JP7354554B2 - Thermal conductive sheet and method for manufacturing the thermal conductive sheet - Google Patents

Description

The present invention relates to a laminate and 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 (for example, see Patent Document 1).

In Patent Document 1, 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 1, the thermally conductive sheet obtained by the method described above can exhibit excellent thermal conductivity even when used at a relatively low clamping pressure.

JP2018-67695A

In recent years, it has become necessary to improve the thickness accuracy of the heat conductive sheet in order to maintain good contact between the heat generating element and the heat dissipating element via the heat conductive sheet and to uniformly transfer heat from the heat generating element to the heat dissipating element. It has been demanded.
However, the thermally conductive sheet manufactured by the conventional method described above has room for improvement in increasing thickness accuracy.
In addition, the heat conductive sheet has room for improvement in the heat conductivity in the thickness direction.

Therefore, an object of the present invention is to provide a laminate that can form a thermally conductive sheet that has sufficient thickness accuracy and can conduct heat well in the thickness direction.
Another object of the present invention is to provide a heat conductive sheet that has sufficient thickness accuracy and can conduct heat well in the thickness direction.

The present inventor conducted extensive studies in order to achieve the above object. The present inventors then stacked a plurality of primary sheets in the thickness direction containing a resin and a particulate filler having a volume average particle diameter within a predetermined range, and the Asker C hardness was within a predetermined range. The inventors have discovered that by using a certain laminate, it is possible to form a thermally conductive sheet that has sufficient thickness accuracy and is capable of good heat transfer in the thickness direction, and has completed the present invention.

That is, the present invention aims to advantageously solve the above problems, and the laminate of the present invention is formed by laminating a plurality of primary sheets containing a resin and a particulate filler in the thickness direction. The laminate is characterized in that the volume average particle diameter of the particulate filler is 40 μm or more and 180 μm or less, and the Asker C hardness of the laminate is 60 or more and 90 or less. In this way, a laminate is formed by laminating a plurality of primary sheets containing a resin and a particulate filler having a volume average particle diameter within a predetermined range in the thickness direction, and has an Asker C hardness within a predetermined range. If so, it is possible to form a thermally conductive sheet that has sufficient thickness accuracy and can conduct heat well in the thickness direction.
In the present invention, "Asker C hardness" is a value measured at a temperature of 25°C using a hardness meter in accordance with the Asker C method of the Japan Rubber Institute Standards (SRIS). It can be measured using the method described in Examples.
In addition, 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, and can be measured, for example, using the method described in the Examples of this specification.

Here, in the laminate of the present invention, it is preferable that the tensile strength of the primary sheet is 1.5 MPa or more. In this way, if the tensile strength of the primary sheet is equal to or higher than the predetermined value, the thermally conductive sheet obtained by slicing will not be deformed during slicing, and the thickness accuracy of the thermally conductive sheet can be further improved.
In the present invention, "tensile strength" is a value obtained in accordance with JIS K6251, and can be measured, for example, using the method described in the Examples of this specification.

Further, in the laminate of the present invention, it is preferable that the particulate filler is expanded graphite. In this way, when the particulate filler is expanded graphite, heat can be transferred even more favorably in the thickness direction of the heat conductive sheet.

Further, in the laminate of the present invention, it is preferable that the content of particulate filler in the primary sheet is 35% by volume or more and 55% by volume or less. In this way, if the content ratio of the particulate filler in the primary sheet is within the above-mentioned predetermined range, the thickness accuracy of the heat conductive sheet can be further improved while further improving heat transfer in the thickness direction of the heat conductive sheet. be able to.
Note that the content ratio (volume %) of the particulate filler in the primary sheet can be measured using the method described in the Examples of this specification.

Furthermore, in the laminate of the present invention, it is preferable that the primary sheet further contains a dispersant. In this way, if the primary sheet further contains a dispersant, the particulate filler can be dispersed and the Asker C hardness can be easily adjusted.

Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the thermally conductive sheet of the present invention is a thermally conductive sheet obtained by slicing any of the above-mentioned laminates, It is characterized in that the standard deviation of the thickness is 3.0 μm or less. In this way, a thermally conductive sheet obtained by slicing any of the above-mentioned laminates and whose standard deviation of thickness is equal to or less than the above-mentioned predetermined value has sufficient thickness accuracy and is well-developed in the thickness direction. It can transfer heat.
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.

Here, the heat conductive sheet of the present invention can have a main surface area of 30 cm ² or more.
In addition, in the present invention, the "principal surface" refers to the surface having the maximum area in the thermally conductive sheet.

In addition, the thermally conductive sheet of the present invention has a ratio of Sa1 to Sa2 (Sa1/Sa2), where the surface roughness Sa of one main surface is Sa1 and the surface roughness Sa of the other main surface is Sa2. is preferably 85/100 or more and 100/85 or less. In this way, if the ratio (Sa1/Sa2) between the surface roughness (Sa1) of one main surface and the surface roughness (Sa2) of the other main surface is within the above predetermined range, the grasping by the robot arm Handling properties such as ease of handling can be improved.
In the present invention, the "surface roughness Sa" is a value obtained in accordance with the international standard ISO 25178, and can be measured, for example, using the method described in the Examples of this specification.

Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the thermally conductive sheet of the present invention is a thermally conductive sheet containing a resin and a particulate filler, wherein the particulate filler is It is characterized in that the volume average particle diameter is 40 μm or more and 180 μm or less, and the Asker C hardness of the thermally conductive sheet is 60 or more and 90 or less. In this way, a thermally conductive sheet that includes a resin and a particulate filler whose volume average particle diameter is within the above predetermined range, and whose Asker C hardness is within the above predetermined range, has sufficient thickness accuracy, and Heat can be transferred well in the thickness direction.

Here, it is preferable that the thermally conductive sheet of the present invention has an average thickness of 200 μm or less. In this way, if the average thickness is equal to or less than the above-mentioned predetermined 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

Moreover, it is preferable that the standard deviation of the thickness of the thermally conductive sheet of the present invention is 3.0 μm or less. In this way, when the standard deviation of the thickness is equal to or less than the above-mentioned predetermined value, the thermally conductive sheet can be brought into closer contact with a substrate such as a heat source.

Furthermore, in the thermally conductive sheet of the present invention, it is preferable that the content of particulate filler in the thermally conductive sheet is 35% by volume or more and 55% by volume or less. In this way, if the content ratio of the particulate filler in the thermally conductive sheet is within the above-mentioned predetermined range, the thickness accuracy of the thermally conductive sheet can be further improved while further improving heat transfer in the thickness direction of the thermally conductive sheet. be able to.

Moreover, it is preferable that the thermally conductive sheet of the present invention has a tensile strength of 1.5 MPa or more. In this way, if the tensile strength is equal to or greater than the predetermined value, the thickness accuracy of the heat conductive sheet can be further improved.

Furthermore, it is preferable that the thermally conductive sheet of the present invention further contains a dispersant. In this way, if a dispersant is further included, the particulate filler can be dispersed and the Asker C hardness can be easily adjusted.

According to the present invention, it is possible to provide a laminate that can form a thermally conductive sheet that has sufficient thickness accuracy and can conduct heat well in the thickness direction.
Further, according to the present invention, it is possible to provide a heat conductive sheet that can conduct heat well in the thickness direction while having sufficient thickness accuracy.

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.

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.
Here, the laminate of the present invention is formed by laminating a plurality of primary sheets in the thickness direction containing a resin and a particulate filler having a volume average particle diameter within a predetermined range, and has an Asker C hardness within a predetermined range. It is a laminate that is inside.
The thermally conductive sheet of the present invention is
(1) A thermally conductive sheet obtained by slicing the above-described laminate of the present invention and having a standard deviation of thickness of a predetermined value or less, and
(2) Either of the two configurations of the thermally conductive sheet may be used, which includes a resin and a particulate filler having a volume average particle diameter within a predetermined range, and has an Asker C hardness within a predetermined range.
Hereinafter, for convenience of explanation, the thermally conductive sheet having the configuration in (1) above will be referred to as "thermal conductive sheet 1", and the thermally conductive sheet having the configuration in (2) above will be referred to as "thermal conductive sheet 2". .

(Thermal conductive sheet 1)
The thermally conductive sheet 1 of the present invention is a thermally conductive sheet obtained by slicing a laminate of the present invention, which will be described later, and is characterized in that the standard deviation of the thickness is less than or equal to a predetermined value.
The heat conductive sheet 1 of the present invention has sufficient thickness accuracy and can conduct heat well in the thickness direction. Therefore, by interposing the thermally conductive sheet 1 of the present invention between the heat generating element and the heat radiating element, the heat generating element and the heat radiating element are brought into close contact with each other, and heat is uniformly transferred from the heat generating element to the heat radiating element. be able to.

<Laminated body>
The laminate of the present invention is formed by laminating a plurality of primary sheets in the thickness direction containing a resin and a particulate filler having a volume average particle diameter within a predetermined range, and has an Asker C hardness within a predetermined range. It is characterized by
By using the laminate of the present invention, it is possible to form a thermally conductive sheet that has sufficient thickness accuracy and can conduct heat well in the thickness direction.
The laminate of the present invention can be used for manufacturing the thermally conductive sheet 1 of the present invention.

<<Primary sheet>>
The primary sheet constituting the laminate of the present invention includes a resin and a particulate filler having a volume average particle diameter within a predetermined range. Note that the primary sheet may optionally further contain additives other than the resin and particulate filler.

-resin-
The resin contained in the primary 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 primary sheet can include at least one of a liquid resin and a solid resin, but from the viewpoint of further improving the thickness accuracy of the heat conductive sheet and better heat transfer in the thickness direction, the primary 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.

--Content ratio of resin--
The content ratio of the resin in the primary sheet is not particularly limited, but is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, and 85% by mass or more. % or less, more preferably 75% by mass or less, even more preferably 65% by mass or less. If the content of the resin in the primary sheet is 30% by mass or more, the thickness accuracy of the heat conductive sheet can be further improved while ensuring flexibility of the heat conductive sheet. On the other hand, if the content of the resin in the primary sheet is 85% by mass or less, heat can be transferred even better 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 of liquid resin in the resin is 95% by mass or less, it will provide 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 done.

-Particulate filler-
The particulate filler contained in the primary 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 it is possible to further improve heat transfer 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 must be 40 μm or more, preferably 45 μm or more, 180 μm or less, preferably 160 μm or less, and 140 μm or less. It is more preferable that the diameter be less than 100 μm. It is presumed that when the volume average particle diameter of the particulate filler is 40 μm or more, a 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 favorably in the thickness direction of the heat conductive sheet. On the other hand, when the volume average particle diameter of the particulate filler is 180 μm or less, the thickness accuracy of the thermally conductive sheet can be sufficiently ensured.

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 better 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). In addition, in the above, for example, when the particulate filler has a scale shape, the "longer axis" refers to the length in the direction of the long axis of the main surface of the scale shape, and the "breadth axis" refers to the length in the direction of the long axis of the main surface. It refers to the length in the orthogonal direction.

<<Content ratio of particulate filler>>
The content of the particulate filler in the primary sheet is not particularly limited, but is preferably 35% by volume or more, more preferably 38% by volume or more, preferably 55% by volume or less, and 50% by volume or more. More preferably, it is less than or equal to % by volume. If the content of the particulate filler in the primary sheet is 35% by volume or more, the thermal conductivity in the thickness direction of the thermally conductive sheet increases, and heat can be transferred even better in the thickness direction of the thermally conductive sheet. . On the other hand, if the content of the particulate filler in the primary sheet is 55% 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 primary sheet is not particularly limited, but is preferably 30% by mass or more, more preferably 35% by mass or more, and even more preferably 40% by mass or more. It is preferably 65% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. If the content of the particulate filler in the primary sheet is 30% by mass or more, the thermal conductivity in the thickness direction of the thermally conductive sheet increases, and it is possible to further improve heat transfer in the thickness direction of the thermally conductive sheet. . On the other hand, if the content of the particulate filler in the primary sheet 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 primary sheet is not particularly limited, but per 100 parts by mass of resin, it is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and 60 parts by mass. It is more preferably at least 150 parts by mass, more preferably at most 120 parts by mass, even more preferably at most 95 parts by mass. If the content of the particulate filler in the primary sheet is 40 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 the thermal conductivity in the thickness direction of the thermally conductive sheet is improved. It can be heated. On the other hand, if the content of the particulate filler in the primary sheet is 150 parts by mass or less per 100 parts by mass of resin, it is possible to further improve the thickness accuracy of the heat conductive sheet while ensuring its flexibility. can.

-Additive-
The primary sheet may further contain known additives that can be used to form a thermally conductive sheet, if necessary. Additives that can be blended into the primary sheet include, but are not particularly limited to, 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 primary 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, based on 100 parts by mass of the above-mentioned resin, and 10 parts by mass. It is preferable to make it less than 1 part.

Further, a dispersant may be added to the primary sheet as an additive. By incorporating a dispersant into the primary sheet, it is possible to improve the dispersibility of the particulate filler and reduce the Asker C hardness of the laminate. Therefore, the dispersant is used for the purpose of adjusting the Asker C hardness of the laminate.
Specific examples of the dispersant include, but are not particularly limited to, alkylammonium salts of high molecular weight copolymers, polymers with acidic or basic attraction groups, polar acid esters of long-chain alcohols, and the like.
Further, as the dispersant, commercially available products such as "BYK-9076" and "BYK-111" manufactured by BYK Chemie Co., Ltd. can also be used.
The blending amount of the dispersant in the primary sheet can be, for example, 0.1 parts by mass or more, preferably 0.2 parts by mass or more, and 0.1 parts by mass or more, preferably 0.2 parts by mass or more, based on 100 parts by mass of the above-mentioned resin. It is more preferably 4 parts by mass or more, can be 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 2 parts by mass or less. If the blending amount of the dispersant in the primary sheet is 0.1 parts by mass or more based on 100 parts by mass of the resin, the Asker C hardness of the laminate can be appropriately reduced and the heat obtained by slicing the laminate can be reduced. The thickness accuracy of the conductive sheet (particularly the thickness accuracy when the thickness of the heat conductive sheet is reduced by reducing the slice width) can be further improved. On the other hand, if the blending amount of the dispersant in the primary sheet is 10 parts by mass or less per 100 parts by mass of the resin, the Asker C hardness of the laminate can be prevented from decreasing excessively, and the laminate can be easily sliced. By suppressing the wobbling of the cutting edge, etc., it is possible to further improve the thickness accuracy of the resulting thermally conductive sheet.

-Properties of primary sheet-
The tensile strength of the primary sheet is preferably 1.5 MPa or more, more preferably 1.8 MPa or more, more preferably 2.5 MPa or less, and still more preferably 2.2 MPa or less. preferable. If the tensile strength is 1.5 MPa or more, the Asker C hardness of the laminate obtained by laminating the primary sheets will increase. Therefore, it is possible to further improve the thickness accuracy of the resulting thermally conductive sheet by suppressing blurring of the cutting edge when slicing the laminate. On the other hand, if the tensile strength is 2.5 MPa or less, the Asker C hardness of the laminate obtained by laminating the primary sheets will not increase excessively. Therefore, the laminate 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 further improved.
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. .

<<Lamination>>
The laminate of the present invention is formed by laminating a plurality of the above-described primary sheets in the thickness direction.
Here, the formation of the laminate by laminating the primary sheets is not particularly limited, and may be performed using a laminating device or manually.
Note that in this specification, "stacking a plurality of primary sheets in the thickness direction" includes folding or winding the primary sheets.
Formation of the laminate by folding the thermally conductive sheet is not particularly limited, and can be performed by folding the primary sheet to a constant width using a folding machine. Furthermore, the formation of a laminate 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 longitudinal direction of the primary sheet. .

<<Asker C hardness of laminate>>
Here, the Asker C hardness of the laminate needs to be 60 or more, preferably 65 or more, more preferably 70 or more, and needs to be 90 or less, and 87 or less. It is preferable that it is, and it is more preferable that it is 85 or less. When the Asker C hardness of the laminate is 60 or more, when slicing the laminate, it will be less affected by the adhesiveness of the resin component of the laminate, and the wobbling of the cutting edge can be suppressed. Sufficient thickness accuracy can be ensured. On the other hand, if the Asker C hardness of the laminate is 90 or less, 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) is sufficiently ensured. be able to.
The Asker C hardness of the laminate can be adjusted by changing the type and content ratio of the materials (resin, particulate filler, etc.) used to manufacture the primary sheet constituting the laminate, and the method for manufacturing the laminate. be able to. For example, when the primary sheet constituting the laminate contains a thermoplastic resin, the Asker C hardness of the laminate can be reduced by performing a heating step, which will be described later, during production of the laminate.

<<Method for manufacturing laminate>>
The method for manufacturing a laminate includes a lamination step of laminating a plurality of the above-described primary sheets in the thickness direction, and optionally further includes other steps other than the lamination step.
Here, in the lamination step, the above-described lamination method can be used as a method for laminating a plurality of primary sheets in the thickness direction.
Note that the laminate obtained in the lamination step can be used as it is for manufacturing the thermally conductive sheet 1 as the laminate of the present invention.
Further, the laminate obtained in the lamination step may be subjected to any other steps and then used to manufacture the thermally conductive sheet 1 as the laminate of the present invention.
Such other steps include, for example, a heating step of heating the laminate obtained in the lamination step.

-Heating 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 passing through the heating process, the Asker C hardness of the laminate can be adjusted. For example, when the laminate contains a thermoplastic resin, the Asker C hardness of the laminate can be reduced by performing a heating step.

<Slice>
The thermally conductive sheet 1 of the present invention is obtained by slicing the laminate of the present invention described above.
The method for slicing the laminate is not particularly limited, and for example, a slicing method using a cutting tool equipped with a blade may be used. Here, the shape of the blade is not particularly limited, and may be single-edged, double-edged, or asymmetrical, but from the viewpoint of ensuring sufficient thickness accuracy of the resulting thermally conductive sheet, it is preferably double-edged. Further, the material of the blade is not particularly limited, but it is preferably made of metal. Examples of cutting tools equipped with such blades include cutters, planes, slicers, and the like.

The angle at which the laminate is sliced is preferably 45° or less with respect to the direction in which the primary sheets are laminated (hereinafter sometimes simply referred to as "the lamination direction"), and with respect to the lamination direction. It is more preferably 30° or less, even more preferably 15° or less with respect to the lamination direction, and particularly preferably approximately 0° with respect to the lamination direction (that is, the direction along the lamination direction). . Here, inside the laminate formed by laminating the above-mentioned primary sheets in the thickness direction, it is presumed that the particulate filler is oriented in a direction substantially perpendicular to the lamination direction. If such a laminate is sliced at an angle of 45° or less with respect to the lamination direction, heat can be transferred even more favorably in the thickness direction of the heat conductive sheet. The reason why heat can be transferred better in the thickness direction of the thermally conductive sheet by slicing the laminate at an angle equal to or less than the above-mentioned predetermined value with respect to the lamination direction is that the particulates in the resulting thermally conductive sheet are While the filler is oriented in the thickness direction (that is, the direction substantially perpendicular to the stacking direction of the primary sheet), the heat transfer path formed by the contact of the particulate filler is well formed mainly in the thickness direction of the thermally conductive sheet. It is speculated that this is because the

In addition, from the viewpoint of easily slicing the laminate and ensuring sufficient thickness accuracy of the resulting thermally conductive sheet, the temperature of the laminate 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.
Furthermore, from the viewpoint of easily slicing the laminate and ensuring sufficient thickness accuracy of the resulting thermally conductive sheet, it is preferable to pressurize the laminate to fix it when slicing. In such pressurization, the surface to which pressure is applied is not particularly limited.

<Properties of thermally conductive sheet 1>
<<Thermal conductivity in the thickness direction>>
The thermal conductivity in the thickness direction of the thermally conductive sheet 1 is preferably 12 W/m·K or more, more preferably 13 W/m·K or more, and even more preferably 15 W/m·K or more. . If the thermal conductivity in the thickness direction of the heat conductive sheet 1 is 12 W/m·K or more, heat can be transferred even better 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 1 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 1 depends on the type of material (resin, particulate filler, etc.) used to manufacture the thermally conductive sheet 1 and its content in the primary sheet, as well as the thermal conductivity of the thermally conductive sheet 1. It can be adjusted by changing manufacturing conditions and the like. For example, by changing the volume average particle diameter and/or content ratio of the particulate filler in the above-mentioned primary sheet, the thermal conductivity in the thickness direction of the thermally conductive sheet 1 can be further increased.

＜＜Average thickness＞＞
The average thickness of the thermally conductive sheet 1 is preferably 70 μm or more, more preferably 80 μm or more, preferably 200 μm or less, more preferably 160 μm or less, and even more preferably 130 μm or less. The thickness is preferably 110 μm or less, particularly preferably 110 μm or less. If the average thickness of the thermally conductive sheet 1 is 70 μm or more, the strength of the thermally conductive sheet can be ensured, and if the average thickness of the thermally conductive sheet 1 is 200 μm or less, the strength in the thickness direction of the thermally conductive sheet can be ensured. It can transfer heat.

<<Standard deviation of thickness>>
The standard deviation of the thickness of the thermally conductive sheet 1 needs to be 3.0 μm or less, preferably 2.8 μm or less, and more preferably 2.6 μm or less. When the standard deviation of the thickness is 3.0 μm or less, the thermally conductive sheet has sufficient thickness accuracy. Therefore, it becomes possible to bring the heating element and the heat radiating element into close contact with each other through the heat conductive sheet 1, and it is possible 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 thermally conductive sheet 1 is not particularly limited, but is, for example, 1.0 μm or more.
The standard deviation of the thickness of the thermally conductive sheet 1 depends on the type of material (resin, particulate filler, etc.) used to manufacture the thermally conductive sheet 1 and its content in the primary sheet, as well as the manufacturing conditions of the thermally conductive sheet 1. It can be adjusted by changing etc. Specifically, in the method for manufacturing the thermally conductive sheet 1, the standard deviation of the thickness of the thermally conductive sheet 1 can be reduced by changing the tensile strength of the primary sheet and/or the Asker C hardness of the laminate. can.

<<Area of main surface>>
The area of the main surface of the thermally conductive sheet 1 can be, for example, 30 cm ² or more, 50 cm ² or more, 80 cm ² or more, 100 cm ² or more, It can be 1000 ^cm2 or less.

<<Surface roughness Sa>>
The surface roughness Sa of at least one main surface of the thermally conductive sheet 1 is preferably 2.80 μm or less, more preferably 2.60 μm or less, even more preferably 2.20 μm or less, and 2. It is particularly preferable that it is .00 μm or less. If the surface roughness Sa of the main surface is 2.80 μm or less, the main surface is sufficiently smooth, so that when the thermally conductive sheet is sandwiched between a heat generating element and a heat radiating element, it can be used as a heat conductive sheet. The heating element and/or the heat radiating element are in good contact with each other, and the interfacial resistance is reduced. Therefore, heat can be transferred even more favorably in the thickness direction of the heat conductive sheet. The lower limit of the surface roughness Sa of the main surface of the thermally conductive sheet 1 is not particularly limited, but is, for example, 1.0 μm or more.
Furthermore, from the viewpoint of better heat transfer in the thickness direction of the heat conductive sheet, it is preferable that the surface roughness Sa of both main surfaces (front and back surfaces) of the heat conductive sheet 1 is equal to or less than the above-mentioned preferred upper limit.
Further, when the surface roughness Sa of one main surface of the thermally conductive sheet 1 is Sa1, and the surface roughness Sa of the other main surface is Sa2, the ratio of Sa1 and Sa2 (Sa1/Sa2) is 85 /100 or more, more preferably 90/100 or more, preferably 100/85 or less, and more preferably 100/90 or more. In this way, if the ratio (Sa1/Sa2) of the surface roughness (Sa1) of one main surface of the thermally conductive sheet 1 to the surface roughness (Sa2) of the other main surface is within the above-mentioned predetermined range, It is possible to improve handling properties such as ease of grasping the thermally conductive sheet with a robot arm.
Note that the surface roughness Sa of the main surface of the thermally conductive sheet 1 can be determined by changing the type and content ratio of materials (resin, particulate filler, etc.) used for manufacturing the thermally conductive sheet 1, and the manufacturing conditions of the thermally conductive sheet 1. It can be adjusted by Specifically, in the method for manufacturing the thermally conductive sheet 1, the surface roughness Sa of the main surface of the thermally conductive sheet 1 is reduced by changing the tensile strength of the primary sheet, the Asker C hardness of the laminate, etc. I can do it.

<<Asker C hardness>>
The Asker C hardness of the thermally conductive sheet 1 is preferably 60 or more, more preferably 65 or more, even more preferably 70 or more, preferably 90 or less, and 87 or less. More preferably, it is 85 or less.

<Method for manufacturing thermally conductive sheet 1>
The thermally conductive sheet 1 can be manufactured using the above-described laminate of the present invention.
Here, the method for manufacturing the thermally conductive sheet 1 includes a slicing step of slicing the above-described laminate of the present invention. Note that the above-mentioned slicing method can be used as a method for slicing the stacked body in the slicing step.
In the method for manufacturing the thermally conductive sheet 1, since the laminate of the present invention having an Asker C hardness within a predetermined range is sliced, the standard deviation of the thickness of the resulting thermally conductive sheet 1 can be easily reduced to below the above-mentioned predetermined value. The thickness accuracy of the heat conductive sheet 1 can be sufficiently ensured. Moreover, in the method for manufacturing the thermally conductive sheet 1, since the above-described laminate of the present invention is sliced, the resulting thermally conductive sheet 1 can conduct heat well in the thickness direction.

(Thermal conductive sheet 2)
The heat conductive sheet 2 of the present invention is a heat conductive sheet containing a resin and a particulate filler, in which the volume average particle diameter of the particulate filler is within a predetermined range, and the Asker C hardness of the heat conductive sheet is within a predetermined range. It is characterized by
The heat conductive sheet 2 of the present invention has sufficient thickness accuracy and can conduct heat well in the thickness direction. Therefore, by interposing the thermally conductive sheet 2 of the present invention between the heat generating element and the heat radiating element, the heat generating element and the heat radiating element are brought into close contact with each other, and heat is uniformly transferred from the heat generating element to the heat radiating element. be able to.
Here, as the resin and particulate filler, the resin and particulate filler described above in the section of "Thermal Conductive Sheet 1" can be used. In addition, suitable examples are also as mentioned above in the section of "thermal conductive sheet 1".
Note that the thermally conductive sheet 2 of the present invention may optionally further contain additives (for example, a dispersant) other than the above-mentioned resin and particulate filler. As the additive, the additive mentioned above in the section of "Thermal Conductive Sheet 1" can be used.
The content ratio of each component of the resin, particulate filler, and optional additives in the thermally conductive sheet 2 is the same as the content ratio of each component in the primary sheet described above in the section of "Thermal conductive sheet 1". It can be set as appropriate within the same range as the range.

<Properties of thermally conductive sheet 2>
<<Asker C hardness>>
The Asker C hardness of the thermally conductive sheet 2 needs to be 60 or more, preferably 65 or more, more preferably 70 or more, needs to be 90 or less, and 87 or less. It is preferably 85 or less, and more preferably 85 or less. The thermally conductive sheet 2 whose Asker C hardness is within the above predetermined range has sufficient thickness accuracy.
Note that a method for adjusting the Asker C hardness of the heat conductive sheet 2 will be described later in connection with the manufacturing method.

<<Tensile strength>>
The tensile strength of the thermally conductive sheet 2 is preferably 1.3 MPa or more, more preferably 1.4 MPa or more, even more preferably 1.5 MPa or more, and preferably 2.3 MPa or less. , more preferably 2.0 MPa or less, and still more preferably 1.8 MPa or less. The heat conductive sheet 2 whose tensile strength is within the above predetermined range has more sufficient thickness accuracy.
In addition, when the thermally conductive sheet 2 exhibits a plurality of different tensile strength values depending on the direction in which it is pulled, it is preferable that the maximum value of the plurality of tensile strength values is within the above-mentioned predetermined range.
The tensile strength of the thermally conductive sheet 2 can be adjusted by changing the type and content ratio of materials (resin, particulate filler, etc.) used for manufacturing the thermally conductive sheet 2 and the manufacturing method of the thermally conductive sheet 2. I can do it. For example, by increasing the resin content in the heat conductive sheet 2, the tensile strength of the heat conductive sheet 2 can be increased.

<<Standard deviation of thickness>>
The standard deviation of the thickness of the thermally conductive sheet 2 is preferably 3.0 μm or less, more preferably 2.8 μm or less, and even more preferably 2.6 μm or less. If the standard deviation of the thickness is 3.0 μm or less, the thermally conductive sheet 2 has sufficient thickness accuracy. Therefore, it becomes possible to bring the heating element and the heat radiating element into close contact with each other through the heat conductive sheet, and it is possible 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 2 is not particularly limited, but is, for example, 1.0 μm or more.
The standard deviation of the thickness of the thermally conductive sheet 2 can be determined by changing the type and content ratio of materials (resin, particulate filler, etc.) used for manufacturing the thermally conductive sheet 2, and the manufacturing conditions of the thermally conductive sheet 2. Can be adjusted.

<<Others>>
The thermal conductivity in the thickness direction, the average thickness, the area of the main surface, and the surface roughness Sa of the thermally conductive sheet 2 can be appropriately set within the ranges described above in the section of the “thermal conductive sheet 1”.

<Method for manufacturing thermally conductive sheet 2>
The method for manufacturing the thermally conductive sheet 2 is such that the resulting thermally conductive sheet contains a resin and a particulate filler whose volume average particle diameter is within the above-mentioned predetermined range, and the Asker C hardness of the thermally conductive sheet is as described above. There is no particular limitation as long as it is within the predetermined range.

As a specific example of the method for manufacturing the thermally conductive sheet 2,
(1) A method of forming a composition containing a resin and a particulate filler into a block shape and then slicing the obtained block body, and
(2) A method of directly forming a composition containing a resin and a particulate filler into a sheet shape,
Examples include.
From the viewpoint of further improving the thickness accuracy of the heat conductive sheet 2 and further improving heat transfer in the thickness direction of the heat conductive sheet 2, it is preferable to use the manufacturing method described in (1) above.

Here, in the manufacturing methods (1) and (2) above, the method for molding the composition into a block shape or sheet shape is not particularly limited, and includes rolling molding, press molding, extrusion molding, injection molding, etc. It can be appropriately selected from known molding methods such as molding depending on the desired shape.
In addition, in the manufacturing method of (1) above, the block body obtained by molding the above composition includes a laminate formed by laminating a plurality of primary sheets made of the above composition in the thickness direction. do. As the method for preparing and laminating the primary sheet, the method for preparing the primary sheet and the laminating method described above in the section of "Thermal Conductive Sheet 1" can be used.

Further, in the manufacturing method (1) above, the method for slicing the block body is not particularly limited, and for example, the slicing method described above in the section of "Thermal Conductive Sheet 1" can be used.

In both of the above manufacturing methods (1) and (2), by changing the types and content ratios of the resin and particulate filler in the composition, and the conditions such as the temperature during molding of the composition, , the Asker C hardness of the resulting thermally conductive sheet 2 can be kept within the above-mentioned predetermined range.
Note that the Asker C hardness of the resulting thermally conductive sheet 2 can be adjusted within the above-mentioned predetermined range by separately subjecting the composition and/or the block to a heat treatment.
However, from the viewpoint of further improving the thickness accuracy of the resulting thermally conductive sheet 2, in the manufacturing method of (1) above, it is preferable to adjust the Asker C hardness of the block body to within the above-mentioned predetermined range before slicing. .

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 Examples and Comparative Examples, the volume average particle diameter of the particulate filler, the content ratio (volume fraction) of the particulate filler in the primary sheet, the tensile strength of the primary sheet, the asker of the block body (laminate), etc. C hardness, average thickness, standard deviation of thickness, surface roughness Sa, area reduction rate from the sliced surface, and thermal conductivity in the thickness direction of the thermally conductive sheet were measured or evaluated according to the following methods, respectively.

<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.
<Tensile strength>
The primary sheet was punched and molded using a dumbbell No. 2 in accordance with JIS K6251 to produce a sample piece. Using a tensile tester (manufactured by Shimadzu Corporation, product name "AG-IS20kN"), pinch the sample piece at 1 cm from both ends and test it perpendicular to the normal line from the surface of the sample piece at a temperature of 23°C. The sample was pulled in the same direction at a tensile speed of 500 mm/min, and the breaking strength (tensile strength) was measured.
<Asker C hardness of laminate>
The Asker C hardness of the laminate was measured at a temperature of 25°C 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). Specifically, the obtained laminate was left standing in a thermostatic chamber kept at a temperature of 25°C for 48 hours or more to be used as a test specimen.Next, the distance of the needle tip from the laminate surface was 2 cm. A hardness meter was installed, the damper was lowered, and the laminate and the damper collided.The Asker C hardness of the laminate 60 seconds after the collision was measured using a hardness meter (manufactured by Kobunshi Keiki Co., Ltd., trade name: "ASKER CL-150LJ") was used to measure twice, and the average value of the measurement results was used.
<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.
<Asker C hardness of thermally conductive sheet>
The Asker C hardness of the thermally conductive sheet is measured in accordance with the Asker C method of the Japan Rubber Institute Standards (SRIS) using a hardness meter (manufactured by Kobunshi Keiki Co., Ltd., product name "ASKER CL-150LJ") at a temperature of 25°C. Specifically, the obtained thermally conductive sheet was cut into a size of 25 mm width x 50 mm length x 0.1 mm thickness, and 90 sheets were stacked to obtain a test piece.The obtained test A thermally conductive sheet layer as a test piece was obtained by leaving the piece in a thermostatic chamber kept at a temperature of 25°C for 48 hours or more.Next, the damper height was adjusted so that the pointer was 95 to 98. The thermally conductive sheet layer and the damper were then collided. The Asker C hardness of the thermally conductive sheet layer 60 seconds after the collision was measured using a hardness meter (manufactured by Kobunshi Keiki Co., Ltd., trade name "ASKER CL-150LJ"). 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>
The surface roughness Sa of the main surface 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, the sample is a thermally conductive sheet cut into a square of arbitrary size of 1 cm square or more, the analysis range is 1 cm x 1 cm, and the three-dimensional shape is determined for both the front and back principal surfaces of the sample. It was measured. 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).
Furthermore, the ratio of Sa1 to Sa2 (Sa1/Sa2) was calculated, where the surface roughness Sa of one main surface of the thermally conductive sheet is Sa1 and the surface roughness Sa of the other main surface is Sa2.
<Area reduction rate from slice surface>
The area of the sliced surface of the laminate formed by slicing the block body (laminated body) and the area of the thermally conductive sheet obtained by the slicing are each measured, and using the following formula, from the sliced surface The area reduction rate was calculated. Note that when slicing is performed normally, the area of the sliced surface of the laminate and the area of the thermally conductive sheet match, but when slicing a particularly soft laminate, the thermally conductive sheet may be compressed by the pressure of the blade during slicing. As a result, a thermally conductive sheet having an area smaller than the area of the sliced surface of the laminate is obtained.
(Area reduction rate) = {(Area of sliced surface of laminate) - (Area of thermally conductive sheet)} ÷ (Area of sliced surface of laminate)
<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 measurement was performed using a thermophysical property measuring device (manufactured by Bethel Co., Ltd., product name: "Thermo Wave Analyzer TA35").
[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.

(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. Then, the content ratio (volume fraction) of the particulate filler in the primary sheet and the tensile strength of the primary sheet were calculated and measured. The results are shown in Table 1.
<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>
Thereafter, the entire upper surface of the obtained block was pressed with a metal plate, leaving a length necessary for slicing, and a pressure of 0.1 MPa was applied in the stacking direction (i.e., from above) to fix the block. . Note that the sides and back of the block were not fixed. At this time, the temperature of the block was 25°C.
Next, a blade 10 having the shape shown in FIG. 1 (double-edged, blade angle 2θ: 20°, maximum thickness of blade part: 3.5 mm, material: super steel) was placed in the press part of a servo press machine (manufactured by Electric Discharge Precision Machining Research Institute). , Rockwell hardness: 91.5, silicone processing on the blade surface: None, total length: 200 mm) was attached, slice width: 100 μm, slicing speed: 200 mm/sec. For example, a thermally conductive sheet having a main surface of 150 mm in length x 80 mm in width was obtained by slicing it in a direction corresponding to the normal to the main surface of the stacked primary sheets. The attitude of the blade at the time of slicing was such that the angle α shown in FIG.
Then, the average thickness, standard deviation of the thickness, surface roughness Sa, area reduction rate from the sliced surface, 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 the formation of the primary sheet of Example 1, 0.9 part of a dispersant (alkylammonium salt of high molecular weight copolymer, "BYK-9076" manufactured by BYK Chemie) was further added and mixed by stirring to obtain a mixture. Except for this, a primary sheet, a block body, and a heat conductive sheet were produced in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1.

(Example 3)
In the formation of the primary sheet in Example 2, the primary sheet, block body, and thermal A conductive sheet was produced and various evaluations were performed. The results are shown in Table 1.

(Example 4)
In the formation of the primary sheet of Example 1, the primary sheet, block body, A thermally conductive sheet was prepared and various evaluations were performed. The results are shown in Table 1.

(Example 5)
In the formation of the primary sheet of Example 1, the primary sheet, block body, A thermally conductive sheet was prepared and various evaluations were performed. The results are shown in Table 1.

(Example 6)
Expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., trade name "EC100", volume average particle size: 200 μm) is crushed in a coffee mill and then classified with a sieve to produce expanded graphite with a volume average particle size of 150 μm. I got it.
In the formation of the primary sheet in Example 1, as a particulate filler, instead of 90 parts of expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., product name "EC300") having a volume average particle diameter of 50 μm, the above obtained A primary sheet, a block body, and a thermally conductive sheet were produced in the same manner as in Example 1, except that 90 parts of expanded graphite having a volume average particle diameter of 150 μm were used, and various evaluations were performed. . The results are shown in Table 1.

(Example 7)
In the formation of the primary sheet in Example 1, the amount of expanded graphite used as a particulate filler was changed from 90 parts to 130 parts, and a dispersant (an alkylammonium salt of a high molecular weight copolymer, "BYK-9076" manufactured by BYK Chemie Co., Ltd.) was changed from 90 parts to 130 parts. A primary sheet, a block body, and a thermally conductive sheet were prepared in the same manner as in Example 1, except that 6.0 parts of ``6.0 parts'') were further added and then stirred and mixed to obtain a mixture, and various evaluations were conducted. I did it. The results are shown in Table 1.

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

(Comparative example 2)
In forming the primary sheet of Example 1, the amount of thermoplastic fluororesin that is liquid at room temperature and pressure was changed from 70 parts to 100 parts, and the amount of thermoplastic fluororesin that is solid at room temperature and pressure was changed to 30 parts. 0 parts, and as a particulate filler, 90 parts of expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., product name "EC300") with a volume average particle diameter of 50 μm was replaced with 90 parts of expanded graphite with a volume average particle diameter of 30 μm. Using 80 parts of a certain expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., product name "EC500"), a plasticizer (bis(2-ethylhexyl) sebacate, manufactured by Daihachi Kagaku Kogyo Co., Ltd., product name "DOS") was used. A primary sheet, a block body, and a heat conductive sheet were produced in the same manner as in Example 1, except that 5 parts of the mixture was further added and then stirred and mixed to obtain a mixture, and various evaluations were performed. The results are shown in Table 1.

(Comparative example 3)
In forming the primary sheet of Example 1, the amount of thermoplastic fluororesin that is liquid at room temperature and pressure was changed from 70 parts to 100 parts, and the amount of thermoplastic fluororesin that is solid at room temperature and pressure was changed to 30 parts. As a particulate filler, 90 parts of expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., product name "EC300") with a volume average particle diameter of 50 μm was replaced with 90 parts of expanded graphite with a volume average particle diameter of 200 μm. A primary sheet, a block body, and a thermally conductive sheet were produced in the same manner as in Example 1, except that 50 parts of a certain expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., product name "EC100") was used, Various evaluations were conducted. The results are shown in Table 1.

(Comparative example 4)
In forming the primary sheet of Example 1, the amount of thermoplastic fluororesin that is liquid at room temperature and pressure was changed from 70 parts to 45 parts, and the amount of thermoplastic fluororesin that is solid at room temperature and pressure was changed to 30 parts. 40 parts, and as a particulate filler, 90 parts of expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., product name "EC300") with a volume average particle diameter of 50 μm was replaced with 90 parts of expanded graphite with a volume average particle diameter of 200 μm. Using 85 parts of a certain expanded graphite (manufactured by Ito Graphite Industries Co., Ltd., product name "EC100"), a plasticizer (bis(2-ethylhexyl) sebacate, manufactured by Daihachi Kagaku Kogyo Co., Ltd., product name "DOS") was used. A primary sheet and a block body were produced in the same manner as in Example 1, except that 5 parts of the mixture was further added and then stirred and mixed to obtain a mixture, and various evaluations were performed. The results are shown in Table 1.
Furthermore, when we attempted to produce a thermally conductive sheet using the block obtained above in the same manner as in Example 1, the blade escaped at about half of the block when slicing the block. I couldn't slice the body all the way.
Therefore, slicing was performed by increasing the slice width by 10 μm, and when the slice width was set to 150 μm, the block body could be sliced to the end to obtain a thermally conductive sheet. Various evaluations were performed using the obtained thermally conductive sheet. The results are shown in Table 1.
Note that when slicing was performed with a slicing width of 140 μm, the blade ran away and only about 80% of the block could be sliced.

(Comparative example 5)
<Formation of primary sheet>
45 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. 40 parts of expanded graphite as a particulate filler (manufactured by Ito Graphite Industries Co., Ltd., product name EC100, volume average particle diameter: 200 μm), and sebacic acid ester as a plasticizer. (manufactured by Daihachi Kagaku Kogyo Co., Ltd., trade name "DOS") 5 parts by mass 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 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. Then, the content ratio (volume fraction) of the particulate filler in the primary sheet and the tensile strength of the primary sheet were calculated and measured. The results are shown in Table 1.
<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 secondary sheet of 150 mm x thickness 0.50 mm (500 μm) 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. In addition, the temperature of the block body was set to room temperature.
<Pressure process>
Using a precision hot press machine (manufactured by Shinto Kogyo Co., Ltd., product name "CYPT-20"), the press plate was heated to 50°C, and the secondary sheet obtained above was pressed for 30 seconds at a pressure of 2.6 MPa. A pressing step was performed to obtain a thermally conductive sheet measuring 150 mm long x 150 mm wide x 0.125 mm (125 μm) thick.
Then, the average thickness, standard deviation of the thickness, surface roughness Sa, area reduction rate from the sliced surface, and thermal conductivity in the thickness direction of the obtained thermally conductive sheet were measured. The results are shown in Table 1.

From Table 1, Example 1 is made by laminating a plurality of primary sheets in the thickness direction containing a resin and a particulate filler having a volume average particle diameter within a predetermined range, and has an Asker C hardness within a predetermined range. It can be seen that by using the laminates No. 6 to 6, it is possible to form a thermally conductive sheet that has sufficient thickness accuracy and is capable of good heat transfer in the thickness direction.
On the other hand, a laminate is used in which a plurality of primary sheets containing a resin and a particulate filler having a volume average particle diameter within a predetermined range are laminated in the thickness direction, and the Asker C hardness is within a predetermined range. It can be seen that in the case of Comparative Examples 1 to 4 where there is no heat conductive sheet, it is not possible to form a heat conductive sheet that has sufficient thickness accuracy and can conduct heat well in the thickness direction.

According to the present invention, it is possible to provide a laminate that can form a thermally conductive sheet that has sufficient thickness accuracy and can conduct heat well in the thickness direction.
Further, according to the present invention, it is possible to provide a heat conductive sheet that can conduct heat well in the thickness direction while having sufficient thickness accuracy.

10 Blade 11 Blade surface 20 Block body 21 Slice surface 30 Heat conductive sheet

Claims (10)

A method for producing a thermally conductive sheet, the method comprising the step of obtaining a thermally conductive sheet by slicing a laminate formed by laminating a plurality of primary sheets containing resin and expanded graphite in the thickness direction,
The volume average particle diameter of the expanded graphite is 40 μm or more and 180 μm or less,
The Asker C hardness of the laminate is 60 or more and 90 or less,
The standard deviation of the thickness of the thermally conductive sheet is 3.0 μm or less,
The ratio of Sa1 to Sa2 (Sa1/Sa2) is 85/100 or more, where the surface roughness Sa of one main surface of the thermally conductive sheet is Sa1 and the surface roughness Sa of the other main surface is Sa2. A method for producing a thermally conductive sheet having a thermal conductivity of 100/85 or less. The method for manufacturing a thermally conductive sheet according to claim 1, wherein the primary sheet has a tensile strength of 1.5 MPa or more. The method for manufacturing a thermally conductive sheet according to claim 1 or 2, wherein the content of the expanded graphite in the primary sheet is 35% by volume or more and 55% by volume or less. The method for producing a thermally conductive sheet according to any one of claims 1 to 3, wherein the primary sheet further contains a dispersant. The method for producing a thermally conductive sheet according to any one of claims 1 to 4, wherein the main surface has an area of 30 cm ² or more. A thermally conductive sheet containing resin and expanded graphite,
The volume average particle diameter of the expanded graphite is 40 μm or more and 180 μm or less,
Asker C hardness of the thermally conductive sheet is 60 or more and 90 or less,
The standard deviation of the thickness of the thermally conductive sheet is 3.0 μm or less,
The ratio of Sa1 to Sa2 (Sa1/Sa2) is 85/100 or more, where the surface roughness Sa of one main surface of the thermally conductive sheet is Sa1 and the surface roughness Sa of the other main surface is Sa2. A thermally conductive sheet that is 100/85 or less. The thermally conductive sheet according to claim 6, having an average thickness of 200 μm or less. The heat conductive sheet according to claim 6 or 7 , wherein the content of the expanded graphite in the heat conductive sheet is 35% by volume or more and 55% by volume or less. The thermally conductive sheet according to any one of claims 6 to 8 , having a tensile strength of 1.3 MPa or more. The thermally conductive sheet according to any one of claims 6 to 9 , further comprising a dispersant.

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