of the material at 50% strain is 97%, and the thermal impedance at 50% strain is 0.08 Kcm 2 / W, the stress required to compress to 50% is 39psi.

[0034] Example 2 (1) Preparation of graphene raw materials: The graphene oxide film is foamed by a plasticizing foaming process, and then reduced by a high temperature treatment at 3200°C to obtain a graphene foam film with a thickness of 350 μm, wherein the diameter of the graphene oxide flakes is 5 to 10 μm; (2) Fiber array construction: A graphene fiber array (thermal conductivity ≥ 1000 W / mK) coated with a mixture of silica gel AB components is laid on the surface of the graphene foam film in the same direction and meets the following requirements: a. Fiber diameter d = 10~15μm; b. The distance between adjacent fibers is s=8μm; (3) Multilayer composite: alternately stack fiber layers and graphene foam films, control the total thickness of the final laminated material to 8 cm, and the angle between adjacent fiber layers to 0-1°; (4) Hot pressing: applying a pressure of 20 MPa to the laminated material obtained in step (3), with the pressure direction perpendicular to the surface of the graphene film, and treating at 80° C. for 4 h to obtain a composite block; (5) Directional slicing: Use wire cutting to slice the composite block obtained in step (4), with the cutting direction perpendicular to the graphene film surface and parallel to the axis of the high thermal conductivity fiber. The cutting thickness is 0.3 mm, and the sheet containing fibers on the surface is removed to obtain a thermal interface material with high compression rebound. Figure 3 As shown, wavy graphene sheets, graphene fibers and silica gel can be seen, and silica gel connects adjacent graphene sheets and graphene fibers.

[0035] The material has a compression rebound rate of 96% at 50% strain and a thermal impedance of 0.084 Kcm at 50% strain. 2 / W, the stress required to compress to 50% is 35psi.

[0036] Example 3 (1) Preparation of graphene raw materials: The graphene oxide film is foamed by plasticizing and foaming process, and then reduced by high temperature treatment at 3000℃ to obtain a graphene foam film with a thickness of 500μm, wherein the diameter of the graphene oxide sheet is 2~6μm; (2) Fiber array construction: An array of asphalt-based carbon fibers (thermal conductivity ≥ 800 W / mK) coated with a mixture of silica gel AB components is laid on the surface of the graphene foam film in the same direction and meets the following requirements: a. Fiber diameter d = 25 ~ 30 μm; b. The distance between adjacent fibers is s=15μm; (3) Multilayer composite: alternately stack fiber layers and graphene foam films, control the total thickness of the final laminated material to 16 cm, and the angle between adjacent fiber layers to 2-3°; (4) Hot pressing: applying a pressure of 40 MPa to the laminated material obtained in step (3), with the pressure direction perpendicular to the surface of the graphene film, and treating at 100° C. for 1 h to obtain a composite block; (5) Directional slicing: The composite block obtained in step (4) is sliced ​​using wire cutting, with the cutting direction being perpendicular to the graphene film surface and parallel to the axis of the high thermal conductivity fiber. The cutting thickness is 1 mm, and the sheet containing fibers on the surface is removed to obtain a thermal interface material with high compression rebound.

[0037] The compression rebound rate of the thermal interface material at 50% strain is 93%, the thermal impedance at 50% strain is 0.095Kcm2 / W, and the stress required to compress to 50% is 41psi.

[0038] Example 4 (1) Preparation of graphene raw materials: The graphene oxide film is foamed by plasticizing and foaming process, and then reduced by high temperature treatment at 2700°C to obtain a graphene foam film with a thickness of 50 μm, wherein the diameter of the graphene oxide flakes is 15-20 μm; (2) Fiber array construction: An array of boron nitride fibers (thermal conductivity ≥ 400 W / mK) coated with a pre-polymerized polyurethane solution is laid on the surface of the graphene foam film in the same direction and meets the following requirements: a. Fiber diameter d = 2~5μm; b. The distance between adjacent fibers is s=4μm; (3) Multilayer composite: alternately stack fiber layers and graphene foam films, control the total thickness of the final laminated material to 4 cm, and the angle between adjacent fiber layers to 0-1°; (4) Hot pressing: applying a pressure of 5 MPa to the laminated material obtained in step (3), with the pressure direction perpendicular to the surface of the graphene film, and treating at 20° C. for 6 h to obtain a composite block; (5) Directional slicing: Use an ultrasonic knife to slice the composite block obtained in step (4), with the cutting direction perpendicular to the graphene film surface and parallel to the axis of the high thermal conductivity fiber. The cutting thickness is 0.2 mm. The sheet containing fibers on the surface is removed to obtain a thermal interface material with high compression rebound.

[0039] The thermal interface material has a compression rebound rate of 90% at 50% strain, a thermal impedance of 0.1 Kcm2 / W at 50% strain, and a stress of 48psi required to compress to 50%.

[0040] Comparative Example 1 (1) Preparation of graphene raw materials: The graphene oxide film is foamed by plasticizing and foaming process, and then reduced by high temperature treatment at 3200°C to obtain a graphene foam film with a thickness of 300 μm, wherein the diameter of the graphene oxide flakes is 5-10 μm; (2) Multilayer composite: a mixed liquid of silica gel AB components is coated on the surface of the graphene foam film, and then the total thickness of the final laminated material is controlled to be 8 cm; (3) Hot pressing: applying a pressure of 20 MPa to the laminated material obtained in step (2), with the pressure direction perpendicular to the surface of the graphene film, and treating at 80°C for 4 h to obtain a composite block; (4) Directional slicing: The composite block obtained in step (3) is sliced ​​using wire cutting, with the cutting direction being perpendicular to the graphene film surface and the cutting thickness being 0.3 mm, to obtain a thermal interface material.

[0041] The compression rebound rate of the thermal interface material at 50% strain is 84%, and the thermal impedance at 50% strain is 0.18Kcm 2 / W, the stress required to compress to 50% is 39psi.

[0042] In Comparative Example 1, no high thermal conductivity fiber was added, and only elastic polymer was used to bond the graphene foam film, resulting in a decrease in compression rebound performance and an increase in thermal resistance. The main reasons are: first, without the fiber, a good bending structure and a stacking structure between graphene sheets cannot be formed. The graphene sheets are loosely arranged in the vertical direction and are easily collapsed without rebounding under the action of external force; second, there is no lateral heat dissipation channel, resulting in slower heat transfer; third, after the silicone is cured, a poor heat conduction channel is formed that runs through the upper and lower parts of the thermal interface material, resulting in an increase in thermal resistance under compression. In contrast, due to the deformation of the graphene film on the fiber surface, a wrapping structure (such as Figure 2 , 3 As shown in the figure, the silicone does not penetrate the entire upper and lower surfaces of the material, so it has little effect on thermal conductivity, but still provides excellent rebound performance.

[0043] Comparative Example 2 (1) Preparation of graphene raw materials: The graphene oxide film is foamed by plasticizing and foaming process, and then reduced by high temperature treatment at 2700°C to obtain a graphene foam film with a thickness of 50 μm, wherein the diameter of the graphene oxide flakes is 15-20 μm; (2) Fiber array construction: Lay the boron nitride fiber (thermal conductivity ≥ 400 W / mK) array on the surface of the graphene foam film in the same direction and meet the following requirements: a. Fiber diameter d = 2~5μm; b. The distance between adjacent fibers is s=4μm; (3) Multilayer composite: alternately stack fiber layers and graphene foam films, control the total thickness of the final laminated material to 4 cm, and the angle between adjacent fiber layers to 0-1°; (4) Hot pressing: applying a pressure of 5 MPa to the laminated material obtained in step (3), with the pressure direction perpendicular to the surface of the graphene film, and treating at 20° C. for 6 h to obtain a composite block; Directional slicing: Use an ultrasonic knife to slice the composite block obtained in step (4), with the cutting direction perpendicular to the graphene film surface and parallel to the axis of the high thermal conductivity fiber. The cutting thickness is 0.2 mm, and the sheet containing fibers on the surface is removed to obtain a thermal interface material.

[0044] The compression rebound rate of the thermal interface material at 50% strain is 14%, and the thermal impedance at 50% strain is 0.11Kcm 2 / W, the stress required to compress to 50% is 41psi.

[0045] In Comparative Example 2, no silica gel is added, and the fiber is wrapped inside the material only by relying on the ππ conjugation effect between the graphene sheets, which cannot play a good rebound effect under compression.

[0046] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the protection scope of the present invention.

Claims

1. A method for preparing a thermal interface material with high compression rebound, characterized in that: The following steps are involved: (1) Preparation of graphene raw materials: The graphene oxide film is foamed by a plasticizing foaming process, and then a graphene foam film with a thickness of 50 to 500 μm is obtained by high-temperature reduction treatment at 2700 to 3200 °C; (2) Fiber array construction: A high thermal conductivity fiber array coated with an elastic polymer precursor is laid on the surface of the graphene foam film in the same direction and meets the following requirements: a. Fiber diameter d = 2 ~ 30 μm; b. The distance between adjacent fibers is s≥4μm and satisfies s / d≥0.5; (3) Multilayer composite: alternately stack fiber layers and graphene foam films, and control the total thickness of the final laminated material to be no less than 4 cm; the fiber angle between adjacent fiber layers is no more than 3°; (4) Hot pressing: applying a pressure of 5 to 40 MPa to the laminated material obtained in step (3), with the pressure direction perpendicular to the surface of the graphene film, and treating at 20 to 100° C. for 1 to 6 hours to obtain a composite block; (5) Directional slicing: Slice the composite block obtained in step (3), with the cutting direction perpendicular to the graphene film surface and parallel to the axis of the high thermal conductivity fiber. The cutting thickness is 0.2~1mm. Remove the sheet containing fibers on the surface to obtain a thermal interface material with high compression rebound.

2. The method according to claim 1, characterized in that The average diameter of the graphene oxide sheets in the graphene oxide film in step (1) is not less than 2 μm.

3. The method according to claim 1, characterized in that The high thermal conductivity fiber array in step (2) is a mixture of one or more of an asphalt-based carbon fiber array, a graphene fiber array, a boron nitride fiber array, and a carbon nanotube fiber array, and the thermal conductivity along the fiber direction is not less than 400 W / mK.

4. The method according to claim 1, characterized in that: The elastic polymer precursor in step (2) is one of uncured silicone and polyurethane.

5. The method according to claim 1, characterized in that The diameter of the high thermal conductivity fibers in the high thermal conductivity fiber array in step (2) is 5-15 μm.

6. The method according to claim 1, characterized in that The slicing method in step (5) is one of wire cutting, ultrasonic knife cutting or laser cutting.

7. A high compression rebound thermal interface material prepared by the method of claim 1, characterized in that: It is composed of wavy graphene sheets, high thermal conductivity fibers and elastic polymers, wherein the wavy graphene sheets are arranged in the vertical direction as a whole, the high thermal conductivity fibers are arranged in the horizontal direction, the elastic polymers are distributed between the graphene sheets and the high thermal conductivity fibers and play a connecting role, and the wavy graphene sheets produce local physical cross-linking at both sides of the fibers.

8. The material according to claim 7, characterized in that The high thermal conductivity fiber is a mixture of one or more of asphalt-based carbon fiber, graphene fiber, boron nitride fiber, and carbon nanotube fiber, and the thermal conductivity along the fiber direction is not less than 400 W / mK.

9. The material according to claim 7, characterized in that The thermal interface material has a compression rebound rate of not less than 90% under 50% strain, and a thermal impedance of not more than 0.1 Kcm under 50% strain. 2 / W.

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