JP7413664B2 - Thermal conductive sheet and its manufacturing method - Google Patents

Description

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

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

As a countermeasure against functional failure due to temperature rise in electronic components, a method is generally adopted to promote heat dissipation by attaching a heat dissipation body such as a metal heat sink, heat sink, or heat dissipation fin to the heat generating body of the electronic component. ing. When using a heat sink, in order to efficiently transfer heat from the heat sink to the heat sink, a sheet-like member with high thermal conductivity (thermal conductive sheet) is interposed between the heat sink and the heat sink. It is in close contact with the heat sink.

Therefore, a thermally conductive sheet used by being sandwiched between a heat generating element and a heat radiating element is required to exhibit excellent thermal conductivity.

Therefore, for example, in Patent Document 1, by pressing a secondary heat conductive sheet obtained by slicing a laminate of primary heat conductive sheets containing a resin and a particulate carbon material at an angle of 45 degrees or less with respect to the lamination direction, As a thermally conductive sheet that can exhibit excellent thermal conductivity even when the pressure applied when sandwiched between a heating element and a heat radiating element is low, the surface roughness Sz of at least one main surface is 3. A thermally conductive sheet with a thickness of 5 μm or less has been obtained.

JP2018-67695A

However, in the thermally conductive sheet described in Patent Document 1, when pressing the secondary thermally conductive sheet to obtain a thermally conductive sheet with a surface roughness Sz of 3.5 μm or less, the orientation of the particulate carbon material in the sheet is changed. Since it collapses and the thermal conductivity decreases, there is room for improvement in terms of improving the thermal conductivity.

Additionally, thermally conductive sheets have been required to have increased tensile strength.

Therefore, an object of the present invention is to provide a thermally conductive sheet that can exhibit excellent thermal conductivity and has high tensile strength.

The present inventor conducted extensive studies in order to achieve the above object. The inventor of the present invention has found that a thermally conductive sheet having a predetermined thermal conductivity and a predetermined surface roughness (arithmetic mean height) Sa can improve tensile strength and exhibit excellent thermal conductivity. The present invention has been completed based on the discovery that the above-mentioned thermally conductive sheet can be easily obtained by using a predetermined manufacturing method.

That is, 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 thermally conductive filler, and has a thickness in the thickness direction. It is characterized by having a thermal conductivity of 12 W/m·K or more, and a surface roughness Sa of 2.5 μm or less on both surfaces. As described above, a thermally conductive sheet having a thermal conductivity in the thickness direction of 12 W/m·K or more and a surface roughness Sa of 2.5 μm or less on both sides can exhibit excellent thermal conductivity and , has excellent tensile strength.
In the present invention, "thermal conductivity" and "surface roughness Sa" can be measured using the methods described in Examples, respectively.

Here, it is preferable that the heat conductive sheet of the present invention has a variation in surface roughness of 0.30 μm or less on both sides. A thermally conductive sheet with surface roughness variation of 0.30 μm or less on both sides has excellent quality stability.
In the present invention, "variation in surface roughness" can be measured using the method described in Examples.

Moreover, it is preferable that the thermally conductive sheet of the present invention has a variation in in-plane tensile strength of 0.10 MPa or less. A thermally conductive sheet having an in-plane tensile strength variation of 0.10 MPa or less has excellent uniformity.
In the present invention, "in-plane tensile strength variation" can be measured using the method described in Examples.

Furthermore, in the thermally conductive sheet of the present invention, it is preferable that the thermally conductive filler includes a particulate carbon material, and the volume average particle diameter of the particulate carbon material is 10 μm or more and 100 μm or less. If a particulate carbon material having a volume average particle diameter of 10 μm or more and 100 μm or less is included, thermal conductivity can be further improved.

Further, in the heat conductive sheet of the present invention, it is preferable that the particulate carbon material is anisotropic graphite. If the particulate carbon material is anisotropic graphite, thermal conductivity can be further improved.

Furthermore, it is preferable that the thermally conductive sheet of the present invention has an area of 3600 mm ² or more in plan view. If the area in plan view is 3600 mm ² or more, productivity can be improved.

The heat conductive sheet of the present invention preferably has an average thickness of 250 μm or less. If the average thickness is 250 μm or less, it is possible to increase the degree of freedom in placement within the device when mounted.
In the present invention, the "average thickness" can be measured using the method described in Examples.

Further, the present invention aims to advantageously solve the above-mentioned problems, and the method for manufacturing a thermally conductive sheet of the present invention involves slicing a resin block containing a resin and a thermally conductive filler using a slicing mechanism. A method for manufacturing a thermally conductive sheet including a step of slicing to obtain a thermally conductive sheet, wherein the slicing mechanism includes a flank surface, a rake surface, and a cutting edge formed of an intersection corner of the flank surface and the rake surface. and a guide member disposed opposite to the rake face, the slice being cut out from the resin block so that the portion cut out from the resin block passes between the rake face and the guide member. It is characterized by doing. In this way, by slicing a resin block using a slicing mechanism equipped with a single-edged cutting blade and a guide member disposed opposite to the rake face of the single-edged cutting blade, a thermally conductive sheet made of sliced pieces of the resin block can be sliced. Since curling can be suppressed, it is possible to obtain a thermally conductive sheet that exhibits excellent thermal conductivity and has excellent tensile strength.

Here, in the method for manufacturing a thermally conductive sheet of the present invention, it is preferable that the static friction coefficient of the surface of the guide member facing the rake surface is 0.4 or less. If the coefficient of static friction of the surface of the guide member facing the rake face is 0.4 or less, the portion cut out from the resin block can be passed between the rake face and the guide member well.
In the present invention, the "static friction coefficient" can be measured using the method described in Examples.

Moreover, in the method for manufacturing a thermally conductive sheet of the present invention, it is preferable that the length of the guide member is 1 cm or more and 5 cm or less. If the length of the guide member is 1 cm or more, it is possible to sufficiently suppress curling of the thermally conductive sheet, exhibit excellent thermal conductivity, and obtain a thermally conductive sheet that has excellent tensile strength. . Further, if the length of the guide member is 5 cm or less, the heat conductive sheet can be easily taken out from between the rake face and the guide member.

In the method for manufacturing a thermally conductive sheet of the present invention, the resin block is preferably sliced at a speed of 25 mm/sec to 200 mm/sec. When the slicing speed is set to 25 mm/sec or more and 200 mm/sec or less, the resin block can be sliced well using a slicing mechanism including a single-edged cutting blade and a guide member.

According to the present invention, it is possible to provide a thermally conductive sheet that can exhibit excellent thermal conductivity and has high tensile strength.

(a) to (c) are explanatory diagrams showing the process of manufacturing a thermally conductive sheet using an example of the method for manufacturing a thermally conductive sheet according to the present invention.

Embodiments of the present invention will be described in detail below.
Here, the thermally conductive sheet of the present invention is used by being sandwiched between a heat generating element such as an electronic component and a heat dissipating body such as a metal heat sink, heat sink, heat sink, or heat dissipating fin. It can be manufactured using a method for manufacturing a thermally conductive sheet.

(thermal conductive sheet)
The thermally conductive sheet of the present invention contains a resin and a thermally conductive filler, and may optionally further contain an additive. Further, the thermally conductive sheet of the present invention needs to have a thermal conductivity in the thickness direction of 12 W/m·K or more, and a surface roughness Sa of 2.5 μm or less on both sides. If the thermal conductivity in the thickness direction is 12 W/m・K or more and the surface roughness Sa is 2.5 μm or less on both sides, it will have excellent thermal conductivity while ensuring a sufficiently high tensile strength. can demonstrate.

<Resin>
Here, as the resin, at least one of a resin that is liquid at room temperature and normal pressure, and a resin that is solid at room temperature and normal pressure can be used. In addition, in this specification, "normal temperature" refers to 23 degreeC, and "normal pressure" refers to 1 atm (absolute pressure).

Examples of resins that are liquid at room temperature and pressure include thermoplastic resins that are liquid at room temperature and pressure, and thermosetting resins that are liquid at room temperature and pressure.
Examples of thermoplastic resins that are liquid at room temperature and pressure include acrylic resins, epoxy resins, silicone resins, and fluororesins.
In addition, examples of thermosetting resins that are liquid 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; phenol resin; unsaturated polyester; diallyl phthalate resin; polyimide silicone resin; polyurethane; thermosetting polyphenylene ether; thermosetting Type-modified polyphenylene ether; etc.

Further, examples of resins that are solid at room temperature and normal pressure include thermoplastic resins that are solid at room temperature and normal pressure, and thermosetting resins that are solid at room temperature and normal 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, polyacrylic acid or Acrylic resin such as its ester; silicone resin; fluororesin; polyethylene; polypropylene; ethylene-propylene copolymer; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymer; polyvinyl alcohol Polyacetal; Polyethylene terephthalate; Polybutylene terephthalate; Polyethylene naphthalate; Polystyrene; Polyacrylonitrile; Styrene-acrylonitrile copolymer; Acrylonitrile-butadiene-styrene copolymer (ABS resin); Styrene-butadiene block copolymer or its hydrogenation 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 ; polyetherketone; polyketone; polyurethane; liquid crystal polymer; ionomer; and the like.
In addition, 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; phenol resin; unsaturated polyester; diallyl phthalate resin; polyimide silicone resin; polyurethane; thermosetting polyphenylene ether; thermosetting Type-modified polyphenylene ether; etc.

Among these, as the resin, it is preferable to use a fluororesin that is liquid at room temperature and pressure, and a fluororesin that is solid at room temperature and pressure.
In addition, the resin mentioned above may be used individually by 1 type, and may use 2 or more types together.

<Thermal conductive filler>
Thermal conductive fillers are not particularly limited, and include, for example, alumina particles, zinc oxide particles, boron nitride particles, aluminum nitride particles, silicon nitride particles, silicon carbide particles, magnesium oxide particles, and particulate carbon materials (e.g. , artificial graphite, flaky graphite, exfoliated graphite, natural graphite, acid-treated graphite, expandable graphite, expanded graphite, carbon black, etc.), as well as carbon nanotubes, vapor-grown carbon fibers, and organic fibers. Examples include carbon fibers obtained by carbonizing carbon fibers, and fibrous materials such as cut products thereof. Among them, thermally conductive fillers include scaly particle materials such as boron nitride particles, artificial graphite, scaly graphite, expandable graphite, and expanded graphite; and carbon nanotubes (hereinafter sometimes referred to as "CNTs"). It is preferable to use at least one kind selected from the group consisting of fibrous carbon nanomaterials such as It is more preferable to use , and it is particularly preferable to use expanded graphite. If these thermally conductive fillers are used, the thermal conductivity of the thermally conductive sheet can be further improved.
In addition, one type of thermally conductive filler may be used alone, or two or more types may be used in combination.

Note that the volume average particle diameter of a particulate material such as a particulate carbon material that can be used as a thermally conductive filler is preferably 10 μm or more and 100 μm or less, and more preferably 30 μm or more and 80 μm or less. If the volume average particle diameter is within the above range, the thermal conductivity of the thermally conductive sheet can be further improved.

The content of the thermally conductive filler is not particularly limited, and, for example, it is preferably 5 parts by mass or more, more preferably 50 parts by mass or more, per 100 parts by mass of the above-mentioned resin. It is more preferably 80 parts by mass or more, preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 100 parts by mass or less. If the content of the thermally conductive filler is at least the above lower limit, the thermal conductivity of the thermally conductive sheet can be sufficiently increased. Moreover, if the content of the thermally conductive filler is below the above upper limit, it is easy to manufacture a thermally conductive sheet with a small surface roughness Sa.

<Additives>
Additives that can be optionally included in the thermally conductive sheet are not particularly limited, and include, for example, flame retardants, plasticizers, toughness improvers, moisture absorbers, adhesive strength improvers, wettability improvers, ion trap agents, etc. can be mentioned.

<Properties of thermally conductive sheet>
The thermally conductive sheet of the present invention needs to have a thermal conductivity in the thickness direction of 12 W/m·K or more, a surface roughness Sa of 2.5 μm or less on both sides, and further have the following properties. It is preferable to have.

[Thermal conductivity in the thickness direction]
The thermal conductivity in the thickness direction of the thermally conductive sheet is preferably 20 W/m·K or more, more preferably 25 W/m·K or more, and even more preferably 30 W/m·K or more. If the thermal conductivity in the thickness direction is greater than or equal to the above lower limit, heat can be transferred favorably from the heat generating element to the heat radiating element.

[Surface roughness Sa]
The heat conductive sheet preferably has a surface roughness Sa of 1.0 μm or more and 2.3 μm or less on both main surfaces (front and back surfaces). If the surface roughness Sa is below the above upper limit, the tensile strength can be sufficiently increased. Furthermore, if the surface roughness Sa is equal to or greater than the above lower limit, it is easy to manufacture the thermally conductive sheet.

Further, the variation in surface roughness Sa on each main surface of the thermally conductive sheet is preferably 0.50 μm or less, more preferably 0.30 μm or less, and even more preferably 0.20 μm or less. preferable. If the variation in the surface roughness Sa is equal to or less than the above upper limit on both sides, the stability of the quality of the thermally conductive sheet can be improved.

[Tensile strength]
Furthermore, the tensile strength of the thermally conductive sheet is preferably 0.45 MPa or more, more preferably 0.50 MPa or more, preferably 1.00 MPa or less, and more preferably 0.7 MPa or less. preferable. If the tensile strength is equal to or greater than the above lower limit, sufficient strength can be ensured. Moreover, if the tensile strength is below the above-mentioned upper limit, manufacturing of a thermally conductive sheet is easy.

The thermally conductive sheet preferably has an in-plane tensile strength variation of 0.10 MPa or less, more preferably 0.08 MPa or less, and even more preferably 0.06 MPa or less. If the variation in in-plane tensile strength is below the above upper limit, the uniformity of the thermally conductive sheet can be sufficiently improved.

[shape]
The area of the heat conductive sheet in plan view is preferably 3,600 mm ² or more, more preferably 10,000 mm ² or more. If the area in plan view is equal to or larger than the above lower limit, productivity can be improved.

Further, the average thickness of the thermally conductive sheet is preferably 250 μm or less, more preferably 150 μm or less, preferably 50 μm or more, and more preferably 80 μm or more. If the average thickness is equal to or less than the above upper limit, the degree of freedom in arrangement within the device during mounting of the thermally conductive sheet can be increased. Further, if the average thickness is equal to or greater than the above lower limit, sufficient strength of the heat conductive sheet can be ensured.

Note that the thermally conductive sheet of the present invention can be manufactured using, for example, the method for manufacturing a thermally conductive sheet of the present invention, and is not particularly limited. The pieces may have a configuration in which they are joined in parallel in the width direction of the pieces.

(Method for manufacturing thermally conductive sheet)
The method for manufacturing a thermally conductive sheet of the present invention is used when manufacturing a thermally conductive sheet that contains a resin and a thermally conductive filler, and may optionally further contain an additive. Among these, the method for manufacturing a thermally conductive sheet of the present invention can be suitably used when manufacturing the thermally conductive sheet of the present invention described above.

The method for manufacturing a thermally conductive sheet of the present invention includes the step of slicing a resin block containing a resin and a thermally conductive filler using a slicing mechanism to obtain a thermally conductive sheet. In addition, in the method for manufacturing a thermally conductive sheet of the present invention, a single-edged cutting blade having a cutting edge consisting of a flank face, a rake face, and an intersection corner of the flank face and the rake face is arranged opposite to the rake face of the single-edged cutting blade. It is necessary to perform slicing using a slicing mechanism equipped with a guide member, such that the portion cut out from the resin block passes between the rake face and the guide member.

In this way, a slicing mechanism including a single-edged cutting blade and a guide member disposed opposite to the rake face of the single-edged cutting blade is used, so that the cut portion passes between the rake face and the guide member. By slicing the resin block, it is possible to prevent the thermally conductive sheet made of sliced pieces of the resin block from curling. Therefore, it is possible to prevent the surface roughness Sa of the thermally conductive sheet from increasing and the tensile strength from decreasing due to curling during slicing. Therefore, a thermally conductive sheet with a small surface roughness Sa and a high tensile strength can be obtained without performing operations such as pressurization after slicing, which may cause a decrease in thermal conductivity. Therefore, it is possible to obtain a thermally conductive sheet that exhibits excellent thermal conductivity and has excellent tensile strength.

In addition, when the content of the thermally conductive filler is large, when a thermally conductive filler with a small volume average particle diameter is used, and when the thickness of the thermally conductive sheet to be manufactured is reduced, the Although the thermally conductive sheet tends to curl, according to the method for manufacturing a thermally conductive sheet of the present invention, curling of the thermally conductive sheet can be sufficiently suppressed even in these cases.

<Resin block>
Here, the resin block that is the material of the thermally conductive sheet contains a resin and a thermally conductive filler, and optionally further contains an additive.
As the resin, thermally conductive filler, and additives, the same ones as those used in the thermally conductive sheet of the present invention described above can be used, and the preferred embodiments thereof are also the same as those of the thermally conductive sheet of the present invention described above. Therefore, the explanation will be omitted below.

[Shape and structure of resin block]
The shape of the resin block is not particularly limited, and can be any shape that allows a thermally conductive sheet of a desired shape to be obtained when sliced. Specifically, for example, when manufacturing a rectangular heat conductive sheet, the shape of the resin block is preferably a rectangular parallelepiped.

The structure of the resin block is not particularly limited, and a resin composition containing a resin, a thermally conductive filler, and optionally an additive may be formed using a known molding device such as a mold. It may have a structure formed by molding it into a desired shape, or it may be obtained by molding a resin composition containing a resin, a thermally conductive filler, and optionally an additive into a sheet shape. The structure may be formed by laminating, folding, or winding sheets.
Note that in a laminate formed by laminating sheets, the adhesive force between the surfaces of the sheets is usually sufficiently obtained by the pressure applied when laminating the sheets. However, if the adhesive strength is insufficient or if it is necessary to sufficiently suppress delamination between the layers of the laminate, lamination may be performed with the surface of the sheet slightly dissolved in a solvent, or the surface of the sheet may be Lamination may be performed with an adhesive applied to the sheet or with an adhesive layer provided on the surface of the sheet, or a laminate in which the sheets are laminated may be further pressed in the lamination direction.

Among these, the structure of the resin block is a resin composition containing a resin and a thermally conductive filler, and optionally further containing an additive, such as the resin block 10 shown in FIGS. 1(a) to (c). After pressurizing the material and forming it into a sheet shape to obtain a sheet 11 containing a resin, a thermally conductive filler, and optional additives, a plurality of the obtained sheets 11 are laminated in the thickness direction. A structure formed by folding or winding the obtained sheet 11 is preferable. In a sheet formed by pressurizing a resin composition and forming it into a sheet shape, the filler is oriented in the in-plane direction of the sheet, so if the laminate obtained by laminating, folding or winding the obtained sheets is sliced, This is because a thermally conductive sheet having anisotropy in thermal conductivity can be obtained. Specifically, in a sheet formed by pressurizing a resin composition containing a thermally conductive filler and forming it into a sheet, the thermally conductive filler is oriented in the in-plane direction, and the thermal conductivity in the in-plane direction is increased. improves. Therefore, if the sheet laminate is sliced in the stacking direction of the laminate, or in a direction perpendicular to both the stacking direction of the laminate and the sheets constituting the laminate, thermal conductivity with excellent thermal conductivity in the thickness direction can be achieved. You can get a seat.
Note that a thermally conductive sheet obtained by slicing a laminate of sheets in the stacking direction of the laminate, or in a direction perpendicular to both the stacking direction of the laminate and the sheets constituting the laminate, does not constitute a laminate. It has a structure in which sliced pieces of sheets (stripes containing resin and thermally conductive filler) are joined in parallel. In other words, the thermally conductive sheet contains a resin and a thermally conductive filler, and has strips having a width approximately equal to the thickness of the sheets that constituted the laminate, and the width direction of the strips is thermally conductive. It has a structure in which the strips are joined in parallel in the width direction in an orientation perpendicular to the thickness direction of the sheet. Here, especially in a heat conductive sheet having such a structure, if it curls during slicing, peeling tends to occur between adjacent strips, and especially on the side where the flank surface of the cutting blade was in contact during slicing, curling may occur. The effect of peeling due to Once a sheet has curled, the curl itself can be eliminated by flattening it by physical processing such as pressing, but it is difficult to recombine the strips that have been separated once. However, according to the method for producing a thermally conductive sheet of the present invention, it is possible to suppress the occurrence of curling, thereby suppressing peeling of strips from each other, thereby obtaining a thermally conductive sheet with low surface roughness and excellent tensile strength. be able to.

<Slice mechanism>
The slicing mechanism includes a single-edged cutting blade and a guide member disposed to face the rake face of the single-edged cutting blade. Specifically, an example of a slicing mechanism includes a cutting edge formed of a rake face 21, a flank face 22, and an intersection corner of the rake face 21 and the flank face 22, as shown in FIGS. 1(a) to 1(c), for example. The guide member 30 is provided to face the rake surface 21 of the single-edged cutting blade 20. In the illustrated example, the single-edged cutting blade 20 and the guide member 30 are provided at both ends in the width direction of the flat guide member 30 so that the rake face 21 and the surface 31 of the guide member 30 are parallel to each other. As shown in FIGS. 1(b) and 1(c), the portion 50 cut out from the resin block 10 during slicing is connected to the rake surface 21 and the rake surface 21 of the guide member 30. It passes through the gap 40 between the side surface 31.

Here, the static friction coefficient of the surface of the guide member facing the rake face is preferably 0.4 or less. If the coefficient of static friction is below the above upper limit value, the portion cut out from the resin block can be passed between the rake face and the guide member well, and the occurrence of curl can be well suppressed.

Further, the length of the guide member is preferably 1 cm or more, more preferably 2 cm or more, and preferably 5 cm or less. If the length of the guide member is equal to or greater than the above lower limit, curling can be sufficiently suppressed. Further, if the length of the guide member is equal to or less than the above upper limit, the heat conductive sheet obtained by slicing the resin block can be easily taken out from between the rake face and the guide member.

Further, the arrangement angle of the guide member is not particularly limited as long as a sufficient distance can be secured between the guide member and the rake face, but from the viewpoint of better suppressing the occurrence of curling, it is preferably parallel to the rake face. It is preferable.

Furthermore, the distance between the guide member and the rake surface is not particularly limited, but is preferably at least 2 times and 40 times the thickness of the thermally conductive sheet to be manufactured. If the distance between the guide member and the rake face is equal to or greater than the above lower limit value, the portion cut out from the resin block can pass between the rake face and the guide member well, and the occurrence of curl can be well suppressed. Can be done. Further, if the distance between the guide member and the rake face is equal to or less than the above upper limit value, the slicing mechanism can be made compact.

The position of the lower end of the guide member (the edge on the side where the cutting edge of the single-edged cutting blade is located) in the vertical direction (in the vertical direction in Fig. 1) is set so that the resin block can be sliced well while suppressing the occurrence of curling. Although there is no particular limitation as long as it can be It is preferable to be at the same position as or above the cutting edge. In addition, from the viewpoint of allowing the part cut out from the resin block to pass well between the rake face and the guide member, the position of the lower end of the guide member in the vertical direction is 5 mm vertically upward from the cutting edge of the single-edged cutting blade. It is preferable that the position be below the position of . Among these, it is particularly preferable that the position of the lower end of the guide member in the vertical direction be the same as the position of the cutting edge of the single-edged cutting blade.

<Slice>
The direction in which the resin block is sliced using the slicing mechanism is not particularly limited, and the clearance angle between the end surface (slice surface) of the sliced resin block and the clearance surface of the single-edged cutting blade is 5° or less. , especially in the direction of 0°. Then, the slicing is performed such that the portion 50 cut out from the resin block 10 passes between the rake face 21 and the guide member 30, as shown in FIGS. 1(b) and 1(c), for example.

Note that the slicing of the resin block using the above-mentioned slicing mechanism is not particularly limited, and is preferably performed while applying pressure to the resin block, and is preferably performed while applying pressure of 0.1 MPa or more and 1.0 MPa or less. It is more preferable to do this while

Further, from the viewpoint of slicing the resin block easily, the temperature of the resin block during slicing is preferably -20°C or more and 30°C or less.

Furthermore, the slicing speed of the resin block is not particularly limited, but is preferably 25 mm/sec or more, more preferably 100 mm/sec or more, preferably 200 mm/sec or less, and 150 mm/sec. It is more preferable to set it as below. If the slicing speed is within the above range, the resin block can be sliced well while increasing the productivity of the heat conductive sheet, and a heat conductive sheet with sufficiently suppressed curling can be obtained.

EXAMPLES Hereinafter, the present invention will be explained in more detail using Examples, but the present invention is not limited to these Examples.
In addition, in the examples and comparative examples, the thermal conductivity, surface roughness Sa, surface roughness variation, tensile strength, in-plane tensile strength variation, average thickness, and thermal resistance value of the thermally conductive sheet, The static friction coefficient of each guide member was measured using the following method.

<Thermal conductivity>
Regarding the thermally conductive sheet, the thermal diffusivity α (m ² /s) in the thickness direction, the specific heat Cp (J/g·K) at constant pressure, and the specific gravity ρ (g/m ³ ) were each measured by the following methods.
[Thermal diffusivity α in the thickness direction]
The measurement was carried out using a thermal diffusion/thermal conductivity measuring device (manufactured by I-Phase Co., Ltd., product name "I-Phase Mobile 1u") in accordance with the provisions of ISO 22007-3.
[Constant pressure specific heat Cp]
Using a differential scanning calorimeter (manufactured by Rigaku, product name "DSC8230"), the specific heat at 25° C. was measured under a temperature increase condition of 10° C./min.
[Specific gravity ρ (density)]
It was measured using an automatic hydrometer (manufactured by Toyo Seiki Co., Ltd., trade name "DENSIMETER-H").
Then, each measured value is expressed by the following formula (I):
λ=α×Cp×ρ...(I)
The thermal conductivity λ (W/m·K) in the thickness direction of the thermally conductive sheet at 25° C. was determined.
<Surface roughness Sa and surface roughness variation>
The surface roughness Sa of the thermally conductive sheet was measured using a three-dimensional shape measuring machine (manufactured by Keyence Corporation, product name: "One-shot 3D measurement macroscope").
Specifically, the three-dimensional shape was measured for an analysis range (1 cm x 1 cm) of five points extracted from the surface of the thermally conductive sheet to be evaluated. Note that when extracting five points, it is desirable that the analysis ranges are separated by 1 cm or more, but if the size of the thermally conductive sheet is small, the analysis ranges may partially overlap. Furthermore, if the size of the thermally conductive sheet is small and an analysis range of 1 cm x 1 cm cannot be secured, the analysis range may be reduced to 0.3 cm x 0.3 cm.
Furthermore, by filtering (2.5 mm) the three-dimensional shape measurement results using software and removing the waviness component, the surface roughness Sa (μm) is automatically calculated, and the average value of the five-point analysis range is calculated. was defined as the surface roughness Sa of the thermally conductive sheet.
The three-dimensional shape was measured on each of the A surface (the surface that was in contact with the rake surface of the cutting blade during slicing) and the B surface (the surface that was in contact with the flank surface of the cutting blade during slicing). Ta.
Further, the difference between the maximum value and the minimum value of the surface roughness Sa was calculated for the analysis range of the five measured points, and the variation in the surface roughness of the heat conductive sheet was determined.
<Tensile strength and in-plane tensile strength variation>
A thermally conductive sheet was punched and molded using a dumbbell No. 2 (dumbbell type, width: 3 mm, length 70 mm) based on JIS K7113, and five sample pieces were produced. Then, using a tensile tester (manufactured by Shimadzu Corporation, product name "AG-IS20kN"), the tensile strength was measured under the conditions of load cell: 50N, distance between chucks: 35mm, speed: 25mm/min, and temperature: 23°C. (Tensile strength) was measured.
The direction in which the sample piece is punched out is the direction in which the long axis of the dumbbell intersects at a 90 degree angle with the strip that constitutes the thermally conductive sheet, and the punching locations are at the center and four corners of the sheet (3 cm inward from the corner). A total of 5 locations were selected (positions within which part of the dumbbell could fit).
The average value of the measured values of the five sample pieces was taken as the tensile strength of the heat conductive sheet, and the difference between the maximum value and the minimum value was taken as the in-plane tensile strength variation of the heat conductive sheet.
Generally, the tensile strength of a curled area deteriorates.
<Average thickness>
Using a film thickness meter (manufactured by Mitutoyo, product name "Digimatic Indicator ID-C112XBS"), measure the thickness at five points in total, the center and four corners of the thermally conductive sheet, and find the average value (μm) of the measured thickness. Ta.
<Thermal resistance value>
The thermal resistance value of the thermally conductive sheet was measured using a thermal resistance tester (manufactured by Hitachi Technology and Services Co., Ltd., product name: "Resin material thermal resistance measuring device").
Specifically, a roughly square sample of 1 cm square size was cut out from a thermally conductive sheet, and the thermal resistance value (℃/W ) was measured. The smaller the thermal resistance value, the better the thermal conductivity of the thermally conductive sheet, and, for example, the better the heat dissipation properties when interposed between a heating element and a heat radiating element.
<Static friction coefficient>
The static friction coefficient was measured in accordance with JIS K7125 using a small tabletop tester (manufactured by Nidec-Shimpo, trade name "FGS-500TV"). Specifically, an aluminum plate was used as the mating material, and the average value of the values measured three times was taken as the static friction coefficient.

(Example 1)
<Preparation of composition>
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 name "DAIEL G-101"). Dynion FC2211'') and 90 parts of expanded graphite as a particulate carbon material (manufactured by Ito Graphite Industries Co., Ltd., trade name ``EC300'', volume average particle diameter: 50 μm) were mixed in a pressure kneader (manufactured by Nippon Spindle). ) for 20 minutes at a temperature of 150°C. Next, the obtained mixture was put into a crusher (manufactured by Osaka Chemical Co., Ltd., trade name "Wonder Crush Mill D3V-10") and crushed for 10 seconds to obtain a composition.
<Formation of pre-thermal conductive sheet>
Next, 50 g of the obtained composition was sandwiched between sandblasted protective films (PET films) with a thickness of 50 μm, and the conditions were as follows: roll gap 1000 μm, roll temperature 50°C, roll linear pressure 50 kg/cm, and roll speed 1 m/min. The sheet was rolled and formed (primary pressing) to obtain a pre-thermal conductive sheet with a thickness of 0.8 mm.
<Formation of laminate>
Subsequently, the obtained pre-thermal conductive sheet was cut into pieces of 150 mm long x 150 mm wide x 0.8 mm thick, and 188 sheets were laminated in the thickness direction of the pre-thermal conductive sheet. Then, by pressing in the stacking direction (secondary pressing) at a temperature of 120° C. and a pressure of 0.1 MPa for 3 minutes, a laminate with a height of about 150 mm was obtained.
<Formation of thermally conductive sheet>
After that, place the laminate so that the stacking direction is horizontal to the ground (the surface on which the laminate is placed), and leave the length necessary for slicing on one end of the laminate in the direction perpendicular to the stacking direction. The entire upper surface of the installed laminate was pressed down with a metal plate, and a pressure of 0.1 MPa was applied from above to fix the laminate. Note that the side and back sides of the laminate were not fixed. At this time, the temperature of the laminate was 25°C.
Next, a cutting blade of the shape shown in Fig. 1 (single edge, blade angle: 20°, maximum blade thickness: 3.5 mm, material: super steel, Rockwell hardness: 91.5, silicone processing on the blade surface: None, total length: 200 mm) and a slicing mechanism (between the guide member and rake surface) consisting of a guide member (length: 50 mm, coefficient of static friction: 0.4) The laminate was placed so that the stacking direction was horizontal, and the laminate was placed in the vertical direction (direction perpendicular to the stacking direction of the laminate) at a slicing speed of 25 mm/sec and a slice width of 100 μm. A thermally conductive sheet measuring 150 mm long x 150 mm wide x 0.10 mm thick (average thickness) was obtained. The attitude of the cutting blade during slicing was such that the extending direction of the flank surface was parallel to the slicing surface of the laminate. Moreover, the obtained thermally conductive sheet had a structure in which sliced pieces (strips) of the pre-thermal conductive sheet were joined in parallel.
Then, various evaluations were performed on the obtained thermally conductive sheet. The results are shown in Table 1.

(Example 2)
A thermally conductive sheet was produced in the same manner as in Example 1 except that the slicing speed was 100 mm/sec.
Then, various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)
A thermally conductive sheet was produced in the same manner as in Example 1 except that the slicing speed was 200 mm/sec.
Then, various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 4)
A thermally conductive sheet was manufactured in the same manner as in Example 1 except that the distance between the guide member of the slicing mechanism and the rake face was changed to 1.5 mm.
Then, various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative example 1)
A thermally conductive sheet was manufactured in the same manner as in Example 1 except that the slice was performed using only the cutting blade without using the guide member. The thermally conductive sheet was curled during slicing into a cylindrical shape with a diameter of 0.5 cm, so it was stretched by hand to form a thermally conductive sheet.
Then, various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

From Table 1, it can be seen that the thermally conductive sheets of Examples 1 to 4 have higher tensile strength and can exhibit excellent thermal conductivity than the thermally conductive sheet of Comparative Example 1.

According to the present invention, it is possible to provide a thermally conductive sheet that can exhibit excellent thermal conductivity and has high tensile strength.

10 resin block 11 sheet 20 cutting blade 21 rake face 22 flank face 30 guide member 31 surface 40 gap 50 part

Claims (11)

A thermally conductive sheet containing a resin and a thermally conductive filler,
The thermal conductivity in the thickness direction is 30 W/m・K or more,
Surface roughness Sa is 1.0 μm or more and 2.5 μm or less on both surfaces ,
A thermally conductive sheet with surface roughness variation of 0.30 μm or less on both sides . The thermally conductive sheet according to claim 1 , having a tensile strength of 0.45 MPa or more and 0.7 MPa or less . The thermally conductive sheet according to claim 1 or 2, wherein the variation in in-plane tensile strength is 0.10 MPa or less. the thermally conductive filler includes a particulate carbon material,
The thermally conductive sheet according to any one of claims 1 to 3, wherein the particulate carbon material has a volume average particle diameter of 10 μm or more and 100 μm or less. The thermally conductive sheet according to claim 4, wherein the particulate carbon material is anisotropic graphite. The thermally conductive sheet according to any one of claims 1 to 5, having an area of 3600 mm ² or more in plan view. The thermally conductive sheet according to any one of claims 1 to 6, having an average thickness of 250 μm or less. A method for producing a thermally conductive sheet comprising the step of slicing a resin block containing a resin and a thermally conductive filler using a slicing mechanism to obtain the thermally conductive sheet according to any one of claims 1 to 7,
The slicing mechanism includes a single-edged cutting blade having a flank face, a rake face, and a cutting edge formed by an intersection corner of the flank face and the rake face, and a guide member disposed opposite to the rake face. ,
A method for manufacturing a thermally conductive sheet, wherein the slicing is performed such that the portion cut out from the resin block passes between the rake face and the guide member. The method for manufacturing a thermally conductive sheet according to claim 8, wherein the surface of the guide member facing the rake surface has a static friction coefficient of 0.4 or less. The method for manufacturing a thermally conductive sheet according to claim 8 or 9, wherein the length of the guide member is 1 cm or more and 5 cm or less. The method for producing a thermally conductive sheet according to any one of claims 8 to 10, wherein the resin block is sliced at a speed of 25 mm/sec or more and 200 mm/sec or less.

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