Thermal conductive sheet

Abstract

To provide a heat conductive sheet which has both of smooth main surfaces, and can satisfactorily transfer heat in a thickness direction while having sufficient thickness accuracy.SOLUTION: A heat conductive sheet contains a resin and a particulate filler, wherein heat conductivity in a thickness direction is 15 W / m K or more, standard deviation of the thickness is 3.5 μm or less, surface roughnesses Sa of both of main surfaces are 3.0 μm or less, and an absolute value of a difference between surface roughness Sa of one main surface and surface roughness Sa of the other main surface is 0.09 μm or more and 0.40 μm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In recent years, heat generation of electronic components such as plasma display panels (PDPs) and integrated circuit (IC) chips has increased with the improvement of their performance. As a result, in electronic devices using such electronic components, it has become necessary to take measures to prevent malfunction due to the temperature rise of the electronic components.

[0003] As a measure to prevent malfunction due to the temperature rise of electronic components, generally, a method of promoting heat dissipation by attaching a heat dissipating body such as a metal heat sink, a heat radiation plate, or heat radiation fins to a heat generating body such as an electronic component is adopted. When using a heat dissipating body, a sheet-like member having heat conductivity (heat conductive sheet) is used to efficiently transfer heat from the heat generating body to the heat dissipating body. For example, a heat conductive sheet containing a resin and particulate fillers is sandwiched between the heat generating body and the heat dissipating body, and the heat generating body and the heat dissipating body are brought into close contact with each other through this heat conductive sheet to transfer heat from the heat generating body to the heat dissipating body. Conventionally, attempts have been made to improve various properties of the heat conductive sheet (see, for example, Patent Documents 1 and 2).

[0004] In Patent Document 1, a resin molded body is supported slidably by a slide surface, and while pressing the resin molded body against the slide surface, the resin molded body is slid with one blade having a tip protruding from the slide surface supported from the side opposite to the resin molded body sandwiching the slide surface, and a method of obtaining a heat conductive sheet by slicing the resin molded body with only one blade is disclosed. According to Patent Document 1, the thickness accuracy of the heat conductive sheet obtained by the above-described method can be improved.

[0005] Patent Document 2 discloses a method for obtaining a thermal conductive sheet by slicing a laminate obtained by stacking primary sheets containing resin and particulate carbon material in the thickness direction at an angle of 45° or less with respect to the stacking direction, and then applying pressure to the sheets obtained by slicing. According to Patent Document 2, the thermal conductive sheet obtained by the above method can exhibit excellent thermal conductivity even when used at relatively low clamping pressure. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5621306 specification [Patent Document 2] Japanese Patent Publication No. 2018-67695 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In recent years, there has been a demand to smooth both main surfaces of the thermal conductive sheet and to improve the thickness accuracy of the thermal conductive sheet, in order to ensure good contact between the heat-generating element and the heat-sinking element via the thermal conductive sheet, while also ensuring uniform heat transfer from the heat-generating element to the heat-sinking element. However, with the conventional method described above, it was difficult to produce a thermal conductive sheet with smooth main surfaces and a uniform thickness while simultaneously enabling the thermal conductive sheet to exhibit excellent thermal conductivity in the thickness direction.

[0008] Therefore, the present invention aims to provide a heat conductive sheet in which both main surfaces are smooth, has sufficient thickness accuracy, and is capable of good heat transfer in the thickness direction, and a method for manufacturing the heat conductive sheet. [Means for solving the problem]

[0009] The inventors diligently conducted research to achieve the above objective. First, the inventors attempted to improve the thickness accuracy of the thermal conductive sheet by applying pressure during slicing using a plane as described in Patent Document 1. However, the inventors' research revealed that applying pressure to the sheet during slicing with a plane makes it difficult to ensure sufficient smoothness of both main surfaces. Based on this, the inventors discovered that in a thermal conductive sheet containing resin and particulate filler, if the standard deviation of the thickness is kept below a predetermined value, the thermal conductivity in the thickness direction is kept above a predetermined value, and the surface roughness Sa of both main surfaces is kept below a predetermined value, a thermal conductive sheet can be obtained in which both main surfaces are smooth, has sufficient thickness accuracy, and can transfer heat well in the thickness direction, thus completing the present invention.

[0010] In other words, the present invention aims to advantageously solve the above problems, and the thermal conductive sheet of the present invention is characterized in that it contains a resin and particulate filler, has a thermal conductivity in the thickness direction of 15 W / m·K or more, has a standard deviation of thickness of 3.5 μm or less, and has a surface roughness Sa of 3.00 μm or less on both main surfaces. Thus, a thermal conductive sheet containing a resin and particulate filler, having a thermal conductivity in the thickness direction of the above value or more, a standard deviation of thickness of the above value or less, and a surface roughness Sa of both main surfaces of the above value or less, has smooth main surfaces, has sufficient thickness accuracy, and can transfer heat well in the thickness direction. In this invention, the "thermal conductivity in the thickness direction" can be calculated using the method described in the examples of this specification. Furthermore, in the present invention, the "standard deviation of thickness" is a value obtained by measuring the thickness at any five points on the thermal conductive sheet and taking these measurements, and can be calculated, for example, using the method described in the examples of this specification. Furthermore, in the present invention, the "surface roughness Sa of both main surfaces" is a value obtained in accordance with the international standard ISO 25178, and can be calculated using the method described in the examples of this specification. In this invention, "both main surfaces" refers to the surface having the largest surface area in the thermal conductive sheet and the surface opposite to that surface.

[0011] In this case, it is preferable that the thermal conductive sheet of the present invention has an average thickness of 250 μm or less. If the average thickness of the thermal conductive sheet is less than or equal to the above value, heat can be transferred even more effectively in the thickness direction of the thermal conductive sheet. In this invention, the "average thickness" is a value obtained by measuring the thickness at any five points on the thermal conductive sheet and taking these measurements, and can be calculated, for example, using the method described in the examples of this specification.

[0012] Furthermore, it is preferable that the heat conductive sheet of the present invention contains particulate filler in a volume ratio of 30% to 55%. If the volume ratio of particulate filler in the heat conductive sheet is within the above range, the thermal conductivity in the thickness direction of the heat conductive sheet increases, allowing for even better heat transfer in the thickness direction of the heat conductive sheet, while also ensuring the flexibility of the heat conductive sheet and further improving the thickness accuracy.

[0013] Furthermore, it is preferable that the heat conductive sheet of the present invention has a volume-average particle diameter of particulate filler of 30 μm or more and 150 μm or less. If the volume-average particle diameter of the particulate filler is within the above range, heat can be transferred more effectively in the thickness direction of the heat conductive sheet, and the smoothness of the main surface and the thickness accuracy of the heat conductive sheet can be further improved. In this invention, the "volume-average particle diameter" can be measured in accordance with JIS Z8825 and represents the particle diameter at which the cumulative volume calculated from the smallest diameter side accounts for 50% of the particle size distribution (volume-based) measured by laser diffraction.

[0014] Furthermore, it is preferable that the thermal conductive sheet of the present invention has an absolute difference of 0.40 μm or less between the surface roughness Sa of one main surface and the surface roughness Sa of the other main surface. If the absolute difference between the surface roughness Sa of one main surface and the surface roughness Sa of the thermal conductive sheet is less than or equal to the above value, handling properties such as ease of gripping by a robot arm can be improved.

[0015] Furthermore, this invention aims to advantageously solve the above problems, and the method for manufacturing a heat conductive sheet of the present invention includes the step of slicing the block body by pressing it against the slide surface while sliding it, with a blade having a tip protruding from the slide surface supported, the blade having a first front surface in contact with the block body, the blade having a back surface intersecting the first front surface, a cutting edge formed from the intersection of the first front surface and the back surface, and a second front surface extending from the edge of the first front surface opposite to the cutting edge side and located on the back side of the first front surface, the length of the first front surface being 0.8 mm or more, and the surface roughness Sa of the first front surface being 1.00 μm or less. Thus, by slicing a block containing resin and particulate filler using a blade whose first surface length and surface roughness Sa are within the above range, a heat conductive sheet can be obtained in which both main surfaces are smooth, has sufficient thickness accuracy, and can conduct heat well in the thickness direction. Furthermore, in the present invention, the "surface roughness Sa of the first front surface" can be measured using the method described in the examples of this specification. In this specification, when slicing a block, the side on which the cutting portion that contacts the block is provided is referred to as the "front side," and the side on which the heat conductive sheet is discharged from the block (the side opposite to the front side on which the cutting portion that first contacts the block is provided) is referred to as the "back side."

[0016] In this invention, it is preferable that the surface roughness Sa of the second surface of the heat conductive sheet is 1.00 μm or less. If the surface roughness Sa of the second surface is less than or equal to the above value, the smoothness of the surface of the heat conductive sheet obtained by slicing the block can be more reliably ensured. In this invention, the "surface roughness Sa of the second front surface" can be calculated, for example, using the method described in the examples of this specification.

[0017] Before the slicing step, the manufacturing method of the heat conduction sheet of the present invention may further include a step of obtaining the block body by laminating a plurality of primary sheets including a resin and particulate fillers in the thickness direction, or by folding or winding the primary sheet. In this specification, "lamination", "folding", or "winding" may be collectively abbreviated as "lamination etc.". [Effect of the Invention]

[0018] According to the present invention, it is possible to provide a heat conduction sheet having smooth both main surfaces, sufficient thickness accuracy, and capable of transferring heat well in the thickness direction, and a manufacturing method of the heat conduction sheet. [Brief Description of the Drawings]

[0019] [Figure 1] It is an explanatory drawing showing a process of manufacturing a heat conduction sheet using an example of the manufacturing method of the heat conduction sheet according to the present invention. [Figure 2] It is a plan view showing a state of slicing a block body (laminated body) at a slide angle β. [Embodiments for Carrying Out the Invention]

[0020] Hereinafter, embodiments of the present invention will be described in detail. The heat conduction sheet of the present invention can be used, for example, by being sandwiched between a heat generating body and a heat radiating body when attaching the heat radiating body to the heat generating body. That is, the heat conduction sheet of the present invention can constitute a heat dissipation device together with a heat radiating body such as a heat sink, a heat radiating plate, and heat radiating fins. And the heat conduction sheet of the present invention can be manufactured, for example, according to the manufacturing method of the heat conduction sheet of the present invention.

[0021] (Heat Conduction Sheet) The thermal conductive sheet of the present invention comprises a resin and particulate filler, and may optionally further contain additives. Furthermore, the thermal conductive sheet of the present invention has a thermal conductivity of 15 W / m·K or more in the thickness direction, a standard deviation of thickness of 3.5 μm or less, and a surface roughness Sa of 3.00 μm or less on both main surfaces. Since the thermal conductive sheet of the present invention has a thermal conductivity of 15 W / m·K or more in the thickness direction, a standard deviation of thickness of 3.5 μm or less, and a surface roughness Sa of 3.00 μm or less on both main surfaces, both main surfaces are smooth, and heat can be transferred well in the thickness direction while maintaining sufficient thickness accuracy.

[0022] <Resin> The resin included in the thermal conductive sheet is not particularly limited, and any resin can be used. For example, both liquid resins and solid resins can be used. One type of resin may be used alone, or two or more types may be used in combination. For example, the thermal conductive sheet may contain at least one of a liquid resin and a solid resin, but from the viewpoint of further improving the thickness accuracy of the thermal conductive sheet and improving heat transfer in the thickness direction even more, it is preferable that the thermal conductive sheet contains both a liquid resin and a solid resin.

[0023] <<Liquid Resin>> Furthermore, as for the liquid resin, there are no particular limitations as long as it is liquid at room temperature and atmospheric pressure; for example, a thermoplastic resin that is liquid at room temperature and atmospheric pressure can be used. In this invention, "room temperature" refers to 23°C, and "atmospheric pressure" refers to 1 atm (absolute pressure).

[0024] 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.

[0025] <<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.

[0026] [Thermoplastic resins that are 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, 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 include: styrene-acrylonitrile copolymer; acrylonitrile-butadiene copolymer (nitrile rubber); acrylonitrile-butadiene-styrene copolymer (ABS resin); styrene-butadiene block copolymer or its hydrogenated derivative; styrene-isoprene block copolymer or its hydrogenated derivative; polyphenylene ether; modified polyphenylene ether; aliphatic polyamides; aromatic polyamides; polyamide-imides; polycarbonates; 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."

[0027] [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.

[0028] <<Resin content ratio>> The resin content in the thermal conductive sheet is not particularly limited, but is preferably 35% by mass or more, more preferably 45% by mass or more, even more preferably 50% 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 35% by mass or more, the thickness accuracy of the thermal conductive sheet can be further improved while ensuring the flexibility of the thermal conductive sheet. On the other hand, if the resin content is 95% by mass or less, heat can be transferred even more effectively in the thickness direction of the thermal conductive sheet.

[0029] <<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, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less. If the proportion of liquid resin in the resin is 30% by mass or more, the thickness accuracy can be further improved while ensuring the flexibility of the thermal conductive sheet. On the other hand, if the proportion of liquid resin in the resin is 95% by mass or less, it provides strength suitable for the primary sheet, making it easier to slice the laminate and further improving the thickness accuracy of the resulting thermal conductive sheet.

[0030] <Particulate filler> The particulate filler included in the thermal conductive sheet is not particularly limited as long as it can impart thermal conductivity to the thermal conductive sheet. Particulate carbon materials with high thermal conductivity are suitably used as such particulate fillers. The particulate filler may be used alone or in combination of two or more types.

[0031] <<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.

[0032] Among the above, it is preferable to use expanded graphite as the particulate carbon material. By using expanded graphite, the thermal conductivity in the thickness direction of the heat conductive sheet is increased, and heat can be transferred more effectively in the thickness direction of the heat conductive sheet. Here, 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.

[0033] <<Properties of particulate fillers>> The particulate filler preferably has a volume-average particle diameter of 30 μm or more, more preferably 40 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. It is presumed that if the volume-average particle diameter of the particulate filler is 30 μm or more, the heat transfer paths of the particulate filler can be formed well in the heat conductive sheet, and the thermal conductivity in the thickness direction of the heat conductive sheet increases. As a result, heat can be transferred even more effectively in the thickness direction of the heat conductive sheet. On the other hand, if the volume-average particle diameter of the particulate filler is 150 μm or less, the smoothness of the main surface and the thickness accuracy of the heat conductive sheet can be further improved.

[0034] Furthermore, the particulate filler 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 filler is greater than 1 and less than or equal to 10, the particulate filler is more likely to orient well 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, heat can be transferred even more effectively in the thickness direction of the thermal conductive sheet. In this invention, the "aspect ratio" can be determined by observing particulate fillers with a scanning electron microscope (SEM), measuring the maximum diameter (long diameter) and the particle diameter in the direction perpendicular to the maximum diameter (short diameter) for any 50 particulate fillers, and calculating the average value of the ratio of the long diameter to the short diameter (long diameter / short diameter).

[0035] <<Percentage of particulate filler content>> The content of particulate filler in the thermal conductive sheet is not particularly limited, but is preferably 30 volume% or more, more preferably 35 volume% or more, particularly preferably 40 volume% or more, preferably 55 volume% or less, more preferably 50 volume% or less, even more preferably 45 volume% or less, and particularly preferably 42 volume% or less. If the content of particulate filler is 30 volume% or more, the thermal conductivity in the thickness direction of the thermal conductive sheet increases, and heat can be transferred more effectively in the thickness direction of the thermal conductive sheet. On the other hand, if the content of particulate filler is 42 volume% or less, the thickness accuracy can be further improved while ensuring the flexibility of the thermal conductive sheet.

[0036] Furthermore, the content of particulate filler in the thermal conductive sheet is not particularly limited, but is preferably 35% by mass or more, more preferably 40% by mass or more, particularly preferably 45% by mass or more, preferably 65% ​​by mass or less, more preferably 55% by mass or less, and particularly preferably 50% by mass or less. If the content of particulate filler is 35% by mass or more, the thermal conductivity in the thickness direction of the thermal conductive sheet increases, and heat can be transferred more effectively in the thickness direction of the thermal conductive sheet. On the other hand, if the content of particulate filler is 65% by mass or less, the thickness accuracy of the thermal conductive sheet can be further improved while ensuring the flexibility of the thermal conductive sheet.

[0037] In addition, the content of particulate 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 120 parts by mass or less, more preferably 110 parts by mass or less, and particularly preferably 100 parts by mass or less per 100 parts by mass of resin. If the content of particulate filler is 60 parts by mass or more per 100 parts by mass of resin, the thermal conductivity in the thickness direction of the thermal conductive sheet increases, and heat can be transferred more effectively in the thickness direction of the thermal conductive sheet. On the other hand, if the content of particulate filler is 120 parts by mass or less per 100 parts by mass of resin, the thickness accuracy of the thermal conductive sheet can be further improved while ensuring the flexibility of the thermal conductive sheet.

[0038] <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; and ion trapping agents such as inorganic ion exchangers. Note that one additive may be used alone, or two or more may be used in combination.

[0039] 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.

[0040] <Properties of thermal conductive sheets> The thermal conductive sheet must have a thermal conductivity in the thickness direction of 15 W / m·K or higher, more preferably 20 W / m·K or higher, and even more preferably 25 W / m·K or higher. If the thermal conductivity in the thickness direction of the thermal conductive sheet is less than 15 W / m·K, heat cannot be transferred well in the thickness direction of the thermal conductive sheet. The upper limit of the thermal conductivity in the thickness direction of the thermal conductive sheet is not particularly limited, but for example, it is 45 W / m·K or lower. Furthermore, the thermal conductivity in the thickness direction of the thermal conductive sheet can be adjusted by changing the type and content ratio of materials (resin, particulate filler, etc.) used in the manufacture of the thermal conductive sheet, as well as the manufacturing conditions of the thermal conductive sheet. For example, the thermal conductivity in the thickness direction of the thermal conductive sheet can be increased by changing the volume-average particle size and / or content ratio of particulate filler in the thermal conductive sheet. Alternatively, for example, the thermal conductivity in the thickness direction of the thermal conductive sheet can be increased by manufacturing the thermal conductive sheet using the thermal conductive sheet manufacturing method of the present invention described later.

[0041] Furthermore, the thermal conductive sheet must have a standard deviation of thickness of 3.5 μm or less, preferably 3.0 μm or less, more preferably 2.7 μm or less, and particularly preferably 2.5 μm or less. If the standard deviation of thickness exceeds 3.5 μm, the thickness accuracy of the thermal conductive sheet is impaired. As a result, it becomes difficult to ensure good contact between the heat-generating element and the heat-sinking element via the thermal conductive sheet, and heat transfer from the heat-generating element to the heat-sinking element cannot be performed uniformly. 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. The standard deviation of the thickness of the thermal conductive sheet can be adjusted by changing the type and content ratio of the materials (resin, particulate filler, etc.) used in the manufacture of the thermal conductive sheet, as well as the manufacturing conditions of the thermal conductive sheet. For example, the standard deviation of the thickness of the thermal conductive sheet can be reduced by manufacturing the thermal conductive sheet using the thermal conductive sheet manufacturing method of the present invention, which will be described later. More specifically, in the thermal conductive sheet manufacturing method of the present invention, the standard deviation of the thickness of the thermal conductive sheet can be reduced by changing the Asker C hardness of the block body, the amount of pressure applied during slicing, the length of the first surface of the blade used for slicing, etc.

[0042] In addition, the thermal conductive sheet preferably has an average thickness of 70 μm or more, more preferably 80 μm or more, preferably 250 μm or less, more preferably 200 μm or less, even more preferably 160 μm or less, and particularly preferably 120 μm or less. If the average thickness is 70 μm or more, the strength of the thermal conductive sheet can be ensured, and if it is 250 μm or less, heat can be transferred even more effectively in the thickness direction of the thermal conductive sheet.

[0043] Furthermore, the thermal conductive sheet has a main surface area of, for example, 30 cm². 2 It can be set to 50cm or more 2 It can be set to 80cm or more 2 It can be set to 100cm or more. 2 It can be set to 1000cm or more. 2 The following is possible:

[0044] Furthermore, the thermal conductive sheet must have a surface roughness Sa of 3.00 μm or less on both main surfaces, preferably 2.80 μm or less, more preferably 2.60 μm or less, even more preferably 2.20 μm or less, and particularly preferably 2.00 μm or less. If the surface roughness Sa of both main surfaces exceeds 3.00 μm, the interfacial resistance increases, making it difficult to achieve good contact between the heat-generating element and the heat-sinking element via the thermal conductive sheet when the thermal conductive sheet is used sandwiched between the heat-generating element and the heat-sinking element, and thus preventing uniform heat transfer from the heat-generating element to the heat-sinking element. Furthermore, there is no particular lower limit to the surface roughness Sa of the main surface of the thermal conductive sheet, but for example, it is 1.0 μm or more. Furthermore, the surface roughness Sa of the main surface of the heat conductive sheet can be adjusted by changing the type and content ratio of the materials (resin, particulate filler, etc.) used in the manufacture of the heat conductive sheet, as well as the manufacturing conditions of the heat conductive sheet. For example, the surface roughness Sa of the heat conductive sheet can be reduced by manufacturing the heat conductive sheet using the heat conductive sheet manufacturing method of the present invention, which will be described later. More specifically, in the heat conductive sheet manufacturing method of the present invention, the surface roughness Sa of the main surface of the heat conductive sheet can be reduced by changing the length of the first front surface of the blade used for slicing, the surface roughness of the first front surface of the blade used for slicing, the length of the second front surface of the blade used for slicing, the surface roughness of the second front surface of the blade used for slicing, etc.

[0045] In addition, the thermal conductive sheet preferably has an absolute difference of 0.40 μm or less between the surface roughness Sa of one main surface and the surface roughness Sa of the other main surface, more preferably 0.30 μm or less, even more preferably 0.20 μm or less, and particularly preferably 0.10 μm or less. If the absolute difference between the surface roughness Sa of one main surface and the surface roughness Sa of the other main surface is 0.40 μm or less, handling properties such as ease of gripping by a robot arm can be improved. The lower limit of the absolute difference between the surface roughness Sa of one main surface and the surface roughness Sa of the other main surface is not particularly limited, but for example, it is 0.01 μm or more.

[0046] (Method of manufacturing a thermal conductive sheet) The thermal conductive sheet of the present invention described above can be manufactured, for example, using the method for manufacturing a thermal conductive sheet of the present invention. Here, the method for manufacturing a thermal conductive sheet of the present invention includes at least the step of slicing the block body by pressing it against the slide surface while sliding it, with a blade supporting a block body containing a resin and particulate filler so as to be slidable on a slide surface and a blade having its tip protruding from the slide surface. Furthermore, according to the method for manufacturing a heat conductive sheet of the present invention, it is possible to obtain a heat conductive sheet in which both main surfaces are smooth, has sufficient thickness accuracy, and is capable of good heat transfer in the thickness direction.

[0047] <Slicing process> In the slicing process, as described above, the block body is supported so as to be slidable by a sliding surface, and with a blade whose tip protrudes from the sliding surface, the block body is pressed against the sliding surface and slid, and the block body is sliced ​​by a blade whose first surface length is 0.8 mm or more and whose first surface roughness Sa is 1.00 μm or less, thereby cutting out a heat conductive sheet from the block body.

[0048] <<Block letters>> The block body comprises a resin and particulate filler, and may optionally further contain additives. Furthermore, the block body preferably has an Asker C hardness of 90 or less. Additionally, the block body preferably has a dynamic friction coefficient of 2.5 or less.

[0049] [Resins, particulate fillers, and additives] The preferred types, properties, and proportions of resin and particulate fillers contained in the block body, as well as optionally included additives, can be the same as those described above for the heat conductive sheet of the present invention.

[0050] [Asker C hardness] Here, the block body preferably has an Asker C hardness of 90 or less, more preferably 85 or less, particularly preferably 80 or less, preferably 30 or more, more preferably 40 or more, even more preferably 50 or more, and particularly preferably 60 or more. If the Asker C hardness is 90 or less, the blade can easily penetrate the block body, thus ensuring greater thickness accuracy of the heat conductive sheet obtained by slicing the block body. On the other hand, if the Asker C hardness is 30 or more, the blade tip vibration caused by the stickiness of the block body during slicing can be suppressed, thereby obtaining a heat conductive sheet with even greater thickness accuracy. Furthermore, the Asker C hardness of the block body can be adjusted by changing the type and proportion of materials (resin, particulate filler, etc.) used in the manufacture of the block body, as well as by changing the manufacturing method of the block body. In this invention, "Asker C hardness" is a value measured at a temperature of 23°C using a hardness tester in accordance with the Asker C method of the Japan Rubber Association Standard (SRIS), and can be measured, for example, using the method described in the examples of this specification.

[0051] [Coefficient of dynamic friction] Here, the coefficient of dynamic friction of the block body is preferably 0.5 or less, more preferably 0.3 or less, preferably 0.05 or more, and more preferably 0.1 or more. If the coefficient of dynamic friction is 0.5 or less, the friction between the block body and the blade can be reduced, enabling smooth slicing. Generally, the coefficient of friction is 0.01 or more. Furthermore, the coefficient of dynamic friction of the block body can be adjusted by changing the type and proportion of materials (resin, particulate filler, etc.) used in the manufacture of the block body, as well as by changing the manufacturing method of the block body. In this invention, the "coefficient of dynamic friction" can be measured in accordance with ASTM D1894, for example, using a surface properties measuring instrument TYPE:14FW (manufactured by Shinto Kagaku Co., Ltd.).

[0052] <<Blade>> The blade used for slicing the block described above may be a "double-edged" blade with cutting edges on both sides of the tip, or a "single-edged" blade with a cutting edge only on the front side. However, from the viewpoint of ensuring sufficient thickness accuracy of the resulting heat conductive sheet, a "single-edged" blade is preferred. Furthermore, the blade shape may be an "asymmetrical blade" having a cross-section that is asymmetrical with respect to the central axis passing through the very tip of the blade, or it may be a "symmetrical blade" having a cross-section that is symmetrical. Furthermore, the number of blades that make up the blade is not particularly limited; for example, it may consist of a "single blade" consisting of one blade, or it may consist of a "double blade" consisting of two blades. Figure 1 shows an example of slicing a block (laminated material) using a plane. As shown in Figure 1, when the blade consists of one blade, it consists of one blade 10. When the blade consists of two blades, it consists of a front blade and a back blade. The front blade and the back blade may have the same height or different heights at the very tips of the blades that protrude from the slit. That is, the tips of the front blade and the back blade may be aligned or offset vertically. The material of the blade used for slicing the block body as described above is not particularly limited, but from the viewpoint of ensuring sufficient smoothness of both main surfaces, it is preferable to use a metal such as ceramic, cemented carbide, high-speed tool steel (HSS), or steel, and cemented carbide is more preferable due to the balance of hardness of the blade itself and the ease of processing the blade.

[0053] The blade used for slicing the block body as described above comprises, for example, as shown in Figure 1, a first front surface 10a that contacts the block body 20, a back surface 10c that intersects with the first front surface 10a, a cutting edge 10d formed at the intersection of the first front surface 10a and the back surface 10c, and a second front surface 10b that extends from the edge 10e of the first front surface 10a opposite to the cutting edge 10d side and is located on the back surface 10c side of the first front surface 10a. In other words, the blade used for slicing a block of material comprises a first front surface and a second front surface. The first front surface is formed on the cutting edge side and is the surface that contacts the block of material being sliced ​​during slicing, while the second front surface is positioned at a predetermined angle to the first front surface and is provided to reduce the contact area with the block of material being sliced.

[0054] Furthermore, as mentioned above, the length of the first front surface of the blade must be 0.8 mm or more, preferably 1.0 mm or more, more preferably 3.0 mm or more, preferably 10.0 mm or less, and more preferably 5.0 mm or less. If the length of the first surface of the blade is less than 0.8 mm, the thickness accuracy of the heat conductive sheet obtained by slicing the block body will be impaired. On the other hand, if the length of the first surface is 10.0 mm or less, the smoothness of the surface of the heat conductive sheet obtained by slicing the block body can be ensured. Furthermore, the surface roughness Sa of the first front surface of the blade must be 1.00 μm or less, preferably 0.80 μm or less, more preferably 0.40 μm or more, and even more preferably 0.50 μm or more. If the surface roughness Sa of the first front surface of the blade exceeds 1.00 μm, the smoothness of the B surface of the heat conductive sheet obtained by slicing the block body will be impaired due to friction between the block body and the front surface. The lower limit of the surface roughness Sa of the first front surface of the blade is not particularly limited, but for example, it is 0.30 μm or more.

[0055] Furthermore, the length of the second front surface of the blade is preferably 20.0 mm or more, more preferably 23.0 mm or more, particularly preferably 25.0 mm or more, preferably 50.0 mm or less, more preferably 40.0 mm or less, and most preferably 30.0 mm or less, as described above. If the length of the second front surface of the blade is 20.0 mm or more, the strength of the heat conductive sheet obtained by slicing the block can be ensured. On the other hand, if the length of the second front surface is 50.0 mm or less, the smoothness of the surface of the heat conductive sheet obtained by slicing the block can be ensured. Furthermore, the surface roughness Sa of the second front surface of the blade is preferably 1.00 μm or less, more preferably 0.80 μm or less, and particularly preferably 0.50 μm or more. If the surface roughness Sa of the second front surface of the blade is 1.00 μm or less, the smoothness of the surface of the heat conductive sheet obtained by slicing the block can be more reliably ensured. Furthermore, the lower limit of the surface roughness Sa of the second front surface of the blade is not particularly limited, but for example, it is 0.50 μm or more.

[0056] Furthermore, the first cutting edge angle of the blade (the angle between the first front surface and the back surface) is not particularly limited and can be, for example, 10° to 45°. For example, as illustrated in Figure 1, the cutting edge angle θ1 can be within the above range. Furthermore, the second cutting edge angle of the blade (the angle between the second front surface and the back surface) is not particularly limited and can be, for example, 10° to 30°. For example, as illustrated in Figure 1, the cutting edge angle θ2 can be within the above range.

[0057] <<Slice>> [Slicing speed] The slicing speed of the block (laminated material) (in other words, the relative speed at which the block and the blade come into contact) must be 5 m / min or more. Furthermore, while there are no particular restrictions on the slicing speed of the block (laminated material), it is preferably 12 m / min or more, more preferably 30 m / min or more, and preferably 120 m / min or less. When the slicing speed of the block (laminated material) is 12 m / min or more, productivity can be improved, and the deterioration of surface roughness caused by the blade compressing the block as it moves can be suppressed. On the other hand, when the slicing speed of the block (laminated material) is 120 m / min or less, the impact of the collision between the block and the blade can be suppressed, allowing for more uniform slicing of the block (especially the part where the blade enters).

[0058] The slicing speed may be controlled by changing the speed at which the block body 20 is driven into (cuts into) the fixed blade 10, as shown in Figure 1; by changing the speed at which the blade is driven into (cuts into) the fixed block body; or by changing the relative speed at which the blade and the block body are driven into (cut into) each other. Furthermore, from the viewpoint of workability, it is desirable to control the slicing speed by machine control.

[0059] [Slice direction] In the above slicing method, it is preferable to slice the block body with a plane parallel to the stacking direction (in other words, such that the main surface of the heat conductive sheet obtained by slicing has a stacked cross-section). For example, as shown in Figure 1, if the block body 20 is sliced ​​with a plane parallel to the stacking direction A of the primary sheet 20a, the desired properties can be made to appear in the thickness direction of the heat conductive sheet obtained by slicing. In this invention, the term "surface parallel to the stacking direction" also includes surfaces having an inclination of approximately 30° or less with respect to the direction parallel to the stacking direction.

[0060] Here, as an example, we will explain the case of slicing using the plane shown in Figure 1. First, the laminated side surface 20b of the block body 20 is supported by the sliding surface 30a so that the block body 20 can slide in a direction parallel to the laminated side surface 20b and the sliding surface 30a of the plane. In other words, according to Figure 1, the laminated body 1 is positioned on the sliding surface 30a such that the lamination direction A is horizontal with respect to a horizontally installed plane, the laminated side surface 20c faces upward and the laminated side surface 20b faces downward, and the top surface 20d faces the blade 10. The blade 10 for slicing has its tip protruding from the sliding surface 30a to an arbitrary extent. In the example in Figure 1, the tip of the blade 10, which has a blade angle θ1, protrudes from the sliding surface 30a at an angle α. Then, according to Figure 1, the block body 20 supported on the slide surface 30a is pressed with arbitrary pressure from the laminated side surface 20c towards the slide surface 30a, and slid in a direction parallel to the slide surface 30a (slide direction, slice direction) at a predetermined slicing speed (slide speed). The sliding speed at this time is the same as the predetermined slicing speed described above. As the block body 20 slides in this manner, the top surface 20d enters the blade 10 at a predetermined sliding speed, and the block body 20 is sliced ​​with a plane parallel to the stacking direction A.

[0061] The pressure applied when pressing the block body against the sliding surface is preferably 0.05 MPa or higher, more preferably 0.10 MPa or higher, particularly preferably 0.20 MPa or higher, preferably 0.50 MPa or lower, more preferably 0.40 MPa or lower, and particularly preferably 0.30 MPa or lower. When the pressure is 0.05 MPa or higher, the thickness accuracy of the heat conductive sheet obtained by slicing the block can be ensured, while when the pressure is 0.50 MPa or lower, the collapse of the block can be suppressed. Furthermore, if the block body is a laminate obtained by laminating primary sheets in a lamination process described later, it is preferable to slice the block body, which is a laminate, while applying pressure in a direction perpendicular to the lamination direction, from the viewpoint of easily slicing the block body and ensuring sufficient thickness accuracy of the resulting heat conductive sheet.

[0062] Furthermore, from the viewpoint of easily slicing the block and ensuring sufficient thickness accuracy of the resulting heat conductive sheet, it is preferable that the temperature of the block during slicing be between -20°C and 80°C, and more preferably between -10°C and 50°C.

[0063] [Slice angle] Here, the slicing angle β (sometimes called the "entry angle" or "penetration angle") between the stacking direction of the block material and the extending direction of the blade can be within the range of 0° to 90°. To explain in more detail with reference to Figure 2, in Figure 2(a), the laminated side surface 20f and the blade 10 come into contact so that the stacking direction A of the primary sheets in the block body 20 (laminated body) is parallel to the extending direction E of the blade 10 (slicing angle β = 0°). In Figures (b) to (d), the stacking direction A of the primary sheets in the block body 20 (laminated body) and the extending direction E of the blade 10 form an angle, and the top surface 20d and the laminated side surface 20f come into contact with the blade 10 so that they enter it (slicing angles β = 15°, 45°, and 75°). Then, in Figure 2(e), the top surface 20d and the blade 10 come into contact so that the stacking direction A of the primary sheets in the block body 20 (laminated body) and the extending direction E of the blade 10 form a right angle (slicing angle β = 90°). From the viewpoint of reducing the impact during the initial collision and improving the thickness surface accuracy, the slice angle β is preferably greater than 0°, more preferably 1° or more, even more preferably 5° or more, even more preferably 30° or more, and particularly preferably 40° or more. Similarly, from the above viewpoint, the slice angle β is preferably less than 90° within the range of 0° to 90°, more preferably 89° or less, even more preferably 85° or less, even more preferably 60° or less, and particularly preferably 50° or less. And the slice angle β is even more preferably 45°.

[0064] The slicing angle may be controlled by changing the angle at which the block body is inserted (cut into) the fixed blade, by changing the angle at which the blade is inserted (cut into) the fixed block body, or by changing the relative angle at which the blade and the block body are brought closer together (cut into).

[0065] As explained above, the method for slicing the block body is not particularly limited, as long as it is a method in which the block body 20 is supported so as to be slidable by a sliding surface 30a, as shown in Figure 1, and the block body 20 is slid while being pressed against the sliding surface 30a while supporting a blade 10 whose tip protrudes from the sliding surface 30a. As described above, the block body 20 is sliced ​​by sliding, for example, in the stacking direction A of the primary sheet 20a while being pressed against the sliding surface 20a, and a new heat conductive sheet (not shown) is generated on the back surface 10c side of the blade 10. Here, the upper main surface of the newly generated heat conductive sheet in Figure 1 is called surface A, and the lower main surface in Figure 1 is called surface B. According to the present invention, at least the length and surface roughness Sa of the first front surface 10a of the blade 10 are adjusted to a predetermined range, and preferably the surface roughness Sa of the second front surface 10b of the blade 10 is adjusted, so that the damage received when the block body 20 is slid in the stacking direction A of the primary sheet 20a while being pressed against the sliding surface 20a (damage received by the lower surface of the block body 20 in Figure 1 (the B surface of the next generated heat conductive sheet) from the second front surface 10b of the blade 10 at the steps 30b and grooves 40) can be reduced. Furthermore, from the viewpoint of preventing damage to the smoothness of the lower surface of the block body 20 (the B-side of the heat conductive sheet that will be generated next), it is preferable to move the block body 20 from the position after sliding back to the position before sliding (the position of the block body 20 in Figure 1) without the block body 20 coming into contact with the sliding surface 30a.

[0066] <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 method for manufacturing a heat-conducting sheet of the present invention, before the slicing step described above, a step (lamination step) can be performed in which multiple primary sheets containing resin and particulate filler are laminated in the thickness direction, or the primary sheets are folded or rolled up to obtain a block body. Furthermore, in the method for manufacturing a heat-conducting sheet of the present invention, a step of heating the block (heating step) can be performed before the slicing step described above. In the method for manufacturing a heat-conductive sheet of the present invention, a step of applying pressure in the thickness direction to the heat-conductive sheet obtained after the slicing step (pressing step) may be performed, provided that the effects of the present invention are not significantly impaired. However, from the viewpoint of suppressing a decrease in the thermal conductivity in the thickness direction of the obtained heat-conductive sheet, it is preferable that the method for manufacturing a heat-conductive sheet of the present invention does not include a pressing step. The following details the lamination process and the heating process, which are other steps in the process.

[0067] <<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.

[0068] [Primary Sheet] The primary sheet comprises a resin and particulate fillers, and may optionally further contain additives.

[0069] —Resins, particulate fillers, and additives— The preferred types, properties, and proportions of resin and particulate fillers 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 heat-conducting sheet of the present invention.

[0070] —Properties of the primary sheet— The primary sheet preferably has a tensile strength of 0.3 MPa or more, more preferably 1.0 MPa or more, even more preferably 1.5 MPa or more, preferably 3.0 MPa or less, more preferably 2.5 MPa or less, and even more preferably 2.0 MPa or less. If the tensile strength is 0.3 MPa or more, the Asker C hardness of the block body obtained by laminating the primary sheets increases. Therefore, by suppressing the wobble of the cutting edge when slicing the block body, a heat conductive sheet with even better thickness accuracy can be obtained. On the other hand, if the tensile strength is 3.0 MPa or less, the Asker C hardness of the block body obtained by laminating the primary sheets does not increase excessively. Therefore, slicing the block body becomes easier, and sufficient thickness accuracy of the obtained heat conductive sheet (especially when the thickness of the heat conductive sheet is reduced by reducing the slice width) can be ensured. Furthermore, the tensile strength of the primary sheet can be adjusted by changing the type and content ratio of materials (resin, particulate filler, etc.) used in the manufacture of the primary sheet, as well as by changing the manufacturing method of the primary sheet. For example, increasing the resin content ratio in the primary sheet can increase the tensile strength of the primary sheet.

[0071] Furthermore, the thickness (average thickness) of the primary sheet is not particularly limited and can be, for example, 0.05 mm or more and 2 mm 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.

[0072] —Method for preparing the primary sheet— 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 and particulate fillers, as well as optionally used additives, using a known molding method such as press molding, rolling, or extrusion molding.

[0073] [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.

[0074] <<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]

[0075] 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, the particle size distribution and volume-average particle diameter, the content (volume fraction) of particulate fillers, the surface roughness Sa of the first and second front surfaces of the blades, the Asker C hardness of the block body, and the average thickness, standard deviation of thickness, surface roughness Sa, and thermal conductivity in the thickness direction of the thermal conductive sheet were measured or evaluated according to the following methods.

[0076] <Volume-average particle size> A suspension was obtained by dissolving the resin components of a thermal conductive sheet (1 g) in methyl ethyl ketone as a solvent, thereby separating and dispersing the particulate filler (expanded graphite) contained in the thermal conductive sheet. Next, the particle size of the particulate filler contained in the suspension was measured using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd., model "LA960"). A particle size distribution curve was then created with the obtained particle size on the x-axis and the particle frequency converted to volume on the y-axis. The particle size at which the cumulative volume calculated from the smallest diameter side reaches 50% (D50) was determined and taken as the volume-average particle size of the particulate filler. <Percentage of particulate filler content (volume fraction)> The volume of each material used in the formation of the primary sheet was calculated by dividing its weight by its specific gravity. The specific gravity of the resin was assumed to be 1.77 for both liquid and solid resins, 2.25 for the particulate filler (expanded graphite), and 1.17 for the additives. <Surface roughness Sa of the first and second front surfaces of the blade> The surface roughness Sa of the first and second front surfaces of the blade was measured using a three-dimensional shape measuring machine (manufactured by Keyence Corporation, product name "One-Shot 3D Measurement Macroscope"). Measurements were taken at 40x magnification, with an observation area of ​​5.7 mm × 7.6 mm. <Asker C hardness of block bodies (laminated bodies)> The Asker C hardness of the block material (laminated material) was measured in accordance with the Asker C method of the Japan Rubber Association Standard (SRIS), using a hardness tester (manufactured by Polymer Instruments Co., Ltd., product name "ASKER CL-150LJ") at a temperature of 25°C. Specifically, the obtained block material (laminated material) was left to stand in a constant temperature room maintained at 25°C for more than 48 hours to prepare as a test specimen. Next, the hardness tester was set up so that the distance of the needle tip from the laminate surface was 2 cm, and the damper was lowered to cause the block material (laminated material) to collide with the damper. The Asker C hardness of the block material (laminated material) 60 seconds after the collision was measured twice using the hardness tester (manufactured by Polymer Instruments Co., Ltd., product name "ASKER CL-150LJ"), and the average value of the measurement results was adopted. <Average thickness> Using a film thickness gauge (Mitutoyo product name "Digimatic Indicator ID-C112XBS"), the thickness of the thermal conductive sheet was measured at five points: approximately the center and the four corners (square). The average value (μm) of the measured thickness was then calculated. <Standard deviation of thickness> Using a film thickness gauge (Mitutoyo product name "Digimatic Indicator ID-C112XBS"), the thickness of the thermal conductive sheet was measured at five points: approximately the center point and the four corners (square). The standard deviation (μm) of the measured thicknesses was then calculated. <Surface roughness Sa of thermal conductive sheet> The surface roughness Sa of the thermal conductive sheet was measured using a three-dimensional shape measuring machine (manufactured by Keyence Corporation, product name "One Shot 3D Measurement Macroscope"). A thermal conductive sheet cut into an approximately square shape of any size (1 cm x 1 cm or larger) was used as the sample, and the analysis range was set to 1 cm x 1 cm. The three-dimensional shape of both the front and back surfaces of the sample was measured. The measurement results were then further filtered (2.5 mm) using software to remove waviness components, and the surface roughness Sa (μm) was automatically calculated. Surface roughness Sa was measured for both surface A (the newly generated surface from a new cutting operation) and surface B (the surface already generated from a previous cutting operation). <Thermal conductivity in the thickness direction> Regarding thermal conductive sheets, the thermal diffusivity α(m) in the thickness direction is... 2( / s), constant-pressure specific heat Cp (J / g·K), and specific gravity ρ (g / m³) 3 The following methods were used to measure each of the following: [Thermal diffusivity α in the thickness direction] The thermal diffusivity of the thermal conductive sheet was measured using a thermal diffusion / thermal conductivity measuring device (ai-Phase Mobile 1u, manufactured by i-Phase Co., Ltd.) in accordance with the provisions of ISO 22007-3. [Specific heat at constant pressure Cp] A differential scanning calorimeter (Rigaku, product name "DSC8230") was used to measure the specific heat at 25°C under a heating condition of 10°C / min. [Specific gravity ρ (density)] The measurement was performed using an automatic hydrometer (manufactured by Toyo Seiki Co., Ltd., product name "DENSIMETER-H"). Then, each measurement value is expressed using the following formula (I): λ = α × Cp × ρ···(I) By substituting these values, the thermal conductivity λ (W / m·K) in the thickness direction of the thermal conductive sheet at 25°C was determined. <Thermal resistance value> The thermal resistance of the thermal conductive sheet was measured using a thermal resistance tester (manufactured by Hitachi Technology & Services, Ltd., product name: "Thermal Resistance Measuring Device for Resin Materials"). A thermal conductive sheet cut into approximately 1 cm squares was used as the sample, and the thermal resistance (°C / W) was measured at a sample temperature of 50°C when pressures of 0.1 MPa and 0.9 MPa were applied. A smaller thermal resistance value indicates superior thermal conductivity of the thermal conductive sheet, for example, superior heat dissipation characteristics when interposed between a heat-generating element and a heat-sinking element.

[0077] (Example 1) <Formation of the primary sheet> Seventy parts of liquid thermoplastic fluororesin at room temperature and pressure (manufactured by Daikin Industries, Ltd., product name "Dai-L G-101"), 30 parts of solid thermoplastic fluororesin at room temperature and pressure (manufactured by 3M Japan Limited, product name "Dinion FC2211"), and 90 parts of expanded graphite as a particulate filler (manufactured by Ito Graphite Industry Co., Ltd., product name "EC300", volume average particle size: 50 μm) were mixed and stirred at 150°C for 20 minutes using a pressurized kneader (manufactured by Nippon Spindle). Next, the resulting mixture was placed in a crusher (manufactured by Osaka Chemical Co., Ltd., product name "Wonder Crush Mill D3V-10") and crushed for 10 seconds. 50 g of the crushed mixture was sandwiched between 50 μm thick polyethylene terephthalate (PET) films (protective films) that had been sandblasted, and rolled under the conditions of a roll gap of 550 μm, a roll temperature of 50°C, a roll linear pressure of 50 kg / cm, and a roll speed of 1 m / min to obtain a primary sheet with a thickness of 0.8 mm. <Lamination process> The obtained primary sheet was cut to 150 mm (length) x 150 mm (width) x 0.8 mm (thickness), and 100 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 80 mm was obtained. The Asker C hardness of the obtained block was then measured. The results are shown in Table 1. <Slicing process> Subsequently, while pressing the side surface (the surface along the lamination direction) of the block (laminated body) against the sliding surface 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 (laminated body) in the lamination direction (in other words, in the direction corresponding to the normal of the main surface of the laminated primary sheet), obtaining a heat conductive sheet measuring 150 mm in length, 150 mm in width, and 0.10 mm in thickness. The above slicing was performed by sliding the block (laminated body) along the sliding surface at a sliding speed of 1000 mm / second. A single-edged blade A with the following properties was used as the slicing blade of the woodworking slicer. The temperature of the block was set to room temperature. <<Properties of Single-Edged Blade A>> Blade angle A (see Figure 1: angle θ1 between the first front surface 10a and the back surface 10c): 40° Blade angle B (see Figure 1: angle θ2 between the second front surface 10b and the back surface 10c): 20° Maximum blade thickness: 9mm Material: Tungsten carbide Rockwell hardness: 90 Silicone coating on the blade surface: None Radius of curvature of the tip R: 10 μm Length of the first front surface: 1.0 mm Surface roughness of the first front surface: Sa: 0.43 μm Length of the second front surface: 25.0 mm Surface roughness Sa of the second front surface: 0.61 μm The average thickness, standard deviation of thickness, surface roughness Sa, and thermal conductivity in the thickness direction of the obtained thermal conductive sheets were then measured. The results are shown in Table 1.

[0078] (Example 2) In Example 1, a primary sheet, a block body, and a heat-conducting sheet were fabricated in the same manner as in Example 1, except that a single-edged blade B with the following properties was used instead of single-edged blade A. Various evaluations were then performed. The results are shown in Table 1. <<Properties of Single-Edged B>> Blade angle A (see Figure 1: angle θ1 between the first front surface 10a and the back surface 10c): 40° Blade angle B (see Figure 1: angle θ2 between the second front surface 10b and the back surface 10c): 20° Maximum blade thickness: 9mm Material: Tungsten carbide Rockwell hardness: 90 Silicone coating on the blade surface: None Radius of curvature of the tip R: 10 μm Length of the first front surface: 3.0 mm Surface roughness of the first front surface: Sa: 0.43 μm Length of the second front surface: 23.0 mm Surface roughness Sa of the second front surface: 0.61 μm

[0079] (Example 3) In Example 1, a primary sheet, a block body, and a heat-conducting sheet were fabricated in the same manner as in Example 1, except that a single-edged blade C with the following properties was used instead of single-edged blade A. Various evaluations were then performed. The results are shown in Table 1. <<Properties of Single-Edged C>> Blade angle A (see Figure 1: angle θ1 between the first front surface 10a and the back surface 10c): 40° Blade angle B (see Figure 1: angle θ2 between the second front surface 10b and the back surface 10c): 20° Maximum blade thickness: 9mm Material: High-speed tool steel (HSS steel) Rockwell hardness: 82 Silicone coating on the blade surface: None Radius of curvature of the tip R: 10 μm Length of the first front surface: 1.0 mm Surface roughness of the first front surface: Sa: 0.75 μm Length of the second front surface: 25.0 mm Surface roughness Sa of the second front surface: 0.86 μm

[0080] (Comparative Example 1) In Example 1, a primary sheet, a block body, and a heat-conducting sheet were fabricated in the same manner as in Example 1, except that a single-edged blade D with the following properties was used instead of single-edged blade A. Various evaluations were then performed. The results are shown in Table 1. <<Properties of Single-Edged D>> Blade angle A (see Figure 1: angle θ1 between the first front surface 10a and the back surface 10c): 40° Blade angle B (see Figure 1: angle θ2 between the second front surface 10b and the back surface 10c): 20° Maximum blade thickness: 9mm Material: High-speed tool steel (HSS steel) Rockwell hardness: 82 Silicone coating on the blade surface: None Radius of curvature of the tip R: 10 μm Length of the first front surface: 1.0 mm Surface roughness of the first front surface: Sa: 1.25 μm Length of the second front surface: 25.0 mm Surface roughness Sa of the second front surface: 0.94 μm

[0081] (Comparative Example 2) In Example 1, instead of pressing the side of the block (laminated body) against a sliding surface with a pressure of 0.3 MPa and slicing it in the lamination direction using a woodworking slicer, the block (laminated body) was sliced ​​in the lamination direction using a woodworking slicer without pressing the side of the block (laminated body) against the sliding surface with a pressure of 0.3 MPa (i.e., only by the weight of the block (laminated body) itself). Except for this difference, a primary sheet, a block, and a thermal conductive sheet were fabricated in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1.

[0082] (Comparative Example 3) In Example 3, instead of using 90 parts of expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., product name "EC300", volume average particle size: 50 μm) as a particulate filler during the formation of the primary sheet, 50 parts of expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., product name "EC100", volume average particle size: 200 μm) were used as particulate fillers. Otherwise, a primary sheet, block body, and thermal conductive sheet were prepared in the same manner as in Example 3, and various evaluations were performed. The results are shown in Table 1.

[0083] (Comparative Example 4) In Example 1, when forming the primary sheet, instead of using 70 parts of liquid thermoplastic fluororesin at room temperature and atmospheric pressure (manufactured by Daikin Industries, Ltd., product name "Daiel G-101") and 30 parts of solid thermoplastic fluororesin at room temperature and atmospheric pressure (manufactured by 3M Japan Limited, product name "Dinion FC2211") as the resin, and 90 parts of expanded graphite as particulate filler (manufactured by Ito Graphite Industry Co., Ltd., product name "EC300", volume average particle size: 50 μm), a thermal conductive sheet measuring 150 mm in length, 150 mm in width, and 0.10 mm in thickness was obtained, instead, 45 parts of liquid thermoplastic fluororesin at room temperature and atmospheric pressure (manufactured by Daikin Industries, Ltd., product name "Daiel G-101") and 40 parts of solid thermoplastic fluororesin at room temperature and atmospheric pressure (manufactured by 3M Japan Limited, product name "Dinion FC2211") were used as the resin. In this experiment, a primary sheet, block, and heat-conducting sheet were prepared in the same manner as in Example 1, except that 85 parts of expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., product name "EC100", volume average particle size: 200 μm) as a particulate filler and 5 parts by mass of sebacate ester (manufactured by Daihachi Chemical Industry Co., Ltd., product name "DOS") as a plasticizer were used to obtain a secondary sheet (sliced ​​from a block) measuring 150 mm in length, 150 mm in width, and 0.50 mm in thickness (500 μm). Then, using a precision hot press machine (manufactured by Shinto Kogyo Co., Ltd., product name "CYPT-20"), the press plate was heated to 50°C and pressed at a pressure of 2.6 MPa for 30 seconds to obtain a heat-conducting sheet measuring 150 mm in length, 150 mm in width, and 0.125 mm in thickness (125 μm). Various evaluations were then performed. The results are shown in Table 1.

[0084] [Table 1]

[0085] Table 1 shows that the thermal conductive sheets of Examples 1-3 have smooth main surfaces. Furthermore, the thermal conductive sheets of Examples 1-3 have low thermal conductivity in the thickness direction, indicating good heat transfer in that direction. Additionally, the thermal conductive sheets of Examples 1-3 have small standard deviations in thickness, demonstrating excellent thickness accuracy. [Industrial applicability]

[0086] According to the present invention, it is possible to provide a heat conductive sheet in which both main surfaces are smooth, has sufficient thickness accuracy, and is capable of good heat transfer in the thickness direction, as well as a method for manufacturing the heat conductive sheet. [Explanation of symbols]

[0087] 10 blades 10a First front side 10b Second front side 10c back side 10d cutting edge 10e edge 20 block letters 20a Primary Sheet 20b Laminated side 20c laminated side 20d Top surface 20e base 20f laminated side 30 units 30a Sliding surface 30b Step 40 grooves A Stacking direction of primary sheet 20a E Blade extension direction θ1 The angle between the first front surface 10a and the back surface 10c (blade angle A) θ2 The angle between the second front surface 10b and the back surface 10c (blade angle B) α angle β slice angle

Claims

1. Containing resin and particulate filler, The thermal conductivity in the thickness direction is 15 W / m·K or higher. The standard deviation of the thickness is 3.5 μm or less. The surface roughness Sa of both main surfaces is 3.00 μm or less. A thermal conductive sheet in which the absolute value of the difference between the surface roughness Sa of one main surface and the surface roughness Sa of the other main surface is 0.09 μm or more and 0.40 μm or less.

2. The thermal conductive sheet according to claim 1, wherein the average thickness is 250 μm or less.

3. The thermal conductive sheet according to claim 1 or 2, wherein the content ratio of the particulate filler is 30% by volume or more and 55% by volume or less.

4. The thermal conductive sheet according to any one of claims 1 to 3, wherein the volume-average particle diameter of the particulate filler is 30 μm or more and 150 μm or less.

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