Composite material, method for producing same, heat conduction member, and heat dissipation structure using same

Abstract

[Problem] To provide a means capable of selectively improving thermal conductivity in a surface direction of a sheet-shaped heat conduction member. [Solution] Provided is a laminate having a pair of metal layers and an intermediate layer which is disposed between the pair of metal layers and which comprises a carbon material, wherein the laminate serves as a composite material and is configured such that the long axis of the carbon material is aligned along the surface direction of the intermediate layer. The composite material is to be used, as a heat conduction member, for a heat dissipation structure or the like.

Description

Composite material and manufacturing method thereof, heat conducting member, and heat dissipation structure using the same

[0001] The present invention relates to a composite material, a manufacturing method thereof, a heat conducting member, and a heat dissipation structure using the same.

[0002] Semiconductor elements mounted in various electronic devices such as personal computers, light-emitting diode (LED) light sources, and thin displays, as well as other devices, generate heat during operation, and if the generated heat accumulates, it can adversely affect the operation of the semiconductor elements and peripheral devices. Furthermore, with the advancement of IoT, the development of high-speed communication networks, and the increasing intelligence of various devices, there is an ever-increasing demand for efficient heat dissipation from electronic devices. Similarly, with regard to secondary batteries used as power sources for driving automotive motors, there is also a growing demand for efficient heat dissipation during operation, from the perspectives of increasing capacity and reducing space required when mounted in the vehicle.

[0003] Various cooling means are used to dissipate heat generated by the operation of the various electronic devices and motor drive power supplies described above. For example, methods for cooling electronic components such as semiconductor elements include attaching a fan to the device to cool the air inside the device housing, and attaching a heat sink such as a heat dissipation fin or heat sink to the semiconductor element to be cooled. Furthermore, motor drive power supplies are cooled using cooling media such as air or water, as well as the above-mentioned fans and heat sinks.

[0004] Conventionally, when a heat sink is attached to a semiconductor element for cooling, a technique of providing a thermally conductive sheet between the semiconductor element and the heat sink has been proposed to efficiently dissipate heat from the semiconductor element. For example, International Publication No. 2018 / 030430 discloses a thermally conductive sheet having a structure in which multiple resin layers are laminated together, each containing a thermally conductive resin layer containing a thermally conductive plate-like filler such as boron nitride or exfoliated graphite, and in which, when the plane perpendicular to the laminated surface is the sheet surface, the long axes of the thermally conductive plate-like fillers are oriented at an angle of 60° or more relative to the sheet surface. According to the disclosure of International Publication No. 2018 / 030430, the above-described configuration can provide a thermally conductive sheet that achieves improved thermal conductivity while reducing the amount of thermally conductive plate-like filler used.

[0005] The thermally conductive sheet disclosed in International Publication No. 2018 / 030430 is intended solely to efficiently conduct heat in the thickness direction of the thermally conductive sheet, as can be seen from the thermal conductivity of the thermally conductive sheet in the thickness direction being 3 W / m·K or greater. Such a thermally conductive sheet is effective as a thermally conductive sheet to be placed between a semiconductor element and a heat sink, as described above. However, since the thermally conductive plate-like filler in this thermally conductive sheet is configured so that its major axis is oriented at an angle of 60 to 90° relative to the sheet surface, the thermal conductivity in the surface direction of the thermally conductive sheet is extremely low. Therefore, this thermally conductive sheet cannot be used in a heat dissipation structure that requires heat dissipation in the surface direction of the thermally conductive sheet.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a means for selectively improving the thermal conductivity of a sheet-shaped heat conducting member in the planar direction.

[0007] The present inventors have conducted extensive research in view of the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by forming a composite material from a laminate having a pair of metal layers and an intermediate layer containing a carbon material disposed between the pair of metal layers, with the major axis of the carbon material oriented in the plane direction of the intermediate layer, thereby completing the present invention.

[0008] That is, one aspect of the present invention is a composite material comprising a laminate having a pair of metal layers and an intermediate layer containing a carbon material disposed between the pair of metal layers, wherein the long axis of the carbon material is oriented in the plane direction of the intermediate layer.

[0009] Fig. 1 is a cross-sectional schematic diagram showing a cross section of a composite material according to one embodiment of the present invention. Fig. 2 is an enlarged view of a bent portion provided in a laminate constituting the composite material shown in Fig. 1. Fig. 3 is an explanatory diagram for explaining the structures of (a) single-layer graphene (graphene sheet) and (b) multi-layer graphene. Fig. 4 is a cross-sectional schematic diagram showing a cross section of a heat dissipation structure according to a conventional technique. Fig. 5 is a cross-sectional schematic diagram showing a cross section of a heat dissipation structure according to one embodiment of the present invention.

[0010] Composite Material One aspect of the present invention is a composite material comprising a laminate having a pair of metal layers and an intermediate layer containing a carbon material disposed between the pair of metal layers, the long axis of the carbon material being oriented in the plane direction of the intermediate layer. The composite material according to this aspect can selectively improve the thermal conductivity of a sheet-shaped heat conduction member in the plane direction. Here, "improving the thermal conductivity of the heat conduction member" means that by providing an intermediate layer to combine the metal material, the thermal conductivity in the plane direction is improved compared to when the heat conduction member is made solely of the metal material. While the use of a metal material with low intrinsic thermal conductivity inevitably leads to a low thermal conductivity of the heat conduction member, even in such cases, the effect of the present invention can be achieved if the presence of the intermediate layer improves the thermal conductivity of the heat conduction member in the plane direction.

[0011] Hereinafter, embodiments of the composite material according to the present invention will be described with reference to the drawings. However, the technical scope of the present invention should be defined based on the claims and is not limited to the following embodiments. Note that the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0012] Fig. 1 is a schematic cross-sectional view of a composite material 10 according to one embodiment of the present invention. Fig. 2 is an enlarged view of a bent portion 130 provided in a laminate 100 constituting the composite material 10 shown in Fig. 1.

[0013] As shown in FIG. 1 , a composite material 10 according to one embodiment of the present invention is composed of a laminate 100 including a pair of aluminum plates 110a and 110b, each constituting a metal layer, and an intermediate layer 120 disposed between the aluminum plates 110a and 110b. The aluminum plates 110a and 110b and the intermediate layer 120 constituting the laminate 100 extend from the front of the paper to the back of the paper in a direction perpendicular to the paper surface. The intermediate layer 120 contains a large number of multilayer graphenes 122, which are powdered carbon materials having a graphene layer structure. Furthermore, as shown in FIG. 2 , the multilayer graphenes 122 are arranged in the intermediate layer 120 such that the long axes of the multilayer graphenes 122 are oriented in the plane direction of the intermediate layer 120. Furthermore, in the composite material 10 according to this embodiment, the laminate 100 includes a plurality of bent portions 130. This provides the laminate 100 with an uneven shape. Note that since the bent portion 130 is formed by bending the laminate 100, in the bent portion 130 shown in FIG. 2, the aluminum plate 110a located inside the bent portion 130 is plastically deformed in the compression direction (solid arrow in FIG. 2), and the aluminum plate 110b located outside the bent portion 130 is plastically deformed in the tensile direction (dashed arrow in FIG. 2).

[0014] The multilayer graphene 122 included in the intermediate layer 120 of the composite material 10 having the configuration shown in FIGS. 1 and 2 has a structure (FIG. 3(b)) in which multiple single-layer graphenes (graphene sheets) shown in FIG. 3(a) are stacked in parallel. Graphene sheets have a structure in which carbon atoms having sp2 hybrid orbitals (sp2 carbons) are arranged in a two-dimensional honeycomb structure, and are therefore characterized by extremely high thermal conductivity in the in-plane direction. As a result, the composite material 10 of the embodiment shown in FIGS. 1 and 2 also has extremely high thermal conductivity in the in-plane direction, as adjacent multilayer graphenes 122 are arranged so that they are in contact with each other and the long axes of the multilayer graphenes 122 are oriented in the in-plane direction of the intermediate layer 120. In other words, the composite material 10 shown in FIGS. 1 and 2 has selectively enhanced thermal conductivity in the in-plane direction relative to the thermal conductivity in its thickness direction (the direction perpendicular to the in-plane direction).

[0015] The constituent materials of the composite material according to this embodiment will be described below.

[0016] [Metal Layer] The composite material according to this embodiment has a pair of metal layers. The metal layer may be any layer containing a metal, and from the viewpoint of excellent thermal conductivity, it is preferably a layer made of a metal or an alloy. Examples of metals constituting the metal layer include aluminum, nickel, iron, stainless steel, titanium, and copper. Other examples include clad materials of nickel and aluminum, and clad materials of copper and aluminum. The effects of the present invention are particularly pronounced when the thermal conductivity of the metal constituting the metal layer is lower than that of the intermediate layer. From this viewpoint, the metal constituting the metal layer preferably contains aluminum, copper, or titanium. Furthermore, from the viewpoints of excellent thermal conductivity and lightweight, it is particularly preferable that the metal constituting the metal layer contains aluminum. The thickness of the metal layer (single layer) is not particularly limited, but is preferably 0.2 to 4 mm, more preferably 0.5 to 3 mm, and even more preferably 1 to 2 mm.

[0017] [Intermediate Layer] The composite material according to this embodiment has an intermediate layer, which is disposed between the pair of metal layers and contains a carbon material.

[0018] (Carbon material) As the carbon material contained in the intermediate layer, conventionally known carbon materials can be used. Here, from the viewpoint of further improving the thermal conductivity in the planar direction, the carbon material preferably contains a powdered carbon material having a graphene laminate structure (hereinafter also referred to as a "flake carbon material"). However, as the carbon material, carbon black, fullerene, carbon nanotube, carbon nanofiber (vapor-grown carbon fiber (VGCF, etc.)), carbon nanohorn, carbon microcoil, carbon nanocoil, etc. may also be used.

[0019] A scaly carbon material has a structure in which a plurality of graphene layers are stacked, but there is no particular limit to the number of stacked graphene layers in the scaly carbon material. In this specification, a scaly carbon material having up to 10 stacked graphene layers is referred to as "graphene." Among graphenes, one having one stacked graphene layer is referred to as "single-layer graphene," and one having two to ten stacked graphene layers is referred to as "multilayer graphene." Furthermore, a scaly carbon material having 11 or more stacked graphene layers is referred to as "graphite."

[0020] Here, as an example, the number of stacked graphene layers in the scaly carbon material is preferably 2 to 100 layers, more preferably 2 to 50 layers, even more preferably 2 to 20 layers, and particularly preferably 2 to 10 layers. Therefore, in the composite material according to this embodiment, the scaly carbon material is preferably multilayer graphene or graphite, and more preferably multilayer graphene. As described above, multilayer graphene or graphite is characterized by particularly excellent thermal conductivity in the planar direction, and further, multilayer graphene is inexpensively available, and therefore is preferably used in the composite material according to this embodiment. Note that, as the scaly carbon material, only one type may be used alone, or two or more types may be used in combination.

[0021] The scaly carbon material has anisotropy with respect to its size. In this specification, when the surface with the largest area among the faces constituting the surface of the scaly carbon material is defined as the XY plane, the longest line segment connecting any two points on the outline of the scaly carbon material in the XY plane is defined as the longest diameter of the scaly carbon material. There are no particular restrictions on the value of the average long diameter of the scaly carbon material, but it is preferably 0.1 to 1000 μm, more preferably 0.1 to 500 μm, and even more preferably 0.1 to 100 μm. The value of the average long diameter of the scaly carbon material refers to the arithmetic mean diameter of the long diameters of several tens of scaly carbon material pieces contained in the intermediate layer 120.

[0022] Furthermore, in this specification, when the face with the largest area among the faces constituting the surface of the scaly carbon material is defined as the XY plane, the maximum dimension of the side constituting the XZ plane or the YZ plane is defined as the short diameter of the scaly carbon material. There are no particular restrictions on the value of the average short diameter of the scaly carbon material, but it is preferably 0.6 to 30 nm, more preferably 0.6 to 15 nm, and even more preferably 0.6 to 3 nm. The value of the average short diameter of the scaly carbon material refers to the arithmetic average value of the short diameters of several tens of scaly carbon material flakes contained in the intermediate layer.

[0023] The ratio of the major axis to the minor axis of the scaly carbonaceous material obtained as described above is defined as the aspect ratio. There are no particular restrictions on the average aspect ratio of the scaly carbonaceous material, but it is preferably greater than 1 and not more than 2,000,000, more preferably 5 to 900,000, and even more preferably 30 to 200,000. The average aspect ratio of the scaly carbonaceous material means the arithmetic mean value of the aspect ratios of several tens of scaly carbonaceous material flakes contained in the composite material.

[0024] The carbon material may be a commercially available product, a processed product of a commercially available product, or a self-prepared material. The manufacturing methods for the above-described multilayer graphene and graphite are widely known, and therefore a detailed description thereof will be omitted here. In recent years, technologies enabling mass production of scaly carbon materials such as multilayer graphene at low cost have been developed, reducing the procurement costs of scaly carbon materials. Therefore, the present embodiment is advantageous in that it allows for the low-cost production of composite materials (thermal conductive members) with excellent in-plane thermal conductivity. Since no technology existed previously that could produce such scaly carbon materials at low cost, it is believed that the motivation to produce composite materials (thermal conductive members) with excellent in-plane thermal conductivity by arranging carbon materials so that they are oriented in the in-plane direction of the film was absent in the prior art.

[0025] There are no particular restrictions on the content of the carbon material in the intermediate layer 120 constituting the composite material 10, but it is preferably 50 to 100 mass%, more preferably 70 to 100 mass%, even more preferably 80 to 100 mass%, particularly preferably 90 to 100 mass%, and most preferably 100 mass%, relative to 100 mass% of the total amount of the constituent components of the intermediate layer 120.

[0026] (Other Compounding Components) The intermediate layer 120 constituting the composite material 10 according to this embodiment essentially contains a carbon material, but may further contain other compounding components. However, since the compounding of other compounding components may reduce the thermal conductivity in the planar direction, it is also preferable not to compound other compounding components.

[0027] Examples of such other blending components include thermally conductive fillers other than carbon materials, binders, etc. For example, when the intermediate layer 120 contains a binder, the carbon materials contained in the intermediate layer 120 are firmly bound to one another. This improves the mechanical strength of the intermediate layer 120, making the thermally conductive network formed by the carbon materials less susceptible to disconnection. As a result, even when used for a long period of time, the decrease in thermal conductivity in the planar direction is minimized, and a composite material 10 with excellent durability is provided.

[0028] Examples of thermally conductive fillers other than carbon materials include carbides, nitrides, oxides, hydroxides, and metals. Examples of carbides include silicon carbide, boron carbide, aluminum carbide, titanium carbide, and tungsten carbide. Examples of nitrides include silicon nitride, boron nitride, aluminum nitride, gallium nitride, chromium nitride, tungsten nitride, magnesium nitride, molybdenum nitride, and lithium nitride. Examples of oxides include iron oxide, silicon oxide (silica), aluminum oxide (alumina) (including aluminum oxide hydrates (e.g., boehmite)), magnesium oxide, titanium oxide, cerium oxide, and zirconium oxide. Examples of oxides include transition metal oxides such as barium titanate, as well as metal ion-doped oxides such as indium tin oxide and antimony tin oxide. Examples of hydroxides include aluminum hydroxide, calcium hydroxide, and magnesium hydroxide. Examples of metals include copper, gold, nickel, tin, iron, and alloys thereof.

[0029] There are no particular restrictions on the content of the thermally conductive filler other than the carbon material in the intermediate layer 120, but it is preferably 1 to 20 mass %, more preferably 2 to 15 mass %, and even more preferably 3 to 10 mass %, relative to 100 mass % of the total amount of the constituent components of the intermediate layer 120.

[0030] Binders are used for the purpose of improving the binding properties of various blended components, protecting them, etc. Examples of binders include thermoplastic polymers such as polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyether nitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and hydrogenated products thereof, styrene-isoprene-styrene block copolymer and hydrogenated products thereof, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PC fluororesins such as vinylidene fluoride-hexafluoropropylene-based fluororubbers (VDF-HFP-based fluororubbers), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-HFP-TFE-based fluororubbers), vinylidene fluoride-pentafluoropropylene-based fluororubbers (VDF-PFP-based fluororubbers), Examples of suitable fluororubbers include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-PFP-TFE-based fluororubbers), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene-based fluororubbers (VDF-PFMVE-TFE-based fluororubbers), and vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), and epoxy resins. Of these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are preferably used.

[0031] There are no particular restrictions on the binder content in the intermediate layer 120, but as mentioned above, a resin binder is typically used as the binder. However, resin binders generally have low thermal conductivity. Therefore, when forming the composite material according to this embodiment, the incorporation of a binder increases thermal resistance and inhibits thermal conduction. From this perspective, the binder content is preferably 1 to 10 mass %, more preferably 1.5 to 5 mass %, and even more preferably 2 to 4 mass %, relative to 100 mass % of the total amount of the components of the intermediate layer 120.

[0032] The intermediate layer 120 preferably has a structure in which adjacent carbon materials are in contact with each other, as shown in FIG. 2 . This is because such contact between adjacent carbon materials can further improve thermal conductivity in the planar direction. Ideally, all carbon materials contained in the intermediate layer 120 are in contact with adjacent carbon materials, but not all carbon materials are necessarily in contact with adjacent carbon materials. In a preferred embodiment of this aspect, when a cross section perpendicular to the planar direction of the intermediate layer 120 is observed, it is preferable that the carbon materials are connected to adjacent carbon materials, thereby forming a thermally conductive network from one end of the planar direction of the intermediate layer 120 to the other end. Quantitatively speaking, it is preferable that, of the particles of the carbon material contained in the intermediate layer 120, preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, particularly preferably 40% or more, and most preferably 50% or more are in contact with adjacent carbon materials.

[0033] The composite material 10 according to the present embodiment is also characterized in that the carbon material is arranged so that its major axis is oriented in the plane direction of the intermediate layer 120, as shown in FIG. 2 . Here, the "major axis of the carbon material" refers to an axis of the carbon material oriented in any direction on the XY plane, and corresponds to the axis in the XY plane in a cross section perpendicular to the plane direction of the intermediate layer 120. Whether the major axis of the carbon material is oriented in the plane direction of the intermediate layer 120 is determined herein from the value of the "orientation rate" measured in the Examples section described later. Specifically, if the orientation rate value is less than 45°, the requirement that "the major axis of the carbon material is oriented in the plane direction of the intermediate layer" is met. The value of this orientation rate is not particularly limited as long as it is less than 45°, but is preferably 40° or less, more preferably 35° or less, even more preferably 30° or less, even more preferably 25° or less, particularly preferably 20° or less, and most preferably 15° or less. If the orientation rate value is within these ranges, sufficiently excellent thermal conductivity in the plane direction can be achieved. On the other hand, there is no particular limitation on the lower limit of the orientation rate, and it is ideally 0°, but in reality, the orientation rate takes a value greater than 0° due to overlapping of the carbon material. From the viewpoint of ease of production, the lower limit of the orientation rate is preferably 3° or more.

[0034] Here, the thermal conductivity of air is very low. For this reason, it is preferable that the intermediate layer 120 according to this embodiment does not contain much air. To express this quantitatively, in the intermediate layer 120 constituting the composite material 10 according to this embodiment, the proportion of voids in a cross section perpendicular to the plane direction is preferably 20% or less, more preferably 19% or less, even more preferably 18% or less, particularly preferably 17% or less, and most preferably 16% or less, as a value per unit area. On the other hand, there is no particular restriction on the lower limit of this void proportion, but it is usually 5% or more. In this specification, the value of the void proportion mentioned above is a value measured by the following method.

[0035] (Method for measuring the porosity of the intermediate layer (proportion of voids in a cross section perpendicular to the surface direction)) A cross section perpendicular to the surface direction of the intermediate layer is observed using a scanning electron microscope (SEM), and the area of ​​voids present in a 20 μm × 20 μm observation field in the obtained SEM observation image is measured. The porosity is then calculated as a percentage of the void area measured in this way relative to the area of ​​the observation field (area of ​​voids / area of ​​observation field × 100 [%]). Note that ion milling is performed as a preparation process for the cross section used for SEM observation.

[0036] There are no particular limitations on the film thickness of the intermediate layer 120 constituting the composite material 10 according to this embodiment, and it can be appropriately determined depending on the desired thermal conductivity of the composite material, the size and physical properties of the installation surface of the substrate or heat source on which the composite material is installed as a thermally conductive member, etc. As an example, the film thickness of the intermediate layer 120 is preferably 100 to 1000 μm, more preferably 200 to 900 μm, even more preferably 300 to 800 μm, and particularly preferably 400 to 700 μm.

[0037] [Structure of Composite Material] As described above with reference to Figure 2, the laminate of the metal layer and the intermediate layer preferably has a bent portion. This allows the carbon material contained in the intermediate layer to be oriented in the planar direction near the bent portion. Note that the laminate may have many bent portions so as to have an uneven shape as shown in Figure 1, but it is sufficient that at least one bent portion is present.

[0038] The thermal conductivity in the in-plane direction of the composite material according to this embodiment is not particularly limited, but is preferably 225 W / m K or more, more preferably 235 W / m K or more, even more preferably 250 W / m K or more, and particularly preferably 275 W / m K or more. In this specification, the thermal conductivity in the in-plane direction of the composite material is a value measured by the method described in the Examples section below.

[0039] <<Method of Manufacturing Composite Material>> There are no particular limitations on the method of manufacturing the composite material according to the present embodiment, and any manufacturing method that can realize a composite material having the structure described above, specifically, that can arrange a carbon material so that it is oriented in the plane direction of an intermediate layer arranged between a pair of metal layers, can be appropriately adopted.

[0040] As an example, the composite material according to this embodiment can be produced by disposing a carbon material, which is a constituent material of an intermediate layer, between a pair of metal layers and applying a shear force in the plane direction to the carbon material. That is, another embodiment of the present invention also provides a method for producing a composite material. The production method includes subjecting a laminate having a pair of metal layers and an intermediate layer sandwiched between the pair of metal layers and containing a carbon material to a roll press process or a bending process, thereby applying a shear force in the plane direction to the carbon material contained in the intermediate layer. According to this production method, the major axis of the carbon material can be oriented in the plane direction of the intermediate layer by simple means.

[0041] Here, the details and preferred embodiments of the metal layer and the carbon material are as described above. There are also no particular limitations on the method for obtaining a laminate by disposing the carbon material between a pair of metal layers.

[0042] In this manufacturing method, as described above, a laminate in which a carbon material is disposed between a pair of metal layers is subjected to roll pressing or bending. This applies a shear force in the plane direction to the carbon material contained in the intermediate layer. As a result, as shown in Figure 2, the major axis of the carbon material is oriented in the plane direction of the intermediate layer, and a composite material according to one embodiment of the present invention is obtained.

[0043] As used herein, "roll press processing" refers to processing using a roll press. A roll press is a machine equipped with at least a pair of cylindrical pressure rolls arranged parallel to each other with their outer peripheral surfaces facing each other, and a rotation drive mechanism for the rolls. In roll press processing, a laminate of the pair of metal layers and an intermediate layer disposed therebetween is sandwiched between the pair of rolls and passed through them to apply pressure. This pressure applies a shear force in the plane direction to the carbon material contained in the intermediate layer. There are no particular limitations on the material and size of the rolls, the type of rotation mechanism, or the arrangement of the rolls and rotation mechanism. There are also no particular limitations on the direction in which the laminate is discharged from between the pair of rolls, and it may be, for example, horizontal or vertical.

[0044] The linear pressure applied by the roll press to the laminate in roll press processing is not particularly limited, but is preferably 1 to 100 MPa, more preferably 10 to 80 MPa, and even more preferably 20 to 60 MPa. When a roll press is used, the linear pressure applied by the roll press to the laminate means a linear pressure calculated from the load obtained by a load cell attached to the roll press and the thickness of the laminate after pressing.

[0045] Meanwhile, in this specification, the term "folding" refers to a type of press working in which the laminate described above is bent without making any cuts, and the portion bent by the bending process becomes the bent portion 130 shown in FIGS. 1 and 2 . Furthermore, particularly near the bent portion 130, a shear force is applied in the plane direction to the carbon material contained in the intermediate layer. As a result, as shown in FIG. 2 , the long axis of the carbon material is oriented in the plane direction, particularly near the bent portion 130. In addition, the metal layer located inside the bent portion 130 undergoes plastic deformation in the compression direction, and the metal layer located outside the bent portion 130 undergoes plastic deformation in the tensile direction.

[0046] <<Uses of Composite Material (Heat Conduction Member and Heat Dissipation Structure)>> The composite material according to one embodiment of the present invention described above has excellent thermal conductivity in the planar direction. Therefore, this excellent thermal conductivity can be utilized as a heat conduction member. Furthermore, this heat conduction member can be disposed near a heat source to form a heat dissipation structure. That is, according to yet another embodiment of the present invention, a heat conduction member is provided that includes the composite material according to one embodiment of the present invention described above. Furthermore, a heat dissipation structure is also provided that includes a heat source and the heat conduction member according to the embodiment disposed so as to contact the heat source. Below, the heat dissipation structure according to this embodiment will be described with reference to the drawings, using as an example a heat dissipation structure for dissipating heat generated from a superbright light-emitting diode (LED) as a heat source.

[0047] In recent years, high-intensity light-emitting diode (LED) lamps have been adopted for the purpose of extending the lifespan and saving power in automotive headlights, and heat sinks are used to cool these high-intensity LEDs. These heat sinks are usually made of metal materials with high thermal conductivity, such as pure aluminum or aluminum alloys, and have a shape such as die-casting, with multiple fins arranged in a row on a flat heat-receiving surface.

[0048] FIG. 4 is a schematic cross-sectional view showing a cross section of such a heat dissipation structure according to the prior art.

[0049] As shown in Figure 4, a conventional heat dissipation structure 1 is used to cool a high-brightness LED module 4 with an output of, for example, 1 W or more. Its basic configuration combines a heat transfer plate 3 made of a good thermal conductor metal or carbon material with a heat sink body 2 made of a thermally conductive resin. The LED module 4 has a structure in which a light emitter 8, which incorporates multiple LED elements and is integrally formed with a lens, is held in the center of a substrate 7, and the substrate 7 is bonded to the heat receiving surface 5 arranged on the heat sink body 2. The heat dissipation structure 1 shown in Figure 4 transfers heat generated from a small heat source when the LED module 4 is driven to the entire heat receiving surface 5 through the heat transfer plate 3 made of a good thermal conductor metal or carbon material and disposed along the heat receiving surface 5 to which the LED module 4 is bonded. The heat is then dissipated into the air by the fins 6 of the heat sink body 2, which are made of a thermally conductive resin with low thermal capacity and high emissivity, thereby suppressing the temperature rise of the LED module 4 (i.e., cooling the LED module 4). The heat dissipation structure 1 having such a configuration is capable of dissipating heat generated by the LED module 4 to a certain extent. However, there is a problem of poor space efficiency because the heat sink body 2 occupies a large volume in the heat dissipation structure 1. Furthermore, because the heat sink body 2 is made of a metal material such as pure aluminum or an aluminum alloy, the heat dissipation structure 1 can also be a factor in increasing the weight of the automobile when applied to, for example, an automobile headlight.

[0050] On the other hand, FIG. 5 is a schematic cross-sectional view showing a cross section of a heat dissipation structure according to one embodiment of the present invention.

[0051] As shown in Fig. 5 , the heat dissipation structure 1 according to one embodiment of the present invention does not include the heat sink body 2, as compared to the heat dissipation structure shown in Fig. 4 . Meanwhile, a composite material 10 according to one embodiment of the present invention (see Fig. 1 ) is disposed as a thermally conductive member, covering the entire surface of the heat transfer plate 3 on the side where the LED module 4 is disposed. With this configuration, the heat dissipation structure 1 according to the embodiment shown in Fig. 5 can rapidly transfer heat generated from a small heat source by driving the LED module 4 in the planar direction of the composite material 10 and efficiently dissipate the heat to the outside. Furthermore, because the heat dissipation structure 1 does not include the heat sink body provided in the heat dissipation structure according to the embodiment shown in Fig. 4 , it has the significant advantage of being able to significantly reduce the volume and weight of the heat dissipation structure.

[0052] Although not shown in FIG. 5 , it is preferable that the heat dissipation structure 1 further includes a heat sink arranged in contact with the composite material 10 as a thermally conductive member. By arranging such a heat sink, more efficient heat dissipation can be achieved. The term "heat sink" as used herein refers to a component that can more efficiently dissipate heat conducted from a heat source (LED module 4 in FIG. 5 ) to the outside via the composite material 10. Examples of such heat sinks include heat sinks, heat pumps, and metal housings for electronic devices. When a heat sink is further arranged on the composite material 10, it is preferable that the heat sink be arranged in a position that does not face the heat source via the composite material (thermally conductive member) arranged in contact with the heat source (i.e., the heat source and the heat sink are spaced apart in the planar direction of the composite material (thermally conductive member)), in order to fully utilize the excellent thermal conductivity of the composite material 10 in the planar direction. In this case, the distance between the heat source and the heat sink in the planar direction of the composite material is preferably 1 cm or more, more preferably 5 cm or more, even more preferably 10 cm or more, particularly preferably 15 cm or more, and most preferably 20 cm or more.

[0053] The above describes a heat dissipation structure according to one embodiment of the present invention, using a heat dissipation structure having a high-brightness light-emitting diode (LED) as a heat source as an example. However, the heat dissipation structure according to this embodiment can be used for the purpose of dissipating heat generated by a wide variety of heat sources, without being limited to this.

[0054] Examples of such heat sources include the above-mentioned LED modules, as well as various lasers (sensors) (conventional heat dissipation means are aluminum plates or combinations thereof with cooling fins, Peltier elements, or chiller water cooling); high-performance infrared cameras (IR) (conventional heat dissipation means are aluminum plates or combinations thereof with cooling fins, Peltier elements, or chiller water cooling); head-up displays (HUDs) (conventional heat dissipation means are combinations of heat sinks and spreaders); smartphone elements and batteries (conventional heat dissipation means are air cooling, heat dissipation sheets, or combinations of heat sinks and spreaders); digital camera elements and batteries (conventional heat dissipation means are combinations of heat sinks, spreaders, and housings); and personal computers (PCs). elements and batteries (wherein the conventional heat dissipation means is a combination of a fan, heat sink, spreader, and housing); elements of electronic control units (ECUs) for vehicles, etc. (wherein the conventional heat dissipation means is a combination of a heat sink, spreader, and housing); elements of insulated gate bipolar transistors (IGBTs), which are the main conversion elements of high-power inverters (wherein the conventional heat dissipation means is a combination of a heat sink, spreader, and housing); rotating parts of motors (wherein the conventional heat dissipation means is a combination of a fan and heat sink, or a combination of either of these with water cooling); light source lamps for thin displays (wherein the conventional heat dissipation means is a heat sink); and large-capacity in-vehicle batteries (wherein the conventional heat dissipation means is a heat dissipation sheet, heat dissipation material, or a combination of air cooling or water cooling with a fan and heat sink).

[0055] By applying the heat dissipation structure according to this embodiment to these heat sources, it is possible to replace the heat dissipation means conventionally applied to each heat source with the composite material (thermal conductive member) according to one embodiment of the present invention. As a result, for example, if a heat sink as a conventional heat dissipation means can be eliminated as described with reference to FIG. 5, the weight and volume of the heat dissipation structure can be significantly reduced. Furthermore, by replacing conventional heat dissipation means such as fans, air cooling, or water cooling with the composite material (thermal conductive member) according to one embodiment of the present invention, it is expected that the weight and volume of the heat dissipation structure can also be significantly reduced compared to a heat dissipation structure equipped with conventional heat dissipation means.

[0056] Furthermore, by manufacturing the composite material (thermal conductive member) by press processing such as bending so that it has an uneven shape suitable for the shape of the various heat sources described above, it is possible to obtain a composite material (thermal conductive member) with a shape that conforms to the shape of the heat source. As a result, it is possible to more efficiently utilize the space around the heat source to achieve heat dissipation, which has the advantage of significantly improving the degree of freedom in space utilization in products such as vehicles equipped with a heat source. In other words, the above-mentioned "uneven shape" is not limited to the regular uneven shape shown in Figure 1, but may be formed irregularly.

[0057] The following embodiments are also included within the scope of the present invention: a composite material according to claim 1 having the features of claim 2; a composite material according to claim 2 having the features of claim 3; a composite material according to any one of claims 1 to 3 having the features of claim 4; a composite material according to any one of claims 1 to 4 having the features of claim 5; a composite material according to claim 5 having the features of claim 6; a composite material according to any one of claims 1 to 6 having the features of claim 7; a heat conduction member comprising a composite material according to any one of claims 1 to 7; and a heat dissipation structure comprising a heat conduction member according to claim 8.

[0058] The present invention will be described in more detail below with reference to examples, although the technical scope of the present invention is not limited to the following examples.

[0059] Example 1-1: Two commercially available aluminum plates (A1050, thicknesses of 2.0 mm and 1.0 mm) were prepared and cut into a size of 60 × 200 mm. These two aluminum plates were then stacked and placed inside a flat press, and pressed at a pressure of 30 MPa to obtain a laminated aluminum plate (thickness 3.0 mm).

[0060] [Comparative Example 1-2] Two commercially available aluminum plates (A1050, thicknesses of 2.0 mm and 1.0 mm) were prepared and cut into a size of 60 × 200 mm. Meanwhile, 1.7 g of commercially available graphene (manufactured by Kanto Chemical Co., Inc., including multilayer graphene) was weighed and evenly placed between the two aluminum plates prepared above. The resulting laminate was then placed inside a flat press and pressed at a pressure of 30 MPa to obtain a composite material (thickness 3.5 mm) having a configuration of aluminum plate / graphene layer / aluminum plate.

[0061] [Example 1-1] Two commercially available aluminum plates (A1050, thicknesses of 2.0 mm and 1.0 mm) were prepared and cut into a size of 60 × 200 mm. Meanwhile, 1.7 g of commercially available graphene (manufactured by Kanto Chemical Co., Inc., including multilayer graphene) was weighed and evenly placed between the two aluminum plates prepared above. The resulting laminate was then placed inside a flat press and pressed at a pressure of 30 MPa. Next, further pressure was applied by passing it through a roll press (linear pressure of 50 MPa) to obtain a composite material (thickness 3.4 mm) having a configuration of aluminum plate / graphene layer / aluminum plate.

[0062] Example 1-2 Two commercially available aluminum plates (A1050, thicknesses of 2.0 mm and 1.0 mm) were prepared and cut into a size of 60 × 200 mm. Meanwhile, 1.7 g of commercially available graphene (manufactured by Kanto Chemical Co., Inc., including multilayer graphene) was weighed and evenly placed between the two aluminum plates prepared above. The resulting laminate was then placed inside a mold capable of forming a concave-convex shape and press-molded at a pressure of 30 MPa to obtain a composite material (thickness 3.4 mm) having an aluminum plate / graphene layer / aluminum plate configuration with the concave-convex shape shown in FIG. 1 .

[0063] Example 1-3 A composite material (thickness: 3.7 mm) having a structure of aluminum plate / graphene layer / aluminum plate having an uneven shape as shown in FIG. 1 was obtained by the same method as in Example 1-2 described above, except that the amount of graphene used was 3.4 g.

[0064] Example of Preparation of Composite Material Using Copper Plate Comparative Example 2 A commercially available copper plate (thickness: 0.5 mm) was prepared and cut into two pieces measuring 50 × 300 mm. These two copper plates were then stacked together and placed inside a flat press, and pressed at a pressure of 30 MPa to obtain a laminated copper plate (thickness: 1.0 mm).

[0065] Example 2 A commercially available copper plate (thickness: 0.5 mm) was prepared and cut into two pieces measuring 50 × 300 mm. Meanwhile, 1.2 g of commercially available graphene (manufactured by Kanto Chemical Co., Inc., including multilayer graphene) was weighed and evenly placed between the two copper plates prepared above. The resulting laminate was then placed inside a mold capable of forming a concave-convex shape and press-molded at a pressure of 30 MPa to obtain a composite material (thickness: 1.3 mm) having a copper plate / graphene layer / copper plate structure with the concave-convex shape shown in FIG. 1 .

[0066] [Comparative Example 3] A commercially available titanium plate (thickness 0.3 mm) was prepared and cut into two pieces measuring 50 × 300 mm. These two titanium plates were then stacked and placed inside a flat press, and pressed at a pressure of 30 MPa to obtain a laminated titanium plate (thickness 0.6 mm).

[0067] Example 3: A commercially available titanium plate (0.3 mm thick) was prepared and cut into two pieces measuring 50 × 300 mm. Meanwhile, 1.2 g of commercially available graphene (manufactured by Kanto Chemical Co., Inc., including multilayer graphene) was weighed and evenly distributed between the two titanium plates prepared above. The resulting laminate was then placed inside a mold capable of forming a concave-convex shape and press-molded at a pressure of 30 MPa to obtain a composite material (0.9 mm thick) having a titanium plate / graphene layer / titanium plate configuration with the concave-convex shape shown in FIG. 1 .

[0068] <<Evaluation Example of Composite Material>> [Measurement of Orientation Ratio of Graphene in Intermediate Layer of Composite Material] For the composite materials produced in Comparative Example 1-2, Example 1-1 to Example 1-3, Example 2, and Example 3 described above, the orientation ratio of graphene was evaluated by the following method.

[0069] Specifically, the composite material was disassembled to remove the intermediate layer, and a pole figure measurement of the graphite (002) plane in the intermediate layer was performed using a micro-X-ray diffraction measurement device. The longitudinal direction (MD) and transverse direction (TD) of the composite material in the obtained pole figure were defined, and the half-width of the diffraction intensity peak was calculated from the cross-sectional profile of the pole figure in the transverse direction (TD), which was used as the orientation ratio. By measuring the half-width of the diffraction intensity peak using such a pole figure while varying the incident angle θ during X-ray diffraction measurement from 0 to 90°, the orientation ratio can be calculated using the following mechanism. That is, if the graphene orientation is random, graphene corresponding to each incident angle θ is uniformly present, resulting in a broad (flat) diffraction intensity peak. On the other hand, if the graphene orientation is aligned in a specific direction, the diffraction intensity is detected biased toward a specific region of the incident angle θ, resulting in a sharp diffraction intensity peak. In this measurement method, a smaller value of the orientation rate means a higher degree of orientation of the long axis of graphene in the plane direction of the composite material (intermediate layer).

[0070] As a result of the above measurement, the orientation rate of graphite in the intermediate layer of the composite material produced in each of the examples was less than 45°. On the other hand, in the intermediate layer of the composite material produced in Comparative Example 1-2, the orientation rate could not be calculated by the above method because the orientation of graphene was random.

[0071] Furthermore, when the intermediate layers of the composite materials prepared in all the examples were observed using a scanning electron microscope (SEM), it was confirmed that adjacent graphenes were in contact with each other.

[0072] [Evaluation of Thermal Conductivity] The thermal conductivity of the composite materials (comparison example 1-1, comparison example 2, and comparison example 3 are laminated metal plates) produced in the above-mentioned comparative examples and examples was evaluated by the following method to evaluate their performance when used as heat conduction members.

[0073] First, the cross-sectional area of ​​each sample was calculated from its thickness. Next, the sample was placed in a thermostatic chamber at 25°C, and a heat source was installed at one end (0 mm position). Thermocouples were also installed at positions 25 mm, 50 mm, 75 mm, and 100 mm from the end where the heat source was installed. 5.0 W of heat was generated from the heat source, and the temperature of each thermocouple was measured when it stabilized. The thermal conductivity was calculated from the temperature of the thermocouple located 50 mm from the heat source according to the following formula. The results are shown in Table 1 below.

[0074] (Thermal conductivity calculation formula) Thermal conductivity [W / m K] = Heat transfer amount [W] x distance [m] x (1 / cross-sectional area [m ２ ])×(1 / temperature difference [K])

[0075]

[0076] The results shown in Table 1 reveal that the composite materials of each example according to one embodiment of the present invention have a configuration in which the long axis of graphene in the intermediate layer is oriented in the plane direction, resulting in very high thermal conductivity in the plane direction. This suggests that the composite material according to the present invention exhibits excellent performance as a thermal conductive member. In contrast, the laminated aluminum plate of Comparative Example 1 exhibited the thermal conductivity of an aluminum plate because it did not have an intermediate layer containing graphene. Furthermore, the composite material of Comparative Example 2, despite having an intermediate layer containing graphene, exhibited a random orientation rate, resulting in a thermal conductivity that was actually lower than that of the laminated aluminum plate.

[0077] Furthermore, it was found that molding the composite material to have a concave-convex shape further improved the thermal conductivity in the in-plane direction. It was also shown that regardless of the metal used to compose the metal layer, the addition of a specific intermediate layer can improve the thermal conductivity when compared with systems using the same metal.

[0078] This application is based on Japanese Patent Application No. 2023-106671, filed on June 29, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0079] REFERENCE SIGNS LIST 1 Heat dissipation structure, 2 Heat sink body, 3 Thermal conduction plate, 4 LED module, 5 Heat receiving surface, 6 Fin, 7 Substrate, 8 Light emitter, 10 Composite material, 100 Laminate, 110a, 110b Aluminum plate (metal layer), 120 Intermediate layer, 122 Multilayer graphene, 130 Bent portion.

Claims

1. A composite material comprising a laminate having a pair of metal layers and an intermediate layer containing a carbon material disposed between the pair of metal layers, wherein the long axis of the carbon material is oriented in the plane direction of the intermediate layer.

2. The composite material of claim 1, wherein said laminate has at least one bend.

3. The composite material according to claim 2, wherein, at the bent portion, one of the pair of metal layers is plastically deformed in a compressive direction and the other is plastically deformed in a tensile direction.

4. The composite material according to claim 1 or 3, wherein the laminate has an uneven shape.

5. The composite material according to claim 1 or 3, wherein the carbon material is a powdered carbon material having a graphene layer structure.

6. The composite material of claim 5, wherein the carbon material is multi-layer graphene or graphite.

7. The composite material according to claim 1 or 3, wherein the constituent material of the metal layer includes aluminum, copper or titanium.

8. A heat conducting member comprising the composite material according to claim 1 or 3.

9. A heat dissipation structure comprising: a heat source; and the heat conduction member according to claim 8, arranged in contact with the heat source.

10. A method for producing a composite material, comprising: subjecting a laminate having a pair of metal layers and an intermediate layer containing a carbon material sandwiched between the pair of metal layers to roll pressing or bending to apply a shear force in the plane direction to the carbon material contained in the intermediate layer.

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