Heat-transfer sheet and method of manufacturing the same

Abstract

To provide a heat-transfer sheet with a small thickness and a low thermal resistance value.SOLUTION: In a heat-transfer sheet, strips containing a resin and a thermally conductive filler are joined in parallel. The thermally conductive filler is oriented in a thickness direction of the heat-transfer sheet. The average thickness is in the range of 15-90 μm. The depth is 20% or more of the average thickness of the heat-transfer sheet. The density of scratches with a width of 100 μm or more and a length of 1000 μm or more is 5 pieces / 10000 mm2 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive sheet and a method for manufacturing the same. [Background technology]

[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 that use these components need to take measures to prevent malfunctions caused by temperature increases in the electronic components.

[0003] To prevent malfunctions of electronic components due to temperature rise, 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-like member (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 sliding the block against the sliding surface. 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-140982 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, thermally conductive sheets are required to exhibit superior thermal conductivity, and to achieve this, the thermal resistance of the thermally conductive sheet itself can be reduced by making the thermally conductive sheet thinner. However, with the above-mentioned conventional methods, it has been difficult to reduce the number of scratches on the manufactured thermally conductive sheet while also reducing the thickness.

[0006] Therefore, an object of the present invention is to provide a thermally conductive sheet that is thin and has a low thermal resistance value. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems, and have discovered that a thermally conductive sheet having a small thickness and a small thermal resistance can be obtained by controlling the average thickness within a predetermined range and the density of predetermined flaws to a certain value or less for a thermally conductive sheet formed by joining strips containing a resin and a thermally conductive filler in parallel, with the thermally conductive filler oriented in the thickness direction of the thermally conductive sheet, and have completed the present invention.

[0008] That is, the present invention aims to advantageously solve the above-mentioned problems, and the present invention provides: [1] a thermally conductive sheet formed by joining strips containing a resin and a thermally conductive filler in parallel, wherein the thermally conductive filler is oriented in the thickness direction of the thermally conductive sheet, the average thickness is 15 μm or more and 90 μm or less, and the density of scratches having a depth of 20% or more of the average thickness of the thermally conductive sheet, a width of 100 μm or more, and a length of 1000 μm or more is 5 / 10000 mm 2 The thermally conductive sheet is as follows: The thermally conductive sheet has a sufficiently small thickness and a sufficiently small thermal resistance value. The average thickness and scratch density of the thermally conductive sheet can be measured according to the method described in the examples of this specification.

[0009] [2] Here, the thermally conductive sheet of [1] above preferably has a tensile strength of 0.10 MPa or more. If the tensile strength is equal to or greater than the lower limit, the thermally conductive sheet is less likely to break and is easier to handle. In this specification, the tensile strength of the thermal conductive sheet refers to the tensile strength when the thermal conductive sheet is assumed to have a thickness of 300 μm, and can be measured according to the method described in the Examples of this specification. By measuring the tensile strength of a thermal conductor sample that is thicker than the thermal conductive sheet of the present invention, it is possible to measure the strength derived from the composition of the thermal conductive sheet, regardless of the thickness of the thermal conductive sheet itself, and therefore the density and depth of scratches on the thermal conductive sheet.

[0010] [3] The present invention also provides a method for producing a thermally conductive sheet, comprising the steps of: supporting a block containing a resin and a thermally conductive filler slidably on a sliding surface; supporting a cutting blade with its cutting edge protruding from the sliding surface; and sliding the block on the sliding surface to slice the block with the cutting blade to obtain a thermally conductive sheet, wherein 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 angle between the flank and the first rake angle, the second rake angle being larger than the first rake angle; and setting the clearance angle of the cutting blade to be between 3° and 15° to slice the block. According to the above manufacturing method, a thermally conductive sheet having a sufficiently small thickness and thermal resistance value can be obtained. In this specification, the term "block" refers to a laminate formed by laminating a plurality of primary sheets containing a resin and a thermally conductive filler in the thickness direction.

[0011] [4] In the method for manufacturing a thermally conductive sheet according to [3] above, it is preferable that the length of the first cutting face along the slicing direction is 0.1 mm or more. If the length of the first cutting face along the slicing direction is equal to or greater than the lower limit, it is possible to reduce the occurrence of scratches on the thermally conductive sheet caused by rubbing against the cutting face when slicing the block body.

[0012] [5] In the method for manufacturing a thermally conductive sheet according to the above [1] or [2], it is preferable that the flank of the cutting blade comprises 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, the second clearance angle being larger than the first clearance angle and corresponding to the clearance angle of the cutting blade. If the flank of the cutting blade satisfies the above, a thermally conductive sheet with an even smaller thickness can be obtained. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a thermally conductive sheet that is thin and has a low thermal resistance value. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing an example of a slicing device that can be used in the method for producing a thermally conductive sheet of the present invention. [Figure 2] 3A to 3C are diagrams showing an example of a method for slicing a block body in the method for producing a thermally conductive sheet of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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 produced, for example, according to the method for producing a thermally conductive sheet of the present invention.

[0016] (thermal conductive sheet) The thermally conductive sheet of the present invention is a thermally conductive sheet formed by joining strips containing a resin and a thermally conductive filler in parallel, with the thermally conductive filler oriented in the thickness direction of the thermally conductive sheet. The thermally conductive sheet of the present invention also has an average thickness of 15 μm to 90 μm, a depth of 20% or more of the average thickness of the thermally conductive sheet, a width of 100 μm or more, and a length of 1000 μm or more, with a density of 5 scratches per 10000 mm 2 The above-mentioned thermally conductive sheet has a small thickness and a small thermal resistance value.

[0017] <Composition of the thermal 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. The resin may be used alone or in combination with two or more types. For example, the thermally conductive sheet may contain at least one of a liquid resin and a solid resin. However, from the viewpoint of further reducing the thickness and thermal resistance value of the thermally conductive sheet, it is preferable that the thermally conductive sheet contain both a liquid resin and a solid resin.

[0018] [Liquid resin] The liquid resin is not particularly limited as long as it is liquid at room temperature and normal pressure, and for example, a thermoplastic resin that is liquid at room temperature and normal pressure can be used. In the present invention, "normal temperature" refers to 23° C., and "normal pressure" refers to 1 atm (absolute pressure).

[0019] 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 thermally conductive sheet. Furthermore, using fluororesin as the liquid resin can improve the heat resistance, oil resistance, and chemical resistance of the resulting thermally conductive sheet. Furthermore, using acrylic resin as the liquid resin can further increase the adhesion of the thermally conductive sheet to metal, ensuring sufficient contact between the thermally conductive sheet and metal components such as heat sinks even when the electronic component package or electronic device is deformed.

[0020] [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.

[0021] {Thermoplastic resin that is solid at room temperature and 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 esters, and polyacrylic acid or its esters; 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; polystyrene; and polyacrylonitrile. Examples of such copolymers 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 included in the "resin".

[0022] {Thermosetting resin that is solid at room temperature and 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.

[0023] [Resin content] The resin content in the thermally conductive sheet is not particularly limited, but is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and is preferably 95% by mass or less, more preferably 85% by mass or less, and even more preferably 75% by mass or less. If the resin content is equal to or greater than the lower limit, the thermally 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 thermally conductive sheet can be further reduced.

[0024] [Liquid resin content] The proportion of liquid resin 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 is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. If the proportion of liquid resin in the resin is equal to or greater than 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 proportion of liquid resin in the resin is equal to or less than the upper limit, the strength suitable for the primary sheet is imparted, making it easier to slice the block, and further improving the thickness uniformity of the resulting thermal conductive sheet. Furthermore, the tensile strength of the sheet can be increased.

[0025] <<Thermal conductive filler>> The thermally 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, carbon materials such as particulate carbon materials and fibrous carbon materials are preferably used as the thermally conductive filler, and particulate carbon materials are more preferably used.

[0026] [Particulate carbon materials] The particulate carbon material is not particularly limited, and examples thereof include graphite such as artificial graphite, scaly 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.

[0027] 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.

[0028] 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 thermally conductive sheet, and the thermal conductivity in the thickness direction of the thermally conductive sheet is increased. As a result, the thermal resistance value of the thermally 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 thermally conductive sheet can be further reduced. In the present invention, the "volume average particle size" can be determined as the particle size (D50) at which the cumulative volume calculated from the smallest diameter side reaches 50% in the particle size distribution measured by a laser diffraction method using a laser diffraction / scattering particle size distribution analyzer.

[0029] 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. When the aspect ratio of the particulate carbon material is within the above range, it is presumed that this is because the particulate carbon material is more likely to be well oriented in the thickness direction in the thermally conductive sheet, thereby increasing the thermal conductivity of the thermally conductive sheet in the thickness direction. As a result, the thermal resistance of the thermally conductive sheet can be further reduced. In the present invention, the "aspect ratio" can be determined by observing particulate carbon material with an SEM (scanning electron microscope), measuring the maximum diameter (long diameter) and the particle diameter (short diameter) in a direction perpendicular to the maximum diameter for 50 randomly selected particulate carbon material particles, and calculating the average value of the ratio of the long diameter to the short diameter (long diameter / short diameter).

[0030] [Thermal conductive filler content] The content of the thermally conductive filler in the thermally conductive sheet is not particularly limited, but is preferably 30% by volume or more, more preferably 35% by volume or more, and particularly preferably 38% by volume or more, and is 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 thermally conductive sheet. If the content of the thermally conductive filler is equal to or greater than the above lower limit, the thermal conductivity of the thermally conductive filler in the thickness direction increases, and the thermal resistance of the thermally conductive sheet can be further reduced. On the other hand, if the content of the thermally conductive filler is equal to or less than the upper limit, the flexibility of the thermally conductive sheet can be ensured and the uniformity of the thickness of the thermally conductive sheet can be further improved.

[0031] 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, and 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, based on the total mass of the 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, further reducing the thermal resistance 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 uniformity of the thickness of the thermally conductive sheet.

[0032] 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, and 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 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 per 100 parts by mass of resin 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.

[0033] <Additives> The thermally conductive sheet of the present invention can further contain known additives that can be used in forming the thermally conductive sheet, if necessary. The additives that can be contained in the thermally 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.

[0034] 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 that it be 10 parts by mass or less.

[0035] <Thermal Conduction Sheet Properties> The thermally conductive sheet of the present invention is formed by joining strips containing a resin and a thermally conductive filler in parallel. In such a thermally conductive sheet, the thermally conductive filler can be easily oriented in the thickness direction of the thermally conductive sheet, thereby improving the thermal conductivity of the thermally conductive sheet.

[0036] The thermally conductive sheet may have a structure in which strips containing a resin and a thermally conductive filler are connected 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 strips in this approximately perpendicular direction is not particularly limited and can be, for example, 50 μm to 2000 μm. The width of the strips 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 has a reduced number of stacks, folds, or windings of the primary sheet. As a result, such a thermally conductive sheet improves the speed of forming the block (laminate) described below and improves productivity. On the other hand, a thermally conductive sheet having a strip width equal to or less than the above-mentioned upper limit has a thermally conductive filler well oriented in the thickness direction in the thermally conductive sheet, thereby improving thermal conductivity and further reducing the thermal resistance of the thermally conductive sheet.

[0037] In the thermally conductive sheet, the thermally conductive filler is preferably 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 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. In addition, 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-mentioned orientation angle.

[0038] The thermally conductive sheet must have an average thickness of 15 μm or more, preferably 20 μm or more, and more preferably 30 μm or more, and must have an average thickness of 90 μm or less, preferably 80 μm or less, and more preferably 70 μm or less. If the thickness of the thermally conductive sheet is equal to or greater than the above-mentioned lower limit, the strength of the thermally conductive sheet can be improved. On the other hand, if the thickness of the thermally conductive sheet is equal to or less than the above-mentioned upper limit, the thermal resistance value of the thermally conductive sheet can be further reduced.

[0039] 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. If the standard deviation of thickness is equal to or less than the above upper limit, a thermally conductive sheet with good thickness uniformity can be obtained. The lower limit of the standard deviation of the 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 the thickness of a 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 the thickness of a thermally conductive sheet can be reduced by manufacturing the thermally conductive sheet using the thermally conductive sheet manufacturing method of the present invention described below. More specifically, in the thermally conductive sheet manufacturing method of the present invention, the standard deviation of the thickness of a 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.

[0040] The thermal conductive sheet has scratches with a depth of 20% or more of the average thickness of the thermal conductive sheet, a width of 100 μm or more, and a length of 1000 μm or more, with a density of 5 scratches per 10,000 mm 2 It must be less than 4 pieces / mm 2 It is preferable that the number of particles is less than 3 / mm 2If the density of scratches is equal to or less than the upper limit, it is possible to obtain a thermally conductive sheet that is difficult to break and has excellent handleability. The density of scratches on the thermally conductive sheet is 0 scratches / mm 2 may be. In addition, in the method for manufacturing a thermal conductive sheet of the present invention, the density of scratches on the thermal conductive sheet can be adjusted by changing the type and content ratio of the materials (resin, thermal conductive filler, etc.) used to manufacture 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.

[0041] 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, allowing the thickness of the thermally conductive sheet to be further reduced. 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 producing the thermally conductive sheet, as well as the production conditions of the thermally conductive sheet.

[0042] 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 (i.e., the short direction of the strips joined in parallel within the thermally conductive sheet) in the thermally conductive sheet manufacturing method described below. Because tensile strength is highly dependent on the sheet thickness, it cannot be simply compared between sheets of various thicknesses. Therefore, in the present invention, the tensile strength was measured using a conventional tensile tester or the like, by preparing a thermal conductor sample thicker than the thermally conductive sheet of the present invention (e.g., 300 μm thick) from the raw material composition of the thermally conductive sheet of the present invention, as described in the examples of this specification. By measuring the tensile strength of a thermal conductor sample that is thicker than the thermal conductive sheet of the present invention, it is possible to measure the strength resulting from the composition of the thermal conductive sheet, regardless of the thickness of the thermal conductive sheet itself or the density and depth of scratches on the thermal conductive sheet. Specifically, the composition of the thermal conductive sheet refers to the content of the thermal conductive filler and the resin composition (the ratio of liquid resin to solid resin), and by changing these, it is possible to control the strength resulting from the composition of the thermal conductive sheet.

[0043] (Method of manufacturing thermal conductive sheets) The thermally conductive sheet of the present invention can be manufactured, for example, by using the thermally conductive sheet manufacturing method of the present invention, which includes at least the steps of: supporting a block containing a resin and a thermally conductive filler slidably on a sliding surface; supporting a cutting blade with its cutting edge protruding 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 the slicing step). Furthermore, according to the method for producing a thermally conductive sheet of the present invention, a thermally conductive sheet having a small thickness and a small thermal resistance value can be obtained.

[0044] 1 shows a slicing apparatus for carrying out a manufacturing method according to one example of the present invention. Note that the illustrated slicing apparatus is merely an example, and the slicing apparatus used in the manufacturing method of the present invention is not limited to the illustrated embodiment, and the dimensions and relative positions of each component are also merely an example 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 drawing. 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 between 3° and 15°. The flank (31) of the cutting blade preferably includes a first flank (31a) that intersects with the first rake face (32a) and has a first clearance angle (θb1), and 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 greater 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 slide surface, and a cutting blade is supported with its cutting edge protruding from the slide surface. The block body is then slid on the slide surface, and the block body is sliced ​​by the cutting blade, thereby cutting out a thermally conductive sheet from the block body.

[0046] <<Block letters>> The block body includes a resin and a thermally conductive filler, and may further include an additive, and is not particularly limited, but is preferably a laminate described below.

[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, can 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 corresponds to 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 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, it is possible to reduce the occurrence of scratches on the sliced ​​heat conduction sheet caused by rubbing against the rake face when slicing the block body.

[0049] The first rake angle of the cutting edge is preferably 40° or more, more preferably 55° or more, and is preferably 75° or less, more preferably 65° or less. If the first rake angle is equal to or greater than the above-mentioned lower limit, scratches caused by the sliced ​​heat conductive sheet rubbing against the rake face when slicing the block body can be reduced. On the other hand, 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 onto the cutting blade when slicing, thereby enabling a thin heat conductive sheet to be obtained 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, when performing the slicing step, 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 is preferably 13° or less, and more preferably 10° or less. If the clearance angle is equal to or greater than the lower limit, the block body can be prevented from riding up onto the cutting blade when slicing, resulting in a thin thermally conductive sheet. If the clearance angle is equal to or less than the upper limit, the rake angle of the cutting blade can be prevented from becoming too small, reducing the occurrence of scratches on the sliced ​​thermally conductive sheet caused by rubbing against the rake face when slicing the block body.

[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, the second clearance angle being 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 flanks that satisfy the above relationship, a thermally conductive sheet with a smaller thickness can be obtained by slicing. In the present invention, a cutting blade having both a first rake face and a second rake face, and a first flank face and a second flank face may be referred to as a "double-edged" cutting blade, and a cutting blade having only either a first rake face and a second rake face, or a first flank face and a second flank face may be referred to as a "single-edged" cutting 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 from the viewpoint of the balance of hardness of the blade itself and the ease of processing the blade.

[0057] <<Slice>> The slicing of the resin block using the above-mentioned cutting blade is not particularly limited, but is preferably carried out 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 climbing onto the cutting blade during slicing, thereby enabling the production of a thermally conductive sheet with an even smaller thickness.

[0060] <Other processes> Other steps that may be optionally included in the method for producing a thermally conductive sheet of the present invention are not particularly limited. For example, in the method for manufacturing a thermally conductive sheet of the present invention, a step (stacking step) can be carried out before the above-mentioned slicing step in which multiple primary sheets containing a resin and a thermally conductive filler are stacked in the thickness direction, or the primary sheets are folded or rolled to obtain a block body. In the method for producing a thermally conductive sheet of the present invention, a step of heating the block (heating step) can be carried out before the slicing step described above. The other steps, namely, the lamination step and the heating step, will be described in detail below.

[0061] <<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 to obtain a block body, which is a laminate. The thermally conductive sheet manufactured through the lamination process has a configuration in which slices of the primary sheets that constitute the laminate are joined in parallel, and the thermally conductive filler is oriented in the thickness direction, resulting in excellent thermal conductivity in the thickness direction.

[0062] [First sheet] The primary sheet comprises a resin and a thermally conductive filler, and may optionally further comprise additives.

[0063] The preferred types, properties, and content ratios of the resin and thermally conductive filler contained in the primary sheet, as well as the optional additives, can be the same as those described above for the block body and the thermally conductive sheet of the present invention.

[0064] 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 thermally conductive sheet.

[0065] 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).

[0066] [Formation of blocks by lamination, etc.] The formation of a block body by stacking primary sheets is not particularly limited and may be performed using a stacking device or manually. 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.

[0067] <<Heating process>> Here, for example, the block 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, from 50°C to 170°C, and the heating time may be, for example, from 1 minute to 8 hours. By undergoing the heating step, the adhesion of the block in the lamination direction can be adjusted. For example, when the block contains a thermoplastic resin, the adhesion of the block in the lamination direction can be increased by performing the heating step. [Example]

[0068] 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.

[0069] <Physical property measurement and evaluation> <<Average thickness and standard deviation of the thermal conductive sheet>> Using a film thickness meter (manufactured by Mitutoyo Corporation, product name "Digimatic Indicator"), the thickness was measured at five points, approximately the center and four corners (squares), of the thermal conductive sheet, and the average value (μm) of the measured thicknesses was calculated. Furthermore, the average thickness of 100 slices of the thermally conductive sheet was measured as described above, and the standard deviation (μm) was calculated.

[0070] <<Density of scratches>> The resulting thermally conductive sheet (150mm x 150mm x 0.06mm) was placed on an inspection stage (200mm x 200mm transparent acrylic plate) and irradiated with light from a white LED bar light (model number "LDL2-275X" manufactured by CCS; color temperature 7,800K; power consumption 27W) at an angle of 40° to the normal to the surface of the thermally conductive sheet (50° to the surface of the thermally conductive sheet). While irradiating with light, an 8K monochrome CMOS line camera (manufactured by Basler; model number "raL8192-12gm"; 8192 pixels x 1 pixel) placed directly above the thermally conductive sheet (i.e., at an imaging angle of 90° to the surface of the thermally conductive sheet) and the white LED bar light were scanned parallel to the surface of the thermally conductive sheet, and a digital image of the surface of the thermally conductive sheet was obtained. The digital image was then subjected to image processing such as smoothing and edge detection using 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 (Keyence Corporation, product name "VK-X2000"). The location corresponding to the coordinates of the scratches obtained in the above inspection was 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 scratches obtained, the number of scratches whose depth is 20% or more of the average thickness of the thermal conductive sheet measured, width is 100 μm or more, and length is 1000 μm or more is calculated, and the number of scratches is calculated by dividing the size of the thermal conductive sheet by 10,000 mm 2 The number of scratches per unit area was calculated and used as the scratch density.

[0071] <<Tensile strength>> A 300 μm thick slice of thermally conductive sheet was punched out using a JIS K7113-compliant dumbbell No. 2 (dumbbell-shaped, 3 mm wide, 70 mm long) to prepare a specimen. Using a tensile testing machine (Shimadzu Corporation, product name "AG-IS20kN"), the specimen was pulled perpendicular to the slicing direction (the short direction of the strips bonded in parallel within the thermally conductive sheet) under the following conditions: load cell: 50 N, chuck distance: 35 mm, speed: 50 mm / min, and temperature: 23°C. The breaking strength (tensile strength) was measured by pulling the specimen in the direction perpendicular to the slicing direction (the short direction of the strips bonded in parallel within the thermally conductive sheet). The average of the measurements for three specimens was recorded as the tensile strength of the thermally conductive sheet.

[0072] <<Bulk thermal resistance value>> The thermal resistance of the thermally conductive sheet was measured using a thermal resistance tester (Hitachi Technology & Services, Ltd., product name "Resin Material Thermal Resistance Measuring Device"). In addition to the thermally conductive sheets of the examples and comparative examples, 50 μm, 100 μm, and 200 μm squares were cut into samples, each approximately 1 cm square. The thermal resistance (°C / W) of these samples was measured at a sample temperature of 50°C and a pressure of 0.3 MPa. From the obtained thermal resistance, an approximation of y = ax + b was calculated, where y is the thermal resistance and x is the thickness of the thermally conductive sheet. The interfacial thermal resistance of the thermally conductive sheet was determined by subtracting b from the thermal resistance measured in the same manner for the thermally conductive sheets of the examples and comparative examples.

[0073] <<Handling>> The handleability was evaluated based on the measurement results of the density of scratches and the tensile strength of the thermal conductive sheet as follows: The lower the density of scratches, the better the handleability, and the higher the tensile strength, the better the handleability. [Table 1]

[0074] Example 1 <Preparation of Composition> 40 parts of a thermoplastic fluororesin (Daikin Industries, Ltd., trade name "Dai-el G-101") that is liquid at room temperature and normal pressure as the fluororesin, 20 parts of a thermoplastic fluororesin (3M Japan Ltd., trade name "Dyneon FC2211") that is solid at room temperature and normal pressure as the fluororesin, 40 parts of a hydroxyl group-containing liquid acrylic polymer (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 (Ito Graphite Industries Co., Ltd., trade name "EC-300", volume average particle size: 50 μm) as the thermally conductive filler were mixed and stirred for 5 minutes using a Hobart mixer (Kodaira Seisakusho Co., Ltd., trade name "ACM-5LVT type") The resulting mixture was vacuum degassed for 30 minutes and then placed in a crusher and crushed for 10 seconds to obtain a composition.

[0075] <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 the 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.

[0076] <Lamination process> The obtained primary sheet was cut into a size of 150 mm length x 150 mm width x 800 μm thickness, and 200 sheets were stacked in the thickness direction of the primary sheet.Furthermore, by pressing in the stacking direction at a temperature of 120°C and a pressure of 0.1 MPa for 3 minutes, a block (laminated body) with a height of approximately 160 mm was obtained.

[0077] <Formation of thermal conductive sheet> The side of the secondary-pressurized block (laminate) was pressed against the lamination direction (the surface along the lamination direction) with a pressure of 0.3 MPa. Using a woodworking slicer (Marunaka Iron Works Co., Ltd., product name "Super Mecha S" ultra-finishing planer), the block was sliced ​​at a speed of 80 mm / s at a 90° angle to the lamination direction (i.e., perpendicular to the normal to the main surface of the laminated primary sheets) at a temperature of 15°C within the slicer's processing space. This resulted in a thermally conductive sheet measuring 150 mm long, 150 mm wide, and 45 μm thick. As shown in Figure 2, the slicing direction (A) of the block (10) was perpendicular to the lamination direction (B) of the primary sheets (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 were as shown in Table 2. The obtained thermally conductive sheet was subjected to various measurements and evaluations according to the methods described above. The results are shown in Table 2.

[0078] (Examples 2-4 and Comparative Examples 1-5) 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 composition, as well as the shape, clearance angle, and rake angle of the cutting blade were changed as shown in Table 2. However, for Comparative Examples 2 and 4, the slicing process was carried out with the intention of producing a thermally conductive sheet as a thin film (thickness 90 μm or less), but the block body got on the cutting blade and could not be sliced ​​at the above thickness, so measurements and evaluation of the thermally conductive sheet were not possible. The results are shown in Table 2.

[0079] 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 does not have a second rake face, the angle between the first rake face and the second rake face is recorded as 0°.

[0080] [Table 2]

[0081] From Table 2, the average thickness is 15 μm or more and 90 μm or less, and the density of the specified scratches is 5 / 10,000 mm 2 It can be seen that the thermally conductive sheet of Example 1-4 below has a smaller thickness and thermal resistance value than the thermally conductive sheet of Comparative Example 1-5. Furthermore, the thermally conductive sheet of Example 1-4 has fewer scratches and a higher tensile strength than the thermally conductive sheet of Comparative Example 1-5, and is therefore easier to handle. [Industrial Applicability]

[0082] According to the present invention, it is possible to provide a thermally conductive sheet that is thin and has a low thermal resistance value. [Explanation of symbols]

[0083] 10 Block Letters 11 First seat 20 Slide surface 30 cutting blade 31 Flank 31a First flank 31b Second flank 32a First rake face 32b Second rake face 33 Cutting edge θa1 First rake angle θa2 Second rake angle θb1 First clearance angle θb2 Second relief angle A Block slice direction B. Stacking direction of primary sheet C Orientation direction of thermally conductive filler

Claims

1. A thermally conductive sheet formed by joining strips containing a resin and a thermally conductive filler in parallel, the thermally conductive filler is oriented in the thickness direction of the thermally conductive sheet, The average thickness is 15 μm or more and 90 μm or less, The density of scratches with a depth of 20% or more of the average thickness of the thermal conductive sheet, a width of 100 μm or more, and a length of 1000 μm or more is 5 / 10000 mm ２ Below is the Thermal conductive sheet.

2. The thermal conductive sheet according to claim 1 , wherein the thermal conductive sheet has a tensile strength of 0.10 MPa or more.

3. A method for manufacturing a thermally conductive sheet, comprising: supporting a block body containing a resin and a thermally conductive filler slidably on a slide surface; supporting a cutting blade disposed so that the cutting edge protrudes from the slide surface; and sliding the block body on the slide surface while supporting the block body; and slicing the block body with the cutting blade to obtain a thermally conductive sheet, The cutting blade is The relief surface and a first rake face intersecting the flank face and having a first rake angle; a second rake face adjacent to the first rake face and having a second rake angle; a cutting edge formed by an intersection angle between the flank and the first rake face; Equipped with the second rake angle is greater than the first rake angle; The clearance angle of the cutting blade is set to 3° or more and 15° or less to slice the block body. A manufacturing method for a thermal conductive sheet.

4. The method for manufacturing a thermally conductive sheet according to claim 3 , wherein the length of the first rake face along the slicing direction is 0.1 mm or more.

5. The flank of the cutting blade is a first flank surface intersecting the first rake face and having a first clearance angle; a second flank adjacent to the first flank and having a second clearance angle; Equipped with the second relief angle is greater than the first relief angle; the first clearance angle corresponds to the clearance angle of the cutting blade; A method for producing the thermal conductive sheet according to claim 3 or 4.

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