WO2016208458A1 - 熱伝導性シート - Google Patents
熱伝導性シート Download PDFInfo
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- WO2016208458A1 WO2016208458A1 PCT/JP2016/067674 JP2016067674W WO2016208458A1 WO 2016208458 A1 WO2016208458 A1 WO 2016208458A1 JP 2016067674 W JP2016067674 W JP 2016067674W WO 2016208458 A1 WO2016208458 A1 WO 2016208458A1
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- heat conductive
- conductive layer
- carbon fiber
- insulating
- thermal
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
- F28F21/02—Constructions of heat-exchange apparatus characterised by the selection of particular materials of carbon, e.g. graphite
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
- B32B7/02—Physical, chemical or physicochemical properties
- B32B7/022—Mechanical properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B25/00—Layered products comprising a layer of natural or synthetic rubber
- B32B25/10—Layered products comprising a layer of natural or synthetic rubber next to a fibrous or filamentary layer
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B25/00—Layered products comprising a layer of natural or synthetic rubber
- B32B25/20—Layered products comprising a layer of natural or synthetic rubber comprising silicone rubber
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
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- B32B27/04—Layered products comprising a layer of synthetic resin as impregnant, bonding, or embedding substance
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/12—Layered products comprising a layer of synthetic resin next to a fibrous or filamentary layer
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
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- B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
- B32B27/20—Layered products comprising a layer of synthetic resin characterised by the use of special additives using fillers, pigments, thixotroping agents
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
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- B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
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- B32B27/40—Layered products comprising a layer of synthetic resin comprising polyurethanes
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- B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
- B32B7/02—Physical, chemical or physicochemical properties
- B32B7/027—Thermal properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
- B32B7/04—Interconnection of layers
- B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B5/00—Non-insulated conductors or conductive bodies characterised by their form
- H01B5/14—Non-insulated conductors or conductive bodies characterised by their form comprising conductive layers or films on insulating-supports
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
- H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
- H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
- H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
- H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
- H01L23/3737—Organic materials with or without a thermoconductive filler
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
- H01L23/42—Fillings or auxiliary members in containers or encapsulations selected or arranged to facilitate heating or cooling
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2262/00—Composition or structural features of fibres which form a fibrous or filamentary layer or are present as additives
- B32B2262/10—Inorganic fibres
- B32B2262/106—Carbon fibres, e.g. graphite fibres
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2264/00—Composition or properties of particles which form a particulate layer or are present as additives
- B32B2264/10—Inorganic particles
- B32B2264/105—Metal
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2264/00—Composition or properties of particles which form a particulate layer or are present as additives
- B32B2264/10—Inorganic particles
- B32B2264/107—Ceramic
- B32B2264/108—Carbon, e.g. graphite particles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2305/00—Condition, form or state of the layers or laminate
- B32B2305/30—Fillers, e.g. particles, powders, beads, flakes, spheres, chips
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/20—Properties of the layers or laminate having particular electrical or magnetic properties, e.g. piezoelectric
- B32B2307/202—Conductive
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/20—Properties of the layers or laminate having particular electrical or magnetic properties, e.g. piezoelectric
- B32B2307/206—Insulating
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/30—Properties of the layers or laminate having particular thermal properties
- B32B2307/302—Conductive
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/50—Properties of the layers or laminate having particular mechanical properties
- B32B2307/514—Oriented
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/50—Properties of the layers or laminate having particular mechanical properties
- B32B2307/536—Hardness
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2457/00—Electrical equipment
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F2255/00—Heat exchanger elements made of materials having special features or resulting from particular manufacturing processes
- F28F2255/06—Heat exchanger elements made of materials having special features or resulting from particular manufacturing processes composite, e.g. polymers with fillers or fibres
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/04—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of carbon-silicon compounds, carbon or silicon
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
- H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
- H01B3/46—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes silicones
Definitions
- the present invention relates to a heat conductive sheet used by being disposed between a heat generator and a heat radiator.
- heat sinks such as heat sinks are used to dissipate the heat generated by heating elements such as semiconductor elements and machine parts.
- a heat conductive sheet may be disposed between the heat generator and the heat radiator.
- a heat conductive sheet for example, a heat conductive sheet in which carbon fibers are filled and oriented as a heat conductive material is disclosed in Japanese Patent Application Laid-Open No. 2005-146057 (Patent Document 1).
- the thermal conductive sheet in which the electrical insulating layer is formed on the thermal conductive sheet in which the carbon fibers are oriented has a high thermal conductivity as compared with the thermal conductive sheet in which the electrical insulating layer is not provided.
- the cured electrical insulating layer has a problem that it has a hard surface and is difficult to fix to an adherend and is not easy to handle.
- the present invention has been made in view of the above problems, and an object thereof is to provide a heat conductive sheet having an insulating property and high heat conductivity. Another object of the present invention is to provide a heat conductive sheet having excellent handling properties.
- the thermally conductive sheet of the present invention that achieves the above object is configured as follows. That is, a carbon fiber oriented heat conductive layer containing carbon fiber powder with fiber axes oriented in the thickness direction of the sheet in the polymer matrix, and an insulating heat conductive filler dispersed in the polymer matrix. And a heat conductive sheet in which an insulating heat conductive layer having insulating properties is laminated.
- the polymer matrix is provided with a carbon fiber oriented heat conductive layer containing carbon fiber powder with fiber axes oriented in the thickness direction of the sheet, it has excellent thermal conductivity in the thickness direction of the sheet. It is difficult to transmit and has excellent thermal conductivity anisotropy.
- the heat conductive sheet oriented flaky graphite powder when using graphite flake powder, it is not limited to one direction, while it exhibits thermal conductivity in the spreading direction of the surface of the flaky graphite powder, carbon fiber When powder is used, the thermal conductivity in the axial direction of the fiber axis, not in the plane direction, can be increased. Therefore, heat conduction in directions other than the fiber axis direction can be suppressed.
- the surface of the flaky graphite powder overlapped and the probability that the graphite powders were in contact with each other was high, which was a factor for increasing the conductivity.
- carbon fiber powder when carbon fiber powder is used, there is a low probability of contact between the carbon fiber powders, but rather, the carbon fiber powders are in contact with each other via a thermally conductive filler.
- the insulating heat conductive filler is dispersed in the polymer matrix and the insulating heat conductive layer having the heat conductivity and the insulating property is provided, it is compared with the heat conductive sheet composed only of the carbon fiber oriented heat conductive layer.
- the insulating property can be improved without greatly reducing the thermal conductivity. Therefore, it can be suitably used for applications that require high insulation.
- the polymer matrix may be composed of a liquid silicone main ingredient and a cured product of a curing agent.
- the polymer matrix is a heat conductive sheet composed of a liquid silicone main ingredient and a cured product of a curing agent, the viscosity can be kept low at the stage of the polymer composition before being cured to form a polymer matrix. Filling with fiber powder or a heat conductive filler can be performed easily. Therefore, it can be set as a heat conductive sheet with high orientation performance.
- the carbon fiber oriented thermal conductive layer has a value (referred to as “E hardness”) measured by a Japanese Industrial Standard JIS K6253 type E hardness tester (referred to as “E hardness”) of 5 to 60, and the insulating thermal conductive layer has carbon fiber oriented thermal conductivity.
- E hardness measured by a Japanese Industrial Standard JIS K6253 type E hardness tester
- the insulating thermal conductive layer has carbon fiber oriented thermal conductivity.
- a thermally conductive sheet that is harder than the layer, has an E hardness of 70 or less, and a thickness of 0.15 to 1.5 mm can be obtained.
- the carbon fiber oriented heat conductive layer has an E hardness measured by a Japanese Industrial Standard JIS K6253 type E hardness tester of 5 to 60, so that it has excellent compressibility and can be closely attached to an adherend. Can be kept low to provide high thermal conductivity. And since an insulation heat conductive layer is harder than a carbon fiber orientation heat conduction layer, it is easy to maintain insulation, without an insulation heat conduction layer being compressed excessively at the time of compression. Since the hardness of the insulating heat conductive layer is 70 or less in terms of E hardness, it has excellent adhesion to the adherend, and when it is too hard, the adhesion deteriorates and the heat conductivity deteriorates. It ’s hard to be.
- the thickness of the insulating heat conductive layer is 0.15 to 1.5 mm, the generation of pinholes that are likely to occur when the insulating heat conductive layer is too thin is suppressed, and the heat transfer that tends to occur when the insulating heat conductive layer is too thick is less likely to occur.
- the hardness of the insulating heat conductive layer can be 20 or more in terms of E hardness.
- the hardness of the insulating heat conductive layer is 20 or more in terms of E hardness, the insulating heat conductive layer is not excessively crushed even during compression, and the insulating property of the heat conductive sheet is stabilized. Since the upper limit of the hardness is 70 or less in terms of E hardness, the thermal resistance can be lowered with the flexibility to follow the adherend.
- the thermal conductivity in the thickness direction of the sheet of the carbon fiber oriented thermal conductive layer is 7 W / m ⁇ K or more and 30 W / m ⁇ K or less, and the insulating thermal conductive layer has a thermal conductivity of 2 W / m ⁇ K or more. It can be set as the heat conductive sheet which is less than 7 W / m * K.
- the thermal conductivity of the insulating heat conductive layer is preferably 5 W / m ⁇ K or more.
- the thermal conductivity is 5 W / m ⁇ K or more, even if the thickness of the insulating thermal conductive layer is increased to about 1.5 mm, the decrease in the thermal conductivity of the thermal conductive sheet is suppressed and high thermal conductivity is achieved. Can be maintained.
- the heat conductivity sheet (W) (unit: W / m ⁇ K) and thickness (T) (unit: mm) of the insulating heat conductive layer should satisfy the relationship of the following formula (1). Can do. 0 ⁇ T ⁇ 0.20W ⁇ 0.19 Expression (1)
- thermal conductivity (W) and the thickness (T) satisfy the formula (1) for the insulating thermal conductive layer, a thermally conductive sheet with high thermal conductivity can be obtained.
- the thickness of the insulating heat conductive layer can be made thinner than the thickness of the carbon fiber oriented heat conductive layer.
- the thickness of the insulating heat conductive layer By reducing the thickness of the insulating heat conductive layer, it is possible to suppress a decrease in the thermal conductivity of the heat conductive sheet. Moreover, the carbon fiber orientation heat conductive layer which becomes relatively thick can be reliably compressed to reduce the thermal resistance.
- the carbon fiber oriented heat conductive layer may include a heat conductive filler having an aspect ratio of 2 or less.
- the carbon fiber powder and other heat conductive fillers can be compared with the case where the carbon fiber powder is filled alone. Both can be highly filled. Therefore, high thermal conductivity can be obtained.
- the heat conductive sheet of the present invention is a heat conductive sheet having both high heat conductivity and insulation. Moreover, according to the heat conductive sheet of this invention, it is easy to fix to a to-be-adhered body and is excellent in the handleability.
- the heat conductive sheet shown as 1st Embodiment consists of the structure on which the carbon fiber orientation heat conductive layer and insulation heat conductive layer which were formed in the sheet form were laminated
- the carbon fiber oriented thermal conductive layer is formed into a sheet by curing a mixed composition in which carbon fiber powder or a thermal conductive filler other than carbon fiber powder is blended into a liquid polymer composition that becomes a polymer matrix.
- the carbon fiber powder has a fiber axis oriented in the thickness direction of the sheet in the polymer matrix. More specifically describing the orientation of the carbon fiber powder in the thickness direction, the ratio of the number of carbon fiber powders having an angle of the fiber axis with respect to the thickness direction of the sheet of less than 30 ° exceeds 50%.
- the hardness of the carbon fiber oriented heat conductive layer is preferably 5 to 60 in terms of E hardness as measured by a Japanese Industrial Standard JIS K6253 type E hardness tester.
- the compressibility of the carbon fiber oriented heat conductive layer deteriorates during actual use, so the laminated insulating heat conductive layer is excessively compressed and the insulating heat conductive layer becomes thinner than expected. There is a possibility that the insulating property may be lowered due to being crushed until it becomes or due to the occurrence of cracks accompanying the deformation. If the insulating heat conductive layer is made harder, the deterioration of the insulation can be suppressed, but then the entire heat conductive sheet becomes hard, the followability to the shape of the heating element and the heat sink deteriorates, and the heating element and the heat sink Adhesiveness with a heat conductive sheet may fall and heat conductivity may fall.
- the E hardness is less than 5, since it is difficult to maintain the shape, the orientation of the carbon fibers is disturbed by compression, and the thermal conductivity may be impaired. If the E hardness is 5 or more, the shape is easily retained and the handleability is improved.
- the hardness of the carbon fiber oriented heat conductive layer is hardened by increasing the filling amount of the carbon fiber powder and the heat conductive filler, in order to bring the hardness of the carbon fiber oriented heat conductive layer to a preferable range.
- a material that is softer than the desired hardness when the carbon fiber oriented heat conductive layer is formed is selected.
- the thickness of the carbon fiber oriented heat conductive layer is preferably 0.25 to 10 mm.
- the thickness is less than 0.25 mm, when the carbon fiber powder is oriented in the mold, the space for the rotation of the carbon fiber powder is insufficient by the mold, and the rotation is hindered so that the orientation is insufficient. There is a risk of becoming. On the other hand, if it exceeds 10 mm, the thermal resistance may increase.
- the thermal conductivity in the thickness direction of the carbon fiber orientation heat conductive layer can be in the range of 7 W / m ⁇ K to 30 W / m ⁇ K.
- the thermal conductivity of the thermal conductive sheet tends to be difficult to increase as the difference increases with respect to the thermal conductivity of the insulating thermal conductive layer. Therefore, if it exceeds 30 W / m ⁇ K, the thermal conductivity difference with respect to the insulating thermal conductive layer becomes too large, and even if the thermal conductivity of the carbon fiber oriented thermal conductive layer is increased, the thermal conductivity of the thermal conductive sheet is almost unchanged. Because it disappears.
- This thermal conductivity can be calculated using a method of an experimental example described later.
- the term “thermal conductivity” refers to the thermal conductivity in the thickness direction of the sheet (the orientation direction of the carbon fiber powder) unless otherwise specified.
- the carbon fiber oriented thermal conductive layer has conductivity because it contains oriented carbon fiber powder.
- the volume resistivity is preferably 10 4 to 10 6 ⁇ ⁇ cm. This is because the conductivity and the thermal conductivity have a certain degree of correlation, and the carbon fiber oriented thermal conductive layer having a conductivity in the range of 10 4 to 10 6 ⁇ ⁇ cm has a high thermal conductivity.
- the volume resistivity can be obtained by measuring the resistance value with a tester when the carbon fiber oriented heat conductive layer is sandwiched between gold-plated metal plates and the initial thickness is compressed to 10%.
- the polymer matrix is a polymer such as resin or rubber, and can be preferably formed by curing a liquid polymer composition comprising a mixed system such as a main agent and a curing agent.
- the polymer composition can contain, for example, uncrosslinked rubber and a crosslinking agent, or can contain uncrosslinked rubber containing a crosslinking agent and a crosslinking accelerator.
- the curing reaction may be room temperature curing or heat curing. If the polymer matrix is silicone rubber, alkenyl group-containing organopolysiloxane and organohydrogenpolysiloxane can be exemplified.
- thermoplastic elastomer if it is a polyester-type thermoplastic elastomer, it can be set as diol and dicarboxylic acid, and if it is a polyurethane-type thermoplastic elastomer, it can be set as diisocyanate and diol.
- polymer compositions polymer matrix before curing
- silicone rubber in which the polymer matrix after curing is particularly flexible and the filling property of the heat conductive filler is good.
- Carbon fiber powder included in the polymer matrix includes carbon fiber powders such as fibers, rods, and needles.
- the crystal plane of graphite is continuous in the fiber axis direction, and has a very high thermal conductivity in the fiber axis direction. Therefore, the thermal conductivity in a specific direction can be increased by aligning the fiber axis direction in a predetermined direction.
- the carbon fiber used in the present invention is graphitized, and examples of the raw material include condensed polycyclic hydrocarbon compounds such as naphthalene, condensed heterocyclic compounds such as PAN (polyacrylonitrile) and pitch, and the like.
- a mesophase pitch By using the mesophase pitch, it is possible to obtain graphitized carbon fiber having a thermal conductivity excellent in the fiber axis direction in which the pitch is oriented in the fiber axis direction due to the anisotropy in the spinning step described later.
- This mesophase pitch is not particularly limited as long as it can be spun.
- mesophase pitch may be used alone, that is, mesophase pitch.
- a graphitized carbon fiber having a content of 100% is most preferable from the viewpoints of high thermal conductivity, spinnability and quality stability.
- the carbon fiber there can be used a carbon fiber that has been subjected to spinning, infusibilization, and carbonization in order and pulverized or cut into a predetermined particle size and then graphitized, or a carbon fiber that has been crushed or cut after carbonization and then graphitized.
- the polycondensation reaction and the cyclization reaction are more likely to proceed during the graphitization process on the surface newly exposed to the pulverization.
- Graphitized carbon fiber with improved properties can be obtained.
- the spun carbon fiber is graphitized and then pulverized
- the carbon fiber after graphitization is stiff and easy to pulverize, and a carbon fiber powder having a relatively narrow fiber length distribution can be obtained by short-time pulverization.
- the fiber diameter of the carbon fiber is not particularly limited, but is preferably 5 to 20 ⁇ m.
- the fiber diameter is in the range of 5 to 20 ⁇ m, it is easy to produce industrially, and the thermal conductivity of the obtained carbon fiber oriented heat conductive layer can be increased.
- the fiber diameter is smaller than 5 ⁇ m or larger than 20 ⁇ m, the productivity is lowered.
- the average fiber length of the carbon fibers is preferably 10 to 500 ⁇ m, more preferably 15 to 200 ⁇ m, and particularly preferably 15 to 120 ⁇ m.
- the average fiber length is shorter than 10 ⁇ m, the contact between the graphitized carbon fibers is reduced in the polymer matrix, and the heat conductivity of the carbon fiber oriented heat conductive layer obtained due to insufficient heat transfer path is lowered.
- the average fiber length is longer than 500 ⁇ m, the carbon fiber becomes bulky, and it becomes difficult to highly fill the polymer matrix.
- the electroconductivity of a carbon fiber orientation heat conductive layer may increase.
- said average fiber length is computable from the particle size distribution which observed the carbon fiber with the microscope.
- the average fiber length of the carbon fibers is preferably 50% or less of the thickness of the carbon fiber oriented heat conductive layer, and the content of carbon fibers having a fiber length exceeding 80% of the thickness of the carbon fiber oriented heat conductive layer is 5%. It is preferable that it is below mass%.
- the content of carbon fiber having a fiber length exceeding 80% of the thickness of the carbon fiber oriented heat conductive layer exceeds 5% by mass, the carbon fiber becomes a length exceeding the compression thickness when the heat conductive sheet is compressed. This is because there is a risk of large intrusion into the insulating heat conductive layer. If the carbon fiber penetrates into the insulating heat conductive layer, the thickness for increasing the insulating property becomes thin and the insulating property may be lowered.
- the carbon fiber penetrates the insulating heat conductive layer, the insulating property is impaired.
- the average fiber length of the carbon fibers is also 50% or less of the thickness of the carbon fiber oriented heat conductive layer, the amount of carbon fibers exceeding the thickness of the carbon fiber oriented heat conductive layer can be reduced even during compression. it can.
- the carbon fiber has a narrow particle size distribution, and it is preferable to use a mixture of a plurality of carbon fibers having different particle size distributions because the thermal conductivity can be increased.
- the aspect ratio of the carbon fiber powder is preferably more than 2.
- the aspect ratio is 2 or less, it is difficult to orient the carbon fiber powder in a specific direction and it is difficult to increase the thermal conductivity. More preferably, the aspect ratio is 5 or more.
- the aspect ratio is a value of “fiber length / fiber diameter” of the carbon fiber powder.
- the thermal conductivity of the carbon fiber is not particularly limited, but the thermal conductivity in the fiber axis direction is preferably 400 W / m ⁇ K or more, more preferably 800 W / m ⁇ K or more, particularly preferably 1000 W / m ⁇ K or more. It is.
- the content of the carbon fiber powder is preferably 75 to 150 parts by mass with respect to 100 parts by mass of the polymer matrix. If the amount is less than 75 parts by mass, it is difficult to increase the thermal conductivity. If the amount exceeds 150 parts by mass, the viscosity of the mixed composition may increase and the orientation may deteriorate.
- Thermally conductive filler is preferably contained separately from the carbon fiber powder in the carbon fiber oriented heat conductive layer, and is a material that imparts heat conductivity to the polymer matrix together with the carbon fiber powder. In particular, it is preferable that a thermally conductive filler having an aspect ratio of 2 or less is included.
- the carbon fiber powder is oriented in the thickness direction of the sheet, and preferably includes other heat conductive fillers, more preferably a heat conductive filler having a small aspect ratio, so that the surfaces of the oriented carbon fiber powders are aligned.
- a heat conductive filler is suitably interposed in the gap, and a carbon fiber oriented heat conductive layer having high heat conductivity can be obtained.
- thermally conductive filler examples include spherical and amorphous powders such as metals, metal oxides, metal nitrides, metal carbides, and metal hydroxides, and spherical graphite.
- the metal examples include aluminum, copper, and nickel.
- the metal oxide examples include aluminum oxide, magnesium oxide, zinc oxide, and quartz.
- the metal nitride examples include boron nitride and aluminum nitride.
- the metal carbide examples include silicon carbide, and examples of the metal hydroxide include aluminum hydroxide.
- thermally conductive fillers aluminum oxide and aluminum are preferable because they have high thermal conductivity and spherical ones are easily available, and aluminum hydroxide is easily available and increases the flame retardancy of the thermally conductive sheet. It is preferable in that it can be performed.
- Such an electrically conductive filler preferably has an aspect ratio of 2 or less. This is because when the aspect ratio exceeds 2, the viscosity is likely to increase and it is difficult to achieve high filling. For these reasons, the shape of the heat conductive filler is preferably spherical.
- the average particle diameter of the heat conductive filler is preferably 0.5 to 35 ⁇ m. When the average particle size exceeds 35 ⁇ m, the size of the carbon fiber powder may approach and the orientation of the carbon fiber powder may be disturbed. On the other hand, a thermally conductive filler having an average particle size of less than 0.5 ⁇ m has a large specific surface area, so that its viscosity is likely to increase and it is difficult to fill it with a high degree. However, if there is no adverse effect on the fillability, a heat conductive filler of less than 0.5 ⁇ m may be included.
- the average particle diameter of the thermally conductive filler can be represented by a volume average particle diameter of a particle size distribution measured by a laser diffraction scattering method (JIS R1629).
- the heat conductive filler is preferably added in the range of 250 to 800 parts by mass, more preferably in the range of 350 to 700 parts by mass with respect to 100 parts by mass of the polymer matrix. If the amount is less than 250 parts by mass, the amount intervening in the gap between the carbon fiber particles may be insufficient, and the thermal conductivity may be deteriorated. On the other hand, even if it exceeds 800 parts by mass, the effect of increasing the thermal conductivity is not increased, and there is a possibility that the heat conduction by the carbon fiber powder may be hindered. In the range of 350 to 700 parts by mass, the heat conductivity is excellent and the viscosity of the mixed composition is also suitable.
- additives can be included as long as the function as a heat conductive sheet is not impaired.
- organic components such as a plasticizer, a dispersant, a coupling agent, and an adhesive may be included.
- the carbon fiber oriented heat conductive layer can be made into a sheet having a relatively low carbon fiber content and excellent tackiness on the sheet surface by including a heat conductive filler together with carbon fiber powder. For this reason, even if the pressure is applied between the heating element and the heat dissipation element, the compressive stress is small, and the substrate is less likely to be distorted or excessive pressure is applied. Further, if the surface of the carbon fiber oriented heat conductive layer is exposed on the surface of the heat conductive sheet, the heat conductive sheet can be easily fixed to the heat generating body or the heat radiating body and has excellent workability.
- the carbon fiber oriented heat conductive layer has tackiness when laminated with the insulating heat conductive layer, it can be easily integrated with the insulating heat conductive layer without providing an adhesive layer. Therefore, there is no cost for providing the adhesive layer, and there is no concern that the thermal conductivity is lowered by the adhesive layer.
- the insulating heat conductive layer is a layer formed by curing a mixed composition in which an insulating heat conductive filler is blended into a liquid polymer composition serving as a polymer matrix, and has an insulating property.
- the insulating property is imparted to the heat conductive sheet laminated with the carbon fiber oriented heat conductive layer.
- the insulating heat conductive layer preferably has a predetermined dielectric breakdown voltage in order to impart insulation to the heat conductive sheet. Dielectric breakdown voltage means that when a sample having electrical insulation is sandwiched between two electrodes and then the voltage is gradually increased, the current increases rapidly, causing a part of the sample to melt and a hole to form or carbonize.
- the dielectric breakdown voltage measured by using a withstand voltage tester (TOS8650, manufactured by Kikusui Electronics Co., Ltd.) based on JIS K6249 is 3 kV. / Mm or more is preferable, and 5 kV / mm or more is more preferable.
- An insulating heat conductive layer in which an insulating heat conductive filler is blended into a polymer matrix is harder than a carbon fiber oriented heat conductive layer and has an E hardness of 70 according to a Japanese Industrial Standard JIS K-6253 type E hardness meter. It is below and it is preferable that it is 20 or more.
- the insulating heat conductive layer When the hardness of the insulating heat conductive layer is softer than that of the carbon fiber oriented heat conductive layer, the insulating heat conductive layer may be excessively compressed during actual use and the insulating property may be impaired. On the other hand, when the hardness of the insulating heat conductive layer exceeds E hardness 70, the adhesion with the adherend deteriorates due to the increase in hardness, and there is a concern about an increase in thermal resistance.
- the hardness of the insulating heat conductive layer is 20 or more in terms of E hardness, a strong insulating heat conductive layer can be obtained, and stable insulation can be maintained even when compressed. And since it has the softness
- the thickness of the insulating heat conductive layer is preferably 0.15 to 1.5 mm, and more preferably 0.25 to 1.5 mm. If the thickness is less than 0.15 mm, a pinhole may be formed, and the insulating property may be impaired due to being too thin. On the other hand, when the thickness exceeds 1.5 mm, the influence of heat transfer inhibition by the insulating heat conductive layer may be increased. Moreover, if the thickness is 0.25 mm or more, the dielectric breakdown voltage is high and stable insulation can be obtained.
- the thermal conductivity of the insulating heat conductive layer is preferably 2 W / m ⁇ K or more and less than 7 W / m ⁇ K, more preferably 5 W / m ⁇ K or more and less than 7 W / m ⁇ K. If the thermal conductivity is less than 2 W / m ⁇ K, the thermal conductivity of the thermal conductive sheet may be greatly reduced. On the other hand, if the amount is 7 W / m ⁇ K or more, the amount of the insulating heat conductive filler to be contained increases, so that the insulating heat conductive layer becomes brittle, and the insulation may be impaired by compression or deformation. By making it 5 W / m ⁇ K or more and less than 7 W / m ⁇ K, a decrease in thermal conductivity can be reduced.
- the thermal conductivity of the insulating thermal conductive layer also indicates the thermal conductivity in the thickness direction.
- the thermal conductivity in the thickness direction can be increased by orienting the long axis of the insulating heat conductive filler having shape anisotropy such as boron nitride in the thickness direction.
- shape anisotropy such as boron nitride
- the insulating heat conductive layer has an isotropic heat conductivity.
- the polymer matrix and the additive can be made of the types of materials described in the carbon fiber oriented heat conductive layer.
- the same polymer matrix as the polymer matrix employed for the carbon fiber oriented heat conductive layer can be used for the insulating heat conductive layer, in which case the chemical structure is the same. Therefore, it can be set as the heat conductive sheet excellent in the adhesiveness of a carbon fiber orientation heat conductive layer and an insulation heat conductive layer.
- a polymer matrix made of a material different from the polymer matrix used for the carbon fiber oriented heat conductive layer can be used for the insulating heat conductive layer.
- silicone is used for the layer on the side that comes into contact with the heat sink, and non-silicone material is used for the layer on the side that comes into contact with an electronic device such as a substrate.
- the transpiration of molecular siloxane can be reduced.
- the carbon fiber oriented heat conductive layer may be made of a material corresponding to each adherend, such as selecting a polymer matrix that easily adheres to each adherend according to the material of the adherend.
- the insulating heat conductive layer is made of a material corresponding to each adherend.
- the insulating thermal conductive filler is a material that imparts thermal conductivity to the polymer matrix in the insulating thermal conductive layer, and insulates the insulating material among the types of materials described in the carbon fiber oriented thermal conductive layer. It can also be used for the conductive layer.
- aluminum oxide is preferable because of its high thermal conductivity and spherical shape
- aluminum hydroxide is preferable because it can enhance the flame retardancy of the heat conductive sheet.
- Spherical ones do not easily increase in viscosity and are easily filled with high viscosity.
- Aluminum oxide and aluminum hydroxide are also preferable from the viewpoint of availability.
- the average particle size of the insulating heat conductive filler is preferably 0.5 to 50 ⁇ m. When the average particle size exceeds 50 ⁇ m, the moldability is significantly lowered. On the other hand, a thermally conductive filler having an average particle size of less than 0.5 ⁇ m has a large specific surface area, so that its viscosity is likely to increase and it is difficult to fill it with a high degree. However, if there is no adverse effect on the fillability, a heat conductive filler of less than 0.5 ⁇ m may be included.
- the insulating heat conductive filler is preferably added in the range of 300 to 2000 parts by mass, more preferably in the range of 500 to 2000 parts by mass with respect to 100 parts by mass of the polymer matrix. If it is less than 300 parts by mass, the thermal conductivity may be lowered. On the other hand, even if it exceeds 2000 parts by mass, the effect of increasing the thermal conductivity is poor, and on the contrary, the formability is lowered, so that it is difficult to form a thin insulating heat conductive layer. In the range of 500 to 1500 parts by mass, the heat conductivity is excellent, and the viscosity of the liquid composition before being cured to form an insulating heat conductive layer is also suitable.
- the insulating heat conductive layer includes an insulating heat conductive filler and does not include carbon fiber powder, so that a sheet having high heat conductivity and high insulation can be obtained. Therefore, insulation can be imparted to the heat conductive sheet.
- it is harder than the carbon fiber oriented heat conductive layer, but has a certain degree of softness. While it is easy to maintain the property, the adhesion to the adherend is also high.
- a heat conductive sheet obtained by laminating a carbon fiber oriented heat conductive layer and an insulating heat conductive layer has the following properties.
- the thermal conductivity of the heat conductive sheet is about 3 to 30 W / m ⁇ K, preferably 10 W / m ⁇ K or more. This is because if it is 10 W / m ⁇ K or more, it has thermal conductivity required as a thermal conductive sheet.
- the preferred thermal conductivity of the carbon fiber oriented thermal conductive layer is 7 W / m ⁇ K to 30 W / m ⁇ K, and the preferred thermal conductivity of the insulating thermal conductive layer is 2 W / m ⁇ K to 7 W / m ⁇ K.
- the difference in thermal conductivity between the two is preferably smaller. As the thermal conductivity difference increases, it tends to be difficult to increase the thermal conductivity of the thermal conductive sheet. Therefore, if the thermal conductivity difference of the carbon fiber orientation thermal conduction layer with respect to the insulating thermal conduction layer becomes too large, the carbon fiber orientation This is because even if the thermal conductivity of the thermal conductive layer is increased, the thermal conductivity of the thermal conductive sheet hardly changes. From this point of view, it is preferable that the thermal conductivity of the carbon fiber oriented thermal conductive layer is 5 times or less in terms of the ratio to the thermal conductivity of the insulating thermal conductive layer.
- the thermal conductive sheet has the above-described thermal conductivity, but also has a predetermined insulating property.
- the dielectric breakdown voltage of the thermally conductive sheet can also be set to 5 kV / mm or more by having an insulating heat conductive layer having a dielectric breakdown voltage of 5 kV / mm or more.
- the ratio of the thickness of the carbon fiber oriented heat conductive layer to the thickness of the insulating heat conductive layer is such that when the thickness of the carbon fiber oriented heat conductive layer is 1, the thickness of the insulating heat conductive layer is in the range of 1 to 0.015. is there.
- “Thickness of carbon fiber oriented thermal conductive layer”: “Thickness of insulating thermal conductive layer” 1: When the insulating thermal conductive layer is made thicker than 1: 1, the insulating thermal conductive layer is compared with the thermal conductivity of the thermal conductive sheet. There is a possibility that the contribution of the increase becomes greater and the thermal conductivity is lowered. On the other hand, if this ratio exceeds 1: 0.015 and the insulating heat conductive layer is thinned, the insulating property may be lowered, or the carbon fiber oriented heat conductive layer may be thick and the thermal resistance may be too high.
- the manufacturing method of a heat conductive sheet As an example of the manufacturing method of a heat conductive sheet, there exists the method of manufacturing a carbon fiber orientation heat conductive layer and an insulation heat conductive layer separately, and bonding them.
- a liquid polymer composition, a carbon fiber powder, and a mixed composition containing a heat conductive filler are placed in a magnetic field, and the carbon fiber powder is placed along the magnetic field.
- the magnetic field alignment manufacturing method include obtaining a carbon fiber alignment heat conductive layer by curing the polymer composition after the alignment.
- Each component constituting the mixed composition in which the carbon fiber powder and the heat conductive filler are uniformly dispersed in the liquid polymer composition is 75 to 150 masses of the carbon fiber powder with respect to 100 mass parts of the polymer composition. And 250 to 800 parts by mass of the thermally conductive filler.
- this addition ratio is converted to volume%, it corresponds approximately to 10 to 25 volume% of carbon fiber powder and 25 to 60 volume% of heat conductive filler with respect to 30 to 50 volume% of the polymer composition. Additives and the like can be appropriately added to this.
- the viscosity of the mixed composition is preferably 10 to 300 Pa ⁇ s. If it is less than 10 Pa ⁇ s, the carbon fiber powder or the thermally conductive filler may be precipitated, and if it exceeds 300 Pa ⁇ s, the fluidity is too low and the carbon fiber powder is not oriented in the magnetic field, or it takes too much time for orientation. It is. However, in some cases, the heat conductivity can be reduced to less than 10 Pa ⁇ s by using a thermally conductive filler that is difficult to settle or by combining an additive such as an anti-settling agent.
- examples of the magnetic force lines generating source for applying the magnetic force lines include superconducting magnets, permanent magnets, electromagnets, coils, and the like.
- Superconducting magnets are preferable in that a magnetic field with high magnetic flux density can be generated.
- the magnetic flux density of the magnetic field generated from these lines of magnetic force is preferably 1 to 30 Tesla. If the magnetic flux density is less than 1 Tesla, it becomes difficult to orient the carbon fiber powder. On the other hand, a magnetic flux density exceeding 30 Tesla is difficult to obtain practically.
- the molded body obtained in the magnetic field orientation manufacturing method may be used as it is as a carbon fiber orientation heat conductive layer, or may be sliced or cut into a final shape.
- a carbon fiber orientation heat conductive layer formed with a mold an extremely thin skin layer made of a polymer matrix may be formed on the surface of the sheet. This skin layer has an effect of suppressing the dropping of the carbon fiber powder and the heat conductive filler.
- a preliminary sheet made of a thin plate by applying a shearing force to the mixed composition is manufactured, and a laminated block in which a plurality of these sheets are laminated and cured is manufactured.
- a laminated slice manufacturing method in which the laminated block is cut.
- a carbon fiber powder, a heat conductive filler, and various additives as necessary are mixed in a liquid polymer composition and stirred, and a mixed composition in which the mixed solid is uniformly dispersed is prepared.
- the mixed composition preferably has a relatively high viscosity of 10 to 1,000 Pa ⁇ s so that a shearing force is applied when it is stretched into a sheet form.
- the mixture composition is stretched flat while applying a shearing force to be formed into a sheet shape.
- a shearing force By applying a shearing force, the carbon fiber powder can be oriented in the shearing direction.
- a sheet forming means for example, a coating applicator such as a bar coater or a doctor blade, or a method of applying the mixed composition on the base film by extrusion molding or ejection from a nozzle can be used.
- the sheet thickness at this time is preferably about 50 to 250 ⁇ m.
- a preliminary sheet can be obtained. In this preliminary sheet, the carbon fiber powder is oriented in one direction within the plane of the sheet.
- the mixed composition is used by using an appropriate curing means for curing the polymer composition such as ultraviolet irradiation or hot pressing. Is cured to form a laminated block. Finally, a laminated block is cut
- the first magnetic field orientation manufacturing method and the second laminated slice manufacturing method are compared.
- the laminated slice manufacturing method it is difficult to produce a flexible and thin carbon fiber oriented heat conductive layer.
- the OO hardness is about 50 or less, even if a blade that is as sharp as possible is used, the sheet is too soft, so that the deformation of the sheet is large due to the pressing force by slicing, and it is difficult to obtain a high-quality thin film sheet.
- the method of freezing is effective, for example, for acrylic gels
- the hardness when slicing cannot be improved in a sheet using silicone as a polymer matrix because the hardness hardly changes even when frozen at ⁇ 40 °. .
- It can be hardened by cooling to a lower temperature (actually to about -60 °), but a special device is required to cool it to a lower temperature beyond -40 °, and it is cooled by frictional heat at the time of slicing. In practice, it is difficult to adopt this, taking into account the fact that it is obstructed.
- the heat conductive sheet is generally used after being compressed by about 10 to 40% for the purpose of surely adhering adherends and lowering the heat resistance. At this time, if the heat conductive sheet is flexible, the stress for compression becomes small, so that the substrate as the adherend is less likely to be distorted by the stress. However, in the laminated slice manufacturing method, since the hardness is limited, it is difficult to obtain a very flexible heat conductive sheet.
- the magnetic field orientation manufacturing method does not include a bonding surface on which a plurality of sheets are bonded, and therefore, the problem that the bonding surface easily peels does not occur. Furthermore, when it is laminated with the insulating heat conductive layer, it is preferable that the surface is sticky, but such a sticky surface is easily formed. Therefore, it is preferable to manufacture by the magnetic field orientation manufacturing method for the reasons as described above.
- the carbon fiber powder and the heat conductive filler are exposed on the cut surface by slicing or cutting on a plane perpendicular to the orientation direction. Since the thermally conductive filler is in contact with the adherend over a wide area, the thermal conductivity can be increased.
- a mixed composition containing a liquid polymer composition and a heat conductive filler is prepared, and then the polymer composition is cured.
- Each component constituting the mixed composition preferably contains 300 to 2000 parts by mass of a thermally conductive filler with respect to 100 parts by mass of the polymer composition.
- this addition ratio is converted to volume%, it corresponds to approximately 50 to 90 volume% of the heat conductive filler in the polymer composition. Additives and the like can be appropriately added to this.
- Examples of the method for forming the insulating heat conductive layer include a bar coater method, a doctor blade method, an extrusion molding method (T-die method, etc.), a calendar molding method, a press molding method, and a casting method. Therefore, it is preferable that the viscosity of the mixed composition be within a range where a thin film can be formed by these methods.
- the bonding between the carbon fiber alignment heat conductive layer and the insulating heat conductive layer can be performed by bonding as long as at least one of the carbon fiber alignment heat conductive layer and the insulating heat conductive layer has adhesiveness derived from the polymer matrix. Can be integrated. From the viewpoint of this bonding, it is preferable that both the carbon fiber orientation heat conductive layer and the insulating heat conductive layer have adhesiveness. Since both the carbon fiber orientation heat conduction layer and the insulating heat conduction layer have a predetermined softness, the surfaces are often sticky enough to be bonded together, but in the absence of such stickiness Can also be laminated via an adhesive or the like.
- a carbon fiber oriented heat conductive layer is first formed into a sheet shape, and a mixed composition to be an insulating heat conductive layer is applied thereon, and then the polymer composition is applied. There is a method of curing. According to this manufacturing method, since the insulating heat conductive layer is cured on the surface of the carbon fiber oriented heat conductive layer, the procedure of bonding them together can be omitted.
- an insulating heat conductive layer is first formed into a sheet shape, and a mixed composition that becomes a carbon fiber alignment heat conductive layer is applied thereon, and then carbon is formed by a magnetic field alignment manufacturing method.
- the heat conductive sheet shown as the second embodiment is a sheet-like heat conductive sheet in which insulating heat conductive layers are laminated on both surfaces of a carbon fiber oriented heat conductive layer. According to this embodiment, since the carbon fiber orientation heat conductive layer containing the carbon fiber which is electroconductive powder is pinched
- a thermally conductive sheet shown as a third embodiment is a sheet-like thermally conductive sheet in which carbon fiber oriented thermally conductive layers are laminated on both sides of an insulating thermally conductive layer. If the carbon fiber oriented heat conductive layer is produced by the above-mentioned laminated slice manufacturing method, or the surface of the carbon fiber oriented heat conductive layer is sliced or cut to expose the carbon fiber powder or the heat conductive filler, the surface tack However, it is possible to obtain a thermally conductive sheet having both surfaces having good slipperiness.
- each embodiment can be combined within a range where there is no problem, and for example, the two heat conductive sheets shown in the first embodiment can be stacked.
- Carbon fiber orientation heat conductive layer 1 It is an addition reaction type silicone as a liquid polymer composition, and a mixture of alkenyl group-containing polyorganosiloxane (main agent) and organohydrogenpolysiloxane (curing agent) (specific gravity: 1.0) is mixed with carbon fiber powder (average Fiber length: 100 ⁇ m, specific gravity: 2.2), spherical aluminum oxide (specific gravity: 4.0) having a particle size of 3 ⁇ m and an aspect ratio of approximately 1 as the heat conductive filler 1, and particles as the heat conductive filler 2 Spherical aluminum oxide (specific gravity: 4.0) having a diameter of 10 ⁇ m and an aspect ratio of approximately 1 was blended in the proportions shown in Table 1 (each expressed in parts by mass), and mixed and stirred so that the composition became uniform. Then, defoaming was performed to prepare a mixed composition for the carbon fiber oriented heat conductive layer 1. In addition, the carbon fiber powder and the heat conductive filler used what surface-treated with the silane
- this mixed composition was molded into a sheet by mold molding. And it left still for 10 minutes in the magnetic field of 8 Tesla by a superconducting magnet so that a magnetic force line might be applied to the thickness direction of a sheet
- This carbon fiber oriented heat conductive layer 1 was prepared as a test piece having a thickness of 2.0 mm and 10.0 mm.
- the average particle diameter of the heat conductive filler indicates the volume average particle diameter of the particle size distribution measured by a laser diffraction scattering method (JIS R1629).
- JIS R1629 The aspect ratio of the thermally conductive filler is observed with an electron microscope.
- the aspect ratio of the heat conductive fillers 1 and 2 and the heat conductive filler 3 described later was approximately 1.0.
- the carbon fiber aligned heat conductive layers 2 to 4 were prepared in the same manner as the carbon fiber aligned heat conductive layer 1 by changing the composition of each component in the mixed composition when the carbon fiber aligned heat conductive layer 1 was manufactured. .
- Table 1 shows the composition (parts by mass) of each component in the mixed composition to be the carbon fiber oriented heat conductive layers 2 to 4.
- the carbon fiber oriented heat conductive layers 2 to 4 were also prepared as test pieces having thicknesses of 2.0 mm and 10.0 mm.
- Insulating heat conduction layer Insulating heat conductive layers 1 to 8 shown below were produced.
- ⁇ Insulating heat conductive layer 1> The same addition reaction type silicone (main agent and curing agent) as that used for the carbon fiber oriented heat conductive layer 1 as a liquid polymer composition, and the same particles as the heat conductive filler 1 as an insulating heat conductive filler Spherical aluminum oxide having a diameter of 3 ⁇ m and an aspect ratio of approximately 1 (specific gravity: 4.0) and a spherical aluminum oxide having a particle diameter of 40 ⁇ m and an aspect ratio of approximately 1 as the insulating thermal conductive filler 3 (specific gravity: 4. 0) were mixed in the proportions shown in Table 2 (respectively expressed in parts by mass), stirred and mixed, and then defoamed to prepare a mixed composition for the insulating heat conductive layer 1.
- the insulating heat conductive filler was also subjected to surface treatment with a silane coupling agent in advance. Subsequently, this mixed composition was molded into a sheet by mold molding and heated at 120 ° C. for 30 minutes to obtain an insulating heat conductive layer 1.
- This insulating heat conductive layer 1 was produced as each test piece having a thickness of 0.10 mm, 0.15 mm, 0.25 mm, 0.50 mm, 0.75 mm, and 10.0 mm.
- Insulating heat conductive layers 2 to 8 were produced in the same manner as the insulating heat conductive layer 1 by changing the composition of the mixed composition at the time of manufacturing the insulating heat conductive layer 1 to the composition (parts by mass) shown in Table 2. .
- the plasticizer added to the insulating heat conductive layers 4 and 5 is dimethylpolysiloxane (silicone oil) (viscosity 100 mPa ⁇ s).
- the insulating heat conductive layers 2 to 8 were prepared as test pieces having thicknesses of 0.5 mm and 10.0 mm, but the insulating heat conductive layer 6 was also prepared as test pieces having thicknesses of 0.25 mm and 0.75 mm.
- thermal conductive sheet The following heat conductive sheets 1 to 21 were prepared.
- the carbon fiber-oriented heat conductive layer 1 without an insulating heat conductive layer was used as a heat conductive sheet 20.
- a heat conductive sheet 21 is formed by laminating a carbon film oriented heat conductive layer 1 and a polyimide film (thermal conductivity is 0.16 W / m ⁇ K, thickness is 50 ⁇ m) as a comparison with the insulating heat conductive layer. .
- the penetration was measured in order to use it as an index of hardness different from the above hardness. More specifically, each test cut into 10 mm in length ⁇ 10 mm in width using a probe for insertion with a cylindrical projection having a diameter of 0.5 mm using a thermomechanical analyzer (manufactured by Shimadzu Corporation, TMA-50) After setting the piece, set the load rate to 1g / min and target load to 0.5g at 23 ° C for 3 minutes (ie, the load increases from 0 to 0.5g in the first 30 seconds, from 30 seconds to 3 minutes) The probe subsidence depth (which is constant at 0.5 g) was measured. The results are shown in Tables 3-5.
- FIG. 1 shows a comparison of a measured penetration value and a measured E hardness value from a test piece having the same configuration as that of the test piece and a thickness of 10.0 mm. More specifically, the penetration value measured for the test pieces having a thickness of 2 mm and 0.5 mm and the E hardness value of the test piece having the same configuration as the test piece and a thickness of 10.0 mm are shown on the graph. The relational expressions for each thickness (two curves in FIG. 1) are derived from these plots. As shown in FIG. 1, the penetration is affected by the thickness of the test piece. If such a relational expression is derived, this relational expression can be used by measuring the penetration of a specimen having a certain thickness. Thus, E hardness can be estimated.
- the E hardness is obtained by substituting the actually measured penetration into the two relational expressions shown in FIG. Even if the thickness is other than 2 mm or 0.5 mm, if a relational expression for a specific length is created in advance in the same manner as both relational expressions, the measured penetration is substituted into the relational expression. Thus, E hardness can be estimated.
- the penetration of the heat conductive sheet in which the carbon fiber oriented heat conductive layer and the insulating heat conductive layer are laminated is the same as that of the heat conductive sheet. It is a value between the degree of penetration and the penetration of a test piece made of an insulating heat conductive layer alone with the same thickness as the heat conductive sheet. The value between these values is also different for the penetration measured from the carbon fiber oriented thermal conductive layer side and the penetration measured from the insulating thermal conductive layer side, and the insulating thermal conductive layer is harder than the carbon fiber oriented thermal conductive layer. For example, the penetration measured from the insulating heat conductive layer side is a lower (hard) value.
- the penetration is measured from both the front and back surfaces of a test piece having a thickness of Lmm
- the penetration on the front side is A ⁇ m
- the penetration on the back side is B ⁇ m
- the layer on the front surface side is a layer having an E hardness that is softer than the E hardness converted from the penetration with a thickness of Lmm.
- this is a layer having an E hardness that is harder than the E hardness converted from the penetration when the thickness is L mm.
- a test piece cut to a length of 10 mm and a width of 10 mm is sandwiched between a heat generating substrate (heat generation amount Q: 25 W) and a heat sink (“FH60-30” manufactured by Alpha Co., Ltd.), and a constant load (2 kgf / cm 2 ) is applied to the heat sink. ) was added.
- a cooling fan air flow 0.01 kg / sec, wind pressure 49 Pa
- the heating substrate is energized with the cooling fan activated.
- Thermal resistance value (° C./W) Thickness in the heat passage direction (m) / (Heat passage cross-sectional area (m 2 ) ⁇ Thermal conductivity (W / m ⁇ K)) Equation (3)
- the values of thermal conductivity thus obtained are shown in Tables 3 to 5.
- Dielectric breakdown voltage which is an index for evaluating insulation, was measured.
- the voltage is gradually increased with a 200 g load applied after the test piece is sandwiched between the two electrodes, the current increases rapidly, and a part of the test piece melts, causing a hole or carbonization.
- the voltage at this time is the dielectric breakdown voltage. More specifically, the dielectric breakdown voltage was measured using a withstand voltage tester (TOS8650, manufactured by Kikusui Electronics Co., Ltd.) based on JIS K6249. Five test pieces were prepared and tested five times. Tables 3 to 5 show average values of 5 times.
- the heat conductive sheet 5 in which the insulating heat conductive layer having the hardness of E18 is laminated has an average value of the dielectric breakdown voltage of 4 kV / mm, but the measurement result is 0 kV / mm only once out of 5 times. became.
- stacked the insulating heat conductive layer of hardness E25, E40, E70, and E80 all had a dielectric breakdown voltage exceeding 5 kV / mm. From these results, it was found that the softer the insulating heat conductive layer, the higher the thermal conductivity.
- the heat conductive sheets 7 and 8 in which the insulating heat conductive layers of various hardnesses are laminated on the carbon fiber oriented heat conductive layer whose hardness is changed to E60 and E75 are seen, the heat conductive sheets 7 and 8 Had a breakdown voltage exceeding 5 kV / mm. Moreover, about heat conductivity, the heat conductivity of the heat conductive sheet 8 was a little low.
- the heat conductive sheet 2 whose dielectric breakdown voltage did not reach the desired value is a combination in which the hardness of the insulating heat conductive layer is softer than that of the carbon fiber oriented heat conductive layer. As a result, it was observed that the insulating heat conductive layer protruded and spread out. From this, it can be seen that if the insulating heat conductive layer is softer than the carbon fiber oriented heat conductive layer, the insulating heat conductive layer is excessively compressed when compressed, resulting in a decrease in insulation.
- the hardness of the insulating heat conductive layer is somewhat harder than that of the carbon fiber oriented heat conductive layer, but it was quite flexible with E18, so that it was considered weak and brittle in strength.
- the thermal conductivity of the carbon fiber oriented thermal conductive layer is E75, and the thermal conductivity of the insulating thermal conductive layer is E80, the thermal conductivity tends to be low. It can be seen that the hardness of the oriented heat conductive layer is preferably E60 or less, and the hardness of the insulating heat conductive layer is preferably E70 or less.
- the heat conductive sheets 1 and 9 to 13 in which the carbon fiber oriented heat conductive layer and the insulating heat conductive layer having various heat conductivities are combined will be compared.
- the thermal conductive sheets 1, 9, and 10 have thermal conductivity of 5.0 W / m ⁇ K and 1.5 W / m ⁇ on the carbon fiber oriented thermal conductive layer with thermal conductivity of 12.9 W / m ⁇ K, respectively. It is a heat conductive sheet in which an insulating heat conductive layer of K, 2.5 W / m ⁇ K is laminated.
- the heat conductive sheet 1 laminated with an insulating heat conductive layer having a thermal conductivity of 5.0 W / m ⁇ K not only has high heat conductivity, but also has a decrease in heat conductivity due to the laminated heat conductive layer. It can be seen that it has a thermal conductivity that is small and very close to the thermal conductivity of the carbon fiber oriented thermal conductive layer. This means that the thermal conductivity is 1.5 W / m ⁇ K, 2.5 W / m ⁇ K, and 5.0 W / m for the carbon fiber oriented thermal conductive layer having a thermal conductivity of 11.5 W / m ⁇ K, respectively. The same applies to the heat conductive sheets 11 to 13 each having the K insulating heat conductive layer laminated.
- the heat conductive sheets 14 and 15 are obtained by laminating insulating heat conductive layers having thicknesses of 0.10 mm and 0.15 mm.
- the thermal conductive sheet 15 having a thickness of the insulating heat conductive layer of 0.15 mm was provided with a dielectric breakdown voltage of 3.0 kV / mm, whereas the thermal conductive sheet 14 having a thickness of 0.10 mm had a dielectric breakdown voltage. It decreased to 1.5 kV / mm. This shows that the thickness of the insulating heat conductive layer is preferably 0.15 mm or more.
- the heat conductive sheets 16 to 19 and the heat conductive sheets 1 and 9 have a heat conductivity of 1.5 W / m on a carbon fiber oriented heat conductive layer having a heat conductivity of 12.9 W / m ⁇ K and a thickness of 2 mm.
- the insulating heat conductive layer of m ⁇ K or 5.0 W / m ⁇ K is a heat conductive sheet in which the thickness is changed to 0.25 mm, 0.50 mm, and 0.75 mm.
- FIG. 2 is a graph in which the thicknesses of these insulating heat conductive layers are plotted on the x axis and the thermal conductivity of the heat conductive sheet is plotted on the y axis.
- the thermal conductivity of the insulating thermal conductive layer is taken as the x axis, and the thickness of each insulating thermal conductive layer at which the thermal conductivity of the thermal conductive sheet obtained here becomes 11.0 W / m ⁇ K is taken as the y axis.
- T (y) (unit: mm) The following equation (1) representing the relationship between 0 ⁇ T ⁇ 0.20W ⁇ 0.19 Expression (1)
- ⁇ Dielectric breakdown voltage> The dielectric breakdown voltage was evaluated as “ ⁇ ” for 3 kV / mm or more and “x” for less than 3 kV / mm. The results are also shown in Tables 3-5.
- the values of the decrease rate of the thermal conductivity thus obtained are shown in Tables 3 to 5.
- the value is less than 15%, the deterioration of the thermal conductivity is small compared to the case of the carbon fiber oriented thermal conductive layer alone, and the adverse effect of providing the insulating thermal conductive layer can be suppressed. 15% or more and less than 35% can suppress the adverse effect of the provision of the insulating heat conductive layer to be somewhat “ ⁇ ”, and 35% or more is more heat-resistant than the carbon fiber oriented heat conductive layer alone. It was evaluated as “x” because of a significant decrease in conductivity. The results are also shown in Tables 3 to 5.
- the heat conductive sheet can be fixed to the adherend by having adhesiveness on the surface, and the mounting operation to the electronic device becomes easy. Therefore, the possibility of fixing to the adherend was evaluated from the viewpoint of handleability.
- the test piece of the heat conductive sheet that was peeled off and dropped within 10 seconds was evaluated as “X” because the handleability was poor, and the test piece that did not fall was evaluated as “ ⁇ ”.
- the insulating heat conductive layer side of the heat conductive sheet 3 is “ ⁇ ” and the handleability is slightly bad, and the insulating heat conductive layer side of the heat conductive sheet 4 is “ ⁇ ”. ", And the result did not adhere to the adherend. From this, it is understood that the hardness of the insulating heat conductive layer is preferably E70 or less.
- the evaluation results of the handling properties of the heat conductive sheets 7 and 8 are slightly worse in the heat conductive sheet 7 having a hardness of E60 on the carbon fiber oriented heat conductive layer side, and in the heat conductive sheet 8 having a hardness of E75. As a result, the heat conductive sheet did not adhere to the adherend. This shows that the hardness of the carbon fiber oriented heat conductive layer is preferably E70 or less.
- the heat conductive sheet in which the carbon fiber oriented heat conductive layer and the insulating heat conductive layer are laminated is Their two or more characteristics are not bad. Further, a heat conductive sheet having a predetermined hardness, thickness, heat conductivity, etc. is a heat conductive sheet having excellent properties such as good handleability and heat conductivity.
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Abstract
Description
即ち、高分子マトリクスに繊維軸がシートの厚み方向に配向している炭素繊維粉末を含む炭素繊維配向熱伝導層と、高分子マトリクスに絶縁性熱伝導性充填材が分散しており熱伝導性と絶縁性とを備える絶縁熱伝導層と、を積層した熱伝導性シートである。
鱗片状黒鉛粉末を配向した熱伝導性シートと比較すると、鱗片黒鉛粉末を用いた場合は一方向に限定されない鱗片黒鉛粉末の面の広がり方向に熱伝導性を発揮するのに対して、炭素繊維粉末を用いた場合は、面方向ではない、繊維軸の軸方向への熱伝導性を高めることができる。そのため、繊維軸方向以外の方向への熱伝導を抑制することができる。
0<T≦0.20W-0.19 ・・・ 式(1)
炭素繊維配向熱伝導層は、高分子マトリクスとなる液状の高分子組成物に、炭素繊維粉末や、炭素繊維粉末以外の熱伝導性充填材を配合した混合組成物を硬化してシート状に形成した層であり、炭素繊維粉末は、その繊維軸が高分子マトリクス中でシートの厚み方向に配向している。この炭素繊維粉末の厚み方向の配向をより具体的に説明すると、シートの厚み方向に対して繊維軸のなす角度が30°未満の炭素繊維粉末の数の割合が50%を超える状態にあることをいう。
高分子マトリクスは、樹脂やゴム等の高分子であり、好ましくは主剤と硬化剤のような混合系からなる液状の高分子組成物を硬化して形成したものとすることができる。したがってこの高分子組成物は、例えば、未架橋ゴムと架橋剤を含むものであったり、架橋剤を含む未架橋ゴムと架橋促進剤を含むものであったりすることができる。また、その硬化反応は常温硬化であっても熱硬化であっても良い。高分子マトリクスがシリコーンゴムであれば、アルケニル基含有オルガノポリシロキサンとオルガノハイドロジェンポリシロキサンなどが例示できる。また、ポリエステル系熱可塑性エラストマーであれば、ジオールとジカルボン酸とすることができ、ポリウレタン系熱可塑性エラストマーであれば、ジイソシアネートとジオールとすることができる。このような高分子組成物(硬化前高分子マトリクス)の中でも、硬化後の高分子マトリクスが特に柔軟であり、熱伝導性充填材の充填性が良い付加反応型のシリコーンゴムを用いることが好ましい。
高分子マトリクスの中に含ませる炭素繊維粉末は、繊維状、棒状、針状等の炭素繊維粉末を含むものである。炭素繊維粉末はグラファイトの結晶面が繊維軸方向に連なっており、その繊維軸方向に極めて高い熱伝導率を備える。そのため、その繊維軸方向を所定の方向に揃えることで、特定方向の熱伝導率を高めることができる。
熱伝導性充填材は、炭素繊維配向熱伝導層において炭素繊維粉末とは別に含有されることが好ましく、炭素繊維粉末とともに高分子マトリクスに熱伝導性を付与する材料である。特にアスペクト比が2以下の熱伝導性充填材が含まれることが好ましい。
熱伝導性シートとしての機能を損なわない範囲で種々の添加剤を含ませることができる。例えば、可塑剤、分散剤、カップリング剤、粘着剤などの有機成分を含んでも良い。またその他の成分として難燃剤、酸化防止剤、着色剤などを適宜添加してもよい。
絶縁熱伝導層は、高分子マトリクスとなる液状の高分子組成物に、絶縁性熱伝導性充填材を配合した混合組成物を硬化してシート状に形成した層であり、絶縁性を有し、炭素繊維配向熱伝導層と積層した熱伝導性シートに対して絶縁性を付与している。
このように絶縁熱伝導層は熱伝導性シートに絶縁性を付与するため、所定の絶縁破壊電圧を備えていることが好ましい。絶縁破壊電圧とは、2つの電極の間に電気絶縁性を有する試料を挟み込んだ後、電圧を徐々に上げていくと電流が急激に増加し、試料の一部が溶けて孔が空いたり炭化したりして通電するようになる際の電圧をいい、より具体的には、JIS K6249に基づき、耐電圧試験器(TOS8650、菊水電子工業株式会社製)を用いて測定した絶縁破壊電圧で3kV/mm以上であることが好ましく、5kV/mm以上であることがより好ましい。
0<T≦0.20W-0.19 ・・・ 式(1)
この関係式を満たす場合には、高い熱伝導率を備える熱伝導性シートとすることができる。
炭素繊維配向熱伝導層と絶縁熱伝導層とを積層した熱伝導性シートは以下の性質を備える。
まず、熱伝導性シートの熱伝導率は、3~30W/m・K程度であり、10W/m・K以上が好ましい。10W/m・K以上であれば熱伝導性シートとして要求される熱伝導性を備えるからである。
熱伝導性シートの製造方法の一例として、炭素繊維配向熱伝導層と絶縁熱伝導層とを別々に製造し、それらを貼合せる方法がある。
積層スライス製法では、柔軟で薄い炭素繊維配向熱伝導層の作製が難しい。例えばOO硬度が50以下程度の場合は可能な限り鋭い刃を用いても、シートが柔らかすぎるためスライスによる押圧力でシートの変形が大きく、品質のよい薄膜シートを得ることが困難である。この問題への対策として冷凍してスライスする方法が挙げられる。しかし、冷凍する方法は例えばアクリルゲルなどでは有効であるが、シリコーンを高分子マトリクスとするシートでは、-40°に冷凍しても硬さがほとんど変わらないため、スライス時の硬さを改善できない。さらに低温まで(実際には-60°程度まで)冷やせば硬くすることができるが、-40°を超えて低い温度まで冷やすためには特殊な装置が必要となり、またスライス時の摩擦熱で冷却が阻害されることなども加味すると現実的には採用が難しい。
絶縁熱伝導層は、液状の高分子組成物と、熱伝導性充填材を含む混合組成物を調製し、次いで高分子組成物を硬化させる。混合組成物を構成する各成分は、高分子組成物100質量部に対し、熱伝導性充填材300~2000質量部を含むことが好ましい。この添加割合を体積%に換算すると、高分子組成物中で熱伝導性充填材およそ50~90体積%に相当する。これに適宜添加剤等を含ませることができる。
炭素繊維配向熱伝導層の表面に高分子マトリクスからなるスキン層が形成されている場合には、表面をスライスやカットをすることで炭素繊維粉末や熱伝導性充填材を表出させた後に、その上に絶縁熱伝導層となる混合組成物を塗布してその高分子組成物を硬化させることとしてもよい。こうすることで層間に介在するスキン層が無くなり熱伝導性シートの熱伝導率を高くすることができる。
熱伝導性シートの製造方法のさらに別の例としては、先ず絶縁熱伝導層をシート状に形成し、その上に炭素繊維配向熱伝導層となる混合組成物を塗布し、磁場配向製法により炭素繊維粉末を配向するとともに高分子組成物を硬化させる方法がある。この製造方法によっても、絶縁熱伝導層の表面で炭素繊維配向熱伝導層を硬化させるため、両者を貼り合わせる手順を省略することができる利点がある。
なお、これらの製造方法は一例であって、これら以外に公知の製造方法を採用することもできる。
以下に示す炭素繊維配向熱伝導層1~4を作製した。
液状の高分子組成物として付加反応型シリコーンであって、アルケニル基含有ポリオルガノシロキサン(主剤)とオルガノハイドロジェンポリシロキサン(硬化剤)の混合物(比重:1.0)に、炭素繊維粉末(平均繊維長:100μm、比重:2.2)、熱伝導性充填材1として粒径3μmでアスペクト比が略1である球状酸化アルミニウム(比重:4.0)と、熱伝導性充填材2として粒径10μmでアスペクト比が略1である球状酸化アルミニウム(比重:4.0)とを表1に示す割合(それぞれ質量部で示す)で配合して、この組成物が均一になるように混合攪拌した後に脱泡して炭素繊維配向熱伝導層1用の混合組成物を調製した。なお、炭素繊維粉末と熱伝導性充填材は予めシランカップリング剤で表面処理したものを用いた。
炭素繊維配向熱伝導層1を製造した際の混合組成物中の各成分の配合を変更して、炭素繊維配向熱伝導層1と同様の方法で炭素繊維配向熱伝導層2~4を作製した。炭素繊維配向熱伝導層2~4となる混合組成物中の各成分の配合(質量部)を表1に示す。この炭素繊維配向熱伝導層2~4も厚みが2.0mmおよび10.0mmの試験片として作製した。
以下に示す絶縁熱伝導層1~8を作製した。
液状の高分子組成物として炭素繊維配向熱伝導層1に用いたものと同じ付加反応型シリコーン(主剤および硬化剤)に、絶縁性熱伝導性充填材として前記熱伝導性充填材1と同じ粒径3μmでアスペクト比が略1である球状酸化アルミニウム(比重:4.0)と、絶縁性熱伝導性充填材3として粒径40μmでアスペクト比が略1である球状酸化アルミニウム(比重:4.0)とを表2で示す割合(それぞれ質量部で示す)で配合し、攪拌混合した後に脱泡して絶縁熱伝導層1用の混合組成物を調製した。絶縁性熱伝導性充填材も予めシランカップリング剤で表面処理したものを用いた。続いて、この混合組成物を、金型成形でシート状に成形し、120℃で30分間加熱して絶縁熱伝導層1を得た。この絶縁熱伝導層1は厚みが0.10mm、0.15mm、0.25mm、0.50mm、0.75mm、10.0mmの各試験片として作製した。
絶縁熱伝導層1を製造した際の混合組成物の配合を表2に示す配合(質量部)に変更して、絶縁熱伝導層1と同様の方法で絶縁熱伝導層2~8を作製した。絶縁熱伝導層4,5に添加した可塑剤は、ジメチルポリシロキサン(シリコーンオイル)(粘度100mPa・s)である。
絶縁熱伝導層2~8は厚みが0.5mmおよび10.0mmの試験片として作製したが、絶縁熱伝導層6については、厚みが0.25mm、0.75mmの試験片も作製した。
以下に示す熱伝導性シート1~21を作製した。
上記炭素繊維配向熱伝導層1~4と、絶縁熱伝導層1~8から、次の表3~5で示すように、炭素繊維配向熱伝導層と絶縁熱伝導層を選択し、その選択した炭素繊維配向熱伝導層と絶縁熱伝導層とを積層して熱伝導性シート1~19を作製した。
炭素繊維配向熱伝導層1~4と絶縁熱伝導層1~8は、何れも表面が微粘着性を有しており、直接重ねるだけで容易に剥がれることはなく一体化することができる。
炭素繊維配向熱伝導層1に、絶縁熱伝導層を設けなかったものを熱伝導シート20とした。
炭素繊維配向熱伝導層1に、絶縁熱伝導層との比較としてのポリイミドフィルム(熱伝導率が0.16W/m・Kで、厚みが50μm)を積層したものを熱伝導性シート21とした。
<硬さの測定>
炭素繊維配向熱伝導層1~4については、タイプEデュロメータを用いて厚みが10.0mmの試験片のE硬度を測定した。その結果を表3~5に示す。また、絶縁熱伝導層1~8については、タイプEデュロメータを用いて厚みが10.0mmの試験片のE硬度を測定した。その結果も表3~5に示す。(注:表3~5で示す炭素繊維配向熱伝導層や絶縁熱伝導層の厚みは10.0mmではないが、E硬度は原則として厚みに依存しないため10.0mm厚での測定結果を記した)
上記硬さとは別の硬さの指標とするため針入度を測定した。より具体的には、熱機械分析装置(島津製作所製、TMA-50)にて直径0.5mmの円柱状の突起を備えた針入用プローブを用い、縦10mm×横10mmにカットした各試験片をセットした後、荷重レートを1g/min、目標荷重を0.5gとして23℃で3分間(即ち、荷重は最初の30秒で0から0.5gに上昇し、30秒から3分まで0.5gで一定である)のプローブの沈み込み深さを測定した。その結果を表3~5に示す。
この図1で示すように、針入度は試験片厚みの影響を受けるが、こうした関係式を導いておけば、ある厚みの試験片の針入度を測定することで、この関係式を利用してE硬度を推測することができる。即ち、厚みが2mmや0.5mmの試験片であれば、図1で示される2つの関係式に実測した針入度を代入すればE硬度が求められる。また、厚みが2mmや0.5mm以外であっても、この両関係式と同様にして予め特定の長さに対する関係式を作成しておけば、その関係式に実測した針入度を代入してE硬度を推測することができる。
この間の値はまた、炭素繊維配向熱伝導層側から測定した針入度と、絶縁熱伝導層側から測定した針入度で異なり、炭素繊維配向熱伝導層よりも絶縁熱伝導層が硬ければ、絶縁熱伝導層側から測定した針入度の方が低い(硬い)値となる。
縦10mm×横10mmにカットした試験片を、発熱基板(発熱量Q:25W)とヒートシンク(株式会社アルファ製「FH60-30」)との間に挟み、ヒートシンクに一定の荷重(2kgf/cm2)を加えた。このヒートシンクの上部には、冷却ファン(風量0.01kg/sec、風圧49Pa)が取り付けられており、ヒートシンク及び発熱基板には温度センサが接続されている。冷却ファンを作動させた状態で、発熱基板に通電する。通電の開始後、5分経過した時点で、発熱基板の温度(T1)及びヒートシンクの温度(T2)を測定し、各温度を次の式(2)に代入することにより各試験片の熱抵抗値を算出した。
熱抵抗値(℃/W)=(T1-T2)/発熱量Q ・・・ 式(2)
熱抵抗値(℃/W)=熱通過方向厚み(m)/(熱通過断面積(m2)×熱伝導率(W/m・K))・・・式(3)
こうして得た熱伝導率の値を表3~5に示す。
絶縁性の評価の指標となる絶縁破壊電圧を測定した。2つの電極の間に試験片を挟み込んだ後に200gの荷重をかけた状態で電圧を徐々に上げていくと、電流が急激に増加し、試験片の一部が溶けて孔が空いたり炭化したりして通電するようになるが、この際の電圧が絶縁破壊電圧である。より具体的には、JIS K6249に基づき、耐電圧試験器(TOS8650、菊水電子工業株式会社製)を用いて絶縁破壊電圧を測定した。試験片はそれぞれ5つ準備して5回試験を行った。表3~5には5回の平均値を示す。
熱伝導性シート表面の粘着性を試験した。水平に配置したステンレス板の上に、縦10mm×横10mmにカットした熱伝導性シートの試験片を置き、その上に剥離フィルムを介して200gの重りを10秒間置いて熱伝導性シートをステンレス板に押し付けた。その後、ステンレス板を180度反転させたときに、10秒の間に試験片が剥離して落下するか否かを試験した。なお、ステンレス板としては、表面仕上げが2Bのものを用い、ステンレス板へ熱伝導性シートを置く際には、炭素繊維配向熱伝導層側を置く場合と、絶縁熱伝導層側を置く場合の両方で試験を行った。表3~5には炭素繊維配向熱伝導層側を置いた場合/絶縁熱伝導層側を置いた場合、の順に評価結果を示す。
<硬さ>
硬さがE30の炭素繊維配向熱伝導層に種々の硬さの絶縁熱伝導層を積層した熱伝導性シート1~6を比較すると、最も柔軟な硬さE10の絶縁熱伝導層を積層した熱伝導性シート2は、熱伝導率では最も良い結果であったが、絶縁破壊電圧が0kV/mmとなり所望の絶縁性を備えていなかった。また、硬さがE18の絶縁熱伝導層を積層した熱伝導性シート5は、絶縁破壊電圧の平均値は4kV/mmであるが、5回のうちの1回だけ0kV/mmという測定結果となった。また、硬さがE25、E40、E70、E80の絶縁熱伝導層を積層した熱伝導性シート1、3、4、6は、何れも絶縁破壊電圧が5kV/mmを超えていた。こうした結果から絶縁熱伝導層が柔らかいほど熱伝導率が高くなる傾向が見られた。
種々の熱伝導率の炭素繊維配向熱伝導層と絶縁熱伝導層とを組合せた熱伝導性シート1、9~13を比較する。熱伝導性シート1、9、10は、熱伝導率が12.9W/m・Kの炭素繊維配向熱伝導層に、それぞれ熱伝導率が5.0W/m・K、1.5W/m・K、2.5W/m・Kの絶縁熱伝導層を積層した熱伝導性シートである。熱伝導率が5.0W/m・Kの絶縁熱伝導層を積層した熱伝導性シート1は、熱伝導率が高いだけでなく、絶縁熱伝導層を積層したことによる熱伝導率の低下が小さく、炭素繊維配向熱伝導層の熱伝導率に極めて近い熱伝導率を備えることがわかる。このことは、熱伝導率が11.5W/m・Kの炭素繊維配向熱伝導層に、熱伝導率がそれぞれ1.5W/m・K、2.5W/m・K、5.0W/m・Kの絶縁熱伝導層を積層した熱伝導性シート11~13でも同様であった。
熱伝導性シート14、15は、厚みが0.10mm、0.15mmの絶縁熱伝導層を積層したものである。絶縁熱伝導層の厚みが0.15mmの熱伝導性シート15は、3.0kV/mmの絶縁破壊電圧を備えていたが、厚みが0.10mmの熱伝導性シート14は、絶縁破壊電圧が1.5kV/mmまで低下していた。このことから、絶縁熱伝導層の厚みは、0.15mm以上であることが好ましいことがわかる。
熱伝導性シート16~19と、熱伝導性シート1、9は、熱伝導率が12.9W/m・Kで厚みが2mmの炭素繊維配向熱伝導層に、熱伝導率が1.5W/m・Kまたは5.0W/m・Kの絶縁熱伝導層について、厚みを0.25mm、0.50mm、0.75mmと変化させたものを積層した熱伝導性シートである。
これらの絶縁熱伝導層の厚みをx軸に、熱伝導性シートの熱伝導率をy軸にプロットしたグラフを図2に示す。
この図3より、近似式としてy=0.20x-0.19を導き出すことができた。
そして、上式から、熱伝導率が11.0W/m・K以上の熱伝導性シートを得るための絶縁熱伝導層の熱伝導率W(x)(単位:W/m・K)と厚さT(y)(単位:mm)
との関係を表す次の式(1)を導出した。
0<T≦0.20W-0.19 ・・・ 式(1)
絶縁破壊電圧については、3kV/mm以上のものについて“○”、3kV/mm未満のものについて“×”と評価した。この結果も表3~5に示す。
絶縁破壊電圧の測定において、測定結果のばらつきの大きさを評価した。より具体的には、平均値が3kV/mmを超えるものの、5回の測定のうち1回以上0kV/mmとなったものを“×”とし、そうでないものを“○”とした。
熱伝導率の高い炭素繊維配向熱伝導層に対してそれよりは熱伝導率が低い絶縁熱伝導層を積層したことによる熱伝導率の低下の程度を評価した。即ち、次の式(4)で示すように炭素繊維配向熱伝導層の熱伝導率から熱伝導性シートの熱伝導率を引き、炭素繊維配向熱伝導層の熱伝導率で割ったものを、炭素繊維配向熱伝導層に対する熱伝導性シートの熱伝導率の低下率(以下単に「熱伝導率の低下率」)と定義し、算出した。
熱伝導率の低下率=(炭素繊維配向熱伝導層の熱伝導率-熱伝導性シートの熱伝導率)/炭素繊維配向熱伝導層の熱伝導率・・・式(4)
熱伝導性シートは、表面に粘着性を有することで被着体に固定することができ、電子機器への装着作業が容易になる。そこで、この被着体への固定の可否を取扱い性という観点から評価した。上記粘着性の試験において、10秒の間に熱伝導性シートの試験片が剥離して落下したものを取扱い性が悪いとして“×”、落下しなかったものを “○”と評価した。
以上のように、種々の観点からの評価を総合した総合評価を各熱伝導性シートについて行った。絶縁性の全くない(絶縁破壊電圧の評価が×)熱伝導性シート2、14、20、および熱伝導率の低下率と取扱い性について×であった熱伝導性シート21は、総合評価を×とした。そうした一方で何れの評価についても×がなかったものを“◎”とした。また、評価に△があるものを“○”、さらに、絶縁破壊電圧の評価以外の何れかの評価に×があるものを“△”と評価した。こうした総合評価も表3~5に示す。
以上より、取扱い性が悪く絶縁性または熱伝導率の低下率の激しい樹脂フィルムを用いる熱伝導性シートと比較して、炭素繊維配向熱伝導層と絶縁熱伝導層を積層した熱伝導性シートはそれらの2つ以上の特性が悪いということはない。また、所定の硬さや、厚み、熱伝導率等を備える熱伝導性シートは、取扱い性も熱伝導性も良く優れた性質を備えた熱伝導性シートである。
Claims (9)
- 高分子マトリクスに繊維軸がシートの厚み方向に配向している炭素繊維粉末を含む炭素繊維配向熱伝導層と、高分子マトリクスに絶縁性熱伝導性充填材が分散しており熱伝導性と絶縁性とを備える絶縁熱伝導層と、を積層した熱伝導性シート。
- 高分子マトリクスが液状シリコーンの主剤と硬化剤の硬化体からなるものである請求項1記載の熱伝導性シート。
- 炭素繊維配向熱伝導層は、日本工業規格であるJIS K6253のタイプEの硬度計によって測定されるE硬度が5~60であり、
絶縁熱伝導層は、炭素繊維配向熱伝導層よりも硬く、E硬度が70以下であり、且つ厚みが0.15~1.5mmである請求項1または請求項2記載の熱伝導性シート。
- 炭素繊維配向熱伝導層のシートの厚み方向の熱伝導率が7W/m・K以上で30W/m・K以下であり、絶縁熱伝導層の熱伝導率が2W/m・K以上で7W/m・K未満であり、炭素繊維配向熱伝導層の厚み方向の熱伝導率を絶縁熱伝導層の熱伝導率よりも高くした請求項1~請求項3何れか1項記載の熱伝導性シート。
- 絶縁熱伝導層の熱伝導率(W)(単位:W/m・K)と、厚み(T)(単位:mm)とが、次の式(1)の関係を満たす請求項1~請求項4何れか1項記載の熱伝導性シート。
0<T≦0.20W-0.19 ・・・ 式(1)
- 絶縁熱伝導層の厚みが炭素繊維配向熱伝導層の厚みよりも薄い請求項1~請求項5何れか1項記載の熱伝導性シート。
- 絶縁熱伝導層の熱伝導率が5W/m・K以上である請求項1~請求項6何れか1項記載の熱伝導性シート。
- 絶縁熱伝導層の硬さがE硬度で20以上である請求項1~請求項7何れか1項記載の熱伝導性シート。
- 炭素繊維配向熱伝導層にアスペクト比が2以下の熱伝導性充填材を含む請求項1~請求項8何れか1項記載の熱伝導性シート。
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JP6723610B2 (ja) | 2020-07-15 |
JPWO2016208458A1 (ja) | 2018-05-24 |
DE112016000807T5 (de) | 2017-11-30 |
DE112016000807B4 (de) | 2022-05-25 |
CN107851623B (zh) | 2021-04-16 |
US20180292148A1 (en) | 2018-10-11 |
US10591229B2 (en) | 2020-03-17 |
CN107851623A (zh) | 2018-03-27 |
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