High thermal conductivity material

Abstract

To provide a material having high thermal conductivity that contains an aluminum nitride fiber sheet and a resin.SOLUTION: An aluminum nitride fiber sheet is made of continuous fiber of aluminum nitride, having a specific surface area of 30 m2 / g or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aluminum nitride fiber sheet and a high thermal conductivity material.

Background Art

[0002] In recent years, miniaturization and weight reduction of electronic devices have been progressing in the automotive and electrical industries. On the other hand, problems such as thermal runaway and thermal fatigue due to an increase in the amount of heat generated have become issues. Metals typified by aluminum have high thermal conductivity, but have problems from the viewpoints of weight and electrical insulation. High thermal conductivity resin materials are superior in terms of weight reduction and electrical insulation compared to high thermal conductivity metal materials, and replacement is expected. Therefore, improvement of the thermal conductivity of resins by compounding a filler having high thermal conductivity and electrical insulation into the resin has been widely studied.

[0003] In order to maintain the advantages such as the light weight and processability of the resin, it is important to add a small amount of a thermal conductivity filler and efficiently form a heat conduction path. From such a viewpoint, particulate, plate-like or fibrous shapes of the thermal conductivity filler have been studied. For example, Patent Document 1 discloses a thermoplastic resin composition in which three high thermal conductivity alumina particles having different particle diameters are compounded. Patent Document 2 discloses a thermoplastic resin composition in which a high thermal conductivity inorganic fiber and a high thermal conductivity inorganic powder are compounded. Patent Document 3 describes the high thermal conductivity and flexibility of a thermal conduction material in which a woven alumina fiber is coated with silicone rubber.

[0004] The present inventors have reported the use of alumina fibers as continuous fiber-like heat conductive fillers (Non-Patent Documents 1, 2, Patent Document 4). Alumina fibers can be obtained by electrospinning a spinning solution in which boehmite particles are dispersed in an aqueous polyvinyl alcohol (PVA) solution and removing the PVA by firing. Then, a sheet in which alumina fibers are combined with a resin is used as a high heat conductive material. In addition, the use of magnesia fibers as continuous fiber-like heat conductive fillers has been reported (Non-Patent Document 3). Magnesia fibers can be obtained by electrospinning a spinning solution in which magnesium diethoxide is heated and dissolved in an aqueous PVA solution and removing the PVA by firing. Then, a sheet in which magnesia fibers are combined with a resin is used as a highly conductive material.

[0005] Aluminum nitride is expected to have a higher thermal conductivity than alumina and magnesia. Patent Document 5 describes the thermal conductivity of a heat conductive material in which aluminum nitride fibers and a resin are combined, but it is 6 W / mK or less, which is insufficient. Since the aspect ratio of the aluminum nitride fibers is small and they are short fibers, it is considered that an effective heat conduction path is not formed, resulting in low thermal conductivity. Although it is described that long fibers may be used to improve the thermal conductivity, when combined with a resin, an aspect ratio of 1,000 or less is preferred. In addition, specific examples of long fiber and resin composites are not shown.

[0006] Patent Document 6 describes the thermal conductivity of a heat conductive material in which aluminum nitride fibers and a resin are combined, but it is 5 W / mK or less, which is insufficient. Since the aspect ratio of the inorganic fibers is small and they are whisker-like (beard-like) short fibers, it is considered that an effective heat conduction path is not formed, resulting in low heat conduction.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Non-Patent Document

[0008]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention has been made in view of such circumstances, and an object thereof is to provide a high thermal conductivity material including an aluminum nitride fiber sheet and a resin.

Means for Solving the Problems

[0010] As a result of intensive studies to achieve the above object, the inventors have found that a composite in which a high thermal conductivity aluminum nitride fiber sheet made of aluminum nitride continuous fibers having a specific surface area of 30 m 2 / g or less is combined with a resin in an appropriate amount is excellent in thermal conductivity, and have completed the present invention.

[0011] That is, the present invention provides the following aluminum nitride fiber sheet and high thermal conductivity material. 1. An aluminum nitride fiber sheet made of continuous aluminum nitride fibers and having a specific surface area of 30 m 2 / g or less. 2. The aluminum nitride fiber sheet according to 1, wherein the continuous aluminum nitride fibers have an aspect ratio exceeding 1,000. 3. The aluminum nitride fiber sheet according to 1 or 2, wherein the continuous aluminum nitride fibers are composed of at least one selected from continuous aluminum nitride fibers oriented in a certain direction, non-oriented non-woven aluminum nitride fibers, and three-dimensionally connected continuous aluminum nitride fibers. 4. The aluminum nitride fiber sheet according to any one of 1 to 3, wherein the average fiber diameter of the continuous aluminum nitride fibers is 90 to 2,000 nm. 5. The aluminum nitride fiber sheet according to 4, wherein the average fiber diameter of the continuous aluminum nitride fibers is 140 to 1,000 nm. 6. The aluminum nitride fiber sheet according to any one of 1 to 5, wherein the specific surface area of the aluminum nitride fiber sheet is 20 m 2 / g or less. 7. A high thermal conductivity material comprising the aluminum nitride fiber sheet according to any one of 1 to 6 and a resin, wherein the aluminum nitride fiber sheet is contained in the high thermal conductivity material in an amount of 15 to 80% by volume. 8. The high thermal conductivity material according to 7, wherein the aluminum nitride fiber sheet is contained in the high thermal conductivity material in an amount of 20 to 75% by volume. 9. The high thermal conductivity material according to 7 or 8, wherein the high thermal conductivity material is in the form of a sheet. 10. The high thermal conductivity material according to 9, wherein the high thermal conductivity material is in the form of a sheet and has a thickness of 20 to 2,000 μm. 11. The high thermal conductivity material according to 10, wherein the high thermal conductivity material is in the form of a sheet and has a thickness of 40 to 1,500 μm. 12. The resin is at least one selected from the group consisting of polyvinyl alcohol, polyvinyl butyral, polyurethane resin, epoxy resin, polyimide resin, styrene resin, and silicone resin, and is any one of the high thermal conductivity materials of 7 to 11. 13. The high thermal conductivity material has a thermal conductivity of 7.0 W / mK or more and is any one of the high thermal conductivity materials of 7 to 12. 14. The high thermal conductivity material of 13 has a thermal conductivity in the direction parallel to the fiber of 10.0 W / mK or more. 15. The high thermal conductivity material is electrically insulating, and the surface resistance value of the high thermal conductivity material is 1×10 13 Ω / □ or more, and is any one of the high thermal conductivity materials of 7 to 14.

Advantages of the Invention

[0012] The high thermal conductivity material of the present invention contains an appropriate amount of aluminum nitride continuous fibers, so it has excellent thermal conductivity.

Brief Description of the Drawings

[0013]

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BEST MODE FOR CARRYING OUT THE INVENTION

[0014] [Aluminum Nitride Fiber Sheet] The aluminum nitride fiber sheet of the present invention is composed of continuous aluminum nitride fibers (hereinafter also referred to as aluminum nitride fibers).

[0015] The specific surface area of the aluminum nitride fiber is 30 m 2 / g or less, preferably 25 m 2 / g or less, and more preferably 20 m 2 / g or less. By reducing the specific surface area, higher thermal conductivity can be obtained. In the present invention, the specific surface area is a measured value by the nitrogen adsorption method (BET method).

[0016] The aluminum nitride fiber may contain components other than aluminum nitride. Examples of components other than aluminum nitride include carbon, calcium oxide, alumina, magnesia, yttrium oxide, selenium oxide, iron oxide, and silicon oxide. When containing components other than aluminum nitride, the content is preferably 5% by mass or less, more preferably 1% by mass or less, and still more preferably 0.1% by mass or less in the aluminum nitride fiber.

[0017] The aluminum nitride fiber is a continuous fiber, and the aspect ratio represented by fiber length ÷ fiber diameter is preferably more than 1,000, and more preferably 2,000 or more. In particular, it is preferably a continuous fiber in which both ends cannot be distinguished due to the long fiber length and the aspect ratio cannot be determined. When the aluminum nitride fiber is combined with a resin, the aluminum nitride fiber is also cut when the composite is cut.

[0018] The aluminum nitride fiber preferably has an average fiber diameter of 90 to 2,000 nm, more preferably 140 to 1,000 nm. If the average fiber diameter is within the above range, the composite with the resin can be easily achieved. In the present invention, the average fiber diameter is a value obtained using image analysis software from a scanning electron micrograph of the aluminum nitride fiber. Further, the aluminum nitride fiber is preferably non-porous.

[0019] The aluminum nitride fiber is preferably sheeted in a state where it is oriented in a certain direction, or in a non-woven fabric state or a three-dimensional connected state where the aluminum nitride fiber is non-oriented. In this case, since there is no need for a process of weaving into a fabric state, it can be easily manufactured.

[0020] [Method for manufacturing an aluminum nitride fiber sheet] The method for manufacturing an aluminum nitride fiber sheet of the present invention (1) A step of producing a fiber sheet containing an aluminum source from a dispersion liquid containing an aluminum source and a water-soluble polymer, and (2) A step of firing the produced fiber sheet containing the aluminum source in a nitrogen atmosphere is included.

[0021] [Step (1)] Step (1) is a step of producing a fiber sheet containing an aluminum source and a water-soluble polymer from a dispersion liquid containing an aluminum source and a water-soluble polymer.

[0022] As the aluminum source, boehmite, alumina, aluminum nitrate, aluminum sulfate, aluminum acetate, aluminum oxalate, aluminum hydroxide, etc. are preferable, and particularly boehmite particles and alumina sol are preferable. Further, instead of the aluminum source, aluminum nitride fibers can also be obtained using aluminum nitride particles as a raw material.

[0023] The boehmite particles are not particularly limited, and examples thereof include "DISPERAL" and "DISPAL" manufactured by Sasol, "Cerasure" (registered trademark) manufactured by Kawai Lime Co., Ltd., and "Boehmite Powder" manufactured by Daimyo Chemical Industry Co., Ltd. etc. The alumina sol particles are not particularly limited, and examples thereof include alumina sols "AS-200", "AS-550", "AS-520" manufactured by Nissan Chemical Industries, Ltd., alumina sols "10A", "10C", "10D", "A2", "CSA-110A", "F-1000", "F-3000" manufactured by Kawaken Fine Chemicals Co., Ltd., and "Biral" (registered trademark) "Al-L7", "Al-ML15", "Al-C20", "AS-l10" etc. manufactured by Taki Chemical Co., Ltd. When using boehmite particles or alumina sol particles as the aluminum source, the primary particle diameter thereof is preferably 2 to 200 nm, more preferably 5 to 100 nm, from the viewpoints of dispersion stability in the spinning solution and sinterability during firing. In the present invention, the primary particle diameter is a measured value by the laser diffraction method. The aluminum source may be used alone or in combination of two or more. The content of the aluminum source is preferably 1 to 40% by mass, more preferably 2 to 30% by mass, still more preferably 3 to 20% by mass in the dispersion liquid.

[0024] The aluminum source may be used alone or in combination of two or more. The content of the aluminum source is preferably 0.5 to 40% by mass, more preferably 1 to 30% by mass, still more preferably 2 to 20% by mass in the dispersion liquid.

[0025] Examples of the water-soluble polymer include PVA, PVA derivatives, cellulose, cellulose derivatives, polyethylene glycol, polypropylene glycol, polyvinylpyrrolidone, poly(meth)acrylic acid, poly(meth)acrylate, polyvinyl acetate emulsion, polyvinylpyrrolidone, ethylene vinyl acetate copolymer emulsion, etc. These may be used alone or in combination of two or more. The content of the water-soluble polymer is preferably 3 to 20% by mass, more preferably 4 to 15% by mass, still more preferably 5 to 10% by mass in the dispersion liquid.

[0026] As the solvent that can be used in the dispersion liquid, water that can dissolve the water-soluble polymer and disperse the aluminum source is preferable. Further, two or more solvents soluble in water may be mixed. Examples of the solvent miscible with water include acetone, methanol, ethanol, isopropyl alcohol, butanol, ethyl methyl ketone (MEK), isobutyl methyl ketone (MIBK), propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether, butyl cellosolve, tetrahydrofuran (THF), 1,4-dioxane, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), cyclohexanone, ethyl lactate, diethylene glycol monoethyl ether, γ-butyrolactone, formic acid, acetic acid, trifluoroacetic acid, and the like. When other solvents are included, the content thereof is not particularly limited as long as the water-soluble polymer can be dissolved.

[0027] The fiber sheet is preferably produced by an electrospinning method, a freeze-drying method, or an emulsification method using the dispersion liquid.

[0028] A method for producing a fiber sheet by an electrospinning method will be described. FIG. 1 is a schematic explanatory view showing the electrospinning method in the present invention. In the electrospinning method, a spinning solution is ejected from a metal nozzle 2 to which a voltage is applied by a voltage supply device 1 to a grounded collector 3. During the scattering of the spinning solution, the solvent volatilizes, and the solid content accumulates on the collector 3 in the form of fibers. The electrospinning method is also called an electrofield spinning method or an electrospinning method.

[0029] The electrospinning method can be carried out using commercially available equipment. The spinning conditions are appropriately selected. For example, the spinning distance 4 (distance between the metal nozzle and the fiber collection collector) can be 5 to 30 cm, the applied voltage between the metal nozzle and the fiber collection collector can be 5 to 50 kV, and the spinning solution injection rate can be 0.1 to 5.0 mL / hour. As the fiber collection collector 3, a drum-shaped or flat-plate-shaped one can be used. When using a drum-shaped fiber collection collector, by rotating the drum at high speed, the fibers ejected from the metal nozzle are wound onto the drum, and a sheet with fibers oriented in a certain direction can be obtained. The rotation speed of the drum-shaped fiber collection collector is, for example, used at 50 to 5,000 revolutions per minute. When using a flat-plate-shaped fiber collection collector or when using a drum-shaped fiber collection collector at a low rotation speed, a non-woven fabric-like sheet composed of non-oriented fibers can be obtained.

[0030] [Step (2)] Step (2) is a step of producing an aluminum nitride fiber sheet by firing a fiber sheet containing an aluminum source and a water-soluble polymer prepared in step (1) under a nitrogen atmosphere and then performing re-firing under an air atmosphere.

[0031] The firing can be carried out using a firing furnace such as an electric furnace or a gas furnace. Also, the firing is preferably carried out under a nitrogen atmosphere under conditions where the carbon component derived from the water-soluble polymer disappears and alumina is reduced to aluminum nitride. The aluminum source is reduced by nitrogen with the carbon derived from the water-soluble polymer to become aluminum nitride. The method of firing a mixture of alumina and a carbon component under nitrogen to obtain aluminum nitride is generally called the reduction nitridation method.

[0032] The firing temperature is preferably a temperature at which the specific surface area of the aluminum nitride fiber sheet can be reduced in order to obtain high thermal conductivity, and is preferably 1,450°C or higher. The upper limit of the firing temperature is not particularly limited, but is preferably a temperature at which aluminum nitride does not melt, preferably 2,200°C or lower, and more preferably 1,600°C or lower in order to maintain the fiber shape. Incidentally, until the firing temperature is reached, it is preferable to raise the temperature at a rate of 20°C / min or lower. As the heating rate, 15°C / min or lower is more preferable, and 10°C / min or lower is more preferable. If the heating rate is within the above range, the disappearance of the carbon component derived from the water-soluble polymer, the reduction of the specific surface area of aluminum nitride, and the formation of pores proceed.

[0033] The firing time in a nitrogen atmosphere is preferably 3 hours or more, more preferably 5 hours or more, and even more preferably 10 hours or more. The upper limit of the firing time is not particularly limited, but is preferably 30 hours, more preferably 20 hours.

[0034] Following the firing in a nitrogen atmosphere, re-firing is performed in an air atmosphere. The re-firing temperature is preferably 700°C or lower, more preferably 600°C or lower. Within the above temperature range, re-oxidation of aluminum nitride is prevented, and the disappearance of carbon derived from the water-soluble polymer proceeds.

[0035] The re-firing time is preferably 1 hour or more, more preferably 3 hours or more, and even more preferably 5 hours or more. The upper limit of the re-firing time is not particularly limited, but is preferably 20 hours, more preferably 10 hours.

[0036] If the firing time and the re-firing time are within the above ranges, the formation of aluminum nitride proceeds, and the disappearance of the carbon component derived from the water-soluble polymer, the reduction of the specific surface area of aluminum nitride, and the formation of pores proceed.

[0037] The average fiber diameter of the aluminum nitride fiber is preferably 90 to 2,000 nm, and more preferably 140 to 1,000 nm. If the average fiber diameter is within the above range, the composite with the resin can be easily achieved, and the smoothness of the resin surface is not impaired.

[0038] Further, the thickness of the aluminum nitride fiber sheet is preferably 10 to 2,000 μm, more preferably 20 to 1,500 μm, and even more preferably 40 to 1,000 μm.

[0039] [High thermal conductivity material] The high thermal conductivity material of the present invention includes the aluminum nitride fiber sheet and a resin. Examples of the resin include PVA, PVA derivatives, polyvinyl acetate, polyvinyl butyral (PVB), polyvinyl pyrrolidone, polyurethane resins such as polyurethane elastomers, epoxy resins, polyimide resins, silicone resins, polyolefin resins such as polyvinylidene fluoride, (meth)acrylic resins such as polymethyl methacrylate, polyester resins such as polyethylene succinate / adipate, polystyrene, high impact polystyrene, acrylonitrile-styrene copolymers, acrylonitrile-butadiene-styrene copolymers, styrene-butadiene-styrene copolymers, polystyrene resins such as methyl methacrylate-styrene copolymers, polyamide resins, polyethylene, polypropylene, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, ethylene-ethyl acrylate copolymers, polycarbonate resins, vinyl chloride resins, polyacrylonitrile, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polylactic acid, poly-3-hydroxybutyric acid, polycaprolactone, polybutylene succinate, polyethylene oxide, polyphenylene ether resins, polyacetal resins, polyether sulfone resins, polysulfone resins, polyphenylene sulfide resins, polyglycolic acid, modified starch, cellulose derivatives such as cellulose acetate and cellulose triacetate, chitin, chitosan, lignin, etc. Among these, PVA, PVB, polystyrene resins, polyurethane resins, epoxy resins, polyimide resins, silicone resins, etc. are preferable. The resin may be used alone or in combination of two or more.

[0040] The lower limit of the content of the aluminum nitride fiber sheet in the high thermal conductivity material of the present invention is 10% by volume, but 15% by volume is more preferable. Further, the upper limit is 75% by volume, but 70% by volume is more preferable. By including the aluminum nitride fiber sheet within the above range, high thermal conductivity can be obtained.

[0041] The high thermal conductivity material of the present invention has high thermal conductivity. Specifically, the thermal conductivity can be 7.0 W / mK or more, preferably 10 W / mK or more, and more preferably 13 W / mK or more.

[0042] The high thermal conductivity material of the present invention can contain electrically insulating high thermal conductivity particles. Examples of such high thermal conductivity particles include aluminum nitride, alumina, magnesia, silica, boron nitride, silicon nitride, silicon carbide, boron carbide, diamond, and the like. The high thermal conductivity particles may be used alone or in combination of two or more.

[0043] The high thermal conductivity material of the present invention can contain inorganic fibers other than aluminum nitride. Examples of the inorganic fibers include glass fibers, alumina fibers, magnesia fibers, silica fibers, ceramic fibers, silicon carbide fibers, and rock fibers. The inorganic fibers may be used alone or in combination of two or more.

[0044] The high thermal conductivity material of the present invention is preferably electrically insulating. Specifically, the surface resistance value can be 1×10 11 Ω / square or more, preferably 1×10 12 Ω / square or more, and more preferably 1×10 13 Ω / square or more.

[0045] [Method for manufacturing a high thermal conductivity material] The high thermal conductivity material of the present invention can be manufactured by impregnating the aluminum nitride fiber sheet with a resin solution to form a composite of aluminum nitride fiber and resin. Note that only one sheet or a plurality of sheets of the aluminum nitride fiber sheet may be included in the composite.

[0046] In order for the obtained composite to exhibit high thermal conductivity, it is necessary to appropriately contain aluminum nitride fibers. The resin concentration in the resin solution is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. When the resin concentration exceeds 40% by mass, particularly when it is 50% by mass or more, the proportion of the resin in the resin solution is large, so the content of the resin in the composite is large, and the content of aluminum nitride fibers becomes low, and high thermal conductivity may not be exhibited. Note that the resin described above may be used alone or in combination of two or more.

[0047] The solvent used for the resin solution is not particularly limited as long as it can dissolve the resin. For example, water, acetone, methanol, ethanol, isopropyl alcohol, butanol, MEK, MIBK, PGME, PGMEA, propylene glycol monoethyl ether, butyl cellosolve, THF, 1,4-dioxane, DMF, DMAc, NMP, cyclohexanone, ethyl lactate, diethylene glycol monoethyl ether, γ-butyrolactone, formic acid, acetic acid, trifluoroacetic acid, etc. may be mentioned. The solvent may be used alone or in combination of two or more.

[0048] Examples of the method of impregnating the fired aluminum nitride fiber sheet with the resin solution include a method of dropping a solution in which the resin is dissolved, a method of dropping a solution in which the monomer is dissolved and reacting the monomer in a subsequent heating step, and the like.

[0049] After impregnating a fired aluminum nitride fiber sheet with a resin solution, if necessary, perform depressurization and heat to remove the solvent and cure the resin to obtain a composite. At this time, depressurization is not necessary as long as the resin can be impregnated without gaps, but when depressurizing, it is preferably 1,000 Pa or less, and more preferably 100 Pa or less. Heating is not particularly limited as long as it can remove the solvent and cure the resin and the resin does not thermally decompose, but it is usually preferably performed at 100 to 140 °C, and more preferably at 110 to 130 °C. Also, the heating time is usually preferably 30 minutes or more, and more preferably 1 hour or more.

[0050] By the above method, a composite of an aluminum nitride fiber sheet and a resin containing the aluminum nitride fiber sheet can be manufactured. The thickness of the composite is preferably 20 to 4,000 μm, preferably 30 to 3,000 μm, and more preferably 40 to 1,500 μm.

[0051] The high thermal conductivity material of the present invention can be used as a heat dissipation material, and for example, can be suitably used as a flexible heat dissipation material for heat dissipation members such as heat dissipation sheets, heat dissipation tapes, heat dissipation circuit boards, heat dissipation housings, heat dissipation sealants, heat sinks, and heat pipes. Also, these heat dissipation members can be suitably used for devices such as LEDs, power semiconductors, CPUs, and lithium-ion batteries. Furthermore, these heat dissipation devices can be suitably used for, for example, digital household appliances such as mobile phones, smartphones, digital cameras, TVs, hard disk recorders, tablet computers, notebook computers, and desktop computers, next-generation automobiles such as hybrid vehicles, electric vehicles, and fuel cell vehicles, next-generation lighting devices such as household lighting, industrial lighting, and in-vehicle lighting, next-generation power generation devices such as solar cells, fuel cells, and geothermal power generation, and next-generation energy carrier manufacturing devices such as hydrogen production by water electrolysis.

Examples

[0052] Hereinafter, the present invention will be described more specifically with reference to production examples, examples, and comparative examples, but the present invention is not limited to the following examples.

[0053] In the following examples, the apparatuses and conditions used for sample preparation and physical property analysis are as follows. (1) Electrospinning method: Infusion pump (syringe pump): FP-1000 manufactured by Merck KGaA, High-voltage power supply: HR-40R0.75 manufactured by Matsueda Precision Co., Ltd. (2) Scanning electron microscope: VE-9800 manufactured by Keyence Corporation, or Miniscope TM3000 manufactured by Hitachi High-Technologies Corporation (3) X-ray diffractometer: MiniFlex 2 manufactured by Rigaku Corporation (Ni filter, CuKα ray, 30 kV, 15 mA) (4) Thermogravimetric analyzer: TG-DTA 2000SA manufactured by BRUKER (5) Thermal diffusivity measurement apparatus: Thermo Wave Analyzer TA-35 manufactured by BETTER Co., Ltd. (6) Specific surface area measurement apparatus: BELSORP-mini II manufactured by MicrotracBEL Corp. (7) Ultra-high insulation resistance meter: SM-8200 manufactured by Hioki E.E. Corporation (8) Firing furnace: High-temperature gas replacement furnace: AHRF-50KC-32P manufactured by Asahi Rika Seisakusho Co., Ltd.

[0054] Also, in the following examples, the reagents used are as follows. · PVA: Polyvinyl alcohol, manufactured by Fuji Film Wako Pure Chemical Corporation (average degree of polymerization: 1,500, saponification degree: 99%) · 10 mass% PVA aqueous solution: Prepared by dissolving the above polyvinyl alcohol in distilled water. · Boehmite powder: DISPERAL P2 manufactured by Sasol (alumina component 72%, primary particle diameter 20 nm) · Alkyl silicate silica: Silicate 40 manufactured by Tama Chemical Industry Co., Ltd. · Yttrium oxide: Reagent yttrium oxide manufactured by Kanto Chemical Co., Inc. · PVB: Polyvinyl butyral, Mobital manufactured by Kuraray Co., Ltd. · Ethanol: Manufactured by Junsei Chemical Co., Ltd. · PU Emulsion: Polyurethane Emulsion, Superflex 300 manufactured by Daiichi Kogyo Seiyaku Co., Ltd., solid content 30% by mass · Silicone Resin: KR-112 manufactured by Shin-Etsu Chemical Co., Ltd., solid content 70% by mass · Toluene: Manufactured by Tokyo Chemical Industry Co., Ltd. · Triglycidyl Isocyanurate: TEPIC manufactured by Nissan Chemical Industries, Ltd. · Phenol Novolak Resin: Phenolite TD213 manufactured by DIC Corporation · NMP: Manufactured by Junsei Chemical Co., Ltd. · 2-Ethyl-4-methylimidazole: Manufactured by Kanto Chemical Co., Inc.

[0055] In the following examples, the average fiber diameter of the aluminum nitride fibers is the average value obtained by measuring the fiber diameter at 10 locations using the image analysis software "Adobe Photoshop CS3" from the scanning electron micrograph of the aluminum nitride fibers. The average fiber length of the aluminum nitride fibers is the average value obtained by measuring the fiber length at 10 locations using the image analysis software "Adobe Photoshop CS3" from the scanning electron micrograph of the aluminum nitride fibers. The aspect ratio of the aluminum nitride fibers was calculated by the formula: aspect ratio = fiber length ÷ fiber diameter.

[0056] [1] Production of Aluminum Nitride Fiber Sheet [Example 1-1] To 10.0 parts by mass of a 10% by mass aqueous PVA solution, 0.598 parts by mass of boehmite powder as an aluminum source was added and stirred to disperse. 2 mL of the obtained aqueous dispersion was used as a spinning solution and filled into a syringe with a metal nozzle attached to the tip. As a collector for fiber collection, a rotating drum with a diameter of 15 cm was used. The metal nozzle and the drum collector were electrically connected to a voltage supply device. A voltage of 20 kV was applied to the metal nozzle side with the drum collector side grounded by the voltage supply device. The distance between the metal nozzle and the drum collector was adjusted to 15 cm. The drum collector was rotated at 4,000 revolutions per minute. By injecting the spinning solution from the syringe toward the rotating drum collector at an extrusion rate of 1.0 mL / h, fibers composed of PVA and boehmite were formed on the rotating drum collector, and a fiber sheet containing an aluminum source was obtained. The fiber sheet containing the aluminum source was placed in an electric furnace, and the temperature was raised to 1,500 °C at a heating rate of 10 °C / min under a nitrogen atmosphere (flow rate: 3.5 L / min). After firing at 1,500 °C for 10 hours, it was cooled to 600 °C and then reheated at 600 °C in the atmosphere for 5 hours. By cooling to room temperature, an aluminum nitride fiber sheet A was obtained. The X-ray diffraction pattern of the aluminum nitride fiber sheet A is shown in FIG. 2. The average fiber diameter of the aluminum nitride fibers in the aluminum nitride fiber sheet A was 170 nm. The specific surface area of the aluminum nitride fiber sheet A was 20.9 m 2 / g. Also, since the fiber length of the aluminum nitride fibers was long, both ends could not be identified, and the aspect ratio could not be calculated.

[0057] [Example 1-2] Aluminum nitride fiber B was produced in the same manner as in Production Example 1 except that the firing time under a nitrogen atmosphere was 4 hours. The formation of aluminum nitride fibers was confirmed from the X-ray diffraction pattern of the aluminum nitride fiber sheet F. The average fiber diameter of the aluminum nitride fibers in the aluminum nitride fiber sheet B was 200 nm. The specific surface area of the aluminum nitride fiber sheet B was 23.7 m2 It was / g. Also, since the fiber length of the aluminum nitride fiber was long, both ends could not be distinguished, and the aspect ratio could not be calculated.

[0058] [Example 1-3] To 10.0 parts by mass of a 10% by mass aqueous PVA solution, 0.598 parts by mass of boehmite powder as an aluminum source and 0.022 parts by mass of silicate 40 were added and stirred to disperse. 2 mL of the obtained aqueous dispersion was used as a spinning solution, and aluminum nitride fiber C was produced in the same manner as in Example 1-1. The X-ray diffraction pattern of the aluminum nitride fiber sheet C is shown in FIG. 3. The average fiber diameter of the aluminum nitride fibers in the aluminum nitride fiber sheet C was 190 nm. The specific surface area of the aluminum nitride fiber sheet C was 25.1 m 2 It was / g. Also, since the fiber length of the aluminum nitride fiber was long, both ends could not be distinguished, and the aspect ratio could not be calculated.

[0059] [Example 1-4] Aluminum nitride fiber D was produced in the same manner as in Example 1-3 except that the firing time under a nitrogen atmosphere was 20 hours. The X-ray diffraction pattern of the aluminum nitride fiber sheet D is shown in FIG. 4. The average fiber diameter of the aluminum nitride fibers in the aluminum nitride fiber sheet D was 200 nm. The specific surface area of the aluminum nitride fiber sheet D was 17.7 m 2 It was / g. Also, since the fiber length of the aluminum nitride fiber was long, both ends could not be distinguished, and the aspect ratio could not be calculated.

[0060] [Example 1-5] To 10.0 parts by mass of a 10% by mass aqueous PVA solution, 0.598 parts by mass of boehmite powder as an aluminum source, 0.022 parts by mass of silicate 40, and 0.0054 parts by mass of yttrium oxide were added and stirred to disperse. 2 mL of the obtained aqueous dispersion was used as a spinning solution, and aluminum nitride fiber E was produced in the same manner as in Example 1-1. The X-ray diffraction pattern of the aluminum nitride fiber sheet E is shown in FIG. 5. The aspect ratio of the aluminum nitride fibers in the aluminum nitride fiber sheet E could not be calculated because the fiber length was so long that both ends could not be distinguished.

[0061] [Example 1-6] Aluminum nitride fibers F were produced in the same manner as in Example 1-1, except that the fiber collector was changed from a drum collector to a flat plate collector. The formation of aluminum nitride fibers was confirmed from the X-ray diffraction pattern of the aluminum nitride fiber sheet F. The average fiber diameter of the aluminum nitride fibers in the aluminum nitride fiber sheet F was 190 nm. The specific surface area of the aluminum nitride fiber sheet F was 18.0 m 2 / g. Also, since the fiber length of the aluminum nitride fibers was long, both ends could not be distinguished and the aspect ratio could not be calculated.

[0062] [Example 1-7] An aluminum nitride fiber sheet G was obtained in the same manner as in Example 1-1, except that the firing temperature was 1,450 °C for 10 hours. The formation of aluminum nitride fibers was confirmed from the X-ray diffraction pattern of the aluminum nitride fiber sheet G. The aspect ratio of the aluminum nitride fibers in the aluminum nitride fiber sheet G could not be calculated because the fiber length was so long that both ends could not be distinguished.

[0063] [Example 1-8] To 10.0 parts by mass of a 10 mass% PVA aqueous solution, 0.598 parts by mass of boehmite powder as an aluminum source and 0.022 parts by mass of yttrium oxide were added and stirred to disperse. 2 mL of the obtained aqueous dispersion was used as a spinning solution, and aluminum nitride fibers H were produced in the same manner as in Example 1-1. The X-ray diffraction pattern of the aluminum nitride fiber sheet H is shown in FIG. 6. The specific surface area of the aluminum nitride fiber sheet H was 12.4 m 2 / g. In the aluminum nitride fiber sheet H, the aspect ratio of the aluminum nitride fibers could not be calculated because the fiber length was long and both ends could not be distinguished.

[0064] [Comparative Example 1-1] A fiber sheet I was obtained in the same manner as in Production Example 1, except that the firing conditions under nitrogen were 1,400 °C for 10 hours. Aluminum nitride could not be obtained from the X-ray diffraction pattern of the fiber sheet I. It is considered that the firing temperature was low and the reduction by nitrogen did not proceed.

[0065] [Comparative Example 1-2] A fiber sheet J was obtained in the same manner as in Production Example 1, except that the re-firing conditions in the air were 800 °C for 10 hours. From the X-ray diffraction pattern of the fiber sheet J, the formation of aluminum nitride was not confirmed, and alumina was confirmed. It is considered that the re-firing temperature was high and the aluminum nitride was re-oxidized to alumina by oxygen.

[0066] [2] Production of high thermal conductivity material In the following examples, the content (volume %) of the aluminum nitride fiber sheet in the composite sheet was measured as the mass % of the aluminum nitride fiber sheet content in the composite sheet by raising the temperature to 500 °C at 10 °C / min using a thermogravimetric analyzer, and the value was calculated from this value and the specific gravities of aluminum nitride and the resin.

[0067] [Example 2-1] PVB was dissolved in ethanol to a solid content of 5.0 mass %, and 136 mass parts of the PVB solution was impregnated into 24.9 mass parts of the aluminum nitride fiber sheet A. Water was removed at 120 °C under vacuum to obtain a sheet A1, which is a sheet-like composite of the aluminum nitride fiber sheet A and PVB. The thickness of the sheet A1 was 114 μm. For the sheet A1, the content of the aluminum nitride fiber sheet in the sheet A1 was measured by raising the temperature to 500 °C at 10 °C / min using a thermogravimetric analyzer. The content of the aluminum nitride fiber sheet in the sheet A1 was 54 volume %. From the scanning electron microscope observation of Sheet A1, it was confirmed that in Sheet A1, the aluminum nitride fibers were continuous fibers, and long fibers were compounded in a state of being oriented in a certain direction.

[0068] [Example 2-2] PVB was dissolved in ethanol to a solid content of 5.0% by mass, and 200 parts by mass of the PVB solution was impregnated into 24.5 parts by mass of the aluminum nitride fiber sheet B. Water was removed at 120 °C under vacuum to obtain Sheet B1, which is a sheet-like composite of the aluminum nitride fiber sheet A and PVB. The thickness of Sheet B1 was 106 μm. From the same measurement method as in Example 2-1, the content of the aluminum nitride fiber sheet in Sheet B1 was 45% by volume. The scanning electron micrograph of Sheet B1 is shown in Fig. 7. In Sheet B1, the aluminum nitride fibers were continuous fibers, and long fibers were compounded in a state of being oriented in a certain direction.

[0069] [Example 2-3] PVB was dissolved in ethanol to a solid content of 5.0% by mass, and 137 parts by mass of the PVB solution was impregnated into 25.1 parts by mass of the aluminum nitride fiber sheet C. Water was removed at 120 °C under vacuum to obtain Sheet C1, which is a sheet-like composite of the aluminum nitride fiber sheet C and PVB. The thickness of Sheet C1 was 154 μm. From the same measurement method as in Example 2-1, the content of the aluminum nitride fiber sheet in Sheet C1 was 54% by volume. From the scanning electron microscope observation of Sheet C1, it was confirmed that in Sheet C1, the aluminum nitride fibers were continuous fibers, and long fibers were compounded in a state of being oriented in a certain direction.

[0070] [Example 2-4] PVB was dissolved in ethanol to a solid content of 5.0% by mass, and 170 parts by mass of the PVB solution was impregnated into 25.5 parts by mass of an aluminum nitride fiber sheet D. Water was removed at 120 °C under vacuum to obtain a sheet D1, which is a sheet-like composite of the aluminum nitride fiber sheet D and PVB. The thickness of the sheet D1 was 130 μm. From the same measurement method as in Example 2-1, the content of the aluminum nitride fiber sheet in the sheet D1 was 47% by volume. Observation of the sheet D1 with a scanning electron microscope confirmed that in the sheet D1, the aluminum nitride fibers were continuous fibers, and the long fibers were combined in an oriented state in a certain direction.

[0071] [Example 2-5] PVB was dissolved in ethanol to a solid content of 7.5% by mass, and 205 parts by mass of the PVB solution was impregnated into 24.8 parts by mass of an aluminum nitride fiber sheet C. Water was removed at 120 °C under vacuum to obtain a sheet C2, which is a sheet-like composite of the aluminum nitride fiber sheet C and PVB. The thickness of the sheet C2 was 128 μm. From the same measurement method as in Example 2-1, the content of the aluminum nitride fiber sheet in the sheet C2 was 35% by volume. Observation of the sheet C2 with a scanning electron microscope confirmed that in the sheet C2, the aluminum nitride fibers were continuous fibers, and the long fibers were combined in an oriented state in a certain direction.

[0072] [Example 2-6] PVB was dissolved in ethanol to a solid content of 2.5% by mass, and 110 parts by mass of the PVB solution was impregnated into 24.7 parts by mass of an aluminum nitride fiber sheet C. Water was removed at 120 °C under vacuum to obtain a sheet C3, which is a sheet-like composite of the aluminum nitride fiber sheet C and PVB. The thickness of the sheet C3 was 189 μm. From the same measurement method as in Example 2-1, the content of the aluminum nitride fiber sheet in the sheet C3 was 73% by volume. The scanning electron micrograph of sheet C3 is shown in Fig. 8. In sheet C3, the aluminum nitride fibers were continuous fibers, and long fibers were combined in an oriented state in a certain direction.

[0073] [Example 2-7] PVB was dissolved in ethanol to a solid content of 20% by mass, and 110 parts by mass of the PVB solution was impregnated into 22.0 parts by mass of the aluminum nitride fiber sheet F2. Water was removed at 120 °C under vacuum to obtain sheet F1, which is a sheet-like composite of the aluminum nitride fiber sheet F and PVB. The thickness of sheet F1 was 120 μm. From the same measurement method as in Example 2-1, the content of the aluminum nitride fiber sheet in sheet F1 was 25% by volume. From the scanning electron microscope observation of sheet F1, in sheet F1, the aluminum nitride fibers were continuous fibers, and long fibers were combined in a non-oriented state.

[0074] [Example 2-8] PVA was dissolved in distilled water to a solid content of 10% by mass, and the PVA solution was impregnated into the aluminum nitride fiber sheet H. Water was removed at 120 °C under vacuum to obtain sheet H1, which is a sheet-like composite of the aluminum nitride fiber sheet H and PVA. The thickness of sheet H1 was 60 μm. For sheet H1, the content of the aluminum nitride fiber sheet in sheet H1 was measured by heating the sheet to 500 °C at a rate of 10 °C / min using a thermogravimetric analyzer. The content of the aluminum nitride fiber sheet in sheet H1 was 25% by volume.

[0075] [Example 2-9] A solution (solid content: 10% by mass) in which a silicone resin was diluted to 1 / 7 with toluene was prepared, and 240.0 parts by mass of the diluted solution was impregnated into 25.0 parts by mass of an aluminum nitride fiber sheet H. Removal of toluene and heat curing of the silicone resin were carried out at 150 °C to obtain Sheet H2, which is a sheet-like composite of the aluminum nitride fiber sheet H and the silicone resin. The thickness of Sheet H2 was 110 μm. Also, the content of the aluminum nitride fiber sheet in Sheet H2 was calculated to be 25% by volume.

[0076] [Example 2-10] A solution (solid content: 10% by mass) in which a PU emulsion was diluted to 1 / 3 with ethanol was prepared, and the aluminum nitride fiber sheet H was impregnated with the diluted solution. Removal of water was carried out at 120 °C under vacuum to obtain Sheet H3, which is a sheet-like composite of the aluminum nitride fiber sheet H and PU. The thickness of Sheet H3 was 59 μm. Regarding Sheet H3, the content of the aluminum nitride fiber sheet in Sheet H3 was measured by heating the temperature from room temperature to 500 °C at 10 °C / min using a thermogravimetric analyzer. The content of the aluminum nitride fiber sheet in Sheet H3 was 27% by volume.

[0077] [Example 2-11] 5.0 parts by mass of triglycidyl isocyanurate, 5.2 parts by mass of phenol novolac resin, and 92.0 parts by mass of NMP were added to a glass container and heated and stirred at 60 °C. The NMP solution was cooled to room temperature, 0.050 parts by mass of 2-ethyl-4-methylimidazole was added, and stirred to prepare an NMP solution with a solid content of 10% by mass. 340 parts by mass of the NMP solution was impregnated into 27.0 parts by mass of the aluminum nitride fiber sheet H. By heating at 100 °C for 5 minutes and then at 180 °C for 1 hour, Sheet H4, which is a sheet-like composite of the aluminum nitride fiber sheet and the epoxy resin, was obtained. The thickness of Sheet H4 was 41 μm. Also, the content of the aluminum nitride fiber sheet in Sheet H4 was calculated to be 25% by volume.

[0078] [Comparative Example 2-1] PVA was dissolved in distilled water to a solid content of 10% by mass and dropped onto a silicone sheet. After drying overnight at room temperature, water removal and heat curing of PVA were carried out at 120 °C to obtain a PVA sheet K1 not containing an aluminum nitride fiber sheet. The thickness of sheet K1 was 109 μm.

[0079] [Comparative Example 2-2] A toluene solution (solid content 10% by mass) in which the silicone resin was diluted to 1 / 7 with toluene was prepared and dropped onto a silicone sheet. After drying overnight at room temperature, toluene removal and heat curing of the silicone resin were carried out at 150 °C to obtain a silicone sheet K2 not containing an aluminum nitride fiber sheet. The thickness of sheet K2 was 111 μm.

[0080] [Comparative Example 2-3] An aqueous solution (solid content 10% by mass) in which the PU emulsion was diluted to 1 / 3 was prepared and dropped onto a silicone sheet. After drying overnight at room temperature, toluene removal and heat curing of PU were carried out at 150 °C to obtain a PU sheet K3 not containing an aluminum nitride fiber sheet. The thickness of sheet K3 was 126 μm.

[0081] [Comparative Example 2-4] An aqueous solution in which PVB was dissolved in ethanol to a solid content of 10% by weight was prepared and dropped onto a silicone sheet. After drying overnight at room temperature, ethanol removal and heat curing of PVB were carried out at 120 °C to obtain a PVB sheet K4 not containing an aluminum nitride fiber sheet. The thickness of sheet K4 was 105 μm.

[0082] [3] Evaluation of high thermal conductivity materials [Examples 3-1 to 3-11] For the sheets obtained in Examples 2-1 to 2-11, the thermal diffusivity was measured using a thermal diffusivity measuring device. The calculation from the thermal diffusivity to the thermal conductivity was based on the specific gravity of aluminum nitride of 3,300 kg / m 3 , the specific heat of aluminum nitride of 725 J / kg °C, and the specific gravity of PVB of 1,100 kg / m 3, the specific heat of PVB is 1,968 J / kg℃, and the specific gravity of the PU resin is 1,200 kg / m 3 , the specific heat of the PU resin is 1,900 J / kg℃, and the specific gravity of PVA is 1,250 kg / m 3 , the specific heat of PVA is 1,968 J / kg℃, and the specific gravity of the silicone resin is 1,060 kg / m 3 , the specific heat of the silicone resin is 1,200 J / kg℃, and the specific gravity of the epoxy resin is 1,400 kg / m 3 , the specific heat of the epoxy resin of 1,400 J / kg℃ was used. The specific gravity and specific heat of the sheet were calculated from the respective contents in the sheet.

[0083] For the sheets obtained in Examples 2-1 to 2-11, the thermal diffusivity was measured and the thermal conductivity was calculated. Table 1 shows the thermal conductivity in the direction parallel to the fiber (average value of 4 locations), the thermal conductivity in the direction perpendicular to the fiber (average value of 4 locations), the thermal conductivity in the plane direction of the sheet in which non-oriented fibers were combined (average of 4 locations), and the thermal conductivity in the sheet thickness direction (average value of 6 locations).

[0084]

Table 1

[0085] From the results shown in Table 1, the high thermal conductivity material of the present invention exhibited a high thermal conductivity of 7.0 W / mK or more.

[0086] [Comparative Examples 3-1 to 3-4] For the sheets obtained in Comparative Examples 2-1 to 2-4, the thermal diffusivity was measured and the thermal conductivity was calculated. Table 2 shows the thermal conductivity in the plane direction of the sheet (average of 4 locations) and the thermal conductivity in the sheet thickness direction (average value of 6 locations).

[0087]

Table 2

[0088] [Example 4-1] The volume resistivity of the sheet obtained in Example 2-1 was measured using a super insulation resistance meter. The obtained volume resistivity (average value of three measurements) was 1.0×10 15 Ω·cm. Since both PVB and aluminum nitride are electrically insulating, it is considered that the composite also exhibited sufficient electrical insulation.

Explanation of symbols

[0089] 1 Voltage supply device 2 Metal nozzle 3 Drum-type collector 4 Spinning distance

Claims

1. Aluminum nitride fiber sheet made of aluminum nitride continuous fibers with a specific surface area of 30 m 2 / g or less and a high thermal conductivity material containing a resin The aluminum nitride fiber sheet is contained in a high thermal conductivity material at 10 to 75% by volume, and the high thermal conductivity material has a thermal conductivity of 7.0 W / mK or more.

2. The high thermal conductivity material according to Claim 1, wherein the continuous aluminum nitride fiber has an aspect ratio exceeding 1,000.

3. The high thermal conductivity material according to Claim 1 or 2, wherein the continuous aluminum nitride fiber is composed of at least one selected from continuous aluminum nitride fibers oriented in a certain direction, non-woven fabric-like continuous aluminum nitride fibers without orientation, and three-dimensionally connected continuous aluminum nitride fibers.

4. The high thermal conductivity material according to any one of Claims 1 to 3, wherein the average fiber diameter of the continuous aluminum nitride fiber is 90 to 2,000 nm.

5. The high thermal conductivity material according to Claim 4, wherein the average fiber diameter of the continuous aluminum nitride fiber is 140 to 1,000 nm.

6. The specific surface area of the aluminum nitride fiber sheet is 20 m 2 / g or less, and the high thermal conductivity material according to any one of claims 1 to 5.

7. The high thermal conductivity material according to any one of Claims 1 to 6, wherein the resin is at least one selected from the group consisting of polyvinyl alcohol, polyvinyl butyral, polyurethane resin, epoxy resin, polyimide resin, styrene resin, and silicone resin.

8. The high thermal conductivity material according to any one of Claims 1 to 7, wherein the aluminum nitride fiber sheet is contained in the high thermal conductivity material at 15 to 70%.

9. The high thermal conductivity material according to any one of Claims 1 to 8, wherein the high thermal conductivity material is in the form of a sheet.

10. The high thermal conductivity material according to Claim 9, wherein the high thermal conductivity material is in the form of a sheet and has a thickness of 20 to 2,000 μm.

11. The high thermal conductivity material according to Claim 10, wherein the high thermal conductivity material is in the form of a sheet and has a thickness of 40 to 1,500 μm.

12. The high thermal conductivity material according to any one of Claims 9 to 11, wherein the continuous aluminum nitride fiber is a continuous aluminum nitride fiber oriented in a certain direction, and the thermal conductivity in the direction parallel to the fiber is 8.9 W / mK or more.

13. The high thermal conductivity material according to Claim 12, wherein the thermal conductivity in the direction parallel to the fiber is 10.0 W / mK or more.

14. The high thermal conductivity material is electrically insulating, and the surface resistance value of the high thermal conductivity material is 1×10 13 Ω / square or more. The high thermal conductivity material according to any one of claims 1 to 13.

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