JP7131142B2 - thermal conductive sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat conductive sheet.

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 heat radiator, in order to efficiently transfer heat from the heat generator to the heat radiator, a sheet-like member with high thermal conductivity (heat conductive sheet) is placed between the heat conductive sheet and the By applying a predetermined pressure, the heating element and the radiator are brought into close contact with each other. Therefore, a thermally conductive sheet that is sandwiched between a heating element and a radiator is required to have high thermal conductivity in addition to high adhesion.

Therefore, as a thermally conductive sheet having excellent adhesion to an adherend and thermal conductivity, a thermally conductive sheet containing a resin and a thermally conductive filler oriented in the thickness direction has been proposed (for example, Patent Document 1 and 2).

Further, in recent years, with the demand for frequent replacement of modules due to the improvement in performance of modules, there has been a demand for frequent replacement of thermally conductive sheets. Therefore, it is required to be able to be easily peeled off from the heat sink (high reworkability) and to improve productivity.

Therefore, in order to improve the balance of the heat transfer properties (thermal conductivity), handleability (strength, tackiness), and shape workability (stress relaxation) of the heat transfer sheet, metal foil is applied to the surface of the heat transfer sheet. It has been proposed to provide such information (see, for example, Patent Literature 3).

Japanese Patent Application Laid-Open No. 2002-026202 JP 2010-254766 A WO2011/158565

However, even if the metal foil is applied to the surface of the heat transfer sheet, there has been a problem that it is impossible to achieve both thermal conductivity and reworkability.

Accordingly, an object of the present invention is to provide a thermally conductive sheet with improved reworkability while maintaining thermal conductivity.

The inventor of the present invention has made intensive studies in order to achieve the above object. The inventors of the present invention have found that if a metal foil having a thickness within a specific range is formed on at least one surface of a predetermined thermally conductive layer, excellent reworkability can be exhibited while maintaining thermal conductivity. Newly discovered, the present invention was completed.

That is, an object of the present invention is to advantageously solve the above problems, and a thermally conductive sheet of the present invention comprises a thermally conductive layer containing a thermoplastic resin and a thermally conductive filler; and a metal foil formed on at least one surface of the metal foil, wherein the thickness of the metal foil is 0.1 μm or more and 1.5 μm or less.
Thus, by forming a metal foil having a thickness within a specific range on at least one surface of a given thermally conductive layer, excellent reworkability can be exhibited while maintaining thermal conductivity.

In the heat conductive sheet of the present invention, the metal foil preferably contains at least one selected from the group consisting of gold, silver, copper and aluminum.
When the metal foil contains at least one selected from the group consisting of gold, silver, copper and aluminum, it is possible to reliably maintain thermal conductivity and exhibit excellent reworkability.

In the heat conductive sheet of the present invention, the surface roughness (Ra) of the heat conductive layer is preferably 1 μm or more and 15 μm or less.
When the surface roughness of the heat conductive layer is 1 μm or more and 15 μm or less, the metal foil can follow the heat conductive layer, and the heat conductivity can be maintained more reliably.

According to the thermally conductive sheet of the present invention, excellent reworkability can be exhibited while maintaining thermal conductivity.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows an example of embodiment of the thermally-conductive sheet of this invention. FIG. 4 is a diagram showing another example of an embodiment of the thermally conductive sheet of the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.
Here, the thermally conductive sheet of the present invention can be used by sandwiching it between the heat generating body and the heat dissipating body, for example, when attaching the heat dissipating body to the heat generating body. That is, the heat conductive sheet of the present invention can constitute a heat dissipation device together with a heat generating body and a heat dissipating body such as a heat sink, a heat dissipating plate, or a heat dissipating fin.

(Thermal conductive sheet)
The thermally conductive sheet of the present invention has a predetermined thermally conductive layer described in detail below, a metal foil formed on one side of the thermally conductive layer, and optionally a metal foil formed on the other side of the thermally conductive layer. It further has a metal foil or other layer formed on the other side of the thermally conductive layer.
FIG. 1 is a diagram showing an example of an embodiment of the heat conductive sheet of the present invention.
In FIG. 1 , a thermally conductive sheet 10 has a thermally conductive layer 1 and a metal foil 2 formed on one surface of the thermally conductive layer 1 .
FIG. 2 is a diagram showing another example of the embodiment of the heat conductive sheet of the present invention.
In FIG. 2 , the thermally conductive sheet 20 has a thermally conductive layer 1 and metal foils 2 and 3 formed on both sides of the thermally conductive layer 1 .
Here, as a method for producing a heat conductive sheet by forming a metal foil on the heat conductive layer, for example, metal foil is attached to both sides of the heat conductive layer, and the bonded material is sandwiched between release PET films. , a method of rubbing with a roller at a predetermined temperature, a method of crimping a metal foil on both sides of the heat conductive layer, a method of pressure pressing, and the like. The method of pressure pressing is to attach metal foil to one or both sides of the heat conductive layer on two metal plates, sandwich it between release PET films, and press it at a pressure of 0.3 MPa or more and 3.0 MPa or less. is preferred. In addition, during pressurization, heating may be performed at preferably 100° C. or lower, more preferably 70° C. or lower, and particularly preferably 50° C. or lower. By applying heat and pressure in this manner, the adhesion between the heat conductive layer and the metal foil can be improved, and the thermal resistance value on the low load side can be further reduced in the thermal resistance test. The thickness of the thermally conductive layer and the metal foil before and after the production of the thermally conductive sheet varies depending on the pressurizing conditions during production of the thermally conductive sheet, but the thickness after production of the thermally conductive sheet is 3% of the thickness before production of the thermally conductive sheet. It is preferably 10% or less.

The thermal resistance value of the heat conductive sheet under a pressure of 0.30 MPa is usually less than 0.31° C./W, preferably less than 0.25° C./W, and less than 0.19° C./W. is more preferred.
The heat resistance value of the heat conductive sheet under pressure of 0.80 MPa is usually less than 0.31° C./W, preferably less than 0.25° C./W, and less than 0.19° C./W. is more preferred.
The heat resistance value of the heat conductive sheet can be measured by the method described in Examples.

<Thermal conduction layer>
The thermally conductive layer includes a thermoplastic resin and a thermally conductive filler, and optionally other ingredients.
The thermoplastic resin and thermally conductive filler are described in detail below.

<<Thermoplastic Resin>>
By containing a thermoplastic resin in the heat conductive layer in the heat conductive sheet of the present invention, the flexibility of the heat conductive sheet is improved in a high temperature environment during use (during heat dissipation), and the heat generating element is generated through the heat conductive sheet. and the radiator can be brought into close contact with each other. A thermosetting resin can also be used in combination with the heat conductive layer provided that the properties and effects of the heat conductive sheet of the present invention are not lost. In this specification, rubber and elastomer shall be included in "resin".
The thermoplastic resin that can be included in the heat conductive layer in the heat conductive sheet of the present invention constitutes the matrix resin of the heat conductive layer and also functions as a binder that binds the heat conductive filler.
Examples of such thermoplastic resins include "thermoplastic resins that are liquid at normal temperature and normal pressure" and "thermoplastic resins that are solid at normal temperature and normal pressure". These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among these, even under relatively low pressure, the interfacial adhesion can be increased to reduce the interfacial thermal resistance, and the thermal conductivity (that is, heat dissipation characteristics) of the thermal conductive layer and thus the thermal conductive sheet can be improved. In view of this, "thermoplastic resin that is liquid at normal temperature and normal pressure" is preferable.
In this specification, "normal temperature" refers to 23°C, and "normal pressure" refers to 1 atm (absolute pressure).

[Thermoplastic resin that is liquid at normal temperature and pressure]
When the heat conductive layer contains a thermoplastic resin that is liquid at normal temperature and pressure, the flexibility of the heat conductive layer can be improved. For example, the heat conductive sheet and the adherend ( 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 layer and, by extension, the heat conductive sheet, even under relatively low pressure, the interfacial adhesion is improved and the interfacial thermal resistance is improved. A thermoplastic fluororesin that is liquid at normal temperature and normal pressure is preferable in that it can be reduced to improve the thermal conductivity (that is, the heat dissipation property) of the thermally conductive layer and thus the thermally conductive sheet.

[[Thermoplastic fluororesin liquid at normal temperature and pressure]]
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.

[[Content ratio]]
The content of the thermoplastic resin that is liquid at room temperature and pressure is 40% by mass or more of the total content of the thermoplastic resin that is liquid at room temperature and pressure and the thermoplastic resin that is solid at room temperature and pressure, which will be described in detail later. It is preferably 60% by mass or more, more preferably 90% by mass or less, and more preferably 75% by mass or less. If the content of the thermoplastic resin, which is liquid at normal temperature and pressure, is within the above range, the flexibility of the thermally conductive layer and thus the thermally conductive sheet can be further increased, for example, by sandwiching the thermally conductive sheet and the thermally conductive sheet. In order to improve the adhesion between the heat conductive sheet and the body (heat generating body, radiator), it is possible to exhibit high thermal conductivity by the heat conductive sheet under a relatively low clamping pressure (for example, 0.5 MPa or less). Because you can.

[Thermoplastic resin that is solid at normal temperature and pressure]
The heat conductive layer (heat conductive sheet) contains a thermoplastic resin that is solid under normal temperature and pressure, so that the heat conductive sheet and the adherend (heat generating element, radiator) to which the heat conductive sheet is adhered adhere to each other. The heat conductive sheet can be made to exhibit higher heat conductivity by increasing the property.

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, and chemical resistance of the heat conductive layer and thus the heat conductive sheet, the thermoplastic resin that is solid at normal temperature and pressure is A solid thermoplastic 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 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., DAIEL G-550 series/G- 600 series, Daiel G-310; KYNAR (registered trademark) series and KYNAR FLEX (registered trademark) series manufactured by ALKEMA; Dyneon FC2211 and FPO3600ULV manufactured by 3M;

[[Content ratio of thermoplastic fluororesin]]
When the thermoplastic resin is a thermoplastic fluororesin, the content of the thermoplastic fluororesin in the heat conductive layer is preferably 30% by mass or more and 60% by mass or less. If the content of the thermoplastic fluororesin is within the above range, the flame retardancy, heat resistance, oil resistance, chemical resistance, etc. of the heat conductive layer and thus the heat conductive sheet can be further improved. When the thermoplastic resin contains both a thermoplastic fluororesin that is liquid under normal temperature and pressure and a thermoplastic fluororesin that is solid under normal temperature and pressure, the total content of each of them may be within the above range. preferable.

<<Thermosetting resin>>
Provided that the properties and effects of the heat conductive sheet of the present invention are not lost, thermosetting resins that can optionally be used in the heat conductive layer include, for example, natural rubber; butadiene rubber; isoprene rubber; nitrile rubber; Nitrile rubber; Chloroprene rubber; Ethylene propylene rubber; Chlorinated polyethylene; Chlorosulfonated polyethylene; Butyl rubber; Halogenated butyl rubber; Polyisobutylene rubber; Epoxy resin; diallyl phthalate resin; polyimide silicone resin; polyurethane; thermosetting polyphenylene ether; thermosetting modified polyphenylene ether; These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.

<<Thermal Conductive Filler>>
When the heat conductive layer in the heat conductive sheet contains a heat conductive filler, the heat conductivity of the heat conductive layer can be further enhanced. Thermally conductive fillers that the thermally conductive layer may contain include carbonaceous materials, inorganic oxide materials, inorganic nitride materials, and the like. Carbonaceous materials or inorganic nitride materials are preferred as thermally conductive fillers. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.

[Carbonaceous material]
Examples of carbonaceous materials include particulate carbon materials and fibrous carbon materials.
When the thermally conductive filler is a carbonaceous material, the content of the carbonaceous material in the thermally conductive layer is preferably 40% by mass or more, more preferably 50% by mass or more, and more preferably 80% by mass. It is preferably 60% by mass or less, more preferably 60% by mass or less. If the content of the carbonaceous material is at least the above lower limit, heat transfer paths can be formed well in the heat conductive layer, so that the heat conductivity of the heat conductive layer and thus the heat conductive sheet can be further enhanced. In addition, if the content of the carbonaceous material is equal to or less than the above upper limit, the reduction in flexibility of the heat conductive layer and thus the heat conductive sheet due to the blending of the carbonaceous material is suppressed, and the heat conductive sheet and the adherend (heat generation) are suppressed. It is possible to improve the adhesion between the heat conductive sheet and the body, heat radiator), so that the heat conductive sheet can exhibit excellent heat conductivity.

[[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 layer, the thermal conductivity of the thermally conductive layer and thus of the thermally conductive sheet can be further improved.

-expanded graphite-
Expanded graphite can be obtained, for example, by heat-treating expandable graphite obtained by chemically treating graphite such as flake graphite with sulfuric acid or the like to expand it, and then pulverizing the expanded graphite. Examples of expanded graphite include EC1500, EC1000, EC500, EC300, EC100, and EC50 (all trade names) manufactured by Ito Graphite Industry Co., Ltd.

-Average particle size-
The average particle size of the particulate carbon material is preferably 0.1 μm or more, more preferably 1 μm or more, preferably 300 μm or less, and more preferably 200 μm or less. If the average particle size of the particulate carbon material is within the above range, the balance between hardness and adhesiveness of the heat conductive layer can be further improved, and handleability can be improved, and the heat resistance of the heat conductive layer can be improved. It can be further lowered to improve the thermal conductivity.
In this specification, the "average particle diameter" is measured by observing the particulate carbon material with a SEM (scanning electron microscope) and measuring the maximum diameter (major diameter) of any 50 particulate carbon materials. It can be obtained by calculating the number average value of the major diameters.

-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).

-Content ratio of particulate carbon material-
The content of the particulate carbon material in the heat conductive layer is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and 50 parts by mass with respect to 100 parts by mass of the thermoplastic resin. It is more preferably 150 parts by mass or less, more preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less. When the content of the particulate carbon material in the heat conductive layer is 20 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin, the hardness and adhesiveness of the heat conductive layer and thus the heat conductive sheet are improved. Balance can be further improved, and handleability can be further improved. Moreover, when the content of the particulate carbon material is 30 parts by mass or more with respect to 100 parts by mass of the thermoplastic resin, the thermal conductivity of the thermally conductive layer and thus of the thermally conductive sheet can be improved. Further, if the content of the particulate carbon material in the thermally conductive layer is 90 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin, the adhesiveness of the thermally conductive layer and thus the thermally conductive sheet is improved, and the particulate Powder falling of the carbon material can be sufficiently prevented.

[[Fibrous carbon material]]
The fibrous carbon material that the heat conductive layer may optionally contain is not particularly limited, and examples thereof include fibrous carbon nanostructures such as carbon nanotubes (hereinafter sometimes referred to as "CNT"), Vapor-grown carbon fibers, carbon fibers obtained by carbonizing organic fibers, cut products thereof, and the like can be used. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
For example, if the thermally conductive layer contains a fibrous carbon material, the thermal conductivity of the thermally conductive layer and thus of the thermally conductive sheet can be improved, and powder falling of the particulate carbon material can be prevented. Although the reason why powder falling off of the particulate carbon material can be prevented by blending the fibrous carbon material is not clear, the formation of a three-dimensional network structure by the fibrous carbon material contributes to heat conduction. It is presumed that this is because detachment of the particulate carbon material is prevented while improving the properties and strength.

Among the materials described above, fibrous carbon nanostructures such as CNTs are preferably used as the fibrous carbon material, and fibrous carbon nanostructures containing CNTs are more preferably used. This is because the use of fibrous carbon nanostructures containing CNTs can further improve the thermal conductivity and strength of the thermally conductive layer and thus the thermally conductive sheet at a relatively low clamping pressure.

-Fibrous carbon nanostructure containing CNT-
A fibrous carbon nanostructure containing CNTs, which can be suitably used as a fibrous carbon material, may consist of CNTs alone, or may consist of CNTs and fibrous carbon nanostructures other than CNTs. It may be a mixture.
The CNTs in the fibrous carbon nanostructure are not particularly limited, and single-walled carbon nanotubes and/or multi-walled carbon nanotubes can be used. Nanotubes are preferred, and single-walled carbon nanotubes are more preferred. This is because the use of single-walled carbon nanotubes can further improve the thermal conductivity and strength of the heat-conducting layer and thus the heat-conducting sheet as compared with the case of using multi-walled carbon nanotubes.

In addition, as a fibrous carbon nanostructure containing CNTs, the ratio (3σ/Av) of the value (3σ) obtained by multiplying the standard deviation (σ) of the diameter by 3 to the average diameter (Av) is greater than 0.20. It is preferable to use carbon nanostructures with a 3σ/Av of less than 0.60, more preferably with a 3σ/Av of greater than 0.25, and with a 3σ/Av of greater than 0.50. is more preferred. If fibrous carbon nanostructures containing CNTs with 3σ/Av of more than 0.20 and less than 0.60 are used, even if the amount of the carbon nanostructures is small, the thermally conductive layer and thus the thermally conductive sheet can be produced. Thermal conductivity and strength can be sufficiently enhanced. Therefore, the increase in hardness (that is, the decrease in flexibility) of the heat conductive layer and thus the heat conductive sheet due to the addition of the fibrous carbon nanostructures containing CNTs is suppressed, and the heat conductive layer and thus the heat conductive sheet are improved. Thermal conductivity and flexibility can be juxtaposed at sufficiently high levels.
The "average diameter (Av) of the fibrous carbon nanostructures" and the "standard deviation of the diameter of the fibrous carbon nanostructures (σ: sample standard deviation)" were each measured using a transmission electron microscope. It can be obtained by measuring the diameter (outer diameter) of 100 randomly selected fibrous carbon nanostructures. The average diameter (Av) and standard deviation (σ) of the fibrous carbon nanostructures containing CNTs can be adjusted by changing the manufacturing method and manufacturing conditions of the fibrous carbon nanostructures containing CNTs. Alternatively, it may be adjusted by combining a plurality of types of fibrous carbon nanostructures containing CNTs obtained by different manufacturing methods.

Then, the fibrous carbon nanostructure containing CNTs is plotted with the diameter measured as described above on the horizontal axis and the frequency on the vertical axis, and when approximated by Gaussian, a normal distribution is obtained. are usually used.

Furthermore, the fibrous carbon nanostructure containing CNTs preferably has a radial breathing mode (RBM) peak when evaluated using Raman spectroscopy. RBM does not exist in the Raman spectrum of a fibrous carbon nanostructure consisting only of multi-walled carbon nanotubes with three or more layers.

Further, the fibrous carbon nanostructure containing CNTs preferably has a ratio of G-band peak intensity to D-band peak intensity (G/D ratio) of 1 or more and 20 or less in Raman spectrum. If the G/D ratio is 1 or more and 20 or less, the thermal conductivity and strength of the thermally conductive layer and thus the thermally conductive sheet can be sufficiently increased even if the amount of the fibrous carbon nanostructure is small. . Therefore, by blending the fibrous carbon nanostructures, the increase in hardness (that is, the decrease in flexibility) of the heat conductive layer and thus the heat conductive sheet is suppressed, and the heat conduction of the heat conductive layer and thus the heat conductive sheet is suppressed. Flexibility and flexibility can be juxtaposed at a sufficiently high level.

Furthermore, the average diameter (Av) of the fibrous carbon nanostructure containing CNTs is preferably 0.5 nm or more, more preferably 1 nm or more, preferably 15 nm or less, and 10 nm or less. It is even more preferable to have When the average diameter (Av) of the fibrous carbon nanostructures is 0.5 nm or more, the aggregation of the fibrous carbon nanostructures can be suppressed and the dispersibility of the carbon nanostructures can be enhanced. Moreover, if the average diameter (Av) of the fibrous carbon nanostructures is 15 nm or less, the thermal conductivity and strength of the thermally conductive layer and thus the thermally conductive sheet can be sufficiently enhanced.

The fibrous carbon nanostructure containing CNTs preferably has an average structure length of 100 μm or more and 5000 μm or less when synthesized. It should be noted that the longer the structure during synthesis, the more likely the CNTs will be damaged during dispersion, such as breakage or cutting.

Furthermore, the BET specific surface area of the fibrous carbon nanostructure containing CNTs is preferably 300 m ² /g or more, more preferably 600 m ² /g or more, and 2500 m ² /g or less. It is preferably 1200 m ² /g or less, and more preferably 1200 m 2 /g or less. Furthermore, in the fibrous carbon nanostructure, the CNTs in which the CNTs are mainly open preferably have a BET specific surface area of 1300 m ² /g or more. If the BET specific surface area of the fibrous carbon nanostructure containing CNTs is 300 m ² /g or more, the thermal conductivity and strength of the thermally conductive layer and thus the thermally conductive sheet can be sufficiently enhanced. Further, if the BET specific surface area of the fibrous carbon nanostructures containing CNTs is 2500 m ² /g or less, the aggregation of the fibrous carbon nanostructures is suppressed and the dispersibility of the CNTs in the heat conductive layer is enhanced. be able to.
In addition, in this specification, "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET method.

Furthermore, according to the super-growth method described later, the fibrous carbon nanostructures containing CNTs are assembled on a substrate having a catalyst layer for growing carbon nanotubes on the surface and aligned in a direction substantially perpendicular to the substrate. Although obtained as a body (oriented aggregate), the mass density of the fibrous carbon nanostructure as the aggregate is preferably 0.002 g/cm ³ or more and 0.2 g/cm ³ or less. If the mass density is 0.2 g/cm ³ or less, the bonds between the fibrous carbon nanostructures become weak, so that the fibrous carbon nanostructures can be uniformly dispersed in the heat conductive layer. Further, if the mass density is 0.002 g/cm ³ or more, the integrity of the fibrous carbon nanostructure can be improved and the separation can be suppressed, which facilitates handling.

Then, the fibrous carbon nanostructure containing CNTs having the properties described above can be produced, for example, by supplying a raw material compound and a carrier gas onto a base material having a catalyst layer for producing carbon nanotubes on its surface, and chemically vaporizing the material. When synthesizing CNTs by the phase growth method (CVD method), the presence of a small amount of oxidizing agent (catalyst activation material) in the system dramatically improves the catalytic activity of the catalyst layer (super-growth method). ; see International Publication No. 2006/011655), it can be efficiently produced. In addition, below, the carbon nanotube obtained by the super growth method may be called "SGCNT."

Here, the fibrous carbon nanostructure containing CNTs produced by the super-growth method may be composed only of SGCNTs, or in addition to SGCNTs, other materials such as non-cylindrical carbon nanostructures may be used. Carbon nanostructures may be included.

-Properties of fibrous carbon material-
The average fiber diameter of the fibrous carbon material that can be contained in the heat conductive layer of the heat conductive sheet is preferably 1 nm or more, more preferably 3 nm or more, preferably 2 μm or less, and 1 μm or less. is more preferable. This is because if the average fiber diameter of the fibrous carbon material is within the above range, the thermal conductivity, flexibility and strength of the thermally conductive layer and thus of the thermally conductive sheet can be paralleled at sufficiently high levels. Here, the aspect ratio of the fibrous carbon material preferably exceeds 10.

In this specification, the "average fiber diameter" refers to the fiber diameter of any 50 fibrous carbon materials observed with a SEM (scanning electron microscope) or TEM (transmission electron microscope). It can be obtained by measuring and calculating the number average value of the measured fiber diameters. In particular, when the fiber diameter is small, it is preferable to observe the same cross section with a TEM (transmission electron microscope).

- Content ratio of fibrous carbon material -
The content of the fibrous carbon material in the heat conductive layer is preferably 0.03% by mass or more, more preferably 0.05% by mass or more, and 2.0% by mass or less. is preferred, and 1.0% by mass or less is more preferred. If the content of the fibrous carbon material in the heat conductive layer is 0.03% by mass or more, the heat conductivity and strength of the heat conductive layer and thus the heat conductive sheet can be sufficiently improved, and the particulate carbon material This is because it is possible to sufficiently prevent the powder from falling off. Furthermore, when the content of the fibrous carbon material in the heat conductive layer is 2.0% by mass or less, the blending of the fibrous carbon material increases the hardness of the heat conductive layer and thus the heat conductive sheet (that is, flexibility is suppressed), and the thermal conductivity and flexibility of the thermally conductive layer and thus of the thermally conductive sheet can be paralleled at a sufficiently high level.

[Inorganic nitride material]
Examples of inorganic nitride materials include boron nitride, silicon nitride, and aluminum nitride. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among these, boron nitride is preferable from the viewpoint of imparting insulating properties and thermal conductivity.
Here, specific examples of commercially available boron nitride particles include, for example, Momentive Performance Materials Japan's "PT" series (eg, "PT-110"); Showa Denko's "Showby N UHP" series (eg, "ShowBN UHP-1"); Dangdong Chemical Engineering Institute Co., Ltd.; , Ltd. "HSL", "HS";

The shape of the thermally conductive inorganic particles includes, for example, plate-like, scale-like, and spherical shapes, preferably plate-like and scale-like, more preferably scale-like.

<<Additives>>
Known additives that can be used for molding the heat conductive layer can be further blended into the heat conductive layer, if necessary. Additives that can be blended in the heat conductive layer are not particularly limited, and examples thereof include flame retardants such as red phosphorus flame retardants and phosphate ester 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; nonionic surfactants, fluorine surfactants, etc. wettability improvers; ion trapping agents such as inorganic ion exchangers; and the like.

<Properties of heat conductive layer>
The heat conductive layer of the present invention is not particularly limited, and preferably has the following properties.

<<Surface Roughness Ra of Heat Conductive Layer>>
The surface roughness Ra of the heat conductive layer is preferably 1 μm or more, more preferably 3 μm or more, and preferably 15 μm or less, more preferably 10 μm or less. If the surface roughness Ra of the thermally conductive sheet of the present invention is within the above range, the metal foil follows the thermally conductive layer, and the thermal conductivity can be more reliably maintained.
Here, the surface roughness Ra of the heat conductive layer is calculated by selecting a preferable range for the surface roughness using, for example, a nanoscale hybrid microscope (VK-X250 manufactured by Keyence Corporation) in accordance with JISB0601. be able to.

<<Thermal resistance value of the thermally conductive layer>>
The thermally conductive layer has a thermal resistance value of less than 0.31° C./W under a pressure of 0.30 MPa. When the value of thermal resistance under pressure of 0.30 MPa is less than 0.31° C./W, excellent thermal conductivity can be obtained under a usage environment in which relatively low pressure is applied.
Here, the thermal resistance value can be measured using a known measuring method that is usually used to measure the thermal resistance of the thermally conductive layer, and a resin material thermal resistance tester (for example, manufactured by Hitachi Technology and Service Co., Ltd. , trade name “C47108”).

It is preferable that the heat conductive layer has a rate of change of +150.0% or less in thermal resistance value when the pressure is changed from 0.80 MPa to 0.30 MPa. When the change rate of the thermal resistance value when the applied pressure is changed from 0.80 MPa to 0.30 MPa is +150.0% or less, the range of increase in the thermal resistance value with a decrease in the applied pressure is small, and it is above a certain level. has a hardness of Therefore, it is possible to improve the balance between hardness and adhesiveness and improve handleability.
The change rate of the thermal resistance value when the applied pressure is decreased from 0.80 MPa to 0.30 MPa can be calculated by the following formula: 100 × (thermal resistance value under 0.30 MPa pressure - 0 Thermal resistance value under pressure of 0.80 MPa)/Heat resistance value under pressure of 0.80 MPa (%).

<<Thermal conductivity of thermally conductive layer>>
The heat conductive layer preferably has a thermal conductivity in the thickness direction of 20 W/m·K or more, more preferably 30 W/m·K or more, and 40 W/m·K or more at 25°C. is more preferred. If the thermal conductivity is 20 W/m·K or more, for example, when a heat conductive sheet is sandwiched between a heating element and a radiator, heat can be efficiently transferred from the heating element to the radiator. can.

<<Thickness of heat conductive layer>>
The thickness of the heat conductive layer is preferably 80 μm or more and 500 μm or less. As long as the heat conductive layer in the heat conductive sheet of the present invention does not impair the handleability, the thinner the thickness, the smaller the bulk thermal resistance of the heat conductive layer and thus the heat conductive sheet. It is possible to improve the heat dissipation characteristics when used for

<<Density of heat conductive layer>>
The heat conductive layer preferably has a density of 1.8 g/cm ³ or less, more preferably 1.6 g/cm ³ or less. This is because a thermally conductive sheet having such a thermally conductive layer is highly versatile and can contribute to weight reduction of electronic components when mounted on products such as electronic components.

<Preparation of heat conductive layer>
The heat conductive layer in the heat conductive sheet of the present invention is, for example, a heat conductive layer including (i) a pre-heat conductive layer forming step, (ii) a laminate forming step, (iii) a slicing step, etc., which will be described in detail below. Prepared by the preparation method.

[(i) Pre-thermal conductive layer forming step]
In the pre-thermally conductive layer forming step, a composition containing a thermoplastic resin, a thermally conductive filler, and optional components such as additives is pressurized and formed into a sheet to obtain a pre-thermally conductive layer.

<<Composition>>
Here, the composition can be prepared by mixing a thermoplastic resin, a thermally conductive filler, and the optional components (additives) described above. As the thermoplastic resin, thermally conductive filler and optional additives, the components described above as the thermoplastic resin, thermally conductive filler and additive that can be contained in the thermally conductive layer of the thermally conductive sheet of the present invention are used. can be used.
Incidentally, when the resin of the heat conductive layer is a crosslinkable resin, the pre-heat conductive layer may be formed using a composition containing a crosslinkable resin, or a crosslinkable resin and a curing agent may be mixed. A pre-heat conductive layer may be formed using the composition to be contained, and the cross-linkable resin may be cross-linked after the pre-heat conductive layer forming step, so that the heat conductive layer contains a cross-linkable resin.

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. A thermoplastic resin may be preliminarily dissolved or dispersed in a solvent to form a resin solution, which may be mixed with other thermally conductive fillers and optional additives. 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.

When the composition further contains a fibrous carbon nanostructure, the fibrous carbon nanostructure tends to aggregate and has low dispersibility. Difficult to disperse well in materials. On the other hand, fibrous carbon nanostructures can be prevented from agglomerating by mixing the dispersion in a solvent (dispersion medium) with other components such as resins, but the dispersion remains in the dispersion state. In the case of mixing, since a large amount of solvent is used when solidifying the solid content after mixing to obtain a composition, the amount of solvent used for preparing the composition may increase. Therefore, when the fibrous carbon nanostructures are blended in the composition used for molding the pre-heat conductive layer, the fibrous carbon nanostructures are dispersed in a solvent (dispersion medium). It is preferable to mix with other components in the state of aggregates (easily dispersible aggregates) of fibrous carbon nanostructures obtained by removing the solvent from the resulting dispersion. The aggregate of fibrous carbon nanostructures obtained by removing the solvent from the dispersion of fibrous carbon nanostructures is composed of the fibrous carbon nanostructures once dispersed in the solvent. Since the dispersibility is superior to that of the previous aggregate of fibrous carbon nanostructures, it becomes an easily dispersible aggregate with high dispersibility. Therefore, by mixing the easily dispersible aggregates with other components such as resins, the fibrous carbon nanostructures can be efficiently and satisfactorily dispersed in the composition without using a large amount of solvent. can.

Here, the dispersion of the fibrous carbon nanostructures is, for example, a coarse dispersion obtained by adding the fibrous carbon nanostructures to a solvent, and a dispersion treatment or crushing effect that can obtain a cavitation effect can be obtained. It can be obtained by subjecting it to dispersion processing. The dispersing treatment that provides the cavitation effect is a dispersing method that utilizes shock waves generated by the bursting of vacuum bubbles generated in water when high energy is applied to the liquid. Specific examples of the dispersion treatment that produces the cavitation effect include dispersion treatment using an ultrasonic homogenizer, dispersion treatment using a jet mill, and dispersion treatment using a high-shear stirring device. In addition, the dispersion treatment that can obtain the crushing effect applies a shearing force to the coarse dispersion to crush and disperse the aggregates of the fibrous carbon nanostructures, and furthermore, by applying back pressure to the coarse dispersion, This is a dispersion method for uniformly dispersing fibrous carbon nanostructures in a solvent while suppressing the generation of air bubbles. The dispersing treatment that provides a crushing effect can be performed using a commercially available dispersing system (for example, the product name "BERYU SYSTEM PRO" (manufactured by Miryu Co., Ltd.)).

In addition, the solvent can be removed from the dispersion by using known solvent removal methods such as drying and filtration. From the viewpoint of removing the solvent quickly and efficiently, filtration such as vacuum filtration is used. It is preferable to

[[Molding of composition]]
The composition prepared as described above can be optionally defoamed and pulverized, and then pressurized to form a sheet. A sheet obtained by pressure-molding the composition in this manner can be used as a pre-heat conductive layer. 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 it 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 roll forming, and more preferably formed into a sheet by passing between rolls while 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 layer]]
In the pre-thermally conductive layer formed by pressurizing the composition and forming it into a sheet, the thermally conductive filler is arranged mainly in the in-plane direction, and the thermal conductivity in the in-plane direction of the pre-thermally conductive layer is particularly improved. Then it is inferred.

[(ii) Laminate forming step]
In the laminate forming step, a plurality of the pre-heat conductive layers obtained in the pre-heat conductive layer forming step are laminated in the thickness direction, or the pre-heat conductive layers are folded or wound, and the thermoplastic resin and the heat conductive layer are formed. Thus, a laminate is obtained in which a plurality of thermally conductive layers containing an elastic filler are formed in the thickness direction. Here, the formation of the laminate by folding the pre-heat conductive layer is not particularly limited, and can be performed by folding the pre-heat conductive layer in a constant width using a folding machine. Moreover, the formation of the laminate by winding the pre-heat conductive layer is not particularly limited. It can be carried out. Moreover, the formation of the laminate by laminating the pre-heat conductive layers is not particularly limited, and can be performed using a lamination 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.

Here, in the laminate obtained in the laminate forming step, the adhesive force between the surfaces of the pre-heat conductive layers is usually sufficient due to the pressure applied when laminating the pre-heat conductive layers and the pressure applied when folding or winding. obtained in

From the viewpoint of suppressing delamination, the obtained laminate is heated at 120° C. or more and 170° C. or less for 2 hours or more and 8 hours or less while being pressed in the lamination direction with a pressure of 0.1 MPa or more and 0.5 MPa or less. is preferred. Here, delamination may be prevented by applying an adhesive or a solvent to the pre-heat conductive layers to bond the pre-heat conductive layers together when forming the laminate. From the standpoint of practical preparation, it is preferred not to use adhesives or solvents.

In the laminate obtained by laminating, folding, or winding the pre-thermally conductive layers, it is presumed that the thermally conductive fillers are arranged in a direction substantially orthogonal to the lamination direction.

[(iii) Slicing step]
In the slicing step, the laminated body obtained in the laminated body forming step is sliced at an angle of 45° or less with respect to the lamination direction to obtain a heat conductive layer composed of sliced pieces of the laminated body. 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 layer 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.

Embodiments of blades that can be used as the blade portion will now be described.
A single blade having a blade portion may be a "double-edged" blade having cutting edges on both front and back sides, or may be a "single-edged" blade having a cutting edge only on the front side.

Also, the cross-sectional shape of the cutting edge is not particularly limited, and may be asymmetrical or symmetrical with respect to the central axis passing through the tip of the cutting edge.

The number of blades constituting the blade portion is not particularly limited, and for example, it may be composed of one blade consisting of one blade, or may be composed of two blades consisting of two blades. good.

Here, each of the two blades may be single-edged or double-edged.
Further, when one or both of the two blades are double-edged, the double-edged blades may be symmetrical or asymmetrical.
In addition, the two blades may be single-stepped blades or double-stepped blades.

The material of the blade is not particularly specified, and may be any of metal, ceramic, and plastic, but cemented carbide is particularly desirable from the standpoint of resistance to impact. The surface of the blade may be coated with silicone, fluorine, or the like for the purpose of improving slipperiness and cutting performance.

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).

From the viewpoint of slicing the laminate easily, the temperature of the laminate during slicing is preferably -20° C. or higher and 40° C. or lower, more preferably 10° C. or higher and 30° C. or lower. Furthermore, for the same reason, the laminate to be sliced is preferably sliced while applying pressure in the direction perpendicular to the lamination direction, and the pressure is 0.1 MPa or more and 0.5 MPa or less in the direction perpendicular to the lamination direction. Slicing while loading is more preferable. It is presumed that the particulate carbon material and the fibrous carbon material are arranged in the thickness direction in the heat conductive layer thus obtained. Therefore, the thermally conductive layer prepared through the above steps has not only thermal conductivity in the thickness direction but also electrical conductivity.

<Metal foil>
The thickness of the metal foil is not particularly limited as long as it is 0.1 μm or more and 1.5 μm or less. It is preferably 0.8 μm or less, more preferably 0.8 μm or less. If the thickness of the metal foil is 0.5 μm or more, reworkability can be further improved. In addition, if the thickness of the metal foil is 1.0 μm or less, it can follow the heat conductive layer more, and the decrease in heat conductivity can be reliably suppressed.
The thickness of the metal foil can be measured by the method described in Examples.

The material of the metal foil is not particularly limited as long as it is a metal, but gold, silver, copper, and aluminum are preferable, and silver is more preferable from the viewpoint of low cost and prevention of rust.

The surface roughness Ra of the metal foil is not particularly limited, but is preferably 0.005 μm or more, more preferably 0.01 μm or more, and preferably 0.2 μm or less, and preferably 0.2 μm or less. It is more preferably 1 μm or less. If the surface roughness Ra of the metal foil is 0.005 μm or more, it can easily follow the unevenness of the heat conductive layer. Further, even if the surface roughness Ra of the metal foil is 0.2 μm or less, it is possible to easily follow the unevenness of the heat conductive layer.
Here, the surface roughness Ra of the metal foil is based on JISB0601, for example, using a nanoscale hybrid microscope (VK-X250 manufactured by Keyence Corporation), for surface roughness, select a preferable range and calculate. can be done.

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, the film thickness of the thermally conductive layer and the metal foil, the surface roughness of the thermally conductive layer and the metal foil, the thermal resistance value of the thermally conductive sheet, and the reworkability of the thermally conductive sheet were measured or evaluated. gone. Here, these were measured or evaluated using the following methods, respectively.

<Thicknesses of Thermal Conductive Layer and Metal Foil>
The film thicknesses of the heat conductive layer and the metal foil were measured with a precision of (1/1000 mm) using a digimatic indicator (ID-C112X) manufactured by Mitutoyo Corporation. The measurement results are shown in Table 1. The values in Table 1 are the thicknesses of the heat conductive layer and the metal foil before forming the metal foil on the heat conductive layer (preparing the heat conductive sheet).

<Surface Roughness Ra of Thermal Conductive Layer and Metal Foil>
The surface roughness Ra of the heat conductive layer and the metal foil was measured using a laser microscope (Keyence Corporation, shape analysis laser microscope, VK-X250 series). Measured at a magnification of 20 times, arbitrarily selected 4 lines with a length of 200 μm, determined the surface roughness Ra with respect to the line roughness, and calculated the average. Table 1 shows the results.

<Thermal resistance value of thermal 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 is used as a sample, and the thermal resistance value (° C./W) when a relatively low pressure of 0.30 MPa is applied at a sample temperature of 50° C. and the sample Thermal resistance values (°C/W) were measured when a relatively high pressure of 0.80 MPa was applied at a temperature of 50°C. The smaller the thermal resistance value, the better the thermal conductivity of the thermally conductive sheet. Furthermore, evaluation was made according to the following evaluation criteria. Table 1 shows the results.
<<Evaluation Criteria>>
A: Less than 0.19 (°C/W) B: 0.19 (°C/W) or more and less than 0.25 (°C/W) C: 0.25 (°C/W) or more and 0.31 (°C/W) Less than D: 0.31 (° C./W) or more

<Evaluation of reworkability of thermal conductive sheet>
A heat conductive sheet is punched into a circle with a diameter of 2 cm, sandwiched between two aluminum plates with a thickness of 5 mm, pressed at 90 ° C. for 30 minutes at a pressure of 0.1 MPa, cooled, and then peeled off the aluminum plate. Reworkability was evaluated according to the following evaluation criteria. Table 1 shows the evaluation results.
In addition, when metal foil is formed on both sides of the heat conductive layer, reworkability is evaluated for both sides (upper side and lower side) of the heat conductive layer, and metal foil is formed on one side of the heat conductive layer. In each case, reworkability was evaluated for one side (upper side or lower side) of the heat conductive layer on which the metal foil was formed.
<<Evaluation Criteria>>
A: There is no transfer of the metal foil to the aluminum plate (transfer of the metal foil to the aluminum plate is 0% in area ratio (area ratio when the area of the metal foil is 100%)).
B: Transfer of the metal foil to the aluminum plate is more than 0% and less than 5% in area ratio (area ratio when the area of the metal foil is 100%).
C: Transfer of the metal foil to the aluminum plate is 5% or more in area ratio (area ratio when the area of the metal foil is 100%).

(Example 1)
<Preparation of readily dispersible aggregates of fibrous carbon nanostructures>
<<Preparation of dispersion>>
400 mg of fibrous carbon nanostructure (SGCNT, Nippon Zeon Co., Ltd., specific surface area: 600 m ² /g) was weighed out, mixed in 2 L of methyl ethyl ketone as a solvent, and stirred for 2 minutes with a homogenizer to obtain a crude dispersion. . Next, using a wet jet mill (manufactured by Joko Co., Ltd., product name “JN-20”), the obtained coarse dispersion is passed through a 0.5 mm channel of the wet jet mill at a pressure of 100 MPa for two cycles. to disperse fibrous carbon nanostructures in methyl ethyl ketone. Then, a dispersion having a solid concentration of 0.20% by mass was obtained.

<<Removal of solvent>>
Thereafter, the dispersion liquid obtained above was filtered under reduced pressure using Kiriyama filter paper (No. 5A) to obtain an easily dispersible aggregate of sheet-like fibrous carbon nanostructures as a fibrous carbon material. .

<Preparation of composition>
70 parts of a thermoplastic fluororesin that is liquid at normal temperature and pressure (manufactured by Daikin Industries, Ltd., trade name "DAIEL G-101"), and a thermoplastic fluororesin that is solid at normal temperature and pressure (manufactured by 3M Japan Co., Ltd., trade name) 30 parts of “Dynion FC-2211”, Mooney viscosity: 27ML ₁₊₄ , 100° C.), and expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., trade name “EC100”) as a particulate carbon material that is a thermally conductive filler. , Volume average particle size: 250 μm, long axis particle size 200 μm in electron microscope observation, uniaxial particle size 10 to 20 μm), and 50 parts of the fibrous carbon obtained above as a fibrous carbon material. 0.5 parts of easily dispersible aggregates of nanostructures were stirred and mixed at a temperature of 150° C. for 20 minutes using a pressure kneader (manufactured by Nihon Spindle). Next, the resulting mixture was put into a crusher and crushed for 10 seconds to obtain a composition.

<Molding of pre-heat conductive layer>
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 layer having a thickness of 0.5 mm.

<Formation of laminate>
Subsequently, the obtained pre-heat conductive layer was cut into a size of 150 mm long × 150 mm wide × 0.5 mm thick, and 120 sheets were laminated in the thickness direction of the pre-heat conductive layer. A laminate having a height of about 60 mm was obtained by pressing (secondary pressure) in the stacking direction for 1 minute.

<Molding of heat conductive layer>
After that, while pressing the laminated side surface of the laminated body obtained by secondary pressurization with a pressure of 0.3 MPa, a slicer for woodworking (manufactured by Marunaka Iron Works Co., Ltd., trade name "super finish planer Super Mecha S") ) at an angle of 0 degrees with respect to the stacking direction (in other words, in the direction normal to the main surface of the laminated pre-heat conductive layer) to obtain a 150 mm length×60 mm width×thickness of 0.5 mm. A thermally conductive layer of 15 mm (150 μm) was obtained.

<Lamination of Metal Foil and Thermal Conductive Layer>
Gold foil (thickness 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.) is attached to both sides of the heat conductive layer obtained above, and the bonded product is a release PET film (manufactured by Unitika Ltd., product name: “Emblet (registered trademark)", thickness 50 μm), and rubbed back and forth 10 times with a roller at a temperature of 50° C. to press the gold foil onto both sides of the heat conductive layer.

(Example 2)
In Example 1, the same procedure as in Example 1 was performed except that the gold foil (thickness: 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.) was replaced with copper foil (thickness: 0.4 μm, manufactured by Horikin Foil Powder Co., Ltd.). preparation of an easily dispersible aggregate of fibrous carbon nanostructures, preparation of a composition, formation of a pre-heat conductive layer, formation of a laminate, formation of a heat conductive layer, and bonding of a metal foil and a heat conductive layer. Lamination was performed.

(Example 3)
In Example 1, the same procedure as in Example 1 was performed except that the gold foil (thickness 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.) was replaced with aluminum foil (thickness 0.3 μm, manufactured by Horikinfaku Co., Ltd.). preparation of an easily dispersible aggregate of fibrous carbon nanostructures, preparation of a composition, formation of a pre-heat conductive layer, formation of a laminate, formation of a heat conductive layer, and bonding of a metal foil and a heat conductive layer. Lamination was performed.

(Example 4)
In Example 1, gold foil (thickness 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.) was replaced with silver foil (thickness 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.) on the upper side of the heat conductive layer, and below the heat conductive layer. Preparation of readily dispersible aggregates of fibrous carbon nanostructures and composition was prepared, the pre-heat conductive layer was formed, the laminate was formed, the heat conductive layer was formed, and the metal foil and the heat conductive layer were laminated.

(Example 5)
In Example 1, in the same manner as in Example 1, except that the gold foil (thickness 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.) was replaced with silver foil (thickness 0.5 μm, manufactured by Imai Gold Leaf Co., Ltd.). Preparation of easily dispersible aggregates of fibrous carbon nanostructures, preparation of compositions, formation of pre-thermal conductive layers, formation of laminates, formation of thermal conductive layers, and lamination of metal foils and thermal conductive layers gone.

(Example 6)
In Example 1, gold foil (thickness 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.) was replaced with silver foil (thickness 1 μm, manufactured by Imai Gold Leaf Co., Ltd.) for the upper side of the heat conductive layer, and for the lower side of the heat conductive layer Preparation of an easily dispersible aggregate of fibrous carbon nanostructures and preparation of a composition in the same manner as in Example 1, except that was replaced with silver foil (thickness: 0.5 μm, manufactured by Imai Kinpaku Co., Ltd.). , formation of a pre-heat conductive layer, formation of a laminate, formation of a heat conductive layer, and lamination of a metal foil and a heat conductive layer were performed.

(Example 7)
In Example 1, gold foil (thickness 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.) was replaced with silver foil (thickness 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.), and the film thickness of the heat conductive layer was changed from 150 μm to 300 μm. Except for the above, in the same manner as in Example 1, preparation of an easily dispersible aggregate of fibrous carbon nanostructures, preparation of a composition, formation of a pre-heat conductive layer, formation of a laminate, formation of a heat conductive layer Molding and lamination of the metal foil and the heat conductive layer were performed.

(Example 8)
In Example 1, in the same manner as in Example 1, except that the gold foil (thickness 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.) was replaced with silver foil (thickness 1.5 μm, manufactured by Imai Gold Leaf Co., Ltd.). Preparation of easily dispersible aggregates of fibrous carbon nanostructures, preparation of compositions, formation of pre-thermal conductive layers, formation of laminates, formation of thermal conductive layers, and lamination of metal foils and thermal conductive layers gone.

(Example 9)
In Example 1, instead of forming gold foil (thickness: 0.3 μm, manufactured by Imai Gold Leaf Co., Ltd.) on both sides of the thermally conductive layer, silver foil (thickness: 1.5 μm, manufactured by Imai Gold Leaf Co., Ltd.) is used for heat conduction. Preparation of readily dispersible aggregates of fibrous carbon nanostructures, preparation of composition, formation of pre-heat conducting layer, formation of pre-heat conductive layer, laminate was formed, the heat conductive layer was formed, and the metal foil and the heat conductive layer were laminated.

(Example 10)
In Example 7, expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., trade name “EC100”, volume average particle diameter: 250 μm, long axis direction in electron microscope observation) as a particulate carbon material that is a thermally conductive filler 50 parts of a particle diameter of 200 μm and a uniaxial particle diameter of 10 to 20 μm) and 0.5 parts of the readily dispersible aggregate of the fibrous carbon nanostructure obtained above as the fibrous carbon material are added. Instead, 150 parts of boron nitride particles (manufactured by Momentive Performance Materials Japan, trade name “PT-110”) were added, and the film thickness of the heat conductive layer was changed from 300 μm to 150 μm. In the same manner as in Example 7, preparation of the composition, formation of the pre-heat conductive layer, formation of the laminate, formation of the heat conductive layer, and lamination of the metal foil and the heat conductive layer were carried out.

(Comparative example 1)
In Example 1, the same procedure as in Example 1 was repeated except that the metal foil was not crimped to any surface of the heat conductive layer, to prepare an easily dispersible aggregate of fibrous carbon nanostructures, and to prepare a composition. Preparation, formation of the pre-thermally conductive layer, formation of the laminate, and formation of the thermally conductive layer were carried out.

(Comparative example 2)
Preparation of an easily dispersible aggregate of fibrous carbon nanostructures and preparation of a composition in the same manner as in Comparative Example 1, except that the film thickness of the heat conductive layer was changed from 150 μm to 300 μm. , formation of the pre-heat conductive layer, formation of the laminate, and formation of the heat conductive layer.

(Comparative Example 3)
In Example 9, "70 parts by mass of thermoplastic fluororesin (G-101) that is liquid at room temperature and pressure and 30 parts by mass of thermoplastic fluororesin (FC-2211) that is solid at room temperature and pressure" Changed to 60 parts by mass of liquid thermoplastic fluororesin (G-101) and 40 parts by mass of thermoplastic fluororesin (FC-2211) which is solid at normal temperature and pressure", silver foil (thickness 1.5 μm, Imai Kinfaku Co., Ltd. ) was replaced with aluminum foil (thickness 5.0 μm, manufactured by Horigane Foil Powder Co., Ltd.) in the same manner as in Example 9, to prepare an easily dispersible aggregate of fibrous carbon nanostructures. , preparation of the composition, formation of the pre-heat conductive layer, formation of the laminate, formation of the heat conductive layer, and lamination of the metal foil and the heat conductive layer.

(Comparative Example 4)
In Example 8, "70 parts by mass of thermoplastic fluororesin (G-101) that is liquid at room temperature and pressure and 30 parts by mass of thermoplastic fluororesin (FC-2211) that is solid at room temperature and pressure" Changed to 60 parts by mass of liquid thermoplastic fluororesin (G-101) and 40 parts by mass of thermoplastic fluororesin (FC-2211) which is solid at normal temperature and pressure", silver foil (thickness 1.5 μm, Imai Kinfaku Co., Ltd. ) was replaced with aluminum foil (thickness 5.0 μm, manufactured by Horigane Foil Powder Co., Ltd.) in the same manner as in Example 8, to prepare an easily dispersible aggregate of fibrous carbon nanostructures. , preparation of the composition, formation of the pre-heat conductive layer, formation of the laminate, formation of the heat conductive layer, and lamination of the metal foil and the heat conductive layer.

From Table 1, it can be seen that in Examples 1 to 10, as compared with Comparative Examples 1 to 4, excellent reworkability can be exhibited while maintaining thermal conductivity.

The heat conductive sheet of the present invention can be used, for example, in heat dissipating materials, heat dissipating parts, cooling parts, temperature control parts, electromagnetic wave shielding members, electromagnetic wave absorbing members, and objects used in various devices and devices. It is suitable as a thermocompression rubber sheet to be interposed between a compression product and a thermocompression bonding device.
Here, the various devices and devices are not particularly limited, but are electronic devices such as servers, server personal computers, and desktop personal computers; portable electronic devices such as notebook computers, electronic dictionaries, PDAs, mobile phones, and portable music players. Display devices such as liquid crystal displays (including backlights), plasma displays, LEDs, organic EL, inorganic EL, liquid crystal projectors, clocks; inkjet printers (ink heads), electrophotographic devices (developing device, fixing device, heat roller, image forming devices such as heat belts; semiconductor devices, semiconductor packages, semiconductor sealing cases, semiconductor die bonding, CPUs, memory, power transistors, power transistor cases and other semiconductor-related parts; rigid wiring boards, flexible wiring boards, ceramic wiring Wiring boards such as boards, build-up wiring boards, multilayer boards (printed wiring boards are also included in wiring boards); manufacturing equipment such as vacuum processing equipment, semiconductor manufacturing equipment, display equipment manufacturing equipment; heat insulating materials, vacuum heat insulating materials , heat insulation devices such as radiation heat insulating materials; DVDs (optical pickups, laser generators, laser receivers), data recording devices such as hard disk drives; image recording devices such as cameras, video cameras, digital cameras, digital video cameras, microscopes, CCDs, etc. devices; battery devices such as charging devices, lithium ion batteries, fuel cells; and the like.

1 thermal conductive layer 2 metal foil 3 metal foil 10 thermal conductive sheet 20 thermal conductive sheet

Claims (3)

A thermally conductive sheet having a thermally conductive layer containing a thermoplastic resin and a thermally conductive filler and metal foils formed on both sides of the thermally conductive layer,
A thermal conductive sheet, wherein each of the metal foils has a thickness of 0.1 μm or more and 1.5 μm or less. 2. The thermally conductive sheet according to claim 1, wherein said metal foil contains at least one selected from the group consisting of gold, silver, copper and aluminum. The thermally conductive sheet according to claim 1 or 2, wherein the thermally conductive layer has a surface roughness (Ra) of 1 µm or more and 15 µm or less.

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