Heat conductive sheet, laminate manufacturing method, and laminate

Abstract

To provide a heat conductive sheet which is excellent in followability at the time of hot press, and handling property.SOLUTION: A heat conductive sheet 20 has a first metal nanowire-containing layer 12, a support 14, and a second metal nanowire-containing layer 16 in this order, wherein the first metal nanowire-containing layer and the second metal nanowire-containing layer contain a metal nanowire and a binder resin, and the first metal nanowire-containing layer and the second metal nanowire-containing layer are B stages.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heat conductive sheet and a method for manufacturing a laminate using the heat conductive sheet. The present invention also relates to a laminate.

Background Art

[0002] In recent years, devices using semiconductor elements have been rapidly becoming more highly functional and miniaturized. Along with this, the amount of heat generated from the semiconductor elements in the devices has increased, and the need to release the generated heat to the outside has been growing. As a method for releasing the heat generated inside the device to the outside, a method of using a heat radiator (for example, a heat spreader, a heat sink, a heat diffusion sheet, etc.) is known. Further, in order to efficiently transfer heat to the heat radiating member, a method of adhering the heat source (heat generating body) of the device and the heat radiator with a heat conductive sheet is known.

[0003] As such a heat conductive sheet, for example, Patent Document 1 describes a heat conductive sheet formed using a heat conductive resin composition containing a deformable aggregate containing heat conductive particles and heat conductive fibers, a binder resin, and a solvent.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When adhering a heating element and a heat dissipating element, the heat conductive sheet described in Patent Document 1 is often adhered by hot pressing. When hot pressing is performed, it deforms according to the shape of the surface of each of the heating element and the heat dissipating element, and is required to adhere to each of the above surfaces. That is, the heat conductive sheet may be required to have followability during hot pressing. In addition, when adhering a heating element and a heat dissipating element, when handling the heat conductive sheet as described above, it is necessary to dispose the heat conductive sheet between the heating element and the heat dissipating element, and it is required to have high handleability of the heat conductive sheet. As a result of studying the heat conductive member described in Patent Document 1, the present inventors have found that there are cases where both followability and handleability during hot pressing cannot be achieved.

[0006] Therefore, an object of the present invention is to provide a heat conductive sheet excellent in followability and handleability during hot pressing. Another object of the present invention is to provide a method for manufacturing a laminate and a laminate.

Means for Solving the Problems

[0007] As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, it has been found that the above problems are solved by the following configuration.

[0008] 〔1〕 A heat conductive sheet having a first metal nanowire-containing layer, a support, and a second metal nanowire-containing layer in this order, The first metal nanowire-containing layer and the second metal nanowire-containing layer contain metal nanowires and a binder resin, The first metal nanowire-containing layer and the second metal nanowire-containing layer are heat conductive sheets that are in the B stage. 〔2〕 The heat conductive sheet according to 〔1〕, wherein the breaking strength of the support is 10 N / mm 2 or more. 〔3〕The heat-conductive sheet according to 〔1〕 or 〔2〕, wherein the metal contained in the metal nanowire is at least one metal selected from the group consisting of copper, silver, and aluminum. 〔4〕The heat-conductive sheet according to any one of 〔1〕 to 〔3〕, wherein in the first metal nanowire-containing layer, at least one of the following requirement 1 and requirement 2 is satisfied. Requirement 1: The metal nanowire is contained in an amount of 40 to 99% by volume. Requirement 2: The metal nanowire is contained in an amount of 70 to 99% by mass. 〔5〕The heat-conductive sheet according to any one of 〔1〕 to 〔4〕, wherein in the second metal nanowire-containing layer, at least one of the following requirement 3 and requirement 4 is satisfied. Requirement 3: The metal nanowire is contained in an amount of 40 to 99% by volume. Requirement 4: The metal nanowire is contained in an amount of 70 to 99% by mass. 〔6〕The heat-conductive sheet according to any one of 〔1〕 to 〔5〕, wherein the binder resin contains one or more resins selected from the group consisting of an epoxy resin, an acrylic resin, a urethane resin, a maleimide resin, an itaconimide resin, and a nadimide resin. 〔7〕The heat-conductive sheet according to any one of 〔1〕 to 〔6〕, wherein the thicknesses of the first metal nanowire-containing layer and the second metal nanowire-containing layer are each independently 5 to 200 μm. 〔8〕The heat-conductive sheet according to any one of 〔1〕 to 〔7〕, wherein the total thickness of the thickness of the first metal nanowire-containing layer and the thickness of the second metal nanowire-containing layer is 80 to 98% of the thickness of the heat-conductive sheet. 〔9〕The heat-conductive sheet according to any one of 〔1〕 to 〔8〕, wherein the support is a metal foil containing at least one metal selected from the group consisting of copper, silver, and aluminum. 〔10〕The heat-conductive sheet according to any one of 〔1〕 to 〔8〕, wherein the support is a C-stage sheet containing a metal nanowire containing at least one metal selected from the group consisting of copper, silver, and aluminum and a binder resin. 〔11〕The thermal conductivity of the cured product obtained by curing the above heat conductive sheet is 10 to 190 Wm -1 K -1 The heat conductive sheet according to any one of 〔1〕~〔10〕. 〔12〕A method for manufacturing a laminate, comprising laminating a heat radiator, the heat conductive sheet according to any one of 〔1〕~〔11〕, and a heat generating body in this order, and performing hot pressing to obtain a laminate. 〔13〕A laminate comprising a heat radiator, a cured product of the heat conductive sheet according to any one of 〔1〕~〔11〕, and a heat generating body in this order.

Advantages of the Invention

[0009] According to the present invention, a heat conductive sheet excellent in followability during hot pressing and handleability can be provided. Further, according to the present invention, a method for manufacturing a laminate and a laminate can also be provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0012] Hereinafter, the meaning of each description in this specification will be represented. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. Also, in this specification, "(meth)acryl" is a notation representing "acryl" or "methacryl".

[0013] [Thermal Conductive Sheet] The thermal conductive sheet of the present invention is a thermal conductive sheet having a first metal nanowire-containing layer, a support, and a second metal nanowire-containing layer in this order. The first metal nanowire-containing layer and the second metal nanowire-containing layer contain metal nanowires and a binder resin. Also, the first metal nanowire-containing layer and the second metal nanowire-containing layer are in the B-stage. The thermal conductive sheet of the present invention will be described with reference to the drawings.

[0014] FIG. 1 is a schematic cross-sectional view showing one aspect of the thermal conductive sheet of the present invention. The thermal conductive sheet 20 of the present invention has a first metal nanowire-containing layer 12, a support 14, and a second metal nanowire-containing layer 16 in this order. The first metal nanowire-containing layer 12 and the second metal nanowire-containing layer 16 contain metal nanowires and a binder resin and are in the B-stage. The first metal nanowire-containing layer 12 is arranged in contact with either the heat radiator or the heat generator during hot pressing, and the second metal nanowire-containing layer 16 is arranged in contact with the other of the heat radiator and the heat generator during hot pressing. When the thermal conductive sheet 20 of the present invention is hot pressed, a thermal conductive member is formed. Also, in the aspect shown in FIG. 1, the support 14 is a copper foil.

[0015] Although the mechanism by which the heat conduction sheet 20 of the present invention is excellent in followability during hot pressing and excellent in handleability is not necessarily clear, the present inventors presume as follows. Since the first metal nanowire-containing layer 12 and the second metal nanowire-containing layer 16 of the heat conduction sheet 20 of the present invention are in the B-stage, fluidity is exhibited by the heat during hot pressing. Therefore, it is considered to be excellent in followability during hot pressing. In addition, since the heat conduction sheet 20 of the present invention has the support 14 between the first metal nanowire-containing layer 12 and the second metal nanowire-containing layer 16, both the first metal nanowire-containing layer 12 and the second metal nanowire-containing layer 16 can be supported, and thus it is considered to be excellent in handleability. Therefore, the heat conduction sheet 20 of the present invention is considered to be excellent in followability during hot pressing and excellent in handleability.

[0016] Hereinafter, the heat conduction sheet of the present invention will be described in detail. Note that the heat conduction sheet of the present invention is not limited to the embodiment shown in FIG. 1, and may be a modified example with various modifications. For example, in the heat conduction sheet of the present invention, the first metal nanowire-containing layer, the support, and the second metal nanowire-containing layer may be modified to the embodiments described in detail later.

[0017] 〔First metal nanowire-containing layer〕 The heat conduction sheet of the present invention has a first metal nanowire-containing layer. The first metal nanowire-containing layer contains metal nanowires and a binder resin. When the first metal nanowire-containing layer contains metal nanowires, the layer formed by the first metal nanowire-containing layer is excellent in thermal conductivity. In addition, the first metal nanowire-containing layer is in the B-stage. Hereinafter, the first metal nanowire-containing layer and its components will be described in detail.

[0018] (Physical properties of the first metal nanowire-containing layer) The first metal nanowire-containing layer is in the B-stage. Generally, the states of thermosetting compounds include the A stage, the B stage, and the C stage. For each stage, refer to the provisions of JIS K6900:1994. In this specification, the A stage refers to a state that is soluble in a specific solvent and fusible, and the B stage refers to a state where its viscosity is 10 4 Pa·s to 10 5 Pa·s at room temperature (25 °C), while the viscosity decreases to 10 2 Pa·s to 10 3 Pa·s at 100 °C, and the C stage refers to a state that does not melt even when heated. The above viscosity is measured by dynamic viscoelasticity measurement (frequency 1 Hz, load 40 g, heating rate 3 °C / min).

[0019] The thickness of the first metal nanowire-containing layer is preferably 5 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. The thickness of the first metal nanowire-containing layer is preferably 200 μm or less, and more preferably 150 μm or less.

[0020] (Metal nanowire) The first metal nanowire-containing layer contains metal nanowires. Metal nanowires refer to those with a metal material, a needle-like or thread-like shape, and a diameter in the nanometer size range. The metal nanowires may be linear or curved. Having a diameter in the nanometer size range means that the diameter of the metal nanowires described later is 1000 nm or less.

[0021] The specific surface area per unit mass of the above metal nanowires is preferably 100 to 50000 m 2 / kg, more preferably more than 100 m 2 / kg and 50000 m 2 / kg or less, even more preferably more than 1000 m 2 / kg and 50000 m 2 / kg or less, particularly preferably more than 2000 m 2 / kg and 30000 m 2 / kg or less, and particularly preferably 3000 m2 / kg over 20,000 m 2 Below / kg is most preferred. Here, the specific surface area per unit mass of the above metal nanowire can be measured by known analytical methods for the obtained specific surface area of the metal nanowire, but in the present invention, the measured value by the krypton gas adsorption method is adopted.

[0022] In the present invention, the metal constituting the above metal nanowire is not particularly limited, but it is preferably a material having an electrical resistivity of 10 -4 Ω·cm or less. Specific examples thereof preferably include gold (Au), silver (Ag), copper (Cu), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), etc. Among these, due to the particularly high thermal conductivity, the metal constituting the metal nanowire is preferably at least one metal selected from the group consisting of Cu, Ag, and Al, and more preferably Cu.

[0023] The diameter (additive average value) of the metal nanowire is preferably 10 to 200 nm, more preferably 10 to 100 nm, and even more preferably 10 to 50 nm. The length (additive average value) of the metal nanowire is preferably 0.3 to 300 μm, more preferably 0.5 to 200 μm, and even more preferably 1 μm to 100 μm. Here, the diameter and length of the above metal nanowire can be obtained, for example, by observing at a magnification of 100 to 500 times using a field emission-scanning electron microscope (FE-SEM). Specifically, the diameter and length of the metal nanowire refer to the additive average value of the measured length values of the diameters and lengths of 100 metal nanowires. More specifically, from the observation image at the above magnification, the operation of observing the diameters and lengths by measuring 10 randomly selected metal nanowires is performed in 10 fields of view, and the additive average values of the diameters and lengths of a total of 100 metal nanowires are calculated.

[0024] The ratio of the length to the diameter of the above metal nanowire (length / diameter) (hereinafter, also referred to as "aspect ratio") is preferably 10 or more, more preferably 100 to 1000.

[0025] The first metal nanowire-containing layer preferably satisfies at least one of the following requirement 1 and requirement 2. Requirement 1: It contains 40 to 99% by volume of metal nanowires. Requirement 2: It contains 70 to 99% by mass of metal nanowires. The above requirement 1 means that the metal nanowires are contained in an amount of 40 to 99% by volume with respect to the total volume of the first metal nanowire-containing layer. The content of the metal nanowires is more preferably 45 to 90% by volume, and even more preferably 50 to 80% by volume with respect to the total volume of the first metal nanowire-containing layer. Also, from the reason that the adhesion to the heat dissipation member becomes better, it is preferable that the metal nanowires are contained in an amount of more than 50% by volume and 99% by volume or less. Also, the above requirement 2 means that the metal nanowires are contained in an amount of 70 to 99% by mass with respect to the total mass of the first metal nanowire-containing layer. The content of the metal nanowires is more preferably 75 to 99% by mass, and even more preferably 80 to 98% by mass with respect to the total mass of the first metal nanowire-containing layer.

[0026] The method for producing the metal nanowires will be described in detail later.

[0027] (Binder resin) The first metal nanowire-containing layer contains a binder resin. The binder resin fills the voids between the metal nanowires contained in the first metal nanowire-containing layer. The binder resin is not particularly limited as long as the first metal nanowire-containing layer is in the B-stage, but a thermosetting resin is preferable. The binder resin preferably contains at least one resin selected from the group consisting of epoxy resins, acrylic resins, urethane resins, maleimide resins, itaconimide resins, and nadimide resins. Among the above resins, in the heat conductive member to be formed, crosslinked resins are preferred and epoxy resins are more preferred from the viewpoint of improving the strength by crosslinking of the resin.

[0028] Specific examples of the epoxy resin include, for example, epoxy resins having a naphthalene skeleton, bisphenol A type epoxy resins, bisphenol F type epoxy resins, phenol novolac type epoxy resins, alicyclic epoxy resins, siloxane type epoxy resins, biphenyl type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, hydantoin type epoxy resins, etc. These may be used alone or in combination of two or more. In particular, from the viewpoint of the moldability of the film, the epoxy resin is preferably an epoxy resin having a naphthalene skeleton, a bisphenol A type epoxy resin, or a bisphenol F type epoxy resin and is liquid at room temperature.

[0029] The binder resin may contain resins other than the above. Examples of the resins other than the above include water-soluble polymers and oil-soluble polymers. Here, "water-soluble" in the water-soluble polymer means that the dissolution amount of the target substance with respect to 100% by mass of water at 25°C is 5% by mass or more, and a more suitable water-soluble polymer means that the dissolution amount is 10% by mass or more. Also, "oil-soluble" in the oil-soluble polymer means that the dissolution amount of the target substance with respect to 100% by mass of water at 25°C is less than 5% by mass.

[0030] Examples of the water-soluble polymer include polyvinyl alcohol (unmodified polyvinyl alcohol and modified polyvinyl alcohol), polyacrylamide and its derivatives, ethylene-vinyl acetate copolymer, styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, polyvinylpyrrolidone, ethylene-acrylic acid copolymer, vinyl acetate-acrylic acid copolymer, carboxymethyl cellulose, methyl cellulose, casein, gelatin, starch derivative, gum arabic, and sodium alginate.

[0031] Examples of the oil-soluble polymer include, for example, a (meth)acrylic acid ester polymer having an alkyl group having 12 to 30 carbon atoms in the side chain described in paragraphs

[0009] to

[0051] of International Publication No. 2018 / 207387, a polymer having heat storage properties described in JP-A-2007-031610, and an olefin copolymer described in paragraphs

[0019] to

[0021] of International Publication No. 2018 / 066605, and these descriptions are incorporated herein. In particular, an olefin copolymer having 3 to 8 carbon atoms is preferable, and an ethylene copolymer with an olefin having 3 to 8 carbon atoms is more preferable.

[0032] Among the above-described water-soluble polymer and oil-soluble polymer, the water-soluble polymer is preferable, polyol is more preferable, polyvinyl alcohol is still more preferable, and modified polyvinyl alcohol is particularly preferable.

[0033] Among polyvinyl alcohols, unmodified polyvinyl alcohol is obtained, for example, by substituting at least a part of the acetate groups of polyvinyl acetate with hydroxyl groups by a saponification reaction. The polyvinyl alcohol may be polyvinyl alcohol in which only a part of the acetate groups of polyvinyl acetate is substituted with hydroxyl groups (partially saponified polyvinyl alcohol), or polyvinyl alcohol in which all of the acetate groups of polyvinyl acetate are substituted with hydroxyl groups (fully saponified polyvinyl alcohol). Modified polyvinyl alcohol means polyvinyl alcohol having a modifying group. The modifying group is preferably at least one group selected from the group consisting of a carboxy group or a salt thereof, and an acetoacetyl group, and more preferably at least one group selected from the group consisting of a carboxy group or a salt thereof, and an acetoacetyl group. As the salt of the carboxy group, a metal salt of the carboxy group is preferable, and a sodium salt of the carboxy group is more preferable. The modified polyvinyl alcohol can be obtained, for example, by saponifying a polymer obtained by copolymerizing a monomer having a modifying group and a vinyl ester (for example, vinyl acetate, etc.). Further, the modified polyvinyl alcohol may be obtained by reacting a hydroxyl group or an acetic acid group in unmodified polyvinyl alcohol with a compound having a modifying group. Examples of polyvinyl alcohol include Kuraray Poval series (e.g., Kuraray Poval PVA-217E, Kuraray Poval KL-318, etc.) manufactured by Kuraray Co., Ltd., Gosenex series (e.g., Gosenex Z-320, etc.) manufactured by Mitsubishi Chemical Corporation, and A series (e.g., AP-17, etc.) manufactured by Nippon Vinyl Acetate Poval Co., Ltd. The degree of polymerization of polyvinyl alcohol is preferably 500 to 5000, more preferably 1000 to 3000, and even more preferably 2000 to 3000.

[0034] The number average molecular weight (Mn) of the above-mentioned water-soluble polymer and oil-soluble polymer is not particularly limited, but from the viewpoint of film strength, it is preferably 20,000 to 300,000, and more preferably 20,000 to 150,000. The measurement of the molecular weight is a value measured by gel permeation chromatography (GPC). The measurement by gel permeation chromatography (GPC) is carried out using HLC (registered trademark)-8020GPC (Tosoh Corporation) as the measuring device, three TSKgel (registered trademark) Super Multipore HZ-H (4.6 mm ID × 15 cm, Tosoh Corporation) columns, and THF (tetrahydrofuran) as the eluent. The measurement conditions are as follows: the sample concentration is 0.45 mass%, the flow rate is 0.35 mL / min, the sample injection volume is 10 μL, and the measurement temperature is 40°C. The measurement is performed using an RI (differential refractive index) detector. The calibration curve is prepared from eight samples of "Standard Sample TSK standard, polystyrene" of Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

[0035] The content of the binder resin is preferably 1 to 50 parts by mass, more preferably 2 to 30 parts by mass, based on 100 parts by mass of the metal nanowire.

[0036] (Other components) The first metal nanowire-containing layer may contain other components other than those described above. For example, when the binder resin contains an epoxy resin, the first metal nanowire-containing layer preferably contains an epoxy resin curing agent. Examples of the epoxy resin curing agent include catalysts that promote the curing reaction of the epoxy resin.

[0037] As the epoxy resin curing agent, for example, imidazole-based, phenol-based, amine-based, acid anhydride-based, organic peroxide-based, etc. can be used. The epoxy resin curing agent may be a high molecular compound. In particular, from the viewpoint of the storage stability (life) of the composition of the present invention at room temperature, a curing agent having latency is preferable, and an imidazole-based curing agent encapsulated and having latency is more preferable. By having good storage stability at room temperature, the management in the supply and use of the heat conductive sheet of the present invention can be made simpler. Specifically, as the epoxy resin curing agent, a microcapsule type latent curing agent obtained by using a latent imidazole modified body as a core and coating its surface with polyurethane can be used. As a commercially available product, for example, Novacure 3941 (manufactured by Asahi Kasei E-Materials Co., Ltd.) can be used. The epoxy resin curing agent may be used alone or in combination of two or more.

[0038] When containing the first metal nanowire-containing layer, epoxy resin and epoxy resin curing agent, the total of these contents is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10 to 20% by mass with respect to the total mass of the first metal nanowire-containing layer.

[0039] The first metal nanowire-containing layer may contain an elastomer as another component. Examples of the elastomer include acrylic rubber (for example, a copolymer of (meth)acrylate and acrylonitrile, etc.), SB (polystyrene-polybutadiene), SBS (polystyrene-polybutadiene-polystyrene), SIS (polystyrene-polyisoprene-polystyrene), SEBS (polystyrene-polyethylene / polybutylene-polystyrene), ABS (acrylonitrile butadiene styrene copolymer), ACM (acrylate rubber), ACS (acrylonitrile chlorinated polyethylene styrene copolymer), acrylonitrile styrene copolymer, syndiotactic 1,2-polybutadiene, polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate, and the like. When the heat conductive member of the present invention contains an elastomer, the content of the elastomer is not particularly limited, but is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the metal nanowire.

[0040] The first metal nanowire-containing layer may contain a coupling agent as another component. Examples of the coupling agent preferably include silane coupling agents such as γ-ureidopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, 3-phenylaminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltrimethoxysilane. These may be used alone or in combination of two or more. When the first metal nanowire-containing layer contains a coupling agent, the content of the coupling agent is not particularly limited, but is preferably 0.01 to 0.2 parts by mass, more preferably 0.015 to 0.15 parts by mass with respect to 100 parts by mass of the metal nanowire.

[0041] The first metal nanowire-containing layer may contain a curing accelerator as another component. The curing accelerator is a component different from the above epoxy resin curing agent. Examples of the curing accelerator include imidazoles and their derivatives, organic phosphorus compounds, secondary amines, tertiary amines, quaternary ammonium salts, and the like. These may be used alone or in combination of two or more. Among these, imidazoles and their derivatives are preferable from the viewpoint of reactivity. Examples of the imidazoles include 2-methylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, and the like. These may be used alone or in combination of two or more. When the heat conductive member of the present invention contains a curing accelerator, the content of the curing accelerator is not particularly limited, but is preferably 0.001 to 0.1 part by mass, more preferably 0.005 to 0.05 part by mass, based on 100 parts by mass of the metal nanowire.

[0042] The first metal nanowire-containing layer may contain metal particles as other components. The metal particles are a component different from the metal nanowires. The metal particles preferably contain at least one metal selected from the group consisting of gold, silver, copper, aluminum, nickel, zinc, and cobalt. Also, the metal particles may contain one or more conductive components other than metals.

[0043] The shape of the metal particles is not particularly limited, and may be either solid or hollow. Also, the average major axis of the minimum circumscribing ellipsoid of the metal particles is preferably 0.01 to 50 μm, more preferably 0.1 to 20 μm. Also, the average major axis of the minimum circumscribing ellipsoid of the metal particles is preferably more than 1 times and less than 10 times the average minor axis for the reason of selecting a shape that efficiently fills the space. Here, the minimum circumscribing ellipsoid refers to the ellipsoid with the minimum volume among the ellipsoids that contain the metal particles inside, and includes an ellipsoid (i.e., a sphere) in which the major axis and the minor axis coincide. Also, the average major axis of the minimum circumscribing ellipsoid can be obtained by observing a cross-section in the thickness direction of the layer formed using the dispersion liquid with a microscope (for example, an electron microscope), measuring the major axes of 100 arbitrary fine particles, and calculating their average. Similarly, the average minor axis of the minimum circumscribing ellipsoid can be obtained by observing a cross-section in the thickness direction of the layer formed using the dispersion liquid with a microscope (for example, an electron microscope), measuring the minor axes of 100 arbitrary fine particles, and calculating their average. Furthermore, the median diameter (D50) described later refers to the median diameter of the diameter when the volume of the metal particles is approximated as a sphere, and can be obtained by the laser diffraction / scattering method or the dynamic light scattering method.

[0044] When the first metal nanowire-containing layer contains metal particles, the content of the metal particles is not particularly limited, but is preferably 1 to 30 parts by mass, more preferably 2 to 20 parts by mass, based on 100 parts by mass of the metal nanowires.

[0045] 〔Support〕 The heat conductive sheet of the present invention has a support. The support is not particularly limited as long as it can support the first metal nanowire-containing layer and the second metal nanowire-containing layer. As the support, for example, a support having a breaking strength of 10 N / mm 2 or more is preferably mentioned. The above breaking strength is more preferably 20 N / mm 2 or more. The upper limit of the above breaking strength is not particularly limited, but for example, 500 N / mm 2 or less can be mentioned, and it is often 300 N / mm 2 or less. The Young's modulus of the support is preferably 0.1 to 200 GPa, more preferably 0.5 to 150 GPa, and even more preferably 0.5 to 130 GPa. The above breaking strength is determined by a tensile test. Specifically, when the support is a metal material, a tensile test is performed based on the test method described in JIS Z 2241. As the test piece, the test piece specified in the above standard is used. The tensile test can be carried out with a universal testing machine. When the support is a resin material, a tensile test is performed based on the test method described in JIS K 7161-1. Furthermore, in the case of a support having pores, a test piece described in the above test method is prepared using the support having pores, and a tensile test is performed.

[0046] As the support as described above, for example, a resin film and a metal foil are preferably mentioned, and a metal foil is preferred. Examples of the resin film include conventionally known resin films, such as polyester films, polyimide films, polyamide films, and polyolefin films. The thickness of the resin film is preferably 5 μm or more, more preferably 10 μm or more. Also, the thickness of the resin film is preferably 200 μm or less, more preferably 100 μm or less. Examples of the metal foil include conventionally known metal foils, such as metal foils containing at least one metal selected from the group consisting of iron, nickel, copper, zinc, silver, and aluminum, and metal foils containing at least one metal selected from the group consisting of copper, silver, and aluminum are preferred. The thickness of the metal foil is preferably 5 μm or more, more preferably 10 μm or more. Also, the thickness of the metal foil is preferably 200 μm or less, more preferably 100 μm or less.

[0047] The support is often sheet-shaped, but may have holes in part or all of it. That is, the support may be a punching sheet or a mesh sheet. For example, when the support is a resin film, if the support has holes, the first metal nanowire-containing layer and the second metal nanowire-containing layer are likely to come into direct contact to form a heat conduction path, which is preferable. Note that in terms of excellent handleability, it is also preferable that the support does not have holes.

[0048] The above support may be a C-stage sheet. Specifically, it may be a C-stage sheet containing metal wires (preferably metal nanowires) and a binder resin. For example, it may be a C-stage sheet containing metal nanowires containing at least one metal selected from the group consisting of copper, silver, and aluminum and a binder resin. The preferred embodiments of the metal nanowires and the binder resin contained in the above C-stage sheet are the same as those of the above first metal nanowire-containing layer. Also, the above C-stage sheet may contain other components described in the first metal nanowire-containing layer and components derived from the above other components. The thickness of the C-stage sheet is preferably 5 μm or more, more preferably 10 μm or more. Also, the thickness of the C-stage sheet is preferably 200 μm or less, more preferably 100 μm or less.

[0049] From the viewpoint of the thermal conductivity of the formed heat-conductive member, the support is preferably a metal foil or the above C-stage sheet.

[0050] 〔Second metal nanowire-containing layer〕 The heat-conductive sheet of the present invention has a second metal nanowire-containing layer. Regarding the second metal nanowire-containing layer, since it is the same as the first metal nanowire-containing layer including its preferred embodiments, the description thereof is omitted. Note that the thickness of the first metal nanowire-containing layer and the thickness of the second metal nanowire-containing layer may be the same or different.

[0051] The second metal nanowire-containing layer preferably satisfies at least one of the following requirement 3 and requirement 4. Requirement 3: Contains 40 to 99% by volume of metal nanowires. Requirement 4: Contains 70 to 99% by mass of metal nanowires. The above requirement 3 means that metal nanowires are contained in an amount of 40 to 99% by volume based on the total volume of the second metal nanowire-containing layer. The content of the metal nanowires is more preferably 45 to 90% by volume, and even more preferably 50 to 80% by volume, based on the total volume of the second metal nanowire-containing layer. Also, for better adhesion to the heat dissipation member, it is preferable that the metal nanowires are contained in an amount exceeding 50% by volume and not exceeding 99% by volume. Also, the above requirement 4 means that metal nanowires are contained in an amount of 70 to 99% by mass based on the total mass of the second metal nanowire-containing layer. The content of the metal nanowires is more preferably 75 to 99% by mass, and even more preferably 80 to 98% by mass, based on the total mass of the second metal nanowire-containing layer.

[0052] Furthermore, the total thickness of the first metal nanowire-containing layer and the second metal nanowire-containing layer is preferably 10.0% or more, more preferably 50.0% or more, still more preferably 65.0% or more, and particularly preferably 80.0% or more with respect to the thickness of the heat conduction sheet in terms of excellent followability during hot pressing. Also, the total thickness of the first metal nanowire-containing layer and the second metal nanowire-containing layer is preferably 99.0% or less, more preferably 98.0% or less with respect to the thickness of the heat conduction sheet in terms of excellent handleability.

[0053] 〔Protective Film〕 The heat conduction sheet of the present invention may have a protective film on at least one of the surface on the side opposite to the support side of the first metal nanowire-containing layer and the surface on the side opposite to the support side of the second metal nanowire-containing layer. When the heat conduction sheet has a protective film, the heat conduction sheet can be stored without being adhered to each other or to other members. The material of the protective film is not particularly limited, and a resin film is preferably mentioned.

[0054] 〔Shape and Properties of Heat Conduction Sheet, etc.〕 The thickness of the heat conduction sheet is preferably 10 μm or more, more preferably 30 μm or more. The thickness of the heat conduction sheet is preferably 500 μm or less, more preferably 400 μm or less, still more preferably 300 μm or less, and particularly preferably 200 μm or less.

[0055] The shape of the heat conduction sheet in the planar direction is not particularly limited, and it may be, for example, square, circular, or a shape along the shapes of the heat dissipating body and the heat generating body.

[0056] The thermal conductivity of the cured product obtained by curing the heat conduction sheet is preferably 5 Wm -1 K -1 or more, more preferably 10 Wm -1 K -1 or more. The thermal conductivity of the above-mentioned cured product is often 190 Wm -1 K -1 or less. In the present invention, the thermal conductivity of the cured product is a value measured using ai-Phase Mobile M3 (manufactured by Ai Phase Co., Ltd.).

[0057] 〔Method for manufacturing thermal conductive sheet〕 The method for manufacturing the thermal conductive sheet of the present invention is not particularly limited as long as the thermal conductive sheet of the present invention can be obtained. For example, a method may be mentioned in which a support is prepared, a coating solution containing metal nanowires and a binder resin is prepared, a first metal nanowire-containing layer is formed on one surface of the support, and a second metal nanowire-containing layer is formed on the other surface of the support. The formation of the first metal nanowire-containing layer and the second metal nanowire-containing layer may be carried out sequentially or simultaneously. Hereinafter, an example of the method for manufacturing the thermal conductive sheet will be described, but the method for manufacturing the thermal conductive sheet of the present invention is not limited to the following method.

[0058] As an example of the method for manufacturing the thermal conductive sheet, a roll-to-roll method will be described. Examples of the method for manufacturing the thermal conductive sheet include a manufacturing method having a coating solution preparation step of preparing a coating solution containing metal nanowires and a binder resin, a coating film formation step of supplying the coating solution onto a temporary support to form a coating film, and a transfer step of transferring the coating film onto a support. The above manufacturing method will be described below.

[0059] First, in the coating solution preparation step, a coating solution containing metal nanowires and a binder resin is prepared. The metal nanowires contained in the above coating solution are as described above. The method for producing the metal nanowires is not particularly limited, but the method described in detail later is preferred. The binder resin contained in the above coating solution is as described above.

[0060] The above coating solution may contain an organic solvent. Examples of the organic solvent contained in the coating liquid include aromatic hydrocarbons such as toluene, xylene, mesitylene, cumene, and p - cymene; aliphatic hydrocarbons such as hexane and heptane; cyclic alkanes such as methylcyclohexane; cyclic ethers such as tetrahydrofuran and 1,4 - dioxane; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and 4 - hydroxy - 4 - methyl - 2 - pentanone; esters such as methyl acetate, ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, γ - butyrolactone, butyl carbitol acetate, and ethyl carbitol acetate; carbonic esters such as ethylene carbonate and propylene carbonate; amides such as N,N - dimethylformamide, N,N - dimethylacetamide, and N - methyl - 2 - pyrrolidone; alcohols such as butyl carbitol and ethyl carbitol. These may be used alone or in combination of two or more.

[0061] The method for preparing the coating liquid is not particularly limited, and the above components may be mixed.

[0062] Next, in the coating film forming step, the above coating liquid is supplied onto a temporary support to form a coating film. The temporary support onto which the above coating liquid is supplied is not particularly limited. Examples of its material include polyethylene terephthalate, polytetrafluoroethylene, polyimide, PEEK (polyether ether ketone), aluminum, glass, alumina, silicon nitride, and stainless steel. In addition, a material obtained by coating or impregnating the above material on a cloth may be used as the temporary support. Further, the above temporary support can be peeled off after the transfer step described later.

[0063] Examples of the method for supplying the above coating liquid onto a temporary support include inkjet printing, screen printing, jet printing method, dispenser, jet dispenser, comma coater, slit coater, die coater, gravure coater, slit coat, relief printing, intaglio printing, gravure printing, stencil printing, bar coater, applicator, spray coater, electrodeposition coating, etc.

[0064] In the above coating film forming step, there may be a step of drying the coating liquid supplied onto the temporary support. Note that by drying the coating liquid, it can be separated from the temporary support as a self-supporting sheet. As the above drying method, drying by leaving at room temperature, heat drying, or reduced-pressure drying can be used. For heat drying or reduced-pressure drying, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, a hot plate pressing device, etc. can be used. The drying temperature and time are preferably adjusted appropriately according to the type and amount of the dispersion medium used. For example, it is preferable to dry at 50 to 300 °C for 1 to 180 minutes. Also, from the viewpoint of suppressing the oxidation of the metal contained in the coating film, it may be dried in an inert atmosphere or a reducing atmosphere. Examples of the inert atmosphere include an atmosphere containing gases such as argon, nitrogen, and water vapor. Examples of the reducing atmosphere include an atmosphere containing hydrogen and formic acid.

[0065] In the transfer step, the coating film is transferred onto the support. The transfer method is not particularly limited. For example, a method of bringing the coating film into contact with the support can be mentioned. More specifically, a method of pressing the coating film against the support with pressure is preferable. For example, vacuum pressing, roller pressing, etc. can be mentioned. After bringing the coating film into contact with the support, it is peeled between the coating film and the temporary support, and the coating film is transferred onto the support to form it. The transfer of the above coating film may be such that after transferring the coating film onto one surface of the support, it is transferred onto the other surface of the support, or the coating film may be brought into contact with both surfaces of the support, the coating film may be formed on both surfaces of the support, and the temporary support may be peeled off. Note that each of the above coating films corresponds to a first metal nanowire-containing layer or a second metal nanowire-containing layer.

[0066] As another example of the method for manufacturing a heat conductive sheet, there is a manufacturing method including a coating liquid preparation step of preparing a coating liquid containing metal nanowires and a binder resin, and a coating film formation step of supplying the coating liquid onto a support to form a coating film. That is, a method of directly supplying the coating liquid onto the support to form a coating film may be used. When forming a coating film on the support, it is preferable to have a step of drying the coating liquid. Examples of the drying method include those described above. Also, when directly forming a coating film on the support, the coating film may be formed sequentially one side at a time, or the coating film may be formed on both sides simultaneously. Each of the above coating films corresponds to a first metal nanowire-containing layer or a second metal nanowire-containing layer.

[0067] Also, the method for manufacturing the heat conductive sheet may not be a roll-to-roll method. For example, a coating film may be formed on a temporary support, and the formed coating film may be transferred onto the support by a flat press or the like. Alternatively, the coating liquid may be supplied to one surface of the support to form a coating film, and the coating liquid may be supplied to the other surface of the support to form a coating film. More specifically, first, the support is placed in a container, the coating liquid is supplied to one surface of the support, and a coating film is formed by the above method. Next, the support with the coating film is taken out of the container, and the support is placed in the container so that the surface on which the coating film is not formed becomes the upper surface. Then, the coating liquid is supplied to the other surface of the support, and a coating film is formed by the above method. The container used in the above procedure is preferably made of a heat-resistant material in terms of being able to perform heat drying in the formation of the coating film. Examples of the heat-resistant material include glass, silicone resin, and polyimide resin.

[0068] 〔Method for Producing Metal Nanowires〕 Hereinafter, a preferable method for obtaining the above metal nanowires will be described. The manufacturing method of the metal nanowires included in the heat conductive member of the present invention has a specific surface area per unit mass of 100 to 50000 m 2Since it becomes easy to adjust to / kg, an anodizing step of forming a porous anodized film on the surface of the valve metal substrate, a metal filling step of filling the pores with metal, an isolation step of isolating the filled metal from the anodized film and the valve metal substrate, and a crushing step of crushing the isolated metal (hereinafter also abbreviated as "isolated metal") to obtain metal nanowires is preferable.

[0069] Next, after explaining the outline of each step in the method for manufacturing metal nanowires using FIGS. 2 to 6, each processing step will be described in detail.

[0070] As shown in FIGS. 2 and 3, in the anodizing step, an anodizing treatment is performed on the surface of the valve metal substrate 1, and an anodized film 3 having pores (micropores) 2 is formed on the surface of the valve metal substrate 1. Next, as shown in FIG. 4, in the metal filling step, the pores 2 are filled with metal 4. Next, as shown in FIG. 5, in the isolation step, the filled metal 4 is isolated from the anodized film 3 and the valve metal substrate 1. Note that the aspect shown in FIG. 5 shows a state in which the isolated metal 5 obtained by the isolation step is recovered (a state in which a part of the isolated metal is adhered). Next, as shown in FIG. 6, in the crushing step, metal nanowires 10 obtained by crushing the isolated metal 5 can be obtained.

[0071] (Valve metal substrate) The valve metal substrate used in the method for manufacturing metal nanowires is not particularly limited as long as it is a substrate containing a valve metal. Here, specific examples of the valve metal include, for example, aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Among these, aluminum is preferable as the valve metal because of its good dimensional stability and relatively low cost. That is, the valve metal substrate is preferably a substrate containing aluminum (hereinafter abbreviated as "aluminum substrate").

[0072] The aluminum base material is not particularly limited, and specific examples thereof include pure aluminum plates; alloy plates mainly composed of aluminum and containing trace amounts of different elements; base materials obtained by vapor-depositing high-purity aluminum on low-purity aluminum (for example, recycled materials); base materials obtained by coating high-purity aluminum on the surfaces of silicon wafers, quartz, glass, etc. by methods such as vapor deposition and sputtering; resin base materials laminated with aluminum; and the like.

[0073] Among the valve metal base materials, the valve metal purity of the surface on the side where the anodizing treatment is performed in the anodizing step described later is preferably 99.5% by mass or more, more preferably 99.9% by mass or more, and even more preferably 99.99% by mass or more. Further, the valve metal purity may be 100% by mass. When the valve metal purity is within the above range, the regularity of the arrangement of the through-holes is likely to be high.

[0074] Also, among the valve metal base materials, the surface on the side where the anodizing treatment is performed in the anodizing step described later is preferably subjected to heat treatment, degreasing treatment, and mirror finishing treatment in advance. Here, for the heat treatment, degreasing treatment, and mirror finishing treatment, the same treatments as those described in paragraphs

[0044] to

[0054] of JP-A No. 2008-270158 can be performed.

[0075] (Anodizing step) The above anodizing step is a step of forming a porous anodized film on the surface of the valve metal base material by subjecting the surface of the valve metal base material to anodizing treatment.

[0076] For the anodizing treatment performed in the above anodizing step, conventionally known methods can be used. However, from the reason that filled metals with little variation in diameter can be isolated in the isolation step described later, it is preferable to use the self-ordering method or the constant voltage treatment. Here, for the self-ordering method and constant voltage treatment of the anodizing treatment, etc., the same treatments as those described in paragraphs

[0056] to

[0108] and [FIG. 3] of JP-A No. 2008-270158 can be performed.

[0077] For anodization treatment, for example, a method of energizing a valve metal substrate as an anode in a solution with an acid concentration of 1 to 10% by mass can be used. The solution used for anodization treatment is preferably an acid solution containing an acid. Examples of the acid contained in the acid solution include sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, amidosulfonic acid, glycolic acid, tartaric acid, malic acid, and citric acid. Among them, sulfuric acid, phosphoric acid, or oxalic acid is preferable, and oxalic acid is more preferable. These acids can be used alone or in combination of two or more.

[0078] The conditions of anodization treatment vary depending on the electrolyte used and thus cannot be determined unconditionally. Generally, the electrolyte concentration is 0.1 to 20% by mass, the liquid temperature is -10 to 30 °C, the current density is 0.01 to 20 A / dm 2 , the voltage is 3 to 300 V, and the electrolysis time is 0.5 to 30 hours. The electrolyte concentration of 0.5 to 15% by mass, the liquid temperature of -5 to 25 °C, the current density of 0.05 to 15 A / dm 2 , the voltage of 5 to 250 V, and the electrolysis time of 1 to 25 hours are preferable. The electrolyte concentration of 1 to 10% by mass, the liquid temperature of 0 to 20 °C, the current density of 0.1 to 10 A / dm 2 , the voltage of 10 to 200 V, and the electrolysis time of 2 to 20 hours are more preferable.

[0079] The treatment time of anodization treatment may be 0.5 minutes to 16 hours, may be 1 minute to 12 hours, or may be 2 minutes to 8 hours.

[0080] The thickness of the anodic oxide film formed by the above anodization process is not particularly limited. From the viewpoint of adjusting the length of the metal nanowire, 0.3 to 300 μm is preferable, 0.5 to 120 μm is more preferable, and 0.5 to 100 μm is even more preferable. The thickness of the anodic oxide film can be calculated as the average value measured at 10 points by cutting the anodic oxide film with a focused ion beam (FIB) in a direction parallel to the thickness direction and taking a surface photograph (magnification: 50,000 times) of the cross section with a field emission scanning electron microscope (FE-SEM).

[0081] The density of the pores formed by the above anodization process is not particularly limited, but is preferably 2 million pores / mm 2 or more, more preferably 10 million pores / mm 2 or more, still more preferably 50 million pores / mm 2 or more, particularly preferably 100 million pores / mm 2 or more. The density of the pores can be measured and calculated by the method described in paragraphs

[0168] and

[0169] of JP-A-2008-270158.

[0082] The average opening diameter of the pores formed by the above anodization process is not particularly limited, but from the viewpoint of adjusting the diameter of the metal nanowires, 5 to 500 nm is preferable, 20 to 400 nm is more preferable, 40 to 200 nm is still more preferable, and 50 to 100 nm is particularly preferable. The average opening diameter of the pores can be calculated as the average value measured at 50 points by obtaining a surface observation image (magnification: 50,000 times) with an FE-SEM.

[0083] (Metal filling step) The above metal filling step is a step of filling the inside of the pores with metal after the above anodization step. Examples of the above metal include the same metals as those described as the metals constituting the above metal nanowires. Examples of the method of filling the inside of the pores with the above metal include the same methods as those described in paragraphs

[0123] to

[0126] and [FIG. 4] of JP-A-2008-270158.

[0084] In the method for manufacturing a metal nanowire, since it is difficult for the manufactured metal nanowire to contain a cavity portion, it is preferable that the metal filling step includes a plating step. Specifically, as a method for filling the metal into the pores, it is preferable to use an electrolytic plating treatment method. For example, an electrolytic plating method or an electroless plating method can be used. Here, in a conventionally known electrolytic plating method used for coloring or the like, it may be difficult to selectively deposit (grow) a metal with a high aspect ratio in the pores. This is presumably because the deposited metal is consumed in the pores, the deposited metal source is not supplied, and even if electrolysis is performed for a certain period of time or more, the plating is difficult to grow. Therefore, in the method for manufacturing a metal nanowire, when filling the metal by an electrolytic plating method, it is preferable to perform pulse electrolysis or provide a pause time during constant potential electrolysis. The pause time is preferably 10 seconds or more, and more preferably 30 to 60 seconds. In addition, in order to promote the stirring of the electrolytic solution, it is also preferable to irradiate the electrolytic solution with ultrasonic waves. Furthermore, the electrolytic voltage is usually 20 V or less, preferably 10 V or less. However, it is more preferable to measure in advance the deposition potential of the target metal in the electrolytic solution used and perform constant potential electrolysis within 1 V of that potential. Note that the apparatus used for constant potential electrolysis is preferably an apparatus capable of also performing cyclic voltammetry. For example, potentiostat apparatuses of Solartron, BAS, Hokuto Denko, and IVIUM can be used. In addition, when filling the metal by an electrolytic plating method, it may be performed by constant current electrolysis.

[0085] As the plating solution, a conventionally known plating solution can be used. Specifically, when depositing copper, an aqueous solution of copper sulfate is generally used. The concentration of copper sulfate is preferably 1 to 300 g / L, and more preferably 100 to 200 g / L. In addition, adding hydrochloric acid to the electrolytic solution can promote deposition. In this case, the hydrochloric acid concentration is preferably 10 to 20 g / L. Also, when depositing gold, it is preferable to use a sulfuric acid solution of tetrachloroauric acid and perform plating by alternating current electrolysis.

[0086] In addition, in the metal filling step, although an electroless plating method can be adopted, the electrolytic plating method is preferable in terms of shortening the time required for the metal filling step.

[0087] In the method for producing metal nanowires, it is also preferable to use a treatment method in which an alternating current electrolytic plating method and a direct current electrolytic plating method are combined in this order as the electrolytic plating method. Here, in the alternating current electrolytic plating method, for example, the voltage is modulated in a sine wave shape at a predetermined frequency and applied. Note that the waveform during the modulation of the voltage is not limited to a sine wave, and for example, it can also be a rectangular wave, a triangular wave, a sawtooth wave, or an inverse sawtooth wave. Also, for the direct current electrolytic plating method, the treatment method in the above-described electrolytic plating method can be appropriately used.

[0088] In the method for producing metal nanowires, for the reason that the time for producing metal nanowires can be shortened, as shown in FIG. 4, it is also preferable that the filling of the metal in the above-described metal filling step is a treatment performed on the region from the bottom of the porous to the middle of the opening among all regions from the bottom of the porous to the opening.

[0089] (Isolation step) The above isolation step is a step of isolating the filled metal from the anodic oxide film and the valve metal substrate after the above metal filling step. Here, the method for isolating the filled metal from the anodic oxide film and the valve metal substrate is not particularly limited, and for example, a method of removing (for example, dissolving, peeling, etc.) the anodic oxide film and the valve metal substrate and isolating the filled metal is preferably mentioned. Therefore, as an aspect after the above isolation step, for example, an aspect in which the filled metal is dispersed in a state of being isolated in the treatment liquid used in the subsequent dissolution step (dissolution treatment) is also included.

[0090] In the method for producing metal nanowires, the method for removing the anodic oxide film and the valve metal substrate is not particularly limited, and for example, it may be a mode of removing by polishing. On the other hand, from the viewpoint that the length of the produced metal nanowires tends to be uniform, the isolation step preferably includes a dissolution step, that is, at least a part of the anodic oxide film and the valve metal substrate is removed by dissolution treatment.

[0091] In the method for producing metal nanowires, for the reason that the shape and size of the produced metal nanowires are maintained, the isolation step preferably includes a one-step removal step of removing the anodic oxide film and removing the valve metal substrate, and it is more preferable that the removal of the anodic oxide film is a step removed by dissolution treatment. Also, for the same reason, the isolation step may be a step including a two-step removal step of removing the valve metal substrate and then removing the anodic oxide film. In this case, in both of the two-step removal steps, it is more preferable that they are steps removed by dissolution treatment.

[0092] For the removal of the valve metal substrate, a dissolution treatment using a treatment liquid that is difficult to dissolve the anodic oxide film and easy to dissolve the valve metal is preferable. In such a treatment liquid, the dissolution rate with respect to the valve metal is preferably 1 μm / min or more, more preferably 3 μm / min or more, and even more preferably 5 μm / min or more. Similarly, the dissolution rate with respect to the anodic oxide film is preferably 0.1 nm / min or less, more preferably 0.05 nm / min or less, and even more preferably 0.01 nm / min or less. Specifically, the treatment liquid preferably contains at least one metal compound having a lower ionization tendency than the valve metal and has a pH of 4 or less or 8 or more. The pH of the treatment liquid is more preferably 3 or less or 9 or more, and even more preferably 2 or less or 10 or more.

[0093] Such treatment liquids are preferably based on an acid or alkaline aqueous solution and contain, for example, compounds of manganese, zinc, chromium, iron, cadmium, cobalt, nickel, tin, lead, antimony, bismuth, copper, mercury, silver, palladium, platinum, gold (such as chloroplatinic acid), fluorides thereof, chlorides thereof, etc. Among them, an acid aqueous solution base is preferred, and it is preferred to blend chlorides. In particular, a treatment liquid obtained by blending mercury chloride into an aqueous hydrochloric acid solution (hydrochloric acid / mercury chloride) and a treatment liquid obtained by blending copper chloride into an aqueous hydrochloric acid solution (hydrochloric acid / copper chloride) are preferred from the viewpoint of the treatment latitude. Note that the composition of such treatment liquids is not particularly limited, and for example, a bromine / methanol mixture, a bromine / ethanol mixture, aqua regia, etc. may be used.

[0094] Also, the acid or alkaline concentration of such treatment liquids is preferably 0.01 to 10 mol / L, and more preferably 0.05 to 5 mol / L. Furthermore, the treatment temperature when using such treatment liquids is preferably -10°C to 80°C, and more preferably 0°C to 60°C.

[0095] Also, the removal of the valve metal substrate is performed by bringing the valve metal substrate after the above metal filling step into contact with the above-described treatment liquid. The method of bringing them into contact is not particularly limited, and examples include the immersion method and the spray method. Among them, the immersion method is preferred. The contact time at this time is preferably 10 seconds to 5 hours, and more preferably 1 minute to 3 hours.

[0096] For the removal of the anodic oxide film, a solvent that selectively dissolves the anodic oxide film without dissolving the metal filled in the pores can be used, and either an alkaline aqueous solution or an acid aqueous solution can be used.

[0097] Here, when using an alkaline aqueous solution, it is preferable to use an aqueous solution of at least one alkali selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide, and it is more preferable to use an aqueous solution of potassium hydroxide. Further, the concentration of the alkaline aqueous solution is preferably 1 to 30% by mass. The temperature of the alkaline aqueous solution is preferably 10 to 60°C, more preferably 20 to 60°C, and even more preferably 30 to 60°C. On the other hand, when using an acidic aqueous solution, it is preferable to use an aqueous solution of an inorganic acid such as chromic acid, sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, oxalic acid, or a mixture thereof, and it is more preferable to use an aqueous solution of chromic acid. Further, the concentration of the acidic aqueous solution is preferably 1 to 30% by mass. The temperature of the acidic aqueous solution is preferably 15 to 80°C, more preferably 20 to 60°C, and even more preferably 30 to 50°C.

[0098] Further, the removal of the anodic oxide film is carried out by bringing it into contact with the above-mentioned alkaline aqueous solution and acidic aqueous solution after the above metal filling step (preferably after removing the valve metal substrate). The method of bringing it into contact is not particularly limited, and examples include the immersion method and the spray method. Among them, the immersion method is preferable. The immersion time in the alkaline aqueous solution and the acidic aqueous solution is preferably 1 to 120 minutes, more preferably 2 to 90 minutes, even more preferably 3 to 60 minutes, and particularly preferably 3 to 30 minutes. Among them, 3 to 20 minutes is preferable, and 3 to 10 minutes is more preferable.

[0099] (Crushing step) The above crushing step is a step of crushing the isolated metal after the above isolation step. The method of crushing the isolated metal is not particularly limited, and for example, a method of crushing by applying an impact to the isolated metal in a liquid is preferably mentioned. The liquid (solvent) used for crushing is not particularly limited as long as it does not alter and dissolve the isolated metal. Examples include water, ethanol, methanol, acetone, methyl ethyl ketone, butanol, ethyl acetate, butyl acetate, tetrahydrofuran, toluene, dimethylformamide, cyclohexane, and cyclohexanone. Among these, water is preferable from the viewpoint of safety. Further, it is preferable that the above-mentioned pulverization step is carried out in water or in an aqueous solution in which the concentration of alkali or acid is less than 1% by mass. Examples of the pulverization treatment include a pulverization treatment using cavitation and a pulverization treatment in which ceramic balls are collided, and apparatuses such as an ultrasonic cleaner, an ultrasonic homogenizer, a jet mill, and a wet atomization device can be used. Among these, a pulverization treatment using cavitation or a pulverization treatment in which ceramic balls are collided is preferable, and a pulverization treatment using cavitation is more preferable.

[0100] In the present invention, the concentration of the isolated metal in the liquid when pressure is pulverized in the liquid is preferably 0.1 to 50% by mass because the treatment becomes uniform and productivity is improved. Further, the concentration of the isolated metal in the liquid when pressure is pulverized in the liquid is more preferably 0.5 to 30% by mass, and even more preferably 1 to 10% by mass because metal nanowires having a higher bonding strength can be obtained at the time of bonding.

[0101] (Drying step) The method for producing metal nanowires preferably further includes a drying step of drying the isolated metal between the above-mentioned isolation step and the above-mentioned pulverization step. Here, the method for drying the isolated metal is not particularly limited, but after removing the anodic oxide film and the valve metal substrate, the isolated metal can be dried by performing separation operations such as filtration using a filter or centrifugation to recover the isolated metal.

[0102] (Protection layer formation step) The method for producing metal nanowires preferably further includes a step of forming a protective layer containing a corrosion inhibitor on the isolated metal after the above-mentioned isolation step (after the above-mentioned drying step if the above-mentioned drying step is included).

[0103] The above-mentioned corrosion inhibitor is not particularly limited, and a known corrosion inhibitor can be applied. Examples of the corrosion inhibitor include compounds containing at least one of a nitrogen atom, an oxygen atom, and a sulfur atom. From the viewpoint of durability, the corrosion inhibitor is preferably a heterocyclic compound containing at least one of a nitrogen atom and an oxygen atom, more preferably a compound containing a 5-membered ring structure containing one or more nitrogen atoms, and particularly preferably at least one compound selected from the group consisting of a compound containing a triazole structure, a compound containing a benzimidazole structure, and a compound containing a thiadiazole structure. The 5-membered ring structure containing one or more nitrogen atoms may be a monocyclic structure or a partial structure constituting a condensed ring.

[0104] In addition, the corrosion inhibitor is preferably a compound containing at least one of a polar group-containing acid and a polar group-containing base because it is likely to adsorb on the surface of the isolated metal. Examples of the polar group of the polar group-containing acid and the polar group-containing base include a carboxylic acid group (carboxy group), a sulfonic acid group (sulfo group), a phosphonic acid group, a phosphate group, a primary to quaternary ammonium base, a carboxylate group, a sulfonate group, a phosphonate group, and a phosphate group.

[0105] The corrosion inhibitor is also preferably a compound containing a carboxy group because it binds to metal ions to form complex ions and the surface of the isolated metal is easily protected.

[0106] Specific examples of the above corrosion inhibitor include imidazole, benzimidazole, 1,2,4-triazole, benzotriazole (BTA), tolyltriazole (TTA), butylbenzyltriazole, alkyldithiothiadiazole, alkylthiol, 2-aminopyrimidine, 5,6-dimethylbenzimidazole, 2-amino-5-mercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole (DMTDA), 2-mercaptopyrimidine, 2-mercaptobenzoxazole, 2-mercaptobenzothiazole (MBT), 2-mercaptobenzimidazole, etc.

[0107] As other specific examples of the above corrosion inhibitor, aliphatic carboxylic acids such as acetic acid, propionic acid, palmitic acid, stearic acid, lauric acid, arachidic acid, terephthalic acid, oleic acid; carboxylic acids such as glycolic acid, lactic acid, oxalic acid, malic acid, tartaric acid, citric acid; aminopolycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), ethylenediaminediacetic acid (EDDA), ethylene glycol diethyl ether diamine tetraacetic acid (GEDA); uric acid; gallic acid; and the like can be mentioned.

[0108] The corrosion inhibitor may be used alone or in an appropriate combination of two or more. Also, for the reason of good stability over time, it is preferable that the above corrosion inhibitor contains a compound containing a nitrogen atom (nitrogen-containing compound), more preferably a nitrogen-containing compound, and even more preferably a heterocyclic compound containing at least one of a nitrogen atom and a sulfur atom.

[0109] The method for forming a protective layer containing such a corrosion inhibitor is not particularly limited. For example, a method of adding and stirring the isolated metal recovered in the above drying step to an aqueous solution containing a corrosion inhibitor; a method of adding a corrosion inhibitor to a washing solvent for washing the isolated metal recovered in the above drying step; and the like can be mentioned.

[0110] (Reduction or removal step) The method for producing the metal nanowire preferably has a step of reducing or removing the surface oxide layer of the isolated metal between the above isolation step and the above crushing step (before the above drying step when the above drying step is included). Examples of the reduction or removal step include a step of performing an immersion treatment using the alkaline aqueous solution and the acidic aqueous solution described in the above removal treatment of the anodic oxide film.

[0111] [Method for producing a laminate] The heat conduction sheet of the present invention can be suitably used for manufacturing a laminate. Specifically, it can be suitably used for a method of manufacturing a laminate in which a heat radiator, the heat conduction sheet of the present invention, and a heat generating body are laminated in this order and hot pressing is performed to obtain a laminate. Hereinafter, a method for manufacturing a laminate will be described.

[0112] 〔Heat radiator〕 The heat radiator is not particularly limited, and examples thereof include a heat spreader, a heat sink, and a heat diffusion sheet. The heat radiator is preferably formed of a heat conductive material. Examples of the heat conductive material include materials having a thermal conductivity of 10 Wm -1 K -1 or more. The thermal conductivity (unit: Wm -1 K -1 ) is a value measured by the flash method at a temperature of 25 °C by a method conforming to Japanese Industrial Standard (JIS) R1611. Examples of such heat conductive materials include carbon materials (e.g., graphite), metals (e.g., silver, copper, aluminum, iron, platinum, stainless steel, nickel), and silicon.

[0113] 〔Heat generating body〕 The heat generating body is not particularly limited, and examples thereof include a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an SRAM (Static Random Access Memory), and a SoC (Systems on a Chip) including RF (Radio Frequency) elements, a camera, an LED (Light Emitting Diode) package, a power semiconductor chip, a current converter, and a battery (particularly a lithium ion secondary battery). Further, the heating element may be a logic integrated circuit such as an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or an ASSP (Application Specific Standard Product).

[0114] Further, the heating element may be a memory. The memory may be a non-volatile memory or a volatile memory. Examples of the memory include a DRAM (Dynamic Random Access Memory), an HMC (Hybrid Memory Cube), an MRAM (Magnetoresistive Random Access Memory), a PCM (Phase-Change Memory), a ReRAM (Resistance Random Access Memory), a FeRAM (Ferroelectric Random Access Memory), and a flash memory.

[0115] The above heating element may be mounted on a device.

[0116] 〔Thermal Conductive Sheet〕 The thermal conductive sheet is the thermal conductive sheet of the present invention, and the preferred embodiment is as described above.

[0117] In the method for manufacturing the above laminate, first, for example, the thermal conductive sheet is cut according to the shape of the heating element, the thermal conductive sheet is brought into contact with the heating element, a heat radiator is brought into contact with the surface of the thermal conductive sheet opposite to the heating element, and the heat radiator, the thermal conductive sheet, and the heating element are laminated in this order. The method of bringing the heating element into contact with the thermal conductive sheet and the method of bringing the thermal conductive sheet into contact with the heat radiator are preferably methods that can fix them in a sufficiently adhered state. For example, a thermal conductive sheet is disposed between the heating element and the heat radiator and fixed with a pressable jig. As described above, in the method for manufacturing the laminate of the present invention, hot pressing is performed in a state where a heat radiator, a heat conductive sheet, and a heating element are laminated in this order. Examples of the hot pressing method include, for example, a method of heating the heating element while being fixed with a jig capable of applying pressure as described above, and a method of heating with an oven or the like. Further, as the hot pressing method, a hot press machine capable of performing heating and pressing may be used.

[0118] When hot pressing is performed as described above, the heat conductive sheet is deformed according to the shapes of the surfaces of the heat radiator and the heating element, and the heat conductive sheet is cured in that state. Then, a laminate having a heat radiator, a cured product of the heat conductive sheet, and a heating element in this order is obtained.

[0119] In the above description, a method of cutting the heat conductive sheet according to the shape of the heating element has been described. However, the heat conductive sheet may be bonded to a heating element array substrate on which the heating elements are arranged, and the heating element array substrate and the heat conductive sheet may be cut so that the heating element and the heat conductive sheet are in contact with each other. Specifically, for example, a heat conductive sheet may be bonded to a semiconductor wafer on which a heating element is formed, and the semiconductor wafer bonded with the heat conductive sheet may be diced.

[0120] [Laminate] The laminate of the present invention has a heat radiator, a cured product of a heat conductive sheet, and a heating element in this order. The laminate of the present invention is obtained by the above-described procedure. Examples of the heat radiator and the heating element are as described above.

[0121] Note that the laminate of the present invention may be included in a device. Examples of the device include electronic devices such as mobile phones (particularly, smartphones), portable information terminals, personal computers (particularly, portable personal computers), cameras, game machines, and remote controls. The heating element included in the device is as described above.

[0122] The laminate of the present invention is applicable to, for example, MEMS (Micro Electro Mechanical Systems) such as acceleration sensors, pressure sensors, vibrators, and gyro sensors. In addition, the laminate of the present invention is applicable to, for example, wireless elements such as GPS (Global Positioning System), FM (Frequency Modulation), NFC (Near field communication), RFEM (RF Expansion Module), MMIC (Monolithic Microwave Integrated Circuit), and WLAN (Wireless Local Area Network), discrete elements, CMOS (Complementary Metal Oxide Semiconductor), CMOS image sensors, camera modules, Passive devices, SAW (Surface Acoustic Wave) filters, RF (Radio Frequency) filters, IPD (Integrated Passive Devices), etc.

[0123] The final product on which the laminate of the present invention is mounted is not particularly limited. For example, smart TVs, mobile communication terminals, mobile phones, smartphones, tablet terminals, desktop personal computers (PCs), notebook PCs, network devices (routers, switching), wired infrastructure devices, digital cameras, game machines, controllers, data centers, servers, mining PCs, high-performance computing (HPC), graphics cards, network servers, storage, chip sets, in-vehicle devices (electronic control devices, driving assistance systems), car navigation systems, portable navigation devices (PNDs), lighting (general lighting, in-vehicle lighting, LED lighting, organic light-emitting diode (OLED) lighting), TVs, displays, display panels (liquid crystal panels, organic electro-luminescence (EL) panels, electronic paper), music playback terminals, industrial devices, industrial robots, inspection devices, medical devices, household appliances, devices for space or aircraft, wearable devices, etc. can be mentioned.

[0124] Note that the laminate of the present invention may be used for applications other than electronic device applications. Examples of applications of the laminate other than electronic devices include building materials suitable for rapid temperature rise during the day or temperature control during heating and cooling indoors (for example, floor materials, roofing materials, wall materials, etc.); clothing suitable for temperature adjustment according to changes in environmental temperature or body temperature changes during exercise or at rest (for example, underwear, outerwear, cold-proof clothing, gloves, etc.); bedding; and applications such as waste heat utilization systems that store unnecessary waste heat and utilize it as thermal energy. Even in the above applications, a cured product of the thermal conductive sheet is disposed between the heating element and the heat dissipating element.

Examples

[0125] The present invention will be described in more detail below based on examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be appropriately changed as long as they do not depart from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0126] [Example 1] The heat conductive sheet used in Example 1 was obtained by the procedure shown below.

[0127] [Fabrication of Metal Nanowires] (Fabrication of Aluminum Substrate) A molten metal was prepared using an aluminum alloy containing Si: 0.06 mass%, Fe: 0.30 mass%, Cu: 0.005 mass%, Mn: 0.001 mass%, Mg: 0.001 mass%, Zn: 0.001 mass%, and Ti: 0.03 mass%, with the balance being Al and inevitable impurities. After performing molten metal treatment and filtration, an ingot with a thickness of 500 mm and a width of 1200 mm was fabricated by the DC (Direct Chill) casting method. Next, the surface was machined off with a surface planer to an average thickness of 10 mm, and then soaked at 550 °C for about 5 hours. When the temperature dropped to 400 °C, it was rolled into a rolled sheet with a thickness of 2.7 mm using a hot rolling mill. Furthermore, after performing heat treatment at 500 °C using a continuous annealing furnace, it was finished to a thickness of 1.0 mm by cold rolling to obtain an aluminum substrate of JIS (Japanese Industrial Standard) 1050 material. After forming the aluminum substrate into a wafer shape with a diameter of 200 mm (8 inches), the following treatments were performed.

[0128] (Electropolishing Treatment) The above aluminum substrate was subjected to electropolishing treatment using an electropolishing solution with the following composition under the conditions of a voltage of 25 V, a solution temperature of 65 °C, and a solution flow rate of 3.0 m / min. The cathode was a carbon electrode, and a GP0110-30R (manufactured by Takasago Seisakusho Co., Ltd.) was used as the power supply. Also, the flow rate of the electrolytic solution was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE Corporation).

[0129] - Electropolishing Solution Composition - · 660 mL of 85 mass% phosphoric acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.) · 160 mL of pure water · 150 mL of sulfuric acid · 30 mL of ethylene glycol

[0130] (Anodizing process) Next, the aluminum substrate after electrolytic polishing was subjected to anodizing treatment by the self-ordering method according to the procedure described in JP-A-2007-204802. The aluminum substrate after electrolytic polishing was subjected to a pre-anodizing treatment for 5 hours under the conditions of a voltage of 40 V, a solution temperature of 16 °C, and a solution flow rate of 3.0 m / min using an electrolytic solution of 0.50 mol / L oxalic acid. Thereafter, the aluminum substrate after the pre-anodizing treatment was subjected to a stripping treatment by immersing it in a mixed aqueous solution of 0.2 mol / L chromic anhydride and 0.6 mol / L phosphoric acid (solution temperature: 50 °C) for 12 hours. Thereafter, a re-anodizing treatment was performed for 5 hours under the conditions of a voltage of 40 V, a solution temperature of 16 °C, and a solution flow rate of 3.0 m / min using an electrolytic solution of 0.50 mol / L oxalic acid to obtain an anodic oxide film with a film thickness of 40 μm. In addition, for both the pre-anodizing treatment and the re-anodizing treatment, the cathode was a stainless steel electrode, and a GP0110-30R (manufactured by Takasago Seisakusho Co., Ltd.) was used as the power supply. Also, a NeoCool BD36 (manufactured by Yamato Scientific Co., Ltd.) was used for the cooling device, and a pair stirrer PS-100 (manufactured by EYELA Tokyo Rika Kikai Co., Ltd.) was used for the stirring and heating device. Furthermore, the flow rate of the electrolytic solution was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE Corporation).

[0131] (Metal filling process) Next, electrolytic plating treatment was performed with the aluminum substrate as the cathode and platinum as the anode. Specifically, a copper plating solution having the following composition was used, and a porous (micropore) internal copper-filled metal-filled microstructure was fabricated by performing constant current electrolysis. Here, for the constant current electrolysis, a plating apparatus manufactured by Yamamoto Plating Tester Co., Ltd. was used, a power supply (HZ-3000) manufactured by Hokuto Denko Corporation was used, cyclic voltammetry was performed in the plating solution to confirm the deposition potential, and then the treatment was performed under the following conditions.

[0132] -Copper plating solution composition and conditions- · Copper sulfate 100 g / L · Sulfuric acid 50 g / L · Hydrochloric acid 15 g / L · Temperature 25 °C · Current density 10 A / dm 2

[0133] After filling the pores with metal, the surface of the anodic oxide film was observed by FE-SEM, and the presence or absence of pore sealing by the metal in 1000 pores was observed to calculate the pore sealing rate (number of sealed pores / 1000 pores), which was 96%. In addition, after filling the pores with metal, the anodic oxide film was cut by FIB in the thickness direction, and the cross-section was photographed by FE-SEM to obtain a surface photograph (magnification: 50,000 times) to confirm the inside of the pores. As a result, it was found that in the sealed pores, the filling height from the bottom of the pores was 35 μm.

[0134] (Isolation process) By immersing in an aqueous solution of potassium hydroxide (concentration: 5 mol / L) at 60 °C for 300 seconds, the filled metal was isolated from the anodic oxide film and the aluminum substrate to obtain the isolated metal. Specifically, by immersing in an aqueous solution of potassium hydroxide (concentration: 5 mol / L) at 60 °C for 300 seconds, the anodic oxide film was dissolved, and at the same time as the dissolution of the anodic oxide film (when 300 seconds had elapsed), the aluminum substrate was peeled off to isolate the filled metal.

[0135] (Drying process) Next, the isolated metal was recovered by suction filtration using a membrane (0.4 μm, PTFE, manufactured by Omnipore), and the isolated metal was dried.

[0136] (Washing / protective layer formation process / reduction or removal process) Next, the isolated metal recovered on the membrane was washed for 1 minute using the washing solvent shown below. In Example 1, since a corrosion inhibitor was added to the washing solvent, a protective layer was formed simultaneously with the washing. Also, in Example 1, since citric acid was used as the corrosion inhibitor, the surface oxide layer of the isolated metal was removed simultaneously with the formation of the protective layer. Thereafter, the isolated metal on the membrane was recovered.

[0137] -Washing Solvent- Aqueous solution containing 1 mass% citric acid

[0138] (Crushing Process) Next, 1 mass% of the recovered isolated metal was added to water, and using a Starburst Mini manufactured by Sugino Machine, the crushing treatment by cavitation (pressure: 50 MPa) was performed once. Thereafter, the isolated metal subjected to the crushing treatment was recovered by suction filtration using a membrane (0.4 μm, PTFE, manufactured by Omnipore), and metal nanowires were produced by drying under reduced pressure for 12 hours. Here, when the specific surface area was measured by the krypton gas adsorption method after performing a decompression treatment at 50 °C for 60 minutes using BELSORP-max manufactured by MicrotracBEL, it was 7000 m 2 / kg.

[0139] [Preparation of Varnish] First, a raw varnish having the following composition was prepared using the metal nanowires obtained by the above procedure. ·Binder resin (bisphenol F type epoxy resin (trade name: EXA-830CRP, manufactured by DIC Corporation)): 4.2 parts by mass ·Epoxy resin curing agent (phenolic resin (trade name: SK Resin HE100C-30, manufactured by Air Water Performance Chemicals Co., Ltd.)): 3.4 parts by mass ·Elastomer (acrylic rubber (trade name: SG-P3, manufactured by Nagase ChemteX Corporation)): 2.4 parts by mass · Coupling agent (γ-ureidopropyltriethoxysilane (trade name: KBE-585A, manufactured by Shin-Etsu Chemical Co., Ltd.)): 0.03 parts by mass · Curing accelerator (1-cyanoethyl-2-phenylimidazole (trade name: 2PZ-CN, manufactured by Shikoku Kasei Kogyo Co., Ltd.)): 0.01 parts by mass · Metal nanowire (metal nanowire obtained by the above procedure): 90 parts by mass

[0140] Next, the prepared raw material varnish was stirred at 100 revolutions per minute for 12 hours at room temperature using a mixing rotor (VMR-3R, manufactured by AS ONE Corporation) to prepare a varnish.

[0141] 〔Preparation of coating solution〕 An organic solvent (cyclohexanone) was added to the varnish prepared by the above procedure, and stirring was performed twice at 800 revolutions per minute for 2 minutes at room temperature using a blender (ARE-400TWIN, manufactured by Shinky Co., Ltd.) to prepare a coating solution with a solid content of 61% by mass.

[0142] 〔Production of heat conduction sheet〕 First, a copper foil (thickness: 10 μm) was placed on the bottom surface of a silicone resin container (width: 2 cm, length: 4 cm, height: 3 cm). Next, the coating solution was supplied onto the copper foil so that the mass of the coating solution was 0.4 g. Next, the container with the coating solution supplied onto the copper foil was placed in a vacuum dryer to remove the solvent contained in the coating solution. The vacuum drying was performed under the conditions of 90°C for 10 minutes. By the above procedure, the first metal nanowire-containing layer of the B stage was formed on one surface of the copper foil.

[0143] Furthermore, the copper foil on which the first metal nanowire-containing layer was formed was taken out from the container and reinstalled in the container so that the side with the first metal nanowire-containing layer was the bottom side of the container. That is, it was installed in the container so that the surface of the copper foil on which the first metal nanowire-containing layer was not formed was the upper surface. Thereafter, by the same procedure as above, the coating solution was supplied onto the copper foil and vacuum drying was performed to form a second metal nanowire-containing layer on the other surface of the copper foil. Using the above procedure, a thermal conductive sheet of Example 1 having a first metal nanowire-containing layer, a copper foil (support), and a second metal nanowire-containing layer in this order was obtained. In the obtained thermal conductive sheet of Example 1, the thicknesses of the first metal nanowire-containing layer and the second metal nanowire-containing layer, and the thickness of the support (copper foil) are shown in the table in the subsequent stage.

[0144] [Example 2] A thermal conductive sheet of Example 2 was obtained in the same procedure as Example 1, except that the support (copper foil) used in Example 1 was changed to the C-stage sheet shown below. The C-stage sheet used for the support was obtained by the following procedure. First, 0.65 g of the above coating solution was supplied to the above container, and vacuum drying was performed to obtain a B-stage sheet. The conditions for vacuum drying were 140 °C for 10 minutes. Thereafter, the B-stage sheet was taken out of the container, and hot pressing was performed to obtain a C-stage sheet. The conditions for hot pressing were a pressing pressure of 60 MPa, a pressing temperature of 180 °C, and a pressing time of 5 minutes under the atmosphere. The thickness of the obtained C-stage sheet is shown in the table in the subsequent stage.

[0145] [Example 3] A thermal conductive sheet of Example 3 was obtained in the same procedure as Example 1, except that the support (copper foil) used in Example 1 was changed to a copper foil with holes (perforated copper foil) having a thickness of 50 μm and holes arranged at a predetermined interval over the entire surface. Note that in the above perforated copper foil, holes with a diameter of 1 mm were arranged in an equilateral triangle shape such that the minimum distance between the centers of the holes was 2 mm.

[0146] [Example 4] A thermal conductive sheet of Example 4 was obtained in the same procedure as Example 1, except that the support (copper foil) used in Example 1 was changed to an aluminum foil with a thickness of 30 μm.

[0147] [Example 5] A heat conduction sheet of Example 5 was obtained in the same procedure as Example 1, except that the thickness of the support (copper foil) used in Example 1 was changed to 50 μm.

[0148] [Example 6] A heat conduction sheet of Example 6 was obtained in the same procedure as Example 1, except that the thicknesses of the first metal nanowire-containing layer and the second metal nanowire-containing layer used in Example 1 were changed to 100 μm. Specifically, when forming the first metal nanowire-containing layer and the second metal nanowire-containing layer in Example 1, the amount of the coating liquid used was set to 1.3 g to obtain the product with the above thickness.

[0149] [Example 7] A heat conduction sheet of Example 7 was obtained in the same procedure as Example 1, except that the thicknesses of the first metal nanowire-containing layer and the second metal nanowire-containing layer used in Example 1 were changed to 5 μm. Specifically, when forming the first metal nanowire-containing layer and the second metal nanowire-containing layer in Example 1, the amount of the coating liquid used was set to 0.065 g to obtain the product with the above thickness.

[0150] [Comparative Example 1] In the procedure for obtaining the C-stage sheet described in Example 2 above, the B-stage sheet before thermocompression was used as Comparative Example 1.

[0151] [Comparative Example 2] The C-stage sheet used in Example 2 above was used as Comparative Example 2.

[0152] [Measurement] [Breaking Strength] The breaking strength of the support used in each of the above examples was measured by the method described above. The breaking strength of each support is shown in the table in the following section.

[0153] [Thermal Conductivity] The thermal conductivity of the cured product of the heat conduction sheet in each example was measured by the method described above. The cured product of the heat conductive sheet was obtained by hot pressing. The conditions of hot pressing were a pressing pressure of 60 MPa, a pressing temperature of 180 °C, and a pressing time of 5 minutes under the atmosphere. In Comparative Example 2, the thermal conductivity of the C-stage sheet was measured as it was.

[0154] [Evaluation] [Followability Evaluation] The followability of the heat conductive sheets used in each example and comparative example was evaluated according to the following procedure. First, a copper plate (5 cm × 5 cm, thickness: 5 mm) simulating a heat radiator, the sheet used in each example and comparative example, and a copper plate (2 cm × 4 cm, thickness: 2 mm) simulating a heat generating body were laminated. After lamination, hot pressing was performed to obtain a laminate having an aluminum plate, a cured product of each sheet, and a copper plate in this order. The conditions of hot pressing were a pressing pressure of 10 MPa, a pressing temperature of 170 °C, and a pressing time of 15 minutes under a nitrogen atmosphere.

[0155] The laminate obtained by the above procedure was analyzed with an ultrasonic imaging device (device name: Fine SAT, model FS200III, manufacturer: Hitachi Power Solutions, measurement method: reflection type, probe frequency: 50 MHz), and the adhesion area between the copper plate and the cured product, and the adhesion area between the other copper plate and the cured product were calculated. Also, the arithmetic mean value of the calculated adhesion areas was calculated. Here, the followability of the first metal nanowire-containing layer and the second metal nanowire-containing layer was evaluated using the ratio of the arithmetic mean value of the adhesion area to the area of the heat conductive sheet. The followability was evaluated based on the following criteria. If the above ratio is large, it can be said that the followability of the first metal nanowire-containing layer and the second metal nanowire-containing layer is high. Practically, an A or B evaluation is preferable, and an A evaluation is more preferable. ·A: The above ratio is 90% or more ·B: The above ratio is 60% or more and less than 90% ·C: The above ratio is less than 60%

[0156] [Handling Property] The handleability of the thermal conductive sheets used in each example and comparative example was evaluated according to the following procedure. At the central portion of the short side of each thermal conductive sheet, in the region 5 mm from the short side, it was pinched with reverse-action tweezers (manufactured by Esco Corporation), and the thermal conductive sheet was lifted up. The handleability was evaluated according to the following criteria. For practical use, an A evaluation or a B evaluation is preferable. · A: The thermal conductive sheet could be lifted up, and no peeling of the metal nanowire layer was observed in the thermal conductive sheet. · B: The thermal conductive sheet could be lifted up, but partial peeling of the metal nanowire layer was observed in the thermal conductive sheet. · C: The thermal conductive sheet could not be lifted up.

[0157] [Results] The configurations, measurement results, and evaluation results of the thermal conductive sheets of each example and comparative example are shown in Table 1. In the table, the "thickness ratio of the metal nanowire layer" is the ratio of the total thickness of the first metal nanowire-containing layer and the second metal nanowire-containing layer to the thickness of the thermal conductive sheet.

[0158]

Table 1

[0159] From the results shown in Table 1, it was confirmed that each example having a support was superior in handleability compared to Comparative Example 1 having no support. Also, from the results shown in Table 1, it was confirmed that when the first metal nanowire-containing layer and the second metal nanowire-containing layer were in the B stage, the followability was excellent. From the comparison between Example 7 and the other examples, when the total thickness of the first metal nanowire-containing layer and the second metal nanowire-containing layer was 50.0% or more (more preferably 80.0% or more) and 98% or less with respect to the thickness of the thermal conductive sheet, it was confirmed that the followability was more excellent.

Explanation of Reference Signs

[0160] 1 Valve metal substrate 2 Porous (micropores) 3 Anodic oxide film 4 Metal 5 Isolated metal 10 Metal nanowire 12 First metal nanowire-containing layer 14 Support 16 Second metal nanowire-containing layer 20 Thermal conductive sheet

Claims

1. A heat conduction sheet having a first metal nanowire-containing layer, a support, and a second metal nanowire-containing layer in this order, wherein the first metal nanowire-containing layer and the second metal nanowire-containing layer contain metal nanowires and a binder resin, and the first metal nanowire-containing layer and the second metal nanowire-containing layer are in the B-stage, the heat conduction sheet.

2. The breaking strength of the support is 10 N / mm ２ or more, the heat conductive sheet according to claim 1.

3. The heat conduction sheet according to claim 1 or 2, wherein the metal contained in the metal nanowires is at least one metal selected from the group consisting of copper, silver, and aluminum.

4. The heat conduction sheet according to claim 1 or 2, wherein the first metal nanowire-containing layer satisfies at least one of the following requirement 1 and requirement 2. Requirement 1: The metal nanowires are contained in an amount of 40 to 99% by volume. Requirement 2: The metal nanowires are contained in an amount of 70 to 99% by mass.

5. The heat conduction sheet according to claim 1 or 2, wherein the second metal nanowire-containing layer satisfies at least one of the following requirement 3 and requirement 4. Requirement 3: The metal nanowires are contained in an amount of 40 to 99% by volume. Requirement 4: The metal nanowires are contained in an amount of 70 to 99% by mass.

6. The heat conduction sheet according to claim 1 or 2, wherein the binder resin contains one or more resins selected from the group consisting of epoxy resins, acrylic resins, urethane resins, maleimide resins, itaconimide resins, and nadimide resins.

7. The heat conduction sheet according to claim 1 or 2, wherein the thicknesses of the first metal nanowire-containing layer and the second metal nanowire-containing layer are each independently 5 to 200 μm.

8. The heat conduction sheet according to claim 1 or 2, wherein the total thickness of the thickness of the first metal nanowire-containing layer and the thickness of the second metal nanowire-containing layer is 80.0 to 98.0% with respect to the thickness of the heat conduction sheet.

9. The heat conduction sheet according to claim 1 or 2, wherein the support is a metal foil containing at least one metal selected from the group consisting of copper, silver, and aluminum.

10. The heat conduction sheet according to claim 1 or 2, wherein the support is a C-stage sheet containing metal nanowires containing at least one metal selected from the group consisting of copper, silver, and aluminum and a binder resin.

11. The thermal conductivity of the cured product obtained by curing the heat conduction sheet is 10 to 190 Wm －１ K －１ The heat conduction sheet according to claim 1 or 2, wherein the heat conduction sheet is made of a material having a thermal conductivity of 10 to 190 Wm

12. A method for manufacturing a laminate, comprising laminating a heat dissipating body, the heat conductive sheet according to claim 1 or 2, and a heating element in this order, and performing hot pressing to obtain a laminate.

13. A laminate having, in this order, a heat dissipating body, a cured product of the heat conductive sheet according to claim 1 or 2, and a heating element.

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