Insulating heat conductive sheet and method for producing same

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

[Technical field]

[0001] The present invention relates to an insulating thermally conductive sheet and a method for producing the same. [Background technology]

[0002] The present disclosure relates to an insulating thermally conductive sheet that has excellent thermal conductivity and transport properties (particularly in-plane thermal conductivity and transport properties) that can quickly diffuse heat generated by heat-generating components such as semiconductor elements, power sources, and light sources inside electrical appliances, thereby mitigating localized temperature increases or transporting heat to locations away from the heat source.

[0003] In recent years, heat dissipation measures have become increasingly important due to the increase in heat density associated with the miniaturization and higher power output of electronic devices. In order to reduce thermal problems in electronic devices, it is important to quickly dissipate the heat generated within the device to the coolant or housing, etc., without adversely affecting surrounding components. For this reason, thermal conductive materials that can conduct heat in a specific direction are required. In many cases, thermal conductive materials are also required to have electrical insulation properties to prevent electrical leakage to the coolant or housing.

[0004] Patent Document 1 describes a thermally conductive sheet having a first surface layer, a second surface layer, and an intermediate layer containing an epoxy resin and an inorganic filler, and describes that the first surface layer and the second surface layer each have a smaller volume content of inorganic filler than the intermediate layer.

[0005] Patent Document 2 discloses a heat dissipation sheet in which a graphite layer is formed on an aromatic polyamide film having a specific thermal conductivity via an adhesive layer.

[0006] Patent Document 3 describes a thermally conductive sheet having a multilayer structure including a layer (A) and a layer (B), in which the layer (A) is a layer made of a composition containing insulating non-spherical particles such as boron nitride particles and an organic polymer compound, and the layer (B) is a layer made of an insulating resin composition such as a polyamideimide resin or an epoxy resin.

[0007] Patent Document 4 describes a heat transfer member including a first surface layer and a second surface layer, and an intermediate layer disposed between these surface layers, and describes that the first surface layer, the second surface layer, and the intermediate layer each include a boron nitride sintered body having a specific degree of orientation of hexagonal boron nitride primary particles, and a thermosetting resin composition impregnated in the boron nitride sintered body.

[0008] Patent Document 5 discloses a multilayer resin sheet having a resin composition layer containing a thermosetting resin and a filler, and an adhesive layer disposed on at least one surface of the resin composition layer, the surface not facing the resin composition layer having an arithmetic mean surface roughness of 1.5 μm or less. The document describes that the adhesive layer may contain an inorganic filler.

[0009] Patent Document 6 discloses an insulating sheet containing insulating particles and a binder resin. The document describes that the insulating sheet contains 75 to 97% by area of ​​insulating particles, 3 to 25% by area of ​​binder resin, and 10% or less by area of ​​voids in the entire cross section perpendicular to the plane direction, and describes that the insulating particles include deformed flat particles. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2016 / 017670 [Patent Document 2] JP 2010-6890 A [Patent Document 3] JP 2011-230472 A [Patent Document 4] International Publication No. 2018 / 181606 [Patent Document 5] JP 2019-14261 A [Patent Document 6] Patent No. 6755421 Summary of the Invention [Problem to be solved by the invention]

[0011] With conventional insulating thermally conductive sheets, it has sometimes been impossible to obtain an insulating thermally conductive sheet having a sufficiently high thermal conductivity and a stable sheet shape. [Means for solving the problem]

[0012] An object of the present invention is to provide an insulating thermally conductive sheet having improved thermal conductivity while maintaining a stable sheet shape, and to provide a method for producing such an insulating thermally conductive sheet.

[0013] The present inventors have found that the above problems can be solved by the following aspects: <Aspect 1> An insulating and thermally conductive sheet containing insulating and thermally conductive particles and a binder resin, With respect to an entire cross section perpendicular to the plane direction, when the total area of ​​the insulating thermally conductive particles and the binder resin is taken as 100 area %, the insulating thermally conductive particles account for 90 to 99 area % and the binder resin accounts for 1 to 10 area %, and In a cross section perpendicular to the plane direction, an area ratio of the binder resin to the insulating thermally conductive particles in a surface portion of the insulating thermally conductive sheet is larger than an area ratio of the binder resin to the insulating thermally conductive particles in a central portion of the insulating thermally conductive sheet. Insulating thermal conductive sheet. <Aspect 2> 2. The insulating thermally conductive sheet of claim 1, wherein the insulating thermally conductive particles include flat insulating thermally conductive particles. <Aspect 3> 3. The insulating and thermally conductive sheet according to claim 1, wherein the binder resin is an aramid resin. <Aspect 4> 4. The insulating thermally conductive sheet according to any one of aspects 1 to 3, wherein the insulating thermally conductive particles include deformed flat insulating thermally conductive particles. <Aspect 5> 5. The insulating thermally conductive sheet according to any one of aspects 1 to 4, wherein the insulating thermally conductive particles are boron nitride particles. <Aspect 6> 6. An insulating thermally conductive sheet according to any one of aspects 1 to 5, having a thermal conductivity of more than 60 W / (m·K) in an in-plane direction. <Aspect 7> 7. The insulating thermally conductive sheet according to any one of aspects 1 to 6, having a thermal conductivity of 3.0 W / (m·K) or more in the thickness direction. <Aspect 8> The insulating and thermally conductive sheet according to any one of aspects 1 to 7, having voids of more than 10% by area over the entire cross section perpendicular to the plane direction. <Aspect 9> Providing a laminate having two A layers containing 7.5% by volume or more of a binder resin and less than 92.5% by volume of insulating thermally conductive particles, and a B layer disposed between the two A layers and containing less than 7.5% by volume of a binder resin and 92.5% by volume or more of insulating thermally conductive particles; roll pressing the laminate; A method for producing the insulating thermally conductive sheet according to any one of aspects 1 to 8, comprising: Effect of the Invention

[0014] According to the present invention, it is possible to provide an insulating thermally conductive sheet having improved thermal conductivity while maintaining a stable sheet shape. Also, according to the present invention, it is possible to provide a method for producing such an insulating thermally conductive sheet. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 shows a schematic diagram of a cross section perpendicular to the plane direction of one embodiment of an insulating thermally conductive sheet according to the present disclosure. [Diagram 2] FIG. 2 shows a schematic diagram of a cross section perpendicular to the plane direction of one embodiment of a laminate used in the method for producing an insulating thermally conductive sheet according to the present disclosure. [Diagram 3]FIG. 3 shows an SEM photograph of a cross section perpendicular to the plane direction of the insulating thermally conductive sheet according to Example 1. As shown in FIG. [Figure 4] FIG. 4 shows an SEM photograph of a cross section perpendicular to the plane direction of the insulating thermally conductive sheet according to Comparative Example 4. [Diagram 5] FIG. 5 shows an SEM photograph of a cross section perpendicular to the plane direction of the insulating thermally conductive sheet according to Comparative Example 5. As shown in FIG. [Figure 6] FIG. 6 shows an SEM photograph of a cross section perpendicular to the plane direction of the insulating thermally conductive sheet according to Comparative Example 6. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <Insulating heat conductive sheet> The insulating and thermally conductive sheet according to the present disclosure comprises: An insulating and thermally conductive sheet containing insulating and thermally conductive particles and a binder resin, With respect to the entire cross section perpendicular to the plane direction, when the total area of ​​the insulating thermally conductive particles and the binder resin is taken as 100%, the insulating thermally conductive particles account for 90 to 99% by area, and the binder resin accounts for 1 to 10% by area, In a cross section perpendicular to the plane direction, the area ratio of the binder resin to the insulating thermally conductive particles in the surface portion of the insulating thermally conductive sheet is greater than the area ratio of the binder resin to the insulating thermally conductive particles in the center portion of the insulating thermally conductive sheet.

[0017] FIG. 1 shows a schematic cross-sectional view perpendicular to the surface direction of one embodiment of the insulating thermally conductive sheet according to the present disclosure (insulating thermally conductive sheet 10). "D" and "S" in FIG. 1 indicate the thickness direction and surface direction of the insulating thermally conductive sheet 10, respectively. Note that the schematic views in FIG. 1 and FIG. 2 are not drawn to scale. The insulating thermally conductive sheet 10 in FIG. 1 has two surface portions 12 and a central portion 14. The two surface portions 12 are adjacent to the main surfaces of the insulating thermally conductive sheet, respectively. The central portion 14 is a portion located between the two surface portions 12 in the thickness direction D of the insulating thermally conductive sheet. In the insulating thermally conductive sheet 10, the binder resin is unevenly distributed in the surface portion 12. That is, the area ratio of the binder resin to the insulating thermally conductive particles in the surface portion 12 of the insulating thermally conductive sheet 10 is larger than the area ratio of the binder resin to the insulating thermally conductive particles in the central portion 14 of the insulating thermally conductive sheet.

[0018] In general, in order to improve the thermal conductivity of an insulating thermally conductive sheet, it is considered to increase the content (or filling rate) of insulating thermally conductive particles. However, in the conventional technology, when the amount of insulating thermally conductive particles relative to the binder resin is large, it is sometimes difficult to mold the sheet into a sheet.

[0019] In response to this, the present inventors have discovered that by adjusting the distribution of the binder resin in the insulating thermally conductive sheet, it is possible to obtain an insulating thermally conductive sheet that retains its sheet shape and exhibits relatively high thermal conductivity, even when the proportion of binder resin is relatively low.

[0020] Specifically, in an insulating thermally conductive sheet containing 90 to 99 area % of insulating thermally conductive particles and 1 to 10 area % of binder resin, when the total area of ​​the insulating thermally conductive particles and binder resin is taken as 100 area %, It has been discovered that by making the area ratio of binder resin to insulating thermally conductive particles in the surface portion of an insulating thermally conductive sheet larger than the area ratio of binder resin to insulating thermally conductive particles in the central portion of the insulating thermally conductive sheet, in a cross section perpendicular to the plane direction, it is possible to obtain an insulating thermally conductive sheet that retains its sheet shape and exhibits relatively high thermal conductivity.

[0021] Without intending to be limited by theory, it is believed that in conventional insulating thermally conductive sheets, the binder resin is distributed relatively uniformly within the sheet, resulting in the binder resin being present between the insulating thermally conductive particles throughout the entire sheet, and as a result, direct contact between the insulating thermally conductive particles is limited. Also, in conventional insulating thermally conductive sheets, even if the binder resin is unevenly distributed on the surface side of the sheet, a relatively large amount of binder resin is also present in the center, resulting in limited direct contact between the insulating thermally conductive particles.

[0022] In contrast, in the insulating thermally conductive sheet of the present invention, the binder resin is extremely reduced in the central portion of the sheet due to the above-mentioned configuration, thereby increasing direct contact between the insulating thermally conductive particles in the central portion, and it is believed that as a result, an insulating thermally conductive sheet having a relatively high thermal conductivity can be obtained.

[0023] Furthermore, in the insulating thermally conductive sheet according to the present disclosure, it is believed that the binder resin is unevenly distributed on the surface portion of the sheet, thereby ensuring good formability and good shape retention of the sheet even when the proportion of insulating thermally conductive particles in the sheet as a whole is relatively high.

[0024] The insulating thermally conductive sheet according to the present disclosure will be described in detail below.

[0025] <Overall structure of the insulating thermal conductive sheet> The insulating thermally conductive sheet according to the present disclosure contains 1 to 10 area % of binder resin when the total area of ​​the insulating thermally conductive particles and the binder resin is 100 area % over the entire cross section perpendicular to the plane direction. When the binder resin content is 10 area % or less, a sufficiently high thermal conductivity can be ensured, and when it is 1 area % or more, good moldability of the sheet and good shape retention of the sheet can be ensured.

[0026] The binder resin contained in the insulating heat conductive sheet according to the present disclosure may be 1.5 area% or more, 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% or less, 8.0 area% or less, 7.0 area% or less, or 6.0 area% or less, 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 1.5 area% or more, it is particularly preferable because the ease of molding and the shape stability of the sheet are ensured.

[0027] In the present disclosure, the "area %" of the binder resin when the total of the insulating thermally conductive particles and the binder resin is taken as 100 area % for the entire cross section perpendicular to the surface direction can be determined by photographing the cross section perpendicular to the surface direction of the insulating thermally conductive sheet by SEM and measuring the area of ​​the insulating thermally 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 is particularly selected so as not to be biased toward either the surface part or the center part of the insulating thermally conductive sheet. In addition, when the insulating thermally conductive sheet has additives other than the insulating thermally conductive particles and the binder resin, the "area %" of the binder resin when the total of the insulating thermally conductive particles and the binder resin is taken as 100 area % can be calculated by setting the above-mentioned constant area so that the additives are not included in the above-mentioned constant area.

[0028] The insulating thermally conductive sheet according to the present disclosure contains 90 to 99 area % of insulating thermally conductive particles when the total area of ​​the insulating thermally conductive particles and the binder resin is 100 area % for the entire cross section perpendicular to the plane direction. When the content of the insulating thermally conductive particles is 90 area % or more, good thermal conductivity is obtained, and when it is 99 area % or less, an increase in viscosity of the resin composition is suppressed, ease of molding is ensured, and shape stability of the sheet is ensured.

[0029] Preferably, the insulating thermally conductive particles contained in the insulating thermally conductive sheet according to the present disclosure may account for 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 % or less, when the total area of ​​the insulating thermally conductive particles and the binder resin is taken as 100 area %, over the entire cross section perpendicular to the plane direction.

[0030] In the present disclosure, for the entire cross section perpendicular to the plane direction, the "area %" of the insulating thermally conductive particles when the total area of ​​the insulating thermally conductive particles and the binder resin is taken as 100 area %, can be determined in the same manner as described above for the binder resin.

[0031] As described below, the insulating heat conductive sheet according to the present disclosure may contain voids and additives (such as fibrous reinforcing materials). The insulating heat conductive sheet according to the present disclosure preferably has insulating heat conductive particles and binder resin in a total amount of 70% or more, 80% or more, 90% or more, or 95% or more over the entire cross section perpendicular to the plane direction.

[0032] <Configuration of the insulating thermally conductive sheet in the thickness direction> As described above, in the electrically insulating thermally conductive sheet according to the present disclosure, the binder resin is unevenly distributed in the surface portion of the sheet.

[0033] The "surface portion" of an insulating heat conductive sheet is a portion adjacent to any one of the main surfaces of the insulating heat conductive sheet. Thus, there is usually one "surface portion" of an insulating heat conductive sheet for each of the two main surfaces of the insulating heat conductive sheet.

[0034] The "surface portion" of the insulating heat conductive sheet may in particular be a portion starting from one of the main surfaces of the insulating heat conductive sheet and extending along the thickness direction of the insulating heat conductive sheet to up to 10% of the thickness of the insulating heat conductive sheet.

[0035] On the other hand, the "center portion" of an insulating thermally conductive sheet is usually the portion located between two surface portions in the thickness direction of the insulating thermally conductive sheet.

[0036] The "central portion" of the insulating heat conductive sheet can particularly be a portion starting from one of the main surfaces of the insulating heat conductive sheet and extending along the thickness direction of the insulating heat conductive sheet to more than 10% to less than 90% of the thickness of the insulating heat conductive sheet.

[0037] (Uneven distribution of binder resin) In the insulating thermally conductive sheet according to the present disclosure, in a cross section perpendicular to the plane direction, the area ratio of the binder resin to the insulating thermally conductive particles in the surface portion of the insulating thermally conductive sheet is greater than the area ratio of the binder resin to the insulating thermally conductive particles in the central portion of the insulating thermally conductive sheet.

[0038] In particular, in a cross section perpendicular to the plane direction, the area ratio of the binder resin to the insulating thermally conductive particles in the surface portion of the insulating thermally conductive sheet 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 times or less, 75 times or less, 50 times or less, or 25 times or less, compared to the area ratio of the binder resin to the insulating thermally conductive particles in the central portion of the insulating thermally conductive sheet.

[0039] In a cross section perpendicular to the plane direction of the insulating thermally conductive sheet, the surface portion of the insulating thermally conductive sheet may contain more than 1 area %, 2.0 area % or more, 2.5 area % or more, or 5.0 area % or more of binder resin, and / or less than 100 area %, 90 area % or less, 75 area % or less, 50 area % or less, 25 area %, or 10 area % or less of binder resin, when the total of the binder resin and the insulating thermally conductive particles is taken as 100 area %.

[0040] It is preferable that the insulating heat conductive sheet contains more than 5 area % and 50 area % or less of the binder resin in the surface portion, when the total of the binder resin and the insulating heat conductive particles is 100 area %. When it is more than 5 area %, the shape retention of the insulating heat conductive sheet is further improved. When it is 50 area % or less, the proportion of the insulating heat conductive particles in the surface portion can be relatively large, which can lead to further improvement in the thermal conductivity of the insulating heat conductive sheet. Furthermore, 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 center portion, thereby reducing the difference in thermal properties (thermal expansion coefficient, thermal shrinkage coefficient, etc.) between these portions, which can further improve the thermal dimensional stability of the insulating heat conductive sheet.

[0041] In a cross section perpendicular to the plane direction of the insulating thermally conductive sheet, the surface portion of the insulating thermally conductive sheet may contain more than 0 area %, 1 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 of the insulating thermally conductive particles, when the total of the binder resin and the insulating thermally conductive particles is taken as 100 area %.

[0042] It is preferable that the insulating heat conductive sheet contains insulating heat conductive particles in an amount of more than 50% by area and not more than 95% by area based on the total amount of the binder resin and the insulating heat conductive particles in the surface portion. When it is 95% by area 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. When it is more than 50% by area, the content of the insulating heat conductive particles in the surface portion increases, so that the thermal conductivity of the insulating heat conductive sheet is further improved. Furthermore, when it is more than 50% by area, the thermal dimensional stability of the insulating heat conductive sheet is further improved.

[0043] In a cross section perpendicular to the plane direction of the insulating thermally conductive sheet, the insulating thermally conductive sheet may contain, in its central portion, more than 0 area %, 0.01 area % or more, 0.1 area % or more, 0.2 area % or more, or 0.3 area % or more of binder resin, when the total of the binder resin and the insulating thermally conductive particles is taken as 100 area %, and / or less than 10 area %, 7.5 area % or less, 5 area % or less, 2.5 area % or less, or 1 area % or less of binder resin.

[0044] It is preferable that the insulating heat conductive sheet contains 0.1% to 5% by area of ​​the binder resin in the center portion of the sheet, based on the total of the binder resin and the insulating heat conductive particles. When the ratio of the binder resin in the center portion is 0.1% by area or more, the flexibility of the insulating heat conductive sheet can be further improved, and the void ratio in the insulating heat conductive sheet can be reduced. When the ratio of the binder resin in the center portion of the sheet is 5% by area or less, it is possible to increase the packing rate of the insulating heat conductive particles, in particular to further increase the direct contact between the insulating heat conductive particles, and therefore the thermal conductivity of the insulating heat conductive sheet can be further improved.

[0045] In addition, the central portion of the insulating thermally conductive sheet, in a cross section perpendicular to the surface direction of the insulating thermally conductive sheet, can contain insulating thermally conductive particles in an amount of 90 area % or more, 92.5 area % 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 of the total of the binder resin and the insulating thermally conductive particles.

[0046] It is preferable that the insulating heat conductive sheet contains insulating heat conductive particles in an amount of 95% by area or more and less than 100% by area of ​​the total of the binder resin and the insulating heat conductive particles in the center part. When it is less than 100% by area, the binder resin can be contained in the center part, so that the flexibility of the insulating heat conductive sheet can be further improved and the void ratio in the insulating heat conductive sheet can be reduced. When it is 95% by area or more, the filling rate of the insulating heat conductive particles increases, so that the thermal conductivity of the insulating heat conductive sheet is further improved.

[0047] The area ratio of the binder resin to the insulating thermally conductive particles in each of the surface and center portions of the insulating thermally conductive sheet can be determined by measuring the areas of the insulating thermally conductive particles and the binder resin present in each of the surface and center portions of the insulating thermally conductive sheet in a certain area in a cross section perpendicular to the surface direction of the insulating thermally conductive sheet. A scanning electron microscope (SEM) can be used for the measurement.

[0048] (Binder resin / insulating thermally conductive particle composition) The insulating thermally conductive sheet according to the present disclosure may have a uniform composition of the binder resin and the insulating thermally conductive particles throughout the entire sheet. That is, the binder resin present in the surface portion of the insulating thermally conductive sheet and the binder resin present in the central portion of the insulating thermally conductive sheet may be the same in type and composition, and the insulating thermally conductive particles present in the surface portion of the insulating thermally conductive sheet and the insulating thermally conductive particles present in the central portion of the insulating thermally conductive sheet may be the same in type and composition.

[0049] On the other hand, the insulating thermally conductive sheet according to the present disclosure may not be uniform (may be non-uniform) throughout the sheet with respect to the composition of the binder resin and / or the composition of the insulating thermally conductive particles. That is, for example, the binder resin present in the surface portion of the insulating thermally conductive sheet and the binder resin present in the central portion of the insulating thermally conductive sheet may be different in type or composition, and / or the insulating thermally conductive particles present in the surface portion of the insulating thermally conductive sheet and the insulating thermally conductive particles present in the central portion of the insulating thermally conductive sheet may be different in type or composition.

[0050] <Void> In one embodiment of the insulating thermally conductive sheet according to the present disclosure, the insulating thermally conductive sheet has voids of more than 10% by area over the entire cross section perpendicular to the plane direction.

[0051] Conventionally, it has been believed that voids in an insulating heat conductive sheet reduce the thermal conductivity of the insulating heat conductive sheet. In particular, when the content of binder resin is suppressed to highly pack the insulating heat conductive particles, the void ratio increases due to steric hindrance between the particles caused by the shape of the insulating heat conductive particles and the amount of binder resin that can fill the voids is reduced, resulting in a decrease in the thermal conductivity of the insulating heat conductive sheet.

[0052] In contrast, the insulating heat conductive sheet according to the present disclosure can achieve a relatively high thermal conductivity even when the entire cross section perpendicular to the plane direction has more than 10% by area of ​​voids. Without intending to be limited by theory, the insulating heat conductive sheet according to the present invention has an improved packing rate of the insulating heat conductive particles in the center part of the sheet due to uneven distribution of the binder resin. Therefore, it is considered that the direct contact between the insulating heat conductive particles increases in the center part of the sheet, and as a result, a relatively high thermal conductivity can be achieved.

[0053] 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% or less by area, more preferably 25% or less by area, and even more preferably 20% or less by area, in the entire cross section perpendicular to the surface direction.

[0054] The "area %" of voids in the entire cross section perpendicular to the surface direction can be calculated by photographing a cross section perpendicular to the surface direction of an insulating thermally conductive sheet using an SEM and measuring the area of ​​voids present in a certain area in the obtained image.

[0055] <Insulating heat conductive particles>

[0056] The insulating heat conductive particles are any particles, particularly inorganic particles, that are insulating and have a higher thermal conductivity than the binder resin. The insulating heat conductive particles are not particularly limited, and examples thereof include particles such as boron nitride, aluminum nitride, aluminum oxide, magnesium oxide, silicon nitride, and silicon carbide, metal silicon particles with an insulated surface, carbon fibers and graphite surface-coated with an insulating material such as resin, and polymer-based fillers. From the viewpoint of thermal conductivity and insulation in the planar direction, it is preferable that the insulating heat conductive particles are boron nitride particles, particularly hexagonal boron nitride particles.

[0057] The average particle size of the insulating thermally conductive particles is preferably 1 to 200 μm, more preferably 5 to 200 μm, further preferably 5 to 100 μm, and particularly preferably 10 to 100 μm.

[0058] The average particle size is the median size (the particle size at which, when a powder is divided into two at a certain particle size, the particles larger than that particle size and the particles smaller than that particle size are equal in quantity; generally known as D50) measured by the laser diffraction method using a laser diffraction / scattering particle size distribution analyzer.

[0059] (flat) The insulating heat conductive sheet according to the present disclosure preferably contains flat insulating heat conductive particles. In the context of the present disclosure, the particles being "flat" means that the particles are in the form of a plate, a scale, or a flake.

[0060] The aspect ratio of the flat insulating thermally conductive particles is preferably 10 to 1000. When the aspect ratio is 10 or more, the important orientation for increasing thermal diffusivity is ensured, and high thermal diffusivity can be obtained, which is preferable. In addition, insulating thermally conductive particles having an aspect ratio of 1000 or less are preferable from the viewpoint of ease of processing, since the increase in viscosity of the composition due to the increase in specific surface area is suppressed.

[0061] The aspect ratio is the longest diameter of a particle divided by the thickness of the particle, i.e., longest diameter / thickness. If a particle is spherical, the aspect ratio is 1, and as the particle becomes more flat, the aspect ratio increases.

[0062] The aspect ratio can be obtained by measuring the major axis and thickness of a particle at a magnification of 1500 times using a scanning electron microscope and calculating the major axis / thickness ratio.

[0063] When the insulating heat conductive sheet contains flat insulating heat conductive particles, the flat insulating heat conductive particles preferably occupy 50% or more by volume of the entire insulating heat conductive particles. When the flat insulating heat conductive particles occupy 50% or more by volume, 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% or more by volume, even more preferably 70% or more by volume, even more preferably 80% or more by volume, and particularly preferably 90% or more by volume, and most preferably, the insulating heat conductive particles are made of flat insulating heat conductive particles.

[0064] (Boron nitride particles) An example of the flat insulating thermally conductive particles is hexagonal boron nitride particles.

[0065] 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, even 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 resin is ensured, which is preferable, and when it is 200 μm or less, the thickness uniformity can be ensured during sheet molding, which is preferable. As the boron nitride particles, boron nitride particles having a single average particle size may be used, or a mixture of multiple types of boron nitride particles having different average particle sizes may be used. The aspect ratio of the boron nitride particles is preferably 10 to 1000.

[0066] When using boron nitride particles as insulating thermally conductive particles, insulating thermally conductive particles other than boron nitride particles may be used in combination. Even in this case, the boron nitride particles preferably occupy 50% by volume or more of the entire insulating thermally conductive particles. If it is 50% by volume or more, it is preferable because good thermal conductivity in the in-plane direction is ensured. The boron nitride particles are more preferably 60% by volume or more, even more preferably 70% by volume or more, even more preferably 80% by volume, and particularly preferably 90% by volume or more, or 95% by volume or more of the entire insulating thermally conductive particles.

[0067] When using boron nitride particles and ceramic particles having isotropic thermal conductivity as insulating thermal conductive particles, the balance between the thermal conductivity in the thickness direction and the thermal conductivity in the in-plane direction of the insulating thermal conductive sheet can be adjusted as necessary, which is a preferred embodiment.In addition, since boron nitride particles are expensive materials, it is convenient to use them in combination with inexpensive materials such as metal silicon particles whose surfaces are thermally oxidized to insulate them, and in this case, the balance between the raw material cost and the thermal conductivity of the insulating thermal conductive sheet can be adjusted as necessary, which is a preferred embodiment.

[0068] (Transformation) In one advantageous embodiment of the insulating and thermally conductive sheet according to the present disclosure, the insulating and thermally conductive particles include deformed, flattened insulating and thermally conductive particles.

[0069] In the insulating heat conductive sheet containing the deformed flat insulating heat conductive particles, the thermal conductivity in the surface direction is further improved. Although there is no intention 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. It is also believed that when the flat insulating heat conductive particles are deformed during the manufacturing process of the insulating heat conductive sheet, the discharge of air bubbles trapped between the particles to the outside of the sheet is promoted, further promoting the reduction of the voids.

[0070] The method for obtaining an insulating heat conductive sheet containing deformed flat insulating heat conductive particles is not particularly limited, but may be, for example, a method of performing roll press treatment on an insulating heat conductive sheet precursor containing flat insulating heat conductive particles (for example, a laminate of sheets obtained by shaping and drying a slurry). In particular, according to the method of performing roll press treatment on an insulating heat conductive sheet precursor highly filled with flat insulating heat conductive particles, it is considered that high shear stress is likely to act between the insulating heat conductive particles, so that the deformation of the particles becomes more significant.

[0071] <Binder resin> The binder resin according to the present disclosure is not particularly limited. Examples of the binder resin include thermoplastic resins such as aramid resins (aromatic polyamides) described below, silicone resins, polyimide resins, phenolic resins, and epoxy resins, which can be used alone or as a mixture of a plurality of them. The binder resin is particularly preferably an aromatic polyamide. Since aromatic polyamides have superior strength compared to aliphatic polyamides, when aromatic polyamides are used as the binder resin, an insulating thermally conductive sheet having particularly excellent retention of insulating thermally conductive particles and stability of the sheet shape can be provided.

[0072] (Thermal properties) From the viewpoint of the thermal properties of the insulating thermally conductive sheet, it is preferable that the binder resin has excellent heat resistance and / or flame retardancy, and in particular, the melting point or thermal decomposition temperature of the binder resin is preferably 150° C. or higher.

[0073] 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, further 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.

[0074] 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.

[0075] When used for heat dissipation inside electronic devices for in-vehicle use, the resin material must also have a high heat resistance. In the case of power semiconductors using silicon carbide, heat resistance of about 300°C is required. Therefore, resins that have a heat resistance of 300°C or higher can be suitably used for in-vehicle use, particularly for heat dissipation around power semiconductors. An example of such a resin is aramid resin.

[0076] (thermoplastic resin) From the viewpoint of flexibility and handling, it is particularly preferable that the binder resin contains a thermoplastic resin. An insulating thermally conductive sheet containing a thermoplastic resin does not require heat curing during production, so it has excellent flexibility and can be relatively easily applied inside an electronic device.

[0077] In addition, 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 there is no intention to be limited by theory, when a thermoplastic resin is used as the binder resin, for example, by performing a heat treatment during a roll press treatment in the manufacture of the insulating heat conductive sheet, the thermoplastic resin is softened, and the discharge of air bubbles trapped between the insulating heat conductive particles is further promoted, and as a result, the effect of reducing the voids can be further improved.

[0078] Examples of thermoplastic resins 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, polyarylate (PAR) resin, polyetherimide (PEI) resin, polyethersulfone (PES) resin, polyamideimide (PAI) resin, polyphenylene sulfide (PPS) resin, polyetheretherketone (PEEK) resin, and polybenzoxazole (PBO).

[0079] (aramid resin) In particular, it is preferable that the binder resin contains aramid resin (aromatic polyamide) or is made of aramid resin. When the binder resin contains aramid resin, it is preferable that the binder resin contains 90% or more by volume of aramid resin. When aramid resin is used as the binder resin, an insulating heat conductive sheet having excellent mechanical strength is obtained while being filled with insulating heat conductive particles at a high rate. 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. In contrast, an insulating heat conductive sheet using aramid resin has excellent mechanical strength while being filled with insulating heat conductive particles, particularly boron nitride particles, at a high rate, and as a result, the sheet itself is thin and has excellent low thermal resistance value of the entire sheet. Also, from the viewpoint of thermal properties, it is preferable that the binder resin contains aramid resin or is made of aramid resin. Aramid resin has a relatively high thermal decomposition temperature, and an insulating heat conductive sheet using aramid resin as a binder resin exhibits excellent flame retardancy.

[0080] Aramid resin is a linear polymeric compound in which 60% or more of the amide bonds are directly bonded to aromatic rings. Examples of aramid resins that can be used include polymetaphenylene isophthalamide and its copolymers, and polyparaphenylene terephthalamide and its copolymers, such as copolyparaphenylene 3,4'-diphenyl ether terephthalamide (also known as copolyparaphenylene 3,4'-oxydiphenylene terephthalamide). A single aramid resin may be used, or multiple aramid resins may be mixed together.

[0081] Regarding the binder resin according to the present disclosure, the binder resins contained in the "surface portion" and the "center portion" of the insulating thermally conductive sheet may be the same or different. In order to prevent damage to the sheet caused by differences in the expansion and contraction rates during heating and cooling or water absorption and drying, it is preferable that the binder resins contained in the "surface portion" and the "center portion" of the insulating thermally conductive sheet are the same. In addition, in the insulating thermally conductive sheet 10 of FIG. 1, it is preferable that the two "surface portions" 12 are the same binder resin.

[0082] <Additives> 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. In addition, a fibrous reinforcing material may be contained in order to increase the strength of the sheet. It is preferable to use short fibers of aramid resin as the fibrous reinforcing material, since the heat resistance of the insulating heat conductive sheet is not reduced by the addition of the reinforcing material. The fibrous reinforcing material is preferably added in a range of 0.5 to 25 parts by volume, more preferably 1 to 20 parts by volume, per 100 parts by volume of the insulating heat conductive sheet. 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.

[0083] <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 is low, which is preferable. In addition, since the insulating heat conductive sheet itself is thin, heat dissipation performance can be expressed in the limited space inside the electronic device.

[0084] (use) The insulating thermally conductive sheet according to the present disclosure can be used, for example, to quickly diffuse heat generated in heat-generating components such as semiconductor elements, power sources, and light sources inside electrical appliances to mitigate local temperature increases, or can be used to transport heat to locations away from the heat source.

[0085] Specifically, examples of methods of using the insulating thermally conductive sheet according to the present disclosure include a method of diffusing heat from a heat source (such as a CPU) by attaching the insulating thermally conductive sheet to the side of the heat source, thereby reducing the temperature of the heat source (chip), or a method of reducing a local increase in the temperature of the housing by attaching the insulating thermally conductive sheet to the side of the housing.

[0086] When the insulating thermally conductive sheet is applied to an electronic device, the application method is not particularly limited. For example, the insulating thermally 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, and thus the surface temperature of the heat source can be efficiently reduced. In addition, by placing the insulating thermally conductive sheet between the heat source and an electronic component with low heat resistance, the heat transferred to the electronic component with low heat resistance can be diffused, thereby protecting the electronic component from heat. In addition, by placing the insulating thermally conductive sheet between the heat source and the liquid crystal display, defects of the liquid crystal display due to local heating, such as color unevenness, can be reduced. Furthermore, by placing the insulating thermally conductive sheet between the heat source and the outer surface of the electronic device, the local temperature rise of the outer surface of the electronic device can be reduced, thereby further improving safety for the user, and for example, low-temperature burns can be avoided.

[0087] (Adhesive layer) An adhesive layer and / or a bonding layer may be disposed on one or both surfaces of the insulating heat conductive sheet. In this case, the adhesive layer and the bonding layer may be publicly known. By disposing an adhesive layer and / or a bonding layer on the surface of the insulating heat conductive sheet, it becomes easier to install the insulating heat conductive sheet inside an electronic device, etc.

[0088] (Thermal conductivity in the in-plane direction) The thermal conductivity of the insulating thermally conductive sheet is preferably greater than 60 W / (m·K), greater than 65 W / (m·K), or greater than 70 W / (m·K) in the in-plane direction. Thermal conductivity of greater than 60 W / (m·K) in the in-plane direction is preferable because it can sufficiently diffuse heat generated by electronic devices and makes it difficult for heat spots to occur. The higher the thermal conductivity in the in-plane direction, the more preferable it is, but the thermal conductivity that can usually be achieved is at most 100 W / (m·K) in the in-plane direction.

[0089] The thermal conductivity of the insulating thermally conductive sheet in the in-plane direction 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) It can be calculated as follows.

[0090] The thermal diffusivity can be measured by an AC light method using an AC light method thermal diffusivity measuring device. The specific heat can be determined by a differential scanning calorimeter. The specific gravity can be determined from the outer dimensions and weight of the insulating thermally conductive sheet.

[0091] (Thermal conductivity in the thickness direction) The thermal conductivity of the insulating thermally conductive sheet in the thickness direction is preferably 3.0 W / (m·K), 3.5 W / (m·K) or more, 4.0 W / (m·K), 4.5 W / (m·K), or 5.0 W / (m·K) or more. There is no particular upper limit to the thermal conductivity in the thickness direction, but it may be 10.0 W / (m·K) or less, or 8.0 W / (m·K) or less.

[0092] The thermal conductivity in the thickness direction of the insulating thermally 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) It can be calculated as follows.

[0093] The thermal diffusivity in the thickness direction can be determined by temperature wave analysis (temperature wave phase delay measurement method). The specific heat can be determined by a differential scanning calorimeter. The specific gravity can be determined from the outer dimensions and weight of the insulating thermally conductive sheet.

[0094] 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 produced, for example, by the production method according to the present disclosure described below.

[0095] ≪Manufacturing method≫ The present invention includes a method for producing an insulating thermally conductive sheet, the method comprising the steps of: Providing a laminate having two A layers containing 7.5 vol% or more of a binder resin and less than 92.5 vol% of insulating thermally conductive particles, and a B layer disposed between the two A layers and containing less than 7.5 vol% of a binder resin and 92.5 vol% or more of insulating thermally conductive particles (Providing step); The laminate is roll-pressed (roll-press process). Includes.

[0096] For the binder resin and the insulating thermally conductive particles used in the manufacturing method according to the present disclosure, the above description of the insulating thermally conductive sheet according to the present disclosure can be referred to.

[0097] <Providing process> In the providing step, a laminate having two layers A and a layer B is provided. Fig. 2 shows a schematic cross-sectional view perpendicular to the plane direction of one embodiment of a laminate (laminate 20) used in the manufacturing method of an insulating thermally conductive sheet according to the present disclosure. This laminate 20 has a layer structure in which a layer B 24 is disposed between two layers A 22.

[0098] (A Layer Composition) The two A layers can each independently contain 1 vol.% or more, 5 vol.% or more, 10 vol.% or more, 25 vol.% or more, 50 vol.% or more, or 75 vol.% or more of insulating thermally conductive particles, and / or can contain less than 92.5 vol.%, less than 90 vol.%, or less than 90 vol.% of insulating thermally conductive particles.

[0099] 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 insulating thermally conductive particles. When it is 90% by volume or less, the content of the binder resin in the surface portion of the insulating thermally conductive sheet to be manufactured can be increased, so that the shape retention and mechanical stability of the insulating thermally conductive sheet can be further improved. When it is 50% by volume or more, the thermal conductivity of the insulating thermally conductive sheet to be manufactured is further improved. Furthermore, when it is 50% by volume or more, the thermal dimensional stability of the insulating thermally conductive sheet to be manufactured is further improved.

[0100] The two A layers can each independently contain 7.5% by volume or more, 10% by volume or more, or 12% by volume or more of a binder resin, and / or can contain 99% by volume or less, 90% by volume or less, 75% by volume or less, 50% by volume or less, or 25% by volume or less of a binder resin.

[0101] 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 produced insulating heat conductive sheet is further improved. When it is 50% by volume or less, it is possible to increase the content of the insulating heat conductive particles in the surface portion, which can further improve the thermal conductivity of the insulating heat conductive sheet. Furthermore, the thermal dimensional stability of the insulating heat conductive sheet when heated can be further improved.

[0102] (B layer composition) Layer B may 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 thermally conductive particles, and / or may contain less than 100% by volume, 99% by volume or less, or 98% by volume or less of insulating thermally conductive particles.

[0103] Layer B preferably contains 95% by volume or more and 99% by volume or less of insulating thermally conductive particles. When it is 99% by volume or less, the content of the binder resin in the center portion can be increased, so that the flexibility of the insulating thermally conductive sheet produced can be further improved, and the porosity in the insulating thermally conductive sheet can be reduced. When it is 95% by volume or more, the filling rate of the insulating thermally conductive particles increases, and the contact between the insulating thermally conductive particles is further promoted, so that the thermal conductivity of the insulating thermally conductive sheet produced can be further improved.

[0104] Layer B may contain more than 0 vol%, 0.1 vol% or more, 0.5 vol% or more, 1 vol% or more, or 2 vol% or more of binder resin, and / or may contain less than 7.5 vol%, 5 vol% or less, or 4 vol% or less of binder resin.

[0105] The B layer preferably contains 1% by volume or more and 5% by volume or less of binder resin. When the ratio of the binder resin in the B layer is 1% by volume or more, the shape stability of the insulating heat conductive sheet to be manufactured can be further improved, and the porosity in the insulating heat conductive sheet can be reduced. When the ratio of the binder resin in the B layer is 5% by volume or less, the packing rate of the insulating heat conductive particles can be increased, and the contact between the insulating heat conductive particles can be further promoted, so that the thermal conductivity of the insulating heat conductive sheet to be manufactured can be further improved.

[0106] (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 produced insulating thermally conductive sheet.

[0107] For example, the thicknesses of the two A layers may each independently be 0.5% or more, 1% or more, 2% or more, 5% or more, 7.5% or more, or 10% or more, and / or 35% or less, 30% or less, 25% or less, or 20% or less, of the total thickness of the laminate.

[0108] Also, for example, the thickness of layer B may be 30% or more, 40% or more, 50% or more, or 60% or more of the total thickness of the laminate, and / or 99% or less, 98% or less, 96% or less, 90% or less, 85% or less, or 80% or less.

[0109] The A layer and B layer constituting the laminate may contain other components in addition to the binder resin and the insulating heat conductive particles. Examples of the other components include flame retardants, discoloration inhibitors, surfactants, coupling agents, colorants, viscosity adjusters, 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.

[0110] (Provided) The method for providing the laminate is not particularly limited. For example, a laminate can be obtained by preparing slurries corresponding to the A layer and the B layer, and successively forming and drying the slurries into sheets on a substrate. Alternatively, precursor sheet members corresponding to the A layer and the B layer, respectively, can be formed in advance from the slurries corresponding to the A layer and the B layer, and the precursor sheet members can be stacked to form the laminate.

[0111] One embodiment of the providing step of providing a laminate comprises: (1) preparing slurry A and slurry B; (2) forming the slurry A into a sheet on a substrate such as a glass plate and drying the sheet to form an A layer (a first A layer); (3) forming a layer B on the layer A by forming the slurry B into a sheet and drying it; and (4) Forming a further A layer (a second A layer) on the B layer by forming the slurry A into a sheet and drying it. Includes.

[0112] (Preparation of Slurry) The slurry can be obtained by mixing the insulating thermally conductive particles, the binder resin, and the solvent. For the insulating thermally conductive particles and the binder resin, the contents described above regarding the insulating thermally conductive sheet can be referenced.

[0113] The contents of the insulating thermally 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) can be set so that the contents of the insulating thermally conductive particles and the binder resin in the A layer and the B layer to be produced are the desired values.

[0114] The slurry may optionally contain additives such as flame retardants, anti-tarnish agents, surfactants, coupling agents, colorants, viscosity modifiers, and / or reinforcing materials (fibrous reinforcing materials).

[0115] 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 the 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.

[0116] The solvent may be any solvent capable of dissolving the binder resin. For example, when an aramid resin is used as the binder resin, 1-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, or dimethylsulfoxide may be used.

[0117] To mix the insulating and thermally conductive particles, the binder resin, and the solvent, a general kneading device such as a paint shaker, a bead mill, a planetary mixer, an agitation type disperser, a planetary agitation mixer, a three-roll mill, a kneader, or a single-screw or twin-screw kneader can be used.

[0118] (Formation of Layer A) In one embodiment, the slurry A is formed into a sheet on a substrate and dried to form an A layer (first A layer).

[0119] In order to form the slurry into a sheet, a method of applying the slurry onto a substrate with a coater (applicator) or a known method such as extrusion molding, injection molding, or lamination molding can be used.

[0120] Drying may be performed 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.

[0121] The substrate is not particularly limited, but is preferably one that has excellent releasability when peeling the A layer, the B layer, and / or the laminate from the substrate. The substrate may be, for example, a glass plate, a polyamide film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polyethylene sulfide film, a polyphenylene oxide film, a polytetrafluoroethylene film, or the like.

[0122] (Formation of layer B) In one embodiment, the slurry B is formed into a sheet on the layer A formed as described above, and then dried to form the layer B.

[0123] 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 shaped and dried on the A layer instead of on a substrate.

[0124] (Further formation of layer A) In one embodiment, a further A layer (a second A layer) is formed on the B layer formed as described above by forming the slurry B into a sheet and drying it.

[0125] The further A layer can be formed in the same manner as described above for the A layer (first A layer), except that the slurry is shaped, dried, etc. on the B layer instead of on the substrate.

[0126] (Precursor sheet member) The slurry formed on the substrate can be peeled off from the substrate and optionally further dried to produce a precursor sheet member (corresponding to layer A or layer B) for producing a laminate. In this case, the laminate can be produced by disposing the precursor sheet member corresponding to layer B between the precursor sheet members corresponding to layer A.

[0127] (Washing process) The laminate and / or the precursor sheet member can be optionally washed with water. By performing the washing with water, the residual solvent in the insulating thermally conductive sheet and, if present, salt can be reduced. The washing with water can be performed, for example, by peeling the laminate and / or the precursor sheet member from the substrate at will and immersing it 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 perform the washing with water.

[0128] The shaped slurry has a relatively large number of voids, and is therefore considered to have high water permeability. Therefore, it is considered that the residual solvent and salt can be removed more efficiently by performing a water washing process before the roll press. The moisture content can be reduced by drying after the water washing or by the roll press process.

[0129] <Roll press process> In the roll press step according to the present disclosure, the laminate provided as described above is roll pressed.

[0130] In the conventional method of stacking and heat pressing a plurality of resin sheets containing insulating heat conductive particles, it may not be possible to obtain a sheet having high thermal conductivity, especially when the filling degree of the insulating heat conductive particles is relatively high. Although there is no intention to be limited by theory, it is believed that the conventional method using heat pressing cannot sufficiently reduce the voids caused by the steric hindrance between the highly filled insulating heat conductive particles, and that the contact between the insulating heat conductive particles is insufficient because a relatively large amount of binder resin remains between the insulating heat conductive particles.

[0131] In contrast, in the method according to the present disclosure in which roll pressing is performed on the laminate, sufficient contact is formed between the insulating thermally conductive particles through the discharge of air bubbles to the outside and / or the deformation of the insulating thermally conductive particles (particularly the deformation of the primary particles constituting the insulating particles), and as a result, it is believed that an insulating thermally conductive sheet having high thermal conductivity can be obtained. In addition, in the case of roll pressing, it is believed that the formation of contact between the insulating thermally conductive particles is further promoted by pressing the highly filled insulating thermally conductive particles against each other and / or by promoting the removal of the binder resin present between the insulating thermally conductive particles.

[0132] The roll press may be performed by a known method, for example, a pressure treatment of the laminate may be performed by a calendar roll machine. The pressure applied to the laminate in the roll press process is preferably 400N / cm to 8000N / cm, more preferably 2000N / cm to 7500N / cm, and even more preferably 5000N / cm to 7000N / cm in terms of line pressure. By setting the line pressure to 400N / cm or more, the insulating thermally conductive particles are easily deformed, and the discharge of air bubbles to the outside of the sheet becomes significant. By setting the line pressure to 8000N / cm or less, the insulating thermally conductive particles are sufficiently deformed to a degree that they are not broken, and are densely packed, and the voids in the sheet can be reduced. The diameter of the roll used in the roll press is preferably, for example, 200mm to 1500mm.

[0133] During the roll press treatment, it is preferable to heat the insulating thermally conductive sheet precursor. The heating temperature can be appropriately set depending on the type of binder resin used. When an aramid resin is used as the binder resin, the heating temperature is preferably 100 to 400°C. By setting the heating temperature to 100°C or higher, the binder resin is easily softened, and the effect of filling the gaps between the insulating thermally conductive particles by the roll press treatment is easily obtained. By setting the heating temperature to 400°C or lower, the strength of the binder resin is less likely to decrease due to thermal history. EXAMPLES

[0134] The present invention will now be described in more detail with reference to examples.

[0135] Example 1 and Comparative Examples 1 to 6 In Example 1 and Comparative Examples 1 to 6, measurements were carried out by the following methods.

[0136] (1) Ratio of insulating thermally conductive particles and binder resin (whole sheet) The ratio of the insulating thermally conductive particles and the binder resin in the entire cross section perpendicular to the surface direction of the insulating thermally conductive sheet was determined by observing the cross section perpendicular to the surface direction with a scanning electron microscope (SEM) at 1000x or 3000x magnification so that both main surfaces of the insulating thermally conductive sheet were included in the observation field, and measuring the area ratio of the binder resin and the insulating thermally 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 cut out with a utility knife from the cross-sectional image printed on paper. Note that the measurement was performed in a range including both main surfaces so as not to be biased toward the surface or center of the insulating thermally conductive sheet.

[0137] (2) Ratio of insulating thermally conductive particles and binder resin (surface and center parts) The contents of binder resin and insulating thermally conductive particles in the "surface portion" and "center portion" were determined by observing a cross section perpendicular to the plane direction using an SEM at 1000x or 3000x magnification so that both main surfaces of the insulating thermally conductive sheet were included in the observation field, and measuring the area ratios of the binder resin and insulating thermally conductive particles present in a certain area in the "surface portion" and "center portion" in the obtained cross-sectional images.

[0138] The "surface portion" refers to a portion of the cross section perpendicular to the surface direction of the insulating heat conductive sheet, starting from each of the two main surfaces of the insulating heat conductive sheet and extending along the thickness direction of the insulating heat conductive sheet to 10% of the thickness of the insulating heat conductive sheet. The "center portion" refers to a portion of the cross section perpendicular to the surface direction of the insulating heat conductive sheet, starting from one of the main surfaces of the insulating heat conductive sheet and extending along the thickness direction of the insulating heat conductive sheet to more than 10% to less than 90% of the thickness of the insulating heat conductive sheet.

[0139] (3) Uneven distribution of binder resin on the surface Based on the area ratio of the binder resin and the insulating thermally conductive particles measured as described above, the uneven distribution of the binder resin in the surface portion of the insulating thermally conductive sheet was evaluated. Specifically, when the area ratio of the binder resin to the insulating thermally conductive particles (binder resin / insulating thermally conductive particles) in the surface portion of the insulating thermally conductive sheet was larger than the area ratio of the binder resin to the insulating thermally conductive particles (binder resin / insulating thermally conductive particles) in the center portion of the insulating thermally conductive sheet, it was judged as "uneven distribution", and when not, it was judged as "not uneven distribution".

[0140] (4) Porosity (area%) The cross section perpendicular to the plane direction was observed by SEM at 1000x or 3000x magnification, and the porosity was calculated from the area ratio of voids present in a certain area of ​​the obtained cross-sectional image.

[0141] (5) Thermal conductivity The thermal conductivity of the insulating thermally conductive sheet was calculated by multiplying the thermal diffusivity, specific gravity, and specific heat in both 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 temperature wave analysis. The measurement device used was an ai-Phase mobile M3 type1 manufactured by ai-Phase. The thermal diffusivity in the surface direction was determined by an optical alternating current method. The measurement device used was a LaserPIT manufactured by Advance Riko. 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 thermally conductive sheet.

[0142] (6) Degree of orientation The degree of orientation of boron nitride was evaluated by the peak intensity ratio of transmission X-ray diffraction (XRD, Rigaku NANO-Viewer) with the main surface of the insulating thermal conductive sheet as the measurement surface. The degree of orientation was defined by the following formula using the (002) peak intensity I(002), which corresponds to the c-axis (thickness) direction of the boron nitride crystal, and the (100) peak intensity I(100), which corresponds to the a-axis (plane). (degree of boron nitride orientation)=I(002) / I(100) The lower the orientation value, the more the boron nitride is oriented in the same direction within the sheet surface.

[0143] (7) Average particle size, aspect ratio (i) The average particle size was measured using a laser diffraction / scattering particle size distribution analyzer (MT3000 manufactured by Microtrack Bell Corporation) with a measurement time of 10 seconds and one measurement, and the D50 value in the volume distribution was obtained. (ii) The aspect ratio was determined by measuring the long diameter and thickness of the particles at a magnification of 1500 times using a scanning electron microscope (Hitachi High-Technologies Corporation, TM3000 Model Microscope) and calculating the aspect ratio.

[0144] Example 1 (Preparation of slurry for layer A) In a state in which 300 parts by volume of 1-methyl-2-pyrrolidone (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was dissolved with 14 parts by volume of the aramid resin "Technora" (copolyparaphenylene-3,4'-diphenyl ether terephthalamide, manufactured by Teijin Limited) as a binder resin and 5 parts by volume of anhydrous calcium chloride (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) as a stabilizer for the dissolved resin, 86 parts by volume of plate-shaped boron nitride particles "HSP" (manufactured by Dandong Chemical Engineering Institute Co., average particle size 40 μm, aspect ratio 20-50) as insulating thermally conductive particles were added and mixed by stirring for 30 minutes with a planetary mixer to obtain slurry A.

[0145] (Preparation of slurry for layer B) 210 parts by volume of 1-methyl-2-pyrrolidone, 3 parts by volume of Technora, and 1 part by volume of anhydrous calcium chloride as a stabilizer were dissolved in the mixture, and 97 parts by volume of HSP was added. The mixture was stirred for 30 minutes in a planetary mixer and passed twice through a three-roll mill to obtain slurry B.

[0146] (film formation) Slurry A was applied onto a glass plate using an applicator with a clearance of 0.12 mm, and dried in air at 80°C for 20 minutes to obtain the bottom layer A. Slurry B was applied onto the resulting coating using an applicator with a clearance of 0.62 mm, and dried in air at 80°C for 1 hour to obtain the middle layer B. Slurry A was further applied onto the coating using an applicator with a clearance of 0.12 mm, and dried in air at 80°C for 1 hour to obtain the top layer A.

[0147] (Desalination) The resulting coating film was peeled off from the glass plate in ion-exchanged water, and then immersed in ion-exchanged water for 30 minutes, followed by drying in the air at 120°C for 1 hour.

[0148] (rolling) After desalting, the coating film was passed twice through a roll press at 220°C and a linear pressure of 600 kgf / cm (approximately 5,880 N / cm) to obtain a self-supporting, flexible, insulating, and thermally conductive sheet with a thickness of 87 μm.

[0149] (Thermal Conductivity) The specific gravity of the obtained insulating thermally conductive sheet was 2.09 g / cm 3 , specific heat is 0.85 J / (g K), and in-plane thermal diffusivity is 42.2 mm 2 / s, thermal diffusivity in thickness direction is 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 thermally conductive sheet according to Example 1 is shown in FIG. 3. As can be seen in FIG. 3, it can be confirmed that the insulating thermally conductive sheet according to Example 1 has a relatively large amount of binder resin in both of the two surface portions compared to the central portion. Also, as can be seen in FIG. 3, in the insulating thermally conductive sheet according to Example 1, there was relatively more contact between the insulating thermally conductive particles in the central portion.

[0150] Comparative Example 1 An insulating thermally conductive sheet was produced in the same manner as in Example 1, except that the bottom layer A was not formed and only the middle layer B and the top layer A were formed. However, the coating was torn during the rolling process, and an insulating thermally conductive sheet could not be obtained.

[0151] Comparative Example 2 An insulating thermally conductive sheet was produced in the same manner as in Example 1, except that the top layer A was not formed and only the bottom layer A and the middle layer B were formed. However, the coating film was torn during the rolling process, and an insulating thermally conductive sheet could not be obtained.

[0152] Comparative Example 3 An insulating thermally conductive sheet was produced in the same manner as in Example 1, except that layer A was not formed as the top and bottom layers, and only layer B was formed as the middle layer. However, the coating film broke during the process of peeling it off from the glass plate, and an insulating thermally conductive sheet could not be obtained.

[0153] Comparative Example 4 In a state in which 350 parts by volume of 1-methyl-2-pyrrolidone (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was dissolved with 5 parts by volume of the aramid resin "Technora" (copolyparaphenylene-3,4'-diphenyl ether terephthalamide, manufactured by Teijin Limited) as a binder resin and 2 parts by volume of anhydrous calcium chloride (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) as a stabilizer for the dissolved resin, 95 parts by volume of scaly boron nitride particles "HSL" (manufactured by Dandong Chemical Engineering Institute Co., average particle size 30 μm, aspect ratio 38) as insulating thermally conductive particles were added and mixed by stirring for 10 minutes using a rotation-revolution mixer to obtain a slurry.

[0154] The obtained slurry was applied to a glass plate using a bar coater with a clearance of 0.14 mm, and dried at 115° C. for 20 minutes. After that, it was immersed in ion-exchanged water for 1 hour for desalting, and 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 with a thickness of 100 μm.

[0155] The obtained precursor sheet member was subjected to compression treatment using a calendar roll machine under 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. 4. As can be seen in Fig. 4, in the insulating heat conductive sheet according to Comparative Example 4, there was no uneven distribution of the binder resin in the surface portion compared to the central portion.

[0156] Comparative Example 5 A 27 μm thick insulating heat conductive sheet 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. 5. As can be seen in Fig. 5, in the insulating heat conductive sheet according to Comparative Example 5, no uneven distribution of the binder resin was observed in the surface portion compared to the center portion.

[0157] Comparative Example 6 In a state in which 10 parts by volume of the aramid resin "Technora" as a binder resin and 2 parts by volume of anhydrous calcium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a stabilizer for the dissolved resin were dissolved in 450 parts by volume of 1-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.), 90 parts by volume of scaly boron nitride particles "PT110" (manufactured by Momentive, average particle size 45 μm, aspect ratio 35) as insulating thermally conductive particles were added, and the mixture was mixed by stirring for 60 minutes with a three-one motor stirrer while heating to 80°C, to obtain a uniform slurry.

[0158] The obtained slurry was applied to a glass plate using a bar coater with a clearance of 0.28 mm to form a sheet, and dried at 70 ° C. for 1 hour. The formed slurry was then peeled off from the glass plate in water, and 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 a compression treatment using a calendar roll machine under conditions of a temperature of 270 ° C. and a linear pressure of 4000 N / cm to obtain an insulating 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. 6. 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 in the surface portion compared to the central portion.

[0159] [Table 1]

[0160] Evaluation As seen in Table 1, the laminate used in the manufacture of the insulating thermally conductive sheet of Example 1 has a configuration (layer configuration = A / B / A) in which an A layer having a volume ratio of binder resin to insulating thermally conductive particles of 86:14 is disposed on each of the two main surfaces of a B layer having a volume ratio of binder resin to insulating thermally conductive particles of 97:3, and good moldability into a sheet was confirmed during the manufacturing process. In contrast, in Comparative Examples 1 and 2, which used laminates having an A layer on only one main surface of the B layer, and Comparative Example 3, which used only the B layer, it was not possible to mold a sheet.

[0161] As can be seen from Table 1, the insulating thermally conductive sheet produced in Example 1 had 2.1% by area of ​​binder resin and 97.9% by area of ​​insulating thermally conductive particles in the entire cross section perpendicular to the surface direction, and the binder resin was unevenly distributed on the surface portion. The insulating thermally conductive sheet of Example 1 showed high thermal conductivity in the surface direction and thickness direction compared to Comparative Examples 4 to 6.

[0162] In particular, the content of the insulating thermally conductive particles in the insulating thermally conductive sheet of Example 1 was equivalent to that of Comparative Example 4, and although the porosity was relatively high, Example 1 exhibited higher thermal conductivity than this example.

[0163] Although there is no intention to be limited by theory, it is believed that in Comparative Examples 4 to 6, the binder resin is uniformly distributed in the sheet, so that the binder resin is present among the insulating thermally conductive particles throughout the entire sheet, and as a result, the advantage of high packing of the insulating thermally conductive particles cannot be fully utilized. In contrast, in the insulating thermally conductive sheet of Example 1, the binder resin is unevenly distributed in the surface portion, so that direct contact between the insulating thermally conductive particles in the center portion of the sheet is increased, and as a result, the thermal conductivity of the entire insulating thermally conductive sheet is improved. [Explanation of symbols]

[0164] 10. Insulating and heat-conducting sheet 12 Surface portion of insulating thermal conductive sheet 14 Center part of insulating thermal conductive sheet 20 Laminate 22 A layer 24 B layer D Thickness direction S plane direction

Claims

1. An insulating and thermally conductive sheet containing insulating and thermally conductive particles and a binder resin, With respect to an entire cross section perpendicular to a plane direction, when the total area of ​​the insulating thermally conductive particles and the binder resin is taken as 100 area %, the insulating thermally conductive particles account for 90 to 99 area % and the binder resin accounts for 1 to 10 area %, In a cross section perpendicular to the plane direction, an area ratio of the binder resin to the insulating thermally conductive particles in a surface portion of the insulating thermally conductive sheet is larger than an area ratio of the binder resin to the insulating thermally conductive particles in a central portion of the insulating thermally conductive sheet, and The insulating and thermally conductive particles include deformed flat insulating and thermally conductive particles. Insulating thermal conductive sheet.

2. An insulating thermally conductive material having two A layers containing 7.5 volume % or more of binder resin and less than 92.5 volume % of insulating thermally conductive particles, and a B layer disposed between the two A layers and containing less than 7.5 volume % of binder resin and 92.5 volume % or more of insulating thermally conductive particles, The thickness of one of the two A layers, the thickness of the B layer, and the thickness of the other of the two A layers are 10 to 20%, 60 to 80%, and 10 to 20%, respectively, relative to the thickness of the insulating thermally conductive sheet; The insulating and thermally conductive sheet according to claim 1 .

3. The insulating and thermally conductive sheet according to claim 1 or 2, wherein the binder resin is an aramid resin.

4. The insulating thermally conductive sheet according to any one of claims 1 to 3, wherein the insulating thermally conductive particles are boron nitride particles.

5. The insulating thermally conductive sheet according to any one of claims 1 to 4, having a thermal conductivity of more than 60 W / (m · K) in an in-plane direction.

6. The insulating thermally conductive sheet according to any one of claims 1 to 5, having a thermal conductivity of 3.0 W / (m · K) or more in the thickness direction.

7. The insulating thermally conductive sheet according to any one of claims 1 to 6, having voids of more than 10% by area over the entire cross section perpendicular to the plane direction.

8. A method for producing an insulating thermally conductive sheet containing insulating thermally conductive particles and a binder resin, comprising: The insulating and thermally conductive sheet is With respect to an entire cross section perpendicular to the plane direction, when the total area of ​​the insulating thermally conductive particles and the binder resin is taken as 100 area %, the insulating thermally conductive particles account for 90 to 99 area % and the binder resin accounts for 1 to 10 area %, and In a cross section perpendicular to the plane direction, an area ratio of the binder resin to the insulating thermally conductive particles in a surface portion of the insulating thermally conductive sheet is larger than an area ratio of the binder resin to the insulating thermally conductive particles in a central portion of the insulating thermally conductive sheet; The method comprises: Providing a laminate having two A layers containing 7.5 vol. % or more of a binder resin and less than 92.5 vol. % of insulating thermally conductive particles, and a B layer disposed between the two A layers and containing less than 7.5 vol. % of a binder resin and 92.5 vol. % or more of insulating thermally conductive particles; roll pressing the laminate; A method comprising:

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