thermal conductive sheet

Abstract

To provide a thermally conductive sheet that has a high compressive rate under low load, and has excellent collapse suppression and thermal conductivity under high load.SOLUTION: A thermally conductive sheet contains a resin, a thermally conductive filler, and rubber particles, the rubber particles having an average diameter of 5 μm or more and 50 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive sheet, and more particularly to a thermally conductive sheet containing a resin, a thermally conductive filler, and rubber particles. [Background technology]

[0002] In recent years, the amount of heat generated by electronic components such as power semiconductors (e.g., IGBT modules) and integrated circuit (IC) chips has increased as their performance has improved. As a result, electronic devices that use these components need to take measures to prevent malfunctions caused by temperature rises in the components.

[0003] Generally, to prevent malfunctions due to temperature rise, a method is adopted to promote heat dissipation by attaching a heat sink, heat sink plate, heat sink fin, or other heat sink made of metal to a heat generating element such as an electronic component. When using a heat sink, the heat generating element and the heat sink are usually attached in close contact with each other through a thermally conductive sheet with high thermal conductivity in between in order to efficiently transfer heat from the heat generating element to the heat sink.

[0004] For example, Patent Document 1 discloses a thermally conductive sheet that contains a resin and a thermally conductive filler, and that has excellent adhesion to an adherend and thermal conductivity, and is formed by aligning the thermally conductive filler in the thickness direction of the thermally conductive sheet.

[0005] Patent Document 2 also describes a thermally conductive adhesive sheet containing a binder resin, an insulating coated carbon fiber, and a thermally conductive filler other than the insulating coated carbon fiber, which is used under a load of 0.5 kgf / cm 2 The application discloses a thermally conductive sheet having a compressibility of 3% to 30% inclusive. According to the application, a typical method is to balance the amounts of binder resin and filler added to achieve both flexibility and compressibility and improve adhesion to the adherend. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2016 / 185688 [Patent Document 2] Japanese Patent Application Publication No. 2018-098515 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the conventional thermally conductive sheets described above have the problem of being difficult to compress under low loads (i.e., having low compressibility under low loads), resulting in poor adhesion to the adherend. Furthermore, in order to improve the adhesion between the thermally conductive sheet and the adherend, it is necessary to increase the compressibility of the thermally conductive sheet, which requires applying a high load to the thermally conductive sheet. However, when used under high loads, the thermally conductive sheet collapses, resulting in a problem of reduced thermal conductivity. Therefore, there has been a demand for a thermally conductive sheet that can suppress collapse in the thickness direction of the thermally conductive sheet even when used under high loads (i.e., has excellent collapse suppression under high loads) and can exhibit high thermal conductivity.

[0008] Therefore, an object of the present invention is to provide a thermally conductive sheet that has high compressibility under low load, and is excellent in terms of suppressing collapse and thermal conductivity under high load. [Means for solving the problem]

[0009] The present inventors conducted extensive research to achieve the above object and discovered that a thermally conductive sheet containing a resin, a thermally conductive filler, and rubber particles having an average diameter within a predetermined range has high compressibility under low loads, and excellent crush resistance and thermal conductivity under high loads, leading to the completion of the present invention.

[0010] The present invention aims to advantageously solve the above-mentioned problems, and provides a thermally conductive sheet comprising a resin, a thermally conductive filler, and rubber particles, the rubber particles having an average diameter of 5 μm to 50 μm. Thus, a thermally conductive sheet comprising a resin, a thermally conductive filler, and rubber particles having an average diameter within the above range has high compressibility under low loads, and excellent crush resistance and thermal conductivity under high loads. In the present invention, the "average diameter" of the rubber particles can be measured using the method described in the examples of this specification.

[0011] Here, the thermally conductive sheet of the present invention has a thickness of T under a pressure of 0.6 MPa. 0.6 The thickness of the heat conductive sheet under a pressure of 0.05 MPa is T 0.05 As a result, the following formula (1): C 0.6 =100×{1-(T 0.6 / T 0.05 )}[%]···(1) The compression ratio C calculated by 0.6 It is preferable that the compressibility of the thermal conductive sheet under low load is 10% or more. If the compressibility calculated by the above formula (1) (hereinafter sometimes abbreviated as "compressibility at 0.6 MPa") is equal to or higher than the above value, the compressibility of the thermal conductive sheet under low load can be further improved. In the present invention, the "thickness" of the thermally conductive sheet can be determined using the method described in the examples of this specification.

[0012] In addition, the thermally conductive sheet of the present invention has a thickness of T under a pressure of 0.9 MPa. 0.9 The thickness of the heat conductive sheet under a pressure of 0.05 MPa is T 0.05 As a result, the following formula (2): C 0.9 =100×{1-(T 0.9 / T 0.05 )}[%]···(2) The compression ratio C calculated by 0.9It is preferable that the compressibility of the thermal conductive sheet under low load is 15% or more. If the compressibility calculated by the above formula (2) (hereinafter sometimes abbreviated as "compressibility at 0.9 MPa") is equal to or higher than the above value, the compressibility of the thermal conductive sheet under low load can be further improved.

[0013] The thermally conductive sheet of the present invention preferably has a thermal conductivity of 10 W / m K or more under a pressure of 0.9 MPa, as measured in accordance with ISO 22007-3. If the thermal conductivity of the thermally conductive sheet under a pressure of 0.9 MPa is equal to or greater than this value, the thermal conductivity of the thermally conductive sheet under a high load can be further improved. In the present invention, the "thermal conductivity" of the thermally conductive sheet can be measured using the method described in the examples of this specification.

[0014] The thermally conductive sheet of the present invention preferably has a thickness of 50 μm or more and 1000 μm or less. If the thickness of the thermally conductive sheet is within the above range, the thermally conductive sheet can be suitably used by being sandwiched between a heat generating element and a heat dissipating element. Furthermore, the strength, durability, and handling properties of the thermally conductive sheet can be improved.

[0015] In the thermal conductive sheet of the present invention, the resin preferably contains a thermoplastic fluororesin that is solid at room temperature and normal pressure. If the resin in the thermal conductive sheet contains a thermoplastic fluororesin that is solid at room temperature and normal pressure, the thermal conductive sheet can be further prevented from collapsing under high loads, and the flame retardancy, heat resistance, oil resistance, and chemical resistance of the thermal conductive sheet can be improved. In this specification, "normal temperature" refers to 23° C., and "normal pressure" refers to 1 atm (absolute pressure).

[0016] In the thermally conductive sheet of the present invention, the content of the thermally conductive filler is preferably 40 to 130 parts by mass per 100 parts by mass of the resin. If the ratio of the thermally conductive filler to the resin in the thermally conductive sheet is within the above range, the compressibility of the thermally conductive sheet under low load can be further increased, and the thermal conductivity of the thermally conductive sheet under high load can be further improved.

[0017] Furthermore, in the thermal conductive sheet of the present invention, the content of the rubber particles is preferably 1 part by mass to 20 parts by mass per 100 parts by mass of the resin. If the ratio of the rubber particles to the resin in the thermal conductive sheet is within the above range, the compressibility of the thermal conductive sheet under low load can be further increased, and the crushing resistance and thermal conductivity of the thermal conductive sheet under high load can be further improved.

[0018] In the thermally conductive sheet of the present invention, the rubber particles preferably have a glass transition temperature (Tg) of 20° C. or lower. If the glass transition temperature of the rubber particles contained in the thermally conductive sheet is equal to or lower than the above value, the compressibility of the thermally conductive sheet under low load can be further improved. In the present invention, the "glass transition temperature" of the rubber particles can be measured using a differential thermal analysis measuring device.

[0019] Furthermore, in the thermally conductive sheet of the present invention, the rubber particles are preferably (meth)acrylic rubber particles. If the rubber particles contained in the thermally conductive sheet are (meth)acrylic rubber particles, the compressibility of the thermally conductive sheet under low load can be further increased, and the crushing resistance and thermal conductivity of the thermally conductive sheet under high load can be further improved. In the present invention, "(meth)acrylic" means acrylic and / or methacrylic. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a thermally conductive sheet that has high compressibility under low load, and is excellent in crush resistance and thermal conductivity under high load. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a perspective view illustrating the structure of an example of a thermally conductive sheet according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view of an example of a thermally conductive sheet taken along the thickness direction. [Figure 3]FIG. 10 is a cross-sectional view along the thickness direction of another example of a thermally conductive sheet. [Figure 4] FIG. 10 is a cross-sectional view along the thickness direction of another example of a thermally conductive sheet. DETAILED DESCRIPTION OF THE INVENTION

[0022] The thermally conductive sheet of the present invention is a thermally conductive sheet containing a resin, a thermally conductive filler, and rubber particles. The thermally conductive sheet of the present invention can be used, for example, by being sandwiched between a heat generating element and a heat sink when attaching the heat sink to the heat generating element.

[0023] (thermal conductive sheet) The thermally conductive sheet of the present invention contains a resin, a thermally conductive filler, and rubber particles, and optionally further contains other components. Specifically, as shown in Fig. 1, the thermally conductive sheet 10 of the present invention has a structure in which rubber particles 20 are partially or entirely embedded in a sheet body 11 that contains a resin, a thermally conductive filler, and optionally further contains other components. The thermally conductive sheet of the present invention is characterized in that the average diameter of the rubber particles is 5 μm or more and 50 μm or less.

[0024] <Resin> The resin contained in the thermally conductive sheet can be at least one of a resin that is liquid at room temperature and normal pressure and a resin that is solid at room temperature and normal pressure.

[0025] Examples of resins that are liquid at room temperature and normal pressure include thermoplastic resins that are liquid at room temperature and normal pressure, and thermosetting resins that are liquid at room temperature and normal pressure. Examples of thermoplastic resins that are liquid at room temperature and normal pressure include acrylic resins, epoxy resins, silicone resins, and fluororesins. Furthermore, examples of thermosetting resins that are liquid at room temperature and normal pressure include natural rubber; butadiene rubber; isoprene rubber; nitrile rubber; hydrogenated nitrile rubber; chloroprene rubber; ethylene propylene rubber; chlorinated polyethylene; chlorosulfonated polyethylene; butyl rubber; halogenated butyl rubber; polyisobutylene rubber; epoxy resin; polyimide resin; bismaleimide resin; benzocyclobutene resin; phenolic resin; unsaturated polyester; diallyl phthalate resin; polyimide silicone resin; polyurethane; thermosetting polyphenylene ether; and thermosetting modified polyphenylene ether.

[0026] Examples of resins that are solid at room temperature and normal pressure include thermoplastic resins that are solid at room temperature and normal pressure, and thermosetting resins that are solid at room temperature and normal pressure. Examples of thermoplastic resins that are solid at room temperature and pressure include acrylic resins such as poly(2-ethylhexyl acrylate), copolymers of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its ester, and polyacrylic acid or its ester; silicone resins; fluororesins; polyethylene; polypropylene; ethylene-propylene copolymers; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymers; polyvinyl alcohol; polyacetal; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; poly Examples include styrene; polyacrylonitrile; styrene-acrylonitrile copolymer; 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; aliphatic polyamides; aromatic polyamides; polyamideimide; polycarbonate; polyphenylene sulfide; polysulfone; polyethersulfone; polyethernitrile; polyetherketone; polyketone; polyurethane; liquid crystal polymer; ionomer; and the like. Furthermore, examples of thermosetting resins that are solid at room temperature and normal pressure include natural rubber; butadiene rubber; isoprene rubber; nitrile rubber; hydrogenated nitrile rubber; chloroprene rubber; ethylene propylene rubber; chlorinated polyethylene; chlorosulfonated polyethylene; butyl rubber; halogenated butyl rubber; polyisobutylene rubber; epoxy resin; polyimide resin; bismaleimide resin; benzocyclobutene resin; phenolic resin; unsaturated polyester; diallyl phthalate resin; polyimide silicone resin; polyurethane; thermosetting polyphenylene ether; and thermosetting modified polyphenylene ether.

[0027] In particular, from the viewpoint of improving the flame retardancy, heat resistance, oil resistance, and chemical resistance of the thermal conductive sheet, it is preferable to use a fluororesin as the resin. Furthermore, the resin preferably contains a resin that is solid at room temperature and normal pressure, more preferably a thermoplastic fluororesin that is solid at room temperature and normal pressure, and even more preferably a thermoplastic fluororesin that is solid at room temperature and normal pressure and a thermoplastic fluororesin that is liquid at room temperature and normal pressure. If the resin contains a resin that is solid at room temperature and normal pressure, the thermal conductive sheet can be further improved in its ability to suppress collapse under high loads. Furthermore, if the resin contains a thermoplastic fluororesin that is solid at room temperature and normal pressure and a thermoplastic fluororesin that is liquid at room temperature and normal pressure, it is possible to obtain a thermal conductive sheet that has appropriate flexibility while improving its flame retardancy, heat resistance, oil resistance, and chemical resistance. The above-mentioned resins may be used alone or in combination of two or more.

[0028] <Thermal conductive filler> The thermally conductive filler contained in the thermally conductive sheet of the present invention is not particularly limited, and known thermally conductive fillers can be used. Specifically, the thermally conductive filler can be a particulate thermally conductive filler, a fibrous thermally conductive filler, or the like. While either the particulate thermally conductive filler or the fibrous thermally conductive filler can be used alone or in combination, it is preferable to use at least a particulate thermally conductive filler from the viewpoint of easily increasing the thermal conductivity of the thermally conductive sheet. Furthermore, from the viewpoint of increasing the thermal conductivity of the thermally conductive sheet while preventing the particulate thermally conductive filler from falling off the thermally conductive sheet, it is more preferable to use a particulate thermally conductive filler and a fibrous thermally conductive filler in combination. In the present invention, a thermally conductive filler being "particulate" means that the aspect ratio, obtained by measuring the major and minor axes of 100 randomly selected thermally conductive fillers and dividing the average major axis by the average minor axis, is 1 or more and less than 5. In addition, in the present invention, a thermally conductive filler being "fibrous" means that the aspect ratio, obtained by measuring the major and minor axes of 100 randomly selected thermally conductive fillers and dividing the average major axis by the average minor axis, is 5 or more.

[0029] <<Granular thermally conductive filler>> Here, the particulate thermally conductive filler is not particularly limited, and examples thereof include alumina particles, zinc oxide particles, boron nitride particles, aluminum nitride particles, silicon nitride particles, silicon carbide particles, magnesium oxide particles, and particulate carbon materials (e.g., artificial graphite, flaky graphite, exfoliated graphite, natural graphite, acid-treated graphite, expandable graphite, expanded graphite, carbon black, etc.). These may be used alone or in combination of two or more. Among these, it is preferable to use particulate carbon materials as the particulate thermally conductive filler, and it is more preferable to use expanded graphite. The use of particulate carbon materials can further improve the thermal conductivity of the thermally conductive sheet.

[0030] Expanded graphite that can be suitably used as a particulate thermally conductive filler can be obtained by, for example, chemically treating graphite such as flake graphite with sulfuric acid or the like to obtain expandable graphite, expanding the graphite by heat treatment, and then pulverizing the expanded graphite. Examples of expanded graphite include EC1500, EC1000, EC500, EC300, EC100, and EC50 (all trade names) manufactured by Ito Graphite Industries Co., Ltd.

[0031] The particulate thermally conductive filler preferably has a volume average particle diameter of 0.1 μm or more, more preferably 1 μm or more, and preferably 300 μm or less, more preferably 250 μm or less. If the volume average particle diameter of the particulate thermally conductive filler is within the above range, the thermal conductivity of the heat conduction sheet can be improved. In the present invention, the "volume average particle size" can be measured in accordance with JIS Z8825, and represents the particle size at which the cumulative volume calculated from the smallest diameter side becomes 50% in the particle size distribution (volume basis) measured by a laser diffraction method.

[0032] [Particulate thermally conductive filler content] The content of the particulate thermally conductive filler in the thermally conductive filler is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more. It can be 100% by mass or less, and preferably 99.9% by mass or less. When the content of the particulate thermally conductive filler in the thermally conductive filler is equal to or greater than the above-mentioned lower limit, the particulate thermally conductive filler is more favorably oriented in the thermally conductive sheet, and the particulate thermally conductive fillers come into contact with each other to form an excellent heat transfer path. As a result, the thermally conductive sheet can exhibit high thermal conductivity. Furthermore, when the content of the particulate thermally conductive filler is 99.9% by mass or less, it is possible to prevent the particulate thermally conductive filler from falling off the thermally conductive sheet.

[0033] <<Fiber-like thermally conductive filler>> The fibrous thermally conductive filler is not particularly limited, and examples thereof include carbon nanotubes (hereinafter sometimes referred to as "CNTs"), vapor-grown carbon fibers, carbon fibers obtained by carbonizing organic fibers, and cut products thereof. These may be used alone or in combination. The inclusion of a fibrous thermally conductive filler in a thermally conductive sheet can further improve the thermal conductivity of the thermally conductive sheet and, when used in combination with a particulate thermally conductive filler, can further prevent the particulate thermally conductive filler from falling off. While the reason why the inclusion of a fibrous thermally conductive filler can prevent the particulate thermally conductive filler from falling off is unclear, it is presumed that the fibrous thermally conductive filler forms a three-dimensional network structure, thereby improving thermal conductivity and strength while preventing the particulate thermally conductive filler from falling off.

[0034] Among the above, it is preferable to use fibrous carbon nanostructures such as CNTs as the fibrous thermally conductive filler, and it is more preferable to use fibrous carbon nanostructures containing CNTs. The use of fibrous carbon nanostructures such as CNTs can further improve the thermal conductivity and strength of the thermally conductive sheet of the present invention.

[0035] Furthermore, fibrous carbon nanostructures containing CNTs that can be suitably used as fibrous thermally conductive fillers may consist of CNTs alone, or may be a mixture of CNTs and fibrous carbon nanostructures other than CNTs. The CNTs in the fibrous carbon nanostructures are not particularly limited and can be single-walled CNTs and / or multi-walled CNTs, but the CNTs are preferably single-walled to five-walled CNTs, and more preferably single-walled CNTs. The use of single-walled CNTs can further improve the thermal conductivity and strength of the thermal conductive sheet compared to the use of multi-walled CNTs.

[0036] Furthermore, fibrous carbon nanostructures containing CNTs can be efficiently produced, for example, by a method (super-growth method; see WO 2006 / 011655) in which, when raw material compounds and a carrier gas are supplied onto a substrate having a catalyst layer for CNT production on its surface to synthesize CNTs by chemical vapor deposition (CVD), the catalytic activity of the catalyst layer is dramatically improved by making a trace amount of oxidant (catalytic activator) present in the system. Note that, hereinafter, carbon nanotubes obtained by the super-growth method may be referred to as "SGCNTs."

[0037] Here, the fibrous carbon nanostructure containing CNTs produced by the super-growth method may be composed only of SGCNTs, or may contain, in addition to SGCNTs, other carbon nanostructures such as non-cylindrical carbon nanostructures.

[0038] [Content of fibrous thermally conductive filler] The content of the fibrous thermally conductive filler in the thermally conductive filler is preferably 0.001% by mass or more, preferably less than 100% by mass, more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 1% by mass or less. When the content of the fibrous thermally conductive filler in the thermally conductive filler is equal to or greater than the above-mentioned lower limit, the thermal conductivity and strength of the thermally conductive sheet can be sufficiently improved, and when used in combination with a particulate thermally conductive filler, powder shedding of the particulate thermally conductive filler can be sufficiently prevented. Furthermore, when the content of the fibrous thermally conductive filler is equal to or less than the above-mentioned upper limit, an excessive increase in the hardness of the thermally conductive sheet (i.e., an excessive decrease in flexibility) due to the incorporation of the fibrous thermally conductive filler can be suppressed.

[0039] <<Thermal conductive filler content>> The content of the thermally conductive filler in the thermally conductive sheet is not particularly limited, but is preferably 40 parts by mass or more, more preferably 60 parts by mass or more, and even more preferably 80 parts by mass or more, and preferably 130 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 110 parts by mass or less, per 100 parts by mass of resin. If the content of the thermally conductive filler in the thermally conductive sheet is equal to or greater than the above-mentioned lower limit, the thermal conductivity of the thermally conductive sheet under high load can be further improved. If the content of the thermally conductive filler in the thermally conductive sheet is equal to or less than the above-mentioned upper limit, the compressibility of the thermally conductive sheet under low load can be further improved.

[0040] <Rubber particles> The rubber particles contained in the thermal conductive sheet of the present invention are a component different from the resin described above, and are particles that exist stably in the thermal conductive sheet and maintain their shape. That is, in the thermal conductive sheet of the present invention, the parts made of resin and the parts made of rubber particles can be clearly distinguished. Here, the rubber particles are not particularly limited, and examples that can be used include polyalkyl acrylate particles, polyalkyl methacrylate particles, specifically (meth)acrylic rubber particles such as polymers of methyl methacrylate, ethyl acrylate, acrylamide, or copolymers thereof; polystyrene rubber particles such as acrylonitrile-styrene copolymer, styrene-ethylene copolymer, and styrene-butylene copolymer; polycarbonate rubber particles such as polyether-polycarbonate copolymer; urethane rubber particles such as polyether-polyurethane, polyester-polyurethane copolymer, and thermoplastic polyurethane (TPU); styrene-butadiene rubber (SBR) rubber particles such as polystyrene-polybutadiene; and ethylene vinyl acetate (EVA) rubber particles such as ethylene-vinyl acetate copolymer. The rubber forming the rubber particles is preferably crosslinked. Among these, from the viewpoint of heat resistance and availability, (meth)acrylic rubber particles are preferred as the rubber particles, polyalkyl acrylate particles and polyalkyl methacrylate particles are more preferred, polyethyl methacrylate, polybutyl methacrylate, polymethoxyethyl acrylate, polyethylene-methyl acrylate or copolymers of the monomers thereof are further preferred, and polybutyl methacrylate is particularly preferred. These may be used alone or in combination of two or more.

[0041] Here, the rubber particles preferably have a core-shell structure consisting of a shell portion with a high degree of cross-linking and a core portion with a low degree of cross-linking. If the rubber particles have such a core-shell structure, the compressibility of the thermal conductive sheet under low load can be further increased, and the crushing suppression and thermal conductivity of the thermal conductive sheet under high load can be further improved.

[0042] The shape of the rubber particles is not particularly limited. For example, the shape of the rubber particles may be spherical or non-spherical (such as bowl-shaped or elliptical). However, from the viewpoint of further increasing the compressibility of the heat conductive sheet under low load and further improving the crushing suppression and thermal conductivity of the heat conductive sheet under high load, it is preferable that the rubber particles be spherical.

[0043] These rubber particles may be synthesized by known methods, or commercially available products may be used. Note that alkyl polyacrylate particles are commercially available, for example, as "Matsumoto Microsphere (registered trademark) S Series" (S-100, S-102) manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.

[0044] [Average diameter] The rubber particles used in the present invention must have an average diameter of 5 μm or more and 50 μm or less, preferably 10 μm or more, more preferably 15 μm or more, and preferably 45 μm or less, and more preferably 40 μm or less. If the average diameter of the rubber particles is less than 5 μm, the compressibility of the thermal conductive sheet under low loads will decrease. On the other hand, if the average diameter of the rubber particles is more than 50 μm, the crush resistance and thermal conductivity of the thermal conductive sheet under high loads will decrease. The rubber particles having the above-mentioned average diameter may be embedded throughout the entire thickness of the thermally conductive sheet as shown in Fig. 2, or may be embedded within the thermally conductive sheet as shown in Figs. 3 and 4. The rubber particles having the above-mentioned average diameter may partially protrude from the surface of the thermally conductive sheet. In particular, it is preferable that the rubber particles are embedded within the thermally conductive sheet.

[0045] [Glass transition temperature] Furthermore, from the viewpoint of further increasing the compressibility of the heat conductive sheet under low load, the rubber particles used in the present invention preferably have a glass transition temperature (Tg) of 20° C. or lower, more preferably 0° C. or lower, and even more preferably −20° C. or lower. The lower limit of the glass transition temperature (Tg) of the rubber particles is not particularly limited, but can be, for example, −120° C. or higher, or −60° C. or higher.

[0046] The content of rubber particles in the thermal conductive sheet is not particularly limited, but is preferably at least 1 part by mass, more preferably at least 2 parts by mass, and even more preferably at least 3 parts by mass, and is preferably no more than 20 parts by mass, more preferably no more than 18 parts by mass, and even more preferably no more than 15 parts by mass, per 100 parts by mass of resin. If the content of rubber particles in the thermal conductive sheet is at least the above-mentioned lower limit per 100 parts by mass of resin, the compressibility of the thermal conductive sheet under low loads can be further improved. Furthermore, if the content of rubber particles in the thermal conductive sheet is no more than the above-mentioned upper limit per 100 parts by mass of resin, the crush resistance and thermal conductivity of the thermal conductive sheet under high loads can be further improved.

[0047] <Other ingredients> The thermally conductive sheet may optionally contain other components in addition to the resin, thermally conductive filler, and rubber particles described above. Examples of such other components include known additives that can be used to form thermally conductive sheets. Known additives that can be used to form thermally conductive sheets include, but are not limited to, flame retardants such as red phosphorus-based flame retardants and phosphate ester-based flame retardants; plasticizers; acid acceptors such as calcium oxide and magnesium oxide; adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides; wettability improvers such as nonionic surfactants and fluorine-based surfactants; and ion trapping agents such as inorganic ion exchangers. The content of the other components in the thermally conductive sheet can be set arbitrarily within a range that provides the desired effects of the present invention.

[0048] <Thermal Conduction Sheet Properties> The thermally conductive sheet is not particularly limited, but preferably has the following properties.

[0049] Thickness The thermally conductive sheet of the present invention preferably has a thickness of 50 μm or more, more preferably 100 μm or more, and even more preferably 150 μm or more, and preferably 1000 μm or less, and more preferably 600 μm or less, at room temperature and normal pressure. If the thickness of the thermally conductive sheet at room temperature and normal pressure is equal to or less than the above upper limit, the thermally conductive sheet can be suitably used by being sandwiched between a heat generating element and a heat dissipating element. Furthermore, if the thickness of the thermally conductive sheet is equal to or greater than the above lower limit, the strength, durability, and handleability of the thermally conductive sheet can be improved.

[0050] [Ratio of average diameter of rubber particles to sheet thickness] Furthermore, in the thermally conductive sheet of the present invention, the ratio of the average diameter of the rubber particles to the thickness of the thermally conductive sheet is preferably 1% or more, more preferably 3% or more, and even more preferably 5% or more, and is preferably 100% or less, more preferably 50% or less, and even more preferably 20% or less. If the ratio of the average diameter of the rubber particles to the thickness of the thermally conductive sheet is equal to or greater than the above-mentioned lower limit, crushing of the thermally conductive sheet in the thickness direction can be suppressed. Furthermore, if the ratio of the average diameter of the rubber particles to the thickness of the thermally conductive sheet is equal to or less than the above-mentioned upper limit, the thermal conductivity of the thermally conductive sheet under high load can be further improved.

[0051] [Compressibility at 0.6 MPa] The thermally conductive sheet of the present invention preferably has a compressibility of 10% or more at 0.6 MPa, more preferably 11% or more, and even more preferably 12% or more. If the compressibility of the thermally conductive sheet at 0.6 MPa is equal to or greater than the above-mentioned lower limit, the compressibility of the thermally conductive sheet under low loads can be further improved. There is no particular upper limit to the compressibility of the thermally conductive sheet at 0.6 MPa, but it can be, for example, 25% or less, or 20% or less.

[0052] [Compressibility at 0.9 MPa] Furthermore, the thermally conductive sheet of the present invention preferably has a compressibility at 0.9 MPa of 15% or more, more preferably 16% or more, and even more preferably 17% or more. If the compressibility at 0.9 MPa of the thermally conductive sheet is equal to or greater than the above-mentioned lower limit, the compressibility of the thermally conductive sheet under low loads can be further improved. Furthermore, the upper limit of the compressibility at 0.9 MPa of the thermally conductive sheet is not particularly limited, but can be, for example, 35% or less, or 30% or less.

[0053] [Thermal Conductivity] Furthermore, the thermal conductivity of the thermally conductive sheet of the present invention under a pressure of 0.9 MPa is preferably 10 W / m·K or more, more preferably 15 W / m·K or more, and even more preferably 20 W / m·K or more. If the thermal conductivity of the thermally conductive sheet under a pressure of 0.9 MPa is equal to or greater than the above-mentioned lower limit, the thermal conductivity of the thermally conductive sheet under a high load can be further improved. Furthermore, there is no particular upper limit to the thermal conductivity of the thermally conductive sheet under a pressure of 0.9 MPa, but it can be, for example, 35 W / m·K or less, or 30 W / m·K or less.

[0054] [Asker C hardness] The thermally conductive sheet of the present invention preferably has an Asker C hardness at a temperature of 25°C of 30 or more, more preferably 40 or more, and even more preferably 50 or more, and preferably 90 or less, and more preferably 85 or less. If the Asker C hardness at a temperature of 25°C of the thermally conductive sheet is within the above range, the flexibility and handleability of the thermally conductive sheet in a room temperature environment can be improved. In the present invention, the "Asker C hardness" of the thermally conductive sheet can be measured by the method described in the examples of this specification.

[0055] <Method of manufacturing thermal conductive sheets> The thermally conductive sheet having the above-described configuration is not particularly limited, and can be manufactured, for example, by a method (Method 1) in which a thermally conductive sheet is made using a composition containing a resin, a thermally conductive filler, and rubber particles, and optionally further containing other components, or a method (Method 2) in which a sheet body is made using a composition containing a resin, a thermally conductive filler, and optionally further containing other components, and then rubber particles are embedded in the sheet body to form a thermally conductive sheet.

[0056] [Method 1] Here, Method 1 is not particularly limited, and a thermally conductive sheet can be produced through, for example, the following steps: a step of pressurizing the composition to form it into a sheet to obtain a pre-sheet (pre-sheet forming step); a step of stacking a plurality of pre-sheets in the thickness direction or folding or rolling the pre-sheet to obtain a laminate (laminate forming step); and a step of slicing the obtained laminate at an angle of 45° or less to the stacking direction to obtain a thermally conductive sheet (slicing step). Method 1 usually produces a thermally conductive sheet in which the average diameter of the rubber particles is 100% or less of the thickness of the thermally conductive sheet.

[0057] -Pre-sheet molding process- In the pre-sheet molding step, a composition containing a resin, a thermally conductive filler, and rubber particles, and optionally further containing other components, is pressed into a sheet to obtain a pre-sheet, where the resin, thermally conductive filler, rubber particles, and other components may be any of those described above as being capable of being contained in the thermally conductive sheet of the present invention.

[0058] The composition is obtained by stirring and mixing the above components. The stirring and mixing can be carried out using known mixing devices such as a kneader, roll, Henschel mixer, Hobart mixer, high-speed mixer, or twin-screw kneader, without any particular limitations. The stirring and mixing may also be carried out in the presence of a solvent such as ethyl acetate or methyl ethyl ketone. The stirring and mixing conditions can be appropriately set. The stirring and mixing temperature can be, for example, from 5°C to 150°C.

[0059] Among the above-mentioned components, fibrous thermally conductive fillers, particularly CNTs, tend to aggregate and have poor dispersibility. Therefore, when mixed directly with other components such as fluororesins or expanded graphite, they are difficult to disperse well in the composition. While agglomeration can be suppressed by mixing the fibrous thermally conductive filler in a dispersion state in a solvent (dispersion medium) with other components such as fluororesins or expanded graphite, mixing the fibrous thermally conductive filler in a dispersion state requires a large amount of solvent to solidify the solids after mixing, which may increase the amount of solvent used to prepare the composition. Therefore, when incorporating a fibrous thermally conductive filler into a composition used to form a pre-sheet, it is preferable to mix the fibrous thermally conductive filler in the form of an aggregate (easily dispersible aggregate) of the fibrous thermally conductive filler obtained by removing the solvent from the dispersion obtained by dispersing the fibrous thermally conductive filler in a solvent (dispersion medium) with the other components. The aggregate of fibrous thermally conductive filler obtained by removing the solvent from the dispersion of fibrous thermally conductive filler is composed of fibrous thermally conductive filler that has been dispersed in a solvent once, and has better dispersibility than the aggregate of fibrous thermally conductive filler before being dispersed in a solvent, resulting in a highly dispersible, easily dispersible aggregate. Therefore, by mixing the easily dispersible aggregate with other components such as a fluororesin or expanded graphite, the fibrous thermally conductive filler can be efficiently dispersed well in the composition without using a large amount of solvent.

[0060] Here, a dispersion of a fibrous thermally conductive filler can be obtained, for example, by subjecting a crude dispersion, which is obtained by adding a fibrous thermally conductive filler to a solvent, to a dispersion treatment that produces a cavitation effect or a dispersion treatment that produces a disintegration effect. Dispersion treatment that produces a cavitation effect is a dispersion method that utilizes shock waves generated when vacuum bubbles generated in water burst when high energy is applied to the liquid. Specific examples of dispersion treatment that produces a cavitation effect include dispersion treatment using an ultrasonic homogenizer, dispersion treatment using a jet mill, and dispersion treatment using a high-shear mixer. Dispersion treatment that produces a disintegration effect applies shear force to the crude dispersion to disintegrate and disperse aggregates of the fibrous thermally conductive filler, and then applies back pressure to the crude dispersion to suppress the generation of bubbles, thereby uniformly dispersing the fibrous thermally conductive filler in the solvent.

[0061] The solvent can be removed from the dispersion by known solvent removal methods such as drying and filtration. From the viewpoint of rapid and efficient solvent removal, filtration such as vacuum filtration is preferred.

[0062] The composition prepared as described above can be optionally degassed and crushed, and then pressed to form into a sheet. If a solvent is used during mixing, it is preferable to remove the solvent before forming into a sheet. For example, if degassing is performed using vacuum degassing, the solvent can be removed simultaneously with degassing.

[0063] Here, the composition can be molded into a sheet using any known molding method, such as press molding, rolling, or extrusion, as long as the molding method applies pressure. Among these, the composition is preferably formed into a sheet by rolling, and more preferably formed into a sheet by passing the composition between rolls while sandwiched between protective films. The protective film is not particularly limited, and a sandblasted polyethylene terephthalate film or the like can be used. The roll temperature can be 5°C or higher and 150°C or higher. The thickness of the pre-sheet is not particularly limited, and can be, for example, 0.05 mm or more and 2 mm or less.

[0064] -Laminate formation process- In the laminate formation step, a laminate is obtained by stacking a plurality of pre-sheets obtained in the pre-sheet molding step in the thickness direction, or by folding or winding the pre-sheets. Here, the formation of the laminate by folding the pre-sheets is not particularly limited, and can be performed by folding the pre-sheets to a fixed width using a folding machine. Furthermore, the formation of the laminate by winding the pre-sheets is not particularly limited, and can be performed by winding the pre-sheets around an axis parallel to the short or long direction of the pre-sheets.

[0065] In general, in the laminate obtained in the laminate-forming step, the adhesive strength between the surfaces of the pre-sheets is sufficiently obtained by the pressure when stacking the pre-sheets and the tensile force when folding or rolling them up. However, if the adhesive strength is insufficient or if it is necessary to sufficiently suppress delamination of the laminate, the laminate-forming step may be performed in a state in which the surfaces of the pre-sheets are slightly dissolved in a solvent, or in a state in which an adhesive is applied to the surfaces of the pre-sheets or an adhesive layer is provided on the surfaces of the pre-sheets.

[0066] The solvent used to dissolve the surface of the pre-sheet is not particularly limited, and any known solvent capable of dissolving resin components such as fluororesin contained in the pre-sheet can be used. Among these, acetone is preferred from the viewpoints of solubility and volatility.

[0067] The adhesive to be applied to the surface of the pre-sheet is not particularly limited, and commercially available adhesives or adhesive resins can be used. Among these, it is preferable to use a resin with the same composition as the resin component, such as a fluororesin, contained in the pre-sheet. 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. Furthermore, 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 adhesive layer may contain a thermally conductive filler insofar as the resulting thermally conductive sheet does not become too hard.

[0068] To prevent delamination, the obtained laminate may be heated at 50° C. to 120° C. for 1 to 60 minutes while being pressed in the lamination direction with a pressure of 0.1 MPa to 0.5 MPa.

[0069] -Slicing process- In the slicing step, the laminate obtained in the laminate-forming step is sliced ​​at an angle of 45° or less relative to the lamination direction to obtain a thermally conductive sheet composed of slices of the laminate. 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 these, the knife processing method is preferred because it is easy to make the thickness of the thermally conductive sheet uniform. The cutting tool used to slice the laminate is not particularly limited, and a slicing member having a smooth plate surface with a slit and a blade portion protruding from the slit portion (for example, a plane or slicer with a sharp blade) can be used.

[0070] From the viewpoint of increasing the thermal conductivity of the thermal conduction sheet, the angle at which the laminate is sliced ​​is preferably 30° or less relative to the stacking direction, more preferably 15° or less relative to the stacking direction, and preferably approximately 0° relative to the stacking direction (i.e., in the direction along the stacking direction).

[0071] Furthermore, from the viewpoint of slicing the laminate easily, the temperature of the laminate during slicing is preferably −20° C. or higher and 40° C. or lower, more preferably −10° C. or higher and 30° C. or lower. Furthermore, for the same reason, the laminate to be sliced ​​is preferably sliced ​​while applying pressure in a direction perpendicular to the stacking direction, more preferably while applying pressure of 0.1 MPa or higher and 0.5 MPa or lower in the direction perpendicular to the stacking direction.

[0072] [Method 2] Here, in Method 2, the pre-sheet molding step, the laminate formation step, and the slicing step can be carried out in the same manner as the pre-sheet molding step, the laminate formation step, and the slicing step in Method 1, respectively, except that a composition that does not contain rubber particles is used as the composition.

[0073] -Embedding process- In the embedding step of Method 2, rubber particles can be embedded in the sheet body obtained in the slicing step by any method to form a thermally conductive sheet. Specifically, in the embedding step, for example, rubber particles can be placed at desired positions on one surface of the sheet body, and then pressed into the sheet body in the thickness direction using a pressing tool such as tweezers, thereby embedding the rubber particles in the sheet body. [Example]

[0074] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified.

[0075] In addition, in the examples and comparative examples, the average diameter of the rubber particles, as well as the Asker C hardness, thickness, compressibility, thermal conductivity, and rate of change in thermal conductivity of the thermal conductive sheet were measured or evaluated using the following methods.

[0076] <Average diameter of rubber particles> The average diameter of the rubber particles was determined as follows. First, 100 rubber particles were observed at a magnification of 20 to 50 times using a laser microscope (Keyence VK-X250). Circles were then drawn on the images of each rubber particle using a planar measurement tool, and the maximum and minimum diameters of the drawn circles were measured using linear measurement. The arithmetic mean value of the maximum and minimum diameters was taken as the diameter of the rubber particles, and the average value of the diameters of 100 rubber particles was taken as the average diameter of the rubber particles. <Asker C hardness of thermal conductive sheet> The Asker C hardness of the thermal conductive sheet was measured in accordance with the Asker C method of the Society of Rubber Industry of Japan standard (SRIS 0101) using a hardness tester (manufactured by Kobunshi Keiki Co., Ltd., product name "ASKER CL-150LJ") in an environment at a temperature of 25°C. <Thermal Conduction Sheet Thickness and Compressibility> The thickness of the thermally conductive sheet was measured with a Digimatic Indicator (ID-C112X, manufactured by Mitutoyo Corporation) with an accuracy of (1 / 1000 mm). Specifically, the thickness of the thermal conductive sheet under no pressure and under a pressure of 0.05 MPa (T 0.05 ), thickness under 0.6 MPa pressure (T 0.6 ), and thickness under 0.9 MPa pressure (T 0.9 ) was measured. The compressibility at 0.6 MPa (C 0.6 ) and compressibility at 0.9 MPa (C 0.9 ) were calculated based on the following formulas (1) and (2), respectively. C 0.6 =100×{1-(T 0.6 / T 0.05 )}[%]···(1) C 0.9 =100×{1-(T 0.9 / T 0.05 )}[%]···(2) The larger the compression ratio, the better the compressibility of the heat conductive sheet under a low load. <Thermal conductivity of the thermal conductive sheet> For the thermal conductive sheet, the thermal diffusivity α(m 2 / s), specific heat at constant pressure C p (J / g K) and specific gravity ρ (g / m 3) were measured by the following methods. [Thermal diffusivity α in the thickness direction] Measurements were performed using a thermal diffusivity and thermal conductivity measuring device (manufactured by iPhase Corporation, product name "iPhase Mobile 1u") in accordance with the provisions of ISO 22007-3. [Constant pressure specific heat C p (J / g·K)] The specific heat was measured using a differential scanning calorimeter (manufactured by Rigaku, product name "DSC8230") under the condition of a temperature increase of 10°C / min. [Specific gravity ρ(g / m 3 )] Specific gravity (density) (g / m) was measured using an automatic hydrometer (manufactured by Toyo Seiki Co., Ltd., product name "DENSIMETER-H"). 3 ) was measured. The obtained measurement value is calculated using the following formula (I): λ=α×C p ×ρ (I) The thermal conductivity λ (W / m K) of the thermal conductive sheet was calculated by substituting

[0077] <Rate of change in thermal conductivity of thermal conductive sheet> The thermal conductivity of the thermally conductive sheet was calculated based on the thermal resistance of the thermally conductive sheet. Specifically, the thermal resistance of the thermally conductive sheet was measured using a resin material thermal resistance tester (manufactured by Hitachi Technology & Services, Ltd.). A sample of the thermally conductive sheet containing rubber particles was cut into a roughly 0.5 cm square. The thermal resistance R1 (°C / W) of the sample was measured at a sample temperature of 50°C under a pressure of 0.05 MPa, and the thermal resistance R2 (°C / W) of the sample was measured under a pressure of 1.5 MPa. Then, from the thermal resistance values ​​R1 and R2, the thermal conductivity C1 (W / m K) of the sample under a pressure of 0.05 MPa and the thermal conductivity C2 (W / m K) of the sample under a pressure of 1.5 MPa were calculated using the following formula when converted to a 1 cm square thermal conductive sheet: Thermal conductivity (W / m K) = [1 / thermal resistance value (°C / W)] × [(sample thickness (mm) / (sample area (mm 2 )] x 1000 I asked for more. Also, the following formula: Rate of change in thermal conductivity = [Thermal conductivity of sample under pressure of 1.5 MPa (C2) / (Thermal conductivity of sample under pressure of 0.05 MPa (C1)] The rate of change in thermal conductivity was determined based on the results and evaluated according to the following criteria. A larger rate of change in thermal conductivity indicates that the thermal conductive sheet is more excellent in terms of its ability to suppress collapse under a high load and its thermal conductivity. A: The rate of change in thermal conductivity is more than 0.5. B: The rate of change in thermal conductivity is more than 0.3 and less than 0.5. C: The rate of change in thermal conductivity is less than 0.3.

[0078] Example 1 <Preparation of easily dispersible aggregates of fibrous carbon nanostructures> [Preparation of dispersion] Fibrous carbon nanostructure (ZEONANO (registered trademark) SG101, manufactured by Zeon Corporation, specific surface area: 600 m 2 400 mg of the carbon nanofibers (carbon nanofibers / g) were weighed out and mixed into 2 L of methyl ethyl ketone as a solvent, and the mixture was stirred for 2 minutes using a homogenizer to obtain a crude dispersion. Next, using a wet jet mill (manufactured by Joko Co., Ltd., product name "JN-20"), the crude dispersion was passed through a 0.5 mm channel of the wet jet mill at a pressure of 100 MPa for two cycles, dispersing the fibrous carbon nanostructures in methyl ethyl ketone. This resulted in a dispersion with a solids concentration of 0.20%. [Solvent removal] Thereafter, the dispersion obtained as described above was filtered under reduced pressure using Kiriyama filter paper (No. 5A) to obtain a sheet-like, easily dispersible aggregate of fibrous carbon nanostructures as a fibrous thermally conductive filler. <Preparation of Composition> A mixture of 70 parts of a thermoplastic fluororesin that is liquid at room temperature and normal pressure (manufactured by Daikin Industries, Ltd., trade name "Dai-el (registered trademark) G-101", hereinafter referred to as "G101") and 10 parts of a thermoplastic fluororesin that is solid at room temperature and normal pressure (manufactured by 3M Japan Ltd., trade name "Dyneon (registered trademark) FC-2211", Mooney viscosity: 27 ml) was used. 1+430 parts of a rubber particle (crosslinked polybutyl acrylate, glass transition temperature (Tg): -40°C, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., trade name "Matsumoto Microsphere S-100", average diameter 20 μm, hereinafter referred to as "S-100"), 3.2 parts of rubber particles, 93 parts of expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., trade name "EC300", volume average particle diameter: 50 μm, average particle diameter in the minor axis direction: 10 to 20 μm, hereinafter referred to as "EC300") as a particulate thermally conductive filler, and 0.5 parts of the easily dispersible aggregates of fibrous carbon nanostructures as a fibrous thermally conductive filler were mixed and stirred at a temperature of 150°C for 20 minutes using a pressure kneader (manufactured by Nippon Spindle). Next, the resulting mixture was placed in a disintegrator and disintegrated for 10 seconds to obtain a composition. <Pre-sheet molding process> Next, 50 g of the obtained composition was sandwiched between sandblasted PET films (protective films) having a thickness of 50 μm, and roll-molded (primary pressing) under the conditions of a roll gap of 550 μm, a roll temperature of 50°C, a roll linear pressure of 50 kg / cm, and a roll speed of 1 m / min to obtain a pre-sheet having a thickness of 0.5 mm. <Laminate formation process> Next, the obtained pre-sheets were cut into 150 mm length x 150 mm width x 0.5 mm thickness, and 300 sheets were stacked in the thickness direction of the pre-sheets.Furthermore, they were pressed (secondary pressing) in the stacking direction at a temperature of 120°C and a pressure of 0.1 MPa for 3 minutes to obtain a laminate with a height of approximately 150 mm. <Slicing process> The laminated side of the secondarily pressurized laminate was then pressed with a pressure of 0.3 MPa and sliced ​​at an angle of 0 degrees to the lamination direction (in other words, in the normal direction to the main surface of the laminated pre-sheets) using a woodworking slicer (Marunaka Iron Works Co., Ltd., product name "Super Mecha S Super Finishing Planer") to obtain a thermally conductive sheet measuring 150 mm in length, 150 mm in width, and 0.3 mm in thickness.

[0079] Example 2 When preparing the composition, the amount of S-100 used was changed from 3.2 parts to 8.0 parts, and the amount of EC300 used was changed from 93 parts to 97 parts. Otherwise, a thermally conductive sheet was produced in the same manner as in Example 1. Then, measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0080] Example 3 A thermally conductive sheet was produced in the same manner as in Example 2, except that the average diameter of S-100 was changed from 20 μm to 30 μm when preparing the composition. Measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0081] Example 4 When preparing the composition, the amount of S-100 used was changed from 3.2 parts to 12.9 parts, the amount of EC300 used was changed from 93 parts to 101 parts, and the amount of the easily dispersible aggregates of fibrous carbon nanostructures used was changed from 0.5 parts to 0.6 parts. Otherwise, a thermally conductive sheet was produced in the same manner as in Example 1. Then, measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0082] Example 5 When preparing the composition, the amount of S-100 used was changed from 3.2 parts to 18.2 parts, the amount of EC300 used was changed from 93 parts to 107 parts, and the amount of the easily dispersible aggregates of fibrous carbon nanostructures used was changed from 0.5 parts to 0.6 parts. Otherwise, a thermally conductive sheet was produced in the same manner as in Example 1. Then, measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0083] (Comparative Example 1) When preparing the composition, S-100 was not used, and the amount of EC300 used was changed from 93 parts to 90 parts. Otherwise, a thermally conductive sheet was produced in the same manner as in Example 1. Then, measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0084] (Comparative Example 2) When preparing the composition, FC-2211 and S-100 were not used, the amount of G101 used was changed from 70 parts to 100 parts, and the amount of EC300 used was changed from 93 parts to 70 parts. Otherwise, a thermally conductive sheet was produced in the same manner as in Example 1. Measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0085] (Comparative Example 3) A thermally conductive sheet was produced in the same manner as in Example 2, except that the average diameter of S-100 was changed from 30 μm to 3 μm when preparing the composition. Measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0086] Comparative Example 4 A thermally conductive sheet was produced in the same manner as in Example 2, except that the average diameter of S-100 was changed from 30 μm to 60 μm when preparing the composition. Measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0087] [Table 1]

[0088] Table 1 shows that in Examples 1 to 5, which use a thermally conductive sheet containing a resin, a thermally conductive filler, and rubber particles with an average diameter within a specified range, a thermally conductive sheet was produced that has high compressibility under low loads and excellent crush resistance and thermal conductivity under high loads. On the other hand, in Comparative Example 1, which used a heat conductive sheet containing no rubber particles, the compressibility of the heat conductive sheet decreased, and it was found that the compressibility under low load decreased. Furthermore, in Comparative Example 2, which used a thermally conductive sheet that did not contain rubber particles, although the Asker hardness, which indicates the flexibility of the thermally conductive sheet, was the same as in Example 2, the compressibility and rate of change of thermal conductivity of the thermally conductive sheet were lower than in Example 2, indicating that the compressibility under low load and the crushing suppression and thermal conductivity under high load were lower. Furthermore, in Comparative Examples 3 and 4, in which the average diameter of the rubber particles was outside the specified range, the rate of change in the compressibility and thermal conductivity of the thermal conductive sheet was reduced, indicating that the compressibility under low load and the crushing suppression and thermal conductivity under high load were reduced. [Industrial Applicability]

[0089] According to the present invention, it is possible to provide a thermally conductive sheet that has high compressibility under low load, and is excellent in crush resistance and thermal conductivity under high load. [Explanation of symbols]

[0090] 10. Thermal Conduction Sheet 11 Seat body 20 rubber particles

Claims

1. The composite material includes a resin, a thermally conductive filler, and rubber particles, The average diameter of the rubber particles is 5 μm or more and 50 μm or less, The content of the thermally conductive filler is 40 parts by mass or more and 130 parts by mass or less per 100 parts by mass of the resin, The content of the rubber particles is 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the resin, the rubber particles are (meth)acrylic rubber particles, the thermally conductive filler is a particulate thermally conductive filler and / or a fibrous thermally conductive filler; the particulate thermally conductive filler is a particulate carbon material; A thermally conductive sheet, wherein the fibrous thermally conductive filler is carbon nanotubes and / or carbon fibers.

2. The thickness of the thermal conductive sheet under a pressure of 0.6 MPa is T ０．６ The thickness of the thermal conductive sheet under a pressure of 0.05 MPa is T ０．０５ As the following formula (1): C ０．６ =100×{1-(T ０．６ / T ０．０５ )}[%]・・・(1) The compression rate C calculated by ０．６ The thermal conductive sheet according to claim 1 , wherein the ρ is 10% or more.

3. The thickness of the thermal conductive sheet under a pressure of 0.9 MPa is T ０．９ The thickness of the thermal conductive sheet under a pressure of 0.05 MPa is T ０．０５ As the following formula (2): C ０．９ =100×{1-(T ０．９ / T ０．０５ )}[%]・・・(2) The compression rate C calculated by ０．９ The thermal conductive sheet according to claim 1 or 2, wherein the SiO 2 content is 15% or more.

4. The thermal conductive sheet according to any one of claims 1 to 3, having a thermal conductivity of 10 W / m·K or more under a pressure of 0.9 MPa, measured in accordance with ISO 22007-3.

5. The thermal conductive sheet according to any one of claims 1 to 4, having a thickness of 50 µm or more and 1000 µm or less.

6. The thermally conductive sheet according to any one of claims 1 to 5, wherein the resin comprises a thermoplastic fluororesin that is solid at room temperature and normal pressure.

7. The thermal conductive sheet according to any one of claims 1 to 6, wherein the rubber particles have a glass transition temperature (Tg) of 20°C or lower.

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