Heat-conductive sheet and method for manufacturing the same

Abstract

To provide a heat-conductive sheet which is less likely to be torn off during usage.SOLUTION: A heat-conductive sheet contains a resin and a particulate filler, and has heat conductivity in a thickness direction of 12 W / m K or more, in which the resin contains a crosslinked resin, and in measurement of a sheet strength on a main surface of the heat-conductive sheet, a sheet strength in a main in-plane direction Y vertical to a main in-plane direction X with the highest sheet strength is 1.0 N / mm2 or more, and the number of micropores that penetrate through the heat-conductive sheet in a thickness direction and have a pore diameter of 48 μm or more and 500 μm or less is 200 pieces or less per 1 cm2 of an area of the heat-conductive sheet in plan view.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a heat conduction sheet and a method for manufacturing the same.

Background Art

[0002] In recent years, heat generation of electronic components such as power semiconductors (such as IGBT modules) and integrated circuit (IC) chips has been increasing along with their performance improvement. As a result, in electronic devices using such electronic components, it has become necessary to take measures against functional failures due to temperature rise of the electronic components.

[0003] As a measure against functional failures due to temperature rise of electronic components, generally, a method of promoting heat dissipation by attaching a heat dissipating body such as a metal heat sink, a heat radiating plate, or heat radiating fins to a heat generating body such as an electronic component is adopted. When using a heat dissipating body, in order to efficiently transfer heat from the heat generating body to the heat dissipating body, a sheet-like member (heat conduction sheet) having high thermal conductivity is interposed, and a predetermined pressure is applied to this heat conduction sheet to bring the heat generating body and the heat dissipating body into close contact with each other.

[0004] From the viewpoint of increasing the thermal conductivity in the thickness direction, the heat conduction sheet can be manufactured, for example, by pressure molding a composition containing a resin and a particulate filler, stacking a plurality of obtained sheet-like molded bodies in the thickness direction, or folding or winding them to form a laminate, and then slicing the laminate. In the heat conduction sheet manufactured by slicing the laminate in this way, it is required to ensure sufficiently high sheet strength. In the heat conduction sheet manufactured by slicing the laminate, when measuring the thermal conductivity of the main surface of the heat conduction sheet, it is relatively easy to improve the sheet strength in the in-plane direction X (the direction perpendicular to the stacking direction of the laminate) where the thermal conductivity is the highest. However, it is difficult to improve the sheet strength in the in-plane direction Y (the direction coinciding with the stacking direction of the laminate) perpendicular to the in-plane direction X.

[0005] Patent Document 1 discloses a heat conduction sheet obtained by slicing a laminate at a predetermined angle. Here, by slicing the laminate at a predetermined angle, the sheet strength in the in-plane direction X and the sheet strength in the in-plane direction Y are made uniform. Further, Patent Document 2 discloses a heat transfer sheet containing a binder component and anisotropic graphite powder, and having a metal vapor deposition film provided on one surface of a base sheet in which the anisotropic graphite powder is oriented in the thickness direction. Here, by providing the metal vapor deposition film, the sheet strength of the heat conduction sheet is improved. Further, Patent Document 3 discloses subjecting a laminate to a crosslinking reaction while applying pressure in the lamination direction.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] Here, when the heat conduction sheet is used in a state of being sandwiched between a heating element and a heat radiating element and heated, by repeating the cycle of pressurization and depressurization, tearing occurs from the portion of the heat conduction sheet where a strong pressure is applied, and it may protrude from between the heating element and the heat radiating element. In an electronic device, the protruding heat conduction sheet can cause a short circuit, so the heat conduction sheet is required to be difficult to tear during use.

[0008] However, the heat conduction sheets of the above prior art have room for improvement in terms of difficulty of tearing during use.

[0009] Therefore, an object of the present invention is to provide a heat conduction sheet that is difficult to tear during use.

Means for Solving the Problems

[0010] The inventor of the present invention has conducted intensive studies to achieve the above object. Then, the inventor has found that in a heat-conductive sheet containing a resin containing a crosslinked resin and a particulate filler and having a thermal conductivity in the thickness direction of a predetermined value or more, if the sheet strength in the in-plane direction Y perpendicular to the in-plane direction X where the sheet strength is the highest is set to a predetermined value or more and the number of predetermined micropores is set to a predetermined value or less, the heat-conductive sheet is less likely to be torn during use, and thus the present invention has been completed.

[0011] That is, the object of this invention is to advantageously solve the above problems, and the heat-conductive sheet of the present invention is a heat-conductive sheet containing a resin and a particulate filler and having a thermal conductivity in the thickness direction of 12 W / m·K or more, wherein the resin contains a crosslinked resin, and in the measurement of the sheet strength of the main surface of the heat-conductive sheet, the sheet strength in the in-plane direction Y perpendicular to the in-plane direction X where the sheet strength is the highest is 1.0 N / mm 2 or more, and the number of micropores having a pore diameter of 48 μm or more and 500 μm or less penetrating the heat-conductive sheet in the thickness direction is 200 or less per 1 cm 2 of the planar view area of the heat-conductive sheet. Thus, a heat-conductive sheet containing a resin containing a crosslinked resin and a particulate filler, having a thermal conductivity in the thickness direction of a predetermined value or more, having a sheet strength in the in-plane direction Y perpendicular to the in-plane direction X where the sheet strength is the highest in the measurement of the sheet strength of the main surface of a predetermined value or more, and having the number of predetermined micropores of a predetermined value or less is less likely to be torn during use. In the present invention, the "thermal conductivity", "sheet strength", and "number of micropores having a pore diameter of 48 μm or more and 500 μm or less penetrating the heat-conductive sheet in the thickness direction" can be measured by the methods described in the examples of this specification.

[0012] Here, for the heat conduction sheet of the present invention, it is preferable that the crosslinked resin is solid under normal temperature and pressure, and the resin further contains a resin that is liquid under normal temperature and pressure. By using a crosslinked resin that is solid under normal temperature and pressure and a resin that is liquid under normal temperature and pressure in combination, the flexibility of the heat conduction sheet can be enhanced.

[0013] Also, for the heat conduction sheet of the present invention, it is preferable that the ratio of the volume of the particulate filler to the total volume of the resin and the particulate filler is 30% by volume or more. If the ratio of the volume of the particulate filler to the total volume of the resin and the particulate filler is 30% by volume or more, the difficulty of tearing during use of the heat conduction sheet can be further increased, and the thermal conductivity of the heat conduction sheet can be enhanced.

[0014] Furthermore, for the heat conduction sheet of the present invention, it is preferable that the surface roughness Sa is 2.4 μm or less. If the surface roughness Sa is equal to or less than the above-mentioned predetermined value, the difficulty of tearing during use of the heat conduction sheet can be further increased. In the present invention, the surface roughness Sa of the heat conduction sheet can be measured by the method described in the examples of this specification.

[0015] Also, this invention aims to advantageously solve the above problems. The manufacturing method of the heat conduction sheet of the present invention includes a pre-heat conduction sheet forming step of pressing a composition containing a resin containing a crosslinkable resin, a particulate filler, and a crosslinking agent into a sheet shape to obtain a pre-heat conduction sheet, a laminate forming step of laminating a plurality of the pre-heat conduction sheets in the thickness direction, or folding or winding the pre-heat conduction sheet to obtain a laminate, a crosslinking reaction step of heating the laminate while applying pressure in the lamination 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 lamination direction to obtain a heat conduction sheet, and is characterized by satisfying at least any one of the following (1) to (3). (1) The content ratio of the crosslinkable resin in the resin is 70% by mass or less. (2) The ratio of the volume of the particulate filler to the total volume of the resin and the particulate filler is 30% by volume or more. (3) The heating temperature in the crosslinking reaction step is 150°C or lower. According to the method for manufacturing a heat conductive sheet of the present invention, a heat conductive sheet that is difficult to tear during use can be manufactured.

[0016] Here, in the method for manufacturing a heat conductive sheet of the present invention, it is preferable that the pressure for pressing the laminate in the lamination direction in the crosslinking reaction step is 0.01 MPa or more. If the pressure for pressing the laminate in the lamination direction in the crosslinking reaction step is equal to or higher than the above predetermined value, the difficulty of tearing during use of the heat conductive sheet can be further enhanced.

[0017] Further, in the method for manufacturing a heat conductive sheet of the present invention, it is preferable that the crosslinking agent contains dibenzoyl peroxide. If the crosslinking agent contains dibenzoyl peroxide, the difficulty of tearing during use of the heat conductive sheet can be further enhanced.

Advantages of the Invention

[0018] According to the present invention, a heat conductive sheet that is difficult to tear during use can be provided.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail. Since the heat conductive sheet of the present invention has heat conductivity, it can be used by being sandwiched between a heating element and a heat radiating element. That is, the heat conductive sheet of the present invention can constitute a heat dissipation device together with a heat radiator such as a heat sink, a heat dissipation plate, and heat dissipation fins as a heat dissipation member. And the heat conductive sheet of the present invention is not particularly limited, but can be efficiently manufactured using the method for manufacturing a heat conductive sheet of the present invention described later.

[0020] (Heat 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, the thermal conductive sheet of the present invention has a thermal conductivity in the thickness direction of 12 W / m·K or more. And, in the thermal conductive sheet of the present invention, the resin contains a crosslinked resin, and in the measurement of the sheet strength of the main surface of the thermal conductive sheet, the sheet strength in the main surface direction Y perpendicular to the main surface direction X where the sheet strength is the highest is 1.0 N / mm or more, and the number of micropores having a pore diameter of 48 μm or more and 500 μm or less that penetrate the thermal conductive sheet in the thickness direction is 200 or less per 1 cm 2 in the plan view area of the thermal conductive sheet. The thermal conductive sheet of the present invention includes a resin containing a crosslinked resin, the sheet strength in a predetermined main surface direction Y is a predetermined value or more, and the number of predetermined micropores is a predetermined value or less per 1 cm 2 in the plan view area, so it is difficult to tear even during use. For example, the thermal conductive sheet of the present invention is less likely to tear even when the cycle of pressurization and depressurization is repeated in a state where it is sandwiched between a heat generating body and a heat radiating body and heated. Therefore, the thermal conductive sheet of the present invention is excellent in durability.

[0021] <Resin> Since the thermal conductive sheet of the present invention contains a resin, the heat generating body and the heat radiating body can be satisfactorily 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).

[0022] <<Crosslinked resin>> The resin contained in the heat-conductive sheet of the present invention contains a crosslinked resin. The crosslinked resin is a resin crosslinked by a crosslinking agent. And, by including a crosslinked resin as the resin, the heat-conductive sheet of the present invention can sufficiently ensure high sheet strength, so that it is difficult to tear during use.

[0023] 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).

[0024] 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. And the crosslinking reaction is not particularly limited, but 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.

[0025] [Crosslinkable resin] The crosslinkable resin is not particularly limited, but for example, a crosslinkable resin that can react 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 (that is, the type of the crosslinking reaction), for example, a resin that is solid under normal temperature and pressure can be used.

[0026] -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.

[0027] --Thermoplastic resin that is solid under normal temperature and pressure-- Examples of thermoplastic resins that are solid under normal 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, polyacrylic acid or its esters; silicone resins; fluorine resins; 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; styrene-acrylonitrile copolymers; acrylonitrile-butadiene-styrene copolymers (ABS resins); styrene-butadiene block copolymers or their hydrogenated products; styrene-isoprene block copolymers or their hydrogenated products; polyphenylene ether; modified polyphenylene ether; aliphatic polyamides; aromatic polyamides; polyamide-imide; polycarbonate; polyphenylene sulfide; polysulfone; polyethersulfone; polyether nitrile; polyether ketone; polyketone; polyurethane; liquid crystal polymers; ionomers; and the like. These may be used alone or in combination of two or more in any ratio. Among these, from the viewpoint of improving the flame retardancy, heat resistance, oil resistance, chemical resistance, etc. of the heat conduction sheet, as the thermoplastic resin that is solid under normal temperature and pressure, it is preferably a thermoplastic fluorine resin that is solid under normal temperature and pressure.

[0028] =Thermoplastic fluorine resin that is solid under normal temperature and pressure= The thermoplastic fluororesin that is solid under normal temperature and pressure is not particularly limited as long as it is a thermoplastic fluororesin that is solid under normal temperature and pressure. Examples of the thermoplastic fluororesin that is solid under normal temperature and pressure include elastomers obtained by polymerizing fluorine-containing monomers such as vinylidene fluoride-based fluororesins, tetrafluoroethylene-propylene-based fluororesins, and tetrafluoroethylene-perfluorovinyl ether-based fluororesins. More specifically, 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, etc. may be mentioned. These may be used alone or in combination of two or more in any ratio. Among these, from the viewpoint of processability, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and acrylic-modified polytetrafluoroethylene are preferred.

[0029] In addition, examples of commercially available thermoplastic fluororesins (fluoroelastomers (fluororubbers)) that are solid under normal temperature and pressure include, for example, Daiel (registered trademark) G-912, G-700 series, Daiel G-550 series / G-600 series, Daiel G-310 manufactured by Daikin Industries, Ltd.; KYNAR (registered trademark) series, KYNAR FLEX (registered trademark) series manufactured by ALKEMA; Dynion FC2211, FPO3600ULV manufactured by 3M; and the like.

[0030] [Crosslinking agent] The crosslinking agent is not particularly limited as long as it can undergo a crosslinking reaction with the above-described crosslinkable resin. Examples include isocyanurates such as triallyl isocyanurate (e.g., TAIC (registered trademark) manufactured by Mitsubishi Chemical Corporation); cyanurates such as triallyl cyanurate; maleimides such as N,N'-m-phenylenedimaleimide; allyl esters of polyvalent 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, triallyl ether of trimethylolpropane, and partial allyl ether of pentaerythritol; allyl-modified resins such as allylated novolac and allylated resol resin; 3- to 5-functional methacrylate compounds and acrylate compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; and the like. These may be used alone or in combination of two or more in any ratio. Among the above, it is preferable to use triallyl isocyanurate as the crosslinking agent. This is because, by using triallyl isocyanurate, the reaction can be more easily carried out, thereby improving the sheet strength of the heat conduction sheet.

[0031] Note that the amount of the crosslinking agent used in the crosslinking reaction is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, still more preferably 0.3 part by mass or more, preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, and still more preferably 0.8 part by mass or less, based on 100 parts by mass of the crosslinkable resin. If the amount of the crosslinking agent used is at least the above lower limit, the crosslinked resin formed can be sufficiently crosslinked by the crosslinking agent, so that the sheet strength of the thermal conductive sheet can be improved and the difficulty of tearing during use can be further increased. On the other hand, if the amount of the crosslinking agent used is at most the above upper limit, it is possible to suppress the excessive crosslinking of the crosslinked resin formed by the crosslinking agent and maintain good flexibility of the thermal conductive sheet.

[0032] 〔Reaction initiator〕 The reaction initiator that can be used in the crosslinking reaction between the crosslinkable resin and the crosslinking agent is not particularly limited. For example, dibenzoyl peroxide (e.g., Niper E manufactured by NOF Corporation), t-butyl peroxyacetate, 2,2-di-(t-butylperoxy)butane, t-butyl peroxybenzoate, t-butyl cumyl peroxide, dicumyl peroxide, di-t-hexyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (e.g., Perhexa 25B-40 (registered trademark) manufactured by NOF Corporation), 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, and the like can be mentioned. These may be used alone or in combination of two or more in any ratio. For example, by using a reaction initiator in the crosslinking reaction, radicals can be generated to smoothly initiate the crosslinking reaction. Among the above, as the reaction initiator, it is preferable to use dibenzoyl peroxide. If dibenzoyl peroxide is used, the cross-linking reaction can be favorably carried out at a low temperature (for example, 150 °C or lower), so the amount of gas generated is reduced, the number of micropores formed in the heat conductive sheet can be reduced, and the difficulty of tearing during use of the heat conductive sheet can be further enhanced.

[0033] In addition, the amount of the reaction initiator used in the cross-linking reaction is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, still more preferably 0.3 part by mass or more, preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, and still more preferably 0.8 part by mass or less with respect to 100 parts by mass of the cross-linkable resin. If the amount of the reaction initiator used is not less than the above lower limit, the formed cross-linked resin is sufficiently cross-linked by the cross-linking agent, so that the sheet strength of the heat conductive sheet can be improved and the difficulty of tearing during use can be further enhanced. On the other hand, if the amount of the reaction initiator used is not more than the above upper limit, the amount of gas generated in the cross-linking reaction can be reduced, so that the number of micropores formed in the heat conductive sheet can be reduced, and the difficulty of tearing during use of the heat conductive sheet can be further enhanced.

[0034] Further, the mass ratio (cross-linking agent / reaction initiator) of the amount of the cross-linking agent used to the amount of the reaction initiator used in the cross-linking reaction can be 1 / 3 or more and 3 / 1 or less.

[0035] 〔Method for forming cross-linked resin〕 The cross-linked resin can be formed by heating the above-mentioned cross-linkable resin, the cross-linking agent, and the reaction initiator used as required to carry out a cross-linking reaction. Regarding the conditions such as the heating temperature and heating time during the cross-linking reaction, they will be described later in the section of "Method for manufacturing heat conductive sheet".

[0036] 〔Content ratio of cross-linked resin〕 The proportion of the crosslinked resin in the resin contained in the heat conductive sheet is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, even more preferably more than 70% by mass, yet even more preferably 85% by mass or more, and particularly preferably 100% by mass. If the proportion of the crosslinked resin in the resin is 30% by mass or more, the sheet strength of the heat conductive sheet can be improved, and the difficulty of tearing during use can be further increased. In addition, the proportion of the crosslinked resin in the resin contained in the heat conductive sheet can be 70% by mass or less, and can also be 60% by mass or less. Note that the amount of the crosslinked resin contained in the heat conductive sheet usually coincides with the amount of the crosslinkable resin used in the production of the heat conductive sheet. Therefore, the proportion of the crosslinked resin in the resin contained in the heat conductive sheet usually coincides with the proportion of the crosslinkable resin in the resin (resin containing a crosslinkable resin and a resin other than the crosslinkable resin) used in the production of the heat conductive sheet.

[0037] <<Other resins>> The resin contained in the heat conductive sheet of the present invention may contain a resin other than the above-described crosslinked resin (hereinafter sometimes referred to as "other resin"). Here, the other resin is a non-crosslinked resin. In addition, as the other resin, a resin that does not undergo a crosslinking reaction with the above-described crosslinking agent (also referred to as a "non-crosslinkable resin") can be used. For example, as the other resin, a resin that does not undergo a peroxide crosslinking reaction with the crosslinking agent can be used. And as the other resin, it is preferable to use a resin that is liquid under normal temperature and pressure. By using a resin that is liquid under normal temperature and pressure in addition to the crosslinked resin that is usually solid under normal temperature and pressure, the flexibility of the heat conductive sheet can be increased.

[0038] 〔Resin that is liquid under normal temperature and pressure〕 The resin that is liquid under normal temperature and pressure is a component that can impart flexibility to the heat conductive sheet. As the resin that is liquid under normal temperature and pressure, for example, a thermoplastic resin that is liquid under normal temperature and pressure can be used.

[0039] - Thermoplastic fluororesin that is liquid under normal temperature and pressure - Since the heat-conducting sheet contains a thermoplastic resin that is liquid under normal temperature and pressure, the flexibility of the heat-conducting sheet can be improved. For example, the adhesiveness between the heat-conducting sheet and the adherend (heating element, heat-radiating body) to which the heat-conducting sheet is adhered can be enhanced, and high heat conductivity can be exhibited by the heat-conducting sheet.

[0040] Examples of the thermoplastic resin that is liquid under normal temperature and pressure include acrylic resin, epoxy resin, silicone resin, fluororesin, etc. These may be used alone or in combination of two or more in any ratio. Among these, in addition to improving the flame retardancy, heat resistance, oil resistance, and chemical resistance of the heat-conducting sheet, the thermoplastic fluororesin that is liquid under normal temperature and pressure is preferable in that it can enhance the interfacial adhesiveness and reduce the interfacial thermal resistance even under a relatively low pressure, thereby improving the heat conductivity (i.e., heat dissipation characteristics) of the heat-conducting sheet.

[0041] The thermoplastic fluororesin that is liquid under normal temperature and pressure is not particularly limited as long as it is a thermoplastic fluororesin that is liquid under normal temperature and pressure. Examples of the thermoplastic fluororesin that is liquid under normal temperature and pressure include vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropentene-tetrafluoroethylene terpolymer, perfluoropropene oxide polymer, tetrafluoroethylene-propylene-vinylidene fluoride copolymer, etc. These may be used alone or in combination of two or more in any ratio. In addition, examples of the commercially available thermoplastic fluororesin that is liquid under normal temperature and pressure include Viton (registered trademark) LM manufactured by DuPont Co., Ltd., Dai-el (registered trademark) G-101 manufactured by Daikin Industries, Ltd., Dynion FC2210 manufactured by 3M Co., Ltd., SIFEL series manufactured by Shin-Etsu Chemical Co., Ltd., etc.

[0042] The viscosity of the thermoplastic fluororesin that is liquid under normal temperature and pressure is not particularly limited. However, from the viewpoints of good kneadability, fluidity, crosslinking reactivity, and excellent moldability, the viscosity (viscosity coefficient) at 80°C is preferably 500 cP or more and 30,000 cP or less, and more preferably 550 cP or more and 25,000 cP or less.

[0043] 〔Content ratio of other resins〕 The ratio of other resins (non-crosslinked resins) in the resin contained in the heat-conductive sheet is preferably 70% by mass or less, more preferably 50% by mass or less, still more preferably 30% by mass or less, and particularly preferably 0% by mass. If the ratio of other resins in the resin is below the above-specified value, by increasing the content of the crosslinked resin in the heat-conductive sheet, the sheet strength can be improved and the difficulty of tearing during use can be further increased. Also, the ratio of other resins in the resin contained in the heat-conductive sheet can be 30% by mass or more, and can also be 40% by mass or more. Note that the ratio of other resins in the resin contained in the heat-conductive sheet generally coincides with the ratio of resins other than the crosslinkable resin (non-crosslinkable resin) in the resin used for manufacturing the heat-conductive sheet (resin containing a crosslinkable resin and a resin other than the crosslinkable resin).

[0044] <Particulate filler> The particulate filler is not particularly limited. For example, alumina particles, zinc oxide particles, boron nitride particles, aluminum nitride particles, silicon nitride particles, silicon carbide particles, magnesium oxide particles, and particulate carbon materials can be used. These particulate fillers may be used alone or in combination of two or more in any ratio.

[0045] From the viewpoint of enhancing the thermal conductivity of the manufactured heat-conductive sheet, it is preferable to use a particulate carbon material as the particulate filler.

[0046] <<Particulate Carbon Material>> The particulate carbon material is not particularly limited, and examples thereof include graphite such as artificial graphite, flaky graphite, exfoliated graphite, natural graphite, acid-treated graphite, negative electrode active material, expandable graphite, and expanded graphite; carbon black; and the like. These may be used alone or in combination of two or more.

[0047] Among those described above, as the particulate carbon material, it is preferable to use expanded graphite. By using expanded graphite, the thermal conductivity of the thermal conductive sheet can be further increased. Here, expanded graphite can be obtained, for example, by chemically treating graphite such as flaky graphite with sulfuric acid or the like to obtain expandable graphite, heat-treating it to expand, and then making it finer. And as expanded graphite, for example, EC1500, EC1000, EC500, EC300, EC100, EC50 (all are trade names) manufactured by Ito Graphite Industry Co., Ltd. and the like can be mentioned.

[0048] <<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, still more preferably 40 μm or more, preferably 180 μm or less, more preferably 160 μm or less, and still more preferably 140 μm or less. If the volume average particle diameter of the particulate filler is at least the above lower limit, it is presumed that the heat transfer path of the particulate filler can be favorably formed in the thermal conductive sheet, and thus the thermal conductivity of the thermal conductive sheet can be increased. On the other hand, if the volume average particle diameter of the particulate filler is at most the above upper limit, the thickness accuracy of the thermal conductive sheet can be ensured sufficiently high. Further, if the volume average particle diameter of the particulate filler is within the above predetermined range, the difficulty of tearing during use of the thermal conductive sheet can be further increased. In the present invention, the "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 smaller diameter side becomes 50% in the particle size distribution (volume basis) measured by the laser diffraction method.

[0049] In addition, the particulate filler preferably has an aspect ratio (major axis / minor axis) greater than 1 and 10 or less, more preferably greater than 1 and 5 or less. If the aspect ratio of the particulate filler is greater than 1 and 10 or less, it is presumed that the particulate filler is likely to be well oriented in the thickness direction in the heat conduction sheet, and the heat conductivity in the thickness direction of the heat conduction sheet can be increased. In the present invention, the "aspect ratio" can be obtained by observing the particulate filler with an SEM (scanning electron microscope), measuring the maximum diameter (major axis) and the particle diameter (minor axis) in the direction orthogonal to the maximum diameter for any 50 particulate fillers, and calculating the average value of the ratio of the major axis to the minor axis (major axis / minor axis). In the above, for example, when the particulate filler has a scale shape, the "major axis" refers to the length in the major axis direction of the main surface of the scale shape, and the "minor axis" refers to the length in the direction orthogonal to the major axis of the main surface.

[0050] <<Content of particulate filler>> And the content of the particulate filler in the heat conductive sheet is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, still more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, particularly preferably 55 parts by mass or more, preferably 200 parts by mass or less, more preferably 150 parts by mass or less, still more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less with respect to 100 parts by mass of the resin. When the content of the particulate filler in the heat conductive sheet is not less than the above lower limit, during the crosslinking reaction step in the method for manufacturing the heat conductive sheet described below, the generated gas is efficiently discharged through the surface or inside of the particulate filler, so that the number of micropores on the surface of the heat conductive sheet is reduced, and the difficulty of tearing during use of the heat conductive sheet can be further increased. Further, when the content of the particulate filler in the heat conductive sheet is not less than the above lower limit value, the thermal conductivity of the heat conductive sheet can be increased. On the other hand, when the content of the particulate filler in the heat conductive sheet is not more than the above upper limit, the flexibility of the heat conductive sheet can be sufficiently maintained, and as a result, the thermal resistance can be reduced. Further, when the content of the particulate filler in the heat conductive sheet is not more than the above upper limit, the proportion of the resin in the heat conductive sheet increases, and the particulate fillers are well bound by the resin, so that the difficulty of tearing during use of the heat conductive sheet can be further increased.

[0051] <<Volume ratio of particulate filler>> The proportion of the volume of the particulate filler in the total volume of the resin and the particulate filler in the heat conductive sheet is preferably 30% by volume or more, preferably 70% by volume or less, more preferably 60% by volume or less, still more preferably 50% by volume or less, and particularly preferably 40% by volume or less. If the proportion of the volume of the particulate filler in the total volume of the resin and the particulate filler in the heat conductive sheet is equal to or greater than the above lower limit, during the crosslinking reaction step in the method for producing the heat conductive sheet described below, the generated gas is efficiently discharged through the surface or inside of the particulate filler, so by reducing the number of micropores on the surface of the heat conductive sheet, the difficulty of tearing during use of the heat conductive sheet can be further increased. Also, if the proportion of the volume of the particulate filler in the total volume of the resin and the particulate filler in the heat conductive sheet is equal to or greater than the above lower limit, the thermal conductivity of the heat conductive sheet can be increased. On the other hand, if the proportion of the volume of the particulate filler in the total volume of the resin and the particulate filler in the heat conductive sheet is equal to or less than the above upper limit, the flexibility of the heat conductive sheet can be sufficiently maintained, and as a result, the thermal resistance can be reduced. Also, if the proportion of the volume of the particulate filler in the total volume of the resin and the particulate filler in the heat conductive sheet is equal to or less than the above upper limit, the proportion of the resin in the heat conductive sheet increases, and the particulate fillers are well bound by the resin, so the difficulty of tearing during use of the heat conductive sheet can be further increased. Also, the proportion of the volume of the particulate filler in the total volume of the resin and the particulate filler in the heat conductive sheet may be 35% by volume or more, or may be 40% by volume or more. Note that among the above "total volume of the resin and the particulate filler in the heat conductive sheet", the volume of the crosslinked resin contained in the resin usually coincides with the volume of the crosslinkable resin used in the production of the heat conductive sheet. Therefore, the above "total volume of the resin and the particulate filler in the heat conductive sheet" usually coincides with the total volume of the resin (including the crosslinkable resin and the resin other than the crosslinkable resin) used in the production of the heat conductive sheet and the particulate filler.

[0052] <Other components> The thermal conductive 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"). And as the other components, as long as they are components that can be used in the production of the thermal conductive sheet, there is no particular limitation. 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 absorbents such as calcium oxide and magnesium oxide; adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides; wetting improvers such as nonionic surfactants and fluorine-based surfactants; ion trap agents such as inorganic ion exchangers; and the like can be mentioned.

[0053] <<Dispersant>> Further, the thermal conductive sheet of the present invention may further contain a dispersant as other components. By using a dispersant, particulate fillers and the like can be well dispersed in the thermal conductive sheet. Also, by using a dispersant, the particulate fillers in the sheet can be uniformly dispersed to enhance the flexibility of the thermal conductive sheet. Therefore, the gas generated during the cross-linking reaction step of the manufacturing method of the thermal conductive sheet described later can be efficiently discharged to the outside, and the number of micropores formed in the thermal conductive sheet can be reduced. Note that the dispersant is a component different from the above-described resin.

[0054] Here, the dispersant is not particularly limited as long as the desired effects of the present invention can be obtained. However, from the viewpoint of further improving the dispersion of particulate fillers and the like in the thermal conductive sheet and further reducing the number of micropores formed in the thermal conductive sheet, it is preferable to use a polymer, and it is more preferable to use a polymer having an amine value (for example, a polymer containing a basic group, etc.).

[0055] And from the viewpoint of further improving the dispersion of particulate fillers and the like in the thermal conductive sheet and further reducing the number of micropores formed in the thermal conductive sheet, it is preferable for the dispersant to have an amine value. The amine value of the dispersant is preferably 5 mg KOH / g or more, more preferably 10 mg KOH / g or more, preferably 50 mg KOH / g or less, and more preferably 20 mg KOH / g or less. If the amine value of the dispersant is within the above-specified range, particulate fillers and the like can be more favorably dispersed in the heat-conductive sheet, and the number of micropores formed in the heat-conductive sheet can be further reduced. In the present invention, the amine value of the dispersant can be measured by titration with potassium hydroxide (KOH).

[0056] Further, from the viewpoint of more favorably dispersing particulate fillers and the like in the heat-conductive sheet and further reducing the number of micropores formed in the heat-conductive sheet, the dispersant preferably has an acid value. The acid value of the dispersant is preferably 3 mg KOH / g or more, more preferably 5 mg KOH / g or more, preferably 80 mg KOH / g or less, and more preferably 50 mg KOH / g or less. If the acid value of the dispersant is within the above-specified range, the difficulty of tearing during use of the produced heat-conductive sheet can be further enhanced. In the present invention, the acid value of the dispersant can be measured by titration with potassium hydroxide (KOH).

[0057] As the dispersant, commercially available products can also be used. For example, "Ajisper 821B" (manufactured by Ajinomoto Fine-Techno Co., Inc.), "BYK-2013" (manufactured by BYK-Chemie) and the like can be preferably used.

[0058] 〔Content of Dispersant〕 The content of the dispersant in the heat-conductive sheet can be, for example, 0 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin. The content of the dispersant in the heat-conductive sheet can be, for example, 0 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the particulate filler.

[0059] 〔Mass Ratio of Dispersant to Particulate Filler〕 In addition, the mass ratio (dispersant / particulate filler) of the dispersant to the particulate filler in the heat conductive sheet can be, for example, 0 / 100 or more, 1 / 100 or more, and 1 / 5 or less.

[0060] <Structure of the heat conductive sheet> The heat conductive sheet of the present invention preferably has a structure in which the above-described particulate filler is oriented in the thickness direction of the heat conductive sheet. In the heat conductive sheet, if the particulate filler is oriented in the thickness direction of the heat conductive sheet, the thermal conductivity in the thickness direction of the heat conductive sheet can be increased. Here, "oriented in the thickness direction of the heat conductive sheet" means a state in which, when an arbitrary cross section of the heat conductive sheet is observed by SEM (scanning electron microscope), in more than half of the particulate fillers in the heat conductive sheet, the major axis is oriented at 0 to 40 degrees with respect to the thickness direction of the sheet (parallel to the thickness direction is defined as 0 degrees).

[0061] <Thermal conductivity> The thermal conductivity in the thickness direction of the heat conductive sheet needs to be 12 W / m·K or more, preferably 13 W / m·K or more, and more preferably 15 W / m·K or more. When the thermal conductivity in the thickness direction of the heat conductive sheet is less than 12 W / m·K, the heat conductive sheet cannot exhibit sufficient thermal conductivity in the thickness direction. On the other hand, when the thermal conductivity in the thickness direction of the heat conductive sheet is 12 W / m·K or more, the heat conductive sheet can exhibit sufficient thermal conductivity in the thickness direction. In addition, the upper limit of the value of the thermal conductivity in the thickness direction of the heat conductive sheet is not particularly limited, but is, for example, 45 W / m·K or less. Note that the thermal conductivity in the thickness direction of the heat conductive sheet can be adjusted by the types and ratios of the materials and components (resin, particulate filler, dispersant, etc.) contained in the heat conductive sheet, as well as the manufacturing method and manufacturing conditions of the heat conductive sheet.

[0062] <Sheet strength> In the measurement of the sheet strength of the main surface of the heat conduction sheet, the sheet strength in the in-plane direction Y perpendicular to the in-plane direction X where the sheet strength is the highest is 1.0 N / mm 2 or more, preferably 1.3 N / mm 2 or more, more preferably 1.5 N / mm 2 or more, still more preferably 1.8 N / mm 2 or more, even more preferably 3.0 N / mm 2 or less, preferably 2.5 N / mm 2 or less is more preferable. When the sheet strength in the in-plane direction Y of the heat conduction sheet is less than 1.0 N / mm 2 , the heat conduction sheet has insufficient strength and is likely to be torn during use. On the other hand, when the sheet strength in the in-plane direction Y of the heat conduction sheet is 1.0 N / mm 2 or more, the heat conduction sheet has sufficient strength and is less likely to be torn during use. Also, if the sheet strength in the in-plane direction Y of the heat conduction sheet is below the above upper limit, the heat conduction sheet will be appropriately crushed when sandwiched between the heating element and the heat sink and pressed, so that the thermal conductivity of the heat conduction sheet can be improved.

[0063] <Asker C hardness> The Asker C hardness of the heat conduction sheet is preferably 50 or more, more preferably 55 or more, still more preferably 60 or more, preferably 100 or less, more preferably 90 or less, and still more preferably 80 or less at 70°C. If the Asker C hardness of the heat conduction sheet is above the above lower limit, the sheet strength of the heat conduction sheet will increase, so that the difficulty of tearing during use of the heat conduction sheet can be further increased. On the other hand, if the Asker C hardness of the heat conduction sheet is below the above upper limit, the heat conduction sheet will be appropriately crushed when sandwiched between the heating element and the heat sink and pressed, so that the thermal conductivity of the heat conduction sheet can be improved. In the present invention, the Asker C hardness of the heat conduction sheet can be measured by the method described in the examples of this specification.

[0064] <Micro holes> The surface of the heat conduction sheet of the present invention has few micropores (also referred to as "pinholes"). The micropores on the surface of the heat conduction sheet are formed, for example, by gas generated during the cross-linking reaction of the resin performed during the production of the heat conduction sheet. And the micropores formed on the surface of the heat conduction sheet can cause tearing during the use of the heat conduction sheet. In contrast, the heat conduction sheet of the present invention is less likely to tear during use because the number of micropores formed on the surface is small.

[0065] Specifically, the number of micropores with a pore diameter of 48 μm or more and 500 μm or less that penetrate the heat conduction sheet in the thickness direction is required to be 200 or less per 1 cm 2 in the plan view area of the heat conduction sheet, preferably 150 or less, more preferably 120 or less, still more preferably 100 or less, and even more preferably 80 or less. When the number of the above micropores in the heat conduction sheet exceeds 200, the heat conduction sheet is likely to tear during use. On the other hand, if the number of the above micropores in the heat conduction sheet is 200 or less, the heat conduction sheet can be made sufficiently difficult to tear during use. Also, the number of the above micropores is not particularly limited, but is usually 10 or more. Note that the number of the above micropores in the heat conduction sheet can be adjusted, for example, by the ratio of the cross-linkable resin in the resin used in the production method of the heat conduction sheet, the ratio of the volume of the particulate filler in the total volume of the resin and the particulate filler, and the conditions (heating temperature, heating time, etc.) of the cross-linking reaction step.

[0066] <Surface roughness Sa> Also, the surface roughness Sa of the heat conduction sheet is preferably 2.4 μm or less, more preferably 2.2 μm or less, and still more preferably 2.0 μm or less. If the surface roughness Sa of the heat conduction sheet is below the above predetermined value, since the number of micropores on the surface of the heat conduction sheet is small, the heat conduction sheet can be made even more difficult to tear during use. Also, the surface roughness Sa of the heat conduction sheet is not particularly limited, but is preferably 1.5 μm or more. Here, it is preferable that the surface roughness Sa of at least one surface in the thickness direction of the heat conduction sheet is within the above-mentioned predetermined range, and it is more preferable that the surface roughness Sa of both surfaces in the thickness direction is within the above-mentioned predetermined range.

[0067] <Thickness of the heat conduction sheet> The thickness of the heat conduction sheet of the present invention is not particularly limited, but is preferably 200 μm or less, more preferably 150 μm or less, still more preferably 100 μm or less, preferably 50 μm or more, more preferably 60 μm or more, and still more preferably 70 μm or more. If the thickness of the heat conduction sheet is below the above upper limit, the thermal conductivity in the thickness direction of the heat conduction sheet can be enhanced. On the other hand, if the thickness of the heat conduction sheet is above the above lower limit, the heat conduction sheet will not be excessively thinned, so that the difficulty of tearing, flame retardancy, strength, and handleability during the use of the heat conduction sheet can be ensured to be sufficiently high.

[0068] (Manufacturing method of the heat conduction sheet) The manufacturing method of the heat conduction sheet of the present invention includes: (A) a pre-heat conduction sheet forming step of pressing a composition containing a resin containing a crosslinkable resin, a particulate filler, and a crosslinking agent into a sheet shape to obtain a pre-heat conduction sheet; (B) a laminate forming step of laminating a plurality of pre-heat conduction sheets in the thickness direction, or folding or winding the pre-heat conduction sheet to obtain a laminate; (C) a crosslinking reaction step of heating the laminate while applying pressure in the lamination direction to perform a crosslinking reaction; and (D) a slicing step of slicing the laminate at an angle of 45° or less with respect to the lamination direction to obtain a heat conduction sheet. Note that the heat conduction sheet of the present invention may optionally further include steps other than the above (A) to (D).

[0069] And the manufacturing method of the heat conduction sheet of the present invention needs to satisfy at least any one of the following (1) to (3). (1) The content ratio of the crosslinkable resin in the resin is 70% by mass or less. (2) The volume ratio of the particulate filler in the total volume of the resin and the particulate filler is 30% by volume or more. (3) The heating temperature in the crosslinking reaction step is 150°C or lower.

[0070] Here, in the method for manufacturing a heat conductive sheet of the present invention, when the content ratio of the crosslinkable resin in the resin is 70% by mass or less, the amount of gas generated in the crosslinking reaction step is reduced, so that the number of micropores (pinholes) formed in the manufactured heat conductive sheet can be reduced, and thus the heat conductive sheet is less likely to tear during use.

[0071] Further, in the method for manufacturing a heat conductive sheet of the present invention, when the volume ratio of the particulate filler in the total volume of the resin and the particulate filler is 30% by volume or more, the gas generated in the crosslinking reaction step is efficiently discharged through the surface or inside of the particulate filler, so that the number of micropores (pinholes) formed in the manufactured heat conductive sheet can be reduced, and thus the heat conductive sheet is less likely to tear during use.

[0072] Furthermore, in the method for manufacturing a heat conductive sheet of the present invention, when the heating temperature in the crosslinking reaction step is 150°C or lower, the amount of gas generated in the crosslinking reaction step is reduced, so that the number of micropores (pinholes) formed in the manufactured heat conductive sheet can be reduced, and thus the heat conductive sheet is less likely to tear during use.

[0073] Therefore, the method for manufacturing a heat conductive sheet of the present invention can manufacture a heat conductive sheet that is less likely to tear during use by satisfying at least one of the above (1) to (3).

[0074] Note that the method for manufacturing a heat conductive sheet of the present invention may satisfy only one of the above (1) to (3), may satisfy only two of the above (1) to (3), or may satisfy all of the above (1) to (3). From the viewpoint of further enhancing the difficulty of tearing of the manufactured heat conductive sheet during use, it is preferable to satisfy at least (3), and it is particularly preferable not to satisfy (1) and to satisfy only (2) and (3).

[0075] Here, from the viewpoint of enhancing the tear resistance during the use of the produced heat-conducting sheet, it is particularly preferable that (1) is not satisfied and only (2) and (3) are satisfied, for the following reasons. First, when (1) is not satisfied, although the number of micropores generated slightly increases compared to the case where (1) is satisfied, since (2) and (3) are satisfied, the number of micropores formed in the produced heat-conducting sheet can be sufficiently reduced. Furthermore, since (1) is not satisfied (that is, the content ratio of the crosslinkable resin in the resin exceeds 70% by mass), the content ratio of the crosslinked resin in the resin contained in the produced heat-conducting sheet becomes high, so the sheet strength of the heat-conducting sheet is improved. Thus, since the number of micropores in the produced heat-conducting sheet can be reduced and the sheet strength of the heat-conducting sheet can be improved, the tear resistance during the use of the heat-conducting sheet can be particularly enhanced.

[0076] Note that according to the method for manufacturing the heat-conducting sheet of the present invention, the above-described heat-conducting sheet of the present invention can be efficiently manufactured.

[0077] <(A) Pre-formed heat-conducting sheet forming step> In the pre-formed heat-conducting sheet forming step, a composition containing a resin containing a crosslinkable resin, a particulate filler, and a crosslinking agent is pressed and formed into a sheet shape to obtain a pre-formed heat-conducting sheet.

[0078] <<Composition>> The above composition contains a resin containing a crosslinkable resin, a particulate filler, and a crosslinking agent. Note that the above composition may further contain a reaction initiator. Furthermore, the above composition may further contain components other than the above-described resin, particulate filler, crosslinking agent, and reaction initiator (other components).

[0079] 〔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 for forming the crosslinked resin described above in the section of "Thermal Conductive Sheet" can be used. Further, as the resin other than the crosslinkable resin (non-crosslinkable resin), for example, a resin other than the crosslinked resin (other resin) that can be contained in the resin described above in the section of "Thermal Conductive Sheet" can be used.

[0080] And when the method for manufacturing the thermal conductive sheet of the present invention satisfies the above (1), the content ratio of the crosslinkable resin in the resin contained in the composition needs to be 70% by mass or less, preferably 60% by mass or less, preferably 30% by mass or more, more preferably 40% by mass or more, and still more preferably 50% by mass or more. When the content ratio of the crosslinkable resin in the resin is 70% by mass or less, by reducing the amount of gas generated in the crosslinking reaction step, the number of micropores (pinholes) formed in the manufactured thermal conductive sheet can be reduced, so that the thermal conductive sheet is less likely to tear during use. On the other hand, if the content ratio of the crosslinkable resin in the resin is 30% by mass or more, the sheet strength of the manufactured thermal conductive sheet can be improved, and the difficulty of tearing during use can be further increased.

[0081] However, when the method for manufacturing the thermal conductive sheet of the present invention does not satisfy (1) and satisfies (2) and (3), the content ratio of the crosslinkable resin in the resin contained in the composition is more than 70% by mass, preferably 85% by mass or more, and particularly preferably 100% by mass. If the content ratio of the crosslinkable resin in the resin is more than 70% by mass, the sheet strength of the manufactured thermal conductive sheet can be improved, and the difficulty of tearing during use can be further increased.

[0082] 〔Particulate Filler〕 Further, as the particulate filler, for example, the particulate filler described above in the section of "Thermal Conductive Sheet" can be used.

[0083] Here, the volume ratio of the particulate filler in the total volume of the resin and the particulate filler in the composition is required or preferably 30% by volume or more, preferably 70% by volume or less, more preferably 60% by volume or less, still more preferably 50% by volume or less, and particularly preferably 40% by volume or less. When the volume ratio of the particulate filler in the total volume of the resin and the particulate filler in the composition is 30% by volume or more, during the cross-linking reaction step described later, the generated gas is efficiently discharged through the surface or inside of the particulate filler, so by reducing the number of micropores on the surface of the produced heat-conducting sheet, the heat-conducting sheet can be made less likely to tear during use. Also, when the volume ratio of the particulate filler in the total volume of the resin and the particulate filler in the composition is 30% by volume or more, the thermal conductivity of the produced heat-conducting sheet can be increased. On the other hand, if the volume ratio of the particulate filler in the total volume of the resin and the particulate filler in the composition is below the above upper limit, the flexibility of the produced heat-conducting sheet can be sufficiently maintained, and as a result, the thermal resistance can be reduced. Also, if the volume ratio of the particulate filler in the total volume of the resin and the particulate filler in the composition is below the above upper limit, the proportion of the resin in the produced heat-conducting sheet increases, and the particulate fillers are well bound by the resin, so the difficulty of tearing during use of the heat-conducting sheet can be further increased. Also, the volume ratio of the particulate filler in the total volume of the resin and the particulate filler in the composition may be 35% by volume or more, or may be 40% by volume or more.

[0084] Note that the content of the particulate filler with respect to 100 parts by mass of the resin in the composition can be set within the same range as the preferred range of the content of the particulate filler with respect to 100 parts by mass of the resin in the heat-conducting sheet described above in the section on "Heat-conducting Sheet".

[0085] 〔Cross-linking agent〕 As the cross-linking agent, a cross-linking agent that can be used for forming the cross-linked resin described above in the section on "Heat-conducting Sheet" can be used.

[0086] In addition, the content of the crosslinking agent with respect to 100 parts by mass of the crosslinkable resin in the composition can be set within the same range as the preferable range of the amount of the crosslinking agent used with respect to 100 parts by mass of the crosslinkable resin described above in the section of "Thermal Conductive Sheet".

[0087] 〔Reaction Initiator〕 As the reaction initiator, a reaction initiator that can be used for the crosslinking reaction for forming the crosslinked resin described above in the section of "Thermal Conductive Sheet" can be used.

[0088] In addition, the content of the reaction initiator with respect to 100 parts by mass of the crosslinkable resin in the composition can be set within the same range as the preferable range of the amount of the reaction initiator used with respect to 100 parts by mass of the crosslinkable resin in the crosslinking reaction described above in the section of "Thermal Conductive Sheet". Moreover, 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 range of the mass ratio of the amount of the crosslinking agent used to the amount of the reaction initiator used (crosslinking agent / reaction initiator) in the crosslinking reaction described above in the section of "Thermal Conductive Sheet", for example.

[0089] 〔Other Components〕 As other components that can be contained in the composition, other components such as a dispersant that can be contained in the thermal conductive sheet described above in the section of "Thermal Conductive Sheet" can be used. Here, the range of the content of the dispersant with respect to 100 parts by mass of the resin in the composition can be set within the same range as the range of the content of the dispersant with respect to 100 parts by mass of the resin in the thermal conductive sheet described above in the section of "Thermal Conductive Sheet", for example. Also, the mass ratio of the dispersant to the particulate filler in the composition (dispersant / particulate filler) can be set within the same range as the preferable range of the mass ratio of the dispersant to the particulate filler (dispersant / particulate filler) in the thermal conductive sheet described above in the section of "Thermal Conductive Sheet", for example.

[0090] 〔Preparation of Composition〕 The composition is not particularly limited and can be prepared by mixing the above-described components. In addition, the mixing of the above-described components can be carried out without particular limitation using known mixing devices such as kneaders; mixers such as Henschel mixers, Hobart mixers, and high-speed mixers; twin-screw kneaders; rolls; etc. Further, the mixing may be carried out in the presence of a solvent such as ethyl acetate. The resin may be previously dissolved or dispersed in the solvent to form a resin solution, which may then be mixed with the particulate filler and the crosslinking agent, as well as the reaction initiator and other components optionally added. And the mixing time can be, for example, 5 minutes or more and 60 minutes or less. Also, the mixing temperature can be, for example, 5°C or more and 150°C or less.

[0091] [[Composition Molding]] Then, the composition prepared as described above can be optionally defoamed and crushed, and then pressed into a sheet form. The sheet-like product obtained by pressure-molding the composition in this way can be used as a pre-thermal conduction sheet. When a solvent is used during mixing, it is preferable to remove the solvent before forming into a sheet. For example, if defoaming is carried out using vacuum defoaming, the removal of the solvent can be carried out simultaneously during defoaming.

[0092] Here, the composition can be formed into a sheet shape using known molding methods such as press molding, rolling molding, or extrusion molding without particular limitation as long as it is a molding method in which pressure is applied. Among them, it is preferable to form the composition into a sheet shape by rolling molding (primary processing), and it is more preferable to pass it between rolls in a state sandwiched between protective films to form a sheet shape. As the protective film, a polyethylene terephthalate (PET) film subjected to sandblasting treatment or the like can be used without particular limitation. Also, the roll temperature can be 5°C or more and 150°C or less, the roll gap can be 50 μm or more and 2500 μm or less, the roll linear pressure can be 1 kg / cm or more and 3000 kg / cm or less, and the roll speed can be 0.1 m / min or more and 20 m / min or less.

[0093] [[Pre-Thermal Conduction Sheet]] In the pre-formed heat conduction sheet formed by pressing the composition into a sheet shape, it is presumed that the particulate filler is mainly oriented in the in-plane direction, and in particular, the in-plane thermal conductivity of the pre-formed heat conduction sheet is improved.

[0094] <(B) Laminated body forming step> In the laminated body forming step, a plurality of pre-formed heat conduction sheets obtained in the pre-formed heat conduction sheet forming step are laminated in the thickness direction, or the pre-formed heat conduction sheet is folded or wound to obtain a laminated body in which a plurality of heat conduction sheets containing a resin and a particulate filler are formed in the thickness direction. Here, the formation of the laminated body by folding the pre-formed heat conduction sheet is not particularly limited and can be performed by folding the pre-formed heat conduction sheet with a folding machine at a constant width. Further, the formation of the laminated body by winding the pre-formed heat conduction sheet is not particularly limited and can be performed by winding the pre-formed heat conduction sheet around an axis parallel to the short side direction or the long side direction of the pre-formed heat conduction sheet. Further, the formation of the laminated body by laminating the pre-formed heat conduction sheets is not particularly limited and can be performed using a laminating device. For example, by using a sheet laminating device (manufactured by Nikkiso Co., Ltd., product name "Hi-Stacker"), it is possible to suppress the entry of air between the layers, so that a good laminated body can be efficiently obtained.

[0095] In the lamination step, it is preferable to apply pressure (secondary pressure) in the lamination direction while heating the obtained laminated body at a temperature lower than the heating temperature in the crosslinking reaction step described later. By performing secondary pressure to apply pressure to the laminated body in the lamination direction while heating at a temperature lower than the heating temperature in the crosslinking reaction step described later, and then performing the crosslinking reaction step described later, the crosslinking reaction can be performed in a state where the fusion between the laminated pre-formed heat conduction sheets is promoted, so that the crosslinking strength between the interfaces of the respective layers in the laminated body can be improved.

[0096] Here, the pressure when applying pressure to the laminated body in the lamination direction can be 0.01 MPa or more, preferably 0.03 MPa or more, more preferably 0.05 MPa or more, can be 0.50 MPa or less, preferably 0.30 MPa or less, and more preferably 0.10 MPa or less.

[0097] Also, the heating temperature of the laminate is not particularly limited as long as it is lower than the heating temperature in 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, and can be 30°C or higher, preferably 40°C or higher, more preferably 50°C or higher. Furthermore, the heating time of the laminate can be, for example, 30 seconds or more and 5 minutes or less.

[0098] In addition, in the laminate obtained by laminating, folding, or winding the pre-heat conductive sheet, it is presumed that the particulate filler is oriented in a direction substantially orthogonal to the lamination direction.

[0099] <(C) Crosslinking reaction step> In the crosslinking reaction step, the laminate is heated while being pressed in the lamination direction to perform a crosslinking reaction. As a result, the crosslinkable resin and the crosslinked body undergo a crosslinking reaction to form a crosslinked resin, so that the sheet strength of the manufactured heat conductive sheet is improved, and it is possible to make it difficult to tear the heat conductive sheet during use.

[0100] Here, the pressure when pressing the laminate in the lamination direction in the crosslinking reaction is preferably 0.01 MPa or more, more preferably 0.02 MPa or more, still more preferably 0.03 MPa or more, preferably 0.5 MPa or less, more preferably 0.1 MPa or less, still more preferably 0.05 MPa or less. If the pressure when pressing the laminate in the lamination direction is at least the above lower limit, the sheet strength in the in-plane direction Y of the manufactured heat conductive sheet can be improved, and the difficulty of tearing during use of the heat conductive sheet can be further enhanced. On the other hand, if the pressure when pressing the laminate in the lamination direction is at most the above upper limit, it is possible to suppress excessive crushing of the laminate.

[0101] In addition, examples of the pressing method include pressing only the upper and lower two surfaces in the lamination direction of the laminate, or pressing four surfaces of the laminate including at least the upper and lower two surfaces in the lamination direction of the laminate. However, from the viewpoint of discharging the gas generated during the crosslinking reaction, it is preferable to press only the upper and lower two surfaces in the lamination direction of the laminate.

[0102] And the heating temperature in the crosslinking reaction step needs to be 150°C or lower, preferably 140°C or lower, more preferably 120°C or lower, still more preferably 110°C or lower, and preferably 90°C or higher, more preferably 92°C or higher, still more preferably 95°C or higher. When the heating temperature in the crosslinking reaction step is 150°C or lower, by reducing the amount of gas generated in the crosslinking reaction step, the number of micropores (pinholes) formed in the manufactured heat conduction sheet can be reduced, so that the heat conduction sheet is less likely to be torn during use. On the other hand, if the heating temperature in the crosslinking reaction step is 90°C or higher, by performing the crosslinking reaction well, the sheet strength of the manufactured heat conduction sheet can be improved, and the difficulty of tearing during use can be further increased.

[0103] In addition, the heating time in the crosslinking reaction step is preferably 1 hour or longer, more preferably 3 hours or longer, still more preferably 5 hours or longer, preferably 24 hours or shorter, more preferably 12 hours or shorter, and still more preferably 8 hours or shorter. If the heating time in the crosslinking reaction step is equal to or longer than the above lower limit, by performing the crosslinking reaction well, the sheet strength of the manufactured heat conduction sheet can be improved, and the difficulty of tearing during use can be further increased. On the other hand, if the heating time in the crosslinking reaction step is equal to or shorter than the above upper limit, excessive progress of the crosslinking reaction can be suppressed, and the flexibility of the heat conduction sheet can be maintained well.

[0104] <(D) Slicing Step> In the slicing step, the laminate that has undergone a crosslinking reaction in the crosslinking reaction step is sliced at an angle of 45° or less with respect to the lamination direction to obtain a heat conduction sheet composed of slices of the laminate. Here, the method of slicing the laminate is not particularly limited, and examples include the multi-blade method, the laser processing method, the water jet method, the knife processing method, and the like. Among these, the knife processing method is preferable in terms of easily making the thickness of the heat conduction sheet uniform. Further, as the cutting tool for slicing the laminate, without being particularly limited, a slicing member having a smooth disk surface with a slit and a blade portion protruding from this slit portion (for example, a cutter or a slicer equipped with a sharp blade) can be used.

[0105] From the viewpoint of enhancing the thermal conductivity of the heat conduction sheet, the angle at which the laminate is sliced is preferably 30° or less with respect to the lamination direction, more preferably 15° or less with respect to the lamination direction, and preferably substantially 0° with respect to the lamination direction (that is, the direction along the lamination direction).

[0106] And in the heat conduction sheet thus obtained, the particulate filler is favorably oriented in the thickness direction, and it is excellent in the thermal conductivity in the thickness direction.

[0107] Further, since the heat conduction sheet manufactured by the manufacturing method of the heat conduction sheet of the present invention is a sheet composed of slices of the laminate, when measuring the sheet strength of the main surface of the heat conduction sheet, the in-plane direction X in which the sheet strength becomes the highest usually coincides with the direction perpendicular to the lamination direction of the laminate. Therefore, the in-plane direction Y perpendicular to the in-plane direction X usually coincides with the lamination direction of the laminate. Furthermore, since the heat conduction sheet manufactured by the manufacturing method of the heat conduction sheet of the present invention is a sheet composed of slices of the laminate, when measuring the thermal conductivity of the main surface of the heat conduction sheet, the in-plane direction X' in which the thermal conductivity becomes the highest usually coincides with the direction perpendicular to the lamination direction of the laminate. Therefore, the in-plane direction Y' perpendicular to the in-plane direction X' usually coincides with the lamination direction of the laminate. Therefore, when measuring the sheet strength of the main surface of the heat conduction sheet, the in-plane direction X in which the sheet strength is the highest usually coincides with the in-plane direction X' in which the thermal conductivity is the highest when measuring the thermal conductivity of the main surface of the heat conduction sheet. And the in-plane direction Y perpendicular to the in-plane direction X in which the sheet strength is the highest usually coincides with the in-plane direction Y' perpendicular to the in-plane direction X' in which the thermal conductivity is the highest.

Example

[0108] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” representing amounts are based on mass unless otherwise specified.

[0109] In each example and each comparative example, the measurement or evaluation of (i) the Asker C hardness of the heat conduction sheet, (ii) the sheet strength of the heat conduction sheet, (iii) the thermal conductivity in the thickness direction of the heat conduction sheet, (iv) the surface roughness Sa of the heat conduction sheet, (v) the number of micropores in the heat conduction sheet, and (vi) the difficulty of tearing during use of the heat conduction sheet was performed by the following methods, respectively.

[0110] <(i) Asker C hardness of the heat conduction sheet> The heat conduction sheets produced in each example and comparative example were used as test specimens after being left at room temperature (25 ° C) for 10 days after the slicing process. This heat conduction sheet was cut into a size of 25 mm in length × 50 mm in width, and a block laminated to a height of 9 mm was used as the test specimen. Specifically, in accordance with the Asker C method of the Japan Rubber Association Standard (SRIS), using a hardness tester (manufactured by Kobunshi Keiki Co., Ltd., trade name “ASKER CL-150LJ”), the measurement was performed while heating the test specimen to 70 ° C on a hot plate. Then, the height of the damper was adjusted so that the pointer was 95 to 98, and the hardness 20 seconds after the collision between the test specimen and the damper was measured 5 times, and the average value was taken as the Asker C hardness of the test specimen.

[0111] <(ii) Sheet strength of the heat conduction 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 bench-top 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 ) to calculate the sheet strength (N / mm 2 ) in the Y direction of the heat conduction sheet. 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". 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)".

[0112] <(iii) Thermal conductivity in the thickness direction of the heat conduction sheet> For the heat conduction sheets produced in each of the examples and comparative examples, the thermal diffusivity α (m 2 / s), specific heat at constant pressure Cp (J / g·K), and specific gravity ρ (g / m 3 ) in the thickness direction were measured by the following method. [Thermal diffusivity α (m 2 / s)] Using a thermal property measuring device (manufactured by BETTER Co., Ltd., product name "Thermo Wave Analyzer TA35"), the thermal diffusivity in the thickness direction was measured. [Specific heat at constant pressure Cp (J / g·K)] Using a differential scanning calorimeter (manufactured by Rigaku, product name "DSC8230"), the specific heat under the temperature rising condition of 10°C / min was measured. [Specific gravity ρ (g / m 3 )] The specific gravity (density) (g / m 3 ) was measured using an automatic specific gravity meter (manufactured by Toyo Seiki Co., Ltd., product name "DENSIMETER-H"). Then, using the obtained measurement values, the following formula (I): λ = α × Cp × ρ ··· (I) was substituted to obtain the thermal conductivity λ (W / m·K) in the thickness direction of the thermal conductive sheet.

[0113] <(iv) Surface roughness Sa of the 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 ranges (1 cm × 1 cm) extracted from the surface of the thermal conductive sheet to be evaluated. When extracting the five points, it is desirable that each analysis range is separated by 1 cm or more, but if the size of the thermal conductive sheet is small, a part of the analysis ranges may overlap. Also, when the size of the thermal conductive sheet is small and an analysis range of 1 cm × 1 cm cannot be secured, the analysis range may be reduced to 0.3 cm × 0.3 cm. Furthermore, a filter process (2.5 mm) was performed on the measurement results of the three-dimensional shape using software to remove the waviness component, and the surface roughness Sa (μm) was automatically calculated. The average value of the five analysis ranges was taken as the surface roughness Sa of the thermal conductive sheet.

[0114] <(v) Number of micropores in the thermal conductive sheet> The number of micropores in the thermal conductive sheets manufactured in each example and comparative example was measured using an appearance inspection device (manufactured by Nagano Automation Co., Ltd., product name "00-6724 Appearance Inspection Device"). Specifically, the back surface of the thermal conductive 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 thermal conductive sheet and the planar view area of the thermal conductive sheet, per 1 cm of the planar view area of the thermal conductive sheet2 The number of micropores per hit was calculated.

[0115] <(vi) Difficulty of tearing during use of the heat conduction sheet> The heat conduction sheets produced in each example and comparative example were sized to 10 mm × 10 mm and placed on a first metal plate (heating element) heated to 120°C. A smooth second metal plate (heat sink) sized to 12 mm × 12 mm was placed on the heat conduction sheet so that the centers overlapped. A cycle test was performed in which a pressure of 250 N was applied from above for 10 seconds and then released for 10 seconds, and this was repeated 50 times as one cycle. The difficulty of tearing during use of the heat conduction sheet was evaluated according to the following criteria based on the degree of protrusion of the heat conduction sheet from the second metal plate when observing the heat conduction sheet from directly above after the above cycle test. When the cycle of pressurization and depressurization is repeated with the heat conduction sheet sandwiched between the heating element and the heat sink and heated, in a heat conduction sheet that is easily torn, tearing occurs particularly from the portion where a strong pressure is applied, and a phenomenon of protruding from between the heating element and the heat sink occurs. Therefore, the smaller the protruding portion of the heat conduction sheet, the more difficult it is for the heat conduction sheet to tear during use. If there is no protrusion of the heat conduction sheet at all, it indicates that the heat conduction sheet is particularly difficult to tear during use. A: There is no protrusion of the heat conduction sheet at all. B: A heat conduction sheet having a side with at least one side exceeding 0 mm and less than 2 mm protrudes. C: A heat conduction sheet having a side with at least one side of 2 mm or more and less than 6 mm protrudes.

[0116] (Example 1) <Preparation of the composition> At normal temperature and pressure, 100 parts (56 volume parts) of a solid fluoroelastomer (fluororubber) (manufactured by 3M Japan, trade name "Dyneon® FPO3600ULV", Mooney viscosity: 3.5 ML1+4, 100 °C) and 60 parts (27 volume parts) of expanded graphite as a particulate filler (manufactured by Ito Graphite Industry Co., Ltd., trade name "EC300", volume average particle diameter: 50 μm) were stirred and mixed at a temperature of 150 °C for 20 minutes using a pressure kneader (manufactured by Nippon Spindle). Next, after lowering the apparatus temperature to 60 °C, 0.5 part of dibenzoyl peroxide (manufactured by NOF Corporation, trade name "Niper E") as a reaction initiator and 0.5 part of triallyl isocyanurate (manufactured by Nippon Kasei Co., Ltd., trade name "TAIC M60") as a crosslinking agent were mixed, and kneaded for 10 minutes while maintaining the material temperature at 60 °C. Next, the mixture obtained above was put into a crusher (manufactured by Sanjo Industry Co., Ltd., product name "Hammer Crusher HN34S") and crushed for 60 seconds to obtain a composition containing a resin, a particulate filler, a crosslinking agent, and a reaction initiator.

[0117] <Preheat conduction sheet forming process> Next, 50 g of the obtained composition was sandwiched between sandblasted PET films (protective films) with a thickness of 50 μm, and roll-formed (primary pressing) 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 preheat conduction sheet with a thickness of 0.5 mm.

[0118] <Laminate formation process> Subsequently, the obtained preheat conduction sheet was cut into a size of 50 mm in length × 50 mm in width × 1.0 mm in thickness, 55 sheets were laminated in the thickness direction of the preheat conduction sheet, and further pressed (secondary pressing) in the lamination direction at a temperature of 80 °C and a pressure of 0.1 MPa for 1 minute to obtain a laminate with a height of 49 mm. By this secondary pressing, the layers of the laminate were made to adhere more closely.

[0119] <Crosslinking reaction process> Subsequently, the obtained laminate was heated in a 100 °C atmosphere for 6 hours under a pressure of 0.03 MPa applied from above and below with a vise to carry out a crosslinking reaction (vulcanization). Note that no particular force was applied to the side surfaces of the laminate so that the generated gas or the like could easily escape.

[0120] <Slicing process> Thereafter, leaving the length necessary for slicing, the entire upper surface of the obtained laminate was pressed 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. Note that the side and back surfaces 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 thickness of the blade part: 3.5 mm, material: super steel, Rockwell hardness: 91.5, no silicon processing on the blade surface, total length: 200 mm) was attached to the press part of a servo press machine (manufactured by Discharge Precision Machining Laboratory), and the laminate was sliced in the lamination direction (in other words, in the direction coinciding with the normal of the main surface of the laminated pre-thermal conductive sheet) under the conditions of a slicing speed of 200 mm / second and a slicing width of 100 μm to obtain a thermal conductive sheet having a length of 150 mm, a width of 60 mm, and a thickness of 0.10 mm. Then, various measurements and evaluations were performed on the obtained thermal conductive sheet according to the above-described method. The results are shown in Table 1.

[0121] (Example 2) In the preparation of the composition of Example 1, when mixing the resin and the particulate filler, 6 parts of a basic group-containing polymer (product name "ADISPER PB821", manufactured by Ajinomoto Fine-Techno Co., Ltd., amine value: 10 mgKOH / g, acid value: 17 mgKOH / g) was further added. Otherwise, in the same manner as in Example 1, "preparation of the composition", "pre-thermal conductive sheet forming process", "laminate forming process", "crosslinking reaction process", and "slicing process" were carried out. Then, the same measurements and evaluations as in Example 1 were performed on the obtained thermal conductive sheet. The results are shown in Table 1.

[0122] (Example 3) In the preparation of the composition of Example 2, when mixing the resin and the particulate filler, the addition amount of the solid fluoroelastomer (manufactured by 3M Japan Ltd., trade name "Dyneon® FPO3600ULV") at normal temperature and pressure was reduced from 100 parts (56 volume parts) to 50 parts (28 volume parts), and 50 parts (28 volume parts) of a liquid thermoplastic fluororesin (manufactured by Daikin Industries, Ltd., trade name "Daiel G-101") was further added at normal temperature and pressure. Otherwise, in the same manner as in Example 2, the "preparation of the composition", "pre-thermal conductive sheet forming step", "laminate forming step", "crosslinking reaction step" and "slicing step" were carried out. Then, the same measurements and evaluations as in Example 2 were performed on the obtained thermal conductive sheet. The results are shown in Table 1.

[0123] (Example 4) The "preparation of the composition", "pre-thermal conductive sheet forming step", "laminate forming step", "crosslinking reaction step" and "slicing step" were carried out in the same manner as in Example 1, except that the "preparation of the composition" was carried out as follows. Then, the same measurements and evaluations as in Example 1 were performed on the obtained thermal conductive sheet. The results are shown in Table 1. <Preparation of the composition> 50 parts (28 volume parts) of a solid fluoroelastomer (fluororubber) (manufactured by 3M Japan Ltd., trade name "Dyneon® FPO3600ULV", Mooney viscosity: 3.5 ML1+4, 100 °C) at normal temperature and pressure, 50 parts (28 volume parts) of a liquid thermoplastic fluororesin (manufactured by Daikin Industries, Ltd., product name "Dai-el G-101") at normal temperature and pressure, 90 parts (40 volume parts) of expanded graphite as a particulate filler (manufactured by Ito Graphite Industry Co., Ltd., trade name "EC300", volume average particle diameter: 50 μm), and 9 parts of a polymer containing a basic group (product name "Adisper PB821", manufactured by Ajinomoto Fine-Techno Co., Inc., amine value: 10 mgKOH / g, acid value: 17 mgKOH / g) were stirred and mixed at a temperature of 150 °C for 20 minutes using a pressure kneader (manufactured by Nippon Spindle). Next, after lowering the apparatus temperature to 60 °C, 0.25 part of dibenzoyl peroxide (manufactured by NOF Corporation, trade name "Niper E") as a reaction initiator and 0.25 part of triallyl isocyanurate (manufactured by Nippon Kasei Co., Ltd., trade name "TAIC M60") as a crosslinking agent were mixed, and the mixture was kneaded for 10 minutes while maintaining the material temperature at 60 °C. Next, the mixture obtained above was put into a crusher (manufactured by Sanjo Industry Co., Ltd., product name "Hammer Crusher HN34S") and crushed for 60 seconds to obtain a composition containing a resin, a particulate filler, a crosslinking agent, and a reaction initiator.

[0124] (Example 5) In the preparation of the composition of Example 4, the addition amount of dibenzoyl peroxide as a reaction initiator was changed from 0.25 part to 0.50 part, the addition amount of triallyl isocyanurate as a crosslinking agent was changed from 0.25 part to 0.50 part, and in the crosslinking reaction step of Example 4, the heating temperature was changed from 100 °C to 150 °C and the heating time was changed from 6 hours to 1 hour. Otherwise, in the same manner as in Example 4, "preparation of the composition", "preheating and forming step of the heat conduction sheet", "laminate forming step", "crosslinking reaction step", and "slicing step" were carried out. Then, the obtained heat conduction sheet was measured and evaluated in the same manner as in Example 4. The results are shown in Table 1.

[0125] (Example 6) In the preparation of the composition of Example 1, when mixing the resin and the particulate filler, the addition amount of the solid fluoroelastomer (manufactured by 3M Japan Ltd., trade name "Dyneon® FPO3600ULV") at normal temperature and pressure was reduced from 100 parts (56 volume parts) to 50 parts (28 volume parts), and 50 parts (28 volume parts) of a liquid thermoplastic fluororesin (manufactured by Daikin Industries, Ltd., trade name "Dai-el G-101") was further added at normal temperature and pressure. Also, in the crosslinking reaction step of Example 1, except that the heating temperature was changed from 100 °C to 180 °C and the heating time was changed from 6 hours to 1 hour, "preparation of the composition", "pre-thermal conductive sheet forming step", "laminate forming step", "crosslinking reaction step" and "slicing step" were carried out in the same manner as in Example 1. Then, the same measurements and evaluations as in Example 1 were performed on the obtained thermal conductive sheet. The results are shown in Table 1.

[0126] (Comparative Example 1) In the preparation of the composition of Example 1, as the particulate filler, 50 parts (22 volume parts) of expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., trade name "EC100") with a volume average particle diameter of 190 μm was used instead of 60 parts (27 volume parts) of expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., trade name "EC300") with a volume average particle diameter of 50 μm. As the initiator, 0.25 part of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (manufactured by NOF Corporation, trade name "Perhexa 25B-40") was used instead of 0.5 part of dibenzoyl peroxide (manufactured by NOF Corporation, trade name "Niper E"). Also, in the crosslinking reaction step of Example 1, except that the heating temperature was changed from 100 °C to 180 °C and the heating time was changed from 6 hours to 1 hour, "preparation of the composition", "pre-thermal conductive sheet forming step", "laminate forming step", "crosslinking reaction step" and "slicing step" were carried out in the same manner as in Example 1. Then, the same measurements and evaluations as in Example 1 were performed on the obtained thermal conductive sheet. The results are shown in Table 1.

[0127] [Table 1]

[0128] From Table 1, it can be seen that the heat-conductive sheets of Examples 1 to 6, which contain a resin containing a crosslinked resin and a particulate filler, have a thermal conductivity in the thickness direction of a predetermined value or more, and in the measurement of the sheet strength of the main surface, the sheet strength in the main surface direction Y perpendicular to the main surface direction X where the sheet strength is the highest is a predetermined value or more, and the number of predetermined micropores is a predetermined value or less, are difficult to tear during use. On the other hand, the heat-conductive sheet of Comparative Example 1, which contains a resin containing a crosslinked resin and a particulate filler, has a thermal conductivity in the thickness direction of a predetermined value or more and the sheet strength in a predetermined main surface direction Y is a predetermined value or more, but the number of predetermined micropores exceeds a predetermined value, and it can be seen that it is easy to tear during use.

Industrial Applicability

[0129] According to the present invention, it is possible to provide a heat-conductive sheet that is difficult to tear during use.

Claims

【Claim 1】 A heat-conductive sheet containing a resin and a particulate filler, having a thermal conductivity in the thickness direction of 12 W / m·K or more, wherein the resin contains a crosslinked resin. In the measurement of the sheet strength of the main surface of the heat conductive sheet, the sheet strength in the in-plane direction Y perpendicular to the in-plane direction X where the sheet strength is the highest is 1.0 N / mm ２ or more, A heat conduction sheet that penetrates in the thickness direction, and the number of micropores having a pore diameter of 48 μm or more and 500 μm or less is 200 or less per 1 cm ２ of the planar view area of the heat conduction sheet.

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