JP2020126972A - Thermally conductive sheet - Google Patents

Abstract

To provide a thermally conductive sheet which is superior in heat conductivity, and which has an excellent isotropy in expansion and contraction in a plane direction.SOLUTION: A thermally conductive filler comprises: an acrylic rubber; and a thermally conductive filler containing a first thermally conductive filler and a second thermally conductive filler smaller than the first thermally conductive filler in particle size. In the thermally conductive sheet, the content of the thermally conductive filler is 30-60 vol.%; the first thermally conductive filler is oriented substantially in a thickness direction; the first thermally conductive filler is a filler containing a boron nitride having a particle size of 20 μm or larger and an aspect ratio of 10 or more; the second thermally conductive filler is a filler containing a material other than boron nitride; the second thermally conductive filler has a particle size of 3-20 μm; and the content of the second thermally conductive filler is 15-45 vol.%.SELECTED DRAWING: Figure 1

Description

The present invention relates to a heat conductive sheet.

In recent years, electronic devices have rapidly become higher in density and thinner, and the influence of heat generated from ICs, power components, and high-brightness LEDs has become a serious problem. On the other hand, for example, as a member that efficiently transfers heat between a heat generating body such as a chip and a heat radiating body, a sheet-shaped molded body (heat conductive sheet) in which a heat conductive filler is dispersed is used I'm out.
In the heat conductive sheet, as a means for increasing the heat conductivity, it is known to orient the heat conductive filler dispersed in the molded body in order to efficiently form the heat conductive path.

For example, in Patent Document 1, a silicone containing 50 to 75% by volume of a heat conductive filler containing two types of boron nitride powders (A) and (B) having different average particle diameters as a heat conductive molded body. A heat conductive molded body has been proposed, which is characterized in that the laminate is cut in the stacking direction.
Further, in Patent Document 1, it is described that boron nitride powder has extremely high thermal conductivity in the lengthwise direction of the scaly particles, and high utilization of the characteristics makes it possible to impart high thermal conductivity.

JP, 2010-260225, A

As described in Patent Document 1, a filler made of boron nitride (hereinafter referred to as BN filler) is a filler having excellent thermal conductivity. Therefore, by orienting the scale-like BN filler in the thickness direction in the heat conductive sheet, the heat conductivity in the thickness direction of the heat conductive sheet can be increased.
On the other hand, when the scale-like BN filler was oriented in the heat conductive sheet, it was revealed by the study of the present inventors that the following problems occur.

When the scale-like BN filler was oriented in the heat conductive sheet, the BN filler was sometimes oriented not only in the thickness direction of the sheet but also in one direction in the plane direction of the sheet. In particular, when the heat conductive sheet was manufactured through an extrusion molding process, the scaly BN filler was easily oriented in one direction in the plane direction.
FIG. 3 is a schematic diagram for explaining a state in which the scaly BN filler is oriented also in one direction in the plane direction of the heat conductive sheet.
The thermal conductive sheet 50 in which the flaky BN filler 54 is dispersed in the matrix component 52 has the thermal conductive filler 54 in the thickness direction (Z direction in FIG. 3) in order to ensure excellent thermal conductivity. It is oriented to. The heat conductive sheet 50 is a heat conductive sheet having a large number of heat conductive paths formed in the thickness direction and having excellent heat conductivity in the thickness direction.
On the other hand, in the manufacturing process of the heat conductive sheet 50, an extrusion process was adopted to orient the scale-like BN filler 54 in the thickness direction. When the heat conductive sheet 50 is manufactured through the extrusion step, as shown in FIG. 3, the scale-like BN filler 54 is not only in the thickness direction of the heat conductive sheet 50 but also in the surface direction (in FIG. 3). , XY direction) in some cases (X direction in FIG. 3).

Thus, the thermal conductive sheet 50 in which the scale-like BN filler 54 is oriented not only in the thickness direction of the thermal conductive sheet 50 but also in one direction in the plane direction has tensile properties in the plane direction of the sheet. It has become clear that variations (anisotropic) occur in the. Specifically, the X direction in which the scaly BN filler 54 is oriented is difficult to expand with a high elastic modulus, and the direction orthogonal to the X direction in the plane direction (Y direction in FIG. 3) is easy to expand with a low elastic modulus. Was there.
And, when the heat conductive sheet has anisotropy in tensile properties in the surface direction, when the heat conductive sheet is assembled between the heat generating body and the heat radiating body, or when the heat conductive sheet is in use, When a load is applied to a part or all of the heat generating element or the heat radiating element, the heat conductive sheet may be deformed unintentionally. As a result, the performance as a heat conductive sheet may not be sufficiently exhibited.

The present invention has been made in view of such problems, and an object thereof is to provide a heat conductive sheet having excellent thermal conductivity and having little variation in tensile properties in the surface direction.

(1) The heat conductive sheet of the present invention is
A heat conductive sheet comprising an acrylic rubber and a heat conductive filler containing a first heat conductive filler and a second heat conductive filler having a particle size smaller than that of the first heat conductive filler,
The content of the heat conductive filler is 30 to 60% by volume,
The first thermally conductive filler is oriented substantially in the thickness direction,
The first thermally conductive filler is a filler made of boron nitride having a particle size of 20 μm or more and an aspect ratio of 10 or more,
The second thermally conductive filler is a filler made of a material other than boron nitride,
The particle diameter of the second heat conductive filler is 3 to 20 μm,
The content of the second heat conductive filler is 15 to 45% by volume,
A heat conductive sheet characterized by the above.

The heat conductive sheet employs acrylic rubber as a matrix component. Therefore, it is suitable as a heat conductive sheet used in a place where siloxane-free is required.
Moreover, the said heat conductive sheet contains the specific 1st thermal conductive filler and the specific 2nd thermal conductive filler whose particle diameter is smaller than a 1st thermal conductive filler.
Therefore, the thermally conductive sheet is suitable for orienting the first thermally conductive filler in the thickness direction, and by orienting the first thermally conductive filler in the thickness direction, excellent thermal conductivity is obtained. Can be secured. In particular, by using the second heat conductive filler together, the first heat conductive filler can be oriented in the thickness direction even if the amount of the first heat conductive filler is not large.

Further, since the second heat conductive filler is used together with the first heat conductive filler, the variation in the tensile properties in the plane direction of the heat conductive sheet is reduced (the tensile properties in the plane direction are made to be isotropic). )be able to.

(2) In the heat conductive sheet, the aspect ratio of the second heat conductive filler is preferably 1.5 or less.
In this case, the thermal conductive sheet tends to have less variation in tensile properties in the surface direction.

(3) In the heat conductive sheet, the content of the second heat conductive filler is preferably 20 to 45% by volume.
In this case, the heat conductive sheet is more suitable for reducing variations in tensile properties in the surface direction.
The second heat conductive filler is also suitable for being interposed between the first heat conductive fillers to enhance the heat conductivity of the heat conductive sheet.
In addition, the second heat conductive filler is interposed between the first heat conductive fillers, and a heat conductive path is easily formed in the surface direction of the heat conductive sheet, so that heat transfer in the surface direction of the heat conductive sheet is facilitated. Variations in performance can also be reduced.

(4) In the heat conductive sheet, the second heat conductive filler is preferably a filler made of magnesium carbonate.
A filler made of magnesium carbonate (magnesite) (hereinafter, also referred to as a magnesite filler) is suitable as a second heat conductive filler because it has relatively excellent thermal conductivity and excellent stability at high temperatures. Is.
In addition, since the magnesite filler has a low Mohs hardness, it does not easily damage the manufacturing equipment (for example, the screw of the extruder) when manufacturing the heat conductive sheet, and the heat is continuously applied for a long period of time. Suitable for forming conductive sheets.

The heat conductive sheet of the present invention has excellent heat conductivity. In addition, the thermal conductive sheet has a small variation in tensile properties in the surface direction.

It is sectional drawing which shows typically an example of the heat conductive sheet which concerns on embodiment of this invention. It is a figure which shows typically an example of the extruder used in manufacture of the heat conductive sheet which concerns on embodiment of this invention. It is a perspective view which shows typically an example of the conventional heat conductive sheet.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
In the present embodiment, the “thermally conductive sheet” is a concept including both a material prepared by molding a raw material composition and a material manufactured by molding a raw material composition and further cut. Is.

FIG. 1 is a sectional view schematically showing an example of a heat conductive sheet according to an embodiment of the present invention, and is a cross sectional view parallel to the thickness direction of the heat conductive sheet. FIG. 1 is a schematic view, and each member (particularly the first heat conductive filler and the second heat conductive filler) does not accurately reflect the actual size.
The heat conductive sheet 1 according to the present embodiment is arranged between a heat generating member such as an IC chip and a heat radiating member such as a heat sink, and one surface is brought into contact with the heat generating member and the other surface is brought into contact with the heat radiating member. To use.

As shown in FIG. 1, the heat conductive sheet 1 has a matrix component 2, a first heat conductive filler 4 and a second heat conductive filler 5, and the first heat conductive filler 4 is The conductive sheet 1 is oriented substantially in the thickness direction (vertical direction in FIG. 1). In the heat conductive sheet 1, a heat conductive path formed by the first heat conductive filler 4 and the second heat conductive filler 5 is formed substantially in the thickness direction of the heat conductive sheet 1. Therefore, the heat conductive sheet 1 has excellent heat conductivity in the thickness direction.
In addition, in the said heat conductive sheet, components other than a heat conductive filler are collectively called a matrix component.

The heat conductive sheet 1 is obtained by slicing a thin rubber sheet, in which the first heat conductive filler 4 in the matrix component 2 is oriented and dispersed in the plane direction thereof, in a state of being folded and adhered in a vertical direction into a sheet shape. is there. A weld line (not shown) may be formed on the heat conductive sheet 1 in a substantially thickness direction.

The matrix component 2 contains acrylic rubber.
The acrylic rubber is a crosslinked product of an acrylic composition containing an uncrosslinked acrylic rubber and a crosslinking agent.
The uncrosslinked acrylic rubber is a copolymer containing (meth)acrylic acid ester as a main component (accounting for 50% by weight or more in all monomer units).
Examples of the uncrosslinked acrylic rubber include a copolymer of (meth)acrylic acid ester and a crosslinking point monomer.
Here, examples of the (meth)acrylic acid ester include ethyl (meth)acrylate, butyl (meth)acrylate, and methoxyethyl (meth)acrylate. Examples of the crosslinking point monomer include chlorine-based monomers such as 2-chloroethyl vinyl ether and vinyl chloroacetate, epoxy-based monomers such as allyl glycidyl ether, and diene-based monomers such as ethylidene norbornene. These (meth)acrylic acid ester and the crosslinking point monomer may be appropriately combined and used.
The uncrosslinked acrylic rubber may be, for example, an ethylene acrylate rubber which is a copolymer of ethylene, methyl acrylate and a third component having a crosslinked carboxyl group.
The uncrosslinked acrylic rubber is preferably a millable type that can be kneaded with a Banbury mixer, a kneader, a roll or the like. This is because it is suitable for producing a heat conductive sheet by the method described below.

The uncrosslinked acrylic rubber may be a commercially available product.
Specific examples of the commercially available products include, for example, Nipol (registered trademark, the same applies hereinafter) AR14, Nipol AR74X, Nipol AR54, Nipol AR12, Nipol AR53L, Nipol AR72LS, Nipol AR42W, Nipol AR32, Nipol AR71, Nipol AR51, Nipol AR31. (Both manufactured by Nippon Zeon Co., Ltd.) and the like.
Moreover, as another specific example of the commercially available product, for example, NOXITE (registered trademark, the same applies hereinafter) A-1095, NOXITE PA-212, NOXITE PA-214, NOXITE A-5098, NOXITE PA-312, NOXITE PA-. 401, NOXITE PA-401L, NOXITE PA-402, NOXITE PA-402L, NOXITE PA-402F, NOXITE PA-403, NOXITE PA-404N, NOXITE PA-422L, NOXITE PA-521, NOXHITE PA-402F. 526, NOXITE PA-524 (all are manufactured by Unimatec Co., Ltd.) and the like.

The uncrosslinked acrylic rubber preferably has a Mooney viscosity (ML ₁₊₄ , 100° C.) of 20 to 60.
This is because this case is suitable for containing a large amount of the thermally conductive filler in the matrix component.
The Mooney viscosity is more preferably 20-40.
The Mooney viscosity may be measured using a Mooney viscometer according to JIS K 6300-1.

Examples of the crosslinking agent include polyvalent amine compounds such as diamine compounds and their carbonates, sulfur, sulfur donors, triazine thiol compounds, polyvalent epoxy compounds, organic carboxylic acid ammonium salts, organic peroxides, dithiocarbamic acid. Conventionally known crosslinking agents such as metal salts, polyvalent carboxylic acids, quaternary onium salts, imidazole compounds and isocyanuric acid compounds can be mentioned.
These may be used alone or in combination of two or more.
The amount of the cross-linking agent to be blended is usually about 0.5 to 2 parts by weight based on 100 parts by weight of the uncrosslinked acrylic rubber.

The acrylic composition preferably contains a crosslinking accelerator.
Examples of the crosslinking accelerator include guanidine compounds, diazabicycloalkene compounds, imidazole compounds, quaternary onium salts, tertiary phosphine compounds, aliphatic monovalent secondary amine compounds, and aliphatic monovalent tertiary amine compounds. Etc.
These may be used alone or in combination of two or more.
When the above crosslinking accelerator is contained, the upper limit of its blending amount is usually about 4 parts by weight with respect to 100 parts by weight of the above-mentioned uncrosslinked acrylic rubber. The amount of the crosslinking accelerator compounded is more preferably 0.5 to 2 parts by weight with respect to 100 parts by weight of the uncrosslinked acrylic rubber.

The acrylic composition preferably contains a lubricant.
By blending the above-mentioned lubricant, it is excellent in processability when producing a heat conductive sheet by the method described later.
Examples of the lubricant include fatty acids such as stearic acid, higher alcohols, fatty acid amides, metal soaps and fatty acid esters.
When the lubricant is blended, the amount thereof is usually about 0.5 to 7 parts by weight with respect to 100 parts by weight of the uncrosslinked acrylic rubber.

The matrix component may contain a component other than the acrylic rubber as long as the performance as the heat conductive sheet is not impaired.
Examples of the other components include resin components other than acrylic rubber, rubber (elastomer) components, and the like. As the above-mentioned other components, for example, general addition of reinforcing agents, fillers, softening agents, plasticizers, antiaging agents, tackifiers, antistatic agents, kneading adhesives, flame retardants, coupling agents, etc. Agents are also included.
On the other hand, when the heat conductive sheet is used in a place where siloxane-free is desired, the matrix component should not contain silicone.

The heat conductive sheet 1 contains, as two kinds of heat conductive fillers, a first heat conductive filler 4 and a second heat conductive filler 5 having a particle diameter smaller than that of the first heat conductive filler 4.
The first thermally conductive filler 4 is made of boron nitride (BN). Therefore, the heat conductive sheet 1 has excellent heat conductivity.
The shape of the first thermally conductive filler 4 is not particularly limited as long as it has a predetermined particle size and aspect ratio. Specific shapes of the first thermally conductive filler 4 include, for example, a scaly shape, a plate shape, a film shape, a fibrous shape, a columnar shape, an elliptical shape, and a flat shape.
Of these, the scale-like shape is preferable. Since it has a high aspect ratio and has isotropic thermal conductivity in the plane direction of the particles, when the scale-like thermally conductive filler is oriented, the thermal conductivity of the thermally conductive sheet becomes high. Is.

The particle diameter of the first heat conductive filler 4 is 20 μm or more. When the particle size is less than 20 μm, it is difficult to form a heat conduction path, and the heat conductivity may be poor.
On the other hand, the preferable upper limit of the particle diameter of the first thermally conductive filler 4 is 100 μm from the viewpoint of workability when manufacturing the thermally conductive sheet. The upper limit of the particle diameter of the first thermally conductive filler 4 is more preferably 40 μm.

The aspect ratio of the first thermally conductive filler 4 is 10 or more. In this case, it is suitable for the second heat conductive filler 5 having a smaller particle diameter than the first heat conductive filler 4 to be dispersed in the gap between the first heat conductive fillers 4 to form a heat conductive path. In addition, the first thermally conductive filler 4 is easily oriented in the matrix component 2.
On the other hand, the upper limit of the aspect ratio of the first thermally conductive filler 4 is preferably 100. In this case, the first thermally conductive filler can be easily filled in the thermally conductive sheet, and the workability in manufacturing the thermally conductive sheet is also excellent.

In the present invention, the “particle diameter” of the heat conductive filler means a value of median diameter (d ₅₀ ) measured by a laser diffraction/scattering method. As a measuring device, for example, Microtrack MT3300EXII manufactured by Microtrack Bell KK can be used.
In the present invention, the “aspect ratio” of the thermally conductive filler means a value obtained by dividing the major axis of the thermally conductive filler by the minor axis. Here, the major axis of the thermally conductive filler refers to the length of the longest part in the thermally conductive filler, and the minor axis of the thermally conductive filler, in the direction orthogonal to the major axis, the most of the thermally conductive filler. The length of the short part.
Here, the major axis and the minor axis of the heat conductive filler are calculated using a microscope image of the heat conductive filler. Then, the calculation of the aspect ratio of the thermally conductive filler is performed by obtaining a microscope image of the thermally conductive filler, randomly selecting 20 thermally conductive fillers from the image, and measuring the major axis and the minor axis of each filler. The aspect ratio is calculated based on the diameter, and the average value is calculated.

The second heat conductive filler 5 has a particle diameter smaller than that of the first heat conductive filler (BN filler) and is made of a material other than boron nitride.
The material of the second thermal conductive filler 5 may be any material other than boron nitride and having thermal conductivity. Specific examples of the material of the second thermally conductive filler 5 include, for example, graphite, carbon fiber, carbon nanotube (CNT), mica, alumina, aluminum nitride, silicon carbide, silica, zinc oxide, magnesium oxide, calcium carbonate, carbonic acid. Examples thereof include magnesium, molybdenum disulfide, copper, aluminum and the like.
The second thermally conductive filler 5 made of these materials may be used alone or in combination of two or more.

Of these, magnesium carbonate (magnesite) is preferable.
Since a filler made of magnesium carbonate (hereinafter, also referred to as a magnesite filler) has a low Mohs hardness, it is less likely to damage a manufacturing apparatus (for example, a screw of an extruder) when manufacturing a heat conductive sheet. In addition, when a high hardness heat conductive filler (for example, a filler made of alumina) is adopted as the heat conductive filler, the filler behaves like an abrasive, and thus a constituent member of a manufacturing apparatus such as a screw. Damage to the manufacturing equipment, and as a result, maintenance of the manufacturing apparatus becomes necessary in a short period of time.

Further, the magnesite filler is chemically stable up to about 500° C., and is unlikely to generate outgas or deteriorate. Therefore, the heat conductive sheet in which the second heat conductive filler 5 is the magnesite filler can exhibit stable performance for a long period of time. Further, the magnesite filler is suitable because it is easy to ensure the electrical insulation of the heat conductive sheet.

As the second heat conductive filler, a filler made of magnesium hydroxide (hereinafter also referred to as magnesium hydroxide filler) or a filler made of magnesium oxide (hereinafter also referred to as magnesium oxide filler) is preferable.
Although the magnesium hydroxide filler is less stable than the magnesite filler, it releases water when it melts, and therefore is suitable as a filler that can impart flame retardancy to the heat conductive sheet.
Magnesium oxide filler is suitable because it has high thermal conductivity and relatively low Mohs hardness, and is unlikely to damage the manufacturing apparatus.

Further, a silica filler (hereinafter, also referred to as silica filler) is preferable as the second heat conductive filler used in combination with a magnesite filler, a magnesium hydroxide filler, a magnesium oxide filler, or the like.
This is because the strength of the heat conductive sheet can be improved by using the silica filler together.
When the silica filler is used in combination with a magnesite filler or the like, the compounding amount thereof is preferably 6 to 10% by volume based on the total amount of the matrix component and the silica filler from the viewpoint of improving the strength described above.

The second thermally conductive filler preferably has an aspect ratio of 1.5 or less.
In this case, the thermal conductive sheet 1 tends to have less variation in tensile properties in the surface direction.
When the aspect ratio of the second heat conductive filler 5 exceeds 1.5, when the heat conductive sheet 1 is manufactured through the extrusion molding process, the above-mentioned variation in the tensile properties in the surface direction is unlikely to be small.
When the variation in tensile properties in the surface direction of the heat conductive sheet 1 is small, as described above, it is possible to avoid unexpected deformation during attachment or use of the heat conductive sheet.
The aspect ratio of the second heat conductive filler is more preferably 1.0 to 1.2.
The shape of the second heat conductive filler 5 is not particularly limited, but one having an aspect ratio of 1.5 or less and having a spherical shape, a cylindrical shape, a prismatic shape, an elliptical shape or the like is preferable.

The particle diameter of the 2nd heat conductive filler 5 is smaller than the particle diameter of the 1st heat conductive filler 4, and is 3-20 micrometers.
When the particle diameter of the second thermally conductive filler 5 is in this range, the second thermally conductive filler 5 is interposed between the first thermally conductive fillers 4 to form a thermally conductive path, and the first thermally conductive filler 4 is heated. It is possible to orient the conductive sheet 1 in the thickness direction.
Further, when the particle diameter of the second heat conductive filler 5 is within this range, the surface roughness of the heat conductive sheet 1 is suppressed, and the contact thermal resistance when contacting the heat generating member or the heat radiating member (heat conductive sheet 1 It is suitable for reducing the thermal resistance of the surface.
On the other hand, when the particle diameter of the second heat conductive filler 5 exceeds 20 μm, the first heat conductive filler 4 becomes difficult to be oriented in the thickness direction of the heat conductive sheet 1.
When the particle diameter of the second heat conductive filler 5 is less than 3 μm, the heat conductive sheet 1 may be inferior in heat conductivity depending on the material of the second heat conductive filler 5.
The particle diameter of the second heat conductive filler 5 is more preferably 5 to 20 μm, further preferably 5 to 15 μm, and particularly preferably 5 to 10 μm.

The total content of the heat conductive filler in the heat conductive sheet 1 is 30 to 60% by volume.
If the total content of the heat conductive filler is less than 30% by volume, sufficient heat conductivity cannot be secured. Further, if the content exceeds 60% by volume, the workability in producing the heat conductive sheet will be poor.
The content of the heat conductive filler in the heat conductive sheet 1 (total content of the heat conductive filler) is preferably 30 to 50% by volume.

The content of the first thermally conductive filler 4 in the thermally conductive sheet 1 is preferably 5 to 20% by volume. In this case, it is suitable for orienting the first thermally conductive filler 4 and ensuring thermal conductivity.
On the other hand, if the content of the first thermally conductive filler 4 is less than 5% by volume, sufficient thermal conductivity may not be ensured even if the first thermally conductive filler is oriented. Moreover, when the said content exceeds 20 volume%, it will become difficult to provide a heat conductive sheet cheaply.

The content of the second thermally conductive filler 5 in the thermally conductive sheet 1 is 15 to 45% by volume.
When the content of the second heat conductive filler 5 is less than 15% by volume, it becomes difficult to orient the first heat conductive filler during molding. On the other hand, when the content of the second heat conductive filler 5 exceeds 45% by volume, the content of the first heat conductive filler becomes too small, and it becomes impossible to secure sufficient heat conductivity.
The content of the second heat conductive filler 5 is preferably 20 to 45% by volume.

The heat conductive sheet 1 of the present embodiment contains the first heat conductive filler 4 and the second heat conductive filler 5 as the heat conductive filler. Here, the particle diameter of the first thermally conductive filler 4 is larger than the particle diameter of the second thermally conductive filler 5, and both have a predetermined particle diameter.
The heat conductive sheet 1 may contain a heat conductive filler other than the first heat conductive filler 4 and the second heat conductive filler 5 as long as the effect of the present invention is not impaired.

The thickness of the heat conductive sheet 1 is not particularly limited, but is, for example, about 0.1 to 3.0 mm.
In this case, the heat conductive sheet 1 can be suitably used as a member that efficiently transfers heat between a heat generating member and a heat radiating member in electric parts, automobile parts, and the like.

As described above, the thermal conductive sheet 1 has a small variation in tensile properties in the plane direction (in-plane anisotropy).
The variation in tensile properties in the surface direction of the heat conductive sheet 1 can be evaluated by, for example, the ratio of the modulus in two orthogonal directions.
Here, the two directions orthogonal to each other are orthogonal to the first direction and the direction in which the modulus of elasticity is relatively low and the modulus is high in the surface direction of the heat conductive sheet 1 (hereinafter, also referred to as the first direction). It is sufficient to set two directions, that is, a direction to be performed (hereinafter, also referred to as a second direction). The ratio of the modulus in the two directions orthogonal to each other is determined by measuring the 5% modulus in each of the first direction and the second direction, and measuring the 5% modulus in the second direction with respect to the first direction (high The 5% modulus ratio (hereinafter referred to as the 5% modulus ratio) in the modulus direction) may be calculated and evaluated.
The first direction in the surface direction of the heat conductive sheet 1 may be determined by the following method. That is,
In the plane direction of the heat conductive sheet 1, four directions (any angle formed between adjacent directions is 45°) passing through one arbitrary point are set, and the modulus of each direction (four directions) is measured. As a result, the direction having the largest modulus may be set as the first direction, and the direction orthogonal to the first direction may be set as the second direction.
Moreover, when the heat conductive sheet 1 is manufactured through an extrusion molding process described below, the heat conductive sheet 1 is relatively hard to extend in the direction orthogonal to the extrusion direction in the extrusion molding process and has a high modulus. Can be the direction of.

In the heat conductive sheet according to the present embodiment, when the 5% modulus ratio is calculated, the value is preferably 2.0 or less. In this case, it is suitable for avoiding the above-mentioned unexpected deformation of the heat conductive sheet. The above 5% modulus ratio is more preferably 1.3 or less, further preferably close to 1.

Next, a method for manufacturing the heat conductive sheet according to the present embodiment will be described with reference to the drawings.
The heat conductive sheet 1 can be manufactured, for example, by performing the following steps (a) to (c).
(A) a step of preparing an acrylic composition containing uncrosslinked acrylic rubber, a crosslinking agent, a crosslinking accelerator, a lubricant, and first and second thermally conductive fillers,
(B) molding the prepared acrylic composition, and
(C) A step of cross-linking the formed acrylic composition and then slicing into a sheet.

First, the step (a) of preparing an acrylic composition is performed. Here, for example, an uncrosslinked acrylic rubber that serves as a matrix component, a crosslinking agent, a crosslinking accelerator, and a lubricant, a first thermally conductive filler and a second thermally conductive filler that are thermally conductive fillers, and further, if necessary. The acrylic composition may be prepared by kneading together various additives to be added with a two-roll mill.
At this time, each component may be supplied in a masterbatch state.

Next, a step (b) of molding the prepared acrylic composition, and a step (c) of crosslinking the molded acrylic composition (uncrosslinked thermally conductive sheet) and then slicing into a sheet shape. And do.
The molding of the acrylic composition may be performed using, for example, an extruder.
FIG. 2 is a diagram schematically showing an example of an extruder used in the production of the heat conductive sheet according to this embodiment. FIG. 2 shows a schematic cross-sectional view of the tip portion of the extruder 100 and the die. It should be noted that FIG. 2 is a schematic diagram, and each component does not accurately reflect the actual dimensions.
The acrylic composition charged into the extruder 100 is stirred and kneaded by the screw 8 and introduced into the first gap 12 of the T die 101 along the flow path 10.

The acrylic composition stirred and kneaded by the extruder 100 is squeezed in the up-down direction (thickness direction) toward the first gap 12, passes through the first gap 12, and becomes a thin belt-shaped precursor sheet. Become. A shearing force acts on the acrylic composition passing through the first gap 12, and at this time, the first thermally conductive filler 4 mixed in the acrylic composition causes the flow direction of the acrylic composition (extrusion direction). ). Therefore, in the precursor sheet that has passed through the first gap 12, the first thermally conductive filler 4 is oriented in the plane direction of the precursor sheet.

The precursor sheet extruded from the ejection port of the first gap 12 passes through the connecting portion 13 and is guided to the second gap 14. The second gap 14 has a larger cross-sectional area of the flow path 10 than the first gap 12 and a longer vertical length. Therefore, the precursor sheet that has passed through the first gap 12 is released in the sheet flow direction that was limited to the extrusion direction, and the flow direction changes to a direction substantially perpendicular to the extrusion direction. This is because the cross-sectional area of the flow channel 10 after passing through the first gap 12 is enlarged, and the length of the flow channel 10 in the vertical direction is increased.
The precursor sheet that has passed through the first gap 12 is extruded toward the second gap 14 through the connecting portion 13 while the flow direction changes to a direction substantially perpendicular to the extrusion direction. As a result, the precursor sheets in the second gap 14 are in a state in which precursor sheets having a small thickness are stacked. At this time, most of the thermally conductive fillers are oriented in the thickness direction of the precursor sheet in the second gap 14 (vertical direction in FIG. 2).
After that, the precursor sheet that has passed through the second gap is subjected to crosslinking treatment by heating or the like. This makes it possible to produce a heat conductive sheet. In addition, after the precursor sheet is crosslinked, so-called secondary crosslinking may be performed if necessary.
Then, the heat conductive sheet is further sliced in a direction perpendicular to the thickness direction to form a thinner heat conductive sheet. The slicing process is an optional process and does not necessarily have to be performed.
Through these steps, the heat conductive sheet 1 having a predetermined thickness and having the heat conductive filler substantially oriented in the thickness direction can be obtained.

In the method of manufacturing the heat conductive sheet, it is preferable that the gap (the vertical dimension in FIG. 2) of the first gap 12 is 0.1 mm or more and 5.0 mm or less. When the gap of the first gap 12 is smaller than 0.1 mm, the extrusion pressure may unnecessarily increase and the raw material composition may be clogged in the first gap 12. On the other hand, if the gap of the first gap 12 is larger than 5.0 mm, the degree of orientation of the first thermally conductive filler with respect to the surface direction of the precursor sheet may decrease.

The gap of the second gap 14 is preferably 2 times or more and 30 times or less than the gap of the first gap 12.
If the gap of the second gap 14 is smaller than twice the gap of the first gap 12, most of the first thermally conductive filler 4 may not be oriented in the thickness direction of the thermally conductive sheet 1. Further, when the gap of the second gap 14 is larger than 30 times the gap of the first gap 12, a situation in which the precursor sheet turbulently flows is likely to occur partially, and as a result, the thickness of the heat conductive sheet 1 is increased. The proportion of the first thermally conductive filler 4 oriented in the depth direction may decrease.
The gap of the second gap 14 is more preferably 5 times or more and 20 times or less than the gap of the first gap 12.

In addition, after the precursor sheet passes through the first gap 12, the center position in the thickness direction of the first gap 12 and the thickness of the second gap 14 so that the precursor sheet can easily flow evenly in the vertical direction of the flow path 10. The center position in the depth direction is preferably substantially the same position in the thickness direction.

The shape of the portion of the first gap 12 that is connected to the inlet is not particularly defined, but the upstream side surface is preferably an inclined surface so that pressure loss is small.
In addition, in order to most efficiently orient the heat conductive filler in the thickness direction of the heat conductive sheet, the side surface of the connecting portion 13 that connects the first gap 12 and the second gap has an inclination angle (extrusion direction and inclined surface). It is desirable to adjust the angle formed by. The inclination angle is preferably 10° to 50°, more preferably 20° to 25°.
It should be noted that the portion of the first gap 12 that is connected to the introduction port does not need to have an upper and lower slope, and only one of them may have a slope. It is not necessary for the side surfaces of the connecting portion 13 to be inclined in both the upper and lower directions, and only one of them may be inclined.

The depths of the first gap 12 and the second gap 14 (that is, the dimensions of the first gap 12 and the second gap 14 in the direction perpendicular to the paper surface in FIG. 2) are substantially the same throughout the T die 101. The depths of the first gap and the second gap are not particularly defined, and various design changes can be made according to the product width of the heat conductive sheet.

(Other embodiments)
The heat conductive sheet according to the embodiment of the present invention can also be manufactured by the following manufacturing method.
That is, after preparing an uncrosslinked acrylic composition as a raw material composition for producing a heat conductive sheet, a sheet in which at least a first heat conductive filler is oriented in the plane direction using this acrylic composition After producing a plurality of sheet-like products by a conventionally known method and stacking a plurality of the sheet-like products to form a block-like product, the block is formed from a direction perpendicular to the direction in which the first thermally conductive filler is oriented. It may be produced by cutting a sheet-like material (a laminate of sheet-like materials).
When the heat conductive sheet is produced by this method, the crosslinking treatment may be performed at an appropriate timing.

Next, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.
The raw materials used in Examples/Comparative Examples are as follows.
-Uncrosslinked acrylic rubber: Nipol AR14 (manufactured by Zeon Corporation)
-Crosslinking agent: Hexamethylenediamine carbamate (Sanfel 6-MC, Sanshin Chemical Industry Co., Ltd.)
・Crosslinking accelerator: Guanidine compound (Suncellar DT, Sanshin Chemical Industry Co., Ltd.)
・Lubricant: Stearic acid

Boron nitride filler: "XGP" manufactured by Denka Co., Ltd. (scale, particle size 35 μm, aspect ratio about 30)
・Magnesite filler A: Magthermo MS-L (manufactured by Kamijima Chemical Co., Ltd., cubic shape, particle diameter 6 μm, aspect ratio 1 to 1.2)
・Magnesite filler B: Magthermo MS-PS (manufactured by Kamijima Chemical Industry Co., Ltd., cubic shape, particle diameter 26 μm, aspect ratio 1 to 1.2)

(Example 1)
With the composition shown in Table 1, a cross-linking agent, a cross-linking accelerator, a lubricant, a BN filler, and a magnesite filler A are kneaded with unrolled acrylic rubber by a two-roll mill to form a ribbon sheet (acrylic composition). Obtained.

Next, the produced ribbon sheet is subjected to vertical alignment die (T die 101) having a 1 mm first gap 12 and a 10 mm second gap 14 in a rubber single screw extruder 100 (see FIG. 2). A sheet having a thickness of 10 mm in which flaky BN filler (first heat conductive filler) was oriented in the thickness direction was prepared, and the sheet was subjected to a crosslinking treatment at 170° C. for 30 minutes. The crosslinked sheet was sliced perpendicularly to the thickness direction to obtain a heat conductive sheet having a thickness of 1000 μm.
The total content of the thermally conductive filler contained in the thermally conductive sheet produced in Example 1 is about 45% by volume.

(Comparative Example 1)
A heat conductive sheet was produced in the same manner as in Example 1 except that the second heat conductive filler (magnesite filler) was not mixed and the raw material components were changed as shown in Table 1. ..
The total content of the thermally conductive filler contained in the thermally conductive sheet produced in Comparative Example 1 is about 40% by volume.

(Comparative example 2)
A heat conductive sheet was produced in the same manner as in Example 1 except that as the second heat conductive filler, magnesite filler B was used instead of magnesite filler A.
The total content of the thermally conductive filler contained in the thermally conductive sheet produced in Comparative Example 2 is about 45% by volume.

[Evaluation test]
(1) Hardness The Asker C hardness of the prepared thermal conductive sheet was measured. The results are shown in Table 2.
(2) Thermal resistance The thermal resistance in the thickness direction of the prepared thermal conductive sheet was measured using TIM TESTER model 1300 at three levels of measurement pressure (0.1 MPa, 0.3 MPa and 0.5 MPa). The measured values are shown in Table 2. In addition, the said measurement was based on the American standard ASTM D5470 by the stationary method.

(3) In-plane anisotropy (5% modulus ratio)
The 5% modulus (strain 5% when the thermal conductive sheets manufactured in Example 1 and Comparative Examples 1 and 2 were pulled in the first direction (X direction) and the second direction (Y direction), respectively. Time stress) was measured. The ratio of the measured value in the first direction and the geodetic value in the second direction (first direction/second direction) was calculated and used as an index of in-plane anisotropy. Here, the first direction and the second direction were set as follows.
First direction: a direction perpendicular to the second direction in the surface direction of the heat conductive sheet (X direction in FIG. 3)
Second direction: extrusion direction during extrusion molding (Y direction in FIG. 3)

Specifically, first, as a measurement sample, a dumbbell-shaped No. 7 measurement sample specified by JIS K 6251 was prepared. As the measurement samples, three samples each for pulling in the X direction (first direction) and three samples for pulling in the Y direction (second direction) were prepared.
Each measurement sample was subjected to a tensile test using a universal material tester Instro 5500, and the 5% modulus in each of the X direction and the Y direction was measured.
At this time, the distance between the chucks of the measurement sample was 20 mm, and the pulling speed was 50 mm/min.
For the measured values, an average value was calculated in each of the X direction and the Y direction, and then the ratio of the two was calculated. The results are shown in Table 2.
In this evaluation, as the calculated ratio is closer to 1, it means that the anisotropy is poor (close to isotropic).

As shown in the results shown in Table 2, it has been clarified that according to the embodiment of the present invention, it is possible to provide a heat conductive sheet having a low thermal resistance value and a tensile property in the plane direction close to isotropic.

1, 51 heat conductive sheet 2, 52 matrix component 4 first heat conductive filler 5 second heat conductive filler 8 screw 10 flow path 12 first gap 13 connection part 14 second gap 54 heat conductive filler 100 extruder 101 T die

Claims (4)

A heat conductive sheet comprising an acrylic rubber and a heat conductive filler containing a first heat conductive filler and a second heat conductive filler having a particle size smaller than that of the first heat conductive filler,
The content of the heat conductive filler is 30 to 60% by volume,
The first thermally conductive filler is oriented substantially in the thickness direction,
The first thermally conductive filler is a filler made of boron nitride having a particle size of 20 μm or more and an aspect ratio of 10 or more,
The second thermally conductive filler is a filler made of a material other than boron nitride,
The particle diameter of the second thermally conductive filler is 3 to 20 μm,
The content of the second thermally conductive filler is 15 to 45% by volume,
A heat conductive sheet characterized by the above. The heat conductive sheet according to claim 1, wherein the second heat conductive filler has an aspect ratio of 1.5 or less. The heat conductive sheet according to claim 1, wherein the content of the second heat conductive filler is 20 to 45% by volume. The heat conductive sheet according to claim 1, wherein the second heat conductive filler is a filler made of magnesium carbonate.