Thermally conductive interface composite material and preparation method thereof

Abstract

A thermally conductive interface composite material is a sheet-like thermal interface material with synergistic graphene / carbon fiber thermal conductivity, wherein: 1) a thermally conductive material layer uniformly composed of graphene-based thermally conductive fillers and carbon fibers and a polyurethane foam layer are alternately distributed in the planar or horizontal direction of the sheet; 2) the interface between the thermally conductive material layer and the polyurethane foam layer is perpendicular or substantially perpendicular to the upper and lower surfaces of the sheet; and 3) the carbon fibers uniformly arranged in the thermally conductive material layer are perpendicular or substantially perpendicular to the upper and lower surfaces of the sheet. The carbon fibers are oriented along the thickness of the sheet, and the graphene and carbon fibers are interconnected through intermolecular forces. The graphene forms a physical connection between the carbon fibers, providing a synergistic thermal conduction path, improving the heat transfer efficiency of the thermally conductive interface composite material in the thickness direction, and having good surface adhesion, reducing interfacial thermal resistance. This material has a simple preparation method, high thermal conductivity, and good operability.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal interface material preparation, and in particular to a thermal interface material with graphene / carbon fiber synergistic heat conduction, namely a thermal interface sheet (or sheet-like thermal interface material). Background Art

[0002] As electronic devices become smaller, more integrated, more intelligent, and more powerful, the heat-generating power density of electronic components, especially chips, continues to increase. This has led to a thorny issue in the thermal management of electronic devices. Thermal interface materials fill the gap between the heat source and the heat sink, enabling rapid heat transfer. Traditional thermally conductive silicone sheets have a thermal conductivity of only 1 to 10 W / mk, which is difficult to meet the heat dissipation requirements. Carbon materials offer advantages such as low density, corrosion resistance, high temperature resistance, and a low thermal expansion coefficient. Highly crystalline carbon has a very high thermal conductivity. For example, graphene has a thermal conductivity of up to 5300 W / mk, and pitch-based carbon fibers have a thermal conductivity of 300 to 1200 W / mk. Carbon materials have become important fillers in the development of high-performance thermal interface materials.

[0003] Conventional thermal interface materials are primarily based on thermally conductive fillers such as flake graphite, expanded graphite, carbon nanotubes, graphene, alumina, and aluminum nitride, prepared through blending or hot pressing. Due to the significant interfacial thermal resistance between fillers, even at high filler loadings (greater than 50 wt.%), the thermal conductivity of the composite material is difficult to achieve 10 W / mK. Establishing a continuous thermal conduction path, reducing interfacial thermal resistance, and establishing vertical orientation are key elements in preparing high-conductivity thermal interface materials. Kojiro Uetani et al. achieved carbon fiber orientation using electrostatic flocking technology and, after compounding with rubber, prepared a vertically oriented thermal interface material. At a carbon fiber loading of 13.2 wt.%, the vertical thermal conductivity reached a maximum of 23.3 W / mK (Advanced Materials, 2014, 26, 5857-5862). However, the carbon fiber loading and orientation are limited by electrostatic flocking technology, making further improvement in thermal conductivity difficult. CN 111500070A discloses a carbon fiber oriented thermal interface material and its preparation method. This patent uses vibration to orient the chopped carbon fibers along the thickness direction of the thermal interface material, forming a longitudinal heat conduction channel. The maximum thermal conductivity reaches only 20.5W / mK. Due to the vibration orientation process and the length of the chopped carbon fibers, it is difficult to form a continuous heat conduction path and the thermal conductivity is difficult to significantly improve.

[0004] CN111363358A discloses an oriented high-thermal-conductivity interface material and its preparation method. This patent utilizes long fiber materials to create a continuous thermal conductivity path. The long fibers are regularly arranged within a predetermined shaped shell. The fibers are then solidified and formed using an adhesive resin. The resulting sheet of oriented high-thermal-conductivity interface material is then cut to the desired thickness. Filled with 60wt% carbon fiber, the thermal conductivity reaches a maximum of 79W / mK. While this method creates a continuous thermal conductivity path, the improvement in thermal conductivity relies solely on increasing the filler content. It is difficult to exceed 80W / mK, and the method lacks the ability to be produced on a continuous scale.

[0005] CN112143465A discloses a high-performance thermal interface material and its preparation method. This method involves mixing metal powder, nitride powder, carbon material, and liquid silicone rubber, forming a sheet structure through casting or calendering, then curling it into a cylindrical shape. After curing, the thermal interface material is cut radially. However, this method cannot ensure good microscopic orientation of the thermally conductive filler, nor can the thermally conductive filler penetrate the thickness direction.

[0006] CN112208173 A discloses a thermal interface material and its preparation method. This patent utilizes graphite micropowder and thermosetting resin to disperse evenly, and then adopts a coating method to achieve horizontal orientation of graphite micropowder in thermosetting resin. The horizontally oriented graphite micropowder / thermosetting resin is further stacked layer by layer, and then pressed into shape. The graphite micropowder is oriented in the thickness direction by cutting to prepare a thermal interface material with a thermal conductivity of 10 to 50 W / mK. However, due to the size of the graphite micropowder, a continuous heat conduction path cannot be constructed, and the thermal conductivity cannot exceed 50 W / mK. In summary, the preparation method and thermal conductivity of traditional thermal interface materials can no longer meet the requirements of high integration, high performance, and high power density of electronic equipment for thermal conductivity and heat dissipation. Based on this, it is of great significance to develop a thermal interface material with low filling amount, high thermal conductivity, simple preparation process, and strong scalability of preparation method. Summary of the Invention

[0007] To address the problems existing in the prior art, the present invention provides a method for preparing a thermal interface material with synergistic graphene / carbon fiber thermal conductivity. This method features a simple preparation process, high efficiency, and extremely high vertical thermal conductivity. By bonding graphene to the carbon fibers, the orientation of the fibers is fixed, creating a continuous, uninterrupted thermal path. Furthermore, by interconnecting the carbon fibers with graphene, the number of thermal paths is increased, achieving a synergistically enhanced thermal conductivity.

[0008] According to a first aspect of the present invention, the present invention provides a thermal interface sheet (or sheet-like thermal interface material, thermally conductive interface composite material), that is, a sheet-like thermal interface material with synergistic thermal conductivity of graphene / carbon fiber, wherein: 1) a thermally conductive material layer uniformly composed of graphene-based thermally conductive fillers and carbon fibers and a polyurethane (PU) foam layer are alternately distributed (or alternately arranged, for example, the two layered materials are alternately distributed or arranged in a vortex manner or a stacked manner) in the plane direction or horizontal direction of the sheet; 2) the interface between the thermally conductive material layer and the polyurethane foam layer is perpendicular or substantially perpendicular to the upper and lower surfaces (i.e., the front and back sides) of the sheet (thermal conductive interface composite material); and 3) the carbon fibers uniformly arranged in the thermally conductive material layer are perpendicular or substantially perpendicular to the upper and lower surfaces (i.e., the front and back sides) of the sheet (thermal conductive interface composite material), and 90-100%, preferably 95-100% (e.g., 96, 97, 98 and 99%, the percentages being based on the total number of carbon fibers) of the carbon fibers have their ends flush with the upper and lower surfaces (i.e., the front and back sides) of the sheet (thermal conductive interface composite material), respectively. Preferably, in addition, the graphene-based thermal conductive filler is fully absorbed in the pores of the polyurethane foam layer, and the graphene-based thermal conductive material is distributed around the carbon fibers.

[0009] Generally, the graphenes described herein include graphene and / or reduced graphene oxide. The graphenes described herein include a combination of graphene and reduced graphene oxide. Generally, high-temperature reduction of graphene oxide removes most of its oxygen-containing functional groups; therefore, reduced graphene oxide can also be referred to as reduced graphene.

[0010] Generally, in a thermally conductive material layer uniformly composed of graphene and carbon fibers, an adhesive (e.g., silicone rubber or cured silicone rubber, or epoxy resin or cured epoxy resin) is impregnated or filled between the carbon fibers, or the gaps between individual carbon fibers are impregnated or filled with an adhesive (e.g., silicone rubber or cured silicone rubber, or epoxy resin or cured epoxy resin). This is to ensure the strength of the entire sheet or to ensure that each carbon fiber is adhered to the adhesive.

[0011] The thermal conductivity of the thermally conductive interface material (sheet) in the thickness direction is 70 to 300 W / mK, preferably 90 to 295 W / mK, more preferably 100 to 290 W / mK, more preferably 110 to 285 W / mK, more preferably 120 to 280 W / mK, for example 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260 and 270 W / mK.

[0012] The test method for thermal conductivity is ASTM E1461-2013.

[0013] The thickness of the polyurethane (PU) foam layer is generally 200 to 900 microns (μm), preferably 250 to 850 microns, preferably 300 to 800 microns, preferably 350 to 750 microns, preferably 400 to 700 microns, such as 500 or 600 microns. Generally, the average size of the foam cells of the polyurethane (PU) foam layer is 120 to 510 microns, preferably 150 to 500 microns, preferably 170 to 480 microns, preferably 180 to 460 microns, preferably 200 to 450 microns, preferably 210 to 420 microns, preferably 220 to 400 microns, and preferably 230 to 380 microns. Preferably, the polyurethane (PU) foam layer is a thin layer of open-cell, flexible polyurethane foam.

[0014] The polyurethane (PU) foam layer described herein may be in the form of a tape (in the form of a roll) or a thin layer (for forming a laminated or sheet-like cube by stacking a plurality of thin layers).

[0015] Generally, the graphene-based thermally conductive filler in the thermally conductive material layer includes a mixture or combination of graphene and (high-temperature) reduced graphene oxide, and the mass ratio of graphene to graphene oxide is 1:10 to 1:1, preferably 1:9 to 1:1, preferably 1:8 to 1:1, preferably 1:7 to 1:1, preferably 1:6 to 1:1, preferably 1:5 to 1:1, preferably 1:4 to 1:1, preferably 1:3 to 1:1, preferably 1:3 to 1:1, preferably 1:2 to 1:1.

[0016] Typically, the carbon fibers are pitch-based carbon fibers, graphene-based carbon fibers, or a combination thereof. Typically, in the sheet, the mass (or weight) of the carbon fibers is 333-1600 wt %, preferably 400-1550 wt %, preferably 500-1500 wt %, preferably 600-1400 wt %, preferably 700-1300 wt %, for example 750, 800, 900, 1000, 1100, 1200, 1250 wt % of the mass (or weight) of the PU foam layer.

[0017] Typically, in the sheet (thermal interface composite material), the total mass (or total weight) of graphene (i.e., both graphene and (high temperature) reduced graphene oxide) is 33-666 wt %, preferably 50-640 wt %, preferably 60-620 wt %, preferably 65-600 wt %, preferably 70-580 wt %, for example 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 350, 370, 400, 420, 450, 470, 500, 520, 540 or 550 wt % of the mass (or weight) of the PU foam layer.

[0018] Generally, the thickness of the above-mentioned thermal interface sheet (thermal conductive interface composite material) or thermal conductive sheet is 50μm to 30mm, preferably 60μm to 25mm, preferably 70μm to 20mm, preferably 80μm to 15mm, preferably 90μm to 12mm, preferably 100μm to 10mm, for example 150, 200, 300, 400, 500, 600, 700, 800, 900μm, 1mm, 1.1mm, 1.5mm, 1.8mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm or 9mm.

[0019] The surface of the thermal interface sheet (thermal interface composite material) or thermal conductive sheet has spiral patterns or lines (formed by cutting a cross section of a roll), or has a layered arrangement structure (formed by cutting a cross section of a laminated body stacked layer by layer).

[0020] From the distribution or texture of the carbon fiber layer, the thermal interface sheet (or sheet-like thermal interface material) is in the form of a roll or a cube formed by stacking multiple layers.

[0021] According to a second aspect of the present invention, the present invention provides a method for preparing a thermal interface sheet (or sheet-like thermal interface material, thermally conductive interface composite material) (described above), namely, a method for preparing the above-described graphene / carbon fiber synergistic thermally conductive sheet-like thermal interface material. The method comprises the following steps:

[0022] 1) dispersing graphene oxide and graphene in water to obtain a mixed dispersion slurry of graphene-graphene oxide, immersing a thin layer of polyurethane (PU) foam tape or sheet into the dispersion slurry so that the thin layer of polyurethane foam tape or sheet fully absorbs (or adsorbs) the slurry, and then taking out the thin layer of polyurethane foam tape or sheet that has absorbed (or adsorbed) the slurry and placing it on a release film (e.g., a film material having a polysiloxane anti-stick coating or a silicone oil coating);

[0023] 2) cutting the carbon fibers so that the length of the cut fibers is equal to or slightly greater than the width of the polyurethane foam tape or sheet (for example, the length of the carbon fibers is 1 to 1.2 times the width of the tape or sheet), placing the cut carbon fibers on the tape or sheet parallel to the width direction of the tape or sheet, gently pressing the fibers with a pressing device (for example, a brush) so that the slurry on the tape or sheet wets the fibers, and evenly coating the wetted carbon fibers with the slurry of step 1) (for example, using a straw to absorb the slurry in step (1)), and then drying the composite foam tape or sheet (for example, drying at a temperature of 60 to 90° C., such as drying in a blast drying oven at 60 to 90° C.). The coating and drying operations can be performed once or repeated two or more times to ensure that a sufficient amount of graphene-graphene oxide composite is adsorbed on the foam tape or sheet as a thermally conductive filler;

[0024] 3) The foamed thin layer tape or sheet obtained in step 2) is rolled up or stacked layer by layer, and then dried (for example, at a temperature of 60 to 90° C., such as in a forced air drying oven at 60 to 90° C.) or without drying to obtain a cylindrical (for example, in the form of a coil) or rectangular (for example, in the form of a stack); then, the frame structure is placed in a high-temperature furnace and heat-treated at a high temperature (for example, under the protection of an inert gas (for example, nitrogen, argon, or helium)). Heat treatment at a temperature of 600-1500°C, preferably 700-1450°C, more preferably 800-1400°C, for a time of generally 1-4 hours, for example 2 or 3 hours. That is, high-temperature thermal reduction is performed to obtain a graphene / carbon fiber thermally conductive carbon skeleton; preferably, the temperature of the heat treatment (i.e., high-temperature thermal reduction) is, for example, 650, 750, 850, 900, 950, 1000, 1100, 1200, 1300 or 1350°C;

[0025] 4) placing the graphene / carbon fiber thermal conductive carbon skeleton into a mold or container (e.g., a polytetrafluoroethylene mold or container), pouring a liquid adhesive (e.g., liquid silicone rubber or liquid epoxy resin) into the mold or container containing the graphene / carbon fiber thermal conductive carbon skeleton and immersing the graphene / carbon fiber thermal conductive carbon skeleton therein; then vacuuming the mold or container so that the liquid adhesive (e.g., liquid silicone rubber or liquid epoxy resin) fully diffuses and penetrates into the graphene / carbon fiber thermal conductive carbon skeleton (to fill the gaps therein); then heating (e.g., heating to 50-120° C. or 60-110° C. or 70-100° C., such as heating in a blast drying oven at 50-120° C.) to cure the adhesive (e.g., curing for 1-5 hours, e.g., 2 or 3 or 4 hours) to obtain a graphene / carbon fiber / adhesive composite material (e.g., a graphene / carbon fiber / silicone rubber composite material, or a graphene / carbon fiber / epoxy resin composite material);

[0026] 5) Cutting the composite material obtained in step 4) using a cutting tool (e.g., an ultrasonic cutter) along the radial direction of the oriented fibers (i.e., cutting or slicing the composite material along the transverse direction of the oriented fibers) to obtain a sheet-like graphene / carbon fiber synergistic thermal interface material, i.e., a thermal interface sheet. After cutting, the ends of the carbon fibers are flush with the two planes (i.e., the front and back surfaces) of the sheet, i.e., the ends are in the same plane as the two planes.

[0027] High-temperature thermal reduction, at temperatures above approximately 600°C (e.g., 600-1500°C, preferably 700-1450°C, and more preferably 800-1400°C), can remove most of the oxygen-containing functional groups on graphene oxide. The carbon atom configuration of graphene oxide after high-temperature reduction differs from that of perfect graphene, and certain lattice defects still exist.

[0028] The temperature of the heat treatment (high temperature thermal reduction) in step 3) is generally higher than 600°C, for example in the range of 600-1500°C, preferably 700-1450°C, more preferably 800-1400°C, for example 900, 1000, 1100, 1200 or 1300°C.

[0029] As liquid silicone rubber, commercially available thermosetting liquid silicone rubber can be used, wherein both a two-component type and a one-component type can be used. In addition, as liquid epoxy resin, commercially available thermosetting liquid aliphatic epoxy resin can be used, wherein both a two-component type and a one-component type can be used.

[0030] Preferably, when preparing the mixed dispersed slurry in step 1), the amount (mass) ratio of graphene to graphene oxide is 1:10 to 1:1, preferably 1:9 to 1:1, preferably 1:8 to 1:1, preferably 1:7 to 1:1, preferably 1:6 to 1:1, preferably 1:5 to 1:1, preferably 1:4 to 1:1, preferably 1:3 to 1:1, preferably 1:3 to 1:1, preferably 1:2 to 1:1. In addition, the amount of water used is sufficient to enable the graphene and graphene oxide to form a stirrable slurry in water or a slurry that can be pipetted with a pipette, for example, to form a slurry having a solids content of 0.2-5 wt%, preferably 0.3-4.5 wt%, more preferably 0.4-4 wt% (e.g., 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.5, 2.8, 3.0, 3.5 or 3.8 wt%).

[0031] Typically, the carbon fiber used in step 2) is pitch-based carbon fiber, graphene carbon fiber, or a combination thereof. Typically, the amount (mass or weight) of the carbon fiber is 333-1600wt% of the mass (or weight) of the PU foam layer, preferably 400-1550wt%, preferably 500-1500wt%, preferably 600-1400wt%, preferably 700-1300wt%, for example 750, 800, 900, 1000, 1100, 1200, or 1250wt%.

[0032] Typically, in step 2), the amount (total mass or total weight) of the graphene thermally conductive filler (i.e., both graphene and graphene oxide) is 33-666 wt %, preferably 50-640 wt %, preferably 60-620 wt %, preferably 65-600 wt %, preferably 70-580 wt %, for example 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 350, 370, 400, 420, 450, 470, 500, 520, 540 or 550 wt % of the mass (or weight) of the PU foam layer. That is, the coating and drying operations are repeated a number of times so that the amount of the graphene thermally conductive filler (relative to the mass or weight of the PU foam layer) is within the range described herein.

[0033] Preferably, the polyurethane foam layer used is an open-cell soft polyurethane foam layer. The polyurethane (PU) foam layer used can be in the form of a tape (presenting a roll) or a thin layer (can be used to form a laminate or sheet by stacking multiple thin layers).

[0034] According to the third aspect of the present invention, the present invention provides a thermal interface sheet or sheet-like thermal interface material prepared by the above method, that is, a sheet-like thermal interface material with synergistic thermal conductivity of graphene / carbon fiber, referred to as a thermal interface sheet or thermal conductive sheet.

[0035] Generally, the thermal conductivity of the thermal interface material (sheet) in the thickness direction is 70 to 300 W / mK, preferably 90 to 295 W / mK, more preferably 100 to 290 W / mK, more preferably 110 to 285 W / mK, more preferably 120 to 280 W / mK, for example 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260 and 270 W / mK.

[0036] The thickness of the polyurethane (PU) foam layer used is generally 200 to 900 microns, preferably 250 to 850 microns, preferably 300 to 800 microns, preferably 350 to 750 microns, preferably 400 to 700 microns. Generally, the average size of the foam cells of the polyurethane (PU) foam layer used is 120 to 510 microns, preferably 150 to 500 microns, preferably 170 to 480 microns, preferably 180 to 460 microns, preferably 200 to 450 microns, preferably 210 to 420 microns, preferably 220 to 400 microns, preferably 230 to 380 microns. Preferably, the polyurethane (PU) foam layer used is an open-cell soft polyurethane foam thin layer.

[0037] The polyurethane (PU) foam layer described herein may be in the form of a strip (in the form of a roll) or a thin layer (which can be stacked to form a laminate or sheet). The polyurethane (PU) foam layer in the form of a strip (in the form of a roll) or a thin layer is an open-cell soft polyurethane foam.

[0038] Generally, the graphene in the thermally conductive material layer includes a mixture of graphene and graphene oxide, and the mass ratio of graphene to graphene oxide is 1:10 to 1:1, preferably 1:9 to 1:1, preferably 1:8 to 1:1, preferably 1:7 to 1:1, preferably 1:6 to 1:1, preferably 1:5 to 1:1, preferably 1:4 to 1:1, preferably 1:3 to 1:1, preferably 1:3 to 1:1, preferably 1:2 to 1:1.

[0039] Typically, the carbon fibers are pitch-based carbon fibers, graphene-based carbon fibers, or a combination thereof. Typically, in the sheet, the mass (or weight) of the carbon fibers is 333-1600 wt %, preferably 400-1550 wt %, preferably 500-1500 wt %, preferably 600-1400 wt %, preferably 700-1300 wt %, for example 750, 800, 900, 1000, 1100, 1200, 1250 wt % of the mass (or weight) of the PU foam layer.

[0040] Typically, in the sheet (thermal interface composite material), the total mass (or total weight) of graphene (i.e., both graphene and graphene oxide) is 33-666 wt %, preferably 50-640 wt %, preferably 60-620 wt %, preferably 65-600 wt %, preferably 70-580 wt %, for example 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 350, 370, 400, 420, 450, 470, 500, 520, 540 or 550 wt % of the mass (or weight) of the PU foam layer.

[0041] Generally, the thickness of the thermal interface sheet or thermal conductive sheet prepared by the above method is as defined above, that is, its thickness is 50 μm to 30 mm, preferably 60 μm to 25 mm, preferably 70 μm to 20 mm, preferably 80 μm to 15 mm, preferably 90 μm to 12 mm, preferably 100 μm to 10 mm, for example, 150, 200, 300, 400, 500, 600, 700, 800, 900 μm, 1 mm, 1.1 mm, 1.5 mm, 1.8 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm or 9 mm. The thickness can be selected according to the specific application.

[0042] When the thermal interface sheet or thermally conductive sheet is a sheet (e.g., a gasket) obtained by cutting or slicing a composite material in roll form, the diameter of the thermal interface sheet or thermally conductive sheet is generally 8-400 mm, preferably 10-350 mm, more preferably 15-300 mm, more preferably 20-250 mm, for example, 30, 50, 80, 100, 130, 150, 180, 200 or 230 mm. In addition, when the above-mentioned thermal interface sheet or thermally conductive sheet is a sheet (square or rectangular cross-section) (such as a gasket) obtained by cutting or slicing from a composite material in the form of a laminate (cube, such as a cube or a cuboid), the length of the thermal interface sheet or thermally conductive sheet is generally 20-400 mm, preferably 30-3500 mm, preferably 40-300 mm, such as 50, 70, 100, 150, 180, 200, 230, 250 or 280 mm, and the width is generally 18-400 mm, preferably 20-400 mm, preferably 30-3500 mm, preferably 40-300 mm, such as 50, 70, 100, 150, 180, 200, 230, 250 or 280 mm.

[0043] The main component of the liquid silicone rubber is vinyl silicone oil (such as Dow Corning's 184), and the crosslinking agent is hydrogen silicone oil. In addition, CN114231039A has a slightly detailed description of silicone rubber and curing agent.

[0044] In this application, cutting, trimming and slicing have the same meaning. Absorbing and adsorbing have the same meaning in this application.

[0045] Advantages of the present invention

[0046] 1. A multi-scale collaborative continuous heat conduction path is constructed in the thermal interface material. A continuous heat conduction path is established through macroscopic carbon fibers that penetrate the thickness of the sheet. At the same time, nanographene is interconnected through carbon fibers to reduce contact thermal resistance, increase the number of heat conduction paths, and improve the thermal conductivity of the sheet.

[0047] 2. The thermally conductive fillers (graphene and graphene oxide) adsorbed in the open cells of the polyurethane foam layer further increase the content of the thermally conductive fillers in the sheet and improve the thermal conductivity of the sheet.

[0048] 3. The synergistic effect of graphene and carbon fiber makes the obtained thermal interface material (thermal interface sheet) have high thermal conductivity and good adhesion to the application surface.

[0049] 4. This invention proposes a new approach to improving the thermal conductivity of composite materials. The invention features a simple preparation process, strong scalability, and ease of scale-up, resolving the challenges of traditional thermal interface materials, which suffer from high filler requirements and low thermal conductivity.

[0050] 5. Compared with existing products, the advantages of the present invention are: the filling amount of thermally conductive filler in the sheet of the present invention is relatively low, and high thermal conductivity is achieved at a relatively low filling amount. This is due to the synergy achieved in the preparation method between graphene and carbon fiber, two types of thermally conductive fillers, which can fully utilize the high thermal conductivity of both types of thermally conductive fillers. In particular, the addition of graphene can significantly improve the thermal conductivity of composite materials with the same carbon fiber filling amount. In addition, the preparation method of the present invention has the advantages of simplicity and strong scalability.

[0051] 6. Compared with the products of the prior art, the sheet of the present invention has a lower density, a thin texture, low hardness, and a very good hand feel; it has good flexibility and can fit well with the heat dissipation surface, thereby improving the heat dissipation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a microscopic morphology image (scanning electron microscope image) of the carbon fiber / graphene synergistic thermal conductive skeleton belt prepared in Example 1.

[0053] Figure 2It is a schematic diagram of the operation process adopted in the embodiment (wherein step 7 obtains a sheet-like graphene / carbon fiber synergistic thermal interface material, i.e., a thermal interface sheet). DETAILED DESCRIPTION

[0054] The present invention further illustrates the technical solution in detail through the following examples, but the present invention is not limited to these examples.

[0055] Unless otherwise specified, the devices used in the examples are all commonly used in the art and commercially available.

[0056] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be understood that the one or more steps mentioned in the present invention do not exclude the presence of other methods and steps before and after the combination step, or other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Unless otherwise specified, the numbering of each method step is only for the purpose of identifying each method step, and is not for limiting the order of arrangement of each method or limiting the scope of implementation of the present invention. Changes or adjustments in their relative relationships, without substantial changes in the technical content, should also be regarded as the scope of implementation of the present invention.

[0057] In the embodiment, the thermal conductivity of the material is measured by a laser flash method using an LFA467 test instrument and the test is performed in accordance with ASTM E1461-2013.

[0058] In a specific embodiment, the preparation of the thermal interface material of the present invention with graphene / carbon fiber synergistic thermal conductivity is as follows: Figure 2 As shown in , the specific process is as follows

[0059] (1) Prepare a graphene oxide aqueous dispersion, add a certain amount of graphene, stir evenly and ultrasonically disperse to obtain a graphene mixed dispersion slurry. Immerse a PU thin layer foam tape of a certain thickness into the slurry to allow the PU thin layer foam tape to fully absorb the slurry, and then take it out and place it on a release film. Cut high carbon fibers and arrange the carbon fibers. The cutting length is the same as or slightly larger than the PU foam tape. The carbon fibers are arranged parallel to the width direction. Use a brush to gently press the fibers to ensure that the graphene mixed slurry on the PU foam tape wets the fibers. Use a straw to absorb the slurry and evenly apply it on the wetted carbon fibers. Place the composite foam tape in a 60-90°C blast drying oven to dry. Repeat the coating and drying operation to obtain a foam tape composited with carbon fibers and graphene.

[0060] (2) The foam strip is rolled up or stacked layer by layer and placed in a 60-90°C forced air drying oven for drying to obtain a cylindrical or rectangular frame structure. The frame structure is placed in a tube furnace and treated at high temperature under inert gas protection (temperature of 600-1500°C for 1-4 hours) to obtain a graphene / carbon fiber thermal conductive carbon skeleton. Liquid silicone rubber (or liquid aliphatic epoxy resin) is poured into and immersed in a polytetrafluoroethylene mold containing the graphene / carbon fiber thermal conductive carbon skeleton, placed in a vacuum drying oven, and vacuum treated at room temperature for 3-12 hours to fully infuse the liquid silicone rubber (or liquid aliphatic epoxy resin) into the graphene / carbon fiber thermal conductive carbon skeleton. The mold is taken out of the vacuum drying oven and placed in a forced air drying oven for curing (temperature of 50-120°C for 1-5 hours) to obtain a graphene / carbon fiber / silicone rubber (or epoxy resin) composite material. The composite material is cut along the radial direction of the oriented fibers using an ultrasonic cutter to obtain a thermal interface material with synergistic thermal conductivity of graphene / carbon fibers.

[0061] The liquid silicone rubber used in the following examples is Dow Corning's 184 type thermosetting silicone rubber, wherein the main component is vinyl silicone oil, the curing agent is hydrogenated silicone oil, and the catalyst is platinum.

[0062] Preparation Example 1

[0063] Preparation of graphene oxide dispersion: A modified Hummers method and static oxidation technology were used.

[0064] The preparation process is as follows:

[0065] 1. Static Oxidation of Flake Graphite: In an ice-water bath, slowly add 55.9 g of KMnO₄ to 520 mL of concentrated H₂SO₄. Maintain the reaction temperature below 10°C during the addition. Continue stirring in the ice-water bath for 2 hours to completely dissolve the KMnO₄. Transfer the reaction mixture to a 35°C water bath and heat for 15 minutes. Then, while stirring continuously, add 13 g of flake graphite. After stirring for 30 minutes, discontinue stirring and continue the reaction at 35°C for 16 hours. Subsequently, add 30% H₂O₂ until no bubbles form, yielding the initial graphite oxide.

[0066] 2. Purification and Exfoliation of Initial Graphite Oxide: After standing for 5 minutes, the supernatant of the initial graphite oxide became colorless and transparent, indicating that the oxidation products had completely precipitated. Adding deionized water to the precipitate again caused the supernatant to become colorless and transparent. The precipitate was allowed to stand for separation and the supernatant was decanted until it became neutral. The precipitate was then diluted with purified water, mechanically stirred, and sonicated for 1 hour to obtain a graphene oxide dispersion, which was used in the following examples.

[0067] In addition, the graphene oxide dispersion can also be prepared using graphene oxide (SE2430W-N) sold by Changzhou Sixth Element Co., Ltd.

[0068] Example 1

[0069] (1) A graphene oxide dispersion was prepared according to the method described in Preparation Example 1: 10 ml of a 4 mg / ml graphene oxide dispersion was prepared in water; then, 10 mg of graphene (Changzhou Sixth Element Co., Ltd., brand SE1231, particle size <10 μm) was added thereto, and the mixture was uniformly and ultrasonically dispersed (using an ultrasonic processing equipment of type CPX8800H-C, with a power of 320 W) to obtain a graphene mixed slurry (solid content 5 mg / ml, 0.50 wt%). 0.15 g of a polyurethane (PU) foam strip with a thickness of 700 μm (Guangzhou Yumi Sports Goods Industrial Co., Ltd., open-cell soft foam with a pore size of 20 μm) was taken. 0-500μm. Cut into 17.5mm wide strips) adsorb the slurry and place it on a polyester PET release film (Dongguan Kunteng Electronic Materials Co., Ltd., PET transparent release film), cut 0.75g of asphalt-based carbon fiber (Hunan Dongying Carbon Material Technology Co., Ltd., average diameter 10-15μm), the carbon fiber extends from both ends of the width of the PU foam strip and is arranged parallel to the width direction, and the graphene slurry is allowed to wet the carbon fiber. The remaining graphene mixed slurry is sucked with a straw and evenly coated on the wetted carbon fiber. The PU composite foam tape is placed in a 90℃ blast drying oven (Shanghai Jinghong Experimental Equipment Co., Ltd., Model DHG-9108A) to dry, thereby obtaining a PU composite foam tape.

[0070] (2) The composite foam tape was rolled into a cylindrical shape (i.e., a frame structure), placed in a tube furnace (Hefei Kejing Material Technology Co., Ltd., model OTF-1200X-S) and treated at 600°C for 1 hour under the protection of inert gas nitrogen (i.e., high-temperature thermal reduction, so that most of the oxygen-containing functional groups were removed) to obtain a graphene / carbon fiber thermal conductive carbon skeleton, and then the skeleton was placed in a polytetrafluoroethylene mold (produced by Nanjing Ruinik Technology Development Co., Ltd., a barrel-shaped container), and the mold containing the skeleton was placed in a vacuum drying oven (Shanghai Yiheng Scientific Instrument Co., Ltd., model DZF6050) and vacuum treated at room temperature for 3 hours to fully infuse liquid silicone rubber (Dow Corning, model 184, viscosity 5100cp, heat curing type) into the graphene / carbon fiber thermal conductive carbon skeleton. The sample was taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 60°C, 1 hour) to obtain a graphene / carbon fiber / silicone rubber composite material. The composite material was cut along the radial direction of the oriented fibers using a metal cutter (i.e., a stainless steel cutter) to obtain a graphene / carbon fiber synergistic thermal interface material (slice) with a thickness of 2 mm and a diameter of 10 mm. The thermal conductivity of the material is listed in Table 1.

[0071] SEM (scanning electron microscope) of thermal interface material Figure 1 As shown in the figure, it can be seen that the carbon fibers in the graphene / carbon fiber thermal conductive carbon skeleton are vertically oriented, establishing a continuous thermal conduction path. The two thermal conductive fillers of different sizes, graphene and carbon fibers, are connected to each other, establishing a stable thermal connection, achieving synergistic heat conduction, improving the quantity and quality of the thermal conduction path, and helping to improve thermal conductivity. In addition, from Figure 1 The distribution state of the graphene-type thermal conductive filler can be judged as follows: on the one hand, the graphene-type thermal conductive filler is fully adsorbed in the pores of the polyurethane foam layer; on the other hand, the graphene-type thermal conductive filler is distributed around the carbon fiber.

[0072] Example 2

[0073] (1) 18.75 ml of a 6 mg / ml graphene oxide dispersion was prepared in water, 37.5 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 8 mg / ml, 0.79 wt%). 0.15 g of a 600 μm thick PU foam tape was adsorbed with the slurry and placed on a release film. 0.75 g of asphalt-based carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was moistened with the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the moistened carbon fiber. The tape was dried in a 60°C forced air drying oven to obtain a PU composite foam tape.

[0074] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 700°C for 2 hours to obtain a graphene / carbon fiber thermal conductive carbon skeleton. The skeleton is then placed in a polytetrafluoroethylene mold. The mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 6 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 60°C, 5 hours) to obtain a graphene / carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fibers using an ultrasonic cutter (Japan HONDA, model ZO-91) to obtain a graphene / carbon fiber synergistic thermal conductive thermal interface material.

[0075] Example 3

[0076] (1) 31.25 ml of a 6 mg / ml graphene oxide dispersion was prepared in water, 62.5 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 8 mg / ml, 0.79 wt%). 0.15 g of a 500 μm thick PU foam tape was taken to absorb the slurry and placed on a release film. 0.75 g of asphalt-based carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was moistened with the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the moistened carbon fiber. The tape was dried in a 70°C forced air drying oven to obtain a PU composite foam tape.

[0077] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 1000°C for 1 hour to obtain a graphene / carbon fiber thermal conductive carbon skeleton. The skeleton is then placed in a polytetrafluoroethylene mold, and the mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 9 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 80°C, 3 hours) to obtain a graphene / carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fibers using a wire cutter (Shandong Zhiwei CNC Machine Tool Co., Ltd., model DK7780) to obtain a graphene / carbon fiber synergistic thermal conductive thermal interface material.

[0078] Example 4

[0079] (1) 31.8 ml of a 10 mg / ml graphene oxide dispersion was prepared in water, 31.8 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 11 mg / ml, 1.09 wt%). 0.15 g of a PU foam tape with a thickness of 400 μm was adsorbed with the slurry and placed on a release film. 0.75 g of asphalt-based carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was moistened with the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the moistened carbon fiber. The tape was dried in a forced air drying oven at 80°C to obtain a PU composite foam tape.

[0080] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 1000°C for 4 hours to obtain a graphene / carbon fiber thermal conductive carbon skeleton. The skeleton is then placed in a polytetrafluoroethylene mold, and the mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 12 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 120°C, 1 hour) to obtain a graphene / carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fibers with a metal cutter (i.e., a stainless steel cutter) to obtain a thermal interface material with synergistic thermal conductivity of graphene / carbon fiber.

[0081] Example 5

[0082] (1) 16.6 ml of a 15 mg / ml graphene oxide dispersion was prepared in water, 250 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 30 mg / ml, 2.91 wt%). 0.15 g of a PU foam tape with a thickness of 300 μm was taken to absorb the slurry and placed on a release film. 0.75 g of asphalt-based carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was moistened with the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the moistened carbon fiber. The tape was dried in a 90°C forced air drying oven to obtain a PU composite foam tape.

[0083] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 1500°C for 1 hour to obtain a graphene / carbon fiber thermal conductive carbon skeleton. The skeleton is then placed in a polytetrafluoroethylene mold. The mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 12 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 120°C, 4 hours) to obtain a graphene / carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fibers using an ultrasonic cutter (Japan HONDA, model ZO-91) to obtain a graphene / carbon fiber synergistic thermal conductive thermal interface material.

[0084] Example 6

[0085] (1) 18.75 ml of a 6 mg / ml graphene oxide dispersion was prepared in water, 37.5 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 8 mg / ml, 0.79 wt%). 0.15 g of a PU foam tape with a thickness of 700 μm was taken to absorb the slurry and placed on a release film. 0.5 g of asphalt-based carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was moistened with the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the moistened carbon fiber. The tape was dried in a blast drying oven at 70°C to obtain a PU composite foam tape.

[0086] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 1500°C for 4 hours to obtain a graphene / carbon fiber thermal conductive carbon skeleton. The skeleton is then placed in a polytetrafluoroethylene mold, and the mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 3 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 80°C, 1 hour) to obtain a graphene / carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fibers using a wire cutter (Shandong Zhiwei CNC Machine Tool Co., Ltd., model DK7780) to obtain a graphene / carbon fiber synergistic thermal conductive thermal interface material.

[0087] Example 7

[0088] (1) 18.75 ml of a 6 mg / ml graphene oxide dispersion was prepared in water, 37.5 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 8 mg / ml, 0.79 wt%). 0.15 g of a PU foam tape with a thickness of 700 μm was taken to absorb the slurry and placed on a release film. 0.5 g of asphalt-based carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was moistened with the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the moistened carbon fiber. The tape was dried in a 90°C forced air drying oven to obtain a PU composite foam tape.

[0089] (2) Cut the composite foam tape and stack it layer by layer, place it in a tube furnace and treat it at 1500℃ for 4 hours under the protection of inert gas to obtain a graphene / carbon fiber thermal conductive carbon skeleton, then place the skeleton in a polytetrafluoroethylene mold, place the mold with the skeleton in a vacuum drying oven, and vacuum treat it at room temperature for 3 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. Take it out of the vacuum drying oven and place it in a blast drying oven for curing (temperature 80℃, 1 hour) to obtain a graphene / carbon fiber / silicone rubber composite material. Use a metal cutter (i.e., a stainless steel cutter) to cut the composite material along the radial direction of the oriented fiber to obtain a thermal interface material with synergistic thermal conductivity of graphene / carbon fiber.

[0090] Example 8

[0091] (1) 18.75 ml of a 6 mg / ml graphene oxide dispersion was prepared in water, 37.5 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 8 mg / ml, 0.79 wt%). 0.15 g of a 300 μm thick PU foam tape was adsorbed with the slurry and placed on a release film. 1 g of asphalt-based carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was allowed to wet the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the wetted carbon fiber. The tape was dried in a 60°C forced air drying oven to obtain a PU composite foam tape.

[0092] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 700°C for 2 hours to obtain a graphene / carbon fiber thermal conductive carbon skeleton. The skeleton is then placed in a polytetrafluoroethylene mold, and the mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 12 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 80°C, 3 hours) to obtain a graphene / carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fibers using a metal cutter (i.e., a stainless steel cutter) to obtain a thermal interface material with synergistic thermal conductivity of graphene / carbon fiber.

[0093] Example 9

[0094] (1) 25 ml of a 10 mg / ml graphene oxide dispersion was prepared in water, 250 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 20 mg / ml, 1.96 wt%). 0.15 g of a 300 μm thick PU foam tape was adsorbed with the slurry and placed on a release film. 2.4 g of asphalt-based carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was allowed to wet the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the wetted carbon fiber. The tape was dried in a 90°C forced air drying oven to obtain a PU composite foam tape.

[0095] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 600°C for 1 hour to obtain a graphene / carbon fiber thermal conductive carbon skeleton, and then the skeleton is placed in a polytetrafluoroethylene mold. The mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 12 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 120°C, 2 hours) to obtain a graphene / carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fibers with a metal cutter (i.e., a stainless steel cutter) to obtain a thermal interface material with synergistic thermal conductivity of graphene / carbon fiber.

[0096] Example 10

[0097] (1) 10 ml of a 4 mg / ml graphene oxide dispersion was prepared in water, 10 mg of graphene was added, and the mixture was stirred evenly for 0.5 h. The mixture was ultrasonically dispersed for 30 min to obtain a graphene mixed slurry (solid content 5 mg / ml, 0.5 wt%). 0.15 g of a PU foam tape with a thickness of 700 μm was adsorbed with the slurry and placed on a release film. 0.5 g of graphene carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was moistened with the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the moistened carbon fiber. The mixture was placed in an 80°C air drying oven for drying to obtain a PU composite foam tape.

[0098] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 800°C for 4 hours to obtain a graphene / carbon fiber thermal conductive carbon skeleton. The skeleton is then placed in a polytetrafluoroethylene mold, and the mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 12 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 80°C, 3 hours) to obtain a graphene / carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fibers using a metal cutter (i.e., a stainless steel cutter) to obtain a thermal interface material with synergistic thermal conductivity of graphene / carbon fiber.

[0099] Example 11

[0100] (1) 18.75 ml of a 6 mg / ml graphene oxide dispersion was prepared in water, 37.5 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 8 mg / ml, 0.79 wt%). 0.15 g of a PU foam tape with a thickness of 700 μm was taken to absorb the slurry and placed on a release film. 0.75 g of graphene carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was allowed to wet the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the wetted carbon fiber. The tape was placed in a 90°C forced air drying oven for drying to obtain a PU composite foam tape.

[0101] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 1500°C for 4 hours to obtain a graphene / carbon fiber thermal conductive carbon skeleton. The skeleton is then placed in a polytetrafluoroethylene mold, and the mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 12 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 60°C, 2 hours) to obtain a graphene / carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fibers using an ultrasonic cutter (Japan HONDA, model ZO-91) to obtain a graphene / carbon fiber synergistic thermal conductive thermal interface material.

[0102] Example 12

[0103] (1) A graphene oxide dispersion was prepared according to the method described in Preparation Example 1: 10 ml of a 4 mg / ml graphene oxide dispersion was prepared in water; then, 10 mg of graphene (Changzhou Sixth Element Co., Ltd., brand SE1231, particle size <10 μm) was added thereto, and the mixture was uniformly and ultrasonically dispersed (using an ultrasonic processing equipment of type CPX8800H-C, with a power of 320 W) to obtain a graphene mixed slurry (solid content 5 mg / ml, 0.50 wt%). 0.15 g of a polyurethane (PU) foam strip with a thickness of 700 μm (Guangzhou Yumi Sports Goods Industrial Co., Ltd., open-cell soft foam with a pore size of 20 μm) was taken. 0-500μm. Cut into 17.5mm wide strips) adsorb the slurry and place it on a polyester PET release film (Dongguan Kunteng Electronic Materials Co., Ltd., PET transparent release film), cut 0.75g of asphalt-based carbon fiber (Hunan Dongying Carbon Material Technology Co., Ltd., average diameter 10-15μm), the carbon fiber extends from both ends of the width of the PU foam strip and is arranged parallel to the width direction, and the graphene slurry is allowed to wet the carbon fiber. The remaining graphene mixed slurry is sucked with a straw and evenly coated on the wetted carbon fiber. The PU composite foam tape is placed in a 90℃ blast drying oven (Shanghai Jinghong Experimental Equipment Co., Ltd., Model DHG-9108A) to dry, thereby obtaining a PU composite foam tape.

[0104] (2) The composite foam tape (17.5 mm wide) prepared in step (1) was cut into thin sheets of 25 mm length per sheet, 50 thin sheets (with the fiber side facing up) were stacked into a 50-layer stack along the length direction (i.e., in the same fiber orientation direction), and the stack was placed in a tubular furnace (Hefei Kejing Material Technology Co., Ltd., model OTF-1200X-S) and treated at 600°C for 1 hour under the protection of inert gas nitrogen (i.e., high-temperature thermal reduction so that most of the oxygen-containing functional groups were removed) to obtain a graphene / carbon fiber thermal conductive carbon skeleton, and then the skeleton was placed in a polytetrafluoroethylene mold (produced by Nanjing Ruinik Technology Development Co., Ltd., container), and the mold containing the skeleton was placed in a vacuum drying oven (Shanghai Yiheng Scientific Instrument Co., Ltd., model DZF6050) and vacuum treated at room temperature for 3 hours to fully infuse liquid silicone rubber (Dow Corning, model 184, viscosity 5100cp, thermosetting type) into the graphene / carbon fiber thermal conductive carbon skeleton. The product was taken out from the vacuum drying oven and placed in a forced air drying oven for curing (temperature 60° C., 1 hour) to obtain a graphene / carbon fiber / silicone rubber composite material.

[0105] The composite material was cut radially along the oriented fibers using an ultrasonic cutter (HONDA, Japan, Model ZO-91) to obtain a 2 mm thick graphene / carbon fiber synergistic thermal interface material (slice). The thermal conductivity of the material is listed in Table 1.

[0106] Example 13

[0107] (1) 25 ml of a 10 mg / ml graphene oxide dispersion was prepared in water, 250 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 20 mg / ml, 1.96 wt%). 0.15 g of a 300 μm thick PU foam tape was adsorbed with the slurry and placed on a release film. 2.4 g of asphalt-based carbon fiber was cut, and the carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The graphene slurry was allowed to wet the carbon fiber. The remaining graphene mixed slurry was sucked with a straw and evenly coated on the wetted carbon fiber. The tape was dried in a 90°C forced air drying oven to obtain a PU composite foam tape.

[0108] (2) The composite foam tape (17.5 mm wide) prepared in step (1) was cut into thin sheets of 25 mm length per sheet, 30 thin sheets (with the fiber side facing up) were stacked in 30 layers along the length direction (i.e., in the same fiber orientation direction), and placed in a tube furnace under inert gas protection at 600 ° C for 1 hour to obtain a graphene / carbon fiber thermal conductive carbon skeleton, and then the skeleton was placed in a polytetrafluoroethylene mold, and the mold containing the skeleton was placed in a vacuum drying oven and vacuum treated at room temperature for 12 hours to fully infuse the liquid silicone rubber into the graphene / carbon fiber thermal conductive carbon skeleton. The resultant was taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 120 ° C, 2 hours) to obtain a graphene / carbon fiber / silicone rubber composite material.

[0109] The composite material was cut along the radial direction of the oriented fibers using a metal cutter (ie, a stainless steel cutter) to obtain a graphene / carbon fiber synergistic thermal conductive thermal interface material with a thickness of 2 mm.

[0110] Comparative Example 1

[0111] (1) 18.75 ml of a 6 mg / ml graphene oxide dispersion was prepared in water, 37.5 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 8 mg / ml, 0.79 wt%). 0.15 g of a PU foam tape was adsorbed with the slurry and placed on a release film. The remaining graphene mixed slurry was taken with a pipette and evenly coated on the PU foam tape. The tape was then dried in a 90°C forced air drying oven to obtain a PU composite foam tape.

[0112] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 700°C for 1 hour to obtain a graphene thermal conductive carbon skeleton. The skeleton is placed in a polytetrafluoroethylene mold, and the mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 3 hours to allow the liquid silicone rubber to be fully infused into the graphene thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 50-120°C, 3 hours) to obtain a graphene / silicone rubber composite material. The composite material is cut radially with a metal cutter (i.e., a stainless steel cutter) to obtain a graphene thermal interface material.

[0113] Comparative Example 2

[0114] (1) Liquid silicone rubber was prepared in water, stirred evenly and vacuum-defoamed. 0.15 g of PU foam tape was taken to absorb the slurry and placed on a release film. 0.75 g of asphalt-based carbon fiber was cut. The carbon fiber extended from both ends of the PU foam and was arranged parallel to the width direction. The liquid silicone rubber was used to wet the carbon fiber. The tape was placed in a 70°C forced air drying oven for 2 hours to obtain a PU composite foam tape.

[0115] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 700°C for 2 hours to obtain a carbon fiber thermal conductive carbon skeleton. The skeleton is placed in a polytetrafluoroethylene mold, and the mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 3 hours to allow the liquid silicone rubber to be fully infused into the graphene / carbon fiber thermal conductive carbon skeleton. The composite material is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 80°C, 3 hours) to obtain a carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fiber using an ultrasonic cutter (Japan HONDA, model ZO-91) to obtain an oriented carbon fiber thermal interface material.

[0116] Comparative Example 3

[0117] (1) 18.75 ml of 6 mg / ml graphene oxide dispersion was prepared in water, 37.5 mg of graphene was added, and the mixture was uniformly and ultrasonically dispersed to obtain a graphene mixed slurry (solid content 8 mg / ml, 0.79 wt%). 0.15 g of PU foam tape was adsorbed with the slurry and placed on a release film. 0.75 g of asphalt-based carbon fiber was cut to a length of 100-2000 μm and fully stirred with the remaining graphene mixed slurry, and evenly coated on the PU foam tape. The tape was placed in an 80°C forced air drying oven for 2 hours to obtain a PU composite foam tape.

[0118] (2) The composite foam tape is rolled into a cylindrical shape and placed in a tube furnace under inert gas protection at 700°C for 2 hours to obtain a thermally conductive carbon skeleton. The skeleton is placed in a polytetrafluoroethylene mold, and the mold containing the skeleton is placed in a vacuum drying oven and vacuum-treated at room temperature for 3 hours to allow the liquid silicone rubber to be fully infused into the thermally conductive carbon skeleton. The composite foam tape is taken out of the vacuum drying oven and placed in a blast drying oven for curing (temperature 80°C, 3 hours) to obtain a carbon fiber / silicone rubber composite material. The composite material is cut along the radial direction of the oriented fibers using a water jet (Nanjing Dadi Water Jet Co., Ltd., model 4020BB) to obtain an oriented carbon fiber thermal interface material.

[0119] Product performance

[0120] The thermal conductivity of the thermal interface materials obtained in Examples 1-11 and Comparative Examples 1-3 was tested using a laser flash method (laser flash spectrometer: NETZSCH, Germany, LFA467). The results are shown in Table 1. The length of the PU foam tape prepared in step (1) was 40 ± 0.5 cm. Table 1 shows that the thermal conductivity of the graphene / carbon fiber synergistic thermal interface materials prepared in the examples is significantly higher than that of thermal interface materials prepared using only carbon fiber or graphene.

[0121] Table 1 - Thermal conductivity of composite materials

[0122]

[0123]

[0124] As can be seen from the results in the above table, due to the specific structural design of the present invention, the sheet of the present invention has a much higher thermal conductivity than that of comparative examples 1-3 at the same filling amount of thermally conductive filler. In addition, the inventors of the present application have found through research that the thermal conductivity of the sheet prepared is jointly determined by the amount of carbon fiber, graphene, and graphene oxide. When the amount of (graphene + graphene oxide) is constant, the thermal conductivity of the sheet is proportional to the amount of carbon fiber added. When the amount of carbon fiber added is constant, the relationship between the thermal conductivity of the sheet and the amount of (graphene + graphene oxide) added is: first increase and then decrease (similar to a parabolic relationship); wherein: (graphene + graphene oxide): carbon fiber is 1:2-15, the effect is better.

[0125] In the present invention, polyurethane is the carrier of the thermal conductive filler. Polyurethane itself does not contribute to thermal conductivity, but it has important functions: (1) providing continuous preparation, and (2) providing a channel for resin impregnation. However, the carbon fiber and polyurethane must maintain a certain amount of relationship. It is necessary to ensure that the carbon fiber is evenly laid on the foam tape, but the surface density of the carbon fiber on the foam tape must be controlled; if the amount of carbon fiber is too large, it is difficult to ensure that the graphene is fully attached to the carbon fiber. Figure 1 In addition, there will be some problems with the bonding of the resin.

[0126] In the present invention, the mass of the carbon fiber is controlled to be 333-1600wt% of the mass of the polyurethane foam layer, preferably 400-1550wt%, preferably 500-1500wt%, preferably 600-1400wt%, preferably 700-1300wt%, for example 750, 800, 900, 1000, 1100, 1200, 1250wt%.

[0127] In the present invention, the addition ratio of (graphene + graphene oxide): carbon fiber in the sheet is controlled to be 1:1.5-20, preferably 1:2-15, and more preferably 1:3-10.

[0128] Through the process method provided by the present invention, the composition of polyurethane, carbon fiber, graphene, and graphene oxide in the sheet is controlled and prepared to obtain a thermally conductive interface material with a specific structure; while ensuring the thermal conductivity of the sheet, the sheet's bonding ability is improved; the obtained sheet has a low density, a light and thin texture, low hardness, and a very good feel; it has good flexibility and can fit well with the heat dissipation surface, thereby improving the heat dissipation effect.

[0129] The inventors of this application also note that Example 4 of CN112477309A (Chinese Application No. 2020112001157) and Examples 8 and 5 of CN105818476A (Chinese Application No. 2016101624533) disclose similar thermally conductive sheets, where the thermal conductivity is measured in the horizontal direction. However, the sheet of the present invention primarily focuses on improving the thermal conductivity of the composite material through its thickness.

[0130] In addition, Example 8 of CN113829684A (Chinese application number 2021110673313) discloses a similar thermally conductive sheet, which specifically discloses that a thermally conductive material is obtained by stacking layers and interlacing carbon fiber filaments. Through the method provided by the present invention, the thermal interface material obtained by a low-cost, continuous preparation method achieves the technical effects of thermal synergy of the filler and more uniform impregnation of the resin, resulting in a thermal interface material with a special structure, which is different from CN113829684A in terms of thermal conduction mechanism, and the thermal conductivity of the thermal interface material obtained by the present invention is improved. Because the curled structure or stacked structure (especially the curled structure) of the present invention has good pressure bearing and structural stability, the toughness is relatively strong, and the use of soft PU and silicone rubber also makes the hardness value relatively low. The hardness of the product of the present invention is less than the hardness of the product of Example 8 of CN113829684A. The sheet of the present invention has a low density, light weight, good hand feel, and especially has good adhesion to the application surface, thereby significantly improving the heat dissipation effect. In addition, the sheet material of the present invention has good toughness through the composite structure of silicone rubber and PU foam, and can withstand repeated bending without cracking. Compared with these products in the prior art, the sheet material of the present invention obtains a specific structure through a special preparation method, which realizes a lower filling amount of thermally conductive filler, but has a high thermal conductivity coefficient. In particular, compared with these products in the prior art, the advantages of the present invention are: the filling amount of thermally conductive filler in the sheet material of the present invention is low, and high thermal conductivity is achieved at a lower filling amount. This is because the preparation method realizes the synergy of two-scale thermally conductive fillers, graphene and carbon fiber, and can fully utilize the high thermal conductivity of the two thermally conductive fillers, especially the addition of graphene can greatly improve the thermal conductivity of composite materials with the same carbon fiber filling amount. In addition, the present invention has the advantages of simplicity and strong scalability in the preparation method.

[0131] The embodiments provided above are merely illustrative and should not be considered as limiting the scope of the present invention. Any equivalent replacement or modification of the technical solution and inventive concept of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a thermally conductive interface composite material, characterized in that: The method comprises the following steps: 1) dispersing graphene oxide and graphene in water to obtain a graphene-graphene oxide mixed dispersion slurry, immersing a thin layer of polyurethane foam or a thin sheet in the slurry so that the thin layer of polyurethane foam or the thin sheet fully absorbs the slurry, and then removing the polyurethane foam thin layer or the thin sheet that has absorbed the slurry and placing it on a release film; when preparing the graphene-graphene oxide mixed dispersion slurry, the mass ratio of graphene to graphene oxide is 1:10 to 1:1; 2) cutting the carbon fibers so that the length of the cut carbon fibers is 1 to 1.2 times the width of the polyurethane foam tape or sheet, placing the cut carbon fibers parallel to the width of the polyurethane foam tape or sheet on the polyurethane foam tape or sheet, pressing the carbon fibers with a pressing device so that the slurry on the polyurethane foam tape or sheet wets the carbon fibers, and evenly coating the wetted carbon fibers with the slurry described in step 1), and then drying the composite foam tape or sheet. The coating and drying operations can be performed once or repeated two or more times to ensure that a sufficient amount of graphene-graphene oxide composite is adsorbed on the polyurethane foam tape or sheet. 3) rolling or stacking the composite foam tape or sheet obtained in step 2) above, and then drying or not drying to obtain a cylindrical or rectangular parallelepiped frame structure; then, placing the frame structure in a high-temperature furnace and performing high-temperature thermal reduction under the protection of an inert gas at high temperature to obtain a graphene / carbon fiber thermal conductive carbon skeleton; 4) placing the graphene / carbon fiber thermal conductive carbon skeleton into a mold or container, pouring a liquid adhesive into the mold or container to submerge the graphene / carbon fiber thermal conductive carbon skeleton therein; then evacuating the mold or container to allow the liquid adhesive to fully diffuse and penetrate the graphene / carbon fiber thermal conductive carbon skeleton; then curing the liquid adhesive by heating to obtain a graphene / carbon fiber / adhesive composite material; the liquid adhesive is a thermosetting liquid silicone rubber or a thermosetting liquid aliphatic epoxy resin; 5) cutting the graphene / carbon fiber / adhesive composite material of step 4) along the radial direction of the oriented carbon fibers using a cutting tool to obtain a sheet-like graphene / carbon fiber synergistically thermally conductive interface composite material; The graphene / carbon fiber synergistically conductive thermal interface composite material comprises: 1) thermal conductive material layers uniformly composed of thermal conductive fillers and the carbon fibers are alternately distributed with polyurethane foam layers; 2) the interface between the thermal conductive material layer and the polyurethane foam layer is perpendicular to the upper and lower surfaces of the sheet-like thermal conductive interface composite material; and 3) the carbon fibers uniformly arranged in the thermal conductive material layer are perpendicular to the upper and lower surfaces of the sheet-like thermal conductive interface composite material, and 90-100% of the carbon fibers have their ends flush with the upper and lower surfaces of the thermal conductive interface composite material, respectively, and this percentage is based on the total number of carbon fibers; the thermal conductive filler includes a combination of graphene and reduced graphene oxide, the total mass of the thermal conductive filler is 33-666wt% of the mass of the polyurethane foam layer; and the mass of the carbon fibers is 333-1600wt% of the mass of the polyurethane foam layer.

2. The preparation method according to claim 1, wherein: The polyurethane foam layer is an open-cell soft polyurethane foam thin layer.

3. The preparation method according to claim 1 or 2, characterized in that: The carbon fiber used in step 2) is pitch-based carbon fiber, graphene carbon fiber, or a combination of the two.

4. The preparation method according to claim 1 or 2, characterized in that: The thickness of the polyurethane foam layer is 200 to 900 microns; and / or The average size of the foam cells of the polyurethane foam layer is 120 to 510 microns.

5. The preparation method according to claim 1 or 2, characterized in that: The temperature of the medium-high temperature thermal reduction in step 3) is 600-1500°C.

6. The preparation method according to claim 1 or 2, characterized in that: The pressing device is a brush.

7. The preparation method according to claim 1 or 2, characterized in that: The drying temperature in step 2) and step 3) is 60-90°C.

8. The preparation method according to claim 1 or 2, characterized in that: In step 4), the heating temperature for curing the liquid adhesive by heating is 50-120°C.

9. The thermally conductive interface composite material prepared by the preparation method according to claim 1, characterized in that: The graphene / carbon fiber synergistic thermal conductive interface composite material: 1) the thermal conductive material layer uniformly composed of the thermal conductive filler and the carbon fiber and the polyurethane foam layer are alternately distributed; 2) the interface between the thermal conductive material layer and the polyurethane foam layer is perpendicular to the upper and lower surfaces of the sheet-like thermal conductive interface composite material; and 3) carbon fibers uniformly arranged in the thermally conductive material layer are perpendicular to the upper and lower surfaces of the sheet-like thermally conductive interface composite material, and 90-100% of the carbon fibers have their ends flush with the upper and lower surfaces of the thermally conductive interface composite material, respectively, and the percentage is based on the total number of carbon fibers; the thermally conductive filler includes a combination of graphene and reduced graphene oxide, and the total mass of the thermally conductive filler is 33 to 666 wt % of the mass of the polyurethane foam layer; and the mass of the carbon fibers is 333 to 1600 wt % of the mass of the polyurethane foam layer.

10. The thermally conductive interface composite material according to claim 9, characterized in that: The thermal conductivity of the thermally conductive interface composite material in the thickness direction is 70 to 300 W / mK.

11. The thermally conductive interface composite material according to claim 9, wherein: The thickness of the thermal conductive interface composite material is 50µm to 30mm.

Images