Thermally conductive sheet

Abstract

Provided is a thermally conductive sheet comprising a matrix and a thermally conductive filler, wherein the thermally conductive filler includes a scaly thermally conductive filler. The scaly thermally conductive filler has a cumulative frequency of 6.6% to 40% for particle sizes of 100 μm or more as measured by image-based particle size distribution measurement.

Description

Thermally conductive sheet

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

[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 components. 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. Thermally conductive sheets generally contain a polymer matrix and a thermally conductive filler dispersed within the polymer matrix. Furthermore, thermally conductive sheets may have anisotropic fillers 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 oriented in the thickness direction of the sheet. Patent Document 2 also discloses that in a thermally conductive sheet containing a matrix composed of an organopolysiloxane having a cross-linked structure and a thermally conductive filler containing 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 fiber axes oriented in the thickness direction of the sheet, and an insulating thermally conductive layer having thermal conductivity and insulation properties and an insulating thermally conductive filler dispersed in a polymer matrix. Patent Document 4 discloses a thermally conductive sheet having multiple unit layers each containing a silicone resin and a thermally conductive filler, in which an anisotropic filler contained as the thermally conductive filler is oriented in the thickness direction of the sheet.

[0005] Patent No. 6844806 Patent No. 6613462 Patent No. 6723610 Patent No. 6978148

[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.

[0008] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by providing a thermally conductive sheet containing a matrix and a thermally conductive filler, which contains a scaly thermally conductive filler as the thermally conductive filler, and by adjusting the cumulative frequency of the scaly thermally conductive filler having a particle size of 100 μm or more to fall within a certain range as measured by image particle size distribution measurement. 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 scaly thermally conductive filler, and wherein the cumulative frequency of particles having a particle size of 100 μm or more in an image particle size distribution measurement is 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 scaly thermally conductive filler has an average particle size of 55 μm or more and 90 μm or less in an image particle size distribution measurement. [4] The thermally conductive sheet according to any one of [1] to [3], wherein the scaly thermally conductive filler is scaly boron nitride. [5] The thermally conductive sheet according to any one of [1] to [4], wherein the scaly thermally conductive filler comprises 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 comprises 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.

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

[0011] Fig. 1 is a schematic cross-sectional view showing an example of a thermally conductive sheet; Fig. 2 is a schematic view showing a dispenser device; Fig. 3 is a schematic view for explaining step (1-2) in a first manufacturing method of a thermally conductive sheet; Fig. 4 is a schematic view for explaining step (1-5) in a first manufacturing method of a thermally conductive sheet.

[0012] [Thermal Conductive Sheet] The thermal 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 thermal conductive sheet of the present invention contains a scaly thermal conductive filler as the thermal conductive filler, and the cumulative frequency of the scaly thermal conductive filler having a particle size of 100 μm or more in an image particle size distribution measurement is 6.6% or more and 40% or less. If the cumulative frequency is less than 6.6%, the scaly thermal conductive filler may not form a sufficient thermal conduction path, resulting in insufficient thermal conductivity of the thermal conductive sheet. Furthermore, if the cumulative frequency exceeds 40%, the flexibility of the thermal conductive sheet may be impaired by the scaly thermal conductive filler having a large particle size. From these perspectives, the cumulative frequency is preferably 6.6% or more and 37% or less, and more preferably 7% or more and 30% or less.

[0014] The average particle size of the scaly thermally conductive filler, as measured by image particle size distribution, is preferably 55 μm or more and 90 μm or less, more preferably 56 μm or more and 89 μm or less, and even more preferably 60 μm or more and 85 μm or less. 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. Furthermore, 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. Furthermore, 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 preferably contained in the thermally conductive sheet as an anisotropic filler, with its major axis oriented in the thickness direction of the thermally conductive sheet. This improves 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, and scaly aluminum oxide powder. 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 scaly graphite powder, the graphite crystal planes are connected in the in-plane direction of the scaly surfaces, providing high thermal conductivity in the in-plane direction. Therefore, by aligning the scaly surfaces in a predetermined direction, it is possible to increase the thermal conductivity in a specific direction. Preferably, the scaly graphite powder has a high degree of graphitization.

[0016] The scaly thermally conductive filler may be used alone or in combination with 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 formulation for the scaly thermally conductive filler, the cumulative frequency can be adjusted within 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 is easier to prevent the viscosity of the curable silicone composition from becoming excessively high due to the influence of the large-particle-sized scaly filler, for example, before the curable silicone composition is cured. Specific examples of using two types of thermally conductive fillers with different average particle sizes in combination are shown below. For example, it is possible to use a scaly thermally conductive filler with an average particle size of approximately 50 μm or less 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 a large number of 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 less and 40% or less when viewed as a whole formulation after the above combination. In this way, when two types of thermally conductive fillers with different average particle sizes are used in combination to increase the cumulative frequency of the thermally conductive fillers with a particle size of 100 μm or more, it is preferable to use the larger average particle size as the larger-particle-sized scaly thermally conductive filler. Alternatively, it is advisable to increase the content of the larger-particle-sized scaly 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, for example, 100 or less in practical use. The aspect ratio of the scaly thermally conductive filler means the length of the major axis / thickness.

[0018] Furthermore, the thermal conductivity of the scaly thermally conductive filler along the longitudinal direction is generally 30 W / m·K or more, preferably 100 W / m·K or more, although not particularly limited. The upper limit of the thermal conductivity of the scaly thermally conductive filler is not particularly limited, but is, for example, 2000 W / m·K or less. The thermal conductivity of the scaly thermally conductive filler may be measured by the laser flash method. The scaly thermally conductive filler may be conductive or insulating. If the scaly thermally conductive filler has insulating properties, the insulation in the thickness direction of the thermally conductive sheet can be improved, making it suitable for use in electrical equipment. In the present invention, being conductive means, for example, a volume resistivity of 1×10 ９ In addition, the term "insulating" refers to a material having a volume resistivity of 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 at or above the above-mentioned lower limit, thermal conductivity is likely to be improved, while by setting the content of the scaly thermally conductive filler at or below the above-mentioned upper limit, flexibility is likely to be improved. Furthermore, the content of the scaly thermally conductive filler is preferably 5 to 45% by volume, more preferably 10 to 35% by volume, and even more preferably 15 to 30% by volume, based on the total volume of the thermally conductive sheet, in terms of volume-based filling rate (volume filling rate).

[0020] The thermally conductive sheet preferably further contains a non-anisotropic filler. By including the non-anisotropic filler, a thermally conductive filler is appropriately interposed between the scaly thermally conductive fillers, thereby further improving the thermal conductivity. The 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 under an environment in which the scaly thermally conductive filler orients in the predetermined 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, and 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, and carbides other than metals. The shapes of the non-anisotropic fillers include spherical and irregular powders. Examples of metals in non-anisotropic fillers include aluminum, copper, and nickel. Examples of metal oxides include aluminum oxide (represented by alumina), magnesium oxide, and zinc oxide. Examples of metal nitrides include aluminum nitride. Examples of metal hydroxides include aluminum hydroxide. 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 insulating non-anisotropic fillers 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. Furthermore, 1 to 20 μm is particularly preferred. By setting the average particle size to 50 μm or less, problems such as disrupting 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 is not unnecessarily large, and even when a large amount is added, the viscosity of the thermally conductive composition is less likely to increase, making it easier to load the non-anisotropic filler with a high amount of filler. The average particle size of the non-anisotropic filler can be measured using a laser diffraction particle size distribution analyzer. The particle size at 50% cumulative volume (D50) is used as the average particle size. The non-anisotropic filler may be used alone or in combination with two or more types. When two or more types of filler are included, 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 weight, more preferably 200 to 800 parts by weight, and even more preferably 250 to 550 parts by weight, per 100 parts by weight of the matrix. By setting the content of the non-anisotropic filler at or above the lower limit, the amount of non-anisotropic filler present in the gaps between the scaly thermally conductive fillers is at or above a certain level, resulting in good thermal conductivity. On the other hand, by setting the content of the non-anisotropic filler at or below the upper limit, the effect of increasing thermal conductivity according to the content can be obtained, and the non-anisotropic filler does not inhibit the thermal conduction of the scaly thermally conductive filler. The content of the non-anisotropic filler, expressed in volume percent, is preferably 20 to 60% by volume, more preferably 35 to 55% by volume, and even more preferably 40 to 50% by volume, based on the total amount 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, a composition consisting of an uncrosslinked rubber and a crosslinking agent, or a composition 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 the 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 in flow orientation. Furthermore, when crosslinked (i.e., cured), as described above, the matrix may be a cured curable polymer composition comprising an uncrosslinked synthetic rubber and a crosslinking agent. Furthermore, thermoplastic elastomers such as polyester-based thermoplastic elastomers and polyurethane-based thermoplastic elastomers, as well as thermosetting elastomers formed by curing a liquid polymer composition containing a base agent and a curing agent, can also be used. For example, a polyurethane-based elastomer formed by curing a polymer composition containing a hydroxyl group-containing polymer and an isocyanate can be used. 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 consist of a polymer compound alone, or may consist 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 matrix content, 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, relative to the total amount of the thermal conductive sheet. When a plasticizer is used, the amount of plasticizer relative to the total amount of the thermal 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 an addition reaction type, or may be other types. When the curable silicone resin is 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 compound is preferably an alkenyl group-containing organopolysiloxane. Specific examples of alkenyl group-containing organopolysiloxanes include organopolysiloxanes terminated at both vinyl ends, such as polydimethylsiloxane terminated at both vinyl ends, polyphenylmethylsiloxane terminated at both vinyl ends, dimethylsiloxane-diphenylsiloxane copolymers terminated at both vinyl ends, dimethylsiloxane-phenylmethylsiloxane copolymers terminated at both vinyl ends, and dimethylsiloxane-diethylsiloxane copolymers terminated at both vinyl ends. The curing agent is not particularly limited as long as it can cure the silicone compound serving as the base compound. However, organohydrogenpolysiloxanes, which are organopolysiloxanes having two or more hydrosilyl groups (SiH), are preferred. The hardness of the thermally conductive sheet can be adjusted by appropriately adjusting the blend ratio of the curing agent to the base compound. Specifically, the hardness of the thermally conductive sheet can be reduced by reducing the blend ratio of the curing agent to the base compound.

[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 %, of the total amount of the thermal conductive sheet. The amount of the silicone oil, relative to the total amount of the thermal conductive sheet, is preferably 1 to 20 volume %, more preferably 3 to 15 volume %, and even more preferably 5 to 10 volume %.

[0034] (Additive Components) 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 more, 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 by 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. When the piercing load is equal to or less than the above upper limit, flexibility after curing is ensured, and, for example, conformability to heat generating bodies and heat dissipating bodies is improved, and heat dissipation properties are likely to be improved. 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 appropriately changed depending on the shape and application of the electronic device in which the thermally conductive sheet is installed. 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 described below, when the thermally conductive sheet is composed of a stack of unit layers, the thickness of each unit layer is not particularly limited, but is preferably 0.1 to 8.5 mm, and 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 a cured version of the 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 includes 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 have to include 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, for example, by 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 Producing Thermally Conductive Sheet) <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 in which the scaly thermally conductive filler is oriented in one direction from a thermally conductive composition containing a curable silicone composition and a scaly thermally conductive filler, 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 manufacturing method comprising the following steps (1-1) to (1-5). In the first manufacturing method, steps (1-1) to (1-5) are preferably performed 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 using a dispenser to dispense the thermally conductive composition obtained in step (1-1) into multiple overlapping sheets to obtain a laminate. Step (1-3): A step of compressing the obtained laminate in the stacking direction. Step (1-4): A step of curing the thermally conductive composition. Step (1-5): A step of cutting the laminate along a direction intersecting the stacking plane.

[0042] <Step (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. Here, the components constituting the thermally conductive composition may be mixed using, for example, a known kneader, kneading roll, mixer, or the like. Furthermore, in the first manufacturing method, an anisotropic filler, such as a scaly thermally conductive filler, is oriented in the discharge direction in step (1-2), thereby increasing the thermal conductivity of the thermally conductive sheet in one direction.

[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. From the viewpoint of further suppressing spreading due to its own weight, a piercing load of 8 gF or more is preferred. Furthermore, from the viewpoint of improving dischargeability from the dispenser, a piercing load of 22 gF or less is preferred, and 20 gF or less is more preferred. 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 described below, or they may be stored in separate tanks and mixed immediately before step (1-2). An organic solvent may be blended into the thermally conductive composition as needed to adjust the piercing load, but it is preferable not to blend an organic solvent.

[0045] Curable silicone compositions are usually liquids, and flexibility can be imparted to the thermally conductive sheet by appropriately adjusting the molecular weight of each component (such as an alkenyl group-containing organopolysiloxane or an 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] <Step (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 pressurized thermally conductive composition 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 of the 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 the MD (Machine Direction), and the horizontal direction is referred to as the TD (Transverse Direction). The MD is the direction perpendicular to the TD. The vertical direction perpendicular to both the MD and TD is referred to as the ZD.

[0047] After the thermally conductive composition R is dispensed at a certain length along the MD, the cutter 58 is moved along the TD (the direction perpendicular to the paper surface in FIG. 3 ) to cut the thermally conductive composition R dispensed from the discharge port 53, as shown in FIG. 3(B), thereby forming a first sheet S1 on the table 57. In the dispenser device 50, the cutter 58 is a wire cutter located below the lower surface 51A. Both ends of the wire cutter are attached to mounting portions 51X and 51Y provided on the head 51. The mounting portions 51X and 51Y are movable along the TD (i.e., the longitudinal direction of the discharge port 53) on the head 51. By moving these mounting portions 51X and 51Y, the cutter 58 can also move along the lateral direction (TD). By moving the cutter 58 along the TD, the thermally conductive composition R dispensed from the discharge port 53 can be cut. 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. Thereafter, as shown in FIG. 3(D), the thermally conductive composition R is dispensed onto the sheet S1, and the table 57 is moved in the reverse direction along the MD (the opposite direction to the forward direction described above). Note that instead of the table 57, the head 51 may be movable. Specifically, the head 51 may be movable in the MD, and may also be movable in the ZD. By moving the head in the MD, the thermally conductive composition R can be dispensed in sheet form along the MD without moving the table 57. Furthermore, by moving the head in the ZD, further thermally conductive composition can be dispensed onto the thermally conductive composition dispensed in sheet form without moving the table 57. Furthermore, in the dispenser device 50, either the table 57 or the head 51 may be movable, or both may be movable. The member onto which the thermally conductive composition is dispensed (the member to be dispensed) does not necessarily have to be the table 57; the table 57 may be omitted, and a member other than the table 57 may be used. Alternatively, it may be a member placed on the table 57. These discharged members may be movable along the ZD or MD in the same way as the table 57.

[0049] After the thermally conductive composition R is dispensed 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 thermally conductive composition R may be cut by a cutter 58 to form the sheet S2, or the sheet S2 may be formed without cutting the thermally conductive composition R. After the sheet S2 is formed on the sheet S1, the table 57 is again moved downward, and the above operation is repeated to obtain a laminate (oriented molded body) 22 in which multiple sheets S1, S2, ... Sn (n is an arbitrary integer) are stacked (see FIG. 4(A)). While FIG. 4 shows an embodiment in which multiple sheets are stacked, the number of stacked sheets (number of layers) is not particularly limited as long as it is two 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. Note that room temperature here means substantially the same as the environmental temperature in which the dispenser device is installed. Therefore, an embodiment in which the thermally conductive composition R is discharged in the dispenser device 50 without being heated by a heating device is also included in the embodiment in which the discharge temperature is room temperature. A specific discharge 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 along a single direction (MD) along the surface of the sheet. As will be described later, the anisotropic filler is also oriented along a single direction along the surface of the unit layer of the thermally conductive sheet, thereby enabling orientation along the thickness direction of the thermally conductive sheet. In step (1-2), for example, the scaly thermally conductive filler may be oriented such that the proportion of the number of scaly thermally conductive fillers whose scale surfaces form an angle of less than 30° with respect to a single direction along the surface (MD, the thickness direction in the thermally conductive sheet described later) exceeds 50%, preferably exceeds 80%, of the total amount of scaly 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 making the sheet thickness 0.1 mm or more, the thermally conductive composition R can be ejected without increasing the ejection pressure, and even thermally conductive compositions containing a large amount of thermally conductive filler can be easily ejected. Furthermore, making the sheet thickness 9.0 mm or less facilitates the enhancement of 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 reduced by the weight of the thermally conductive composition itself, resulting in a thickness that is, for example, 80 to 100% of the ejected thickness (thickness of the sheet without lamination).

[0053] <Step (1-3)> In step (1-3), the laminate 22 obtained in step (1-2) may be compressed by applying pressure in the stacking 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. Because the multiple sheets are uncured, compressing them by applying pressure allows them to be firmly bonded together. The laminate 22 is preferably deformed to a thickness of 75 to 97% of its original thickness (assuming it is 100%). Compression within the above range facilitates strong bonding of the sheets without excessive deformation of the laminate 22. It is more preferable that the laminate 22 be deformed to a thickness of 85 to 95%. The laminate 22 undergoes plastic compression deformation when compressed, and therefore, even when the compressed and deformed laminate is released from pressure, the thickness of the laminate 22 remains within the above range. The laminate can be compressed by applying pressure using, for example, a roller or a press. The pressure to be applied is not particularly limited, but, as an example, when a roller is used, the pressure is preferably 0.3 to 3 kgf / 50 mm.

[0054] <Step (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 preferably carried out at a temperature of, for example, about 50 to 150°C. The heating time is, for example, about 10 minutes to 10 hours. If a solvent is blended into the thermally conductive composition, the solvent is preferably volatilized by heating during curing, for example.

[0055] <Step (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. Examples of the blade 18 that can be used include double-edged or single-edged blades such as razor blades or utility knives, round blades, wire blades, and saw blades. The laminate 22 is cut using the blade 18 by, for example, pushing, shearing, rotating, sliding, or other methods. The cutting direction in step (1-5) is preferably the same as the stacking direction, but may deviate from 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 manufactured by a second manufacturing method. The second manufacturing method comprises the following steps (2-1) to (2-3). Step (2-1): A step of preparing a block-shaped thermally conductive composition containing a curable silicone composition and a scaly thermally conductive filler. Step (2-2): A 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] <Step (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 the 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 similar to step (1-1) in the first manufacturing method described above, and therefore a detailed description is omitted. Next, the thermally conductive composition is extruded into a block shape while applying shear force, thereby orienting the anisotropic filler, such as the scaly thermally conductive filler, along the MD (extrusion direction). Specifically, the thermally conductive composition is fed from an extruder or the like into a die having a slit, and then passed through the slit to orient it in the MD. Other known devices may also be used.

[0058] <Step (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 in the same manner as in step (1-4) in the first manufacturing method described above, and the heating temperature and heating time are the same as in step (1-4) in the first manufacturing method. The thickness of the block obtained by the 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 refers to the thickness in the direction perpendicular to the extrusion direction (ZD direction).

[0059] <Step (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 step (1-5) in the first manufacturing method, so a detailed description will be omitted. Unlike the thermally conductive sheets obtained by the first manufacturing method and the third manufacturing method described below, the thermally conductive sheet obtained by the second manufacturing method does not have multiple unit layers, but consists of a single layer including 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 Step> 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 the 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.

[0062] The viscosity of the thermally conductive composition in the third manufacturing method can be determined depending on the sheet forming means 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. Note that 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 during application of 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., in the planar direction). The thermally conductive composition may be applied to the substrate film using, for example, a coating applicator such as a bar coater or doctor blade, or by extrusion molding or discharge from a nozzle. This method applies shear force along the coating direction of the thermally conductive composition. Due to this shear force, the anisotropic filler in the thermally conductive composition is oriented in the coating direction.

[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, as in 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 manufacturing method, if a solvent is blended into the thermally conductive composition, the solvent may be volatilized, for example, by heating during curing.

[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 perspectives, the thickness of the primary sheet is more preferably 0.3 to 0.8 mm.

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

[0067] (Lamination Process) Next, multiple primary sheets are laminated 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 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 to each other by the activated one surface. Furthermore, from the viewpoint of further improving adhesiveness, it is preferable that both overlapping surfaces are irradiated with VUV. That is, it is preferable that one VUV-irradiated surface of a primary sheet be overlapped with another primary sheet so that the VUV-irradiated surface contacts the other primary sheet. In this case, it is preferable that the other surface of the other primary sheet that contacts the one surface is also irradiated with VUV.

[0068] In the third manufacturing method, the primary sheets can be bonded simply by stacking them as described above, but to achieve stronger bonding, they may be pressed in the stacking direction. Pressurization should be performed at a pressure that does not significantly deform the primary sheets, and can be performed using, for example, a roller or press. For example, when using a roller, a pressure of 0.3 to 3 kgf / 50 mm is preferred. The stacked primary sheets may be heated as needed, for example, when applying pressure. However, since primary sheets activated by VUV irradiation can be bonded without heating, it is preferable not to heat the stacked primary sheets. Therefore, the temperature during pressing is, for example, 0 to 50°C, preferably about 10 to 40°C.

[0069] (Cutting step) 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. Furthermore, while the first to third manufacturing methods have been described above as methods for manufacturing the thermally conductive sheet of the present invention, the method is not limited to these manufacturing methods, 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] (Method of Using the Thermally Conductive Sheet) The thermally conductive sheet is not particularly limited, but is preferably used inside electronic devices, etc. 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, and 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 of 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.

[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] A base resin made of an alkenyl group-containing organopolysiloxane, a curing agent made of a hydrogen organopolysiloxane, and a viscosity of the mixture at 25°C: 300 mPa·s [Silicone oil] Dimethyl silicone oil [Additive components] Platinum catalyst [Non-anisotropic filler] Alumina (1): irregular, 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, average particle size 1 μm [Scaly 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 sieving boron nitride (3) through a 45 μm mesh sieve Boron nitride (5): Average particle size 88.6 μm, obtained by sieving boron nitride (3) with a mesh size of 75 μm. Boron nitride (6): Average particle size 92.8 μm, obtained by sieving boron nitride (3) with a mesh size of 85 μm.

[0074] [Example 1] (Step 1) To a curable silicone resin containing an alkenyl group-containing organopolysiloxane (main component) and a hydrogen organopolysiloxane (curing agent) (total 100 parts by mass), 0.2 parts by mass of a 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) were blended. 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] (Step 2) The obtained thermally conductive composition was filled into the tank of the dispenser device shown in FIG. 2 and supplied to the head at a pressure of 0.5 MPa. The thermally conductive composition was discharged at 25°C from a rectangular discharge port with a length L1 of 50 mm and a length L2 of 3 mm. At this time, the table was moved in the forward direction of the MD at a speed of 100 mm / min, and a sheet-like thermally conductive composition was discharged in a length of 50 mm with a thickness of 3 mm. After discharging the 50 mm length, the sheet-like thermally conductive composition was cut with a cutter to form a first sheet on the table. Thereafter, the table was moved downward, and subsequently moved in the reverse direction of the MD at a speed of 100 mm / min. The thermally conductive composition was discharged in the same thickness and length, and then cut with a cutter. A second sheet was stacked on top of the first sheet. This operation was repeated until 20 sheets were stacked to obtain a laminate.

[0076] (Steps 3 to 5) Next, in an environment of 25°C, the laminate was pressed with a roller at a pressure of 1.5 kgf / 50 mm to obtain a compressed and deformed laminate, which was then heated at 80°C for 480 minutes to harden. Next, the laminate was 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, thereby obtaining a thermally conductive sheet in the form of a sheet with a thickness of 2 mm for each unit layer. The contents of each component in the thermally conductive sheet, the average particle size of the total amount of boron nitride,

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

[0078] [Average Particle Size of Boron Nitride and Frequency of Boron Nitride Particles with Particle Sizes of 100 μm or More] The particle size distribution of scaly boron nitride used to determine the cumulative frequency of particles with particle sizes of 100 μm or more was measured using the following method. First, a scaly thermally conductive filler was dispersed in ion-exchanged water as a test sample before being incorporated into a thermally conductive composition. 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 to 0.90", and focus limit "0.15". The cumulative frequency of particles with a particle size of 100 μm or more was determined from the obtained particle size distribution. The arithmetic mean value of the particle sizes of the total amount of boron nitride used to prepare the particle size distribution was taken 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) having a disk-shaped member with a diameter of 3 mm and a thickness of 1 mm at its tip was pressed against the thermally conductive sheet from the tip side of the piercing rod 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 material of the piercing rod was stainless steel. The measurement was carried out at 25°C.

[0081]

[0082] As is clear from the above examples, the thermally conductive sheets satisfying the requirements of the present invention had 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 a particle size of 100 μm or more. Furthermore, the sheet produced in Comparative Example 3 had insufficient flexibility due to a high occurrence frequency of boron nitride particles with a particle size of 100 μm or more.

[0083] REFERENCE SIGNS LIST 10 Thermally conductive sheet 11 Matrix 13 Unit layer 14 Anisotropic filler 15 Non-anisotropic filler 18 Blade 22, 22B, 22C Laminate 50 Dispenser device 51 Head 52 Supply path 53 Discharge port 54 Connection path 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, wherein the thermally conductive filler comprises a flaky thermally conductive filler, and wherein the cumulative frequency of particles having a particle size of 100 μm or more in an image particle size distribution measurement of the flaky thermally conductive filler is 6.6% or more and 40% or less.

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

3. A 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 measured by image particle size distribution measurement.

4. The thermally conductive sheet according to claim 1 or 2, wherein the flaky thermally conductive filler is flaky boron nitride.

5. The thermally conductive sheet according to claim 1 or 2, wherein the scaly thermally conductive filler comprises boron nitride particles 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. A 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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