Method for manufacturing a thermal conductive sheet and thermal conductive sheet

Abstract

To provide a thermally conductive sheet that is resistant to tearing during use.SOLUTION: There is provided a method for manufacturing a thermally conductive sheet, the method involving a crosslinking reaction using a composition including a resin containing a crosslinkable resin, a particulate filler and a crosslinking agent. During the crosslinking reaction of a laminate of sheet materials made of the above composition, the entire surface of the laminate is fixed with a jig, and a value of pressure applied in the direction of lamination is set to more than 1.0 MPa.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a thermal conductive sheet and to a thermal conductive sheet. [Background technology]

[0002] In recent years, electronic components such as power semiconductors (IGBT modules, etc.) and integrated circuit (IC) chips have been generating increasing amounts of heat as their performance has improved. As a result, electronic devices using these components require measures to prevent functional failures caused by temperature increases in the electronic components.

[0003] To prevent malfunctions caused by temperature increases in electronic components, a common method is to promote heat dissipation by attaching heat sinks, heat dissipation plates, or heat fins made of metal to the heat-generating elements of electronic components. When using heat sinks, a sheet-like material with high thermal conductivity (thermal conductive sheet) is used as an intermediary to efficiently transfer heat from the heat-generating element to the heat sink. A predetermined pressure is then applied to this thermal conductive sheet to ensure close contact between the heat-generating element and the heat sink.

[0004] Thermal conductive sheets have always been required to have excellent strength. For example, in Patent Documents 1 and 2, a crosslinking agent and a reaction initiator were added to a composition containing a resin and particulate filler, the material was formed into a sheet, and heat was applied to the laminated structure to promote the crosslinking reaction. The resulting laminate was then sliced ​​to obtain a crosslinked vertically oriented sheet. Thermal conductive sheets manufactured in this way had high sheet strength. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-055893 [Patent Document 2] Japanese Patent Publication No. 2021-155636 [Overview of the project] [Problems that the invention aims to solve]

[0006] When a thermal conductive sheet is used in a heated state, sandwiched between a heating element and a heat sink, repeated cycles of pressurization and depressurization can cause the thermal conductive sheet to tear in areas under strong pressure, causing it to protrude from between the heating element and the heat sink. In electronic equipment, protruding thermal conductive sheets can cause short circuits, so thermal conductive sheets must be resistant to tearing during use.

[0007] However, the conventional thermal conductive sheets described above had room for improvement in terms of their resistance to tearing during use.

[0008] Therefore, the present invention aims to provide a method for manufacturing a heat-conductive sheet that is difficult to tear during use, and a heat-conductive sheet that is difficult to tear during use. [Means for solving the problem]

[0009] The inventors diligently conducted research to achieve the above objective. They then discovered that when manufacturing a thermal conductive sheet according to a crosslinking reaction method using a composition containing a crosslinkable resin, a particulate filler, and a crosslinking agent, fixing the entire surface of the laminate made of the above composition with a jig during the crosslinking reaction, and further applying a pressure of more than 1.0 MPa in the lamination direction, can effectively increase the resistance of the resulting thermal conductive sheet to tearing during use, thus completing the present invention.

[0010] In other words, the present invention aims to advantageously solve the above problems, and the present invention provides a method for manufacturing a heat conductive sheet, comprising: a pre-heat conductive sheet molding step of pressurizing a composition containing a crosslinkable resin, a particulate filler, and a crosslinking agent to form a sheet to obtain a pre-heat conductive sheet; a laminate forming step of stacking a plurality of the pre-heat conductive sheets in the thickness direction, or folding or winding the pre-heat conductive sheets to obtain a laminate; a crosslinking reaction step of heating the laminate while pressurizing it in the stacking direction to perform a crosslinking reaction; and a slicing step of slicing the laminate at an angle of 45° or less with respect to the stacking direction to obtain a heat conductive sheet, wherein in the crosslinking reaction step, the entire surface of the laminate is fixed with a jig, and the pressure applied in the stacking direction is greater than 1.0 MPa. Thus, by forming a composition containing a crosslinkable resin, a particulate filler, and a crosslinking agent into a sheet and then forming a laminate, and by fixing the entire surface of the laminate with a jig and further applying a pressure of more than 1.0 MPa in the lamination direction to allow the crosslinking reaction to proceed in the laminate, the resistance to tearing of the resulting thermal conductive sheet during use can be effectively increased.

[0011] In this invention, it is preferable that the crosslinking reaction step is carried out under a vacuum atmosphere in the method for manufacturing the thermal conductive sheet. By carrying out the crosslinking reaction step under a vacuum atmosphere, the strength of the thermal conductive sheet can be increased.

[0012] Furthermore, in the method for manufacturing the thermal conductive sheet of the present invention, it is preferable that the pressure in the crosslinking reaction step be 2.0 MPa or higher. By setting the pressure in the crosslinking reaction step to 2.0 MPa or higher, the occurrence of large open pores on the surface of the thermal conductive sheet can be effectively suppressed, and as a result, the resistance to tearing of the resulting thermal conductive sheet during use can be more effectively enhanced.

[0013] Furthermore, this invention aims to advantageously solve the above problems, and the thermal conductive sheet of the present invention is a thermal conductive sheet comprising a crosslinked resin and a particulate filler, wherein the angle of the particulate filler in the longitudinal direction with respect to the surface of the thermal conductive sheet is 60° or more and 90° or less, and when the tensile strength on the main surface of the thermal conductive sheet is measured, the direction in the main surface in which the tensile strength is highest is defined as the X direction, and the direction in the main surface in which the tensile strength is perpendicular to the X direction is defined as the Y direction, and the tensile strength in the X direction is defined as Sx(MPa) and the tensile strength in the Y direction is defined as Sx(MPa) or more, and the value of (Sx / Sy) is 3.2 or less. The thermal conductive sheet of the present invention is difficult to tear during use. The angle of the particulate filler in the longitudinal direction with respect to the surface of the thermal conductive sheet, and the values ​​of the tensile strength Sx and Sy of the thermal conductive sheet can be measured by the methods described in the examples of this specification, respectively.

[0014] Here, the thermal conductive sheet of the present invention has a number of micropores with a pore diameter of 48 μm or more and 500 μm or less, and the number of micropores is such that the total planar area of ​​the thermal conductive sheet is 1 cm². 2 It is preferable that the number of micropores per sheet be 12 or less. A thermal conductive sheet with 12 or fewer micropores is less likely to tear during use and is of higher quality. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a heat-conducting sheet that is less likely to tear during use. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be described in detail below. Because the thermal conductive sheet of the present invention has thermal conductivity, it can be used by sandwiching it between a heat-generating element and a heat-sinking element. That is, the thermal conductive sheet of the present invention can be used as a heat-dissipating member to constitute a heat dissipation device together with heat-sinking elements such as heat sinks, heat sinks, and heat sinking fins. Furthermore, the thermal conductive sheet of the present invention is not particularly limited, but can be efficiently manufactured using the thermal conductive sheet manufacturing method of the present invention described later.

[0017] (Thermal Conductive Sheet) The thermal conductive sheet of the present invention contains a resin and a particulate filler. Further, the thermal conductive sheet of the present invention may optionally further contain components other than the resin and the particulate filler. Also, in the thermal conductive sheet of the present invention, the angle of the particulate filler with respect to the surface of the thermal conductive sheet in the long axis direction is 60° or more and 90° or less. And, when measuring the tensile strength on the main surface of the thermal conductive sheet, the in-plane direction in which the tensile strength is the highest is defined as the X direction, and the in-plane direction perpendicular to the X direction is defined as the Y direction. As the tensile strength Sx (MPa) in the X direction and the tensile strength Sy (MPa) in the Y direction, Sx (MPa) is 5.0 MPa or more, and further, the value of (Sx / Sy) is 3.2 or less. The thermal conductive sheet of the present invention is difficult to tear during use because it satisfies the above characteristics. More specifically, the thermal conductive sheet of the present invention is difficult to tear even when the cycle of pressurization and depressurization is repeated in a state where it is sandwiched between a heating element and a heat radiator and heated. Therefore, the thermal conductive sheet of the present invention is excellent in durability.

[0018] [Resin]< Since the thermal conductive sheet of the present invention contains a resin, the heating element and the heat radiator can be well adhered to each other through the thermal conductive sheet. In this specification, rubber and elastomer are included in "resin". The resin that the thermal conductive sheet of the present invention may contain constitutes a matrix resin and also functions as a binder for binding the particulate filler. And the resin contained in the thermal conductive sheet of the present invention contains a crosslinked resin and optionally contains a resin other than the crosslinked resin (other resins).

[0019] [[Crosslinked Resin]]<< The resin contained in the thermal conductive sheet of the present invention contains a crosslinked resin. The crosslinked resin is a crosslinkable resin crosslinked by a crosslinking agent. And, since the thermal conductive sheet of the present invention contains a crosslinked resin as the resin, the sheet strength can be ensured to be sufficiently high, so it is difficult to tear during use.

[0020] Here, the crosslinked resin is usually solid under normal temperature and pressure. In this specification, "normal temperature" refers to 23°C, and "normal pressure" refers to 1 atm (absolute pressure).

[0021] And the crosslinked resin is formed by subjecting a crosslinkable resin and a crosslinking agent to a crosslinking reaction. In the crosslinking reaction, a reaction initiator can be used. The crosslinking reaction is not particularly limited, and for example, a peroxide crosslinking reaction in which the reaction is carried out in the presence of an organic peroxide as a reaction initiator can be used.

[0022] 〔Crosslinkable resin〕 The crosslinkable resin is not particularly limited, and for example, a crosslinkable resin capable of reacting with a crosslinking agent by a peroxide crosslinking reaction can be used. And as the crosslinkable resin, depending on the types of the crosslinking agent and the reaction initiator (i.e., the type of the crosslinking reaction), for example, a resin that is solid under normal temperature and pressure can be used.

[0023] -Resin that is solid under normal temperature and pressure- As the resin that is solid under normal temperature and pressure, for example, a thermoplastic resin that is solid under normal temperature and pressure can be used.

[0024] --Thermoplastic resin that is solid under normal temperature and pressure-- Examples of thermoplastic resins that are solid at room temperature and pressure include acrylic resins such as poly(2-ethylhexyl acrylate), copolymers of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its esters, and polyacrylic acid or its esters; silicone resins; fluororesins; polyethylene; polypropylene; ethylene-propylene copolymers; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymers; polyvinyl alcohol; polyacetal; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; and styrene. Examples include acrylonitrile copolymers; acrylonitrile-butadiene-styrene copolymers (ABS resin); styrene-butadiene block copolymers or their hydrogenated versions; styrene-isoprene block copolymers or their hydrogenated versions; acrylonitrile-butadiene copolymers or their hydrogenated versions, butadiene rubber; polyphenylene ethers; modified polyphenylene ethers; aliphatic polyamides; aromatic polyamides; polyamide-imides; polycarbonates; polyphenylene sulfides; polysulfones; polyethersulfones; polyethernitriles; polyether ketones; polyketones; polyurethanes; liquid crystal polymers; ionomers; and others. These may be used individually or in combination of two or more in any ratio. Among these, from the viewpoint of improving the flame retardancy, heat resistance, oil resistance, and chemical resistance of the heat conductive sheet, a thermoplastic fluororesin that is solid at room temperature and atmospheric pressure is preferred as the thermoplastic resin that is solid at room temperature and atmospheric pressure. Furthermore, from the viewpoint of increasing strength, an acrylonitrile-butadiene copolymer or its hydrogenated version is preferred.

[0025] =Thermoplastic fluororesin that is solid at room temperature and atmospheric pressure= The thermoplastic fluororesin that is solid at room temperature and pressure is not particularly limited as long as it is a thermoplastic fluororesin that is solid at room temperature and pressure. Examples of thermoplastic fluororesins that are solid at room temperature and pressure include vinylidene fluoride-based fluororesins, tetrafluoroethylene-propylene-based fluororesins, tetrafluoroethylene-purple orovinyl ether-based fluororesins, and elastomers obtained by polymerizing fluorine-containing monomers. More specifically, examples include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, ethylene-chlorofluoroethylene copolymer, tetrafluoroethylene-perfluorodioxole copolymer, polyvinyl fluoride, tetrafluoroethylene-propylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, acrylic-modified polytetrafluoroethylene, ester-modified polytetrafluoroethylene, epoxy-modified polytetrafluoroethylene, and silane-modified polytetrafluoroethylene. These may be used individually or in combination of two or more in any ratio.

[0026] Examples of commercially available thermoplastic fluororesins (fluoroelastomers (fluororubber)) that are solid at room temperature and pressure include Daikin Industries, Ltd.'s Daiel® G-912, G-700 series, Daiel G-550 series / G-600 series, and Daiel G-310; ALKEMA's KYNAR® series and KYNAR FLEX® series; and 3M's Dynion FC2211 and FPO3600ULV.

[0027] [Crosslinking agent] The crosslinking agent is not particularly limited as long as it can crosslink with the crosslinkable resins mentioned above, and examples include isocyanurates such as triallyl isocyanurate (e.g., TAIC® manufactured by Mitsubishi Chemical Corporation); cyanurates such as triallyl cyanurate; maleimides such as N,N'-m-phenylenedimaleimide; allyl esters of polyhydric acids such as diallyl phthalate, diallyl isophthalate, diallyl maleate, diallyl fumarate, diallyl sebacate, and triallyl phosphate; diethylene glycol bisallyl carbonate; allyl ethers such as ethylene glycol diallyl ether, trimethylolpropane triallyl ether, and pentaerythritol partial allyl ether; allyl-modified resins such as allylated novolac and allylated resol resins; and 3- to 5-functional methacrylate and acrylate compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate. These may be used individually or in combination of two or more in any ratio. Among the options mentioned above, triallyl isocyanurate is preferred as the crosslinking agent. This is because using triallyl isocyanurate allows for easier reaction, thereby improving the sheet strength of the thermal conductive sheet.

[0028] The amount of crosslinking agent used in the crosslinking reaction is preferably 0.1 parts by mass or more, more preferably 0.4 parts by mass or more, even more preferably 0.6 parts by mass or more, preferably 10 parts by mass or less, more preferably 7.5 parts by mass or less, and even more preferably 3.5 parts by mass or less, per 100 parts by mass of crosslinkable resin. If the amount of crosslinking agent used is above the lower limit, the formed crosslinked resin will be sufficiently crosslinked by the crosslinking agent, thereby improving the sheet strength of the thermal conductive sheet and further increasing its resistance to tearing during use. Also, if the amount of crosslinking agent used is above the lower limit, the thermal conductive sheet will be sufficiently resistant to crushing when pressure is applied, making it even more resistant to tearing during use. On the other hand, if the amount of crosslinking agent used is below the upper limit, excessive crosslinking of the formed crosslinked resin by the crosslinking agent can be suppressed, and the flexibility of the thermal conductive sheet can be maintained well. Also, if the amount of crosslinking agent used is below the upper limit, gas generation during the crosslinking reaction can be suppressed, and the surface of the thermal conductive sheet can be made smooth.

[0029] [Reaction initiator] The reaction initiators that can be used in the crosslinking reaction between a crosslinkable resin and a crosslinking agent are not particularly limited, and include, for example, dibenzoyl peroxide (e.g., Niper E manufactured by Nippon Oil & Fats Co., Ltd.), t-butyl peroxyacetate, 2,2-di-(t-butylperoxy)butane, t-butyl peroxybenzoate, t-butylcumyl peroxide, dicumyl peroxide, di-t-hexyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (e.g., Perhexa 25B-40® manufactured by Nippon Oil & Fats Co., Ltd.), di-t-butyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexene-3, t-butyl hydroperoxide, t-butyl peroxyisobutyrate, lauroyl peroxide, dipropionyl peroxide, p-menthane hydroperoxide, and other organic peroxides that function as radical reaction initiators. These may be used individually or in combination of two or more in any ratio. For example, by using a reaction initiator in a crosslinking reaction, radicals are generated, which can help to initiate the crosslinking reaction smoothly. Among the above, dibenzoyl peroxide is preferred as the reaction initiator. Using dibenzoyl peroxide allows the crosslinking reaction to proceed well at low temperatures (e.g., 150°C or below), which reduces the amount of gas generated and the number of micropores formed in the thermal conductive sheet, thereby further increasing the resistance to tearing when the thermal conductive sheet is in use.

[0030] The amount of reaction initiator used in the crosslinking reaction is preferably 0.3 parts by mass or more, more preferably 0.6 parts by mass or more, even more preferably 0.9 parts by mass or more, preferably 12 parts by mass or less, more preferably 8.5 parts by mass or less, and even more preferably 5.5 parts by mass or less, per 100 parts by mass of crosslinkable resin. If the amount of reaction initiator used is above the lower limit above, the formed crosslinked resin will be sufficiently crosslinked by the crosslinking agent, thereby improving the sheet strength of the thermal conductive sheet and further increasing its resistance to tearing during use. Also, if the amount of reaction initiator used is above the lower limit above, the density of the crosslinked structure can be sufficiently increased to effectively increase the sheet strength, so that the thermal conductive sheet is less likely to be crushed when pressure is applied. If the thermal conductive sheet is less likely to be crushed, a certain space can be maintained between the thermal conductive sheet and the heat generating element or heat sink when the thermal conductive sheet is used. On the other hand, if the amount of reaction initiator used is below the upper limit above, the amount of gas generated in the crosslinking reaction can be reduced, thereby reducing the number of micropores formed in the thermal conductive sheet, and further increasing the resistance to tearing during use of the thermal conductive sheet. Furthermore, if the amount of reaction initiator used is below the above upper limit, gas generation during the crosslinking reaction can be suppressed, and the surface of the thermal conductive sheet can be made smooth.

[0031] Furthermore, the mass ratio of the amount of crosslinking agent used to the amount of reaction initiator used in the crosslinking reaction (crosslinking agent / reaction initiator) can be between 1 / 3 and 1 / 3.

[0032] [Method for forming crosslinked resins] Crosslinked resins can be formed by heating the crosslinkable resin described above, a crosslinking agent, and a reaction initiator used as needed to carry out a crosslinking reaction. The heating temperature, heating time, and other conditions for the crosslinking reaction will be described later in the section on "Method for Manufacturing Thermal Conductive Sheets".

[0033] [Percentage of cross-linked resin content] The proportion of crosslinked resin in the resin contained in the thermal conductive sheet is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 85% by mass or more, and particularly preferably 100% by mass. If the proportion of crosslinked resin in the resin is above the lower limit of the above value, the sheet strength of the thermal conductive sheet can be improved, further increasing its resistance to tearing during use. The amount of crosslinked resin contained in the thermal conductive sheet is usually equal to the amount of crosslinkable resin used in the manufacture of the thermal conductive sheet. Therefore, the proportion of crosslinked resin in the resin contained in the thermal conductive sheet is usually equal to the proportion of crosslinkable resin in the resin used in the manufacture of the thermal conductive sheet (a resin containing both crosslinkable resin and other resins).

[0034] <<Other resins>> Furthermore, the resin contained in the heat conductive sheet of the present invention may include resins other than the crosslinked resin described above (hereinafter sometimes referred to as "other resins"). Here, the other resins are resins that have not been crosslinked (non-crosslinked resins). In addition, resins that do not react with the crosslinking agent described above (also referred to as "non-crosslinkable resins") can be used as the other resins. For example, resins that do not react with the crosslinking agent using peroxide can be used as the other resins. Furthermore, other resins can be used, for example, liquid resins at room temperature and atmospheric pressure. While not particularly limited, various resins described in Japanese Patent Publication No. 2021-155636 can be used as liquid resins at room temperature and atmospheric pressure.

[0035] <Particulate filler> The particulate filler is not particularly limited, and examples include alumina particles, zinc oxide particles, boron nitride particles, aluminum nitride particles, silicon nitride particles, silicon carbide particles, magnesium oxide particles, and particulate carbon materials. The particulate carbon material is not particularly limited, and examples include artificial graphite, flaky graphite, flake graphite, natural graphite, acid-treated graphite, negative electrode active material, expandable graphite, expanded graphite, and other types of graphite; carbon black; etc. These may be used individually or in combination of two or more types. These particulate fillers may be used individually or mixed in any ratio of two or more types.

[0036] Furthermore, from the viewpoint of improving the thermal conductivity of the manufactured thermal conductive sheet, the aspect ratio (long axis / short axis) of the particulate filler is preferably greater than 1 and less than or equal to 10, and more preferably greater than 1 and less than or equal to 5. It is presumed that if the aspect ratio of the particulate filler is greater than 1 and less than or equal to 10, the particulate filler will be more likely to be well oriented in the thickness direction within the thermal conductive sheet, thereby improving the thermal conductivity in the thickness direction of the thermal conductive sheet. In this invention, the "aspect ratio" can be determined by observing the particulate packing material with a scanning electron microscope (SEM), measuring the maximum diameter (long axis) and the particle diameter in the direction perpendicular to the maximum diameter (short axis) for any 50 particulate packing materials, and calculating the average value of the ratio of the long axis to the short axis (long axis / short axis). In the above, for example, if the particulate packing material is in the shape of a scale, the "long axis" refers to the length in the direction of the long axis of the main surface of the scale shape, and the "short axis" refers to the length in the direction perpendicular to the long axis of the main surface.

[0037] <<Properties of particulate filler>> The volume-average particle diameter of the particulate filler is preferably 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, even more preferably 40 μm or more, preferably 180 μm or less, more preferably 160 μm or less, and even more preferably 140 μm or less. If the volume-average particle diameter of the particulate filler is above the lower limit, it is presumed that good heat transfer paths of the particulate filler can be formed in the thermal conductive sheet, thereby improving the thermal conductivity of the thermal conductive sheet. On the other hand, if the volume-average particle diameter of the particulate filler is below the upper limit, a sufficiently high thickness accuracy of the thermal conductive sheet can be ensured. Furthermore, if the volume-average particle diameter of the particulate filler is within the above predetermined range, the resistance to tearing during use of the thermal conductive sheet can be further improved. In this invention, "volume-average particle diameter" can be measured in accordance with JIS Z8825 and represents the particle diameter at which the cumulative volume calculated from the smallest diameter side accounts for 50% of the particle size distribution (volume-based) measured by laser diffraction.

[0038] <<Content of particulate filler>> Furthermore, the content of particulate filler in the thermal conductive sheet is preferably 70 parts by mass or more, more preferably 90 parts by mass or more, even more preferably 110 parts by mass or more, preferably 400 parts by mass or less, and more preferably 350 parts by mass or less, per 100 parts by mass of resin. If the content of particulate filler in the thermal conductive sheet is above the lower limit, the gas generated during the crosslinking reaction step in the thermal conductive sheet manufacturing method described later can be efficiently discharged through the surface or interior of the particulate filler, thereby reducing the number of micropores on the surface of the thermal conductive sheet and further increasing its resistance to tearing during use. Also, if the content of particulate filler in the thermal conductive sheet is above the lower limit, the thermal conductivity of the thermal conductive sheet can be increased. On the other hand, if the content of particulate filler in the thermal conductive sheet is below the upper limit, the flexibility of the thermal conductive sheet can be sufficiently maintained, and as a result, thermal resistance can be reduced. Furthermore, if the amount of particulate filler in the thermal conductive sheet is below the above upper limit, the proportion of resin in the thermal conductive sheet increases, and the particulate fillers are well bonded together by the resin, which further improves the resistance of the thermal conductive sheet to tearing during use.

[0039] <<Percentage of particulate filler volume>> In a thermal conductive sheet, the ratio of the volume of particulate filler to the total volume of resin and particulate filler is preferably 25% by volume or more, more preferably 30% by volume or more, more preferably 85% by volume or less, and even more preferably 80% by volume or less. If the ratio of the volume of particulate filler to the total volume of resin and particulate filler in the thermal conductive sheet is above the lower limit, the gas generated during the crosslinking reaction step in the thermal conductive sheet manufacturing method described later can be efficiently discharged through the surface or interior of the particulate filler, thereby reducing the number of micropores on the surface of the thermal conductive sheet and further increasing its resistance to tearing during use. Also, if the ratio of the volume of particulate filler to the total volume of resin and particulate filler in the thermal conductive sheet is above the lower limit, the thermal conductivity of the thermal conductive sheet can be increased. On the other hand, if the ratio of the volume of particulate filler to the total volume of resin and particulate filler in the thermal conductive sheet is below the upper limit, the flexibility of the thermal conductive sheet can be sufficiently maintained, and as a result, the thermal resistance can be reduced. Furthermore, if the ratio of the volume of particulate filler to the total volume of resin and particulate filler in the thermal conductive sheet is below the above upper limit, the proportion of resin in the thermal conductive sheet increases, and the particulate fillers are well bonded together by the resin, which further improves the resistance of the thermal conductive sheet to tearing during use. Of the "total volume of resin and particulate filler in the thermal conductive sheet" mentioned above, the volume of crosslinked resin contained in the resin usually matches the volume of crosslinkable resin used in the manufacture of the thermal conductive sheet. Therefore, the "total volume of resin and particulate filler in the thermal conductive sheet" usually matches the total volume of the resin and particulate filler used in the manufacture of the thermal conductive sheet.

[0040] <Other ingredients> The heat-conducting sheet of the present invention may optionally further contain components other than the above-described resin and particulate filler (hereinafter sometimes referred to as "other components"). The other components are not particularly limited as long as they can be used in the production of the heat-conducting sheet. For example, fibrous carbon materials; flame retardants such as red phosphorus-based flame retardants and phosphate ester-based flame retardants; plasticizers such as fatty acid ester-based plasticizers; toughness improvers such as urethane acrylate; moisture absorbers such as calcium oxide and magnesium oxide; adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides; wettability improvers such as nonionic surfactants and fluorine-based surfactants; ion trappers such as inorganic ion exchangers; dispersants; acid acceptors, etc. can be mentioned.

[0041] <Structure of the heat-conducting sheet> The heat-conducting sheet of the present invention requires that the angle of the long axis direction of the above-described particulate filler with respect to the surface of the heat-conducting sheet be 60° or more and 90° or less. If the angle of the long axis direction of the particulate filler with respect to the surface of the heat-conducting sheet in the heat-conducting sheet is 60° or more and 90° or less, the thermal conductivity in the thickness direction of the heat-conducting sheet can be increased. Here, the "angle of the long axis direction of the particulate filler with respect to the surface of the heat-conducting sheet" is preferably 70 degrees or more, more preferably 80 degrees or more, and even more preferably 85 degrees or more. If the angle is at least the above lower limit value, the thermal conductivity can be further increased, and the smoothness and strength of the surface of the heat-conducting sheet can be increased. Incidentally, the "angle of the long axis direction of the particulate filler with respect to the surface of the heat-conducting sheet" can be increased by increasing the pressure in the crosslinking reaction step described later.

[0042] <Tensile strength Sx (MPa) in the X direction> When measuring the tensile strength on the main surface of the heat-conducting sheet of the present invention, taking the in-plane direction X in which the tensile strength is the highest as the X direction, the tensile strength Sx (MPa) in the X direction is required to be 5.0 MPa or more, and more preferably 5.5 MPa or more. The upper limit of the value of the tensile strength Sx in the X direction is not particularly limited, but usually can be 12.0 MPa or less. The tensile strength Sx in the X direction can be increased by fixing the entire surface of the laminate with a jig, adjusting the pressure, or adjusting the resin composition or the amount of the crosslinking agent in the crosslinking reaction process described later.

[0043] <The value (Sx / Sy) obtained by dividing the tensile strength Sx (MPa) in the X direction by the tensile strength Sy (MPa) in the Y direction> For the heat-conducting sheet of the present invention, taking the in-plane direction perpendicular to the in-plane direction X as the Y direction, when the tensile strength in the Y direction is denoted as the tensile strength Sy, the value of (Sx / Sy) needs to be 3.2 or less, and preferably 3.0 or less. If the value of (Sx / Sy) is below the above upper limit value, the deviation of the tensile strength in the in-plane direction of the sheet is small. Therefore, when it is used sandwiched between a heating element and a heat sink, it has excellent thermal conductivity and is less likely to be torn due to the pressure applied by the heating element and the heat sink. The reason is not clear, but it is presumed that because the deviation of the tensile strength in the in-plane direction of the sheet is small, even when the sheet is pressurized, the stress difference that may occur between the direction with relatively weak strength and the direction with relatively strong strength becomes small, so that the sheet is less likely to be torn due to such a stress difference. The lower limit of the value of (Sx / Sy) is not particularly limited, but for example, it can be 1.1 or more. The value of (Sx / Sy) can be increased by fixing the entire surface of the laminate with a jig, adjusting the pressure, or adjusting the resin composition or the amount of the crosslinking agent in the crosslinking reaction process described later.

[0044] In the heat conductive sheet and the method for manufacturing the heat conductive sheet of the present invention, the X direction usually coincides with the direction perpendicular to the stacking direction of the laminate. Therefore, the Y direction perpendicular to the X direction usually coincides with the stacking direction of the laminate.

[0045] <Micropore> The surface of the heat-conducting sheet of the present invention has few micropores (also referred to as "pinholes"). Micropores on the surface of a heat-conducting sheet are formed, for example, by gases generated during the cross-linking reaction of the resin carried out during the manufacture of the heat-conducting sheet. These micropores formed on the surface of a heat-conducting sheet can cause the sheet to tear during use. In contrast, the heat-conducting sheet of the present invention is less likely to tear during use because it has fewer micropores formed on its surface.

[0046] Specifically, the number of micropores with a pore diameter of 48 μm to 500 μm corresponds to the planar area of ​​the thermal conductive sheet per 1 cm². 2 The number of hits is preferably 12 or less, more preferably 5 or less, and even more preferably no micropores at all. If the number of micropores in the thermal conductive sheet is below the above upper limit, the thermal conductive sheet is less likely to tear during use and is of high quality. The number of micropores in the thermal conductive sheet can be adjusted, for example, by the proportion of crosslinkable resin in the resin used in the manufacturing method of the thermal conductive sheet, the proportion of the volume of particulate filler to the total volume of resin and particulate filler, and the conditions of the crosslinking reaction process (heating temperature, heating time, pressure, etc.).

[0047] <Thickness of the thermal conductive sheet> The thickness of the thermal conductive sheet of the present invention is not particularly limited, but is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less, preferably 50 μm or more, more preferably 60 μm or more, and most preferably 70 μm or more. If the thickness of the thermal conductive sheet is below the above upper limit, the thermal conductivity in the thickness direction of the thermal conductive sheet can be increased. On the other hand, if the thickness of the thermal conductive sheet is above the above lower limit, the thermal conductive sheet will not become excessively thin, so the resistance to tearing, flame retardancy, strength, and handling properties of the thermal conductive sheet during use can be sufficiently ensured.

[0048] (Method of manufacturing a thermal conductive sheet) The present invention provides a method for manufacturing a thermal conductive sheet, comprising: a pre-thermal conductive sheet molding step of pressurizing a composition containing a crosslinkable resin, a particulate filler, and a crosslinking agent to form a sheet to obtain a pre-thermal conductive sheet; a laminate formation step of stacking multiple pre-thermal conductive sheets in the thickness direction, or folding or winding the pre-thermal conductive sheets to obtain a laminate; a crosslinking reaction step of heating the laminate while applying pressure in the stacking direction to perform a crosslinking reaction; and a slicing step of slicing the laminate at an angle of 45° or less with respect to the stacking direction to obtain a thermal conductive sheet. Furthermore, the manufacturing method of the present invention is characterized in that, in the crosslinking reaction step, the entire surface of the laminate is fixed with a jig, and the pressure applied in the stacking direction is greater than 1.0 MPa. The thermal conductive sheet of the present invention may optionally further include steps other than those listed above.

[0049] In the present invention, according to the method for manufacturing a thermal conductive sheet, in the crosslinking reaction step, the entire surface of the laminate is fixed with a jig, and the pressure applied in the lamination direction is set to more than 1.0 MPa. This makes it possible to increase the angle of the particulate filler in the longitudinal direction relative to the thermal conductive sheet surface, and the tensile strength Sx (MPa) in the X direction, while keeping the value of (Sx / Sy) low. Furthermore, since the number of micropores (pinholes) formed in the thermal conductive sheet can be reduced, the thermal conductive sheet can be made less likely to tear during use.

[0050] <Pre-heat conductive sheet molding process> In the pre-heat-conducting sheet molding process, a composition containing a crosslinkable resin, a particulate filler, and a crosslinking agent is pressurized and molded into a sheet to obtain a pre-heat-conducting sheet.

[0051] <<Composition>> The above composition comprises a resin containing a crosslinkable resin, a particulate filler, and a crosslinking agent. The above composition may further contain a reaction initiator. Furthermore, the above composition may further contain components other than the resin, particulate filler, crosslinking agent, and reaction initiator (other components).

[0052] 〔resin〕 Here, the resin contained in the composition contains a crosslinkable resin and optionally contains a resin other than the crosslinkable resin (non-crosslinkable resin). As the crosslinkable resin, for example, a crosslinkable resin that can be used to form the crosslinkable resin described above in the "Thermal Conductive Sheet" section can be used. As the resin other than the crosslinkable resin (non-crosslinkable resin), for example, a resin other than the crosslinkable resin that can be included in the resin described above in the "Thermal Conductive Sheet" section (other resins) can be used.

[0053] [Particulate filler] Furthermore, as particulate fillers, for example, the particulate fillers described above in the "Thermal Conductive Sheet" section can be used.

[0054] Here, the ratio of the volume of particulate filler to the total volume of resin and particulate filler in the composition is preferably 25% by volume or more, preferably 30% by volume or less, more preferably 85% by volume or less, and even more preferably 80% by volume or less. If the ratio of the volume of particulate filler to the total volume of resin and particulate filler in the composition is equal to or greater than the above lower limit, the gas generated during the crosslinking reaction process described later can be efficiently discharged through the surface or interior of the particulate filler, thereby reducing the number of micropores on the surface of the manufactured thermal conductive sheet and making it less likely to tear during use. Furthermore, if the ratio of the volume of particulate filler to the total volume of resin and particulate filler in the composition is equal to or greater than the above lower limit, the thermal conductivity of the manufactured thermal conductive sheet can be improved. On the other hand, if the ratio of the volume of particulate filler to the total volume of resin and particulate filler in the composition is equal to or less than the above upper limit, the flexibility of the manufactured thermal conductive sheet can be sufficiently maintained, and as a result, the thermal resistance can be reduced. Furthermore, if the ratio of the volume of particulate filler to the total volume of resin and particulate filler in the composition is less than or equal to the above upper limit, the proportion of resin in the manufactured thermal conductive sheet will increase, and the particulate fillers will be well bonded together by the resin, thereby further improving the resistance to tearing when using the thermal conductive sheet.

[0055] The content of particulate filler per 100 parts by mass of resin in the composition can be set within the same range as the preferred range for the content of particulate filler per 100 parts by mass of resin in the thermal conductive sheet described above in the "thermal conductive sheet" section.

[0056] [Crosslinking agent] As the crosslinking agent, you can use the crosslinking agent that can be used to form the crosslinked resin described above in the "Thermal Conductive Sheet" section.

[0057] The amount of crosslinking agent per 100 parts by mass of crosslinkable resin in the composition can be set within the same range as the preferred range for the amount of crosslinking agent used per 100 parts by mass of crosslinkable resin as described above in the "Thermal Conductive Sheet" section.

[0058] [Reaction initiator] As a reaction initiator, you can use a reaction initiator that can be used in the crosslinking reaction for forming the crosslinked resin described above in the "Thermal Conductive Sheet" section.

[0059] The amount of reaction initiator per 100 parts by mass of crosslinkable resin in the composition can be set within the same range as the preferred range for the amount of reaction initiator used per 100 parts by mass of crosslinkable resin in the crosslinking reaction described above in the "Thermal Conductive Sheet" section. Furthermore, the mass ratio of the crosslinking agent to the reaction initiator in the composition (crosslinking agent / reaction initiator) can be set within the same range as the mass ratio of the amount of crosslinking agent used to the amount of reaction initiator used in the crosslinking reaction described above in the "thermal conductive sheet" section (crosslinking agent / reaction initiator).

[0060] [Other ingredients] Other components that may be included in the composition include dispersants and other components that may be included in the thermal conductive sheet as described in the "Thermal Conductive Sheet" section.

[0061] [Preparation of the composition] The composition is not particularly limited and can be prepared by mixing the above-mentioned components. The mixing of the above-mentioned components can be carried out using known mixing equipment such as a kneader, mixer (e.g., Henschel mixer, Hobart mixer, high-speed mixer), twin-shaft kneader, or rolls, without any particular limitations. The mixing may also be carried out in the presence of a solvent such as ethyl acetate. The resin may be dissolved or dispersed in the solvent beforehand to form a resin solution, which can then be mixed with the particulate filler, crosslinking agent, and optionally added reaction initiator and other components. The mixing time can be, for example, 5 minutes to 60 minutes. The mixing temperature can be, for example, 5°C to 150°C.

[0062] <<Formation of the composition>> The composition prepared as described above can be optionally degassed and crushed, and then pressed to form a sheet. A sheet formed by pressing the composition in this way can be used as a pre-heat-conducting sheet. If a solvent is used during mixing, it is preferable to remove the solvent before forming the sheet. For example, if degassing is performed using vacuum degassing, the solvent can be removed at the same time as degassing.

[0063] Here, the composition can be formed into a sheet using known molding methods such as press molding, rolling molding, or extrusion molding, as long as the molding method involves applying pressure. In particular, it is preferable to form the composition into a sheet by rolling molding (primary processing), and it is more preferable to form it into a sheet by passing it between rolls while sandwiched between protective films. The protective film is not particularly limited, and can be a sandblasted polyethylene terephthalate (PET) film or the like. The roll temperature can be 5°C to 150°C, the roll gap can be 50 μm to 2500 μm, the roll linear pressure can be 1 kg / cm to 3000 kg / cm, and the roll speed can be 0.1 m / min to 20 m / min.

[0064] <<Pre-heat conductive sheet>> Furthermore, in a pre-heat-conductive sheet formed by pressurizing the composition into a sheet, the particulate filler is mainly oriented in the in-plane direction, and it is presumed that the in-plane thermal conductivity of the pre-heat-conductive sheet is particularly improved.

[0065] <(B) Laminate formation process> In the laminate formation process, multiple pre-heat conductive sheets obtained in the pre-heat conductive sheet molding process are laminated in the thickness direction, or the pre-heat conductive sheets are folded or wound to obtain a laminate in which multiple heat conductive sheets containing resin and particulate filler are formed in the thickness direction. Here, the formation of a laminate by folding the pre-heat conductive sheets is not particularly limited and can be done by folding the pre-heat conductive sheets to a certain width using a folding machine. Similarly, the formation of a laminate by winding the pre-heat conductive sheets is not particularly limited and can be done by winding the pre-heat conductive sheets around an axis parallel to the short or long direction of the pre-heat conductive sheets. Furthermore, the formation of a laminate by laminating pre-heat conductive sheets can be done using a laminating device without particular limitations. For example, using a sheet laminating device (manufactured by Nikkiso Co., Ltd., product name "High Stacker") can suppress the intrusion of air between layers, thereby efficiently obtaining a good laminate.

[0066] In the lamination process, it is preferable to heat the resulting laminate at a temperature lower than the heating temperature of the crosslinking reaction process described later, while applying pressure in the lamination direction (secondary pressurization). By performing secondary pressurization, which involves heating the laminate at a temperature lower than the heating temperature of the crosslinking reaction process described later, and then carrying out the crosslinking reaction process described later, the crosslinking reaction can be performed while promoting fusion between the laminated pre-heat-conductive sheets, thereby improving the crosslinking strength between the interfaces of each layer in the laminate.

[0067] Here, the pressure applied to the laminate in the stacking direction can be 0.01 MPa or more, preferably 0.03 MPa or more, more preferably 0.05 MPa or more, and can be 0.50 MPa or less, preferably 0.30 MPa or less, and more preferably 0.10 MPa or less.

[0068] Furthermore, the heating temperature of the laminate is not particularly limited as long as it is lower than the heating temperature of the crosslinking reaction step described later, but it can be less than 90°C, preferably 85°C or lower, more preferably 80°C or lower, can be 30°C or higher, preferably 40°C or higher, and more preferably 50°C or higher. Furthermore, the heating time for the laminate can be, for example, 30 seconds to 5 minutes.

[0069] Furthermore, in laminates obtained by laminating, folding, or winding pre-heat-conductive sheets, it is presumed that the particulate filler is oriented in a direction approximately perpendicular to the lamination direction.

[0070] <(C) Crosslinking reaction process> In the crosslinking reaction step, the laminate is heated while being pressurized in the lamination direction to carry out the crosslinking reaction. At this time, the entire surface of the laminate is fixed with a jig, and the pressure applied in the lamination direction is set to more than 1.0 MPa. In the crosslinking reaction step, the crosslinkable resin undergoes a crosslinking reaction to form a crosslinked resin, which improves the sheet strength of the manufactured thermal conductive sheet and makes it less likely to tear during use. Here, the crosslinking reaction step is preferably carried out under a vacuum atmosphere from the viewpoint of making the surface of the resulting thermal conductive sheet even smoother, increasing the strength of the resulting thermal conductive sheet, and further increasing the resistance of the resulting thermal conductive sheet to crushing.

[0071] Here, the pressure applied to the laminate in the lamination direction during the crosslinking reaction must be greater than 1.0 MPa, preferably 2.0 MPa or higher, more preferably 2.5 MPa or higher, preferably 5.0 MPa or lower, and more preferably 4.0 MPa or lower. If the pressure applied to the laminate in the lamination direction during the crosslinking reaction is greater than or equal to the lower limit above, the sheet strength in the main plane direction X of the manufactured thermal conductive sheet can be improved, and the formation of micropores on the surface of the thermal conductive sheet during the crosslinking reaction can be suppressed. This further enhances the resistance of the thermal conductive sheet to tearing during use. Furthermore, if the pressure applied to the laminate in the lamination direction during the crosslinking reaction is greater than or equal to the lower limit above, the smoothness of the thermal conductive sheet surface can be improved. And, if the pressure applied to the laminate in the lamination direction during the crosslinking reaction is greater than or equal to the lower limit above, the sheet strength can be effectively increased, so that the thermal conductive sheet is less likely to collapse when pressure is applied. On the other hand, if the pressure applied to the laminate in the lamination direction during the crosslinking reaction is less than or equal to the upper limit above, it is possible to suppress excessive compression of the laminate and collapse of the laminated structure.

[0072] Furthermore, in the crosslinking reaction process, when fixing the entire surface of the laminate with a jig, flat plates are placed on the bottom and top surfaces in the lamination direction of the laminate to sandwich it, and flat plates are also placed on all sides of the laminate to prevent the sides from moving when the laminate is pressed using the upper and lower plates. The shape of the laminate is not particularly limited, but for example, if the laminate is cubic or rectangular, flat plates made of a rigid material such as a metal plate are placed in close contact with all four sides. Also, for example, if the laminate is octagonal prism-shaped, flat plates are placed in close contact with all eight sides. In this way, by fixing the entire surface of the laminate with a jig during the crosslinking reaction, the formation of micropores on the surface of the thermal conductive sheet can be effectively suppressed, thereby further increasing the resistance to tearing of the thermal conductive sheet during use.

[0073] Furthermore, the heating temperature in the crosslinking reaction process must be 180°C or lower, more preferably 170°C or lower, even more preferably 160°C or lower, preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 110°C or higher. If the heating temperature in the crosslinking reaction process is below the above upper limit, the amount of gas generated in the crosslinking reaction process can be reduced, thereby reducing the number of micropores (pinholes) formed in the manufactured thermal conductive sheet, making the thermal conductive sheet less likely to tear during use. On the other hand, if the heating temperature in the crosslinking reaction process is above the above lower limit, the crosslinking reaction can be carried out well, improving the sheet strength of the manufactured thermal conductive sheet and further increasing its resistance to tearing during use.

[0074] Furthermore, the heating time in the crosslinking reaction step is preferably 1 hour or more, more preferably 3 hours or more, even more preferably 5 hours or more, preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 8 hours or less. If the heating time in the crosslinking reaction step is above the lower limit above, the crosslinking reaction can be carried out well, improving the sheet strength of the manufactured thermal conductive sheet and further increasing its resistance to tearing during use. On the other hand, if the heating time in the crosslinking reaction step is below the upper limit above, the crosslinking reaction can be prevented from progressing excessively, and the flexibility of the thermal conductive sheet can be maintained well.

[0075] <(D) Slicing process> In the slicing process, the laminate that has undergone the crosslinking reaction in the crosslinking reaction process is sliced ​​at an angle of 45° or less with respect to the lamination direction to obtain a heat conductive sheet made of sliced ​​pieces of the laminate. The method of slicing the laminate is not particularly limited, and examples include the multi-blade method, laser processing method, water jet method, and knife processing method. Among these, the knife processing method is preferred because it makes it easier to ensure a uniform thickness of the heat conductive sheet. Furthermore, the cutting tool used when slicing the laminate is not particularly limited, and a slicing member having a smooth surface with a slit and a blade portion protruding from the slit portion (for example, a plane or slicer with a sharp blade) can be used.

[0076] Furthermore, from the viewpoint of improving the thermal conductivity of the thermal conductive sheet, the slicing angle of the laminate is preferably 30° or less with respect to the lamination direction, more preferably 15° or less with respect to the lamination direction, and preferably approximately 0° with respect to the lamination direction (i.e., in the direction along the lamination direction).

[0077] Furthermore, the thermal conductive sheet obtained in this way is less likely to tear during use. In addition, the granular filler in the thermal conductive sheet obtained in this way is well oriented in the thickness direction, resulting in excellent thermal conductivity in the thickness direction. [Examples]

[0078] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" used to express quantities refer to mass unless otherwise specified.

[0079] In each example and comparative example, various attributes were measured or evaluated by the following methods.

[0080] <Orientation angle of particulate filler> The orientation angle of the particulate filler in the thermal conductive sheet was determined by observing a cross-section of the thermal conductive sheet, cut into a regular octagon, using a scanning electron microscope (SEM, Hitachi High-Technologies "SU-3500") at a magnification that captured the entire sheet from top to bottom. The magnification at this time was 700x. Fifty lines were drawn along the long axis of the particulate filler in this cross-section, and the average angle of the long axis relative to the surface of the composite sheet was calculated. If the angle was 90° or greater, a supplementary angle was used. This was performed for eight surfaces, and the value with the largest result among the eight surfaces was taken as the orientation angle of the particulate filler in the composite sheet.

[0081] <Thermal conductivity in the thickness direction of the thermal conductive sheet> For the thermal conductive sheets manufactured in each example and comparative example, the thermal diffusivity α(m) in the thickness direction is as follows: 2 ( / s), constant-pressure specific heat Cp (J / g·K) and specific gravity ρ (g / m 3 The following method was used to measure the following: [Thermal diffusivity α(m 2 / s)] The thermal diffusivity in the thickness direction was measured using a thermophysical property measuring device (manufactured by Bethel Co., Ltd., product name "ThermoWave Analyzer TA35"). [Specific heat at constant pressure Cp (J / g·K)] The specific heat was measured under a heating condition of 10°C / min using a differential scanning calorimeter (Rigaku, product name "DSC8230"). [Specific gravity ρ(g / m 3 )] Specific gravity (density) (g / m³) was measured using an automatic hydrometer (manufactured by Toyo Seiki Co., Ltd., product name "DENSIMETER-H"). 3 ) was measured. Then, using the obtained measurements, the following equation (I): λ = α × Cp × ρ···(I) By substituting these values, the thermal conductivity λ (W / m·K) in the thickness direction of the thermal conductive sheet was determined.

[0082] <Surface roughness Sa of thermal conductive sheet> The surface roughness Sa of the thermal conductive sheets manufactured in each example and comparative example was measured using a three-dimensional shape measuring machine (manufactured by Keyence Corporation, product name "One Shot 3D Measurement Macroscope"). Specifically, the three-dimensional shape was measured for five analysis areas (1 cm × 1 cm) extracted from the surface of the thermal conductive sheet being evaluated. Ideally, each analysis area should be at least 1 cm apart when selecting the five points; however, if the thermal conductive sheet is small, some overlap in the analysis areas is acceptable. Furthermore, if the thermal conductive sheet is too small to secure a 1 cm × 1 cm analysis area, the analysis area may be reduced to 0.3 cm × 0.3 cm. Furthermore, the three-dimensional shape measurement results were filtered (2.5 mm) using software to remove waviness components, and the surface roughness Sa (μm) was automatically calculated. The average value of the five analysis points was then used as the surface roughness Sa of the thermal conductive sheet.

[0083] <Compression ratio of thermal conductive sheets> The compressibility of the thermal conductive sheets manufactured in each example and comparative example was measured using a thermal resistance tester (manufactured by Hitachi Technology & Services, Ltd., product name "Thermal Resistance Measuring Device for Resin Materials"). Here, a thermal conductive sheet cut into a roughly square shape of 1 cm was used as a sample, and the thickness value of the thermal conductive sheet before pressurization (T0.1) was measured. At a sample temperature of 50°C, the thickness value of the thermal conductive sheet under a pressure of 0.9 MPa (T0.9) was measured. The compressibility value (C) of the thermal conductive sheet was calculated by substituting the measured values ​​into the following formula (1). A lower compressibility of the thermal conductive sheet means that the thermal conductive sheet is less likely to collapse when subjected to pressure during use. C=100×{1-(T0.9 / T0.1)}[%]...(1)

[0084] <Sheet strength of thermal conductive sheet> The heat conduction sheets produced in each of the examples and comparative examples were punched out in a size of 20 mm in the X direction and 50 mm in the Y direction to obtain test pieces. For the obtained test pieces, a tensile test was conducted using a small desktop testing machine (manufactured by Nidec-Shimpo Corporation, "FGS-500TV", using FGP-50 as a digital force gauge), with a tensile speed of 20 mm / min, to pull the test pieces in the Y direction. The distance between the chucks was set to 30 mm. The maximum strength (N) during the tensile test was divided by the cross-sectional area of the test body (width 20 mm × thickness 0.1 mm = 2 mm 2 ), and the sheet strength (N / mm 2 ) in the Y direction of the heat conduction sheet was calculated. In the above, the "X direction" means "the in-plane direction of the main surface where the sheet strength is the highest when measuring the sheet strength for the main surface of the heat conduction sheet". And since the heat conduction sheets produced in each of the examples and comparative examples are composed of sliced pieces of the laminate, when measuring the sheet strength for the main surface of the heat conduction sheet by the same method as described above, the "X direction" was found to coincide with the direction perpendicular to the lamination direction of the laminate. Also, the "Y direction" means "the in-plane direction perpendicular to the X direction (the direction coinciding with the lamination direction of the laminate)".

[0085] <Number of micropores in the heat conduction sheet> The number of micropores in the heat conduction sheets produced in each of the examples and comparative examples was measured using an appearance inspection device (manufactured by Nagano Automation Co., Ltd., product name "0O-6724 Appearance Inspection Device"). Specifically, the back surface of the heat conduction sheet placed on the pedestal was illuminated with an LED light, and the entire sheet was photographed with a camera. The obtained image was binarized by image processing to identify the white parts. Among these white parts, those with both the maximum diameter and the minimum diameter being 48 μm or more and 500 μm or less were regarded as micropores, and the number thereof was measured. From the number of micropores in the entire obtained heat conduction sheet and the planar view area of the heat conduction sheet, the number of micropores per 1 cm 2 of the planar view area of the heat conduction sheet was calculated. A: No micropores are present. B: There are 1 to 5 micropores. C: There are 6 to 12 micropores. D: 13 or more micropores.

[0086] (Example 1) <Preparation of Composition> 100 parts of a solid fluoroelastomer (fluororubber) (manufactured by 3M Japan, product name "Dyneon® FPO3600ULV", specific gravity: 1.77) as a crosslinkable resin at room temperature and pressure, and 140 parts of expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., product name "EC300", volume average particle size: 50 μm, aspect ratio: greater than 1 and less than or equal to 5, specific gravity: 2.25) as a particulate filler were mixed by stirring at 150°C for 20 minutes using a pressurized kneader (manufactured by Nippon Spindle). Next, after lowering the apparatus temperature to 60°C, 1.08 parts of dibenzoyl peroxide (manufactured by NOF Corporation, trade name "Perhexa 25B-40") as a reaction initiator, 0.72 parts of triallyl isocyanurate (manufactured by Nippon Chemical Corporation, trade name "TAIC") as a crosslinking agent, and 1.00 part of magnesium oxide (manufactured by Kyowa Chemical Industry Co., Ltd., trade name "Kyowa Mag 150") as an acid acceptor were mixed and kneaded for 10 minutes while maintaining the material temperature at 60°C. Next, the mixture obtained above was put into a pulverizer (manufactured by Sansho Industry Co., Ltd., product name "Hammer Crusher HN34S") and pulverized for 60 seconds to obtain a composition containing a crosslinkable resin, particulate filler, crosslinking agent, and reaction initiator.

[0087] <Pre-heat conductive sheet molding process> Next, 50 g of the obtained composition was sandwiched between 50 μm thick PET films (protective films) that had been sandblasted, and rolled (primary pressurized) under the conditions of a roll gap of 550 μm, a roll temperature of 50°C, a roll linear pressure of 50 kg / cm, and a roll speed of 1 m / min to obtain a pre-heat-conductive sheet with a thickness of 1.0 mm.

[0088] <Laminate formation process> Next, the obtained pre-heat conductive sheets were cut to 50 mm x 50 mm x 1.0 mm thickness, and 55 sheets were stacked in the thickness direction. Furthermore, by pressing (secondary pressurization) in the stacking direction at a temperature of 80°C and a pressure of 0.1 MPa for 1 minute, a laminate with a height of 49 mm was obtained. This secondary pressurization made the interlayers of the laminate more tightly bonded.

[0089] <Crosslinking reaction process> Next, the resulting laminate was placed on a flat plate constituting the pressure platform. The laminate was oriented so that its bottom surface was in contact with the flat plate. The four sides of the laminate were then covered with 2cm thick aluminum plates to prevent movement of the laminate. The aluminum plates were fixed in place to prevent movement even if the volume of the laminate changed. Furthermore, a flat plate constituting the pressure plate, paired with the flat plate constituting the pressure platform, was placed on top so that it was in contact with the top surface of the laminate. Then, the pressure plate was brought closer to the pressure platform, and a pressure of 3.0 MPa was applied in the lamination direction of the laminate. In this state, that is, with all six sides of the rectangular laminate fixed by jigs (molds) and a pressure of 3.0 MPa applied, the crosslinking reaction (vulcanization) was carried out by heating at 150°C in a vacuum atmosphere for 6 hours. Specifically, the crosslinking reaction process was carried out using a vacuum heat pressurization apparatus (apparatus name "VS02-1515", manufactured by Mikado Technos Co., Ltd.).

[0090] <Slicing process> Subsequently, leaving the necessary length for slicing, the entire top surface of the resulting laminate was pressed down with a metal plate, and a pressure of 0.1 MPa was applied in the lamination direction (i.e., from above) to fix the laminate in place. The sides and back of the laminate were not fixed. At this time, the temperature of the laminate was 25°C. Next, a cutting blade (double-edged, blade angle 2θ: 20°, maximum blade thickness: 3.5 mm, material: carbide, Rockwell hardness: 91.5, silicon coating on blade surface: none, total length: 200 mm) was attached to the press section of a servo press machine (manufactured by Discharge Precision Machining Laboratory), and the laminate was sliced ​​in the direction of the lamination of the laminate (in other words, in the direction that coincides with the normal to the main surface of the laminated pre-heat conductive sheet) at a slicing speed of 200 mm / second and a slice width of 100 μm to obtain a heat conductive sheet measuring 50 mm in length, 50 mm in width, and 0.10 mm in thickness. Then, the obtained thermal conductive sheets were subjected to various measurements and evaluations according to the method described above. The results are shown in Table 1.

[0091] (Example 2) The pressure applied in the stacking direction during the crosslinking reaction process was changed to 1.0 MPa. Otherwise, the same operations, measurements, and evaluations as in Example 1 were performed. The results are shown in Table 1.

[0092] (Example 3) The atmosphere during the crosslinking reaction process was set to atmospheric pressure. Otherwise, the same operations, measurements, and evaluations as in Example 1 were performed. The results are shown in Table 1.

[0093] (Example 4) In preparing the composition, the amount of reaction initiator was increased to 5.60 parts and the amount of crosslinking agent to 3.73 parts compared to Example 1. Otherwise, the same operations, measurements, and evaluations as in Example 1 were performed. The results are shown in Table 1.

[0094] (Example 5) In preparing the composition, 300 parts of hexagonal boron nitride (h-BN) particles (manufactured by Dandong Chemical Engineering, trade name "HSL", volume-average particle size: 30 μm, aspect ratio: 1.2, specific gravity: 2.27) were added as particulate filler. Otherwise, the same operations, measurements, and evaluations as in Example 1 were performed. The results are shown in Table 1.

[0095] (Example 6) In preparing the composition, 100 parts of acrylonitrile-butadiene copolymer hydrogenated (manufactured by Nippon Zeon Co., Ltd., trade name "ZP2000L", specific gravity: 1, labeled "hydrogenated nitrile rubber" in Table 1) were added as the crosslinkable resin, the amount of expanded graphite was changed to 120 parts, the amount of reaction initiator was changed to 7.00 parts, and the amount of crosslinking agent was changed to 5.00 parts. Except for these points, the same operations, measurements, and evaluations as in Example 1 were carried out. The results are shown in Table 1.

[0096] (Comparative Example 1) In the crosslinking reaction process, the sides of the laminate were not covered with aluminum plates during crosslinking. Aside from these points, the same operations as in Example 1 were attempted. However, the laminate collapsed during the lamination process, making slicing impossible and thus preventing the acquisition of a thermal conductive sheet. The results are shown in Table 1.

[0097] (Comparative Example 2) The pressure during the crosslinking reaction process was set to 0.8 MPa. Aside from these points, the same operations, measurements, and evaluations as in Example 1 were performed. The results are shown in Table 1.

[0098] [Table 1]

[0099] Table 1 shows that in Examples 1 to 6, when manufacturing a thermal conductive sheet according to a crosslinking reaction using a composition containing a crosslinkable resin, a particulate filler, and a crosslinking agent, the entire surface of the laminate of the sheet-like material made of the above composition was fixed with a jig during the crosslinking reaction, and the pressure applied in the lamination direction was greater than 1.0 MPa, a thermal conductive sheet that was less likely to tear during use was formed. On the other hand, in Comparative Example 1, where the entire surface of the laminate was not fixed with a jig during the crosslinking reaction, and in Comparative Example 2, where the pressure applied in the lamination direction was 1.0 MPa or less, it was found that a heat-conducting sheet that was resistant to tearing during use could not be formed. [Industrial applicability]

[0100] According to the present invention, it is possible to provide a heat-conducting sheet that is less likely to tear during use.

Claims

1. A pre-heat-conducting sheet molding step to obtain a pre-heat-conducting sheet by pressurizing a composition comprising a resin containing a crosslinkable resin which is a solid thermoplastic resin at room temperature and atmospheric pressure, a particulate filler blended such that its proportion to the total volume of the resin is 30% by volume or more and 80% by volume or less, and a crosslinking agent, A laminate formation step is to obtain a laminate by stacking multiple pre-heat conductive sheets in the thickness direction, or by folding or winding the pre-heat conductive sheets. A crosslinking reaction step is performed by heating the laminate while applying pressure in the stacking direction, A method for manufacturing a thermal conductive sheet, comprising a slicing step of slicing the laminate at an angle of 45° or less with respect to the lamination direction to obtain a thermal conductive sheet, In the crosslinking reaction step, the entire surface of the laminate is fixed with a jig, and the pressure applied in the lamination direction is set to more than 1.0 MPa, The aforementioned crosslinking reaction step is carried out under a vacuum atmosphere. A method for manufacturing a heat conductive sheet.

2. The method for manufacturing a thermal conductive sheet according to claim 1, wherein the pressure in the crosslinking reaction step is 2.0 MPa or more.

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