JP7434712B2 - Thermal conductive sheet and its manufacturing method - Google Patents

Description

The present invention relates to a thermally conductive sheet and a method for manufacturing a thermally conductive sheet.

In recent years, the amount of heat generated by electronic components such as plasma display panels (PDP) and integrated circuit (IC) chips has increased as their performance has improved. As a result, in electronic devices using electronic components, it is necessary to take measures against functional failures caused by temperature rises in the electronic components.

As a countermeasure against functional failure due to temperature rise in electronic components, a method is generally adopted to promote heat dissipation by attaching a heat dissipation body such as a metal heat sink, heat sink, or heat dissipation fin to the heat generating body of the electronic component. ing. When using a heat radiator, a sheet-like member having thermal conductivity (thermal conductive sheet) is used to efficiently transfer heat from the heat radiator to the heat radiator. For example, by sandwiching a heat conductive sheet containing resin and particulate filler between a heat generating element and a heat radiating element, and bringing the heat generating element and the heat radiating element into close contact via this heat conducting sheet, the heat generating element can be transferred from the heat radiating element to the heat radiating element. and conduct heat transfer. Conventionally, attempts have been made to improve various properties of thermally conductive sheets (see, for example, Patent Documents 1 and 2).

In Patent Document 1, a resin molded body is slidably supported by a slide surface, and one blade whose tip protrudes from the slide surface is supported from the opposite side of the resin molded body across the slide surface. A method is disclosed in which a heat conductive sheet is obtained by sliding the molded body while pressing it against a sliding surface and slicing the resin molded body with only one blade. According to Patent Document 1, the thickness accuracy of the thermally conductive sheet obtained by the method described above can be improved.

In Patent Document 2, a laminate obtained by laminating primary sheets 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 laminate obtained by slicing is A method for obtaining a thermally conductive sheet by pressurizing a sheet is disclosed. According to Patent Document 2, the thermally conductive sheet obtained by the method described above can exhibit excellent thermal conductivity even when used at a relatively low clamping pressure.

Patent No. 5621306 specification JP2018-67695A

Here, in recent years, both main surfaces of the heat conductive sheet are made smooth in order to ensure good contact between the heat generating element and the heat radiating element via the heat conductive sheet and to ensure uniform heat transfer from the heat generating element to the heat radiating element. At the same time, it is required to improve the thickness accuracy of the heat conductive sheet.
However, with the conventional method described above, it is difficult to produce a thermally conductive sheet that has both smooth principal surfaces and a uniform thickness while also making the thermally conductive sheet exhibit excellent thermal conductivity in the thickness direction. there were.

Accordingly, the present invention provides a thermally conductive sheet that has both smooth principal surfaces and is capable of good heat transfer in the thickness direction while having sufficient thickness accuracy, and a method for manufacturing the thermally conductive sheet. The purpose is to

The present inventor conducted extensive studies in order to achieve the above object. First, the present inventors attempted to improve the thickness accuracy of a thermally conductive sheet by applying pressure during slicing using a plane described in Patent Document 1 mentioned above. However, according to studies conducted by the present inventors, it has become clear that if the sheet is pressurized during slicing using a plane, it is difficult to ensure sufficient smoothness on both principal surfaces. On top of that, the present inventor has determined that in a thermally conductive sheet containing a resin and a particulate filler, 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 both principal surfaces are If the surface roughness Sa is set to a predetermined value or less, a thermally conductive sheet can be obtained in which both principal surfaces are smooth, which has sufficient thickness accuracy and which can conduct heat well in the thickness direction. They discovered this and completed the present invention.

That is, the present invention aims to advantageously solve the above problems, and the thermally conductive sheet of the present invention contains a resin and a particulate filler, and has a thermal conductivity in the thickness direction of 15 W/m·K. The standard deviation of the thickness is 3.5 μm or less, and the surface roughness Sa of both main surfaces is 3.00 μm or less. In this way, it contains a resin and a particulate filler, has a thermal conductivity in the thickness direction equal to or higher than the above value, has a standard deviation of thickness equal to or lower than the above value, and has a surface roughness Sa of both main surfaces. A heat conductive sheet in which the thickness is less than or equal to the above value has both principal surfaces smooth, has sufficient thickness accuracy, and can conduct 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.
In addition, in the present invention, the "standard deviation of thickness" is a value obtained by measuring the thickness at five arbitrary points of a thermally conductive sheet, and is obtained from these measured values. It can be calculated using a method.
Furthermore, in the present invention, the "surface roughness Sa of both principal 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, "both principal surfaces" refers to the surface having the largest area in the thermally conductive sheet and the surface opposite to the surface.

Here, it is preferable that the thermally conductive sheet of the present invention has an average thickness of 250 μm or less. If the average thickness of the heat conductive sheet is less than or equal to the above value, heat can be transferred even more favorably in the thickness direction of the heat conductive sheet.
In the present invention, the "average thickness" is a value obtained by measuring the thickness at five arbitrary points of the thermally conductive sheet, and is obtained from these measured values, for example, by the method described in the Examples of this specification. It can be calculated using

Further, in the thermally 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 thermally conductive sheet is within the above range, the thermal conductivity in the thickness direction of the thermally conductive sheet increases, and it is possible to conduct heat even better in the thickness direction of the thermally conductive sheet. At the same time, it is possible to further improve the thickness accuracy while ensuring the flexibility of the heat conductive sheet.

Moreover, in the thermally conductive sheet of the present invention, it is preferable that the volume average particle diameter of the particulate filler is 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 better in the thickness direction of the heat conductive sheet, and the main surface smoothness and thickness accuracy of the heat conductive sheet can be further improved. can be done.
In the present invention, the "volume average particle diameter" can be measured in accordance with JIS Z8825, and in the particle size distribution (volume basis) measured by laser diffraction method, the cumulative volume calculated from the small diameter side is 50 It represents the particle size in %.

Furthermore, in the thermally conductive sheet of the present invention, it is preferable that 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. If the absolute value of the difference between the surface roughness Sa of one main surface of the thermally conductive sheet and the surface roughness Sa of the other main surface is less than or equal to the above value, handling properties such as ease of grasping with a robot arm will be improved. can be done.

Further, the present invention aims to advantageously solve the above-mentioned problems, and the method for manufacturing a thermally conductive sheet of the present invention includes supporting a block body containing a resin and a particulate filler so as to be slidable by a sliding surface. and slicing the block body with the blade by sliding the block body while pressing it against the slide face while supporting a blade whose tip portion protrudes from the slide face, the blade is a cutting edge consisting of a first front surface that contacts the block body, a back surface that intersects with the first front surface, and an intersection corner of the first front surface and the back surface; , a second front surface extending from an edge of the first front surface opposite to the cutting edge side and located closer to the back surface than the first front surface; The first front surface has a length of 0.8 mm or more, and the first front surface has a surface roughness Sa of 1.00 μm or less. In this way, if a block body containing resin and particulate filler is sliced in a predetermined manner using a blade whose first front surface length and surface roughness Sa are within the above range, both main surfaces can be sliced. It is possible to obtain a heat conductive sheet that has a smooth surface, has sufficient thickness accuracy, and is capable of good heat transfer in the thickness direction.
Further, 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 body, "the surface on the side where the cutting part in contact with the block body is provided" is referred to as the "front surface", and the side from which the thermally conductive sheet is discharged from the block body is referred to as the "front surface". The surface (the surface opposite to the front surface where the cutting part that first contacts the block body is provided) is defined as the "back surface."

Here, in the method for manufacturing a thermally conductive sheet of 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 equal to or less than the above value, the smoothness of the surface of the heat conductive 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.

In the method for manufacturing a thermally conductive sheet of the present invention, prior to the slicing step, a plurality of primary sheets containing a resin and a particulate filler are laminated in the thickness direction, or the primary sheets are folded. It can further include the step of obtaining the block body by tatami or rolling.
In addition, in this specification, "lamination,""folding," or "winding" may be collectively abbreviated as "lamination, etc."

According to the present invention, there is provided a thermally conductive sheet that has both smooth main surfaces and can conduct heat well in the thickness direction while having sufficient thickness accuracy, and a method for manufacturing the thermally conductive sheet. be able to.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows the process of manufacturing a thermally conductive sheet using an example of the manufacturing method of a thermally conductive sheet according to this invention. FIG. 3 is a plan view showing how a block body (laminated body) is sliced at a slide angle β.

Embodiments of the present invention will be described in detail below.
The thermally conductive sheet of the present invention can be used, for example, by being sandwiched between a heat generating element and a heat radiating element when the heat radiating element is attached to the heating element. That is, the thermally conductive sheet of the present invention can constitute a heat radiating device together with a heat radiating body such as a heat sink, a heat radiating plate, and a heat radiating fin.
The thermally conductive sheet of the present invention can be manufactured, for example, according to the method for manufacturing a thermally conductive sheet of the present invention.

(thermal conductive sheet)
The thermally conductive sheet of the present invention contains a resin and a particulate filler, and may optionally further contain an additive. Furthermore, the thermally 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 principal surfaces of 3. .00 μm or less. The thermally 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 principal surfaces. Since it is 3.00 μm or less, both main surfaces are smooth, and heat can be transferred well in the thickness direction while having sufficient thickness accuracy.

<Resin>
The resin contained in the thermally conductive sheet is not particularly limited, and any resin can be used. For example, as the resin, both liquid resin and solid resin can be used. In addition, one type of resin may be used alone, or two or more types may be used in combination. For example, the thermally 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 thermally conductive sheet and better heat transfer in the thickness direction, the thermally conductive sheet is , it is preferable to include both a liquid resin and a solid resin.

<<Liquid resin>>
The liquid resin is not particularly limited as long as it is liquid at room temperature and pressure, and for example, a thermoplastic resin that is liquid at room 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).

Examples of liquid resins include fluororesins, silicone resins, acrylic resins, and epoxy resins. These may be used alone or in combination of two or more. Among these, as the liquid resin, silicone resins and fluororesins are preferred, and fluororesins are more preferred. If at least one of a silicone resin and a fluororesin is used as the liquid resin, the flame retardance of the thermally conductive sheet can be improved. Moreover, if a fluororesin is used as the liquid resin, the heat resistance, oil resistance, and chemical resistance of the resulting thermally conductive sheet can be improved.

<<Solid resin>>
The solid resin is not particularly limited as long as it is not liquid at room temperature and pressure, and for example, a thermoplastic resin that is solid at room temperature and pressure, and a thermosetting resin that is solid at room temperature and pressure can be used.

[Thermoplastic resin that is solid at room temperature and pressure]
Examples of thermoplastic resins that are solid at room temperature and normal pressure include poly(2-ethylhexyl acrylate), a copolymer of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its ester, and polyacrylic acid or its ester. Acrylic resins; silicone resins; fluororesins; polyethylene; polypropylene; ethylene-propylene copolymers; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymers; polyvinyl alcohol; polyacetals ; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; styrene-acrylonitrile copolymer; acrylonitrile-butadiene copolymer (nitrile rubber); acrylonitrile-butadiene-styrene copolymer (ABS resin); styrene- Butadiene block copolymer or its hydrogenated product; Styrene-isoprene block copolymer or its hydrogenated product; Polyphenylene ether; Modified polyphenylene ether; Aliphatic polyamides; Aromatic polyamides; Polyamideimide; Polycarbonate; Polyphenylene sulfide; Polysulfone ; polyether sulfone; polyether nitrile; polyether ketone; polyketone; polyurethane; liquid crystal polymer; ionomer; and the like. These may be used alone or in combination of two or more.
Note that in the present invention, rubber is included in the "resin".

[Thermosetting resin that is solid at room temperature and pressure]
Examples of thermosetting resins that are solid at normal temperature and normal pressure include natural rubber; butadiene rubber; isoprene rubber; nitrile rubber; hydrogenated nitrile rubber; chloroprene rubber; ethylene propylene rubber; chlorinated polyethylene; chlorosulfonated polyethylene; butyl rubber; Halogenated butyl rubber; polyisobutylene rubber; epoxy resin; polyimide resin; bismaleimide resin; benzocyclobutene resin; phenolic resin; unsaturated polyester; diallyl phthalate resin; polyimide silicone resin; polyurethane; thermosetting polyphenylene ether; thermosetting modification Examples include polyphenylene ether; etc. These may be used alone or in combination of two or more.

<<Resin content ratio>>
The content ratio of the resin in the thermally 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, and 95% by mass or more. % or less, more preferably 85% by mass or less, even more preferably 75% by mass or less. When the resin content is 35% by mass or more, the thickness accuracy of the heat conductive sheet can be further improved while ensuring the flexibility of the heat conductive sheet. On the other hand, if the resin content is 95% by mass or less, heat can be transferred even more favorably in the thickness direction of the heat conductive sheet.

<<Content ratio of liquid resin>>
Further, 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 is preferably 30% by mass or more, and 40% by mass or more. It is more preferably 50% by mass or more, even more preferably 60% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, It is more preferably 85% by mass or less, 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 thickness accuracy can be further improved while ensuring the flexibility of the heat conductive sheet. On the other hand, if the content ratio of liquid resin in the resin is 95% by mass or less, it will give suitable strength to the primary sheet, making it easier to slice the laminate and further improving the thickness accuracy of the resulting thermally conductive sheet. can be improved.

<Particulate filler>
The particulate filler contained in the thermally conductive sheet is not particularly limited as long as it can impart thermal conductivity to the thermally conductive sheet. As such a particulate filler, a particulate carbon material having high thermal conductivity can be suitably used. In addition, one type of particulate filler may be used alone, or two or more types may be used in combination.

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

Among those mentioned 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 increases, and heat can be transferred even more favorably in the thickness direction of the heat conductive sheet. Here, the expanded graphite can be obtained by, for example, expanding graphite obtained by chemically treating graphite such as flaky graphite with sulfuric acid or the like, heat-treating it to expand it, and then refining the graphite. Examples of the expanded graphite include EC1500, EC1000, EC500, EC300, EC100, and EC50 (all trade names) manufactured by Ito Graphite Industries.

<<Properties of particulate filler>>
The volume average particle diameter of the particulate filler is preferably 30 μm or more, more preferably 40 μm or more, preferably 150 μm or less, more preferably 100 μm or less, and 80 μm or less. is more preferable, 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 heat conductive sheet, but the heat conduction in the thickness direction of the heat conductive sheet is rate increases. As a result, heat can be transferred even more favorably 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 main surface smoothness and thickness accuracy of the thermally conductive sheet can be further improved.

Further, the aspect ratio (major axis/breadth axis) of the particulate filler is preferably greater than 1 and less than or equal to 10, more preferably greater than 1 and less than or equal to 5. If the aspect ratio of the particulate filler is more than 1 and less than or equal to 10, it is presumed that the particulate filler is easily oriented in the thickness direction in the thermally conductive sheet, but the thermal conductivity in the thickness direction of the thermally conductive sheet is increases. As a result, heat can be transferred even more favorably in the thickness direction of the heat conductive sheet.
In the present invention, "aspect ratio" refers to the maximum diameter (lengthwise axis) and the direction perpendicular to the maximum diameter of any 50 particulate fillers observed by observing the particulate filler with a SEM (scanning electron microscope). It can be determined by measuring the particle diameter (breadth axis) of and calculating the average value of the ratio of the long axis to the short axis (long axis/breadth axis).

<<Content ratio of particulate filler>>
The content ratio of the particulate filler in the thermally 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, It is 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 the particulate filler is 30% by volume or more, the thermal conductivity in the thickness direction of the thermally conductive sheet increases, and it is possible to conduct heat even more favorably in the thickness direction of the thermally conductive sheet. On the other hand, if the content of the particulate filler is 42% by volume or less, the thickness accuracy can be further improved while ensuring the flexibility of the thermally conductive sheet.

The content of the particulate filler in the thermally conductive sheet is not particularly limited, but is preferably 35% by mass or more, more preferably 40% by mass or more, particularly 45% by mass or more. It is preferably 65% by mass or less, more preferably 55% by mass or less, particularly preferably 50% by mass or less. If the content of the particulate filler is 35% by mass or more, the thermal conductivity in the thickness direction of the thermally conductive sheet increases, and it is possible to conduct heat even more favorably in the thickness direction of the thermally conductive sheet. On the other hand, if the content of the particulate filler is 65% by mass or less, the thickness accuracy of the heat conductive sheet can be further improved while ensuring the flexibility of the heat conductive sheet.

In addition, the content of the particulate filler in the thermally conductive sheet is not particularly limited, but per 100 parts by mass of resin, it is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, and 80 parts by mass. It is particularly preferably at least 120 parts by mass, more preferably at most 110 parts by mass, and particularly preferably at most 100 parts by mass. 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 thermally conductive sheet increases, and it is possible to conduct heat even better in the thickness direction of the thermally conductive sheet. can. 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, the thickness accuracy of the heat conductive sheet can be further improved while ensuring the flexibility of the heat conductive sheet.

<Additives>
The thermally conductive sheet of the present invention may further contain known additives that can be used for forming the thermally conductive sheet, if necessary. Additives that can be added to the thermally conductive sheet include, without particular limitation, plasticizers such as fatty acid esters such as sebacic acid ester; flame retardants such as red phosphorus flame retardants and phosphate ester flame retardants. ; Toughness improvers such as urethane acrylate; Moisture absorbers such as calcium oxide and magnesium oxide; Adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides; Nonionic surfactants, fluorine surfactants wettability improvers such as; ion trapping agents such as inorganic ion exchangers; and the like. In addition, one type of additive may be used alone, or two or more types may be used in combination.

When the thermally conductive sheet further contains an additive, the amount of the additive can be, for example, 0.1 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the above-mentioned resin, and 10 parts by mass. It is preferable to make it less than 1 part.

<Properties of thermally conductive sheet>
The thermal conductivity of the thermally conductive sheet in the thickness direction must be 15 W/m・K or more, more preferably 20 W/m・K or more, and preferably 25 W/m・K or more. More preferred. If the thermal conductivity in the thickness direction of the heat conductive sheet is less than 15 W/m·K, heat cannot be transferred well in the thickness direction of the heat conductive sheet. The upper limit of the thermal conductivity value in the thickness direction of the thermally conductive sheet is not particularly limited, but is, for example, 45 W/m·K or less.
The thermal conductivity in the thickness direction of the thermally conductive sheet can be adjusted by changing the type and content ratio of the materials (resin, particulate filler, etc.) used to manufacture the thermally conductive sheet, as well as the manufacturing conditions of the thermally conductive sheet. can do. For example, by changing the volume average particle diameter and/or content ratio of the particulate filler in the heat conductive sheet, the thermal conductivity in the thickness direction of the heat conductive sheet can be increased. Further, for example, by manufacturing a thermally conductive sheet using the method for manufacturing a thermally conductive sheet of the present invention described later, the thermal conductivity in the thickness direction of the thermally conductive sheet can be increased.

In addition, the standard deviation of the thickness of the thermally conductive sheet is required to be 3.5 μm or less, preferably 3.0 μm or less, more preferably 2.7 μm or less, and 2.5 μm or less. It is particularly preferable that If the standard deviation of the thickness is more than 3.5 μm, the thickness accuracy of the thermally conductive sheet will be impaired. Therefore, it is difficult to bring the heating element and the heat radiating element into good contact with each other through the heat conductive sheet, and it is also impossible to uniformly transfer heat from the heating element to the heat radiating element. The lower limit of the standard deviation of the thickness of the heat conductive sheet is not particularly limited, but is, for example, 1 μm or more.
The standard deviation of the thickness of the thermally conductive sheet can be adjusted by changing the type and content ratio of the materials (resin, particulate filler, etc.) used to manufacture the thermally conductive sheet, as well as the manufacturing conditions of the thermally conductive sheet. Can be done. For example, by manufacturing a thermally conductive sheet using the method for manufacturing a thermally conductive sheet of the present invention, which will be described later, the standard deviation of the thickness of the thermally conductive sheet can be reduced. More specifically, in the method for manufacturing a thermally conductive sheet of the present invention, the Asker C hardness of the block, the amount of pressure applied during slicing, the length of the first front surface of the blade used for slicing, etc. may be changed. Therefore, the standard deviation of the thickness of the heat conductive sheet can be reduced.

In addition, the average thickness of the thermally conductive sheet is preferably 70 μm or more, more preferably 80 μm or more, preferably 250 μm or less, more preferably 200 μm or less, and 160 μm or less. It is even more preferable that the thickness be 120 μm or less. If the average thickness is 70 μm or more, the strength of the heat conductive sheet can be ensured, and if it is 250 μm or less, heat can be transferred even better in the thickness direction of the heat conductive sheet.

Further, the area of the main surface of the thermally conductive sheet can be, for example, 30 cm ² or more, 50 cm ² or more, 80 cm ² or more, or 100 cm ² or more. , 1000 cm ² or less.

The thermally conductive sheet needs to have a surface roughness Sa of both main surfaces of 3.00 μm or less, preferably 2.80 μm or less, more preferably 2.60 μm or less, It is more preferably 2.20 μm or less, particularly preferably 2.00 μm or less. If the surface roughness Sa of both main surfaces is more than 3.00 μm, the interfacial resistance will be high, and when the heat conductive sheet is sandwiched between the heat generating element and the heat radiating element, the heat generating element This makes it difficult to bring the heat radiator into good contact with the heat radiator, making it impossible to uniformly transfer heat from the heat generator to the heat radiator. The lower limit of the surface roughness Sa of the main surface of the thermally conductive sheet is, for example, 1.0 μm or more, although it is not particularly limited.
In addition, the surface roughness Sa of the main surface of the thickness of the thermally conductive sheet is determined by changing the type and content ratio of the materials (resin, particulate filler, etc.) used for manufacturing the thermally conductive sheet, and the manufacturing conditions of the thermally conductive sheet. It can be adjusted by For example, the surface roughness Sa of the thermally conductive sheet can be reduced by manufacturing the thermally conductive sheet using the method for manufacturing a thermally conductive sheet of the present invention, which will be described later. More specifically, in the method for manufacturing a thermally conductive sheet of the present invention, 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, and the length of the first front surface of the blade used for slicing; By changing the length of the second front surface of the blade used, 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 thermally conductive sheet is reduced. be able to.

In addition, in the thermally 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, and preferably 0.30 μm or less. It is more preferable that it is, it is even more preferable that it is 0.20 μm or less, and it is particularly preferable that it is 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, it is possible to improve handling properties such as ease of grasping with a robot arm. can. 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.

(Method for manufacturing thermally conductive sheet)
The thermally conductive sheet of the present invention described above can be manufactured using, for example, the method for manufacturing a thermally conductive sheet of the present invention. Here, in the method for manufacturing a thermally conductive sheet of the present invention, a block body containing a resin and a particulate filler is slidably supported by a sliding surface, and a blade whose tip portion protrudes from the sliding surface is supported. , at least the step of sliding the block body while pressing it against the slide surface and slicing the block body with the blade (slicing step).
According to the method for manufacturing a thermally conductive sheet of the present invention, it is possible to obtain a thermally conductive sheet that has both smooth principal surfaces, has sufficient thickness accuracy, and can conduct heat well in the thickness direction. Can be done.

<Slicing process>
In the slicing process, as described above, the block body is slidably supported by the slide surface, and the block body is slid while being pressed against the slide surface while supporting the blade whose tip portion protrudes from the slide surface. By slicing the block body with a blade whose first front surface has a length of 0.8 mm or more and a surface roughness Sa of the first front surface of 1.00 μm or less, heat is generated from the block body. Cut out the conductive sheet.

＜＜Block font＞＞
The block body contains a resin and a particulate filler, and may optionally further contain an additive. Further, the block body preferably has an Asker C hardness of 90 or less. Furthermore, it is preferable that the block body has a dynamic friction coefficient of 2.5 or less.

[Resin, particulate filler, and additive]
Suitable types, properties and content ratios of the resin and particulate filler contained in the block body, as well as optional additives, are the same as the suitable types, properties and content ratios described above for the thermally conductive sheet of the present invention. can do.

[Asker C hardness]
Here, the Asker C hardness of the block body is preferably 90 or less, more preferably 85 or less, particularly preferably 80 or less, preferably 30 or more, and 40 or more. It is more preferable that it is, it is still more preferable that it is 50 or more, and it is especially preferable that it is 60 or more. If the Asker C hardness is 90 or less, the blade can easily penetrate into the block, so that the thickness accuracy of the heat conductive sheet obtained by slicing the block can be more fully ensured. On the other hand, if the Asker C hardness is 30 or more, it is possible to obtain a thermally conductive sheet with even better thickness accuracy by suppressing the wobbling of the cutting edge due to the stickiness of the block during slicing.
Note that the Asker C hardness of the block body can be adjusted by changing the type and content ratio of materials (resin, particulate filler, etc.) used for manufacturing the block body, and the method for manufacturing the block body.
In addition, in the present invention, "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 Institute Standards (SRIS), and for example, in the present specification. It can be measured using the method described in Examples.

[Dynamic friction coefficient]
Here, the dynamic friction coefficient of the block body is preferably 0.5 or less, more preferably 0.3 or less, preferably 0.05 or more, and preferably 0.1 or more. More preferred. If the dynamic friction coefficient is 0.5 or less, the friction generated between the block body and the blade can be reduced, and smooth slicing becomes possible. Further, the friction coefficient is generally 0.01 or more.
Note that the coefficient of dynamic friction of the block body can be adjusted by changing the type and content ratio of materials (resin, particulate filler, etc.) used for manufacturing the block body, and the method for manufacturing the block body.
In the present invention, the "dynamic coefficient of friction" can be measured using, for example, a surface property measuring machine TYPE: 14FW (manufactured by Shinto Kagaku Co., Ltd.) in accordance with ASTM D1894.

＜＜Blade＞＞
The shape of the blade used for slicing the block body described above may be a "double-edged" shape in which both sides of the blade are cutting edges, or only the front side (front surface side) of the blade is a cutting edge. A "single edge" may be used, but a "single edge" is preferable from the viewpoint of ensuring sufficient thickness accuracy of the resulting thermally conductive sheet.
Further, the shape of the blade may be an "asymmetrical blade" having a cross section that is asymmetrical with respect to the central axis passing through the tip of the cutting edge, or may be a "symmetrical blade" having a symmetrical cross section.
Further, the number of blades constituting the blade is not particularly limited, and for example, it may be composed of a "single-blade" consisting of one blade, or a "double-blade" consisting of two blades. It's okay. FIG. 1 shows an example of slicing a block body (laminate) using a plane. As shown in FIG. 1, when the blade is composed of one blade, it is composed of one blade 10. In addition, when the blade is composed of two blades, it is composed of a front blade and a back blade. The front blade and the back blade may have the same or different heights between the leading edges of the cutting edges protruding from the slit portion. That is, the tips of the front blade and the back blade may be aligned or may be vertically offset.
The material of the blade used for slicing the above-mentioned block body is not particularly limited, but from the viewpoint of ensuring sufficient smoothness of both main surfaces, ceramic, cemented carbide, high speed tool steel (high speed steel), steel, etc. It is preferably made of metal, and cemented carbide is more preferable from the viewpoint of the hardness balance of the cutter itself and ease of machining of the cutter.

For example, as shown in FIG. 1, the blade used to slice the block body described above has a first front surface 10a that contacts the block body 20, and a back surface 10c that intersects with the first front surface 10a. , a cutting edge 10d consisting of the intersection corner of the first front surface 10a and the back surface 10c, and a first main extending from the edge 10e of the first front surface 10a on the opposite side to the cutting edge 10d side. and a second front surface 10b located closer to the back surface 10c than the 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 a surface that is formed on the blade edge side and comes into contact with the block body that is the object to be sliced during slicing, and the second front surface is formed at a predetermined angle with respect to the first front surface. This is a surface provided to reduce the area of contact with the block body which is the body to be sliced.

Further, 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, and more preferably 3.0 mm or more. , is preferably 10.0 mm or less, 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 conductive sheet obtained by slicing the block body will be impaired. On the other hand, when the length of the first front 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 needs to be 1.00 μm or less as described above, preferably 0.80 μm or less, and more preferably 0.40 μm or more. It is preferably 0.50 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 side of the thermally conductive sheet obtained by slicing the block body will be impaired due to friction between the block body and the front surface. It will be done. The lower limit of the surface roughness Sa of the first front surface of the blade is not particularly limited, but is, for example, 0.30 μm or more.

Further, as described above, 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, It is preferably 50.0 mm or less, more preferably 40.0 mm or less, and even 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 conductive 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 conductive sheet obtained by slicing the block body can be ensured.
Further, 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. .
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 conductive 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, for example, 0.50 μm or more, although it is not particularly limited.

Further, the first blade angle of the blade (the angle formed 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 FIG. 1, the blade angle θ1 can be within the above range.
Further, the second blade angle (the angle formed between 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 set within the above range.

＜＜Slice＞＞
[Slice speed]
The speed at which the block (laminate) is sliced (in other words, the relative speed at which the block and the blade are brought into contact) needs to be 5 m/min or more. Further, the speed at which the block body (laminate) is sliced is not particularly limited, but is preferably 12 m/min or more, more preferably 30 m/min or more, and, for example, 120 m/min or less. It is preferable.
When the speed of slicing the block body (laminate) is 12 m/min or more, productivity can be improved and deterioration of surface roughness caused by the blade moving forward while compressing the block body can be suppressed. can. In addition, if the speed at which the block body (laminate) is sliced is 120 m/min or less, the impact caused by the collision between the block body and the blade is suppressed from increasing, and the block body (especially the part where the blade enters) is suppressed. It can be sliced more evenly.

Note that the slicing speed may be controlled by changing the speed at which the block body 20 enters (cuts into) the fixed blade 10, as shown in FIG. It may be controlled by changing the speed at which the blade advances (cuts); it may also be controlled by changing the relative speed at which the blade and block body mutually advance (cut). Furthermore, from the viewpoint of workability, it is desirable to control the slicing speed by mechanical control.

[Slice direction]
In the above-mentioned slicing, it is preferable to slice the block body in a plane parallel to the lamination direction (in other words, so that the main surface of the thermally conductive sheet obtained by slicing has a lamination cross section). For example, as shown in FIG. 1, if the block body 20 is sliced in a plane parallel to the stacking direction A of the primary sheet 20a, the desired characteristics can be exhibited in the thickness direction of the thermally conductive sheet obtained by slicing. Because you can.
In the present invention, "a plane parallel to the stacking direction" includes a plane having an inclination of about 30 degrees or less with respect to a direction parallel to the stacking direction.

Here, as an example, a case of slicing using a plane shown in FIG. 1 will be described.
First, the laminated side surface 20b of the block body 20 is supported by the slide surface 30a so that the block body 20 can be slid in a direction in which the laminated side surface 20b and the slide surface 30a of the plane are parallel to each other. In other words, according to FIG. 1, the stacking direction A is also horizontal with respect to the plane installed horizontally, the stacking side surface 20c faces upward, the stacking side surface 20b faces downward, and the top surface 20d faces the blade 10. The body 1 is placed on the slide surface 30a. Further, the tip of the slicing blade 10 protrudes from the slide surface 30a to an arbitrary extent. In the example shown in FIG. 1, the tip of the blade 10 having a blade angle θ1 protrudes from the slide surface 30a at an angle α.
According to FIG. 1, while pressing the block body 20 supported on the slide surface 30a from the laminated side surface 20c side to the slide surface 30a side with an arbitrary pressure, at a predetermined slicing speed (slide speed), Slide in a direction parallel to the slide surface 30a (slide direction, slice direction). Note that the sliding speed at this time is the same as the predetermined slicing speed described above.
By sliding the block body 20 in this manner, the top surface 20d enters the blade 10 at a predetermined sliding speed, and the block body 20 is sliced in a plane parallel to the stacking direction A.

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, and 0.50 MPa or less. It is preferably at most 0.40 MPa, more preferably at most 0.40 MPa, particularly preferably at most 0.30 MPa.
When the pressure is 0.05 MPa or more, the thickness accuracy of the heat conductive sheet obtained by slicing the block body can be ensured, while when the pressure is 0.50 MPa or less, the block body is suppressed from being crushed. can do.
In addition, when the block body is a laminate obtained by laminating primary sheets in the lamination process described below, the block body can be easily sliced to ensure sufficient thickness accuracy of the resulting thermally conductive sheet. It is preferable to slice the block body, which is a stacked body, while applying pressure in a direction perpendicular to the stacking direction.

In addition, from the viewpoint of easily slicing the block body and ensuring sufficient thickness accuracy of the resulting thermally conductive sheet, the temperature of the block body during slicing is preferably -20°C or more and 80°C or less, More preferably, the temperature is -10°C or higher and 50°C or lower.

[Slice angle]
Here, the slice angle β (sometimes referred to as "entering angle" or "penetrating angle") between the stacking direction of the block body and the extending direction of the blade can be within the range of 0° to 90°. .
To explain more specifically according to FIG. 2, in FIG. 2(a), the stacking is performed so that the stacking direction A of the primary sheets in the block body 20 (laminate) and the extending direction E of the blade 10 are parallel to each other. The side surface 20f and the blade 10 are in contact (slice angle β=0°). In Figures (b) to (d), the stacking direction A of the primary sheets 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 stacked side surface 20f are aligned with the blade 10. (slice angle β=15°, 45° and 75°). In FIG. 2E, the top surface 20d and the blade 10 are in contact with each other such that the stacking direction A of the primary sheets in the block body 20 (laminate) and the extending direction E of the blade 10 are perpendicular to each other ( slice angle β = 90°).
From the viewpoint of reducing the impact at the time of the first collision and improving the thickness surface accuracy, the slice angle β is preferably greater than 0°, more preferably 1° or more, and more preferably 5° or more. The angle is more preferably 30° or more, even more preferably 40° or more. Similarly, from the above point of view, the slice angle β is preferably less than 90° within the range of 0° to 90°, more preferably 89° or less, and even more preferably 85° or less. The angle is preferably 60° or less, more preferably 50° or less, and particularly preferably 50° or less. It is even more preferred that the slice angle β is 45°.

Note that the slicing 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 block body enters (cuts into) the fixed block body. It may be controlled by changing the angle, or it may be controlled by changing the relative angle at which the blade and the block body approach each other (make the cut).

As explained above, the method of slicing a block body includes, for example, as shown in FIG. There is no particular limitation as long as the method is to slide the block body 20 while pressing it against the slide surface 30a while supporting the block body 20.
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, so that the heat conductive sheet (not shown) is sliced onto the back surface 10c of the blade 10. Newly generated on the side. Here, the main surface on the upper side in FIG. 1 of the newly generated thermally conductive sheet is defined as the A side, and the main surface on the lower side in FIG. 1 as the B side.
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 of the second front surface 10b of the blade 10 is adjusted to within a predetermined range. Since Sa is adjusted, the damage caused when the block body 20 is slid in the stacking direction A of the primary sheets 20a while pressing it against the slide surface 20a (the lower surface of the block body 20 in FIG. Damage to the B side of the heat conductive sheet from the second front surface 10b of the blade 10 at the step 30b or the groove 40 can be reduced.
In addition, from the viewpoint of suppressing the loss of smoothness of the lower surface of the block body 20 in FIG. In order to return to the position (the position of the block body 20 in FIG. 1), it is preferable to move the block body 20 without contacting the slide surface 30a.

<Other processes>
Other steps that may be optionally included in the method for manufacturing a thermally conductive sheet of the present invention are not particularly limited.
For example, in the method for manufacturing a thermally conductive sheet of the present invention, before the slicing step described above, a plurality of primary sheets containing resin and particulate filler are laminated in the thickness direction, or this primary sheet is folded. A process (lamination process) of obtaining a block body by tatami matting or rolling can be carried out.
Moreover, in the method for manufacturing a thermally conductive sheet of the present invention, a step of heating the block body (heating step) can be performed before the above-mentioned slicing step.
In addition, in the method for manufacturing a thermally conductive sheet of the present invention, a step (pressing step) of pressing the thermally conductive sheet obtained after the slicing step in the thickness direction is carried out unless the effect of the present invention is significantly impaired. It's okay. However, from the viewpoint of suppressing a decrease in thermal conductivity in the thickness direction of the obtained thermally conductive sheet, it is preferable that the method for manufacturing a thermally conductive sheet of the present invention does not include a pressing step.
Hereinafter, the lamination process and heating process as other processes will be explained in detail.

<<Lamination process>>
As described above, in the lamination step, a plurality of primary sheets are laminated in the thickness direction, or the primary sheets are folded or rolled to obtain a block body which is a laminate.

[Primary sheet]
The primary sheet includes a resin and a particulate filler, and may optionally further include additives.

-Resins, particulate fillers, and additives-
Preferred types, properties, and content ratios of the resin and particulate filler contained in the primary sheet, as well as optional additives, are the same as those described above for the block body and the thermally conductive sheet of the present invention. It can be the same as the content ratio.

-Properties of primary sheet-
The tensile strength of the primary sheet is preferably 0.3 MPa or more, more preferably 1.0 MPa or more, even more preferably 1.5 MPa or more, and 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 obtained by laminating the primary sheets will increase. Therefore, it is possible to suppress the wobbling of the cutting edge when slicing the block body, and thereby obtain a heat conductive sheet with even better thickness accuracy. On the other hand, if the tensile strength is 3.0 MPa or less, the Asker C hardness of the block obtained by laminating the primary sheets will not increase excessively. Therefore, the block body can be easily sliced, and the thickness accuracy of the resulting thermally conductive sheet (particularly, the thickness accuracy when the thickness of the thermally conductive sheet is reduced by reducing the slice width) can be sufficiently ensured.
Note that the tensile strength of the primary sheet can be adjusted by changing the type and content ratio of materials (resin, particulate filler, etc.) used for manufacturing the primary sheet, and the method for manufacturing the primary sheet. For example, by increasing the resin content in the primary sheet, the tensile strength of the primary sheet can be increased.

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 thermally conductive sheet.

-Preparation method of 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. .

[Formation of block body by lamination etc.]
Formation of a block body by laminating primary sheets or the like is not particularly limited, and may be performed using a laminating device or manually. Furthermore, the formation of the block body by folding the heat conductive sheet is not particularly limited, and can be performed by folding the primary sheet into a constant width using a folding machine. Furthermore, the formation of a block body by winding the primary sheet is not particularly limited, and can be performed by winding the primary sheet around an axis parallel to the transverse direction or the longitudinal direction of the primary sheet. .

<<Heating process>>
Here, for example, the block body obtained through the above-described lamination process may be subjected to the slicing process as it is, or may be further heated and then subjected to the slicing process. 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 performing the heating process, the adhesion of the blocks in the stacking direction can be adjusted. For example, when the block body contains a thermoplastic resin, the adhesion of the block body in the stacking direction can be increased by performing a heating step.

EXAMPLES Hereinafter, the present invention will be specifically explained based on Examples, but the present invention is not limited to these Examples. In the following description, "%" and "part" representing amounts are based on mass unless otherwise specified.
In the Examples and Comparative Examples, the particle size distribution and volume average particle diameter, the content ratio (volume fraction) of the particulate filler, the surface roughness Sa of the first front surface and the second front surface of the blade, The Asker C hardness of the block, the average thickness, standard deviation of thickness, surface roughness Sa, and thermal conductivity in the thickness direction of the thermally conductive sheet were measured or evaluated according to the following methods, respectively.

<Volume average particle diameter>
By placing 1 g of the thermally conductive sheet in methyl ethyl ketone as a solvent and dissolving the resin components of the thermally conductive sheet, a suspension in which the particulate filler (expanded graphite) contained in the thermally conductive sheet is separated and dispersed is created. Obtained. Next, the particle size of the particulate filler contained in the suspension was measured using a laser diffraction/scattering particle size distribution measuring device (manufactured by Horiba, model "LA960"). Then, a particle size distribution curve was created, with the obtained particle diameter as the horizontal axis and the volume-converted particle frequency as 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 is 50% was determined, and this was taken as the value of the volume average particle diameter of the particulate filler.
<Content ratio of particulate filler (volume fraction)>
The content ratio (volume fraction) of the particulate filler in the primary sheet was calculated by dividing the weight of each material used when forming the primary sheet by the specific gravity of the material as the volume of the material. The calculation was performed assuming that the specific gravity of the resin is 1.77 for both the liquid resin and the solid resin, the specific gravity of the particulate filler (expanded graphite) is 2.25, and the specific gravity of the additive is 1.17.
<Surface roughness Sa of the first front surface and 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 x 7.6 mm.
<Asker C hardness of block body (laminate)>
The Asker C hardness of the block body (laminate) is measured using a hardness meter (manufactured by Kobunshi Keiki Co., Ltd., product name "ASKER CL-150LJ") in accordance with the Asker C method of the Japan Rubber Institute Standards (SRIS). The test was carried out at a temperature of 25°C.Specifically, the obtained block body (laminated body) was left standing in a thermostatic chamber kept at a temperature of 25°C for 48 hours or more to form a test specimen.Next, the laminated surface A hardness meter was installed so that the distance between the needle tip and the damper was 2 cm, and the damper was lowered to cause the block body (laminate) to collide with the damper. 60 seconds after the collision, the block body (laminate) was The Asker C hardness was measured twice using a hardness meter (manufactured by Kobunshi Keiki Co., Ltd., trade name "ASKER CL-150LJ"), and the average value of the measurement results was used.
<Average thickness>
Using a film thickness meter (manufactured by Mitutoyo, product name "Digimatic Indicator ID-C112XBS"), measure the thickness at a total of five points, approximately the center point and the four corners (squares) of the thermally conductive sheet, and calculate the average value of the measured thickness. (μm) was determined.
<Standard deviation of thickness>
Using a film thickness meter (manufactured by Mitutoyo, product name "Digimatic Indicator ID-C112XBS"), measure the thickness at a total of five points, approximately the center point and the four corners (squares) of the thermally conductive sheet, and calculate the standard deviation of the measured thickness. (μm) was determined.
<Surface roughness Sa of thermally conductive sheet>
The surface roughness Sa of the thermally conductive sheet was measured using a three-dimensional shape measuring machine (manufactured by Keyence Corporation, product name: "One-shot 3D measurement macroscope"). Here, a thermally conductive sheet cut into a substantially square of arbitrary size of 1 cm square or more was used as a sample, the analysis range was 1 cm x 1 cm, and the three-dimensional shape was measured on the front and back surfaces of the sample. Then, the measurement results of the three-dimensional shape were further filtered (2.5 mm) using software to remove the waviness component, thereby automatically calculating the surface roughness Sa (μm). The surface roughness Sa was measured for each of side A (the surface newly generated by inserting a new blade) and surface B (the surface already generated by inserting the previous blade).
<Thermal conductivity in the thickness direction>
Regarding the heat conductive sheet, the thermal diffusivity α (m ² /s) in the thickness direction, specific heat Cp (J/g·K) at constant pressure, and specific gravity ρ (g/m ³ ) were each measured by the following methods.
[Thermal diffusivity α in the thickness direction]
The thermal diffusivity of the thermally conductive sheet was measured using a thermal diffusion/thermal conductivity measuring device (ai-Phase Mobile 1u, manufactured by i-Phase Co., Ltd.) based on the provisions of ISO 22007-3.
[Constant pressure specific heat Cp]
Using a differential scanning calorimeter (manufactured by Rigaku, product name "DSC8230"), the specific heat at 25° C. was measured under a temperature increase condition of 10° C./min.
[Specific gravity ρ (density)]
It was measured using an automatic hydrometer (manufactured by Toyo Seiki Co., Ltd., trade name "DENSIMETER-H").
Then, each measured value is expressed by the following formula (I):
λ=α×Cp×ρ...(I)
The thermal conductivity λ (W/m·K) in the thickness direction of the thermally conductive sheet at 25° C. was determined.
<Thermal resistance value>
The thermal resistance value of the thermally 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 thermally conductive sheet cut out into a 1 cm square approximately was used as a sample, and the thermal resistance value (°C/W) was measured when pressures of 0.1 MPa and 0.9 MPa were applied at a sample temperature of 50°C. . The smaller the thermal resistance value is, the more excellent the thermal conductivity of the thermally conductive sheet is, and, for example, the better the heat dissipation property when interposed between a heating element and a heat radiating element is shown.

(Example 1)
<Formation of primary sheet>
70 parts of a thermoplastic fluororesin that is liquid at room temperature and normal pressure (manufactured by Daikin Industries, Ltd., product name "Daiel G-101") and a thermoplastic fluororesin that is solid at room temperature and normal pressure (manufactured by 3M Japan Ltd., product) as a resin. 30 parts of Dyneon FC2211) and 90 parts of expanded graphite as a particulate filler (manufactured by Ito Graphite Industries Co., Ltd., product name EC300, volume average particle diameter: 50 μm) were mixed in a pressure kneader (Nippon Spindle). The mixture was stirred and mixed for 20 minutes at a temperature of 150° C. 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 sandblasted polyethylene terephthalate (PET) films (protective films) with a thickness of 50 μm, roll gap 550 μm, roll temperature 50° C., roll linear pressure 50 kg/cm, and roll speed 1 m/cm. A primary sheet having a thickness of 0.8 mm was obtained by rolling and forming under the conditions of 10 minutes.
<Lamination process>
The obtained primary sheet was cut into 150 mm long x 150 mm wide x 0.8 mm thick, 100 sheets were laminated in the thickness direction of the primary sheet, and further processed in the laminating direction at a temperature of 120°C and a pressure of 0.1 MPa for 3 minutes. By pressing, a block body (laminate) having a height of about 80 mm was obtained. Then, the Asker C hardness of the obtained block body was measured. The results are shown in Table 1.
<Slicing process>
After that, while pressing the side surface (the surface along the stacking direction) of the block body (laminate) against the slide surface with a pressure of 0.3 MPa, use a wood slicer (manufactured by Marunaka Iron Works Co., Ltd., product name: "Super Finish Planer"). Super Mecha S'') is used to slice the block body (laminate) in the stacking direction (in other words, in the direction that corresponds to the normal to the main surface of the stacked primary sheets) into 150 mm length x width slices. A thermally conductive sheet measuring 150 mm x 0.10 mm in thickness was obtained. Note that the above-mentioned slicing was performed by sliding the block body (laminate) on the sliding surface at a sliding speed of 1000 mm/sec. A single-edged blade A having the following properties was used as the slicing blade of a woodworking slicer. In addition, the temperature of the block body was set to room temperature.
<<Properties of single-edged 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 second front surface 10b and back surface 10c): 20°
Maximum thickness of blade: 9mm
Material: Cemented carbide (tungsten carbide)
Rockwell hardness: 90
Silicon processing on the blade surface: None Radius of curvature at the tip: 10 μm
Length of first front surface: 1.0mm
Surface roughness Sa of first front surface: 0.43μm
Length of second front surface: 25.0mm
Surface roughness Sa of second front surface: 0.61 μm
Then, the average thickness, standard deviation of thickness, surface roughness Sa, and thermal conductivity in the thickness direction of the obtained thermally conductive sheet were measured. The results are shown in Table 1.

(Example 2)
In Example 1, a primary sheet, a block body, and a heat conductive sheet were produced in the same manner as in Example 1, except that instead of using single edge A, single edge B having the following properties was used, and various evaluations were performed. went. 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 second front surface 10b and back surface 10c): 20°
Maximum thickness of blade: 9mm
Material: Cemented carbide (tungsten carbide)
Rockwell hardness: 90
Silicon processing on the blade surface: None Radius of curvature at the tip: 10 μm
Length of first front surface: 3.0mm
Surface roughness Sa of first front surface: 0.43μm
Length of second front surface: 23.0mm
Surface roughness Sa of second front surface: 0.61 μm

(Example 3)
In Example 1, a primary sheet, a block body, and a heat conductive sheet were produced in the same manner as in Example 1, except that instead of using single edge A, single edge C having the following properties was used, and various evaluations were performed. went. 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 second front surface 10b and back surface 10c): 20°
Maximum thickness of blade: 9mm
Material: High speed tool steel (high speed steel)
Rockwell hardness: 82
Silicon processing on the blade surface: None Radius of curvature at the tip: 10 μm
Length of first front surface: 1.0mm
Surface roughness Sa of first front surface: 0.75 μm
Length of second front surface: 25.0mm
Surface roughness Sa of second front surface: 0.86 μm

(Comparative example 1)
In Example 1, a primary sheet, a block body, and a heat conductive sheet were produced in the same manner as in Example 1, except that instead of using single edge A, single edge D having the following properties was used, and various evaluations were performed. went. 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 second front surface 10b and back surface 10c): 20°
Maximum thickness of blade: 9mm
Material: High speed tool steel (high speed steel)
Rockwell hardness: 82
Silicon processing on the blade surface: None Radius of curvature at the tip: 10 μm
Length of first front surface: 1.0mm
Surface roughness Sa of first front surface: 1.25 μm
Length of second front surface: 25.0mm
Surface roughness Sa of second front surface: 0.94 μm

(Comparative example 2)
In Example 1, instead of slicing the block body (laminate) in the stacking direction using a wood slicer while pressing the side surface of the block body (laminate) against the slide surface with a pressure of 0.3 MPa, the block body (laminate) was sliced in the stacking direction. Without pressing the side surface of the block body (laminate) against the sliding surface with a pressure of 0.3 MPa (that is, using only the weight of the block body (laminate)), use a woodworking slicer to move the block body (laminate) in the stacking direction. A primary sheet, a block body, and a thermally conductive sheet were produced in the same manner as in Example 1 except that they were sliced into slices, and various evaluations were performed. The results are shown in Table 1.

(Comparative example 3)
In Example 3, when forming the primary sheet, instead of using 90 parts of expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., product name "EC300", volume average particle diameter: 50 μm) as a particulate filler, particulate A primary sheet and a block body were prepared in the same manner as in Example 3, except that 50 parts of expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., product name "EC100", volume average particle diameter: 200 μm) was used as a filler. , and a thermally conductive sheet were produced and various evaluations were performed. The results are shown in Table 1.

(Comparative example 4)
In Example 1, when forming the primary sheet, 70 parts of a thermoplastic fluororesin (manufactured by Daikin Industries, Ltd., product name "Daiel G-101"), which is liquid at room temperature and normal pressure, and a solid at room temperature and normal pressure, were used as the resin. 30 parts of thermoplastic fluororesin (manufactured by 3M Japan Ltd., product name "Dyneon FC2211"), and expanded graphite as a particulate filler (manufactured by Ito Graphite Industries Ltd., product name "EC300", volume average particle diameter: 50 μm) to obtain a thermally conductive sheet of 150 mm long x 150 mm wide x 0.10 mm thick, a thermoplastic fluororesin (manufactured by Daikin Industries, Ltd., product name: Daiel G-101'') 45 parts, a thermoplastic fluororesin solid at room temperature and pressure (3M Japan Ltd., product name ``Dyneon FC2211''), 40 parts, expanded graphite as a particulate filler (Ito Graphite Industries Ltd.) Co., Ltd., product name "EC100", volume average particle diameter: 200 μm), and 5 parts by mass of sebacic acid ester (manufactured by Daihachi Kagaku Kogyo Co., Ltd., product name "DOS") as a plasticizer. After obtaining a secondary sheet (block body sliced) of 150 mm x width 150 mm x thickness 0.50 mm (500 μm), a precision hot press machine (manufactured by Shinto Kogyo Co., Ltd., product name "CYPT-20") was used. Using a press plate, heat the press plate to 50 ° C. and press the secondary sheet for 30 seconds at a pressure of 2.6 MPa (post-processing step) to form a sheet of 150 mm long x 150 mm wide x 0.125 mm thick (125 μm). A primary sheet, a block body, and a heat conductive sheet were produced in the same manner as in Example 1, except that a heat conductive sheet was obtained, and various evaluations were performed. The results are shown in Table 1.

From Table 1, it can be seen that both main surfaces of the thermally conductive sheets of Examples 1 to 3 are smooth. It can also be seen that the thermally conductive sheets of Examples 1 to 3 have low thermal conductivity in the thickness direction and can conduct heat well in the thickness direction. Furthermore, it can be seen that the thermally conductive sheets of Examples 1 to 3 have excellent thickness accuracy because the standard deviation of the thickness is small.

According to the present invention, there is provided a thermally conductive sheet that has both smooth main surfaces and can conduct heat well in the thickness direction while having sufficient thickness accuracy, and a method for manufacturing the thermally conductive sheet. be able to.

10 Blade 10a First front surface 10b Second front surface 10c Back surface 10d Cutting edge 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 Stand 30a Slide surface 30b Step 40 Groove A Stacking direction E of the primary sheet 20a Extension direction of the blade θ1 Angle between the first front surface 10a and the back surface 10c (blade angle A)
θ2 Angle between the second front surface 10b and the back surface 10c (blade angle B)
α angle β slice angle

Claims (3)

A block body containing a resin and a particulate filler is slidably supported by a slide surface, and the block body is slid while being pressed against the slide surface while supporting a blade whose tip portion protrudes from the slide surface. A method for manufacturing a thermally conductive sheet, the method comprising: slicing the block body with the blade;
The blade includes a first front surface that contacts the block body, a back surface that intersects with the first front surface, and an intersection corner between the first front surface and the back surface. a cutting edge; and a second front surface extending from an edge of the first front surface opposite to the cutting edge side and located closer to the back surface than the first front surface. ,
The length of the first front surface is 0.8 mm or more,
A method for manufacturing a thermally conductive sheet, wherein the first front surface has a surface roughness Sa of 1.00 μm or less. The method for manufacturing a thermally conductive sheet according to claim 1 , wherein the second front surface has a surface roughness Sa of 1.00 μm or less. Prior to the slicing step, a step of laminating a plurality of primary sheets containing a resin and a particulate filler in the thickness direction, or folding or winding the primary sheets to obtain the block body. The method for manufacturing a thermally conductive sheet according to claim 1 or 2 , further comprising:

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