Multilayer graphene-metal composite longitudinal heat conductor and preparation method thereof

Abstract

The present invention discloses a multilayer graphene-metal composite longitudinal heat conductor and a preparation method thereof. The preparation method comprises: preparing a combination, comprising a stacked graphene layer and a metal layer, which are bonded as a whole by wax; slicing to obtain a heat-conducting substrate; forming a metal coating, and there are uncovered areas on the surface to expose all wax layers; removing the wax, and then covering the uncovered areas with the metal coating to obtain a graphene longitudinal heat conductor. The preparation method provided by the present invention uses wax that can be removed by flow as a temporary bonding material, forms a combination by stacking and hot pressing, and obtains a heat-conducting substrate after slicing, and then coats the metal coating to combine it into a whole, and then removes the wax by heat treatment, so that there is no colloid residue or carbide between the metal layer and the graphene layer, and there is no surface defect caused by carbonization of the adhesive, and a high-quality multilayer graphene-metal composite longitudinal heat conductor can be obtained.

Description

Technical Field

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

[0002] As people's requirements for computing performance and electronic equipment become higher and higher, electronic components continue to develop in the direction of miniaturization and high integration, resulting in a sharp increase in the power density of electronic equipment, which brings serious heat dissipation problems. According to statistics, electronic equipment failures caused by overheating account for 55% of all failures. Therefore, it is urgent to develop high-performance thermal conductive materials to manage the heat of electronic equipment and reduce the probability of failure during use.

[0003] Graphene is a carbon atom with sp 2 The two-dimensional material with a regular hexagonal honeycomb lattice formed by hybrid orbitals has an in-plane thermal conductivity of up to 5300 W m-2 at room temperature. -1 K -1 , and has low thermal expansion coefficient, low density, and good mechanical properties, so it is considered to be an ideal thermal conductive raw material. Metal materials, such as copper, have high thermal conductivity and good processability and have been widely used in heat dissipation devices. Therefore, the composite of graphene and metal materials is considered to be an effective way to prepare high-performance heat dissipation materials.

[0004] Some existing technologies provide technical solutions for combining carbon thermal conductive materials such as graphene with metal thin layers by winding or stacking to form a composite longitudinal thermal conductor. For example, a graphene and copper coil is prepared by winding, and then combined by sintering. However, in one type of technical solution, since the metal material and the graphene material cannot be firmly bonded, it is difficult to form a composite thermal conductive material with a larger lateral size and a thinner longitudinal thickness, which seriously limits the application of this form of composite material. If a traditional resin adhesive is used to pre-bond graphene and copper, the adhesive needs to be sintered because the adhesive will seriously affect thermal expansion. Traditional adhesives will produce carbonization during the sintering process, and carbon impurities will be precipitated through the copper plating layer to the surface of the material, causing carbon impurities to be produced on the surface of the material, thereby seriously affecting the performance of the material.

[0005] Therefore, how to obtain a longitudinal heat conductor with overall strength while avoiding the negative effects of adhesive materials has become a difficult problem facing researchers in this field. Summary of the invention

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

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0008] In a first aspect, the present invention provides a method for preparing a multilayer graphene-metal composite longitudinal thermal conductor, comprising:

[0009] Prepare a composite body, the composite body comprising a graphene layer and a metal layer cyclically stacked in a specified direction, the graphene layer and the metal layer being bonded together by wax;

[0010] Slicing the assembly along the specified direction to obtain a thermally conductive matrix;

[0011] The heat-conducting substrate is subjected to surface metallization to form a metal plating layer, wherein the metal plating layer at least covers at least one cut surface of the heat-conducting substrate to fix the graphene layer and the metal layer together, and an uncovered area exists on the surface of the heat-conducting substrate, and the uncovered area exposes all edges of the wax layer;

[0012] The wax between the graphene layer and the metal layer is removed by at least heating, the uncovered area is used as a channel for removing the wax, and the uncovered area is then supplemented with a metal coating to obtain a graphene longitudinal heat conductor.

[0013] In a second aspect, the present invention further provides a multi-layer graphene-metal composite longitudinal heat conductor obtained by the above-mentioned preparation method, comprising a heat-conducting substrate composed of a metal layer and a graphene layer stacked in multiple cycles, and a metal coating bonded to the surface of the heat-conducting substrate, wherein the metal coating is bonded to the side edges of the metal layer and the graphene layer so that the metal layer and the graphene layer are combined into the heat-conducting substrate;

[0014] There is a gap between the metal layer and the graphene layer, and the gap does not contain carbonized residues or colloidal residues.

[0015] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention at least include:

[0016] The preparation method provided by the present invention uses a wax that can flow and be removed as a temporary adhesive material, forms a combination by stacking and hot pressing, obtains a heat-conducting substrate after slicing, and then coats it with a metal coating to combine it into a whole. After that, the wax is removed by heat treatment, so that there is no colloid residue or carbide between the metal layer and the graphene layer, and there is no surface defect caused by carbonization of the adhesive, so that a high-quality multi-layer graphene-metal composite longitudinal heat conductor can be obtained.

[0017] 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 the present application and implement them according to the contents of the specification, the following is a description of the preferred embodiments of the present invention in conjunction with detailed drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1a It is a schematic diagram of part of the process of the preparation method provided by a typical embodiment of the present invention;

[0019] Figure 1b It is a schematic diagram of part of the process of the preparation method provided by a typical embodiment of the present invention;

[0020] Figure 1c It is a schematic diagram of part of the process of the preparation method provided by a typical embodiment of the present invention;

[0021] Figure 1d It is a schematic diagram of part of the process of the preparation method provided by a typical embodiment of the present invention;

[0022] Figure 2 This is a photo of the overall state of a graphene-copper composite longitudinal heat conductor provided by a typical implementation case of the present invention;

[0023] Figure 3 This is a photo of the overall state of a graphene-copper composite longitudinal heat conductor provided by a typical comparative case of the present invention;

[0024] Figure 4 This is a graph showing the test results of the thermal diffusion coefficient of a graphene-copper composite longitudinal thermal conductor provided by a typical implementation example of the present invention;

[0025] Figure 5 This is a graph showing the test results of the thermal diffusion coefficient of another graphene-copper composite longitudinal thermal conductor provided by a typical implementation example of the present invention;

[0026] Figure 6 This is a graph showing the test results of the thermal diffusion coefficient of a graphene-copper composite longitudinal thermal conductor provided by a typical control case of the present invention. DETAILED DESCRIPTION

[0027] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[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 protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0029] Moreover, relational terms such as “first” and “second” are merely used to distinguish one component or method step from another with the same name, but do not necessarily require or imply any such actual relationship or order between these components or method steps.

[0030] See also Figure 1a-1d As shown, an embodiment of the present invention provides a method for preparing a multilayer graphene-metal composite longitudinal thermal conductor, which comprises the following steps:

[0031] Use the first method to form a combination:

[0032] A wax layer is provided on the surface of the graphene layer and the metal layer;

[0033] stacking the graphene layer containing the wax layer and the metal layer in a specified direction to obtain a first preform;

[0034] Performing a hot pressing process on the first preform, so that the wax in the wax layer combines the graphene layer and the metal layer into one, thereby obtaining the assembly;

[0035] Or use the second method to form a combination:

[0036] The graphene layer and the metal layer are stacked in sequence, and then the melted wax is brought into contact with the edge of the graphene layer during vacuum heating so that the wax penetrates into the graphene layer and / or between the graphene layer and the metal layer to obtain a second preform;

[0037] The second preform is subjected to hot pressing treatment to obtain the assembly.

[0038] After obtaining the assembly, the assembly is sliced ​​along the specified direction to obtain a thermally conductive matrix. In this step, the slicing can be performed completely parallel to the stacking direction, or it can be performed at a certain angle inclined to the stacking direction (i.e., the specified direction), generally not exceeding 45°, and preferably not exceeding 30°. These embodiments can all obtain a thermally conductive matrix with a longitudinal layer structure. The completely parallel method has the shortest thermal conductivity path, but since the bonding area is smaller, the overall bonding during the preparation process is not as good as the inclined method.

[0039] The heat-conducting substrate is subjected to surface metallization to form a metal plating layer, wherein the metal plating layer at least covers at least one cut surface of the heat-conducting substrate to fix the graphene layer and the metal layer together, and an uncovered area exists on the surface of the heat-conducting substrate, and the uncovered area exposes all edges of the wax layer;

[0040] The wax between the graphene layer and the metal layer is removed by at least heating, the uncovered area is used as a channel for removing the wax, and the uncovered area is then supplemented with a metal coating to obtain a graphene longitudinal heat conductor.

[0041] During the early research and development process, the inventor of the present invention used a colloid bonding method to stack the graphene layer and the metal layer into one. The stacking method can be stacking or winding, and then cutting along a specified direction perpendicular to the layer to obtain a plurality of thin sheets. At this time, the role of the colloid is to temporarily combine the metal layer and the graphene layer, and then the metal layer and the graphene layer are completely combined by forming a metal coating by electroplating or chemically plating the cut surface of the thin sheet. Finally, the colloid is carbonized or partially gasified through sintering and other treatment methods to prevent the colloid from affecting the thermal expansion coefficient of the thermal conductor.

[0042] However, in the actual research process, it was found that the presence of colloid and the carbonization process will lead to problems such as carbide penetration, which can easily have a serious impact on the surface quality and thermal conductivity. Therefore, it is necessary to develop a new technical solution that can obtain a high-performance composite thermal conductor with a certain degree of ease of processing while avoiding affecting the quality of the thermal conductor.

[0043] To solve the above problems, in some typical cases of the present invention, paraffin can be used to replace the adhesive layer. After the stack is cut, the surface is coated with a metal coating as a bonding layer, and the side of each paraffin layer is exposed. After the temperature is raised to the melting point of the paraffin, the paraffin with a high thermal expansion coefficient can be directly discharged due to its low viscosity, thereby avoiding the influence of carbonization of the adhesive during the high-temperature debonding process. The final product is a high-quality composite thermal conductor with no impurities on the surface. In addition, the process omits the high-energy consumption and high-pollution step of long-term high-temperature debonding (even if it is necessary to gasify and remove the wax in some preferred schemes, the heating temperature is lower, the heating time is shorter, and no decomposition products are produced), which not only reduces carbon emissions, but also allows the wax to be recycled, further reducing material costs.

[0044] Of course, the choice of wax is not limited to paraffin wax, other waxes with similar physical properties are also available.

[0045] The above scheme can avoid the generation of impurities on the surface of the material during the removal of the adhesive layer, and the process consumes low energy. The cost of wax is much lower than that of the adhesive film. In addition, the production efficiency of the product can be further improved. Since the wax has good fluidity after melting, the thickness of the adhesive layer can be significantly reduced by adjusting the pressure during the hot pressing process, and the density of the material is less affected after removal, thereby obtaining a higher thermal conductivity. In contrast, it is difficult to use the fluidity of the glue to significantly reduce the thickness of the adhesive layer by gluing, and the cross-sectional density of the final product is not as good as the technical solution proposed in the present invention, and there is a difference in thermal conductivity.

[0046] In addition, the solution provided by the present invention also has good processability. If there is a problem in the production process, the paraffin can be removed by heating it to the melting temperature of the paraffin, and secondary processing can be achieved by re-applying the paraffin. For example, if a defect occurs during the preparation process using the preparation method provided by the present invention, the graphene layers and metal layers can be separated by heating before slicing, and then the surface can be cleaned to reuse these materials, which can reduce the scrap rate and improve economic efficiency.

[0047] In some embodiments, the wax layer coating process may specifically include:

[0048] The molten wax is brought into contact with the surface of the graphene layer and the metal layer to form an adhesion layer;

[0049] The graphene layer and the metal layer having the adhesion layer are actively cooled to obtain the graphene layer and the metal layer with the wax layer covering the surface.

[0050] The above steps can be performed, for example, using an ordinary gluing machine, wherein the graphene layer and the metal layer are passed through the gluing machine respectively, and the melted paraffin in the glue tank of the gluing machine is applied to the surface of the graphene layer and the surface of the metal layer. The temperature in the gluing machine is maintained at 80°C-150°C. After gluing, the cold plate is quickly cooled to solidify the paraffin, so that the paraffin on the surface will be more uniform, and the paraffin will evenly form a solidified adhesive layer on the surface of the graphene layer and the copper foil to form a whole.

[0051] In some embodiments, the graphene layer and the metal layer are stacked in a manner including winding or lamination.

[0052] In some embodiments, the hot pressing treatment is performed in a negative pressure environment, and the surface pressure of the negative pressure environment is below -0.1 MPa.

[0053] In some embodiments, the hot pressing treatment includes a continuous first hot pressing stage and a second hot pressing stage; the temperature of the first hot pressing stage is 80-100°C, the time is 25-40min, the temperature of the second hot pressing stage is 120-135°C, the time is 25-40min, and the pressure applied to the preform gradually increases from the beginning of the first hot pressing stage to the end of the second hot pressing stage.

[0054] In some embodiments, the pressure applied to the preform is in the range of 0.8-8 MPa.

[0055] In the above-mentioned hot pressing treatment steps, the temperature and pressure are gradually increased, with the purpose of squeezing out more wax and maintaining only a thin layer to serve as interlayer bonding and reduce the gap after subsequent wax removal. Compared with colloid, due to the high-temperature fluidity of wax, the gap formed will be smaller, and the bonding force can achieve the same effect as colloid. Therefore, the gap can be reduced while ensuring that the same thin thermal conductor is cut out, thereby increasing the thermal conductive cross-sectional area per unit size, thereby improving the thermal conductivity performance.

[0056] In some embodiments, the slice thickness of the thermally conductive substrate may be 0.27-10 mm.

[0057] In order to ensure the overall strength, in some embodiments, the thickness of the metal coating needs to be controlled to be above 10 μm.

[0058] The specific method of forming the metal plating layer may be, for example, chemical plating, electroplating, physical plating, or a combination of the above methods, and the present invention is not limited thereto.

[0059] In some embodiments, the thermally conductive substrate has a first cut surface and a second cut surface facing away from each other, and the process of forming the metal coating and removing the wax specifically includes:

[0060] Shielding the first cut surface, and performing metal plating on the second cut surface, with the first cut surface serving as the uncovered area;

[0061] Heating the heat-conductive substrate so that the wax flows out from the first cut surface and / or is vaporized and removed;

[0062] or,

[0063] Completely plating the heat-conducting substrate so that the metal plating layer wraps the heat-conducting substrate;

[0064] Cutting the side surface of the heat conductive substrate (which can be understood as a side surface in a hexahedron that is not the first cut surface and the second cut surface and is not perpendicular to the specified direction) to remove at least part of the metal plating on the side surface, exposing all the side edges of the wax layer to form an exposed surface;

[0065] Heating the heat-conductive substrate to make the wax flow out from the exposed surface and / or be vaporized and removed;

[0066] The exposed surface may then be selectively subjected to secondary plating to fully cover the thermally conductive substrate.

[0067] In some embodiments, the preparation method may further include the following steps:

[0068] After the wax flows out by heating, the temperature is further increased to gasify and remove the remaining wax.

[0069] In some embodiments, the preparation method may further include the following steps:

[0070] After the heating, a solvent is used to perform ultrasonic cleaning on the remaining wax.

[0071] The inventors of the present invention have tried to directly use solvents for solvent ultrasonic cleaning, but due to the small gaps, it is difficult to completely penetrate, so the direct solvent cleaning method cannot completely remove the wax; the preferred removal method is to first heat and flow, then vaporize, and then perform solvent cleaning after vaporization, which can better remove the wax and finally have fewer residual impurities, so the impact on product performance is also smaller.

[0072] An embodiment of the present invention also provides a multi-layer graphene-metal composite longitudinal thermal conductor obtained by the above-mentioned preparation method, which includes a thermally conductive substrate composed of a metal layer and a graphene layer stacked in multiple cycles, and a metal coating bonded to the surface of the thermally conductive substrate, wherein the metal coating is bonded to the sides of the metal layer and the graphene layer so that the metal layer and the graphene layer are combined into the thermally conductive substrate; there is a gap between the metal layer and the graphene layer, and the gap does not contain carbonized residues or colloidal residues.

[0073] 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 do not limit the scope of the present invention.

[0074] Example 1

[0075] This embodiment illustrates a preparation process of a graphene-copper composite longitudinal thermal conductor, which is specifically as follows:

[0076] Step 1: Apply the melted paraffin in the glue tank of the glue machine to the surface of the graphene layer and the copper foil. The temperature in the glue machine is maintained at 80℃-150℃. After gluing, the cold plate is quickly cooled to solidify the paraffin. In this way, the paraffin on the surface will be more uniform. The paraffin evenly forms a solidified glue layer on the graphene layer and the copper foil surface to form a whole. Then use a fully automatic composite lamination machine to perform sequential lamination of the graphene layer and the copper foil through a mechanical arm, that is, a cycle structure of graphite layer-metal layer-graphite layer-metal layer..., and the lamination thickness is 1-200mm. The thickness of the paraffin after application here is between 40-60μm.

[0077] Step 2: Use a vacuum hot press to evacuate to -0.1MPa. The wax melts under negative pressure and can impregnate the graphite layer, which can significantly improve the integrity of the material. Then heat up to 85°C and keep warm for 30 minutes. Then heat up to 125°C and keep warm for 30 minutes. During the heating process, the hot press gradually increases the applied pressure. The pressure range is 5-50t. After reaching the set maximum pressure of 50t, stop pressurizing, stop heating, and cool down to remove the air and gaps between the films, so that the materials are completely fitted and air-free.

[0078] Step 3: Trim and slice the substrate using a single-wire cutting machine and a multi-wire cutting machine to obtain a thermally conductive substrate with a thickness of 0.27 mm, and perform solvent ultrasonic cleaning on the thermally conductive substrate.

[0079] Step 4: Electroless copper plating is performed on the surface of the thermal conductive substrate. The specific process route is sensitization-activation-electroless plating. In order to enhance the fluidity of the plating solution and increase the contact area between the plating solution and the material, the electroless plating is performed under ultrasonic conditions. The sensitization process is to form a reducing liquid film on the surface of the material. For example, it can be performed in a 30 g / L SnCl2 and 50 ml / L hydrochloric acid solution, soaked at room temperature for 30 min, and washed with deionized water several times until neutral; the activation solution consists of 0.25 g / L PdCl2 and 10 ml / L hydrochloric acid. This process can reduce Pd to the surface of the material, which promotes the copper plating reaction. Soaked at room temperature for 30 min, washed with deionized water several times until neutral. The composition of the chemical plating solution is 15 g / L copper sulfate pentahydrate, 15 g / L potassium sodium tartrate, 14 g / L EDTA, 0.01 g / L potassium ferrocyanide, 0.02 g / L 2,2'-bipyridine, 10 ml / L 36 wt% HCHO and 2 ml / L OP-10; the plating temperature is 50°C, the pH value is 12.5-13.0 (adjusted by NaOH), and the immersion is carried out under ultrasonic conditions for 10 min. After completion, it is washed with deionized water several times until neutral and placed in a vacuum oven for 24 hours, and the temperature is controlled at 40-45°C. The coating thickness is adjusted to 10μm by the number of chemical plating times. During copper plating, one end face of the thermal conductor is shielded and maintained as it is without chemical plating.

[0080] Step 5: Place the heat conductor in an oven for wax removal treatment, with a temperature range of 150-550°C. The specific process is to first heat it to 150°C, keep it warm for 30 minutes, and completely melt and precipitate the wax; then heat it to 200 degrees, keep it warm for 30 minutes, further promote the melting and precipitation of the wax, and then directly heat it to 550 degrees, keep it warm for 1 hour, directly gasify the wax, and completely remove the paraffin in the heat conductor. After completion, cool it to room temperature, take out the material, and ultrasonically clean it with ether, chloroform, volatile oil and other wax-soluble solutions to dissolve the residual wax, and then copper-plate the uncoppered end face again for thorough copper coating. Finally, a graphene / copper composite longitudinal heat conductor with high longitudinal thermal conductivity, low thermal expansion coefficient, good mechanical properties and no carbide precipitation on the surface is obtained.

[0081] The morphology of the graphene / copper composite longitudinal thermal conductor obtained in this embodiment is as follows Figure 2 As shown, the surface is smooth and bright, does not affect the effective heat conduction area, and the preparation success rate is extremely high, with almost no scrap.

[0082] Based on the method of this embodiment, the slice thickness is changed to measure the thermal diffusion coefficient, such as Figure 4 As shown, when the thickness of the final graphene / copper composite longitudinal thermal conductor is 2.93 mm, the thermal diffusion coefficient is 574.369 mm 2 / s, such as Figure 5 As shown, when the thickness of the graphene / copper composite longitudinal thermal conductor is 4.18 mm, the thermal diffusion coefficient is 582.090 mm 2 / s, usually the thickness change has little effect on the actual thermal diffusion coefficient, mainly because the thicker the thickness, the more accurate the measurement of the thermal diffusion coefficient of the material, that is, the measured value is closer to the actual value.

[0083] Comparative Example 1

[0084] As a comparison, this comparative example provides a preparation process of a graphene / copper composite longitudinal heat conductor, which is substantially the same as that of Example 1, except that:

[0085] Epoxy glue is used to replace paraffin as the bonding material of the graphene layer and the copper layer, and the graphene layer and the copper layer are bonded by hot pressing and then sliced, and then copper-plated. In the removal process, high-temperature sintering (400°C, 2h) is used to carbonize and eliminate the epoxy glue. The size of the slice, the thickness of the coating, and the process conditions are all the same as those in Example 1.

[0086] The surface state of the graphene / copper composite longitudinal heat conductor obtained in this comparative example is as follows Figure 3 As shown, surface discoloration, pits and other defects can be observed. These defects lead to an increase in the scrap rate on the one hand, and also affect the thermal conductivity on the other hand.

[0087] like Figure 6 As shown in Figure 2, when the thickness of the finished product is controlled at 3 mm, the thermal diffusion coefficient is 502.348 mm 2 / s.

[0088] Example 2

[0089] This embodiment is substantially the same as the first embodiment, and the main difference is that the method of forming the assembly is different, as shown below:

[0090] Step 1: Use a fully automatic composite lamination machine to laminate the graphene layer and copper foil through a mechanical arm, with a lamination thickness of 1-200mm. The thickness of the paraffin after application here is 40-60μm, preferably 40μm, and then select a certain amount of wax blocks, the amount of wax blocks is determined according to the mass of a layer of 40-60μm and the number of layers to be laminated, and then place the laminated graphene film and wax blocks together in a container close to the size of the graphene film, evacuate, and then heat to 85-150 degrees to dissolve and melt the paraffin, impregnate the graphite film layer, and then return to normal pressure, and repeat the above steps many times again, so that the paraffin fully penetrates into the graphite film layer.

[0091] Step 2: Then directly proceed to the hot pressing step (the steps in step 1 can be performed in a vacuum hot press), evacuate to -0.1MPa, and then pause the vacuum (when the vacuum is paused, the wax will begin to melt and gradually enter the graphite layer, better combining into a whole). Under the negative pressure state, the wax can be impregnated with the graphite layer after it melts, which can significantly improve the integrity of the material. Then heat it to 85℃, keep it warm for 30min, then heat it to 125℃, keep it warm for 30min, and gradually increase the pressure during hot pressing. The pressure range is 5-50t. After reaching the set maximum pressure of 50t, stop pressurizing, stop heating, and cool it down statically to remove the air and gap between the films, so that the material is completely fitted without air. After the hot pressing is completed, wait for the material to cool down and put it in a freezer with a freezing temperature below 0 degrees to demold the laminated graphite material from the container.

[0092] The remaining steps are the same as those in Example 1.

[0093] The corresponding graphene / copper composite longitudinal thermal conductor can be obtained by adopting different methods. Compared with the method of coating with a wax layer and then hot pressing and extruding in Example 1, the method of impregnating molten wax in this embodiment is more uniform, the wax used is less and more precise, and the process is easier to implement.

[0094] Specifically, the process of directly coating to form a wax layer and then solidifying to form a whole and then hot pressing the laminated sheets in Example 1 has the problem of large paraffin loss and long time consumption. In addition, during the wax coating process, the wax is easy to flow when the graphite film or metal film is rapidly solidified at room temperature, resulting in uneven distribution of wax on the surface, which may affect the subsequent interlayer adhesion. In the final cutting step, the interlayer bonding force at some positions may be insufficient, and the cut layers may be scattered, resulting in defective products. However, through the method adopted in this embodiment, the wax penetrates into the interlayer through the infiltration of the graphene film, which is more uniform, has better adhesion, and the interlayers of the cut thermal conductor are more neat, and it is also easier to eliminate the wax, reduce the process difficulty, and improve the yield rate and the appearance of the thermal conductor.

[0095] Example 3

[0096] This embodiment is substantially the same as the first embodiment, and the main difference is that the subsequent copper plating and paraffin removal steps are different, as shown below:

[0097] Step 5: Copper-plating the heat conductor completely, cutting the designated direction of the copper-plated heat conductor, cutting off the copper plated on the side of the heat conductor, the cutting thickness should be greater than the copper plating thickness, that is, the cutting thickness is greater than the metal plating layer of 1-50μm, and copper plating is performed again after the paraffin flows out. After the copper plating is completed, the material is taken out and ultrasonically cleaned with a solution of polar liquid ether, chloroform, volatile oil, etc. that can dissolve the wax, so that the residual wax is dissolved and precipitated, and then the uncopper-plated side is copper-plated again for thorough copper coating. Finally, a graphene / copper composite longitudinal heat conductor with high longitudinal thermal conductivity, low thermal expansion coefficient, good mechanical properties and no carbide precipitation on the surface is obtained.

[0098] The remaining steps are exactly the same as those in Example 1.

[0099] This embodiment removes the wax by cutting the exposed side after complete copper plating. Compared with the partial copper plating in Embodiment 1, it is easier to implement, the copper plating steps are simpler, and the copper plating is more complete. It is not easy to have the phenomenon of incomplete and uneven copper plating in a certain part. In addition, since the two cut surfaces in this embodiment are combined by copper plating, compared with the single cut surface copper plating method in Embodiments 1 and 2, the overall bonding is stronger, and it is less likely to become loose and scrapped during the process transfer, which can reduce the scrap rate to a certain extent.

[0100] Based on the above embodiments, it can be clearly seen that the preparation method provided in the embodiments of the present invention uses a wax that can be flowed and removed as a temporary adhesive material, forms a combination by stacking and hot pressing, and obtains a thermally conductive substrate after slicing, and removes the wax by heat treatment after coating it with a metal coating to combine it into a whole, so that there is no colloid residue or carbide between the metal layer and the graphene layer, and there is no surface defect caused by carbonization of the adhesive, so that a high-quality multi-layer graphene-metal composite longitudinal thermal conductor can be obtained.

[0101] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a multilayer graphene-metal composite longitudinal thermal conductor, characterized in that: include: Covering the surfaces of the graphene layer and the metal layer with a wax layer, and stacking the graphene layer and the metal layer containing the wax layer in a specified direction to obtain a first preform; The first preform is subjected to hot pressing treatment to press out part of the wax, so that the wax in the wax layer combines the graphene layer and the metal layer into one, thereby obtaining a combination; or, the graphene layer and the metal layer are stacked in sequence, and then the melted wax is brought into contact with the edge of the graphene layer during vacuum heating treatment, so that the wax penetrates into the graphene layer and / or between the graphene layer and the metal layer, thereby obtaining a second preform; The second preform is subjected to hot pressing to press out part of the wax, thereby obtaining a composite body; the composite body comprises a graphene layer and a metal layer cyclically stacked in a specified direction, and the graphene layer and the metal layer are bonded together by the wax; Slicing the assembly along the specified direction to obtain a thermally conductive matrix; The heat-conducting substrate is subjected to surface metallization to form a metal plating layer, wherein the metal plating layer at least covers at least one cut surface of the heat-conducting substrate to fix the graphene layer and the metal layer together, and an uncovered area exists on the surface of the heat-conducting substrate, and the uncovered area exposes all edges of the wax layer; At least heating is used to remove the wax between the graphene layer and the metal layer, and then the temperature is continuously increased to vaporize and remove the residual wax, and then a solvent is used to perform ultrasonic cleaning on the residual wax, and the uncovered area is used as a removal channel for the wax, and then the uncovered area is supplemented with a metal coating to obtain a graphene longitudinal heat conductor.

2. The preparation method according to claim 1, characterized in that: The wax layer coating process specifically includes: The molten wax is brought into contact with the surface of the graphene layer and the metal layer to form an adhesion layer; The graphene layer and the metal layer having the adhesion layer are actively cooled to obtain the graphene layer and the metal layer with the wax layer covering the surface.

3. The preparation method according to claim 1, characterized in that: The hot pressing treatment includes a first hot pressing stage and a second hot pressing stage in succession; The temperature of the first hot pressing stage is 80-100°C and the time is 25-40 minutes. The temperature of the second hot pressing stage is 120-135°C and the time is 25-40 minutes. From the beginning of the first hot pressing stage to the end of the second hot pressing stage, the pressure applied to the preform gradually increases.

4. The preparation method according to claim 3, characterized in that: The pressure applied to the preform is in the range of 0.8-8 MPa.

5. The preparation method according to claim 1, characterized in that: The slice thickness of the thermally conductive substrate is 0.27-10 mm.

6. The preparation method according to claim 1, characterized in that: The thickness of the metal plating layer is above 10 μm.

7. The preparation method according to claim 1, characterized in that: The heat conductive substrate has a first section and a second section facing away from each other, and the process of forming the metal coating and removing the wax specifically includes: Shielding the first cut surface, and performing metal plating on the second cut surface, with the first cut surface serving as the uncovered area; Heating the heat-conductive substrate so that the wax flows out from the first cut surface and / or is vaporized and removed; or, Completely plating the heat-conducting substrate so that the metal plating layer wraps the heat-conducting substrate; Cutting the side of the heat-conducting substrate to remove at least a portion of the metal plating on the side, exposing the entire side of the wax layer to form an exposed surface; Heating the heat-conductive substrate to make the wax flow out from the exposed surface and / or be vaporized and removed; The exposed surface is then subjected to secondary plating to fully cover the thermally conductive substrate.

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