Manufacturing method of thermally conductive sheet

Abstract

A method for producing a thermally conductive sheet with improved productivity is provided. [Solution] The present invention relates to a method for producing a thermally conductive sheet, which includes the steps of: discharging a mixture of carbon fibers and a curable rubber composition onto a plane in multiple rows; forming a carbon fiber-containing sheet in which the carbon fibers are oriented; forming a laminate by stacking multiple carbon fiber-containing sheets with an adhesive in between; forming a cured laminate of the laminate; and cutting the cured laminate into sheets obliquely with respect to the orientation direction of the carbon fibers so as to cut the carbon fibers. In the laminate formation step, multiple carbon fiber-containing sheets are stacked in opposite directions from the inner bottom surface of a container to form the laminate, and the inner bottom surface is inclined at an acute angle θ1 with respect to a plane perpendicular to the height direction of the container. The laminate is formed within the container in the shape of a parallelogram, with one pair of opposing interior angles being (90-θ1) degrees and another pair of opposing interior angles being an obtuse angle, and the remaining four faces are rectangular.

Description

[Technical Field]

[0001] The present invention relates to a method for producing 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 solutions to the problems of electronic component failure and shortened lifespan caused by heat generation around the circuit board.

[0003] A known method for achieving rapid heat dissipation from a circuit board is to interpose 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. Thermally conductive sheets that contain a thermally conductive filler dispersed in a rubber-like elastic material such as resin or rubber have been widely used. Recently, a thermally conductive sheet in which carbon fibers as a thermally conductive filler are oriented obliquely relative to the thickness direction of the thermally conductive sheet, and a method for manufacturing the same, have become known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-42619 Summary of the Invention [Problem to be solved by the invention]

[0005] The manufacturing method for thermally conductive sheets described in Patent Document 1 can produce thermally conductive sheets with low hardness and high thermal conductivity, but there is still room for improvement. The manufacturing method includes a cutting step in which a block formed by alternately stacking carbon fiber-containing sheets, in which carbon fibers are oriented horizontally, and adhesive is cut into sheets obliquely relative to the orientation direction. There is a need for a manufacturing method like this that can increase the portion that can be used as a product.

[0006] In order to solve the above problems, an object of the present invention is to provide a method for producing a thermally conductive sheet that increases the portion that can be used as a product and improves productivity. [Means for solving the problem]

[0007] (1) In order to achieve the above object, a method for producing a thermally conductive sheet according to one embodiment includes the steps of: A method for manufacturing a thermally conductive sheet, comprising: a sheet-like rubber-like elastic body; and carbon fibers embedded in the rubber-like elastic body and oriented in a direction oblique to a thickness direction of the rubber-like elastic body, wherein at least one end of at least a portion of the carbon fibers is exposed on a surface of the rubber-like elastic body, a discharge step of discharging the mixture of carbon fibers and a curable rubber composition onto a flat surface of a flat body in a plurality of rows along a predetermined direction; a sheet forming step of forming the mixture discharged onto the plane into a sheet to form a carbon fiber-containing sheet in which the carbon fibers are oriented in the predetermined direction; a laminate formation step of forming a laminate by stacking a plurality of the carbon fiber-containing sheets with an adhesive disposed between the carbon fiber-containing sheets; a cured body forming step of forming a cured body by curing the laminate; a cutting step of cutting the cured body into sheets in a direction oblique to the orientation direction of the carbon fibers so as to cut the carbon fibers; Including, The laminate forming step is a step of forming the laminate by stacking a plurality of the carbon fiber-containing sheets in a cylindrical container from an inner bottom surface of the container in opposite directions, The inner bottom surface is inclined at an acute angle θ1 with respect to a plane perpendicular to the height direction of the container, Within the container, the stack is formed in the shape of a parallelogram, with two opposing surfaces having a pair of opposing interior angles of (90-θ1) degrees and another pair of opposing interior angles being obtuse angles, and the remaining four surfaces being rectangular, forming a hexahedron. (2) In another embodiment of the method for producing a thermally conductive sheet, preferably, The method further includes a coating step of forming a coated body by hardening at least a surface of the surface of the cured body surrounding the outer periphery in the cutting direction, prior to the cutting step, In the cutting step, the coating may be cut into sheets in a direction oblique to the orientation direction of the carbon fibers. (3) In another embodiment of the method for producing a thermally conductive sheet, the method may further include a fixing step of fixing the coating body onto a fixing body after the coating step and before the cutting step. (4) In the method for producing a thermally conductive sheet according to another embodiment, the acute angle θ1 may preferably be greater than 0 degrees and equal to or less than 45 degrees. (5) In another embodiment of the method for producing a thermally conductive sheet, preferably, prior to the cured body forming step, the inside of a mold containing the laminate may be subjected to a decompression treatment, and then the cured body may be formed. (6) In another embodiment of the method for producing a thermally conductive sheet, preferably, The method further includes a mixing step of mixing the curable rubber composition and the carbon fibers to obtain the mixture prior to the discharging step, The mixing step may be a step of enclosing the curable rubber composition and the carbon fibers in a bag and performing non-shear mixing together with the bag to obtain the mixture. (7) In another embodiment of the method for producing a thermally conductive sheet, the ejection step may preferably be a step of ejecting the mixture onto the plane in multiple rows so as to reciprocate along the predetermined direction. [Effects of the Invention]

[0008] According to the present invention, it is possible to increase the portion that can be used as a product and improve productivity. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 shows a plan view of a thermally conductive sheet manufactured by a manufacturing method according to one embodiment, a cross-sectional view taken along line AA, and a partially enlarged view of part B thereof. [Figure 2] FIG. 2 shows a flow diagram of a method for producing a thermally conductive sheet according to one embodiment. [Figure 3] FIG. 3 is a schematic diagram showing a discharging step in the method for producing a thermally conductive sheet according to one embodiment. [Figure 4] FIG. 4 is a schematic diagram showing a sheet forming step in the method for producing a thermally conductive sheet according to one embodiment. [Figure 5] FIG. 5 is a schematic diagram showing a laminate formation step in the method for producing a thermally conductive sheet according to one embodiment. [Figure 6] FIG. 6 is a schematic diagram showing the cured body forming step in the method for producing a thermally conductive sheet according to one embodiment. [Figure 7] FIG. 7 shows a schematic diagram of the covering step and the fixing step in the method for producing a thermally conductive sheet according to one embodiment. [Figure 8] FIG. 8 is a schematic diagram showing a cutting step in the method for producing a thermally conductive sheet according to one embodiment. [Figure 9] FIG. 9 is a schematic diagram showing a mixing step in a method for producing a thermally conductive sheet according to another embodiment. [Explanation of symbols]

[0010] 1···Thermal conductive sheet, 10···Rubber-like elastomer, 20···Carbon fiber, 30···Adhesive layer, 70···Mixture, 72, 74···Film (an example of a flat body), 76···Carbon fiber-containing sheet, 80···Adhesive, 85···Container, 87···Inner bottom surface, 90···Laminate, 95···Hardened body, 100···Coating body, 110···Film, 120···Fixed body, 140···Bag body, θ1···Acute angle. DETAILED DESCRIPTION OF THE INVENTION

[0011] (First embodiment) Next, embodiments of the present invention will be described with reference to the drawings. Note that the embodiments described below do not limit the claimed invention, and not all of the elements and combinations thereof described in the embodiments are necessarily essential to the solution of the present invention. In this specification and claims, a numerical range expressed by "to" means a numerical range in which the numbers before and after "to" are the lower and upper limits.

[0012] 1. Thermally conductive sheet FIG. 1 shows a plan view of a thermally conductive sheet manufactured by a manufacturing method according to one embodiment, a cross-sectional view taken along line AA, and a partially enlarged view of part B thereof.

[0013] The thermally conductive sheet 1 according to this embodiment is a sheet that conducts heat from a heat source to a cooling-side member, enabling heat dissipation from the heat source. In this embodiment, the thermally conductive sheet 1 is a sheet that is disposed between a heat source and a cooling-side member, such that one surface 11 in the thickness direction of the rubber-like elastomer 10 contacts the heat source and the other surface 12 in the thickness direction contacts the cooling-side member. The thermally conductive sheet 1 includes a sheet-like rubber-like elastomer 10 and carbon fibers 20 embedded in a direction oblique to the thickness direction of the rubber-like elastomer 10 (the vertical direction in FIG. 1 ). The carbon fibers 20 are preferably amorphous carbon fibers. Preferably, both ends of the carbon fibers 20 are exposed on the surfaces 11 and 12 of the rubber-like elastomer 10. In this embodiment, the thermally conductive sheet 1 is a member formed into a single sheet by stacking a plurality of rubber-like elastomers 10 in a planar view. The thermally conductive sheet 1 preferably includes an adhesive layer 30 disposed between the plurality of rubber-like elastomers 10. Next, each component of the thermally conductive sheet 1 will be described.

[0014] (1) Rubber-like elastic body The rubber-like elastic body 10 is not particularly limited and can be appropriately selected depending on the performance required of the thermally conductive sheet, and examples thereof include thermosetting or thermoplastic materials. Examples of thermosetting materials (resins or rubbers) include silicone rubber, silicone resin, polyurethane resin, and epoxy resin. Examples of thermoplastic materials (resins or rubbers) include synthetic rubber, polyethylene resin, polyurethane resin, ABS resin, and soft polyvinyl chloride resin. These materials may be used alone or in combination of two or more. Among these, silicone rubber is particularly preferred because of its excellent moldability, weather resistance, and heat resistance, as well as its adhesion and conformability to heat sources such as electronic components.

[0015] The rubber-like elastomer 10 may contain the above-mentioned material and a filler with higher thermal conductivity than the material. As a result, the rubber-like elastomer 10 has higher thermal conductivity than a material made of resin alone, thereby improving thermal conductivity from the heat source to the cooling side component. The filler may be particulate, fibrous, plate-like, or needle-like filler, such as aluminum oxide (Al2O3), aluminum nitride (AlN), cubic boron nitride (cBN), hexagonal boron nitride (hBN), zinc oxide, silicon carbide, aluminum hydroxide, or diamond. Fillers with high insulating properties are preferred.

[0016] (2) Carbon fiber The carbon fibers 20 are embedded in the rubber-like elastomer 10, preferably oriented such that the angle θ2 (hereinafter also referred to as the orientation angle) relative to the sheet surface of the rubber-like elastomer 10 (the horizontal direction in FIG. 1) is greater than 0 degrees and less than 90 degrees, preferably 45 degrees or greater but less than 90 degrees, and even more preferably 45 to 70 degrees. Here, "orientation" refers to a state in which the carbon fibers 20 face in the same direction from surface 11 to surface 12 in a cross-sectional view when the thermally conductive sheet 1 is cut in the thickness direction so that the carbon fibers 20 are inclined relative to the sheet surface of the thermally conductive sheet 1, regardless of whether the carbon fibers 20 face in the same direction. Note that θ2 is not limited to the above range as long as the carbon fibers 20 are oriented at least in a diagonal direction relative to the thickness direction of the rubber-like elastomer 10 (the vertical direction in FIG. 1), i.e., in a direction other than the vertical and horizontal directions. The value of angle θ1 in FIG. 1 is equal to the value of acute angle θ1, described below, as the relationship between θ2 and the value of Equation 1 below holds. (θ1 + θ2) = 90 (Equation 1)

[0017] The carbon fibers 20 may include amorphous carbon, graphite, carbon nanotubes, diamond-like carbon, or a mixture of two or more thereof. Among these, amorphous carbon fibers are preferred, which are made from amorphous pitch as a raw material and are configured so that the crystal arrangement remains random even after high-temperature firing. The amorphous carbon fibers themselves have an amorphous structure. Therefore, amorphous carbon fibers have high compressive strength and high impact strength. The fiber length of the carbon fibers 20 is preferably 3 to 10 mm, more preferably 5 to 7.5 mm. The fiber diameter of the carbon fibers is preferably 1 to 50 μm, more preferably 5 to 25 μm.

[0018] Each surface at both ends of the carbon fiber 20 is preferably flush with each of the surfaces 11, 12 of the rubber-like elastomer 10, and does not significantly protrude or recess from each of the surfaces 11, 12. The diameter of each of the carbon fibers 20 at both longitudinal ends is preferably slightly larger than the diameter of the carbon fiber 20 itself. Therefore, even if an external force is applied in the direction in which the carbon fiber 20 is pulled out (the orientation direction of the carbon fiber 20), the carbon fiber 20 can be prevented from being pulled out of the rubber-like elastomer 10. Furthermore, in the thermally conductive sheet 1, the carbon fiber 20 has both ends that come into contact with a heat-generating or heat-receiving member, thereby increasing the contact area between the carbon fiber 20 and the heat-generating member (and heat-receiving member), thereby increasing the thermal conductivity. The diameter (fiber diameter) of the carbon fiber 20 is not particularly limited and is preferably 1 to 50 μm, more preferably 1 to 10 μm. The carbon fibers 20 are preferably contained in an amount within a range of 30 to 70 parts by mass, more preferably within a range of 40 to 60 parts by mass, and even more preferably within a range of 45 to 57 parts by mass, relative to 100 parts by mass of the rubber-like elastic body 10.

[0019] (3) Adhesive layer The adhesive layer 30 is formed by curing an adhesive 80 applied between carbon fiber-containing sheets 76 in a laminate formation process (described later) during a curing process. The adhesive 80 is not particularly limited, but is preferably uncured liquid rubber. The adhesive layer 30 is preferably a rubber layer obtained by curing uncured liquid rubber, more preferably a silicone rubber layer. The uncured liquid rubber is a highly fluid rubber that can be cured by a desired method. Examples of methods for curing uncured liquid rubber include heating, light irradiation, electron beam irradiation, and curing with a catalyst or curing agent. Examples of 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 preferred because it is less likely to undergo dimensional changes or warping after curing, has small compression set, and has high heat resistance. The liquid silicone rubber may be either a condensation type or an addition type.

[0020] The thickness of the thermally conductive sheet 1 is not particularly limited, but is preferably 0.1 to 5.0 mm, more preferably 0.1 to 2.0 mm, and even more preferably 0.1 to 1.0 mm.

[0021] 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.

[0022] The method for producing a thermally conductive sheet according to this embodiment includes at least the following steps: a discharging step (S110) of discharging a mixture of carbon fiber and a curable rubber composition onto a flat surface of a planar body in multiple rows along a predetermined direction; a sheet-forming step (S120) of forming a sheet by shaping the mixture onto the flat surface to form a carbon fiber-containing sheet in which the carbon fibers are oriented in a predetermined direction; a laminate-forming step (S130) of stacking multiple carbon fiber-containing sheets with an adhesive disposed between them to form a laminate; a cured body-forming step (S140) of curing the laminate to form a cured body; and a cutting step (S150) of cutting the cured body into sheets obliquely to the carbon fiber orientation direction so as to cut the carbon fibers. The method may also include a coating step (S141) of forming a coated body by hardening at least the outer periphery of the surface of the cured body in the cutting direction, preferably prior to the cutting step. More preferably, the method may also include a fixing step (S142) of fixing the coated body to a flat surface after the coating step and prior to the cutting step. S110 to S150 will be described in detail below with reference to FIGS.

[0023] FIG. 2 shows a flow diagram of a method for producing a thermally conductive sheet according to one embodiment. FIG. 3 shows a schematic diagram of a discharge step in the method for producing a thermally conductive sheet according to one embodiment. FIG. 4 shows a schematic diagram of a sheet formation step in the method for producing a thermally conductive sheet according to one embodiment. FIG. 5 shows a schematic diagram of a laminate formation step in the method for producing a thermally conductive sheet according to one embodiment. FIG. 6 shows a schematic diagram of a cured body formation step in the method for producing a thermally conductive sheet according to one embodiment. FIG. 7 shows a schematic diagram of a coating step and a fixing step in the method for producing a thermally conductive sheet according to one embodiment. FIG. 8 shows a schematic diagram of a cutting step in the method for producing a thermally conductive sheet according to one embodiment.

[0024] (1) Discharge process (S110) In this process, a mixture 70 of premixed carbon fibers 20 and a curable rubber composition, which is the rubber-like elastomer 10 before curing, is extruded in multiple rows along a predetermined direction Do (left-right direction in FIG. 3 ) onto the flat surface of a film (an example of a flat body) 72. The curable rubber composition is not particularly limited, but is preferably a composition that cures to form the rubber-like elastomer 10 upon application of heat, light, or electron beams, and more preferably a curable silicone rubber composition that cures to form silicone rubber. By using a curable rubber composition with the properties described above, it is possible to reduce the risk of portions of the rubber-like elastomer 10 melting or softening due to the action of heat during use of the thermally conductive sheet 1. The curable rubber composition preferably contains not only a primary rubber material but also a secondary material (e.g., a catalyst or a filler other than the carbon fibers 20) that promotes the curing of the rubber material.

[0025] This step is a step of discharging the mixture 70 in multiple rows onto the flat surface of a film (an example of a flat body) 72, preferably reciprocating along a predetermined direction Do (see FIG. 3). A flat body refers to an object having at least one flat surface. In one example of the discharging step (S110) in this embodiment, the mixture 70 is discharged onto the film 72 in a state in which the film 72 is placed in a recess 41 of a lower mold 40 constituting a mold 60 used in the sheet forming step (S120) described below (see the cross-sectional view along line CC in FIG. 3(b)). Note that the film 72 may be placed in, for example, a commercially available resin discharging device, instead of in the recess 41 of the lower mold 40, and after discharging is completed, the film 72 may be grasped and moved into the mold 60.

[0026] In the discharge step (S110), the mixture 70 is discharged linearly along a predetermined direction Do using a syringe or the like, and then discharged in multiple rows aligned in a direction perpendicular to the predetermined direction Do (see FIG. 3(a)), forming a sheet-like mixture 70 on a film 72 (see FIG. 3(b)). The mixture 70 is a composition that will become a rubber-like elastomer 10 after curing. In the discharge step (S110), the mixture 70 containing carbon fibers 20 is discharged along the predetermined direction Do, thereby orienting the carbon fibers 20 along the predetermined direction Do. Hereinafter, the predetermined direction Do will also be referred to as the orientation direction Do or the discharge direction Do. This step may be performed manually or automatically.

[0027] 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.

[0028] (2) Sheet forming step (S120) In this step, the mixture 70 extruded onto the film 72 is molded into a sheet to form a carbon fiber-containing sheet 76 in which the carbon fibers 20 are oriented in a predetermined direction Do (see FIG. 4). More specifically, first, the flat surface of a film (an example of a flat body) 74 is placed on the mixture 70 extruded onto the film 72. The film 74 is preferably made of the same material as the above-mentioned film 72. Next, an upper mold 50 constituting the mold 60 is prepared and placed on the side of the depression 41 of the lower mold 40, and the lower mold 40 and the upper mold 50 are closed (see FIGS. 4(c) and (d)). The upper mold 50 has a depression 51 on the surface opposite the depression 41 of the lower mold 40. After clamping the mold 60, the mold 60 is heated and the mixture 70 is molded (see FIG. 4(e)). As a result, the mixture 70 hardens 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 fiber-containing sheet 76 (see FIG. 4(f)). The carbon fiber-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. 4(f)).

[0029] The carbon fiber-containing sheet 76 has a hardness higher than that of the mixture 70 and is in a fully cured or semi-cured state. In this step, for example, the curable rubber composition can be fully cured or semi-cured by heating. Heating may be performed in multiple stages. For example, when the curable rubber composition is a curable silicone rubber composition, the heating temperature during the first heating step can be set preferably in the range of 110 to 150°C, more preferably in the range of 120 to 140°C. Furthermore, the heating temperature during the second heating step can be set higher than the heating temperature during the first heating step, preferably in the range of 180 to 230°C, more preferably in the range of 195 to 215°C.

[0030] (3) Laminate formation process (S130) In this step, the formed carbon fiber-containing sheets 76 are bonded together via an adhesive 80 to form a laminate 90 (see FIG. 5( g )). That is, the laminate 90 is formed by alternately laminating carbon fiber-containing sheets 76 and adhesives 80. The carbon fiber-containing sheets 76 to be laminated may be a single carbon fiber-containing sheet 76 obtained in the sheet formation step, or may be a plurality of carbon fiber-containing sheets 76 obtained by dividing the carbon fiber-containing sheet 76. The adhesive 80 is preferably applied to the sheet surfaces of the carbon fiber-containing sheets 76 during or before lamination. The adhesive 80 is not particularly limited, but is preferably a composition that hardens to form the adhesive layer 30 upon application of heat, light, or electron beams, and more preferably liquid silicone rubber. Using such a composition as the adhesive 80 reduces the risk of the adhesive layer 30 melting or softening due to heat during use of the thermally conductive sheet 1.

[0031] The laminate formation step is a step of forming a laminate 90 by stacking a plurality of carbon fiber-containing sheets 76 in a cylindrical container 85 in the opposite direction from the inner bottom surface 87 of the container 85 (see FIG. 5(h)). The inner bottom surface 87 is inclined at an acute angle θ1 with respect to a plane perpendicular to the height direction of the container 85. The acute angle θ1 is greater than 0 degrees and less than 90 degrees, preferably greater than 0 degrees and equal to or less than 45 degrees, and more preferably 20 to 45 degrees. Therefore, the interior angle of the laminate 90 and a cured product 95 described later is the angle θ2 formed by the wall in the height direction of the container 85 and the inner bottom surface 87 (hereinafter, also simply referred to as the interior angle θ2). θ2 is (90-θ1) degrees.

[0032] This tilting process forms a laminate 90 in the shape of a parallelogram (hereinafter also referred to simply as a parallelogram) on two opposing surfaces of the container 85, with one pair of opposing interior angles θ2 being (90-θ1) degrees and another pair of opposing interior angles being obtuse angles, and the remaining four surfaces being rectangular. In this application, the term "parallelogram" does not include rectangles or squares, but is also interpreted to include rhombuses. Furthermore, in this application, the term "rectangle" refers to a quadrilateral with right angles and includes rectangles and squares. For example, the laminate 90 in FIG. 5(h) is a hexahedron in which two of the four opposing side surfaces are parallelogram-shaped, and the top, bottom, and remaining two side surfaces are rectangular. By tilting the inner bottom surface 87 at an acute angle θ1 with respect to a plane perpendicular to the height direction of the container 85, the orientation direction Do of the carbon fibers 20 inside the laminate 90 can be tilted at an acute angle θ1 from the horizontal direction.

[0033] The container 85 may be used as a mold 89 in the subsequent hardened body forming step.

[0034] (4) Cured body formation process (S140) This step involves curing the formed laminate 90 to form a cured body 95 (see FIG. 6(j)). FIG. 6(j) shows an example of a front view, a plan view, and a right side view of the cured body 95, when the parallelogram-shaped side of the cured body 95 is viewed from the front. More specifically, if the carbon fiber-containing sheet 76 has already cured, only the adhesive 80 will cure to form the adhesive layer 30. On the other hand, if the carbon fiber-containing sheet 76 is in a semi-cured state, this step will cure not only the adhesive 80 but also the carbon fiber-containing sheet 76 (more specifically, the curable rubber composition in the sheet). Examples of curing methods include heating. When only the adhesive 80 is to be cured and liquid silicone rubber is used as the adhesive 80, the heating temperature can be set to a range of preferably 110 to 150°C, more preferably 120 to 140°C.

[0035] When forming the hardened body 95, a heat press or the like may be performed. When performing the heat press, any mold may be used. Furthermore, the container 85 from the previous laminate formation step may be used as a mold 89 (lower mold), or an upper lid 86 shaped to be able to seal the container 85 may be used as a mold 89 (upper mold) (see FIG. 6(i)).

[0036] Furthermore, prior to the cured body forming step, the inside of a mold containing the laminate 90 may be depressurized, and then the cured body 95 may be formed by heat pressing or the like. The depressurization may be performed, for example, to a gauge pressure in the range of -95 to -85 kPa. The time for which the depressurization is performed is not particularly limited, but is preferably 5 to 15 minutes.

[0037] (5) Coating process (S141) This step is a step prior to the cutting step described below, in which at least the surface surrounding the outer periphery of the surface of the cured body 95 in the cutting direction Dc is hardened with a coating 110 to obtain a coated body 100. The coating 110 is not particularly limited as long as it can cover the cured body 95, but is preferably a thermosetting material (resin or rubber). Examples of such materials include silicone rubber, silicone resin, polyurethane resin, and epoxy resin.

[0038] When the cured body 95 is coated with a thermosetting resin material, the cured body 95 is immersed in a container 105 containing a coating material 108, preferably in a state where the coating 110 is not yet hardened (see FIG. 7(k)). The container 105 is then subjected to a curing process, thereby obtaining a coated body 100 in which the cured body 95 is coated with a cured coating 110 of the coating material 108. After curing is complete, the coated body 100 is removed from the container 105. Note that FIG. 7(k) shows a schematic front cross-sectional view of the container 105 in which the cured body 95 is immersed. The dimensions of the container 105 are preferably adjusted to allow the cured body 95 to be fixed in any of the width, height, and length directions of the cured body 95. FIG. 7(k) shows, as an example, a container 105 in which the cured body 95 can be fixed along the width direction w of the side surface of the parallelogram. This step is optional.

[0039] (6) Fixing process (S142) This step is a step of fixing the coated body 100 obtained in the coating step described above onto a fixing body 120 prior to the cutting step described later (see FIG. 7(l)). The fixing body 120 may be, for example, a plate, block, or the like having a flat surface to which the coated body 100 can be fixed and formed of a hard material, preferably a plate or block made of metal or resin, and more preferably a metal plate or metal block. The method for fixing the coated body 100 is not particularly limited, and examples include adhesion using an adhesive. By performing this step, the cutting of the coated body 100 can be performed more stably. This step is optional. In FIG. 7(l), the coated body 100 is fixed onto the fixing body 120 in a state rotated 90 degrees, but this is not limited thereto. For example, the coated body 100 may be fixed onto the fixing body 120 in a state where it is not rotated or where it is rotated 180 degrees.

[0040] (7) Cutting process (S150) In this step, the formed cured body 95 or coated body 100 is cut into sheets to form a thermally conductive sheet 1 (see FIG. 8(m)). In FIG. 8(m), dotted lines indicate the cutting direction Dc, and dashed lines indicate straight lines perpendicular to the cutting direction Dc. In the cutting step, the cured body 95 or coated body 100 is cut in a direction oblique to the orientation direction Do of the carbon fibers 20 oriented therein (cutting direction Dc). The cutting direction Dc is not particularly limited as long as it is parallel or perpendicular to the orientation direction Do. As a result, in the thermally conductive sheet 1 with the surface on the cutting direction Dc side as the horizontal plane, the carbon fibers 20 are oriented at an angle formed by the line of the cutting direction Dc and the line of the orientation direction Do. In FIG. 8, the cured body 95 is cut in the direction of a line (a line in the horizontal direction in FIG. 8) that is not parallel to the orientation direction Do, among the sides that form the interior angle θ2, the cut is made in the direction of a line that is not parallel to the orientation direction Do. In this case, the orientation angle of the carbon fibers 20 in the thermally conductive sheet 1 is θ2. By carrying out the cutting step after carrying out each step as described above, it is possible to reduce the amount of material that is discarded when the material is cut into sheets.

[0041] When the coated body 100 is cut in this step, slices 130 are obtained in which the periphery of the thermally conductive sheet 1 is covered with the coating 110. The thickness of the slices 130 is not particularly limited, but is preferably 0.1 to 1.5 mm.

[0042] The cutting may be performed multiple times to obtain a desired sheet thickness. Various known cutting methods can be used, including a thin blade such as a cutter or similar cutting means, a filamentary cutting means, or an optical cutting means such as a laser, or a method of splitting the sheet using a band machine or the like.

[0043] After the cutting process, the process may include a process of chamfering the sheet edges, and if the coating 100 is cut, a process of removing the coating 110 that covers the periphery of the thermally conductive sheet 1 from the slice 130, and may further include finishing processes such as further cutting, grinding and / or polishing.

[0044] (Second embodiment) Next, a method for manufacturing a thermally conductive sheet according to a second embodiment will be described. Portions common to the previous embodiment will be assigned the same reference numerals, and duplicated descriptions will be omitted. The difference from the method for manufacturing a thermally conductive sheet according to the first embodiment is that it includes a mixing step (S100) in which, prior to the discharge step, the material is sealed in a bag 140 and subjected to non-shear mixing together with the bag 140 to obtain a mixture 70.

[0045] FIG. 9 is a schematic diagram showing a mixing step in a method for producing a thermally conductive sheet according to another embodiment.

[0046] (8) Mixing process (S100) In this process, the curable rubber composition and carbon fibers are mixed to obtain mixture 70. The curable rubber composition and carbon fibers are enclosed in bag 140, and non-shear mixing is performed on the bag 140 to obtain mixture 70. Bag 140 is preferably mixed inside mixer 150, which is capable of non-shear mixing. There are no particular restrictions on the material of bag 140, as long as it will not break inside mixer 150 and can seal the curable rubber composition and carbon fibers.

[0047] Non-shear mixing refers to mixing that is not based on shear action or the action of agitating blades or the like, but rather on mixing that is based on rotation and / or deformation of the mixing vessel. In other words, it refers to mixing that uses three-dimensional movement in irregular directions, rather than mixing that is based on rotation in only one or a specific direction. The mixer used in this embodiment can suitably be, for example, a rocking mixer. A rocking mixer is a mixer that applies force in directions other than the direction of rotation, for example, a mixer in which the rotating shaft itself vibrates up and down and left and right, or the mixing vessel itself deforms, generating three-dimensional convection.

[0048] The mixing time is not particularly limited, but is preferably 10 to 40 minutes, more preferably 15 to 35 minutes, and even more preferably 20 to 30 minutes.

[0049] 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. [Industrial Applicability]

[0050] The method for producing a thermally conductive sheet according to the present invention can be used for, for example, 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.

Claims

1. A method for manufacturing a thermally conductive sheet, comprising: a sheet-like rubber-like elastic body; and carbon fibers embedded in the rubber-like elastic body and oriented in a direction oblique to a thickness direction of the rubber-like elastic body, wherein at least one end of at least a portion of the carbon fibers is exposed on a surface of the rubber-like elastic body, a discharge step of discharging the mixture of carbon fibers and a curable rubber composition onto a flat surface of a flat body in a plurality of rows along a predetermined direction; a sheet forming step of forming the mixture discharged onto the plane into a sheet to form a carbon fiber-containing sheet in which the carbon fibers are oriented in the predetermined direction; a laminate formation step of forming a laminate by stacking a plurality of the carbon fiber-containing sheets with an adhesive disposed between the carbon fiber-containing sheets; a cured body forming step of forming a cured body by curing the laminate; a cutting step of cutting the cured body into sheets in a direction oblique to the orientation direction of the carbon fibers so as to cut the carbon fibers; Including, The laminate forming step is a step of forming the laminate by stacking a plurality of the carbon fiber-containing sheets in a cylindrical container from an inner bottom surface of the container in opposite directions, The inner bottom surface is inclined at an acute angle θ1 with respect to a plane perpendicular to the height direction of the container, A method for manufacturing a thermally conductive sheet, characterized in that the laminate is formed in the container so that two opposing surfaces are parallelogram-shaped, with one pair of opposing interior angles being (90-θ1) degrees and another pair of opposing interior angles being obtuse angles, and the remaining four surfaces are hexahedral, with rectangles.

2. The method further includes a coating step of forming a coated body by hardening at least a surface of the surface of the cured body surrounding the outer periphery in the cutting direction, prior to the cutting step, 2. The method for producing a thermally conductive sheet according to claim 1, wherein in the cutting step, the coating is cut into sheets in a direction oblique to the orientation direction of the carbon fibers.

3. 3. The method for producing a thermally conductive sheet according to claim 2, further comprising a fixing step of fixing the coating body on a fixing body after the coating step and before the cutting step.

4. 2. The method for manufacturing a thermally conductive sheet according to claim 1, wherein the acute angle θ1 is greater than 0 degrees and equal to or less than 45 degrees.

5. 2. The method for producing a thermally conductive sheet according to claim 1, wherein, prior to the cured body forming step, the inside of a mold containing the laminate is subjected to a decompression treatment, and then the cured body is formed.

6. The method further includes a mixing step of mixing the curable rubber composition and the carbon fibers to obtain the mixture prior to the discharging step, 2. The method for manufacturing a thermally conductive sheet according to claim 1, wherein the mixing step is a step of enclosing the curable rubber composition and the carbon fibers in a bag and performing non-shear mixing together with the bag to obtain the mixture.

7. 2. The method for manufacturing a thermally conductive sheet according to claim 1, wherein the discharging step is a step of discharging the mixture onto the flat surface in a plurality of rows so as to reciprocate along the predetermined direction.

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