Heat-conducting sheet

Abstract

A heat-conducting sheet containing a resin and a heat-conductive filler, wherein the heat-conductive filler is aligned in the thickness direction of the heat-conducting sheet, the average thickness is 30-300 μm inclusive, and the density of scratches having a depth of 10 μm or more, a width of 100 μm or more, and a length of 1,000 μm or more is more than 0.0 per 10,000 mm2 but not more than 5.0 per 10,000 mm2.

Description

thermal conductive sheet

[0001] The present invention relates to a thermally conductive sheet.

[0002] In recent years, the amount of heat generated by electronic components such as plasma display panels (PDPs) and integrated circuit (IC) chips has increased as their performance has improved. As a result, electronic devices using these components need to take measures to prevent malfunctions caused by temperature increases in the electronic components.

[0003] To address functional failures caused by temperature rise in electronic components, a common approach is to promote heat dissipation by attaching a heat sink, heat sink plate, heat sink fin, or other heat sink made of metal to the heat-generating element of the electronic component. When using a heat sink, a thermally conductive sheet (thermal conduction sheet) is used to efficiently transfer heat from the heat-generating element to the heat sink. For example, Patent Document 1 discloses a method for manufacturing a thermally conductive sheet, which includes a step of slicing a block containing a resin and a particulate filler by supporting the block on a sliding surface and a blade with a tip protruding from the sliding surface, by pressing the block against the sliding surface and sliding the block with the blade. The blade contacts the block on a first front surface having a length greater than or equal to a certain level and a surface roughness less than or equal to a certain level. According to Patent Document 1, the thermally conductive sheet obtained by the above method has smooth main surfaces, sufficient thickness accuracy, and excellent heat transfer in the thickness direction.

[0004] Furthermore, Patent Document 2 discloses a method for slicing a laminate, in which a laminate of primary composite sheets containing an organic polymer compound and an inorganic material is sliced ​​using a blade in a plane parallel to the lamination direction, characterized in that the slicing speed is 5 m / min or more. According to Patent Document 2, the thermal conductive sheet obtained by the above method has a low thermal resistance value in the thickness direction.

[0005] JP 2020-140982 A JP 2018-089733 A

[0006] Here, it is preferable that the thermally conductive sheet has few scratches. However, with the above-mentioned conventional methods, it has been difficult to manufacture a sheet with a low thermal resistance while reducing the number of scratches on the manufactured thermally conductive sheet.

[0007] Therefore, an object of the present invention is to provide a thermally conductive sheet that has few scratches and a low thermal resistance value.

[0008] The present inventors have conducted extensive research to solve the above problems, and have discovered that a thermally conductive sheet containing a resin and a thermally conductive filler, in which the thermally conductive filler is oriented in the thickness direction of the thermally conductive sheet, can have fewer scratches and a low thermal resistance by controlling the average thickness within a predetermined range and the density of scratches within a predetermined range, thereby completing the present invention.

[0009] That is, the present invention aims to advantageously solve the above-mentioned problems, and the present invention provides: [1] a thermally conductive sheet containing a resin and a thermally conductive filler, wherein the thermally conductive filler is oriented in the thickness direction of the thermally conductive sheet, the average thickness is 30 μm or more and 300 μm or less, and the density of scratches having a depth of 10 μm or more, a width of 100 μm or more, and a length of 1000 μm or more is 0.0 scratches / 10000 mm ２ Super, 5.0 pieces / 10000mm ２ The thermal conductive sheet has few scratches and a sufficiently small thermal resistance. The average thickness and scratch density of the thermal conductive sheet can be measured according to the method described in the examples of this specification.

[0010] [2] Here, the thermally conductive sheet of [1] above preferably has a bulk thermal resistance of 0.070°C / W or less. If the bulk thermal resistance is equal to or less than the upper limit, the thermally conductive sheet has excellent thermal conductivity. Note that the bulk thermal resistance refers to the thermal resistance of the thermally conductive sheet itself, and the sum of the bulk thermal resistance and the interfacial thermal resistance at the interface between the thermally conductive sheet and the heat generating element / heat sink is the total thermal resistance of the thermally conductive sheet.

[0011] According to the present invention, a thermally conductive sheet with few scratches and a small thermal resistance value can be provided.

[0012] 1 is a diagram showing an example of a slicing device that can be used in the production of the thermally conductive sheet of the present invention. 2 is a diagram showing an example of a method for slicing a block body in an example of a production method for producing the thermally conductive sheet of the present invention. The block body in the diagram represents a block body as a laminate of primary sheets, which will be described later.

[0013] Hereinafter, embodiments of the present invention will be described in detail. The thermally conductive sheet of the present invention can be used, for example, by being sandwiched between a heat generating body and a heat dissipating body when attaching the heat dissipating body to the heat generating body. That is, the thermally conductive sheet of the present invention can be used together with a heat dissipating body such as a heat sink, a heat dissipating plate, or a heat dissipating fin to form a heat dissipating device. The thermally conductive sheet of the present invention can be manufactured, for example, according to the manufacturing method described below.

[0014] (Thermal Conduction Sheet) The thermal conduction sheet of the present invention is a thermal conduction sheet containing a resin and a thermally conductive filler, and the thermally conductive filler is oriented in the thickness direction of the thermal conduction sheet. The thermal conduction sheet of the present invention has an average thickness of 30 μm to 300 μm, and a density of scratches having a depth of 10 μm or more, a width of 100 μm or more, and a length of 1000 μm or more of 0.0 scratches / 10000 mm ２ Super, 5.0 pieces / 10000mm ２ The above thermal conductive sheet has few scratches and a small thermal resistance value.

[0015] <Composition of Thermally Conductive Sheet> <<Resin>> The resin contained in the thermally conductive sheet is not particularly limited, and any resin can be used. For example, either a liquid resin or a solid resin can be used as the resin. Note that one type of resin may be used alone, or two or more types may be used in combination. For example, the thermally conductive sheet may contain at least one of a liquid resin and a solid resin. However, from the viewpoint of reducing scratches on the thermally conductive sheet and further reducing the thermal resistance value, it is preferable that the thermally conductive sheet contain both a liquid resin and a solid resin.

[0016] [Liquid Resin] The liquid resin is not particularly limited as long as it is liquid at room temperature and atmospheric pressure, and for example, a thermoplastic resin that is liquid at room temperature and atmospheric pressure can be used. In the present invention, "room temperature" refers to 23°C, and "atmospheric pressure" refers to 1 atm (absolute pressure).

[0017] Examples of liquid resins include fluororesins, silicone resins, acrylic resins, and epoxy resins. These may be used alone or in combination. Among these, silicone resins and fluororesins are preferred as liquid resins, with fluororesins being more preferred. Using at least one of silicone resin and fluororesin as the liquid resin can improve the flame retardancy of the thermal conductive sheet. Furthermore, using fluororesin as the liquid resin can improve the heat resistance, oil resistance, and chemical resistance of the resulting thermal conductive sheet. Furthermore, using acrylic resin as the liquid resin can further enhance the adhesion of the thermal conductive sheet to metal, ensuring sufficient contact between the thermal conductive sheet and metal components such as heat sinks even when the electronic component package or electronic device is deformed.

[0018] [Solid Resin] The solid resin is not particularly limited as long as it is not a liquid at room temperature and normal pressure. For example, a thermoplastic resin that is solid at room temperature and normal pressure, or a thermosetting resin that is solid at room temperature and normal pressure can be used.

[0019] {Thermoplastic resins that are solid at room temperature and normal pressure} Examples of thermoplastic resins that are solid at room temperature and normal pressure include acrylic resins such as poly(2-ethylhexyl acrylate), a copolymer of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its ester, and polyacrylic acid or its ester; silicone resin; fluororesin; polyethylene; polypropylene; ethylene-propylene copolymer; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymer; polyvinyl alcohol; polyacetal; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; and polyacrylonitrile. Examples of such materials include styrene-acrylonitrile copolymers, acrylonitrile-butadiene copolymers (nitrile rubbers), acrylonitrile-butadiene-styrene copolymers (ABS resins), styrene-butadiene block copolymers or hydrogenated products thereof, styrene-isoprene block copolymers or hydrogenated products thereof, polyphenylene ethers, modified polyphenylene ethers, aliphatic polyamides, aromatic polyamides, polyamideimides, polycarbonates, polyphenylene sulfides, polysulfones, polyethersulfones, polyethernitriles, polyetherketones, polyketones, polyurethanes, liquid crystal polymers, and ionomers. These may be used alone or in combination of two or more. In the present invention, rubber is considered to be included in the term "resin."

[0020] {Thermosetting resins that are solid at room temperature and normal pressure} 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, thermosetting modified polyphenylene ether, etc. These may be used alone or in combination of two or more.

[0021] [Resin Content] The resin content in the thermal conductive sheet is not particularly limited, but is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and is preferably 95% by mass or less, more preferably 85% by mass or less, even more preferably 75% by mass or less, and particularly preferably 60% by mass or less. If the resin content is equal to or greater than the lower limit, the thermal conductive sheet can be easily formed. On the other hand, if the resin content is equal to or less than the upper limit, the thermal resistance of the thermal conductive sheet can be further reduced.

[0022] [Liquid Resin Content] The liquid resin content in the resin (i.e., the proportion of liquid resin in the total of solid resin and liquid resin) is not particularly limited, but is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and particularly preferably 60% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. If the liquid resin content in the resin is above the lower limit, the thickness and thermal resistance of the thermal conductive sheet can be further reduced while maintaining the flexibility of the thermal conductive sheet. On the other hand, if the liquid resin content in the resin is below the upper limit, the thermal conductive sheet is provided with strength suitable for the primary sheet, making it easier to slice the block, and further improving the thickness uniformity of the resulting thermal conductive sheet. This also increases the tensile strength of the sheet.

[0023] <<Thermal Conductive Filler>> The thermal conductive filler imparts excellent thermal conductivity to the thermally conductive sheet of the present invention. The thermally conductive filler is not particularly limited, and known thermally conductive fillers such as metal fillers and carbon fillers can be used. Among these, it is preferable to use carbon materials such as particulate carbon materials and fibrous carbon materials as the thermally conductive filler, and it is more preferable to use particulate carbon materials.

[0024] [Particulate Carbon Material] The particulate carbon material is not particularly limited, and examples thereof include graphite such as artificial graphite, flake graphite, exfoliated graphite, natural graphite, acid-treated graphite, expandable graphite, and expanded graphite; carbon black; etc. These may be used alone or in combination of two or more.

[0025] Among the above-mentioned materials, it is preferable to use expanded graphite as the particulate carbon material. By using expanded graphite, the thermal resistance value of the thermal conductive sheet can be further reduced. Here, expanded graphite can be obtained by, for example, chemically treating graphite such as flake graphite with sulfuric acid or the like to obtain expandable graphite, which is then heat-treated to expand it and then refined. Examples of expanded graphite include EC1500, EC1000, EC500, EC300, EC100, and EC50 (all trade names) manufactured by Ito Graphite Industries Co., Ltd.

[0026] The particulate carbon material preferably has a volume average particle diameter of 10 μm or more, more preferably 15 μm or more, and preferably 150 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, and particularly preferably 60 μm or less. It is presumed that if the volume average particle diameter of the particulate carbon material is equal to or greater than the above-mentioned lower limit, a good heat transfer path of the particulate carbon material can be formed in the thermal conductive sheet, and the thermal conductivity in the thickness direction of the thermal conductive sheet is increased. As a result, the thermal resistance value of the thermal conductive sheet can be further reduced. On the other hand, if the volume average particle diameter of the particulate carbon material is equal to or less than the above-mentioned upper limit, the thickness of the thermal conductive sheet can be further reduced. In the present invention, the "volume average particle diameter" can be determined as the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter side reaches 50% in the particle size distribution measured by laser diffraction using a laser diffraction / scattering particle size distribution analyzer.

[0027] Furthermore, the aspect ratio (major axis / minor axis) of the particulate carbon material is preferably greater than 1 and less than 10, more preferably greater than 1 and less than 5. It is presumed that when the aspect ratio of the particulate carbon material is within the above range, the particulate carbon material is more likely to be well oriented in the thickness direction in the thermal conductive sheet, thereby increasing the thermal conductivity of the thermal conductive sheet in the thickness direction. As a result, the thermal resistance value of the thermal conductive sheet can be further reduced. In the present invention, the "aspect ratio" can be determined by observing the particulate carbon material with a scanning electron microscope (SEM), measuring the maximum diameter (major axis) and the particle diameter (minor axis) in the direction perpendicular to the maximum diameter for 50 randomly selected particles of the particulate carbon material, and calculating the average value of the ratio of the major axis to the minor axis (major axis / minor axis).

[0028] [Thermal Conductive Filler Content] The thermal conductive filler content in the thermal conductive sheet is not particularly limited, but is preferably 30% by volume or more, more preferably 35% by volume or more, particularly preferably 38% by volume or more, and preferably 55% by volume or less, more preferably 50% by volume or less, even more preferably 45% by volume or less, and particularly preferably 43% by volume or less, relative to the entire thermal conductive sheet. If the thermal conductive filler content is above the lower limit, the thermal conductivity of the thermal conductive filler in the thickness direction is increased, thereby further reducing the thermal resistance of the thermal conductive sheet. On the other hand, if the thermal conductive filler content is below the upper limit, the flexibility of the thermal conductive sheet can be maintained while further improving the thickness uniformity of the thermal conductive sheet.

[0029] The content of the thermally conductive filler in the thermally conductive sheet is not particularly limited, but is preferably 35% by mass or more, more preferably 40% by mass or more, particularly preferably 45% by mass or more, and preferably 65% ​​by mass or less, more preferably 55% by mass or less, and particularly preferably 50% by mass or less, relative to the entire thermally conductive sheet. If the content of the thermally conductive filler is equal to or greater than the above-mentioned lower limit, the thermal conductivity of the thermally conductive filler in the thickness direction can be increased, thereby further reducing the thermal resistance value of the thermally conductive sheet. On the other hand, if the content of the thermally conductive filler is equal to or less than the above-mentioned upper limit, the flexibility of the thermally conductive sheet can be maintained while further improving the thickness uniformity of the thermally conductive sheet.

[0030] In addition, the content of the thermally conductive filler in the thermally conductive sheet is not particularly limited, but is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, particularly preferably 80 parts by mass or more, and preferably 220 parts by mass or less, more preferably 210 parts by mass or less, and particularly preferably 200 parts by mass or less, per 100 parts by mass of resin. If the content of the thermally conductive filler per 100 parts by mass of resin is above the above-mentioned lower limit, the thermal conductivity of the thermally conductive filler in the thickness direction can be increased, and the thermal resistance value of the thermally conductive sheet can be further reduced. On the other hand, if the content of the thermally conductive filler per 100 parts by mass of resin is below the above-mentioned upper limit, the flexibility of the thermally conductive sheet can be maintained while further improving the thickness uniformity of the thermally conductive sheet.

[0031] <Additives> The thermal conductive sheet of the present invention can further contain known additives that can be used to form the thermal conductive sheet, if necessary. The additives that can be contained in the thermal conductive sheet are not particularly limited, and examples thereof include plasticizers such as fatty acid esters (e.g., sebacic acid esters); flame retardants such as red phosphorus flame retardants and phosphate ester flame retardants; toughness improvers such as urethane acrylates; moisture absorbents such as calcium oxide and magnesium oxide; adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides; wettability improvers such as nonionic surfactants and fluorine-based surfactants; ion trapping agents such as inorganic ion exchangers; and antioxidants such as phenolic antioxidants. The additives may be used alone or in combination.

[0032] If the thermal conductive sheet further contains an additive, the amount of the additive can be, for example, 0.1 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the above-mentioned resin, and it is preferable to set it to 10 parts by mass or less.

[0033] <Properties of the Thermally Conductive Sheet> In the thermally conductive sheet of the present invention, the thermally conductive filler is oriented in the thickness direction of the thermally conductive sheet. Here, the orientation angle of the thermally conductive filler in the thermally conductive sheet is preferably 60° or more, and preferably 90° or less, with the direction parallel to the thickness direction of the thermally conductive sheet being 90°. If the orientation angle of the thermally conductive filler is within the above range, the thermally conductive filler is well oriented in the thickness direction in the thermally conductive sheet, thereby improving thermal conductivity and further reducing the thermal resistance value of the thermally conductive sheet. Note that when the thermally conductive filler has an aspect ratio (major axis / minor axis) of greater than 1, it is preferable that the major axis (major axis) of the thermally conductive filler is oriented in the thickness direction of the thermally conductive sheet at the above orientation angle.

[0034] In a thermally conductive sheet, the method for orienting the thermally conductive filler in the thickness direction of the thermally conductive sheet is not particularly limited. As described below in the section "Method for manufacturing a thermally conductive sheet," orientation may be performed by extrusion molding or the like, or orientation may be performed by slicing a laminate formed by stacking thin sheets that have been oriented in the in-plane direction by pressing in the stacking direction.

[0035] When the orientation operation by slicing the laminate is performed, the thermally conductive sheet of the present invention is formed by joining strips containing a resin and a thermally conductive filler in parallel. Such a thermally conductive sheet facilitates orientation of the thermally conductive filler in the thickness direction of the thermally conductive sheet, further improving the thermal conductivity of the thermally conductive sheet. Furthermore, the thermally conductive sheet may have a structure in which strips containing a resin and a thermally conductive filler are joined in parallel in one direction approximately perpendicular to the thickness direction of the thermally conductive sheet (a direction at an angle of approximately 90° to the thickness direction). The width of the strip in this approximately perpendicular direction is not particularly limited and can be, for example, 50 μm or more and 2000 μm or less. The width of the strip may depend on the thickness of the primary sheet in the manufacturing method described below. Therefore, a thermally conductive sheet having a strip width equal to or greater than the above-mentioned lower limit further reduces the number of stacks, folds, or windings of the primary sheet. As a result, such a thermally conductive sheet improves the speed of block (laminate) formation described below, thereby improving productivity. On the other hand, in a thermally conductive sheet in which the width of the strip is equal to or less than the above upper limit, the thermally conductive filler is well oriented in the thickness direction within the thermally conductive sheet, thereby improving the thermal conductivity and further reducing the thermal resistance value of the thermally conductive sheet.

[0036] The thermal conductive sheet must have an average thickness of 30 μm or more, preferably 40 μm or more, more preferably 50 μm or more, and may be greater than 90 μm. The average thickness must be 300 μm or less, preferably 260 μm or less, more preferably 220 μm or less, and particularly preferably 180 μm or less. If the thickness of the thermal conductive sheet is equal to or greater than the lower limit, the strength of the thermal conductive sheet can be improved. On the other hand, if the thickness of the thermal conductive sheet is equal to or less than the upper limit, the thermal resistance value of the thermal conductive sheet can be further reduced.

[0037] Furthermore, the thermally conductive sheet preferably has a standard deviation of thickness of 3.5 μm or less, more preferably 3.0 μm or less, and even more preferably 2.7 μm or less. A thermally conductive sheet with good thickness uniformity can be obtained if the standard deviation of thickness is equal to or less than the above upper limit. The lower limit of the standard deviation of thickness of the thermally conductive sheet is not particularly limited, but is, for example, 1 μm or more. The standard deviation of thickness refers to the standard deviation of the average thickness of multiple thermally conductive sheets manufactured using the same manufacturing method. The standard deviation of thickness of the thermally conductive sheet can be adjusted by changing the type and content of materials (resin, thermally conductive filler, etc.) used in manufacturing the thermally conductive sheet, as well as the manufacturing conditions of the thermally conductive sheet. For example, the standard deviation of thickness of the thermally conductive sheet can be reduced by manufacturing the thermally conductive sheet using the thermally conductive sheet manufacturing method described below. More specifically, the standard deviation of thickness of the thermally conductive sheet can be reduced by changing the content of the liquid resin, the shape of the cutting blade, the clearance angle, the rake angle, etc. in the thermally conductive sheet manufacturing method described below.

[0038] The density of scratches on the thermal conductive sheet that are 10 μm or more deep, 100 μm or more wide, and 1000 μm or more long is 0.0 / 10000 mm ２ It is necessary to have a density of more than 5.0 pieces / 10,000 mm. ２ It is necessary that the number of pieces is 4.0 pieces / 10,000 mm or less. ２ It is preferable that the number of pieces is 3.0 pieces / 10,000 mm or less. ２ If the density of scratches is equal to or less than the upper limit, it is possible to obtain a thermal conductive sheet that is difficult to break and has excellent handleability. ２If the thickness is greater than 1 / 2 mm, the thermal conductive sheet can be manufactured more easily, and the yield during the manufacturing of the thermal conductive sheet can be improved. The density of scratches on the thermal conductive sheet can be adjusted by changing the type and content of materials (resin, thermally conductive filler, etc.) used in manufacturing the thermal conductive sheet, as well as the first and second rake angles of the cutting blade, the length of the first rake face along the slicing direction, etc., in the manufacturing method of the thermal conductive sheet described below. The measurement of the density of scratches on the thermal conductive sheet may be performed on the thermal conductive sheet after slicing, or may be performed on the thermal conductive sheet after the sliced ​​sheet has been cut to the size actually used. When measuring the thermal conductive sheet after cutting to the size actually used, the measurement should be performed on a thermal conductive sheet having a total area of ​​10,000 mm ２ The number of scratches on the minimum number of sheets that meet the above criteria is measured and the number of scratches is measured over a 10,000 mm ２ This is converted into the per-flaw density.

[0039] The thermal conductive sheet preferably has a bulk thermal resistance of 0.070°C / W or less, more preferably 0.050°C / W or less, and even more preferably 0.040°C / W or less. The lower limit of the bulk thermal resistance is not particularly limited, but is generally 0.010°C / W or more. If the bulk thermal resistance is equal to or less than the upper limit, the thermal resistance of the thermal conductive sheet can be further reduced.

[0040] The thermally conductive sheet preferably has a tensile strength of 0.10 MPa or more, more preferably 0.11 MPa or more, even more preferably 0.12 MPa or more, and preferably 0.50 MPa or less. If the tensile strength is equal to or greater than the above-mentioned lower limit, a thermally conductive sheet that is less likely to break and has excellent handleability can be obtained. Furthermore, if the tensile strength is equal to or less than the above-mentioned upper limit, the block body can be easily sliced, further reducing scratches on the thermally conductive sheet. The tensile strength of the thermally conductive sheet can be adjusted by changing the type and content of materials (resin, thermally conductive filler, etc.) used in the production of the thermally conductive sheet, as well as the production conditions of the thermally conductive sheet.

[0041] In the present invention, the tensile strength of a thermally conductive sheet refers to the tensile strength in a direction perpendicular to the slicing direction of a block containing a resin and a thermally conductive filler in the thermally conductive sheet manufacturing method of the present application described below. Because tensile strength is highly dependent on sheet thickness, simple comparisons between sheets of various thicknesses are not possible. Therefore, in the present invention, as described in the examples of this specification, a thermal conductor sample thicker than the thermally conductive sheet of the present invention (e.g., 300 μm thick) was prepared from the raw material composition of the thermally conductive sheet, and the tensile strength of the thermal conductor sample was measured using a conventional tensile tester. By measuring the tensile strength of a thermal conductor sample thicker than the thermally conductive sheet of the present invention, the strength derived from the composition of the thermally conductive sheet can be measured without depending on the thickness of the thermally conductive sheet itself, and therefore the density and depth of scratches on the thermally conductive sheet. Specifically, the composition of the thermally conductive sheet refers to the content of the thermally conductive filler and the resin composition (the ratio of liquid resin to solid resin), and by changing these, the strength derived from the composition of the thermally conductive sheet can be controlled.

[0042] The thermal conductive sheet of the present invention preferably has a tensile strength of 0.01 MPa or more, more preferably 0.05 MPa or more, even more preferably 0.08 MPa or more, and preferably 0.60 MPa or less, more preferably 0.40 MPa or less, and even more preferably 0.20 MPa or less, when the tensile strength is equal to or greater than the lower limit. A thermal conductive sheet that is less likely to break and has excellent handleability can be obtained. Furthermore, a thermal conductive sheet that is equal to or less than the upper limit can be easily sliced, further reducing scratches on the thermal conductive sheet. The virtual tensile strength of the thermal conductive sheet, like the tensile strength, can be adjusted by changing the type and content of materials (e.g., resin, thermally conductive filler) used in the production of the thermal conductive sheet, as well as the production conditions of the thermal conductive sheet.

[0043] (Method for Manufacturing Thermally Conductive Sheet) The thermally conductive sheet of the present invention described above can be manufactured using, for example, the following manufacturing method. Here, the method for manufacturing a thermally conductive sheet of the present invention includes at least a step of slidably supporting a block containing a resin and a thermally conductive filler on a sliding surface, supporting a cutting blade positioned so that the cutting edge protrudes from the sliding surface, sliding the block on the sliding surface, and slicing the block with the cutting blade to obtain a thermally conductive sheet (hereinafter also referred to as a slicing step). Furthermore, the method for manufacturing a thermally conductive sheet of the present invention can obtain a thermally conductive sheet with few scratches and a low thermal resistance value.

[0044] FIG. 1 shows a slicing device that can be used in the manufacture of a thermally conductive sheet according to one embodiment of the present invention. The illustrated slicing device is merely an example, and the slicing device used in the manufacture of a thermally conductive sheet according to the present invention is not limited to the illustrated embodiment. The dimensions and relative positions of each component are also merely exemplary and are not limited to the illustrated embodiment. The slicing device has a cutting blade (30) attached to a slide base having a slide surface (20) that slidably supports a block body (10). FIG. 1 shows the slicing device and block body (10) as a cross-sectional view taken along a plane parallel to the plane of the illustration. The cutting blade (30) includes a flank (31), a first rake face (32a) that intersects with the flank (31) and has a first rake angle (θa1), a second rake face (32b) that is adjacent to the first rake face (32a) and has a second rake angle (θa2), and a cutting edge (33) formed by the intersection angle between the flank (31) and the first rake face (32a). Here, the second rake angle (θa2) is greater than the first rake angle (θa1). The clearance angle (θb) of the cutting blade is set to be 3° or greater and 15° or less. It is preferable that the flank (31) of the cutting blade includes, in addition to the first flank (31a) that intersects with the first rake face (32a) and has the first clearance angle (θb1), a second flank (31b) that is adjacent to the first flank and has a second clearance angle (θb2). The second clearance angle (θb2) is preferably larger than the first clearance angle (θb1). In this case, the first clearance angle (θb1) corresponds to the clearance angle (θb) of the cutting blade.

[0045] <Slicing process> In the slicing process, as described above, the block body is slidably supported by the sliding surface, and a cutting blade is supported with its cutting edge protruding from the sliding surface. In this state, the block body is slid on the sliding surface, and the block body is sliced ​​by the cutting blade, thereby cutting out a thermally conductive sheet from the block body.

[0046] <<Block Body>> The block body contains a resin and a thermally conductive filler, and may further contain optional additives.

[0047] [Resin, Thermally Conductive Filler, and Additives] The suitable types, properties, and content ratios of the resin and thermally conductive filler contained in the block body, as well as the optional additives contained therein, may be the same as the suitable types, properties, and content ratios described above for the thermally conductive sheet of the present invention.

[0048] <<Cutting Blade>> The cutting blade used to slice the block body described above has a cutting edge located at one end in the extension direction and is usually used so that the extension direction of the cutting blade coincides with the slicing direction. The cutting blade has a flank, a first rake face that intersects with the flank and has a first rake angle, a second rake face that is adjacent to the first rake face and has a second rake angle, and a cutting edge formed by the intersection angle between the flank and the first rake face, where the second rake angle is greater than the first rake angle. By having the first rake face and second rake face that satisfy the above relationship, the occurrence of scratches on the sliced ​​heat conduction sheet due to rubbing against the rake face when slicing the block body can be reduced.

[0049] The first rake angle of the cutting blade is preferably 40° or more, more preferably 55° or more, and preferably 75° or less, and more preferably 65° or less. If the first rake angle is equal to or greater than the above-mentioned lower limit, the occurrence of scratches on the sliced ​​thermally conductive sheet due to rubbing against the rake face when slicing the block body can be reduced. Furthermore, if the first rake angle is equal to or less than the above-mentioned upper limit, the clearance angle of the cutting blade can be prevented from becoming too small, and the block body can be prevented from riding up on the cutting blade when slicing, thereby enabling the production of a thermally conductive sheet with a small thickness by slicing.

[0050] The angle between the first rake face and the second rake face is preferably 1° or more, more preferably 5° or more. There is no particular upper limit to the angle between the first rake face and the second rake face, but it is generally preferably 20° or less.

[0051] The length of the cutting blade along the slicing direction of the first rake face is preferably 0.1 mm or more, and is preferably 5.0 mm or less, more preferably 3.0 mm or less, even more preferably 1.5 mm or less, and particularly preferably 1.0 mm or less. If the length of the first rake face along the slicing direction is within the above range, scratches caused by the heat conduction sheet rubbing against the rake face when slicing the block can be reduced.

[0052] Furthermore, during the slicing process, the clearance angle of the cutting blade is set to 3° or more and 15° or less. The clearance angle is preferably 4° or more, more preferably 5° or more, and preferably 13° or less, and more preferably 10° or less. If the clearance angle is equal to or greater than the above-mentioned lower limit, the block body is prevented from riding up onto the cutting blade during slicing, and a thin thermally conductive sheet can be obtained by slicing. If the clearance angle is equal to or less than the above-mentioned upper limit, the rake angle of the cutting blade is prevented from becoming too small, and scratches caused by the sliced ​​thermally conductive sheet rubbing against the rake face during slicing the block body can be reduced.

[0053] Furthermore, the flank of the cutting blade preferably includes a first flank that intersects with the first rake face and has a first clearance angle, and a second flank that is adjacent to the first flank and has a second clearance angle, and the second clearance angle is preferably larger than the first clearance angle. Here, the first clearance angle corresponds to the clearance angle of the cutting blade. By having the first and second flank faces that have the above relationship, a thermally conductive sheet with a smaller thickness can be obtained by slicing. In the present invention, a cutting blade that includes both a first rake face and a second rake face, and a first flank face and a second flank face, is sometimes referred to as a "double-edged blade," and a cutting blade that includes only either a first rake face and a second rake face or a first flank face and a second flank face is sometimes referred to as a "single-edged blade."

[0054] The angle between the first flank and the second flank is preferably 0.5° or more, and more preferably 1° or more. There is no particular upper limit to the angle between the first flank and the second flank, but it is generally preferably 10° or less.

[0055] The cutting edge angle (the angle between the first rake face and the flank face) of the cutting edge is not particularly limited, and can be, for example, 10° or more and 35° or less.

[0056] The material of the cutting blade is not particularly limited, but from the viewpoint of reducing the thickness of the heat conductive sheet and improving the uniformity of the thickness, it is preferable that the cutting blade be made of a metal such as ceramic, cemented carbide, high-speed tool steel (high-speed steel), or steel, and cemented carbide is more preferable in terms of the balance of hardness of the blade itself and the ease of processing the blade.

[0057] <<Slicing>> The slicing of the resin block using the above-mentioned cutting blade is not particularly limited, but is preferably performed while applying pressure to the resin block, and more preferably while applying a pressure of 0.1 MPa or more and 1.0 MPa or less.

[0058] In addition, from the viewpoint of slicing the resin block easily, the temperature of the resin block when slicing is preferably set to be −20° C. or higher and 40° C. or lower.

[0059] Furthermore, the slicing speed of the resin block is not particularly limited, but is preferably 50 mm / sec or more, more preferably 60 mm / sec or more, and even more preferably 70 mm / sec or more. By setting the slicing speed at or above the lower limit, the productivity of the resin sheet can be increased and the thickness uniformity of the resulting resin sheet can be further improved. The slicing speed of the resin block is typically 600 mm / sec or less. Setting the slicing speed at or below the upper limit prevents the block from riding on the cutting blade during slicing, thereby enabling the production of a thermally conductive sheet with an even smaller thickness.

[0060] <Other Steps> The method for producing a thermally conductive sheet of the present invention may optionally include other steps, but are not limited to these. For example, in the production of a thermally conductive sheet of the present invention, a step of orienting the thermally conductive filler in the thickness direction of the thermally conductive sheet (orientation step) may be carried out before the slicing step described above. The orientation method carried out in the orientation step is not particularly limited, but may be an extrusion molding method or a step of stacking multiple primary sheets containing a resin and a thermally conductive filler in the thickness direction, or folding or rolling the primary sheets to obtain a block (lamination step). Furthermore, the block (laminate) obtained in the lamination step may be subjected to a heating step (heating step) before the slicing step described above. The extrusion molding step, lamination step, and heating step as other steps are described in detail below.

[0061] <<Extrusion Molding Step>> When orienting a thermally conductive filler by extrusion molding, for example, a block is obtained by extrusion molding from a composition containing at least a resin and a thermally conductive filler, according to the method described in JP 2022-037939 A. During this process, the resin flows when extruded through a die, and the thermally conductive filler is oriented along the flow direction.

[0062] <<Lamination Process>> As described above, in the lamination process, a plurality of primary sheets are laminated in the thickness direction, or the primary sheets are folded or rolled up to obtain a block body that is a laminate. The thermally conductive sheet manufactured through the lamination process has a configuration in which slices of the primary sheets that constituted the laminate are joined in parallel, and since the thermally conductive filler is oriented in the thickness direction, it has excellent thermal conductivity in the thickness direction.

[0063] [Primary Sheet] The primary sheet comprises a resin and a thermally conductive filler, and may optionally further comprise additives.

[0064] The suitable types, properties and content ratios of the resin and thermally conductive filler contained in the primary sheet, as well as the optional additives contained therein, can be the same as those described above for the block body and the thermally conductive sheet of the present invention.

[0065] The thickness (average thickness) of the primary sheet is not particularly limited and can be, for example, 50 μm or more and 2000 μm or less. The "thickness (average thickness)" of the primary sheet can be measured in the same manner as the "average thickness" of the thermal conductive sheet.

[0066] The method for preparing the primary sheet is not particularly limited. The primary sheet can be obtained, for example, by molding a composition containing a resin, a thermally conductive filler, and optional additives using a known molding method such as press molding, rolling molding, or extrusion molding. In this way, when producing the primary sheet, by performing a pressing operation in the sheet surface direction, a structure can be formed in the primary sheet in which the thermally conductive filler is oriented in a direction perpendicular to the sheet thickness direction (i.e., in the sheet surface direction).

[0067] [Formation of a block body by lamination, etc.] The formation of a block body by laminating primary sheets, etc., is not particularly limited and may be performed using a lamination device or by manual labor. Furthermore, the formation of a block body by folding a thermally conductive sheet is not particularly limited and may be performed by folding the primary sheet at a fixed width using a folding machine. Furthermore, the formation of a block body by winding a primary sheet is not particularly limited and may be performed by winding the primary sheet around an axis parallel to the short or long direction of the primary sheet.

[0068] <<Heating Step>> Here, for example, the block body obtained through the lamination step described above may be subjected to the slicing step as is, or may be further heated before being subjected to the slicing step. The heating temperature in the heating step may be, for example, 50°C or higher and 170°C or lower, and the heating time may be, for example, 1 minute or higher and 8 hours or lower. By undergoing the heating step, the adhesion of the block body in the lamination direction can be adjusted. For example, when the block body contains a thermoplastic resin, the adhesion of the block body in the lamination direction can be increased by performing the heating step.

[0069] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. In the examples and comparative examples, various measurements and evaluations were carried out by the following methods.

[0070] <Measurement and Evaluation of Physical Properties> <<Average Thickness and Standard Deviation of Thickness of Thermally Conductive Sheet>> Using a film thickness meter (manufactured by Mitutoyo Corporation, product name "Digimatic Indicator"), the thickness of the thermally conductive sheet was measured at five points, approximately at the center and at each of the four corners (squares), and the average value (μm) of the measured thicknesses was calculated. In addition, the average thickness of 100 slices of the thermally conductive sheet was measured as described above, and the standard deviation (μm) was calculated.

[0071] <<Scratch Density>> The obtained thermally conductive sheet (150 mm x 150 mm x 0.06 mm) was placed on an inspection stage (200 mm x 200 mm transparent acrylic plate), and the thermally conductive sheet was illuminated at an angle of 40 ° relative to the perpendicular to the surface of the thermally conductive sheet (50 ° relative to the surface of the thermally conductive sheet) using a white LED bar light (model number "LDL2-275X" manufactured by CCS; color temperature 7,800 K; power consumption 27 W). Then, while irradiating light, an 8K monochrome CMOS line camera (manufactured by Basler; model number "raL8192-12gm"; 8192 pix x 1 pix) and a white LED bar light were installed directly above the thermally conductive sheet (i.e., at an imaging angle of 90 ° relative to the surface of the thermally conductive sheet). While scanning parallel to the surface of the thermally conductive sheet, the surface of the thermally conductive sheet was photographed with the camera to obtain a digital image of the surface of the thermally conductive sheet. The digital image was then subjected to image processing such as smoothing and edge detection in an image processing unit (original software) to detect scratches, and the number of scratches, their width, length, and position coordinates were obtained. Next, the inspected thermal conductive sheet was removed from the inspection stage and placed on the stage of a laser microscope (manufactured by Keyence Corporation, product name "VK-X2000"). The locations corresponding to the position coordinates of the scratches obtained in the above inspection were measured at 10x magnification over a height range of 200 μm, and a profile of the depth direction of the scratches was obtained. The depth of the scratches was measured from the obtained profile. From the width, length, and depth of the obtained scratches, the number of scratches with a depth of 10 μm or more, a width of 100 μm or more, and a length of 1000 μm or more was calculated, and the number of scratches was calculated based on the size of the inspected thermal conductive sheet. ２ The number of scratches per unit area was calculated and used as the scratch density.

[0072] <<Tensile Strength and Virtual Tensile Strength>> A thermally conductive sheet sliced ​​to a thickness of 300 μm was punched out using a No. 2 dumbbell (dumbbell-shaped, 3 mm wide, 70 mm long) conforming to JIS K7113 to prepare a sample. Using a tensile tester (manufactured by Shimadzu Corporation, product name "AG-IS20kN"), the sheet was pulled in a direction perpendicular to the slicing direction under the following conditions: load cell: 50 N, chuck distance: 35 mm, speed: 50 mm / min, and temperature: 23°C, and the breaking strength (tensile strength) was measured. The average value of the measurements for three sample pieces was taken as the tensile strength of the thermally conductive sheet. Furthermore, the virtual tensile strength of the thermally conductive sheet was calculated from the tensile strength measurement results according to the following formula: Virtual tensile strength = tensile strength (MPa) × average thickness of thermally conductive sheet (μm) / 300 (μm).

[0073] <<Bulk Thermal Resistance Value>> The thermal resistance value of the thermal conductive sheet was measured using a thermal resistance tester (Hitachi Technology & Services Co., Ltd., product name "Resin Material Thermal Resistance Measuring Device"). In addition to the thermal conductive sheets of the examples and comparative examples, 50 μm, 100 μm, and 200 μm thermal conductive sheets were cut into approximately 1 cm squares and used as samples. The thermal resistance values ​​(°C / W) of these samples were measured at a sample temperature of 50°C and a pressure of 0.3 MPa was applied. From the obtained thermal resistance values, an approximation of y = ax + b was calculated, where y is the thermal resistance value and x is the thickness of the thermal conductive sheet, and b was used as the interface thermal resistance value of the thermal conductive sheet. The bulk thermal resistance value was determined by subtracting the value of b from the thermal resistance value measured in the same manner for the thermal conductive sheets of the examples and comparative examples.

[0074] <<Handling Efficiency>> Handling ease was evaluated based on the resulting scratch density and virtual tensile strength as follows: A film with a lower scratch density exhibits better handling ease, and a film with a higher virtual tensile strength exhibits better handling ease.

[0075]

[0076] Example 1 Preparation of Composition 40 parts of a thermoplastic fluororesin that is liquid at room temperature and normal pressure (manufactured by Daikin Industries, Ltd., trade name "Dai-el G-101") as the fluororesin, 20 parts of a thermoplastic fluororesin that is solid at room temperature and normal pressure (manufactured by 3M Japan Ltd., trade name "Dyneon FC2211"), 40 parts of a hydroxyl group-containing liquid acrylic polymer having a weight average molecular weight of 6000 (manufactured by Toagosei Co., Ltd., trade name "ARUFON (registered trademark) UH-2190") that is liquid at room temperature and normal pressure as the acrylic resin, and 90 parts of expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., trade name "EC-300", volume average particle size: 50 μm) as the thermally conductive filler were stirred and mixed for 5 minutes using a Hobart mixer (manufactured by Kodaira Seisakusho Co., Ltd., trade name "ACM-5LVT type"). The resulting mixture was vacuum degassed for 30 minutes and then charged into a crusher and crushed for 10 seconds to obtain a composition.

[0077] <Formation of Primary Sheet> Next, 1 kg of the obtained composition was sandwiched between sandblasted PET films (protective films) having a thickness of 50 μm, and roll-molded (primary pressing) under conditions of a roll gap of 600 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 primary sheet having a thickness of 800 μm.

[0078] <Lamination step> The obtained primary sheet was cut into a size of 150 mm length × 150 mm width × 800 μm thickness, and 200 sheets were laminated in the thickness direction of the primary sheet. Further, by pressing in the lamination direction at a temperature of 120°C and a pressure of 0.1 MPa for 3 minutes, a block body (laminate body) with a height of approximately 160 mm was obtained.

[0079] <Formation of Thermally Conductive Sheet> Then, while pressing the side (surface along the stacking direction) of the secondary-pressurized block (laminated body) with a pressure of 0.3 MPa, the block was sliced ​​at an angle of 90° to the stacking direction (in other words, in a direction perpendicular to the normal to the main surface of the stacked primary sheets) at a speed of 80 mm / s using a woodworking slicer (manufactured by Marunaka Iron Works Co., Ltd., product name "Super Finishing Planer Super Mecha S") with the temperature in the slicer's processing space at 15°C, to obtain a thermally conductive sheet measuring 150 mm long x 150 mm wide x 45 μm thick. As shown in FIG. 2, the slicing direction (A) of the block (10) is perpendicular to the stacking direction (B) of the primary sheet (11). The first and second clearance angles, first and second rake angles, shape, and length of the first rake face of the cutting blade used for slicing are as shown in Table 2. The resulting thermally conductive sheet was then subjected to various measurements and evaluations according to the methods described above. The results are shown in Table 2.

[0080] (Examples 2 to 5 and Comparative Examples 1 to 4) Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the types and amounts of materials blended when preparing the compositions, as well as the shape, clearance angle, and rake angle of the cutting blade, were changed as shown in Table 2. The results are shown in Table 2.

[0081] The modified nitrile rubber used was acrylonitrile-butadiene rubber (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol 1072J") which is solid at room temperature and normal pressure; the liquid nitrile rubber used was acrylonitrile-butadiene rubber (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol 1312") which is liquid at room temperature and normal pressure; the epoxy resin used was bisphenol A diglycidyl ether (manufactured by Mitsubishi Chemical Corporation, trade name "jER") which is liquid at room temperature and normal pressure; and the antioxidant used was a combination of an aromatic secondary amine antioxidant (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrac CD") and a benzimidazole antioxidant (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrac MBZ"). In addition, when the cutting blade did not have a second rake face, the angle between the first rake face and the second rake face was recorded as 0°.

[0082]

[0083] From Table 2, when the average thickness is 30 μm or more and 300 μm or less, and the density of the predetermined scratches is 0.0 pieces / 10,000 mm ２ Super, 5.0 pieces / 10000mm ２ It can be seen that the thermal conductive sheet of Example 1-5 below has both fewer scratches and a smaller thermal resistance value compared to the thermal conductive sheet of Comparative Example 1-4. Furthermore, the thermal conductive sheet of Example 1-5 has fewer scratches and a larger virtual tensile strength than the thermal conductive sheet of Comparative Example 1-3, and therefore is easier to handle.

[0084] According to the present invention, a thermally conductive sheet with few scratches and a small thermal resistance value can be provided.

[0085] REFERENCE SIGNS LIST 10 Block body 11 Primary sheet 20 Slide surface 30 Cutting blade 31 Flank surface 31a First flank surface 31b Second flank surface 32a First rake surface 32b Second rake surface 33 Cutting edge θa1 First rake angle θa2 Second rake angle θb1 First relief angle θb2 Second relief angle A Slicing direction of block body B Stacking direction of primary sheet C Orientation direction of thermally conductive filler

Claims

1. A thermally conductive sheet containing a resin and a thermally conductive filler, wherein the thermally conductive filler is oriented in the thickness direction of the thermally conductive sheet, the average thickness is 30 μm or more and 300 μm or less, and the density of scratches with a depth of 10 μm or more, a width of 100 μm or more, and a length of 1000 μm or more is 0.0 / 10000 mm ２ Super, 5.0 pieces / 10000mm ２ Below is a thermal conductive sheet.

2. The thermal conductive sheet according to claim 1, having a bulk thermal resistance of 0.070°C / W or less.

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