Manufacturing method of thermally conductive sheet

Abstract

To provide a manufacturing method of a thermally conductive sheet that allows large slices to be obtained.SOLUTION: In a manufacturing method of a thermally conductive sheet according to the present invention, a workpiece exhibiting anisotropic thermal conductivity is produced using a resin composition containing a resin and an anisotropic inorganic filler having a major axis and a minor axis, the workpiece is sliced to obtain slices having a higher thermal conductivity in the thickness direction than in the planar direction, and a thermally conductive sheet whose thickness direction coincides with the thickness direction of the slices is produced. The manufacturing method of thermally conductive sheet according to the present invention includes a workpiece production process in which the workpiece is produced in a direction in which a first direction having low thermal conductivity intersects with a second direction having a higher thermal conductivity than the first direction, and a slice acquisition process in which the workpiece is sliced around an axis extending along the first direction to obtain strip-shaped slices.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, in the field of electronics, thermally conductive sheets have been known that include a polymer matrix layer formed from a polymer matrix composition containing a polymer matrix (e.g., silicone resin) and an anisotropic inorganic filler having a major axis and a minor axis (e.g., boron nitride filler) (for example, Patent Document 1 below).

[0003] The thermally conductive sheet is used, for example, to dissipate heat generated by a semiconductor element incorporated in a semiconductor module.

[0004] The following Patent Document 1 describes that the thermally conductive sheet is produced according to the following procedure. (1) A polymer matrix composition containing the polymer matrix and the anisotropic inorganic filler (plurality of anisotropic inorganic fillers) is prepared. (2) Using a coating applicator (e.g., a bar coater), the polymer matrix resin is molded into a sheet having a rectangular shape in plan view while applying shear force to the polymer matrix resin composition along the coating direction (flow direction) (obtaining a primary sheet). Furthermore, by preparing the primary sheet while applying shear force as described above, each of the anisotropic inorganic fillers is arranged in the primary sheet such that its major axis is oriented in a direction perpendicular to the thickness direction of the primary sheet (i.e., a direction parallel to the surface direction of the primary sheet). (3) A plurality of the primary sheets are stacked in the thickness direction so that the orientation direction of the long axis of the anisotropic inorganic filler in one primary sheet is approximately the same as the orientation direction of the long axis of the anisotropic inorganic filler in another primary sheet, thereby obtaining a laminated block as the workpiece. That is, a rectangular parallelepiped workpiece is obtained. (4) The laminated block (workpiece) is cut along the lamination direction of the primary sheet so as to intersect with the long axis of the anisotropic inorganic filler, thereby obtaining the polymer matrix layer (slice piece). (5) The thermally conductive sheet is prepared so as to include the slices. The slice contains the anisotropic inorganic filler in such a manner that the major axis is oriented in the thickness direction of the slice. Generally, the anisotropic inorganic filler has higher thermal conductivity in the long axis direction than in the short axis direction. Therefore, a thermally conductive sheet including such slices can exhibit good thermal conductivity in the thickness direction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-145134 Summary of the Invention [Problem to be solved by the invention]

[0006] In the above manufacturing method, the slices are obtained by cutting the rectangular workpiece along the stacking direction of the primary sheet, so the planar dimensions of the obtained slices are the same as the dimensions of one side of the rectangular workpiece. Therefore, the above manufacturing method is suitable for obtaining a plurality of slices having the same dimensions from one workpiece.

[0007] The thermally conductive sheet may be formed by directly using a small sheet cut out from a sliced ​​piece, or by stacking a plurality of small sheets. When cutting the small sheets from the slices, it is difficult to use up the entire slice, including the outer periphery. Therefore, in consideration of improving yield, it is preferable to cut out large slice pieces from the workpiece. However, in the manufacturing method described above, in which slices are cut out from a rectangular parallelepiped workpiece, only slices having a fixed size (dimensions) can be obtained.

[0008] Therefore, an object of the present invention is to provide a method for producing a thermally conductive sheet that can produce large slices. [Means for solving the problem]

[0009] That is, the method for producing a thermally conductive sheet according to the present invention includes the steps of: A method for producing a thermally conductive sheet, comprising: preparing a workpiece exhibiting anisotropic thermal conductivity using a resin composition containing a resin and an anisotropic inorganic filler having a major axis and a minor axis; slicing the workpiece to obtain slices having higher thermal conductivity in a thickness direction than in a plane direction; and producing a thermally conductive sheet having a thickness direction that coincides with the thickness direction of the slices, a workpiece fabrication step of fabricating the workpiece in a direction in which a first direction having a low thermal conductivity and a second direction having a higher thermal conductivity than the first direction intersect; and a slice obtaining step of slicing the workpiece around an axis extending along the first direction to obtain strip-shaped slices. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for producing a thermally conductive sheet that can produce slices having larger planar dimensions than those obtained by conventional methods. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a flow diagram illustrating a method for producing a thermally conductive sheet according to an embodiment of the present invention. [Figure 2A] FIG. 3 is a perspective view showing a rectangular parallelepiped resin sheet obtained in the resin sheet preparation step. [Figure 2B]FIG. 10 is a perspective view showing a disk-shaped resin sheet cut out from a rectangular parallelepiped resin sheet. [Figure 2C] FIG. 10 is a perspective view showing a state in which a plurality of disc-shaped resin sheets are stacked. [Figure 2D] FIG. 10 is a top view showing how a thermally conductive sheet is cut out in a spiral shape from a cylindrical resin sheet laminate. [Figure 2E] FIG. 10 is a perspective view showing a donut-shaped resin sheet cut out from a rectangular parallelepiped resin sheet. [Figure 2F] FIG. 10 is a perspective view showing a state in which a plurality of doughnut-shaped resin sheets are stacked. [Figure 2G] FIG. 10 is a top view showing how a thermally conductive sheet is cut out in a spiral shape from a cylindrical resin sheet laminate. [Figure 3] FIG. 1 is a perspective view showing a cylindrical laminate obtained by stacking rectangular parallelepiped resin sheets in a spiral shape. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following, one embodiment of the present invention will be simply referred to as the present embodiment.

[0013] [Method for manufacturing thermally conductive sheets] The method for manufacturing a thermally conductive sheet according to this embodiment involves producing a workpiece exhibiting anisotropic thermal conductivity using a resin composition containing a resin and an anisotropic inorganic filler having a major axis and a minor axis, slicing the workpiece to obtain slices having higher thermal conductivity in the thickness direction than in the planar direction, and manufacturing a thermally conductive sheet whose thickness direction coincides with the thickness direction of the slices. As shown in Figure 1, the method for manufacturing a thermally conductive sheet according to this embodiment includes a workpiece preparation step (S1) for preparing a workpiece in which a first direction having low thermal conductivity intersects with a second direction having higher thermal conductivity than the first direction, and a slice acquisition step (S2) for slicing the workpiece around an axis extending along the first direction to obtain strip-shaped slices.

[0014] As the resin, various known resins can be used. Examples of the resin include a thermoplastic resin, a thermoplastic elastomer, and a thermosetting resin.

[0015] Examples of the thermoplastic resin include polyethylene, polypropylene, ethylene-α-olefin copolymers (such as ethylene-propylene copolymers), polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, polyvinyl acetal, fluorinated copolymers (such as polyvinylidene fluoride and polytetrafluoroethylene), polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene copolymer (ABS) resins, polyphenylene-ether copolymers (PPE) resins, modified PPE resins, aliphatic polyamides, aromatic polyamides, polyimide, polyamideimide, polymethacrylic acid, polymethacrylic acid esters (such as polymethyl methacrylate ester), polyacrylic acids, polycarbonate, polyphenylene sulfide, polysulfone, polyethersulfone, polyethernitrile, polyetherketone, polyketone, liquid crystal polymers, and ionomers.

[0016] Examples of the thermoplastic elastomer include a styrene-butadiene block copolymer or a hydrogenated product thereof, a styrene-isoprene block copolymer or a hydrogenated product thereof, a styrene-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, a vinyl chloride-based thermoplastic elastomer, a polyester-based thermoplastic elastomer, a polyurethane-based thermoplastic elastomer, and a polyamide-based thermoplastic elastomer.

[0017] Examples of the thermosetting resin include epoxy resin, phenol resin, polyimide resin, unsaturated polyester resin, diallyl phthalate resin, and crosslinked rubber. The crosslinked rubber means a rubber obtained by subjecting raw rubber to a crosslinking treatment.

[0018] The resin is preferably a thermosetting resin. As the resin, it is preferable to use the epoxy resin among the thermosetting resins. That is, the resin composition is preferably a thermosetting resin composition containing an epoxy resin as the resin. The thermosetting resin composition may contain 60% by mass or more, or 70% by mass or more of the epoxy resin as the resin. The thermosetting resin composition may contain 95% by mass or less, or 85% by mass or less of the epoxy resin as the resin. Furthermore, the thermosetting resin composition may contain 100 mass % of the epoxy resin as the resin. That is, in the thermosetting resin composition, all of the resins may be the epoxy resins.

[0019] Examples of the epoxy resin include various known epoxy resins such as triphenylmethane type epoxy resin, cresol novolac type epoxy resin, bisphenol A type epoxy resin, modified bisphenol A type epoxy resin, bisphenol F type epoxy resin, modified bisphenol F type epoxy resin, bisphenol AD ​​type epoxy resin, modified bisphenol AD ​​type epoxy resin, dicyclopentadiene type epoxy resin, phenol novolac type epoxy resin, and biphenyl type epoxy resin.

[0020] The softening point of the epoxy resin is preferably 30°C or higher, more preferably 40°C or higher, and even more preferably 50°C or higher. The softening point of the epoxy resin may be 80°C or lower, 70°C or lower, or 60°C or lower.

[0021] As the epoxy resin, it is preferable to use the triphenylmethane type epoxy resin, since it has a softening point within the above range. Commercially available triphenylmethane epoxy resins include, for example, products manufactured by Nippon Kayaku Co., Ltd. under the trade names "EPPN-501H," "EPPN-501HY," and "EPPN-502H."

[0022] In this specification, the softening point of the epoxy resin can be measured by the ring and ball method of JIS 7234-1986.

[0023] When the epoxy resin is used as the resin, the thermosetting resin may contain a curing agent for the epoxy resin. As the curing agent for the epoxy resin, for example, a phenol-based curing agent, an amine-based curing agent, an acid anhydride-based curing agent, or the like can be used. The phenol-based curing agent, the amine-based curing agent, and the acid anhydride-based curing agent may be used alone or in combination of two or more.

[0024] Examples of the phenol-based curing agent include phenol novolac resin, aralkyl-type phenol resin, dicyclopentadiene-modified phenol resin, naphthalene-type phenol resin, bisphenol-type phenol resin, and triphenylmethane-type phenol resin. The phenol-based curing agent is preferably the phenol novolac resin. Commercially available phenol novolac resins include those manufactured by Gunei Chemical Industry Co., Ltd. under the trade name "GS-200" and those manufactured by Meiwa Kasei Co., Ltd. under the trade names "H-4" and "HF-1M".

[0025] Examples of the amine-based curing agent include diaminodiphenyl sulfone, dicyandiamide, diaminophenylmethane, and triethylenetetramine.

[0026] Examples of the acid anhydride curing agent include phthalic anhydride, trimellitic anhydride, and maleic anhydride.

[0027] When the resin composition is the thermosetting resin composition, the thermosetting resin composition contains the epoxy resin as the resin, and the resin contains a curing agent for the epoxy resin, the resin preferably contains 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more of the curing agent for the epoxy resin per 100 parts by mass of the epoxy resin. Furthermore, the resin preferably contains 80 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 65 parts by mass or less of a curing agent for the epoxy resin per 100 parts by mass of the epoxy resin.

[0028] The resin may further contain additives, such as a curing accelerator that accelerates the curing reaction between the epoxy resin and the curing agent, a dispersant, a tackifier, an antiaging agent, an antioxidant, a processing aid, a stabilizer, an antifoaming agent, a flame retardant, a thickener, and a pigment.

[0029] The thermosetting resin preferably further contains a curing accelerator as an additive. Examples of the curing accelerator include tetraphenylphosphonium tetraphenylborate, imidazoles, triphenylphosphate (TPP), and amine-based curing accelerators. Examples of the amine-based curing accelerator include boron trifluoride monoethylamine.

[0030] The thermosetting resin preferably contains 0.01 parts by mass or more and 3.00 parts by mass or less, and more preferably 0.02 parts by mass or more and 1.50 parts by mass or less, of the curing accelerator per 100 parts by mass of the thermosetting resin.

[0031] As described above, the anisotropic inorganic filler has a major axis and a minor axis. The anisotropic inorganic filler is an inorganic filler whose thermal conductivity characteristics differ between the major axis direction and the minor axis direction. That is, the anisotropic inorganic filler is an inorganic filler whose thermal conductivity is directionally dependent. Examples of the particle shape of the anisotropic inorganic filler include plate-like, needle-like, and oval-spherical shapes. The anisotropic inorganic filler is preferably a plate-like inorganic filler having a plate-like particle shape or a needle-like inorganic filler having a needle-like particle shape. The anisotropic inorganic filler is more preferably the plate-like inorganic filler.

[0032] An example of the plate-like inorganic filler is boron nitride filler (h-BN). The plate-like inorganic filler may also be an alumina filler, silicon carbide filler, silicon dioxide filler, magnesium oxide filler, diamond filler, aluminum nitride filler, silicon nitride filler, gallium nitride filler, or the like, which has been processed into a plate-like particle shape. Among these various plate-like inorganic fillers, it is preferable to use boron nitride filler (h-BN).

[0033] The boron nitride filler (h-BN) has a hexagonal crystal structure and is a plate-like (more specifically, scale-like) inorganic filler that exhibits large anisotropy in thermal conductivity in the long axis direction (the (002) plane direction in Miller indices; hereinafter, simply referred to as the (002) plane direction). Specifically, the boron nitride filler has a thermal conductivity of 100 to 200 W / m K in the long axis direction (the (002) plane direction), and a thermal conductivity of 1 to 2 W / m K in the short axis direction (the (100) plane direction perpendicular to the (002) plane direction; hereinafter, simply referred to as the (100) plane direction). That is, in the boron nitride filler, the thermal conductivity in the long axis direction ((002) plane direction) is about 100 times higher than the thermal conductivity in the short axis direction ((100) plane direction).

[0034] Examples of the needle-like inorganic filler include whisker-like fillers. Examples of the whisker-like filler include aluminum nitride whiskers, alumina whiskers, calcium carbonate whiskers, and calcium metasilicate whiskers. The whisker-like filler is a highly thermally conductive inorganic filler having a relatively high thermal conductivity at 20°C. The whisker-like filler particles generally have a thickness of 2 to 3 μm and a length of several tens of μm to several thousands of μm. Among the various whisker-like fillers mentioned above, the aluminum nitride whiskers exhibit a particularly high thermal conductivity at 20° C. (170 W / (m·K) or more). Therefore, when the whisker-like filler is used as the anisotropic inorganic filler, it is preferable to use aluminum nitride whiskers in order to ensure that the thermally conductive sheet exhibits good thermal conductivity.

[0035] As the anisotropic inorganic filler, the plate-like inorganic filler and the needle-like inorganic filler may be used in combination. By using the plate-like inorganic filler and the needle-like inorganic filler in combination, the needle-like inorganic filler can be interposed between adjacent plate-like inorganic fillers in the resin composition, and the adjacent plate-like inorganic fillers can be connected by the interposed needle-like inorganic filler. In this way, adjacent plate-like inorganic fillers are connected by the needle-like inorganic fillers, thereby forming a good heat conduction path in the orientation direction of the long axes of the plate-like inorganic fillers.

[0036] The resin composition may contain an isotropic inorganic filler in addition to the anisotropic inorganic filler. The isotropic inorganic filler does not have a major axis and a minor axis like the anisotropic inorganic filler, and the thermal conductivity characteristics do not depend on the direction. The particle shape of the isotropic inorganic filler may be spherical, cubic, or the like. The isotropic inorganic filler is preferably a spherical inorganic filler having a spherical particle shape, from the viewpoint of being easily dispersed in the resin when the resin composition is obtained.

[0037] Examples of the spherical inorganic filler include alumina filler, silicon carbide filler, silicon dioxide filler, magnesium oxide filler, diamond filler, aluminum nitride filler, silicon nitride filler, gallium nitride filler, etc., which have been processed into spherical particle shapes.

[0038] In the following description, the anisotropic inorganic filler and the isotropic inorganic filler will be collectively referred to simply as "inorganic filler."

[0039] The anisotropic inorganic filler preferably accounts for 70% by mass or more of the total mass of the inorganic filler, more preferably 80% by mass or more, and even more preferably 90% by mass or more. Furthermore, from the viewpoint of further increasing the thermal conductivity in the thickness direction of the thermally conductive sheet, it is particularly preferable that the anisotropic inorganic filler in the resin composition accounts for 100% by mass of the total mass of the inorganic filler. That is, it is particularly preferable that the resin composition contains only the anisotropic inorganic filler as the inorganic filler. Furthermore, the resin composition preferably contains only the plate-like inorganic filler as the anisotropic inorganic filler, and the plate-like inorganic filler preferably contains only the boron nitride filler.

[0040] The resin composition preferably contains 30% by volume or more of the inorganic filler, more preferably 40% by volume or more, even more preferably 50% by volume or more, and particularly preferably 55% by volume or more. The resin composition preferably contains 90% by volume or less of the inorganic filler, more preferably 85% by volume or less, and even more preferably 80% by volume or less.

[0041] Hereinafter, the workpiece preparing step S1 and the slice obtaining step S2 in the method for producing a thermally conductive sheet according to this embodiment will be described in more detail with reference to FIGS. 2A to 2F. In the following, a method for manufacturing a thermally conductive sheet will be described, mainly taking as an example a method in which a disk-shaped or doughnut-shaped resin sheet obtained by extruding the resin composition into a sheet is stacked to produce a cylindrical or cylindrical workpiece, and then the workpiece is sliced ​​along the periphery (outer periphery or inner periphery) of the workpiece; however, the method for manufacturing a thermally conductive sheet is not limited to this. Furthermore, when a resin sheet is produced by extrusion using a resin composition containing an anisotropic inorganic filler such as a plate-like inorganic filler, the anisotropic inorganic filler in the resin sheet becomes oriented so that the long axis direction is along the planar direction of the resin sheet. Therefore, the thickness direction of the resin sheet, i.e., the direction along the central axis of the cylindrical or cylindrical workpiece, becomes the first direction in which the thermal conductivity is relatively low, and the planar direction of the resin sheet that intersects this first direction at right angles, i.e., the radial direction of the cylindrical or cylindrical workpiece, becomes the second direction in which the thermal conductivity is relatively high.

[0042] In the following, we will first explain a first example in which a cylindrical body is produced as the workpiece in the workpiece preparation step S1, and then slices are obtained from this cylindrical workpiece in the slice obtaining step S2 (see Figures 2A to 2D). Next, we will explain a second example in which a cylindrical body is produced as the workpiece in the workpiece preparation step S1, and then slices are obtained from this cylindrical workpiece in the slice obtaining step S2 (see Figure 2A and Figures 2E to 2G). In the case of the cylindrical workpiece, the outer peripheral surface serves as the slicing surface, and in the case of the cylindrical workpiece, at least one of the outer peripheral surface and the inner peripheral surface serves as the slicing surface.

[0043] In the following, an example will be described in which the resin composition is a thermosetting resin composition containing an epoxy resin as the resin, and the anisotropic inorganic filler contains the plate-like inorganic filler (more specifically, boron nitride filler) having a plate-like particle shape. Although the plate-like inorganic filler is shown in FIG. 2A, the plate-like inorganic filler is not shown in FIGS. 2B to 2G.

[0044] (Workpiece preparation step S1 according to the first example) In the workpiece preparation step S1 in the first example, a thermosetting resin composition containing the epoxy resin and the plate-like inorganic filler is extruded to prepare a resin sheet whose thickness direction is perpendicular to the extrusion direction (hereinafter referred to as the resin sheet preparation step S1a). The resin sheet preparation step S1a can be performed using an extruder equipped with one or more screws and a die disposed downstream of the one or more screws. The die has a rectangular opening at one end in the extrusion direction. More specifically, the die has a rectangular opening with the horizontal direction as the longitudinal direction and the vertical direction as the lateral direction, that is, a horizontally elongated rectangular opening. The resin sheet preparation step S1a can be performed by kneading the epoxy resin and the plate-like inorganic filler while flowing them in the axial direction in the one or more screws to obtain the thermosetting resin composition, and then extruding the thermosetting resin composition from the horizontally elongated rectangular opening of the die. As a result, a rectangular parallelepiped resin sheet 10 as shown in FIG. 2A can be obtained. In the following description, the rectangular parallelepiped resin sheet 10 will also be simply referred to as a resin sheet.

[0045] The die may be a flat die (T die) or a circular die (annular die). The resin sheet may be produced so that its thickness is thinner than the die lip distance (the dimension of the die opening in the thickness direction of the sheet) by increasing the sheet take-up speed faster than the extrusion speed of the resin composition from the die. When the die lip spacing is T and the average thickness of the resin sheet is t, the draw-down ratio, which is calculated as the ratio (t / T) of the average thickness t of the extruded sheet to the die lip spacing T, may be 1 or less, 0.9 or less, or 0.8 or less. The withdrawal ratio is usually set to 0.3 or more. Such drawing is effective in improving the orientation of anisotropic inorganic fillers such as the plate-like inorganic filler.

[0046] The extrusion through the die may be carried out so that the thickness of the resin sheet is greater than the die lip distance T immediately after being extruded from the die. That is, extrusion through the die may be carried out so as to cause so-called die swell. When the thickness of the resin sheet immediately after extrusion is t0, the swell ratio, calculated as the ratio (t0 / T) of the thickness t0 of the resin sheet immediately after extrusion to the die lip spacing T, may be 1.1 or more, 1.2 or more, or 1.5 or more. The swell ratio is usually 3 or less. When the die swell is generated as described above, the effect of drawing down is more pronounced, and the orientation of the anisotropic inorganic filler such as the plate-like inorganic filler can be further improved.

[0047] The resin sheet extruded from the die may be compressed in the thickness direction by passing it through a pair of rolls (squeezing rolls) arranged with a gap slightly narrower than the thickness of the resin sheet. Furthermore, when compressing the resin sheet by passing it between the pair of rolls, the peripheral speed of at least one of the pair of rollers may be slower than the moving speed of the resin sheet so that a shear force is applied in the extrusion direction of the resin sheet. This makes it possible to further improve the orientation of the anisotropic inorganic filler such as the plate-like inorganic filler.

[0048] Here, in order to ensure that the thermally conductive sheet manufactured by the thermally conductive sheet manufacturing method according to this embodiment exhibits good thermal conductivity, the thermosetting resin composition contains the plate-like inorganic filler in a high mass ratio, as described above. As described above, even if the epoxy resin and the plate-like inorganic filler are kneaded while flowing in the axial direction in the one or more screws, the plate-like inorganic filler is not contained in the thermosetting resin composition in a state where all of the plate-like inorganic filler is oriented with its major axis aligned with the extrusion direction, since the mass ratio of the plate-like inorganic filler in the thermosetting resin composition is high. That is, the particles are contained in the thermosetting resin composition in such a manner that the major axes are oriented in various directions (hereinafter simply referred to as various directions) other than the extrusion direction.

[0049] Therefore, even in the rectangular parallelepiped resin sheet 10 obtained by extruding the thermosetting resin composition from the horizontally elongated rectangular opening of the die, the plate-like inorganic filler is contained in a form in which the long axes are oriented in various directions (see Figure 2A).

[0050] In the workpiece manufacturing process S1 according to the first example, the rectangular parallelepiped-shaped resin sheet 10 obtained in the resin sheet manufacturing step S1a is then cut along the line α as shown in FIG. 2A to obtain a disk-shaped resin sheet 10' as shown in FIG. 2B. The disc-shaped resin sheet 10' can be cut out from the rectangular parallelepiped resin sheet 10 by, for example, punching press using a hollow cylindrical mold. In the following, cutting out the disc-shaped resin sheet 10' from the rectangular parallelepiped resin sheet 10 will be referred to as a raw material sheet cutting step S1b.

[0051] The raw material sheet cutting step S1b can be performed using, for example, a blade such as a cutter.

[0052] In the workpiece manufacturing step S1 according to the first example, next, multiple disk-shaped resin sheets 10' obtained in the raw material sheet cutting step S1b are stacked in the thickness direction to obtain a cylindrical resin sheet laminate 20' (cylindrical workpiece) as shown in Figure 2C (hereinafter referred to as resin sheet laminate manufacturing step S1c). In FIG. 2C, the central axis of the cylindrical resin sheet laminate 20' is indicated as CA.

[0053] In the resin sheet laminate fabrication step S1c, a plurality of stacked disc-shaped resin sheets 10' are bonded to each other and integrated to obtain a cylindrical resin sheet laminate 20'.

[0054] In the resin sheet laminate fabrication step S1c, a plurality of disc-shaped resin sheets 10' are stacked on one another in the thickness direction, and then hot pressed to apply pressure in the stacking direction. This allows the epoxy resin contained in each of the disk-shaped resin sheets 10' to melt, and the overlapping disk-shaped resin sheets 10' can be bonded together by the molten epoxy resin. As a result, a cylindrical resin sheet laminate 20' can be obtained in which the overlapping disk-shaped resin sheets 10' are integrated together.

[0055] The heat pressing can be carried out using, for example, an SFV type vacuum compression molding machine (manufactured by Shinto Metal Industries Co., Ltd., hereinafter referred to as "press machine").

[0056] As described above, when a plurality of disc-shaped resin sheets 10′ are stacked in the thickness direction and then heat-pressed to apply pressure in the stacking direction, the plate-like inorganic filler particles are arranged in a plane (specifically, a plane F) whose major axis is perpendicular to the central axis CA of the cylindrical resin sheet laminate 20′. co ) along the direction of the Therefore, in the cylindrical resin sheet laminate 20′, the thermal conductivity in the direction along the central axis CA is low, and the plane F intersecting (specifically, perpendicular to) the central axis CA co The thermal conductivity in the direction along the central axis CA is higher than the thermal conductivity in the direction along the central axis CA. Therefore, in FIG. 2C, the direction along the central axis CA is shown as the first direction, and the plane F co The direction along the arrow is shown as the second direction. That is, the cylindrical resin sheet laminate 20' has a low thermal conductivity in the first direction, and a higher thermal conductivity in the second direction than the thermal conductivity in the first direction.

[0057] Here, "the plate-like inorganic fillers are arranged such that the long axes thereof are aligned in a direction along a plane perpendicular to the central axis CA of the cylindrical resin sheet laminate 20'" means that when the cylindrical resin sheet laminate 20' cut in the thickness direction is observed in cross section, in a randomly selected rectangular region of 100 μm × 100 μm, 70% or more of the plate-like inorganic fillers contained in the region have long axes that form an angle of 45° or less with respect to a plane perpendicular to the central axis CA. The cross section of the rectangular parallelepiped resin sheet 10 cut in the thickness direction can be observed using an image taken at a magnification of 500 to 1000 times using a scanning electron microscope (SEM).

[0058] When the cross-section of the cylindrical resin sheet laminate 20' is observed, it is preferable that 70% or more of the plate-like inorganic fillers contained in the rectangular region have an angle of the long axis of 30° or less with respect to the plane, more preferably 20° or less, and even more preferably 10° or less. Furthermore, it is more preferable that 80% or more of the plate-like inorganic filler particles contained in the region have the angle of the major axis relative to the plane of 20° or less, and even more preferable that the angle is 10° or less. Since the plate-like inorganic filler is contained in the cylindrical resin sheet laminate 20' in the above-described form, the long axis of the plate-like inorganic filler is more aligned in the thickness direction in the slices obtained in the slice obtaining step S2 described below. Therefore, in a thermally conductive sheet produced using such slices, a more favorable thermal conduction path is formed in the thickness direction. This allows the thermally conductive sheet to have even better thermal conductivity in the thickness direction.

[0059] In order to sufficiently bond and integrate the stacked disc-shaped resin sheets 10' to each other, it is preferable to carry out the heat pressing while heating at a temperature that is at least 10°C lower than the softening point of the epoxy resin contained in the disc-shaped resin sheet 10', more preferably at a temperature that is at least 5°C lower than the softening point of the epoxy resin, and even more preferably at a temperature that is at least the softening point of the epoxy resin.

[0060] Multiple rectangular parallelepiped-shaped resin sheets 10 may be stacked so that the extrusion directions of adjacent rectangular parallelepiped-shaped resin sheets 10 on the top and bottom are aligned, or may be stacked so that the extrusion directions of adjacent rectangular parallelepiped-shaped resin sheets 10 on the top and bottom are different. A plurality of rectangular parallelepiped resin sheets 10 are preferably stacked so that the extrusion directions intersect.

[0061] Incidentally, the thermally conductive sheet produced using the sliced ​​pieces containing the epoxy resin is in a semi-cured, B-stage state before the sheet surface is attached to the surface of the adherend. Such a thermally conductive sheet is used by subjecting it to a heat treatment to transition it from a semi-cured B-stage state to a fully cured C-stage state, thereby adhering the sheet surface to the adherend surface of the adherend. Therefore, when the disc-shaped resin sheet 10' contains the epoxy resin as described above, it is necessary to carry out the heat pressing so that it does not reach a C-stage state, which is a completely hardened state, in order to ensure adhesion to the adherend surface. That is, when a plurality of disc-shaped resin sheets 10' containing the epoxy resin are stacked in the thickness direction and then hot pressed, it is necessary to maintain the semi-cured B-stage state. Therefore, it is preferable that the heat pressing is carried out at a temperature lower than the curing temperature of the epoxy resin. For example, the heat pressing is preferably carried out at a press temperature of 120°C or less, more preferably 100°C or less, and even more preferably 80°C or less.

[0062] The pressure applied during the heat pressing can be 0.5 MPa or more and 2.0 MPa or less.

[0063] By carrying out the workpiece fabrication step S1 according to the first example as described above, a cylindrical resin sheet laminate 20' (cylindrical workpiece) as shown in FIG. 2C can be obtained.

[0064] (Slice piece obtaining step S2 according to the first example) In the sliced ​​piece obtaining process S2 in the first example, the outer peripheral surface of a cylindrical resin sheet laminate 20' (cylindrical workpiece) as shown in Figure 2D is sliced ​​along the circumferential direction to obtain strip-shaped sliced ​​pieces from the cylindrical resin sheet laminate 20'. That is, in the slice obtaining step S2 according to the first example, the cylindrical resin sheet laminate 20' is sliced ​​around the central axis CA (ie, the axis extending along the first direction) to obtain strip-shaped slices.

[0065] When the workpiece is a cylindrical resin sheet laminate 20' as shown in Figure 2D, the slicing is performed so that the slice pieces are cut out in a spiral shape (see the dotted line in Figure 2D) when viewed in the direction of the central axis (CA) of the cylindrical resin sheet laminate 20', as shown in Figure 2D. More specifically, as shown in FIG. 2D, the slices are cut out in a spiral shape using a blade such as a cutter, starting from an arbitrary point (point A) on the outer peripheral surface of the cylindrical resin sheet laminate 20′. The blade for cutting the slices may be arranged so that the cutting edge is perpendicular to the slicing direction, or may be arranged so that the cutting edge is oblique. The cutting edge of the blade may be straight. The blade may have a cutting edge shaped like an inverted V. More specifically, the blade may have an inverted V shape with the central part in the width direction protruding in the slicing direction. Furthermore, the blade may have a plurality of projections and recesses on the cutting edge, like a tape cutter, and the projections and recesses may be arranged alternately in the width direction. The blade may have a curved cutting edge. Additionally, the slicing may be performed using a cutting tool such as a hand saw or a wire saw.

[0066] The slices can be cut out from the cylindrical resin sheet laminate 20' using a cutter, for example, by holding the cylindrical resin sheet laminate 20' so that it can rotate in the circumferential direction, abutting the cutting edge of the cutter against the outer peripheral surface of the cylindrical resin sheet laminate 20', and then rotating the cylindrical resin sheet laminate 20' in the circumferential direction.

[0067] The slices may be cut to a thickness of, for example, 30 μm or more, 50 μm or more, 100 μm or more, or 200 μm or more. Furthermore, the slices may be cut to a thickness of, for example, 1000 μm or less, 750 μm or less, or 450 μm or less.

[0068] The slice obtaining step S2 according to the first example is preferably carried out while heating the portion of the cylindrical resin sheet laminate 20' to be sliced. By heating the portion of the cylindrical resin sheet laminate 20' to be sliced, the portion (hereinafter simply referred to as the slice portion) can be adjusted to a hardness suitable for cutting out slices. Here, when the cylindrical resin sheet laminate 20' contains an epoxy resin as the resin, as in this example, the cylindrical resin sheet laminate 20' is particularly hard. Therefore, if slicing is performed without heating the sliced ​​area, this hardness may cause the cylindrical resin sheet laminate 20' to collapse during slicing, and there is a concern that slices of sufficient dimensions may not be able to be cut out. However, even if the cylindrical resin sheet laminate 20' contains epoxy resin as the resin, the sliced ​​portion can be softened to a hardness suitable for cutting by heating the sliced ​​portion, so that slices having sufficient dimensions can be cut out. That is, slices with sufficient dimensions can be obtained.

[0069] The sliced ​​area is preferably heated to a temperature that is at least 10°C below the softening point of the epoxy resin, more preferably at least 5°C below the softening point of the epoxy resin, and even more preferably at least the softening point of the epoxy resin. By heating the sliced ​​portion at the above temperature, it becomes easier to cut out the slices from the cylindrical resin sheet laminate 20'. The sliced ​​portions can be heated, for example, by applying hot air from a dryer to the sliced ​​portions. The sliced ​​portions can also be heated by heating the cutting edge of a cutter used to cut out the slices.

[0070] Here, if the sliced ​​portion is heated to an excessively high temperature, the curing reaction of the epoxy resin will proceed excessively. If the curing reaction of the epoxy resin proceeds excessively in this way, the sliced ​​portions become too hard and brittle, and are prone to crumbling. In such a case, it becomes difficult to cut out the slices having large planar dimensions from the cylindrical resin sheet laminate 20'. Moreover, if the curing reaction of the epoxy resin proceeds excessively, the epoxy resin may reach a C-stage state, which is a completely cured state. In such a case, a thermally conductive sheet made from slices cut out from the cylindrical resin sheet laminate 20' will not be able to exhibit sufficient adhesiveness to the adherend surface of the adherend. In this way, from the viewpoint of preventing the curing reaction of the epoxy resin from proceeding excessively, it is preferable that the slicing of the portion is carried out at a temperature lower than the curing temperature of the epoxy resin. For example, the heating of the sliced ​​portion is preferably carried out at a temperature of not more than 10°C above the softening point of the epoxy resin, more preferably at a temperature of not more than 7°C above the softening point of the epoxy resin, and even more preferably at a temperature of not more than 5°C above the softening point of the epoxy resin.

[0071] In this manner, slices can be obtained from the cylindrical resin sheet laminate 20' (cylindrical workpiece) shown in FIG. 2C.

[0072] When the sliced ​​piece is observed in cross section in the thickness direction, in a randomly selected horizontally elongated rectangular region of 100 μm width x 10 μm height, it is preferable that 70% or more of the plate-like inorganic filler contained in the region has an angle of 45° or less, more preferably 30° or less, and even more preferably 20° or less, of the long axis with respect to one plane of the sliced ​​piece (the surface to be adhered to the substrate of the thermally conductive sheet produced using the sliced ​​piece). Furthermore, it is preferable that 80% or more of the plate-like inorganic fillers contained in the region have an angle of the major axis of 30° or less with respect to one plane of the slice piece, and it is more preferable that the angle is 20° or less. By including the plate-like inorganic filler in the above-described form, the major axes of the plate-like inorganic filler are aligned more along the thickness direction in the sliced ​​pieces. Therefore, such slices have better heat conduction paths through their thickness. This allows the thermally conductive sheet produced using the sliced ​​pieces to have even better thermal conductivity in the thickness direction. The cross-section of the slice cut in the thickness direction can be observed using an image taken at a magnification of 500 to 1000 times using a scanning electron microscope (SEM).

[0073] Next, the workpiece preparing step S1 according to the second example and the sliced ​​piece obtaining step S2 according to the second example will be described.

[0074] (Workpiece preparation step S1 according to the second example) In the workpiece fabrication step S1 according to the second example, a rectangular parallelepiped resin sheet 10 as shown in FIG. 2A is obtained in the same manner as in the resin sheet fabrication step S1a of the workpiece fabrication step S1 according to the first example. In the workpiece preparation step S1 according to the second example, the rectangular parallelepiped-shaped resin sheet 10 obtained in the resin sheet preparation step S1a is then cut along the lines α and β as shown in FIG. 2A to obtain a donut-shaped resin sheet 10'' as shown in FIG. 2E. The donut-shaped resin sheet 10'' can be cut out from the rectangular parallelepiped resin sheet 10, for example, by punching press using a mold in which a solid cylinder having a diameter smaller than the diameter of the hollow cylinder is placed inside the hollow cylinder. In the following, cutting out the doughnut-shaped resin sheet 10'' from the rectangular parallelepiped resin sheet 10 will be referred to as a raw material sheet cutting step S1b'.

[0075] The raw material sheet cutting step S1b' can be performed in the same manner as the raw material sheet cutting step S1b.

[0076] In the workpiece manufacturing step S1 of the second example, similar to the workpiece manufacturing step S1 of the first example, multiple donut-shaped resin sheets 10'' obtained in the raw material sheet cutting step S1b' are stacked in the thickness direction to obtain a cylindrical resin sheet laminate 20'' (cylindrical workpiece) as shown in Figure 2F (hereinafter referred to as resin sheet laminate manufacturing step S1c'). In FIG. 2F, the central axis of the cylindrical resin sheet laminate 20'' is also indicated as CA.

[0077] In the resin sheet laminate manufacturing step S1c', similar to the resin sheet laminate manufacturing step S1c of the first example, multiple stacked donut-shaped resin sheets 10'' are bonded together and integrated to obtain a cylindrical resin sheet laminate 20''. Furthermore, in the resin sheet laminate manufacturing step S1c', as in the resin sheet laminate manufacturing step S1c of the first example, it is preferable to perform heat pressing so that multiple donut-shaped resin sheets 10'' are stacked in the thickness direction and press pressure is applied in the stacking direction. As a result, in the cylindrical resin sheet laminate 20″ obtained in the workpiece fabrication step S1 according to the second example, the plate-like inorganic filler has a long axis that is perpendicular to the central axis CA of the cylindrical resin sheet laminate 20″ (specifically, the plane F cy ) along the direction of the Therefore, the cylindrical resin sheet laminate 20'' also has a low thermal conductivity in the direction along the central axis CA, and the plane F intersecting (specifically, perpendicular to) the central axis CA cy The thermal conductivity in the direction along the central axis CA is higher than the thermal conductivity in the direction along the central axis CA. Therefore, in FIG. 2F, the direction along the central axis CA is shown as the first direction, and the plane F cy The direction along the arrow is shown as the second direction. That is, the cylindrical resin sheet laminate 20'' also has a low thermal conductivity in the first direction, and a higher thermal conductivity in the second direction than the thermal conductivity in the first direction. In addition, "the plate-like inorganic filler is arranged in a direction along a plane whose long axis is perpendicular to the central axis CA of the cylindrical resin sheet laminate 20''" also means the same as that explained for the cylindrical resin sheet laminate 20'.

[0078] By carrying out the workpiece fabrication step S1 according to the second example as described above, a cylindrical resin sheet laminate 20'' (cylindrical workpiece) as shown in FIG. 2F can be obtained.

[0079] The cylindrical workpiece can also be made of one long rectangular parallelepiped resin sheet 10 (strip-shaped resin sheet). For example, a cylindrical laminate may be produced by spirally stacking resin sheets 10. Specifically, the thermosetting resin composition is extruded into a sheet form from a flat die corresponding to the radial dimension of a cylinder, and the resulting rectangular parallelepiped resin sheet 10 is spirally wound and stacked so that the flat portions of the resulting sheet 10 overlap each other, thereby producing a laminate similar to one produced by stacking multiple doughnut-shaped resin sheets 10''.

[0080] In this case, the rectangular parallelepiped-shaped resin sheets 10 can be laminated immediately after being formed by extruding the thermosetting resin composition in a molten state from the die, before the rectangular parallelepiped-shaped resin sheets 10 cool and solidify. Therefore, when stacking the rectangular parallelepiped resin sheets 10 in a spiral shape, a load can be applied in the stacking direction using a roller or the like to achieve thermal adhesion between the layers. Therefore, in such a case, not only can the process of cutting out a donut-shaped resin sheet 10'' from a rectangular parallelepiped resin sheet 10 using a punching press or the like be omitted, but the process of performing heat pressing as described above can also be omitted.

[0081] (Slice piece obtaining step S2 according to the second example) In the slice obtaining process S2 of the second example, at least one of the outer and inner surfaces of a cylindrical resin sheet laminate 20'' (cylindrical workpiece) as shown in Figure 2G is sliced ​​circumferentially to obtain strip-shaped slices from the cylindrical resin sheet laminate 20''. That is, in the slice obtaining step S2 according to the second example, the cylindrical resin sheet laminate 20'' is sliced ​​around the central axis CA (ie, the axis extending along the first direction) to obtain strip-shaped slices. More specifically, as shown in FIG. 2G, the slices are cut out in a spiral shape using a cutter or the like, starting from at least one of an arbitrary point (point A) on the outer peripheral surface and an arbitrary point (point B) on the inner peripheral surface of the cylindrical resin sheet laminate 20''. That is, when the workpiece is a cylindrical resin sheet laminate 20'', the slices may be cut out in a spiral shape only from point A on the outer peripheral surface of the cylindrical resin sheet laminate 20'', or the slices may be cut out in a spiral shape only from point B on the inner peripheral surface of the cylindrical resin sheet laminate 20'', or the slices may be cut out in a spiral shape from both point A on the outer peripheral surface and point B on the inner peripheral surface of the cylindrical resin sheet laminate 20''. The cutting of the slices from both point A on the outer peripheral surface and point B on the inner peripheral surface may be carried out, for example, by cutting one slice in a spiral shape from point A on the outer peripheral surface of the cylindrical resin sheet laminate 20'', and then cutting another slice in a spiral shape from point B on the inner peripheral surface.

[0082] As described above, except that the slices are cut out from at least one of the outer peripheral surface and the inner peripheral surface of the cylindrical resin sheet laminate 20'', the slice obtaining process S2 of the second example can be carried out in the same manner as the slice obtaining process S2 of the first example.

[0083] In this manner, slices can be obtained from the cylindrical resin sheet laminate 20'' (cylindrical workpiece) shown in FIG. 2F.

[0084] Here, when a rectangular parallelepiped resin sheet laminate is used as the workpiece and slices are obtained by cutting the rectangular parallelepiped resin sheet laminate from one side along the stacking direction of the resin sheets, the planar dimensions of the slices are limited by the dimensions of one side of the rectangular parallelepiped resin sheet laminate. However, in the manufacturing method of the thermally conductive sheet described above, as shown in Figure 2D, the outer surface of the cylindrical resin sheet laminate 20' is sliced ​​spirally along the circumferential direction to cut out strip-shaped slices, or as shown in Figure 2G, at least one of the outer surface and inner surface of the cylindrical resin sheet laminate 20'' is sliced ​​spirally along the circumferential direction to cut out strip-shaped slices. Therefore, according to the above method, slices having various planar dimensions can be obtained without being limited by the dimensions of one side, as is the case when a rectangular parallelepiped resin sheet laminate is used as the workpiece. That is, slices having large planar dimensions can be obtained from one workpiece without being limited by the dimensions of one side surface. This makes it possible to produce a thermally conductive sheet with large planar dimensions from a single workpiece.

[0085] Furthermore, as described above, in the cylindrical resin sheet laminate 20' and the cylindrical resin sheet laminate 20'', the plate-like inorganic filler is arranged so that the long axes are oriented in various directions when the cylindrical resin sheet laminate 20' and the cylindrical resin sheet laminate 20'' are viewed from above. Furthermore, as described above, the anisotropic inorganic filler is arranged in the thickness direction such that the major axis is aligned along a plane perpendicular to the central axis CA of the cylindrical resin sheet laminate 20' and the cylindrical resin sheet laminate 20''. Therefore, as described above, the slices cut into strips from the cylindrical resin sheet laminate 20' and the cylindrical resin sheet laminate 20'' can exhibit good thermal conductivity in the thickness direction of the slices. That is, a thermally conductive sheet made using the sliced ​​pieces can exhibit good thermal conductivity in the thickness direction.

[0086] In the workpiece preparation step S1, a cylindrical workpiece can be obtained in a manner other than the second example. For example, in the workpiece preparation step S1, a cylindrical workpiece can be obtained according to the following procedure. (1) A rectangular parallelepiped resin sheet 10 is produced according to the resin sheet production step S1a described above. (2) Rectangular parallelepiped resin sheets 10 are stacked in a spiral shape so as to have a hollow portion in the center, to obtain a cylindrical laminate S (see FIG. 3). (3) The cylindrical laminate S is pressed in the height direction (the direction perpendicular to the lamination direction of the resin sheet 10) to produce a cylindrical workpiece in which the extrusion direction of the rectangular parallelepiped-shaped resin sheet 10 is the circumferential direction. The above (2) can be implemented by spirally winding the rectangular parallelepiped resin sheet 10 around a rod-shaped member. After the rectangular parallelepiped resin sheet 10 is spirally wound to obtain a laminate, the rod-shaped member can be removed from the laminate to obtain a cylindrical laminate S as shown in FIG. 3. Furthermore, the pressing in (3) above is preferably carried out by hot pressing. The heat pressing can be carried out in the same manner as described in the workpiece fabrication step S1 according to the first example.

[0087] The cylindrical workpiece produced by the above-described procedure is pressed in the height direction, so that the plate-like inorganic filler particles are arranged in a direction along a plane whose long axis is perpendicular to the central axis of the cylindrical workpiece. That is, even in the cylindrical workpiece, the direction along the central axis is the first direction with low thermal conductivity, and the direction along a plane perpendicular to the central axis is the second direction with higher thermal conductivity than the first direction. Therefore, the cylindrical workpiece also has a first direction and a second direction.

[0088] In obtaining a cylindrical workpiece as described above, one rectangular parallelepiped-shaped resin sheet 10 may be spirally wound or multiple rectangular parallelepiped-shaped resin sheets 10 may be spliced ​​together and spirally wound.

[0089] Furthermore, in the workpiece preparation step S1, obtaining a cylindrical workpiece can be carried out in a manner other than the first example described above, and obtaining a cylindrical workpiece can be carried out in a manner other than the second example described above.

[0090] For example, the workpiece preparation step S1 may be carried out by kneading the plate-like inorganic filler and the epoxy resin using a kneader or the like to obtain a thermosetting resin composition, pouring the thermosetting resin composition into a disk-shaped mold to prepare a plurality of disk-shaped resin sheets 10′, and then stacking the plurality of disk-shaped resin sheets 10′ to obtain a cylindrical resin sheet laminate 20′. Alternatively, the workpiece preparation step S1 may be carried out by pouring the thermosetting resin composition into a doughnut-shaped mold to prepare a plurality of doughnut-shaped resin sheets 10'', and then stacking the plurality of doughnut-shaped resin sheets 10'' to obtain a cylindrical resin sheet laminate 20''.

[0091] When the thermosetting resin composition is poured into a disk-shaped mold or a doughnut-shaped mold, it is preferable to pour the thermosetting resin composition from the center of the mold. By pouring the thermosetting resin composition into these molds in this manner, the thermosetting resin composition can be made to flow from the center toward the periphery of the molds. This makes it easier to incorporate the plate-like inorganic filler into the disk-shaped resin sheet 10' and the doughnut-shaped resin sheet 10'' in such a way that the major axis is aligned with the flow direction of the thermosetting resin composition when viewed from above. That is, in the disk-shaped resin sheet 10' and the doughnut-shaped resin sheet 10'', it becomes easier to incorporate the plate-shaped inorganic filler in such a manner that the major axes are oriented radially when viewed from above.

[0092] It is preferable to pour the thermosetting resin composition into the disk-shaped mold or doughnut-shaped mold while rotating the disk-shaped mold or doughnut-shaped mold, or the die through which the thermosetting resin composition is extruded.

[0093] Even when a disk-shaped resin sheet 10' and a donut-shaped resin sheet 10'' are obtained as described above, a cylindrical resin sheet laminate 20' and a cylindrical resin sheet laminate 20'' may be obtained in the same manner as described above. That is, after obtaining a first laminate in which multiple disk-shaped resin sheets 10' are stacked, the first laminate may be heat-pressed in the stacking direction to obtain a cylindrical resin sheet laminate 20'. In addition, after obtaining a second laminate in which multiple doughnut-shaped resin sheets 10'' are stacked, the second laminate may be heat-pressed in the stacking direction to obtain a cylindrical resin sheet laminate 20''.

[0094] In the above, an example was described in which a thermosetting resin, epoxy resin, was used as the resin and a plate-like inorganic filler was used as the anisotropic inorganic filler, but the resin may be a thermosetting resin other than epoxy resin, a thermoplastic resin, or a thermoplastic elastomer. The anisotropic inorganic filler may contain the needle-like inorganic filler in addition to the plate-like inorganic filler, or may contain the needle-like inorganic filler instead of the plate-like inorganic filler. As described above, even when the resin is a resin other than an epoxy resin, when the anisotropic inorganic filler contains the needle-shaped inorganic filler in addition to the plate-shaped inorganic filler, or when the anisotropic inorganic filler contains the needle-shaped inorganic filler instead of the plate-shaped inorganic filler, the manufacturing method of the thermally conductive sheet of this embodiment can be carried out in the same manner as described above. When a thermosetting resin other than an epoxy resin, a thermoplastic resin, or a thermoplastic elastomer is used as the resin, the heat pressing temperature and the heating temperature of the sliced ​​portion may be set based on the glass transition temperature Tg of these resins instead of the softening point of the epoxy resin.

[0095] In addition, although the above description has been given of an example in which the workpiece is columnar or cylindrical, the shape of the workpiece is not limited to these. The shape of the workpiece may be a polygonal prism, such as a quadrangular prism, a hexagonal prism, or an octagonal prism.

[0096] [Thermal conductive sheet] The thermally conductive sheet according to this embodiment is a thermally conductive sheet manufactured by the method for manufacturing a thermally conductive sheet according to this embodiment. More specifically, the thermally conductive sheet according to this embodiment is a thermally conductive sheet including strip-shaped slices obtained in the slice obtaining step. The thermally conductive sheet according to this embodiment may include one strip-shaped slice, or may include two or more strip-shaped slices. When the thermally conductive sheet according to this embodiment includes two or more strip-shaped slices, the two or more strip-shaped slices may be stacked in the thickness direction. The thermally conductive sheet according to this embodiment may be a thermally conductive sheet with metal foil, which includes the strip-shaped slices and metal foil supporting the strip-shaped slices.

[0097] Examples of metals for forming the metal foil include copper, aluminum, nickel, and iron. The metal foil may also be formed from an alloy of the above metals.

[0098] When the thermally conductive sheet includes the metal foil, the thermally conductive sheet according to this embodiment is used, for example, to dissipate heat generated by a semiconductor element incorporated in a semiconductor module. In one example, the semiconductor module includes a semiconductor element and the thermally conductive sheet. The semiconductor module has an abutment surface with a heat dissipation member, such as a heat sink, to which heat generated by the semiconductor element is transferred. The thermally conductive sheet is interposed between the semiconductor element and the heat dissipation member, such as the heat sink, and forms the abutment surface. In this case, the exposed surface of the metal foil in the thermally conductive sheet abuts against the heat dissipation member. By arranging the thermally conductive sheet on the semiconductor module in the above manner, heat generated in the semiconductor element can be quickly transferred to a heat sink or the like.

[0099] As described above, the strip-shaped slice obtained in the slice obtaining step contains the anisotropic inorganic filler in such a manner that the long axis is oriented in the thickness direction of the slice. The thermally conductive sheet according to this embodiment includes the strip-shaped slices as described above, and therefore has an excellent thermally conductive path formed in the thickness direction. Therefore, as described above, the thermally conductive sheet according to this embodiment can exhibit good thermal conductivity when interposed between the heat sink and the heat radiator.

[0100] In the thermally conductive sheet according to this embodiment, the strip-shaped slice pieces may be electrically insulating. The dielectric breakdown voltage (BDV) of the strip-shaped slice is preferably 45 kV / mm or more. When the strip-shaped slices have the above-mentioned BDV, a thermally conductive sheet including such strip-shaped slices can exhibit excellent electrical insulation properties. The BDV can be measured based on JIS K6911:1995.

[0101] The matters disclosed by this specification include the following.

[0102] (1) A method for producing a thermally conductive sheet, comprising: preparing a workpiece having anisotropic thermal conductivity using a resin composition containing a resin and an anisotropic inorganic filler having a major axis and a minor axis; slicing the workpiece to obtain slices having a higher thermal conductivity in a thickness direction than in a plane direction; and producing a thermally conductive sheet having a thickness direction that coincides with the thickness direction of the slices, a workpiece fabrication step of fabricating the workpiece in a direction in which a first direction having a low thermal conductivity and a second direction having a higher thermal conductivity than the first direction intersect; a slice obtaining step of slicing the workpiece around an axis extending along the first direction to obtain strip-shaped slices. A method for manufacturing a thermally conductive sheet.

[0103] According to this configuration, slices having large planar dimensions can be obtained without being limited by the dimensions of one side, as in the case where a rectangular parallelepiped resin sheet laminate is used as the workpiece. By using such slices having large planar dimensions, a thermally conductive sheet having large planar dimensions can be obtained. Furthermore, the second direction of the workpiece produced in the workpiece producing step coincides with the thickness direction of the strip-shaped slice obtained in the slice obtaining step. Therefore, a thermally conductive sheet manufactured using the strip-shaped slices can exhibit good thermal conductivity in the thickness direction.

[0104] (2) the resin composition is a thermosetting resin composition containing an epoxy resin as the resin, In the slice obtaining step, the slice is obtained while heating the portion of the workpiece to be sliced. A method for producing the thermally conductive sheet according to (1) above.

[0105] According to this configuration, the workpiece can be made to have an appropriate hardness, which makes it easier to obtain the slices from the workpiece.

[0106] (3) The anisotropic inorganic filler is a plate-like inorganic filler having a plate-like particle shape. A method for producing the thermally conductive sheet according to (1) or (2) above.

[0107] According to this configuration, it becomes easier to orient the major axes of the anisotropic inorganic filler in the workpiece so as to follow the second direction. As a result, the thermally conductive sheet produced using the strip-shaped slices obtained from the workpiece can exhibit even better thermal conductivity in the thickness direction.

[0108] (4) The workpiece manufacturing step includes: extruding the resin composition containing the plate-like inorganic filler to produce a resin sheet whose thickness direction is perpendicular to the extrusion direction; and manufacturing the workpiece by stacking and pressing a plurality of the resin sheets. A method for producing the thermally conductive sheet according to (3) above.

[0109] According to this configuration, it becomes easier to orient the major axes of the anisotropic inorganic filler in the workpiece so as to follow the second direction. As a result, the thermally conductive sheet produced using the strip-shaped slices obtained from the workpiece can exhibit even better thermal conductivity in the thickness direction.

[0110] (5) The workpiece manufacturing step includes: extruding the resin composition containing the plate-like inorganic filler to produce a resin sheet whose thickness direction is perpendicular to the extrusion direction; stacking the resin sheets in a spiral shape to form a cylindrical laminate; and pressing the cylindrical laminate to produce a cylindrical workpiece in which the extrusion direction is a circumferential direction. A method for producing the thermally conductive sheet according to (3) above.

[0111] According to this configuration, it becomes easier to orient the major axes of the anisotropic inorganic filler in the workpiece so as to follow the second direction. As a result, the thermally conductive sheet produced using the strip-shaped slices obtained from the workpiece can exhibit even better thermal conductivity in the thickness direction.

[0112] The method for producing a thermally conductive sheet according to the present invention is not limited to the above-described embodiment. Furthermore, the method for producing a thermally conductive sheet according to the present invention is not limited to the above-described effects. The method for producing a thermally conductive sheet according to the present invention can be modified in various ways without departing from the gist of the present invention. [Example]

[0113] The present invention will now be described in more detail with reference to examples, comparative examples, and reference examples. The following examples are intended to explain the present invention in more detail, but are not intended to limit the scope of the present invention.

[0114] Example 1 62 parts by weight of an epoxy resin (triphenylmethane-type epoxy resin (trade name "EPPN-502H" manufactured by Nippon Kayaku Co., Ltd.)), 38 parts by weight of a phenolic curing agent (bisphenol-based phenolic resin (trade name "H-4" manufactured by Meiwa Kasei Co., Ltd.)), and 1 part by weight of a curing accelerator (tetraphenylphosphonium tetraphenylborate (trade name "TPP-K (registered trademark)" manufactured by Hokko Chemical Industry Co., Ltd.)) were mixed. Next, 60% by volume of an inorganic filler (boron nitride filler (BN filler)) was further added, and the mixture was added to methyl ethyl ketone so that the solid content was 57% by weight. The mixture was stirred (1000 rpm) at room temperature for 6 minutes to prepare a varnish. The varnish was coated on a carrier sheet and dried to obtain a rectangular resin sheet measuring 70 x 70 mm and 15 mm thick.

[0115] Eighty disk-shaped resin sheets cut from the rectangular parallelepiped resin sheet were stacked in the thickness direction, and a heat press was performed to apply pressure in the stacking direction to obtain a cylindrical resin sheet laminate. The heat press was performed using an SFV-type vacuum compression molding machine, with the set temperature of the SFV-type vacuum compression molding machine set at 120°C and the press pressure at 40 MPa. Slices A were then cut out from the outer periphery of the cylindrical resin sheet laminate using a cutter.

[0116] (Comparative Example 1) Eighty rectangular parallelepiped resin sheets obtained in Example 1 were stacked in the thickness direction, and a heat press was performed under the same conditions as in Example 1 so as to apply a pressure in the stacking direction, thereby obtaining a rectangular parallelepiped resin sheet laminate. Then, sample X was cut out from the plane of the rectangular parallelepiped resin sheet laminate using a cutter.

[0117] (Reference example 1) A slice B was cut out from the outer peripheral surface of the rectangular parallelepiped resin sheet laminate obtained in Comparative Example 1 using a cutter.

[0118] <Thermal conductivity> Using the slices A, sample X, and slices B obtained in Example 1, Comparative Example 1, and Reference Example 1, the thermal conductivity in the thickness direction of each sheet was determined. The thermal conductivity value was calculated by multiplying the thermal diffusivity measured for the thermal diffusivity measurement sample using a xenon flash analyzer (NETZSCH, LFA-447) by the specific heat measured by heat flux DSC in accordance with JIS 7123:1987 and the density measured by the immersion method in accordance with JIS K 7122:1999. The thermal diffusivity value was calculated by arithmetically averaging the thermal diffusivity values ​​measured for three measurement samples. The thermal diffusivity measurement was performed five times for each measurement sample, and the arithmetic average of the three values ​​for each measurement sample, excluding the maximum and minimum values, was used as the measured value. The results of measuring the thermal conductivity are shown in Table 1 below.

[0119] [Table 1]

[0120] Comparative Example 1 in Table 1 essentially shows the thermal conductivity in the horizontal direction of the sheet of sliced ​​piece A of Example 1. Since Example 1 exhibits a thermal conductivity superior to that of Comparative Example 1, it is clear that anisotropy of thermal conductivity occurs in sliced ​​piece A. Moreover, Example 1 showed a thermal conductivity equivalent to that of Reference Example 1. That is, Example 1, which satisfies the constituent requirements of the present invention, shows that the long axis of the inorganic filler in slice piece A is oriented in the sheet thickness direction, similar to Reference Example 1 based on the conventional method.

[0121] (Reference example 2) A cylindrical resin sheet laminate was obtained in the same manner as in Example 1, except that the raw materials for the thermosetting resin composition were changed to 62 parts by mass of an epoxy resin (triphenylmethane-type epoxy resin (trade name "EPPN-502H" manufactured by Nippon Kayaku Co., Ltd.)), 38 parts by mass of a phenol-based curing agent (bisphenol-based phenolic resin (trade name "H-4" manufactured by Meiwa Kasei Co., Ltd.)), and 60% by volume of an inorganic filler (boron nitride filler (BN filler)).

[0122] (Reference example 3) A cylindrical resin sheet laminate was obtained in the same manner as in Example 1, except that the raw materials for the thermosetting resin composition were changed to 62 parts by mass of an epoxy resin (triphenylmethane-type epoxy resin (trade name "EPPN-502H" manufactured by Nippon Kayaku Co., Ltd.)), 38 parts by mass of a phenol-based curing agent (bisphenol-based phenolic resin (trade name "HF-1M" manufactured by Meiwa Kasei Co., Ltd.)), and 60% by volume of an inorganic filler (boron nitride filler (BN filler)).

[0123] (Reference example 4) A cylindrical resin sheet laminate was obtained in the same manner as in Example 1, except that the raw materials for the thermosetting resin composition were changed to 62 parts by mass of an epoxy resin (triphenylmethane-type epoxy resin (trade name "EPPN-501HY" manufactured by Nippon Kayaku Co., Ltd.)), 38 parts by mass of a phenol-based curing agent (novolac-type phenol-based curing agent (trade name "GS-200" manufactured by Gun-ei Chemical Co., Ltd.)), and 60% by volume of an inorganic filler (boron nitride filler (BN filler)).

[0124] The cylindrical resin sheet laminates obtained in Reference Examples 2 to 4 were used to study the heating temperature of the portion of the resin sheet laminate to be sliced. Specifically, the resin sheet laminate and a cutter used to cut the slices were heated at temperatures below the softening point of the epoxy resin contained in the resin sheet laminate: -15°C, -10°C, -5°C, and above the softening point, and an evaluation was made as to whether slices could be continuously cut from the cylindrical resin sheet laminates of Reference Examples 2 to 4. The evaluation results are shown in Table 2. <Evaluation criteria> 〇: No cracks in the resin are observed and it is possible to slice it to 5cm or more. ×: When sliced, the resin cracked, making it impossible to obtain continuous sheets.

[0125] [Table 2]

[0126] The results in Table 2 show that if the heating temperature is raised to near the softening point of the epoxy resin, it is possible to cut out slices continuously.

[0127] From the above, it can be seen that the present invention can provide a method for producing a thermally conductive sheet that can produce large slices. [Explanation of symbols]

[0128] 10 Rectangular parallelepiped resin sheet, 10' disk-shaped resin sheet, 10'' donut-shaped resin sheet, 20' cylindrical resin sheet laminate (cylindrical workpiece), 20'' cylindrical resin sheet laminate (cylindrical workpiece), CA center axis, F co plane, F cy Plane, SP A Tangent plane at point A, SP B Tangent plane at point B.

Claims

1. A method for producing a thermally conductive sheet, comprising: preparing a workpiece exhibiting anisotropic thermal conductivity using a resin composition containing a resin and an anisotropic inorganic filler having a major axis and a minor axis; slicing the workpiece to obtain slices having higher thermal conductivity in a thickness direction than in a plane direction; and producing a thermally conductive sheet having a thickness direction that coincides with the thickness direction of the slices, a workpiece fabrication step of fabricating the workpiece in a direction in which a first direction having a low thermal conductivity and a second direction having a higher thermal conductivity than the first direction intersect; a slice obtaining step of slicing the workpiece around an axis extending along the first direction to obtain strip-shaped slices. A method for manufacturing a thermally conductive sheet.

2. the resin composition is a thermosetting resin composition containing an epoxy resin as the resin, In the slice obtaining step, the slice is obtained while heating the portion of the workpiece to be sliced. A method for producing the thermally conductive sheet according to claim 1.

3. The anisotropic inorganic filler is a plate-like inorganic filler having a plate-like particle shape. A method for producing the thermally conductive sheet according to claim 1 or 2.

4. The workpiece manufacturing step includes: extruding the resin composition containing the plate-like inorganic filler to produce a resin sheet whose thickness direction is perpendicular to the extrusion direction; and forming the workpiece by stacking and pressing a plurality of the resin sheets. A method for producing the thermally conductive sheet according to claim 3.

5. The workpiece manufacturing step includes: extruding the resin composition containing the plate-like inorganic filler into a strip shape to produce a resin sheet whose thickness direction is perpendicular to the extrusion direction; stacking the resin sheets in a spiral shape to form a cylindrical laminate; and pressing the cylindrical laminate to produce a cylindrical workpiece in which the extrusion direction is a circumferential direction. A method for producing the thermally conductive sheet according to claim 3.

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