Thermally conductive sheet and method for manufacturing the same

Abstract

A thermally conductive sheet having a plurality of unit layers each containing a silicone resin and a thermally conductive filler, and being stacked in a manner that the unit layers are bonded to each other, and the volume content of the silicone resin is 32% by volume or less, and the compression load on a sheet area of 25.4 mm x 25.4 mm is 7.0 kgf or less when compressed by 30% in the vertical direction from the bonding surface of the unit layers bonded to each other. According to the present application, the thermal conductivity can be improved compared to the past, and the softness can be improved in a thermally conductive sheet configured using a silicone resin as a base component and stacking a plurality of unit layers.

Description

Technical Field

[0001] This invention relates to a thermally conductive sheet and a method for manufacturing the same. Background Technology

[0002] In electronic devices such as computers, automotive parts, and mobile phones, heat sinks and other heat dissipation devices are commonly used to release heat generated from heat-generating components such as semiconductor components or mechanical parts. It is known that thermally conductive sheets are placed between the heat-generating component and the heat sink to improve heat transfer efficiency. When thermally conductive sheets are placed inside electronic devices, they are usually compressed for use, thus requiring a high degree of flexibility.

[0003] Generally, thermally conductive sheets contain a polymer matrix and a thermally conductive filler dispersed in the polymer matrix. Furthermore, regarding thermally conductive sheets, in order to improve thermal conductivity in a specific direction, there are cases where anisotropic fillers with anisotropic shapes are oriented in one direction.

[0004] A thermally conductive sheet with anisotropic filler oriented in one direction can be manufactured, for example, by producing multiple primary sheets obtained by stretching or otherwise orienting the anisotropic filler along the surface direction of the sheet, stacking multiple primary sheets to form a single unit, and then cutting them vertically. This manufacturing method (hereinafter also referred to as the "flow orientation method") allows for the production of thermally conductive sheets composed of multiple stacked unit layers of specific thicknesses. Furthermore, the anisotropic filler can be oriented in the thickness direction of the sheet (for example, see Patent Document 1).

[0005] Furthermore, from the perspective of thermal conductivity and heat resistance, thermally conductive sheets widely use silicone resin as a polymer matrix. By dispersing thermally conductive fillers such as anisotropic fillers in the silicone resin and orienting the anisotropic fillers in the thickness direction of the sheet, the thermal conductivity is improved.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-27144 Summary of the Invention

[0009] [The problem the invention aims to solve]

[0010] However, in recent years, with the increasing sophistication of electronic devices and the resulting increase in heat generation, there is a need for thermally conductive sheets with higher thermal conductivity than ever before, requiring superior heat dissipation. From the perspective of improving thermal conductivity, increasing the content of thermally conductive filler in the thermally conductive sheet (i.e., reducing the content of the resin that forms the matrix) is considered. Furthermore, flexible thermally conductive sheets can be made by using silicone resin as the resin. However, if silicone resin is used as the resin, the following problem exists: it is difficult to manufacture thermally conductive sheets from a composition (composite) of silicone resin with added solvent and highly filled with thermally conductive filler, resulting in the inability to obtain thermally conductive sheets with high thermal conductivity.

[0011] In addition, the use of volatile solvents is also considered to obtain a composition of silicone resin highly filled with thermally conductive fillers. However, due to the influence of volatile solvents, the following problems may sometimes occur: the sheets are difficult to stack, or the sheets become hard and lose their flexibility.

[0012] Therefore, the objective of this invention is to improve the thermal conductivity and flexibility of a thermally conductive sheet that is constructed by using silicone resin as a matrix component and stacking multiple unit layers.

[0013] [Technical means to solve the problem]

[0014] The inventors conducted in-depth research and found that the above-mentioned problems can be solved by having the following structure, thereby completing the present invention. That is, the present invention provides the following [1] to

[11] .

[0015] [1] A thermally conductive sheet having multiple unit layers, each comprising a silicone resin and a thermally conductive filler, and stacked in such a manner that the multiple unit layers are bonded to each other, wherein the volume content of the silicone resin is 32% or less, and when compressed by 30% in the direction perpendicular to the bonding surface of the multiple unit layers, the compressive load on the sheet area of ​​25.4 mm × 25.4 mm is 7.0 kgf or less.

[0016] [2] As described in [1] above, the multiple unit layers are stacked along one direction along the surface direction of the sheet.

[0017] [3] As described in [1] or [2] above, the thermally conductive sheet contains anisotropic filler.

[0018] [4] As described in [3] above, the thermally conductive sheet also contains anisotropic filler.

[0019] [5] As described in [3] or [4] above, the anisotropic filler is oriented in the thickness direction of the sheet.

[0020] [6] As described in any of [3] to [5] above, the anisotropic filler is selected from at least one of fibrous materials and flake materials.

[0021] [7] As described in [6] above, the normal direction of the scale surface of the scale-like material is toward the stacking direction of the plurality of unit layers.

[0022] [8] As described in any of [1] to [7] above, the adjacent unit layers are directly fixedly bonded to each other.

[0023] [9] A method for manufacturing a thermally conductive sheet includes: step (1), molding a liquid composition comprising a curable siloxane composition, a thermally conductive filler and a volatile compound into a sheet to obtain a sheet-shaped body; step (2), with the sheet-shaped body disposed between two films, at least one of which is a breathable film, evaporating a portion of the volatile compound contained in the sheet-shaped body and curing the curable siloxane composition to obtain a primary sheet; step (4), preparing a plurality of the primary sheets and stacking the plurality of primary sheets, thereby joining the plurality of primary sheets to form a laminated block; and step (5), cutting the laminated block along the stacking direction into a sheet to obtain a thermally conductive sheet.

[0024]

[10] A method for manufacturing a thermally conductive sheet includes: step (1), molding a liquid composition comprising a curable siloxane composition, a thermally conductive filler and a volatile compound into a sheet shape to obtain a sheet-shaped molded body; step (2'), evaporating a portion of the volatile compound contained in the sheet-shaped molded body and curing the curable siloxane composition to obtain a primary sheet; step (3), preparing a plurality of the primary sheets and irradiating at least one side of each primary sheet with vacuum ultraviolet light; step (4'), stacking the plurality of primary sheets in such a way that the side irradiated by vacuum ultraviolet light is in contact with another primary sheet, thereby joining the plurality of primary sheets to form a stacked block; and step (5), cutting the stacked block into a sheet shape along the stacking direction to obtain a thermally conductive sheet.

[0025]

[11] The method for manufacturing a thermally conductive sheet as described in [9] or

[10] above, wherein the thermally conductive filler includes anisotropic filler, the anisotropic filler is oriented along the surface direction of the primary sheet, and the laminate is cut in a direction orthogonal to the direction in which the anisotropic filler is oriented.

[0026] [Invention Effects]

[0027] According to the present invention, the thermal conductivity and flexibility of the thermally conductive sheet constructed by using silicone resin as a matrix component and stacking multiple unit layers can be improved compared to the past. Attached Figure Description

[0028] Figure 1 This is a schematic cross-sectional view showing the thermally conductive sheet of the first embodiment.

[0029] Figure 2 This is a schematic perspective view showing an example of a method for manufacturing a thermally conductive sheet.

[0030] Figure 3 This is a schematic cross-sectional view showing the thermally conductive sheet of the second embodiment. Detailed Implementation

[0031] The thermally conductive sheet according to embodiments of the present invention will be described in detail below.

[0032] [First Implementation]

[0033] Figure 1 This refers to a thermally conductive sheet according to the first embodiment. The thermally conductive sheet 10 of the first embodiment includes a plurality of unit layers 13, each containing a silicone resin 11 and a thermally conductive filler. The plurality of unit layers 13 are stacked along a direction in the planar direction (that is, a direction perpendicular to the thickness direction z, also referred to as the "stack direction x"), and adjacent unit layers 13 are bonded to each other. In each unit layer 13, the silicone resin 11 serves as a matrix component for retaining the thermally conductive filler, and the thermally conductive filler is dispersedly incorporated into the silicone resin 11.

[0034] The thermally conductive sheet 10 contains anisotropic filler 14 and non-anisotropic filler 15 as thermally conductive fillers. The anisotropic filler 14 is oriented in the thickness direction z of the sheet 10. The presence of the anisotropic filler 14 oriented in the thickness direction z of the sheet improves the thermal conductivity in the thickness direction z. Furthermore, the thermally conductive sheet 10 also contains the non-anisotropic filler 15, further improving its thermal conductivity.

[0035] When the thermally conductive sheet 10 of the present invention is compressed by 30% in the direction perpendicular to the joint surface where it is joined with the plurality of unit layers, the compression load on the sheet area of ​​25.4 mm × 25.4 mm is 7.0 kgf or less. If the compression load exceeds 7.0 kgf, the flexibility is insufficient, making it difficult to compress and use in electronic devices or the like.

[0036] From the viewpoint of improving flexibility, the aforementioned compression load is preferably 5.0 kgf or less, more preferably 3.0 kgf or less. Furthermore, from the viewpoint of properly manufacturing the thermally conductive sheet 10 to prevent each unit layer 13 from expanding due to the pressure when stacking the unit layers 13, the aforementioned compression load is preferably 0.5 kgf or more.

[0037] Furthermore, the aforementioned compression load was measured when the joint surface where multiple unit layers are joined is compressed by 30% in the vertical direction. Specifically, compression can be performed along the thickness direction of the thermally conductive sheet 10. In addition, the term "compression of 30%" means compressing a thickness equivalent to 30% of the initial thickness of the thermally conductive sheet 10 before compression.

[0038] (Organic silicone resin)

[0039] There are no particular limitations as long as the silicone resin 11 is an organopolysiloxane, but a curable silicone resin is preferred. When the silicone resin 11 is curable, it can be obtained by curing the curable siloxane composition. The silicone resin 11 can be of addition reaction type or other types. When it is of addition reaction type, the curable siloxane composition preferably consists of a polysiloxane compound as the main agent and a curing agent for curing the main agent.

[0040] The polysiloxane used as the main agent is preferably an alkenyl-containing organopolysiloxane. Specifically, examples include: vinyl-terminated polydimethylsiloxane, vinyl-terminated polyphenylmethylsiloxane, vinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer, vinyl-terminated dimethylsiloxane-phenylmethylsiloxane copolymer, vinyl-terminated dimethylsiloxane-diethylsiloxane copolymer, and other vinyl-terminated organopolysiloxanes.

[0041] As a curing agent, there are no particular limitations as long as it can cure the polysiloxane compound used as the main agent, but it is preferred to be an organosiloxane having two or more hydrosilyl groups (SiH), i.e., an organohydrosiloxane.

[0042] The hardness of the primary film can be adjusted by appropriately changing the ratio of the curing agent to the main agent. Specifically, the hardness of the primary film can be reduced by decreasing the ratio of the curing agent to the main agent.

[0043] The volume percentage (volume basis percentage) of the silicone resin relative to the total amount of the thermally conductive sheet is 32% or less. If the volume percentage of the silicone resin exceeds 32%, the volume percentage of the thermally conductive filler decreases, and the thermal conductivity of the thermally conductive sheet decreases. From the viewpoint of further improving the thermal conductivity of the thermally conductive sheet, the volume percentage of the silicone resin is preferably 31% or less. When the volume percentage of the silicone resin is reduced as described above, it is not possible to obtain a suitable composite of silicone resin and thermally conductive filler, making it difficult to manufacture the thermally conductive sheet. However, in this invention, the volume percentage of the silicone resin can be reduced by employing the specific manufacturing method described below.

[0044] Furthermore, from the viewpoint of being able to manufacture thermally conductive sheets, the volume content of the silicone resin is preferably 18% by volume or more.

[0045] On the other hand, from the viewpoint of improving thermal conductivity, the volume content of the thermally conductive filler relative to the total amount of the thermally conductive sheet is preferably 68% by volume or more, and more preferably 69% by volume or more. Furthermore, the content of the thermally conductive filler is the sum of anisotropic filler and non-anisotropic filler.

[0046] In this invention, adjacent unit layers 13 are bonded to each other, but each unit layer 13 is preferably directly and fixedly bonded to the adjacent unit layer 13. That is, adjacent unit layers 13 are preferably directly bonded without the use of adhesives or other materials other than unit layers. With this configuration, since each unit layer 13 uses silicone resin 11 as a matrix component as described above, the silicone resin 11 is bonded to each other.

[0047] While silicone resins 11 typically have difficulty bonding with high adhesion, in this embodiment, as described below, adjacent unit layers 13 can be bonded to each other due to the specific manufacturing method used to produce the thermally conductive sheet. Therefore, peeling does not occur at the interface between unit layers 13. Furthermore, since the unit layers 13 are bonded to each other without any other components in between, the thermally conductive sheet 10 exhibits high flexibility.

[0048] (Anisotropic filler material)

[0049] The anisotropic filler 14 is a filler with an anisotropic shape and is an orientable filler. Preferably, the anisotropic filler 14 is selected from at least one type of fibrous material and flake material. Generally, the anisotropic filler 14 has a high aspect ratio, exceeding 2, and more preferably 5 or more. By making the aspect ratio greater than 2, the anisotropic filler 14 is easily oriented in the thickness direction z, which easily improves the thermal conductivity of the thermally conductive sheet 10.

[0050] Furthermore, there is no specific upper limit to the aspect ratio, but for practical purposes it is 100.

[0051] Furthermore, the aspect ratio is the ratio of the length of the major axis of the anisotropic filler 14 to the length of the minor axis. For fibrous materials, it means fiber length / fiber diameter, and for flake materials, it means the length / thickness of the major axis of the flake material.

[0052] The content of anisotropic filler 14 in the thermally conductive sheet is preferably 10 to 500 parts by weight relative to 100 parts by weight of silicone resin, more preferably 50 to 350 parts by weight. Furthermore, if expressed as a volume percentage, the content of anisotropic filler 14 is preferably 2 to 50% by volume relative to the total amount of the thermally conductive sheet, more preferably 10 to 40% by volume.

[0053] By setting the content of the anisotropic filler 14 to 10 parts by mass or more, the thermal conductivity can be easily improved. By setting it to 500 parts by mass or less, the viscosity of the liquid composition can be made appropriate, and the orientation of the anisotropic filler 14 can be made good.

[0054] When the anisotropic filler 14 is a fibrous material, its average fiber length is preferably 10 to 500 μm, more preferably 20 to 350 μm. If the average fiber length is set to 10 μm or more, the anisotropic fillers in each thermally conductive sheet 10 are in proper contact with each other, thereby ensuring the heat transfer path and improving the thermal conductivity of the thermally conductive sheet 10.

[0055] On the other hand, if the average fiber length is set to 500 μm or less, the volume of the anisotropic filler becomes smaller, allowing for high-level filling of the silicone resin. Furthermore, even if the anisotropic filler 14 is conductive, the conductivity of the thermally conductive sheet 10 is prevented from becoming excessively high.

[0056] Furthermore, the aforementioned average fiber length can be calculated by observing the anisotropic filler material under a microscope. More specifically, for example, for the anisotropic filler material 14 separated by dissolving the matrix component of the thermally conductive sheet 10, the fiber lengths of any 50 anisotropic fillers can be measured using an electron microscope or an optical microscope, and their average value (arithmetic mean) can be taken as the average fiber length. In this case, large shearing is not applied to avoid pulverizing the fibers. In addition, when it is difficult to separate the anisotropic filler material 14 from the thermally conductive sheet 10, an X-ray CT device can also be used to measure the fiber length of the anisotropic filler material 40 and calculate the average fiber length.

[0057] Furthermore, the diameter of the anisotropic filler 14 can also be measured in the same manner using an electron microscope or optical microscope, or an X-ray CT device.

[0058] Furthermore, in this invention, "arbitrary" means randomly selected.

[0059] Furthermore, when the anisotropic filler 14 is a flake-like material, its average particle size is preferably 10 to 400 μm, more preferably 15 to 300 μm. Particularly preferred is 20 to 200 μm. By setting the average particle size to 10 μm or more, the anisotropic fillers 14 in the thermally conductive sheet 10 can easily contact each other, ensuring a heat transfer path and improving the thermal conductivity of the thermally conductive sheet 10. On the other hand, if the average particle size is set to 400 μm or less, the volume of the anisotropic filler 14 is reduced, allowing for a high degree of filling of the anisotropic filler 14 in the silicone resin 11.

[0060] Furthermore, the average particle size of the flake-like material can be observed under a microscope for anisotropic fillers, and the major axis can be used as the diameter for calculation. More specifically, the major axis of any 50 anisotropic fillers can be measured using an electron microscope, optical microscope, or X-ray CT device in the same manner as the average fiber length mentioned above, and their average value (arithmetic mean) can be set as the average particle size.

[0061] Furthermore, the thickness of the anisotropic filler 14 can also be measured in the same manner using an electron microscope, an optical microscope, or an X-ray CT device.

[0062] As long as the anisotropic filler 14 is made of a known material with thermal conductivity, it is acceptable. Furthermore, the anisotropic filler 14 can be either conductive or insulating. If the anisotropic filler 14 is insulating, it can be well used in electrical machinery because it improves the insulation of the thermally conductive sheet 10 in the thickness direction z. Moreover, in this invention, "conductive" means, for example, a volume resistivity of 1 × 10⁻⁶. 9 For cases below Ω·cm. Furthermore, "insulating" refers to, for example, a volume resistivity greater than 1×10⁻⁶. 9 The case of Ω·cm.

[0063] Specifically, anisotropic filler material 14 can be exemplified by: carbon-based materials such as carbon fibers and flake carbon powder; metal materials or metal oxides such as metal fibers; boron nitride or metal nitrides; metal carbides; metal hydroxides; poly(p-phenylbenzoazole) fibers, etc. Among these, carbon-based materials are preferred because they have a lower specific gravity and better dispersibility in the silicone resin 11; graphitized carbon materials with high thermal conductivity are more preferred. Furthermore, from the viewpoint of insulation, boron nitride and poly(p-phenylbenzoazole) fibers are preferred. Zyrazole fibers, more preferably boron nitride. Boron nitride is not particularly limited, but it is preferably used in the form of a flake-like material. The flake-like boron nitride may or may not agglomerate, and preferably at least a portion of it contains unagglomerated boron nitride.

[0064] The anisotropic filler 14 is not particularly limited, but its thermal conductivity along the anisotropic direction (i.e., the major axis direction) is generally 30 W / m·K or higher, preferably 100 W / m·K or higher. The upper limit of the thermal conductivity of the anisotropic filler 14 is not particularly limited, but is, for example, 2000 W / m·K or lower. The thermal conductivity is measured by laser flash method.

[0065] Anisotropic filler 14 can be used alone or in combination with two or more types. For example, at least two anisotropic fillers 14 with different average particle sizes or average fiber lengths can be used as anisotropic fillers 14. It is believed that if anisotropic fillers of different sizes are used, the smaller anisotropic filler will enter between the relatively larger anisotropic fillers, thereby allowing the anisotropic filler to be filled into the polysiloxane resin at a high density and improving the heat transfer efficiency.

[0066] The carbon fiber used as the anisotropic filler 14 is preferably graphitized carbon fiber. Furthermore, as a flake-shaped carbon powder, flake-shaped graphite powder is preferred. Among these, the anisotropic filler 14 is more preferably graphitized carbon fiber.

[0067] Graphitized carbon fibers have graphite crystal planes connected along the fiber axis, exhibiting high thermal conductivity in this direction. Therefore, aligning the fiber axis with a specific direction can improve the thermal conductivity in that particular direction. Furthermore, flake graphite powder has graphite crystal planes connected in-plane in the flake direction, exhibiting high thermal conductivity in this direction. Therefore, aligning the flake surface with a specific direction can improve the thermal conductivity in that particular direction. Graphitized carbon fibers and flake graphite powder preferably have a high degree of graphitization.

[0068] As graphitized carbon materials such as the aforementioned graphitized carbon fibers, graphitized carbon materials obtained by graphitizing the following raw materials can be used. Examples include: condensed ring hydrocarbon compounds such as naphthalene, PAN (polyacrylonitrile), condensed heterocyclic compounds such as pitch, etc. Graphitized mesophase pitch or polyimide or polyindole with a high degree of graphitization are particularly preferred. For example, by using mesophase pitch, in the following spinning step, the pitch is oriented in the fiber axis direction due to its anisotropy, thereby obtaining graphitized carbon fibers with excellent thermal conductivity in that fiber axis direction.

[0069] Regarding the form in which the mesophase pitch in graphitized carbon fibers is used, there are no particular limitations as long as spinning is possible. Mesophase pitch can be used alone or in combination with other raw materials. However, in terms of high heat transfer, spinnability, and quality stability, the most preferred form is graphitized carbon fibers with 100% mesophase pitch content, where the mesophase pitch is used alone.

[0070] Graphitized carbon fibers can be produced by sequentially spinning, infusing, and carbonizing, followed by pulverization or cutting into specific particle sizes before graphitization, or by carbonization followed by pulverization or cutting before graphitization. When pulverization or cutting occurs before graphitization, the newly exposed surfaces facilitate condensation and cyclization reactions during graphitization, thus increasing the degree of graphitization and obtaining graphitized carbon fibers with further improved thermal conductivity. Conversely, when the spun carbon fibers are graphitized and then pulverized, the graphitized fibers are relatively hard and easy to pulverize; a short pulverization time can yield carbon fiber powder with a relatively narrow fiber length distribution.

[0071] The average fiber length of the graphitized carbon fiber is preferably 50–500 μm, more preferably 70–350 μm. Furthermore, the aspect ratio of the graphitized carbon fiber is greater than 2, as described above, and preferably 5 or more. The thermal conductivity of the graphitized carbon fiber is not particularly limited, but the thermal conductivity along the fiber axis is preferably 400 W / m·K or more, more preferably 800 W / m·K or more.

[0072] The anisotropic filler 14 is oriented in the thickness direction z of the thermally conductive sheet in each unit layer. To explain more specifically the orientation of the anisotropic filler 14 in the thickness direction z, when the anisotropic filler 14 is a fibrous filler, it means that the ratio of the number of anisotropic fillers in which the angle between the long axis of the fibrous filler and the thickness direction z of the thermally conductive sheet 10 is less than 30° is greater than 50% of the total amount of anisotropic filler, and this ratio is preferably greater than 80%.

[0073] Furthermore, when the anisotropic filler 14 is a flake-shaped filler, it means that the ratio of the number of anisotropic fillers in which the angle between the flake surface and the thickness direction z of the thermally conductive sheet 10 is less than 30° is greater than 50% of the total amount of anisotropic filler, and this ratio is preferably greater than 80%. In other words, it means that the ratio of the number of anisotropic fillers in which the angle between the normal direction of the flake surface and the sheet surface (xy plane) of the thermally conductive sheet is less than 30° is greater than 50% of the total amount of anisotropic filler, and this ratio is preferably greater than 80%.

[0074] Furthermore, regarding the orientation of the anisotropic filler 14, from the viewpoint of improving thermal conductivity, it is preferable to set the angle between the long axis and the thickness direction z, or the angle between the scale surface and the thickness direction z, to 0° or more but less than 5°. On the other hand, from the viewpoint of reducing the load when compressing the thermally conductive sheet 10, it is also acceptable to tilt it within a range of 5° or more but less than 30°. Furthermore, these angles are the average of the orientation angles of a certain number (e.g., any 50 anisotropic fillers 14).

[0075] Furthermore, regarding the anisotropic filler 14, when the anisotropic filler 14 is not either fibrous or scaly, it means that the ratio of the number of anisotropic fillers whose long axis forms an angle of less than 30° with respect to the thickness direction z of the thermally conductive sheet 10 is greater than 50% of the total amount of anisotropic filler, and this ratio is preferably greater than 80%.

[0076] Furthermore, when the anisotropic filler 14 is a flake-like material, the anisotropic filler 14 is preferably oriented with the normal direction of the flake surface facing a specific direction, specifically, preferably facing the stacking direction x of the plurality of unit layers 13. By oriented the normal direction towards the stacking direction x in this way, the thermal conductivity of the thermally conductive sheet 10 in the thickness direction z is improved. In addition, the thermal conductivity along the surface direction of the thermally conductive sheet 10 and in a direction orthogonal to the stacking direction x is also improved.

[0077] Furthermore, the so-called normal direction of the scale surface toward the stacking direction x means that the ratio of the number of carbon fiber powders in which the angle between the normal direction and the stacking direction x is less than 30° is greater than 50%, and this ratio is preferably greater than 80%.

[0078] Furthermore, when the anisotropic filler 14 is a flake-like material, as described in the manufacturing method below, shear force is applied and it is simultaneously formed into a flake shape, thereby causing the normal direction of the flake surface to face the lamination direction x.

[0079] <Anisotropic filler>

[0080] The anisotropic filler 15 is a thermally conductive filler included in the thermally conductive sheet 10 in addition to the anisotropic filler 14. It is a material that, together with the anisotropic filler 14, imparts thermal conductivity to the thermally conductive sheet 10. In this embodiment, by including the anisotropic filler 15, a thermally conductive sheet 10 with high thermal conductivity can be obtained, where the gaps between the oriented anisotropic fillers 14 are separated by filler.

[0081] The non-anisotropic filler 15 is a filler whose shape is not substantially anisotropic. It is a filler that will not be oriented in a specific direction even when the anisotropic filler 14 is oriented in a specific direction under the action of shear force, etc.

[0082] The aspect ratio of the anisotropic filler 15 is 2 or less, more preferably 1.5 or less. In this embodiment, by including anisotropic filler 15 with such a low aspect ratio, a thermally conductive sheet 10 with high thermal conductivity and appropriate intervening of thermally conductive filler in the gaps between the anisotropic filler 14 can be obtained. Furthermore, by setting the aspect ratio to 2 or less, the viscosity of the liquid composition described below can be prevented from increasing, thus preventing it from becoming highly filled.

[0083] The anisotropic filler 15 may also be conductive, but it is preferable to be insulating. In the thermally conductive sheet 10, it is preferable that both the anisotropic filler 14 and the anisotropic filler 15 are insulating. If both the anisotropic filler 14 and the anisotropic filler 15 are insulating, it is easy to further improve the insulation of the thermally conductive sheet 10 in the thickness direction z.

[0084] Specific examples of the anisotropic filler 15 include: metals, metal oxides, metal nitrides, metal hydroxides, carbon materials, oxides other than metals, nitrides, carbides, etc. Furthermore, examples of the shape of the anisotropic filler 14 include: spherical, amorphous powder, etc.

[0085] In the anisotropic filler 15, examples of metals include aluminum, copper, and nickel; examples of metal oxides include aluminum oxide, magnesium oxide, and zinc oxide; examples of metal nitrides include aluminum nitride; examples of metal hydroxides include aluminum hydroxide; and examples of carbon materials include spherical graphite. Examples of oxides, nitrides, and carbides other than metals include quartz, boron nitride, and silicon carbide.

[0086] Among these, aluminum oxide or aluminum is preferred in terms of high thermal conductivity and easy availability of spherical shapes, while aluminum hydroxide is preferred in terms of easy availability and ability to improve the flame retardancy of the thermally conductive sheet.

[0087] As an insulating anisotropic filler 15, examples of the above include: metal oxides, metal nitrides, metal hydroxides, and metal carbides, with aluminum oxide and aluminum hydroxide being particularly preferred.

[0088] The anisotropic filler 15 can be used alone or in combination with two or more of the above-mentioned types.

[0089] The average particle size of the anisotropic filler 15 is preferably 0.1 to 50 μm, more preferably 0.3 to 35 μm. By setting the average particle size to 50 μm or less, it is less likely to cause adverse conditions such as interference with the orientation of the anisotropic filler 14. Furthermore, by setting the average particle size to 0.1 μm or more, the specific surface area of ​​the anisotropic filler 15 will not increase excessively, and even with large-scale blending, the viscosity of the liquid composition is not easily increased, making it easy to highly fill the anisotropic filler 15.

[0090] Furthermore, from the viewpoint of increasing the filling amount of anisotropic filler, it is preferable to use two or more fillers with different particle sizes. For example, it is preferable to use anisotropic filler with a small particle size of 0.1 μm to 2 μm and anisotropic filler with a large particle size of more than 2 μm and less than 50 μm. When using two anisotropic fillers with different average particle sizes, the amount of the small particle size anisotropic filler relative to the large particle size anisotropic filler (amount of small particle size anisotropic filler / amount of large particle size anisotropic filler) is preferably 0.05 to 5, more preferably 0.2 to 1.0.

[0091] If a certain amount of small-particle-size anisotropic filler is used, it is usually difficult to form a primary sheet for making a thermally conductive sheet. However, according to the following method of manufacturing a thermally conductive sheet according to the present invention, even when a certain amount of small-particle-size anisotropic filler is used, a thermally conductive sheet can be appropriately manufactured.

[0092] Furthermore, the average particle size of the anisotropic filler 15 can be measured by observation using an electron microscope or the like. More specifically, the particle size of any 50 anisotropic fillers can be measured using an electron microscope, an optical microscope, or an X-ray CT device in the same manner as the measurement of the anisotropic fillers described above, and their average value (arithmetic mean) can be taken as the average particle size.

[0093] The content of the anisotropic filler 15 in the thermally conductive sheet 10 is preferably in the range of 50 to 1500 parts by mass relative to 100 parts by mass of silicone resin, and more preferably in the range of 200 to 800 parts by mass. By setting it to 50 parts by mass or more, the amount of anisotropic filler 15 interposed between the anisotropic fillers 14 is made to a certain amount or more, thereby improving the thermal conductivity. On the other hand, by setting it to 1500 parts by mass or less, the effect of improving the thermal conductivity corresponding to the content can be obtained, and the anisotropic filler 15 will not hinder the heat transfer of the anisotropic filler 14. In addition, by setting it to the range of 200 to 800 parts by mass, the thermal conductivity of the thermally conductive sheet 10 is excellent, and the viscosity of the liquid composition is also good. Furthermore, if the content of the anisotropic filler 15 is expressed as a volume % (%), it is preferably 20 to 75% by volume relative to the total amount of the thermally conductive sheet, and more preferably 30 to 60% by volume.

[0094] Furthermore, the content of the anisotropic filler 15, which has an average particle size of 0.1 μm or more and 2 μm or less, is preferably 180 to 500 parts by weight relative to 100 parts by weight of the silicone resin, and particularly preferably 200 to 420 parts by weight. This is because, within this range, the puncture load of the liquid composition can be reduced.

[0095] Furthermore, in this embodiment, each unit layer 13 has substantially the same composition. Therefore, the content of anisotropic filler, non-anisotropic filler, and silicone resin in each unit layer is the same as that in the thermally conductive sheet, and the content of anisotropic filler, non-anisotropic filler, and silicone resin in each unit layer is also as described above.

[0096] (Added ingredients)

[0097] In the thermally conductive sheet 10, various additives may be incorporated into the silicone resin 11 without impairing its function. Examples of additives include at least one selected from dispersants, coupling agents, adhesives, flame retardants, antioxidants, colorants, and precipitation inhibitors. Furthermore, when the curable siloxane composition is cured as described above, a curing catalyst that promotes curing may also be incorporated as an additive. Examples of curing catalysts include platinum-based catalysts. Moreover, resin components other than silicone resin may be mixed into the silicone resin 11 as additives without impairing the effects of the present invention.

[0098] (thermal conductive sheet)

[0099] The thermal conductivity of the thermally conductive sheet 10 in the thickness direction z is, for example, 4.5 W / (m·K) or higher, preferably 8.0 W / (m·K) or higher, and more preferably 12.0 W / (m·K) or higher. By setting these lower limits or higher, the thermal conductivity of the thermally conductive sheet 10 in the thickness direction z becomes excellent. There is no particular upper limit to the thermal conductivity of the thermally conductive sheet 10 in the thickness direction z, for example, it is 50 W / (m·K) or lower. Furthermore, the thermal conductivity is measured according to the method of ASTM D5470-06.

[0100] The O0-type hardness of the thermally conductive sheet 10 is, for example, 62 or less. By ensuring the O0-type hardness of the thermally conductive sheet 10 is 62 or less, flexibility is ensured, for example, resulting in good conformability to heat-generating and heat-dissipating elements, thereby facilitating good heat dissipation. Furthermore, from the viewpoint of improving flexibility and thus enhancing conformability, the O0-type hardness of the thermally conductive sheet 10 is preferably 50 or less, and more preferably 45 or less.

[0101] Furthermore, the hardness of the thermally conductive sheet 10 is not particularly limited, but may be 15 or higher, preferably 18 or higher, and more preferably 25 or higher.

[0102] In this embodiment, anisotropic filler 14 is exposed on two surfaces 10A and 10B of the thermally conductive sheet 10. Furthermore, the exposed anisotropic filler 14 may also protrude from the two surfaces 10A and 10B respectively. By exposing the anisotropic filler 14 on the two surfaces 10A and 10B, the thermally conductive sheet 10 makes the two surfaces 10A and 10B non-adhesive surfaces. Moreover, the thermally conductive sheet 10 is cut using a cutting tool, making the two surfaces 10A and 10B cut surfaces, thus exposing the anisotropic filler 14 on the two surfaces 10A and 10B.

[0103] Either or both of the two surfaces 10A and 10B may be used as the adhesive surface without exposing the anisotropic filler 14.

[0104] The thickness of the thermally conductive sheet 10 can be appropriately varied depending on the shape or application of the electronic device on which the thermally conductive sheet 10 is to be mounted. There is no particular limitation on the thickness of the thermally conductive sheet 10; for example, it can be used in the range of 0.1 to 50 mm.

[0105] Furthermore, the thickness of each unit layer 13 is not particularly limited, but is preferably 0.1 to 10 mm, more preferably 0.3 to 5.0 mm. Moreover, the thickness of the unit layer 13 is the length of the unit layer 13 along the stacking direction x.

[0106] The thermally conductive sheet 10 is used inside electronic devices. Specifically, the thermally conductive sheet 10 is placed between a heat-generating element and a heat-dissipating element, conducting the heat emitted by the heat-generating element to the heat-dissipating element for dissipation. Examples of heat-generating elements include various electronic components such as CPUs, power amplifiers, and power supplies used inside electronic devices. Examples of heat-dissipating elements include heat sinks, heat pipes, and the metal casing of electronic devices. The two surfaces 10A and 10B of the thermally conductive sheet 10 are in close contact with the heat-generating element and the heat-dissipating element, respectively, and are used under compression.

[0107] <Manufacturing Method of Thermally Conductive Sheets>

[0108] (Manufacturing Method 1)

[0109] The manufacturing method of the thermally conductive sheet of the present invention is not particularly limited, but preferably a first manufacturing method including each of the following steps (1), (2), (4) and (5).

[0110] That is, the first manufacturing method of the thermally conductive sheet of the present invention is a manufacturing method of a thermally conductive sheet comprising the following steps:

[0111] Step (1) involves molding a liquid composition containing a curable siloxane composition, a thermally conductive filler, and a volatile compound into a sheet to obtain a sheet-shaped molded body.

[0112] Step (2) involves placing the sheet-shaped molded body between two films, at least one of which is a breathable membrane, allowing a portion of the volatile compound contained in the sheet-shaped molded body to evaporate, and curing the curable siloxane composition to obtain a single sheet.

[0113] Step (4) involves preparing multiple of the aforementioned primary sheets and stacking them together to form a laminated block; and

[0114] Step (5) involves cutting the aforementioned stacked block into sheets along the stacking direction to obtain a thermally conductive sheet.

[0115] <Step (1)>

[0116] Step (1) is the following steps, namely, molding the liquid composition containing the curable siloxane composition, the thermally conductive filler, and the volatile compound into a sheet to obtain a sheet-shaped molded body. Here, the curable siloxane composition, as described above, is a raw material for organosilicon resin.

[0117] In addition to curable siloxane compositions and thermally conductive fillers, liquid compositions also contain volatile compounds. By using liquid compositions containing volatile compounds, it is possible to manufacture liquid compositions with a higher content of thermally conductive fillers than conventional liquid compositions. Furthermore, by following specific steps, a thermally conductive sheet with a higher content of thermally conductive fillers (i.e., a lower content of silicone resin) can be obtained.

[0118] In this specification, volatile compounds refer to compounds possessing at least one of the following properties: in thermogravimetric analysis, when heated at a rate of 2°C / min, the temperature T1 at which 90% weight loss occurs is in the range of 70–300°C; and the boiling point (at 1 atmosphere) is in the range of 60–200°C. Here, the temperature T1 at which 90% weight loss occurs means the temperature at which 90% of the weight of the sample before thermogravimetric analysis is lost (i.e., the temperature at which the sample becomes 10% of its original weight before the determination), with the sample weight set to 100%.

[0119] Examples of volatile compounds include volatile silane compounds and volatile solvents, with volatile silane compounds being preferred.

[0120] Examples of the aforementioned volatile silane compounds include alkoxysilane compounds. Alkoxysilane compounds are compounds having a structure in which 1 to 3 of the four bonds in the silicon atom (Si) are bonded to alkoxy groups, and the remaining bonds are bonded to organic substituents. Examples of alkoxy groups present in alkoxysilane compounds include methoxy, ethoxy, propoxy, butoxy, pentoxy, and hexoxy. Alkoxysilane compounds can also contain alkoxysilanes in the form of dimers.

[0121] From the viewpoint of ease of acquisition, alkoxysilane compounds having methoxy or ethoxy groups are preferred. From the viewpoint of improving affinity with thermally conductive fillers as inorganic materials, the number of alkoxy groups in the alkoxysilane compound is preferably 3. More preferably, the alkoxysilane compound is selected from at least one of trimethoxysilane compounds and triethoxysilane compounds.

[0122] Examples of functional groups contained in the organic substituents of alkoxysilane compounds include: acryloyl, alkyl, carboxyl, vinyl, methacryl, aromatic, amino, isocyanate, isocyanurate, epoxy, hydroxy, and mercapto. When using an addition-reaction type organopolysiloxane containing a platinum catalyst as a precursor to the aforementioned matrix, it is preferable to select an alkoxysilane compound that is unlikely to affect the curing reaction of the organopolysiloxane forming the matrix. Specifically, when using an addition-reaction type organopolysiloxane containing a platinum catalyst, the organic substituents of the alkoxysilane compound preferably do not contain amino, isocyanate, isocyanurate, hydroxy, or mercapto groups.

[0123] Regarding alkoxysilane compounds, from the perspective of easily and highly filling thermally conductive fillers by improving the dispersibility of the thermally conductive filler, alkylalkoxysilane compounds containing alkyl groups bonded to silicon atoms are preferred, i.e., alkoxysilane compounds having alkyl groups as organic substituents. The number of carbon atoms in the alkyl group bonded to silicon atoms is preferably 4 or more. Furthermore, from the viewpoint that the alkoxysilane compound itself has relatively low viscosity and thus lowers the viscosity of the thermally conductive composition, the number of carbon atoms in the alkyl group bonded to silicon atoms is preferably 16 or less.

[0124] Alkoxysilane compounds may be used in one or more forms. Specific examples of alkoxysilane compounds include: alkyl-containing alkoxysilane compounds, vinyl-containing alkoxysilane compounds, acryloyl-containing alkoxysilane compounds, methacryloyl-containing alkoxysilane compounds, aromatic-containing alkoxysilane compounds, amino-containing alkoxysilane compounds, isocyanate-containing alkoxysilane compounds, isocyanurate-containing alkoxysilane compounds, epoxy-containing alkoxysilane compounds, and mercapto-containing alkoxysilane compounds.

[0125] Examples of alkyl-containing alkoxysilane compounds include: methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, cyclohexylmethyldimethoxysilane, n-octyltriethoxysilane, and n-decyltrimethoxysilane. Among alkyl-containing alkoxysilane compounds, at least one is preferably selected from isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, cyclohexylmethyldimethoxysilane, n-octyltriethoxysilane, and n-decyltrimethoxysilane, more preferably at least one is selected from n-octyltriethoxysilane and n-decyltrimethoxysilane, and particularly preferably n-decyltrimethoxysilane.

[0126] Examples of vinyl-containing alkoxysilane compounds include vinyltrimethoxysilane and vinyltriethoxysilane. Examples of acryloyl-containing alkoxysilane compounds include 3-acryloyloxypropyltrimethoxysilane. Examples of methacryloxysilane compounds include 3-methacryloyloxypropylmethyldimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, and 3-methacryloyloxypropyltriethoxysilane. Examples of aromatic-containing alkoxysilane compounds include phenyltrimethoxysilane and phenyltriethoxysilane. Examples of amino-containing alkoxysilane compounds include: N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane. Examples of isocyanate-containing alkoxysilane compounds include: 3-isocyanopropyltriethoxysilane. Examples of isocyanate-containing alkoxysilane compounds include: tris(trimethoxysilylpropyl)isocyanate. Examples of epoxy-containing alkoxysilane compounds include: 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-epoxypropoxypropylmethyldimethoxysilane, 3-epoxypropoxypropyltrimethoxysilane, and 3-epoxypropoxypropyltriethoxysilane. Examples of alkoxysilane compounds containing mercapto groups include 3-mercaptopropyltrimethoxysilane.

[0127] Furthermore, the specific example of the alkoxysilane compound mentioned above is just one example and is not limited to this.

[0128] As the aforementioned volatile solvent, a solvent with a boiling point (at 1 atmosphere) of 60–200°C can be used, preferably a solvent with a boiling point of 100–130°C. Furthermore, the volatile solvent preferably has a boiling point that is at least 10°C higher than the curing temperature of the organopolysiloxane, and more preferably has a boiling point that is at least 20°C higher.

[0129] The type of volatile solvent can be appropriately selected to meet the above requirements, for example, aromatic compounds such as toluene are preferred.

[0130] The content of volatile compounds in the liquid composition is preferably 5 to 100 parts by weight relative to 100 parts by weight of the curable siloxane composition used as a raw material for organosilicon resin, and more preferably 15 to 70 parts by weight.

[0131] Simply adjust the content of the curable siloxane composition and the thermally conductive filler in the liquid composition so that the content of the silicone resin and the thermally conductive filler in the thermally conductive sheet formed by the liquid composition is within the above-mentioned range.

[0132] Specifically, when the total of all components in the liquid composition, excluding volatile compounds, is set to 100% by volume, the curable siloxane composition is preferably 32% by volume or less, more preferably 31% by volume or less. Furthermore, when the total of all components in the liquid composition, excluding volatile compounds, is set to 100% by volume, the thermally conductive filler is preferably 68% by volume or more, more preferably 69% by volume or more.

[0133] The liquid composition is prepared by mixing a curable siloxane composition, a thermally conductive filler (i.e., anisotropic filler 14 and non-anisotropic filler 15), and a volatile compound. The liquid composition is typically a slurry. Additional components may be added to the liquid composition as needed. Here, the components constituting the liquid composition can be mixed using, for example, a known kneader, mixing roller, mixer, or vibratory mixer.

[0134] In step (1), the liquid composition prepared as described above is molded into a sheet to form a sheet-shaped body.

[0135] The viscosity of the liquid composition can be determined according to the sheet forming method and the required sheet thickness. When the liquid composition is coated onto a substrate and formed into a sheet, the viscosity of the liquid composition is preferably 50 to 10000 Pa·s. If the viscosity is set to 50 Pa·s or higher, the anisotropic filler can be easily oriented in the planar direction of the sheet by applying shear force. Furthermore, setting it to 10000 Pa·s or lower improves coatability.

[0136] Furthermore, the viscosity is the viscosity measured using a rotational viscometer (Burlburton viscometer DV-E, spindle SC4-14) at a rotational speed of 1 rpm, and the measurement temperature is the temperature at which the liquid composition is coated.

[0137] The puncture load of the liquid composition is preferably 0.1 to 120 gf, more preferably 5.0 to 60 gf, and even more preferably 10 to 40 gf. If the puncture load is within the above range, the liquid composition can be appropriately coated onto a substrate and formed into a sheet. The puncture load of the liquid composition can be determined by the method described in the examples.

[0138] Curable siloxane compositions are typically liquids, and the aforementioned viscosity can be achieved by appropriately adjusting the molecular weight and other properties of the components constituting the curable siloxane composition (such as alkenyl-containing organopolysiloxanes and organohydrogen polysiloxanes).

[0139] Subsequently, a shear force is applied to the liquid composition while simultaneously shaping it into a sheet, thereby producing a sheet-shaped body. This orients the anisotropic filler 14 in a direction parallel to the sheet surface (i.e., the planar direction). Here, the liquid composition can be applied to the substrate film, for example, using a rod coater or applicator, extrusion molding, or ejection from a nozzle. This method applies a shear force along the coating direction of the liquid composition. The anisotropic filler 14 in the liquid composition is oriented in the coating direction by this shear force. Furthermore, the substrate film can be a breathable membrane.

[0140] In addition, as other methods to obtain sheet-shaped molded articles, methods such as sandwiching a liquid composition between two films and stretching it by stretching rollers can also be applied.

[0141] <Step (2)>

[0142] Step (2) is the following steps, namely, in the state of placing the sheet-shaped molded body obtained by step (1) between two films, at least one of which is a breathable membrane, a portion of the volatile compound contained in the sheet-shaped molded body is volatilized, and the curable siloxane composition is cured to obtain a single sheet.

[0143] In step (2), a sheet-shaped body is disposed between two membranes. Specifically, the two membranes are disposed in such a way that they are in contact with two surfaces of the sheet-shaped body. At least one of the two membranes is a breathable membrane.

[0144] When the curable siloxane composition contained in the sheet-shaped molded body is cured by using a breathable membrane, the volatile compounds can be properly volatilized, and the generation of bubbles in the primary sheet formed by the sheet-shaped molded body can be suppressed. In addition, the surface of the primary sheet has fewer irregularities, making it easier to form a laminate in step (4).

[0145] Here, "permeability" refers to the property that liquids cannot pass through but gases can. The oxygen permeability of the permeable membrane is preferably, for example, 1 × 10⁻⁶. -16 mol·m / (m 2 (·s·Pa) or higher. Furthermore, the moisture permeability of the aforementioned breathable membrane is more preferably 1×10⁻⁶. -15 mol·m / (m 2 (·s·Pa) or above. Here, the air permeability is the value obtained according to the air permeability test method of JIS K7126-2:2006.

[0146] Examples of breathable membranes include porous membranes formed by mixing polymers with fillers or by mixing polymers with each other. In addition, any breathable membrane is acceptable, even non-porous membranes.

[0147] There are no particular limitations on the polymers constituting the breathable membrane, and examples include: low-density polyethylene, linear low-density polyethylene, poly(4-methylpent-1-ene), ethyl cellulose, polytetrafluoroethylene, or fluorinated resins such as fluorinated resins. Among these, non-porous breathable membranes formed of poly(4-methylpent-1-ene) and porous breathable membranes formed of fluorinated resins are preferred. By using a breathable membrane formed of poly(4-methylpent-1-ene) and a fluorinated resin, volatile compounds can be appropriately volatilized when the curable siloxane composition is cured, resulting in excellent release properties when the breathable membrane is peeled off from a single sheet. Furthermore, non-porous breathable membranes formed of poly(4-methylpent-1-ene) are particularly preferred. If a non-porous, breathable membrane formed of poly(4-methylpent-1-ene) is used, the release properties are particularly excellent when a liquid composition is coated, as the liquid resin does not penetrate into the pores. Furthermore, since there are no pores on the membrane surface, no unevenness caused by pores is formed, thus a single sheet with a good surface condition and fewer unevenness can be obtained.

[0148] It is permissible if at least one of the two membranes used in step (2) is a breathable membrane, or both of them may be breathable membranes. In addition, one of the two membranes may be a breathable membrane and the other may be a non-breathable membrane such as a polyester membrane or a polyolefin membrane.

[0149] In step (2), the sheet-shaped body obtained in step (1) is placed between the two films, and the method for achieving this state is not particularly limited. For example, when the sheet-shaped body is made by coating a liquid composition onto a substrate film in step (1), the substrate film can be placed as one of the two films, with the other film in contact with the sheet-shaped body. Furthermore, when the sheet-shaped body is obtained using a single component in step (1), two films are prepared, and the sheet-shaped body is placed between the two films.

[0150] In step (2), with a sheet-shaped molded body disposed between the two films, a portion of the volatile compounds contained in the sheet-shaped molded body is volatilized, and the curable siloxane composition is cured to obtain a single sheet. Here, the curing of the curable siloxane composition is carried out by heating, through which a portion of the volatile compounds is volatilized.

[0151] The primary sheet manufactured without causing the volatile compounds to evaporate has excessive softness and loss of resilience. When the primary sheet is laminated in step (4), it causes the primary sheet to collapse, making it difficult to manufacture a thermally conductive sheet.

[0152] On the other hand, regarding the primary sheet manufactured by completely evaporating the volatile compound, when the primary sheet is stacked in step (4), the bonding between the sheets is poor, resulting in difficulty in manufacturing a thermally conductive sheet.

[0153] In step (2), when the volatile compound contained in the sheet-shaped molded body before evaporation is set to 100% by mass, the evaporation rate of the volatile compound is preferably 10 to 80% by mass, and more preferably 30 to 80% by mass. By setting the evaporation rate of the volatile compound to the above range, the sheet has appropriate softness, and the bonding between the sheets becomes good, making it easy to obtain a sheet with suitable thermal conductivity.

[0154] The amount of volatilization can be adjusted by changing the heating temperature and time during curing. For example, the heating temperature can be around 65–100°C. Furthermore, the heating time is approximately 2–24 hours.

[0155] As described above, a primary sheet can be obtained by curing the curable siloxane composition contained in the sheet-shaped molded body. In the primary sheet, as described above, the anisotropic filler is oriented along the surface direction. After obtaining the primary sheet, the two films disposed on its surface can be peeled off.

[0156] The thickness of the primary sheet obtained by curing is preferably in the range of 0.1 to 10 mm. By setting the thickness of the primary sheet within the above range, the anisotropic filler 14 can be appropriately oriented in the planar direction by shear force. Furthermore, by setting the thickness of the primary sheet to 0.1 mm or more, it can be easily peeled off from the film. Moreover, by setting the thickness of the primary sheet to 10 mm or less, deformation of the primary sheet due to its own weight is prevented. From these points of view, the thickness of the primary sheet is more preferably 0.3 to 5.0 mm.

[0157] The OO-type hardness of the primary sheet is preferably 6 or higher. By setting it to 6 or higher, when the primary sheets are stacked, even under pressure, the primary sheets will hardly expand, and a laminated block with sufficient thickness can be produced. From this point of view, the OO-type hardness of the primary sheet is more preferably 10 or higher, and even more preferably 15 or higher.

[0158] Furthermore, from the viewpoint of ensuring the flexibility of the obtained thermally conductive sheet, the OO-type hardness of the primary sheet is preferably 55 or less, more preferably 50 or less, and even more preferably 40 or less.

[0159] <Step (4)>

[0160] Step (4) is the following steps, namely, preparing multiple single sheets obtained in step (2) above, and stacking multiple single sheets, thereby joining multiple single sheets to form a stacked block.

[0161] like Figure 2As shown in (a) and (b), multiple primary sheets 21 are stacked in the same orientation direction as the anisotropic filler 14. Here, it is known that if the volatile compounds are allowed to completely evaporate from a primary sheet highly filled with thermally conductive filler, the surface tends to become dry due to the exposure of the thermally conductive filler, resulting in poor surface adhesion. Since the primary sheet contains a certain amount of volatile compounds, the surface does not become dry, and multiple primary sheets can be joined by stacking. Therefore, it is unnecessary to use adhesives or primers to join the primary sheets together. When adhesives or primers are used, they may penetrate to a certain depth into the primary sheet, thereby reducing the flexibility of the thermally conductive sheet. However, the thermally conductive sheet of the present invention exhibits good flexibility because it does not require the use of adhesives or primers during its manufacturing process.

[0162] The primary sheets 21 can be joined by overlapping as described above, or pressure can be applied in the stacking direction x of the primary sheets 21 to make the joint more secure. Pressure should be applied at a level that will not cause significant deformation of the primary sheets 21; for example, pressure can be applied using rollers or a press. As an example, when using rollers, it is preferable to set the pressure to 0.3 to 3 kgf / 50 mm.

[0163] The laminated primary sheet 21 can be appropriately heated, for example, during pressurization, but since bonding can be achieved even without heating, the laminated primary sheet 21 is preferably not heated. Therefore, the stamping temperature is, for example, 0 to 50°C, preferably around 10 to 40°C.

[0164] <Step (5)>

[0165] Step (5) is the following steps, namely, cutting the laminated block obtained in step (4) into a sheet along the lamination direction to obtain a thermally conductive sheet.

[0166] like Figure 2 As shown in (c), the laminate 22 is cut along the lamination direction x of the primary sheet 21 using the cutter 18 to obtain the thermally conductive sheet 10. At this time, the laminate 22 can be cut in a direction orthogonal to the orientation direction of the anisotropic filler 14. The cutter 18 can be, for example, a double-edged or single-edged blade such as a razor or slicing blade, a circular blade, a wire cutter, a serrated blade, etc. The laminate 22 is cut using the cutter 18 by methods such as pressing, shearing, rotating, or sliding.

[0167] From the viewpoint of causing the residual volatile compounds to volatilize, it is preferable to heat-treat the thermally conductive sheet obtained after cutting, which can be carried out at a heating temperature of 100 to 150°C and a heating time of 2 to 48 hours.

[0168] The first manufacturing method, comprising steps (1), (2), (4), and (5), has been described above. Alternatively, the step of irradiating vacuum ultraviolet light, as described in the second manufacturing method below, i.e., step (3), can be placed between steps (2) and (4) in the first manufacturing method. By performing step (3), the bonding strength between the primary sheets is improved when the secondary sheets are stacked in step (4), making it easier to manufacture the thermally conductive sheet of the present invention.

[0169] (Second Manufacturing Method)

[0170] The manufacturing method of the thermally conductive sheet of the present invention is preferably a second manufacturing method comprising each of the following steps (1), (2'), (3), (4'), and (5).

[0171] That is, the second manufacturing method of the thermally conductive sheet of the present invention is a manufacturing method of a thermally conductive sheet comprising the following steps:

[0172] Step (1) involves molding a liquid composition containing a curable siloxane composition, a thermally conductive filler, and a volatile compound into a sheet to obtain a sheet-shaped molded body.

[0173] Step (2') involves evaporating a portion of the volatile compounds contained in the sheet-shaped molded body and curing the curable siloxane composition to obtain a single sheet.

[0174] Step (3) involves preparing multiple primary wafers and irradiating at least one side of each primary wafer with vacuum ultraviolet light.

[0175] Step (4') involves stacking the plurality of primary sheets in such a way that one surface of the primary sheet, which has been irradiated by vacuum ultraviolet light, is in contact with another primary sheet, thereby joining the plurality of primary sheets to form a stacked block; and

[0176] Step (5) involves cutting the aforementioned stacked block into sheets along the stacking direction to obtain a thermally conductive sheet.

[0177] Regarding step (1), it is as described in the first manufacturing method above.

[0178] <Step (2')>

[0179] Step (2') is the following steps, namely, to volatilize a portion of the volatile compounds contained in the sheet-shaped molded body obtained by step (1), and to cure the above-mentioned curable siloxane composition to obtain a single sheet.

[0180] The primary sheet manufactured without causing the volatile compounds to evaporate has excessive softness and loss of resilience. When the primary sheet is laminated in step (4'), it causes the primary sheet to collapse, making it difficult to manufacture a thermally conductive sheet.

[0181] On the other hand, regarding the primary sheet manufactured by completely evaporating the volatile compound, when the primary sheet is stacked in step (4'), the adhesion between the sheets is poor, resulting in difficulty in manufacturing a thermally conductive sheet.

[0182] There are no particular limitations on the method for evaporating a portion of the volatile compounds contained in the sheet-shaped molded body. For example, the volatile compounds can be evaporated in the same manner as in step (2) above, with the sheet-shaped molded body disposed between two films, at least one of which is a breathable membrane. Alternatively, the volatile compounds can be evaporated with one side of the sheet-shaped molded body being an open system. The state of one side of the sheet-shaped molded body being an open system means, for example, that a membrane is provided on one side of the sheet-shaped molded body, and no object is provided on the other side. Specifically, in step (1), a sheet-shaped molded body can be formed by coating a liquid composition onto a substrate film, and then heated in this state to evaporate the volatile compounds.

[0183] In step (2'), when the volatile compound contained in the sheet-shaped molded body before evaporation is set to 100% by mass, the amount of volatile compound volatilization is preferably 10 to 80% by mass, and more preferably 30 to 80% by mass. By setting the amount of volatile compound volatilization within the above range, the sheet has appropriate softness, and the bonding between the sheets becomes good, making it easy to obtain a sheet with suitable thermal conductivity.

[0184] The amount of volatilization can be adjusted by changing the heating temperature and time during curing. For example, the heating temperature can be around 65–100°C. Furthermore, the heating time is approximately 2–24 hours.

[0185] <Step (3)>

[0186] Step (3) involves preparing multiple primary wafers obtained in step (2') and irradiating at least one side of each primary wafer with vacuum ultraviolet light. In step (3), at least one side of the cured primary wafer is irradiated with VUV. VUV stands for vacuum ultraviolet light, referring to ultraviolet light with a wavelength of 10–200 nm. Examples of VUV light sources include excimer Xe lamps and excimer ArF lamps.

[0187] The cured primary sheet, as described above, contains an organosilicon resin (organopolysiloxane), and when irradiated with VUV, the VUV-irradiated surface is activated. The primary sheet is then overlapped with another primary sheet, as described below, with one of its activated surfaces becoming the overlapping surface, thereby enabling a strong bond between the primary sheets.

[0188] The underlying principle is unclear, but it is presumed that when exposed to VUV, the C-Si bonds of the organopolysiloxane in the silicone resin transform into Si-O bonds such as Si-OH, which then allow for strong bonding between the primary layers. In other words, the primary layers (unit layers 13, 13) can be bonded together by intermolecular bonds formed by the organopolysiloxane.

[0189] VUV irradiation conditions are not particularly limited as long as they are sufficient to activate the surface of the primary film; for example, conditions that allow for a cumulative light intensity of 5–100 mJ / cm² are acceptable. 2 Preferably, the cumulative light intensity is 10–50 mJ / cm². 2 The method of irradiating VUV.

[0190] <Step (4')>

[0191] Step (4') is the following steps, namely, stacking multiple primary sheets in such a way that one of the primary sheets irradiated by vacuum ultraviolet light is in contact with another primary sheet, thereby joining multiple primary sheets to form a stacked block.

[0192] like Figure 2 As shown in (a) and (b), multiple primary sheets 21 are stacked in such a manner that the anisotropic filler 14 has the same orientation. Here, each primary sheet 21, as described above, only requires that any one of its overlapping surfaces be pre-irradiated with VUV. By irradiating one surface with VUV, adjacent primary sheets 21, 21 can be joined together through this activated surface. Furthermore, from the viewpoint of further improving the bonding strength, it is preferable that both surfaces of the overlapping surfaces are irradiated with VUV.

[0193] That is, such as Figure 2 As shown in (a), a primary sheet 21 can overlap with another primary sheet 21 in such a way that one surface 21A, which is irradiated by VUV, is in contact with the other primary sheet 21. In this case, it is preferable that the other surface 21B of the other primary sheet 21, which is in contact with one surface 21A, is also irradiated by VUV.

[0194] The primary sheets 21 can be joined by overlapping them as described above, or pressure can be applied in the stacking direction x of the primary sheets 21 to make the joint more secure. Pressure should be applied at a level that will not cause significant deformation of the primary sheets 21; for example, pressure can be applied using rollers or a press. As an example, when using rollers, it is preferable to set the pressure to 0.3 to 3 kgf / 50 mm.

[0195] The primary sheet 21 being stacked can be appropriately heated, for example, during pressurization. However, since the primary sheet 21 activated by VUV irradiation can be bonded even without heating, the primary sheet 21 being stacked is preferably not heated. Therefore, the stamping temperature is, for example, 0 to 50°C, preferably around 10 to 40°C.

[0196] By performing step (5), a thermally conductive sheet can be obtained, which involves cutting the laminated block obtained in step (4) into sheets along the lamination direction to obtain the thermally conductive sheet. Furthermore, the details of step (5) are as described in the first manufacturing method above.

[0197] [Second Implementation]

[0198] Subsequently, for the thermally conductive sheet of the second embodiment of the present invention, using Figure 3 Please provide an explanation.

[0199] In the first embodiment, the thermally conductive sheet 10 contains both anisotropic filler 14 and non-anisotropic filler 15 as thermally conductive filler, but the thermally conductive sheet 30 in this embodiment is as follows: Figure 3 The diagram shows that it does not contain anisotropic filler. That is, each unit layer 33 of the thermally conductive sheet in the second embodiment contains anisotropic filler 34 oriented in the thickness direction of the sheet 30, but does not contain anisotropic filler.

[0200] Except for the absence of anisotropic filler, the other components of the thermally conductive sheet 30 in the second embodiment are the same as those of the thermally conductive sheet 10 in the first embodiment described above, so its description is omitted.

[0201] In this embodiment, similar to the first embodiment, the volume fraction of the silicone resin in the thermally conductive sheet 20 is 32% by volume or less, and the compressive load on the sheet area of ​​25.4mm × 25.4mm is 5.0kgf or less when compressed by 30% in the vertical direction. Therefore, since the volume fraction of the thermally conductive filler can be increased, the thermal conductivity is excellent, and the flexibility is good, making it suitable for use in electronic devices and other applications after compression. Furthermore, each unit layer 33 hardly expands due to the pressure when stacking the unit layers 33, allowing for the appropriate manufacture of the thermally conductive sheet 20.

[0202] Furthermore, the thermally conductive sheet of the present invention is not limited to the configuration of the first and second embodiments described above, and may have various forms. For example, in the first embodiment, the thermally conductive sheet contains both anisotropic filler and non-anisotropic filler as thermally conductive fillers, but the thermally conductive sheet may also contain only non-anisotropic filler and not anisotropic filler.

[0203] Furthermore, when there is no anisotropic filler, it is not necessary to apply shear force to orient the anisotropic filler when forming a sheet. As long as it is a method that can form the liquid composition into a sheet, a sheet can be formed by any method.

[0204] In the above description, it is stated that each unit layer in the thermally conductive sheet has a substantially identical composition, but the composition of each unit layer may also be different.

[0205] For example, in the first embodiment, each unit layer contains both anisotropic filler and non-anisotropic filler, but some unit layers may contain both anisotropic filler and non-anisotropic filler, and some unit layers may contain either anisotropic filler or non-anisotropic filler.

[0206] In addition, for example, some unit layers may have only anisotropic filler material, and some unit layers may have only non-anisotropic filler material 15.

[0207] Furthermore, the content of thermally conductive filler in each unit layer does not need to be the same; the content of thermally conductive filler in some unit layers can differ from that in other unit layers. Additionally, the type of thermally conductive filler in some unit layers can also differ from that in other unit layers.

[0208] As mentioned above, in each unit layer, the thermal conductivity of some unit layers can be made higher than that of others by appropriately adjusting the presence, content, and type of thermally conductive filler. In this case, unit layers with higher thermal conductivity and unit layers with lower thermal conductivity can be arranged alternately, but it is not necessary for them to be arranged alternately.

[0209] The composition of each unit layer, except for the thermally conductive filler, can also be changed. For example, the type of silicone resin in some unit layers can be changed to the type of silicone resin in other unit layers. In addition, the presence, type, and amount of additives in some unit layers can be different from those in other unit layers.

[0210] For example, the hardness (OO type hardness) of a portion of the unit layer can be made different from that of the other unit layers by making at least a portion of the type or amount of silicone resin or thermally conductive filler different from the other unit layers.

[0211] Example

[0212] The present invention will now be described in more detail by way of examples, but the present invention is not limited to these examples in any way.

[0213] In this embodiment, the physical properties of the thermally conductive sheet are evaluated using the following method.

[0214] [Compression load]

[0215] The compressive load (kgf) on a 25.4 mm × 25.4 mm thermally conductive sheet was measured. The compressive load was measured by measuring the load when compressed by 30% in the vertical direction from the joint surface where multiple unit layers are joined together.

[0216] Thermal conductivity

[0217] The thermal conductivity of the thermally conductive sheet was determined according to the method of ASTM D5470-06.

[0218] [Puncture load]

[0219] The liquid composition was defoamed, and then 30g of the liquid composition was introduced into a cylindrical container with a diameter of 25mm. Next, a puncture rod with a disc-shaped member at the tip with a diameter of 3mm was pressed against the liquid composition introduced into the container at a speed of 10mm / min from the tip of the puncture rod. The load (gf) was measured when the tip of the puncture rod reached a depth of 12mm from the liquid surface. The measurement was performed at 25°C.

[0220] In this embodiment, the thermally conductive sheet is made using the following components.

[0221] [Curing Siloxane Composition]

[0222] Addition-reaction type organopolysiloxanes, including alkenyl-containing organopolysiloxanes as the main agent and organohydrogen-containing organopolysiloxanes as curing agents.

[0223] [Anisotropic filler material]

[0224] Boron nitride: flaky, average particle size 30 μm, aspect ratio 10–15

[0225] Graphitized carbon fiber: fibrous, with an average fiber length of 100 μm, an aspect ratio of 10, and a thermal conductivity of 500 W / m·K.

[0226] Flake-shaped carbon powder: flake-shaped, average particle size 130 μm, aspect ratio 10–15, thermal conductivity 100 W / m·K

[0227] [Anisotropic filler material]

[0228] Alumina A: Average particle size 3μm, spherical, aspect ratio 1.0

[0229] Alumina B: Average particle size 0.5 μm, spherical, aspect ratio 1.0

[0230] [Volatile compounds]

[0231] n-Decyltrimethoxysilane: In thermogravimetric analysis, the temperature at which 90% weight loss occurs (T1) when the temperature is increased by 2°C / min is 187°C.

[0232] [Example 1]

[0233] A liquid composition was obtained by mixing 110 parts by weight of an alkenyl-containing organopolysiloxane (main agent) and an organohydrogen polysiloxane (curing agent) as a curable siloxane composition, 200 parts by weight of boron nitride (flake-like, average particle size 20 μm) as an anisotropic filler, 430 parts by weight of alumina A (spherical, average particle size 3 μm, aspect ratio 1.0) as an anisotropic filler, 200 parts by weight of alumina B (spherical, average particle size 0.5 μm, aspect ratio 1.0) as a non-anisotropic filler, and 35 parts by weight of n-decyltrimethoxysilane as a volatile compound.

[0234] A liquid composition is applied in one direction onto a substrate film consisting of a breathable membrane ("TPX membrane" manufactured by Mitsui Chemicals) using a rod coater at 25°C. The major axis of the anisotropic filler is oriented towards the coating direction, and the minor axis is oriented towards the normal direction of the coated surface. A breathable membrane ("TPX membrane" manufactured by Mitsui Chemicals) is then placed on the side of the sheet without the substrate film. Subsequently, the sheet is heated at 80°C for 16 hours while sandwiched between two membranes, causing some of the volatile compounds to evaporate and the curable siloxane composition contained in the sheet to cure, thereby obtaining a single sheet with a thickness of 1.5 mm.

[0235] The two sides of each of the obtained primary wafers were irradiated using a VUV irradiation device (excimer MINI, manufactured by Hamamatsu Hotniks Co., Ltd.) at room temperature (25°C) and in atmospheric conditions with a cumulative light intensity of 20 mJ / cm². 2 The sheets were then irradiated with VUV under specific conditions. Subsequently, 100 sheets irradiated with VUV were stacked and pressed at 1.6 kgf / 50 mm using rollers at 25°C to obtain a laminated block. The laminated block was then sliced ​​using a cutting blade in a direction parallel to the stacking direction and perpendicular to the orientation direction of the anisotropic filler, yielding thermally conductive sheets with each unit layer having a thickness of 1500 μm and a thickness of 2 mm.

[0236] The evaluation results are shown in Table 1. The "ratio of curable siloxane composition in the liquid composition other than volatile compounds" in the column of the liquid composition shown in Table 1 is the same as the ratio (volume %) of silicone resin in the thermally conductive sheet when the composition is used to form the thermally conductive sheet.

[0237] [Examples 2-16]

[0238] The composition of the liquid composition was changed to that shown in Table 1 or Table 2, and the thermally conductive sheet was otherwise obtained in the same manner as in Example 1.

[0239] [Example 17]

[0240] The thickness of the primary sheet was changed to 9 mm, and the thermally conductive sheet was otherwise obtained in the same manner as in Example 1.

[0241] [Compare Examples 1, 3, and 5]

[0242] The composition of the liquid composition was changed as shown in Table 3, and the thermally conductive sheet was obtained in the same manner as in Example 1.

[0243] [Compare Examples 2, 4, and 6]

[0244] The composition of the liquid composition was changed to that shown in Table 3, but the liquid composition became powder and could not be formed into a single sheet.

[0245] Table 1

[0246]

[0247] Table 2

[0248]

[0249] Table 3

[0250]

[0251] In the thermally conductive sheets of Examples 1-17, the volume content of silicone resin is 32% or less, resulting in a higher content of thermally conductive filler and thus higher thermal conductivity. Furthermore, the load at 30% compression is 5.0 kgf or less, and the flexibility is also good. Therefore, it is believed that thermally conductive sheets with good physical property balance can be obtained through specific manufacturing steps using a liquid composition containing volatile compounds.

[0252] In contrast, the thermally conductive sheets of Comparative Examples 1, 3, and 5 had a silicone resin volume content exceeding 32% by volume, resulting in a lower content of thermally conductive filler and lower thermal conductivity compared to the examples incorporating the same anisotropic filler. Furthermore, Comparative Examples 2, 4, and 6 could not form a single sheet, thus failing to produce a thermally conductive sheet. This is presumably because, unlike the examples, they did not use volatile compounds in the liquid composition, preventing the formation of a suitable composite.

[0253] Explanation of symbols in attached drawings

[0254] 10,30: Thermal conductive sheet

[0255] 10A, 21A: One face

[0256] 10B, 21B: The other side

[0257] 11: Organosilicon resin

[0258] 13,33: Unit layer

[0259] 14,34: Anisotropic fillers

[0260] 15: Anisotropic fillers

[0261] 18: Knives

[0262] 21:1 film

[0263] 22: Stacked Blocks

Claims

1. A thermally conductive sheet comprising a plurality of unit layers, each comprising an organosilicon resin and a thermally conductive filler, wherein the plurality of unit layers are stacked in a manner that they are bonded together. The volume content of the organosilicon resin is less than 32% by volume. The thermally conductive filler contains anisotropic and non-anisotropic fillers. The non-anisotropic fillers include small-particle-size non-anisotropic fillers with an average particle size of 0.1 μm or more and 2 μm or less, and large-particle-size non-anisotropic fillers with an average particle size of more than 2 μm and 50 μm or less. The amount of the small-particle-size non-anisotropic filler relative to the amount of the large-particle-size non-anisotropic filler, i.e., the ratio of the amount of small-particle-size non-anisotropic filler to the amount of large-particle-size non-anisotropic filler, is 0.2 to 1.

0. The content of the non-anisotropic filler relative to 100 parts by weight of the silicone resin is 200 to 800 parts by weight. When compressed by 30% from a direction perpendicular to the joint surface where the multiple unit layers interlock, the compressive load on a sheet area of ​​25.4 mm × 25.4 mm is less than 7.0 kgf. The thermally conductive sheet is manufactured through the following process: The step of obtaining a sheet-like molded article by molding a liquid composition comprising a curable siloxane composition, a thermally conductive filler, and a volatile compound, and The process of causing a portion of the volatile compound to evaporate from the sheet-like molded body. The volatile compound is an alkoxysilane compound, which is at least one selected from trimethoxysilane compounds and triethoxysilane compounds having an alkyl group having 4 or more carbon atoms bonded to a silicon atom.

2. The thermally conductive sheet as claimed in claim 1, wherein the plurality of unit layers are stacked along one direction along the surface direction of the sheet.

3. The thermally conductive sheet as described in claim 1 or 2, wherein the anisotropic filler is oriented in the thickness direction of the sheet.

4. The thermally conductive sheet as described in claim 1 or 2, wherein the anisotropic filler is selected from at least one of fibrous materials and flake materials.

5. The thermally conductive sheet as described in claim 4, wherein the average fiber length of the fibrous material is 10–500 μm.

6. The thermally conductive sheet as described in claim 4, wherein the average particle size of the flake-like material is 10–400 μm.

7. The thermally conductive sheet as claimed in claim 4, wherein the normal direction of the scale surface of the scale-like material is oriented toward the stacking direction of the plurality of unit layers.

8. The thermally conductive sheet as claimed in claim 1 or 2, wherein the aspect ratio of the anisotropic filler exceeds 2.

9. The thermally conductive sheet as described in claim 1 or 2, wherein the content of the anisotropic filler is 2 to 50% by volume.

10. The thermally conductive sheet as described in claim 1 or 2, wherein the content of the anisotropic filler is 20-75% by volume.

11. The thermally conductive sheet as described in claim 1 or 2, wherein the silicone resin is a cured silicone resin.

12. The thermally conductive sheet as claimed in claim 11, wherein the curable silicone resin is obtained by curing a curable silicone composition composed of an alkenyl-containing organopolysiloxane and an organohydrogen polysiloxane.

13. The thermally conductive sheet as described in claim 1 or 2, wherein the content of the silicone resin is 18-32% by volume.

14. The thermally conductive sheet as described in claim 1 or 2, wherein adjacent unit layers are directly fixedly bonded to each other.

15. The thermally conductive sheet as described in claim 1 or 2, wherein adjacent unit layers are directly bonded to each other without passing through materials other than the unit layers.

16. A method for manufacturing a thermally conductive sheet, comprising the following steps: Step (1) involves molding a liquid composition comprising a curable siloxane composition, a thermally conductive filler, and a volatile compound into a sheet to obtain a sheet-shaped molded body. In step (2), while the sheet-shaped molded body is disposed between two films, at least one of which is a breathable membrane, a portion of the volatile compounds contained in the sheet-shaped molded body is volatilized, and the curable siloxane composition is cured to obtain a single sheet. Step (4) involves preparing multiple primary wafers and stacking them together to form a stacked block; and... Step (5) involves cutting the laminated block into sheets along the lamination direction to obtain a thermally conductive sheet containing silicone resin and thermally conductive filler. The volatile compound is an alkoxysilane compound, which is at least one selected from trimethoxysilane compounds and triethoxysilane compounds having an alkyl group having 4 or more carbon atoms bonded to a silicon atom. The thermally conductive filler contains anisotropic and non-anisotropic fillers. The non-anisotropic fillers contain non-anisotropic fillers with an average particle size of 0.1 μm or more and 2 μm or less, and non-anisotropic fillers with an average particle size of more than 2 μm and 50 μm or less. The amount of the non-anisotropic filler relative to the amount of the non-anisotropic filler, i.e., the amount of the non-anisotropic filler / the amount of the non-anisotropic filler, is 0.2 to 1.

0. The content of the non-anisotropic filler is 200 to 800 parts by mass relative to 100 parts by mass of the silicone resin.

17. A method for manufacturing a thermally conductive sheet, comprising the following steps: Step (1) involves molding a liquid composition comprising a curable siloxane composition, a thermally conductive filler, and a volatile compound into a sheet to obtain a sheet-shaped molded body. Step (2') involves evaporating a portion of the volatile compounds contained in the sheet-shaped molded body while curing the curable siloxane composition to obtain a single sheet. Step (3) involves preparing multiple primary sheets and irradiating at least one side of each primary sheet with vacuum ultraviolet light. The step (4') involves stacking the plurality of primary sheets such that one surface irradiated by vacuum ultraviolet light is in contact with another primary sheet, thereby bonding the plurality of primary sheets to form a stacked block; and Step (5) involves cutting the laminated block into sheets along the lamination direction to obtain a thermally conductive sheet containing silicone resin and thermally conductive filler. The volatile compound is an alkoxysilane compound, which is at least one selected from trimethoxysilane compounds and triethoxysilane compounds having an alkyl group having 4 or more carbon atoms bonded to a silicon atom. The thermally conductive filler contains anisotropic and non-anisotropic fillers. The non-anisotropic fillers contain non-anisotropic fillers with an average particle size of 0.1 μm or more and 2 μm or less, and non-anisotropic fillers with an average particle size of more than 2 μm and 50 μm or less. The amount of the non-anisotropic filler relative to the amount of the non-anisotropic filler, i.e., the amount of the non-anisotropic filler / the amount of the non-anisotropic filler, is 0.2 to 1.

0. The content of the non-anisotropic filler is 200 to 800 parts by mass relative to 100 parts by mass of the silicone resin.

18. The method for manufacturing a thermally conductive sheet as described in claim 16 or 17, wherein the puncture load of the liquid composition in step (1) is 0.1 to 120 gf.

19. The method for manufacturing a thermally conductive sheet as described in claim 16, wherein the breathable membrane is a non-porous breathable membrane formed of poly(4-methylpent-1-ene).

20. The method for manufacturing a thermally conductive sheet as described in claim 16, wherein the amount of volatile compound volatilized in step (2) is 10 to 80% by mass when the amount of volatile compound contained in the sheet-shaped molded body before volatilization is set to 100% by mass.

21. The method for manufacturing a thermally conductive sheet as described in claim 17, wherein the amount of volatile compound volatilized in step (2') is 10 to 80% by mass when the amount of volatile compound contained in the sheet-shaped molded body before volatilization is set to 100% by mass.

22. The method for manufacturing a thermally conductive sheet as described in claim 17, wherein in step (3), the cumulative light intensity is 5-100 mJ / cm. 2 It is irradiated with vacuum ultraviolet light in this way.

23. The method for manufacturing a thermally conductive sheet as described in claim 16 or 17, wherein the anisotropic filler in the primary sheet is oriented along the surface direction of the primary sheet. The laminated block is cut along a direction orthogonal to the direction in which the anisotropic filler is oriented.

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