JP2022095514A - Insulating heat conductive sheet and manufacturing method thereof - Google Patents

Abstract

To provide an insulating heat conductive sheet having a stable sheet shape and improved heat conductivity, and a manufacturing method of the insulating heat conductive sheet.SOLUTION: An insulating heat conductive sheet 10 containing insulating heat conductive particles and a binder resin includes 90 to 99 area% of the insulating heat conductive particles and 1 to 10 area% of the binder resin when the total of the insulating heat conductive particles and the binder resin is 100 area% for the entire cross section perpendicular to the plane direction, and the area ratio of the binder resin to the insulating heat conductive particles in a surface portion 12 of the insulating heat conductive sheet is larger than the area ratio of the binder resin to the insulating heat conductive particles in a central portion 14 of the insulating heat conductive sheet for the cross section perpendicular to the plane direction.SELECTED DRAWING: Figure 1

Description

The present invention relates to an insulating heat conductive sheet and a method for manufacturing the same.

The present disclosure is to rapidly diffuse the heat generated in heat-generating components such as semiconductor elements, power supplies, and light sources inside electrical products to mitigate a local temperature rise, or to transport heat to a location away from the heat-generating source. The present invention relates to an insulating heat conductive sheet having excellent heat conductivity and heat transport characteristics (particularly heat conductivity and heat transport characteristics in the in-plane direction).

In recent years, the importance of heat dissipation measures has increased due to the increase in heat generation density due to the thinning, shortening, and increasing output of electronic devices. In order to reduce heat troubles in electronic devices, it is important to promptly diffuse the heat generated in the devices to the coolant, housing, etc. so as not to adversely affect the peripheral members. Therefore, a heat conductive member capable of conducting heat in a specific direction is required. In many cases, the heat conductive member is also required to have electrical insulation in order to prevent leakage to the coolant and the housing.

Patent Document 1 describes a heat conductive sheet including a first surface layer, a second surface layer, and an intermediate layer containing an epoxy resin and an inorganic filler, and describes the first surface layer and the second surface layer. Each describes that the layer has a smaller volume content of the inorganic filler than the intermediate layer.

Patent Document 2 discloses a heat-dissipating sheet in which a graphite layer is formed on an aromatic polyamide film having a specific thermal conductivity via an adhesive layer.

Patent Document 3 describes a heat conductive sheet having a multilayer structure including a layer (A) and a layer (B), in which the layer (A) is an insulating non-spherical particle such as boron nitride particles and an organic polymer compound. It is described that the layer (B) is a layer made of an insulating resin composition such as a polyamideimide resin and an epoxy resin.

Patent Document 4 describes a heat transfer member including a first surface layer and a second surface layer, and an intermediate layer arranged between these surface layers, and describes the first surface layer and the second surface layer. The surface layer and the intermediate layer each have a boron nitride sintered body in which the degree of orientation of hexagonal boron nitride primary particles has a specific value, and a thermosetting resin composition impregnated in the boron nitride sintered body. It is stated that it is included.

Patent Document 5 is arranged on at least one surface of a resin composition layer containing a thermosetting resin and a filler, and has an arithmetic average surface roughness of 1 on the surface not facing the resin composition layer. A multilayer resin sheet having an adhesive layer having a thickness of .5 μm or less is disclosed. The document describes that the adhesive layer may contain an inorganic filler.

Patent Document 6 discloses an insulating sheet containing insulating particles and a binder resin. The document describes that the insulating sheet contains 75-97 area% insulating particles, 3-25 area% binder resin, and 10 area% or less voids in the entire cross section perpendicular to the plane direction. It is described that the insulating particles include deformed flat particles.

International Publication No. 2016/017670 Japanese Unexamined Patent Publication No. 2010-6890 Japanese Unexamined Patent Publication No. 2011-230472 International Publication No. 2018/181606 Japanese Unexamined Patent Publication No. 2019-14261 Japanese Patent No. 6755421

With the conventional insulating heat conductive sheet, it may not be possible to obtain an insulating heat conductive sheet having a sufficiently high thermal conductivity and a stable sheet shape.

An object of the present invention is to provide an insulating heat conductive sheet having a stable sheet shape and improved heat conductivity. It is also an object of the present invention to provide a method for producing such an insulating heat conductive sheet.

The inventors have found that the above problems are solved by the following aspects:
<Aspect 1>
An insulating heat conductive sheet containing insulating heat conductive particles and a binder resin.
When the total of the insulating heat conductive particles and the binder resin is 100 area%, 90 to 99 area% of the insulating heat conductive particles and 1 to 10 area% of the entire cross section perpendicular to the plane direction. Contains the binder resin and
For a cross section perpendicular to the plane direction, the area ratio of the binder resin to the insulating heat conductive particles on the surface portion of the insulating heat conductive sheet is the binder to the insulating heat conductive particles in the central portion of the insulating heat conductive sheet. Larger than the area ratio of the resin,
Insulating heat conductive sheet.
<Aspect 2>
The insulating heat conductive sheet according to aspect 1, wherein the insulating heat conductive particles include flat insulating heat conductive particles.
<Aspect 3>
The insulating heat conductive sheet according to aspect 1 or 2, wherein the binder resin is an aramid resin.
<Aspect 4>
The insulating heat conductive sheet according to any one of aspects 1 to 3, wherein the insulating heat conductive particles include deformed flat insulating heat conductive particles.
<Aspect 5>
The insulating heat conductive sheet according to any one of aspects 1 to 4, wherein the insulating heat conductive particles are boron nitride particles.
<Aspect 6>
The insulating heat conductive sheet according to any one of aspects 1 to 5, which has a thermal conductivity of more than 60 W / (m · K) in the in-plane direction.
<Aspect 7>
The insulating heat conductive sheet according to any one of aspects 1 to 6, which has a thermal conductivity of 3.0 W / (m · K) or more in the thickness direction.
<Aspect 8>
The insulating heat conductive sheet according to any one of aspects 1 to 7, which has a void of more than 10 area% for the entire cross section perpendicular to the plane direction.
<Aspect 9>
Two A layers containing 7.5% by volume or more of the binder resin and less than 92.5% by volume of insulating heat conductive particles, and less than 7.5% by volume arranged between the two A layers. To provide a laminate having a binder resin and a B layer containing 92.5% by volume or more of insulating heat conductive particles, and
Roll pressing the laminate,
The method for producing an insulating heat conductive sheet according to any one of aspects 1 to 8, comprising the method for producing an insulating heat conductive sheet.

According to the present invention, it is possible to provide an insulating heat conductive sheet having a stable sheet shape and improved heat conductivity. Further, according to the present invention, it is possible to provide a method for producing such an insulating heat conductive sheet.

FIG. 1 shows a schematic view in a cross section perpendicular to the plane direction of one embodiment of the insulating heat conductive sheet according to the present disclosure. FIG. 2 shows a schematic view in a cross section perpendicular to the plane direction of one embodiment of the laminate used in the method for manufacturing an insulating heat conductive sheet according to the present disclosure. FIG. 3 shows an SEM photograph of a cross section perpendicular to the plane direction of the insulating heat conductive sheet according to the first embodiment. FIG. 4 shows an SEM photograph of a cross section perpendicular to the plane direction of the insulating heat conductive sheet according to Comparative Example 4. FIG. 5 shows an SEM photograph of a cross section perpendicular to the plane direction of the insulating heat conductive sheet according to Comparative Example 5. FIG. 6 shows an SEM photograph of a cross section perpendicular to the plane direction of the insulating heat conductive sheet according to Comparative Example 6.

≪Insulated heat conductive sheet≫
The insulating heat conductive sheet according to the present disclosure is
An insulating heat conductive sheet containing insulating heat conductive particles and a binder resin.
When the total of the insulating heat conductive particles and the binder resin is 100 area%, 90 to 99 area% of the insulating heat conductive particles and 1 to 10 area% of the binder resin are used for the entire cross section perpendicular to the plane direction. Contains and
With respect to the cross section perpendicular to the plane direction, the area ratio of the binder resin to the insulating heat conductive particles in the surface portion of the insulating heat conductive sheet is the area ratio of the binder resin to the insulating heat conductive particles in the central portion of the insulating heat conductive sheet. Larger than the area ratio.

FIG. 1 shows a schematic cross-sectional view perpendicular to the plane direction of one embodiment of the insulating heat conductive sheet according to the present disclosure (insulating heat conductive sheet 10). “D” and “S” in FIG. 1 indicate the thickness direction and the surface direction of the insulating heat conductive sheet 10, respectively. The schematic views of FIGS. 1 and 2 are not in scale. The insulating heat conductive sheet 10 of FIG. 1 has two surface portions 12 and a central portion 14. Each of the two surface portions 12 is a portion adjacent to the main surface of the insulating heat conductive sheet. The central portion 14 is a portion located between the two surface portions 12 in the thickness direction D of the insulating heat conductive sheet. In the insulating heat conductive sheet 10, the binder resin is unevenly distributed on the surface portion 12. That is, the area ratio of the binder resin to the insulating heat conductive particles in the surface portion 12 of the insulating heat conductive sheet 10 is larger than the area ratio of the binder resin to the insulating heat conductive particles in the central portion 14 of the insulating heat conductive sheet. It has become.

Generally, in order to improve the thermal conductivity of the insulating heat conductive sheet, it is conceivable to increase the content (or filling rate) of the insulating heat conductive particles. However, in the conventional technique, when the amount of the insulating heat conductive particles with respect to the binder resin is large, it may be difficult to mold the particles into a sheet shape.

On the other hand, the inventors of the present invention maintain the sheet shape and relatively by adjusting the distribution of the binder resin in the insulating heat conductive sheet even when the proportion of the binder resin is relatively low. It has been found that an insulating heat conductive sheet showing high thermal conductivity can be obtained.

Specifically, 90 to 99 area% of the insulating heat conductive particles and 1 to 10 area% of the entire cross section perpendicular to the plane direction, where the total of the insulating heat conductive particles and the binder resin is 100 area%. In the insulating heat conductive sheet containing the binder resin of
For the cross section perpendicular to the plane direction, the area ratio of the binder resin to the insulating heat conductive particles on the surface portion of the insulating heat conductive sheet, and the area ratio of the binder resin to the insulating heat conductive particles in the central portion of the insulating heat conductive sheet. It has been found that an insulating heat conductive sheet that retains the sheet shape and exhibits a relatively high heat conductivity can be obtained by making the size larger than the above.

Although not intended to be limited by theory, in conventional insulating heat conductive sheets, the binder resin is relatively evenly distributed in the sheet, so that the binder resin is present between the insulating heat conductive particles throughout the sheet. As a result, it is considered that the direct contact between the insulating heat conductive particles was restricted. Further, in the conventional insulating heat conductive sheet, even when the binder resin is unevenly distributed on the surface side of the sheet, a relatively large amount of the binder resin is also present in the central portion, and as a result, the insulating heat conductive sheet is present. It is probable that the direct contact between the particles was restricted.

On the other hand, in the insulating heat conductive sheet according to the present invention, the binder resin is extremely reduced in the central portion of the sheet due to the above configuration, whereby the insulating heat conductive particles are formed in the central portion. It is considered that the direct contact with each other is increasing, and as a result, an insulating heat conductive sheet having a relatively high thermal conductivity can be obtained.

Further, in the insulating heat conductive sheet according to the present disclosure, even when the ratio of the insulating heat conductive particles in the entire sheet is relatively large due to the uneven distribution of the binder resin on the surface portion of the sheet, the sheet is used. It is considered that good formability and good shape retention of the sheet can be ensured.

The insulating heat conductive sheet according to the present disclosure will be described in detail below.

<Overall configuration of insulating heat conductive sheet>
The insulating heat conductive sheet according to the present disclosure contains 1 to 10 area% of the binder resin when the total of the insulating heat conductive particles and the binder resin is 100 area% for the entire cross section perpendicular to the plane direction. .. When the content of the binder resin is 10 area% or less, a sufficiently high thermal conductivity can be ensured, and when it is 1 area% or more, the sheet has good formability and the sheet has good formability. Shape retention can be ensured.

The binder resin contained in the insulating heat conductive sheet according to the present disclosure is 1.5 area% when the total of the insulating heat conductive particles and the binder resin is 100 area% with respect to the entire cross section perpendicular to the plane direction. It may be 2.0 area% or more, 2.5 area% or more, 3.0 area% or more, 4.0 area% or more, or 5.0 area% or more, and / or 9.0 area%. Hereinafter, it may be 8.0 area% or less, 7.0 area% or less, or 6.0 area% or less. When the content of the binder resin is 1.5 area% or more, the ease of molding is ensured and the shape stability of the sheet is ensured, which is particularly preferable.

In the present disclosure, the "area%" of the binder resin when the total of the insulating heat conductive particles and the binder resin is 100 area% with respect to the entire cross section perpendicular to the surface direction is perpendicular to the surface direction of the insulating heat conductive sheet. It can be determined by taking an image of the cross section by SEM and measuring the area of the insulating heat conductive particles and the binder resin present in a certain area in the acquired image. The area to be measured is selected so as to reflect the average content over the entire cross section, and in particular, is selected so as not to be biased to either the surface portion or the central portion of the insulating heat conductive sheet. When the insulating heat conductive sheet has additives other than the insulating heat conductive particles and the binder resin, the fixed area should be set so that the additive is not contained in the fixed area. Therefore, the "area%" of the binder resin can be calculated when the total of the insulating heat conductive particles and the binder resin is 100 area%.

The insulating heat conductive sheet according to the present disclosure is 90 to 99 area% of the insulating heat conductive particles when the total of the insulating heat conductive particles and the binder resin is 100 area% with respect to the entire cross section perpendicular to the plane direction. Contains. When the content of the insulating heat conductive particles is 90 area% or more, good heat conductivity is obtained, and when it is 99 area% or less, the increase in the viscosity of the resin composition is suppressed and molding is easy. The property is ensured and the shape stability of the sheet is ensured.

Preferably, the insulating heat conductive particles contained in the insulating heat conductive sheet according to the present disclosure have a total area of 100 area% of the insulating heat conductive particles and the binder resin with respect to the entire cross section perpendicular to the plane direction. , 92 area% or more, 93 area% or more, 94 area% or more, or 95 area% or more, and / or less than 99 area%, 98.5 area% or less, 98 area% or less, or 97 area. It may be less than or equal to%.

In the present disclosure, the "area%" of the insulating heat conductive particles when the total of the insulating heat conductive particles and the binder resin is 100 area% with respect to the entire cross section perpendicular to the plane direction is the same as that described above for the binder resin. It can be determined in the same way.

As will be described later, the insulating heat conductive sheet according to the present disclosure may contain voids and additives (fibrous reinforcing material, etc.). The insulating heat conductive sheet according to the present disclosure preferably has an insulating heat of 70 area% or more, 80 area% or more, 90 area% or more, or 95 area% or more in total for the entire cross section perpendicular to the plane direction. It has conductive particles and a binder resin.

<Structure in the thickness direction of the insulating heat conductive sheet>
As described above, in the insulating heat conductive sheet according to the present disclosure, the binder resin is unevenly distributed on the surface portion of the sheet.

The "surface portion" of the insulating heat conductive sheet is a portion close to any one of the main surfaces of the insulating heat conductive sheet. Therefore, there is usually one "surface portion" of the insulating heat conductive sheet for each of the two main surfaces of the insulating heat conductive sheet.

The "surface portion" of the insulating heat conductive sheet is, in particular, starting from one of the main surfaces of the insulating heat conductive sheet and along the thickness direction of the insulating heat conductive sheet of the insulating heat conductive sheet. It can be a portion up to 10% of the thickness.

On the other hand, the "central portion" of the insulating heat conductive sheet is usually a portion located between the two surface portions in the thickness direction of the insulating heat conductive sheet.

The "central portion" of the insulating heat conductive sheet is, in particular, starting from one of the main surfaces of the insulating heat conductive sheet and along the thickness direction of the insulating heat conductive sheet. It can be a portion of more than 10% to less than 90% of the thickness of.

(Uneven distribution of binder resin)
In the insulating heat conductive sheet according to the present disclosure, the area ratio of the binder resin to the insulating heat conductive particles on the surface portion of the insulating heat conductive sheet is the central portion of the insulating heat conductive sheet in the cross section perpendicular to the plane direction. Is larger than the area ratio of the binder resin to the insulating heat conductive particles in.

In particular, for a cross section perpendicular to the plane direction, the area ratio of the binder resin to the insulating heat conductive particles on the surface portion of the insulating heat conductive sheet is the binder resin to the insulating heat conductive particles in the central portion of the insulating heat conductive sheet. It may be 1.1 times or more, 1.5 times or more, 2 times or more, 3 times or more, 4 times or more, 5 times or more, or 10 times or more, and / or 100, as compared with the area ratio of 100. It may be times or less, 75 times or less, 50 times or less, or 25 times or less.

In the cross section perpendicular to the plane direction of the insulating heat conductive sheet, the surface portion of the insulating heat conductive sheet exceeds 1 area%, 2 when the total of the binder resin and the insulating heat conductive particles is 100 area%. .0 area% or more, 2.5 area% or more, or 5.0 area% or more, and / or less than 100 area%, 90 area% or less, 75 area% or less, 50 area% or less, 25 area%, or 10 It can contain a binder resin having an area% or less.

It is preferable that the insulating heat conductive sheet contains a binder resin of more than 5 area% and 50 area% or less on the surface portion thereof, where the total of the binder resin and the insulating heat conductive particles is 100 area%. .. When it exceeds 5 area%, the shape retention of the insulating heat conductive sheet is further improved. Further, when the area is 50 area% or less, the proportion of the insulating heat conductive particles on the surface portion can be relatively large, so that the heat conductivity of the insulating heat conductive sheet can be further improved. Further, when it is 50 area% or less, it is possible to reduce the difference in the content of the insulating heat conductive particles between the surface portion and the central portion, thereby reducing the difference between these portions. Since the difference in thermal characteristics (thermal expansion rate, thermal shrinkage rate, etc.) is reduced, the thermal dimensional stability of the insulating heat conductive sheet can be further improved.

In the cross section perpendicular to the plane direction of the insulating heat conductive sheet, the surface portion of the insulating heat conductive sheet exceeds 0 area% and 1 when the total of the binder resin and the insulating heat conductive particles is 100 area%. Area% or more, 10 area% or more, 25 area% or more, 50 area% or more, 75 area% or more, or 80 area% or more, and / or 98 area% or less, 95 area% or less, or 94 area% or less. It can contain insulating heat conductive particles.

It is preferable that the insulating heat conductive sheet contains the insulating heat conductive particles of more than 50 area% and 95 area% or less with respect to the total of the binder resin and the insulating heat conductive particles on the surface portion thereof. When the area is 95% or less, the content of the binder resin in the surface portion can be increased, so that the shape retention of the insulating heat conductive sheet can be further improved. Further, when the area is more than 50 area%, the content of the insulating heat conductive particles in the surface portion is increased, so that the thermal conductivity of the insulating heat conductive sheet is further improved. Further, when the area is more than 50 area%, the thermal dimensional stability of the insulating heat conductive sheet is further improved.

In the cross section perpendicular to the plane direction of the insulating heat conductive sheet, the insulating heat conductive sheet exceeds 0 area% in the central portion thereof when the total of the binder resin and the insulating heat conductive particles is 100 area%. , 0.01 area% or more, 0.1 area% or more, 0.2 area% or more, or 0.3 area% or more, and / or less than 10 area%, 7.5 area% or less, 5 area% or less, It can contain a binder resin of 2.5 area% or less, or 1 area% or less.

It is preferable that the insulating heat conductive sheet contains a binder resin of 0.1 area% or more and 5 area% or less with respect to the total of the binder resin and the insulating heat conductive particles in the central portion thereof. When the ratio of the binder resin in the central portion is 0.1 area% or more, the flexibility of the insulating heat conductive sheet can be further improved, and the porosity in the insulating heat conductive sheet is reduced. be able to. Further, when the ratio of the binder resin in the central portion of the sheet is 5 area% or less, the filling rate of the insulating heat conductive particles is increased, and in particular, the direct contact between the insulating heat conductive particles is further increased. Since it can be increased, the thermal conductivity of the insulating heat conductive sheet can be further improved.

Further, the central portion of the insulating heat conductive sheet has a cross section perpendicular to the plane direction of the insulating heat conductive sheet, and has an area of 90 area% or more and 92.5 area with respect to the total of the binder resin and the insulating heat conductive particles. % Or more, 95 area% or more, 98 area% or more, or 99 area% or more, and / or less than 100 area%, 99.9 area% or less, 99.8 area% or less, or 99.7 area% or less. It can contain insulating heat conductive particles.

It is preferable that the insulating heat conductive sheet contains 95 area% or more and less than 100 area% of the insulating heat conductive particles in the central portion thereof with respect to the total of the binder resin and the insulating heat conductive particles. When it is less than 100 area%, the binder resin can be contained in the central portion, so that the flexibility of the insulating heat conductive sheet can be further improved, and the porosity in the insulating heat conductive sheet can be increased. Can be reduced. Further, when the area is 95 area% or more, the filling rate of the insulating heat conductive particles increases, so that the heat conductivity of the insulating heat conductive sheet is further improved.

The area ratio of the binder resin to the insulating heat conductive particles at the surface portion and the center portion of the insulating heat conductive sheet is the insulating heat conduction in a fixed area in the cross section perpendicular to the plane direction of the insulating heat conductive sheet. It can be determined by measuring the areas of the insulating heat conductive particles and the binder resin present on the surface portion and the central portion of the sheet, respectively. A scanning electron microscope (SEM) can be used for the measurement.

(Composition of binder resin / insulating heat conductive particles)
The insulating heat conductive sheet according to the present disclosure may be uniform throughout the sheet with respect to the composition of the binder resin and the insulating heat conductive particles. That is, the binder resin present in the surface portion of the insulating heat conductive sheet and the binder resin existing in the central portion of the insulating heat conductive sheet may be the same in terms of type and composition, and the insulating heat conductive sheet. The insulating heat conductive particles present in the surface portion of the above and the insulating heat conductive particles present in the central portion of the insulating heat conductive sheet may be the same in terms of type and composition.

On the other hand, the insulating heat conductive sheet according to the present disclosure may not be uniform (may be non-uniform) over the entire sheet with respect to the composition of the binder resin and / or the composition of the insulating heat conductive particles. That is, for example, the binder resin present in the surface portion of the insulating heat conductive sheet and the binder resin existing in the central portion of the insulating heat conductive sheet may be different in terms of type or composition, and / or. The insulating heat conductive particles present on the surface portion of the insulating heat conductive sheet and the insulating heat conductive particles present on the central portion of the insulating heat conductive sheet may be different in type or composition.

<Gap>
In one embodiment of the insulating heat conductive sheet according to the present disclosure, the insulating heat conductive sheet has a void of more than 10 area% for the entire cross section perpendicular to the plane direction.

Conventionally, it has been considered that the voids in the insulating heat conductive sheet reduce the thermal conductivity of the insulating heat conductive sheet. In particular, when the content of the binder resin is suppressed and the insulating heat conductive particles are highly filled, the steric obstacle between the particles due to the shape of the insulating heat conductive particles and the amount of the binder resin that can fill the voids. It was thought that the void ratio would increase due to the decrease in heat, and as a result, the thermal conductivity of the insulating heat conductive sheet would decrease.

On the other hand, in the insulating heat conductive sheet according to the present disclosure, relatively high thermal conductivity can be achieved even when the entire cross section perpendicular to the plane direction has a void of more than 10 area%. .. Although not intended to be limited by theory, in the insulating heat conductive sheet according to the present invention, the filling rate of the insulating heat conductive particles in the central portion of the sheet is improved due to the uneven distribution of the binder resin. Therefore, it is considered that the direct contact between the insulating heat conductive particles increases in the central portion of the sheet, and as a result, a relatively high thermal conductivity can be achieved.

As described above, the insulating heat conductive sheet according to the present disclosure exhibits a relatively high thermal conductivity even when the porosity is relatively high. On the other hand, it is preferable that the voids in the insulating heat conductive sheet are reduced as much as possible. Preferably, the insulating heat conductive sheet has voids of 30 area% or less, more preferably 25 area% or less, still more preferably 20 area% or less, with respect to the entire cross section perpendicular to the plane direction.

The "area%" of the voids in the entire cross section perpendicular to the plane direction is the area of the voids existing in a certain area in the acquired image obtained by photographing the cross section perpendicular to the plane direction of the insulating heat conductive sheet by SEM. It can be calculated by measuring.

<Insulating heat conductive particles>

The insulating heat conductive particles are arbitrary particles that are insulating and have a higher heat conduction than the binder resin, particularly inorganic particles. The insulating heat conductive particles are not particularly limited, and are, for example, particles such as boron nitride, aluminum nitride, aluminum oxide, magnesium oxide, silicon nitride, and silicon carbide, metal silicon particles having an insulated surface, and insulating properties such as resin. Examples thereof include carbon fibers and graphite surface-coated with a material, and polymer-based fillers. From the viewpoint of thermal conductivity and insulating properties in the plane direction, the insulating thermal conductive particles are preferably boron nitride particles, particularly hexagonal boron nitride particles.

The average particle size of the insulating heat conductive particles is preferably 1 to 200 μm, more preferably 5 to 200 μm, still more preferably 5 to 100 μm, and particularly preferably 10 to 100 μm.

The average particle size is the median diameter measured by the laser diffraction method using a laser diffraction / scattering type particle size distribution measuring device (when a powder is divided into two from a certain particle size, the particles are larger than the particle size. The particle size is such that small particles are equal in quantity, also commonly referred to as D50).

(Flat)
The insulating heat conductive sheet according to the present disclosure preferably contains flat insulating heat conductive particles. For the present disclosure, "flat" means that the particles are plate-like, scaly, or flaky in shape.

The aspect ratio of the flat insulating heat conductive particles is preferably 10 to 1000. When the aspect ratio is 10 or more, it is preferable because important orientation for enhancing the thermal diffusivity is secured and high thermal diffusivity can be obtained. Further, the insulating heat conductive particles having an aspect ratio of 1000 or less are preferable from the viewpoint of ease of processing because the increase in the viscosity of the composition due to the increase in the specific surface area is suppressed.

The aspect ratio is a value obtained by dividing the major axis of the particles by the thickness of the particles, that is, the major axis / thickness. When the particles are spherical, the aspect ratio is 1, and the aspect ratio increases as the degree of flatness increases.

The aspect ratio can be obtained by measuring the major axis and thickness of the particles at a magnification of 1500 times using a scanning electron microscope and calculating the major axis / thickness.

When the insulating heat conductive sheet contains flat insulating heat conductive particles, the flat insulating heat conductive particles preferably occupy 50% by volume or more with respect to the entire insulating heat conductive particles. When it is 50% by volume or more, good thermal conductivity in the in-plane direction can be ensured. The ratio of the flat insulating heat conductive particles to the entire insulating heat conductive particles is more preferably 60% by volume or more, further preferably 70% by volume or more, still more preferably 80% by volume or more, and particularly preferably 90% by volume. As described above, most preferably, the insulating heat conductive particles are composed of flat insulating heat conductive particles.

(Boron nitride particles)
Examples of the flat insulating heat conductive particles include hexagonal boron nitride particles.

The average particle size of the boron nitride particles is, for example, 1 μm or more, preferably 1 to 200 μm, more preferably 5 to 200 μm, still more preferably 5 to 100 μm, and particularly preferably 10 to 100 μm. When it is 1 μm or more, the specific surface area of the boron nitride particles is small and compatibility with the resin is ensured, which is preferable. When it is 200 μm or less, the thickness uniformity can be ensured during sheet molding. Therefore, it is preferable. As the boron nitride particles, boron nitride particles having a single average particle size may be used, or a plurality of types of boron nitride particles having different average particle sizes may be mixed and used. The aspect ratio of the boron nitride particles is preferably 10 to 1000.

When boron nitride particles are used as the insulating heat conductive particles, insulating heat conductive particles other than the boron nitride particles may be used in combination. Even in that case, the boron nitride particles preferably occupy 50% by volume or more of the total insulating heat conductive particles. When it is 50% by volume or more, good thermal conductivity in the in-plane direction is ensured, which is preferable. The boron nitride particles with respect to the entire insulating heat conductive particles are more preferably 60% by volume or more, further preferably 70% by volume or more, still more preferably 80% by volume or more, and particularly preferably 90% by volume or more, or 95% by volume or more. be.

When boron nitride particles and ceramic particles having isotropic thermal conductivity are used in combination as the insulating thermal conductive particles, the thermal conductivity in the thickness direction and the thermal conductivity in the in-plane direction of the insulating thermal conductive sheet This is a preferred embodiment because the balance can be adjusted as needed. Further, since the boron nitride particles are an expensive material, it is convenient to use them together with an inexpensive material such as metal silicon particles whose surface is thermally oxidized and insulated. In this case, an insulating heat conductive sheet is used. This is a preferable embodiment because the balance between the raw material cost and the thermal conductivity of the above can be adjusted as needed.

(Transformation)
In one advantageous embodiment of the insulating heat conductive sheet according to the present disclosure, the insulating heat conductive particles include deformed flat insulating heat conductive particles.

In an insulating heat conductive sheet containing deformed flat insulating heat conductive particles, the thermal conductivity in the plane direction is further improved. Although not intended to be limited by theory, it is believed that the deformation of the flat insulating heat conductive particles fills the gaps between the particles and reduces the voids inside the sheet. In addition, when the flat insulating heat conductive particles are deformed in the process of manufacturing the insulating heat conductive sheet, the discharge of bubbles trapped between the particles to the outside of the sheet is promoted, and the reduction of voids is further promoted. It is also possible that it will be done.

The method for obtaining an insulating heat conductive sheet containing deformed flat insulating heat conductive particles is not particularly limited, and for example, an insulating heat conductive sheet precursor containing flat insulating heat conductive particles is used. Examples thereof include a method of performing a roll press treatment on a body (for example, a laminated body of sheets obtained by shaping and drying a slurry). In particular, according to the method of performing a roll press treatment on an insulating heat conductive sheet precursor that is highly filled with flat insulating heat conductive particles, high shear stress is likely to act between the insulating heat conductive particles. , It is considered that the deformation of particles becomes more remarkable.

<Binder resin>
The binder resin according to the present disclosure is not particularly limited. Examples of the binder resin include thermoplastic resins described later such as aramid resins (aromatic polyamides), and thermosetting resins such as silicone resins, polyimide resins, phenol resins, and epoxy resins, which are used alone. , Or a mixture of a plurality of them can be used. The binder resin is particularly preferably an aromatic polyamide. Since the aromatic polyamide has excellent strength as compared with the aliphatic polyamide, when the aromatic polyamide is used as the binder resin, the retention of the insulating heat conductive particles and the stability of the sheet shape are particularly excellent. An insulating heat conductive sheet can be provided.

(Thermal characteristics)
From the viewpoint of the thermal properties of the insulating heat conductive sheet, it is preferable that the binder resin has excellent heat resistance and / or flame retardancy. In particular, it is preferable that the melting point or the thermal decomposition temperature of the binder resin is 150 ° C. or higher.

The melting point of the binder resin is measured by a differential scanning calorimeter. The melting point of the binder resin is more preferably 200 ° C. or higher, still more preferably 250 ° C. or higher, and particularly preferably 300 ° C. or higher. The lower limit of the melting point of the binder resin is not particularly limited, but is, for example, 600 ° C. or lower, 500 ° C. or lower, or 400 ° C. or lower.

The thermal decomposition temperature of the binder is measured by a differential scanning calorimeter. The thermal decomposition temperature of the binder resin is more preferably 200 ° C. or higher, further preferably 300 ° C. or higher, particularly preferably 400 ° C. or higher, and most preferably 500 ° C. or higher. The lower limit of the thermal decomposition temperature of the binder resin is not particularly limited, but is, for example, 1000 ° C. or lower, 900 ° C. or lower, or 800 ° C. or lower.

When used for heat dissipation inside electronic devices for automobiles, the heat resistant temperature of the resin material is also required to be high. In the case of a power semiconductor using silicon carbide, heat resistance of around 300 ° C. is required. Therefore, the resin having a heat resistance of 300 ° C. or higher can be suitably used for in-vehicle applications, especially for heat dissipation around power semiconductors. Examples of such a resin include an aramid resin.

(Thermoplastic resin)
From the viewpoint of flexibility and handleability, it is particularly preferable that the binder resin contains a thermoplastic resin. Since the insulating heat conductive sheet containing the thermoplastic resin does not require heat curing at the time of manufacture, it has excellent flexibility and can be relatively easily applied to the inside of an electronic device.

Further, when the binder resin contains a thermoplastic resin, it is considered that the voids in the insulating heat conductive sheet can be further reduced, which is particularly preferable. Although not intended to be limited by theory, when a thermoplastic resin is used as the binder resin, the thermoplastic resin is softened by heat treatment, for example, during the roll press treatment during the production of the insulating heat conductive sheet. It is considered that the discharge of the bubbles trapped between the insulating heat conductive particles is further promoted, and as a result, the effect of reducing the voids can be further enhanced.

Examples of the thermoplastic resin that can be used as the binder resin according to the present disclosure include aramid resin, polyvinylidene fluoride (PVDF), thermoplastic polyimide resin, polytetrafluoroethylene (PTFE) resin, liquid crystal polymer (LCP) resin, and poly. Arilate (PAR) resin, polyetherimide (PEI) resin, polyethersulfone (PES) resin, polyamideimide (PAI) resin, polyphenylene sulfide (PPS) resin, polyether ether ketone (PEEK) resin, and polybenzoxazole ( PBO) and the like can be mentioned.

(Aramid resin)
In particular, it is preferable that the binder resin contains an aramid resin (aromatic polyamide) or is made of an aramid resin. When the binder resin contains an aramid resin, it is preferably contained in an amount of 90% by volume or more with respect to the binder resin. When an aramid resin is used as the binder resin, an insulating heat conductive sheet having further excellent mechanical strength while being filled with a high proportion of insulating heat conductive particles is obtained. In the conventional insulating heat conductive sheet, the thickness of the sheet itself is large, and as a result, the thermal resistance value may become high. On the other hand, the insulating heat conductive sheet using the aramid resin is excellent in mechanical strength while being filled with insulating heat conductive particles, particularly boron nitride particles in a high ratio, and as a result, the thickness of the sheet is excellent. It is thin and has excellent low thermal resistance of the entire sheet. Further, from the viewpoint of thermal characteristics, it is preferable that the binder resin contains an aramid resin or is made of an aramid resin. The aramid resin has a relatively high thermal decomposition temperature, and the insulating heat conductive sheet using the aramid resin as the binder resin exhibits excellent flame retardancy.

The aramid resin is a linear polymer compound in which 60% or more of the amide bonds are directly bonded to the aromatic ring. As the aramid resin, for example, polymetaphenylene isophthalamide and its copolymer, polyparaphenylene terephthalamide and its polymer can be used, for example, copolyparaphenylene 3,4'-diphenyl ether terephthalamide (also known as copoly). Paraphenylene (3,4'-oxydiphenylene terephthalamide) can be mentioned. The aramid resin may be used alone or in combination of two or more.

Regarding the binder resin according to the present disclosure, the binder resins contained in the "surface portion" and the "central portion" of the insulating heat conductive sheet may be the same or different. The binder resin contained in the "surface part" and "center part" of the insulating heat conductive sheet is different from the viewpoint of preventing the sheet from being destroyed due to the difference in expansion / contraction rate during heating / cooling and water absorption / drying. , It is preferable that they are the same. Further, in the insulating heat conductive sheet 10 of FIG. 1, it is preferable that the two "surface portions" 12 are the same binder resin.

<Additive>
The insulating heat conductive sheet of the present invention may contain a flame retardant, a discoloration inhibitor, a surfactant, a coupling agent, a colorant, a viscosity modifier, and / or a reinforcing material. Further, in order to increase the strength of the sheet, a fibrous reinforcing material may be contained. It is preferable to use aramid resin staple fibers as the fibrous reinforcing material because the heat resistance of the insulating heat conductive sheet does not decrease due to the addition of the reinforcing material. The fibrous reinforcing material is preferably added in the range of 0.5 to 25 parts by volume with respect to 100 parts by volume of the insulating heat conductive sheet, and more preferably added in the range of 1 to 20 parts by volume. When a reinforcing material or the like is added, the ratio of the binder resin to 100 parts by volume of the insulating heat conductive sheet is preferably not less than 3 parts by volume.

<Insulating heat conductive sheet>
The thickness of the insulating heat conductive sheet is not particularly limited, but may be, for example, 300 μm or less, 200 μm or less, 150 μm or less, 100 μm or less, or 90 μm or less. The lower limit of the thickness of the insulating heat conductive sheet is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more. When the thickness of the insulating heat conductive sheet is 100 μm or less, the thermal resistance value of the insulating heat conductive sheet itself becomes low, which is preferable. Further, since the insulating heat conductive sheet itself is thin, heat dissipation performance can be exhibited in the limited space inside the electronic device.

(use)
The insulating heat conductive sheet according to the present disclosure shall be used, for example, to rapidly diffuse the heat generated in a semiconductor element inside an electric product or a heat generating component such as a power source or a light source to alleviate a local temperature rise. Or can be used to transport heat away from the heat source.

Specifically, as an example of the method of using the insulating heat conductive sheet according to the present disclosure, the heat of the heat generating source is diffused by attaching the insulating heat conductive sheet to the heat generating source (CPU, etc.) side, thereby spreading the heat of the heat generating source. (Chip) A usage method for reducing the temperature, or a usage method for reducing a local increase in the housing temperature by attaching an insulating heat conductive sheet to the housing side can be mentioned.

When the insulating heat conductive sheet is applied to an electronic device, the application method is not particularly limited. For example, the insulating heat conductive sheet may be placed in direct contact with a heat source, such as a semiconductor inside an electronic device, or via another heat conductor, thus reducing the surface temperature of the heat source. It can be reduced efficiently. In addition, by arranging an insulating heat conductive sheet between the heat generation source and the electronic component with low heat resistance, the heat transferred to the electronic component with low heat resistance is diffused, thereby protecting the electronic component from heat. Can be done. Further, by arranging the insulating heat conductive sheet between the heat generation source and the liquid crystal display, it is possible to reduce defects of the liquid crystal display due to local heating, for example, color unevenness. In addition, by placing an insulating heat conductive sheet between the heat source and the outer surface of the electronic device, it is possible to reduce the local temperature rise of the outer surface of the electronic device, thereby providing safety to the user. The sex can be further improved, for example, low temperature burns can be avoided.

(Adhesive layer)
An adhesive layer and / or an adhesive layer may be arranged on one surface or both surfaces of the insulating heat conductive sheet. In this case, the adhesive layer and the adhesive layer may be known. By arranging the adhesive layer and / or the adhesive layer on the surface of the insulating heat conductive sheet, it becomes easier to install the insulating heat conductive sheet inside an electronic device or the like.

(Thermal conductivity in the in-plane direction)
The thermal conductivity of the insulating heat conductive sheet is more than 60 W / (m · K), more than 65 W / (m · K), 70 W / (m · K) or more, or 70 W / (m · K) in the in-plane direction. ) It is preferable that it is super. When the thermal conductivity is more than 60 W / (m · K) in the in-plane direction, the heat generated by the electronic device can be sufficiently diffused and heat spots are less likely to occur, which is preferable. The higher the thermal conductivity in the in-plane direction, the more preferable, but the thermal conductivity that can usually be achieved is at most 100 W / (m · K) in the in-plane direction.

The in-plane thermal conductivity of the insulating heat conductive sheet can be calculated by multiplying the thermal diffusivity, the specific gravity, and the specific heat. That is,
(Thermal conductivity) = (Thermal diffusivity) x (Specific heat) x (Specific gravity)
Can be calculated by.

The above heat diffusivity can be measured by the optical AC method using an optical AC method heat diffusivity measuring device. The specific heat can be determined by a differential scanning calorimeter. Further, the specific gravity can be obtained from the outer dimensions and weight of the insulating heat conductive sheet.

(Thermal conductivity in the thickness direction)
The thermal conductivity of the insulating heat conductive sheet is 3.0 W / (m · K), 3.5 W / (m · K) or more, 4.0 W / (m · K), 4.5 W / in the thickness direction. It is preferably (m · K) or 5.0 W / (m · K) or higher. The upper limit of the thermal conductivity in the thickness direction is not particularly limited, but may be 10.0 W / (m · K) or less, or 8.0 W / (m · K) or less.

The thermal conductivity in the thickness direction of the insulating heat conductive sheet can be calculated by multiplying all of the thermal diffusivity, the specific gravity and the specific heat. That is,
(Thermal conductivity) = (Thermal diffusivity) x (Specific heat) x (Specific gravity)
Can be calculated by.

The thermal diffusivity in the thickness direction can be obtained by a temperature wave analysis method (phase delay measurement method of temperature waves). The specific heat can be determined by a differential scanning calorimeter. Further, the specific gravity can be obtained from the outer dimensions and weight of the insulating heat conductive sheet.

The method for producing the insulating heat conductive sheet according to the present disclosure is not particularly limited. The insulating heat conductive sheet according to the present disclosure can be manufactured, for example, by the manufacturing method according to the present disclosure described below.

≪Manufacturing method≫
The present invention includes a method for producing an insulating heat conductive sheet, which comprises the following steps:
Two A layers containing 7.5% by volume or more of the binder resin and less than 92.5% by volume of insulating heat conductive particles, and less than 7.5% by volume arranged between the two A layers. To provide a laminate having a binder resin and a B layer containing 92.5% by volume or more of insulating heat conductive particles (providing step), and
Roll pressing the above laminate (roll pressing process)
including.

For the binder resin and the insulating heat conductive particles used in the production method according to the present disclosure, the above description of the insulating heat conductive sheet according to the present disclosure can be referred to.

<Providing process>
In the providing step, a laminate having two A layers and a B layer is provided. FIG. 2 shows a schematic cross-sectional view perpendicular to the plane direction of one embodiment (laminate 20) of the laminate used in the method for manufacturing an insulating heat conductive sheet according to the present disclosure. The laminated body 20 has a layer structure in which the B layer 24 is arranged between the two A layers 22.

(Structure of layer A)
Each of the two A layers independently contains 1% by volume or more, 5% by volume or more, 10% by volume or more, 25% by volume or more, 50% by volume or more, or 75% by volume or more of insulating heat conductive particles. And / or can contain insulating heat conductive particles of less than 92.5% by volume, 90% by volume or less, or less than 90% by volume.

It is preferable that one of the two A layers, particularly both of the two A layers, contains 50% by volume or more and 90% by volume or less of the insulating heat conductive particles. When it is 90% by volume or less, the content of the binder resin in the surface portion of the manufactured insulating heat conductive sheet can be increased, so that the shape retention and mechanical stability of the insulating heat conductive sheet are further improved. Can be improved. Further, when it is 50% by volume or more, the thermal conductivity of the manufactured insulating heat conductive sheet is further improved. Further, when it is 50% by volume or more, the thermal dimensional stability of the manufactured insulating heat conductive sheet is further improved.

The two A layers can independently contain 7.5% by volume or more, 10% by volume or more, or 12% by volume or more of the binder resin, and / or 99% by volume or less and 90% by volume or less. , 75% by volume or less, 50% by volume or less, or 25% by volume or less of the binder resin can be contained.

It is preferable that one of the two A layers, particularly both of the two A layers, contains 10% by volume or more and 50% by volume or less of the binder resin. When it is 10% by volume or more, the shape retention of the manufactured insulating heat conductive sheet is further improved. Further, when it is 50% by volume or less, the content of the insulating heat conductive particles in the surface portion can be increased, so that the thermal conductivity of the insulating heat conductive sheet can be further improved. .. Further, the thermal dimensional stability of the insulating heat conductive sheet when heated can be further improved.

(Structure of layer B)
The B layer can contain 92.5% by volume or more, 93% by volume or more, 94% by volume or more, or 95% by volume or more of insulating heat conductive particles, and / or less than 100% by volume, 99% by volume. Insulating heat conductive particles of% or less, or 98% by volume or less can be contained.

The B layer preferably contains 95% by volume or more and 99% by volume or less of insulating heat conductive particles. When it is 99% by volume or less, the content of the binder resin in the central portion can be increased, so that the flexibility of the manufactured insulating heat conductive sheet can be further improved, and the insulating heat can be further improved. The porosity in the conductive sheet can be reduced. Further, when it is 95% by volume or more, the filling rate of the insulating heat conductive particles increases and the contact between the insulating heat conductive particles is further promoted, so that the heat conduction of the manufactured insulating heat conductive sheet is further promoted. The rate is further improved.

The B layer can contain a binder resin of more than 0% by volume, 0.1% by volume or more, 0.5% by volume or more, 1% by volume or more, or 2% by volume or more, and / or 7.5. It can contain less than 5% by volume, 5% by volume or less, or 4% by volume or less of the binder resin.

The B layer preferably contains 1% by volume or more and 5% by volume or less of the binder resin. When the ratio of the binder resin in the B layer is 1% by volume or more, the shape stability of the manufactured insulating heat conductive sheet can be further improved, and the porosity in the insulating heat conductive sheet can be increased. Can be reduced. Further, when the ratio of the binder resin in the B layer is 5% by volume or less, the filling rate of the insulating heat conductive particles can be increased, and the contact between the insulating heat conductive particles can be further promoted. Therefore, the thermal conductivity of the manufactured insulating heat conductive sheet is further improved.

(thickness)
The thicknesses of the A layer and the B layer can be appropriately set so that the binder resin exhibits a desired uneven distribution pattern in the manufactured insulating heat conductive sheet.

For example, the thicknesses of the two layers A are independently 0.5% or more, 1% or more, 2% or more, 5% or more, 7.5% or more, or 10% with respect to the total thickness of the laminated body. It may be more than or equal to and / or may be 35% or less, 30% or less, 25% or less, or 20% or less.

Further, for example, the thickness of the B layer may be 30% or more, 40% or more, 50% or more, or 60% or more, and / or 99% or less, 98% with respect to the total thickness of the laminated body. Hereinafter, it may be 96% or less, 90% or less, 85% or less, or 80% or less.

The layers A and B constituting the laminate can contain other components other than the binder resin and the insulating heat conductive particles. Other components include flame retardants, discoloration inhibitors, surfactants, coupling agents, colorants, viscosity modifiers, and / or reinforcing materials. The "other components" are preferably 25% by volume or less, 10% by volume or less, 5% by volume or less, 2.5% by volume or less, or 1% by volume or less in each of the A layer and the B layer.

(Provided)
The method for providing the above-mentioned laminate is not particularly limited. For example, a laminated body can be obtained by preparing slurries corresponding to the A layer and the B layer, respectively, and sequentially shaping and drying the respective slurries on the substrate in the form of a sheet. Alternatively, a precursor sheet member corresponding to each of the A layer and the B layer is formed in advance from the slurry corresponding to the A layer and the B layer, and these precursor sheet members are superposed to form a laminated body. You can also.

One embodiment of the providing step of providing a laminate is
(1) Preparing slurry A and slurry B,
(2) Forming and drying the slurry A in the form of a sheet on a substrate such as a glass plate to form the A layer (first A layer).
(3) The slurry B is formed into a sheet on the A layer and dried to form the B layer, and the slurry B is formed.
(4) The slurry A is formed into a sheet on the B layer and dried to form a further A layer (second A layer).

(Preparation of slurry)
The slurry can be obtained by mixing insulating heat conductive particles, a binder resin, and a solvent. For the insulating heat conductive particles and the binder resin, the above-mentioned contents regarding the insulating heat conductive sheet can be referred to.

The content of the insulating heat conductive particles and the binder resin in the slurry A (slurry for forming the A layer) and the slurry B (slurry for forming the B layer) is the insulating property in the manufactured A layer and B layer. The contents of the heat conductive particles and the binder resin can be set to be desired values, respectively.

Additives such as flame retardants, discoloration inhibitors, surfactants, coupling agents, colorants, viscosity modifiers, and / or reinforcing materials (fibrous reinforcing materials) may be optionally added to the slurry. can.

Anhydrous calcium chloride or anhydrous lithium chloride may be added to the slurry. By adding anhydrous calcium chloride or anhydrous lithium chloride, the solubility of the binder resin in a solvent may be improved. In particular, when an aramid resin is used as the binder resin, it is preferable to add anhydrous calcium chloride or anhydrous lithium chloride, and in this case, the solubility of the aramid resin in the solvent can be further improved.

As the solvent, a solvent capable of dissolving the binder resin can be used. For example, when an aramid resin is used as the binder resin, 1-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide, or dimethyl sulfoxide can be used.

For mixing insulating heat conductive particles, binder resin and solvent, for example, paint shaker, bead mill, planetary mixer, stirring type disperser, self-rotating stirring mixer, three-roll, kneader, single-screw or twin-screw kneader, etc. A general kneading device can be used.

(Formation of layer A)
In one embodiment, the slurry A is formed into a sheet on the substrate and dried to form the A layer (first A layer).

In order to shape the slurry into a sheet, a known method such as extrusion molding, injection molding, or laminating molding can be used in addition to the method of applying the slurry on the substrate by a coater (applicator).

Drying may be carried out by a known method. The drying temperature may be, for example, 50 ° C. to 120 ° C., and the drying time may be, for example, 1 minute to 3 hours, or 10 minutes to 1 hour.

The base material is not particularly limited, but a base material having excellent peelability when peeling the A layer, the B layer, and / or the laminate from the base material is preferable. The substrate may be, for example, a glass plate, a polyamide film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polyethylene sulfate film, a polyphenylene oxide film, a polytetrafluoroethylene film, or the like.

(Formation of layer B)
In one embodiment, the slurry B is formed into a sheet on the layer A formed as described above, and dried to form the layer B.

The B layer can be formed in the same manner as described above for the A layer (first A layer) except that the slurry is formed and dried on the A layer instead of the base material. ..

(Formation of additional layer A)
In one embodiment, the slurry B is formed into a sheet on the B layer formed as described above, and dried to form a further A layer (second A layer).

Further, the A layer can be formed in the same manner as described above for the A layer (first A layer) except that the slurry is formed and dried on the B layer instead of the base material. ..

(Precursor sheet member)
It is also possible to exfoliate the slurry shaped on the substrate from the substrate and optionally further dry it to produce a precursor sheet member (corresponding to layer A or layer B) for producing the laminate. can. In this case, the laminated body can be manufactured by arranging the precursor sheet member corresponding to the B layer between the precursor sheet members corresponding to the A layer.

(Washing treatment)
The laminated body and / or the precursor sheet member can be arbitrarily washed with water. By performing the washing treatment with water, the residual solvent in the insulating heat conductive sheet and, if present, the salt can be reduced. The water washing treatment can be performed, for example, by appropriately peeling the laminated body and / or the precursor sheet member from the substrate and immersing the laminated body and / or the precursor sheet member in ion-exchanged water for 10 minutes to 3 hours. When anhydrous calcium chloride or anhydrous lithium chloride is added in the mixing step, it is preferable to carry out a washing treatment with water.

Since the shaped slurry has a relatively large number of voids, it is considered that the water permeability is high. Therefore, it is considered that the residual solvent and salt can be removed more efficiently by performing the washing treatment with water before the roll press. The water content can be reduced by washing with water and then drying, or by a roll press treatment.

<Roll press process>
In the roll press process according to the present disclosure, the laminate provided as described above is roll pressed.

In the conventional method of laminating and heat-pressing a plurality of resin sheets containing insulating heat conductive particles, a sheet having high thermal conductivity can be obtained, especially when the filling degree of the insulating heat conductive particles is relatively high. Was not possible in some cases. Although not intended to be limited by theory, conventional thermal press methods cannot sufficiently reduce voids due to steric obstruction between highly filled insulating heat conductive particles and also provide insulating heat. Since a relatively large amount of the binder resin remains between the conductive particles, it is considered that the contact between the insulating heat conductive particles is insufficient.

On the other hand, in the method according to the present disclosure in which the laminated body is roll-pressed, bubbles and the like are discharged to the outside and / or deformation of the insulating heat conductive particles (particularly, deformation of the primary particles constituting the insulating particles). ) Etc., it is considered that sufficient contact is formed between the insulating heat conductive particles, and as a result, an insulated heat conductive sheet having high thermal conductivity can be obtained. Further, in the case of the roll press treatment, the highly filled insulating heat conductive particles are pressed against each other, and / or the elimination of the binder resin existing between the insulating heat conductive particles is promoted. It is also possible that this further promotes the formation of contacts between the insulating heat conductive particles.

The roll press may be performed by a known method, and for example, a pressure treatment of the laminated body may be performed by a calendar roll machine. The pressure applied to the laminate in the roll press step is linear pressure, preferably 400 N / cm to 8000 N / cm, more preferably 2000 N / cm to 7500 N / cm, and further preferably 5000 N / cm to 7000 N / cm. .. By setting the linear pressure to 400 N / cm or more, the insulating heat conductive particles are likely to be deformed, and the bubbles are remarkably discharged to the outside of the sheet. When the linear pressure is 8000 N / cm or less, the insulating heat conductive particles are sufficiently deformed and densely filled to the extent that they are not destroyed, and the voids in the sheet can be reduced. The diameter of the roll used in the roll press is preferably, for example, 200 mm to 1500 mm.

During the roll press treatment, it is preferable to heat the insulating heat conductive sheet precursor. The heating temperature can be appropriately set according to the type of binder resin used and the like. When an aramid resin is used as the binder resin, the heating temperature is preferably 100 to 400 ° C. When the heating temperature is 100 ° C. or higher, the binder resin is easily softened, and the effect of filling the gaps between the insulating heat conductive particles is easily obtained by the roll press treatment. By setting the heating temperature to 400 ° C. or lower, the strength of the binder resin is less likely to decrease due to the heat history.

Hereinafter, the invention according to the present disclosure will be described in more detail by way of examples.

<< Example 1, Comparative Examples 1 to 6 >>
In Example 1 and Comparative Examples 1 to 6, the measurement was carried out by the following method.

(1) Ratio of insulating heat conductive particles and binder resin (whole sheet)
The ratio of the insulating heat conductive particles and the binder resin to the entire cross section perpendicular to the plane direction of the insulating heat conductive sheet is the insulating heat in the observation field of the cross section perpendicular to the plane direction by a scanning electron microscope (SEM). It was determined by observing at 1000 times or 3000 times so that both main surfaces of the conductive sheet were inserted, and measuring the area ratio of the binder resin and the insulating heat conductive particles present in a certain area of the obtained cross-sectional image. .. The area ratio was calculated from the weight ratio of each piece of paper obtained by cutting out a cross-sectional image printed on paper with a utility knife. In the measurement, the range including both main surfaces was set so that the measurement target was not biased to the surface portion or the central portion of the insulating heat conductive sheet.

(2) Ratio of insulating heat conductive particles and binder resin (surface part and center part)
The contents of the binder resin and the insulating heat conductive particles in the "surface part" and the "central part" are such that the main surfaces of both the insulating heat conductive sheets have a cross section perpendicular to the plane direction and the observation field of view by SEM. Observe at 1000 times or 3000 times so as to enter, and in the obtained cross-sectional image, measure the area ratio of the binder resin and the insulating heat conductive particles existing in a certain area in the "surface portion" and the "central portion", respectively. By that, it was decided.

The "surface portion" starts from each of the two main surfaces of the insulating heat conductive sheet in the cross section perpendicular to the surface direction of the insulating heat conductive sheet, and is along the thickness direction of the insulating heat conductive sheet. The portion up to 10% of the thickness of the insulating heat conductive sheet was used. Further, the "central portion" starts from one of the main surfaces of the insulating heat conductive sheet in the cross section perpendicular to the surface direction of the insulating heat conductive sheet and is oriented in the thickness direction of the insulating heat conductive sheet. Along with this, the thickness of the insulating heat conductive sheet was set to a portion of more than 10% to less than 90%.

(3) Uneven distribution of the binder resin on the surface portion The uneven distribution of the binder resin on the surface portion of the insulating heat conductive sheet was evaluated based on the area ratio of the binder resin and the insulating heat conductive particles measured as described above. Specifically, the area ratio of the binder resin to the insulating heat conductive particles on the surface portion of the insulating heat conductive sheet (binder resin / insulating heat conductive particles) is the insulating heat conduction in the central portion of the insulating heat conductive sheet. When it was larger than the area ratio of the binder resin to the particles (binder resin / insulating heat conductive particles), it was defined as "unevenly distributed", and when it was not, it was defined as "not unevenly distributed".

(4) Porosity (area%)
The porosity was calculated from the area ratio of the voids existing in a certain area of the obtained cross-sectional image obtained by observing the cross section perpendicular to the plane direction at 1000 times or 3000 times by SEM.

(5) Thermal Conductivity The thermal conductivity of the insulating heat conductive sheet was calculated by multiplying the thermal diffusivity, specific gravity and specific heat in each of the thickness direction and the surface direction.
(Thermal conductivity) = (Thermal diffusivity) x (Specific heat) x (Specific gravity)
The thermal diffusivity in the thickness direction was determined by the temperature wave analysis method. As the measuring device, ai-Phase mobile M3 type 1 manufactured by iPhase was used. The thermal diffusivity in the plane direction was determined by the optical exchange method. A LaserPIT manufactured by Advanced Riko was used as the measuring device. The specific heat was determined using a differential scanning calorimeter (DSCQ10 manufactured by TA Instruments). The specific gravity was determined from the outer dimensions and weight of the insulating heat conductive sheet.

(6) Degree of Orientation The degree of orientation of boron nitride was evaluated by the peak intensity ratio of transmitted X-ray diffraction (XRD, NANO-Viewer manufactured by Rigaku) with the main surface of the insulating heat conductive sheet as the measurement surface. Using the (002) peak intensity I (002) corresponding to the c-axis (thickness) direction of the boron nitride crystal and the (100) peak intensity I (100) corresponding to the a-axis (plane), the degree of orientation is as follows. Was defined.
(Boron Nitride Orientation) = I (002) / I (100)
The lower the degree of orientation, the more the boron nitride is oriented in the same direction as in the sheet surface.

(7) Average particle size, aspect ratio (i) As the average particle size, a laser diffraction / scattering type particle size distribution measuring device (MT3000 manufactured by Microtrac Bell Co., Ltd.) is used, the measurement time is 10 seconds, and the number of measurements is 1. The measurement was performed once and the D50 value in the volume distribution was obtained.
(Ii) The aspect ratio was determined by measuring the major axis and thickness of the particles at a magnification of 1500 times using a scanning electron microscope (TM3000 type Microscope manufactured by Hitachi High-Technologies Corporation).

<Example 1>
(Preparation of layer A slurry)
1-Methyl-2-pyrrolidone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) 300 parts by volume of aramid resin "Technora" as a binder resin (copolyparaphenylene 3,4'-diphenyl ether terephthalamide, manufactured by Teijin Co., Ltd.) Plate-shaped boron nitride particles "HSP" (HSP) as insulating heat conductive particles with 14 parts by volume and 5 parts by volume of anhydrous calcium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a stabilizer for the dissolved resin dissolved. 86 parts by volume (manufactured by Dandong Chemical Engineering Institute Co., average particle size 40 μm, aspect ratio 20 to 50) was added and mixed by stirring with a planetary mixer for 30 minutes to obtain slurry A.

(Preparation of B layer slurry)
In a state where 3 parts by volume of "Technora" and 1 part by volume of anhydrous calcium chloride as a stabilizer are dissolved in 210 parts by volume of 1-methyl-2-pyrrolidone, 97 parts by volume of "HSP" is added, and 30 parts by planetarimixer is used. The mixture was stirred for 1 minute and passed through a three-roll mill twice to obtain slurry B.

(Film formation)
Slurry A was applied onto a glass plate using an applicator having a clearance of 0.12 mm and dried in the air at 80 ° C. for 20 minutes to obtain the lowest layer A. Slurry B was applied onto the obtained coating film using an applicator having a clearance of 0.62 mm, and dried in the air at 80 ° C. for 1 hour to obtain a layer B of an intermediate layer. Further, the slurry A was applied onto the coating film using an applicator having a clearance of 0.12 mm and dried in the air at 80 ° C. for 1 hour to obtain the uppermost layer A.

(Desalting)
The obtained coating film was peeled off from the glass plate in ion-exchanged water and immersed as it was in ion-exchanged water for 30 minutes. Then, it was dried in the air at 120 ° C. for 1 hour.

(rolling)
By passing the desalted coating film twice through a roll press at 220 ° C. and a linear pressure of 600 kgf / cm (about 5,880 N / cm), a flexible insulating heat conductive sheet having a thickness of 87 μm and having self-reliance is obtained. rice field.

(Thermal conductivity)
The obtained insulating heat conductive sheet has a specific gravity of 2.09 g / cm ³ , a specific heat of 0.85 J / (g · K), an in-plane thermal conductivity of 42.2 mm ² / s, and a thermal diffusion in the thickness direction. The ratio was 3.0 mm ² / s, the thermal conductivity in the in-plane direction was 75 W / (m · K), and the thermal conductivity in the thickness direction was 5.4 W / (m · K). A cross-sectional SEM photograph of the insulating heat conductive sheet according to the first embodiment is shown in FIG. As can be seen in FIG. 3, it can be confirmed that in the insulating heat conductive sheet according to the first embodiment, a relatively large amount of the binder resin is present in any of the two surface portions as compared with the central portion. Further, as can be seen in FIG. 3, in the insulating heat conductive sheet according to the first embodiment, relatively many contacts between the insulating heat conductive particles were confirmed in the central portion.

<Comparative Example 1>
An insulating heat conductive sheet was produced by the same method as in Example 1 except that only the intermediate layer B and the uppermost layer A were formed without forming the lowermost layer A. The coating film was torn in the rolling process, and an insulating heat conductive sheet could not be obtained.

<Comparative Example 2>
An insulating heat conductive sheet was produced by the same method as in Example 1 except that the film formation of the lowermost layer A and the layer B of the intermediate layer was performed without forming the film of the uppermost layer A. The coating film was torn in the rolling process, and an insulating heat conductive sheet could not be obtained.

<Comparative Example 3>
An insulating heat conductive sheet was produced by the same method as in Example 1 except that the film formation of the uppermost layer and the lowermost layer A was not carried out and only the film formation of the intermediate layer B was carried out. The coating film was torn in the peeling process, and an insulating heat conductive sheet could not be obtained.

<Comparative Example 4>
1-Methyl-2-pyrrolidone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) 350 parts by volume of aramid resin "Technora" as a binder resin (copolyparaphenylene 3,4'-diphenyl ether terephthalamide, manufactured by Teijin Co., Ltd.) Scale-like boron nitride particles "HSL" (HSL) as insulating heat conductive particles with 5 parts by volume and 2 parts by volume of anhydrous calcium chloride as a stabilizer for dissolved resin (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) dissolved. A slurry was obtained by adding 95 parts by volume of Dandong Chemical Engineering Institute Co., having an average particle size of 30 μm and an aspect ratio of 38) and stirring with a rotating / revolving mixer for 10 minutes.

The obtained slurry was applied onto a glass plate using a bar coater having a clearance of 0.14 mm, shaped, and dried at 115 ° C. for 20 minutes. Then, after immersing in ion-exchanged water for 1 hour and desalting, the sheet-shaped slurry was peeled off from the glass plate in water. The peeled sheet was dried at 100 ° C. for 30 minutes to obtain a precursor sheet member having a thickness of 100 μm.

The obtained precursor sheet member was subjected to compression treatment with a calendar roll machine under the conditions of a temperature of 280 ° C. and a linear pressure of 4000 N / cm to obtain a flexible insulating heat conductive sheet having a thickness of 37 μm. A cross-sectional SEM photograph of the insulating heat conductive sheet according to Comparative Example 4 is shown in FIG. As can be seen in FIG. 4, in the insulating heat conductive sheet according to Comparative Example 4, the binder resin was not unevenly distributed on the surface portion with respect to the central portion.

<Comparative Example 5>
An insulating heat conductive sheet having a thickness of 27 μm was obtained in the same manner as in Comparative Example 4, except that the aramid resin was 8 parts by volume and the scaly boron nitride particles were 92 parts by volume. A cross-sectional SEM photograph of the insulating heat conductive sheet according to Comparative Example 5 is shown in FIG. As can be seen in FIG. 5, in the insulating heat conductive sheet according to Comparative Example 5, the binder resin was not unevenly distributed on the surface portion with respect to the central portion.

<Comparative Example 6>
1-Methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.) 450 parts by volume, 10 parts by volume of aramid resin "Technora" as a binder resin, and anhydrous calcium chloride as a stabilizer for dissolved resin (Fujifilm Wako Jun) (Made by Yakuhin Co., Ltd.) With 2 parts by volume dissolved, add 90 parts by volume of scaly boron nitride particles "PT110" (manufactured by Momentive, average particle size 45 μm, aspect ratio 35) as insulating heat conductive particles. Mixing was performed by stirring with a three-one motor stirrer for 60 minutes while heating at 80 ° C. to obtain a uniform slurry.

The obtained slurry was applied onto a glass plate using a bar coater having a clearance of 0.28 mm, shaped into a sheet, and dried at 70 ° C. for 1 hour. Then, the shaped slurry was peeled off from the glass plate in water and then dried at 100 ° C. for 1 hour to obtain an insulating heat conductive sheet precursor having a thickness of 100 μm. The obtained insulating heat conductive sheet precursor was subjected to compression treatment with a calendar roll machine under the conditions of a temperature of 270 ° C. and a linear pressure of 4000 N / cm to obtain an insulated heat conductive sheet having a thickness of 48 μm. A cross-sectional SEM photograph of the insulating heat conductive sheet according to Comparative Example 6 is shown in FIG. As can be seen in FIG. 6, in the insulating heat conductive sheet according to Comparative Example 6, the binder resin was not unevenly distributed on the surface portion with respect to the central portion.

≪Evaluation≫
As can be seen in Table 1, the laminate used for producing the insulating heat conductive sheet of Example 1 has two main surfaces of the B layer having a volume ratio of the binder resin and the insulating heat conductive particles of 97: 3. Each has a structure in which an A layer having a volume ratio of the binder resin and the insulating heat conductive particles of 86:14 is arranged (layer structure = A / B / A), and in the manufacturing process, Good formability on the sheet was confirmed. On the other hand, in Comparative Example 1 and Comparative Example 2 using a laminate having the A layer on only one main surface of the B layer, and Comparative Example 3 using only the B layer, a sheet is formed. I couldn't.

Further, as can be seen in Table 1, the insulating heat conductive sheet produced in Example 1 has 2.1 area% of binder resin and 97.9 area% of insulating heat in the entire cross section perpendicular to the plane direction. It had conductive particles, and the binder resin was unevenly distributed on the surface portion. The insulating heat conductive sheet of Example 1 showed higher thermal conductivity in the plane direction and the thickness direction as compared with Comparative Examples 4 to 6.

In particular, although the content of the insulating heat conductive particles in the insulating heat conductive sheet of Example 1 is the same as that of Comparative Example 4 and the porosity is relatively high, Example 1 is more than this example. Also showed high heat conduction.

Although not intended to be limited by theory, in Comparative Examples 4 to 6, since the binder resin is uniformly distributed in the sheet, the binder resin is present between the insulating heat conductive particles throughout the sheet. As a result, it is considered that the advantages of high filling of the insulating heat conductive particles cannot be fully utilized. On the other hand, in the insulating heat conductive sheet according to the first embodiment, the binder resin is unevenly distributed on the surface portion, so that the direct contact between the insulating heat conductive particles in the central portion of the sheet increases. As a result, it is considered that the thermal conductivity of the entire insulating heat conductive sheet is improved.

10 Insulating heat conductive sheet 12 Surface part of insulating heat conductive sheet 14 Central part of insulating heat conductive sheet 20 Laminated body 22 A layer 24 B layer D Thickness direction S plane direction

Claims (9)

An insulating heat conductive sheet containing insulating heat conductive particles and a binder resin.
When the total of the insulating heat conductive particles and the binder resin is 100 area%, 90 to 99 area% of the insulating heat conductive particles and 1 to 10 area% of the entire cross section perpendicular to the plane direction. Contains the binder resin and
For a cross section perpendicular to the plane direction, the area ratio of the binder resin to the insulating heat conductive particles on the surface portion of the insulating heat conductive sheet is the binder to the insulating heat conductive particles in the central portion of the insulating heat conductive sheet. Larger than the area ratio of the resin,
Insulating heat conductive sheet. The insulating heat conductive sheet according to claim 1, wherein the insulating heat conductive particles include flat insulating heat conductive particles. The insulating heat conductive sheet according to claim 1 or 2, wherein the binder resin is an aramid resin. The insulating heat conductive sheet according to any one of claims 1 to 3, wherein the insulating heat conductive particles include deformed flat insulating heat conductive particles. The insulating heat conductive sheet according to any one of claims 1 to 4, wherein the insulating heat conductive particles are boron nitride particles. The insulating heat conductive sheet according to any one of claims 1 to 5, which has a thermal conductivity of more than 60 W / (m · K) in the in-plane direction. The insulating heat conductive sheet according to any one of claims 1 to 6, which has a thermal conductivity of 3.0 W / (m · K) or more in the thickness direction. The insulating heat conductive sheet according to any one of claims 1 to 7, which has a gap of more than 10 area% for the entire cross section perpendicular to the plane direction. Two A layers containing 7.5% by volume or more of the binder resin and less than 92.5% by volume of insulating heat conductive particles, and less than 7.5% by volume arranged between the two A layers. To provide a laminate having a binder resin and a B layer containing 92.5% by volume or more of insulating heat conductive particles, and
Roll pressing the laminate,
The method for producing an insulating heat conductive sheet according to any one of claims 1 to 8, comprising the method for producing an insulating heat conductive sheet.

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