JP7159643B2 - Method for manufacturing thermally conductive sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a heat conductive sheet.

In recent years, electronic components such as power semiconductors (such as IGBT modules) and integrated circuit (IC) chips have been increasing in heat generation as their performance has improved. As a result, in electronic equipment using electronic components, it is necessary to take measures against functional failure due to temperature rise of the electronic components.

As a countermeasure against functional failure due to temperature rise of electronic components, generally, a method of accelerating heat dissipation is adopted by attaching a radiator such as a metal heat sink, radiator plate, or radiator fin to the heat generating body of the electronic component. ing. When using a radiator, in order to efficiently transfer heat from the heating element to the radiator, a sheet-like member with high thermal conductivity (thermally conductive sheet) is placed between the thermally conductive sheet. A predetermined pressure is applied to the heat generating member and the heat dissipating member. As the thermally conductive sheet, a sheet molded using a composite material sheet having excellent thermal conductivity is used.

In addition, electromagnetic noise and static electricity caused by mutual interference between electronic devices may cause functional failures in the electronic devices. As a countermeasure against functional failure due to such electromagnetic noise and static electricity, a highly conductive thermal conductive sheet can be attached directly to an electronic device or electronic component, or used as a material (packaging material, etc.) that comes into contact with an electronic device or electronic component. is adopted. In this way, by using a thermally conductive sheet with high electrical conductivity, it is possible to prevent the propagation of noise generated between electronic devices and to prevent electrification.

Therefore, the thermally conductive sheet is required to exhibit high thermal conductivity and electrical conductivity with an orientation according to the application and the place of use.

For example, in Patent Document 1, a laminate obtained by laminating primary sheets obtained by performing spherical molding and pressing on a composition containing an acrylic ester copolymer resin and a particulate carbon material such as graphite particles is laminated in the thickness direction. A technique for producing a thermally conductive sheet having excellent thermal conductivity and flexibility by slicing is disclosed.

For slicing, there is a technique of cutting using a wire saw device as described below.
For example, wire saws are used as means for cutting wafers from semiconductor ingots. This wire saw is arranged in a state in which a large number of cutting wires are arranged across a roll at equal intervals, and a large number of thin pieces are simultaneously cut out from one process.
This wire saw is provided with a guide roller having a large number of guide grooves for supporting the wire. For example, in Patent Document 2, the guide roller is composed of an inner roller and an outer roller mounted on the outer periphery of the inner roller. It is described that only the outer roller can be replaced while it is attached to the support device.
As a wire saw, a fixed-abrasive type wire saw is used in which abrasive grains such as white alumina, green silicon carbide, or diamond are fixed to the peripheral surface of a core wire. The fixed abrasive type wire saw includes an electrodeposition wire saw in which abrasive grains are fixed by electrodeposition and a resin bond wire saw in which abrasive grains are fixed using a resin as a binder. At present, resin-bonded wire saws are the mainstream of wire saws.
Further, for example, Patent Document 3 discloses a saw wire with abrasive grains, in which a paint obtained by kneading a binder made of an organic or inorganic material and abrasive grains is applied to the surface of a core wire (core wire) and fixed by baking, wherein the core wire is It is disclosed to use a saw wire with abrasive grains having fine dents on the surface and the abrasive grains entering the dents and being fixed to the core wire.

In addition, in order to solve the problem that abrasive grains tend to fall off due to wear and vibration of the resin layer due to contact with the workpiece when cutting silicon ingots using a wire saw, for example, patented Document 3 discloses a wire saw in which fine dents are formed on the surface of the core wire and abrasive grains are made to enter the dents and are fixed to the core wire. A wire saw is disclosed in which a resin layer for cutting is formed and an abrasive grain layer is adhered.

In addition, in order to solve the problem that cutting powder generated during cutting process accumulates in the gaps between abrasive grains and causes clogging, which reduces sharpness, for example, Patent Document 5 discloses that abrasive grains are distributed in a dense portion. A wire saw is disclosed in which a rough portion is formed in a helical shape so that chips generated by the cutting action of a dense portion are discharged to the rough portion.

JP 2014-1388 A JP-A-9-216222 JP-A-10-328932 JP-A-2000-246542 JP-A-2000-271872

However, in the technique described in the above-mentioned Patent Document 1, in order for the heat conductive sheet to exhibit high thermal conductivity, it is necessary to orient the particulate carbon material such as graphite particles in the heat conductive sheet vertically. , a smooth board surface having a slit and a blade portion protruding from the slit portion are used to slice and cut one by one. In addition, slicing increases the number of slices and increases the amount of heat accumulated in the sheet due to frictional heat generated during slicing, which increases the degree of curling of the sheet and may tear the curled sheet when it is unfolded. There was a problem that workability and yield deteriorated.

Accordingly, an object of the present invention is to provide a method for producing a thermally conductive sheet that can improve workability and yield when producing a thermally conductive sheet having high thermal conductivity.

The present inventors have made intensive studies to achieve the above object. Then, by slicing the laminate using a multi-wire saw device, it was found that the workability and yield when manufacturing a thermally conductive sheet with high thermal conductivity can be significantly improved, and the present invention was completed. .

That is, an object of the present invention is to advantageously solve the above-mentioned problems. Using a multi-wire saw device having wires arranged in a plurality of rows, a laminate having a plurality of heat conductive layers containing a thermoplastic resin and a heat conductive filler formed in the thickness direction is cut in the stacking direction of the laminate (Fig. 1 The direction of the arrow in ) includes a slicing step of slicing at an angle of 45° or less. Such a method for producing a thermally conductive sheet can improve workability and yield when producing a thermally conductive sheet with high thermal conductivity.

In the method for producing a heat conductive sheet of the present invention, the laminate further has a resin coating layer containing at least one of a thermosetting resin and a hot-melt resin, and the resin coating layer comprises at least the extension of the wire. It is preferably formed on the laminate side surface having a normal extending substantially in the same direction as the direction. A resin coating layer containing at least one of a thermosetting resin and a hot-melt resin has at least a normal line extending in substantially the same direction as the direction in which the wires extend. is formed on the side surface of the laminate that penetrates), the impact on the plurality of heat conductive layers in the heat conductive sheet obtained through the slicing process (for example, the heat conductive sheet is collected in the collection layer tank 4 in FIG. 1 The resin coating layer can absorb the impact during the slicing process, preventing the heat conductive sheet from tearing during the slicing process, and fixing the laminate against the vibration of the wire during the slicing process. can do.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the heat conductive sheet which can improve the workability|operativity and yield at the time of manufacturing a heat conductive sheet with high thermal conductivity can be provided.

It is a figure which shows an example of embodiment of the multi-wire saw apparatus used for the manufacturing method of the heat conductive sheet of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.
The thermally conductive sheet manufactured by the manufacturing method of the present invention can be used, for example, by sandwiching it between the heat generating element and the heat dissipating element when attaching the heat dissipating element to the heat generating element. That is, the heat conductive sheet manufactured by the manufacturing method of the present invention has a high heat dissipation capability as a heat dissipation member, together with a heat dissipation body such as a heat sink, a heat dissipation plate, and a heat dissipation fin. Fewer heat dissipation devices can be constructed.
Further, the thermally conductive sheet can also be used as a thermally radiating sheet, for example, by attaching it to a heating element alone. That is, the heat conductive sheet can be used alone or in combination with a radiator to form a heat radiator. The thermally conductive sheet can be manufactured, for example, by using the method for manufacturing a thermally conductive sheet of the present invention, which will be described later.

(Manufacturing method of heat conductive sheet)
The method for producing a thermally conductive sheet of the present invention includes at least a slicing step, and if necessary, further includes a pre-thermally conductive sheet forming step, a laminate forming step, and other steps.

<Thermal conductive sheet>
The thermally conductive sheet is a thermally conductive sheet obtained by slicing a laminate in which a plurality of thermally conductive layers (hereinafter sometimes referred to as "pre-thermally conductive sheets") are formed in the thickness direction, and the thermally conductive layer contains a thermoplastic resin and a thermally conductive filler (thermally conductive filler). Thereby, the thermally conductive sheet of the present invention has high thermal conductivity.

<<Thermoplastic Resin>>
The thermoplastic resin that can be contained in the heat conductive layer in the heat conductive sheet manufactured by the heat conductive sheet manufacturing method of the present invention constitutes the matrix resin of the heat conductive layer, and the heat conductive filler (heat conductive filler ) and the like.
Examples of such thermoplastic resins include "thermoplastic resins that are liquid at normal temperature and normal pressure" and "thermoplastic resins that are solid at normal temperature and normal pressure". These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
In this specification, "normal temperature" refers to 23°C, and "normal pressure" refers to 1 atm (absolute pressure).

[Thermoplastic resin that is liquid at normal temperature and pressure]
Since the heat conductive layer (heat conductive sheet) contains a thermoplastic resin that is liquid at normal temperature and pressure, the flexibility of the heat conductive layer (heat conductive sheet) can be improved. sheet) and the adherend (heating element, radiator) to which the thermally conductive layer (thermally conductive sheet) is adhered can be enhanced, and the thermally conductive sheet can exhibit higher thermal conductivity. .

Examples of thermoplastic resins that are liquid at normal temperature and pressure include acrylic resins, epoxy resins, silicone resins, and fluorine resins. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among these, from the viewpoint of improving the flame retardancy, heat resistance, oil resistance, chemical resistance, etc. of the heat conductive layer and thus the heat conductive sheet, Liquid thermoplastic fluororesins are preferred.

[[Thermoplastic fluororesin liquid at normal temperature and pressure]]
The thermoplastic fluororesin that is liquid at normal temperature and pressure is not particularly limited as long as it is a thermoplastic fluororesin that is liquid at normal temperature and pressure. Examples of thermoplastic fluororesins that are liquid at normal temperature and pressure include vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropentene-tetrafluoroethylene terpolymer, perfluoropropene oxide polymer, tetrafluoroethylene-propylene-vinylidene fluoride copolymer, and the like. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Examples of commercially available thermoplastic fluororesins that are liquid at normal temperature and pressure include Viton (registered trademark) LM manufactured by DuPont Co., Ltd., Daiel (registered trademark) G-101 manufactured by Daikin Industries, Ltd., and 3M. Dynion FC2210 manufactured by Co., Ltd., SIFEL series manufactured by Shin-Etsu Chemical Co., Ltd., and the like can be mentioned.

The viscosity of the thermoplastic fluororesin, which is liquid at normal temperature and normal pressure, is not particularly limited. coefficient) is preferably 500 cP or more and 30000 cP or less, more preferably 550 cP or more and 25000 cP or less.

Incidentally, the molecular weight of a thermoplastic fluororesin that is liquid at normal temperature and normal pressure is generally smaller than that of a thermoplastic fluororesin that is solid at normal temperature and pressure, which will be described later. Therefore, for example, when the heat conductive sheet contains a thermoplastic fluororesin that is liquid under normal temperature and pressure and a thermoplastic fluororesin that is solid under normal temperature and pressure, gel permeation chromatography (GPC) is used. Of the two different peaks obtained, the peak on the low molecular weight side usually indicates a thermoplastic fluororesin that is liquid at normal temperature and pressure, and the peak on the high molecular weight side indicates a thermoplastic fluororesin that is solid at normal temperature and pressure. .

[[Content ratio]]
The content of the thermoplastic resin that is liquid at room temperature and pressure is 40% by mass or more of the total content of the thermoplastic resin that is liquid at room temperature and pressure and the thermoplastic resin that is solid at room temperature and pressure, which will be described in detail later. It is preferably 60% by mass or more, more preferably 90% by mass or less, and more preferably 75% by mass or less. If the content of the thermoplastic resin, which is liquid at normal temperature and pressure, is within the above range, the flexibility of the thermally conductive layer and thus the thermally conductive sheet can be further increased, for example, by sandwiching the thermally conductive sheet and the thermally conductive sheet. Since the adhesion between the body (heat generating body and radiator) can be improved, the thermal conductive sheet can exhibit high thermal conductivity under relatively low clamping pressure (e.g., 0.5 MPa or less). It is from.

[Thermoplastic resin that is solid at normal temperature and pressure]
Since the heat conductive layer (heat conductive sheet) contains a thermoplastic resin that is solid at normal temperature and pressure, the heat conductive layer (heat conductive sheet) and the adherend (heat generation) to which the heat conductive layer (heat conductive sheet) is adhered It is possible to increase the adhesion between the heat conductive sheet and the body, radiator), so that the heat conductive sheet can exhibit high thermal conductivity.

Examples of thermoplastic resins that are solid under normal temperature and pressure include poly(2-ethylhexyl acrylate), copolymers of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its esters, polyacrylic acid or its esters. Acrylic resin such as acrylic resin; silicone resin; fluorine resin; polyethylene; polypropylene; ethylene-propylene copolymer; polymethylpentene; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; styrene-acrylonitrile copolymer; acrylonitrile-butadiene-styrene copolymer (ABS resin); Styrene-isoprene block copolymer or hydrogenated product thereof; Polyphenylene ether; Modified polyphenylene ether; Aliphatic polyamides; Aromatic polyamides; Polyamideimide; Polycarbonate; ether ketone; polyketone; polyurethane; liquid crystal polymer; These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among these, from the viewpoint of improving the flame retardancy, heat resistance, oil resistance, and chemical resistance of the heat conductive layer and thus the heat conductive sheet, the thermoplastic resin that is solid at normal temperature and pressure is A solid thermoplastic fluororesin is preferred.

[[Thermoplastic fluororesin solid at normal temperature and pressure]]
The thermoplastic fluororesin that is solid at normal temperature and normal pressure is not particularly limited as long as it is a thermoplastic fluororesin that is solid at normal temperature and normal pressure. Thermoplastic fluororesins that are solid under normal temperature and pressure include, for example, vinylidene fluoride fluororesins, tetrafluoroethylene-propylene fluororesins, tetrafluoroethylene-perfluorovinyl ether fluororesins, and the like, which are produced by polymerizing fluorine-containing monomers. The resulting elastomer and the like can be mentioned. More specifically, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polychloro trifluoroethylene, ethylene-chlorofluoroethylene copolymer, tetrafluoroethylene-perfluorodioxole copolymer, polyvinyl fluoride, tetrafluoroethylene-propylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, Vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, acrylic-modified polytetrafluoroethylene, ester-modified polytetrafluoroethylene, epoxy-modified polytetrafluoroethylene and silane-modified polytetrafluoroethylene , and so on. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among these, a vinylidene fluoride-hexafluoropropylene copolymer is preferable from the viewpoint of workability.

In addition, commercially available thermoplastic fluororesins that are solid under normal temperature and pressure include, for example, DAIEL (registered trademark) G-912 and G-700 series manufactured by Daikin Industries, Ltd., DAIEL G-550 series/G- 600 series, Daiel G-310; KYNAR (registered trademark) series and KYNAR FLEX (registered trademark) series manufactured by ALKEMA; Dyneon FC2211 and FPO3600ULV manufactured by 3M;

[[Content ratio of thermoplastic fluororesin]]
When the thermoplastic resin is a thermoplastic fluororesin, the content of the thermoplastic fluororesin in the thermally conductive layer (thermally conductive sheet) is preferably 30% by mass or more and 60% by mass or less. If the content of the thermoplastic fluororesin is within the above range, the flame retardancy, heat resistance, oil resistance, chemical resistance, etc. of the thermally conductive sheet can be further improved. When the thermoplastic resin contains both a thermoplastic fluororesin that is liquid under normal temperature and pressure and a thermoplastic fluororesin that is solid under normal temperature and pressure, the total content of each of them may be within the above range. preferable.

<<Thermal Conductive Filler (Thermal Conductive Filler)>>
By including a thermally conductive filler (thermally conductive filler) in the thermally conductive layer in the thermally conductive sheet manufactured by the method for manufacturing a thermally conductive sheet of the present invention, the thermal conductivity of the thermally conductive layer (thermally conductive sheet) is further increased. can be enhanced. Examples of thermally conductive fillers (thermally conductive fillers) that the thermally conductive layer (thermally conductive sheet) may contain include carbonaceous materials, inorganic oxide materials, and inorganic nitride materials. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.

[Carbonaceous material]
Examples of carbonaceous materials include particulate carbon materials and fibrous carbon materials.
When the thermally conductive filler (thermally conductive filler) is a carbonaceous material, the content of the carbonaceous material in the thermally conductive layer (thermally conductive sheet) is preferably 40% by mass or more, and 50% by mass or more. is more preferably 80% by mass or less, and more preferably 60% by mass or less. If the content of the carbonaceous material is at least the above lower limit, heat transfer paths can be well formed in the heat conductive layer (heat conductive sheet), so that the heat conductivity of the heat conductive layer and thus the heat conductive sheet can be further enhanced. can be done. In addition, if the content of the carbonaceous material is equal to or less than the above upper limit, the reduction in flexibility of the heat conductive layer and thus the heat conductive sheet due to the blending of the carbonaceous material is suppressed, and the heat conductive layer (heat conductive sheet) and It is possible to improve the adhesion between the adherend (heat generating body, radiator) and the thermal conductive sheet to exhibit excellent thermal conductivity.

[[particulate carbon material]]
The particulate carbon material is not particularly limited, and examples thereof include graphite such as artificial graphite, flake graphite, exfoliated graphite, natural graphite, acid-treated graphite, expansive graphite, and expanded graphite; carbon black; can be used. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among these, expanded graphite is preferred. If expanded graphite is used for the thermally conductive layer (thermally conductive sheet), the thermal conductivity of the thermally conductive layer and thus of the thermally conductive sheet can be further improved.

-expanded graphite-
Expanded graphite can be obtained, for example, by heat-treating expandable graphite obtained by chemically treating graphite such as flake graphite with sulfuric acid or the like to expand it, and then pulverizing the expanded graphite. Examples of expanded graphite include EC1500, EC1000, EC500, EC300, EC100, and EC50 (all trade names) manufactured by Ito Graphite Industry Co., Ltd.

-Average particle size-
The average particle diameter of the particulate carbon material is preferably 50 μm or more, more preferably 150 μm or more, preferably 300 μm or less, and more preferably 200 μm or less in terms of volume average particle diameter. If the average particle size of the particulate carbon material is at least the above lower limit, the heat transfer path of the particulate carbon material in the thermally conductive layer (thermally conductive sheet) can be better formed, and heat can be conducted even at a relatively low sandwiching pressure. This is because the layer and thus the thermally conductive sheet can exhibit more excellent thermal conductivity. Also, if the average particle size of the particulate carbon material is equal to or less than the above upper limit, it is possible to ensure good flexibility of the heat conductive layer and thus the heat conductive sheet.
In the present specification, the "volume average particle size" is measured using a laser diffraction method using, for example, a laser diffraction/scattering particle size distribution analyzer (manufactured by Horiba, model "LA-960"). It can be obtained as the particle diameter (D50) when the cumulative volume calculated from the small diameter side is 50% in the obtained particle diameter distribution. Here, the measurement of the average particle diameter of the particulate carbon material is not particularly limited, and any method such as dissolving the resin using a good solvent for the resin contained in the heat conductive sheet may be used. can be used to remove the particulate carbon material from the thermally conductive sheet.

-aspect ratio-
The aspect ratio (major axis/minor axis) of the particulate carbon material is preferably 1 or more and 10 or less, more preferably 1 or more and 5 or less.
In this specification, the “aspect ratio” refers to an arbitrary 50 Measure the maximum diameter (major diameter) and the particle diameter (minor diameter) in the direction perpendicular to the maximum diameter (minor diameter) of each particulate carbon material, and calculate the average value of the ratio of the major diameter to the minor diameter (major diameter/minor diameter). can be obtained by

[[Fibrous carbon material]]
The fibrous carbon material that the heat conductive layer (heat conductive sheet) may optionally contain is not particularly limited, and examples thereof include carbon nanotubes (hereinafter sometimes referred to as "CNT") and vapor-grown carbon. Fibers, carbon fibers obtained by carbonizing organic fibers, cut products thereof, and the like can be used. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
For example, if the thermally conductive sheet contains a fibrous carbon material, the thermal conductivity of the thermally conductive sheet can be improved, and powder falling of the particulate carbon material can be prevented. Although the reason why powder falling off of the particulate carbon material can be prevented by blending the fibrous carbon material is not clear, the formation of a three-dimensional network structure by the fibrous carbon material contributes to heat conduction. It is presumed that this is because detachment of the particulate carbon material is prevented while improving the properties and strength.

Among the materials described above, fibrous carbon nanostructures such as CNTs are preferably used as the fibrous carbon material, and fibrous carbon nanostructures containing CNTs are more preferably used. This is because the use of fibrous carbon nanostructures containing CNTs can further improve the thermal conductivity and strength of the thermally conductive layer and thus the thermally conductive sheet at a relatively low clamping pressure.

-Fibrous carbon nanostructure containing CNT-
A fibrous carbon nanostructure containing CNTs, which can be suitably used as a fibrous carbon material, may consist of CNTs alone, or may consist of CNTs and fibrous carbon nanostructures other than CNTs. It may be a mixture.
The CNTs in the fibrous carbon nanostructure are not particularly limited, and single-walled carbon nanotubes and/or multi-walled carbon nanotubes can be used. Nanotubes are preferred, and single-walled carbon nanotubes are more preferred. This is because the use of single-walled carbon nanotubes can further improve the thermal conductivity and strength of the thermal conductive sheet compared to the use of multi-walled carbon nanotubes.

-aspect ratio-
Here, the aspect ratio (major axis/minor axis) of the fibrous carbon material is preferably greater than 10.
In the present invention, the "aspect ratio of the fibrous carbon material" refers to the maximum diameter (major diameter) of 100 fibrous carbon materials randomly selected using a TEM (transmission electron microscope) and the maximum diameter perpendicular to the maximum diameter. It can be obtained by measuring the particle diameter (minor diameter) in the direction to which the particle diameter extends, and calculating the average value of the ratio of the major diameter to the minor diameter (major diameter/minor diameter).

-Specific surface area-
Further, the specific surface area of the fibrous carbon material is preferably 300 m ² /g or more, more preferably 600 m ² /g or more, preferably 2500 m ² /g or less, and 1200 m ² /g or less. is more preferable. If the specific surface area of the fibrous carbon material is at least the above lower limit, the fibrous carbon material can more favorably form a three-dimensional network structure in the heat conductive sheet. As a result, the thermal conductivity of the thermally conductive sheet can be compatible at a higher level. In addition, if the specific surface area of the fibrous carbon material is equal to or less than the above upper limit, aggregation of the fibrous carbon material can be suppressed, and the dispersibility of the fibrous carbon material in the heat conductive sheet can be enhanced.
In the present invention, the "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET method.

-Preparation of fibrous carbon material-
As the fibrous carbon material, a commercially available product may be used. For example, fibrous carbon nanostructures containing CNTs are efficiently produced according to the Super Growth (SG) method (see International Publication No. 2006/011655). can be produced commercially. In addition, below, the CNT obtained by the SG method may also be referred to as "SGCNT".
Here, the fibrous carbon nanostructure containing SGCNTs produced by the super-growth method may be composed only of SGCNTs, or in addition to SGCNTs, other materials such as non-cylindrical carbon nanostructures may be used. Carbon nanostructures may be included.

- Content ratio of fibrous carbon material -
The content of the fibrous carbon material in the heat conductive layer (heat conductive sheet) is preferably 0.03% by mass or more, more preferably 0.05% by mass or more. It is preferably 0% by mass or less, more preferably 1.0% by mass or less. If the content of the fibrous carbon material is at least the above lower limit, heat transfer paths can be well formed in the heat conductive layer (heat conductive sheet), so that the heat conductivity of the heat conductive layer and thus the heat conductive sheet is further enhanced. This is because the strength can be further increased while the strength can be increased. Further, if the content ratio of the fibrous carbon material is equal to or less than the above upper limit, it is possible to suppress the decrease in the flexibility of the heat conductive layer and thus the heat conductive sheet due to the blending of the fibrous carbon material, and the heat conductive layer (heat conductive sheet) and the adherend (heat generating element, heat dissipating element) can be enhanced to allow the thermally conductive sheet to exhibit excellent thermal conductivity.

<<Additives>>
Known additives that can be used to form the thermally conductive layer (thermally conductive sheet) can be further blended into the thermally conductive layer (thermally conductive sheet), if necessary. Additives that can be blended in the heat conductive layer (heat conductive sheet) are not particularly limited, and examples thereof include flame retardants such as red phosphorus flame retardants and phosphate ester flame retardants; fatty acid ester plasticizers; plasticizers such as; 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 wettability improvers such as system surfactants; ion trap agents such as inorganic ion exchangers; and the like.

<Pre-thermal conductive sheet forming process>
In the pre-thermal conductive sheet molding step, a composition containing a thermoplastic resin, a thermally conductive filler (thermally conductive filler), and further containing optional components such as additives is pressurized into a sheet, and pre-heated. Get a conductive sheet.

<<Composition>>
Here, the composition can be prepared by mixing a thermoplastic resin, a thermally conductive filler (thermally conductive filler), and the optional components (additives) described above. As the thermoplastic resin, the thermally conductive filler (thermally conductive filler) and optional additives, the thermoplastic resin and the thermally conductive filler that can be contained in the thermally conductive sheet produced by the method for producing the thermally conductive sheet of the present invention. The components described above as (thermally conductive filler) and additives can be used.
Incidentally, when the resin of the heat conductive layer (heat conductive sheet) is a crosslinked resin, the pre-heat conductive sheet may be formed using a composition containing a crosslinkable resin, or a crosslinkable resin may be used. and a curing agent to form a pre-thermally conductive sheet, and after the pre-thermally conductive sheet forming step, the crosslinkable resin is crosslinked to form a crosslinkable resin in the thermally conductive layer (thermally conductive sheet). may be included.

The mixing of the above-described components is not particularly limited, and can be performed using a known mixing device such as a kneader; a Henschel mixer; a Hobart mixer, a mixer such as a high-speed mixer; can. Mixing may also be performed in the presence of a solvent such as ethyl acetate. A thermoplastic resin may be previously dissolved or dispersed in a solvent to form a resin solution, which may be mixed with other thermally conductive fillers and optional additives. And mixing time can be 5 minutes or more and 60 minutes or less, for example. Moreover, the mixing temperature can be, for example, 5° C. or higher and 150° C. or lower.

When the composition further contains a fibrous carbon nanostructure, the fibrous carbon nanostructure tends to aggregate and has low dispersibility. Difficult to disperse well in materials. On the other hand, fibrous carbon nanostructures can be prevented from agglomerating by mixing the dispersion in a solvent (dispersion medium) with other components such as resins, but the dispersion remains in the dispersion state. In the case of mixing, since a large amount of solvent is used when solidifying the solid content after mixing to obtain a composition, the amount of solvent used for preparing the composition may increase. Therefore, when the fibrous carbon nanostructures are added to the composition used for forming the pre-heat conductive sheet, the fibrous carbon nanostructures are dispersed in a solvent (dispersion medium). It is preferable to mix with other components in the state of aggregates (easily dispersible aggregates) of fibrous carbon nanostructures obtained by removing the solvent from the resulting dispersion. The aggregate of fibrous carbon nanostructures obtained by removing the solvent from the dispersion of fibrous carbon nanostructures is composed of the fibrous carbon nanostructures once dispersed in the solvent. Since the dispersibility is superior to that of the previous aggregate of fibrous carbon nanostructures, it becomes an easily dispersible aggregate with high dispersibility. Therefore, by mixing the easily dispersible aggregates with other components such as resins, the fibrous carbon nanostructures can be efficiently and satisfactorily dispersed in the composition without using a large amount of solvent. can.

Here, the dispersion of the fibrous carbon nanostructures is, for example, a coarse dispersion obtained by adding the fibrous carbon nanostructures to a solvent, and a dispersion treatment or crushing effect that can obtain a cavitation effect can be obtained. It can be obtained by subjecting it to dispersion processing. The dispersing treatment that provides the cavitation effect is a dispersing method that utilizes shock waves generated by the bursting of vacuum bubbles generated in water when high energy is applied to the liquid. Specific examples of the dispersion treatment that produces the cavitation effect include dispersion treatment using an ultrasonic homogenizer, dispersion treatment using a jet mill, and dispersion treatment using a high-shear stirring device. In addition, the dispersion treatment that can obtain the crushing effect applies a shearing force to the coarse dispersion to crush and disperse the aggregates of the fibrous carbon nanostructures, and furthermore, by applying back pressure to the coarse dispersion, This is a dispersion method for uniformly dispersing fibrous carbon nanostructures in a solvent while suppressing the generation of air bubbles. The dispersing treatment that provides a pulverizing effect can be performed using a commercially available dispersing system (for example, product name "BERYU SYSTEM PRO" (manufactured by Miryu Co., Ltd.)).

In addition, the solvent can be removed from the dispersion by using known solvent removal methods such as drying and filtration. From the viewpoint of removing the solvent quickly and efficiently, filtration such as vacuum filtration is used. It is preferable to

[Molding of composition]
The composition prepared as described above can be optionally defoamed and pulverized, and then pressurized to form a sheet. A sheet-like product obtained by pressure-molding the composition in this way can be used as a pre-heat conductive sheet. In addition, when a solvent is used during mixing, it is preferable to form the sheet after removing the solvent. For example, if defoaming is performed using vacuum defoaming, the solvent is removed at the same time as defoaming. It can be carried out.

Here, the composition is not particularly limited as long as it is a molding method in which pressure is applied, and it can be molded into a sheet using a known molding method such as press molding, rolling molding, or extrusion molding. . Above all, the composition is preferably formed into a sheet by roll forming, and more preferably formed into a sheet by passing between rolls while sandwiched between protective films. The protective film is not particularly limited, and a sandblasted polyethylene terephthalate (PET) film or the like can be used. In addition, the roll temperature is 5° C. or higher and 150° C. or lower, the roll gap is 50 μm or higher and 2500 μm or lower, the roll linear pressure is 1 kg/cm or higher and 3000 kg/cm or lower, and the roll speed is 0.1 m/min or higher and 20 m/min or lower. can.

In the pre-thermally conductive sheet formed by pressurizing the composition and molding it into a sheet, the thermally conductive filler (thermally conductive filler) is arranged mainly in the in-plane direction, and particularly in the in-plane direction of the pre-thermally conductive sheet. It is presumed that the thermal conductivity is improved.
The thickness of the pre-heat conductive sheet is not particularly limited, and can be, for example, 0.05 mm or more and 2 mm or less. Further, when the thermally conductive filler (thermally conductive filler) contains a particulate carbon material, the thickness of the pre-thermally conductive sheet is , preferably more than 4 times and 5000 times or less the average particle diameter of the particulate carbon material.

<Laminate formation process>
In the laminate forming step, a plurality of pre-thermally conductive sheets obtained in the pre-thermally conductive sheet forming step are laminated in the thickness direction, or the pre-thermally conductive sheets are folded or wound to form a thermoplastic resin and a heat conductive sheet. A laminate is obtained in which a plurality of thermally conductive layers containing a filler are formed in the thickness direction. Here, the formation of the laminate by folding the pre-heat conductive sheet is not particularly limited, and can be performed by folding the pre-heat conductive sheet to a certain width using a folding machine. Moreover, the formation of the laminate by winding the pre-heat conductive sheet is not particularly limited. It can be carried out. Moreover, the formation of the laminate by laminating the pre-thermally conductive sheets is not particularly limited, and can be performed using a laminating apparatus. For example, if a sheet lamination apparatus (manufactured by Nikkiso Co., Ltd., product name: "High Stacker") is used, it is possible to prevent air from entering between layers, so that a good laminate can be obtained efficiently.

Here, in the laminate obtained in the laminate forming step, the adhesive force between the surfaces of the pre-heat conductive sheets is usually determined by the pressure during lamination of the pre-heat conductive sheets and the pressure during folding or winding. sufficiently obtained.

From the viewpoint of suppressing delamination, the obtained laminate is heated at 120° C. or more and 170° C. or less for 2 hours or more and 8 hours or less while being pressed in the lamination direction with a pressure of 0.1 MPa or more and 0.5 MPa or less. is preferred. Here, delamination may be prevented by applying an adhesive or a solvent to the pre-heat conductive sheets and bonding the pre-heat conductive sheets together when forming the laminate. From a manufacturing point of view, it is preferred not to use adhesives or solvents.

In the laminate obtained by laminating, folding, or winding the pre-thermally conductive sheets, it is presumed that the thermally conductive fillers (thermally conductive fillers) are arranged in a direction substantially orthogonal to the stacking direction.
Moreover, the laminate preferably further has a resin coating layer as described later.

<<Resin coating layer>>
In the present invention, at least the side surface of the laminate (the side surface 1a of the laminate and the opposite surface thereof in FIG. 1) having a normal extending in substantially the same direction as the extending direction of the wire is covered with a resin coating layer. It is preferable to slice using a multi-wire saw device, and four surfaces of the laminate (side surface 1a of the laminate and its opposing surface, and main surface 1b of the laminate and its opposing surface in FIG. 1) are covered with a resin coating layer. It is more preferable to slice the cut (embedded) laminate using a multi-wire saw device described later.
By using a laminate in which at least the laminate side surface (laminate side surface 1a and the opposite surface in FIG. 1) having a normal extending in substantially the same direction as the wire extending direction is covered with a resin coating layer, the slicing process can be performed. The resin coating layer can absorb the impact on the heat conductive layer in the heat conductive sheet obtained through the process (for example, the impact when the heat conductive sheet is collected in the collecting layer tank 4 in FIG. 1), and during the slicing process In addition, the laminate can be fixed against the vibration of the wire during the slicing process.
In addition, the resin coating layer contains at least one of a thermosetting resin and a hot-melt resin.

As a method for forming a laminate covered with a resin coating layer, for example, (i) a resin (thermosetting resin, hot melt resin) liquid is poured into a container in which a laminate having a heat conductive layer laminated thereon is placed. (ii) a method of applying with a brush, a spray, or the like; Among these methods, (i) the method of pouring the resin liquid into a container in which the laminate having the heat conductive layer is placed is preferable because the laminate covered with the resin coating layer can be formed in a short time.

[Thermosetting resin, hot melt resin]
Moreover, the thermosetting resin composition for forming the resin coating layer usually contains a thermosetting resin and a curing agent. The thermosetting resin is not particularly limited as long as it exhibits thermosetting properties when combined with a curing agent. Cyclic olefin polymers, aromatic polyether polymers, benzocyclobutene polymers, cyanate ester polymers, polyimides, and the like. These may be used individually by 1 type, and may use 2 or more types together by arbitrary ratios.
Among these, thermosetting epoxy resins and thermosetting (meth)acrylic resins are preferable from the viewpoint of adhesion to the heat conductive layer.

The hot-melt resin for forming the resin coating layer also includes a so-called hot-melt adhesive that has a shear storage elastic modulus of 1 MPa or more and 500 MPa or less at 23° C. and does not exhibit stickiness at room temperature. Among these, hot-melt adhesives are preferable from the viewpoint of easy formation of a laminate. Specific examples of hot melt adhesives include "Aron Melt Adhesive PPET Series" manufactured by Toagosei Co., Ltd., "3M Scotch-Weld Hot Melt Adhesives" manufactured by 3M, "Hot Melt Adhesives" manufactured by Nissin Chemical Industry Co., Ltd. ”, and the like are preferably exemplified.

The thickness of the resin coating layer (thermosetting resin coating layer, hot melt resin coating layer) is preferably 1 mm or more, more preferably 2 mm or more, particularly preferably 3 mm or more, and 10 cm or less. It is preferably 5 cm or less, more preferably 3 cm or less, and particularly preferably 3 cm or less. When the thickness of the resin coating layer (thermosetting resin coating layer, hot-melt resin coating layer) is at least the lower limit value, crushing due to slicing of the laminate can be effectively suppressed, and the resin coating layer (thermosetting When the thickness of the flexible resin coating layer and the hot-melt resin coating layer) is equal to or less than the above upper limit, the amount of resin used can be suppressed, so that the manufacturing cost can be reduced.
In addition, from the viewpoint of suppressing vibration of the laminate and preventing sheet breakage in the slicing process, the four surfaces of the laminate (the side surface 1a of the laminate and its opposing surface, and the main surface 1b of the laminate and its opposing surface in FIG. 1) are made of resin. When covered (embedded) with a coating layer, it has a normal that extends substantially in the same direction as the wire extending direction than the thickness of the resin coating layer that covers the main surface 1b of the laminate and the opposing surface thereof. It is preferable that the thickness of the resin coating layer covering the side surface of the laminate (the side surface 1a of the laminate and the opposite surface thereof in FIG. 1) is thick.

The melting point or glass transition temperature of the resin (thermosetting resin, hot melt resin) is preferably 40° C. or higher. Resins (thermosetting resins, hot-melt resins) having a melting point or glass transition temperature of 40° C. or higher are solid in a normal state and can increase the initial adhesive strength due to the cohesive force during crystallization. Further, the melting point or glass transition temperature of the resin (thermosetting resin, hot melt resin) is preferably 150° C. or less. By using a resin (thermosetting resin, hot-melt resin) with a melting point or glass transition temperature of 150°C or less, the melting of the laminate due to heat during heating and melting of the resin (thermosetting resin, hot-melt resin) is suppressed. It is possible to suppress the breakage of the sheet due to the slicing of the laminate.

<Slicing process>
In the slicing step, the laminate laminated in the above-described laminate forming step or the like is sliced at an angle of 45° or less with respect to the lamination direction to obtain a heat conductive sheet composed of sliced pieces of the laminate. Here, the device for slicing the laminate must be a multi-wire saw device.

The angle at which the laminate is sliced must be 45° or less with respect to the stacking direction of the laminate. It is preferably 30° or less with respect to the stacking direction of the laminate, more preferably 15° or less with respect to the stacking direction of the laminate, and is approximately 0° with respect to the stacking direction of the laminate (that is, It is particularly preferable that it is a direction along the stacking direction of the laminate.

Then, the thermally conductive sheet containing the thermoplastic resin and the thermally conductive filler (thermally conductive filler) obtained through the slicing process is usually a strip containing the thermoplastic resin and the thermally conductive filler (thermally conductive filler). It has a configuration in which pieces (sliced pieces of the pre-heat-conductive sheet constituting the laminate) are joined in parallel.

When slicing a laminate in which a predetermined surface (at least a laminate side surface having a normal extending in substantially the same direction as the wire extending direction) is covered with the resin coating layer, the resin coating layer is removed. is preferred. Since the resin coating layer does not have a large adverse effect on thermal conductivity, it is possible to use the sheet covered with the resin coating layer as a thermal conductive sheet, but removing the resin coating layer results in a higher quality sheet. This is because a good thermally conductive sheet can be obtained. Moreover, since the thermoplastic resin contained in the heat conductive sheet is a fluororesin, it can be easily removed for removing the resin coating layer.

<<Multi-wire saw device>>
The multi-wire saw device is provided with wires stretched (arranged) in a plurality of rows between a plurality of main rollers arranged at a predetermined distance (for example, a multi-wire saw as shown in FIG. 1). If it is a wire saw device), a commercially available device can be used as appropriate and is not particularly limited. The slicing conditions are different from cutting conditions for extremely hard materials such as silicon ingots. However, the slicing process can be suitably performed by appropriately setting conditions for the multi-wire saw device that do not affect the in-plane film thickness, heat conduction characteristics, yield, breakage, and productivity of the thermally conductive sheet having rubber elasticity. becomes possible.

FIG. 1 is a diagram showing an example of an embodiment of a multi-wire saw device used in the method of manufacturing a heat conductive sheet of the present invention.
In FIG. 1, the multi-wire saw device X has a plurality of main rollers 3 (3a, 3b, 3c), wires 2, and the like. The wire 2 is wound around the main rollers 3 to form a wire row between the main rollers 3 .
The multi-wire saw device X includes wires 2 stretched in multiple rows between at least two main rollers 3a and 3b arranged at a predetermined distance. A workpiece (laminated body) 1 is arranged so as to face the wire 2 between the rollers 3, and the wire 2 is run between the main rollers 3. A plurality of thermally conductive sheets are obtained from a workpiece 1 (laminated body) with a wire 2 while pressing the body) at a predetermined pressing speed.
The first main roller 3a and the second main roller 3b are arranged with a predetermined distance therebetween, and the wire 2 is stretched in a plurality of rows between these main rollers 3 in a planar shape. By rotating the main roller 3 at a predetermined rotational speed, the wire 2 can be run in the longitudinal direction (extending direction) of the wire 2 . Also, the wire 2 can be reciprocated by changing the direction of rotation of the main roller 3 .
The workpiece (laminate) 1 is cut by moving the workpiece (laminate) 1 while supplying the cutting fluid to the wire 2 running at high speed. This is done by pressing the (laminate) against each other. At this time, the tension of the wire 2, the speed at which the wire 2 travels (running speed), and the speed at which the workpiece (laminate) 1 is lowered toward the wire 2 (feed speed) are controlled appropriately. .
Below the wire 2, a recovery layer tank 4 may be provided for the purpose of recovering the heat conductive sheet, and for recovering chips from the workpiece 1 and machining fluid generated during cutting.

[Wire (wire saw)]
High tensile strength metal wire such as piano wire is normally used as the core wire of the wire (wire saw), but it is also possible to use a core wire in which the surface of the high tensile strength metal is plated with a soft metal such as copper or copper alloy. can.
Wire processing methods include a fixed-abrasive method in which a wire to which abrasive grains are attached is used for cutting, and a free-abrasive grain method in which a wire coated with a slurry containing an abrasive is used for cutting. The wire used in the fixed abrasive method will be described in detail below.

An adhesive resin layer may be provided between the core wire and the abrasive grain layer, and a spiral concave portion may be formed in the adhesive resin layer. In this case, a mixture of a liquid resin and abrasive grains is coated on the surface on which the spiral recesses are formed, and then passed through a die of a predetermined inner diameter to be cured. Spiral recesses corresponding to the spiral recesses of the adhesive resin layer are formed by surface tension when passing through the die. Further, if a volatile component is added to the resin of the abrasive grain layer, it is possible to form helical recesses corresponding to the helical recesses of the adhesive resin layer even with shrinkage during curing.

By forming the helical concave portion in the adhesive resin layer, the surface area of the adhesive resin layer is increased, the adhesive strength between the adhesive resin layer and the abrasive grain layer is improved, and the abrasive grains during the cutting process are improved. is prevented from falling off, extending the life of the wire. Furthermore, since the outer surface of the abrasive grain layer is formed with spiral recesses, the ability to discharge shavings during cutting is improved, and good sharpness can be maintained.

The thickness of the adhesive resin layer is preferably 3 μm or more and 10 μm or less. If the thickness of the adhesive resin layer is too thin, it is not possible to form a helical concave portion with a required depth. , there is a problem with the strength of the core wire. Furthermore, it is preferable that this adhesive resin layer has a two-layer structure of a thermosetting resin and a photosensitive resin. Since the thermosetting resin has the effect of crimping the core wire due to condensation during curing, by forming the core wire side of the adhesive resin layer with a thermosetting resin, the adhesive strength between the core wire and the adhesive resin layer is increased. . On the other hand, since the thermosetting resin contains volatile components, if the thermosetting resin is used on the abrasive grain layer side, the helical recesses cannot be stably formed. Since the photosensitive resin does not contain a volatile component, the spiral concave portion can be stably formed by forming the abrasive grain layer side of the adhesive resin layer with the photosensitive resin.

The depth of the helical concave portion formed in the adhesive resin layer is preferably 2 μm or more and 20% or less of the average grain size of the abrasive grains. If the depth of the recesses is less than 2 μm, the effect of the recesses is small because the recesses are shallow. It will be buried in the resin inside, and the effect of providing the concave portion will be lost. By forming spiral recesses only in this bonding resin layer and partially burying the abrasive grains therein, the core wire is not damaged and there is no risk of wire breakage. In this case, the abrasive grains of the abrasive grain layer in the portions corresponding to the recesses function to improve the wear resistance of the recesses. The life of the wire is reached when the abrasive grain layer wears out and becomes uniform as a result of the use of the wire.

The resin bond wire can be manufactured using conventionally known wire manufacturing equipment and methods, except for some steps. When a soft metal-plated core wire is used as the core wire, the high tensile strength metal wire as the core material is plated with copper, a copper alloy, gold, tin, zinc, or an alloy thereof. The adhesive resin layer formed on the core wire is formed by applying a known method of passing the core wire through liquid resin contained in a container while feeding the core wire at a constant speed, coating the core wire with the liquid resin, and curing the core wire. . Here, when the adhesive resin layer has a two-layer structure of a thermosetting resin layer and a photosensitive resin layer, the core wire is first passed through a liquid thermosetting resin contained in a container, and the core wire is coated with the liquid thermosetting resin. A thermosetting resin is coated and cured to form a first adhesive resin layer, and then passed through a liquid photosensitive resin contained in a container to form a liquid photosensitive resin layer on the first adhesive resin layer. A second adhesive resin layer can be formed by coating with an adhesive resin and curing it. In order to form a helical concave portion in this adhesive resin layer, while feeding the core wire with the adhesive resin layer formed thereon at a constant speed, for example, a die with a non-circular hole is pressed in a plane perpendicular to the core wire axis direction. It is possible to adopt a method of passing the core wire while rotating it, a method of sandwiching the core wire with a pressing tool and relatively rotating the core wire and the pressing tool, and the like.

A known method can be used to form the abrasive grain layer. For example, a core wire in which a helical recess is formed in an adhesive resin layer is passed through a mixture of abrasive grains and liquid resin contained in a container to coat the adhesive resin layer with the mixture of abrasive grains and liquid resin. The wire is manufactured by passing the core wire through a die of a predetermined inner diameter, curing the liquid resin after passing through the die, and fixing the abrasive grain layer to the core wire. Moreover, as the resin constituting the abrasive grain layer, a photosensitive resin or a thermosetting resin can be used. However, it is desirable to use a photosensitive resin in order to shorten the curing time of the liquid resin and improve production efficiency.

<Properties of heat conductive sheet>
<<Thermal resistance value>>
The heat conductive sheet preferably has a thermal resistance value of less than 0.31° C./W under a pressure of 0.80 MPa, more preferably less than 0.25° C./W, and more preferably less than 0.19° C./W. It is particularly preferred that it is less than. When the thermal resistance value under a pressure of 0.80 MPa is less than 0.31° C./W, it can have excellent thermal conductivity under a usage environment in which relatively high pressure is applied.
Here, the thermal resistance value of the thermally conductive sheet can be measured using a commonly used known measurement method, using a resin material thermal resistance tester (for example, manufactured by Hitachi Technology and Service Co., Ltd., trade name "C47108"). ) can be measured.

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified.
In the examples and comparative examples, the Mooney viscosity of the resin that is solid under normal temperature and normal pressure; the film thickness of the heat conductive sheet; the thermal resistance value of the heat conductive sheet; the surface roughness Ra of the heat conductive sheet; Each test was measured or evaluated using the following methods.

<Mooney viscosity of solid resin under normal temperature and pressure>
The Mooney viscosity (ML ₁₊₄ , 100°C) of a resin that is solid at normal temperature and pressure is measured at a temperature of 100°C according to JIS-K6300 using a Mooney viscometer (manufactured by Shimadzu Corporation, product name “MOONEY VISCOMETER SMV-202”). It was measured. In general, the lower the Mooney viscosity of a resin that is solid at normal temperature and normal pressure, the higher the flexibility.

<Film thickness of thermally conductive sheet>
The film thickness of the heat conductive sheet was measured with an accuracy of (1/1000 mm) using a film thickness gauge (manufactured by Mitutoyo Co., Ltd., product name "Digimatic Indicator (ID-C112X)". Then, the surface of the heat conductive sheet The average value (μm) of the values measured at five points above was taken as the film thickness of the thermally conductive sheet.The results are shown in Table 1.

<Thermal resistance value of thermal conductive sheet>
The thermal resistance value of the thermal conductive sheet was measured using a resin material thermal resistance tester (manufactured by Hitachi Technology and Service Co., Ltd., product name “C47108”). Here, a thermally conductive sheet cut into a square of 1 cm square is used as a sample, and the thermal resistance value (° C./W) when a relatively low pressure of 0.05 MPa is applied at a sample temperature of 50 ° C. and the sample temperature of 50 C., and the thermal resistance value (.degree. C./W) when a relatively high pressure of 0.80 MPa was applied was measured. The smaller the thermal resistance value, the better the thermal conductivity of the thermally conductive sheet. Furthermore, evaluation was made according to the following evaluation criteria. Table 1 shows the results.
<<Evaluation Criteria>>
A: Less than 0.19 (°C/W) B: 0.19 (°C/W) or more and less than 0.25 (°C/W) C: 0.25 (°C/W) or more and 0.31 (°C/W) Less than D: 0.31 (° C./W) or more

<Surface Roughness Ra of Heat Conductive Sheet>
The surface roughness Ra of the heat conductive sheet was measured using a laser microscope (Keyence Corporation, shape analysis laser microscope, VK-X250 series). Measured at a magnification of 20 times, arbitrarily selected 4 lines with a length of 200 μm, determined the surface roughness Ra with respect to the line roughness, and calculated the average. Table 1 shows the results.

<Curl test of heat conductive sheet>
A curl test was performed by observing the thermally conductive sheet immediately after the slicing process, and evaluation was made according to the following evaluation criteria. Table 1 shows the results.
<<Evaluation Criteria>>
A: No curling (degree of curling (distance from horizontal surface to edge of sheet): less than 3 cm).
B: Slightly curled, but flattened when pressed by hand (degree of curl (swelling distance from horizontal surface to edge of sheet): 3 to 5 cm).
C: Curled and must be spread by hand (curling degree (curvature radius): 3 cm to 5 cm).
D: Curled and may be torn if unrolled carefully (curling degree (curvature radius): less than 3 cm).

(Example 1)
<Preparation of readily dispersible aggregates of fibrous carbon nanostructures>
<<Preparation of dispersion>>
400 mg of fibrous carbon nanostructure (SGCNT, Nippon Zeon Co., Ltd., specific surface area: 600 m ² /g) was weighed out, mixed in 2 L of methyl ethyl ketone as a solvent, and stirred for 2 minutes with a homogenizer to obtain a crude dispersion. . Next, using a wet jet mill (manufactured by Joko Co., Ltd., product name “JN-20”), the obtained coarse dispersion is passed through a 0.5 mm channel of the wet jet mill at a pressure of 100 MPa for two cycles. to disperse fibrous carbon nanostructures in methyl ethyl ketone. Then, a dispersion having a solid concentration of 0.20% by mass was obtained.

<<Removal of solvent>>
Thereafter, the dispersion liquid obtained above was filtered under reduced pressure using Kiriyama filter paper (No. 5A) to obtain an easily dispersible aggregate of sheet-like fibrous carbon nanostructures as a fibrous carbon material. .

<Preparation of composition>
70 parts of a thermoplastic fluororesin that is liquid at normal temperature and pressure (manufactured by Daikin Industries, Ltd., trade name "DAIEL G-101"), and a thermoplastic fluororesin that is solid at normal temperature and pressure (manufactured by 3M Japan Co., Ltd., trade name) 30 parts of "Dynion FC-2211", Mooney viscosity: 27 ML ₁₊₄ , 100 ° C.) and expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., 50 parts of "EC100" (trade name, volume average particle diameter: 250 μm), and 0.5 parts of the easily dispersible aggregate of the fibrous carbon nanostructures obtained above as the fibrous carbon material, Using a pressure kneader (manufactured by Nippon Spindle Co., Ltd.), the mixture was stirred and mixed at a temperature of 150° C. for 20 minutes. Next, the resulting mixture was put into a crusher and crushed for 10 seconds to obtain a composition.

<Formation of pre-thermal conductive sheet>
Next, 50 g of the resulting composition was sandwiched between sandblasted PET films (protective films) having a thickness of 50 μm, and the roll gap was 550 μm, the roll temperature was 50° C., the roll linear pressure was 50 kg/cm, and the roll speed was 1 m/min. to obtain a pre-heat conductive sheet having a thickness of 0.5 mm.

<Formation of laminate>
Subsequently, the obtained pre-thermal conductive sheet was cut into a size of 150 mm long x 150 mm wide x 0.5 mm thick, and 300 sheets were laminated in the thickness direction of the pre-thermal conductive sheet. A laminate having a height (thickness) of about 150 mm was obtained by pressing (secondary pressure) in the stacking direction for 1 minute.

<Formation of thermal conductive sheet: slicing (multi-wire cutting) process>
A layer (thickness 5 mm) made of a hot melt adhesive "manufactured by 3M: product name "Scotch-Weld 3747": softening temperature 104 ° C." The hot melt adhesive liquid is poured into a container in which the laminate is placed so that the hot melt adhesive liquid is formed on the surface, and the laminate main surface 1b and the opposite surface), and then cooled to room temperature to cure. let me
In addition, as a multi-wire saw device, the slicing process was performed using a "small multi-wire cutting machine: RTD6400" manufactured by Meyer Burger. A resin-bonded diamond wire of 140 μm was used as the core wire, and 100 wires were set in parallel with a wire tension of 10 N and a gap of 150 μm. Glycol solution containing a surfactant was used as a lubricant for cutting.
After that, among the four surfaces of the laminate obtained by secondary pressure, the laminate surface having a normal extending in substantially the same direction as the wire extending direction (for example, the laminate side surface 1a in FIG. while pressing the surface) with a pressure of 0.1 MPa, using a multi-wire saw device, at an angle of 0 degrees with respect to the lamination direction of the laminate (thickness direction of the laminate) (in other words, the laminated pre-heat conduction The laminate was sliced at a 0 degree angle to the normal direction of the major surface of the sheet). The cutting (slicing) speed was 1.0 mm/min. Rinse the sliced heat conductive sheet with ion-exchanged water to remove cutting lubricant (glycol solution containing surfactant) and cutting waste, blow off moisture, and heat conductive sheets of length 150 mm x width 150 mm x thickness 0.15 mm. 99 sheets were obtained.

Of the 99 sheets obtained, one of the ends (the first sheet) was designated as "Example 1", the 50th sheet was designated as "Example 2", and the other end (the last 99th sheet) was designated as " It was evaluated as "Example 3".

(Comparative Examples 1 to 3)
In Examples 1 to 3, instead of forming the thermally conductive sheet through the slicing (multi-wire cutting) step, the thermally conductive sheet was formed through the following slicing (plane slicing) step. A thermally conductive sheet was formed in the same manner as in Examples 1 to 3, and the obtained thermally conductive sheet was measured and evaluated.
<Formation of thermal conductive sheet: slicing (plane slicing) process>
While pressing the side surface of the laminate obtained by secondary pressure (the side surface of the laminate along approximately the same direction as the plane slicing direction) with a pressure of 0.3 MPa, a slicer for woodworking (manufactured by Marunaka Iron Works Co., Ltd., At an angle of 0 degrees with respect to the lamination direction (in other words, 0 degrees with respect to the normal direction of the main surface of the laminated pre-heat conductive sheet) at an angle of ) and sliced the laminate. Then, 100 thermally conductive sheets of length 150 mm×width 150 mm×thickness 0.15 mm were obtained.

Table 1 shows the results. From Table 1, 99 thermal conductive sheets (Examples 1 to 3) obtained by slicing using a multi-wire saw device can be sliced in 60 seconds. On the other hand, it took 8 minutes or more (500 seconds) to slice 99 conventional thermal conductive sheets (Comparative Examples 1 to 3) sliced with a knife. Moreover, as can be seen from the results of measuring the surface roughness Ra of the heat conductive sheet, the cross sections of the slices of Examples 1 to 3 are good. Further, the thermal resistance values of the thermal conductive sheets of Examples 1-3 are substantially the same as the thermal resistance values of the conventional thermal conductive sheets of Comparative Examples 1-3.
Here, when slicing with a knife (conventional method), it curls, and after fixing the curl and flattening one sheet, it is sandwiched between release PET (manufactured by Unitika, EMBLET, thickness 50 μm) to make one product sheet. It took 10 seconds for each one. Moreover, it took 30 minutes or more to obtain 99 product sheets.
In Comparative Examples 1 to 3, as the number of slices increased, sheet heat accumulation due to frictional heat generated during slicing increased, and the results of the curl test deteriorated (Comparative Example 1: B, Comparative Example 2: C, Comparative Example 3: D) can be seen.
It is presumed that the above-mentioned curl is caused by extending the sliced surface and rounding the surface opposite to the sliced surface.
As a result of the above, it is clear that slicing (multi-wire cutting) using a multi-wire saw device has a very epoch-making effect in increasing production efficiency.

The conventional process of slicing with a blade can be replaced with multiple wire saws wrapped around a roll to produce a large number of thermally conductive sheets at once. It made it possible to manufacture a heat conductive sheet.
Moreover, high thermal conductivity, high strength, and high flexibility (low hardness) can be imparted to the obtained thermally conductive sheet.

1 Workpiece (Laminate)
1a Laminate side face 1b Laminate main surface 2 Wire 3 Main roller 3a First main roller 3b Second main roller 3c Third main roller 4 Recovery layer tank X Multi-wire saw device

Claims (2)

A multi-wire saw device having wires arranged in a plurality of rows between main rollers of a plurality of main rollers arranged at predetermined distances is used to form a heat conductive layer containing a thermoplastic resin and a heat conductive filler in the thickness direction. A method for producing a heat conductive sheet, comprising a slicing step of slicing a plurality of laminated bodies at an angle of 45° or less with respect to the lamination direction of the laminated body,
The laminate further has a resin coating layer containing at least one of a thermosetting resin and a hot melt resin,
The resin coating layer is formed at least on a side surface of the laminate having a normal extending in substantially the same direction as the wire extending direction,
A method for manufacturing a heat conductive sheet . 2. The method for producing a heat conductive sheet according to claim 1, wherein the resin coating layer has a thickness of 1 mm or more and 10 cm or less.

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