Highly oriented graphene heat conduction sheet and method of making same

Abstract

The application discloses a kind of high orientation graphene heat conduction sheet and preparation method thereof, it is related to heat dissipation material technical field.The preparation method includes the following steps: preparation grid film forming tool;Preparation graphene oxide slurry;Grid film forming tool is immersed in graphene oxide slurry and pre-drying, slurry fills up tool gap;Then directional freeze-drying is carried out, form unidirectional temperature gradient, obtain graphene oxide tool;Again, cover the cover plate with micropore on its upper and lower, sequentially carry out three-stage heat treatment, through low temperature, medium temperature and high temperature stage, prepare graphene bulk;Finally, cut into sheet along the direction perpendicular to height, and coating phase change type adhesive on surface, obtain high orientation graphene heat conduction sheet.The preparation method of the application can effectively improve the orientation and thermal conductivity of graphene heat conduction sheet, the interface thermal resistance of high orientation heat conduction sheet prepared by the preparation method is low, the heat dissipation efficiency is high, and excellent compression resilience can also be possessed under the condition of maintaining low modulus.

Description

Technical Field

[0001] This invention relates to the field of heat dissipation materials technology, and in particular to a highly oriented graphene thermal conductive sheet and its preparation method. Background Technology

[0002] Currently, chip iterations and upgrades are rapid, and chip packaging forms are becoming increasingly diversified. Many assembly schemes have emerged where bare chip dies are directly connected to heat sinks without shielding. Applications such as intelligent driving in new energy vehicles and the wind power and wind energy industries place extremely high demands on the thermal conductivity and low-stress compression adaptability of TIM1.5 thermal conductive materials.

[0003] Although currently used graphene thermal conductive sheets have significantly improved thermal conductivity compared to traditional filler-type thermal conductive materials, most commercially available graphene thermal conductive sheets are made by laminating graphene films with adhesives and then cutting them. The orientation of the graphene is determined by the raw graphene film, lacking the ability to be re-aligned in the later stages. Furthermore, the adhesives between the graphene films reduce upward thermal conductivity pathways and create significant horizontal thermal resistance, thus drastically weakening graphene's inherent ultra-high thermal conductivity. Therefore, the thermal conductivity of most high-end graphene thermal conductive sheets on the market is currently around 100 W / mK, and their thermal resistance is insufficient to meet the heat dissipation requirements of rapidly iterating high-power chips. In addition, existing drying methods for graphene thermal conductive films have the following drawbacks: First, during the evaporation process of ordinary thermal drying or air drying, huge capillary forces are generated at the gas-liquid interface, pulling and compressing the fragile porous graphene network, causing its pore structure to collapse and graphene sheets to stack and agglomerate, forming a disordered network structure. Secondly, the direct rapid freezing method with liquid nitrogen will form a large number of tiny, disordered ice crystals, creating an isotropic porous network, which is not conducive to the long-distance rapid transfer of phonons and has relatively low thermal conductivity.

[0004] Existing technologies also attempt to improve thermal conductivity by increasing the density of graphene film stacks. However, this approach sacrifices the compressive resilience of the thermally conductive sheet at low modulus, which cannot meet the requirements of TIM1.5 thermally conductive materials. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the purpose of this invention is to provide a highly oriented graphene thermal conductive sheet and its preparation method, so as to achieve the high orientation and low thermal resistance of the graphene thermal conductive sheet, and to have excellent compression resilience while maintaining low modulus.

[0006] This invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a highly oriented graphene thermal conductive sheet, comprising the following steps:

[0008] S1. Prepare a grid film forming fixture. The grid film forming fixture is made of metal with a melting point of 500~1900℃. The grid film forming fixture includes a U-shaped frame, which is fixedly connected as a whole by connectors. The grid film forming fixture is provided with through holes running vertically through the top and bottom.

[0009] S2. An anti-sagging agent is added to the graphene oxide dispersion, followed by jet dispersion and ultrasonic treatment to obtain a graphene oxide slurry; the thixotropic index of the graphene oxide slurry is 3-4.8.

[0010] S3. After immersing the grid film forming fixture in the graphene oxide slurry, pull it vertically upwards so that the graphene oxide slurry adheres to the surface of the grid film forming fixture and is then pre-dried.

[0011] S4. Repeat step S3 until the graphene oxide slurry fills the gaps in the grid film forming fixture.

[0012] S5. The grid film-forming fixture with graphene oxide attached obtained in step S4 is subjected to directional freeze-drying, so that its bottom contacts a cold source to form a unidirectional temperature gradient and is cooled to -50~-100℃ at a rate of 0.5-10℃ / min, and then kept at the temperature for 12-96 hours to obtain the graphene oxide fixture.

[0013] S6. Seal the upper and lower ends of the graphene oxide fixture with two cover plates respectively, and then perform heat treatment: first, heat to 200-500℃ at a heating rate of 0.5-6℃ / min and hold for 2-9 hours; then continue heating to 1100-1900℃ at a heating rate of 3-10℃ / min and hold for 5-11 hours; finally, continue heating to 2700-3300℃ at a heating rate of 5-20℃ / min and hold for 10-28 hours to obtain a graphene block; the material of the cover plates is the same as that of the grid film forming fixture, and the cover plates are distributed with micropores.

[0014] S7. Cut the graphene block into graphene sheets of the required thickness along a direction perpendicular to its height, and coat the upper and lower surfaces of the graphene sheets with a phase change adhesive to form an adhesive layer, thereby obtaining a highly oriented graphene thermal conductive sheet.

[0015] Furthermore, the material of the grid film-forming fixture is aluminum or an aluminum-silicon alloy. In step S5, materials with too low a melting point will melt and disappear prematurely, while materials with too high a melting point will not be able to melt and disappear later, affecting the final formation of the graphene block.

[0016] Preferably, the surface roughness of the grid film-forming fixture is Ra0.8-5.3. The roughness of the grid film-forming fixture is adjusted by plasma treatment of its surface, so that the graphene oxide slurry can more easily adhere to the surface of the grid film-forming fixture without affecting the orientation of the graphene oxide. When the roughness is too small, the graphene oxide slurry is not easy to adhere; when the roughness is too large, the concave holes will obviously introduce additional pores and will also be detrimental to the orientation of the graphene oxide.

[0017] Furthermore, the U-shaped frame includes at least two rectangular frames, which are nested sequentially from the center outwards, with their dimensions increasing sequentially. The connector connects the rectangular frames, and the space between the rectangular frames and the connector forms the through hole.

[0018] Furthermore, the connector is an X-shaped structure composed of a first connector and a second connector, with the first and second connectors located on the two diagonals of the rectangular frame and connecting the corners of two adjacent rectangular frames. The U-shaped frame design of at least two rectangular frames maintains strong deformation recovery in terms of mechanical properties, ensuring that the prepared graphene thermal conductive sheet has good resilience.

[0019] Furthermore, the thickness of the rectangular frame, the first connector, and the second connector is 0.04-0.3 mm, and the distance between two adjacent rectangular frames is 0.2-1 mm. If the thickness of the rectangular frame, the first connector, and the second connector is too thin, they are prone to deformation and the gaps will not be parallel and perpendicular; if they are too thick, the gaps will not be filled by the subsequent expansion and repair of graphene oxide.

[0020] Furthermore, the rectangular frame is a square structure, and the height of the rectangular frame and the connector is twice the width of the rectangular frame.

[0021] Further, in step S2, the concentration of the graphene oxide dispersion is 20-60 mg / ml; the amount of anti-sagging agent added is 0.1-2% of the mass of the graphene oxide slurry.

[0022] Further, in step S2, the pressure of the jet dispersion is 13000-17000 psi, the flow rate is 0.3-1.1 L / min, and the ultrasonic treatment time is 5-15 min.

[0023] Preferably, the anti-sagging agent is one or more of fumed silica, polyamide wax, cellulose ether, and organobentonite.

[0024] Specifically, in step S2, vertically pulling the graphene sheet upwards utilizes fluid action, which helps the graphene oxide sheets to be regularly arranged on the tooling surface, thus improving the orientation effect.

[0025] Preferably, in step S3, the immersion time is 3-9 seconds.

[0026] Preferably, in step S3, the pre-drying temperature is 40-60℃ and the time is 1-12 hours.

[0027] Preferably, in step S5, the cover plate is provided with a plurality of micropores, the pore diameter of the micropores is 0.1-0.3mm, and the porosity of the cover plate is 40-70%.

[0028] Specifically, in step S5, directional freeze-drying ensures that heat from the sample can only be removed in a single direction through the bottom cold source, thus establishing a stable and uniform unidirectional temperature gradient from bottom to top within the sample. During the freezing process, water turns into ice crystals and cools down at a slower rate. The ice crystals have ample time to preferentially grow in the direction most favorable for energy, growing into large, oriented columnar or layered ice crystals along the temperature gradient (from the cold end to the hot end). These large, oriented ice crystals push graphene sheets between the ice crystal boundaries, forming a highly ordered, oriented layered or honeycomb-like porous structure. The direction of ice crystal growth determines the orientation of the channels. When the ice crystals sublimate, the spaces they originally occupied become pores, and their morphology is directly replicated into the framework structure of the graphene network. After subsequent heat treatment, these oriented channels collapse to form highly oriented graphene layers, providing a high-speed highway for phonon (heat carrier) transport and greatly improving in-plane thermal conductivity.

[0029] Specifically, in step S6, the first heating is a low-temperature thermal reduction stage, which causes the oxygen-containing functional groups in graphene oxide to decompose and escape in the form of gases such as carbon dioxide and water vapor, resulting in a dramatic volume expansion. However, due to the limitations of the grid film-forming tooling, a dense porous structure can be formed without the need for densification processes such as pressure roller extrusion. The second heating is a medium-temperature thermal reduction stage, where the grid film-forming tooling melts away at high temperatures, and the graphene oxide is further reduced and carbonized, resulting in an adhesive-free, integrated graphene oxide / graphene bulk, which is beneficial for preserving the ultra-high thermal conductivity of graphene itself. The third heating is a high-temperature graphitization stage, where, at ultra-high temperatures, a large number of defects remaining in the graphene oxide are repaired, the carbon lattice structure becomes more complete, the grain size increases, and the carbon atoms rearrange in an oriented manner, ultimately obtaining a graphene bulk with high orientation and high thermal conductivity.

[0030] Further, in step S6, the phase change adhesive comprises the following components in parts by weight: 100 parts polyethylene glycol, 0.3-2 parts coupling agent, 100-800 parts amino silicone oil, and 200-500 parts solvent.

[0031] Preferably, the molecular weight of the polyethylene glycol is 1000-4000.

[0032] Preferably, the coupling agent is KH-550.

[0033] Preferably, the viscosity of the amino silicone oil is 20,000-80,000 and the ammonia value is 0.3-2.6%.

[0034] Preferably, the solvent is ethyl acetate or xylene.

[0035] Preferably, the thickness of the adhesive layer is 10-60 micrometers.

[0036] Preferably, the preparation method of the phase change adhesive is as follows: polyethylene glycol, coupling agent and amino silicone oil are heated to 70-90℃ and melt-blended, and then diluted with solvent after cooling to room temperature.

[0037] The phase change adhesive is a weak phase change material. At room temperature, the phase change adhesive can adhere to the graphene sheet surface to form an isolation layer to prevent mutual adhesion. When the chip generates heat during operation, it can become weakly viscous instead of flowing out as a pure liquid, increasing the wettability of the graphene thermal conductive sheet interface and reducing the interface thermal resistance. At the same time, its weak viscous effect is conducive to its adhesion and fixation on the chip surface, enhancing usability.

[0038] Furthermore, the thickness of the graphene sheet is 0.3-2.2 mm.

[0039] Secondly, the present invention also discloses a highly oriented graphene thermal conductive sheet, which is prepared by the above-described method for preparing highly oriented graphene thermal conductive sheets.

[0040] The present invention has the following technical effects:

[0041] This invention utilizes a U-shaped grid film-forming tool made of a metal with a specific melting point as a guiding template, combined with a unique directional freeze-drying and stepped heat treatment process, to successfully prepare a highly oriented, adhesive-free, integrated graphene thermal conductive sheet. This graphene thermal conductive sheet constructs a highly efficient "highway" for phonon transport, exhibiting low interfacial thermal resistance and high heat dissipation efficiency. Simultaneously, this unique preparation path and structural design enable the graphene thermal conductive sheet to achieve ultra-high thermal conductivity while also possessing low bulk modulus and rapid compression resilience, perfectly resolving the inherent contradiction between high thermal conductivity and low modulus and high resilience. Furthermore, the phase change adhesive used further optimizes interfacial wettability, effectively reducing contact thermal resistance. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a top view of the grid film forming fixture A provided in Embodiment 1 of the present invention;

[0044] Figure 2 This is a schematic diagram of the main structure of the grid film forming fixture A provided in Embodiment 1 of the present invention;

[0045] Figure 3 This is a schematic diagram of the structure of the cover plate provided in Embodiment 1 of the present invention;

[0046] Figure 4 This is a top view of the grid film forming fixture B provided in Comparative Example 3 of the present invention.

[0047] Figure 5 This is a schematic diagram of the chip heating and heat dissipation simulation fixture provided by the present invention;

[0048] Figure descriptions: 1-Grid film forming fixture A; 11-U-shaped frame; 111-Rectangular frame A; 12-Connector; 121-First connector; 122-Second connector; 13-Through hole A; 2-Cover plate; 21-Micropore; 3-Grid film forming fixture B; 31-Rectangular frame B; 32-Transverse support; 33-Through hole B; 4-Filling layer; 5-Heating end; 6-Heat source; 7-Heat dissipation layer. Detailed Implementation

[0049] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] It should be understood that, when used in this specification and the appended claims, the terms “comprising” and “including” indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0051] Example 1:

[0052] A fabrication process for a highly oriented graphene thermal conductive sheet includes the following steps:

[0053] S1. Prepare a grid film forming fixture A1, such as... Figure 1 and Figure 2 As shown, the grid film forming fixture A1 includes a U-shaped frame 11 fixedly connected by X-shaped connectors 12. The U-shaped frame 11 includes nine rectangular frames A111, which are nested sequentially from the center outwards, with their sizes increasing sequentially. The X-shaped connectors 12 include a first connector 121 and a second connector 122, which are located on the two diagonals of the rectangular frames A111 and connect the corners of adjacent rectangular frames A111. The space between the multiple rectangular frames A111 and the X-shaped connectors forms a through hole A13 that runs vertically through the grid film forming fixture A1. The grid film forming fixture A1 is made of aluminum (melting point 660℃). The thickness of the rectangular frames A111, the first connector 121, and the second connector 122 is 0.3mm, and the spacing between two adjacent rectangular frames A111 is 1mm. 111 has the same length and width, and its height is twice the length (or width). The grid film forming tool A1 is pretreated with plasma to make its surface roughness Ra5.3.

[0054] S2. An anti-sagging agent was added to a graphene oxide dispersion with a concentration of 60 mg / mL. The dispersion was performed using a jet disperser at a pressure of 13000 psi and a flow rate of 1.1 L / min, followed by ultrasonic treatment for 15 minutes to obtain a graphene oxide slurry with a thixotropic index of 4.8. In this embodiment, the anti-sagging agent was fumed silica, accounting for 2% of the mass of the graphene oxide slurry.

[0055] S3. Immerse the grid film forming fixture A1 in the graphene oxide slurry for 3 seconds, then pull it out vertically upwards at a uniform speed to allow the graphene oxide to adhere to the surface of the fixture. Then place it in a 60°C constant temperature oven for pre-drying for 1 hour.

[0056] S4. Repeat step S3 until the graphene oxide fills the gaps in the grid film forming fixture A1.

[0057] S5. Place the grid film forming fixture A1 with graphene oxide attached obtained in step S4 into a directional freeze dryer for directional freeze drying, so that its bottom contacts the cold source to form a unidirectional temperature gradient, and programmatically cool it down to -100°C at a rate of 10°C / min, and keep it at this temperature for 96 hours to form a highly oriented graphene network and obtain the graphene oxide fixture.

[0058] S6. Seal the upper and lower surfaces of the graphene oxide fixture with two cover plates 2, and then perform heat treatment: First, heat to 500℃ at a heating rate of 6℃ / min and hold for 2 hours; then continue heating to 1900℃ at a heating rate of 10℃ / min and hold for 5 hours; finally, heat to 3300℃ at a heating rate of 20℃ / min and hold for 10 hours to obtain the graphene bulk. Figure 3 As shown, the material of the cover plate 2 is the same as that of the grid film forming tooling A1, and the cover plate 2 is provided with a plurality of micropores 21 arranged at equal intervals. The diameter of the micropores is 0.2mm, and the porosity of the cover plate 2 is 50%.

[0059] S7. The graphene block is laser-cut into 0.6 mm thick graphene sheets along a direction perpendicular to its height. A phase change adhesive is sprayed onto the upper and lower surfaces of the graphene sheets to form an adhesive layer with a thickness of 60 micrometers. The phase change adhesive, by weight, consists of 100 parts of polyethylene glycol (molecular weight 4000), 2 parts of coupling agent (KH-550), 800 parts of amino silicone oil (viscosity 80000 mPa·s, ammonia value 0.3%), and 500 parts of solvent (ethyl acetate). The preparation method is to heat polyethylene glycol, coupling agent, and amino silicone oil to 90°C to melt and blend them, cool them to room temperature, and then add solvent to dilute them, finally obtaining a highly oriented graphene thermal conductive sheet.

[0060] Example 2:

[0061] A fabrication process for a highly oriented graphene thermal conductive sheet includes the following steps:

[0062] S1. Prepare a grid film forming fixture, which includes a U-shaped frame fixedly connected by X-shaped connectors. The U-shaped frame includes two rectangular frames, which are nested from the center outwards and their sizes increase sequentially. The X-shaped connectors include a first connector and a second connector, which are located on the two diagonals of the rectangular frames and connect the corners of two adjacent rectangular frames. The space between the multiple rectangular frames and the X-shaped connectors forms a through hole that runs vertically through the grid film forming fixture. The grid film forming fixture is made of aluminum-silicon alloy (melting point 577℃). The thickness of the rectangular frames, the first connector, and the second connector is 0.04mm. The distance between two adjacent rectangular frames is 0.2mm. The length and width of the rectangular frames are the same, and their height is twice the length (or width). The grid film forming fixture is pretreated with plasma to make its surface roughness Ra0.8.

[0063] S2. An anti-sagging agent was added to a graphene oxide dispersion with a concentration of 20 mg / mL. The dispersion was then performed using a jet disperser at a pressure of 17000 psi and a flow rate of 0.3 L / min, followed by ultrasonic treatment for 5 minutes to obtain a graphene oxide slurry with a thixotropic index of 3.0. In this example, the anti-sagging agent was polyamide wax, which accounted for 0.1% of the mass of the graphene oxide slurry.

[0064] S3. Immerse the grid film forming fixture in the graphene oxide slurry for 9 seconds, then pull it out vertically upwards at a uniform speed to allow the graphene oxide to adhere to the surface of the fixture. Then place it in a 40°C constant temperature oven for pre-drying for 12 hours.

[0065] S4. Repeat step S3 until the graphene oxide fills the gaps in the grid film forming fixture.

[0066] S5. The grid film forming apparatus with graphene oxide attached obtained in step S4 is subjected to directional freeze drying in a directional freezer so that its bottom contacts the cold source to form a unidirectional temperature gradient. The temperature is programmed to drop to -50°C at a rate of 0.5°C / min and held at this temperature for 12 hours to form a highly oriented graphene network and obtain graphene oxide tooling.

[0067] S6. The upper and lower surfaces of the graphene oxide fixture are sealed with two aluminum-silicon alloy cover plates of the same material, each with micropores, and then subjected to heat treatment: First, the temperature is increased to 200℃ at a heating rate of 0.5℃ / min and held for 9 hours; then, the temperature is increased to 1100℃ at a heating rate of 3℃ / min and held for 11 hours; finally, the temperature is increased to 2700℃ at a heating rate of 5℃ / min and held for 28 hours to obtain a graphene bulk. In this embodiment, the pore size of the micropores is 0.1mm, and the porosity of the cover plates is 70%.

[0068] S7. The graphene block is laser-cut into 0.3 mm thick graphene sheets along a direction perpendicular to its height. A phase change adhesive is sprayed onto the upper and lower surfaces of the graphene sheets to form an adhesive layer with a thickness of 10 micrometers. The phase change adhesive, by weight, consists of 100 parts polyethylene glycol (molecular weight 1000), 0.3 parts coupling agent (KH-550), 100 parts amino silicone oil (viscosity 20000 mPa·s, ammonia value 2.6%), and 200 parts solvent (xylene). The preparation method is to heat polyethylene glycol, coupling agent, and amino silicone oil to 70°C to melt and blend them, cool them to room temperature, and then add solvent to dilute them, finally obtaining a highly oriented graphene thermal conductive sheet.

[0069] Example 3:

[0070] A fabrication process for a highly oriented graphene thermal conductive sheet includes the following steps:

[0071] S1. Prepare a grid film forming fixture. The grid film forming fixture has a through hole running vertically. Its structure includes a U-shaped frame fixedly connected by X-shaped connectors. The U-shaped frame includes 9 rectangular frames, which are nested sequentially from the center outwards, and their sizes increase sequentially. The X-shaped connectors include a first connector and a second connector. The first connector and the second connector are located on the two diagonals of the rectangular frames respectively and connect the corners of two adjacent rectangular frames. The space between the multiple rectangular frames and the X-shaped connectors forms the through hole running vertically through the grid film forming fixture. The grid film forming fixture is made of aluminum (melting point 660℃). The thickness of the rectangular frames, the first connector and the second connector is 0.3mm. The distance between two adjacent rectangular frames is 1mm. The length and width of the rectangular frames are the same, and their height is twice the length (or width). The grid film forming fixture is pretreated by plasma to make its surface roughness Ra3.6.

[0072] S2. An anti-sagging agent was added to a graphene oxide dispersion with a concentration of 40 mg / mL. The dispersion was then performed using a jet disperser at a pressure of 15000 psi and a flow rate of 0.7 L / min, followed by ultrasonic treatment for 15 minutes to obtain a graphene oxide slurry with a thixotropic index of 4.0. In this example, the anti-sagging agent was organobentonite, which accounted for 1% of the mass of the graphene oxide slurry.

[0073] S3. Immerse the grid film forming fixture in the graphene oxide slurry for 5 seconds, then pull it out vertically upwards at a uniform speed to allow the graphene oxide to adhere to the surface of the fixture. Then place it in a 50°C constant temperature oven for pre-drying for 6 hours.

[0074] S4. Repeat step S3 until the graphene oxide fills the gaps in the grid film forming fixture.

[0075] S5. The grid film forming apparatus with graphene oxide attached obtained in step S4 is subjected to directional freeze drying in a directional freezer so that its bottom contacts the cold source to form a unidirectional temperature gradient. The temperature is programmed to drop to -75°C at a rate of 5°C / min and held at this temperature for 48 hours to form a highly oriented graphene network and obtain graphene oxide tooling.

[0076] S6. The upper and lower surfaces of the graphene oxide fixture are sealed with two aluminum cover plates of the same material and containing micropores, and then heat-treated: first, the temperature is increased to 350℃ at a heating rate of 3℃ / min and held for 5 hours; then, the temperature is increased to 1500℃ at a heating rate of 6℃ / min and held for 8 hours; finally, the temperature is increased to 3000℃ at a heating rate of 12℃ / min and held for 18 hours to obtain a graphene bulk. In this embodiment, the pore size of the micropores is 0.3mm, and the porosity of the cover plates is 40%.

[0077] S7. The graphene block is laser-cut into 1.0 mm thick graphene sheets along a direction perpendicular to its height. A phase change adhesive is sprayed onto the upper and lower surfaces of the graphene sheets to form an adhesive layer with a thickness of 30 micrometers. The phase change adhesive, by weight, consists of 100 parts of polyethylene glycol (molecular weight 2000), 1 part of coupling agent (KH-550), 400 parts of amino silicone oil (viscosity 50000 mPa·s, ammonia value 1.0%), and 350 parts of solvent (ethyl acetate). The preparation method is to heat polyethylene glycol, coupling agent, and amino silicone oil to 80°C to melt and blend them, cool them to room temperature, and then add solvent to dilute them, finally obtaining a highly oriented graphene thermal conductive sheet.

[0078] To further verify the technical effects of the present invention, comparative examples are set up based on Example 1 as follows:

[0079] Comparative Example 1

[0080] The only difference between Comparative Example 1 and Example 1 is that the material of the grid film forming tool in step S1 is epoxy resin board (melting point 180°C).

[0081] Comparative Example 2

[0082] The only difference between Comparative Example 2 and Example 1 is that the material of the grid film forming tool in step S1 is a zirconia ceramic sheet (melting point 2710°C).

[0083] Comparative Example 3

[0084] The only difference between Comparative Example 3 and Example 1 is the grid film forming fixture in step S1, such as... Figure 4 As shown, in this embodiment, the grid film forming fixture B3 is in the shape of a straight line, comprising a rectangular frame B31 and transverse supports 32 disposed inside the rectangular frame B31. These supports are arranged horizontally and parallel to each other at equal intervals within the rectangular frame B31. The thickness of the rectangular frame B31 and the transverse supports 32 is 0.3 mm, and the spacing between the transverse supports 32 is 1 mm. A through hole B33 is formed between the rectangular frame B31 and the transverse supports 32, connecting the upper and lower surfaces of the grid film forming fixture B3. The length, width, and height of the grid film forming fixture B3 are consistent with those of the grid film forming fixture A1 in Embodiment 1.

[0085] Comparative Example 4

[0086] The only difference between Comparative Example 4 and Example 1 is that in step S2, a planetary disperser is used for dispersion and ultrasonication for 15 minutes.

[0087] Comparative Example 5

[0088] The only difference between Comparative Example 5 and Example 1 is that in step S7, a layer of ordinary vinyl silicone oil is sprayed onto the upper and lower surfaces of the graphene sheet instead of the phase change adhesive.

[0089] Comparative Example 6

[0090] The only difference between Comparative Example 6 and Example 1 is that no anti-sagging agent was added in step S2.

[0091] Comparative Example 7

[0092] The only difference between Comparative Example 7 and Example 1 is that the mass percentage of the anti-sagging agent in the graphene oxide slurry preparation in step S2 is 3%.

[0093] Comparative Example 8

[0094] The only difference between Comparative Example 8 and Example 1 is that the drying method in step S5 is to dry at room temperature (25°C) for 96 hours.

[0095] Comparative Example 9

[0096] The only difference between Comparative Example 9 and Example 1 is that the drying method in step S5 is to directly immerse the sample in liquid nitrogen for rapid freezing and drying for 96 hours.

[0097] Comparative Example 10

[0098] The difference between Comparative Example 10 and Example 1 is that no cover plate was used in step S6.

[0099] Comparative Example 11

[0100] Commercially available graphene thermal conductive sheets with a thermal conductivity of 130 W / mk (currently the highest thermal conductivity on the market) are formed by bonding and oriented layers together with adhesives.

[0101] To further verify the technical effects of the present invention, the thermal conductivity and mechanical properties of the graphene thermal conductive sheets of Examples 1-3 and Comparative Examples 1-11 were tested.

[0102] The thermal conductivity test method is as follows:

[0103] Prepare a chip temperature rise and heat dissipation simulation fixture, such as... Figure 5 As shown, the bottom is a 30*30mm heating end 5, with the heat source 6 located in the middle at a 10*10mm position; the middle layer is a graphene thermal conductive sheet filling layer 4, with an area of ​​30*30mm; the top is a metal heat dissipation layer 7 of the same area. By inputting a certain power into the heating end 5, heat is generated by the heat source 6, and the temperature T1 of the heat source 6 is recorded. After the temperature of the heat dissipation layer 7 stabilizes, the temperatures T2 at the four corners of the heat dissipation layer 7 and the time t1 from the start of power input to the temperature stabilization of the heat dissipation layer 7 are recorded. The smaller the temperature difference T1-T2 and the shorter the time t1, the better the thermal conductivity of the graphene thermal conductive sheet in the filling layer 4.

[0104] Mechanical performance testing includes bulk modulus testing and springback testing.

[0105] The bulk modulus test was conducted according to the ISO 3386 standard.

[0106] The rebound test method is as follows: Place the sample in a tensile testing machine, select the compression model, compress it to 70% and hold for 60 seconds. After removing the compression force, observe the time t2 required for the heat-conducting sheet to rebound to 96%.

[0107] The test results are shown in Table 1 below:

[0108] Table 1 Performance Test Results

[0109]

[0110] As shown in Table 1, the highly oriented graphene thermal conductive sheets prepared in Examples 1-3 exhibit better thermal conductivity than those in Comparative Examples 1-11. Both longitudinal and transverse thermal conduction are faster, resulting in a shorter temperature stabilization time. Their thermal conductivity is significantly superior to that of the graphene thermal conductive sheets in Comparative Examples 1-11. Furthermore, the highly oriented graphene thermal conductive sheets prepared in Examples 1-3 can rapidly rebound under low bulk modulus conditions, with a rebound time of less than 1 second.

[0111] Therefore, this invention demonstrates that the highly oriented graphene thermal conductive sheet prepared by this invention possesses excellent thermal conductivity and can achieve rapid rebound characteristics under low bulk modulus conditions. This unique combination of properties gives it significant advantages in the field of thermal management. Compared to traditional thermal conductive materials, the product of this invention not only improves heat conduction efficiency but also enhances the structural stability and service life of the material through a rapid rebound mechanism, providing innovative solutions for fields such as heat dissipation in electronic devices and thermal management of new energy vehicle batteries.

[0112] 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 person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered 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 highly oriented graphene thermal conductive sheet, characterized in that, Includes the following steps: S1. Prepare a grid film forming fixture. The grid film forming fixture is made of metal with a melting point of 500~1900℃. The grid film forming fixture includes a U-shaped frame, which is fixedly connected as a whole by connectors. The grid film forming fixture is provided with through holes running vertically through the top and bottom. S2. An anti-sagging agent is added to the graphene oxide dispersion, followed by jet dispersion and ultrasonic treatment to obtain a graphene oxide slurry; the thixotropic index of the graphene oxide slurry is 3-4.

8. S3. After immersing the grid film forming fixture in the graphene oxide slurry, pull it vertically upwards so that the graphene oxide slurry adheres to the surface of the grid film forming fixture and is then pre-dried. S4. Repeat step S3 until the graphene oxide slurry fills the gaps in the grid film forming fixture. S5. The grid film-forming fixture with graphene oxide attached obtained in step S4 is subjected to directional freeze-drying, so that its bottom contacts a cold source to form a unidirectional temperature gradient and is cooled to -50~-100℃ at a rate of 0.5-10℃ / min, and then kept at the temperature for 12-96 hours to obtain the graphene oxide fixture. S6. Seal the upper and lower ends of the graphene oxide fixture with two cover plates respectively, and then perform heat treatment: first, heat to 200-500℃ at a heating rate of 0.5-6℃ / min and hold for 2-9 hours; then continue heating to 1100-1900℃ at a heating rate of 3-10℃ / min and hold for 5-11 hours; finally, continue heating to 2700-3300℃ at a heating rate of 5-20℃ / min and hold for 10-28 hours to obtain a graphene block; the material of the cover plates is the same as that of the grid film forming fixture, and the cover plates are distributed with micropores. S7. Cut the graphene block into graphene sheets of the required thickness along the direction perpendicular to the height, and coat the upper and lower surfaces of the graphene sheets with a phase change adhesive to form an adhesive layer, thereby obtaining a highly oriented graphene thermal conductive sheet. The material of the grid film forming tool is aluminum or aluminum-silicon alloy; The U-shaped frame includes at least two rectangular frames, which are nested sequentially from the center outwards, with their sizes increasing sequentially. The connector is an X-shaped structure connector composed of a first connector and a second connector, with the first connector and the second connector located on the two diagonals of the rectangular frames respectively, connecting the corners of two adjacent rectangular frames. The space between the rectangular frames and the connector forms the through hole. In step S2, the concentration of the graphene oxide dispersion is 20-60 mg / ml; the amount of the anti-sagging agent added is 0.1-2% of the mass of the graphene oxide slurry. In step S2, the pressure of the jet dispersion is 13000-17000 psi, and the flow rate is 0.3-1.1 L / min; the ultrasonic treatment time is 5-15 min. In step S7, the phase change adhesive comprises the following components in parts by weight: 100 parts polyethylene glycol, 0.3-2 parts coupling agent, 100-800 parts amino silicone oil, and 200-500 parts solvent.

2. The method for preparing the highly oriented graphene thermal conductive sheet as described in claim 1, characterized in that, The thickness of the rectangular frame, the first connector, and the second connector is 0.04-0.3mm, and the distance between two adjacent rectangular frames is 0.2-1mm.

3. The method for preparing the highly oriented graphene thermally conductive sheet as described in claim 1, characterized in that, The rectangular frame has a square structure, and the height of the rectangular frame and the connector is twice the width of the rectangular frame.

4. The method for preparing the highly oriented graphene thermal conductive sheet as described in claim 1, characterized in that, The thickness of the graphene sheet is 0.3-2.2 mm.

5. A highly oriented graphene thermal conductive sheet, characterized in that, It is prepared by the method for preparing highly oriented graphene thermal conductive sheets according to any one of claims 1-4.

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