Thermal conductivity sheet

Abstract

To provide a thermal conductivity sheet that has low hardness and high thermal conductivity.SOLUTION: The present invention relates to a thermal conductivity sheet 1 that includes a sheet-shaped rubber-like elastomer 10 and carbon fibers 20 embedded diagonally to the thickness direction of the rubber-like elastomer 10, and the carbon fibers 20 are amorphous carbon fibers and both ends 21, 22 are exposed on the surfaces 11, 12 of the rubber-like elastomer 10, and a plurality of rubber-like elastomers 10 containing the carbon fibers 20 are laminated with a layer of silicone rubber 30 sandwiched between them.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a thermally conductive sheet. [Background technology]

[0002] Control systems for automobiles, aircraft, ships, and home and commercial electronic devices are becoming more precise and complex, and as a result, the integration density of small electronic components on circuit boards is steadily increasing. As a result, there is a strong demand for a solution to the problems of electronic component failure and shortened lifespan caused by heat generation around the circuit board.

[0003] In order to realize rapid heat dissipation from a circuit board, a method of interposing a thermally conductive sheet between a heat source such as a circuit board and a cooling member such as a heat sink or a cooling fan has been known. As a thermally conductive sheet, one in which a thermally conductive filler is dispersed in a rubber-like elastic body such as resin or rubber is widely used. In recent years, a thermally conductive sheet in which carbon fibers as a thermally conductive filler are oriented in the thickness direction of the thermally conductive sheet has also become known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-56299 A Summary of the Invention [Problem to be solved by the invention]

[0005] In such a thermally conductive sheet, further improvement in thermal conductivity is required. In general, in order to obtain a high thermal conductivity, the filling rate of the thermally conductive filler such as carbon fiber contained in the thermally conductive sheet is increased. However, when the filling rate of the thermally conductive filler is increased, the thermally conductive sheet may become hard and lose flexibility. When the thermally conductive sheet is hard, the adhesion to the heat source and the cooling member may decrease, and the thermal conductivity may decrease. In addition, the conventionally known thermally conductive sheet as described above is manufactured by slicing a flexible sheet precursor formed so that the carbon fibers are oriented in one direction in the plane, on a plane perpendicular to the orientation direction. The thermally conductive sheet manufactured in this way has a large surface roughness on the cut surface, so that the thermal resistance at the contact interface with the heat source and / or cooling member increases, and the thermal conductivity in the thickness direction of the thermally conductive sheet may decrease. This applies not only to circuit boards but also to other heat sources such as electronic components, electronic device bodies, and battery cells.

[0006] In order to solve the above problems, an object of the present invention is to provide a thermally conductive sheet that can achieve low hardness and high thermal conductivity. [Means for solving the problem]

[0007] (1A) In one embodiment for achieving the above object, a thermally conductive sheet comprises a sheet-like rubber-like elastomer and carbon fibers embedded obliquely to the thickness direction of the rubber-like elastomer, the carbon fibers being amorphous carbon fibers having both ends exposed on the surface of the rubber-like elastomer, and a plurality of the rubber-like elastomers containing the carbon fibers being laminated with a layer of silicone rubber sandwiched therebetween. (2A) In the thermally conductive sheet according to another embodiment, the carbon fibers may be embedded so as to be oriented at an angle greater than 0° and equal to or less than 70° with respect to the thickness direction. (3A) In another embodiment of the thermally conductive sheet, the carbon fibers may preferably have a larger diameter at both ends exposed on the surface of the rubber-like elastomer than the diameter of the region embedded in the rubber-like elastomer. (4A) In the thermally conductive sheet according to another embodiment, the rubber-like elastic body may preferably be silicone rubber. (5A) In the thermally conductive sheet according to another embodiment, preferably, the surface roughness Ra of the surface perpendicular to the thickness direction may be 1.0 μm or more and 1.8 μm or less. (1) In order to achieve the above object, one embodiment of a thermally conductive sheet is a thermally conductive sheet comprising a sheet-like rubber-like elastomer and carbon fibers embedded in a direction oblique to the thickness direction of the rubber-like elastomer, the carbon fibers being amorphous carbon fibers having both ends exposed on the surface of the rubber-like elastomer. (2) In the thermally conductive sheet according to another embodiment, the carbon fibers may be embedded and oriented at an angle greater than 0° and equal to or less than 70° with respect to the thickness direction. (3) In another embodiment of the thermally conductive sheet, the diameter of the two ends of the carbon fiber exposed on the surface of the rubber-like elastomer may be larger than the diameter of the region embedded in the rubber-like elastomer. (4) In the thermally conductive sheet according to another embodiment, at least one of the surfaces perpendicular to the thickness direction may preferably have an uneven shape. (5) The thermally conductive sheet according to another embodiment may preferably further include a protective film for protecting the surfaces of the recesses that form the uneven shape. (6) In the thermally conductive sheet according to another embodiment, the rubber-like elastic body may preferably be silicone rubber. (7) In the thermally conductive sheet according to another embodiment, the surface roughness Ra of the surface perpendicular to the thickness direction may be preferably 1.0 μm or more and 1.8 μm or less. (8) A method for producing a thermally conductive sheet according to one embodiment for achieving the above object is a method for producing a thermally conductive sheet as described above, comprising the steps of: discharging a curable rubber composition containing carbon fibers made of amorphous carbon fibers onto a flat surface of a planar body in a plurality of rows along a predetermined direction; forming a carbon-containing sheet in which the carbon fibers are oriented in the predetermined direction by molding the curable rubber composition discharged onto the flat surface of the planar body into a sheet and curing the curable rubber composition; stacking a plurality of the carbon-containing sheets with uncured liquid rubber disposed between the carbon-containing sheets, curing the uncured liquid rubber, and forming a stacked block body with the orientation of the carbon fibers aligned; and cutting the block body into sheets in a direction oblique to the orientation direction of the carbon fibers so as to cut the carbon fibers. (9) In the method for producing a thermally conductive sheet according to another embodiment, the cutting step may preferably include cutting the sheet at an angle of 20° or more and less than 90° with respect to the orientation direction of the carbon fibers. (10) According to another embodiment, the method for producing a thermally conductive sheet may further include a step of forming an uneven shape on at least one of the cut surfaces of the sheet obtained by the cutting step. (11) The method for producing a thermally conductive sheet according to another embodiment may preferably further include a protective film arranging step of arranging a protective film on the surfaces of the recesses that form the uneven shape to protect the surfaces. (12) In the method for producing a thermally conductive sheet according to another embodiment, the uncured liquid rubber may preferably be liquid silicone rubber. Effect of the Invention

[0008] According to the present invention, it is possible to provide a thermally conductive sheet that can achieve low hardness and high thermal conductivity. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 shows a plan view and an enlarged view of a part B of a thermally conductive sheet according to a first embodiment of the present invention. [Diagram 2] FIG. 2 shows a cross-sectional view taken along line AA of the thermally conductive sheet of FIG. 1, an enlarged view of a part C thereof, and an enlarged view of a part D thereof. [Diagram 3] FIG. 3 shows an example of a flow of main steps in the method for producing a thermally conductive sheet according to the first embodiment of the present invention. [Figure 4] FIG. 4 shows the state of each step of the manufacturing method shown in FIG. 3 in plan view and cross section. [Diagram 5] FIG. 5 shows cross-sectional views of the process steps subsequent to FIG. [Figure 6] FIG. 6 shows in cross section the state of each process subsequent to FIG. [Figure 7] FIG. 7 is a perspective view showing the state of each process subsequent to FIG. [Figure 8] FIG. 8 shows a cross-sectional view of a thermally conductive sheet according to a second embodiment of the present invention taken in the same direction as FIG. 2, and an enlarged view of a portion G thereof. [Figure 9] FIG. 9 shows an example of a flow of main steps in the method for producing a thermally conductive sheet according to the second embodiment of the present invention. [Figure 10] FIG. 10 shows a cross-sectional view of a part of the process of the manufacturing method shown in FIG. [Figure 11] FIG. 11 shows a plan view of a thermally conductive sheet according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Next, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below does not limit the invention according to the claims, and all of the elements and combinations thereof described in the embodiment are not necessarily essential to the solution of the present invention.

[0011] (First embodiment) 1. Thermally conductive sheet Fig. 1 shows a plan view of a thermally conductive sheet according to a first embodiment of the present invention and an enlarged view of a part B. Fig. 2 shows a cross-sectional view of the thermally conductive sheet shown in Fig. 1 taken along line AA, an enlarged view of a part C thereof, and an enlarged view of a part D thereof.

[0012] The thermally conductive sheet 1 according to this embodiment is a sheet that allows heat to be dissipated from a heat source by conducting heat from the heat source to a member on the cooling side. In this embodiment, the thermally conductive sheet 1 is a sheet that is used by being disposed between a heat source and a member on the cooling side so that one surface 11 in the thickness direction of the rubber-like elastic body 10 contacts the heat source and the other surface 12 in the thickness direction contacts the member on the cooling side. The thermally conductive sheet 1 includes a sheet-like rubber-like elastic body 10 and carbon fibers 20 embedded in a diagonal direction with respect to the thickness direction of the rubber-like elastic body 10 (the vertical direction in FIG. 2). The carbon fibers 20 are amorphous carbon fibers, and both ends 21, 22 thereof are exposed on the surfaces 11, 12 of the rubber-like elastic body 10. In this embodiment, the thermally conductive sheet 1 is a member in which a plurality of rubber-like elastic bodies 10 are laminated to form a single sheet shape in a plan view. The thermally conductive sheet 1 is preferably arranged such that silicone rubber 30 obtained by curing uncured liquid rubber is disposed between the plurality of rubber-like elastic bodies 10. The uncured liquid rubber acts as an adhesive that bonds together the rubber-like elastic bodies 10. Next, each of the components of the thermally conductive sheet 1 will be described.

[0013] (1) Rubber-like elastomer The rubber-like elastic body 10 is not particularly limited and can be appropriately selected according to the performance required for the thermal conductive sheet, and examples thereof include thermosetting resins and thermoplastic resins. Examples of thermosetting resins include elastomeric thermosetting resins such as silicone rubber, silicone resin, polyurethane resin, and epoxy resin. Examples of thermoplastic resins include elastomeric thermoplastic resins such as synthetic rubber, polyethylene resin, polyurethane resin, ABS resin, and soft polyvinyl chloride resin. These may be used alone or in combination of two or more. Among these, silicone rubber is particularly preferred in terms of excellent moldability, weather resistance, and heat resistance, as well as adhesion and followability to a heat source such as an electronic component. The rubber-like elastic body 10 may contain the above-mentioned resin material and a filler having a higher thermal conductivity than the resin material. As a result, the rubber-like elastic body 10 has a higher thermal conductivity than a material composed only of a resin material, and therefore the thermal conductivity from the heat source to the member on the cooling side can be increased. As the filler, particulate, fibrous, plate-like or needle-like fillers such as aluminum oxide (Al2O3), aluminum nitride (AlN), cubic boron nitride (cBN), hexagonal boron nitride (hBN), zinc oxide, silicon carbide, aluminum hydroxide, and diamond can be selected. Fillers with high insulating properties are preferred.

[0014] (2) Carbon fiber The carbon fibers 20 are embedded in the rubber-like elastic body 10, preferably oriented such that the angle θ1 with respect to the thickness direction of the rubber-like elastic body 10 (the vertical direction in FIG. 2) is greater than 0° and equal to or less than 70°. The surfaces of both ends of the carbon fibers 20 are preferably flush with the surfaces 11, 12 of the rubber-like elastic body 10, respectively, and do not significantly protrude or recess from the surfaces 11, 12. The carbon fibers 20 preferably have a diameter Φ1 of both ends 21, 22 exposed to the surfaces 11, 12 of the rubber-like elastic body 10 larger than a diameter Φ2 of a region 23 embedded in the rubber-like elastic body 10. The size of Φ1 relative to Φ2 is preferably 1<Φ1 / Φ2<2, and more preferably 1.5<Φ1 / Φ2<2. In the thermally conductive sheet 1, the diameter Φ1 of both ends 21, 22 of the carbon fibers 20 is larger than the diameter Φ2 of the remaining region 23. Therefore, even if an external force is applied in a direction in which the carbon fibers 20 are pulled out (the orientation direction of the carbon fibers 20), the carbon fibers 20 can be prevented from being pulled out of the rubber-like elastic body 10. In addition, in the thermally conductive sheet 1, the both ends 21, 22 of the carbon fibers 20 having the diameter Φ1 come into contact with the heat source or the member on the cooling side, so that the contact area between the carbon fibers 20 and the heat source or the member on the cooling side is increased, and the thermal conductivity can be increased. Note that the orientation angle θ1 of the carbon fibers 20 is not limited to the above range as long as the carbon fibers 20 are oriented at least obliquely with respect to the thickness direction of the rubber-like elastic body 10.

[0015] The carbon fiber 20 is an amorphous carbon fiber made of amorphous pitch as a raw material, and is configured so that the crystal arrangement remains random even after high-temperature firing. In the case of the amorphous carbon fiber, the structure of the carbon fiber itself is also amorphous. Therefore, the amorphous carbon fiber has high compressive strength and high impact strength. However, the carbon fiber 20 is not limited to being composed only of amorphous carbon fiber, and may be a mixture of amorphous carbon fiber and other carbon fibers such as carbon nanotubes, graphite nanofibers, and diamond fibers. The fiber length of the carbon fiber 20 is preferably 0.002 mm to 10 mm, more preferably 0.005 mm to 7.5 mm. The fiber diameter of the carbon fiber is preferably 1 μm to 50 μm, more preferably 5 μm to 25 μm.

[0016] (3) Silicone rubber The silicone rubber 30 is a silicone rubber having low fluidity or in a solid state obtained by curing an uncured liquid rubber. The uncured liquid rubber is a rubber having high fluidity that can be cured by a desired method. Examples of the curing method of the uncured liquid rubber include heating, light irradiation, electron beam irradiation, and curing by a catalyst or a curing agent. Examples of the uncured liquid rubber include liquid silicone rubber, liquid natural rubber, liquid isoprene rubber, liquid butadiene rubber, liquid styrene-butadiene rubber, liquid butyl rubber, liquid nitrile rubber, liquid ethylene-propylene rubber, liquid chloroprene rubber, liquid chlorosulfonated polyethylene rubber, liquid urethane rubber, and liquid fluororubber. Among these, liquid silicone rubber is preferable because it is less likely to cause dimensional changes or warping after curing, has a small compression set, and is highly heat resistant. The liquid silicone rubber may be either a condensation type or an addition type.

[0017] The thermally conductive sheet 1 preferably has an arithmetic mean roughness Ra of 1.0 μm or more and 1.8 μm or less on the surfaces 11 and 12 perpendicular to the thickness direction (the vertical direction in FIG. 2). The thermally conductive sheet 1 preferably has a ten-point mean roughness Rz of 7.7 μm or more and 18 μm or less on the surfaces 11 and 12. The arithmetic mean roughness Ra is a value measured according to JIS B 0601-2001. The ten-point mean roughness Rz is a value measured according to JIS B 0601-1994. By reducing the surface roughness of the thermally conductive sheet 1 in this way, the surfaces 11 and 12 perpendicular to the thickness direction of the thermally conductive sheet 1 become flat, so that the heat source and the carbon fibers 20 can be in more reliable contact with each other, and the thermal conductivity can be increased.

[0018] 2. Manufacturing method of thermal conductive sheet Next, a method for producing a thermally conductive sheet according to an embodiment of the present invention will be described.

[0019] The manufacturing method of the thermally conductive sheet 1 includes a discharge step of discharging a curable rubber composition containing carbon fibers 20 made of amorphous carbon fibers onto the flat surface of a planar body in multiple rows along a predetermined direction; a shaping step of molding the curable rubber composition discharged onto the flat surface of the planar body into a sheet and curing it to form a carbon-containing sheet in which the carbon fibers 20 are oriented in a predetermined direction; a lamination step of stacking multiple carbon-containing sheets with uncured liquid rubber disposed between the carbon-containing sheets and curing the uncured liquid rubber to form a stacked block body with the orientation of the carbon fibers 20 aligned; and a cutting step of cutting the block body into sheets in a direction oblique to the orientation direction of the carbon fibers 20 so as to cut the carbon fibers.

[0020] FIG. 3 shows an example of a flow of main steps of the manufacturing method of the thermal conductive sheet according to the first embodiment of the present invention. FIG. 4 shows the status of each step of the manufacturing method in FIG. 3 in plan view and cross-sectional view. FIG. 5 shows the status of each step following FIG. 4 in cross-sectional view. FIG. 6 shows the status of each step following FIG. 5 in cross-sectional view. FIG. 7 shows the status of each step following FIG. 6 in perspective view. Note that in FIG. 4 and FIG. 7, the carbon fibers 20 are exaggerated for the purpose of explaining the manufacturing process.

[0021] The thermally conductive sheet 1 can be manufactured through a discharging step (S100), a molding step (S110), a laminating step (S120), and a cutting step (S130). Steps S100 to S130 will be described in detail below with reference to FIGS.

[0022] (1) Discharge process (S100) This step is a step of discharging a curable rubber composition 70 containing carbon fibers 20 made of amorphous carbon fibers onto a plane of a film (one example of a flat body) 72 in a plurality of rows along a predetermined direction Do (left-right direction in FIG. 4(a)) (see FIG. 4). A flat body means one having at least one flat surface. In this embodiment, the discharging step (S100) is preferably performed by discharging the curable rubber composition 70 onto the film 72 in a state in which the film 72 is placed in a recess 41 of a lower die 40 constituting a die 60 used in a molding step (S110) described later (see the cross-sectional view of line EE in FIG. 4(b)). In addition, in the discharging step (S100), the curable rubber composition 70 discharged in a straight line along the predetermined direction Do using a syringe or the like is discharged in a plurality of rows so as to be aligned in a direction perpendicular to the predetermined direction Do (see FIG. 4(a)), and a sheet-like curable rubber composition 70 is formed on the film 72 (see FIG. 4(b)). The curable rubber composition 70 is a composition that becomes a rubber-like elastomer 10 after curing. In the discharge step (S100), the curable rubber composition 70 containing the carbon fibers 20 is discharged along a predetermined direction Do, so that the carbon fibers 20 can be oriented along the predetermined direction Do. Hereinafter, the predetermined direction Do is also referred to as an orientation direction Do or a discharge direction Do. The film 72 is preferably a film made of a resin. Examples of resins include polyethylene terephthalate (PET), polyethylene naphthalate, polyethylene isophthalate, polybutylene terephthalate, polyacetate, polycarbonate, polyphenylene sulfide, polyamide, polyvinyl chloride, and polyvinylidene chloride. Among these, a PET film is more preferable as the film 72.

[0023] (2) Molding process (S110) In this step, the curable rubber composition 70 discharged onto the film 72 is molded into a sheet and cured to form a carbon-containing sheet 76 in which the carbon fibers 20 are oriented in a predetermined direction Do (see FIG. 5). More specifically, first, a flat surface of a film (one example of a flat body) 74 is superimposed on the curable rubber composition 70 discharged onto the film 72. The film 74 is preferably made of the same material as the film 72 described above. Next, an upper die 50 constituting the mold 60 is prepared and superimposed on the recess 41 side of the lower die 40, and the lower die 40 and the upper die 50 are closed (see FIGS. 5(c) and (d)). The upper die 50 has a recess 51 on the surface facing the recess 41 of the lower die 40. After the mold 60 is clamped, it is heated to mold the curable rubber composition 70 (see FIG. 5(e)). As a result, the curable rubber composition 70 is cured to form a rubber-like elastic body 10 containing the carbon fibers 20. Then, the mold 60 is opened, and the films 72, 74 are peeled off to form a carbon-containing sheet 76 (see FIG. 5(f)). The carbon-containing sheet 76 is a sheet containing the carbon fibers 20 oriented in the rubber-like elastic body 10 along a predetermined direction Do (the left-right direction in FIG. 5(f)).

[0024] (3) Lamination process (S120) In this step, a plurality of carbon-containing sheets 76 are laminated with the uncured liquid rubber 80 disposed between the carbon-containing sheets 76, and the uncured liquid rubber 80 is cured to form a laminated block body 90 with the carbon fibers 20 aligned (see FIG. 6). More specifically, first, the uncured liquid rubber 80 is placed on the carbon-containing sheet 76, and another carbon-containing sheet 76 is laminated (see FIG. 6(g)). At this time, the two carbon-containing sheets 76 are laminated so that the orientation direction Do of the carbon fibers 20 contained in the two carbon-containing sheets 76 laminated with the uncured liquid rubber 80 in between are the same direction. This operation is repeated to laminate a plurality of carbon-containing sheets 76 with the uncured liquid rubber 80 in between (see FIG. 6(h)). The uncured liquid rubber 80 becomes the silicone rubber 30 after curing, and is preferably a liquid silicone rubber. In this embodiment, the uncured liquid rubber 80 plays the role of an adhesive that bonds the carbon-containing sheets 76 together. Then, with the carbon-containing sheets 76 stacked, the uncured liquid rubber 80 is cured to form a block body 90 (see FIG. 6(i)). The block body 90 is a laminate in which the carbon-containing sheets 76 are stacked such that the orientation directions Do of the carbon fibers 20 contained in each of the carbon-containing sheets 76 are the same (see FIG. 7(j)).

[0025] (4) Cutting process (S130) This step is a step of cutting the block body 90 into sheets in an oblique direction with respect to the orientation direction Do of the carbon fibers 20 (left and right direction in FIG. 7(j)) (see FIG. 7). More specifically, the block body 90 is cut into a predetermined thickness at an angle θ2 of 20° or more and less than 90° with respect to the orientation direction Do of the carbon fibers 20 (see FIG. 7(j)). The predetermined thickness is preferably 0.01 mm to 10 mm, and more preferably 0.05 mm to 5 mm. In the cutting step (S130), the cutting means is not particularly limited as long as it is capable of cutting into a predetermined thickness, such as a known cutter or slicer, but slicing using a band machine slicer (a device that rotates a band-shaped blade called a band knife in a ring at high speed) or slicing using a rotary blade is preferred. In the cutting step (S130), the carbon fibers 20 are pulled by the cutting means when they are cut, so that the diameter Φ1 of the cut surfaces 21, 22 can be made larger than the diameter Φ2 of the region 23 embedded in the rubber-like elastic body 10 (see Figs. 1 and 2). In the cutting step (S130), it is preferable to cut the carbon fibers 20 by the cutting means so that the arithmetic mean roughness Ra of the cut surface is 1.0 μm or more and 1.8 μm or less. In addition, in the cutting step (S130), it is preferable to cut the carbon fibers 20 by the cutting means so that the ten-point mean roughness Rz of the cut surface is 7.7 μm or more and 18 μm or less. By cutting the block body 90 in this way in the cutting step (S130), the thermally conductive sheet 1 can be manufactured (see Fig. 7(k)). Note that Fig. 7(l) shows a view from the direction of the arrow F in Fig. 7(k).

[0026] The thermally conductive sheet 1 manufactured in this manner has the carbon fibers 20 embedded in a direction oblique to the thickness direction (the vertical direction in FIG. 7(l)). In addition, in the thermally conductive sheet 1, both ends of the carbon fibers 20 are exposed on the cut surface (i.e., the surfaces 11, 12 of the rubber-like elastic body 10). The diameter Φ1 of both ends 21, 22 exposed on the cut surface of the carbon fibers 20 is larger than the diameter Φ2 of the region 23 embedded in the rubber-like elastic body 10. Therefore, according to the thermally conductive sheet 1 manufactured in this manner, the contact area between the carbon fibers 20 and the heat source or the member on the cooling side is increased, and the thermal conductivity can be increased. Furthermore, according to the thermally conductive sheet 1, for example, even if an external force is applied in the direction in which the carbon fibers 20 are pulled out (the orientation direction Do of the carbon fibers 20), it is possible to prevent the carbon fibers 20 from being pulled out of the rubber-like elastic body 10. Moreover, since the thermally conductive sheet 1 is cut in the cutting step (S130) so as to reduce surface roughness, the cut surface becomes flat, and the heat source and the carbon fibers 20 can contact each other more reliably. This can further increase the thermal conductivity. Furthermore, since the thermally conductive sheet 1 has high thermal conductivity as described above, it is not necessary to increase the packing rate of the carbon fibers 20 in order to increase the thermal conductivity. Therefore, the thermally conductive sheet 1 can suppress the increase in hardness caused by increasing the packing rate of the carbon fibers 20, and can achieve low hardness and high thermal conductivity.

[0027] Second embodiment 1. Thermally conductive sheet Next, a description will be given of a thermally conductive sheet according to a second embodiment. The same reference numerals will be used to designate parts common to the previous embodiment, and duplicated descriptions will be omitted.

[0028] FIG. 8 shows a cross-sectional view of a thermally conductive sheet according to a second embodiment of the present invention taken in the same direction as FIG. 2, and an enlarged view of a portion G thereof.

[0029] The thermally conductive sheet 1a according to the second embodiment has a similar structure to the thermally conductive sheet 1 according to the first embodiment, but differs from the thermally conductive sheet 1 according to the first embodiment in that at least one of the surfaces perpendicular to the thickness direction has an uneven shape. In this embodiment, the thermally conductive sheet 1a is a sheet that is used by being disposed between a heat source and a member on the cooling side such that surface 13 of the rubber-like elastomer 10 contacts the heat source and surface 12 contacts the member on the cooling side.

[0030] In the thermally conductive sheet 1a, one of the surfaces 12, 13 perpendicular to the thickness direction of the rubber-like elastic body 10 (the vertical direction in FIG. 8) has an uneven shape. Hereinafter, the surface 13 is also referred to as the uneven surface 13. The uneven surface 13 is a surface in which the convex portions 14 and the concave portions 16 are arranged adjacent to each other to form an uneven shape (see the enlarged view of part G in FIG. 8). Each surface at both ends of the carbon fiber 20 is preferably flush with the surfaces of the convex portions 14 and the surface 12 of the rubber-like elastic body 10, respectively, and does not protrude or sink significantly from the surfaces of the convex portions 14 and the surface 12. The thermally conductive sheet 1a preferably includes a protective film 18 that protects the surfaces of the concave portions 16. There are no particular restrictions on the material of the protective film 18, and examples thereof include thermosetting resins or thermoplastic resins similar to the materials of the rubber-like elastic body 10 described above. These may be used alone or in combination of two or more types. The protective film 18 may be made of the same resin as the films 72 and 74. Among these, the protective film 18 is particularly preferably made of silicone rubber, which has excellent moldability, weather resistance, and heat resistance, and is also excellent in adhesion and conformity to a heat source such as an electronic component. The protective film 18 may contain the above-mentioned resin material and a filler having higher thermal conductivity than the resin material, as in the rubber-like elastic body 10. As the filler, the same filler as in the rubber-like elastic body 10 can be used. The thickness of the predetermined thickness protective film 18 is preferably 0.005 mm to 0.5 mm, and more preferably 0.01 mm to 0.25 mm. Such a thermally conductive sheet 1a can also achieve the same effect as the thermally conductive sheet 1 according to the first embodiment. The thermally conductive sheet 1a is compressed in the thickness direction between the heat source and the member on the cooling side. For example, the thermally conductive sheet 1a has an uneven surface 13 formed so that only the areas in contact with the heat source are convex portions 14 and the other areas are concave portions 16, thereby ensuring that the convex portions 14 are in contact with the heat source during compression and reducing the load on the concave portions 16 that are not in contact with the heat source.Furthermore, since the thermally conductive sheet 1a is provided with the protective film 18 in the recesses 16, even if an external force is applied in a direction in which the carbon fibers 20 are pulled out (the orientation direction of the carbon fibers 20), the carbon fibers 20 in the recesses 16 can be prevented from being pulled out from the rubber-like elastic body 10. The shapes of the protrusions 14 and the recesses 16 are not particularly limited as long as the uneven surface 13 forms at least an uneven shape. Furthermore, the protective film 18 does not have to be provided in all of the recesses 16 as long as it is provided in at least one of the multiple recesses 16.

[0031] 2. Manufacturing method of thermal conductive sheet Next, a method for producing a thermally conductive sheet according to a second embodiment will be described. The same reference numerals will be used to designate parts common to the previous embodiment, and duplicated descriptions will be omitted.

[0032] Fig. 9 shows an example of a flow of main steps of a method for producing a thermally conductive sheet according to a second embodiment of the present invention, and Fig. 10 shows cross-sectional views of some steps of the production method shown in Fig. 9.

[0033] The manufacturing method of the thermally conductive sheet 1a according to the second embodiment includes a discharge step (S100), a molding step (S110), a lamination step (S120), a cutting step (S130), a concave-convex surface forming step (S140), and a protective film arranging step (S150). The thermally conductive sheet 1a can be manufactured by further performing the concave-convex surface forming step (S140) and the protective film arranging step (S150) on the thermally conductive sheet 1 according to the first embodiment. The discharge step (S100), the molding step (S110), the lamination step (S120), and the cutting step (S130) are the same as those in the manufacturing method of the thermally conductive sheet 1 according to the first embodiment, and therefore detailed explanations are omitted. Hereinafter, S140 to S150 will be described in detail with reference to FIG. 9 and FIG. 10.

[0034] (5) Uneven surface formation process (S140) This step is a step of forming an uneven shape on at least one of the cut surfaces 12, 13 cut into a sheet shape in the cutting step (S130) (see Figs. 10(l) and (m)). In this embodiment, an uneven shape is formed on one cut surface 13 of the thermally conductive sheet 1 cut into a sheet shape in the cutting step (S130). More specifically, a known uneven processing means is used to form the uneven surface 13 in which the convex portions 14 and the concave portions 16 are adjacently arranged (see the enlarged view of part H in Fig. 10(m)). The uneven processing means is not particularly limited as long as it is a means capable of forming the uneven surface 13. It is preferable that the uneven surface 13 is formed so that the area in contact with the heat source becomes the convex portions 14 and the area not in contact with the heat source becomes the concave portions 16 depending on the application of the thermally conductive sheet 1a.

[0035] (6) Protective film placement process (S150) This step is a step of placing a protective film 18 on the surface of the recess 16 (see the enlarged view of part I in FIG. 10(n)). In the protective film placing step (S150), when the protective film 18 is placed on the surface of the recess 16, a known adhesive may or may not be used. In this manner, the thermally conductive sheet 1a can be manufactured.

[0036] Third embodiment Thermally conductive sheet and manufacturing method thereof Next, a description will be given of a thermally conductive sheet according to a third embodiment. The same reference numerals will be used to designate parts common to the previous embodiment, and duplicated descriptions will be omitted.

[0037] FIG. 11 shows a plan view of a thermally conductive sheet according to a third embodiment of the present invention.

[0038] The thermally conductive sheet 1b according to this embodiment is a sheet in which the thermally conductive sheet 1 according to the first embodiment and a foamed silicone rubber sheet (one example of a foamed rubber sheet) 95 are fixed together. In the thermally conductive sheet 1b, a foamed silicone rubber sheet 95 is disposed on the outer periphery of the thermally conductive sheet 1 in order to prevent the carbon fibers 20 from falling off from the cut surface of the outer periphery of the thermally conductive sheet 1. When adhesive tape, silicone rubber, or the like is printed on the surface of the thermally conductive sheet 1, the thermal conductivity characteristics of the thermally conductive sheet 1 may decrease. For this reason, the use of the outer periphery that is not related to thermal conduction results in a structure in which the thermal conductivity characteristics are less likely to decrease.

[0039] When foamed silicone rubber sheet 95 is used, it foams during vulcanization, thereby eliminating any gaps between thermally conductive sheet 1 and the periphery of the frame inside foamed silicone rubber sheet 95. In other words, the foamed silicone rubber penetrates into the minute gaps between the periphery of the frame of foamed silicone rubber sheet 95 and the outer periphery of thermally conductive sheet 1, thereby exerting adhesion between foamed silicone rubber sheet 95 and thermally conductive sheet 1.

[0040] Thermally conductive sheet 1b can be manufactured as follows. Before or after manufacturing of thermally conductive sheet 1, a square is cut out from the inside of an unvulcanized silicone rubber sheet. The rectangular thermally conductive sheet 1 is placed in the cut-out area. After placement, the silicone rubber sheet is vulcanized by heating. In this way, thermally conductive sheet 1b is completed.

[0041] (Other embodiments) As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to these and can be practiced in various modifications.

[0042] The thermally conductive sheet 1, 1a may have at least one of the surfaces 11, 12, 13 perpendicular to the thickness direction coated with a resin. The resin used for this coating is not particularly limited, and may be, for example, a thermosetting resin or a thermoplastic resin similar to the material of the rubber-like elastic body 10 described above. Also, like the rubber-like elastic body 10, the thermally conductive sheet 1, 1a may contain the above-mentioned resin material and a filler having a higher thermal conductivity than the resin material. As the filler, the same filler as that of the rubber-like elastic body 10 can be used. According to the thermally conductive sheet 1, 1a configured in this manner, the coating of the surfaces 11, 12, 13 can further suppress the carbon fiber 20 from falling off from the rubber-like elastic body 10. Also, the thermally conductive sheet 1, 1a can reduce the decrease in thermal conductivity caused by the coating by including a filler having a high thermal conductivity in the resin material used for the coating. When the surfaces 11, 12, 13 of the thermally conductive sheets 1, 1a are coated with the above-mentioned resin material, the thermally conductive sheets 1, 1a can be manufactured by coating the surfaces 11, 12, 13 after the cutting step (S130).

[0043] Although the thermally conductive sheet 1a has a protective film 18 on the surface of the recesses 16, the protective film 18 may be provided only on the surface of some of the multiple recesses 16, or the protective film 18 may not be provided on the surface of any of the recesses 16.

[0044] In the thermally conductive sheet 1a, one of the surfaces 12 and 13 perpendicular to the thickness direction of the rubber-like elastic body 10 (the vertical direction in FIG. 8) has an uneven shape on the surface 13, but both the surfaces 12 and 13 may have an uneven shape. In this case, the thermally conductive sheet 1a may have a protective film 18 on the surface of the recesses 16 formed on the surface 12. Also, the thermally conductive sheet 1a may have a protective film 18 only on the surfaces of some of the recesses 16 among the multiple recesses 16 formed on the surface 12, or may not have a protective film 18 on the surfaces of any of the recesses 16. Also, the thermally conductive sheet 1a may have an uneven shape only on the surface 12, without having an uneven shape on the surface 13.

[0045] After the molding step (S110), a trimming step may be performed to trim off excess areas of the carbon-containing sheet 76. [Industrial Applicability]

[0046] The thermally conductive sheet according to the present invention can be used, for example, in automobiles, industrial robots, power generation equipment, various electronic devices such as PCs and household electrical appliances, automobile batteries, rechargeable household batteries, batteries for electronic devices such as PCs, etc. [Explanation of symbols]

[0047] 1, 1a, 1b...thermal conductive sheet, 10...rubber-like elastomer, 11, 12, 13...surface, 16...recess, 18...protective film, 20...carbon fiber, 21, 22...both ends (of carbon fiber), 23...region embedded in rubber-like elastomer (of carbon fiber), 70...curable rubber composition, 72, 74...film (an example of a planar body), 76...carbon-containing sheet, 80...uncured liquid rubber, 90...block body, Φ1...diameter of both ends of carbon fiber, Φ2...diameter of region of carbon fiber embedded in rubber-like elastomer.

Claims

1. A sheet-like rubber-like elastic body; Carbon fibers embedded in the rubber-like elastic body in a direction oblique to the thickness direction; A thermally conductive sheet comprising: the carbon fiber is an amorphous carbon fiber, both ends of which are exposed on the surface of the rubber-like elastic body; A thermally conductive sheet, comprising a plurality of the rubber-like elastomers containing the carbon fibers laminated with a layer of silicone rubber sandwiched therebetween.

2. The thermally conductive sheet according to claim 1 , wherein the carbon fibers are embedded and oriented at an angle greater than 0° and equal to or less than 70° with respect to the thickness direction.

3. The thermally conductive sheet according to claim 1 or 2, characterized in that the diameter of the carbon fibers at both ends exposed on the surface of the rubber-like elastomer is larger than the diameter of the region embedded in the rubber-like elastomer.

4. 4. The thermally conductive sheet according to claim 1, wherein the rubber-like elastic body is a silicone rubber.

5. 5. The thermally conductive sheet according to claim 1, wherein the surface roughness Ra of the surface perpendicular to the thickness direction is 1.0 μm or more and 1.8 μm or less.

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