Thermally-conductive sheet

Abstract

This thermally-conductive sheet contains a polymer matrix and an anisotropic carbon material. The content of the anisotropic carbon material is 20 to 40 vol.% with respect to the total amount of the thermally-conductive sheet. The anisotropic carbon material is exposed on the surface of the thermally-conductive sheet, and the carbon material coverage on the surface of the thermally-conductive sheet is 65% or more.

Description

Thermal conductive sheet

[0001] This invention relates to a thermally conductive sheet.

[0002] In recent years, with the increasing density of wiring in multilayer printed circuit boards, the increasing density of wiring in semiconductor packages, the increasing density of electronic component mounting, and the increased heat generation per unit area due to the high integration of semiconductor elements themselves, there has been a demand for improved heat dissipation from semiconductor packages. It is known that semiconductor packages dissipate heat by sandwiching a heat dissipation material between the heat-generating element, such as a semiconductor chip, and a heat sink, also called a heat spreader, and ensuring close contact. Conventionally, thermally conductive grease has been widely used as the heat dissipation material placed between the semiconductor chip and the heat spreader.

[0003] Semiconductor packages are typically heated to a certain temperature or higher during use. Because the substrate, semiconductor chip, heat spreader, and other components have different thermal expansion coefficients, warping can occur when heated. Recently, with the increasing size of chips, the warping of the semiconductor chip has led to a larger gap between the semiconductor chip and the heat spreader. Thermal conductive grease cannot accommodate such warping, resulting in gaps and other problems. Therefore, the use of thermal conductive sheets as an alternative to thermal conductive grease is being considered.

[0004] The thermal conductive sheets used in the above applications are required to have both enhanced heat dissipation and improved flexibility to follow warping. This is because if the flexibility to follow surrounding components is poor, there is a concern that they will not be able to follow warping, similar to thermal conductive grease, and may delaminate from the semiconductor chip or heat spreader.

[0005] Furthermore, due to their characteristics, thermally conductive sheets are required to have excellent thermal conductivity in the thickness direction. For example, Patent Document 1 discloses an invention relating to a thermally conductive sheet that can sufficiently improve thermal conductivity in the thickness direction, wherein anisotropic fillers are oriented in the thickness direction, the anisotropic fillers are exposed on the sheet surface, and the exposed anisotropic fillers are arranged so that 3.5 to 45% of them are tilted. Patent Document 2 discloses an invention relating to a thermally conductive sheet that can sufficiently lower the thermal resistance value, which includes anisotropic fillers and has a reflectivity of 0.30% or more on the sheet surface. Furthermore, Patent Document 3 discloses a thermally conductive sheet with reduced contact thermal resistance, wherein fibrous fillers are oriented in the thickness direction, the average height of the protruding peaks of the sheet is 3 μm or less, and the contact thermal resistance is 1.4 kgf / cm². ２ Under pressure: 2.1 kgf / cm² ２ The contact thermal resistance under pressure is 0.10 degrees Celsius / cm². ２ An invention relating to a thermally conductive sheet with a thermal conductivity of 0.25 / W or less has been disclosed, and it has been stated that the surface of the thermally conductive sheet is a polished surface.

[0006] Japanese Patent Publication No. 6650175, Japanese Patent Publication No. 7424713, Japanese Unexamined Patent Publication No. 2023-152928

[0007] By the way, when designing a thermally conductive sheet, in order to reduce thermal resistance, it is necessary to lower both the bulk thermal resistance, which is the thermal resistance of the thermally conductive sheet itself, and the interfacial thermal resistance, which is the thermal resistance of the interface between the thermally conductive sheet and the adherend. One way to lower bulk thermal resistance is to make the thermally conductive sheet thinner. On the other hand, in order to reduce interfacial thermal resistance, it is necessary to give the thermally conductive sheet flexibility.

[0008] However, when a thermally conductive sheet is made flexible and then thinned, it becomes difficult to finish the sheet surface smoothly, leading to a deterioration of the interfacial thermal resistance. Possible causes include, for example, the thermally conductive filler falling off during the sheet-making process, the sheet surface becoming rough, or the sheet thickness becoming uneven. Therefore, there is a trade-off between reducing bulk thermal resistance by thinning the thermally conductive sheet and reducing interfacial thermal resistance by adding flexibility to the thermally conductive sheet.

[0009] Therefore, the object of the present invention is to provide a thermally conductive sheet with low bulk thermal resistance and interfacial thermal resistance.

[0010] As a result of diligent research, the inventors have found that the above problems can be solved by ensuring that the carbon material coverage on the surface of a thermally conductive sheet containing a polymer matrix and an anisotropic carbon material is above a certain level. That is, the present invention provides the following [1] to

[10] .

[0011] [1] A thermally conductive sheet comprising a polymer matrix and an anisotropic carbon material, wherein the content of the anisotropic carbon material is 20% by volume or more and 40% by volume or less with respect to the total amount of the thermally conductive sheet, the anisotropic carbon material is exposed on at least one surface of the thermally conductive sheet, and the carbon material coverage rate on the surface of the thermally conductive sheet is 65% or more. [2] The thermally conductive sheet according to [1], wherein the type E hardness is 25 or more and 45 or less. [3] The thermally conductive sheet according to [1] or [2], wherein the polymer matrix comprises a polymer dispersant. [4] The thermally conductive sheet according to [3], wherein the polymer dispersant comprises at least one selected from the group consisting of alkoxysiloxane compounds, aromatic ring-containing siloxane compounds, and hydroxyl group-containing siloxane compounds. [5] The thermally conductive sheet according to any one of [1] to [4], wherein the anisotropic carbon material comprises at least one of carbon fibers and flake graphite. [6] The thermal conductive sheet according to [5], wherein the anisotropic carbon material comprises the carbon fibers and the flake graphite. [7] The thermal conductive sheet according to [6], wherein the carbon fiber content is 20% to 28% by volume relative to the total amount of the thermal conductive sheet, and the flake graphite content is 1% to 12% by volume relative to the total amount of the thermal conductive sheet. [8] The thermal resistance value at a 30 psi load is 0.12°C・cm ２ A thermally conductive sheet according to any one of items [1] to [7], wherein the thermal conductivity is less than or equal to / W. [9] A thermally conductive sheet according to any one of items [1] to [8], wherein the polymer matrix comprises a silicone resin.

[10] A thermally conductive sheet according to any one of items [1] to [9], wherein the thickness is 0.05 mm or more and 0.5 mm or less.

[0012] According to the present invention, it is possible to provide a thermally conductive sheet with low bulk thermal resistance and low interfacial thermal resistance.

[0013] This is a schematic diagram of a thermal resistance measuring machine.

[0014] [Thermal Conductive Sheet] The thermal conductive sheet of the present invention comprises a polymer matrix and an anisotropic carbon material, wherein the content of the anisotropic carbon material, expressed as a volume-based packing density (volume packing density), is 20% by volume or more and 40% by volume or less of the total amount of thermal conductive sheet. Furthermore, the anisotropic carbon material is exposed on the surface of the sheet, and the carbon material coverage rate on the surface of the sheet is 65% or more.

[0015] In this invention, by exposing an anisotropic carbon material on at least one surface of a thermally conductive sheet, covering the surface with the exposed anisotropic carbon material, and ensuring a carbon material coverage rate of 65% or more, the interfacial thermal resistance can be sufficiently reduced. On the other hand, if the carbon material coverage rate is less than 65%, the amount of carbon material covering the surface of the thermally conductive sheet becomes insufficient, making it difficult to reduce the interfacial thermal resistance. The carbon material coverage rate can be measured by obtaining an image of the surface of the thermally conductive sheet using a scanning electron microscope, performing image analysis on the image, and determining the area of ​​the thermally conductive sheet surface covered by the carbon material in the image, as described later. Details of the method for measuring the carbon material coverage rate are as described in the examples.

[0016] As described above, the thermal conductive sheet only needs to have anisotropic carbon material exposed on at least one of its main surfaces (the surface perpendicular to the thickness direction) and a carbon material coverage rate of 65% or more. Preferably, the thermal conductive sheet has anisotropic carbon material exposed on both sides and a carbon material coverage rate of 65% or more.

[0017] The carbon material coverage rate is preferably 67% or more, and more preferably 70% or more. On the other hand, from the viewpoint of easily imparting a certain degree of flexibility to the thermal conductive sheet, the carbon material coverage rate is preferably 90% or less, more preferably 87% or less, and even more preferably 85% or less. The carbon material coverage rate can be set to a desired range by appropriately adjusting the type and content of the carbon material, the manufacturing method of the thermal conductive sheet, etc. Specifically, the carbon material coverage rate can be increased by increasing the content of the anisotropic carbon material, which will be described later, within a certain range. In addition, the carbon material coverage rate can be increased by increasing the number of polishing cycles in the manufacturing process of the thermal conductive sheet.

[0018] (Anisotropic Carbon Material) As described above, the anisotropic carbon material content of the thermal conductive sheet of the present invention is 20% to 40% by volume relative to the total amount of the thermal conductive sheet, expressed as a volume-based packing rate (volume packing rate). If the anisotropic carbon material content is less than 20% by volume, the amount of anisotropic carbon material oriented in the thickness direction of the thermal conductive sheet and the amount of anisotropic carbon material covering the surface of the thermal conductive sheet will be insufficient. Therefore, it becomes difficult to expose the anisotropic carbon material on the surface of the thermal conductive sheet or to achieve a carbon material coverage rate of 65% or more, and furthermore, it becomes difficult to impart excellent thermal conductivity to the thermal conductive sheet. Also, if the anisotropic carbon material content exceeds 40% by volume, it becomes difficult to orient the anisotropic carbon material in the thickness direction of the thermal conductive sheet, and the degree of orientation deteriorates, which may prevent a sufficient reduction in the bulk thermal resistance. From the above perspective, the content of anisotropic carbon material is preferably 25% by volume or more and 37% by volume or less, and more preferably 27% by volume or more and 35% by volume or less.

[0019] The anisotropic carbon material is preferably dispersed in the polymer matrix. Furthermore, as described above, the anisotropic carbon material is exposed to and covers the surface (main surface) of the thermal conductive sheet, and it is preferable that the carbon material covering the surface is composed of the anisotropic carbon material. The anisotropic carbon material is preferably oriented in the thickness direction of the thermal conductive sheet. This makes it easier to improve the thermal conductivity of the thermal conductive sheet, especially the bulk thermal conductivity. When the anisotropic carbon material is oriented in the thickness direction, its long axis does not need to be strictly parallel to the thickness direction; it is acceptable for the long axis to be slightly tilted relative to the thickness direction to still be oriented in the thickness direction. Specifically, anisotropic carbon material with a long axis tilt of less than 20° is also considered to be oriented in the thickness direction, and such anisotropic carbon material is expected to be oriented in the thickness direction if it constitutes the majority of the thermal conductive sheet (for example, more than 60%, preferably more than 80%, of the total number of anisotropic fillers, including other anisotropic fillers described later).

[0020] Anisotropic carbon materials are fillers that have anisotropy in shape and are carbon materials that can be oriented. Examples of anisotropic carbon materials include fibrous materials such as carbon fibers and flaky materials such as flaky graphite. Anisotropic carbon materials have a high aspect ratio, specifically an aspect ratio greater than 2, and preferably an aspect ratio of 5 or higher. By making the aspect ratio greater than 2, it becomes easier to orient the anisotropic carbon material in one direction, such as the thickness direction, and it is easier to improve the thermal conductivity in one direction, such as the thickness direction. Furthermore, there is no particular upper limit to the aspect ratio, but practically it is 100. The aspect ratio is the ratio of the length in the long axis direction to the length in the short axis direction of the anisotropic carbon material. In the case of fibrous materials, it means fiber length / fiber diameter, and in the case of flaky materials, it means the length in the long axis direction of the flaky material / thickness.

[0021] When the anisotropic carbon material is a fibrous material, its average fiber length is, for example, 10 μm to 500 μm, preferably 10 μm to 300 μm, more preferably 20 μm to 200 μm, and even more preferably 30 μm to 100 μm. If the average fiber length is 10 μm or more, the anisotropic carbon materials will be in appropriate contact with each other within the thermal conductive sheet, ensuring a heat transfer path and resulting in good thermal conductivity of the thermal conductive sheet. On the other hand, if the average fiber length is 500 μm or less, the bulk of the anisotropic carbon material will be reduced, allowing for high-density filling of the binder component. Furthermore, it is preferable that the average fiber length of the fibrous material be shorter than the thickness of the thermal conductive sheet. A shorter average fiber length prevents the fibrous material from protruding excessively from the surface of the thermal conductive sheet. The above average fiber length can be calculated by observing the anisotropic carbon material under a microscope. More specifically, for example, by using an electron microscope or an optical microscope to measure the fiber lengths of 50 arbitrary anisotropic carbon materials, the average fiber length can be taken as the average value (arithmetic mean).

[0022] Furthermore, when the anisotropic carbon material is a flaky material, its average particle size is preferably 5 μm to 1000 μm, more preferably 8 μm to 750 μm, and even more preferably 10 μm to 500 μm. In particular, when the orientation method described later is the magnetic field orientation method, it is preferably 5 μm to 300 μm, more preferably 8 μm to 200 μm, and even more preferably 10 μm to 100 μm. By setting the average particle size to 5 μm or more, the anisotropic carbon materials in the thermal conductive sheet can easily come into contact with each other, ensuring a heat transfer path and improving the thermal conductivity of the thermal conductive sheet. On the other hand, if the average particle size is 1000 μm or less, the bulk of the thermal conductive sheet is reduced, making it possible to fill the binder component with a high amount of anisotropic carbon material. Furthermore, when the orientation method is the flow orientation method, the average particle size of the flake-like material is preferably 5 μm or more and 1000 μm or less, more preferably 10 μm or more and 750 μm or less, and even more preferably 15 μm or more and 500 μm or less. By setting the average particle size to 5 μm or more, the anisotropic carbon materials come into contact with each other in the thermal conductive sheet, ensuring a heat transfer path and improving the thermal conductivity of the thermal conductive sheet. On the other hand, if the average particle size is 1000 μm or less, the bulk of the thermal conductive sheet is reduced, making it possible to fill the binder component with a high concentration of anisotropic carbon material. The average particle size of the flake-like material is D50, which can be calculated by observing the flake-like material under a microscope and taking the longest axis as the diameter. More specifically, for example, by measuring the longest axis of 500 or more arbitrary flake-like materials using an electron microscope or optical microscope, it means the particle size corresponding to the cumulative frequency of 50%. Specifically, the particle size can be determined from a particle size distribution curve using a flaky material as a sample, with the horizontal axis representing particle size and the vertical axis representing the cumulative frequency. This particle size distribution curve is a number-based particle size distribution curve obtained by sequentially accumulating the particles of the flaky material, starting from the smallest particle size.

[0023] Anisotropic carbon materials can be any known material with thermal conductivity, but if orientation is achieved by magnetic field orientation as described later, it is preferable to have diamagnetism. On the other hand, if orientation is achieved by flow orientation, diamagnetism is not required. Examples of anisotropic carbon materials include carbon fibers and flaky graphite.

[0024] Carbon fibers are preferably graphitized carbon fibers. In graphitized carbon fibers, the crystal planes of graphite are continuous in the fiber axis direction, and they have high thermal conductivity in the fiber axis direction. Therefore, by aligning the fiber axis direction in a predetermined direction, the thermal conductivity in a specific direction can be increased. In addition, in flaky graphite, the crystal planes of graphite are continuous in the in-plane direction of the flaky surface, and it has high thermal conductivity in the in-plane direction. Therefore, by aligning the flaky surface in a predetermined direction, the thermal conductivity in a specific direction can be increased. Graphitized carbon fibers and flaky graphite preferably have a high degree of graphitization.

[0025] As the anisotropic carbon materials such as the above-mentioned graphitized carbon fibers and flaky graphite, those obtained by graphitizing the following raw materials can be used. For example, condensed polycyclic hydrocarbon compounds such as naphthalene, PAN (polyacrylonitrile), condensed heterocyclic compounds such as pitch, etc. can be mentioned, but it is particularly preferable to use graphitized mesophase pitch, polyimide, or polybenzazole with a high degree of graphitization. For example, by using mesophase pitch, in the spinning process described later, the pitch is oriented in the fiber axis direction due to its anisotropy, and graphitized carbon fibers having excellent thermal conductivity in the fiber axis direction can be obtained. The usage mode of mesophase pitch in graphitized carbon fibers is not particularly limited as long as it can be spun. Mesophase pitch may be used alone or in combination with other raw materials. However, using mesophase pitch alone, that is, graphitized carbon fibers with a mesophase pitch content of 100% are most preferable in terms of high thermal conductivity, spinnability, and quality stability.

[0026] Graphitized carbon fibers can be those obtained by sequentially performing spinning, non-melting, and carbonization treatments, pulverizing or cutting them to a predetermined particle size, and then graphitizing them, or those obtained by graphitizing them after pulverizing or cutting them after carbonization. When pulverizing or cutting before graphitization, since the polycondensation reaction and cyclization reaction easily proceed during the graphitization treatment on the newly exposed surface due to pulverization, graphitized carbon fibers with a higher degree of graphitization and further improved thermal conductivity can be obtained. On the other hand, when pulverizing after graphitizing the spun carbon fibers, since the carbon fibers after graphitization are rigid, they are easy to pulverize, and carbon fiber powder with a relatively narrow fiber length distribution can be obtained by pulverizing for a short time.

[0027] The anisotropic carbon material is not particularly limited, but the thermal conductivity along the direction having anisotropy (i.e., the long axis direction) is generally 30 W / (m·K) or more, preferably 60 W / (m·K) or more, more preferably 100 W / (m·K) or more, and still more preferably 200 W / (m·K) or more. The upper limit of the thermal conductivity of the anisotropic carbon material is not particularly limited, but for example, it is 2000 W / (m·K) or less. The thermal conductivity can be measured by a laser flash method or the like.

[0028] The anisotropic carbon material may be used alone or in combination of two or more. For example, as the anisotropic carbon material, an anisotropic carbon material having at least two different average particle sizes or average fiber lengths may be used. When using anisotropic carbon materials of different sizes, it is considered that the small anisotropic carbon materials can enter between the relatively large anisotropic carbon materials, so that the anisotropic carbon materials can be filled densely in the binder component and the heat conduction efficiency can be improved.

[0029] The anisotropic carbon material preferably contains at least one of carbon fibers and flake graphite, and more preferably contains both carbon fibers and flake graphite. Including both carbon fibers and flake graphite makes it easier to increase the carbon material coverage. When both carbon fibers and flake graphite are included, the content ratio of flake graphite to carbon fibers (flak graphite / carbon fiber) is, on a volume basis, for example, 0.01 or more and 1 or less, preferably 0.02 or more and 0.5 or less, and more preferably 0.1 or more and 0.3 or less. Setting the flake graphite / carbon fiber ratio to the lower limit above makes it easier to adjust the carbon material coverage to a certain level or higher. Also, setting the flake graphite / carbon fiber ratio to the upper limit above makes it easier to densely pack the anisotropic carbon material, for example, in the magnetic field orientation method described later.

[0030] The carbon fiber content in the thermal conductive sheet, expressed as a volume-based packing rate, is preferably 10% to 35% by volume, more preferably 15% to 30% by volume, and even more preferably 20% to 28% by volume, relative to the total amount of the thermal conductive sheet. The flake graphite content in the thermal conductive sheet, expressed as a volume-based packing rate, is preferably 0.5% to 15% by volume, more preferably 1% to 12% by volume, and even more preferably 2% to 10% by volume, relative to the total amount of the thermal conductive sheet. If at least one of the carbon fiber content and the flake graphite content is above the above lower limit, the carbon material coverage rate can be increased, making it easier to reduce the interfacial thermal resistance and further reduce the bulk thermal resistance. Furthermore, if at least one of the carbon fiber content and the flake graphite content is below the above upper limit, the carbon fibers and flake graphite can be oriented in the thickness direction of the thermal conductive sheet, making it easier to reduce bulk thermal resistance. From the viewpoint of further reducing bulk thermal resistance, it is preferable that the carbon fiber content is 20% to 28% by volume of the total thermal conductive sheet, and the flake graphite content is 1% to 12% by volume of the total thermal conductive sheet.

[0031] The anisotropic carbon material content in the thermally conductive sheet is preferably 70 parts by mass or more and 500 parts by mass or less per 100 parts by mass of polymer matrix, more preferably 100 parts by mass or more and 300 parts by mass or less, and even more preferably 130 parts by mass or more and 250 parts by mass or less. A content of 70 parts by mass or more of anisotropic carbon material makes it easier to improve thermal conductivity. Furthermore, a content of 500 parts by mass or less makes it easier to achieve an appropriate viscosity in the mixed composition described later, and improves the orientation of the anisotropic carbon material. In addition, it improves the dispersibility of the anisotropic carbon material in the polymer matrix.

[0032] (Other Fillers) The thermally conductive sheet of the present invention may contain fillers other than the anisotropic carbon material described above (hereinafter also referred to as "other fillers"). Examples of other fillers include anisotropic fillers other than anisotropic carbon material (hereinafter also referred to as "other anisotropic fillers") and non-anisotropic fillers. Any material other than carbon material may be used as the other filler. Furthermore, the other fillers are preferably dispersed in a polymer matrix. Specific examples of other anisotropic fillers include metal materials represented by metal fibers, metal oxides, boron nitride and metal nitrides, metal carbides, metal hydroxides, poly(p-phenylenebenzoxazole) fibers, etc. Specifically, the aspect ratio of the other anisotropic fillers is preferably greater than 2, and preferably 5 or more. The upper limit of the aspect ratio is not particularly limited, but practically it is 100.

[0033] The content of other anisotropic fillers is preferably less than that of the anisotropic carbon material described above. Specifically, it is preferably 30% by volume or less, and more preferably 10% by volume or less, based on the total amount of anisotropic fillers, including the anisotropic carbon material. By keeping the content of other anisotropic fillers below a certain level, it becomes easier to reduce bulk thermal resistance and interfacial thermal resistance. The reason for this is not entirely clear, but it is presumed that because anisotropic carbon material has lower hardness compared to other anisotropic fillers, when a polishing process, for example, is carried out as described later, a larger amount of anisotropic carbon material is exposed on the surface of the thermal conductive sheet, making it easier to adjust the carbon material coverage rate to a certain level or higher. Note that the thermal conductive sheet of the present invention does not have to contain other fillers. That is, the content of other anisotropic fillers may be 0% by volume according to the above criteria.

[0034] Non-anisotropic fillers, in particular, can be used in combination with anisotropic fillers oriented in one direction, such as the thickness direction, to interpose in the gaps between oriented anisotropic fillers and further increase thermal conductivity. Non-anisotropic fillers are fillers that do not substantially have anisotropy in shape, and even in environments where anisotropic fillers such as anisotropic carbon materials are oriented in a predetermined direction, such as under magnetic field line generation or shear force application described later, non-anisotropic fillers do not align in that predetermined direction.

[0035] The non-anisotropic filler has an aspect ratio of 2 or less, preferably 1.5 or less. When used in combination with anisotropic fillers, non-anisotropic fillers with a low aspect ratio are more easily positioned in the gaps of the anisotropic fillers, thus improving thermal conductivity. Furthermore, by setting the aspect ratio to 2 or less, it becomes possible to prevent an increase in the viscosity of the mixed composition described later, thereby enabling high-filling.

[0036] Specific examples of non-anisotropic fillers include metals, metal oxides, metal nitrides, metal hydroxides, non-metallic oxides, nitrides, and carbides. The shape of non-anisotropic fillers can be spherical, polyhedral, or amorphous powder. Examples of metals in non-anisotropic fillers include aluminum, copper, and nickel; examples of metal oxides include aluminum oxide (represented by alumina), magnesium oxide, and zinc oxide; and examples of metal nitrides include aluminum nitride. An example of a metal hydroxide is aluminum hydroxide. Examples of non-metallic oxides, nitrides, and carbides include quartz, boron nitride, and silicon carbide. Among these, aluminum oxide and aluminum are preferred because they have high thermal conductivity and are readily available in spherical form. Non-anisotropic fillers may be used individually or in combination of two or more types.

[0037] The average particle size of the non-anisotropic filler is preferably, for example, 0.1 μm to 200 μm, more preferably 0.5 μm to 100 μm, and more preferably 1 μm to 70 μm. Furthermore, when the non-anisotropic filler is used in combination with the anisotropic filler, the average particle size of the non-anisotropic filler is preferably 0.1 μm to 50 μm, more preferably 0.5 μm to 35 μm, and even more preferably 1 μm to 15 μm. By setting the average particle size to 50 μm or less, problems such as disrupting the orientation of the anisotropic filler are less likely to occur even when used in combination with the anisotropic filler. In addition, by setting the average particle size to 0.1 μm or more, the specific surface area of ​​the non-anisotropic filler does not become unnecessarily large, the viscosity of the mixed composition does not increase easily even when a large amount is added, and it becomes easier to fill the mixture with the non-anisotropic filler to a high degree. For example, the non-anisotropic filler may consist of at least two non-anisotropic fillers having different average particle sizes. The average particle size of the non-anisotropic filler can be measured by observation using an electron microscope or the like. More specifically, for example, the particle sizes of 500 or more arbitrary non-anisotropic fillers can be measured using an electron microscope or optical microscope, and D50 can be determined in the same way as for the flake-like filler.

[0038] The content of the anisotropic filler in the thermal conductive sheet, expressed as a volume-based filling rate (volume filling rate), is preferably 5% to 40% by volume, more preferably 15% to 35% by volume, and even more preferably 20% to 33% by volume, relative to the total amount of the thermal conductive sheet.

[0039] The content of the anisotropic filler, expressed in parts by mass, is preferably 100 parts by mass or more and 700 parts by mass or less per 100 parts by mass of polymer matrix, more preferably 150 parts by mass or more and 500 parts by mass or less, and even more preferably 250 parts by mass or more and 350 parts by mass or less. A content of 100 parts by mass or more allows for good thermal conductivity of the thermal conductive sheet. On the other hand, a content of 700 parts by mass or less allows the anisotropic filler to be appropriately dispersed in the binder component, thereby enhancing thermal conductivity according to the content. Furthermore, it prevents the viscosity of the mixed composition from increasing excessively.

[0040] (Polymer Matrix) The polymer matrix is ​​a matrix made of organic polymers, such as elastomers or rubbers, and preferably a liquid polymer composition (curable polymer composition) consisting of a mixed system of a main component and a curing agent, which is cured to form the matrix. The curable polymer composition may consist of, for example, uncrosslinked rubber and a crosslinking agent, or it may contain monomers, prepolymers, and a curing agent. Furthermore, the curing reaction may be room temperature curing or thermal curing.

[0041] The polymer matrix preferably contains a silicone resin. The silicone resin is an organopolysiloxane. In this invention, using an organopolysiloxane makes the polymer matrix flexible after curing and improves the packing properties of fillers such as anisotropic carbon materials. The organopolysiloxane is preferably a silicone rubber. Furthermore, the organopolysiloxane is preferably a curable silicone, and more preferably an addition-reaction type silicone. In the case of an addition-reaction type silicone, the curable polymer composition consists of an alkenyl group-containing organopolysiloxane (main component) and a hydrogen organopolysiloxane (curing agent), and the polymer matrix can be formed by curing these components. In the curable polymer composition, the mixing ratio of the curing agent to the main component (curing agent / main component) is preferably 0.2 / 9.8 or more and 5 / 5 or less by mass ratio, more preferably 0.5 / 9.5 or more and 4 / 6 or less, and even more preferably 0.7 / 9.3 or more and 4 / 6 or less. If the curing agent / main component is above the lower limit value mentioned above, the E hardness described later will be above a certain level, making it easier to thin the thermal conductive sheet. Also, if the curing agent / main component is below the upper limit value mentioned above, the E hardness described later will be below a certain level, making it easier to impart a certain degree of flexibility to the thermal conductive sheet.

[0042] In addition to silicone rubber, various synthetic rubbers can be used as rubbers. Specific examples include acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, styrene-butadiene rubber, butadiene rubber, fluororubber, and butyl rubber. When using these rubbers, the synthetic rubber may be crosslinked or left uncrosslinked (i.e., uncured) in the thermal conductive sheet. Uncrosslinked rubber is mainly used in flow orientation. When crosslinking (i.e., curing) is performed, as explained above, the polymer matrix may be a curable polymer composition consisting of uncrosslinked rubber made from these synthetic rubbers and a crosslinking agent, which is then cured. As for elastomers, thermoplastic elastomers such as polyester-based thermoplastic elastomers and polyurethane-based thermoplastic elastomers, as well as thermosetting elastomers formed by curing a mixed liquid polymer composition consisting of a main component and a curing agent, can also be used. For example, a polyurethane-based elastomer formed by curing a polymer composition containing a polymer having hydroxyl groups and an isocyanate can be cited.

[0043] The polymer matrix may contain a plasticizer. Plasticizers are preferably used when synthetic rubber is used, and the inclusion of a plasticizer can increase the flexibility of the polymer matrix before crosslinking. For example, when the organic polymer is an organopolysiloxane, silicone oil may be used as a plasticizer. The polymer matrix preferably contains a polymer dispersant. The polymer matrix contains a polymer dispersant, which makes it easier to disperse anisotropic carbon material and increases the coverage of carbon material on the surface. That is, the polymer composition for forming the polymer matrix may consist of the above-mentioned organic polymer alone (for example, a main component and a curing agent), or it may be a mixture containing a plasticizer and a polymer dispersant in addition to the above-mentioned organic polymer, but among these, a mixture containing a polymer dispersant in addition to the main component and curing agent is preferred.

[0044] The polymeric dispersant preferably contains at least one selected from the group consisting of alkoxysiloxane compounds, aromatic ring-containing siloxane compounds, and siloxane compounds having hydroxyl groups. The polymeric dispersant may contain one of these alone or two or more in combination. Among the above, aromatic ring-containing siloxane compounds are preferred as polymeric dispersants from the viewpoint of improving the dispersibility of anisotropic carbon materials.

[0045] Alkoxysiloxane compounds used as polymer dispersants have two or more siloxane bonds (also called siloxane skeletons) and a structure in which an alkoxy group is bonded to at least one silicon atom. Alkoxysiloxane compounds have a structure in which an organic substituent is bonded to at least one silicon atom among the silicon atoms constituting the siloxane bonds. The alkoxysiloxane compound is preferably an organopolysiloxane compound. By having an alkoxy group and an organic substituent, the alkoxysiloxane compound can improve compatibility with organopolysiloxanes constituting curable polymer compositions. The number of repeating units n of the siloxane skeleton is preferably 11 or more. The number of repeating units n of the siloxane skeleton (-Si-O-) is preferably 11 or more and 350 or less, more preferably 20 or more and 300 or less, even more preferably 50 or more and 270 or less, and even more preferably 100 or more and 250 or less. If the number of repeating units n of the siloxane skeleton is greater than or equal to the lower limit, the compatibility with the organopolysiloxane forming the matrix is ​​increased, and the amount of volatile components can be suppressed. Also, if the number of repeating units n of the siloxane skeleton is less than or equal to the upper limit, it becomes easier to adjust the viscosity of the composition to a lower level. Examples of alkoxy groups and organic substituents of the alkoxysiloxane compound are those exemplified in the description of alkoxysilane compounds later, and from the viewpoint of compatibility with the organopolysiloxane constituting the curable polymer composition, it is preferable to have at least an alkyl group.

[0046] Examples of alkoxysiloxane compounds include methyl methoxysiloxane oligomers, methylphenyl methoxysiloxane oligomers, methyl epoxy methoxysiloxane oligomers, methyl mercaptomethoxysiloxane oligomers, and methyl acryloyl methoxysiloxane oligomers. One or more alkoxysiloxane compounds can be used.

[0047] In aromatic ring-containing siloxane compounds, the aromatic ring can be a conjugated aromatic six-membered ring consisting of three to six members, and specific examples are described later. As an aromatic ring-containing siloxane compound, an aromatic ring-containing siloxane compound having the structure represented by the following formula (1) can also be used. In formula (1), R １ Each of these is independently a group represented by A-B, or a monovalent hydrocarbon group having 1 to 4 carbon atoms, and multiple R １ at least one of R １ A is a group represented by A-B. A is a divalent organic group bonded to a silicon atom. B has three to six conjugated aromatic six-membered rings. When the atoms constituting A are defined as follows: the atom bonded to the aromatic six-membered ring of B is the α-position atom, the atom bonded to the α-position atom is the β-position atom, and the atom bonded to the β-position atom other than the α-position atom is the γ-position atom, then any of the α-position atom, β-position atom, and γ-position atom is a heteroatom, and n is an integer of 1 or more. Note that A may also have heteroatoms in parts other than the α-position atom, β-position atom, and γ-position atom. Here, the heteroatoms are not particularly limited and include, for example, oxygen atoms, nitrogen atoms, sulfur atoms, and boron atoms, among which oxygen atoms are preferred from the viewpoint of effectively improving the fluidity of the aromatic ring-containing siloxane compound.

[0048] The aromatic ring-containing siloxane compound having the structure represented by formula (1) above has three to six conjugated aromatic six-membered rings and possesses a large conjugated system in its molecular structure. Therefore, the aromatic ring-containing siloxane compound has high adsorption properties to fillers having π electrons, especially anisotropic carbon materials, due to π-π interactions, and thus easily disperses anisotropic carbon materials.

[0049] A is preferably a divalent organic group having 11 or less carbon atoms, more preferably a divalent organic group having 10 or less carbon atoms. Thus, an aromatic ring-containing siloxane compound in which the carbon number of A is a certain number or less is preferable because it is easy to enhance the dispersibility of the filler. The lower limit of the carbon number of A is not particularly limited, but A is preferably a divalent organic group having 4 or more carbon atoms. Further, as described above, since A has a hetero atom, it has a structural unit having a hetero atom. Examples of the structural unit include ether, ester, amide, urethane, thioether, thioester, etc. Among them, from the viewpoints of improving the dispersibility with respect to the filler and improving the fluidity, ether or ester is preferable, ether is more preferable, and cyclic ether is particularly preferable. Note that the cyclic ether is an ether having a structure in which the carbon of the cyclic hydrocarbon is substituted with oxygen.

[0050] Further, from the viewpoints of improving the dispersibility of the filler and improving the fluidity, A preferably has a cyclic ether structure represented by the following formula (5-1) or an ester skeleton represented by the following formula (5-2). In formula (5-1), *1 and *2 are bonds, and R ４ is a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, preferably a hydrogen atom. Two Rs ４ may be the same or different. R ３ is a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, preferably a hydrocarbon group having 1 to 4 carbon atoms, more preferably a hydrocarbon group having 1 to 3 carbon atoms, and still more preferably an ethyl group. R ５ is a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, preferably a hydrogen atom. The oxygen atom in formula (5-1) is the above-mentioned β-position atom or γ-position atom, preferably the β-position atom. In formula (5-2), *3 and *4 are bonds. The oxygen atom having the bond of *3 is the above-mentioned α-position atom, β-position atom or γ-position atom. Among the above, A preferably has a skeleton represented by formula (5-1).

[0051] Furthermore, A is preferably one of the structures represented by the following formulas (6) to (10) from the viewpoint of improving the dispersibility and fluidity of the filler, and more preferably one of the structures represented by the following formula (6) or (7). In equations (6) to (10), *5 is a bond that attaches to the aromatic six-membered ring of B, and *6 is a bond that attaches to the silicon atom in equation (1).

[0052] In formula (1), B has three to six conjugated aromatic six-membered rings. Conjugation refers to a molecular structure in which unsaturated bonds and single bonds alternate, leading to stabilization through p-orbital interactions and electron delocalization (spread throughout the entire conjugated system). Note that three to six conjugated aromatic six-membered rings are included in the concept of polycyclic aromatic structure described above. When the number of aromatic six-membered rings is six or less, the fluidity of the aromatic ring-containing siloxane compound is improved, and when the number of aromatic six-membered rings is three or more, the adsorption to the filler is improved, and the dispersibility of the filler is improved. From the viewpoint of improving both adsorption to the filler and fluidity in a balanced manner, it is preferable that the number of aromatic six-membered rings be four to five.

[0053] The conjugated aromatic six-membered rings, consisting of three to six aromatic six-membered rings, may be a fused ring compound or a non-fused ring compound, but it is preferable that they be a fused ring compound. Thus, when B contains a fused ring compound, or when B is a fused ring compound, it is preferable from the viewpoint of improving adsorption to the filler and enhancing dispersibility.

[0054] Examples of the fused ring compound include anthracene, anthracene derivatives, phenanthrene, phenanthrene derivatives, triphenylene, triphenylene derivatives, pyrene, pyrene derivatives, tetracene, tetracene derivatives, picene, picene derivatives, perylene, perylene derivatives, pentaphene, pentaphene derivatives, pentacene, pentacene derivatives, hexaphene, hexaphene derivatives, and the like. Among these, pyrene, pyrene derivatives, perylene, or perylene derivatives are preferred. Here, derivative means having substituents; for example, anthracene derivative means anthracene having substituents, and the same applies to other derivatives. When the fused ring compound has substituents, at least one of the hydrogen atoms constituting the fused ring compound is substituted with substituents. Examples of substituents include organic groups having 1 to 10 carbon atoms. From the viewpoint of improving the fluidity of the aromatic ring-containing siloxane compound in the present invention, it is preferable that the fused ring compound does not have substituents. Therefore, it is particularly preferable that B is pyrene or perylene. Furthermore, the fused ring compound only needs to have at least one carbon atom constituting the fused ring bonded to A.

[0055] In the present invention, B can be any of the above-mentioned structures without particular limitation, but preferred structures of B are shown below. In equations (11) to (14) above, * represents a bond that combines with A.

[0056] Among the compounds of formulas (11) to (14) above, any of the compounds of formulas (11) to (13) that are condensed ring compounds are preferred, and among them, pyrene of formula (11) or perylene of formula (12) is more preferred, and pyrene of formula (11) is even more preferred.

[0057] In equation (1), at least one R １ This is the group represented by A-B above, and the remaining R １ R is a hydrocarbon group having 1 to 4 carbon atoms. In formula (1), multiple R １Of these, the number of groups represented by A-B is preferably 1 to 5, more preferably 1 or 2, and the remainder is preferably a monovalent hydrocarbon group having 1 to 4 carbon atoms. If there are multiple groups represented by A-B, these multiple A-B groups may be the same or different. Also, in formula (1), at least one R at the end of the molecular chain １ It is preferable that the group is represented by A-B. Examples of monovalent hydrocarbon groups having 1 to 4 carbon atoms include methyl, ethyl, propyl, and butyl groups, with methyl being preferred. If there are multiple monovalent hydrocarbon groups having 1 to 4 carbon atoms, these multiple monovalent hydrocarbon groups having 1 to 4 carbon atoms may be the same or different.

[0058] In formula (1), n ​​represents the number of repeating units of the siloxane skeleton, and n is an integer of 1 or more. n is not particularly limited as long as it is an integer of 1 or more, but is preferably 400 or less, more preferably 300 or less, even more preferably 250 or less, and preferably 10 or more, more preferably 40 or more, and even more preferably 200 or more. When the number of repeating units n of the siloxane skeleton is greater than or equal to the lower limit, the compatibility with the organopolysiloxane forming the matrix is ​​increased, and the amount of volatile components can be suppressed. Also, when the number of repeating units n of the siloxane skeleton is less than or equal to the upper limit, it becomes easier to adjust the viscosity of the composition to a low level, and the fluidity is improved.

[0059] (Siloxane Compounds Having Hydroxyl Groups) The polymeric dispersant may be a siloxane compound having hydroxyl groups. The siloxane compound having hydroxyl groups has hydroxyl groups on part of the ends of the main chain, on the side chains, or on both. That is, the siloxane compound having hydroxyl groups in the present invention may be a siloxane compound having hydroxyl groups on part of the ends of the main chain or on the side chains, or it may be a siloxane compound having hydroxyl groups on part of the ends of the main chain and on both the side chains. The siloxane compound having hydroxyl groups is a hydroxyl-containing siloxane compound other than a siloxane compound having hydroxyl groups on both ends of the main chain. Here, the ends of the main chain refer to the ends of the longest part of the molecular chain (the straight-chain part with the most constituent atoms in the molecular structure) in the molecular structure.

[0060] Siloxane compounds having hydroxyl groups with this specific structure readily react or interact with functional groups on the surface of fillers due to the presence of hydroxyl groups. However, since these hydroxyl-containing siloxane compounds do not have hydroxyl groups at both ends, they do not react or interact with the filler at either end. Therefore, it is believed that this can improve the dispersibility of the filler in the composition and effectively reduce viscosity.

[0061] The hydroxyl group-containing siloxane compound of the present invention may have only one hydroxyl group or two or more hydroxyl groups. While there is no particular upper limit to the number of hydroxyl groups, it is preferably 6 or less, and more preferably 3 or less. Among these, siloxane compounds having two hydroxyl groups are particularly preferred due to their high viscosity-reducing effect. The number of hydroxyl groups in the hydroxyl group-containing siloxane compound of the present invention may be as few as one; one embodiment includes a siloxane compound having a hydroxyl group only at one end of the main chain. The hydroxyl group may be bonded to the siloxane skeleton via an organic group such as a hydrocarbon group.

[0062] The siloxane compound having a hydroxyl group is preferably an organopolysiloxane compound. The siloxane compound having a hydroxyl group has a siloxane skeleton (-Si-O-), and it is preferable that the number of repeating units n of the siloxane skeleton is 11 or more. Preferably, the number of repeating units n of the siloxane skeleton is 11 or more and 350 or less, more preferably 20 or more and 300 or less, even more preferably 50 or more and 270 or less, and even more preferably 100 or more and 250 or less. When the number of repeating units n of the siloxane skeleton is above the lower limit, the compatibility with the organopolysiloxane forming the matrix is ​​increased, and the amount of volatile components can be suppressed. Also, when the number of repeating units n of the siloxane skeleton is below the upper limit, it is easier to adjust the viscosity of the composition to a low level. In addition to the organic group having a hydroxyl group described above, hydrocarbon groups may also be bonded to the Si constituting the siloxane skeleton, and examples of hydrocarbon groups include alkyl groups such as methyl groups.

[0063] The polymer dispersant in the present invention is contained in a polymer composition, and when the total amount of the polymer composition (i.e., polymer matrix) is 100% by mass, the content of the polymer dispersant in the polymer composition is preferably 1% by mass or more and 45% by mass or less, more preferably 3% by mass or more and 35% by mass or less, and even more preferably 5% by mass or more and 25% by mass or less, from the viewpoint of effectively lowering the viscosity of the composition. Here, the total amount of the polymer composition means the total amount of components that form the polymer matrix, and the polymer composition includes not only organic polymers such as organopolysiloxanes but also additives such as plasticizers and polymer dispersants, but does not include components that volatilize during manufacturing or fillers such as anisotropic carbon materials. Therefore, the total amount of the polymer composition can also be said to be the amount obtained by subtracting the amount of fillers and volatile substances from the total amount of the mixed composition for forming the heat conductive layer.

[0064] The polymer matrix content, expressed as a volume-based filling rate (volume filling rate), is preferably 25% to 60% by volume, more preferably 30% to 55% by volume, and even more preferably 35% to 50% by volume, relative to the total amount of thermal conductive sheet.

[0065] (Additives) The thermal conductive sheet of the present invention may further contain various additives, to the extent that they do not impair its function as a thermal conductive sheet. Examples of additives include at least one selected from flame retardants, antioxidants, colorants, and settling inhibitors. Furthermore, when the curable polymer composition is crosslinked or cured as described above, additives such as crosslinking accelerators, curing accelerators, and curing catalysts may be added to promote crosslinking and curing. If the polymer matrix is ​​an organopolysiloxane, a platinum catalyst may be used as the curing catalyst.

[0066] (Bulk thermal resistance value) The thermal conductive sheet of the present invention has a bulk thermal resistance value of 0.07°C·cm ２ It is preferable that the temperature is 0.05°C / cm² or less. ２ It is more preferable that the temperature is less than or equal to / W, and 0.04°C / cm². ２It is even more preferable that the value is less than or equal to / W. If the bulk thermal resistance value is less than or equal to the above upper limit, it can be said that the bulk thermal resistance of the thermal conductive sheet has been reduced, and it is possible to make the thermal conductive sheet into a thin film while providing the sheet with excellent thermal conductivity. In the present invention, the lower the bulk thermal resistance value, the better, and 0°C・cm ２ Anything above 1W is acceptable, but in practice, for example, 0.005°C / cm² is sufficient. ２ / W or higher, preferably 0.01°C / cm ２ It is / W or greater.

[0067] (Interfacial thermal resistance value) The thermal conductive sheet of the present invention has an interfacial thermal resistance value of 0.075°C·cm. ２ Preferably, the temperature is 0.07°C / cm² or less. ２ It is more preferable that the temperature is less than or equal to / W, and 0.065°C / cm². ２ It is even more preferable that the interfacial thermal resistance is less than or equal to the above upper limit. If the interfacial thermal resistance is less than or equal to the above upper limit, it can be said that the interfacial thermal resistance of the thermal conductive sheet has been reduced, and both the flexibility and thermal conductivity of the thermal conductive sheet can be made excellent. In this invention, the lower the interfacial thermal resistance, the better. ２ Anything above / W is acceptable, but in practical terms, for example, 0.007°C·cm is sufficient. ２ / W or higher, preferably 0.02°C / cm² ２ It is / W or greater.

[0068] (Overall thermal resistance) The thermally conductive sheet of the present invention has a thermal resistance of 0.12°C·cm at a load of 30 psi (hereinafter also referred to as "overall thermal resistance"). ２ Preferably, the temperature is 0.11°C / cm² or less. ２ It is more preferable that the temperature is less than or equal to 0.1°C / cm². ２ It is even more preferable that the thermal resistance is less than or equal to / W. When the overall thermal resistance is less than or equal to the above upper limit, the efficiency of heat transfer from the heat-generating element to the heat-sinking element via the thermal conductive sheet is improved, and excellent thermal conductivity can be obtained. In this invention, the lower the overall thermal resistance, the better. ２ Anything above 1W is acceptable, but in practical terms, for example, 0.02°C / cm² is sufficient. ２ / W or higher, preferably 0.03°C / cm² ２It is 1W or more. Note that all of the above thermal resistance values ​​can be obtained by the measurement methods described in the examples.

[0069] (Thickness of the thermally conductive sheet) The thermally conductive sheet of the present invention is preferably 0.05 mm or more and 0.5 mm or less in thickness, more preferably 0.06 mm or more and 0.4 mm or less, and even more preferably 0.07 mm or more and 0.3 mm or less. If the thickness of the thermally conductive sheet is below the above upper limit, the thermally conductive sheet can be made into a thin film, and the bulk thermal resistance can also be reduced. Furthermore, the thermally conductive sheet can be installed in narrow gaps, such as inside electronic equipment. On the other hand, if the thickness of the thermally conductive sheet is above the above lower limit, a certain degree of thermal conductivity can be guaranteed.

[0070] (E Hardness) The thermal conductive sheet of the present invention preferably has a Type E hardness (hereinafter also referred to as "E hardness") of 25 or more and 45 or less as defined in JIS K6253, more preferably 27 or more and 45 or less, and even more preferably 28 or more and 43 or less. If the E hardness is above the lower limit, as will be described later, it becomes easier to thin the thermal conductive sheet when cutting it by slicing or the like to obtain a sheet-like molded body. Also, if the E hardness is below the upper limit, a certain degree of flexibility is imparted to the thermal conductive sheet, making it easier to reduce the interfacial thermal resistance.

[0071] [Method for Manufacturing a Thermally Conductive Sheet] The method for manufacturing the thermally conductive sheet of the present invention is not particularly limited, but for example, it can be manufactured by a method comprising the following steps (A) and (B). Step (A): A step of obtaining a molded body comprising a binder and an anisotropic carbon material dispersed in the binder. Step (B): A step of polishing the surface of the molded body. Each step will be described in more detail below.

[0072] (Step (A)) In Step (A), it is preferable to obtain an oriented molded body in which an anisotropic carbon material or the like is oriented along one direction which is the thickness direction of the thermal conductive sheet, and then cut the oriented molded body into a sheet to obtain a sheet-like molded body. It is then preferable to polish the sheet-like molded body in Step (B). The molded body may be obtained by mixing a polymer composition and an anisotropic carbon material to obtain a mixed composition, and then curing the mixed composition, but it is preferable to further mix a volatile substance into the mixed composition. Furthermore, other components such as additives may be added to the mixed composition as needed. Preferred embodiments of Step (A) will be described in detail below.

[0073] The method of mixing the above components is not particularly limited, as long as a mixed composition can be obtained by mixing the above components. The polymer composition, anisotropic carbon material, volatile substances added as needed, and other components added as needed may be mixed in any order to obtain the mixed composition. The polymer composition may consist of, for example, a main agent and a curing agent (for example, in the case of addition-reaction type silicones, an alkenyl group-containing organopolysiloxane and a hydrogen organopolysiloxane). In such cases, the main agent, curing agent, anisotropic carbon material, volatile substances added as needed, and other components may be mixed in any order to obtain the mixed composition. The mixed composition may be in the form of a one-component type or a two-component type consisting of a first agent and a second agent. In the two-component type, the first agent and the second agent are mixed at the time of use to obtain the mixed composition.

[0074] <Volatile Substances> The volatile substances used in this invention may be any components that volatilize during heating for curing of the polymer composition described later. By volatilizing during heating for curing, the volatile substances allow for a higher proportion of fillers, such as anisotropic carbon materials, in the thermally conductive sheet. Furthermore, the viscosity of the mixed composition decreases due to the inclusion of volatile substances. This makes it easier to increase the amount of filler and ensures proper dispersion even at high concentrations. Moreover, it becomes easier to orient anisotropic carbon materials in a predetermined direction through methods such as magnetic field orientation, as described later.

[0075] Furthermore, it is preferable that the volatile substance is a miscible substance that is compatible with or dissolves in the polymer composition. When the volatile substance is a miscible substance, the polymer composition and the volatile substance can be mixed uniformly, making it easier to reduce viscosity or increase the amount of filler used. Moreover, the bubbles formed by the volatilization of the volatile substance can be made fine and uniform.

[0076] The volatile substance is preferably a substance that is liquid at room temperature (25°C) and 1 atmosphere. Examples of volatile substances include alkoxysilane compounds, hydrocarbon solvents, and alkoxysiloxane compounds. These compounds can increase the solubility or compatibility with polymer compositions, making it easier to reduce the viscosity of the mixed composition or increase the amount of filler used. They also make it easier to create fine and uniform bubbles formed by the volatilization of the volatile substance. The volatile substance may be used alone or in combination of two or more types.

[0077] It is preferable to use an alkoxysilane compound as the volatile substance. Using an alkoxysilane compound results in a smooth surface and good appearance of the heat-conductive sheet obtained by curing. The alkoxysilane compound used as the volatile substance is a compound having a structure in which one to three of the four bonds of a silicon atom (Si) are bonded to an alkoxy group, and the remaining bond is bonded to an organic substituent. The presence of an alkoxy group and an organic substituent enhances the compatibility of the alkoxysilane compound with polymer compositions, particularly those composed of organopolysiloxanes. Examples of alkoxy groups in alkoxysilane compounds include methoxy, ethoxy, protoxy, butoxy, pentoxy, and hexatoxy groups. The alkoxysilane compound may also be included in the curable polymer composition as a dimer.

[0078] Among alkoxysilane compounds, those having at least one of a methoxy group and an ethoxy group are preferred from the viewpoint of availability. The number of alkoxy groups in the alkoxysilane compound is preferably two or three, and more preferably three, from the viewpoint of compatibility and solubility with polymer compositions. Specifically, the alkoxysilane compound is preferably at least one selected from trimethoxysilane compounds, triethoxysilane compounds, dimethoxysilane compounds, and diethoxysilane compounds.

[0079] Examples of functional groups included in the organic substituents of alkoxysilane compounds include acryloyl groups, alkyl groups, carboxyl groups, vinyl groups, methacrylic groups, aromatic groups, amino groups, isocyanate groups, isocyanurate groups, epoxy groups, hydroxyl groups, and mercapto groups. When using a platinum catalyst as a curing catalyst for a polymer composition composed of organopolysiloxanes, it is preferable to select and use an alkoxysilane compound that does not easily affect the curing reaction of the organopolysiloxane. Specifically, when using an addition reaction type organopolysiloxane utilizing a platinum catalyst, it is preferable that the organic substituent of the alkoxysilane compound does not contain amino groups, isocyanate groups, isocyanurate groups, hydroxyl groups, or mercapto groups.

[0080] From the viewpoint of compatibility with polymer compositions composed of organopolysiloxanes, alkoxysilane compounds preferably include alkylalkoxysilane compounds having an alkyl group bonded to a silicon atom, i.e., alkoxysilane compounds having an alkyl group as an organic substituent. Therefore, dialkyldialkoxysilane compounds and alkyltrialkoxysilane compounds are preferred, and alkyltrialkoxysilane compounds are preferred among them. The number of carbon atoms of the alkyl group bonded to the silicon atom is preferably 1 to 16. Furthermore, in trialkoxysilane compounds such as trimethoxysilane compounds and triethoxysilane compounds, the number of carbon atoms of the alkyl group is preferably 6 or more, more preferably 8 or more, preferably 12 or less, and more preferably 10 or less. On the other hand, in dialkoxysilane compounds such as dimethoxysilane compounds and diethoxysilane compounds, the number of carbon atoms of the alkyl group may be 1 or more, preferably 10 or less, more preferably 6 or less, and more preferably 4 or less.

[0081] Examples of alkyl group-containing alkoxysilane compounds include methyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, di-n-propyldimethoxysilane, di-n-propyldiethoxysilane, isobutyltrimethoxysilane, isobutyltrimethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, methylcyclohexyldimethoxysilane, methylcyclohexyldiethoxysilane, n-octyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, and n-decyltriethoxysilane. Among alkyl group-containing alkoxysilane compounds, n-decyltrimethoxysilane and n-octyltriethoxysilane are even more preferred from the viewpoint of compatibility with organopolysiloxanes constituting the polymer composition.

[0082] Alkoxysiloxane compounds used as volatile substances have two or more siloxane bonds and a structure in which an alkoxy group is bonded to at least one silicon atom. Alkoxysiloxane compounds have a structure in which an organic substituent is bonded to at least one silicon atom among the silicon atoms constituting the siloxane bond. By having an alkoxy group and an organic substituent, alkoxysiloxane compounds can improve compatibility with organopolysiloxanes constituting polymer compositions. Examples of alkoxy groups and organic substituents of alkoxysiloxane compounds are those exemplified in the description of alkoxysilane compounds above, and from the viewpoint of compatibility with organopolysiloxanes constituting polymer compositions, it is preferable to have at least an alkyl group.

[0083] Examples of alkoxysiloxane compounds include methyl methoxysiloxane oligomers, methylphenyl methoxysiloxane oligomers, methyl epoxy methoxysiloxane oligomers, methyl mercaptomethoxysiloxane oligomers, and methyl acryloyl methoxysiloxane oligomers. One or more alkoxysiloxane compounds can be used.

[0084] Aromatic hydrocarbon solvents are used as volatile substances. Among these, aromatic hydrocarbon solvents are preferred from the viewpoint of compatibility with polymer compositions. Examples of aromatic hydrocarbon solvents include those having about 6 to 10 carbon atoms, such as toluene, xylene, mesitylene, ethylbenzene, propylbenzene, butylbenzene, and t-butylbenzene, with toluene and xylene being preferred.

[0085] In the mixed composition, the content of volatile substances per 100 parts by mass of the polymer composition is preferably 6 parts by mass or more and 60 parts by mass or less. A content of 6 parts by mass or more makes it easier to exert the effects of the volatile substances, for example, allowing for the formation of an appropriate amount of fine bubbles in the polymer matrix. Furthermore, a content of 60 parts by mass or less allows for obtaining effects commensurate with the amount of volatile substances used. From these viewpoints, the above content of volatile substances is more preferably 8 parts by mass or more and 50 parts by mass or less, and even more preferably 10 parts by mass or more and 35 parts by mass or less. It is preferable that some or all of the volatile substances volatilize upon heating during curing. Therefore, volatile substances do not necessarily have to be contained in the thermal conductive sheet, but they may be contained in the thermal conductive sheet in an amount less than that contained in the mixed composition.

[0086] Further details regarding components other than volatile substances in the mixed composition (i.e., polymer composition, anisotropic carbon material, and other additives) are as described above. The content of anisotropic carbon material in the mixed composition is also as described above. However, while the amounts of each component shown above are based on 100 parts by mass of the polymer matrix, in the case of the mixed composition, the amounts are based on 100 parts by mass of the polymer composition.

[0087] In step (A), it is preferable to form an oriented molded article from the mixed composition as described above. The mixed composition is preferably cured to form an oriented molded article. The oriented molded article can be obtained more specifically by a magnetic field orientation method or a flow orientation method, but among these, the magnetic field orientation method is preferred.

[0088] <Magnetic Field Orientation Method> In the magnetic field orientation method, a mixed composition containing a polymer composition such as a liquid curable silicone composition that will become a silicone matrix after curing, and a filler containing at least anisotropic carbon material, is injected into the inside of a mold or the like, and then placed in a magnetic field. The anisotropic carbon material is then oriented along the magnetic field, and the polymer composition is cured to obtain an oriented molded body. The oriented molded body is preferably in the shape of a block. In addition, a release film may be placed in the part of the mold that comes into contact with the mixed composition. For example, a resin film with good release properties or a resin film on one side that has been treated with a release agent can be used as the release film. Using a release film makes it easier to remove the oriented molded body from the mold.

[0089] In the magnetic field orientation method, the viscosity of the mixed composition used is preferably 10 to 600 Pa·s in order to achieve magnetic field orientation. A viscosity of 10 Pa·s or higher prevents the sedimentation of fillers such as anisotropic carbon materials. A viscosity of 600 Pa·s or lower ensures good fluidity, allowing the anisotropic fillers to be properly oriented by the magnetic field without causing problems such as excessive orientation time. Viscosity is measured using a rotational viscometer (Brookfield viscometer DV-E, spindle SC4-14) at 25°C and a rotational speed of 10 rpm. However, when using fillers that are less prone to sedimentation or when combining with additives such as sedimentation inhibitors, the viscosity of the mixed composition may be less than 10 Pa·s.

[0090] In magnetic field orientation manufacturing methods, examples of magnetic field source for applying magnetic field lines include superconducting magnets, permanent magnets, and electromagnets, but superconducting magnets are preferred because they can generate a magnetic field with a high magnetic flux density. The magnetic flux density of the magnetic field generated from these magnetic field source sources is preferably 1 to 30 Tesla. Setting the magnetic flux density to 1 Tesla or higher makes it possible to easily orient anisotropic fillers such as anisotropic carbon materials. Setting it to 30 Tesla or lower makes practical manufacturing possible.

[0091] Curing of polymer compositions such as curable silicone compositions is preferably carried out by heating, for example, at a temperature of about 50 to 150°C. The heating time is, for example, about 10 minutes to 3 hours.

[0092] <Flow Orientation Method> In the flow orientation method, a preliminary sheet is produced in which anisotropic filler is oriented in the planar direction by applying shear force to the mixed composition. Multiple sheets of this preliminary sheet are then stacked to produce a laminated block, and this laminated block is used as an oriented molded body. More specifically, in the flow orientation method, first, as described above, a mixed composition containing at least a polymer composition and a filler containing at least anisotropic carbon material is prepared. Here, the polymer compound used in the polymer composition may be a polymer compound that is liquid at room temperature (23°C) or a polymer compound that is solid at room temperature. The mixed composition has a relatively high viscosity so that shear force is applied when it is stretched into a sheet, and the viscosity of the mixed composition is preferably 3 to 500 Pa·s. In order to obtain the above viscosity, it is preferable that a solvent is added to the mixed composition.

[0093] Next, the mixed composition is flattened and stretched while applying shear force to form a sheet (preliminary sheet). Applying shear force allows anisotropic fillers, such as anisotropic carbon materials, to be oriented in the shear direction. As a means of forming the sheet, for example, the mixed composition may be coated onto a base film using a coating applicator such as a bar coater or doctor blade, or by extrusion molding or discharge from a nozzle, and then dried or semi-cured as needed. The thickness of the preliminary sheet is preferably about 50 to 250 μm. In the preliminary sheet, the anisotropic fillers are oriented in one direction along the surface direction of the sheet. Next, multiple preliminary sheets are stacked and laminated so that the orientation direction is the same, and then the preliminary sheets are bonded to each other by heat pressing or the like while curing the mixed composition as needed by heating or ultraviolet irradiation to form a laminated block, and this laminated block is used as an oriented molded body.

[0094] Next, the oriented molded body obtained above is cut perpendicular to the direction in which the anisotropic filler is oriented, by slicing or other means, to obtain a sheet-like molded body. Slicing can be done, for example, with a shear blade or laser.

[0095] (Process (B)) In process (B), the molded body, such as the sheet-like molded body obtained in process (A), is polished. The molded body is usually a sheet-like molded body as described above, and it is preferable that one or both sides of the sheet-like molded body be polished. Surface polishing can be performed using, for example, abrasive paper, abrasive film, abrasive cloth, or abrasive belt. In this manufacturing method, by polishing the surface of the sheet-like molded body, it is possible to expose the anisotropic carbon material on the surface of the thermal conductive sheet and to increase the carbon material coverage rate. The properties of the abrasive paper are preferably such that the average particle size (D50) of the contained abrasive grains is 0.1 to 100 μm, and more preferably 1 to 60 μm. By using abrasive paper with an average particle size of 0.1 μm or more, it is possible to expose the anisotropic carbon material on the surface of the thermal conductive sheet and to achieve a carbon material coverage rate of 65% or more. Furthermore, by using abrasive paper with an average particle size of 100 μm or less, it is possible to prevent scratches on the surface of the thermal conductive sheet that would be practically problematic. Also, for the same reasons as above, the grit size of the abrasive grains of the abrasive paper is preferably #120 to 20000, preferably #300 to 15000, and more preferably #320 to 6000. For the polishing method, methods such as polishing by continuously contacting the surface of the thermal conductive sheet with abrasive paper in the same linear direction, polishing by reciprocating a certain distance, polishing by rotating in the same direction, or polishing by contacting in various directions can be used. The degree of polishing can be determined by observing the surface condition, for example, but in the case of reciprocating polishing, 50 to 500 reciprocations are preferred, 60 to 400 reciprocations are more preferred, and 70 to 300 reciprocations are even more preferred. Specifically, it is preferable to polish to the extent that the anisotropic carbon material is exposed on the surface of the thermal conductive sheet, or that the carbon material coverage rate is 65% or more.

[0096] It is preferable to polish the surface of the thermally conductive sheet in two separate polishing steps. In this case, the average particle size of the abrasive paper used in the first polishing step is preferably 3 to 40 μm larger, more preferably 5 to 30 μm larger, and even more preferably 10 to 25 μm larger than the average particle size of the abrasive paper used in the second polishing step. It is also preferable that the particle size of the abrasive paper differs between the first and second polishing steps. It is more preferable that the particle size of the abrasive paper used in the first polishing step is larger than that of the abrasive paper used in the second polishing step. It is preferable that the particle size of the abrasive paper used in the first polishing step is 500 to 8000 greater than that of the abrasive paper used in the second polishing step, more preferably 800 to 5000 greater, and even more preferably 1000 to 3500 greater. Furthermore, the number of polishing cycles in the first polishing step is preferably 20 to 200 times greater than the number of polishing cycles in the second polishing step, more preferably 30 to 170 times greater, and even more preferably 50 to 150 times greater. Dividing the polishing process into two steps as described above allows for rough polishing in the first step and fine polishing in the second step, making it easier to expose anisotropic carbon material on the surface of the thermal conductive sheet and to achieve a carbon material coverage rate of 65% or more.

[0097] [Applications of Thermally Conductive Sheets] Thermally conductive sheets are interposed between a heat-generating element and a heat sink, transferring heat generated by the heat-generating element to the heat sink and then releasing the heat from the heat sink. Thermally conductive sheets are used in electronic equipment applications, semiconductor applications, etc., and are preferably used in semiconductor applications. In semiconductor applications, thermally conductive sheets can be used in any application, but are preferably used in applications that are directly applied to semiconductor chips such as silicon dies, referred to as TIM1, for example, between a semiconductor chip and a heat spreader. Of course, they may also be used in applications that are not directly applied to semiconductor chips, referred to as TIM2, in which case the thermally conductive sheet may be used, for example, between a heat spreader and a cooling unit such as a heat sink or heat pipe. In addition, thermally conductive sheets may be used between various electronic components that act as heat-generating elements and heat sinks such as heat spreaders, heat sinks, heat pipes, heat pumps, and metal housings of electronic equipment. Thermally conductive sheets are best used by being placed between two components (adhered objects), such as a heat sink and a heat generating element, and are best used in a state where they are in close contact with each component (adhered object) and compressed.

[0098] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0099] [Physical Properties] The physical properties of the thermal conductive sheet were measured using the following method.

[0100] (E Hardness) The thermally conductive sheets obtained in each example and comparative example were stacked until the test specimens reached a thickness of 10 mm to create measurement samples. The E hardness of the measurement samples was measured using a Type E durometer in accordance with the Japanese Industrial Standard JIS K 6253.

[0101] (Thickness) The thickness (initial thickness) of the thermal conductive sheet was measured using a thickness gauge.

[0102] (Carbon material coverage) The surface of the thermally conductive sheet was observed using a scanning electron microscope (SEM). Images obtained by SEM were captured using a field emission scanning electron microscope (model S-4800, manufactured by Hitachi High-Technologies Corporation) with an acceleration voltage of 10 kV, a probe current of 20 μA in High mode, and a magnification of 150x, using a YAG backscattered electron detector. In addition, as a setting before image acquisition, the ABCC (Auto Brightness Contrast Control) settings were adjusted to Contrast: 5 and Brightness: 4, and the contrast and brightness were measured. The captured images were analyzed using ImageJ. In the captured SEM images, the entire thermal conductive sheet was selected, and values ​​with a brightness threshold of 85 or less were considered voids present on the thermal conductive sheet surface, while values ​​with a threshold of 190 or less were considered carbon material and voids present on the thermal conductive sheet surface. The ratio of carbon material present on the thermal conductive sheet surface was calculated by subtracting these values. The measurement and analysis were performed five times, and the average value was taken as the carbon material coverage rate. In this example and comparative example, the front and back surfaces of the sheet were assumed to have similar coverage rates, and measurements were performed on one side of the sheet.

[0103] (Overall Thermal Resistance) The overall thermal resistance was measured using a thermal resistance measuring instrument as shown in Figure 1, in the following manner. Specifically, for each sample, a test piece S with dimensions of 30 mm x 30 mm and a thickness of 1 mm was prepared for this test. Each test piece S was then attached to a copper block 22 with a measuring surface of 25.4 mm x 25.4 mm and its sides covered with insulating material 21, sandwiched between upper copper blocks 23, and a load of 30 psi was applied by a load cell 26. Here, the lower copper block 22 is in contact with a heater 24. The upper copper block 23 is covered with insulating material 21 and connected to a heat sink 25 with a fan. Next, the heater 24 was heated at a heat output of 25 W, and after 12 minutes when the temperature reached a near-steady state, the temperature of the upper copper block 23 (θ) was measured. ｊ０ ), the temperature of the lower copper block 22 (θ ｊ１ The thermal resistance of each sample was determined by measuring the heat output (Q) of the heater and the following equation (1): Thermal resistance = (θ ｊ１ -θ ｊ０) / Q ...Equation (1) In Equation (1), θ ｊ１ The temperature of the lower copper block 22, θ ｊ０ Q is the temperature of the upper copper block 23, and Q is the amount of heat generated.

[0104] (Bulk Thermal Resistance) Three types of thermally conductive sheets with different thicknesses were prepared, and the overall thermal resistance of each sheet was measured using the measurement method described above. The thicknesses of the sheets were 2.0 mm, 1.0 mm, and 0.5 mm, respectively. After measuring the overall thermal resistance of each sheet, an approximate straight line was obtained using the least squares method, with the thermal resistance at a load that reduces the thickness of each sheet to 20% of its original thickness plotted on the vertical axis and the thickness of each sheet at that load plotted on the horizontal axis. The bulk thermal conductivity of the thermally conductive sheet was then calculated from the slope of the obtained approximate straight line. The bulk thermal resistance of the thermally conductive sheet was determined from the bulk thermal conductivity and the thickness of the sheet.

[0105] (Interfacial thermal resistance) The interfacial thermal resistance was determined by subtracting the bulk thermal resistance from the total thermal resistance.

[0106] The following components were used as raw materials for the thermal conductive sheet.

[0107] (Main component and curing agent) Curable silicone: Addition reaction type organopolysiloxane consisting of an alkenyl group-containing organopolysiloxane as the main component and a hydrogen organopolysiloxane as the curing agent (however, containing a catalytic amount of platinum catalyst). (Volatile substance) n-decyltrimethoxysilane

[0108] (Anisotropic carbon materials) Graphitized carbon fiber: Average fiber length (arithmetic mean) 85 μm, aspect ratio 8.5, thermal conductivity 900 W / (m·K) Flake graphite powder: Average particle size (D50) = 15 μm, aspect ratio 10, thermal conductivity 550 W / (m·K)

[0109] (Other fillers) Aluminum oxide 1: Polyhedral shape, average particle size (D50) = 0.5 μm, aspect ratio 1.0, non-anisotropic filler Aluminum oxide 2: Polyhedral shape, average particle size (D50) = 3.0 μm, aspect ratio 1.0, non-anisotropic filler (Polymer dispersant) Pyrene dispersant: Organopolysiloxane containing pyrene as shown by the synthesis method described later, number average molecular weight 17,000

[0110] (Synthesis of Pyrene Dispersant) 98.6 g of an organosiloxane compound having a 1,3-diol group (n=210), 1.4 g of 1-pyrenecarboxaldehyde, 50 g of toluene as a solvent, and 0.6 g of a catalyst (Organo Corporation, "Amberlyst 15 dry") were reacted at 100°C for 24 hours in a nitrogen atmosphere. After the reaction, the catalyst was removed by filtration through a 5.0 μm PTFE filter, and the filtrate was concentrated using a rotary evaporator and a vacuum dryer to obtain pyrene dispersant 1. The reaction equation is shown below. １ The following reactions were confirmed to have occurred by 1H NMR measurement. A JEOL "ECX-400" NMR analyzer was used, and measurements were performed with deuterated chloroform as the solvent, at a sample concentration of 1% by weight, at 25°C, a measurement frequency of 400 MHz, and 8 cumulative measurements.

[0111] [Example 1] A mixed composition was obtained by mixing each component in a planetary mixer at 25°C for 50 minutes according to the formulation shown in Table 1. The curable silicone was prepared by mixing 65 parts by mass of alkenyl group-containing organopolysiloxane as the main component and 26 parts by mass of hydrogen organopolysiloxane as the curing agent.

[0112] *The units for the values ​​of each component in Table 1 are parts by mass. The same applies to Tables 2 to 5 described later.

[0113] Next, the mixed composition was injected into a mold set to a thickness sufficiently greater than that of the thermally conductive sheet. An 8T magnetic field was applied in the thickness direction to orient the carbon fibers and flake graphite in the thickness direction, and then the curable silicone was cured by heating at 80°C for 8 hours to obtain a block-shaped oriented molded body. Next, using a shearing blade, the block-shaped oriented molded body was sliced ​​perpendicular to the orientation surface into a sheet with a thickness of 100 μm to obtain a sheet-shaped molded body in which the anisotropic carbon material was exposed. Subsequently, both surfaces of the sheet-shaped molded body were polished back and forth 75 times with coarse abrasive paper A (grit #800) having an average abrasive particle size (D50) of 20 μm, and then polished back and forth 10 more times with coarse abrasive paper B (grit #4000) having an average abrasive particle size (D50) of 3 μm, and then heated at 150°C for 2 hours to obtain a thermally conductive sheet having the composition as described in Table 6.

[0114] [Example 2] A thermally conductive sheet having the composition described in Table 6 was obtained using the same procedure as in Example 1, except that the number of reciprocating polishing cycles was changed as shown in Table 6.

[0115] [Examples 3-6] Except for mixing 64 parts by mass of the main component and 27 parts by mass of the curing agent to prepare a curable silicone, and changing the number of reciprocating polishing steps and the thickness of the thermal conductive sheet as shown in Table 6, a thermal conductive sheet having the formulation shown in Table 6 was obtained using the same procedure as in Example 1.

[0116] [Example 7] A heat-conductive sheet having the formulation shown in Table 6 was obtained by following the same procedure as in Example 1, except that a curable silicone was prepared by mixing 56 parts by mass of the main component and 26 parts by mass of the curing agent, and the formulation of each component of the mixed composition was changed as shown in Table 2.

[0117]

[0118] [Comparative Examples 1-3] Except for mixing 49 parts by mass of the main component and 60 parts by mass of the curing agent to prepare a curable silicone, changing the composition of each component of the mixed composition as shown in Table 3, and changing the thickness of the thermal conductive sheet as shown in Table 7, a thermal conductive sheet having the composition shown in Table 7 was obtained using the same procedure as in Example 1.

[0119]

[0120] [Comparative Example 4] A heat-conductive sheet having the formulation shown in Table 7 was obtained by following the same procedure as in Example 1, except that a curable silicone was prepared by mixing 65 parts by mass of the main component and 35 parts by mass of the curing agent, and the formulation of each component of the mixed composition was changed as shown in Table 4.

[0121]

[0122] [Comparative Example 5] A thermally conductive sheet having the formulation shown in Table 7 was obtained using the same procedure as in Comparative Example 1, except that the formulation of each component of the mixed composition was changed as shown in Table 5.

[0123]

[0124] [Comparative Example 6] A thermally conductive sheet having the composition shown in Table 7 was obtained using the same procedure as in Comparative Example 1, except that the number of reciprocating polishing cycles was changed as shown in Table 7.

[0125]

[0126] *In Tables 6 and 7, "○" indicates that a pyrene dispersant was included, and "×" indicates that a pyrene dispersant was not included. Also, "Other fillers" refers to alumina.

[0127] As is clear from the above results, the thermally conductive sheets prepared in the examples had an anisotropic carbon material content within a certain range, the anisotropic carbon material was exposed on the surface of the sheet, and the anisotropic carbon material coverage rate on the surface of the sheet was 65% or more, resulting in low bulk thermal resistance and interfacial thermal resistance. In contrast, the thermally conductive sheets prepared in the comparative examples had a carbon material coverage rate of less than 65%, making it impossible to lower at least one of the bulk thermal resistance and interfacial thermal resistance. In particular, the thermally conductive sheet prepared in Comparative Example 5 had too little anisotropic carbon material content, resulting in a significantly low anisotropic carbon material coverage rate.

Claims

1. A thermally conductive sheet comprising a polymer matrix and an anisotropic carbon material, wherein the content of the anisotropic carbon material is 20% by volume or more and 40% by volume or less of the total amount of the thermally conductive sheet, the anisotropic carbon material is exposed on at least one surface of the thermally conductive sheet, and the carbon material coverage rate on the surface of the thermally conductive sheet is 65% or more.

2. The thermal conductive sheet according to claim 1, wherein the Type E hardness is 25 or more and 45 or less.

3. The thermally conductive sheet according to claim 1 or 2, wherein the polymer matrix comprises a polymer dispersant.

4. The thermally conductive sheet according to claim 3, wherein the polymer dispersant comprises at least one selected from the group consisting of alkoxysiloxane compounds, aromatic ring-containing siloxane compounds, and siloxane compounds having a hydroxyl group.

5. The thermally conductive sheet according to claim 1 or 2, wherein the anisotropic carbon material comprises at least one of carbon fibers and flaky graphite.

6. The thermally conductive sheet according to claim 5, wherein the anisotropic carbon material comprises the carbon fibers and the flaky graphite.

7. The thermal conductive sheet according to claim 6, wherein the carbon fiber content is 20% by volume or more and 28% by volume or less with respect to the total amount of the thermal conductive sheet, and the flake graphite content is 1% by volume or more and 12% by volume or less with respect to the total amount of the thermal conductive sheet.

8. The thermal resistance value at a 30 psi load is 0.12°C·cm. ２ A thermally conductive sheet according to claim 1 or 2, wherein the thermal conductivity is less than or equal to / W.

9. The thermally conductive sheet according to claim 1 or 2, wherein the polymer matrix comprises a silicone resin.

10. The thermally conductive sheet according to claim 1 or 2, wherein the thickness is 0.05 mm or more and 0.5 mm or less.

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