Thermally conductive sheet

Abstract

To provide a thermally conductive sheet which is excellent in thermal conductivity, compressibility, and surface smoothness.SOLUTION: A thermally conductive sheet contains a resin and aluminum nitride. The thermally conductive sheet has an orientation angle of the aluminum nitride to a main surface of 60° or more and 90° or less, the aluminum nitride has a scale shape, and a volume average particle size of the aluminum nitride is 20 μm or more and 100 μm or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, the amount of heat generated by electronic components such as power semiconductors (e.g., IGBT modules) and integrated circuit (IC) chips has increased as their performance has improved. As a result, electronic devices that use these components need to take measures to prevent malfunctions caused by temperature increases in the electronic components.

[0003] To prevent malfunctions caused by temperature rise in electronic components, a common method is to promote heat dissipation by attaching a heat sink, heat sink plate, heat dissipation fin, or other heat sink made of metal to the heat-generating body of the electronic component.When using a heat sink, in order to efficiently transfer heat from the heat-generating body to the heat sink, a sheet-like member with high thermal conductivity (thermal conduction sheet) is placed between the heat-generating body and the heat sink, and a predetermined pressure is applied to this thermal conduction sheet to bring the heat-generating body and the heat sink into close contact.

[0004] Various studies have been conducted to improve the properties of thermally conductive sheets, such as thermal conductivity. For example, Patent Document 1 discloses a thermally conductive sheet containing resin and non-spherical ceramic particles, in which the orientation degree of specific crystal lattice planes of the non-spherical ceramic particles is adjusted to a desired range, thereby achieving both high thermal conductivity and high electrical insulation. Furthermore, Patent Document 2 discloses a resin composition and a resin molded product containing fibrous aluminum nitride. The resin composition and resin molded product described in Patent Document 2 can achieve higher thermal conductivity at the same additive amount compared to compositions made using finely powdered aluminum nitride with a low aspect ratio. In other words, they can achieve higher thermal conductivity with a smaller loading. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-123278 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-138056 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, a thermally conductive sheet is required to have not only high thermal conductivity but also excellent compressibility and a smooth surface. However, the above-mentioned conventional thermally conductive sheets have room for improvement in terms of simultaneously achieving high levels of thermal conductivity, compressibility, and surface smoothness.

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

[0008] The present inventors have conducted extensive research to achieve the above object, and have discovered that, in the manufacture of a thermally conductive sheet, by orienting flaky aluminum nitride particles having a predetermined volume average particle diameter in a predetermined direction in a resin matrix, a thermally conductive sheet having excellent thermal conductivity, compressibility, and surface smoothness can be obtained, leading to the completion of the present invention.

[0009] The present invention aims to advantageously solve the above-mentioned problems. [1] The thermally conductive sheet of the present invention is a thermally conductive sheet containing resin and aluminum nitride, characterized in that the orientation angle of the aluminum nitride relative to the main surface of the thermally conductive sheet is 60° to 90°, the aluminum nitride is flaky, and the volume-average particle diameter of the aluminum nitride is 20 μm to 100 μm. The thermally conductive sheet of the present invention has excellent thermal conductivity, compressibility, and surface smoothness. The "orientation angle of aluminum nitride" can be measured using the method described in the Examples. The "volume-average particle diameter of aluminum nitride" can be measured in accordance with JIS Z8825 and refers to the particle diameter at which the cumulative volume calculated from the smallest diameter side becomes 50% in the particle size distribution (volume basis) measured by laser diffraction.

[0010] [2] Here, in the thermally conductive sheet of [1] above, the aspect ratio of the main surface of the aluminum nitride is preferably 1.1 or more and 3.0 or less. If the aspect ratio of the main surface of the aluminum nitride is within the above range, the thermally conductive sheet will have even better thermal conductivity. The aspect ratio of the main surface of the aluminum nitride can be measured according to the method described in the Examples.

[0011] [3] In the thermally conductive sheet of [1] or [2] above, the volume fraction of the aluminum nitride is preferably 60% by volume or more and 80% by volume or less. A thermally conductive sheet with an aluminum nitride volume fraction within the above range has better thermal conductivity, compressibility, and surface smoothness. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a thermally conductive sheet that is excellent in thermal conductivity, compressibility, and surface smoothness. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail. Because the thermally conductive sheet of the present invention has thermal conductivity, it can be sandwiched between a heat generating body and a heat dissipating body. For example, the thermally conductive sheet of the present invention can be used to form an electronic device by being interposed between a heat generating body such as a semiconductor, an electronic display, or a general electronic component and a heat dissipating body such as a heat sink, a heat dissipating plate, or a heat dissipating fin to bond them together.

[0014] (thermal conductive sheet) The thermally conductive sheet of the present invention is a thermally conductive sheet for bonding a heat sink and a heat generating element by heating and pressurizing the sheet while the sheet is placed between the heat sink and the heat generating element, and includes a resin and aluminum nitride. Furthermore, in this thermally conductive sheet, the orientation angle of the aluminum nitride with respect to the main surface is 60° to 90°, the aluminum nitride is flaky, and the volume average particle diameter of the aluminum nitride is 20 μm to 100 μm. This thermally conductive sheet exhibits high thermal conductivity due to the oriented structure of the aluminum nitride. Furthermore, since the aluminum nitride is flaky and has a size equal to or greater than the lower limit, the sheet exhibits excellent compressibility. Furthermore, since the size of the aluminum nitride is equal to or less than the upper limit, the sheet exhibits excellent surface smoothness.

[0015] <Resin> The thermal conductive sheet of the present invention contains a resin, which allows the heat generating element and the heat dissipating element to be well adhered to each other via the thermal conductive sheet. In this specification, rubber and elastomer are included in the term "resin." The resin that can be contained in the thermally conductive sheet of the present invention constitutes a matrix resin and also functions as a binder that binds aluminum nitride.

[0016] The resin is not particularly limited, and any resin can be used. For example, either a liquid resin or a solid resin can be used. The resin may be used alone or in combination of two or more types. For example, both a liquid resin and a solid resin can be used. When both a liquid resin and a solid resin are used in combination, the ratio of the liquid resin to the solid resin is not particularly limited, but may be, for example, in the range of 20 / 80 to 80 / 20 by mass.

[0017] [Liquid resin] The liquid resin is not particularly limited as long as it is liquid at room temperature and normal pressure, and for example, a thermoplastic resin that is liquid at room temperature and normal pressure can be used. In the present invention, "normal temperature" refers to 23° C., and "normal pressure" refers to 1 atm (absolute pressure).

[0018] Examples of liquid resins include fluororesins, silicone resins, acrylic resins, epoxy resins, and acrylonitrile-butadiene copolymers (nitrile rubbers). These may be used alone or in combination of two or more. Among these, acrylonitrile-butadiene copolymers are preferably used.

[0019] [Solid resin] The solid resin is not particularly limited as long as it is not a liquid at room temperature and normal pressure, and for example, a thermoplastic resin that is solid at room temperature and normal pressure, or a thermosetting resin that is solid at room temperature and normal pressure can be used.

[0020] Examples of thermoplastic resins that are solid at room temperature and pressure include acrylic resins such as poly(2-ethylhexyl acrylate), copolymers of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its esters, and polyacrylic acid or its esters; silicone resins; fluororesins; polyethylene; polypropylene; ethylene-propylene copolymers; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymers; polyvinyl alcohol; polyacetal; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; and polyacrylonitrile. Examples of suitable polymers include styrene-acrylonitrile copolymers, acrylonitrile-butadiene copolymers (nitrile rubbers), acrylonitrile-butadiene-styrene copolymers (ABS resins), styrene-butadiene block copolymers or hydrogenated products thereof, styrene-isoprene block copolymers or hydrogenated products thereof, polyphenylene ethers, modified polyphenylene ethers, aliphatic polyamides, aromatic polyamides, polyamideimides, polycarbonates, polyphenylene sulfides, polysulfones, polyethersulfones, polyethernitriles, polyetherketones, polyketones, polyurethanes, liquid crystal polymers, and ionomers. These may be used alone or in combination. Among these, acrylonitrile-butadiene copolymers are particularly preferred.

[0021] Examples of thermosetting resins that are solid at room temperature and normal pressure include natural rubber, butadiene rubber, isoprene rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene propylene rubber, chlorinated polyethylene, chlorosulfonated polyethylene, butyl rubber, halogenated butyl rubber, polyisobutylene rubber, epoxy resin, polyimide resin, bismaleimide resin, benzocyclobutene resin, phenolic resin, unsaturated polyester, diallyl phthalate resin, polyimide silicone resin, polyurethane, thermosetting polyphenylene ether, thermosetting modified polyphenylene ether, etc. These may be used alone or in combination of two or more.

[0022] <Resin content> The resin content in the thermal conductive sheet must be 20% by volume or more, preferably 24% by volume or more, and 60% by volume or less, preferably 32% by volume or less, based on the total volume of the resin and aluminum nitride (described later). If the resin content in the thermal conductive sheet is equal to or greater than the lower limit, the flexibility and surface smoothness of the thermal conductive sheet can be further improved. If the resin content in the thermal conductive sheet is equal to or less than the upper limit, the thermal conductivity of the thermal conductive sheet can be improved.

[0023] <Aluminum nitride> Aluminum nitride is a so-called filler component that can impart thermal conductivity, mechanical strength, etc. to the thermal conductive sheet. As the aluminum nitride, flaky aluminum nitride is used. The flaky aluminum nitride may be produced by nitriding raw aluminum according to a known method, or commercially available aluminum nitride may be used. Known nitriding methods include, for example, a direct nitriding method in which the object to be nitrided is directly reacted with nitrogen or ammonia, and a reduction-nitriding method in which aluminum oxide (alumina) is heated in a nitrogen or ammonia atmosphere while being carbon-reduced, thereby simultaneously carrying out a nitriding reaction.

[0024] Here, the aspect ratio (major axis / minor axis) of the main surface of the scaly aluminum nitride is preferably 1.1 or more, more preferably 1.3 or more, even more preferably 1.5 or more, and is preferably 3.0 or less, more preferably 2.5 or less, and more preferably 2.2 or less. If the aspect ratio of the main surface of the scaly aluminum nitride is within the above range, it is presumed that this is because the aluminum nitride is more likely to be well oriented in the thickness direction in the thermal conductive sheet, and the thermal conductivity of the thermal conductive sheet in the thickness direction can be improved.

[0025] The volume average particle diameter of the aluminum nitride must be 20 μm or more, preferably 35 μm or more, and must be 100 μm or less, preferably 90 μm or less. If the volume average particle diameter of the aluminum nitride is above the above lower limit, it is presumed that a good heat transfer path of the aluminum nitride can be formed in the thermal conductive sheet, thereby improving the thermal conductivity of the electronic device. If the volume average particle diameter of the aluminum nitride is above the above lower limit, it is presumed that when pressure is applied in the thickness direction, the scaly aluminum nitride of a certain size tilts, thereby efficiently absorbing pressure, thereby improving the compressibility of the thermal conductive sheet. If the volume average particle diameter of the aluminum nitride is below the above upper limit, the surface smoothness of the thermal conductive sheet can be improved.

[0026] <<Aluminum nitride content>> The content of aluminum nitride in the thermal conductive sheet must be 60% by volume or more, preferably 68% by volume or more, and 80% by volume or less, preferably 76% by volume or less, based on the total of the resin and aluminum nitride. When the content of aluminum nitride in the thermal conductive sheet is equal to or greater than the lower limit, the thermal conductivity of the thermal conductive sheet can be improved. When the content of aluminum nitride in the thermal conductive sheet is equal to or less than the upper limit, the compressibility and flexibility of the thermal conductive sheet can be further improved. When the content of aluminum nitride in the thermal conductive sheet is equal to or less than the upper limit, the orientation of aluminum nitride in the thermal conductive sheet can be improved, thereby improving the thermal conductivity of the thermal conductive sheet. This effect on orientation is significantly greater with aluminum nitride than with fillers other than aluminum nitride (e.g., boron nitride) that may be contained in the thermal conductive sheet. Specifically, as will be apparent from the examples described below, the Asker C hardness is significantly higher when the content of aluminum nitride is 70% by volume than when it is 60% by volume. This tendency is more pronounced with aluminum nitride than with other fillers such as boron nitride. The higher the hardness of a thermally conductive sheet, the higher its strength. However, the hardness of the composition makes it difficult for the aluminum nitride to form an oriented structure within the sheet. Therefore, in the present invention, which uses aluminum nitride as an essential component, the appropriate proportion of aluminum nitride was selected to achieve good thermal conductivity.

[0027] <Other ingredients> The thermally conductive sheet of the present invention may optionally further contain components other than the resin and aluminum nitride (hereinafter, sometimes referred to as "other components"). The other components are not particularly limited as long as they are components that can be used in the manufacture of a thermally conductive sheet, and examples thereof include fibrous carbon materials; flame retardants such as red phosphorus-based flame retardants and phosphate ester-based flame retardants; plasticizers such as fatty acid ester-based plasticizers; toughness improvers such as urethane acrylates; moisture absorbents such as calcium oxide and magnesium oxide; adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides; wettability improvers such as nonionic surfactants and fluorine-based surfactants; ion trapping agents such as inorganic ion exchangers; and antioxidants. The upper limit of the content of the other components is not particularly limited, but may be, for example, 5.0% by mass or less, 1.0% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, based on the total mass of the thermally conductive sheet (100% by mass).

[0028] <Thermal Conduction Sheet Structure> The thermally conductive sheet of the present invention has a structure in which the aluminum nitride is oriented at an angle of 60° to 90° relative to the main surface of the thermally conductive sheet. If the aluminum nitride is oriented in the thickness direction of the thermally conductive sheet, the thermal conductivity of the thermally conductive sheet in the thickness direction can be improved.

[0029] The orientation angle of aluminum nitride is preferably 70° or more, more preferably 75° or more, and even more preferably 78° or more. If the orientation angle of aluminum nitride is equal to or greater than the lower limit, the thermal conductivity of the heat conductive sheet can be improved. The upper limit of the orientation angle of aluminum nitride is not particularly limited, and may be 90°.

[0030] <Thermal Conduction Sheet Properties> <<Thermal conductivity>> The thermal conductivity of the thermal conductive sheet in the thickness direction is preferably 6 W / m K or more, and more preferably 10 W / m K or more. There is no particular upper limit to the thermal conductivity of the thermal conductive sheet in the thickness direction, but it is, for example, 45 W / m K or less. The thermal conductivity of the thermally conductive sheet in the thickness direction can be adjusted, for example, by adjusting the ratio of aluminum nitride and resin contained in the thermally conductive sheet.

[0031] <<Thermal Conduction Sheet Thickness>> The thickness of the thermally conductive sheet of the present invention is not particularly limited, but is preferably 50 μm or more, more preferably 100 μm or more, more preferably 200 μm or more, and preferably 500 μm or less, more preferably 450 μm or less, and even more preferably 400 μm or less. If the thickness of the thermally conductive sheet is equal to or greater than the above lower limit, the thermally conductive sheet does not become excessively thin, thereby increasing the strength of the thermally conductive sheet. If the thickness of the thermally conductive sheet is equal to or less than the above upper limit, the thermal properties of the thermally conductive sheet in the thickness direction can be improved.

[0032] <<Surface roughness of thermal conductive sheet>> The thermally conductive sheet preferably has a surface roughness of 3.7 μm or less, more preferably 3.5 μm or less. The lower limit of the surface roughness is not particularly limited, but may be, for example, 2.0 μm or more. If the surface roughness is equal to or less than the upper limit, the interface resistance of thermal conduction between the sheet and the adherend can be reduced.

[0033] <<Asker C hardness of thermal conductive sheets>> The thermally conductive sheet preferably has an Asker C hardness at a temperature of 25°C of 60 or more, more preferably 65 or more, and preferably 80 or less, more preferably 75 or less. If the Asker C hardness at a temperature of 25°C is within the above range, the sheet can be satisfactorily used by being sandwiched between a heat generating element and a heat dissipating element.

[0034] <<Compressibility of the thermal conductive sheet>> The thermal conductive sheet of the present invention has a thickness of T when pressed at 0.9 MPa in the thickness direction. 0.9The thickness of the thermally conductive sheet before pressure is defined as T0, and the compression ratio of the thermally conductive sheet calculated by the following formula (1) is preferably 3% or more, more preferably 5% or more, and is preferably 25% or less, more preferably 18% or less. Compression rate (%)=100×[1-(T 0.9 / T0)][%]···(1) If the compression ratio is equal to or greater than the lower limit, the thermally conductive sheet has excellent adhesion to the heat generating element and the heat dissipating element. If the compression ratio is equal to or less than the upper limit, the thermally conductive sheet has adequate strength and excellent durability. The compression ratio can be controlled depending on the composition and manufacturing method of the thermally conductive sheet. The above compression ratio is a value that can be measured for a 0.3 mm thick thermally conductive sheet using the method described in the Examples.

[0035] <Method of manufacturing thermal conductive sheets> The thermally conductive sheet of the present invention can be efficiently produced by a production method including the following steps: (A) a pre-thermally conductive sheet forming step of pressing a composition containing a resin and aluminum nitride into a sheet to obtain a pre-thermally conductive sheet; (B) a laminate forming step of stacking multiple pre-thermally conductive sheets in the thickness direction or folding or rolling the pre-thermally conductive sheets to obtain a laminate; and (C) a slicing step of slicing the laminate at an angle of 45° or less to the stacking direction to obtain a thermally conductive sheet. The thermally conductive sheet of the present invention may optionally include further steps other than the above steps (A) to (C).

[0036] <(A) Pre-heat conductive sheet forming process> In the pre-thermal conductive sheet forming step, a composition containing a resin and aluminum nitride is pressed and formed into a sheet to obtain a pre-thermal conductive sheet.

[0037] <<Composition>> The composition includes a resin and aluminum nitride. The composition may further include any additives.

[0038] 〔resin〕 Here, the resin contained in the composition may be, for example, any of the various resins described above in the "Thermal Conductive Sheet" section, in the proportions described above. The amount of resin contained in the composition corresponds to the range of the "resin content" in the thermal conductive sheet described above.

[0039] [Aluminum nitride] As the aluminum nitride, for example, the aluminum nitride described above in the section "Thermal Conduction Sheet" can be used in the proportions described above.

[0040] [Other ingredients] As other components that can be contained in the composition, other components that can be contained in the thermally conductive sheet described above in the section "Thermal Conductive Sheet" can be used.

[0041] [Preparation of Composition] The composition is not particularly limited and can be prepared by mixing the above-mentioned components. The mixing of the above-mentioned components can be carried out using known mixing devices, such as kneaders; mixers such as Henschel mixers, Hobart mixers, and high-speed mixers; twin-screw kneaders; and roll mixers. The mixing may also be carried out in the presence of a solvent such as ethyl acetate. The resin may be dissolved or dispersed in a solvent in advance to form a resin solution, which is then mixed with aluminum nitride and other optional components. The mixing time may be, for example, 5 minutes to 60 minutes. The mixing temperature may be, for example, 5°C to 150°C.

[0042] <<Molding of the composition>> The composition prepared as described above can be optionally degassed and crushed, and then pressed to form into a sheet. The sheet-shaped composition thus pressure-molded can be used as a pre-heat conductive sheet. If a solvent is used during mixing, it is preferable to remove the solvent before forming into a sheet. For example, if degassing is performed using vacuum degassing, the solvent can be removed simultaneously during degassing.

[0043] Here, the composition can be formed into a sheet using any known forming method, such as press molding, rolling, or extrusion, as long as the forming method involves applying pressure. Among these, the composition is preferably formed into a sheet by rolling (primary processing), and more preferably by a predetermined roll forming method in which the composition is passed between a first roll and a second roll having a faster peripheral speed than the first roll. The peripheral speed ratio of the second roll to the first roll ("peripheral speed of the second roll" / "peripheral speed of the first roll") is preferably 1.03 / 1 or more and 2 / 1 or less. The distance between the first roll and the second roll can be, for example, 1 mm or more and 3 mm or less.

[0044] <<Pre-heat conductive sheet>> In the pre-heat conductive sheet obtained by pressing the composition into a sheet, the aluminum nitride is oriented mainly in the in-plane direction, which is thought to improve the thermal conductivity of the pre-heat conductive sheet in the in-plane direction in particular.

[0045] <(B) Laminate formation process> In the laminate formation process, multiple pre-thermally conductive sheets obtained in the pre-thermally conductive sheet forming process are stacked in the thickness direction, or the pre-thermally conductive sheets are folded or rolled to obtain a laminate in which multiple thermally conductive sheets containing resin and aluminum nitride are formed in the thickness direction. Here, the formation of the laminate by folding the pre-thermally conductive sheets is not particularly limited and can be performed by folding the pre-thermally conductive sheets at a constant width using a folding machine. Furthermore, the formation of the laminate by rolling the pre-thermally conductive sheets is not particularly limited and can be performed by rolling the pre-thermally conductive sheets around an axis parallel to the short or long direction of the pre-thermally conductive sheets. Furthermore, the formation of the laminate by stacking the pre-thermally conductive sheets is not particularly limited and can be performed using a lamination device.

[0046] In the lamination step, the obtained laminate (hereinafter also referred to as a first laminate) is preferably pressed in the lamination direction (secondary pressing) while being heated to form a second laminate.

[0047] The pressure applied to the laminate in the stacking direction can be 0.05 MPa or more and 0.90 MPa or less. Alternatively, isostatic pressing can be performed using an apparatus such as an autoclave. The pressure of the isostatic pressing is preferably in the range of 0.3 MPa or more and 0.9 MPa or less.

[0048] The heating temperature of the laminate is not particularly limited, but can be 30° C. or higher, preferably 40° C. or higher, and more preferably 50° C. or higher, and can be 170° C. or lower, and preferably 160° C. or lower. The heating time of the laminate can be, for example, 10 seconds or longer and 60 minutes or shorter.

[0049] It is presumed that in the laminate obtained by stacking, folding or rolling the pre-heat-conductive sheets, the aluminum nitride is oriented in a direction substantially perpendicular to the stacking direction.

[0050] <(C) Slicing process> In the slicing step, the laminate obtained in the laminate-forming step is sliced ​​at an angle of 45° or less relative to the lamination direction to obtain a thermally conductive sheet consisting of slices of the laminate. The method for slicing the laminate is not particularly limited, and examples thereof include a multi-blade method, a laser processing method, a water jet method, and a knife processing method. The cutting tool used to slice the laminate is not particularly limited, and a slicing member having a smooth plate surface with a slit and a blade protruding from the slit (for example, a plane or slicer with a sharp blade) can be used.

[0051] From the viewpoint of increasing the thermal conductivity of the thermal conduction sheet, the angle at which the laminate is sliced ​​is preferably 30° or less relative to the stacking direction, more preferably 15° or less relative to the stacking direction, and preferably approximately 0° relative to the stacking direction (i.e., in the direction along the stacking direction).

[0052] In the thermally conductive sheet obtained in this manner, the aluminum nitride is oriented at an angle of 60° to 90° relative to the main surface of the thermally conductive sheet, and the thermal conductivity in the thickness direction is excellent. In addition, the thermally conductive sheet obtained through the above process has a structure in which the strips are joined in parallel to each other. [Example]

[0053] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. In each example and each comparative example, various attributes were measured or evaluated by the following methods.

[0054] <Aspect ratio of the main surface of aluminum nitride> The "aspect ratio" of the main surface of the aluminum nitride used in the examples and comparative examples was determined by observing the aluminum nitride with a scanning electron microscope (SEM), measuring the maximum diameter (long diameter) and the particle diameter (short diameter) in the direction perpendicular to the maximum diameter for the main surface of any 50 aluminum nitride particles, and calculating the average value of the ratio of the long diameter to the short diameter (long diameter / short diameter). Note that, in the above, the "long diameter" refers to the length in the direction of the long axis of the main surface of the aluminum nitride, and the "short diameter" refers to the length in the direction perpendicular to the long axis of the main surface.

[0055] <Volume average particle size of aluminum nitride> Measurement was carried out in accordance with JIS Z8825, and the particle size at which the cumulative volume calculated from the smallest diameter side was 50% was obtained based on the volume-based particle size distribution.

[0056] <Orientation angle of aluminum nitride> The orientation angle of aluminum nitride in the thermally conductive sheets prepared in the Examples and Comparative Examples was determined by observing a cross section of a thermally conductive sheet cut into a regular octagon using a scanning electron microscope (SEM, Hitachi High-Technologies Corporation, "SU-3500") at a magnification that fit the entire sheet from top to bottom. The magnification was 700x. Specifically, 50 lines were drawn along the long axis of the aluminum in the cross section, and the average angle of the long axis relative to the surface of the thermally conductive sheet was calculated. If the angle was 90° or greater, a supplementary angle was used. This was performed on eight surfaces, and the largest value among the eight surfaces was taken as the orientation angle of aluminum nitride in the thermally conductive sheet.

[0057] <Thermal conductivity> [Thermal diffusivity α in the thickness direction] The thermal diffusivity of the thermal conductive sheet was measured using a thermal diffusivity / thermal conductivity measuring device (ai-Phase Mobile 1u, manufactured by ai-Phase Corporation) in accordance with the provisions of ISO22007-3. [Constant pressure specific heat Cp] Using a differential scanning calorimeter (manufactured by Rigaku, product name "DSC8230"), the specific heat was measured at 25°C under conditions of a temperature increase of 10°C / min. [Specific gravity ρ (density)] Measurement was carried out using an automatic hydrometer (manufactured by Toyo Seiki Co., Ltd., trade name "DENSIMETER-H"). Then, each measurement value is calculated using the following formula (I): λ=α×Cp×ρ (I) The thermal conductivity λ (W / m K) of the thermal conductive sheet in the thickness direction at 25°C was calculated by substituting the above equation.

[0058] <Surface roughness Sa of the thermal conductive sheet> The surface roughness Sa of the thermal conductive sheet was measured using a three-dimensional shape measuring instrument (Keyence Corporation, product name "One-Shot 3D Measurement Macroscope"). The sample was a thermal conductive sheet cut into an arbitrary square shape of 1 cm or larger, with an analysis area of ​​1 cm x 1 cm. The three-dimensional shape of each of the front and back surfaces of the sample was measured. The three-dimensional shape measurement results were then further filtered (2.5 mm) using software to remove waviness, and the surface roughness Sa (μm) was automatically calculated.

[0059] <Asker C hardness> The Asker C hardness was measured in accordance with the Asker C method of the Society of Rubber Science and Technology of Japan (SRIS) using a hardness tester (manufactured by Kobunshi Keiki Co., Ltd., product name "ASKER CL-150LJ") at a temperature of 25°C. Specifically, a laminate (50 mm long x 50 mm wide x approximately 6 mm thick) made by stacking 20 thermally conductive sheets to a thickness of approximately 6 mm was left to stand in a thermostatic chamber maintained at a temperature of 25°C for 48 hours or more to prepare a test specimen. Next, the hardness tester was placed so that the needle tip was 2 cm from the top surface of the test specimen, and a damper was lowered to allow the top surface of the test specimen to collide with the damper. The Asker C hardness of the test specimen 60 seconds after the collision was measured twice using a hardness tester (manufactured by Kobunshi Keiki Co., Ltd., product name "ASKER CL-150LJ"), and the average of the measurement results was used.

[0060] <Compression ratio> The compressibility of the thermally conductive sheets manufactured in each example and comparative example was measured using a thermal resistance tester (Hitachi Technology and Services, Ltd., product name: "Resin Material Thermal Resistance Measuring Device"). A thermally conductive sheet cut into a roughly 1 cm square was used as a sample, and the thickness (T0) of the thermally conductive sheet before pressure was applied was measured. Then, at a sample temperature of 50°C, a pressure of 0.9 MPa was applied in the thickness direction, and the thermal resistance and thickness of the thermally conductive sheet were measured in each state. The thickness of the sample before pressure was T0, and the thickness of the sample after pressure of 0.9 MPa was T 0.9 Let T0 and T 0.9 The compression ratio (%) was calculated according to the following formula (1). Compression rate (%)=100×[1-(T 0.9 / T0)][%]···(1)

[0061] Example 1 <Preparation of Composition> As a thermoplastic resin, 30 parts of nitrile butadiene rubber (manufactured by Nippon Zeon Corporation under the trade name "Nipole 1312," specific gravity: 1.0) that is liquid at room temperature and normal pressure and 30 parts of nitrile butadiene rubber (manufactured by Nippon Zeon Corporation under the trade name "Nipole 3350," specific gravity: 1.0) that is solid at room temperature and normal pressure were prepared. The prepared thermoplastic resin, 480 parts of flaky aluminum nitride (manufactured by Furukawa Electronics Corporation under the trade name "Furukawa Electronics Corporation," reduced flaky aluminum nitride, volume average particle size: 80 μm, aspect ratio: 2.1, specific gravity: 3.4) as a so-called filler, and 0.5 parts of 2,2,4-trimethyl-1,2-dihydroquinoline polymer (manufactured by Ouchi Shinko Chemical Industry Co., Ltd. under the trade name "Nocrac 224") as an antioxidant were kneaded at 120°C for 20 minutes using a pressure kneader (manufactured by Nippon Spindle Co., Ltd.) to obtain a composition.

[0062] <Pre-heat conductive sheet forming process> Next, 500 g of the obtained composition was rolled into a sheet using a first roll and a second roll under the following conditions: a gap between the first roll and the second roll of 2 mm, a roll temperature of 25°C, a sheet discharge speed (peripheral speed of the first roll) of 2 m / min, and a peripheral speed ratio of the second roll to the first roll (second roll / first roll): 1.15 / 1. The rolling process was repeated while maintaining the same sheet conveyance direction. A total of 10 rolling processes were performed to obtain a pre-heat-conductive sheet with a thickness of 2 mm.

[0063] <First laminate formation process> Next, the obtained pre-heat conductive sheet was cut into a size of 50 mm length x 50 mm width, and 50 sheets were stacked in the thickness direction to obtain a first stack having a height of about 50 mm.

[0064] <Second laminate formation process> The obtained first laminate was wrapped in release PET (polyethylene terephthalate) and sealed with tape, then vacuum-packaged in a PET retort pouch. This was then heated and pressurized in an autoclave (Hanida Iron Works, small autoclave "DANDELION") at a temperature of 150°C and a pressure of 0.8 MPa (absolute pressure) from all directions for 30 minutes to obtain a second laminate.

[0065] <Slicing process> The second stack was then placed so that the stacking direction was perpendicular to the ground (the surface on which the second stack was placed), and the entire top surface of the placed second stack was pressed down with a metal plate, leaving a length required for slicing at one end in a direction perpendicular to the stacking direction of the second stack, and a pressure of 0.1 MPa was applied from above to fix the second stack. Note that the stacking direction of the second stack refers to the normal direction of the main surface of the stacked primary sheets. The sides and back of the second stack were not fixed. At this time, the temperature of the second stack was 25°C. Next, a slicing mechanism (0.5 mm gap between the guide member and the rake face) consisting of a cutting blade (single-edged, cutting angle: 20°, maximum blade thickness: 3.5 mm, material: carbide, Rockwell hardness: 91.5, no silicon processing on the blade surface, total length: 200 mm) and a guide member (length: 50 mm, static friction coefficient: 0.4) was attached to the press portion of a servo press (manufactured by Electrical Discharge Precision Machining Laboratory). The second laminate, placed so that the lamination direction was perpendicular to the ground, was sliced ​​in the lamination direction at a slicing speed of 25 mm / s and a slice width of 300 μm to obtain a thermally conductive sheet measuring 50 mm long x 50 mm wide x 0.30 mm thick (average thickness). The cutting blade was positioned so that the extension direction of the flank was parallel to the sliced ​​surface of the second laminate. The resulting thermally conductive sheet consisted of multiple layers joined in parallel in a direction perpendicular to the thickness direction of the thermally conductive sheet (at a 90° angle to the thickness direction). The width of the strip in the perpendicular direction was approximately the same as the thickness of the primary sheet. The obtained thermal conductive sheet was subjected to various measurements and evaluations as described above. The results are shown in Table 1.

[0066] Example 2 Various measurements and evaluations were carried out in the same manner as in Example 1, except that the flaky aluminum nitride added in <Preparation of composition> was changed to reduced flaky aluminum nitride having a volume average particle size of 30 μm (manufactured by Furukawa Electronics Co., Ltd., aspect ratio: 1.6, specific gravity: 3.4). The results are shown in Table 1.

[0067] Example 3 Except for changing the amount of flaky aluminum nitride added in <Preparation of composition> to 500 parts, various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0068] Example 4 Except for changing the amount of flaky aluminum nitride added in <Preparation of composition> to 300 parts, various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0069] (Comparative Example 1) Various measurements and evaluations were carried out in the same manner as in Example 1, except that in <Preparation of composition>, 480 parts of spherical aluminum nitride having a particle size of 80 μm (manufactured by Tokuyama, specific gravity: 3.4) was added instead of the scaly aluminum nitride. The results are shown in Table 1. Note that the shape of the aluminum nitride used in this example was spherical, which does not fit the concept of "orientation," so the orientation angle was not measured.

[0070] (Comparative Example 2) Various measurements and evaluations were carried out in the same manner as in Example 1, except that in <Preparation of composition>, 480 parts of flaky aluminum nitride having a particle diameter of 120 μm (manufactured by Furukawa Electronics, reduced flaky aluminum nitride, aspect ratio: 2.5, specific gravity: 3.4) was added instead of the flaky aluminum nitride having a particle diameter of 80 μm. The results are shown in Table 1.

[0071] (Comparative Example 3) Various measurements and evaluations were carried out in the same manner as in Example 1, except that in <Preparation of composition>, 300 parts of flaky aluminum nitride having a particle diameter of 120 μm (manufactured by Furukawa Electronics, reduced flaky aluminum nitride, aspect ratio: 2.5, specific gravity: 3.4) was added instead of the flaky aluminum nitride having a particle diameter of 80 μm. The results are shown in Table 1.

[0072] Comparative Example 4 Various measurements and evaluations were carried out in the same manner as in Example 1, except that in <Preparation of composition>, 540 parts of flaky alumina having a particle size of 10 μm (manufactured by Kinseimatec Co., Ltd., "Seraph", aluminum oxide, aspect ratio: 1.2, specific gravity: 3.9) was added instead of the flaky aluminum nitride having a particle size of 80 μm. The results are shown in Table 1.

[0073] (Comparative Example 5) In the <Preparation of Composition>, the 80 μm particle diameter flaky aluminum nitride was replaced with reduced flaky aluminum nitride (aspect ratio: 1.2, specific gravity: 3.4) having a volume average particle diameter of 10 μm obtained as follows. Here, the above aluminum nitride was obtained by carrying out a reduction-nitridation method using alumina having a volume average particle diameter of 10 μm ("Ceraph", manufactured by Kinsei Matec Co., Ltd., specific gravity: 3.9) according to the method described in the examples of JP 2010-138056 A. Except for this, various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0074] [Table 1]

[0075] Table 1 shows that the thermal conductive sheets of Examples 1 to 4, which contain resin and flaky aluminum nitride with a volume average particle diameter of a predetermined size and in which the aluminum nitride is oriented at a predetermined orientation angle, had excellent thermal conductivity, compressibility, and surface smoothness. On the other hand, in Comparative Example 1, in which spherical aluminum nitride was used instead of scaly aluminum nitride, the thermal conductivity and compressibility of the thermal conductive sheet could not be improved. Furthermore, in Comparative Examples 2 and 3, in which scaly aluminum nitride with a large volume average particle diameter was used, the thermal conductive sheets had poor surface smoothness and were poor in compressibility or thermal conductivity. Furthermore, in Comparative Example 4, in which scaly alumina was used instead of scaly aluminum nitride, the thermal conductivity of the thermal conductive sheet could not be sufficiently improved. Furthermore, in Comparative Example 5, in which scaly aluminum nitride with a small volume average particle diameter was used, the compressibility and thermal conductivity could not be improved in a balanced manner compared to Examples 1 to 4. [Industrial Applicability]

[0076] According to the present invention, it is possible to provide a thermally conductive sheet that is excellent in thermal conductivity, compressibility, and surface smoothness.

Claims

1. A thermally conductive sheet containing a resin and aluminum nitride, an orientation angle of the aluminum nitride with respect to the main surface of the thermal conductive sheet is 60° or more and 90° or less; The aluminum nitride has a flaky shape, The volume average particle diameter of the aluminum nitride is 20 μm or more and 100 μm or less. Thermal conductive sheet.

2. 2. The thermal conductive sheet according to claim 1, wherein the aspect ratio of the main surface of the aluminum nitride is 1.1 or more and 3.0 or less.

3. 3. The thermal conductive sheet according to claim 1, wherein the volume fraction of the aluminum nitride is 60% by volume or more and 80% by volume or less.

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