JP2020019883A - Thermally conductive sheet - Google Patents

Abstract

To provide a thermally conductive sheet capable of suppressing collapse in the thickness direction of a thermally conductive sheet even when used under high load and capable of maintaining high thermal conductivity.SOLUTION: There is provided a thermally conductive sheet 11 which comprises: a sheet body 12 containing a resin and a carbon material and having a plurality of hole parts 15 extending in the thickness direction of the thermally conductive sheet 11; and a plurality of reinforcement parts 21 filled with at least one of a metal and an inorganic oxide in the hole parts 15, wherein the sum of the average area of a cross section orthogonal to a thickness direction of the thermally conductive sheet 11 of each of the plurality of reinforcement parts 21 is less than 1% with respect to an area of one surface in the thickness direction of the thermally conductive sheet 11.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heat conductive sheet, and more particularly, to a heat conductive sheet containing a resin and a carbon material.

  2. Description of the Related Art In recent years, heat generation of electronic components such as power semiconductors (IGBT modules and the like) and integrated circuit (IC) chips has been increasing with higher performance. As a result, in electronic devices using electronic components, it is necessary to take measures against functional failure due to a rise in temperature of the electronic components.

  Here, in general, as a measure against functional failure due to temperature rise, a method of promoting heat radiation by attaching a heat radiator such as a metal heat sink, a heat radiating plate, and a heat radiating fin to a heat generating element such as an electronic component is adopted. ing. When using a heat radiator, the heat radiator and the heat radiator are usually interposed with a heat conductive sheet having high thermal conductivity in order to efficiently transfer heat from the heat radiator to the heat radiator. We adhere.

  Patent Documents 1 and 2, for example, include a resin and a heat conductive filler, and have the heat conductive filler oriented in the thickness direction of the heat conductive sheet. A heat conductive sheet having excellent heat conductivity is disclosed.

  Patent Literature 3 discloses a heat conductive sheet in which a heat conductive filler is filled in a through hole extending in a thickness direction of a heat conductive sheet formed of a matrix resin, thereby increasing the heat conductivity in the thickness direction. Have been.

  Patent Literature 4 discloses a bonding heat conductive material having high heat conductivity and adhesive strength, which is obtained by forming a through hole in an adhesive film and filling the obtained through hole with a heat conductive paste. A film is disclosed. The through-hole filled with the heat conductive paste functions as a heat conductive path connecting the semiconductor chip and the frame.

JP 2002-026202 A JP 2010-254766 A JP-A-5-259671 JP-A-2004-140170

  However, when the conventional heat conductive sheet is used under a high load, the heat conductive sheet is crushed, and as a result, there is a problem that the heat conductivity of the heat conductive sheet is reduced. Therefore, even when used under a high load, there has been a demand for a heat conductive sheet capable of suppressing collapse of the heat conductive sheet in the thickness direction and maintaining high heat conductivity.

  Therefore, an object of the present invention is to provide a heat conductive sheet that can suppress collapse in the thickness direction of the heat conductive sheet and maintain high heat conductivity even when used under a high load.

  The present inventors have conducted intensive studies to achieve the above object. And the present inventors are a heat conductive sheet including a resin and a carbon material, the sheet body including a plurality of holes including the resin and the carbon material, and extending in a thickness direction of the heat conductive sheet. A plurality of reinforcing portions filled with at least one of a metal and an inorganic oxide in the hole portion, and the sum of the average areas of the cross sections orthogonal to the thickness direction of the heat conductive sheet of each of the plurality of reinforcing portions. It has been found that if the heat conductive sheet has a specific relationship with the area of one surface in the thickness direction of the heat conductive sheet, the collapse of the heat conductive sheet in the thickness direction can be suppressed, and high heat conductivity can be maintained. The present invention has been completed.

  That is, an object of the present invention is to advantageously solve the above-described problems, and a heat conductive sheet of the present invention is a heat conductive sheet including a resin and a carbon material, wherein the resin and the carbon material are used. Comprising a sheet body having a plurality of holes extending in the thickness direction of the heat conductive sheet, and a plurality of reinforcing portions filled with at least one of a metal and an inorganic oxide in the holes, The sum of the average areas of the cross sections orthogonal to the thickness direction of the heat conductive sheet of each of the plurality of reinforcing portions is less than 1% with respect to the area of one surface in the thickness direction of the heat conductive sheet. As described above, the reinforcing member is formed by filling at least one of the metal and the inorganic oxide in the hole of the sheet main body, and the average area of the cross section orthogonal to the thickness direction of the heat conductive sheet of each of the plurality of reinforcing members. If the total is less than 1% of the area of one surface in the thickness direction of the heat conductive sheet, collapse of the heat conductive sheet in the thickness direction can be suppressed, and high heat conductivity is maintained. be able to.

  Further, in the heat conductive sheet of the present invention, the ratio [(L / T) × 100] of the length (L) of the reinforcing portion in the thickness direction of the heat conductive sheet to the thickness (T) of the heat conductive sheet is 50. % Is preferable. When the ratio of the length (L) of the reinforcing portion in the thickness direction of the heat conductive sheet to the thickness (T) of the heat conductive sheet is 50% or more, the collapse of the heat conductive sheet in the thickness direction can be further suppressed.

Further, in the heat conductive sheet of the present invention, the heat conductivity of the heat conductive sheet under a pressure of 1.5 MPa is preferably 2.5 W / mK or more. If the thermal conductivity of the heat conductive sheet under a pressure of 1.5 MPa is 2.5 W / mK or more, the heat conductive sheet can be suitably used even under a high load.
In the present invention, “thermal conductivity” can be measured by the method described in the examples of the present specification.

  Further, in the heat conductive sheet of the present invention, it is preferable that the reinforcing portion has a major axis of a cross section orthogonal to a thickness direction of the heat conductive sheet of 0.1 mm or more and 2 mm or less. When the major axis of the cross section of the reinforcing portion orthogonal to the thickness direction of the heat conductive sheet is equal to or larger than the lower limit, the collapse of the heat conductive sheet in the thickness direction can be suitably suppressed. Also. When the major axis of the cross section of the reinforcing portion perpendicular to the thickness direction of the heat conductive sheet is equal to or less than the upper limit, the thermal conductivity of the heat conductive sheet can be suitably maintained.

Further, in the heat conductive sheet of the present invention, it is preferable that the arrangement density of the reinforcing portions is 1 piece / cm ² or more. When the arrangement density of the reinforcing portions is 1 piece / cm ² or more, the collapse of the heat conductive sheet in the thickness direction can be more favorably suppressed.

  And in the heat conductive sheet of the present invention, the content ratio of the carbon material in the sheet main body is preferably 15% by mass or more and 80% by mass or less. When the content ratio of the carbon material in the sheet body is equal to or more than the above lower limit, the carbon material is more favorably oriented in the sheet body, and the carbon materials contact each other to form a good conduction path. As a result, high thermal conductivity can be exhibited by the thermal conductive sheet. When the content ratio of the carbon material is equal to or less than the upper limit, flexibility can be imparted to the sheet body.

  ADVANTAGE OF THE INVENTION According to this invention, even when it uses under a heavy load, the heat conductive sheet which can suppress the crush of the heat conductive sheet in the thickness direction and can maintain high heat conductivity can be provided.

It is a perspective view showing roughly the heat conductive sheet concerning one embodiment of the present invention. It is a front view of the heat conductive sheet shown in FIG. It is an enlarged view of the part shown by A in FIG. FIG. 4 is a sectional view taken along line BB of FIG. 3. It is a top view of the heat conductive sheet shown in FIG. It is an expanded sectional view which follows the DD line of the part shown by C in FIG. FIG. 2 is a front view schematically showing an example of a usage mode of the heat conductive sheet shown in FIG. 1. It is sectional drawing which shows the modification of the reinforcement part in the heat conductive sheet of this invention schematically.

  The heat conductive sheet of the present invention is a heat conductive sheet containing a resin and a carbon material. The heat conductive sheet of the present invention can be used, for example, sandwiched between the heat generator and the heat radiator when the heat radiator is attached to the heat generator.

(Heat conductive sheet)
Here, the heat conductive sheet according to one embodiment of the present invention will be described.
The heat conductive sheet 11 whose perspective view is shown in FIG. 1 includes a sheet body 12 containing a resin and a carbon material. And the sheet main body 12 is provided with a plurality of holes 15 penetrating in the thickness direction of the heat conductive sheet 11. The heat conductive sheet 11 includes a plurality of reinforcing portions 21 in which the holes 15 are filled with at least one of a metal and an inorganic oxide.

FIG. 2 is a front view, FIG. 3 is an enlarged view of a portion indicated by A in FIG. 2, and FIG. 4 is a cross-sectional view taken along line BB in FIG. S (S = S ₁ + S ₂ ... + S _n ), the sum of the average areas of the cross sections orthogonal to the thickness direction of the heat conductive sheet 11 of each of the plurality of reinforcing portions 21, and one surface in the thickness direction of the heat conductive sheet 11. When the area to S _M, the sum S of the average area of the cross section perpendicular to the thickness direction of the plurality of reinforcing portions 21 each of the heat conducting sheet 11, with respect to the area S _M in the thickness direction one surface of the heat conduction sheet 11 Less than 1%, that is, (S / S _M ) × 100 <1 (%), and preferably less than 0.9%. If the sum S of the average areas of the cross sections orthogonal to the thickness direction of the heat conductive sheet 11 of each of the plurality of reinforcing portions 21 is less than 1% with respect to the area _SM of one surface in the thickness direction of the heat conductive sheet 11, Even when used under a high load, the heat conductive sheet 11 can be suppressed from crushing in the thickness direction of the heat conductive sheet 11 and can maintain high heat conductivity.

<Seat body>
Here, the seat body 12 will be described in detail. FIG. 5 is a plan view, and FIG. 6 is an enlarged cross-sectional view taken along line D-D of a portion indicated by C in FIG. It is formed in a sheet shape having a plurality of holes 15 extending in the thickness direction. The sheet body 12 is made of a material containing a resin and a carbon material, and optionally further containing an additive.

[resin]
Here, the resin included in the sheet body 12 is not particularly limited, and a known resin that can be used for a conventional heat conductive sheet, for example, a thermoplastic resin can be used.

〔Thermoplastic resin〕
Examples of the thermoplastic resin include a thermoplastic resin which is solid at normal temperature and normal pressure, and a thermoplastic resin which is liquid at normal temperature and normal pressure. Above all, as the thermoplastic resin, it is preferable to use at least a solid thermoplastic resin at normal temperature and normal pressure, and it is preferable to use a solid thermoplastic fluororesin at normal temperature and normal pressure and / or a solid thermoplastic silicone resin at normal temperature and normal pressure. It is more preferable to use a thermoplastic fluororesin which is solid at least under normal temperature and normal pressure. If a solid thermoplastic resin is used at normal temperature and normal pressure, the flexibility of the heat conductive sheet 11 can be further improved in a high temperature environment, and the heat conductive sheet and the heat generating body and the heat radiating body can be more closely adhered. In addition, the handleability of the heat conductive sheet 11 can be improved in a normal temperature environment. Further, if a solid thermoplastic fluororesin at normal temperature and normal pressure and a solid thermoplastic silicone resin at normal temperature and normal pressure are used, in addition to the above effects, the heat resistance, oil resistance, and chemical resistance of the heat conductive sheet 11 are further improved. Can be done.
In this specification, “normal temperature” refers to 25 ° C., and “normal pressure” refers to 1 atm.

([Solid thermoplastic resin under normal temperature and normal pressure])
Here, examples of the thermoplastic resin which is solid at normal temperature and pressure include poly (2-ethylhexyl acrylate), a copolymer of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or an ester thereof, and polyacrylic acid. Or an acrylic resin such as an ester thereof; silicone resin; fluororesin; polyethylene; polypropylene; ethylene-propylene copolymer; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymer; Alcohol; polyacetal; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; styrene-acrylonitrile copolymer; acrylonitrile-butadiene copolymer (nitrilego). Acrylonitrile-butadiene-styrene copolymer (ABS resin); styrene-butadiene block copolymer or hydrogenated product thereof; styrene-isoprene block copolymer or hydrogenated product thereof; polyphenylene ether; modified polyphenylene ether; Polyamides; Aromatic polyamides; Polyamide imide; Polycarbonate; Polyphenylene sulfide; Polysulfone; Polyethersulfone; Polyethernitrile; Polyetherketone; Polyketone; Polyurethane; Liquid crystal polymer; These may be used alone or in combination of two or more.

  Further, as the resin, it is preferable to use at least one of a solid thermoplastic fluororesin at normal temperature and normal pressure and a solid thermoplastic silicone resin at normal temperature and normal pressure, and it is preferable to use a solid thermoplastic fluororesin at least at normal temperature and normal pressure It is more preferable to use a solid thermoplastic fluororesin at room temperature and pressure and a liquid thermoplastic fluororesin at room temperature and pressure. If at least one of a solid thermoplastic fluororesin at normal temperature and normal pressure and a solid thermoplastic silicone resin at normal temperature and normal pressure is used, the flexibility of the heat conductive sheet 11 can be further improved in a high temperature environment, And the heat generating body and the heat radiating body can be brought into better contact with each other. In addition, when at least one of a thermoplastic fluororesin solid at normal temperature and normal pressure and a thermoplastic silicone resin solid at normal temperature and normal pressure is used, the handleability of the heat conductive sheet 11 can be improved in a normal temperature environment.

[(Thermoplastic fluororesin solid at normal temperature and normal pressure)]
As a solid thermoplastic fluororesin at normal temperature and pressure, for example, vinylidene fluoride-based fluororesin, tetrafluoroethylene-propylene-based fluororesin, tetrafluoroethylene-purplefluorovinylether-based fluororesin, or the like, by polymerizing a fluorine-containing monomer. And the resulting elastomers. More specifically, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, vinylidene fluoride Ride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorofluoroethylene copolymer, tetrafluoroethylene-perfluorodioxole copolymer Coalesce, polyvinyl fluoride, tetrafluoroethylene-propylene copolymer, acrylic modified polytetrafluoroethylene, ester modified polytetrafluoroethylene Epoxy-modified product of polytetrafluoroethylene and polytetrafluoroethylene silane modified product, and the like. These may be used alone or in combination of two or more.
Among these, a vinylidene fluoride-hexafluoropropylene copolymer is preferred from the viewpoint of processability.
In the present invention, rubber and elastomer are included in “resin”.

([Thermoplastic fluororesin liquid at normal temperature and pressure])
Examples of the thermoplastic fluororesin liquid at normal temperature and pressure include vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and vinylidene fluoride-hexafluoropentene-tetrafluoroethylene ternary polymer. Copolymers, perfluoropropene oxide polymers, tetrafluoroethylene-propylene-vinylidene fluoride copolymers and the like can be mentioned.

  Here, the viscosity of the liquid thermoplastic fluororesin at normal temperature and normal pressure is not particularly limited, but from the viewpoint of fluidity, kneadability, and moldability, at a temperature of 105 ° C., preferably 500 cP or more and 30000 cP or less, More preferably, it is 550 cP or more and 25000 cP or less.

[[Blending ratio]]
In addition, the mixing ratio in terms of mass when the thermoplastic fluororesin solid at room temperature and normal pressure and the thermoplastic fluororesin liquid at normal temperature and normal pressure are not particularly limited, and the resin is solid at normal temperature and normal pressure. Thermoplastic fluororesin: The thermoplastic fluororesin liquid at normal temperature and pressure can be adjusted to 40:60 to 70:30.

[Carbon material]
The carbon material contained in the sheet body 12 is not particularly limited, and a known carbon material can be used. Specifically, as the carbon material, a particulate carbon material, a fibrous carbon material, or the like can be used. In addition, any one of the particulate carbon material and the fibrous carbon material may be used alone or both may be used, but from the viewpoint of easily increasing the thermal conductivity of the heat conductive sheet 11, It is preferable to use at least a particulate carbon material. That is, the carbon material preferably contains at least a particulate carbon material. In addition, from the viewpoint of preventing the particulate carbon material from falling off the thermal conductive sheet 11 while further improving the thermal conductivity of the thermal conductive sheet 11, it is preferable to use the particulate carbon material and the fibrous carbon material together. More preferred. That is, it is more preferable that the carbon material further contains a fibrous carbon material in addition to the particulate carbon material.

(Fibrous carbon material)
Here, the fibrous carbon material is not particularly limited, and for example, carbon nanotubes, vapor-grown carbon fibers, carbon fibers obtained by carbonizing organic fibers, and cut products thereof can be used. . These may be used alone or in combination of two or more.
When the sheet body 12 contains the fibrous carbon material, the thermal conductivity of the heat conductive sheet 11 can be further improved, and when the fibrous carbon material is used together with the particulate carbon material, the powder of the particulate carbon material can be reduced. It can also be prevented more. It is not clear why the fibrous carbon material can prevent the powdered carbon material from falling off, but the fibrous carbon material forms a three-dimensional network structure, and thus has a thermal conductivity. It is presumed that this is because desorption of the particulate carbon material is prevented while increasing the strength.

  Among the above, a fibrous carbon nanostructure such as a carbon nanotube is preferably used as the fibrous carbon material, and a fibrous carbon nanostructure containing a carbon nanotube is more preferably used. If a fibrous carbon nanostructure such as a carbon nanotube is used, the heat conductivity and strength of the heat conductive sheet 11 of the present invention can be further improved.

([Fibrous carbon nanostructure containing carbon nanotubes])
Here, the fibrous carbon nanostructure containing carbon nanotubes, which can be suitably used as the fibrous carbon material, may be composed of only carbon nanotubes (hereinafter, sometimes referred to as “CNT”). Alternatively, a mixture of CNT and a fibrous carbon nanostructure other than CNT may be used.
The CNTs in the fibrous carbon nanostructure are not particularly limited, and single-walled carbon nanotubes and / or multi-walled carbon nanotubes can be used. And more preferably a single-walled carbon nanotube. When the single-walled carbon nanotube is used, the thermal conductivity and the strength of the heat conductive sheet 11 can be further improved as compared with the case where the multi-walled carbon nanotube is used.

  For example, a fibrous carbon nanostructure containing CNT is prepared by supplying a raw material compound and a carrier gas onto a base material having a catalyst layer for producing carbon nanotubes on the surface thereof, and performing chemical vapor deposition (CVD). In synthesizing CNTs, a method of dramatically improving the catalytic activity of a catalyst layer by the presence of a trace amount of an oxidizing agent (catalytic activator) in the system (super growth method; WO 2006/011655) ) Can be efficiently produced. Hereinafter, the carbon nanotube obtained by the super growth method may be referred to as “SGCNT”.

  Here, the fibrous carbon nanostructure containing CNTs manufactured by the super growth method may be composed of only SGCNT, or may be other carbon such as a non-cylindrical carbon nanostructure in addition to SGCNT. Nanostructures may be included.

[[Properties of fibrous carbon material]]
The average fiber diameter of the above-mentioned fibrous carbon material is preferably 1 nm or more, more preferably 3 nm or more, preferably 2 μm or less, and more preferably 1 μm or less. If the average fiber diameter of the fibrous carbon material is within the above range, the heat conductivity, hardness and strength of the heat conductive sheet 11 can be made to be sufficiently high at the same time.

  In the present invention, the “average fiber diameter” is obtained by observing a cross section in the thickness direction of the heat conductive sheet 11 with a SEM (scanning electron microscope) or a TEM (transmission electron microscope), and selecting any fifty fibrous carbon. It can be obtained by measuring the fiber diameter of the material and calculating the number average value of the measured fiber diameters. In particular, when the fiber diameter is small, it is preferable to observe the same cross section with a TEM (transmission electron microscope).

[[Content ratio of fibrous carbon material]]
The content ratio of the fibrous carbon material in the carbon material is preferably 0.001% by mass or more, preferably less than 100% by mass, more preferably 20% by mass or less, and more preferably 10% by mass or less. %, More preferably 0.5% by mass or less. When the content ratio of the fibrous carbon material in the carbon material is equal to or more than the above lower limit, the thermal conductivity and strength of the heat conductive sheet 11 can be sufficiently improved, and when used together with the particulate carbon material, Powdering of the carbon material can be sufficiently prevented. When the content ratio of the fibrous carbon material is equal to or less than the upper limit, the hardness of the heat conductive sheet 11 is prevented from being excessively increased (that is, the flexibility is excessively decreased) due to the compounding of the fibrous carbon material. be able to.

(Particulate carbon material)
The above-mentioned particulate carbon material is not particularly limited, and examples thereof include graphite such as natural graphite, artificial graphite, flaky graphite, exfoliated graphite, acid-treated graphite, expandable graphite, and expanded graphite; carbon black. ; Etc. can be used. These may be used alone or in combination of two or more.
Above all, it is preferable to use expanded graphite as the particulate carbon material. If expanded graphite is used, the thermal conductivity of the heat conductive sheet 11 can be further improved.

[[Expanded graphite]]
Here, expanded graphite that can be suitably used as the particulate carbon material is, for example, expandable graphite obtained by chemically treating graphite such as flaky graphite with sulfuric acid, etc. Can be obtained.

[[Particle size of particulate carbon material]]
Further, the particle diameter of the particulate carbon material is preferably 20 μm or more, more preferably 30 μm or more, and preferably 300 μm or less in terms of volume average particle diameter. When the particle diameter of the particulate carbon material is equal to or larger than the lower limit, the particulate carbon material is easily oriented in a desired direction in the sheet body 12 and a good heat transfer path is easily formed. Therefore, the bulk thermal resistance of the heat conductive sheet 11 can be further reduced, and higher thermal conductivity can be exhibited. Further, if the particle diameter of the particulate carbon material is equal to or less than the upper limit, the surface of the sheet body 12 is made smoother, and the heat transfer from the heating element to the sheet body 12 when in contact with the heating element is improved. Can be.
In the present invention, the “volume average particle size” can be measured according to JIS Z8825, and the cumulative volume calculated from the smaller diameter side is 50% in the particle size distribution (volume basis) measured by a laser diffraction method. Represents the particle size.

[[Content ratio of particulate carbon material]]
The content ratio of the particulate carbon material in the carbon material is more preferably 80% by mass or more, further preferably 90% by mass or more, and still more preferably 99.5% by mass or more. It can be 100% by mass or less, and preferably 99.9% by mass or less. When the content ratio of the particulate carbon material in the carbon material is equal to or more than the lower limit, the particulate carbon material is more favorably oriented in the sheet body 12, and the particulate carbon materials come into contact with each other to form a good heat transfer path. Form. As a result, the heat conductive sheet 11 can exhibit high thermal conductivity. Further, when the content ratio of the particulate carbon material is 99.9% by mass or less, powder of the particulate carbon material from the sheet body 12 can be prevented from falling off.

[Content ratio of carbon material]
The content ratio of the carbon material in the sheet body 12 is preferably 15% by mass or more, more preferably 20% by mass or more, preferably 80% by mass or less, and more preferably 60% by mass or less. More preferably, there is. When the content ratio of the carbon material in the sheet body 12 is equal to or more than the lower limit value, the carbon materials are more favorably oriented in the sheet body 12, and the carbon materials contact each other to form a good conduction path. As a result, the sheet body 12 can exhibit higher thermal conductivity. When the content ratio of the carbon material is equal to or less than the upper limit, the hardness can be more easily adjusted by imparting flexibility to the sheet body 12.

<Additives>
If necessary, the sheet body 12 of the present invention may further contain known additives that can be used for forming the sheet body 12. The additive that can be blended in the sheet body 12 is not particularly limited, and is, for example, a plasticizer such as a fatty acid ester such as sebacate; a flame retardant such as a red phosphorus-based flame retardant and a phosphate ester-based flame retardant. A toughness improving agent such as urethane acrylate; a hygroscopic agent such as calcium oxide and magnesium oxide; an adhesion improving agent such as a silane coupling agent, a titanium coupling agent and an acid anhydride; a nonionic surfactant and a fluorine surfactant And an ion trapping agent such as an inorganic ion exchanger.

<Reinforcing part>
Subsequently, the reinforcing portion 21 will be described in detail. The reinforcing portion 21 is formed by filling the hole portion 15 of the sheet body 12 with at least one of a metal inorganic oxide. As shown in FIGS. 3 and 4, the reinforcing portion 21 has a columnar shape having a circular cross section orthogonal to the thickness direction of the heat conductive sheet 11, and extends between both main surfaces of the heat conductive sheet 11. Are there.

[metal]
Here, examples of the metal include gold, silver, copper, aluminum, nickel, and the like. Among them, silver is preferable because of its high thermal conductivity. As the metal, one kind may be used alone, or two or more kinds may be used in combination at an arbitrary ratio.

  The Mohs hardness of the metal is not particularly limited, but is preferably 2 or more, more preferably 3 or more, preferably 7 or less, and more preferably 5 or less. When the Mohs' hardness of the metal is equal to or more than the above lower limit, the collapse of the heat conductive sheet 12 in the thickness direction under a high load can be satisfactorily suppressed. If the Mohs hardness of the metal is equal to or less than the above upper limit, when the heat conductive sheet 11 is used between a heat generator and a heat radiator described later, damage to the surface of the heat generator and the heat radiator is further prevented. can do.

[Inorganic oxide]
Further, examples of the inorganic oxide is not particularly limited, for example, glass (SiO _2), glass precursors, and the like. As the inorganic oxide, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.
And glass and / or a glass precursor as an inorganic oxide are usually formed using a liquid composition containing glass and / or a glass precursor.

Here, the liquid composition containing glass and / or a glass precursor is liquid under the conditions of a temperature of 25 ° C. and a pressure (absolute pressure) of 1 atm, and can be solidified to form a glass layer. There is no particular limitation, and a liquid composition containing glass and / or a glass precursor and optionally further containing a solvent and an additive can be used. Above all, from the viewpoint of easy formation of a glass layer, it is preferable to use liquid glass as the liquid composition.
In addition, as a glass precursor contained in a liquid composition, tetraethoxysilane etc. are mentioned, for example.

  Here, the liquid glass is not particularly limited, and examples thereof include a liquid glass containing silicon dioxide, alumina, and a solvent, and a liquid glass containing tetraethoxysilane, a metal catalyst, and water. More specifically, examples of the liquid glass include “Heatless Glass” and “Shidak Cital B4373” manufactured by Sumitomo Chemical Co., Ltd., and “Fine Crystal (Quartz for NOM Series)” manufactured by Mokutec Kamemura Corporation. Can be used.

  The Mohs hardness of the inorganic oxide is not particularly limited, but is preferably 2 or more, more preferably 3 or more, preferably 7 or less, and more preferably 5 or less. When the Mohs hardness of the inorganic oxide is equal to or higher than the lower limit, the collapse of the heat conductive sheet 12 under a high load can be further suppressed. Further, if the Mohs hardness of the inorganic oxide is equal to or less than the upper limit, when the heat conductive sheet 11 is used between the heat generating body 81 and the heat radiating body 82, the surface of the heat generating body and the heat radiating body may be damaged. Further, it can be prevented.

  In addition, as shown in FIG. 4, assuming that the major axis of the cross section orthogonal to the thickness direction of the heat conductive sheet 11 of the reinforcing portion 21 is d, the major axis (d) is preferably 0.1 mm or more, and preferably 2 mm or less. Preferably, there is. When the major axis (d) of the cross section of the reinforcing portion 21 perpendicular to the thickness direction of the heat conductive sheet 11 is within the above range, the thermal conductivity of the heat conductive sheet 11 can be suitably maintained.

The arrangement density of the reinforcing portions 21 is not particularly limited, but is preferably 1 piece / cm ² or more, and more preferably 2 pieces / cm ² or more. If the arrangement density of the reinforcing portions 21 is 1 piece / cm ² or more, the collapse of the heat conductive sheet 11 in the thickness direction and the decrease in thermal conductivity can be suppressed in a well-balanced manner.

<<< Asker C hardness >>
The sheet body 12 preferably has an Asker C hardness at a temperature of 25 ° C. of 30 or more, and more preferably 90 or less. When the Asker C hardness of the sheet main body 12 is within the above range, the flexibility and the handleability of the heat conductive sheet 11 in a room temperature environment can be improved.
In the present invention, “Asker C hardness” can be measured by the method described in the examples of the present specification.

  The heat conductive sheet 11 is not particularly limited, but preferably has the following properties.

<Thickness>
The heat conductive sheet 11 preferably has a sheet thickness (T) of 0.1 mm or more, more preferably 0.15 mm or more, preferably 1 mm or less, and preferably 0.5 mm or less under normal temperature and normal pressure. Is more preferable. When the thickness of the heat conductive sheet 11 under normal temperature and normal pressure is equal to or less than the upper limit, the heat conductive sheet 11 can be suitably used by sandwiching the heat conductive sheet 11 between a heat generator and a heat radiator described later. Further, when the sheet thickness of the heat conductive sheet 11 is equal to or more than the above lower limit, the strength, durability and handling properties of the heat conductive sheet 11 are more excellent.
In the present invention, “sheet thickness” can be measured by the method described in Examples of the present invention.

<Change rate of sheet thickness>
And the rate of change of the sheet thickness of the heat conductive sheet 11 is preferably 0.4 or more, more preferably 0.5 or more, preferably 0.9 or less, and 0.8 or less. Is more preferable. If the rate of change of the sheet thickness of the heat conductive sheet 11 is within the above range, the heat conductive sheet 11 can be more suitably used by sandwiching it between a heat generator and a heat radiator described later.
In the present invention, the “rate of change in sheet thickness” can be measured by the method described in Examples in the present specification.

<Thermal conductivity>
Further, the thermal conductive sheet 11 has a thermal conductivity under a pressure of 0.05 MPa of preferably 10 W / mK or more, more preferably 15 W / mK or more, and preferably 30 W / mK or less. , 25 W / mK or less.
Moreover, the thermal conductivity of the heat conductive sheet 11 under 1.5 MPa pressure is preferably 5 W / mK or more, more preferably 10 W / mK or more, and preferably 20 W / mK or less. , 15 W / mK or less.
If the thermal conductivity of the heat conductive sheet 11 under the pressure of 0.05 MPa and the thermal conductivity under the pressure of 1.5 MPa are within the above ranges, respectively, the heat conductive sheet 11 is sandwiched between a heating element and a heat radiating element described later. It can be more preferably used.
In the present invention, the “thermal conductivity” can be determined by the measuring method described in the examples of the present specification.

<Change rate of thermal conductivity>
In the heat conductive sheet 11, the rate of change of the thermal conductivity is preferably 0.3 or more, and more preferably 0.5 or more. When the rate of change of the thermal conductivity is equal to or higher than the lower limit, the heat conductive sheet 11 can exhibit excellent thermal conductivity even under a high load.
In the present invention, the “rate of change in thermal conductivity” can be determined by the method described in the examples of the present specification.

<Ratio of change rate of sheet thickness to change rate of thermal conductivity>
Furthermore, in the heat conductive sheet 11, the ratio of the change rate of the sheet thickness to the change rate of the heat conductivity [(change rate of sheet thickness) / (change rate of heat conductivity)] is 0.95 or more. Preferably, it is 0.98 or more, more preferably 1.5 or less, more preferably 1.3 or less, and most preferably 1. When the ratio between the rate of change of the sheet thickness and the rate of change of the thermal conductivity is within the above range, the collapse of the heat conductive sheet 11 in the thickness direction and the decrease in thermal conductivity can be suppressed in a well-balanced manner.

The heat conductive sheet 11 having the above configuration can be used, for example, as a sheet for efficiently transmitting heat from a heating element to a radiator.
Specifically, as shown in a front view of the usage mode in FIG. 7, when attaching the heat radiator 82 to the heat radiator 81, the heat conductive sheet 11 is used by being sandwiched between the heat radiator 81 and the heat radiator 82. can do. According to the present invention, even when the thermal conductive sheet 11 is sandwiched between the heat generating body 81 and the heat radiating body 82 and used under a high load, the collapse of the thermal conductive sheet 11 in the thickness direction can be suppressed, and the thermal conductivity can be reduced. The high thermal conductivity of the conductive sheet 11 can be maintained.

  As described above, the heat conductive sheet according to one embodiment of the present invention has been described, but the heat conductive sheet of the present invention is not limited to the above-described embodiment. Specifically, the above-described reinforcing portion is not limited to the configuration described in the above embodiment. Thus, with reference to FIG. 8, a description will be given of a modified example of the reinforcing portion in the heat conductive sheet of the present invention.

(Modified example of reinforcing part)
FIG. 8 is a cross-sectional view schematically showing a modified example of the reinforcing portion in the heat conductive sheet of the present invention. The same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof will not be repeated.

  In the heat conductive sheet of the present invention, the above-mentioned hole is not particularly limited as long as it extends in the thickness direction of the heat conductive sheet. Therefore, the hole may be a hole that is open at both ends, may be a hole that is open at one end, and may be a hole that is closed at the other end, or may be a hole that is closed at both ends. Hole may be provided. 8A, the reinforcing portion 21 may be configured such that only one end of the reinforcing portion 21 is exposed from the surface of the heat conductive sheet 11, for example, as shown in FIG. (B), the reinforcing portion 21 may be embedded in the seat body 12. Further, the shape of the reinforcing portion is not limited to the column shape, and may be, for example, a polygonal column shape.

  Here, assuming that the thickness of the heat conductive sheet 11 is T and the length of the reinforcing portion 21 in the thickness direction of the heat conductive sheet 11 is L, the thickness (T) of the heat conductive sheet 11 The ratio [(L / T) × 100] of the length (L) in the thickness direction is preferably 50% or more, and 100%, that is, as shown in FIG. More preferably, it penetrates through the thickness direction of the heat conductive sheet 11. If the ratio of the length (L) of the reinforcing portion 21 in the thickness direction of the heat conductive sheet 11 to the thickness (T) of the heat conductive sheet 11 is 50% or more, the collapse of the heat conductive sheet in the thickness direction is more preferable. Can be suppressed.

<Production method of heat conductive sheet>
And the manufacturing method of the above-mentioned heat conductive sheet 11 is not particularly limited, for example,
(1) a step of pressing a composition containing a resin and a carbon material into a sheet to obtain a pre-sheet (pre-sheet forming step);
(2) a step of laminating a plurality of pre-sheets in the thickness direction or folding or winding the pre-sheets to obtain a laminate (laminate forming step);
(3) a step of slicing the obtained laminate at an angle of 45 ° or less with respect to the lamination direction to obtain a pre-sheet body (pre-sheet body forming step);
(4) a step of forming a hole in the obtained pre-sheet body to obtain a sheet body (sheet body forming step);
(5) a step of filling a hole formed in the sheet body with a filler to form a reinforcing section (reinforcing section forming step);
Can be produced by a production method including:

[(1) Pre-sheet molding step]
In the pre-sheet forming step, a composition containing a resin and a carbon material and optionally containing an additive is pressurized and formed into a sheet to obtain a pre-sheet. Here, as the resin, the carbon material, and the additive, those described above as the resin, the carbon material, and the additive that can be included in the heat conductive sheet of the present invention can be used.

  The composition is obtained by stirring and mixing the above components. The stirring and mixing are not particularly limited, and can be performed using a known mixing device such as a kneader, a roll, a Henschel mixer, a Hobart mixer, a high-speed mixer, a twin-screw kneader, or the like. The stirring and mixing may be performed in the presence of a solvent such as ethyl acetate or methyl ethyl ketone. The stirring and mixing conditions can be appropriately set, for example, with reference to examples described later. The stirring and mixing temperature can be, for example, 5 ° C. or more and 150 ° C. or less.

  In addition, among the above-mentioned components, particularly, the fibrous carbon material is easily aggregated and has low dispersibility. Therefore, when mixed with other components such as a fluororesin or expanded graphite as it is, the composition is favorably contained in the composition. Difficult to disperse. On the other hand, when the fibrous carbon material is mixed with another component such as a fluororesin or expanded graphite in the state of a dispersion dispersed in a solvent (dispersion medium), the occurrence of aggregation can be suppressed. In the case of mixing in the state described above, a large amount of solvent is used when the solid content is solidified after mixing to obtain a composition, and thus the amount of the solvent used for preparing the composition may increase. Therefore, when a fibrous carbon material is added to the composition used for forming the pre-sheet, the fibrous carbon material is obtained by removing the solvent from a dispersion obtained by dispersing the fibrous carbon material in a solvent (dispersion medium). It is preferable to mix the obtained fibrous carbon material with other components in the state of an aggregate (easily dispersible aggregate). The aggregate of the fibrous carbon material obtained by removing the solvent from the dispersion of the fibrous carbon material is composed of the fibrous carbon material once dispersed in the solvent, and the fibrous carbon material before being dispersed in the solvent. Is more excellent in dispersibility than the aggregate of the above, so that an easily dispersible aggregate having high dispersibility is obtained. Therefore, if the easily dispersible aggregate and other components such as fluororesin and expanded graphite are mixed, the fibrous carbon material can be dispersed well in the composition efficiently without using a large amount of solvent. Can be done.

  Here, for the dispersion of the fibrous carbon material, for example, a coarse dispersion obtained by adding the fibrous carbon material to a solvent is subjected to a dispersion treatment in which a cavitation effect is obtained or a dispersion treatment in which a crushing effect is obtained. Can be obtained. Note that the dispersion treatment for obtaining the cavitation effect is a dispersion method using a shock wave generated by bursting a vacuum bubble generated in water when high energy is applied to a liquid. Specific examples of the dispersion treatment that can achieve the cavitation effect include dispersion treatment with an ultrasonic homogenizer, dispersion treatment with a jet mill, and dispersion treatment with a high-shear stirring device. In addition, the dispersion treatment for obtaining the crushing effect is performed by applying a shearing force to the coarse dispersion to crush and disperse the aggregates of the fibrous carbon material, and further applying a back pressure to the coarse dispersion to remove bubbles. This is a dispersion method of uniformly dispersing the fibrous carbon material in a solvent while suppressing generation.

  Further, the removal of the solvent from the dispersion can be performed by using a known solvent removal method such as drying and filtration, but from the viewpoint of quickly and efficiently removing the solvent, a filtration method such as vacuum filtration is used. It is preferable to carry out.

  The composition prepared as described above can be arbitrarily defoamed and crushed, and then pressurized to form a sheet. When a solvent is used at the time of mixing, it is preferable to form the sheet after removing the solvent. For example, if defoaming is performed using vacuum defoaming, the solvent is removed at the same time as defoaming. be able to.

Here, the composition is not particularly limited as long as it is a molding method to which pressure is applied, and can be formed into a sheet by using a known molding method such as press molding, rolling molding, or extrusion molding. Above all, the composition is preferably formed into a sheet by rolling, and more preferably formed into a sheet by passing between rolls in a state sandwiched between protective films. The protective film is not particularly limited, and a sand blasted polyethylene terephthalate film or the like can be used. Further, the roll temperature can be 5 ° C. or more and 150 ° C.
The thickness of the pre-sheet is not particularly limited, and may be, for example, 0.05 mm or more and 2 mm or less.

[(2) Laminate forming step]
In the laminate forming step, a plurality of presheets obtained in the presheet forming step are laminated in the thickness direction, or the presheet is folded or wound to obtain a laminate. Here, the formation of the laminate by folding the pre-sheet is not particularly limited, and can be performed by folding the pre-sheet at a constant width using a folding machine. In addition, the formation of the laminate by winding the presheet is not particularly limited, and can be performed by winding the presheet around an axis parallel to the short direction or the long direction of the presheet.

  Here, usually, in the laminate obtained in the laminate forming step, the adhesive force between the surfaces of the pre-sheets is sufficiently obtained by the pressure at the time of laminating the pre-sheets and the pulling force at the time of folding or winding. However, when the adhesive strength is insufficient or when it is necessary to sufficiently suppress delamination of the laminate, the laminate forming step may be performed with the surface of the pre-sheet slightly dissolved with a solvent, The laminate forming step may be performed with the adhesive applied to the surface of the pre-sheet or with the adhesive layer provided on the surface of the pre-sheet.

  The solvent used for dissolving the surface of the presheet is not particularly limited, and a known solvent that can dissolve a resin component such as a fluororesin contained in the presheet can be used. Above all, it is preferable to use acetone from the viewpoint of solubility and volatility.

The adhesive applied to the surface of the pre-sheet is not particularly limited, and a commercially available adhesive or a tacky resin can be used. Above all, it is preferable to use a resin having the same composition as a resin component such as a fluororesin contained in the pre-sheet as the adhesive. The thickness of the adhesive applied to the surface of the pre-sheet can be, for example, 10 μm or more and 1000 μm or less.
Further, the adhesive layer provided on the surface of the pre-sheet is not particularly limited, and a double-sided tape or the like can be used.
Here, the adhesive or the adhesive layer may contain a thermally conductive filler as long as the resulting thermally conductive sheet is not too hard.

  In addition, from the viewpoint of suppressing delamination, the obtained laminate is heated at 120 ° C or higher and 170 ° C or lower for 2 to 8 hours while being pressed in the stacking direction at a pressure of 0.1 MPa or higher and 0.5 MPa or lower. Good.

[(3) Pre-sheet body forming step]
In the pre-sheet body forming step, the laminate obtained in the laminate forming step is sliced at an angle of 45 ° or less with respect to the laminating direction to obtain a pre-sheet body composed of slices of the laminate. Here, the method for slicing the laminate is not particularly limited, and examples thereof include a multi-blade method, a laser processing method, a water jet method, and a knife processing method. Among them, the knife processing method is preferable because the thickness of the pre-sheet body is easily made uniform. Further, the cutting tool for slicing the laminated body is not particularly limited, and a slicing member having a smooth board surface having a slit and a blade portion protruding from the slit portion (for example, provided with a sharp blade Canna or slicer).

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

  In addition, from the viewpoint of easily slicing the laminate, the temperature of the laminate at the time of slicing is preferably from -20 ° C to 20 ° C, more preferably from -10 ° C to 0 ° C. Further, for the same reason, it is preferable that the laminated body to be sliced is sliced while applying pressure in a direction perpendicular to the laminating direction, and a pressure of 0.1 MPa or more and 0.5 MPa or less in a direction perpendicular to the laminating direction. It is more preferable to slice while loading.

[(4) Sheet body forming step]
In the sheet body forming step, one surface of the pre-sheet body is irradiated with laser light to form a sheet body having a hole extending in the thickness direction of the sheet body. Here, the number of irradiations and the irradiation position of the laser beam are not particularly limited, and may be any number of irradiations and irradiation positions. Further, the spot diameter of the laser beam and the irradiation time of the laser beam may be appropriately adjusted according to the shape, size, and the like of the target reinforcing portion.
As the laser, for example, a CO ₂ laser, a UV-YAG laser, or the like can be used. Particularly preferred is a CO ₂ laser having a wavelength of 10.6 μm. The irradiation output is preferably from 10 to 100 W, and can be appropriately adjusted according to the size and depth of the hole. For example, a hole can be formed by the following procedure.
(1) Adjust the irradiation position of the laser beam irradiation device so that the laser beam can be irradiated perpendicularly to the surface of the pre-sheet body. (2) The laser irradiation conditions are programmed according to the properties (thickness, density, hardness, etc.) of the holes and the number, spacing, and size of the holes in the pre-sheet body. (3) The laser irradiation can be performed at a position where the laser beam is positioned by sliding the stage, and while the stage is being slid, the pre-sheet body is intermittently irradiated with a laser beam to form a plurality of holes at a desired position. Form a part.

[(5) Reinforcing part forming step]
In the reinforcing portion forming step, at least one of a metal and an inorganic oxide is filled in the hole formed in the sheet body to form a reinforcing portion. The reinforcing portion is preferably formed by filling and curing a paste-like material such as a silver paste. Further, as the metal and the inorganic oxide that can be used for filling, those described above as the metal and the inorganic oxide that can form the reinforcing portion can be used.
Then, by drying the filler, the heat conductive sheet 11 shown in the present embodiment is obtained.
Further, two heat conductive sheets 11 obtained by the above-described method are prepared, and they are bonded by an arbitrary bonding method to form a heat conductive sheet as shown in FIG. 8B.

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

  In Examples and Comparative Examples, the height of the reinforcing portion in the thickness direction of the heat conductive sheet, the arrangement density of the reinforcing portion, the average area of a cross section orthogonal to the thickness direction of the heat conductive sheet of the reinforcing portion, Asker C hardness, sheet thickness , And thermal conductivity were measured or evaluated using the following methods, respectively.

<Height of the reinforcement section in the thickness direction of the heat conductive sheet>
First, for the depth of the hole, a cross section was obtained using a cross section polisher (registered trademark) “IB-0902CP” cross-section sample preparation device manufactured by JEOL Ltd. Microscope “VK-X250 series”). The depth of the hole was defined as the height of the reinforcing portion in the thickness direction of the heat conductive sheet.

<Arrangement density of reinforcement>
The number of holes formed per 1 cm square of the surface of the sheet body was measured using the above laser microscope. Then, the number of reinforcing portions per 1 cm square on one surface of the heat conductive sheet was defined as the arrangement density of the reinforcing portions.

<Average area of cross section orthogonal to thickness direction of thermal conductive sheet of reinforcement>
The opening area of each hole was measured using the above laser microscope. Since the hole had a cylindrical shape, the opening area of the hole was defined as an average area of a cross section of the reinforcing portion orthogonal to the thickness direction of the heat conductive sheet. Then, based on the surface area (s _m ) of the heat conductive sheet and the sum (s) of the average areas of the cross sections orthogonal to the thickness direction of the heat conductive sheet of each reinforcing portion, the surface area (s _m ) of the heat conductive sheet is determined. The ratio [(s / s _m ) × 100 (%)] of the total area (s) of the average areas of the cross sections of the reinforcement sections perpendicular to the thickness direction of the heat conductive sheet was determined.

<Asker C hardness>
The Asker C hardness of the sheet body is 23 ° C. using a hardness tester (manufactured by Kobunshi Keiki Co., Ltd., product name “ASKER CL-150LJ”) in accordance with the Asker C method of the Japan Rubber Association Standard (SRIS 0101). Was measured under the following environment.

<Sheet thickness>
The sheet thickness of the heat conductive sheet was measured with an accuracy of (1/1000 mm) using a Digimatic Indicator (ID-C112X) manufactured by Mitutoyo Corporation.
Specifically, the sheet thickness of the thermal conductive sheet under a pressure of 0.05 MPa and the sheet thickness of the thermal conductivity sheet under a pressure of 1.5 MPa were measured. Then, the rate of change in sheet thickness was determined based on the following equation.
Rate of change in sheet thickness = (sheet thickness of thermal conductive sheet under 1.5 MPa pressure) / (sheet thickness of thermal conductive sheet under 0.05 MPa pressure)
The rate of change in sheet thickness was evaluated based on the following.
A: Change rate of sheet thickness exceeds 0.6 B: Change rate of sheet thickness exceeds 0.5 and less than 0.6 C: Change rate of sheet thickness is less than 0.5

<Thermal conductivity>
The thermal conductivity of the heat conductive sheet was calculated based on the thermal resistance value of the heat conductive sheet. Specifically, the thermal resistance of the heat conductive sheet was measured using a resin material thermal resistance tester (manufactured by Hitachi Technology and Service Co., Ltd.). At this time, a heat conductive sheet cut into a 0.5 cm square substantially square including a reinforcing portion was used as a sample, and the sample had a thermal resistance R ₁ (° C./W) under a pressure of 0.05 MPa at a sample temperature of 50 ° C. And the thermal resistance R ₂ (° C./W) of the sample under 1.5 MPa pressure.
Then, from the thermal resistance values R ₁ and R ₂ , the thermal conductivity C ₁ (W / mK) of the sample under a pressure of 0.05 MPa and the thermal conductivity C ₂ of the sample under a pressure of 1.5 MPa (W / mK) was obtained from the following formula as a value when converted to a 1 cm square of the heat conductive sheet.
Thermal conductivity (W / mK) = [1 / thermal resistance value (° C./W)]×[(sample thickness (mm) / (sample area (mm ² )) × 1000)
Then, the rate of change of the thermal conductivity was determined based on the following equation.
Rate of change of thermal conductivity = [Thermal conductivity of sample under 1.5 MPa pressurization (C ₂ ) / (Thermal conductivity of sample under 0.05 MPa pressurization (C ₁ )]]
Then, the rate of change of the thermal conductivity was evaluated based on the following criteria.
A: The rate of change of thermal conductivity exceeds 0.5 B: The rate of change of thermal conductivity exceeds 0.3 and less than 0.5 C: The rate of change of thermal conductivity is less than 0.3

Further, the following evaluation was performed based on the ratio of the rate of change of the thickness of the sheet to the rate of change of the thermal conductivity [(change rate of thickness of the sheet) / (change rate of thermal conductivity)].
A: [(change rate of sheet thickness) / (change rate of thermal conductivity)] exceeds 0.95 or more and less than 1.2 B: [(change rate of sheet thickness) / (change rate of thermal conductivity) )] Exceeds 1.2 and less than 2.0 C: [(change rate of sheet thickness) / (change rate of thermal conductivity)] exceeds 2.0 [(change rate of sheet thickness) / (heat (Rate of change in conductivity)], the closer to 1 the value, the more well-balanced suppression of collapse in the thickness direction of the heat conductive sheet and reduction in heat conductivity can be achieved.

(Example 1)
<Preparation of easily dispersible aggregate of fibrous carbon nanostructure>
[Preparation of dispersion]
400 mg of a fibrous carbon nanostructure (ZEONANO (registered trademark) SG101, manufactured by Zeon Corporation, specific surface area: 600 m ² / g) is weighed, mixed in 2 L of methyl ethyl ketone as a solvent, stirred for 2 minutes with a homogenizer, and coarsely dispersed. A liquid was obtained. Next, using a wet jet mill (manufactured by Joko Co., Ltd., product name “JN-20”), the obtained coarse dispersion liquid was passed through a 0.5 mm flow path of the wet jet mill at a pressure of 100 MPa for 2 cycles. Thus, the fibrous carbon nanostructure was dispersed in methyl ethyl ketone. Then, a dispersion having a solid content concentration of 0.20% by mass was obtained.

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

[Preparation of composition]
70 parts of a thermoplastic fluororesin liquid (manufactured by Daikin Industries, Ltd., trade name "Daiel G-101") at normal temperature and normal pressure, and a solid thermoplastic fluororesin (manufactured by 3M Japan Co., Ltd. under normal temperature and normal pressure) "Dynion FC-2211", Mooney viscosity: 27 ML _{1 + 4} , 100 ° C), 30 parts, and expanded graphite as a particulate carbon material as a thermally conductive filler (trade name "EC50", manufactured by Ito Graphite Industry Co., Ltd.) , Volume average particle diameter: 250 μm), and 0.5 part of the above-mentioned easily dispersible aggregate of fibrous carbon nanostructures as a fibrous carbon material, using a pressure kneader (manufactured by Nippon Spindle). The mixture was stirred and mixed at a temperature of 150 ° C. for 20 minutes. Next, the obtained mixture was put into a crusher and crushed for 10 seconds to obtain a composition.

[(1) Pre-sheet molding step]
Next, 50 g of the obtained composition is sandwiched between 50 μm-thick PET films (protective films) that have been subjected to sandblasting, and the conditions are as follows: roll gap 550 μm, roll temperature 50 ° C., roll linear pressure 50 kg / cm, roll speed 1 m / min. To form a pre-sheet having a thickness of 0.5 mm.

[(2) Laminate forming step]
Subsequently, the obtained pre-sheet is cut into a size of 150 mm (length) × 150 mm (width) × 0.5 mm (thickness), 120 sheets are laminated in the thickness direction of the pre-sheet, and further pressed at a temperature of 120 ° C. and a pressure of 0.1 MPa for 3 minutes in the lamination direction. By performing (secondary pressurization), a laminate having a height of about 60 mm was obtained.

[(3) Pre-sheet body forming step]
Then, while pressing the laminated side surface of the secondary-pressed laminate at a pressure of 0.3 MPa, a slicer for woodworking (trade name “Super Finished Planer Super Mecha S” manufactured by Marunaka Ironworks Co., Ltd.) is used. Then, by slicing at an angle of 0 degree with respect to the laminating direction (in other words, in the direction of the normal to the main surface of the laminated pre-sheet), a pre-sheet main body of 150 mm long × 60 mm wide × 0.15 mm thick is obtained. Was.

[(4) Sheet body forming step]
A sheet body having one hole per 1 cm square of the surface of the sheet body was formed on the surface of the obtained pre-sheet body using a CO ₂ laser beam machine (VLS 6.60, manufactured by Universal Laser Systems). Specifically, a hole was formed in a central portion of a 1 cm × 1 cm square of the sheet body using a CO ₂ laser processing machine.

[(5) Reinforcing part forming step]
Then, the sheet main body was placed on a flat copper plate having a thickness of 1 mm. Then, a silver paste (Mohs hardness: 2.5, manufactured by Nihon Handa Co., Ltd.) as a filler is dropped on the upper portion of the sheet body, and the surface of the sheet body is lightened with a 1 mm thick copper plate so as not to be damaged. Filled with silver paste. Thereafter, the filler was sintered at 250 ° C. for 20 minutes to obtain a heat conductive sheet. Various physical properties were evaluated using the obtained heat conductive sheet. Table 1 shows the results.

(Example 2)
The same operation as in Example 1 was performed except that the hole was filled with liquid glass (Quartz for NOM, Mohs hardness: 4) manufactured by Moktec Kamemura Co., Ltd. Various physical properties were evaluated using the obtained heat conductive sheet, and the results are shown in Table 1.

(Example 3)
Four holes were formed per 1 cm square of the surface of the sheet body. Specifically, a hole was formed in a central portion of four squares obtained by dividing a square of 1 cm × 1 cm in surface of the sheet body into four using a CO ₂ laser processing machine. Otherwise, the same operation as in Example 1 was performed to obtain a heat conductive sheet. And various physical properties were evaluated using the obtained heat conductive sheet. Table 1 shows the results.

(Example 4)
The same operation as in Example 1 was performed, except that the depth of the hole was set to 50% of the thickness of the heat conductive sheet by setting the depth of the hole formed in the sheet body to 0.075 mm. I got And various physical properties were evaluated using the obtained heat conductive sheet. Table 1 shows the results.

(Example 5)
The same operation as in Example 1 was performed except that the depth of the hole was made 30% of the thickness of the heat conductive sheet by setting the depth of the hole formed in the sheet body to 0.045 mm. I got And various physical properties were evaluated using the obtained heat conductive sheet. Table 1 shows the results.

(Comparative Example 1)
A heat conductive sheet was obtained by performing the same operation as in Example 1 except that no hole was formed in the sheet body. And various physical properties were evaluated using the obtained heat conductive sheet. Table 1 shows the results.

(Comparative Example 2)
Twenty holes were formed per 1 cm square of the surface of the sheet body. Specifically, a CO ₂ laser processing machine is applied to the central portion of each of a total of 20 squares obtained by dividing a square of 1 cm × 1 cm in the surface of the sheet body into five equal parts in the vertical direction and four equal parts in the horizontal direction. A hole was formed using the same. Otherwise, the same operation as in Example 1 was performed to obtain a heat conductive sheet. And various physical properties were evaluated using the obtained heat conductive sheet. Table 1 shows the results.

From the above results, the ratio of the total area (s) of the average area of the cross sections orthogonal to the thickness direction of the heat conductive sheet of each reinforcing portion to the surface area (s _m ) of the heat conductive sheet was less than 1%. It can be seen that the heat conductive sheet is excellent in both suppressing the collapse in the thickness direction and suppressing the decrease in the thermal conductivity.

  ADVANTAGE OF THE INVENTION According to this invention, even when it uses under a heavy load, the heat conductive sheet which can suppress the crush of the heat conductive sheet in the thickness direction and can maintain high heat conductivity can be provided.

DESCRIPTION OF SYMBOLS 11 Thermal conductive sheet 12 Sheet main body 15 Hole 21 Reinforcing part 81 Heating body 82 Heat radiator

Claims (6)

A heat conductive sheet containing a resin and a carbon material,
A sheet body including the resin and the carbon material, and having a plurality of holes extending in a thickness direction of the heat conductive sheet;
A plurality of reinforcing portions filled with at least one of a metal and an inorganic oxide in the hole portion,
A heat conductive sheet, wherein the sum of the average areas of the cross sections of the plurality of reinforcing portions orthogonal to the thickness direction of the heat conductive sheet is less than 1% with respect to the area of one surface in the thickness direction of the heat conductive sheet.   2. The ratio ((L / T) × 100) of the length (L) of the reinforcing portion in the thickness direction of the heat conductive sheet to the thickness (T) of the heat conductive sheet is 50% or more. 3. Heat conduction sheet.   The heat conductive sheet according to claim 1 or 2, wherein the heat conductive sheet has a thermal conductivity of 2.5 W / mK or more under 1.5 MPa pressure.   The heat conductive sheet according to any one of claims 1 to 3, wherein the reinforcing portion has a major axis in a cross section orthogonal to a thickness direction of the heat conductive sheet of 0.1 mm or more and 2 mm or less. The heat conductive sheet according to any one of claims 1 to 4, wherein an arrangement density of the reinforcing portions is 1 piece / cm ² or more.   The heat conductive sheet according to any one of claims 1 to 5, wherein a content ratio of the carbon material in the sheet body is from 15% by mass to 80% by mass.

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