Heat 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 conduction sheet and a method for manufacturing the heat conduction sheet.

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 their higher performance. As a result, in electronic devices using such electronic components, it has become necessary to take measures against functional failures caused by temperature rise of the electronic components.

[0003] As a measure against functional failures caused by 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 thermal conductivity (heat conduction sheet) is used to efficiently transfer heat from the heat generating body to the heat dissipating body. For example, a heat conduction sheet containing a resin and particulate fillers is sandwiched between a heat generating body and a heat dissipating body, and the heat generating body and the heat dissipating body are brought into close contact with each other through this heat conduction 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 conduction sheet (see, for example, Patent Documents 1 and 2).

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

[0005] In Patent Document 2, a method for obtaining a heat conduction sheet is disclosed, in which a laminate obtained by laminating a primary sheet containing a resin and a particulate carbon material in the thickness direction is sliced at an angle of 45° or less with respect to the lamination direction, and then the sheet obtained by slicing is pressed. According to Patent Document 2, the heat conduction sheet obtained by the above method can exhibit excellent heat conductivity even when used at a relatively low clamping pressure.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] Here, in recent years, from the viewpoint of making the heat generating body and the heat radiating body adhere well through the heat conduction sheet and uniformly transferring heat from the heat generating body to the heat radiating body, it has been required to smooth both main surfaces of the heat conduction sheet and improve the thickness accuracy of the heat conduction sheet. However, with the above conventional method, it has been difficult to produce a heat conduction sheet having smooth both main surfaces and a uniform thickness while causing the heat conduction sheet to exhibit excellent heat conductivity in the thickness direction.

[0008] Therefore, an object of the present invention is to provide a heat conduction sheet capable of smoothly transferring heat in the thickness direction while having smooth both main surfaces and sufficient thickness accuracy, and a method for manufacturing the heat conduction sheet.

Means for Solving the Problems

[0009] The inventor has conducted intensive studies to achieve the above object. First, the inventors attempted to improve the thickness accuracy of the heat conduction sheet by applying pressure during slicing using the cannabis described in Patent Document 1 above. However, according to the studies by the inventors, it became clear that when pressure is applied to the sheet during slicing using cannabis, it is difficult to sufficiently ensure the smoothness of both main surfaces. Then, the inventor found that in a heat conduction sheet containing a resin and a particulate filler, if the standard deviation of the thickness is set to a predetermined value or less, the thermal conductivity in the thickness direction is set to a predetermined value or more, and the surface roughness Sa of both main surfaces is set to a predetermined value or less, a heat conduction sheet with smooth main surfaces, sufficient thickness accuracy, and good heat transfer in the thickness direction can be obtained, and thus completed the present invention.

[0010] That is, the object of this invention is to advantageously solve the above problems. The heat conduction sheet of the present invention contains a resin and a particulate filler, has a thermal conductivity in the thickness direction of 15 W / m·K or more, a standard deviation of the thickness of 3.5 μm or less, and a surface roughness Sa of both main surfaces of 3.00 μm or less. Thus, a heat conduction sheet containing a resin and a particulate filler, having a thermal conductivity in the thickness direction of the above value or more, a standard deviation of the 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, sufficient thickness accuracy, and can transfer heat well in the thickness direction. In the present invention, the "thermal conductivity in the thickness direction" can be calculated using the method described in the examples of this specification. Also, in the present invention, the "standard deviation of the thickness" is a value obtained by measuring the thickness at any five points of the heat conduction sheet 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 the present invention, the "both main surfaces" refers to the surface having the largest area in the heat conduction sheet and the surface facing that surface.

[0011] Here, the thermal conductive sheet of the present invention preferably 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 more favorably in the thickness direction of the thermal conductive sheet. In the present invention, the "average thickness" is a value obtained by measuring the thicknesses at any five points of the thermal conductive sheet, and can be calculated, for example, using the method described in the examples of this specification.

[0012] Also, in the thermal conductive sheet of the present invention, the content ratio of the particulate filler is preferably 30% by volume or more and 55% by volume or less. If the volume ratio of the particulate filler in the thermal conductive sheet is within the above range, the thermal conductivity in the thickness direction of the thermal conductive sheet increases, and heat can be transferred more favorably in the thickness direction of the thermal conductive sheet. At the same time, while ensuring the flexibility of the thermal conductive sheet, the thickness accuracy can be further improved.

[0013] Also, in the thermal conductive sheet of the present invention, the volume average particle diameter of the particulate filler is preferably 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 favorably in the thickness direction of the thermal conductive sheet, and the smoothness of the main surface and the thickness accuracy of the thermal conductive sheet can be further improved. In the present 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 small-diameter side is 50% in the particle size distribution (volume basis) measured by the laser diffraction method.

[0014] Furthermore, in the thermal conductive sheet of the present invention, 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 preferably 0.40 μm or less. If 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 of the thermal conductive sheet is less than or equal to the above value, the handleability such as the ease of gripping with a robot arm can be improved.

[0015] The present invention also aims to advantageously solve the above problems. The method for manufacturing a heat conduction sheet according to the present invention includes a step of slidably supporting a block body containing a resin and a particulate filler by a sliding surface, and while supporting a blade with its tip protruding from the sliding surface, sliding the block body while pressing it against the sliding surface to slice the block body with the blade. The blade includes a first front surface that contacts the block body, a back surface that intersects the first front surface, a blade tip formed by an intersection corner of the first front surface and the back surface, and a second front surface that extends from an edge on the side opposite to the blade tip side of the first front surface and is located on the back surface side with respect to the first front surface. The length of the first front surface is 0.8 mm or more, and the surface roughness Sa of the first front surface is 1.00 μm or less. Thus, if the block body containing a resin and a particulate filler is sliced by a predetermined method using a blade whose first front surface has a length and surface roughness Sa within the above ranges, a heat conduction sheet with smooth both main surfaces, sufficient thickness accuracy, and capable of transferring heat well in the thickness direction can be obtained. 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, during slicing of the block body, the "surface on the side where the cutting part in contact with the block body is provided" is defined as the "front surface", and the surface on the side from which the heat conduction sheet is discharged from the block body (the surface on the side opposite to the front surface where the cutting part in contact with the block body is first provided) is defined as the "back surface".

[0016] Here, in the method for manufacturing a heat conduction sheet according to the present invention, it is preferable that the surface roughness Sa of the second front surface is 1.00 μm or less. If the surface roughness Sa of the second front surface is below the above value, the smoothness of the surface of the heat conduction sheet obtained by slicing the block body can be more reliably ensured. In the present 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 can 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, "laminating", "folding", or "winding" may be collectively abbreviated as "laminating etc.".

Advantages 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 favorably conducting heat in the thickness direction, and a manufacturing method of the heat conduction sheet.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

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 contains a resin and particulate fillers, and may further optionally contain additives. Further, the thermal conductive sheet of the present invention has a thermal conductivity in the thickness direction of 15 W / m·K or more, a standard deviation of the thickness of 3.5 μm or less, and a surface roughness Sa of both main surfaces of 3.00 μm or less. And, since the thermal conductive sheet of the present invention has a thermal conductivity in the thickness direction of 15 W / m·K or more, a standard deviation of the thickness of 3.5 μm or less, and a surface roughness Sa of both main surfaces of 3.00 μm or less, both main surfaces are smooth, and while having sufficient thickness accuracy, heat can be transferred well in the thickness direction.

[0022] <resin> The resin contained in the thermal conductive 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 thermal conductive sheet can 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 enabling better heat transfer in the thickness direction, it is preferable that the thermal conductive sheet contains both a liquid resin and a solid resin.

[0023] <<liquid resin>> And, as the liquid resin, as long as it is liquid under normal temperature and pressure, it is not particularly limited, and 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).

[0024] Examples of the liquid resin include a fluororesin, a silicone resin, an acrylic resin, and an epoxy resin. These may be used alone or in combination of two or more. Among them, as the liquid resin, a silicone resin and a fluororesin are preferable, and a fluororesin is more preferable. If at least one of a silicone resin and a fluororesin is used as the liquid resin, the flame retardancy of the heat conductive sheet can be improved. Further, if a fluororesin is used as the liquid resin, the heat resistance, oil resistance, and chemical resistance of the obtained heat conductive sheet can be improved.

[0025] <<Solid resin>> The solid resin is not particularly limited as long as it is not liquid under normal temperature and pressure. For example, a thermoplastic resin that is solid under normal temperature and pressure and a thermosetting resin that is solid under normal temperature and pressure can be used.

[0026] [Thermoplastic resin that is solid under normal temperature and pressure] Examples of thermoplastic resins that are solid at normal 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; fluorine resins; 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; polyacrylonitrile; styrene-acrylonitrile copolymers; acrylonitrile-butadiene copolymers (nitrile rubber); acrylonitrile-butadiene-styrene copolymers (ABS resin); styrene-butadiene block copolymers or their hydrogenated products; styrene-isoprene block copolymers or their hydrogenated products; polyphenylene ether; modified polyphenylene ether; aliphatic polyamides; aromatic polyamides; polyamide-imide; polycarbonate; polyphenylene sulfide; polysulfone; polyether sulfone; polyether nitrile; polyether ketone; polyketone; polyurethane; liquid crystal polymer; ionomer; etc. These may be used alone or in combination of two or more. In the present invention, rubber is included in "resin".

[0027] [Thermosetting resins that are solid at normal temperature and pressure] Examples of thermosetting resins that are solid at normal temperature and pressure include, for example, 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; phenol resin; unsaturated polyester; diallyl phthalate resin; polyimide silicone resin; polyurethane; thermosetting polyphenylene ether; thermosetting modified polyphenylene ether; and the like. These may be used alone or in combination of two or more.

[0028] <<Content ratio of resin>> The content ratio of the resin in the heat conductive sheet is not particularly limited, but it is preferably 35% by mass or more, more preferably 45% by mass or more, still more preferably 50% by mass or more, preferably 95% by mass or less, more preferably 85% by mass or less, and still more preferably 75% by mass or less. If the content ratio of the resin is 35% by mass or more, the flexibility of the heat conductive sheet can be ensured while further improving the thickness accuracy of the heat conductive sheet. On the other hand, if the content ratio of the resin is 95% by mass or less, heat can be transferred better in the thickness direction of the heat conductive sheet.

[0029] <<Content ratio of liquid resin>> Also, the content ratio of the liquid resin in the resin (in other words, the ratio of the liquid resin in the total of the solid resin and the liquid resin) is not particularly limited, but it is preferably 30% by mass or more, more preferably 40% by mass or more, still 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, still more preferably 85% by mass or less, and particularly preferably 80% by mass or less. If the content ratio of the liquid resin in the resin is 30% by mass or more, the flexibility of the heat conduction sheet can be ensured while further improving the thickness accuracy. On the other hand, if the content ratio of the liquid resin in the resin is 95% by mass or less, the strength suitable for the primary sheet is imparted, so that the laminate is easier to slice, and the thickness accuracy of the obtained heat conduction sheet can be further improved.

[0030] <Particulate filler> The particulate filler contained in the heat conduction sheet is not particularly limited as long as it can impart heat conductivity to the heat conduction sheet. And as such a particulate filler, a particulate carbon material having high heat conductivity can be preferably used. The particulate filler may be used alone or in combination of two or more.

[0031] <<Particulate carbon material>> The particulate carbon material is not particularly limited, and for example, graphite such as artificial graphite, flaky graphite, exfoliated graphite, natural graphite, acid-treated graphite, expandable graphite, expanded graphite; carbon black; etc. can be used. These may be used alone or in combination of two or more.

[0032] Among the above, as the particulate carbon material, it is preferable to use expanded graphite. By using expanded graphite, the thermal conductivity in the thickness direction of the thermal conductive sheet is increased, and heat can be transferred better in the thickness direction of the thermal conductive sheet. Here, expanded graphite can be obtained, for example, by chemically treating graphite such as flake graphite with sulfuric acid or the like to obtain expandable graphite, heat-treating it to expand, and then making it finer. And as expanded graphite, for example, EC1500, EC1000, EC500, EC300, EC100, EC50 (all are trade names) manufactured by Ito Graphite Industry Co., Ltd. etc. can be mentioned.

[0033] <<Properties of Particulate Filler>> 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, still more preferably 80 μm or less, and particularly preferably 60 μm or less. If the volume average particle diameter of the particulate filler is 30 μm or more, it is presumed that the heat transfer path of the particulate filler can be formed well in the thermal conductive sheet, and the thermal conductivity in the thickness direction of the thermal conductive sheet increases. As a result, heat can be transferred better in the thickness direction of the thermal conductive sheet. On the other hand, if the volume average particle diameter of the particulate filler is 150 μm or less, the flatness of the main surface and the thickness accuracy of the thermal conductive sheet can be further improved.

[0034] Also, the particulate filler preferably has an aspect ratio (major axis / minor axis) of more than 1 and 10 or less, more preferably more than 1 and 5 or less. If the aspect ratio of the particulate filler is more than 1 and 10 or less, it is presumed that the particulate filler is likely to be oriented well in the thickness direction in the thermal conductive sheet, and the thermal conductivity in the thickness direction of the thermal conductive sheet increases. As a result, heat can be transferred better in the thickness direction of the thermal conductive sheet. In the present invention, the "aspect ratio" can be obtained by observing particulate fillers with an SEM (scanning electron microscope), measuring the maximum diameter (major axis) and the particle diameter (minor axis) in the direction orthogonal to the major axis for any 50 particulate fillers, and calculating the average value of the ratio of the major axis to the minor axis (major axis / minor axis).

[0035] <<Content ratio of particulate filler>> The content ratio of particulate fillers in the heat conductive sheet is not particularly limited, but is preferably 30% by volume or more, more preferably 35% by volume or more, particularly preferably 40% by volume or more, preferably 55% by volume or less, more preferably 50% by volume or less, still more preferably 45% by volume or less, and particularly preferably 42% by volume or less. When the content ratio of particulate fillers is 30% by volume or more, the thermal conductivity in the thickness direction of the heat conductive sheet increases, and heat can be transferred more favorably in the thickness direction of the heat conductive sheet. On the other hand, when the content ratio of particulate fillers is 42% by volume or less, the flexibility of the heat conductive sheet can be ensured while further improving the thickness accuracy.

[0036] Also, the content ratio of particulate fillers in the heat 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. When the content ratio of particulate fillers is 35% by mass or more, the thermal conductivity in the thickness direction of the heat conductive sheet increases, and heat can be transferred more favorably in the thickness direction of the heat conductive sheet. On the other hand, when the content ratio of particulate fillers is 65% by mass or less, the flexibility of the heat conductive sheet can be ensured while further improving the thickness accuracy of the heat conductive sheet.

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

[0038] <Additive> If necessary, known additives that can be used in the formation of the heat conductive sheet can be further blended into the heat conductive sheet of the present invention. The additives that can be blended into the heat conductive sheet are not particularly limited, and examples include plasticizers such as fatty acid esters such as sebacic acid ester; flame retardants such as red phosphorus-based flame retardants and phosphate ester-based flame retardants; toughness improvers such as urethane acrylate; moisture absorbents such as calcium oxide and magnesium oxide; adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides; wettability improvers such as nonionic surfactants and fluorine-based surfactants; ion trap agents such as inorganic ion exchangers; and the like. Note that the additives may be used alone or in combination of two or more.

[0039] When the heat conductive sheet further contains an additive, the blending amount of the additive can be, for example, 0.1 part by mass or more and 20 parts by mass or less, preferably 10 parts by mass or less, based on 100 parts by mass of the resin described above.

[0040] <Properties of the heat conductive sheet> The thermal conductive sheet needs to have a thermal conductivity in the thickness direction of 15 W / m·K or more, more preferably 20 W / m·K or more, and even more preferably 25 W / m·K or more. If the thermal conductivity of the thermal conductive sheet in the thickness direction 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 value of the thermal conductivity of the thermal conductive sheet in the thickness direction is not particularly limited, but for example, it is 45 W / m·K or less. Note that the thermal conductivity in the thickness direction of the thermal conductive sheet can be adjusted by changing the types and content ratios of the materials (resins, particulate fillers, etc.) used in the production of the thermal conductive sheet, as well as the production conditions of the thermal conductive sheet. For example, by changing the volume average particle diameter and / or the content ratio of the particulate filler in the thermal conductive sheet, the thermal conductivity in the thickness direction of the thermal conductive sheet can be increased. Also, for example, by manufacturing the thermal conductive sheet using the manufacturing method of the thermal conductive sheet of the present invention described later, the thermal conductivity in the thickness direction of the thermal conductive sheet can be increased.

[0041] In addition, the standard deviation of the thickness of the thermal conductive sheet needs to be 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 the thickness exceeds 3.5 μm, the thickness accuracy of the thermal conductive sheet is impaired. Therefore, it becomes difficult to bring the heat generating body and the heat radiating body into good contact through the thermal conductive sheet, and heat transfer from the heat generating body to the heat radiating body cannot be performed uniformly. The lower limit of the value 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. Incidentally, the standard deviation of the thickness of the heat conduction sheet can be adjusted by changing the types and content ratios of the materials (resins, particulate fillers, etc.) used in the production of the heat conduction sheet, as well as the production conditions of the heat conduction sheet. For example, by manufacturing a heat conduction sheet using the method for manufacturing a heat conduction sheet of the present invention described later, the standard deviation of the thickness of the heat conduction sheet can be reduced. More specifically, in the method for manufacturing a heat conduction sheet of the present invention, by changing the Asker C hardness of the block body, the pressing amount during slicing, the length of the first front surface of the blade used for slicing, etc., the standard deviation of the thickness of the heat conduction sheet can be reduced.

[0042] In addition, the heat conduction 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, still 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 heat conduction sheet can be ensured, and if it is 250 μm or less, heat can be transferred more favorably in the thickness direction of the heat conduction sheet.

[0043] Also, the heat conduction sheet can have a main surface area of, for example, 30 cm 2 or more, 50 cm 2 or more, 80 cm 2 or more, 100 cm 2 or more, and 1000 cm 2 or less.

[0044] And, for the thermal conductive sheet, the surface roughness Sa of both main surfaces needs to be 3.00 μm or less, preferably 2.80 μm or less, more preferably 2.60 μm or less, still more preferably 2.20 μm or less, and particularly preferably 2.00 μm or less. When the surface roughness Sa of both main surfaces exceeds 3.00 μm, the interfacial resistance increases, and when the thermal conductive sheet is used by sandwiching it between a heat generating body and a heat radiating body, it becomes difficult to make the heat generating body and the heat radiating body adhere well through the thermal conductive sheet, and heat transfer from the heat generating body to the heat radiating body cannot be performed uniformly. And, the lower limit of the value of the surface roughness Sa of the main surface of the thermal conductive sheet is not particularly limited, but is, for example, 1.0 μm or more. Incidentally, the surface roughness Sa of the main surface 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 production of the thermal conductive sheet, as well as the production conditions of the thermal conductive sheet. For example, by manufacturing the thermal conductive sheet using the manufacturing method of the thermal conductive sheet of the present invention described later, the surface roughness Sa of the thermal conductive sheet can be reduced. More specifically, in the manufacturing method of the thermal conductive sheet of the present invention, 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., the surface roughness Sa of the main surface of the thermal conductive sheet can be reduced.

[0045] In addition, for the thermal conductive sheet, 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 preferably 0.40 μm or less, more preferably 0.30 μm or less, still more preferably 0.20 μm or less, and particularly preferably 0.10 μm or less. If 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 0.40 μm or less, the handleability such as the ease of gripping with a robot arm can be improved. And, the lower limit of 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 not particularly limited, but is, for example, 0.01 μm or more.

[0046] (Method for manufacturing a heat conduction sheet) The heat conduction sheet of the present invention described above can be manufactured, for example, using the method for manufacturing a heat conduction sheet of the present invention. Here, the method for manufacturing a heat conduction sheet of the present invention supports a block body containing a resin and a particulate filler so as to be slidable by a sliding surface, and while supporting a blade having a tip protruding from the sliding surface, slides the block body while pressing it against the sliding surface, and slices the block body with the blade (slicing step), at least including. And according to the method for manufacturing a heat conduction sheet of the present invention, it is possible to obtain a heat conduction sheet having smooth both main surfaces, sufficient thickness accuracy, and capable of transferring heat well in the thickness direction.

[0047] <Slicing step> In the slicing step, as described above, the block body is supported so as to be slidable by the sliding surface, and while supporting a blade having a tip protruding from the sliding surface, the block body is slid while pressing it against the sliding surface, and the block body is sliced by a blade having a length of the first front surface of 0.8 mm or more and a surface roughness Sa of the first front surface of 1.00 μm or less, thereby cutting out a heat conduction sheet from the block body.

[0048] <<Block body>> The block body contains a resin and a particulate filler, and may further optionally contain an additive. Further, the block body preferably has an Asker C hardness of 90 or less. Furthermore, the block body preferably has a coefficient of kinetic friction of 2.5 or less.

[0049] [Resin, particulate filler, and additive] The suitable types, properties, and content ratios of the resin, particulate filler, and optionally contained additive contained in the block body can be the same as the suitable types, properties, and content ratios described above for the heat conduction 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, still more preferably 50 or more, and particularly preferably 60 or more. If the Asker C hardness is 90 or less, the blade can easily cut into the block body, so that the thickness accuracy of the heat conduction sheet obtained by slicing the block body can be more sufficiently ensured. On the other hand, if the Asker C hardness is 30 or more, a heat conduction sheet with even better thickness accuracy can be obtained by suppressing the blade edge deviation caused by the adhesiveness of the block body during slicing. Note that the Asker C hardness of the block body can be adjusted by changing the types and content ratios of the materials (resins, particulate fillers, etc.) used in the manufacture of the block body and the manufacturing method of the block body. In the present invention, the "Asker C hardness" is a value measured at a temperature of 23 °C using a hardness meter 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 kinetic friction] Here, the block body preferably has a coefficient of kinetic friction of 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 kinetic friction is 0.5 or less, the friction generated between the block body and the blade can be reduced, enabling smooth slicing. Generally, the coefficient of friction is 0.01 or more. Note that the coefficient of kinetic friction of the block body can be adjusted by changing the types and content ratios of the materials (resins, particulate fillers, etc.) used in the manufacture of the block body and the manufacturing method of the block body. In the present invention, the "coefficient of kinetic friction" can be measured in accordance with ASTM D1894, for example, using a surface property measuring machine TYPE: 14FW (manufactured by Shin-Tech Co., Ltd.).

[0052] <<Blade>> The shape of the blade used for slicing the above-described block body may be a "double-edge" in which both sides of the blade tip are cutting edges, or a "single-edge" in which only the front side (front surface side) of the blade is a cutting edge. However, from the viewpoint of sufficiently ensuring the thickness accuracy of the obtained heat conduction sheet, a "single-edge" is preferable. Further, the shape of the blade may be an "asymmetric blade" having an asymmetric cross-section with respect to the central axis passing through the tip of the blade tip, or a "symmetric blade" having a symmetric cross-section. Also, the number of blades constituting the blade is not particularly limited. For example, it may be composed of a "single blade" consisting of one blade, or a "double blade" consisting of two blades. FIG. 1 shows an example when slicing a block body (laminated body) using a cutter. As shown in FIG. 1, when the blade is composed of one blade, it is composed of one blade 10. When the blade is composed of two blades, it is composed of a front blade and a back blade. The heights of the tips of the front blade and the back blade protruding from the slit portion may be the same or different. That is, the tip portions of the front blade and the back blade may be aligned or may be displaced vertically. The material of the blade used for slicing the above-described block body is not particularly limited. However, from the viewpoint of sufficiently ensuring the smoothness of both main surfaces, it is preferably made of a metal such as ceramic, cemented carbide, high-speed tool steel (high-speed steel), or steel. Cemented carbide is more preferable due to the balance of the hardness of the blade itself and the ease of machining of the blade.

[0053] The blade used for slicing the above-described block body, for example, as shown in FIG. 1, includes a first front surface 10a in contact with the block body 20, a back surface 10c intersecting the first front surface 10a, a blade tip 10d formed by the intersection angle portion of the first front surface 10a and the back surface 10c, and a second front surface 10b extending from an edge 10e on the side opposite to the blade tip 10d side of the first front surface 10a and located on the back surface 10c side with respect to the first front surface 10a. That is, the blade used for slicing the block body includes 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 body, which is the object to be sliced, during slicing. The second front surface forms a predetermined angle with respect to the first front surface and is the surface provided to reduce the contact area with the block body, which is the object to be sliced.

[0054] Also, the length of the first front surface of the blade needs to be 0.8 mm or more as described above, 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 front surface of the blade is less than 0.8 mm, the thickness accuracy of the heat conduction sheet obtained by slicing the block body will be impaired. On the other hand, if the length of the first front surface is 10.0 mm or less, the smoothness of the surface of the heat conduction sheet obtained by slicing the block body can be ensured. Furthermore, the surface roughness Sa of the first front surface of the blade needs to be 1.00 μm or less as described above, preferably 0.80 μm or less, more preferably 0.40 μm or more, and 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 conduction sheet obtained by slicing the block body due to the friction between the block body and the front surface will be impaired. And 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] Also, the length of the second front surface of the blade is preferably 20.0 mm or more as described above, 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 more preferably 30.0 mm or less. When the length of the second front surface of the blade is 20.0 mm or more, the strength of the heat conduction sheet obtained by slicing the block body can be ensured. On the other hand, when the length of the second front surface is 50.0 mm or less, the smoothness of the surface of the heat conduction sheet obtained by slicing the block body 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 as described above. When 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 conduction sheet obtained by slicing the block body can be more reliably ensured. The lower limit of the surface roughness Sa of the second front surface of the blade is not particularly limited, but is, for example, 0.50 μm or more.

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

[0057] <<Slice>> [Slice speed] The speed at which the block body (laminated body) is sliced (in other words, the relative speed when the block body and the blade are brought into contact) needs to be 5 m / min or more. The speed at which the block body (laminated body) is sliced is not particularly limited, but is preferably 12 m / min or more, more preferably 30 m / min or more, and is preferably 120 m / min or less, for example. When the slicing speed of the block body (laminated body) is 12 m / min or more, productivity can be improved, and deterioration of the surface roughness due to the blade advancing while compressing the block body can be suppressed. Further, when the slicing speed of the block body (laminated body) is 120 m / min or less, an increase in the impact in the collision between the block body and the blade can be suppressed, and the block body (particularly the portion where the blade enters) can be sliced more uniformly.

[0058] Note that, as shown in FIG. 1, the slicing speed may be controlled by changing the speed at which the block body 20 enters (cuts into) the fixed blade 10; it may also be controlled by changing the speed at which the blade enters (cuts into) the fixed block body; or it may be controlled by changing the relative speed at which the blade and the block body enter (cut into) each other. Further, from the viewpoint of workability, it is desirable to control the slicing speed by machine control.

[0059] [Slicing direction] In the above slicing, it is preferable to slice the block body with a plane parallel to the lamination direction (in other words, so that the main surface of the heat conduction sheet obtained by slicing has a laminated cross section). For example, as shown in FIG. 1, if the block body 20 is sliced with a plane parallel to the lamination direction A of the primary sheet 20a, desired characteristics can be exhibited in the thickness direction of the heat conduction sheet obtained by slicing. Note that in the present invention, the "plane parallel to the lamination direction" also includes a plane having an inclination of about 30° or less with respect to the direction parallel to the lamination direction.

[0060] Here, as an example, the case of slicing using the cutter shown in FIG. 1 will be described. 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 in which the laminated side surface 20b and the sliding surface 30a of the cutter are parallel. That is, according to FIG. 1, the lamination direction A is also horizontal with respect to the horizontally installed cutter, 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 laminate 1 is arranged on the sliding surface 30a. Further, the tip of the blade 10 for slicing protrudes from the sliding surface 30a to an arbitrary extent. In the example of FIG. 1, the tip of the blade 10 having the blade angle θ1 protrudes from the sliding surface 30a at an angle α. Then, according to FIG. 1, while pressing the block body 20 supported by the sliding surface 30a from the laminated side surface 20c side to the sliding surface 30a side with an arbitrary pressure, it is slid in a direction parallel to the sliding surface 30a (sliding direction, slicing direction) at a predetermined slicing speed (sliding speed). Note that the speed at which it is slid at this time is as described above for the predetermined slicing speed. By sliding the block body 20 in this way, the top surface 20d enters the blade 10 at a predetermined sliding speed, and the block body 20 is sliced by a plane parallel to the lamination direction A.

[0061] The pressure when pressing the block body against the sliding surface is preferably 0.05 MPa or more, more preferably 0.10 MPa or more, particularly preferably 0.20 MPa or more, preferably 0.50 MPa or less, more preferably 0.40 MPa or less, and particularly preferably 0.30 MPa or less. When the pressure is 0.05 MPa or more, the thickness accuracy of the heat conduction sheet obtained by slicing the block body can be ensured. On the other hand, when the pressure is 0.50 MPa or less, it is possible to suppress the block body from being crushed. In addition, when the block body is a laminate obtained by laminating a primary sheet or the like in the laminating step described later, from the viewpoint of easily slicing the block body and sufficiently ensuring the thickness accuracy of the obtained heat conduction sheet, it is preferable to slice the block body, which is a laminate, while applying pressure in a direction perpendicular to the laminating direction.

[0062] Also, from the viewpoint of easily slicing the block body and sufficiently ensuring the thickness accuracy of the obtained heat conduction sheet, the temperature of the block body during slicing is preferably -20°C or higher and 80°C or lower, and more preferably -10°C or higher and 50°C or lower.

[0063] [Slicing Angle] Here, the slicing angle β (sometimes referred to as the "entry angle" or "penetration angle") formed between the laminating direction of the block body and the extending direction of the blade can be within the range of 0° to 90°. More specifically described according to FIG. 2, in FIG. 2(a), the laminated side surface 20f and the blade 10 are in contact (slicing angle β = 0°) such that the laminating direction A of the primary sheet in the block body 20 (laminate) and the extending direction E of the blade 10 are parallel. In FIGS. (b) to (d), the laminating direction A of the primary sheet in the block body 20 (laminate) and the extending direction E of the blade 10 form an angle, and the top surface 20d and the laminated side surface 20f enter the blade 10 and are in contact (slicing angles β = 15°, 45°, and 75°). And in FIG. 2(e), the top surface 20d and the blade 10 are in contact (slicing angle β = 90°) such that the laminating direction A of the primary sheet in the block body 20 (laminate) and the extending direction E of the blade 10 are perpendicular. From the perspective 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, still more preferably 5° or more, even more preferably 30° or more, and particularly preferably 40° or more. Similarly, from the above perspective, the slice angle β is preferably less than 90°, more preferably 89° or less, still more preferably 85° or less, even more preferably 60° or less, and particularly preferably 50° or less within the range of 0° to 90°. And it is even more preferable that the slice angle β is 45°.

[0064] Note that the slice angle may be controlled by changing the angle at which the block body enters (cuts into) the fixed blade, or by changing the angle at which the blade enters (cuts into) the fixed block body, or by changing the relative angle at which the blade and the block body approach each other and enter (cut into).

[0065] As described above, the method of slicing the block body is not particularly limited as long as, for example, as shown in FIG. 1, the block body 20 is slidably supported by the slide surface 30a and the block body 20 is slid while being pressed against the slide surface 30a in a state where the blade 10 with the tip protruding from the slide surface 30a is supported. 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 slide surface 20a, and a heat conduction sheet (not shown) is newly generated on the back surface 10c side of the blade 10. Here, the upper main surface of the newly generated heat conduction sheet in FIG. 1 is defined as surface A, and the lower main surface in FIG. 1 is defined as 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 within a predetermined range, and preferably, the surface roughness Sa of the second front surface 10b of the blade 10 is adjusted. Therefore, when the block body 20 is slid in the stacking direction A of the primary sheet 20a while pressing against the sliding surface 20a, the damage received (the damage received by the lower surface of the block body 20 in FIG. 1 (the B surface of the heat conduction sheet to be generated next) from the second front surface 10b of the blade 10 in the step 30b and the groove 40) can be reduced. In addition, from the viewpoint of suppressing the impairment of the smoothness of the lower surface of the block body 20 in FIG. 1 (the B surface of the heat conduction sheet to be generated next), in order to return the block body 20 from the position after sliding to the position before sliding (the position of the block body 20 in FIG. 1), it is preferable to move the block body 20 in a state where it does not contact the sliding surface 30a.

[0066] <Other processes> The other processes that the manufacturing method of the heat conduction sheet of the present invention may optionally include are not particularly limited. For example, in the manufacturing method of the heat conduction sheet of the present invention, before the slicing process described above, a step (lamination step) of laminating a plurality of primary sheets containing a resin and a particulate filler in the thickness direction, or folding or winding this primary sheet to obtain a block body can be carried out. Also, in the manufacturing method of the heat conduction sheet of the present invention, before the slicing process described above, a step (heating step) of heating the block body can be carried out. In the manufacturing method of the heat conduction sheet of the present invention, as long as the effects of the present invention are not significantly impaired, a step (pressing step) of pressing the heat conduction sheet obtained after the slicing process in the thickness direction may be carried out. However, from the viewpoint of suppressing the decrease in the thermal conductivity in the thickness direction of the obtained heat conduction sheet, the manufacturing method of the heat conduction sheet of the present invention preferably does not include the pressing step. Hereinafter, the lamination step and the heating step as other processes will be described in detail.

[0067] <<Lamination step>> As described above, in the lamination step, a plurality of primary sheets are laminated in the thickness direction, or the primary sheet is folded or wound to obtain a block body as a laminate.

[0068] [Primary sheet] The primary sheet contains a resin and a particulate filler, and may optionally further contain an additive.

[0069] - Resin, particulate filler, and additive - The preferred types, properties, and content ratios of the resin, particulate filler, and optionally contained additive in the primary sheet can be the same as the preferred types, properties, and content ratios described above for the block body and the heat conductive 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, still more preferably 1.5 MPa or more, preferably 3.0 MPa or less, more preferably 2.5 MPa or less, and still 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 sheet or the like increases. Therefore, it is possible to obtain a heat conductive sheet with even better thickness accuracy by suppressing the blade vibration when slicing the block body. 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 sheet or the like does not increase excessively. Therefore, slicing of the block body becomes easy, and sufficient thickness accuracy (particularly, thickness accuracy when reducing the thickness of the heat conductive sheet by reducing the slice width) of the obtained heat conductive sheet can be ensured. Note that the tensile strength of the primary sheet can be adjusted by changing the types and content ratios of the materials (resin, particulate filler, etc.) used in the production of the primary sheet and the production method of the primary sheet. For example, by increasing the content ratio of the resin in the primary sheet, the tensile strength of the primary sheet can be increased.

[0071] Further, 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. Note that the "thickness (average thickness)" of the primary sheet can be measured in the same manner as the "average thickness" of the heat conduction 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, a particulate filler, and optionally used additives by a known molding method such as press molding, rolling molding, or extrusion molding.

[0073] [Formation of a block body by lamination, etc.] The formation of a block body by laminating the primary sheet, etc. is not particularly limited and may be carried out using a laminating device or manually. Also, the formation of a block body by folding the heat conduction sheet is not particularly limited and can be carried out by folding the primary sheet with a folding machine to a certain width. Further, the formation of a block body by winding the primary sheet is not particularly limited and can be carried out by winding the primary sheet around an axis parallel to the short side direction or the long side direction of the primary sheet.

[0074] <<Heating step>> Here, for example, the block body obtained through the above-mentioned lamination step may be directly subjected to the slicing step, or may be subjected to the slicing step after further heating the block body. The heating temperature in the heating step can be, for example, 50°C or more and 170°C or less, and the heating time can be, for example, 1 minute or more and 8 hours or less. By going through the heating step, the adhesion in the lamination direction of the block body can be adjusted. For example, when the block body contains a thermoplastic resin, the adhesion in the lamination direction of the block body can be increased by carrying out the heating step.

Examples

[0075] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” representing amounts are based on mass unless otherwise specified. Then, in the examples and comparative examples, the particle size distribution, volume average particle diameter, content ratio (volume fraction) of the particulate filler, surface roughness Sa of the first front surface and the second front surface of the blade, Asker C hardness of the block body, and the average thickness, standard deviation of the 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, respectively.

[0076] <Volume average particle diameter> 1 g of the thermal conductive sheet was placed in methyl ethyl ketone as a solvent, and the resin component of the thermal conductive sheet was dissolved to obtain a suspension in which the particulate filler (expanded graphite) contained in the thermal conductive sheet was separated and dispersed. Next, the particle diameter of the particulate filler contained in the suspension was measured using a laser diffraction / scattering type particle size distribution measuring device (manufactured by Horiba, Ltd., model “LA960”). Then, a particle size distribution curve was created with the obtained particle diameter on the horizontal axis and the volume-converted particle frequency on the vertical axis. Then, in the particle size distribution curve, the particle diameter (D50) at which the cumulative volume calculated from the small-diameter side becomes 50% was determined, and this value was taken as the volume average particle diameter of the particulate filler. <Content ratio (volume fraction) of particulate filler> The content ratio (volume fraction) of the particulate filler in the primary sheet was calculated by taking the value obtained by dividing the weight of each material used at the time of forming the primary sheet by the specific gravity of the material as the volume of the material. The specific gravity of the resin was calculated as 1.77 for both the liquid resin and the solid resin, the specific gravity of the particulate filler (expanded graphite) was 2.25, and the specific gravity of the additive was 1.17. <Surface roughness Sa of the first front surface and the second front surface of the blade> The surface roughness Sa of the first front surface and the second front surface of the blade was measured using a three-dimensional shape measuring machine (manufactured by Keyence Corporation, product name “One Shot 3D Measurement Macroscope”). The measurement was performed at a magnification of 40 times, and the observation range was 5.7 mm × 7.6 mm. <Asker C hardness of the block body (laminated body)> The measurement of the Asker C hardness of the block body (laminated body) was carried out at a temperature of 25°C in accordance with the Asker C method of the Japan Rubber Association Standard (SRIS), using a hardness tester (manufactured by Kobunshi Keiki Co., Ltd., product name "ASKER CL-150LJ"). Specifically, the obtained block body (laminated body) was left standing in a thermostatic chamber maintained at a temperature of 25°C for 48 hours or more to obtain a test piece. Next, the hardness tester was installed so that the distance from the tip of the needle to the laminated surface was 2 cm, the damper was lowered, and the block body (laminated body) was made to collide with the damper. The Asker C hardness of the block body (laminated body) 60 seconds after the collision was measured twice using a hardness tester (manufactured by Kobunshi Keiki 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 Corporation, product name "Digital Indicator ID-C112XBS"), the thicknesses at five points, namely, the approximate center point and the four corners (squares) of the heat conduction sheet were measured, and the average value (μm) of the measured thicknesses was obtained. <Standard deviation of thickness> Using a film thickness gauge (Mitutoyo Corporation, product name "Digital Indicator ID-C112XBS"), the thicknesses at five points, namely, the approximate center point and the four corners (squares) of the heat conduction sheet were measured, and the standard deviation (μm) of the measured thicknesses was obtained. <Surface roughness Sa of the heat conduction sheet> The surface roughness Sa of the heat conduction sheet was measured using a three-dimensional shape measuring machine (manufactured by Keyence Corporation, product name "One Shot 3D Measurement Macroscope"). Here, a heat conduction sheet cut into a substantially square of any size of 1 cm square or more was used as a sample, the analysis range was 1 cm × 1 cm, and the three-dimensional shapes of the front and back surfaces of the sample were measured respectively. Then, the measurement results of the three-dimensional shape were further subjected to filter processing (2.5 mm) with software to remove the waviness component, and the surface roughness Sa (μm) was automatically calculated. In addition, the surface roughness Sa was measured for each of the A surface (the surface newly generated by the insertion of a new blade) and the B surface (the surface already generated by the insertion of the previous blade). <Thermal conductivity in the thickness direction> For the heat conduction sheet, the thermal diffusivity α (m in the thickness direction 2 / s), specific heat at constant pressure Cp (J / g·K), and specific gravity ρ (g / m 3 ) were measured by the following methods, respectively. [Thermal diffusivity α in the thickness direction] The thermal diffusivity of the thermal conductive sheet was measured using a thermal diffusivity / thermal conductivity measuring device (manufactured by AI Phases Co., Ltd., ai-Phase Mobile 1u) based on the provisions of ISO22007-3. [Specific heat at constant pressure Cp] Using a differential scanning calorimeter (manufactured by Rigaku, product name "DSC8230"), the specific heat at 25°C was measured under the condition of a temperature increase rate of 10°C / min. [Specific gravity ρ (density)] It was measured using an automatic specific gravity meter (manufactured by Toyo Seiki Co., Ltd., product name "DENSIMETER-H"). Then, each measured value was substituted into the following formula (I): λ = α × Cp × ρ ··· (I) to obtain the thermal conductivity λ (W / m·K) in the thickness direction of the thermal conductive sheet at 25°C. [Thermal resistance value] The thermal resistance value of the thermal conductive sheet was measured using a thermal resistance tester (manufactured by Hitachi Technology and Services Co., Ltd., product name "Resin Material Thermal Resistance Measuring Device"). Here, a thermal conductive sheet cut out into a substantially square of 1 cm square was used as a sample, and the thermal resistance values (°C / W) when pressures of 0.1 MPa and 0.9 MPa were applied at a sample temperature of 50°C were measured. The smaller the thermal resistance value, the better the thermal conductivity of the thermal conductive sheet, for example, indicating excellent heat dissipation characteristics when interposed between a heating element and a heat sink.

[0077] (Example 1) [Formation of the primary sheet] 70 parts of a thermoplastic fluororesin that is liquid at normal temperature and pressure (manufactured by Daikin Industries, Ltd., product name "Dai-el G-101"), 30 parts of a thermoplastic fluororesin that is solid at normal temperature and pressure (manufactured by 3M Japan Ltd., product name "Dyneon FC2211"), and 90 parts of expanded graphite as a particulate filler (manufactured by Ito Graphite Industries, Ltd., product name "EC300", volume average particle diameter: 50 μm) were stirred and mixed at a temperature of 150 °C for 20 minutes using a pressure kneader (manufactured by Nippon Spindle). Next, the obtained mixture was put into 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 polyethylene terephthalate (PET) films (protective films) with a thickness of 50 μm that had been subjected to sandblasting treatment, and rolled and formed 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 into a size of 150 mm in length × 150 mm in width × 0.8 mm in thickness, 100 sheets were laminated in the thickness direction of the primary sheet, and further pressed in the lamination direction at a temperature of 120 °C and a pressure of 0.1 MPa for 3 minutes to obtain a block body (laminated body) with a height of approximately 80 mm. Then, the Asker C hardness of the obtained block body was measured. The results are shown in Table 1. <Slicing process> Thereafter, while pressing the side surface (the surface along the lamination direction) of the block body (laminated body) against the sliding surface with a pressure of 0.3 MPa, a woodworking slicer (manufactured by Marunaka Tekko Co., Ltd., product name "Super Finishing Plane Super Meka S") was used to slice the block body (laminated body) in the lamination direction (in other words, in the direction that coincides with the normal line of the main surface of the laminated primary sheets) to obtain a heat conduction sheet with a size of 150 mm in length × 150 mm in width × 0.10 mm in thickness. The above slicing was performed by sliding the block body (laminated body) on the sliding surface under the condition of a sliding speed of 1000 mm / sec. A single-edge blade A with the following properties was used as the slicing blade of the woodworking slicer. The temperature of the block body was set to room temperature. <<Properties of single-edge blade A>> Cutting edge angle A (see Fig. 1: angle θ1 formed by the first front surface 10a and the back surface 10c): 40° Cutting edge angle B (see Fig. 1: angle θ2 formed by the second front surface 10b and the back surface 10c): 20° Maximum thickness of the cutting edge: 9 mm Material: Cemented carbide (tungsten carbide) Rockwell hardness: 90 Silicon processing of the cutting edge surface: None Radius of curvature R of the tip: 10 μm Length of the first front surface: 1.0 mm Surface roughness Sa of the first front surface: 0.43 μm Length of the second front surface: 25.0 mm Surface roughness Sa of the second front surface: 0.61 μm Then, the average thickness, standard deviation of the thickness, surface roughness Sa, and thermal conductivity in the thickness direction of the obtained thermal conductive sheet were measured. The results are shown in Table 1.

[0078] (Example 2) In Example 1, except that single-edge B with the following properties was used instead of single-edge A, a primary sheet, a block body, and a thermal conductive sheet were produced in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1. <<Properties of single-edge B>> Cutting edge angle A (see Fig. 1: angle θ1 formed by the first front surface 10a and the back surface 10c): 40° Cutting edge angle B (see Fig. 1: angle θ2 formed by the second front surface 10b and the back surface 10c): 20° Maximum thickness of the cutting edge: 9 mm Material: Cemented carbide (tungsten carbide) Rockwell hardness: 90 Silicon processing of the cutting edge surface: None Radius of curvature R of the tip: 10 μm Length of the first front surface: 3.0 mm Surface roughness Sa of the first front surface: 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 conduction sheet were produced and various evaluations were performed in the same manner as in Example 1, except that a single-edge C with the following properties was used instead of the single-edge A. The results are shown in Table 1. <<Properties of Single-Edge C>> Cutting edge angle A (see Fig. 1: angle θ1 formed by the first front surface 10a and the back surface 10c): 40° Cutting edge angle B (see Fig. 1: angle θ2 formed by the second front surface 10b and the back surface 10c): 20° Maximum thickness of the cutting edge: 9 mm Material: High-speed tool steel (HSS) Rockwell hardness: 82 Silicon processing of the cutting edge surface: None Radius of curvature R of the tip: 10 μm Length of the first front surface: 1.0 mm Surface roughness Sa of the first front surface: 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 conduction sheet were produced and various evaluations were performed in the same manner as in Example 1, except that a single-edge D with the following properties was used instead of the single-edge A. The results are shown in Table 1. <<Properties of Single-Edge D>> Cutting edge angle A (see Fig. 1: angle θ1 formed by the first front surface 10a and the back surface 10c): 40° Cutting edge angle B (see Fig. 1: angle θ2 formed by the second front surface 10b and the back surface 10c): 20° Maximum thickness of the cutting edge: 9 mm Material: High-speed tool steel (HSS) Rockwell hardness: 82 Silicon processing of the cutting edge surface: None Radius of curvature R of the tip: 10 μm Length of the first front surface: 1.0 mm Surface roughness Sa of the first front surface: 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 slicing the block body (laminated body) in the lamination direction using a wood slicer while pressing the side surface of the block body (laminated body) against the sliding surface with a pressure of 0.3 MPa, without pressing the side surface of the block body (laminated body) against the sliding surface (i.e., only with the self-weight of the block body (laminated body)), a primary sheet, a block body, and a heat conduction sheet were produced in the same manner as in Example 1, except that slicing was performed in the lamination direction of the block body (laminated body) using a wood slicer, and various evaluations were conducted. The results are shown in Table 1.

[0082] (Comparative Example 3) In Example 3, when forming the primary sheet, instead of using 90 parts of expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., product name "EC300", volume average particle diameter: 50 μm) as the particulate filler, 50 parts of expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., product name "EC100", volume average particle diameter: 200 μm) was used as the particulate filler. A primary sheet, a block body, and a heat conduction sheet were produced in the same manner as in Example 3, except for this, and various evaluations were conducted. 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 a thermoplastic fluororesin that is liquid at normal temperature and pressure (manufactured by Daikin Industries, Ltd., product name "Dail G-101"), 30 parts of a thermoplastic fluororesin that is solid at normal temperature and pressure (manufactured by 3M Japan Ltd., product name "Dyneon FC2211"), and 90 parts of expanded graphite as a particulate filler (manufactured by Ito Graphite Industry Co., Ltd., product name "EC300", volume average particle diameter: 50 μm) to obtain a heat conduction sheet with a length of 150 mm × width of 150 mm × thickness of 0.10 mm, 45 parts of a thermoplastic fluororesin that is liquid at normal temperature and pressure (manufactured by Daikin Industries, Ltd., product name "Dail G-101"), 40 parts of a thermoplastic fluororesin that is solid at normal temperature and pressure (manufactured by 3M Japan Ltd., product name "Dyneon FC2211"), 85 parts of expanded graphite as a particulate filler (manufactured by Ito Graphite Industry Co., Ltd., product name "EC100", volume average particle diameter: 200 μm), and 5 parts by mass of sebacic acid ester as a plasticizer (manufactured by Daihachi Chemical Industry Co., Ltd., trade name "DOS") were used to obtain a secondary sheet (sliced block body) with a length of 150 mm × width of 150 mm × thickness of 0.50 mm (500 μm). Then, using a precision hot press machine (manufactured by Shin Dong Industries 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 for the secondary sheet (post-treatment process) to obtain a heat conduction sheet with a length of 150 mm × width of 150 mm × thickness of 0.125 mm (125 μm). In the same manner as in Example 1, a primary sheet, a block body, and a heat conduction sheet were produced and various evaluations were performed. The results are shown in Table 1.

[0084]

Table 1

[0085] From Table 1, it can be seen that the heat conduction sheets of Examples 1 to 3 have smooth both main surfaces. Also, it can be seen that the heat conduction sheets of Examples 1 to 3 have a small thermal conductivity in the thickness direction and can transfer heat well in the thickness direction. Furthermore, since the values of the standard deviation of the thickness of the heat conduction sheets of Examples 1 to 3 are small, it can be seen that they are excellent in thickness accuracy.

Industrial Applicability

[0086] According to the present invention, it is possible to provide a heat conductive sheet having smooth both main surfaces, sufficient thickness accuracy, and capable of efficiently transferring heat in the thickness direction, and a method for manufacturing the heat conductive sheet.

Explanation of Signs

[0087] 10 blades 10a First front surface 10b Second front surface 10c Back surface 10d Blade tip 10e Edge 20 Block body 20a Primary sheet 20b Laminated side surface 20c Laminated side surface 20d Top surface 20e Bottom surface 20f Laminated side surface 30 Base 30a Slide surface 30b Step 40 Groove A Laminating direction of the primary sheet 20a E Extending direction of the blade θ1 Angle formed by the first front surface 10a and the back surface 10c (blade angle A) θ2 Angle formed by the second front surface 10b and the back surface 10c (blade angle B) α Angle β Slicing angle

Claims

1. Contains a resin and a particulate filler, The thermal conductivity in the thickness direction is 15 W / m K or more, 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 thermally conductive sheet, wherein the absolute value of the difference between the surface roughness Sa of one principal surface and the surface roughness Sa of the other principal surface is 0.09 μm or more and 0.40 μm or less.

2. The thermal conductive sheet according to claim 1 , having an average thickness of 250 μm or less.

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

4. The thermal conductive sheet according to claim 1 , wherein the particulate filler has a volume average particle diameter of 30 μm or more and 150 μm or less.

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