Thermal conductive sheet

Abstract

The present invention aims to provide a thermal conductive sheet that is less prone to scratches and has a low thermal resistance value. [Solution] A thermal conductive sheet comprising a resin and a thermal conductive filler, wherein the thermal conductive filler is oriented in the thickness direction of the thermal 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 scratches / 10000 mm 2 Super, 5.0 pieces / 10000mm 2 The following is a thermal conductive sheet.

Description

[Technical Field]

[0001] This invention relates to a thermal conductive sheet. [Background technology]

[0002] In recent years, electronic components such as plasma display panels (PDPs) and integrated circuit (IC) chips have been generating increasing amounts of heat as their performance has improved. As a result, electronic devices using these components require measures to prevent functional failures caused by temperature increases in the electronic components.

[0003] To prevent malfunctions caused by temperature rise in electronic components, a common method is to promote heat dissipation by attaching heat sinks, heat sinks, or heat fins made of metal to the heat-generating elements of electronic components. When using heat sinks, a sheet-like material with thermal conductivity (thermal conductive 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 thermal conductive sheet, which includes a step of slicing the block body with the blade while pressing it against the slide surface, with the block body being supported by a blade whose tip protrudes from the slide surface, and the blade contacting the block body with a first surface having a certain length and a certain surface roughness. According to Patent Document 1, the thermal conductive sheet obtained by the above method has smooth main surfaces and can transfer heat well in the thickness direction while having sufficient thickness accuracy.

[0004] Furthermore, Patent Document 2 discloses a method for slicing a laminate of primary composite sheets containing an organic polymer compound and an inorganic material, using a blade to slice the laminate 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. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-140982 [Patent Document 2] Japanese Patent Publication No. 2018-089733 [Overview of the project] [Problems that the invention aims to solve]

[0006] In this context, it is preferable that the thermal conductive sheet has few defects. However, with the conventional method described above, it has been difficult to produce a sheet with a low thermal resistance value while reducing the number of defects in the manufactured thermal conductive sheet.

[0007] Therefore, the present invention aims to provide a thermal conductive sheet that has fewer scratches and a low thermal resistance value. [Means for solving the problem]

[0008] The inventors diligently conducted research with the aim of solving the above problems. As a result, the inventors discovered that a thermal conductive sheet with fewer defects and a low thermal resistance can be obtained by setting the average thickness within a predetermined range and the density of defects within a predetermined range for a thermal conductive sheet containing a resin and a thermal conductive filler, wherein the thermal conductive filler is oriented in the thickness direction of the thermal conductive sheet, and thus completed the present invention.

[0009] In other words, the present invention aims to advantageously solve the above problems, and the present invention is a thermal conductive sheet comprising [1] a resin and a thermal conductive filler, wherein the thermal conductive filler is oriented in the thickness direction of the thermal 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 scratches / 10000 mm 2 Super, 5.0 pieces / 10000mm 2 The following is a thermal conductive sheet. The above thermal conductive sheet has few scratches and a sufficiently low thermal resistance value. The average thickness and density of defects in the thermal conductive sheet can be measured according to the methods described in the examples of this specification.

[0010] [2] Here, it is preferable that the thermal conductive sheet described in [1] above has a bulk thermal resistance of 0.070°C / W or less. If the bulk thermal resistance is below the above upper limit, the thermal conductive sheet has excellent thermal conductivity. Note that the bulk thermal resistance value refers to the thermal resistance value of the thermal conductive sheet itself, and the sum of the bulk thermal resistance value and the interfacial thermal resistance value at the interface between the thermal conductive sheet and the heat-generating / heat-sinking element is the total thermal resistance value of the thermal conductive sheet. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a thermal conductive sheet with fewer scratches and a low thermal resistance value. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows an example of a slicing apparatus that may be used in the manufacture of the heat conductive sheet of the present invention. [Figure 2] This figure shows an example of a method for slicing a block body in a manufacturing method for an example of a heat conductive sheet according to the present invention. In the figure, the block body refers to a block body that is a laminate of primary sheets, which will be described later. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described in detail below. The thermal conductive sheet of the present invention can be used, for example, by being sandwiched between a heat-generating element and a heat-sinking element when attaching a heat-sinking element to a heat-generating element. That is, the thermal conductive sheet of the present invention can be used to constitute a heat dissipation device together with heat-sinking elements such as heat sinks, heat-sinking plates, and heat-sinking fins. Furthermore, the thermal conductive sheet of the present invention can be manufactured, for example, according to the manufacturing method described later.

[0014] (Thermal conductive sheet) The heat-conducting sheet of the present invention is a heat-conducting sheet containing a resin and a heat-conductive filler, and the heat-conductive filler is oriented in the thickness direction of the heat-conducting sheet. Further, the heat-conducting sheet of the present invention has an average thickness of 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 pieces / 10000 mm 2 super, 5.0 pieces / 10000 mm 2 or less. The above heat-conducting sheet has few scratches and a small heat resistance value.

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

[0016] [Liquid resin] And, as the liquid resin, as long as it is liquid under normal temperature and pressure, it is not particularly limited. For example, a thermoplastic resin that is liquid under normal temperature and pressure can be used. In the present invention, "normal temperature" refers to 23°C, and "normal 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 individually or in combination of two or more. Among these, silicone resins and fluororesins are preferred as liquid resins, with fluororesins being more preferred. Using at least one of silicone resins and fluororesins 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. Moreover, 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 dissipation pairs, even during deformation of electronic component packages and electronic devices.

[0018] [Solid resin] As for the solid resin, there are no particular limitations as long as it is not liquid at room temperature and atmospheric pressure. For example, thermoplastic resins that are solid at room temperature and atmospheric pressure, and thermosetting resins that are solid at room temperature and atmospheric pressure can be used.

[0019] {A thermoplastic resin that is solid at room temperature and atmospheric 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, 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 include: styrene-acrylonitrile copolymer; acrylonitrile-butadiene copolymer (nitrile rubber); acrylonitrile-butadiene-styrene copolymer (ABS resin); styrene-butadiene block copolymer or its hydrogenated product; styrene-isoprene block copolymer or its hydrogenated product; polyphenylene ether; modified polyphenylene ether; aliphatic polyamides; aromatic polyamides; polyamide-imide; polycarbonate; polyphenylene sulfide; polysulfone; polyethersulfone; polyethernitrile; polyether ketone; polyketone; polyurethane; liquid crystal polymer; ionomer; and others. These may be used individually or in combination of two or more. In this invention, rubber is included in the term "resin".

[0020] {A thermosetting resin that is solid at room temperature and atmospheric pressure} Examples of thermosetting resins that are solid at room temperature and 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, and the like. These may be used individually 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, 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 above the lower limit, the formation of the thermal conductive sheet becomes easier. On the other hand, if the resin content is below the upper limit, the thermal resistance value of the thermal conductive sheet can be further reduced.

[0022] [Percentage of liquid resin content] Furthermore, the proportion of liquid resin in the resin (in other words, 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, particularly preferably 60% by mass or more, 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 above the lower limit, the thickness and thermal resistance of the thermal conductive sheet can be further reduced while ensuring the flexibility of the thermal conductive sheet. On the other hand, if the proportion of liquid resin in the resin is below the upper limit, it provides strength suitable for a primary sheet, making it easier to slice the block and further improving the uniformity of the thickness of the resulting thermal conductive sheet. In addition, the tensile strength of the sheet can be increased.

[0023] <<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. In particular, 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 of graphite such as artificial graphite, flake graphite, flaked graphite, natural graphite, acid-treated graphite, expandable graphite, and expanded graphite; carbon black; etc. may be used. These may be used individually or in combination of two or more.

[0025] Among the above, it is preferable to use expanded graphite as the particulate carbon material. By using expanded graphite, the thermal resistance value of the heat conductive sheet can be further reduced. Expanded graphite can be obtained, for example, by chemically treating graphite such as flake graphite with sulfuric acid 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 are product 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, 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. If the volume-average particle diameter of the particulate carbon material is above the lower limit, it is presumed that a good heat transfer path can be formed in the thermal conductive sheet, and the thermal conductivity in the thickness direction of the thermal conductive sheet increases. As a result, the thermal resistance 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 below the upper limit, the thickness of the thermal conductive sheet can be further reduced. In this invention, the "volume-average particle diameter" can be determined using a laser diffraction / scattering particle diameter distribution analyzer, specifically as the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter side reaches 50% in the particle diameter distribution measured using the laser diffraction method.

[0027] Furthermore, the particulate carbon material preferably has an aspect ratio (major axis / minor axis) greater than 1 and less than or equal to 10, and more preferably greater than 1 and less than or equal to 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 within the thermal conductive sheet, thereby increasing the thermal conductivity of the thermal conductive sheet in the thickness direction. As a result, the thermal resistance of the thermal conductive sheet can be further reduced. In this invention, the "aspect ratio" can be determined by observing particulate carbon material with a scanning electron microscope (SEM), measuring the maximum diameter (major diameter) and the particle diameter in the direction perpendicular to the maximum diameter (minor diameter) for any 50 particulate carbon materials, and calculating the average value of the ratio of major diameter to minor diameter (major diameter / minor diameter).

[0028] [Percentage of thermally conductive filler content] The proportion of thermal conductive filler 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, 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. If the proportion of thermal conductive filler is above the above lower limit, the thermal conductivity in the thickness direction of the thermal conductive filler increases, and the thermal resistance of the thermal conductive sheet can be further reduced. On the other hand, if the proportion of thermally conductive filler is below the above upper limit, it is possible to further improve the uniformity of the thickness of the thermally conductive sheet while ensuring the flexibility of the thermally conductive sheet.

[0029] Furthermore, while the proportion of thermal conductive filler in the thermal conductive sheet is not particularly limited, it is preferably 35% by mass or more, more preferably 40% by mass or more, particularly preferably 45% by mass or more, 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 thermal conductive sheet. If the proportion of thermal conductive filler is above the lower limit, the thermal conductivity in the thickness direction of the thermal conductive filler increases, and the thermal resistance of the thermal conductive sheet can be further reduced. On the other hand, if the proportion of thermal conductive filler is below the upper limit, the uniformity of the thickness of the thermal conductive sheet can be further improved while ensuring the flexibility of the thermal conductive sheet.

[0030] In addition, the content of the thermal conductive filler in the thermal 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, 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 thermal conductive filler per 100 parts by mass of resin is above the lower limit, the thermal conductivity in the thickness direction of the thermal conductive filler will increase, and the thermal resistance value of the thermal conductive sheet can be further reduced. On the other hand, if the content of the thermal conductive filler per 100 parts by mass of resin is below the upper limit, the uniformity of the thickness of the thermal conductive sheet can be further improved while ensuring the flexibility of the thermal conductive sheet.

[0031] <Additives> The thermal conductive sheet of the present invention may further contain known additives that can be used in the formation of the thermal conductive sheet, as needed. The additives that can be incorporated into the thermal conductive sheet are not particularly limited, but include, for example, plasticizers such as fatty acid esters like sebacate; flame retardants such as red phosphorus-based flame retardants and phosphate ester-based flame retardants; toughness modifiers such as urethane acrylate; hygroscopic agents such as calcium oxide and magnesium oxide; adhesion enhancers such as silane coupling agents, titanium coupling agents, and acid anhydrides; wettability enhancers such as nonionic surfactants and fluorine-based surfactants; ion trapping agents such as inorganic ion exchangers; and anti-aging agents such as phenolic antioxidants. Note that one additive may be used alone, or two or more may be used in combination.

[0032] Furthermore, if the heat conductive sheet contains additional additives, the amount of additives 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 resin described above, and is preferably 10 parts by mass or less.

[0033] <Properties of thermal conductive sheets> In the heat-conducting sheet of the present invention, the heat-conducting filler is oriented in the thickness direction of the heat-conducting sheet. Here, the orientation angle of the heat-conducting filler in the heat-conducting sheet is preferably 60° or more, and preferably 90° or less, with the direction parallel to the thickness direction of the heat-conducting sheet being defined as 90°. If the orientation angle of the heat-conducting filler is within the above range, the heat-conducting filler in the heat-conducting sheet is well oriented in the thickness direction, thereby improving heat conductivity and further reducing the thermal resistance of the heat-conducting sheet. Furthermore, if the thermally conductive filler has an aspect ratio (major axis / minor axis) 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 orientation angle described above.

[0034] In a thermal conductive sheet, the method for orienting the thermal conductive filler in the thickness direction of the thermal conductive sheet is not particularly limited, but orientation operations may be performed by extrusion molding or the like, as described later in the section on "Methods for Manufacturing Thermal Conductive Sheets," or orientation operations may be performed by slicing a laminate, which is made by stacking thin sheets oriented in the in-plane direction by pressing, in the direction of stacking.

[0035] When the above-described orientation operation is performed by slicing the laminate, the thermal conductive sheet of the present invention is formed by joining strips containing resin and thermal conductive filler in parallel. With such a thermal conductive sheet, it is easy to orient the thermal conductive filler in the thickness direction of the thermal conductive sheet, so the thermal conductivity of the thermal conductive sheet can be further improved. Furthermore, the thermal conductive sheet may have a structure in which strips containing resin and thermal conductive filler are connected in parallel in one substantially perpendicular direction to the thickness direction of the thermal conductive sheet (a direction at an angle of approximately 90° to the thickness direction). The width of the strips in this substantially perpendicular direction is not particularly limited and can be, for example, 50 μm or more and 2000 μm or less. The width of the strips may depend on the thickness of the primary sheet in the manufacturing method described later. Therefore, thermal conductive sheets with strip widths greater than or equal to the lower limit have a further reduction in the number of layers, folds, or turns of the primary sheet. As a result, such thermal conductive sheets have an improved block (laminated) formation speed, as described later, and improved productivity. On the other hand, thermal conductive sheets with strip widths less than or equal to the upper limit have improved thermal conductivity because the thermal conductive filler is well oriented in the thickness direction within the thermal conductive sheet, and the thermal resistance value of the thermal conductive sheet can be further reduced.

[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, may exceed 90 μm, 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 above 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 below the upper limit, the thermal resistance value of the thermal conductive sheet can be further reduced.

[0037] Furthermore, the standard deviation of the thickness of the thermal conductive sheet is preferably 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 the thickness is below the above upper limit, a thermal conductive sheet with good thickness uniformity can be obtained. The lower limit of the standard deviation of the thickness of the thermal conductive sheet is not particularly limited, but for example, it is 1 μm or more. Note that the standard deviation of thickness refers to the standard deviation of the average thickness of multiple thermal conductive sheets manufactured by the same manufacturing method. The standard deviation of the thickness of the heat conduction sheet can be adjusted by changing the types and content ratios of the materials (such as resins and heat conduction fillers) used in the production of the heat conduction sheet, as well as the production conditions of the heat conduction sheet. For example, by manufacturing the heat conduction sheet using the manufacturing method of the heat conduction sheet described later, the standard deviation of the thickness of the heat conduction sheet can be reduced. More specifically, in the manufacturing method of the heat conduction sheet described later, by changing the content ratio of the liquid resin, as well as the shape, relief angle, and rake angle of the cutting blade, etc., the standard deviation of the thickness of the heat conduction sheet can be reduced.

[0038] The density of scratches on the heat conduction sheet with a depth of 10 μm or more, a width of 100 μm or more, and a length of 1000 μm or more should be 0.0 pieces / 10000 mm 2 or less, and preferably 5.0 pieces / 10000 mm 2 or less, and more preferably 4.0 pieces / mm 2 or less, and even more preferably 3.0 pieces / mm 2 or less. If the density of the above scratches is below the above upper limit value, a heat conduction sheet that is difficult to break and has excellent handling properties can be obtained. Also, if the density of the above scratches is more than 0.0 pieces / 10000 mm 2 or more, the production of the heat conduction sheet is even easier, and the yield during the production of the heat conduction sheet can be improved. Note that the density of scratches on the heat conduction sheet can be adjusted by changing the types and content ratios of the materials (such as resins and heat conduction fillers) used in the production of the heat conduction sheet, as well as the first and second rake angles of the cutting blade, the length along the slicing direction of the first rake face, etc. in the manufacturing method of the heat conduction sheet described later. The measurement of the density of scratches on the heat conduction sheet may be performed on the heat conduction sheet after slicing, or may be performed on the heat conduction sheet after cutting the sliced sheet into the actual size for use. When measuring the heat conduction sheet after cutting it into the size for use, the number of scratches is measured for the minimum number of sheets with a total area of 10000 mm 2 or more, and converted to the scratch density per 10000 mm 2 for calculation.

[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 value is below the above upper limit, the thermal resistance of the thermal conductive sheet can be further reduced.

[0040] The thermal conductive sheet preferably has a tensile strength of 0.10 MPa or higher, more preferably 0.11 MPa or higher, even more preferably 0.12 MPa or higher, and preferably 0.50 MPa or lower. If the tensile strength is above the lower limit, a thermal conductive sheet that is less prone to breakage and has excellent handling properties can be obtained. Furthermore, if the tensile strength is below the upper limit, the block becomes easier to slice, and damage to the thermal conductive sheet can be further reduced. The tensile strength of a thermal conductive sheet can be adjusted by changing the type and proportion of materials (resin, thermal conductive filler, etc.) used in the manufacture of the thermal conductive sheet, as well as the manufacturing conditions of the thermal conductive sheet.

[0041] In this invention, the tensile strength of the thermal conductive sheet refers to the tensile strength in the direction perpendicular to the slicing direction of the block body containing the resin and thermal conductive filler in the thermal conductive sheet manufacturing method of this application, which will be described later. Since tensile strength is an attribute that is highly dependent on the sheet thickness, it is not possible to simply compare sheets of various thicknesses. Therefore, in this invention, as described in the examples of this specification, a thermal conductive material sample with a greater thickness than the thermal conductive sheet of this invention (for example, a thickness of 300 μm) was prepared from the composition that serves as the raw material for the thermal conductive sheet of this invention, and the tensile strength of this thermal conductive material sample was measured using a general tensile testing machine or the like. By measuring the tensile strength of a thermal conductive material 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, independent of the thickness of the thermal conductive sheet itself, and consequently, the density and depth of scratches on the thermal conductive sheet. Specifically, the composition of the thermal conductive sheet refers to the content of thermal conductive filler and the resin composition (ratio of liquid resin to solid resin), and the strength derived from the composition of the thermal conductive sheet can be controlled by changing these.

[0042] The thermal conductive sheet of the present invention preferably has a tensile strength of 0.01 MPa or higher, more preferably 0.05 MPa or higher, even more preferably 0.08 MPa or higher, preferably 0.60 MPa or lower, more preferably 0.40 MPa or lower, and even more preferably 0.20 MPa or lower. If the virtual tensile strength is above the lower limit, a heat conductive sheet that is less prone to breakage and has excellent handling properties can be obtained. Furthermore, if the virtual tensile strength is below the upper limit, the block becomes easier to slice, and damage to the heat conductive sheet can be further reduced. The virtual tensile strength of the heat conductive sheet can be adjusted, similar to the tensile strength, by changing the type and content ratio of materials (resin, heat conductive filler, etc.) used in the manufacture of the heat conductive sheet, as well as the manufacturing conditions of the heat conductive sheet.

[0043] (Method of manufacturing a thermal conductive sheet) The thermal conductive sheet of the present invention described above can be manufactured, for example, by the following manufacturing method. Here, the manufacturing method of the thermal conductive sheet of the present invention includes at least the step of slicing the block body containing a resin and a thermal conductive filler with the cutting blade, while supporting a cutting blade positioned so that the cutting edge protrudes from the sliding surface, and obtaining a thermal conductive sheet (hereinafter also referred to as the slicing step). Furthermore, according to the method for manufacturing a thermal conductive sheet of the present invention, a thermal conductive sheet with fewer scratches and a low thermal resistance value can be obtained.

[0044] Figure 1 shows a slicing apparatus that may be used in the manufacture of a thermal conductive sheet according to an example of the present invention. However, the slicing apparatus shown is just one example, and the slicing apparatus used in the manufacture of the thermal conductive sheet of the present invention is not limited to the illustrated configuration, nor are the dimensions and relative positions of the components limited to the illustrated configuration. The slicing device has a cutting blade (30) mounted on a slide table having a slide surface (20) that slidably supports a block body (10). Figure 1 shows a cross-sectional view of the slicing device and the block body (10) cut by a plane parallel to the illustrated plane. The cutting blade (30) comprises a relief surface (31), a first rake face (32a) intersecting the relief surface (31) and having a first rake angle (θa1), a second rake face (32b) adjacent to the first rake face (32a) and having a second rake angle (θa2), and a cutting edge (33) formed by the intersection of the relief surface (31) and the first rake face (32a). Here, the second rake angle (θa2) is greater than the first rake angle (θa1). The relief angle (θb) of the cutting blade is set to 3° or more and 15° or less. Preferably, the relief surface (31) of the cutting blade comprises a first relief surface (31a) that intersects the first rake face (32a) and has a first relief angle (θb1), as well as a second relief surface (31b) adjacent to the first relief surface and having a second relief angle (θb2). Preferably, the second relief angle (θb2) is larger than the first relief angle (θb1). In this case, the first relief angle (θb1) corresponds to the relief angle (θb) of the cutting blade.

[0045] <Slicing process> In the slicing process, as described above, the block is supported so as to be slidable by a sliding surface, and a cutting blade positioned so that its cutting edge protrudes from the sliding surface is also supported. The block is then slid on the sliding surface, and the block is sliced ​​by the cutting blade, thereby cutting out a heat conductive sheet from the block.

[0046] <<Block letters>> The block body comprises a resin and a thermally conductive filler, and may optionally further contain additives.

[0047] [Resins, thermally conductive fillers, and additives] The preferred types, properties, and proportions of resin and thermally conductive filler contained in the block body, as well as optionally included additives, can be the same as those described above for the thermally conductive sheet of the present invention.

[0048] <<Cutting blade>> The cutting blade used for slicing the block body described above has its cutting edge positioned at one end in the direction of extension, and is usually used so that the direction of extension of the cutting blade is the slicing direction. The cutting blade comprises a flank, a first rake face intersecting the flank and having a first rake angle, a second rake face adjacent to the first rake face and having a second rake angle, and a cutting edge formed from the intersection of the flank and the first rake face, where the second rake angle is larger than the first rake angle. By having a first rake face and a second rake face having the above relationship, the occurrence of scratches caused by the sliced ​​heat conductive sheet rubbing against the rake face during slicing of 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, preferably 75° or less, and more preferably 65° or less. If the first rake angle is greater than or equal to the lower limit, the occurrence of scratches caused by the sliced ​​heat conductive sheet rubbing against the rake face during slicing of the block can be reduced. Also, if the first rake angle is less than or equal to the upper limit, it prevents the relief angle of the cutting blade from becoming too small and prevents the block from riding up onto the cutting blade during slicing, thereby enabling the production of heat conductive sheets with a smaller thickness through slicing.

[0050] The angle between the first rake face and the second rake face is preferably 1° or more, and 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 preferable to be 20° or less.

[0051] The cutting blade preferably has a length of 0.1 mm or more, 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, along the slicing direction of the first rake face. If the length of the cutting blade along the slicing direction of the first rake face is within the above range, the occurrence of scratches caused by the heat conductive sheet rubbing against the rake face during slicing of the block can be reduced.

[0052] Furthermore, when performing the slicing process, the cutting blade is set to have a relief angle of 3° to 15°. Preferably, the relief angle is 4° or more, more preferably 5° or more, preferably 13° or less, and more preferably 10° or less. If the relief angle is greater than or equal to the lower limit, it prevents the block from riding up onto the cutting blade during slicing, allowing for the production of a thinner heat conductive sheet. Conversely, if the relief angle is less than or equal to the upper limit, it prevents the rake angle of the cutting blade from becoming too small, reducing the occurrence of scratches on the sliced ​​heat conductive sheet caused by friction against the rake surface during slicing.

[0053] Furthermore, the relief surface of the cutting blade preferably comprises a first relief surface that intersects the first rake surface and has a first relief angle, and a second relief surface adjacent to the first relief surface and having a second relief angle, with the second relief angle being larger than the first relief angle. Here, the first relief angle corresponds to the relief angle of the cutting blade described above. By having a first relief surface and a second relief surface having the above relationship in the cutting blade, a heat conductive sheet with an even smaller thickness can be obtained by slicing. In this invention, a cutting blade having both a first rake face and a second rake face, as well as a first relief face and a second relief face, is sometimes referred to as a "double-edged" cutting blade, while a cutting blade having only one of the first rake face and the second rake face, or the first relief face and the second relief face, is sometimes 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 preferable to be 10° or less.

[0055] Furthermore, the cutting edge angle (the angle between the first rake face and the flank face) of the cutting blade 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 it be made of a metal such as ceramic, cemented carbide, high-speed tool steel (HSS steel), or steel, and cemented carbide is more preferable due to the balance of the hardness of the blade itself and the ease of processing the blade.

[0057] <<Slice>> The slicing of the resin block using the cutting blade described above 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 to 1.0 MPa.

[0058] Furthermore, from the viewpoint of easily slicing the resin block, it is preferable that the temperature of the resin block during slicing be between -20°C and 40°C.

[0059] Furthermore, the slicing speed of the resin block is not particularly limited, but is preferably 50 mm / second or more, more preferably 60 mm / second or more, and even more preferably 70 mm / second or more. Setting the slicing speed above the lower limit increases the productivity of resin sheets and further improves the uniformity of the thickness of the resulting resin sheets. Typically, the slicing speed of the resin block is 600 mm / second or less. Setting the slicing speed below the upper limit prevents the block from riding up on the cutting blade during slicing, thereby allowing for the production of even thinner heat-conducting sheets.

[0060] <Other processes> Other steps that may be optionally included in the method for manufacturing a thermal conductive sheet of the present invention are not particularly limited. For example, in the manufacturing of the thermal conductive sheet of the present invention, a step (orientation operation step) can be performed to orient the thermal conductive filler in the thickness direction of the thermal conductive sheet before the slicing step described above. The orientation method performed in the orientation operation step is not particularly limited, but may be an extrusion molding method, or it may be a process (lamination step) in which multiple primary sheets containing resin and thermal conductive filler are laminated in the thickness direction, or the primary sheets are folded or rolled up to obtain a block body. Furthermore, the block body (laminated body) obtained in the lamination process described above can be subjected to a heating process (heating process) before the slicing process described above. The following describes in detail the other processes, including the extrusion molding process, the lamination process, and the heating process.

[0061] <<Extrusion Molding Process>> When performing the orientation operation of a thermally conductive filler by extrusion molding, for example, a block body is obtained by extrusion molding from a composition containing at least a resin and a thermally conductive filler, according to the method described in Japanese Patent Application Publication No. 2022-037939. At this time, the resin flows when extruded into the die, and the thermally conductive filler is oriented along the direction of this flow.

[0062] <<Lamination process>> As described above, in the lamination process, multiple primary sheets are stacked in the thickness direction, or these primary sheets are folded or rolled up to obtain a laminated block. The thermal conductive sheet manufactured through the lamination process has a structure in which slices of the primary sheets that made up the laminate are joined in parallel, and because the thermal 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 contain additives.

[0064] The preferred types, properties, and proportions of resin and thermally conductive filler contained in the primary sheet, as well as optionally included additives, 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 way 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 forming a composition containing a resin, a thermally conductive filler, and optionally used additives using a known molding method such as press molding, rolling, or extrusion molding. In this way, by performing a pressing operation in the sheet surface direction during the production of the primary sheet, a structure can be formed within the primary sheet in which the thermally conductive filler is oriented in a direction perpendicular to the sheet thickness direction (i.e., the sheet surface direction).

[0067] [Formation of block bodies by stacking, etc.] The formation of a block body by laminating primary sheets is not particularly limited and may be carried out using a lamination device or by hand. Furthermore, the formation of a block body by folding a heat conductive sheet is not particularly limited and can be carried out by folding the primary sheet to a certain width using a folding machine. In addition, the formation of a block body by winding a primary sheet is not particularly limited and can be carried out by winding the primary sheet around an axis parallel to the short or long direction of the primary sheet.

[0068] <<Heating process>> Here, for example, the block body obtained through the lamination process described above may be subjected to the slicing process as is, or it may be subjected to the slicing process after further heating. The heating temperature in the heating process can be, for example, 50°C to 170°C, and the heating time can be, for example, 1 minute to 8 hours. By going through the heating process, the adhesion in the lamination direction of the block body can be adjusted. For example, if the block body contains a thermoplastic resin, the adhesion in the lamination direction of the block body can be greatly improved by performing the heating process. [Examples]

[0069] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" used to express quantities refer to mass unless otherwise specified. In the examples and comparative examples, various measurements and evaluations were performed using the following methods.

[0070] <Physical property measurement and evaluation> <<Average thickness and standard deviation of thermal conductive sheets>> Using a film thickness gauge (manufactured by Mitutoyo Corporation, product name "Digimatic Indicator"), the thickness of the thermal conductive sheet was measured at five points: approximately the center point and the four corners (square). The average value (μm) of the measured thickness was then calculated. Furthermore, the average thickness of 100 sliced ​​thermal conductive sheets was measured as described above, and its standard deviation (μm) was calculated.

[0071] <<Density of wounds>> The obtained thermal conductive sheet (150mm x 150mm x 0.06mm) was placed on an inspection stage (200mm x 200mm transparent acrylic plate), and light was shone onto the thermal conductive sheet using a white LED bar light (model number "LDL2-275X" manufactured by CCS Corporation; color temperature 7,800K; power consumption 27W) at an illumination angle of 40° to the perpendicular to the surface of the thermal conductive sheet (50° relative to the surface of the thermal conductive sheet). While illuminating the sheet, an 8K monochrome CMOS line camera (manufactured by Basler Corporation; model number "raL8192-12gm"; 8192 pixels x 1 pixel) and the white LED bar light were scanned parallel to the surface of the thermal conductive sheet, and the surface of the thermal conductive sheet was photographed with the camera to obtain a digital image of the thermal conductive sheet surface. Subsequently, image processing such as smoothing and edge detection was performed on this digital image using image processing software (original software) to detect scratches, and the number of scratches, their width, length, and their 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 location of the defect obtained in the above inspection was measured at 10x magnification within a height range of 200 μm to obtain a profile of the defect in the depth direction. The depth of the defect 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 measured from the size of the thermal conductive sheet inspected. 2 The number of wounds per area was calculated and defined as the wound density.

[0072] <<Tensile strength and virtual tensile strength>> A thermal conductive sheet was sliced ​​to a thickness of 300 μm using a dumbbell-shaped die (Dumbbell No. 2, width 3 mm, length 70 mm) conforming to JIS K7113, and then punched out to prepare a sample. Using a tensile testing machine (Shimadzu Corporation, product name "AG-IS20kN"), the sample 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, temperature: 23 °C, and the breaking strength (tensile strength) was measured. The average of the measured values ​​from three sample pieces was taken as the tensile strength of the thermal conductive sheet. Furthermore, the virtual tensile strength of the thermal conductive sheet was calculated from the tensile strength measurement results according to the following formula. Virtual tensile strength = Tensile strength (MPa) × Average thickness of thermal conductive sheet (μm) / 300 (μm)

[0073] <<Bulk Thermal Resistance Value>> The thermal resistance of the thermal conductive sheets was measured using a thermal resistance tester (manufactured by Hitachi Technology & Services, Ltd., product name "Resin Material Thermal Resistance Measuring Device"). In addition to the thermal conductive sheets used in the examples and comparative examples, 50 μm, 100 μm, and 200 μm thermal conductive sheets were prepared by cutting them into approximately 1 cm squares. 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 values, an approximate formula y = ax + b was calculated, where y: thermal resistance and x: thickness of the thermal conductive sheet, with b being the interfacial thermal resistance value of the thermal conductive sheet. The bulk thermal resistance value was then calculated by subtracting the value of b from the thermal resistance values ​​measured similarly for the thermal conductive sheets in the examples and comparative examples.

[0074] <<Handling>> Based on the density of scratches and virtual tensile strength obtained, the handling properties were evaluated as follows. Note that a lower scratch density indicates better handling, and a higher virtual tensile strength indicates better handling.

[0075] [Table 1]

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

[0077] <Formation of the primary sheet> Next, 1 kg of the obtained composition was sandwiched between sandblasted PET films (protective films) with a thickness of 50 μm, and rolled (primary pressurized) 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 with a thickness of 800 μm.

[0078] <Lamination process> The obtained primary sheet was cut to a size of 150 mm in length, 150 mm in width, and 800 μm in thickness. 200 sheets were stacked in the thickness direction of the primary sheet, and then pressed in the stacking direction for 3 minutes at a temperature of 120°C and a pressure of 0.1 MPa to obtain a block (laminated) with a height of approximately 160 mm.

[0079] <Formation of a thermally conductive sheet> Subsequently, while pressing the side surface (the surface along the lamination direction) of the secondarily pressurized block (laminated body) with a pressure of 0.3 MPa, a woodworking slicer (manufactured by Marunaka Iron Works Co., Ltd., product name "Super Finishing Planer Super Mecha S") was used to slice the block at a speed of 80 mm / second at a 90° angle to the lamination direction (in other words, perpendicular to the normal of the main surface of the laminated primary sheet), while the temperature in the processing space of the slicer was 15°C. This resulted in obtaining a heat conductive sheet measuring 150 mm in length, 150 mm in width, and 45 μm in thickness. As shown in Figure 2, the slicing direction (A) of the block (10) is perpendicular to the lamination direction (B) of the primary sheet (11). The first and second relief 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. Then, various measurements and evaluations were performed on the obtained thermal conductive sheet according to the method described above. The results are shown in Table 2.

[0080] (Examples 2-5 and Comparative Examples 1-4) Except for changing the types and amounts of materials used in the composition preparation, as well as the shape, relief angle, and rake angle of the cutting blade, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 2.

[0081] As the modified nitrile rubber, solid acrylonitrile-butadiene rubber (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol 1072J") was used at room temperature and atmospheric pressure; as the liquid nitrile rubber, liquid acrylonitrile-butadiene rubber (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol 1312") was used at room temperature and atmospheric pressure; as the epoxy resin, liquid bisphenol A diglycidyl ether (manufactured by Mitsubishi Chemical Corporation, trade name "jER") was used at room temperature and atmospheric pressure; and as the antioxidant, an aromatic secondary amine antioxidant (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrack CD") and a benzimidazole antioxidant (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrack MBZ") were used in combination. Furthermore, if the cutting blade does not have a second rake face, the angle between the first rake face and the second rake face is described as 0°.

[0082] [Table 2]

[0083] Table 2 shows that the average thickness is between 30 μm and 300 μm, and the specified defect density is 0.0 defects / 10000 mm². 2 Super, 5.0 pieces / 10000mm 2 The thermal conductive sheets of Examples 1-5, as shown below, exhibit both fewer scratches and lower thermal resistance compared to the thermal conductive sheet of Comparative Example 1-4. Furthermore, the thermal conductive sheets of Examples 1-5 have fewer scratches or higher virtual tensile strength compared to the thermal conductive sheet of Comparative Example 1-3, resulting in superior handling properties. [Industrial applicability]

[0084] According to the present invention, it is possible to provide a thermal conductive sheet with fewer scratches and a low thermal resistance value. [Explanation of symbols]

[0085] 10 Block letters 11 Primary Seat 20 sliding surfaces 30 cutting blade 31 Escape 31a First escape route 31b Second escape route 32a First rake face 32b Second rake face 33 cutting edge θa1 First rake angle θa² Second rake angle θb1 First relief angle θb2 Second relief angle Slicing direction of block body A B Stacking direction of the primary sheet C Orientation direction of the thermally conductive filler

Claims

1. A thermal conductive sheet comprising a resin and a thermally conductive filler, The thermally conductive filler is oriented in the thickness direction of the thermally conductive sheet, The average thickness is between 30 μm and 300 μm. 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 scratches / 10000 mm². ２ Super, 5.0 pieces / 10000mm ２ The following is: Thermal conductive sheet.

2. The thermal conductive sheet according to claim 1, wherein the bulk thermal resistance value is 0.070°C / W or less.

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