JP7234560B2 - Heat-conducting sheet and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat conductive sheet and a manufacturing method thereof.

In recent years, electronic components such as power semiconductors (such as IGBT modules) and integrated circuit (IC) chips have been increasing in heat generation as their performance has improved. As a result, in electronic equipment using electronic components, it is necessary to take measures against functional failure due to temperature rise of the electronic components.

As a countermeasure against functional failure due to temperature rise of electronic components, generally, a method of accelerating heat dissipation is adopted by attaching a radiator such as a metal heat sink, radiator plate, or radiator fin to the heat generating body of the electronic component. ing. When using a radiator, in order to efficiently transfer heat from the heating element to the radiator, a sheet-shaped member with high thermal conductivity (thermally conductive sheet) is placed between the thermally conductive sheet. A predetermined pressure is applied to the heat generating member and the heat dissipating member.

In the method of slicing a laminate to produce a thermally conductive sheet, when the thermal conductivity is measured on the main surface of the thermally conductive sheet, the main surface in-plane direction X (relative to the lamination direction of the laminate) where the thermal conductivity is the highest It is relatively easy to improve the sheet strength in the direction perpendicular to the surface), but the sheet strength in the direction Y perpendicular to the direction X in the direction X (the direction coinciding with the lamination direction of the laminate) is improved. It is difficult to improve.

Patent Literature 1 discloses a heat conductive sheet obtained by slicing a laminate at a predetermined angle. Here, the sheet strength in the main in-plane direction X and the sheet strength in the main in-plane direction Y are made uniform by slicing the laminate at a predetermined angle.
Further, Patent Document 2 discloses a heat transfer sheet in which a metal deposition film is provided on one surface of a base sheet containing a binder component and anisotropic graphite powder, in which the anisotropic graphite powder is oriented in the thickness direction. is disclosed. Here, the sheet strength of the heat conductive sheet is improved by providing the metal deposition film.
Further, Patent Literature 3 discloses that a laminate is subjected to a cross-linking reaction while being pressurized in the lamination direction.

Japanese Patent No. 6156337 Japanese Patent No. 5678596 Japanese Patent No. 5423455

However, in the conventional heat conductive sheet, when the heat conductivity is measured on the main surface of the heat conductive sheet, the main in-plane direction X (the direction perpendicular to the lamination direction of the laminate) in which the heat conductivity is the highest ), there is room for improvement in terms of improving the sheet strength in the main in-plane direction Y (the direction coinciding with the lamination direction of the laminate).

Accordingly, an object of the present invention is to provide a thermally conductive sheet having high sheet strength in the main in-plane direction Y (the direction coinciding with the stacking direction of the laminate).
Another object of the present invention is to provide a method for producing a thermally conductive sheet, which can efficiently produce a thermally conductive sheet having high sheet strength in the main in-plane direction Y (the direction coinciding with the stacking direction of the laminate). and

The inventor of the present invention has made intensive studies in order to achieve the above object. Then, the present inventors found that the sheet strength in the main in-plane direction X and the sheet strength in the main in-plane direction Y of the heat conductive sheet containing a resin and a particulate filler and in which the particulate filler is oriented in the thickness direction are The ratio of the sheet strength in the main in-plane direction X to the sheet strength in the main in-plane direction Y (sheet strength in the main in-plane direction X/sheet strength in the main in-plane direction Y) is set to a predetermined value or more. The present inventors have found that a heat conductive sheet having a high sheet strength in the main in-plane direction Y can be obtained by setting the value to be equal to or more than the value, and completed the present invention.

That is, an object of the present invention is to advantageously solve the above problems, and a heat conductive sheet of the present invention includes a resin and a particulate filler, and the particulate filler is oriented in the thickness direction. The sheet strength in the main in-plane direction X in which the thermal conductivity is the highest when the thermal conductivity is measured on the main surface of the thermally conductive sheet, and the sheet strength perpendicular to the main in-plane direction X The sheet strength in the main in-plane direction Y is 0.8 MPa or more, and the ratio of the sheet strength in the main in-plane direction X to the sheet strength in the main in-plane direction Y (the sheet strength in the main in-plane direction X /Sheet strength in the main in-plane direction Y) is 2.3 or more. The sheet strength in the main in-plane direction X and the sheet strength in the main in-plane direction Y are both 0.8 MPa or more, and the ratio of the sheet strength in the main in-plane direction X to the sheet strength in the main in-plane direction Y is 2.3 or more. By doing so, a heat conductive sheet having a high sheet strength in the main in-plane direction Y can be obtained.
Here, the "particulate filler" means a filler having an aspect ratio of 10 or less, and the "main surface of the heat conductive sheet" means at least one surface of the heat conductive sheet.
The "thermal conductivity" and "sheet strength" can be measured by the methods described in Examples.

Moreover, the heat conductive sheet of the present invention preferably has a gel fraction of 30% or more. If the gel fraction is 30% or more, cross-linking within the sheet can improve strength and solvent resistance.
The gel fraction can be measured by the method described in Examples.

In addition, the thermally conductive sheet of the present invention has a ratio of the thickness of the thermally conductive sheet pressurized at 0.9 MPa to the thickness of the thermally conductive sheet pressurized at 0.05 MPa (thickness of the thermally conductive sheet pressurized at 0.9 MPa /thickness of the heat conductive sheet pressurized at 0.05 MPa) is preferably 90% or more. If the ratio of the thickness of the heat conductive sheet pressurized at 0.9 MPa to the thickness of the heat conductive sheet pressurized at 0.05 MPa is 90% or more, the compressive strength of the heat conductive sheet can be improved.

Furthermore, the heat conductive sheet of the present invention preferably contains a resin that is liquid under normal temperature and normal pressure. If the resin contains a resin that is liquid under normal temperature and normal pressure, the adhesion (tacking) of the thermally conductive sheet can be improved.

An object of the present invention is to advantageously solve the above problems. a pre-heat conductive sheet forming step of forming a sheet into a pre-heat conductive sheet to obtain a pre-heat conductive sheet; , a laminate forming step for obtaining a laminate, a pressurizing step for pressurizing the laminate, a cross-linking reaction step for performing a cross-linking reaction by reacting the laminate under temperature conditions at which the cross-linking agent can react, and and a slicing step of obtaining a heat conductive sheet by slicing at an angle of 45° or less with respect to the stacking direction. According to such a manufacturing method, it is possible to efficiently manufacture a heat conductive sheet having a high sheet strength in the main in-plane direction Y.

Here, in the method for producing a heat conductive sheet of the present invention, in the pressurizing step, the obtained laminate is heated at a temperature of 30° C. or higher and 180° C. or lower, and at a pressure of 0.01 MPa or more and 0.01 MPa or more in the lamination direction. It is preferable to pressurize at a pressure of 50 MPa or less. By heating the laminate at a temperature of 30° C. or higher and 180° C. or lower and applying a pressure of 0.01 MPa or higher and 0.50 MPa or lower in the lamination direction, a heat conductive sheet having a high sheet strength in the main in-plane direction Y can be obtained. It can be manufactured more efficiently.

Here, in the method for producing a heat conductive sheet of the present invention, in the cross-linking reaction step, the cross-linking reaction is preferably performed while applying pressure to the laminate at 0.03 MPa or more in the stacking direction. If the cross-linking reaction is performed while the laminate is pressed at 0.03 MPa or more in the lamination direction, a heat conductive sheet having high sheet strength in the main in-plane direction Y can be produced more efficiently.

According to the present invention, it is possible to provide a thermally conductive sheet having high sheet strength in the main in-plane direction Y (the direction coinciding with the stacking direction of the laminate).
Further, according to the present invention, there is provided a method for producing a thermally conductive sheet that can efficiently produce a thermally conductive sheet having high sheet strength in the main in-plane direction Y (the direction coinciding with the stacking direction of the laminate). can be done.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.
Since the thermally conductive sheet of the present invention has thermal conductivity, it can be used by sandwiching it between a heating element and a radiator. That is, the heat conductive sheet of the present invention can be used as a heat radiating member to constitute a heat radiating device together with a heat radiating body such as a heat sink, a heat radiating plate, or a heat radiating fin.
The thermally conductive sheet of the present invention contains a resin and a particulate filler, the particulate filler is oriented in the thickness direction, and the main surface of the thermally conductive sheet has a thermal conductivity of When measured, the sheet strength in the main in-plane direction X at which the thermal conductivity is the highest and the sheet strength in the main in-plane direction Y perpendicular to the main in-plane direction X are both 0.8 MPa or more, As long as the ratio of the sheet strength in the main in-plane direction X to the sheet strength in the main in-plane direction Y (the sheet strength in the main in-plane direction X/the sheet strength in the main in-plane direction Y) is 2.3 or more. Although it can be manufactured according to any manufacturing method without any particular limitation, it can be efficiently manufactured according to the manufacturing method of the heat conductive sheet of the present invention, which will be described later.

(Thermal conductive sheet)
The thermally conductive sheet of the present invention contains a resin and a particulate filler, and further contains optional other ingredients. Furthermore, the thermally conductive sheet of the present invention has a structure in which the particulate filler is oriented in the thickness direction, and when the thermal conductivity is measured on the main surface of the thermally conductive sheet, the main surface of the thermally conductive sheet has the highest thermal conductivity. The sheet strength in the in-plane direction X and the sheet strength in the main in-plane direction Y perpendicular to the in-plane direction X are both 0.8 MPa or more, and the sheet strength in the main in-plane direction with respect to the sheet strength in the main in-plane direction Y The sheet strength ratio in the direction X (the sheet strength in the main in-plane direction X/the sheet strength in the main in-plane direction Y) is 2.3 or more. In the thermally conductive sheet of the present invention, the thermally conductive path is formed by the particulate filler oriented in the thickness direction of the thermally conductive sheet, and the thermal conductivity can be exhibited. The sheet strength of Y is all 0.8 MPa or more, and the ratio of the sheet strength in the main in-plane direction X to the sheet strength in the main in-plane direction Y is 2.3 or more. Sheet strength can be improved.

<Resin>
Since the thermally conductive sheet of the present invention contains a resin, the heat generating body and the radiator can be brought into close contact with each other through the thermally conductive sheet. In this specification, rubber and elastomer shall be included in "resin".
The resin that can be contained in the heat conductive sheet of the present invention constitutes the matrix resin and also functions as a binder that binds the particulate filler.
Examples of such resins include "resins that are solid under normal temperature and normal pressure" and "resins that are liquid under normal temperature and normal pressure". These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios. In the cross-linking reaction step described later, the "resin that is solid under normal temperature and pressure" undergoes a cross-linking reaction, and the "resin that is liquid under normal temperature and pressure" does not participate in the cross-linking reaction of the "resin that is solid under normal temperature and pressure". Adhesion can be imparted. This means, for example, that the "resin that is solid at normal temperature and normal pressure" is a peroxide cross-linking system, the "resin that is liquid at normal temperature and pressure" is a polyol cross-linking system, and the cross-linking agent used is a peroxide cross-linking agent. It is done in some cases.
In this specification, "normal temperature" refers to 23°C, and "normal pressure" refers to 1 atm (absolute pressure).
In addition, when a “resin that is solid at normal temperature and pressure” undergoes a cross-linking reaction and a “resin that is liquid under normal temperature and pressure” is cross-linked in a different reaction system, the strength of the sheet can be arbitrarily adjusted by adjusting the amount of the cross-linking agent. and stickiness can be easily balanced.

<<Resin that is solid at normal temperature and pressure>>
Since the heat conductive sheet contains a resin that is solid under normal temperature and normal pressure, it is possible to maintain the strength of the sheet. can be improved.
As the resin that is solid under normal temperature and normal pressure, for example, a thermoplastic resin that is solid under normal temperature and normal pressure can be used.
The content of the resin that is solid at normal temperature and pressure is preferably 10% by mass or more, more preferably 20% by mass or more, of the total content of the resin that is solid at normal temperature and pressure and the resin that is liquid at normal temperature and pressure, which will be described later. is more preferably 80% by mass or more, and particularly preferably 100% by mass (all of which is a solid resin). If the content of the resin that is solid at normal temperature and normal pressure is within the above range, the strength of the sheet can be improved.

[Thermoplastic resin that is solid at normal temperature and pressure]
Since the thermally conductive sheet contains a thermoplastic resin that is solid under normal temperature and normal pressure, the adhesion between the thermally conductive sheet and the adherend (heating element, radiator) to which the thermally conductive sheet is adhered is enhanced, High thermal conductivity can be exhibited by the thermally conductive sheet.

Examples of thermoplastic resins that are solid under normal temperature and pressure include poly(2-ethylhexyl acrylate), copolymers of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its esters, polyacrylic acid or its esters. Acrylic resin such as acrylic resin; silicone resin; fluorine resin; polyethylene; polypropylene; ethylene-propylene copolymer; polymethylpentene; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; styrene-acrylonitrile copolymer; acrylonitrile-butadiene-styrene copolymer (ABS resin); Styrene-isoprene block copolymer or hydrogenated product thereof; Polyphenylene ether; Modified polyphenylene ether; Aliphatic polyamides; Aromatic polyamides; Polyamideimide; Polycarbonate; ether ketone; polyketone; polyurethane; liquid crystal polymer; These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among these, from the viewpoint of improving the flame retardancy, heat resistance, oil resistance, chemical resistance, etc. of the heat conductive sheet, thermoplastic resins that are solid at room temperature and pressure A fluororesin is preferred.

[[Thermoplastic fluororesin solid at normal temperature and pressure]]
The thermoplastic fluororesin that is solid at normal temperature and normal pressure is not particularly limited as long as it is a thermoplastic fluororesin that is solid at normal temperature and normal pressure. Thermoplastic fluororesins that are solid at normal temperature and pressure include, for example, vinylidene fluoride fluororesins, tetrafluoroethylene-propylene fluororesins, tetrafluoroethylene-purple vinyl ether fluororesins, and the like, which are obtained by polymerizing fluorine-containing monomers. The resulting elastomer and the like can be mentioned. More specifically, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polychloro trifluoroethylene, 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 , and so on. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among them, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, acrylic-modified polytetrafluoroethylene, from the viewpoint of workability , is preferred.

In addition, commercially available thermoplastic fluororesins (fluoroelastomers (fluororubbers)) that are solid under normal temperature and pressure include, for example, DAIEL (registered trademark) G-912 and G-700 series manufactured by Daikin Industries, Ltd. Dai-El G-550 series / G-600 series, Dai-El G-310; KYNAR (registered trademark) series manufactured by ALKEMA, KYNAR FLEX (registered trademark) series; Dyneon FC2211, FPO3600ULV manufactured by 3M;

<<Resin that is liquid at normal temperature and pressure>>
When the thermally conductive sheet contains resin that is liquid at normal temperature and normal pressure, the flexibility of the sheet can be improved.
As the resin that is liquid at normal temperature and normal pressure, for example, a thermoplastic resin that is liquid at normal temperature and normal pressure can be used.

[Thermoplastic fluororesin that is liquid at normal temperature and pressure]
When the heat conductive sheet contains a thermoplastic resin that is liquid at normal temperature and normal pressure, the flexibility of the heat conductive sheet can be improved. It is possible to increase the adhesion between the heat generating body and the heat dissipating body, and to exhibit higher thermal conductivity by the heat conductive sheet.

Examples of thermoplastic resins that are liquid at normal temperature and pressure include acrylic resins, epoxy resins, silicone resins, and fluorine resins. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among these, in addition to improving the flame retardancy, heat resistance, oil resistance, and chemical resistance of the heat conductive sheet, even under relatively low pressure, the interfacial adhesion is increased and the interfacial thermal resistance is reduced. A thermoplastic fluororesin that is liquid at normal temperature and normal pressure is preferable because it can improve the thermal conductivity (that is, the heat dissipation property) of the heat conductive sheet.

The thermoplastic fluororesin that is liquid at normal temperature and pressure is not particularly limited as long as it is a thermoplastic fluororesin that is liquid at normal temperature and pressure. Examples of thermoplastic fluororesins that are liquid at normal temperature and pressure include vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropentene-tetrafluoroethylene terpolymer, perfluoropropene oxide polymer, tetrafluoroethylene-propylene-vinylidene fluoride copolymer, and the like. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Examples of commercially available thermoplastic fluororesins that are liquid at normal temperature and pressure include Viton (registered trademark) LM manufactured by DuPont Co., Ltd., Daiel (registered trademark) G-101 manufactured by Daikin Industries, Ltd., and 3M. Dynion FC2210 manufactured by Co., Ltd., SIFEL series manufactured by Shin-Etsu Chemical Co., Ltd., and the like can be mentioned.

The viscosity of the thermoplastic fluororesin, which is liquid at normal temperature and pressure, is not particularly limited. coefficient) is preferably 500 cP or more and 30,000 cP or less, more preferably 550 cP or more and 25,000 cP or less.

<Particulate filler>
When the thermally conductive sheet of the present invention contains a particulate filler, the thermal conductivity of the thermally conductive sheet can be further enhanced.
Examples of particulate fillers include particulate carbon materials, particulate inorganic materials, particulate metal materials, and the like.

<<Content ratio of particulate filler>>
The content of the particulate filler in the thermally conductive sheet is preferably 20 parts by mass or more, more preferably 50 parts by mass or more, and 80 parts by mass or more with respect to 100 parts by mass of the resin. It is particularly preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and particularly preferably 100 parts by mass or less. If the content of the particulate filler is at least the above lower limit, the thermal conductivity can be improved. Also, if the content of the particulate filler is equal to or less than the above upper limit, a sheet with high strength can be produced.

<<particulate carbon material>>
The particulate carbon material is not particularly limited, and examples thereof include graphite such as artificial graphite, flake graphite, exfoliated graphite, natural graphite, acid-treated graphite, expansive graphite, and expanded graphite; carbon black; can be used. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among these, expanded graphite is preferred. If expanded graphite is used for the thermally conductive sheet, the thermal conductivity of the thermally conductive sheet can be further improved.

-expanded graphite-
Here, the expanded graphite that can be suitably used as the particulate carbon material is, for example, expandable graphite obtained by chemically treating graphite such as flake graphite with sulfuric acid or the like, heat-treating it to expand it, and then making it fine. can be obtained by Examples of commercially available expanded graphite include EC-1500, EC-1000, EC-500, EC-300, EC-100, EC-50, and EC-10 manufactured by Ito Graphite Industry Co., Ltd. first name), etc.

-Average particle size-
The average particle size of the particulate carbon material is preferably 10 µm or more, more preferably 30 µm or more, preferably 250 µm or less, and more preferably 100 µm or less.
If the average particle diameter of the particulate carbon material is at least the above lower limit, the thermal conductivity and the like of the thermally conductive sheet can be further improved. Further, if the average particle size of the particulate carbon material is equal to or less than the above upper limit, the strength and shape retention ability of the heat conductive sheet can be further enhanced.

-aspect ratio-
The aspect ratio (major axis/minor axis) of the particulate carbon material is preferably 1 or more and 10 or less, more preferably 1 or more and 5 or less.
In this specification, the "aspect ratio" refers to the maximum diameter (major diameter) and the maximum diameter of any 50 particulate carbon materials observed with a SEM (scanning electron microscope). It can be obtained by measuring the particle diameter (short diameter) in the orthogonal direction and calculating the average value of the ratio of the long diameter to the short diameter (long diameter/short diameter).

<Other ingredients>
If necessary, the thermally conductive sheet can further contain other components that can be used for molding the thermally conductive sheet. Other components that can be blended in the heat conductive sheet are not particularly limited, and include, for example, cross-linking agents; reaction initiators; fibrous carbon materials; red phosphorus flame retardants, phosphate flame retardants, and the like. Flame retardants; plasticizers such as fatty acid ester plasticizers; toughness improvers such as urethane acrylate; moisture absorbers such as calcium oxide and magnesium oxide; adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides wettability improvers such as nonionic surfactants and fluorine-based surfactants; ion trapping agents such as inorganic ion exchangers; and the like.

<<crosslinking agent>>
The cross-linking agent that the heat conductive sheet may optionally contain is not particularly limited, and examples thereof include isocyanurates such as triallyl isocyanurate (for example, TAIC (registered trademark) manufactured by Mitsubishi Chemical Corporation); Cyanurates such as lucyanurate; maleimides such as N,N'-m-phenylene dimaleimide; allyl esters; diethylene glycol bisallyl carbonate; allyl ethers such as ethylene glycol diallyl ether, triallyl ether of trimethylolpropane, and partial allyl ether of pentaerythritol; Tri- to penta-functional methacrylate compounds and acrylate compounds such as methylolpropane trimethacrylate and trimethylolpropane triacrylate; These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
For example, if the thermal conductive sheet contains a cross-linking agent, the strength can be further improved by heating and reacting.
Among those mentioned above, it is preferable to use triallyl isocyanurate as the cross-linking agent. This is because if triallyl isocyanurate is used, the strength can be improved by making the reaction easier.

<<Reaction initiator>>
The reaction initiator that the heat conductive sheet may optionally contain is not particularly limited, and examples thereof include dibenzoyl peroxide, t-butylperoxyacetate, 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 (for example, NOF Perhexa 25B-40 (registered trademark) manufactured by Co., Ltd.), di-t-butyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexene-3, t-butyl hydroperoxide , t-butyl peroxyisobutyrate, lauroyl peroxide, dipropionyl peroxide, p-menthane hydroperoxide, and other organic peroxides functioning as radical reaction initiators. These may be used singly or in combination of two or more at any ratio.
For example, if the thermally conductive sheet contains a reaction initiator, radicals are generated and the cross-linking reaction can be started smoothly.
Among those mentioned above, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane is preferably used as the reaction initiator. This is because the use of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane suppresses the initiation of the reaction at low temperatures and enables efficient cross-linking.

<Structure and Properties of Heat Conductive Sheet>
The heat conductive sheet of the present invention has the following structure and properties without being particularly limited.

<<Structure of Thermally Conductive Sheet>>
The thermally conductive sheet of the present invention has a structure in which the above-described particulate filler is oriented in the thickness direction of the thermally conductive sheet. Here, "oriented in the thickness direction of the heat conductive sheet" means that the cross section of the heat conductive sheet (secondary sheet) is first observed using a SEM (scanning electron microscope), and the particulate filler in the sheet is It refers to the state in which it is oriented in the thickness direction.

<<Sheet strength of the thermally conductive sheet in the main in-plane direction X>>
The sheet strength of the heat conductive sheet in the main in-plane direction X must be 0.8 MPa or more, preferably 1.5 MPa or more, more preferably 2.0 MPa or more, and 20.0 MPa. It is preferably 10.0 MPa or less, particularly preferably 7.0 MPa or less. If the sheet strength in the main in-plane direction X of the heat conductive sheet is equal to or less than the above upper limit, the sheet can be moderately crushed by the pressure when the sheet is mounted on a device, and a sheet exhibiting good heat conductivity can be obtained. Further, if the sheet strength in the direction X in the main surface of the heat conductive sheet is equal to or higher than the above lower limit value, it is possible to obtain a sheet that is strong enough not to be damaged by an external force applied during mounting.
Here, the sheet strength of the heat conductive sheet in the main in-plane direction X can be measured by the method described in Examples.

<<Sheet strength in main in-plane direction Y of thermally conductive sheet>>
The sheet strength of the heat conductive sheet in the main in-plane direction Y must be 0.8 MPa or more, preferably 1.5 MPa or more, more preferably 2.0 MPa or more, and 3.0 MPa. It is preferably 2.5 MPa or less, more preferably 2.5 MPa or less. If the sheet strength in the in-plane direction Y of the heat conductive sheet is equal to or less than the above upper limit, the sheet can be moderately crushed by the pressure when the sheet is mounted on a device, and a sheet exhibiting good heat conductivity can be obtained. Further, if the sheet strength in the direction Y of the main surface of the heat conductive sheet is equal to or higher than the above lower limit value, it is possible to obtain a sheet that is strong enough not to be damaged by an external force applied during mounting.
Here, the sheet strength of the heat conductive sheet in the main in-plane direction Y can be measured by the method described in Examples.

<<Thermal resistance value of the thermally conductive sheet>>
The heat resistance value of the heat conductive sheet is preferably 1.50 (° C./W) or less, more preferably 1.00 (° C./W) or less, under pressure of 0.05 MPa. It is more preferably 0.50 (° C./W) or less, and particularly preferably 0.50 (° C./W) or less. When the thermal resistance value under pressure of 0.05 MPa is equal to or less than the above upper limit value, excellent thermal conductivity can be obtained under a usage environment in which relatively low pressure is applied.
The heat resistance value of the heat conductive sheet is preferably 0.80 (° C./W) or less, more preferably 0.40 (° C./W) or less, under pressure of 0.30 MPa. It is more preferably 0.30 (° C./W) or less, and particularly preferably 0.30 (° C./W) or less. When the thermal resistance value under pressure of 0.30 MPa is equal to or less than the above upper limit value, excellent thermal conductivity can be obtained.
The heat resistance value of the heat conductive sheet is preferably 0.50 (° C./W) or less, more preferably 0.25 (° C./W) or less, under pressure of 0.90 MPa. It is more preferably 0.20 (° C./W) or less, and particularly preferably 0.20 (° C./W) or less. When the thermal resistance value under pressure of 0.90 MPa is equal to or less than the above upper limit value, excellent thermal conductivity can be obtained under a usage environment in which relatively high pressure is applied.
Here, the thermal resistance value of the thermally conductive sheet can be measured by the method described in Examples.

<<Gel fraction of thermally conductive sheet>>
The gel fraction of the heat conductive sheet is preferably 30% or more, more preferably 50% or more, particularly preferably 70% or more, and preferably 99% or less. % or less.
If the gel fraction of the thermally conductive sheet is equal to or higher than the above lower limit, cross-linking within the sheet is advanced, so that the strength and solvent resistance can be improved.
Here, the gel fraction of the heat conductive sheet can be measured by the method described in Examples.

<<Thickness of thermally conductive sheet>>
The thickness of the heat conductive sheet under pressure of 0.05 MPa is preferably 140 μm or more, more preferably 143 μm or more, particularly preferably 145 μm or more, and 160 μm or less. It is preferably 150 μm or less, more preferably 150 μm or less. If the thickness of the thermally conductive sheet is equal to or less than the above upper limit, the thermal resistance of the sheet can be reduced. Moreover, if the thickness of the thermally conductive sheet is equal to or greater than the above lower limit, the strength of the sheet can be improved.

The thickness of the heat conductive sheet under pressure of 0.30 MPa is preferably 135 μm or more, more preferably 140 μm or more, and preferably 150 μm or less, more preferably 145 μm or less. preferable. If the thickness of the thermally conductive sheet is equal to or less than the above upper limit, the thermal resistance of the sheet can be reduced. Moreover, if the thickness of the thermally conductive sheet is equal to or more than the above lower limit, the strength of the sheet can be improved.

The thickness of the heat conductive sheet under pressure of 0.90 MPa is preferably 130 μm or more, more preferably 135 μm or more, and preferably 145 μm or less, more preferably 140 μm or less. preferable. If the thickness of the thermally conductive sheet is equal to or less than the above upper limit, the thermal resistance of the sheet can be reduced. Moreover, if the thickness of the thermally conductive sheet is equal to or greater than the above lower limit, the strength of the sheet can be improved.

The thermally conductive sheet has a ratio of the thickness of the thermally conductive sheet pressurized at 0.9 MPa to the thickness of the thermally conductive sheet pressurized at 0.05 MPa (thickness of the thermally conductive sheet pressurized at 0.9 MPa / at 0.05 MPa The thickness of the pressurized heat conductive sheet) is preferably 90% or more, more preferably 93% or more, particularly preferably 95% or more, and preferably 98% or less. , 97% or less. If the thickness of the heat conductive sheet is equal to or less than the above upper limit, the sheet is appropriately compressed according to the pressure during mounting, and the thermal resistance of the sheet can be reduced. Further, when the thickness of the heat conductive sheet is equal to or more than the above lower limit value, the compressive strength of the heat conductive sheet can be improved.

<<Adhesion of thermal conductive sheet (tacking)>>
The adhesion (tacking) of the heat conductive sheet is preferably 0.6 N or more, more preferably 0.8 N or more, particularly preferably 1.0 N or more, and 1.5 N or less. It is preferably 1.2N or less, more preferably 1.2N or less.
If the adhesiveness (tacking) of the thermally conductive sheet is at least the above lower limit, the adhesiveness of the thermally conductive sheet can be improved. It can be adhered to the frame with good adhesion.
Here, the adhesion (tacking) of the heat conductive sheet can be measured by the method described in Examples.

<Preparation of heat conductive sheet>
For example, the heat conductive sheet of the present invention includes (i) a pre-heat conductive sheet forming step, (ii) a laminate forming step, (iii) a pressing step, (iv) a cross-linking reaction step, and (v), which will be described in detail below. ) prepared by a heat conductive sheet preparation method including a slicing step, and the like.

<<(i) Pre-thermal conductive sheet forming step>>
In the pre-thermal conductive sheet forming step, a composition containing a resin, a particulate filler, a cross-linking agent, and optionally other components is pressurized and formed into a sheet to obtain a pre-thermal conductive sheet.

〔Composition〕
Here, the composition can be prepared by mixing the resin, particulate filler, cross-linking agent, and any other ingredients. The resin, particulate filler, cross-linking agent, and optional other components include the above resin, the above-described particulate filler, the above-described cross-linking agent, and the above-described Other ingredients described above can be used.

The mixing of the above-described components is not particularly limited, and can be performed using known mixing devices such as kneaders; mixers such as Henschel mixers, Hobart mixers, and high-speed mixers; twin-screw kneaders; can. Mixing may also be performed in the presence of a solvent such as ethyl acetate. The resin may be pre-dissolved or dispersed in a solvent and mixed with the particulate filler, cross-linking agent, and any other ingredients as a resin solution. And mixing time can be 5 minutes or more and 60 minutes or less, for example. Moreover, the mixing temperature can be, for example, 5° C. or higher and 150° C. or lower.

[Molding of composition]
The composition prepared as described above can be optionally defoamed and pulverized, and then pressurized to form a sheet. A sheet-like product obtained by pressure-molding the composition in this way can be used as a pre-heat conductive sheet. In addition, when a solvent is used during mixing, it is preferable to form the sheet after removing the solvent. For example, if defoaming is performed using vacuum defoaming, the solvent is removed at the same time as defoaming. It can be carried out.

Here, the composition is not particularly limited as long as it is a molding method in which pressure is applied, and can be molded into a sheet using a known molding method such as press molding, rolling molding, or extrusion molding. . Above all, the composition is preferably formed into a sheet by rolling (primary processing), and more preferably formed into a sheet by passing between rolls sandwiched between protective films. The protective film is not particularly limited, and a sandblasted polyethylene terephthalate (PET) film or the like can be used. In addition, the roll temperature is 5° C. or higher and 150° C. or lower, the roll gap is 50 μm or higher and 2500 μm or lower, the roll linear pressure is 1 kg/cm or higher and 3000 kg/cm or lower, and the roll speed is 0.1 m/min or higher and 20 m/min or lower. can.

[Pre-thermal conductive sheet]
In the pre-thermally conductive sheet formed by pressurizing the composition and forming it into a sheet, the particulate filler is oriented mainly in the in-plane direction, and in particular, the thermal conductivity of the pre-thermally conductive sheet in the in-plane direction is improved. guessed.

<<(ii) Laminate forming step>>
In the laminate forming step, a plurality of pre-thermally conductive sheets obtained in the pre-thermally conductive sheet forming step are laminated in the thickness direction, or the pre-thermally conductive sheets are folded or wound, and the resin and the particulate filler are formed. A laminate is obtained in which a plurality of thermally conductive sheets containing is formed in the thickness direction. Here, the formation of the laminate by folding the pre-heat conductive sheet is not particularly limited, and can be performed by folding the pre-heat conductive sheet to a certain width using a folding machine. Moreover, the formation of the laminate by winding the pre-heat conductive sheet is not particularly limited. It can be carried out. Moreover, the formation of the laminate by laminating the pre-thermally conductive sheets is not particularly limited, and can be performed using a laminating apparatus. For example, if a sheet lamination apparatus (manufactured by Nikkiso Co., Ltd., product name: "High Stacker") is used, it is possible to prevent air from entering between layers, so that a good laminate can be obtained efficiently.

<<(iii) Pressurizing step>>
In the pressurizing step, the obtained laminate is pressurized.
In the pressurizing step, the obtained laminate is subjected to a pressure of 0.01 MPa or more and 0.50 MPa or less, preferably 0.03 MPa or more and 0.30 MPa or less, more preferably 0.05 MPa or more and 0.10 MPa or less in the lamination direction. While pressing with, at a temperature of 30 ° C. or higher and 180 ° C. or lower, preferably 40 ° C. or higher and 150 ° C. or lower, more preferably 60 ° C. or higher and 100 ° C. or lower, heating for 1 minute or more and 5 minutes or less (performing secondary pressurization ) is preferred.
In this way, after performing secondary pressurization in which pressure is applied while heating at a temperature lower than the crosslinking reaction temperature described later, the crosslinking reaction step described later is performed, thereby promoting the fusion of the sheets between the sheets. As a result, the cross-linking strength between the interfaces of each layer in the laminate can be improved.

In the laminate obtained by laminating, folding, or winding the pre-heat conductive sheets, it is presumed that the particulate filler is oriented in a direction substantially perpendicular to the lamination direction.

<<(iv) Cross-linking reaction step>>
In the cross-linking reaction step, a cross-linking reaction (vulcanization) is performed by reacting the laminate pressurized in the pressurizing step under temperature conditions at which the cross-linking agent can react.
In the cross-linking reaction step, the cross-linking reaction (vulcanization) is preferably performed while applying pressure to the laminate in the stacking direction at 0.03 MPa or more, preferably 0.05 MPa or more, more preferably 0.20 MPa or more.
Examples of the method of pressurization include pressing only the top and bottom two surfaces of the laminate in the stacking direction, or pressing four surfaces of the laminate including at least the top and bottom two surfaces in the stacking direction of the laminate. From the viewpoint of releasing generated gas, it is preferable to pressurize only the upper and lower surfaces of the laminate in the stacking direction.
The temperature for the cross-linking reaction is not particularly limited as long as it is a temperature at which the cross-linking agent can react. It is preferably 220° C. or lower, more preferably 200° C. or lower, and particularly preferably 180° C. or lower.

<<(v) Slicing step>>
In the slicing step, the laminate crosslinked in the crosslinking reaction step is sliced at an angle of 45.degree. Here, the method for slicing the laminate is not particularly limited, and examples thereof include a multi-blade method, a laser processing method, a water jet method, a knife processing method, and the like. Among them, the knife processing method is preferable because the thickness of the heat conductive sheet can be easily made uniform. Also, the cutting tool for slicing the laminate is not particularly limited, and a slicing member having a smooth board surface with a slit and a blade protruding from the slit (for example, a sharp blade) A planer or slicer) can be used.

From the viewpoint of enhancing the thermal conductivity of the heat conductive sheet, the angle at which the laminate is sliced is preferably 30° or less with respect to the stacking direction, and more preferably 15° or less with respect to the stacking direction. Preferably, the angle is approximately 0° with respect to the stacking direction (that is, the direction along the stacking direction).

In the heat conductive sheet thus obtained, the particulate filler is well oriented in the thickness direction, and the heat conductivity in the thickness direction is excellent.

EXAMPLES The present invention will be specifically described below 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.

In each example and each comparative example, (i) appearance evaluation of the heat conductive sheet (secondary sheet), (ii) sheet strength of the heat conductive sheet, (iii) thermal resistance value and thickness of the heat conductive sheet, (iv) The adhesion (tacking) of the heat conductive sheet, (v) the gel fraction of the heat conductive sheet, and (vi) the volume fraction of the particulate filler in the heat conductive sheet are measured or evaluated using the following methods. went. Table 1 shows the results.

<(i) Appearance evaluation of heat conductive sheet (secondary sheet)>
The appearance of the heat conductive sheet (secondary sheet) was visually evaluated according to the following criteria.
○: A state in which no tear of 1 mm or more is observed on the surface of the secondary sheet.
x: The surface of the secondary sheet (especially the laminated portion) has a tear of 1 mm or more.

<(ii) Sheet strength of thermal conductive sheet>
A specimen of 20 mm×50 mm was punched out of the thermally conductive sheet in the X and Y directions to obtain a test piece. The resulting test piece was subjected to a tensile test at a tensile speed of 20 mm/min using a small desktop testing machine (manufactured by Nidec-Shimpo Corporation, "FGS-500TV", using FGP-50 as a digital force gauge). gone. In addition, the distance between chucks was set to 30 mm. The sheet strength (N/mm) of the heat conductive sheet was calculated by dividing the maximum strength (N) in the tensile test by the thickness (mm) of the test piece.
The “X direction” means “the direction in which the thermal conductivity is the highest when the thermal conductivity is measured on the main surface of the thermally conductive sheet (the direction perpendicular to the stacking direction of the laminate)”. , "Y-direction" means "a direction perpendicular to the X-direction (a direction coinciding with the lamination direction of the laminate)".
Here, thermal conductivity can be measured by the following method.
<<Thermal conductivity>>
Thermal diffusivity α (m ² /s), constant pressure specific heat Cp (J/g·K), and specific gravity ρ (g/m ³ ) were measured in the main surface of each heat conductive sheet by the following methods.
[Thermal diffusivity α (m ² /s)]
Thermal diffusivity was measured using a thermophysical property measuring device (manufactured by Bethel Co., Ltd., product name “Thermo Wave Analyzer TA35”).
[Constant pressure specific heat Cp (J / g K)]
A differential scanning calorimeter (manufactured by Rigaku, product name “DSC8230”) was used to measure the specific heat under the condition of temperature increase of 10° C./min.
[Specific gravity ρ (g/m ³ )]
The specific gravity (density) (g/m ³ ) was measured using an automatic hydrometer (trade name “DENSIMETER-H” manufactured by Toyo Seiki Co., Ltd.).
Then, using the obtained measured value, the following formula (I):
λ=α×Cp×ρ (I)
to obtain the thermal conductivity λ (W/m·K) of the thermally conductive sheet.

<(iii) Thermal resistance value and thickness of thermally conductive sheet>
The thermal resistance value of the thermal conductive sheet was measured using a resin material thermal resistance tester (manufactured by Hitachi Technology and Service Co., Ltd.). Here, a thermally conductive sheet cut into a square of 1.0 cm ² was used as a sample, and the thermal resistance value when three pressures of 0.05 MPa, 0.3 MPa, and 0.9 MPa were applied at a sample temperature of 50 ° C. (°C/W) was measured. The smaller the thermal resistance value, the better the thermal conductivity of the thermally conductive sheet. Furthermore, similarly to the measurement of the thermal resistance value (°C/W) of the thermal conductive sheet, the thickness (mm) of the thermal conductive sheet when three levels of pressure of 0.05 MPa, 0.3 MPa, and 0.9 MPa were applied was also measured. , at the same time, was measured using the resin material heat resistance tester.

<(iv) Adhesion (Tacking) of Thermally Conductive Sheet>
The adhesion (tacking) of the heat conductive sheet was measured using a probe tack tester (manufactured by Lesca Co., Ltd., trade name "TAC1000"). Specifically, the tip of a flat-shaped probe with a diameter of 10 mm was pressed against the heat conductive sheet for 10 seconds with a load of 0.5 N (50 gf), and the force required to separate the probe from the heat conductive sheet was measured at a measurement temperature of 25°C. . The larger the measured value of the adhesion (tacking) of the thermally conductive sheet, the higher the adhesion and the better the adhesion to the frame.

<(v) Gel fraction of thermal conductive sheet>
A predetermined amount (X) (approximately 500 mg) of the thermally conductive sheet was precisely weighed, immersed in 100 ml of ethyl acetate at room temperature for 3 days, filtered through a 200-mesh wire mesh to remove insoluble matter, and air-dried at room temperature for 15 hours. Then, the sample was dried at 100° C. for 2 hours, cooled to normal temperature, and then the mass (Y) of the sample was measured. The gel fraction was calculated by substituting X and Y into the following formula. Table 1 shows the results.
Gel fraction (%) = (Y) / (X) x 100

<(vi) Volume fraction of particulate filler in heat conductive sheet>
The volume fraction of the particulate filler in the heat conductive sheet was calculated using the added amount and the specific gravity.

(Example 1)
<Preparation of composition>
1000 parts of a fluoroelastomer (fluororubber) (manufactured by 3M Japan Ltd., trade name “Dyneon (registered trademark) FPO3600ULV”, Mooney viscosity: 3.5ML1+4, 100°C) as a resin that is solid under normal temperature and pressure, and a particulate filler 500 parts of expanded graphite (manufactured by Ito Graphite Kogyo Co., Ltd., trade name "EC100", volume average particle size: 200 μm), using a pressure kneader (manufactured by Nihon Spindle), at a temperature of 150 ° C. for 20 minutes. Stir mixed. Next, after lowering the device temperature to 60° C., 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (manufactured by NOF Corporation, trade name “Perhexa 25B- 40”) and 30 parts of triallyl isocyanurate (manufactured by Nippon Kasei Co., Ltd., trade name “TAIC”) as a cross-linking agent were mixed and kneaded for 10 minutes while the material temperature was maintained at 60°C. Next, the mixture obtained above is put into a pulverizer (manufactured by Sansho Industry Co., Ltd., product name "Hammer Crusher HN34S") and pulverized for 60 seconds to remove the resin, particulate filler, cross-linking agent, and reaction initiation. A composition containing the agent was obtained.

<Molding of pre-thermal conductive sheet>
Next, 50 g of the resulting composition was sandwiched between sandblasted PET films (protective films) having a thickness of 50 μm, and the roll gap was 550 μm, the roll temperature was 50° C., the roll linear pressure was 50 kg/cm, and the roll speed was 1 m/min. to obtain a pre-heat conductive sheet having a thickness of 0.5 mm.

<Formation of laminate>
Subsequently, the obtained pre-heat conductive sheet was cut into a size of 50 mm long × 50 mm wide × 0.5 mm thick, and 100 sheets were laminated in the thickness direction of the pre-heat conductive sheet. A laminate with a height of 49 mm was obtained by pressing (secondary pressure) in the stacking direction for 1 minute. By this secondary pressurization, the layers of the laminate were brought into closer contact with each other.

<Crosslinking reaction>
Subsequently, the resulting laminate was subjected to a cross-linking reaction (vulcanization) in an atmosphere of 180° C. for 1 hour while a pressure of 0.03 MPa was applied from above and below with a vise.
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.

After that, leaving a 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 (that is, from above) to fix the laminate. . 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 blade: 3.5 mm, material: carbide, Rockwell hardness: 91 5, silicon processing of the blade surface: none, total length: 200 mm), and the lamination direction of the laminate (in other words, the main surface of the laminated pre-heat conductive sheet) under the conditions of a slicing speed of 200 mm / sec and a slice width of 100 μm. ) to obtain a heat conductive sheet of length 150 mm x width 60 mm x thickness 0.10 mm.
Then, the obtained heat conductive sheet was subjected to the above-described measurements according to the above-described method. Table 1 shows the results.

(Example 2)
In Example 1, instead of mixing 25 parts of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane as a reaction initiator and 30 parts of triallyl isocyanurate as a cross-linking agent, Example except that 12.5 parts of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane as a reaction initiator and 15 parts of triallyl isocyanurate as a cross-linking agent were mixed. In the same manner as in 1, "preparation of composition", "molding of pre-thermally conductive sheet", "formation of laminate", "crosslinking reaction" and "molding of thermally conductive sheet" were carried out.

(Example 3)
In Example 2, instead of using 1000 parts of fluoroelastomer (fluororubber) (manufactured by 3M Japan Ltd., trade name "Dyneon (registered trademark) FPO3600ULV"), fluoroelastomer (fluororubber) (manufactured by 3M Japan Ltd., trade name " Dyneon (registered trademark) FPO3600ULV”) and 500 parts of a thermoplastic fluororesin that is liquid at normal temperature and pressure (manufactured by Daikin Industries, Ltd., trade name “Daiel G-101”). In the same manner as in Example 2, "preparation of composition", "formation of pre-heat conductive sheet", "formation of laminate", "crosslinking reaction" and "formation of heat conductive sheet" were carried out.

(Example 4)
Instead of mixing 12.5 parts of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane as a reaction initiator and 15 parts of triallyl isocyanurate as a cross-linking agent in Example 3 In addition, 6.3 parts of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane as a reaction initiator and 7.5 parts of triallyl isocyanurate as a cross-linking agent were mixed. In the same manner as in Example 3, "preparation of composition", "formation of pre-heat conductive sheet", "formation of laminate", "crosslinking reaction" and "formation of heat conductive sheet" were carried out.

(Example 5)
In Example 1, 1000 parts of fluoroelastomer (fluororubber) (manufactured by 3M Japan, trade name “Dyneon (registered trademark) FPO3600ULV”), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane Instead of using 25 parts and 30 parts of triallyl isocyanurate, 300 parts of fluoroelastomer (fluororubber) (manufactured by 3M Japan, trade name “Dyneon (registered trademark) FPO3600ULV”) and liquid heat at normal temperature and pressure Plastic fluororesin (manufactured by Daikin Industries, Ltd., trade name "Dai-El G-101") 700 parts, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane 7.5 parts, triallyl In the same manner as in Example 1, except that 9 parts of isocyanurate was used, "preparation of composition", "molding of pre-heat conductive sheet", "formation of laminate", "crosslinking reaction" and "heat Molding of conductive sheet” was performed.

(Example 6)
In Example 5, instead of using 7.5 parts of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and 9 parts of triallyl isocyanurate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane was used. "Preparation of composition", "Preparation of composition", " Preformation of heat conductive sheet”, “Formation of laminate”, “Crosslinking reaction” and “Formation of heat conductive sheet” were carried out.

(Comparative example 1)
In Example 1, instead of performing "crosslinking reaction (vulcanization) using a reaction initiator and a crosslinker", "crosslinking reaction (vulcanization) using a reaction initiator and a crosslinker" was not performed. Except for this, in the same manner as in Example 1, "preparation of composition", "formation of pre-heat conductive sheet", "formation of laminate", "crosslinking reaction" and "formation of heat conductive sheet" were carried out. .

(Comparative example 2)
In Example 3, instead of performing the "crosslinking reaction (vulcanization) using the reaction initiator and the crosslinker", the "crosslinking reaction (vulcanization) using the reaction initiator and the crosslinker" was not performed. Except for this, in the same manner as in Example 3, "preparation of composition", "molding of pre-thermally conductive sheet", "formation of laminate", "crosslinking reaction" and "molding of thermally conductive sheet" were carried out. .

(Comparative Example 3)
In Example 5, instead of performing "crosslinking reaction (vulcanization) using a reaction initiator and a crosslinker", "crosslinking reaction (vulcanization) using a reaction initiator and a crosslinker" was not performed. Except for this, in the same manner as in Example 5, "preparation of composition", "formation of pre-heat conductive sheet", "formation of laminate", "crosslinking reaction" and "formation of heat conductive sheet" were carried out. .

(Comparative Example 4)
In Example 1, "Preparation of composition", "Preheat Formation of conductive sheet", "Formation of laminate", "Cross-linking reaction" and "Formation of thermally conductive sheet" were carried out.

ADVANTAGE OF THE INVENTION According to this invention, the heat conductive sheet which improved the sheet strength of the principal in-plane direction Y (the direction which corresponds to the lamination direction of a laminated body) can be provided.

Claims (6)

A thermal conductive sheet containing a resin and a particulate filler, wherein the particulate filler is oriented in the thickness direction,
The resin contains at least a resin that is solid under normal temperature and normal pressure,
The particulate filler is expanded graphite,
A content ratio of the particulate filler in the heat conductive sheet is 20 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the resin,
The heat conductive sheet has a gel fraction of 38% or more and 95% or less,
When the thermal conductivity is measured on the main surface of the heat conductive sheet, the sheet strength in the main in-plane direction X where the thermal conductivity is the highest and the sheet in the main in-plane direction Y perpendicular to the main in-plane direction X Both strengths are 0.8 MPa or more,
A ratio of the sheet strength in the main in-plane direction X to the sheet strength in the main in-plane direction Y (the sheet strength in the main in-plane direction X/the sheet strength in the main in-plane direction Y) is 2.3 or more. Thermally conductive sheet. The ratio of the thickness of the thermally conductive sheet pressurized at 0.9 MPa to the thickness of the thermally conductive sheet pressurized at 0.05 MPa (thickness of the thermally conductive sheet pressurized at 0.9 MPa/heat conduction sheet pressurized at 0.05 MPa 2. The heat conductive sheet according to claim 1 , wherein the sheet thickness) is 90% or more. 3. The thermally conductive sheet according to claim 1 , wherein the resin further contains a resin that is liquid under normal temperature and normal pressure. A pre-thermal conductive sheet forming step of pressurizing a composition containing a resin, a particulate filler, and a cross-linking agent to form a sheet, thereby obtaining a pre-thermal conductive sheet;
a laminate forming step of obtaining a laminate by laminating a plurality of the pre-heat conductive sheets in the thickness direction, or by folding or winding the pre-heat conductive sheets;
a pressurizing step of pressurizing the laminate;
A cross-linking reaction step of performing a cross-linking reaction by reacting the laminate under a temperature condition of 150° C. or more and 220° C. or less while pressurizing the laminate at 0.03 MPa or more in the lamination direction ;
a slicing step of obtaining a heat conductive sheet by slicing the laminate at an angle of 45° or less with respect to the lamination direction ,
The resin contains at least a resin that is solid under normal temperature and normal pressure,
The particulate filler is expanded graphite,
A content ratio of the particulate filler in the heat conductive sheet is 20 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the resin,
A method for producing a thermally conductive sheet, wherein the thermally conductive sheet has a gel fraction of 38% or more and 95% or less . 5. The method according to claim 4 , wherein in the pressurizing step, the obtained laminate is heated at a temperature of 30° C. or higher and 180° C. or lower and pressurized in the lamination direction at a pressure of 0.01 MPa or higher and 0.50 MPa or lower. A method for manufacturing a heat conductive sheet. The method for producing a heat conductive sheet according to claim 4 or 5 , wherein in the cross-linking reaction step, the cross-linking reaction is performed while applying pressure of 0.03 MPa or more to the laminate in the stacking direction.