Thermally conductive sheet

Abstract

To provide a thermally conductive sheet excellent in both flexibility and thermal conductivity.SOLUTION: A thermally conductive sheet comprising a matrix and a thermally conductive filler, wherein the thermally conductive filler comprises a scaly thermally conductive filler, and the scaly thermally conductive filler has a cumulative frequency of a particle size of 100 μm or more in image particle size distribution measurement of 6.6% or more and 40% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive sheet. [Background technology]

[0002] In electronic devices such as computers, automobile parts, and mobile phones, heat sinks and other heat dissipators are commonly used to dissipate heat generated by heat-generating elements such as semiconductor devices and mechanical parts. It is known that a thermally conductive sheet is placed between the heat generating element and the heat dissipating element to improve the efficiency of heat transfer to the heat dissipating element. Thermally conductive sheets are generally compressed when placed inside electronic devices, requiring high flexibility. A thermally conductive sheet generally contains a polymer matrix and a thermally conductive filler dispersed in the polymer matrix. In some thermally conductive sheets, the anisotropic filler, which has an anisotropic shape, is oriented in one direction to enhance thermal conductivity in a specific direction.

[0003] For example, Patent Document 1 discloses a thermally conductive sheet containing a silicone resin and an anisotropic filler that is oriented in the thickness direction of the sheet. Furthermore, Patent Document 2 discloses that in a thermally conductive sheet including a matrix composed of an organopolysiloxane having a crosslinked structure and a thermally conductive filler including graphitized carbon fibers dispersed in the matrix, the thermally conductive filler is oriented in the thickness direction of the thermally conductive sheet by applying a magnetic field.

[0004] Patent Document 3 discloses a thermally conductive sheet formed by laminating a carbon fiber oriented thermally conductive layer containing carbon fiber powder in a polymer matrix with the fiber axes oriented in the thickness direction of the sheet, and an insulating thermally conductive layer having thermal conductivity and insulation properties, in which an insulating thermally conductive filler is dispersed in a polymer matrix. Patent Document 4 discloses that in a thermally conductive sheet having a plurality of unit layers each containing a silicone resin and a thermally conductive filler, the anisotropic filler contained as the thermally conductive filler is oriented in the thickness direction of the sheet. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6844806 [Patent Document 2] Patent No. 6613462 [Patent Document 3] Patent No. 6723610 [Patent Document 4] Patent No. 6978148 Summary of the Invention [Problem to be solved by the invention]

[0006] However, although conventional thermally conductive sheets have excellent flexibility, further improvement in thermal conductivity is desired.

[0007] Therefore, an object of the present invention is to provide a thermally conductive sheet that is excellent in both flexibility and thermal conductivity. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by including a scaly thermally conductive filler as the thermally conductive filler in a thermally conductive sheet containing a matrix and a thermally conductive filler, and by adjusting the cumulative frequency of scaly thermally conductive filler having a particle size of 100 μm or more in an image particle size distribution measurement to fall within a certain range. That is, the present invention provides the following [1] to [7].

[0009] [1] A thermally conductive sheet comprising a matrix and a thermally conductive filler, wherein the thermally conductive filler comprises a flaky thermally conductive filler, and the flaky thermally conductive filler has a cumulative frequency of particles having a particle size of 100 μm or more in an image particle size distribution measurement of 6.6% or more and 40% or less. [2] The thermally conductive sheet according to [1], wherein the matrix is ​​a silicone resin. [3] The thermally conductive sheet according to [1] or [2], wherein the average particle size of the scaly thermally conductive filler is 55 μm or more and 90 μm or less as measured by image particle size distribution measurement. [4] The thermally conductive sheet according to any one of [1] to [3], wherein the flaky thermally conductive filler is flaky boron nitride. [5] The thermally conductive sheet according to any one of [1] to [4], wherein the scaly thermally conductive filler contains boron nitride having at least two different average particle sizes. [6] The thermally conductive sheet according to any one of [1] to [5], wherein the thermally conductive filler further contains a non-anisotropic filler. [7] The thermally conductive sheet according to any one of [1] to [6], wherein the major axes of the scaly thermally conductive filler are oriented in the thickness direction of the thermally conductive sheet. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a thermally conductive sheet that is excellent in both flexibility and thermal conductivity. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic cross-sectional view showing an example of a thermally conductive sheet. [Figure 2] FIG. 1 is a schematic diagram showing a dispenser device. [Figure 3] FIG. 2 is a schematic diagram illustrating step (1-2) in the first method for producing a thermally conductive sheet. [Figure 4] FIG. 3 is a schematic diagram illustrating step (1-5) in the first method for producing a thermally conductive sheet. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Thermal conductive sheet] The thermally conductive sheet of the present invention comprises a matrix and a thermally conductive filler. Each component will be described in detail below.

[0013] (Thermal conductive filler) The thermally conductive sheet of the present invention contains a scaly thermally conductive filler as the thermally conductive filler, and the cumulative frequency of the scaly thermally conductive filler having a particle size of 100 μm or more in an image particle size distribution measurement is 6.6% to 40%. If the cumulative frequency is less than 6.6%, the scaly thermally conductive filler may not form sufficient heat conduction paths, resulting in insufficient thermal conductivity of the thermally conductive sheet. If the cumulative frequency exceeds 40%, the scaly thermally conductive filler with large particle sizes may impair the flexibility of the thermally conductive sheet. From these perspectives, the cumulative frequency is preferably 6.6% to 37%, more preferably 7% to 30%.

[0014] The scaly thermally conductive filler preferably has an average particle size of 55 μm to 90 μm, more preferably 56 μm to 89 μm, and even more preferably 60 μm to 85 μm, as measured by image particle size distribution measurement. When the average particle size is equal to or greater than the lower limit, the thermal conductivity of the thermally conductive sheet is likely to be improved. When the average particle size is equal to or less than the upper limit, the flexibility of the thermally conductive sheet is likely to be improved. The cumulative frequency of particles with a particle size of 100 μm or more and the average particle size described above are measured for all of the scaly thermally conductive fillers contained in the thermally conductive sheet. Details of the image particle size distribution measurement are as described in the Examples. The particle size referred to above refers to the length in the major axis direction, and the average particle size is its arithmetic mean.

[0015] The scaly thermally conductive filler is contained in the thermally conductive sheet as an anisotropic filler, and the major axis of the filler is preferably oriented in the thickness direction of the thermally conductive sheet, thereby improving the heat dissipation properties of the thermally conductive sheet. Examples of scaly thermally conductive fillers include scaly carbon powder, scaly silicon carbide powder, scaly aluminum nitride powder, scaly boron nitride, scaly aluminum oxide powder, etc. Among these, from the viewpoint of thermal conductivity, it is preferable to include at least one selected from scaly graphite powder and scaly boron nitride powder, and it is more preferable to include scaly boron nitride. In flake graphite powder, the crystal planes of graphite are aligned in the in-plane direction of the flake surfaces, and the flake surfaces have high thermal conductivity in the in-plane direction. Therefore, by aligning the flake surfaces in a specific direction, the thermal conductivity in a specific direction can be increased. Preferably, the flake graphite powder has a high degree of graphitization.

[0016] The scaly thermally conductive filler may be used alone or in combination of two or more types. However, it is preferable that the scaly thermally conductive filler contains at least two types of boron nitride having different average particle sizes. By adopting such a blending method for the scaly thermally conductive filler, the cumulative frequency can be adjusted to a certain range, making it easier to improve the flexibility and thermal conductivity of the thermally conductive sheet. Here, the two different average particle sizes preferably differ from each other by at least 2 μm, more preferably by at least 3 μm, and even more preferably by at least 10 μm. Furthermore, the two different average particle sizes preferably differ from each other by at most 50 μm, more preferably by at most 30 μm. When the difference between the two different average particle sizes is 50 μm or less, it becomes easier to prevent the viscosity of the curable silicone composition from becoming excessively high due to the influence of the large particle size of the scaly filler before the curable silicone composition is cured. A specific example of the combined use of two types of thermally conductive fillers with different average particle sizes is shown below. For example, a scaly thermally conductive filler with an average particle size of approximately 50 μm or less can be used in combination with a scaly thermally conductive filler with an average particle size of 65 μm or more. A scaly thermally conductive filler with an average particle size of approximately 50 μm or less contains almost no components with a particle size of 100 μm or more. Therefore, by combining a scaly thermally conductive filler with a particle size of 65 μm or more that contains many components with a particle size of 100 μm or more, it is easy to adjust the cumulative frequency of particles with a particle size of 100 μm or more to 6.6% or more and 40% or less when considering the overall formulation after the above combination. When two types of thermally conductive fillers with different average particle sizes are used in combination to increase the cumulative frequency of thermally conductive fillers with particle sizes of 100 μm or more, it is preferable to use the large-particle-size, flaky thermally conductive filler with the larger average particle size, or to increase the content of the large-particle-size, flaky thermally conductive filler of the two types.

[0017] The aspect ratio of the scaly thermally conductive filler is not particularly limited as long as it exceeds 2, but is preferably 5 or more. When the aspect ratio is equal to or greater than the above-mentioned lower limit, the thermal conductivity in the thickness direction is likely to be improved. In addition, the aspect ratio of the scaly thermally conductive filler is practically, for example, 100 or less. The aspect ratio of the scaly thermally conductive filler means the length of the major axis / thickness.

[0018] Furthermore, although there are no particular limitations on the thermal conductivity of the scaly thermally conductive filler, the thermal conductivity along the longitudinal direction is generally 30 W / m K or more, and preferably 100 W / m K or more. There are no particular limitations on the upper limit of the thermal conductivity of the scaly thermally conductive filler, but it is, for example, 2000 W / m K or less. The thermal conductivity of the scaly thermally conductive filler can be measured by the laser flash method. Furthermore, the scaly thermally conductive filler may be conductive or insulating. If the scaly thermally conductive filler has insulating properties, the insulating properties in the thickness direction of the thermally conductive sheet can be improved, making it suitable for use in electrical devices. In the present invention, being conductive means, for example, a filler having a volume resistivity of 1×10 9Ω·cm or less. Also, having insulating properties means that the volume resistivity is, for example, 1×10 9 This refers to a case where the resistance exceeds Ω·cm.

[0019] The content of the scaly thermally conductive filler in the thermally conductive sheet is preferably 3 to 250 parts by mass, more preferably 5 to 200 parts by mass, and even more preferably 10 to 170 parts by mass, per 100 parts by mass of the matrix. By setting the content of the scaly thermally conductive filler to at least the above-mentioned lower limit, thermal conductivity is likely to be improved, while by setting the content of the scaly thermally conductive filler to at most the above-mentioned upper limit, flexibility is likely to be improved. Furthermore, the content of the scaly thermally conductive filler, in terms of volume-based filling rate (volume filling rate), is preferably 5 to 45% by volume, more preferably 10 to 35% by volume, and even more preferably 15 to 30% by volume, relative to the total amount of the thermally conductive sheet.

[0020] The thermally conductive sheet preferably further contains a non-anisotropic filler, which allows a thermally conductive filler to be appropriately interposed between the flake-like thermally conductive fillers, thereby further improving the thermal conductivity. A non-anisotropic filler is a filler that has substantially no anisotropy in shape, and is a filler that does not orient in a predetermined direction even in an environment in which a scaly thermally conductive filler would orient in that direction, such as under the action of shear force described below.

[0021] The aspect ratio of the non-anisotropic filler is preferably 2 or less, more preferably 1.5 or less. By setting the aspect ratio to 2 or less, an increase in the viscosity of the thermally conductive composition described below can be prevented, enabling high loading. The aspect ratio of the non-anisotropic filler can be determined by the major axis / minor axis ratio of the non-anisotropic filler.

[0022] The non-anisotropic filler may be conductive, but is preferably insulating, and in the thermally conductive sheet, the fillers (i.e., the scaly thermally conductive filler and the non-anisotropic filler) to be blended are preferably insulating. If these are insulating, it becomes easier to improve the insulation in the thickness direction of the thermally conductive sheet.

[0023] Examples of non-anisotropic fillers include metals, metal oxides, metal nitrides, metal hydroxides, carbon materials, oxides, nitrides, carbides, etc. The shape of the non-anisotropic filler may be spherical or irregular powder. In the non-anisotropic filler, examples of metals include aluminum, copper, nickel, etc.; examples of metal oxides include aluminum oxide, such as alumina, magnesium oxide, and zinc oxide; and examples of metal nitrides include aluminum nitride. Examples of metal hydroxides include aluminum hydroxide. Furthermore, examples of carbon materials include spherical graphite. Examples of oxides, nitrides, and carbides other than metals include quartz, boron nitride, and silicon carbide. Among the above, examples of non-anisotropic fillers having insulating properties include metal oxides, metal nitrides, metal hydroxides, and metal carbides. Among the above-mentioned non-anisotropic fillers, aluminum oxide, aluminum nitride, and aluminum hydroxide are preferred, with aluminum oxide and aluminum hydroxide being preferred because they have high thermal conductivity and are readily available in spherical form, and aluminum hydroxide being preferred because it is readily available and can enhance the flame retardancy of the thermally conductive sheet. Of these, aluminum oxide is more preferred.

[0024] The average particle size of the non-anisotropic filler is preferably 0.1 to 50 μm, more preferably 0.5 to 35 μm, and particularly preferably 1 to 20 μm. By setting the average particle size to 50 μm or less, problems such as disturbance of the orientation of the scaly thermally conductive filler are less likely to occur. Furthermore, by setting the average particle size to 0.1 μm or more, the specific surface area of ​​the non-anisotropic filler does not become larger than necessary, and even if a large amount is added, the viscosity of the thermally conductive composition is less likely to increase, making it easier to fill a large amount of the non-anisotropic filler. The average particle size of the non-anisotropic filler can be measured using a laser diffraction particle size distribution analyzer. The particle size when the cumulative volume is 50% (D50) is used as the average particle size. The non-anisotropic filler may be used alone or in combination of two or more. When two or more types of each filler are used, the average particle size of each filler is calculated without distinguishing between them.

[0025] The content of the non-anisotropic filler in the thermally conductive sheet is preferably in the range of 50 to 1500 parts by mass, more preferably in the range of 200 to 800 parts by mass, and even more preferably in the range of 250 to 550 parts by mass, per 100 parts by mass of the matrix. By setting the content of the non-anisotropic filler at or above the above-mentioned lower limit, the amount of non-anisotropic filler present in the gaps between the scaly thermally conductive filler is at or above a certain amount, resulting in good thermal conductivity. On the other hand, by setting the content of the non-anisotropic filler at or below the above-mentioned upper limit, the effect of increasing thermal conductivity according to the content can be obtained, and the non-anisotropic filler does not inhibit thermal conduction by the scaly thermally conductive filler. The content of the non-anisotropic filler, expressed in volume %, is preferably 20 to 60% by volume, more preferably 35 to 55% by volume, and even more preferably 40 to 50% by volume, relative to the total volume of the thermally conductive sheet.

[0026] In the above explanation, the thermally conductive filler contained in the thermally conductive sheet of the present invention has been described as a scaly thermally conductive filler and a non-anisotropic filler, but the thermally conductive sheet of the present invention may also contain an anisotropic filler other than the above-mentioned scaly thermally conductive filler. Examples of anisotropic fillers other than the scaly thermally conductive filler include fibrous thermally conductive fillers.

[0027] (matrix) The matrix used in the thermally conductive sheet is a polymeric compound such as elastomer or rubber, preferably formed by curing a liquid polymeric composition (curable polymeric composition) consisting of a mixture of a base resin and a curing agent. The curable polymeric composition may be, for example, one consisting of uncrosslinked rubber and a crosslinking agent, or one containing a monomer, prepolymer, or the like and a curing agent. The curing reaction may be either room temperature curing or heat curing.

[0028] Various synthetic rubbers can be used as rubber, including acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, styrene-butadiene rubber, butadiene rubber, fluororubber, butyl rubber, and silicone resin. When using these rubbers, the synthetic rubbers may be crosslinked or left uncrosslinked (i.e., uncured) in the thermally conductive sheet. Uncrosslinked rubbers are primarily used for flow orientation. Furthermore, when crosslinking (i.e., curing) is performed, as explained above, the matrix may be a cured curable polymer composition comprising an uncrosslinked synthetic rubber and a crosslinking agent. The elastomer may be a thermoplastic elastomer such as a polyester thermoplastic elastomer or a polyurethane thermoplastic elastomer, or a thermosetting elastomer formed by curing a liquid polymer composition containing a base agent and a curing agent, such as a polyurethane elastomer formed by curing a polymer composition containing a hydroxyl group-containing polymer and an isocyanate. Among the above, it is preferable to use silicone resin, for example, because the matrix after curing is particularly flexible and the thermally conductive filler has good filling properties.

[0029] The polymer composition for forming the matrix may be composed of a polymer compound alone, or may be composed of a polymer compound and a plasticizer. Plasticizers are preferably used when synthetic rubber is used, and the inclusion of a plasticizer can increase the flexibility of the matrix when not crosslinked. The content of the matrix, expressed as a volume-based filling rate (volume filling rate), is preferably 10 to 45% by volume, more preferably 15 to 35% by volume, and even more preferably 20 to 30% by volume, based on the total volume of the thermally conductive sheet. When a plasticizer is used, the amount of the plasticizer relative to the total amount of the thermally conductive sheet is preferably 1 to 20% by volume, more preferably 3 to 15% by volume, and even more preferably 5 to 10% by volume.

[0030] (silicone resin) The silicone resin is not particularly limited as long as it is an organopolysiloxane, but preferably includes a curable silicone resin. The curable silicone resin is obtained by curing a curable silicone composition. The curable silicone resin may be of an addition reaction type, or may be other types. When the curable silicone resin is of an addition reaction type, the curable silicone composition for obtaining the curable silicone resin preferably comprises a silicone compound as a main component and a curing agent that cures the main component.

[0031] The silicone compound used as the base agent is preferably an alkenyl group-containing organopolysiloxane.Specific examples of the alkenyl group-containing organopolysiloxane include organopolysiloxanes having vinyl groups at both ends, such as polydimethylsiloxane having vinyl groups at both ends, polyphenylmethylsiloxane having vinyl groups at both ends, dimethylsiloxane-diphenylsiloxane copolymer having vinyl groups at both ends, dimethylsiloxane-phenylmethylsiloxane copolymer having vinyl groups at both ends, and dimethylsiloxane-diethylsiloxane copolymer having vinyl groups at both ends. The curing agent is not particularly limited as long as it can cure the silicone compound that is the main component, but organohydrogenpolysiloxane, which is an organopolysiloxane having two or more hydrosilyl groups (SiH), is preferred. The hardness of the thermally conductive sheet can be adjusted by appropriately adjusting the ratio of the curing agent to the base resin. Specifically, the hardness of the thermally conductive sheet can be reduced by reducing the ratio of the curing agent to the base resin.

[0032] The silicone resin may also contain silicone oil. When silicone oil is contained, it is preferable that the silicone resin contains silicone oil in addition to the above-mentioned curable silicone resin. Examples of silicone oil include straight silicone oils such as dimethyl silicone oil and phenylmethyl silicone oil, as well as non-reactive modified silicone oils in which a non-reactive organic group is introduced into a main chain having a polysiloxane structure, a side chain bonded to the main chain, or the end of the main chain. A non-reactive organic group is an organic group that does not have an addition reaction group. Examples of non-reactive modified silicone oils include polyether-modified silicone oil, aralkyl-modified silicone oil, fluoroalkyl-modified silicone oil, long-chain alkyl-modified silicone oil, higher fatty acid ester-modified silicone oil, higher fatty acid amide-modified silicone oil, and phenyl-modified silicone oil. Among the above, straight silicone oil is preferred as the silicone oil, and among straight silicone oils, dimethyl silicone oil is more preferred.

[0033] The content of the silicone resin, expressed in volume % (filling rate), is preferably 10 to 45 volume %, more preferably 15 to 35 volume %, and even more preferably 20 to 30 volume %, relative to the total volume of the thermally conductive sheet. The amount of silicone oil relative to the total amount of the thermally conductive sheet is preferably 1 to 20% by volume, more preferably 3 to 15% by volume, and even more preferably 5 to 10% by volume.

[0034] (Additional ingredients) Various additives may be further blended into the matrix as long as they do not impair the function of the thermally conductive sheet. Examples of additives include at least one selected from dispersants, coupling agents, adhesives, flame retardants, antioxidants, colorants, anti-settling agents, etc. For example, when curing the curable silicone composition as described above, a curing catalyst that accelerates curing may be blended as an additive. Examples of curing catalysts include platinum-based catalysts.

[0035] (thermal conductivity) The thermal conductivity of the thermally conductive sheet in the thickness direction is, for example, 5 W / (m·K) or more, preferably 10 W / (m·K) or more, more preferably 10.2 W / (m·K) or more, and even more preferably 11 W / (m·K) or more. By setting the thermal conductivity to the above lower limit or higher, the thermal conductivity of the thermally conductive sheet in the thickness direction can be made excellent. There is no particular upper limit, but the thermal conductivity of the thermally conductive sheet in the thickness direction is, for example, 50 W / (m·K) or less. The thermal conductivity is measured according to a method in accordance with ASTM D5470-06.

[0036] (Piercing load) The piercing load of the thermally conductive composition is preferably 25 gF or less, more preferably 22 gF or less, and even more preferably 20 gF or less. Having a piercing load below the upper limit ensures flexibility after curing, and, for example, improves conformability to heat generating bodies and heat dissipating bodies, making it easier to achieve good heat dissipation. The piercing load of the thermally conductive sheet is not particularly limited, but is, for example, 5 gF or more, preferably 8 gF or more. The piercing load is measured by the method described in the Examples below.

[0037] (Thickness) The thickness of the thermally conductive sheet is changed as appropriate depending on the shape and application of the electronic device it is to be mounted in. The thickness of the thermally conductive sheet is not particularly limited, but is preferably in the range of 0.1 to 5 mm, for example. Furthermore, as will be described later, when the thermally conductive sheet is composed of a laminate of unit layers, the thickness of each unit layer is not particularly limited, but is preferably 0.1 to 8.5 mm, more preferably 0.5 to 6 mm. The thickness of the unit layer is the length of the unit layer along the stacking direction of the unit layers.

[0038] An example of a thermally conductive sheet is shown in FIG. 1. In FIG. 1, a thermally conductive sheet 10 includes a plurality of unit layers 13, each containing a matrix 11 and a thermally conductive filler. The plurality of unit layers 13 are stacked along a direction x, with adjacent unit layers 13 bonded to each other. In each unit layer 13, the matrix serves as a matrix resin that holds the thermally conductive filler, and the matrix 11 is formulated so that the thermally conductive filler is dispersed therein. The matrix 11 is preferably made of a silicone resin, and more preferably contains the cured curable silicone composition described above. The direction x in which the unit layers 13 are stacked is perpendicular to the thickness direction z of the thermally conductive sheet and is a direction along the surface direction.

[0039] The thermally conductive sheet 10 shown in FIG. 1 contains an anisotropic filler 14 and a non-anisotropic filler 15 as thermally conductive fillers in each unit layer 13. The anisotropic filler 14 is oriented in the thickness direction z of the sheet-like thermally conductive sheet 10. That is, the anisotropic filler 14 is oriented in one direction along the surface direction of each unit layer 13. By including the anisotropic filler 14 oriented in the thickness direction z, the thermally conductive sheet 10 has improved thermal conductivity in the thickness direction. Furthermore, by including the non-anisotropic filler 15 in the thermally conductive sheet 10, the thermal conductivity can be further improved. However, the thermally conductive sheet 10 does not necessarily need to contain the non-anisotropic filler 15 .

[0040] The thermally conductive sheet 10 preferably has the anisotropic filler 14 exposed on both sides 10A and 10B in the thickness direction z. The exposed anisotropic filler 14 may protrude from each of the two sides 10A and 10B. By exposing the anisotropic filler 14 on both sides 10A and 10B of the thermally conductive sheet 10, both sides 10A and 10B become non-adhesive surfaces. Note that, as described below, when the thermally conductive sheet is cut with, for example, a blade, both sides 10A and 10B become cut surfaces, and the anisotropic filler 14 is exposed on both sides 10A and 10B. However, either one or both of the two sides 10A and 10B may be an adhesive surface without exposing the anisotropic filler 14. The thermally conductive sheet illustrated in FIG. 1 can be manufactured by, for example, either the first or third manufacturing method described below. However, the configuration of the thermally conductive sheet of the present invention is not limited to the above, and may be, for example, a thermally conductive sheet that does not include unit layers and is made of a single layer that is not a laminate.

[0041] (Method for manufacturing thermally conductive sheets) <First manufacturing method> The thermally conductive sheet of the present invention is not particularly limited, but may be produced, for example, by preparing an oriented molded body from a thermally conductive composition containing a curable silicone composition and a scaly thermally conductive filler, in which the scaly thermally conductive filler is oriented in one direction, appropriately curing the oriented molded body, and then cutting the oriented molded body. More specifically, the method for producing the thermally conductive sheet is preferably a first production method including the following steps (1-1) to (1-5): In the first production method, it is preferable to carry out steps (1-1) to (1-5) in this order. Step (1-1): A step of preparing a thermally conductive composition containing a curable silicone composition and a scaly thermally conductive filler Step (1-2): A step of obtaining a laminate by discharging the thermally conductive composition obtained in step (1-1) into a sheet shape using a dispenser device so that multiple overlapping sheets are formed. Step (1-3): Step of compressing the obtained laminate in the lamination direction Step (1-4): Step of curing the thermally conductive composition Step (1-5): Cutting the laminate along a direction intersecting the laminate surface

[0042] <Process (1-1)> In step (1-1), a thermally conductive composition is prepared by mixing at least a curable silicone composition, which is a raw material for a curable silicone resin, with a scaly thermally conductive filler. In addition to the above components, the thermally conductive composition may contain at least one of an anisotropic filler other than the scaly thermally conductive filler, a non-anisotropic filler, silicone oil, and an additive. The components constituting the thermally conductive composition may be mixed using, for example, a known kneader, kneading roll, or mixer. Furthermore, in the first manufacturing method, the anisotropic filler such as the scaly thermally conductive filler is oriented in the discharge direction in the step (1-2), and therefore the thermal conductivity of the thermally conductive sheet in one direction can be increased.

[0043] The thermally conductive composition prepared in step (1-1) is not particularly limited, but preferably has a piercing load of 5 to 25 gF at a piercing speed of 10 mm / min. If the piercing load is 5 gF or more, when multiple sheet-shaped thermally conductive compositions dispensed from a dispenser are stacked, the thermally conductive composition does not spread under its own weight, preventing problems such as the inability to obtain a laminate having a certain thickness or disturbance of orientation. Furthermore, a piercing load of 25 gF or less allows the thermally conductive composition to be dispensed from the dispenser. Furthermore, a piercing load of 25 gF or less makes the thermally conductive sheet flexible after curing. To further suppress spreading under its own weight, the piercing load is preferably 8 gF or more. Furthermore, to improve the dischargeability from the dispenser, the piercing load is preferably 22 gF or less, more preferably 20 gF or less. The piercing load is measured using a piercing rod with a diameter of 3 mm.

[0044] When the curable silicone composition is composed of a base agent and a curing agent for curing the base agent, step (1-1) may include preparing a first liquid containing at least a scaly thermally conductive filler blended with the base agent, and a second liquid containing at least a scaly thermally conductive filler blended with the curing agent. In addition to the scaly thermally conductive filler, the first and second liquids may also contain at least one of an anisotropic filler other than the scaly thermally conductive filler, a non-anisotropic filler, silicone oil, and an additive. The first and second liquids may be mixed and stored in a tank, as described below, or may be stored in separate tanks and mixed immediately before step (1-2). The thermally conductive composition may contain an organic solvent as needed to adjust the piercing load to the above range, but it is preferable not to contain an organic solvent.

[0045] Curable silicone compositions are typically liquids, and flexibility can be imparted to the thermally conductive sheet by appropriately adjusting the molecular weight of each component (such as the alkenyl-group-containing organopolysiloxane and organohydrogenpolysiloxane) that makes up the curable silicone composition. Furthermore, while an organic solvent may be blended into the thermally conductive composition as needed to adjust the viscosity to the above range, it is preferable not to blend an organic solvent. The same applies to the second and third production methods described below.

[0046] <Process (1-2)> The thermally conductive composition obtained in step (1-1) may be filled into a tank 56 (see FIG. 2) of a dispenser device 50. Then, by driving a pump (not shown), the thermally conductive composition in a pressurized state is supplied to a head 51 via a supply path 52, and the thermally conductive composition R is discharged to the outside from a discharge port 53, as shown in FIG. 3(A). At this time, as shown in FIG. 3(A), by moving a table 57 in one direction MD (also referred to as the "forward direction") while the thermally conductive composition R is being discharged, the thermally conductive composition R is discharged in a sheet form onto the table 57. In this specification, the direction in which the thermally conductive composition is discharged is referred to as MD (Machine Direction), and the horizontal direction is referred to as TD (Transverse Direction). MD is the direction perpendicular to TD. Furthermore, the vertical direction perpendicular to both MD and TD is referred to as ZD.

[0047] After the thermally conductive composition R is discharged at a certain length along the MD, the cutter 58 is moved along the TD (the direction perpendicular to the paper surface in Figure 3) to cut the thermally conductive composition R discharged from the discharge port 53, as shown in Figure 3(B), and a first sheet body S1 is formed on the table 57. In the dispenser device 50, the cutter 58 is a wire cutter arranged below the lower surface 51A. Both ends of the wire cutter are attached to attachment portions 51X and 51Y provided on the head 51. The attachment portions 51X and 51Y are movable along the TD (i.e., the longitudinal direction of the discharge port 53) in the head 51, and by moving these attachment portions 51X and 51Y, the cutter 58 can also move along the lateral direction (TD). By moving the cutter 58 in the TD, it becomes possible to cut the thermally conductive composition R discharged from the discharge port 53. Although not shown, the thermally conductive composition R discharged from the discharge port 53 does not have to be cut for each layer formed, and in that case, the thermally conductive composition discharged in sheet form (sheet body S) may be folded to form a laminate. In this case, the cutter 58 may be omitted from the dispenser device 50.

[0048] Next, as shown in Fig. 3(C), the table 57 is moved downward. After that, as shown in Fig. 3(D), the thermally conductive composition R is discharged onto the sheet body S1, and the table 57 is moved in the reverse direction along the MD (the direction opposite to the forward direction described above). Note that the head 51 may be movable instead of the table 57. Specifically, the head 51 may be movable in the MD, and may further be movable in the ZD. By moving the head in the MD, the thermally conductive composition R can be ejected in sheet form along the MD without moving the table 57. Furthermore, by moving the head in the ZD, it becomes possible to eject further thermally conductive composition onto the thermally conductive composition ejected in sheet form without moving the table 57. In addition, in the dispenser device 50, only one of the table 57 and the head 51 may be movable, or both may be movable. The member onto which the thermally conductive composition is discharged (discharged member) does not have to be the table 57, and the table 57 may be omitted and a member other than the table 57 may be used. It may also be a member placed on the table 57. These discharged members only need to be able to move along the ZD or MD in the same way as the table 57.

[0049] After the thermally conductive composition R has been discharged at a certain length along the MD, a second sheet S2 is formed on the sheet S1, as shown in Fig. 3(E). At this time, the sheet S2 may be formed by cutting the thermally conductive composition R with a cutter 58, or the sheet S2 may be formed without cutting the thermally conductive composition R. After sheet body S2 is formed on sheet body S1, table 57 is moved downward again, and the above operation is repeated to obtain a laminate (oriented formed body) 22 in which multiple sheet bodies S1, S2, ... Sn (n is an arbitrary integer) are stacked (see Figure 4(A)). Note that Figure 4 shows an embodiment in which a large number of sheet bodies are stacked, but the number of stacked sheet bodies (number of layers) is not particularly limited as long as it is 2 or more, and may be, for example, 10 or more, or may be approximately 1000 or less, or may be approximately 100 or less.

[0050] In step (1-2), the temperature (discharge temperature) when the thermally conductive composition R is discharged from the discharge port 53 is preferably room temperature. By setting the discharge temperature to room temperature in step (1-2), there is no need to provide a heating device or the like in the dispenser device 50, and the device can be simplified. Here, room temperature means substantially the same as the ambient temperature where the dispenser device is installed. Therefore, an embodiment in which the thermally conductive composition R is dispensed in the dispenser device 50 without being heated by a heating device is also included in the embodiment in which the dispensing temperature is room temperature. A specific dispensing temperature is, for example, about 0 to 40°C, and preferably about 10 to 30°C.

[0051] In step (1-2), the thermally conductive composition R is discharged along the MD, so that the anisotropic filler, such as the scaly thermally conductive filler blended into the thermally conductive composition R, is oriented in the discharge direction (MD). As a result, in each of the sheets S1, S2, ..., Sn, the anisotropic filler is oriented in a direction (MD) that is parallel to the in-plane direction of the sheet. As will be described later, the anisotropic filler is also oriented in a direction that is parallel to the in-plane direction in each unit layer of the thermally conductive sheet, which enables it to be oriented in the thickness direction of the thermally conductive sheet. In step (1-2), the scale-like thermally conductive fillers are preferably oriented so that the proportion of the number of scale-like thermally conductive fillers whose scale surfaces form an angle of less than 30° with respect to one direction along the surface direction (MD, the thickness direction in the thermally conductive sheet described below) exceeds 50%, and preferably exceeds 80%, of the total amount of the scale-like thermally conductive fillers.

[0052] In the laminate obtained in step (1-2), the thickness of each sheet S1, S2, ... Sn is not particularly limited, but is preferably 0.1 to 9.0 mm. By setting the thickness of the sheet to 0.1 mm or more, the thermally conductive composition R can be discharged without increasing the discharge pressure, and even thermally conductive compositions containing a large amount of thermally conductive filler can be easily discharged. Furthermore, setting the thickness to 9.0 mm or less makes it easier to improve the orientation of the anisotropic filler. From these perspectives, the thickness of each sheet S1, S2, ... Sn is more preferably 0.5 to 7 mm. Note that the thickness of each sheet in the laminate may be thinner than the discharged thickness of the sheet (the thickness of the sheet without lamination) due to compression by the weight of the thermally conductive composition itself to be laminated. As a result, the thickness of each sheet is, for example, 80 to 100% of the discharged thickness, preferably 90 to 100%.

[0053] <Process (1-3)> In step (1-3), the laminate 22 obtained in step (1-2) may be compressed by applying pressure in the lamination direction. In step (1-3), compressing the laminate 22 by applying pressure allows the multiple sheets S1, S2, ... Sn to adhere to each other, preventing peeling between the sheets. Note that, since the multiple sheets are uncured, they can be firmly bonded to each other by compressing them by applying pressure. When the original thickness of the laminate 22 is taken as 100%, it is preferable that the laminate 22 be compressed to a thickness of 75 to 97%. By compressing and deforming within the above range, the laminate 22 is not excessively deformed, and the sheets can be easily firmly bonded to each other. It is more preferable that the laminate 22 be compressed and deformed to a thickness of 85 to 95%. Furthermore, when the laminate 22 is compressed, it undergoes plastic compression deformation. Therefore, even when the compressed and deformed laminate is released from the pressure, the thickness of the laminate 22 will be maintained within the above range. The laminate can be compressed by applying pressure using, for example, a roller or a press. The pressure when applying pressure is not particularly limited, but as an example, when using a roller, the pressure is preferably 0.3 to 3 kgf / 50 mm.

[0054] <Process (1-4)> Next, in step (1-4), the laminate that has been compressively deformed in step (1-3) is cured. Curing is preferably carried out by heating. Specifically, it is advisable to carry out curing at a temperature of, for example, about 50 to 150° C. The heating time is, for example, about 10 minutes to 10 hours. When a solvent is blended in the thermally conductive composition, the solvent may be evaporated by heating during curing, for example.

[0055] <Process (1-5)> Next, as shown in FIG. 4(B), the cured laminate 22 is cut with a blade 18 along the stacking direction of the sheets S1, S2, ..., Sn to obtain the thermally conductive sheet 10. In this case, the laminate 22 is preferably cut in a direction perpendicular to the orientation direction of the anisotropic filler. As the blade 18, for example, a double-edged or single-edged blade such as a razor blade or a utility knife, a round blade, a wire blade, a saw blade, or the like can be used. The laminate 22 is cut with the blade 18 by, for example, pushing, shearing, rotating, sliding, or the like. The cutting direction in step (1-5) is preferably a direction that coincides with the stacking direction, but may be deviated from the direction that coincides with the stacking direction as long as it intersects with the stacking surface of the laminate 22.

[0056] (Second manufacturing method) The thermally conductive sheet of the present invention may be produced by a second production method, which includes the following steps (2-1) to (2-3). Step (2-1): preparing a block-shaped thermally conductive composition containing a curable silicone composition and a scaly thermally conductive filler Step (2-2): Step of curing the block-shaped thermally conductive composition Step (2-3): A step of cutting the block-shaped thermally conductive composition along a direction intersecting the extrusion direction

[0057] <Process (2-1)> In step (2-1), a thermally conductive composition is prepared by mixing at least a curable silicone composition, which is a raw material for a curable silicone resin, with a scaly thermally conductive filler. In addition to the above components, the thermally conductive composition may also contain at least one of an anisotropic filler other than the scaly thermally conductive filler, a non-anisotropic filler, silicone oil, and an additive component. The specific mixing method is the same as in step (1-1) in the first manufacturing method described above, and therefore a detailed description thereof will be omitted. Next, the thermally conductive composition is extruded into a block shape while applying shear force, thereby orienting the anisotropic filler, such as the flaky thermally conductive filler, along the MD (extrusion direction). Specifically, the thermally conductive composition is fed from an extruder or the like into a die with slits, and then passed through the slits to orient it in the MD. Other known devices may also be used.

[0058] <Process (2-2)> In step (2-2), the block-shaped thermally conductive composition obtained in step (2-1) is cured. The thermally conductive composition may be cured by heating, as in step (1-4) in the first production method described above, and the heating temperature and heating time are the same as in step (1-4) in the first production method. The thickness of the block obtained by the above curing is not particularly limited, but is, for example, 10 to 250 mm, preferably 30 to 200 mm, and more preferably 60 to 150 mm. The thickness of the block is the thickness in the direction perpendicular to the extrusion direction (ZD direction).

[0059] <Process (2-3)> In step (2-3), the block (oriented molded body) obtained in step (2-2) is cut along the ZD direction to obtain a thermally conductive sheet. The specific cutting method is the same as in step (1-5) in the first manufacturing method, so a detailed description will be omitted. The thermally conductive sheet obtained by the second manufacturing method differs from the thermally conductive sheets obtained by the first manufacturing method and the third manufacturing method described below in that it does not have multiple unit layers, but consists of a single layer containing a matrix and a thermally conductive filler.

[0060] (Third manufacturing method) The thermally conductive sheet of the present invention may be manufactured by a third manufacturing method. The third manufacturing method includes a primary sheet preparation step of preparing a plurality of primary sheets, each containing a silicone resin and a scaly thermally conductive filler; a VUV irradiation step of irradiating the primary sheets with VUV; a lamination step of stacking the VUV-irradiated primary sheets to obtain a laminated block; and a cutting step of cutting the laminated block to obtain a thermally conductive sheet. Each step is described in detail below.

[0061] <Primary sheet preparation process> In the primary sheet preparation step, a thermally conductive composition is prepared by mixing at least a curable silicone composition, which is a raw material for a curable silicone resin, with a scaly thermally conductive filler. In addition to the above components, the thermally conductive composition may contain at least one of an anisotropic filler other than the scaly thermally conductive filler, a non-anisotropic filler, silicone oil, and an additive component. The specific mixing method is the same as in step (1-1) in the first manufacturing method described above, and therefore a detailed description thereof will be omitted.

[0062] The viscosity of the thermally conductive composition in the third manufacturing method can be determined depending on the means of sheet formation and the desired sheet thickness. When forming a sheet by applying the thermally conductive composition to a substrate, the viscosity of the thermally conductive composition is preferably 50 to 10,000 Pa·s. By setting the viscosity to 50 Pa·s or more, the application of shear force makes it easier to orient the scaly thermally conductive filler in the plane direction of the primary sheet. Furthermore, setting the viscosity to 10,000 Pa·s or less improves coatability. In the third manufacturing method, the viscosity is measured using a rotational viscometer (Brookfield viscometer DV-E, spindle SC4-14) at a rotational speed of 1 rpm, and the measurement temperature is the temperature at the time of coating the thermally conductive composition.

[0063] Next, the thermally conductive composition is formed into a sheet while applying shear force, thereby orienting the anisotropic filler, such as the scaly thermally conductive filler, in a direction parallel to the sheet surface (i.e., the planar direction). The thermally conductive composition can be applied to the substrate film, for example, using a coating applicator such as a bar coater or doctor blade, or by extrusion molding or ejection from a nozzle. This method applies shear force along the coating direction of the thermally conductive composition. The anisotropic filler in the thermally conductive composition is oriented in the coating direction due to this shear force.

[0064] Next, the thermally conductive composition formed into a sheet is cured to obtain a primary sheet. In the primary sheet, the anisotropic filler is oriented along the surface direction as described above. The thermally conductive composition may be cured by heating, similar to step (1-4) in the first manufacturing method described above, and the heating temperature and heating time are the same as those described above. In the third production method, when a solvent is blended into the thermally conductive composition, the solvent may be evaporated by heating during curing, for example.

[0065] The thickness of the primary sheet obtained by curing is preferably in the range of 0.1 to 2.0 mm. By setting the thickness of the primary sheet within this range, the anisotropic filler can be properly oriented in the plane direction by shear force. Furthermore, by setting the thickness of the primary sheet to 0.1 mm or more, it can be easily peeled from the base film. Furthermore, by setting the thickness of the primary sheet to 2.0 mm or less, deformation of the primary sheet due to its own weight can be prevented. From these viewpoints, the thickness of the primary sheet is more preferably 0.3 to 0.8 mm.

[0066] (VUV irradiation process) Next, at least one surface of the cured primary sheet is irradiated with VUV. VUV stands for vacuum ultraviolet light, and refers to ultraviolet light with a wavelength of 10 to 200 nm. Examples of VUV light sources include an excimer Xe lamp and an excimer ArF lamp. As described above, the cured primary sheet contains a silicone resin (organopolysiloxane), and when irradiated with VUV, the irradiated surface is activated. As described below, the primary sheet is overlapped with another primary sheet so that one activated surface becomes the overlapping surface, thereby firmly bonding the primary sheets together. The VUV irradiation conditions are not particularly limited as long as they can activate the surface of the primary sheet. For example, the cumulative light dose is 5 to 100 mJ / cm 2 Preferably, the cumulative light amount is 10 to 50 mJ / cm 2 It is recommended to irradiate VUV so that

[0067] (Lamination process) Next, multiple primary sheets are stacked so that the orientation direction of the anisotropic filler is the same to obtain a laminated block. Here, as described above, it is sufficient that either one of the overlapping surfaces of each primary sheet that contacts each other has been previously irradiated with VUV. By irradiating one surface with VUV, adjacent primary sheets are bonded together by that activated surface. Furthermore, from the viewpoint of further improving adhesion, it is preferable that both overlapping surfaces are irradiated with VUV. In other words, the primary sheet is preferably superimposed so that one side that has been irradiated with VUV comes into contact with another primary sheet, and in this case, it is preferable that the other side of the other primary sheet that comes into contact with the one side is also irradiated with VUV.

[0068] In the third manufacturing method, the primary sheets can be bonded simply by overlapping them as described above, but to bond them more firmly, pressure may be applied in the stacking direction of the primary sheets. The pressure should be such that the primary sheets do not deform significantly, and can be applied using, for example, a roller or press. For example, when using a roller, the pressure is preferably 0.3 to 3 kgf / 50 mm. The laminated primary sheets may be heated appropriately, for example, when applying pressure, but it is preferable not to heat the laminated primary sheets because primary sheets activated by VUV irradiation can be bonded without heating. Therefore, the temperature during pressing is, for example, 0 to 50°C, preferably about 10 to 40°C.

[0069] (cutting process) Next, the laminated block obtained in the lamination step is cut with a blade along the lamination direction of the primary sheet to obtain a thermally conductive sheet. The specific cutting method is the same as in step (1-5) in the first manufacturing method, so a detailed description will be omitted.

[0070] In the first to third manufacturing methods, examples have been described in which a curable silicone composition that is cured by heating and silicone oil are used as raw materials for the silicone resin, but the raw materials for the silicone resin are not limited to the curable silicone composition and silicone oil, and materials other than the curable silicone composition and silicone oil may also be used. Although the first to third manufacturing methods have been described above as the manufacturing method of the thermally conductive sheet of the present invention, the manufacturing method is not limited to these, and the thermally conductive sheet may be manufactured by other manufacturing methods. For example, the matrix may be formed from a resin other than silicone resin.

[0071] (How to use the thermal conductive sheet) The thermally conductive sheet is not particularly limited, but is preferably used inside electronic devices. Specifically, the thermally conductive sheet is interposed between a heat generating element and a heat dissipating element, and transfers heat generated by the heat generating element to the heat dissipating element by thermal conduction, where the heat is dissipated from the heat dissipating element. Here, examples of the heat generating element include various electronic components used inside electronic devices, such as CPUs, power amplifiers, and power supplies. Examples of the heat dissipating element include heat sinks, heat pumps, and metal housings for electronic devices. The thermally conductive sheet is used by being in close contact with and compressed against the heat generating element and the heat dissipating element, respectively. [Example]

[0072] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0073] The raw materials used in the examples and comparative examples are as follows. [Silicone resin] The base resin is an alkenyl-containing organopolysiloxane, and the curing agent is a hydrogen organopolysiloxane. The viscosity of this mixture at 25°C is 300 mPa·s. [Silicone oil] Dimethyl Silicone Oil [Additional ingredients] platinum catalyst [Non-anisotropic filler] Alumina (1): irregular shape, average particle size 3 μm Alumina (2): Spherical, average particle size 3.5 μm Alumina (3): Spherical, average particle size 0.5 μm Aluminum nitride: spherical, average particle size 5 μm Aluminum hydroxide: irregular shape, average particle size 1 μm [Scale-like thermally conductive filler] Boron nitride (1): average particle size 43.9 μm Boron nitride (2): average particle size 52.5 μm Boron nitride (3): average particle size 69.2 μm Boron nitride (4): Average particle size 72.3 μm, obtained by passing boron nitride (3) through a sieve with a mesh size of 45 μm Boron nitride (5): Average particle size 88.6 μm, obtained by passing boron nitride (3) through a sieve with a mesh size of 75 μm Boron nitride (6): Average particle size 92.8 μm, obtained by passing boron nitride (3) through a sieve with an opening of 85 μm

[0074] [Example 1] (Process 1) An alkenyl-containing organopolysiloxane (base resin) and a hydrogen organopolysiloxane (curing agent) (total 100 parts by mass) were blended with 0.2 parts by mass of platinum catalyst, 115 parts by mass of alumina (1), 215 parts by mass of alumina (2), and 306.5 parts by mass of alumina (3). Furthermore, 93.5 parts by mass of boron nitride (1) and 93.5 parts by mass of boron nitride (3) were blended, and these components were mixed to obtain a thermally conductive composition.

[0075] (Process 2) The obtained thermally conductive composition was filled into the tank of the dispenser shown in Figure 2 and supplied to the head at a pressure of 0.5 MPa. The thermally conductive composition was dispensed at 25°C from a rectangular discharge port with a length L1 of 50 mm and a length L2 of 3 mm. The table was moved forward in the MD direction at a speed of 100 mm / min, and a 50 mm long sheet of the thermally conductive composition was dispensed with a thickness of 3 mm. After dispensing the 50 mm length, the sheet of the thermally conductive composition was cut with a cutter to form a first sheet on the table. The table was then moved downward, and subsequently moved in the reverse MD direction at a speed of 100 mm / min. The thermally conductive composition was dispensed with the same thickness and length, and then cut with a cutter. A second sheet was placed on top of the first sheet. This operation was repeated until 20 sheets were stacked to obtain a laminate.

[0076] (Steps 3~5) Next, the laminate was compressed and deformed using a roller at 1.5 kgf / 50 mm in a 25°C environment, and then cured by heating at 80°C for 480 minutes. The laminate was then sliced ​​parallel to the lamination direction and perpendicular to the orientation direction of the anisotropic filler, and further heated at 150°C for 300 minutes to volatilize the n-decyltrimethoxysilane, yielding a thermally conductive sheet with a thickness of 2 mm for each unit layer.

[0077] [Examples 2 to 7, Comparative Examples 1 to 3] The same procedure as in Example 1 was carried out, except that the formulation of the thermally conductive composition was changed so that the formulation of the thermally conductive sheet would be as shown in Table 1.

[0078] [Average particle size of boron nitride, frequency of boron nitride particles with particle size of 100 μm or more] The particle size distribution of the scaly boron nitride flakes used to determine the cumulative frequency of particles with particle sizes of 100 μm or more was measured by the following method. First, as a test sample, a scaly thermally conductive filler before being blended into a thermally conductive composition was dispersed in ion-exchanged water. Next, the frequency distribution of the test sample was measured using an image measuring device (Microtrac MT3300EX II, manufactured by MicrotracBEL) and analysis software (PartAn SI, manufactured by MicrotracBEL). The measurement and analysis conditions were: "Sieve correction correlation (none)," display mode "Frequency," particle size calculation "FLength," distribution display "Volume %," particle classification settings: minimum diameter "5 μm," maximum diameter "300 μm," number of classifications "142," roundness "0.60-0.90," and focus limit "0.15." The cumulative frequency of particles with a particle size of 100 μm or greater was calculated from the obtained particle size distribution. The arithmetic mean particle size of the total amount of boron nitride used to generate the particle size distribution was used as the average particle size of the total amount of boron nitride. The average particle size of each boron nitride was also measured using the same procedure.

[0079] [Thermal Conductivity] The thermal conductivity of the thermally conductive sheet was measured by a method in accordance with ASTM D5470-06.

[0080] [Piercing load] The piercing load of the thermally conductive composition was measured by the following method. A piercing rod (rod diameter 1 mm) with a disk-shaped member at the tip, 3 mm in diameter and 1 mm thick, was pressed against the thermally conductive sheet from the tip side at a speed (piercing speed) of 10 mm / min, and the load (gF) was measured when the tip of the piercing rod reached a depth of 12 mm from the liquid surface. The piercing rod was made of stainless steel. Measurements were carried out at 25°C.

[0081] [Table 1]

[0082] As is clear from the above examples, the thermally conductive sheets that satisfy the requirements of the present invention have low puncture resistance, excellent flexibility, and high thermal conductivity. In contrast, the sheets produced in Comparative Examples 1 and 2 had low thermal conductivity due to a low occurrence frequency of boron nitride particles with particle sizes of 100 μm or more, and the sheet produced in Comparative Example 3 had insufficient flexibility due to a high occurrence frequency of boron nitride particles with particle sizes of 100 μm or more. [Explanation of symbols]

[0083] 10. Thermally conductive sheet 11. Matrix 13 Unit Layer 14 Anisotropic Filler 15 Non-anisotropic filler 18 Cutlery 22, 22B, 22C laminate 50 Dispenser device 51 head 52 Supply route 53 Discharge port 54 Connecting Road 56 Tank 57 Table 58 Cutter R Thermally conductive composition S, S1, S2,..., Sn sheet body

Claims

1. A thermally conductive sheet comprising a matrix and a thermally conductive filler, the thermally conductive filler includes a flaky thermally conductive filler; The thermally conductive sheet, wherein the scaly thermally conductive filler has a cumulative frequency of particles having a particle size of 100 μm or more of 6.6% or more and 40% or less in an image particle size distribution measurement.

2. The thermally conductive sheet according to claim 1 , wherein the matrix is ​​a silicone resin.

3. The thermally conductive sheet according to claim 1 or 2, wherein the scaly thermally conductive filler has an average particle size of 55 μm or more and 90 μm or less, as determined by image particle size distribution measurement.

4. 3. The thermally conductive sheet according to claim 1, wherein the flaky thermally conductive filler is flaky boron nitride.

5. 3. The thermally conductive sheet according to claim 1, wherein the scaly thermally conductive filler comprises boron nitride having at least two different average particle sizes.

6. The thermally conductive sheet according to claim 1 or 2, wherein the thermally conductive filler further comprises a non-anisotropic filler.

7. The thermally conductive sheet according to claim 1 or 2, wherein the major axes of the scaly thermally conductive filler are oriented in the thickness direction of the thermally conductive sheet.

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