JP7689713B2 - High thermal conductivity materials - Google Patents

Description

The present invention relates to an aluminum nitride fiber sheet and a highly thermally conductive material.

In recent years, electronic devices have become smaller and lighter in the automotive and electrical industries. However, problems such as thermal runaway and thermal fatigue caused by increased heat generation have arisen. Metals such as aluminum have high thermal conductivity, but have issues in terms of weight and electrical insulation. Highly thermally conductive resin materials are superior to highly thermally conductive metal materials in terms of weight reduction and electrical insulation, and are expected to replace these materials. Therefore, there has been extensive research into improving the thermal conductivity of resins by compounding highly thermally conductive and electrically insulating fillers with the resin.

In order to maintain the advantages of resins, such as their light weight and workability, it is important to add a small amount of thermally conductive filler and efficiently form a thermal conduction path. From this perspective, particulate, plate-like, or fibrous shapes of thermally conductive fillers are being considered. For example, Patent Document 1 discloses a thermoplastic resin composition that combines three highly thermally conductive alumina particles with different particle sizes. Patent Document 2 discloses a thermoplastic resin composition that combines highly thermally conductive inorganic fibers and highly thermally conductive inorganic powders. Patent Document 3 describes high thermal conductivity and flexibility for a thermally conductive material in which woven alumina fibers are coated with silicone rubber.

The present inventors have reported the use of alumina fiber as a continuous fibrous thermally conductive filler (Non-Patent Documents 1, 2, Patent Document 4). A spinning solution in which boehmite particles are dispersed in a polyvinyl alcohol (PVA) aqueous solution is electrostatically spun, and the PVA is removed by baking to obtain alumina fiber. The alumina fiber is then composited with resin to obtain a sheet, which is then used as a highly thermally conductive material. The present inventors have also reported the use of magnesia fiber as a continuous fibrous thermally conductive filler (Non-Patent Document 3). A spinning solution in which magnesium diethoxide is heated and dissolved in a PVA aqueous solution is electrostatically spun, and the PVA is removed by baking to obtain magnesia fiber. The magnesia fiber is then composited with resin to obtain a sheet, which is then used as a highly conductive material.

Aluminum nitride is expected to have a thermal conductivity higher than that of alumina and magnesia. Patent Document 5 describes the thermal conductivity of a thermally conductive material made by combining aluminum nitride fibers and resin, but it is insufficient at 6 W/mK or less. It is believed that the low thermal conductivity is due to the aluminum nitride fibers being short fibers with a small aspect ratio, which do not form an effective thermal conduction path. It describes that long fibers can be used to improve thermal conductivity, but when combined with resin, an aspect ratio of 1,000 or less is preferable. Furthermore, no specific examples of long fiber and resin composites are given.

Patent Document 6 describes the thermal conductivity of a thermally conductive material made of a composite of aluminum nitride fibers and resin, but it is insufficient at 5 W/mK or less. It is believed that the low thermal conductivity is due to the inorganic fibers having a small aspect ratio and being short whisker-like fibers, which do not form an effective thermal conduction path.

Japanese Patent Application Publication No. 5-132576 Japanese Patent Application Publication No. 8-283456 Patent No. 4343355 International Publication No. 2018-135517 JP 2020-1981 A JP 2018-154534 A

Koji Nakane et al., SENI GAKKAISHI Vol. 71, No. 1, 67 (2015) Koji Nakane et al., Journal of Textile Engineering, 65(4), 77-82 (2019) Koji Nakane et al., Journal of Materials Science: Materials in Electronics 30, 20566-20573(2019)

The present invention was made in consideration of these circumstances, and aims to provide a highly thermally conductive material that contains an aluminum nitride fiber sheet and a resin.

As a result of extensive research to achieve the above-mentioned objective, the inventors discovered that a composite comprising a highly thermally conductive aluminum nitride fiber sheet made of continuous aluminum nitride fibers with a specific surface area of 30 ^m2 /g or less and an appropriate amount of resin has excellent thermal conductivity, and thus completed the present invention.

That is, the present invention provides the following aluminum nitride fiber sheet and highly thermally conductive 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 aluminum nitride continuous fibers have an aspect ratio of more than 1,000.
3. The aluminum nitride fiber sheet according to 1 or 2, wherein the aluminum nitride continuous fibers are at least one selected from the group consisting of aluminum nitride continuous fibers oriented in a certain direction, non-oriented nonwoven fabric-like aluminum nitride continuous fibers, and aluminum nitride continuous fibers connected in a three-dimensional shape.
4. The aluminum nitride fiber sheet according to any one of 1 to 3, wherein the average fiber diameter of the aluminum nitride continuous fibers is 90 to 2,000 nm.
5. The aluminum nitride fiber sheet according to 4, wherein the average fiber diameter of the aluminum nitride continuous 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 highly thermally conductive material comprising an aluminum nitride fiber sheet according to any one of 1 to 6 and a resin,
The highly thermally conductive material contains the aluminum nitride fiber sheet at 15 to 80 volume % of the highly thermally conductive material.
8. The highly thermally conductive material according to 7, wherein the aluminum nitride fiber sheet is contained in the highly thermally conductive material in an amount of 20 to 75 volume %.
9. The highly thermally conductive material according to 7 or 8, wherein the highly thermally conductive material is in a sheet form.
10. The highly thermally conductive material of 9, wherein the highly thermally conductive material is in a sheet shape and has a thickness of 20 to 2,000 μm.
11. The highly thermally conductive material of 10, wherein the highly thermally conductive material is in a sheet shape and has a thickness of 40 to 1,500 μm.
12. The highly thermally conductive material according to any one of 7 to 11, 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.
13. Any of the highly thermally conductive materials of 7 to 12, having a thermal conductivity of 7.0 W/mK or more.
14. A highly thermally conductive material having a thermal conductivity parallel to the fibers of 10.0 W/mK or more.
15. The highly thermally conductive material according to any one of 7 to 14, wherein the highly thermally conductive material is electrically insulating and has a surface resistance of 1×10 ¹³ Ω/□ or more.

The highly thermally conductive material of the present invention has excellent thermal conductivity because it contains a moderate amount of aluminum nitride continuous fibers.

FIG. 1 is a schematic diagram illustrating an electrospinning method according to the present invention. FIG. 2 is an X-ray diffraction diagram of the aluminum nitride fiber sheet A obtained in Example 1-1. FIG. 1 is an X-ray diffraction diagram of the aluminum nitride fiber sheet C obtained in Example 1-3. FIG. 1 is an X-ray diffraction diagram of the aluminum nitride fiber sheet D obtained in Example 1-4. FIG. 1 is an X-ray diffraction diagram of the aluminum nitride fiber sheet E obtained in Example 1-5. FIG. 1 is an X-ray diffraction diagram of the aluminum nitride fiber sheet H obtained in Example 1-8. 1 is a scanning electron microscope photograph of the sheet B1 obtained in Example 2-2. 1 is a scanning electron microscope photograph of sheet C3 obtained in Example 2-6.

[Aluminum nitride fiber sheet]
The aluminum nitride fiber sheet of the present invention is made of continuous aluminum nitride fibers (hereinafter also referred to as aluminum nitride fibers).

The aluminum nitride fiber has a specific surface area of 30 ^m2 /g or less, preferably 25 ^m2 /g or less, and more preferably 20 ^m2 /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 value measured by a nitrogen adsorption method (BET method).

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 components other than aluminum nitride are contained, the content of the components other than aluminum nitride is preferably 5 mass% or less, more preferably 1 mass% or less, and even more preferably 0.1 mass% or less in the aluminum nitride fiber.

The aluminum nitride fiber is a continuous fiber, and preferably has an aspect ratio, expressed as fiber length divided by fiber diameter, of more than 1,000, and more preferably 2,000 or more. In particular, it is preferable for the fiber to be a continuous fiber whose fiber length is so long that both ends cannot be distinguished and whose aspect ratio cannot be determined. When the aluminum nitride fiber is composited with a resin, the aluminum nitride fiber is also cut when the composite is cut.

The aluminum nitride fibers preferably have an average fiber diameter of 90 to 2,000 nm, and more preferably 140 to 1,000 nm. If the average fiber diameter is within the above range, it is easy to achieve composite with resin. In the present invention, the average fiber diameter is a value determined from a scanning microscope photograph of the aluminum nitride fibers using image analysis software. In addition, it is preferable that the aluminum nitride fibers are non-porous.

It is preferable that the aluminum nitride fibers are oriented in a certain direction, or that the aluminum nitride fibers are formed into a sheet in a non-oriented nonwoven fabric or three-dimensional connected state. In this case, since there is no need for a process of weaving into a fabric, it can be easily manufactured.

[Method of manufacturing aluminum nitride fiber sheet]
The method for producing an aluminum nitride fiber sheet of the present invention comprises the steps of:
The method includes (1) a step of preparing 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 baking the prepared aluminum source-containing fiber sheet in a nitrogen atmosphere.

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

Preferable examples of the aluminum source include boehmite, alumina, aluminum nitrate, aluminum sulfate, aluminum acetate, aluminum oxalate, and aluminum hydroxide, with boehmite particles and alumina sol being particularly preferable. Aluminum nitride fibers can also be obtained using aluminum nitride particles as a raw material instead of the aluminum source.

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

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

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

A solvent that can be used in the dispersion liquid is preferably water, which can dissolve the water-soluble polymer and disperse the aluminum source. Furthermore, two or more solvents that dissolve in water may be mixed. Examples of solvents that can be mixed 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, and trifluoroacetic acid. When other solvents are included, the content is not particularly limited as long as the water-soluble polymer can be dissolved in them.

The fiber sheet is preferably produced using the dispersion by electrostatic spinning, freeze-drying or emulsification.

A method for producing a fiber sheet by electrostatic spinning is described below. Figure 1 is a schematic diagram showing the electrostatic spinning method of the present invention. In electrostatic spinning, a spinning solution is ejected from a metal nozzle 2 to which a voltage is applied by a voltage supply device 1 onto a grounded collector 3. The solvent evaporates as the spinning solution scatters, and the solids are accumulated in the form of fibers on the collector 3. Electrostatic spinning is also called electrospinning or electrospinning.

Electrostatic spinning can be performed using a commercially available device. The spinning conditions can be appropriately selected, for example, the spinning distance 4 (distance between the metal nozzle and the fiber collector) can be 5 to 30 cm, the voltage applied between the metal nozzle and the fiber collector can be 5 to 50 kV, and the spinning solution injection amount can be 0.1 to 5.0 mL/hour. The fiber collector 3 can be drum-shaped or flat. When a drum-shaped fiber collector is used, the fiber injected from the metal nozzle is wound around the drum by rotating the drum at high speed, and a sheet in which the fibers are oriented in a certain direction can be obtained. The rotation speed of the drum-shaped fiber collector is, for example, 50 to 5,000 rpm. When a flat fiber collector is used or when a drum-shaped fiber collector is used at a low rotation speed, a nonwoven sheet made of unoriented fibers can be obtained.

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

The calcination can be carried out in a calcination furnace such as an electric furnace or a gas furnace. The calcination is preferably carried out in a nitrogen atmosphere under conditions that eliminate the carbon components derived from the water-soluble polymer and reduce the alumina 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 obtaining aluminum nitride by calcining a mixture of alumina and carbon components under nitrogen is generally called the reduction-nitridation method.

The firing temperature is preferably a temperature at which the specific surface area of the aluminum nitride fiber sheet can be reduced 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 below which the aluminum nitride does not melt, and is preferably 2,200°C or lower, but more preferably 1,600°C or lower to maintain the fiber shape. It is preferable to increase the temperature at a rate of 20°C/min or lower until the firing temperature is reached. The rate of increase is more preferably 15°C/min or lower, and more preferably 10°C/min or lower. If the rate of increase is within the above range, the carbon components derived from the water-soluble polymer disappear, and the specific surface area of the aluminum nitride decreases and becomes non-porous.

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. There is no particular upper limit to the firing time, but it is preferably 30 hours, and more preferably 20 hours.

Following firing in a nitrogen atmosphere, re-firing is performed in an air atmosphere. The re-firing temperature is preferably 700°C or less, and more preferably 600°C or less. This temperature range prevents re-oxidation of aluminum nitride and promotes the loss of carbon derived from the water-soluble polymer.

The re-firing time is preferably 1 hour or more, more preferably 3 hours or more, and even more preferably 5 hours or more. There is no particular upper limit to the re-firing time, but it is preferably 20 hours, and more preferably 10 hours.

If the firing time and re-firing time are within the above ranges, the production of aluminum nitride will progress, the carbon components derived from the water-soluble polymer will disappear, and the specific surface area of the aluminum nitride will decrease and it will become non-porous.

The aluminum nitride fibers preferably have an average fiber diameter of 90 to 2,000 nm, and more preferably 140 to 1,000 nm. If the average fiber diameter is within this range, it is easy to combine with the resin, and the smoothness of the resin surface is not impaired.

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.

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

The lower limit of the content of the aluminum nitride fiber sheet in the highly thermally conductive material of the present invention is 10 volume percent, with 15 volume percent being more preferred. The upper limit is 75 volume percent, with 70 volume percent being more preferred. By including the aluminum nitride fiber sheet in the above range, high thermal conductivity can be obtained.

The highly thermally conductive 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.

The highly thermally conductive material of the present invention may contain electrically insulating highly thermally conductive particles. Examples of such highly thermally conductive particles include aluminum nitride, alumina, magnesia, silica, boron nitride, silicon nitride, silicon carbide, boron carbide, diamond, and the like. The highly thermally conductive particles may be used alone or in combination of two or more types.

The highly thermally conductive material of the present invention may contain inorganic fibers other than aluminum nitride. Examples of 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 types.

The highly thermally conductive material of the present invention is preferably electrically insulating. Specifically, the surface resistivity can be 1× ¹⁰ Ω/□ or more, preferably 1× ¹⁰ Ω/□ or more, and more preferably 1× ¹⁰ Ω/□ or more.

[Method of manufacturing highly thermally conductive material]
The highly thermally conductive material of the present invention can be produced by impregnating the aluminum nitride fiber sheet with a resin solution to form a composite of the aluminum nitride fiber and the resin. The composite may contain only one aluminum nitride fiber sheet or multiple aluminum nitride fiber sheets.

In order for the resulting composite to exhibit high thermal conductivity, it is necessary to include a moderate amount of aluminum nitride fiber. The resin concentration in the resin solution is preferably 40 mass% or less, more preferably 30 mass% or less, and even more preferably 20 mass% or less. If the resin concentration exceeds 40 mass%, particularly 50 mass% or more, the proportion of resin in the resin solution is high, so the resin content in the composite is high and the aluminum nitride fiber content is low, and high thermal conductivity may not be exhibited. The above-mentioned resins may be used alone or in combination of two or more types.

The solvent used in the resin solution is not particularly limited as long as it can dissolve the resin. Examples include 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, and trifluoroacetic acid. The solvent may be used alone or in combination of two or more.

Methods for impregnating a fired aluminum nitride fiber sheet with a resin solution include dripping a solution containing dissolved resin, dripping a solution containing dissolved monomer, and then reacting the monomer in a subsequent heating process.

After impregnating the fired aluminum nitride fiber sheet with the resin solution, a composite can be obtained by reducing the pressure as necessary and heating to remove the solvent and harden the resin. At this time, reducing the pressure is not necessary as long as the resin can be impregnated without any gaps, but if reducing the pressure, it is preferable to set the pressure at 1,000 Pa or less, and more preferably at 100 Pa or less. There are no particular restrictions on heating as long as it is possible to remove the solvent and harden the resin and the resin does not thermally decompose, but it is usually preferable to perform heating at 100 to 140°C, and more preferably at 110 to 130°C. The heating time is usually preferably 30 minutes or more, and more preferably 1 hour or more.

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

The highly thermally conductive material of the present invention can be used as a heat dissipation material, and 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. These heat dissipation members can be suitably used in devices such as LEDs, power semiconductors, CPUs, and lithium-ion batteries. These heat dissipation devices can be suitably used in digital home appliances such as mobile phones, smartphones, digital cameras, televisions, hard disk recorders, tablet computers, notebook computers, and desktop computers, next-generation automobiles such as hybrid automobiles, electric automobiles, and fuel cell automobiles, next-generation lighting devices such as home 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 production devices such as hydrogen production by water electrolysis.

The present invention will be explained in more detail below with reference to manufacturing examples, examples, and comparative examples, but the present invention is not limited to the following examples.

In the following examples, the apparatus and conditions used for sample preparation and analysis of physical properties are as follows.
(1) Electrostatic spinning method: Infusion pump (syringe pump): FP-1000 manufactured by Melquest Co., Ltd., High voltage power supply: HR-40R0.75 manufactured by Matsusada 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 diffraction device: Rigaku MiniFlex 2 (Ni filter, CuKα radiation, 30 kV, 15 mA)
(4) Thermogravimetric analyzer: BRUKER TG-DTA 2000SA
(5) Thermal diffusivity measuring device: Thermowave analyzer TA-35 manufactured by Bethel Corporation
(6) Specific surface area measuring device: BELSORP-mini II manufactured by Microtrack Bell Co., Ltd.
(7) Super insulation resistance meter: Hioki SM-8200
(8) Firing furnace: High-temperature gas replacement furnace: Asahi Rika Seisakusho AHRF-50KC-32P

In the following examples, the reagents used are as follows:
PVA: Polyvinyl alcohol, Fujifilm Wako Pure Chemical Industries, Ltd. (average polymerization degree: 1,500, saponification degree: 99%)
10% by weight PVA aqueous solution: prepared by dissolving the polyvinyl alcohol in distilled water.
Boehmite powder: DISPERAL P2 manufactured by Sasol (alumina content 72%, primary particle size 20 nm)
Alkyl silicate silica: silicate 40 manufactured by Tama Chemical Industry Co., Ltd.
Yttrium oxide: Kanto Chemical Co., Ltd. Reagent yttrium oxide PVB: Polyvinyl butyral, manufactured by Kuraray Co., Ltd. Ethanol: Manufactured by Junsei Chemical Co., Ltd. PU emulsion: Polyurethane emulsion, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Superflex 300, solid content 30% by mass
Silicone resin: Shin-Etsu Chemical Co., Ltd. KR-112, solid content 70% by mass
・Toluene: Tokyo Chemical Industry Co., Ltd. ・Triglycidyl isocyanurate: Nissan Chemical Co., Ltd. TEPIC
Phenol novolac resin: Phenolite TD213 manufactured by DIC Corporation
NMP: manufactured by Junsei Chemical Co., Ltd. 2-Ethyl-4-methylimidazole: manufactured by Kanto Chemical Co., Ltd.

In the following examples, the average fiber diameter of the aluminum nitride fiber is the average of 10 measurements of fiber diameter taken from a scanning microscope photograph of the aluminum nitride fiber using the image analysis software "Adobe Photoshop CS3". The average fiber length of the aluminum nitride fiber is the average of 10 measurements of fiber length taken from a scanning microscope photograph of the aluminum nitride fiber using the image analysis software "Adobe Photoshop CS3". The aspect ratio of the aluminum nitride fiber was calculated as aspect ratio = fiber length ÷ fiber diameter.

[1] Production of aluminum nitride fiber sheet [Example 1-1]
0.598 parts by mass of boehmite powder as an aluminum source was added to 10.0 parts by mass of a 10% by mass PVA aqueous solution, and the mixture was stirred to disperse. 2 mL of the resulting aqueous dispersion was used as a spinning solution, and filled into a syringe with a metal nozzle attached to the tip. A rotating drum with a diameter of 15 cm was used as a collector for collecting fibers. 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 being earthed, 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. The spinning solution was extruded from the syringe toward the rotating drum collector at an extrusion speed of 1.0 mL/h, forming fibers made of PVA and boehmite 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 heated to a firing temperature of 1,500°C at a heating rate of 10°C/min in a nitrogen atmosphere (flow rate 3.5 L/min). After firing at 1,500°C for 10 hours, the sheet was allowed to cool to 600°C and then re-fired in air at 600°C for 5 hours. Aluminum nitride fiber sheet A was obtained by cooling to room temperature. The X-ray diffraction diagram of aluminum nitride fiber sheet A is shown in Figure 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 ^m2 /g. Since the aluminum nitride fibers were too long, both ends could not be distinguished, and the aspect ratio could not be calculated.

[Example 1-2]
Except for changing the firing time in the nitrogen atmosphere to 4 hours, aluminum nitride fibers B were produced in the same manner as in Production Example 1. From the X-ray diffraction diagram of aluminum nitride fiber sheet F, the formation of aluminum nitride fibers was confirmed.
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 m ² /g. In addition, since the fiber length of the aluminum nitride fibers was so long that both ends could not be distinguished, the aspect ratio could not be calculated.

[Examples 1-3]
To 10.0 parts by mass of a 10% by mass PVA aqueous 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 dispersed by stirring. 2 mL of the resulting 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 diagram of aluminum nitride fiber sheet C is shown in FIG.
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 ^m2 /g. Since the aluminum nitride fibers were too long, both ends could not be distinguished, and the aspect ratio could not be calculated.

[Examples 1 to 4]
Aluminum nitride fiber sheet D was produced in the same manner as in Example 1-3, except that the firing time in the nitrogen atmosphere was set to 20 hours. The X-ray diffraction diagram of aluminum nitride fiber sheet D is shown in FIG.
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 /g. In addition, 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.

[Examples 1 to 5]
To 10.0 parts by mass of a 10% by mass PVA aqueous 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 dispersed by stirring. 2 mL of the resulting 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 diagram of aluminum nitride fiber sheet E is shown in FIG.
The aspect ratio of the aluminum nitride fibers in the aluminum nitride fiber sheet E could not be calculated because the fiber lengths were so long that both ends could not be distinguished.

[Examples 1 to 6]
Aluminum nitride fiber F was produced in the same manner as in Example 1-1, except that the collector for collecting the fibers was changed from a drum collector to a flat collector. The X-ray diffraction pattern of aluminum nitride fiber sheet F confirmed the production of aluminum nitride fibers.
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 ^m2 /g. In addition, since the fiber length of the aluminum nitride fibers was so long that both ends could not be distinguished, the aspect ratio could not be calculated.

[Examples 1 to 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. From the X-ray diffraction diagram of the aluminum nitride fiber sheet G, the formation of aluminum nitride fibers was confirmed.
The aspect ratio of the aluminum nitride fibers in the aluminum nitride fiber sheet G could not be calculated because the fiber lengths were so long that both ends could not be distinguished.

[Examples 1 to 8]
To 10.0 parts by mass of a 10% by 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 dispersed by stirring. 2 mL of the resulting aqueous dispersion was used as a spinning solution, and aluminum nitride fiber H was produced in the same manner as in Example 1-1. The X-ray diffraction diagram of aluminum nitride fiber sheet H is shown in Figure 6. The specific surface area of aluminum nitride fiber sheet H was 12.4 ^m2 /g.
The aspect ratio of the aluminum nitride fibers in the aluminum nitride fiber sheet H could not be calculated because the fiber lengths were so long that both ends could not be distinguished.

[Comparative Example 1-1]
Fiber sheet I was obtained in the same manner as in Production Example 1, except that the firing conditions under nitrogen were changed to 1,400° C. for 10 hours. From the X-ray diffraction pattern of fiber sheet I, aluminum nitride was not obtained. This is thought to be because the firing temperature was low and reduction by nitrogen did not proceed.

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

[2] Production of Highly Thermally Conductive Material In the following examples, the aluminum nitride fiber sheet content (volume %) in the composite sheet was determined by measuring the aluminum nitride fiber sheet content in the composite sheet in mass % by heating the sheet at 10°C/min up to 500°C using a thermogravimetric analyzer, and calculating from this value and the specific gravities of the aluminum nitride and resin.

[Example 2-1]
PVB was dissolved in ethanol to a solid content of 5.0 mass %, and 24.9 mass parts of aluminum nitride fiber sheet A were impregnated with 136 mass parts of the PVB solution. Water was removed under vacuum at 120° C. to obtain sheet A1, which was a sheet-like composite of aluminum nitride fiber sheet A and PVB. Sheet A1 had a thickness of 114 μm.
The aluminum nitride fiber sheet content in sheet A1 was measured by increasing the temperature of sheet A1 at 10° C./min to 500° C. The aluminum nitride fiber sheet content in sheet A1 was 54% by volume.
Observation of Sheet A1 with a scanning electron microscope confirmed that the aluminum nitride fibers in Sheet A1 were continuous fibers, and that the long fibers were compounded in a state where they were oriented in a fixed direction.

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

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

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

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

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

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

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

[Example 2-9]
A solution (solid content 10 mass%) was prepared by diluting silicone resin with toluene to 1/7, and 240.0 mass parts of the diluted solution was impregnated into 5.0 mass parts of aluminum nitride fiber sheet H2. The toluene was removed and the silicone resin was heat-cured at 150°C to obtain sheet H2, which was a sheet-like composite of aluminum nitride fiber sheet H and silicone resin. The thickness of sheet H2 was 110 μm. The content of aluminum nitride fiber sheet in sheet H2 was calculated to be 25 volume %.

[Example 2-10]
The PU emulsion was diluted with ethanol by one-third to prepare a solution (solid content: 10 mass%), and the aluminum nitride fiber sheet H was impregnated with the diluted solution. Water was removed under vacuum at 120° C. to obtain a sheet-like composite of the aluminum nitride fiber sheet H and PU, sheet H3. The thickness of sheet H3 was 59 μm.
The aluminum nitride fiber sheet content in Sheet H3 was measured by increasing the temperature of Sheet H3 to 500° C. at 10° C./min using a thermogravimetric analyzer. The aluminum nitride fiber sheet content in Sheet H3 was 27% by volume.

[Example 2-11]
In a glass container, 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 and heated and stirred at 60°C. The NMP solution was cooled to room temperature, and 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. 27.0 parts by mass of aluminum nitride fiber sheet H was impregnated with 340 parts by mass of the NMP solution. The sheet was heated at 100°C for 5 minutes and then at 180°C for 1 hour to obtain sheet H4, which is a sheet-like composite of aluminum nitride fiber sheet and epoxy resin. The thickness of sheet H4 was 41 μm. The aluminum nitride fiber sheet content in sheet H4 was calculated to be 25% by volume.

[Comparative Example 2-1]
PVA was dissolved in distilled water to a solid content of 10% by mass, and the solution was dropped onto a silicone sheet. After drying overnight at room temperature, water was removed and the PVA was heat-cured at 120° C. to obtain a PVA sheet K1 that did not contain an aluminum nitride fiber sheet. The thickness of the sheet K1 was 109 μm.

[Comparative Example 2-2]
A toluene solution (solid content 10 mass%) was prepared by diluting the silicone resin with toluene to 1/7, and the solution was dropped onto the silicone sheet. After drying overnight at room temperature, the toluene was removed and the silicone resin was heat-cured at 150°C to obtain a silicone sheet K2 that did not contain an aluminum nitride fiber sheet. The thickness of the sheet K2 was 111 μm.

[Comparative Example 2-3]
The PU emulsion was diluted by one third to prepare an aqueous solution (solid content 10 mass%) and dropped onto a silicone sheet. After drying overnight at room temperature, toluene was removed and the PU was heat-cured at 150°C to obtain a PU sheet K3 that did not contain an aluminum nitride fiber sheet. The thickness of the sheet K3 was 126 μm.

[Comparative Example 2-4]
An aqueous solution of PVB was prepared by dissolving it in ethanol to a solid content of 10% by weight, and the solution was dropped onto a silicone sheet. After drying overnight at room temperature, the ethanol was removed and the PVB was heat-cured at 120°C to obtain a PVB sheet K4 that did not contain an aluminum nitride fiber sheet. The thickness of the sheet K4 was 105 μm.

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

Thermal diffusivity was measured and thermal conductivity was calculated for the sheets obtained in Examples 2-1 to 2-11. Table 1 shows the thermal conductivity parallel to the fibers (average of four locations), the thermal conductivity perpendicular to the fibers (average of four locations), the thermal conductivity in the planar direction of the sheet containing non-oriented fibers (average of four locations), and the thermal conductivity in the thickness direction of the sheet (average of six locations).

The results shown in Table 1 show that the highly thermally conductive material of the present invention exhibits a high thermal conductivity of 7.0 W/mK or more.

[Comparative Examples 3-1 to 3-4]
The thermal diffusivity was measured and the thermal conductivity was calculated for the sheets obtained in Comparative Examples 2-1 to 2-4. Table 2 shows the thermal conductivity in the planar direction of the sheet (average of four locations) and the thermal conductivity in the thickness direction of the sheet (average of six locations).

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

1 Voltage supply device 2 Metal nozzle 3 Drum type collector 4 Spinning distance

Claims (14)

A highly thermally conductive material comprising an aluminum nitride fiber sheet made of continuous aluminum nitride fibers having a specific surface area of 30 ^m2 /g or less and a resin,
The highly thermally conductive material contains the aluminum nitride fiber sheet at a volume ratio of 10 to 75% and has a thermal conductivity of 7.0 W/mK or more. The highly thermally conductive material according to claim 1, wherein the aluminum nitride continuous fibers have an aspect ratio of more than 1,000. The highly thermally conductive material according to claim 1 or 2, wherein the aluminum nitride continuous fibers are at least one selected from the group consisting of aluminum nitride continuous fibers oriented in a certain direction, non-oriented nonwoven aluminum nitride continuous fibers, and aluminum nitride continuous fibers connected in a three-dimensional manner. A highly thermally conductive material according to any one of claims 1 to 3, in which the average fiber diameter of the aluminum nitride continuous fibers is 90 to 2,000 nm. The highly thermally conductive material according to claim 4, wherein the average fiber diameter of the aluminum nitride continuous fibers is 140 to 1,000 nm. 6. The highly thermally conductive material according to claim 1, wherein the aluminum nitride fiber sheet has a specific surface area of 20 m ² /g or less. The highly thermally conductive 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. The highly thermally conductive material according to any one of claims 1 to 7, wherein the aluminum nitride fiber sheet is contained in the highly thermally conductive material at 15 to 70%. The highly thermally conductive material according to any one of claims 1 to 8, wherein the highly thermally conductive material is in sheet form. The highly thermally conductive material according to claim 9, wherein the highly thermally conductive material is in sheet form and has a thickness of 20 to 2,000 μm. The highly thermally conductive material according to claim 10, wherein the highly thermally conductive material is in sheet form and has a thickness of 40 to 1,500 μm. A highly thermally conductive material according to any one of claims 9 to 11, in which the aluminum nitride continuous fibers are oriented in a certain direction and the thermal conductivity in the direction parallel to the fibers is 8.9 W/mK or more. The highly thermally conductive material according to claim 12, wherein the thermal conductivity parallel to the fibers is 10.0 W/mK or more. The highly thermally conductive material according to any one of claims 1 to 13 , wherein the highly thermally conductive material is electrically insulating and has a surface resistivity of 1 x 10 ¹³ Ω/□ or more.

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