Graphene longitudinal thermal conductor, preparation method and application thereof

Abstract

The present invention discloses a graphene longitudinal heat conductor, its preparation method and application. The graphene longitudinal heat conductor includes a resin layer and a graphene heat conductive layer, which are tightly combined; the extension direction of the graphene sheet in the graphene heat conductive layer is consistent with the thickness direction of the graphene longitudinal heat conductor; the graphene heat conductive layer includes a plurality of first graphene sublayers stacked in sequence, and any two first graphene sublayers are separated by a second graphene sublayer; the first graphene sublayer and the second graphene sublayer are tightly combined. The graphene longitudinal heat conductor provided by the present invention connects the first graphene sublayers on both sides through the second graphene sublayer, and the plurality of sublayers are stacked together to form a complete and continuous whole-surface graphene heat conductive layer. The bonding force between the graphene heat conductive layer and the resin layer is excellent, and no hole structure is generated to lose the heat conductive cross-sectional area. Therefore, it has both mechanical strength and excellent longitudinal heat conductive performance, and has broad application prospects in the field of heat dissipation applications of electronic products.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal conductive materials, and in particular to a graphene longitudinal thermal conductor, a preparation method thereof, and applications thereof. Background Art

[0002] With the development of science and technology and the continuous advancement of technology, electronic components are becoming increasingly lightweight and integrated. While electronic products have achieved advantages such as small size, light weight and high performance, the heat generated by electronic components such as CPU, GPU and battery is also increasing simultaneously. Excessive heat will affect the performance and service life of electronic components, thereby greatly reducing the user experience of electronic products.

[0003] Graphene, a new material that has emerged in recent years, has garnered significant attention across industries due to its exceptional thermal conductivity. Graphene-based thermal conductive materials are now a widespread phenomenon. In the electronics industry, graphene-modified thermal conductive materials, due to their superior thermal conductivity, are considered a key non-metallic solution to heat dissipation issues in electronic components.

[0004] Graphene thermal conductive materials currently available on the market are widely used in the mobile phone industry. Their working principle is to transfer heat in a planar direction through the graphene thermal conductive material, then transfer the heat to other heat dissipation materials, and then transfer the heat to the outer casing. The heat is then transferred to the outside world through the heat dissipation casing, avoiding heat accumulation in a specific area and preventing damage to the performance and lifespan of electronic components due to excessive temperatures. However, because heat transfer on graphene thermal conductive materials is mainly in a planar direction, it cannot directly transfer heat quickly in a vertical direction. This results in a long heat transfer time, high temperature of electronic products, and poor user experience.

[0005] Some existing technologies, such as Chinese invention patent publication number CN112477356A, provide a graphene longitudinal thermal conductor and its preparation method. This involves creating multiple pores on the graphene surface, then stacking and bonding multiple graphene sheets with solder paste. The sheets are then cut along the stacking direction to produce a graphene longitudinal thermal conductor with the thermal conductivity extending along its thickness. However, this method requires drilling holes into the graphene to ensure a good bond with the solder material. These holes reduce the graphene's actual thermal conductivity area, affecting its ultimate thermal conductivity. Furthermore, the solder paste and graphene do not bond tightly, making it prone to cracking during production, processing, and application, hindering its application prospects. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide a graphene longitudinal thermal conductor, a preparation method and applications thereof.

[0007] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0008] In a first aspect, the present invention provides a graphene longitudinal heat conductor, comprising a cyclically stacked resin layer and a graphene heat conductive layer, wherein the resin layer and the graphene heat conductive layer are tightly combined;

[0009] The extending direction of the graphene sheets in the graphene heat conducting layer is consistent with the thickness direction of the graphene longitudinal heat conductor;

[0010] The graphene heat conductive layer includes a plurality of first graphene sublayers stacked in sequence, and a second graphene sublayer is provided between any two of the first graphene sublayers, wherein the first graphene sublayers are formed by graphitizing a graphene oxide film;

[0011] The first graphene sublayer and the second graphene sublayer are tightly bonded.

[0012] In a second aspect, the present invention further provides a method for preparing a graphene longitudinal thermal conductor, comprising:

[0013] Providing graphene oxide slurry and coating it to form a film to obtain a graphene oxide film;

[0014] stacking a plurality of graphene oxide films and placing graphene paper between any two adjacent graphene oxide films to form a composite body;

[0015] The assembly is subjected to a high-temperature graphitization treatment and a calendering treatment, so that the graphene oxide film is graphitized and combined with the graphene paper to form a graphene thermal conductive layer in which multiple first graphene sublayers are stacked and a second graphene sublayer is disposed between any two first graphene sublayers;

[0016] Covering the surface of the graphene thermal conductive layer with a resin layer to form a single layer precursor;

[0017] stacking the single-layer precursors in multiple layers, such that the resin layer in one single-layer precursor contacts the graphene thermally conductive layer in another adjacent single-layer precursor, and combining the single-layer precursors by heat pressing to form a multi-layer precursor;

[0018] The multilayer precursor is cut along the stacking direction to obtain a sheet-like graphene longitudinal heat conductor.

[0019] In a third aspect, the present invention further provides an application of the above-mentioned graphene longitudinal heat conductor in the field of heat dissipation of electronic components.

[0020] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least:

[0021] The graphene longitudinal heat conductor provided by the present invention connects the first graphene sublayers on both sides through the second graphene sublayer. Multiple sublayers are stacked together to form a complete and continuous full-surface graphene heat conductive layer. The bonding force between the graphene heat conductive layer and the resin layer is excellent, and no pore structure is generated to lose the heat conductive cross-sectional area. Therefore, it has both mechanical strength and excellent longitudinal thermal conductivity, and has broad application prospects in the field of heat dissipation applications of electronic products.

[0022] The above description is only an overview of the technical solution of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of this application and implement them according to the contents of the specification, the following is an explanation of the preferred embodiments of the present invention with detailed drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of a graphene longitudinal heat conductor provided by a typical embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of a heat dissipation performance testing device for a heat conductor provided in a typical test case of the present invention;

[0025] Figure 3 This is a test curve diagram of the heat dissipation capacity of the heat conductor provided by a typical embodiment of the present invention and a comparative example;

[0026] Figure 4 This is a micron-CT characterization image of a graphene longitudinal thermal conductor provided by a typical embodiment of the present invention. DETAILED DESCRIPTION

[0027] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The following will further explain this technical solution, its implementation process and principles.

[0028] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0029] The present invention discloses a graphene longitudinal heat conductor. The main difference between the graphene longitudinal heat conductor and other graphene-modified heat-conducting materials currently on the market is that the heat conduction direction of the graphene longitudinal heat conductor is perpendicular to the heat source. Through the excellent thermal conductivity of graphene, heat is directly transferred in the vertical direction, and the amount of heat conducted in the planar direction is relatively small, thereby maximizing the utilization of the longitudinal thermal conductivity of graphene to achieve the effect of rapid heat conduction and cooling.

[0030] Therefore, if Figure 1As shown, an embodiment of the present invention provides a graphene longitudinal heat conductor, which includes a cyclically stacked resin layer and a graphene heat conductive layer, wherein the resin layer and the graphene heat conductive layer are tightly bonded; the extension direction of the graphene sheets in the graphene heat conductive layer is consistent with the thickness direction of the graphene longitudinal heat conductor; the graphene heat conductive layer includes a plurality of first graphene sublayers stacked in sequence, and a second graphene sublayer is provided between any two of the first graphene sublayers, wherein the first graphene sublayers are formed by graphitizing a graphene oxide film; and the first graphene sublayer and the second graphene sublayer are tightly bonded.

[0031] The graphene thermal conductive layer comprises multiple graphene sheets, which are preferentially arranged parallel to the plane of the graphene thermal conductive layer. This is a common microscopic arrangement of graphene films; this arrangement facilitates heat conduction along the plane of the graphene thermal conductive layer. In this technical solution, the plane of the graphene layers aligns with the thickness of the graphene thermal conductor, making it extremely easy for heat to be transferred along the thickness of the graphene thermal conductor. This overcomes the problem that conventional graphene thermal conductors can only conduct heat along the plane.

[0032] It should be pointed out that the so-called consistent direction means that the two directions are usually parallel, but it is not strictly limited to this. For example, the so-called extension direction of multiple graphene sheets has a distribution trend that is parallel to the thickness direction of the graphene longitudinal thermal conductor, but not all graphene sheets are strictly arranged in this direction. It is sufficient if the whole has this trend; and the so-called consistency does not necessarily mean completely parallel. For example, a slight tilt is acceptable (regardless of whether the tilt is caused by processing accuracy, such as cutting tilt, or a deliberate tilt setting). The acceptable tilt angle is based on fully realizing longitudinal heat conduction. For example, an inclination angle within ±30° is acceptable. Appropriate tilt, such as a tilt of 15-30°, will increase the contact area of ​​each layer at the same thickness, which is beneficial to mechanical properties. Of course, if it can be strictly controlled, an angle with no tilt at all is most helpful for improving thermal conductivity efficiency.

[0033] In some embodiments, the first graphene sublayer comprises a rough side and a smooth side that are opposite to each other;

[0034] The rough surfaces of the two first graphene sub-layers at the end faces are facing away from the center of the graphene heat conducting layer and are combined with the resin layer.

[0035] In some embodiments, the number of cyclic stacking of the resin layer and the graphene thermal conductive layer is 800-1200; and it is not limited thereto. The above-mentioned number of stacking is a number commonly used in the specific implementation of the present invention. In actual implementation, the number of stacking can be adaptively adjusted based on the required size of the thermal conductor (such as length and width).

[0036] In some embodiments, the resin layer is doped with a thermal conductive additive, and the mass fraction of the thermal conductive additive in the resin layer is 2-25%. However, this is not limiting. In practice, the optimal doping amount may vary depending on the thermal conductive additive. For example, a preferred embodiment is to dope graphene at a mass fraction of approximately 10%.

[0037] In some embodiments, the thermal conductive additive includes any one of metal thermal conductive materials, carbon thermal conductive materials, oxide thermal conductive materials, and nitride thermal conductive materials, or a combination of two or more thereof.

[0038] like Figure 2 As shown, corresponding to the structure of the above-mentioned graphene longitudinal heat conductor, an embodiment of the present invention further provides a method for preparing the graphene longitudinal heat conductor, which includes the following steps:

[0039] Providing graphene oxide slurry and coating it to form a film to obtain a graphene oxide film;

[0040] stacking a plurality of graphene oxide films and placing graphene paper between any two adjacent graphene oxide films to form a composite body;

[0041] The assembly is subjected to a high-temperature graphitization treatment and a calendering treatment, so that the graphene oxide film is graphitized and combined with the graphene paper to form a graphene thermal conductive layer in which multiple first graphene sublayers are stacked and a second graphene sublayer is disposed between any two first graphene sublayers;

[0042] Covering the surface of the graphene thermal conductive layer with a resin layer to form a single layer precursor;

[0043] stacking the single-layer precursors in multiple layers, such that the resin layer in one single-layer precursor contacts the graphene thermally conductive layer in another adjacent single-layer precursor, and combining the single-layer precursors by heat pressing to form a multi-layer precursor;

[0044] The multilayer precursor is cut along the stacking direction to obtain a sheet-like graphene longitudinal heat conductor.

[0045] In some embodiments, the graphene oxide film includes a smooth surface and a rough surface opposite to each other, and when forming the assembly, the graphene oxide film at both end surfaces of the assembly exposes the rough surface;

[0046] In some embodiments, the smooth surface corresponds to the surface of the graphene oxide slurry when coated into a film.

[0047] In some embodiments, the graphene oxide sheets contained in the graphene oxide slurry have a planar size of 0.5-5 μm.

[0048] In some embodiments, the thickness of the graphene oxide film is 0.5-3 mm, and the thickness of the graphene paper is 0.1-0.3 mm.

[0049] In some embodiments, the resin layer has a thickness of 0.04-0.06 mm.

[0050] Based on the above technical solution, the key technical means of the present invention is to add a second graphene sublayer (graphene paper) between the first graphene sublayers. The main function of the graphene paper is to conduct heat quickly. By utilizing the principle of its own high thermal conductivity, the subsequent graphitization step can be carried out faster and better, and heat can be better transferred and water vapor can be removed.

[0051] This is because the coated graphene oxide film is a film coated with a mixed slurry of water and graphene oxide, and contains water molecules. Even after drying, a small amount of water molecules are still bound due to the action of the surface groups of graphene oxide. Removing water molecules at high temperature can make the film purer and thus bring better thermal conductivity and mechanical bonding properties. This is because water molecules act as oxidants at high temperatures and affect the graphitization process of graphene oxide being reduced to graphene, thereby affecting the surface morphology of the film, causing the film to expand, thereby affecting the thermal conductivity and bonding strength of the material.

[0052] Moreover, in the common preparation method of graphene oxide film, smooth and rough surfaces are easily produced, and the smooth surface corresponds to the surface of the liquid film during the coating process, and the rough surface corresponds to the side in contact with the substrate; in the specific structure provided by the present invention, through the bridging effect of the graphene paper, the first graphene sublayer at both end surfaces can be combined with the graphene paper through its smooth surface, and the rough surfaces exposed on the two end surfaces are used to combine with the resin layer, thereby achieving excellent graphene-resin bonding strength, thereby bringing excellent mechanical properties, and bringing great convenience to production, processing and assembly during thermal conductivity applications.

[0053] Moreover, in the above-mentioned setting method, the smooth surface is relatively facing inward, mainly to achieve better contact with the graphene paper, to achieve better inter-sublayer heat transfer through the combination of calendering, and thus to achieve better thermal conductivity; if the rough surface is relatively facing inward, not only will the above-mentioned bonding problem occur, but there will also be more microscopic gaps between it and the graphene paper, which will not transfer heat well and further lose thermal conductivity.

[0054] In addition, if there is no graphene paper, the heat conduction will be uneven. For example, the water vapor is not completely removed within the set time, the graphitization is incomplete, etc., which may affect the yield. If the time is increased, the efficiency will also be reduced and the cost will increase.

[0055] As some typical application examples of the above technical solutions, the preparation process of the graphene longitudinal heat conductor provided by the embodiments of the present invention may include steps 1-10 as follows:

[0056] 1. By repeatedly homogenizing the graphene oxide under high pressure, the graphene oxide size is trimmed so that the slurry concentration and viscosity meet the corresponding requirements, thereby obtaining a graphene oxide slurry;

[0057] 2. Degassing is performed by an online degassing machine before coating, and then the graphene oxide slurry is coated into graphene oxide films of different thicknesses by an automatic coating dryer;

[0058] 3. Stack at least two layers of graphene oxide film together with the smooth surfaces facing each other. A layer of graphene paper is sandwiched between each two adjacent layers of graphene oxide film, and the stacking height is gradually increased. Place in an oven for drying. Generally, no more than 10 layers of graphene oxide film are stacked, and 2-4 layers are preferred. Too many layers will cause the subsequent film to be too thick, affecting product performance and other problems. The graphene paper is used to quickly conduct heat during the subsequent graphitization process and remove a small amount of water vapor carried during the coating process.

[0059] 4. Graphitization: The two stacked graphene films are combined into a single layer, and the epoxy groups of the graphene oxide are removed to convert it into the first graphene sublayer. This step uses a multi-stage heat treatment process to graphitize the material and fully carbonize the impurities.

[0060] 5. Calendering: The graphene film, which was originally laminated into two layers, is calendered into a single layer. This step mainly uses a vacuum press to calender the graphitized material to obtain a graphene thermal conductive layer.

[0061] 6. Use a fully automatic composite lamination machine to heat-press the graphene film and thermally conductive epoxy resin adhesive and cool them. Remove the PET release film on the surface of the thermally conductive epoxy resin adhesive. Use a robotic arm to perform multi-layer lamination. When laminating, keep the multiple layers facing the same direction, that is, the lower graphene thermal conductive layer is in contact with the upper epoxy resin adhesive.

[0062] 7. Use a vacuum hot press to vacuum-press the laminated graphene thermal conductive layer to remove the air and gaps between the films, so that the materials are completely fitted and air-free. This step preferably uses existing equipment to perform multi-directional six-sided heating for more uniform heat conduction.

[0063] 8. Use a single-wire cutting machine to trim the vacuum hot-pressed assembly according to the corresponding size to maintain the uniform size of the overall material; of course, if the size itself meets the requirements, this step can be omitted.

[0064] 9. Adjust the direction of the trimmed material so that the graphene arrangement direction changes from plane to vertical, and then slice it along the stacking direction using a multi-wire saw to obtain a graphene longitudinal thermal conductive sheet monomer of the required thickness;

[0065] 10. Using a self-designed separation and cleaning composite machine, the graphene longitudinal thermal conductive sheet monomers are cleaned and peeled off, and PET double-sided tape is applied one by one as a protective film, thus completing the preparation of the graphene longitudinal thermal conductor.

[0066] The above content illustrates the preparation process of the graphene longitudinal thermal conductor provided by the present invention. Regarding the specific process conditions, in some embodiments, the temperature range of the high-temperature graphitization treatment is room temperature during treatment - 4000°C, the heating rate is 0.01-15°C / min, and the heating time is 0.5-10h;

[0067] In some embodiments, the calendering process causes the density of the graphene thermal conductive layer to be between 1.6 g / cm 3 and / or reducing the thickness of the graphene thermal conductive layer to 40-60% of the assembly;

[0068] In some embodiments, the pressure of the calendering treatment is not less than 100T, and more preferably 100-200T.

[0069] In some embodiments, the autoclave treatment is performed under vacuum conditions;

[0070] In some embodiments, the pressure of the autoclave is 50-200°F and the temperature range is 50-300°C.

[0071] In some embodiments, the cutting fluid used is continuously filtered during the cutting process;

[0072] In some embodiments, the graphene longitudinal thermal conductor obtained by cutting has a thickness of more than 0.2 mm.

[0073] In some specific implementation cases, during the above exemplary preparation process:

[0074] In step 1, the graphene oxide is sheared. The preferred size range of the sheared graphene oxide is 0.5-5 μm, the slurry concentration range is 0.1-10 wt %, and the slurry viscosity is 50,000-150,000 mPa·s. Of course, the slurry performance parameters in actual applications are not limited to these, as long as they can achieve good film formation and good planar thermal conductivity.

[0075] In the second step of coating, the coating thickness is 1-5mm, the coating speed is 0.5-5m / min, and the thickness of the film after forming is about 60% of the liquid film during coating. The specific value varies according to the change of solid content.

[0076] During the drying process in step 3, the temperature is increased at a rate of 1-5°C / min, and the temperature in the oven is 50-750°C. The heating process is, for example, 2 hours, and the temperature is kept at this temperature for 1-3 hours. Of course, the drying process can remove a large amount of water or other types of dispersions, and is not limited to the parameter range of this example.

[0077] During the graphitization process in step 4, the preferred multi-stage heat treatment process parameter ranges are as follows:

[0078] The temperature range is room temperature-4000°C, the heating rate is 0.01-15°C / min, and the heating time is 0.5-10h. The specific multi-stage graphitization heating process can refer to the graphitization process of graphene oxide in the prior art and be adaptively adjusted.

[0079] During the calendering process in step 5, the preferred pressure range is 100-200T; the pressure should not be lower than 100T, otherwise the density of the material after pressing will be less than 1.6g / cm 3 There are many gaps between layers or in the microscopic space, which affects the thermal conductivity of the product. Theoretically, within the limit range, the higher the pressure, the higher the density of the material after pressing and the higher the thermal conductivity coefficient. However, the higher the pressure, the cost of the equipment used will increase sharply, which is not conducive to production. Another reference standard is that the thickness of the film after calendering is reduced to about 50% of the original.

[0080] In the composite lamination process of step 6, the epoxy resin glue is preferably one or more of metal thermal conductive epoxy resin glue (thermal conductive filling materials are Fe, Mg, Al, Cu, Ag, etc.), carbon-based thermal conductive epoxy resin glue (thermal conductive filling materials are carbon nanotubes, graphene, graphite, etc.), oxide thermal conductive epoxy resin glue (Al2O3, ZnO, BeO, SiO2, etc.) and nitride epoxy resin glue (thermal conductive filling materials are AlN, BN, Si3N4, etc.);

[0081] During the vacuum hot pressing process in step 7, the preferred pressure parameter range is set at 50-200t, and the temperature parameter range is set at 50-300℃. The specific process is to put the material in, first heat it to 80 degrees, maintain it for 30-60min, then heat it to 150 degrees, maintain it for 30min, and then perform hot pressing, hot pressing 1-2 times, with a pressure of about 20-30t, and then hold the pressure for 30-60min. The holding pressure is one-fifth of the hot pressing, and the hot pressing process is kept in vacuum throughout. Of course, this implementation condition is the hot pressing condition preferred by the inventor of the present invention in research and development practice. The process conditions that can achieve good hot pressing vary with the influence of factors such as material composition, layer thickness, number of stacking, etc., and are not limited to the scope of the above examples.

[0082] In the single-wire cutting process in step 8, the preferred cutting speed range is 3-20 mm / s;

[0083] In the 9th step of the multi-wire sawing machine slicing process, the preferred cutting thickness range is greater than 0.2mm to ensure mechanical strength, so that it is not easy to crack or separate between layers. The multi-wire sawing machine used has a cutting fluid filtration function to prevent the material debris generated during the cutting process from affecting the subsequent cutting and ensure the surface quality of the material after cutting.

[0084] Corresponding to the above-mentioned graphene longitudinal heat conductor and its preparation method, an embodiment of the present invention further provides an application of the graphene longitudinal heat conductor provided or prepared by any of the above-mentioned embodiments in the field of heat dissipation of electronic components.

[0085] The technical solution of the present invention is further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0086] Example 1

[0087] This embodiment illustrates a preparation process of a graphene longitudinal heat conductive sheet, which specifically includes the following steps:

[0088] 1. High-pressure homogenization. Through multiple high-pressure homogenizations, the graphene oxide is sheared to a size of about 1 micron, and the aqueous slurry concentration reaches 6wt% and the slurry viscosity is not less than 90,000mPa·s;

[0089] 2. Degassing. Degas the graphene oxide slurry through an online degassing machine;

[0090] 3. The graphene oxide slurry was then coated into a graphene oxide film with a thickness of 3 mm using an automatic coating dryer at a coating speed of 0.8 m / min;

[0091] 4. Stack two layers of graphene oxide film together, with the smooth sides facing each other, and sandwich them between two layers of graphene paper. Then, stack them layer by layer with the rough side facing outward. The total number of layers is 4. The obtained laminated assembly is then placed in an oven for drying. The specific drying process includes:

[0092] Heat the temperature from room temperature to 100°C in an oven for 2 hours and keep warm for 1 hour;

[0093] In an oven, heat from 100-120°C for 2 hours and keep warm for 1 hour;

[0094] In an oven, heat from 120-140°C for 2 hours and keep warm for 1 hour;

[0095] In an oven from 140-200°C for 2 hours;

[0096] In an oven from 200-240°C for 2 hours;

[0097] In an oven, heat from 240-300°C for 2 hours and keep warm for 1 hour;

[0098] In an oven, heat from 300-550°C for 2 hours and keep warm for 2 hours;

[0099] In the oven, heat from 550-750℃ for 2 hours and keep warm for 2 hours.

[0100] 5. Graphitization. A multi-stage heat treatment process is used to graphitize the composite material. The specific multi-stage heat treatment process includes:

[0101] The first stage: room temperature - 650 ° C, heating time 0.5h;

[0102] The second stage: 650-1600℃, heating time 0.5h;

[0103] The third stage: 1600-2000℃, heating time 1h;

[0104] The fourth stage: 2000-2200℃, heating time 2h;

[0105] The fifth stage: 2200-2600℃, heating time 1.5h;

[0106] The sixth stage: 2600-3000℃, heating time 5h;

[0107] Stage 7: 3000-3200℃, heating time 1-2h;

[0108] Section 8: 3100℃, heating time 1h.

[0109] 6. Calendering: Use a vacuum flat press to calender the graphitized material to obtain a graphene thermal conductive film with a thickness of about 2 mm.

[0110] 7. Use a fully automatic composite lamination machine to hot-press and cool the graphene thermal conductive film and graphene thermal conductive epoxy film, remove the PET release film on the surface of the graphene thermal conductive epoxy film, and laminate them using a robotic arm. The thickness of the laminate is 8.5 cm.

[0111] 8. Through the self-modified vacuum hot press, after loading, the temperature is first raised to 80 degrees and maintained for 30 minutes, then raised to 150 degrees and maintained for 30 minutes, and then vacuumed for hot pressing, hot pressing twice, the pressure is 20t, and then the pressure is maintained for 60 minutes. The pressure is one-fifth of the hot pressing. The vacuum is maintained throughout the hot pressing process and the temperature is maintained at 150 degrees. The air and gaps between the films are removed to make the materials completely fit and air-free. After vacuum hot pressing treatment, the material thickness is 6cm.

[0112] 9. Use a single-wire cutting machine with a cutting speed of 5 mm / s to trim the material after vacuum hot pressing to the corresponding size to keep the overall material size uniform. The cutting size is based on the required size of the thermal conductive sheet.

[0113] 10. Adjust the direction of the trimmed material so that the graphene arrangement direction changes from plane to vertical, and then slice it through a multi-wire saw. The thickness of the cut sheet is 0.27mm. In order to prevent material debris from contaminating the cutting fluid during the cutting process and ensure the cutting quality, a cutting fluid filtration function is added to the multi-wire saw to ensure the purity of the cutting fluid and obtain a graphene longitudinal thermal conductive sheet monomer of the required thickness.

[0114] 11. Use a separation and cleaning composite all-in-one machine to clean the graphene longitudinal thermal conductive sheet monomers, separate them piece by piece, and attach PET double-sided tape to complete the preparation of the graphene longitudinal thermal conductor.

[0115] After testing, the overall thermal conductivity of the prepared graphene longitudinal thermal conductor was 598.6W / mK.

[0116] Comparative Example 1

[0117] This comparative example is substantially the same as Example 1, except that:

[0118] There is no longer a graphene paper between the multilayer graphene oxide films. Instead, two adjacent graphene oxide films are directly brought into contact with each other, and then stacked and subsequently produced under the same conditions.

[0119] Whether to add graphene paper mainly affects the overall processing efficiency when the graphene film is formed. In the comparative example, there is no graphene paper, and the required drying time needs to be significantly extended by several times to dozens of times to achieve good drying, and the final composite effect may deteriorate, thereby affecting the quality of the graphene thermal conductive layer.

[0120] Within the same processing time, the graphene thermal conductive layer produced by the method of sandwiching graphene paper in Example 1 has better thermal conductivity than the thermal conductive layer without sandwiched graphene paper in Comparative Example 1, and the thermal conductivity of the subsequent thermal conductor will also be good. Within the same processing time, if the product does not fail in processing, the average thermal conductivity of the multiple graphene longitudinal thermal conductors successfully obtained is about 450W / mK. In addition to the decrease in thermal conductivity, this comparative example also faces the problem of low yield, and is prone to preparation failure, poor bonding between layers, and other undesirable phenomena.

[0121] Comparative Example 2

[0122] This comparative example is substantially the same as Example 1, except that:

[0123] The graphene oxide on the end faces is set with the smooth side facing outward, and then stacked and subsequently produced under the same conditions.

[0124] The thermal conductivity of the graphene longitudinal thermal conductor obtained in this embodiment is about 530 W / mK. Although it is somewhat different from that in Example 1, it is still a relatively high thermal conductivity. The main problem faced by this comparative example is similar to that in the above-mentioned comparative example 1, mainly in terms of the low yield of the preparation. This may be related to the peel strength. The bonding between the smooth surface and the resin layer is not as good as that in Example 1. The peel strength may be insufficient during the support cutting process, and some loss will occur when a complete overall thermal conductive thin layer is finally cut out.

[0125] Test Case

[0126] In the above, the thermal conductivity of the graphene longitudinal heat conductors provided in the examples and comparative examples was tested, and the specific testing method was as follows:

[0127] Thermal conductivity: The thermal conductivity of the material was measured using the conventional laser flash method. Considering the high thermal conductivity of the material and the anisotropy of graphene, a NETZSCH 467 laser thermal conductivity meter was used with a 10mmx10mm mold to measure the thermal conductivity of the sample through the thickness direction.

[0128] In addition, actual heat dissipation capacity tests were also conducted: In order to characterize the actual heat transfer performance of the material, a CPU heat dissipation simulation device was built, such as Figure 2To ensure test stability, the thermal interface material between the metal housing and the heating element was kept constant, while the material between the metal housing and the heat sink was changed. The temperature of the heating element was compared at the same power to characterize the actual heat transfer performance of the material.

[0129] We compared the graphene longitudinal thermal conductor with a thickness of 0.266 mm and the graphene with a thickness of 0.161 mm and a thermal conductivity of 1 W m - 1 K -1 The commercial thermal conductive silicone pad is compared with the heating power of the heating plate, and the heating power is set to 24V*4A. Figure 3 As shown, when both samples were heated at the same power for 3 minutes, the graphene longitudinal thermal conductor used as the TIM's heating element maintained a 3.83°C cooler temperature than the commercial silicone pad. Notably, the commercial silicone pad was almost half the thickness of the graphene longitudinal thermal conductor. Therefore, given comparable thicknesses, the graphene longitudinal thermal conductor provided by the present invention significantly outperformed the commercial silicone pad in heat dissipation.

[0130] And micro-CT test was performed:

[0131] In order to gain a more intuitive and accurate understanding of the structure of the graphene longitudinal thermal conductor and the interlayer bonding conditions, the present invention conducted a micron-CT test on the material for non-destructive 3D imaging, such as Figure 4 As shown. CT imaging is based on the different absorption rates of materials to X-rays, so the black gaps in the figure are epoxy resin glue. Figure 4 In the figure, the orderly arranged graphene films can be seen, which meets the expected goals of the present invention; and the layers are well adhered to each other without falling off.

[0132] Based on the above embodiments and comparative examples, it can be clearly seen that the graphene longitudinal heat conductor provided by the present invention connects the first graphene sublayers on both sides through the second graphene sublayer, and multiple sublayers are stacked together to form a complete and continuous whole-surface graphene heat conductive layer. The bonding force between the graphene heat conductive layer and the resin layer is excellent, and no hole structure is generated to lose the heat conductive cross-sectional area. Therefore, it has both mechanical strength and excellent longitudinal thermal conductivity, and has broad application prospects in the field of heat dissipation applications of electronic products.

[0133] It should be understood that the above embodiments are merely illustrative of the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications made in accordance with the spirit and substance of the present invention are intended to be encompassed within the scope of protection of the present invention.

Claims

1. A graphene longitudinal heat conductor, characterized in that: The invention comprises a cyclically stacked resin layer and a graphene heat-conducting layer, wherein the resin layer and the graphene heat-conducting layer are tightly combined; The extending direction of the graphene sheets in the graphene heat conducting layer is consistent with the thickness direction of the graphene longitudinal heat conductor; The graphene heat conductive layer includes a plurality of first graphene sublayers stacked in sequence, and a second graphene sublayer is provided between any two of the first graphene sublayers, wherein the first graphene sublayers are formed by graphitizing a graphene oxide film, and the second graphene sublayer is selected from graphene paper; The first graphene sublayer and the second graphene sublayer are tightly bonded.

2. The graphene longitudinal heat conductor according to claim 1, characterized in that: The first graphene sublayer comprises a rough surface and a smooth surface opposite to each other; The rough surfaces of the two first graphene sub-layers at the end faces are facing away from the center of the graphene heat conducting layer and are combined with the resin layer.

3. The graphene longitudinal heat conductor according to claim 1, characterized in that The number of cyclic stacking of the resin layer and the graphene thermal conductive layer is 800-1200; And / or, the resin layer is doped with a thermal conductive additive, and the mass fraction of the thermal conductive additive in the resin layer is 5-25%.

4. The graphene longitudinal heat conductor according to claim 3, characterized in that: The thermal conductive additive includes any one of metal thermal conductive materials, carbon thermal conductive materials, oxide thermal conductive materials, and nitride thermal conductive materials, or a combination of two or more thereof.

5. A method for preparing a graphene longitudinal thermal conductor, characterized in that: include: Providing graphene oxide slurry and coating it to form a film to obtain a graphene oxide film; stacking a plurality of graphene oxide films and placing graphene paper between any two adjacent graphene oxide films to form a composite body; The assembly is subjected to a high-temperature graphitization treatment and a calendering treatment, so that the graphene oxide film is graphitized and combined with the graphene paper to form a graphene thermal conductive layer in which multiple first graphene sublayers are stacked and a second graphene sublayer is disposed between any two first graphene sublayers; Covering the surface of the graphene thermal conductive layer with a resin layer to form a single layer precursor; stacking the single-layer precursors in multiple layers, such that the resin layer in one single-layer precursor contacts the graphene thermally conductive layer in another adjacent single-layer precursor, and combining the single-layer precursors by heat pressing to form a multi-layer precursor; The multilayer precursor is cut along the stacking direction to obtain a sheet-like graphene longitudinal heat conductor.

6. The preparation method according to claim 5, characterized in that The graphene oxide film includes a smooth surface and a rough surface facing each other. When forming the assembly, the rough surfaces of the graphene oxide films at both end surfaces of the assembly are exposed, and the smooth surface corresponds to the surface of the graphene oxide slurry when the film is coated.

7. The preparation method according to claim 6, characterized in that The planar size of the graphene oxide sheets contained in the graphene oxide slurry is 0.5-5 μm; And / or, the thickness of the graphene oxide film is 0.5-3 mm, and the thickness of the graphene paper is 0.1-0.3 mm; And / or, the thickness of the resin layer is 0.04-0.06 mm.

8. The preparation method according to claim 5, characterized in that The temperature range of the high-temperature graphitization treatment is from room temperature to 4000°C, the heating rate is 0.01-15°C / min, and the heating time is 0.5-10h; And / or, the calendering process makes the density of the graphene thermal conductive layer between 1.6 g / cm 3 and / or, reducing the thickness of the graphene thermal conductive layer to 40-60% of the assembly.

9. The preparation method according to claim 8, characterized in that The pressure of the calendering treatment is not less than 100T.

10. The preparation method according to claim 9, characterized in that The pressure of the calendering treatment is 100-200T.

11. The preparation method according to claim 5, characterized in that The hot pressing treatment is carried out under vacuum conditions; And / or, the pressure of the hot pressing treatment is 50-200°C and the temperature range is 50-300°C.

12. The preparation method according to claim 5, characterized in that During the cutting process, the cutting fluid used is continuously filtered.

13. Application of the graphene longitudinal heat conductor according to any one of claims 1 to 4 in the field of heat dissipation of electronic components.

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