Ceramic powder, resin composition, and ceramic powder manufacturing method

Abstract

To provide a ceramic powder exhibiting excellent fluidity during mixture with a resin, that exhibits high thermal conductivity, and to provide a manufacturing method therefor and a resin composition comprising the ceramic powder.SOLUTION: A ceramic powder having a circularity C50 of 0.83 or more of 50% accumulation from a low circularity side of an accumulation circularity distribution on a number basis has a circularity C10 of less than 0.81 of 10% accumulation from the low circularity side of the accumulation circularity distribution on the number basis.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a ceramic powder, a resin composition, and a method for producing the ceramic powder. [Background technology]

[0002] Heat generated by passing electricity through electronic components is desired to be dissipated quickly because it is likely to adversely affect the performance of the electronic components. Therefore, it is desired that the material constituting the thermally conductive member for dissipating heat exhibits high thermal conductivity. One of the thermally conductive members is a thermally conductive resin composition containing a resin and inorganic particles, and ceramic particles are used as the inorganic particles. For example, Patent Document 1 discloses a particulate material with high thermal conductivity, which is mainly composed of alumina, has a volume average particle size of 70 to 200 μm, a sphericity of 0.89 to less than 0.99, an alpha content rate of 40 to 85%, and has a result of equipment wear test of 0.017 g or less. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 170307 Summary of the Invention [Problem to be solved by the invention]

[0004] When mixing thermally conductive particles with resin, it is preferable to mix the thermally conductive particles and resin uniformly in order to ensure uniform characteristics of the component, and for this purpose, the thermally conductive particles are required to have high fluidity when mixed with the resin. In addition, although Patent Document 1 also shows thermally conductive materials, further study is thought to be necessary to further improve thermal conductivity.

[0005] The present disclosure has been made in consideration of the above circumstances, and its object is to provide a ceramic powder that has high thermal conductivity and excellent fluidity when mixed with a resin, a method for producing the same, and a resin composition containing the ceramic powder. [Means for solving the problem]

[0006] Aspect 1 of the present invention is The cumulative circularity C50 of 50% from the low circularity side of the cumulative circularity distribution based on the number is 0.83 or more, This ceramic powder has a circularity C10 of less than 0.81 for the cumulative 10% from the low circularity side of the cumulative circularity distribution based on number.

[0007] Aspect 2 of the present invention is The ceramic powder according to aspect 1, wherein a cumulative 50% particle size D50 from the fine particle side of a volume-based cumulative particle size distribution is 70 to 250 μm.

[0008] Aspect 3 of the present invention is The cumulative circularity C90 of 90% from the low circularity side in the cumulative circularity distribution based on the number of particles; In the ceramic powder according to aspect 1 or 2, the circularity C10 and the circularity C50 satisfy the following formula (1): (C90-C10) / C50≧0.11 ···(1)

[0009] A fourth aspect of the present invention is The ceramic powder according to any one of aspects 1 to 3, which is an alumina powder containing 90% or more of an α-alumina phase.

[0010] A fifth aspect of the present invention is A resin composition comprising the ceramic powder according to any one of the first to fourth aspects.

[0011] A sixth aspect of the present invention is A method for producing a ceramic powder according to any one of aspects 1 to 4, Mixing and granulating the raw material powders by wet granulation to obtain a mixture; drying the mixture at 30° C. or more and 150° C. or less to obtain a dry powder having a moisture content of 3% by mass or more and 55% by mass or less; and firing the dried powder. Effect of the Invention

[0012] According to the present disclosure, it is possible to provide a ceramic powder having high thermal conductivity and excellent fluidity when mixed with a resin, a method for producing the same, and a resin composition containing the ceramic powder. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the cumulative circularity distribution based on the number of alumina raw material particles 1 and alumina raw material particles 2 used in the examples. [Diagram 2] FIG. 2 is a scanning electron microscope (SEM) photograph of the alumina raw material particles 1 used in the examples. [Diagram 3] FIG. 3 is a scanning electron microscope (SEM) photograph of the alumina raw material particles 2 used in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present inventors have conducted extensive research to obtain a ceramic powder that has high thermal conductivity and excellent fluidity when mixed with a resin. As a result, they have found that the shape of the ceramic powder should be such that the circularity C50 at 50% cumulative from the low circularity side of the cumulative circularity distribution based on the number of particles and the circularity C10 at 10% cumulative from the low circularity side are each within a predetermined range. The ceramic powder according to this embodiment will be described in detail below.

[0015] [Ceramic powder] [C50, the cumulative 50% circularity from the low circularity side of the cumulative circularity distribution based on the number of pieces, and C10, the cumulative 10% circularity from the low circularity side of the cumulative circularity distribution based on the number of pieces] The ceramic powder according to this embodiment has a cumulative 50% circularity C50 (hereinafter sometimes referred to as "circularity C50") from the low circularity side of the cumulative circularity distribution based on the number of particles of 0.83 or more, and a cumulative 10% circularity C10 (hereinafter sometimes referred to as "circularity C10") from the low circularity side of the cumulative circularity distribution based on the number of particles of 0.81 or less. By making the circularity C50 0.83 or more, the fluidity when mixed with the resin is ensured, and by making the circularity C10 less than 0.81 and making the ceramic powder with low circularity exist at a small ratio, the contact area between the particles is increased, and as a result, a resin composition in which the ceramic powder is uniformly dispersed and exhibits high thermal conductivity can be realized.

[0016] The circularity C50 is preferably 0.84 or more. In addition, by using a ceramic powder containing a large amount of spherical particles with a relatively low circularity, it is possible to achieve higher thermal conductivity while ensuring excellent flowability when mixed with a resin. From this viewpoint, the circularity C50 is preferably less than 0.89. The circularity C50 is more preferably 0.88 or less, and even more preferably 0.87 or less.

[0017] In addition, the circularity C10 is preferably 0.80 or less, more preferably 0.78 or less, from the viewpoint of increasing the contact area between particles and ensuring high thermal conductivity. On the other hand, in the viewpoint of ensuring flowability when mixed with resin, the circularity C10 is preferably 0.75 or more, more preferably 0.76 or more. The circularity is determined by the method described in the examples below.

[0018] [(C90-C10) / C50] It is preferable that the circularity C90 of the cumulative 90% from the low circularity side of the cumulative circularity distribution, the circularity C10, and the circularity C50 satisfy the following formula (1). (C90-C10) / C50≧0.11 ···(1)

[0019] (C90-C10) / C50 (hereinafter sometimes referred to as "span value") is an index showing the spread of the circularity distribution, and the higher the span value, the wider the circularity distribution. The ceramic powder of this embodiment preferably has a span value of 0.11 or more. That is, by specifying the individual values ​​of the circularity C10 and the circularity C50, and by having a span value of 0.11 or more and a spread in the circularity distribution, it is possible to realize higher thermal conductivity while ensuring excellent fluidity when mixed with a resin. The above span value is more preferably 0.12 or more, and even more preferably 0.15 or more. In addition, from the viewpoint of achieving both high thermal conductivity and reduced viscosity of the resin composition, the above span value is preferably 0.30 or less.

[0020] Examples of ceramics constituting the ceramic powder include oxide-based ceramics such as alumina, magnesia, magnesia spinel, zirconia, silica, titania, ceria, yttria, zinc oxide, and beryllium oxide, and nitride-based ceramics such as aluminum nitride, boron nitride, silicon nitride, titanium nitride, etc. The ceramic powder may be composed of one type of ceramic powder among these, or may be composed of multiple types of ceramic powder.

[0021] The ceramic powder preferably contains an alumina powder, more preferably consists of an alumina powder, and further preferably consists of an alumina powder containing 90% or more of an α-alumina phase as described below.

[0022] [D50, the cumulative 50% particle size from the fine side of the cumulative particle size distribution based on volume] The ceramic powder according to the present embodiment preferably has a cumulative 50% particle size D50 (hereinafter sometimes referred to as "D50") from the fine particle side of the cumulative particle size distribution based on volume of 70 to 250 μm. The reason why a resin composition having a high thermal conductivity can be obtained by setting the D50 of the ceramic powder contained in the resin composition to a certain value or more is considered as follows.

[0023] When the D50 of a ceramic powder increases, the sum of the surface areas of the ceramic powder per unit mass (total surface area) decreases. Therefore, when a resin composition is produced by mixing a ceramic powder with a resin, the sum of the areas where the ceramic powder contacts the resin (total area) can be reduced by using a ceramic powder with a larger average particle size, even if the volume ratio is the same. The interface between the ceramic powder and the resin scatters propagating phonons, so it is believed that the thermal conductivity can be increased by reducing the total area.

[0024] From the above viewpoint, the ceramic powder according to the embodiment of the present invention preferably has a D50 of 70 μm or more. By having a D50 of 70 μm or more, the total area of ​​the interface when mixed with a resin at a predetermined ratio can be reduced compared to when the D50 is less than 70 μm, and a resin composition with high thermal conductivity can be obtained, which is preferable. The D50 of the ceramic powder is preferably more than 130 μm, more preferably more than 160 μm, even more preferably more than 160 μm, and even more preferably more than 170 μm. On the other hand, from the viewpoint of ensuring the kneadability with the resin, the D50 is preferably 250 μm or less, more preferably 220 μm or less. The D50 of the ceramic powder is measured by the method described in the examples described later.

[0025] The ceramic powder is preferably an alumina powder containing 90% or more of α-alumina phase. Since α-alumina has high thermal conductivity, the thermal conductivity of the alumina powder can be increased by increasing the content of α-alumina phase in the alumina powder. When the α-alumina content index is as high as 90% or more, the alumina powder can achieve high thermal conductivity. The α-alumina content of the alumina powder is preferably 95% or more, and most preferably 100%. The α-alumina content of the alumina powder may be 90% or more and less than 95%. Within this range, it is easier to produce an alumina powder that exhibits thermal conductivity not significantly different from that of alumina powder containing 100% α-alumina phase.

[0026] In this specification, the term "alpha-alumina ratio" refers to the content (volume %) of alpha-alumina relative to the total alumina contained in the alumina powder. The alpha phase ratio was measured by measuring the alumina powder by powder X-ray diffraction and calculating the peak height (I 25.6 ) and the peak heights of the γ, η, χ, κ, θ and δ phases at 2θ = 46° (I 46 ) and calculate using the following formula (2). αization rate=I 25.6 / (I 25.6 +I 46 )×100(%) (2)

[0027] In addition, although it is most desirable for the alumina powder according to this embodiment to have an alpha conversion rate of 100%, it may contain alumina other than alpha alumina (delta alumina, theta alumina, etc.) in an amount of, for example, about 10% or less, without interfering with the objective of this embodiment.

[0028] The alumina other than α-alumina may be contained in any form. For example, both α-alumina and alumina other than α-alumina may be contained inside one alumina powder particle. Also, a certain alumina powder particle may consist of only α-alumina, and another alumina powder particle may consist of only alumina other than α-alumina, and these alumina powder particles may be mixed together.

[0029] [Method of manufacturing ceramic powder] The method for producing the ceramic powder according to the present embodiment is not particularly limited as long as it can produce a ceramic powder having the above-mentioned circularity distribution. mixing and granulating the ceramic powder by wet granulation to obtain a mixture; drying the mixture at 30° C. or more and 150° C. or less to obtain a dry powder having a moisture content of 3% by mass or more and 55% by mass or less; and firing the dried powder.

[0030] Hereinafter, the method for producing the ceramic powder will be described by taking the case of producing an alumina powder as an example, but is not limited thereto. When producing an alumina powder as the ceramic powder, the alumina raw material particles constituting the alumina powder can be produced by the above-mentioned method. Hereinafter, the case of producing α-alumina raw material particles as the alumina raw material particles will be described. That is, the α-alumina raw material particles can be produced by, for example, mixing and granulating an α-alumina precursor and α-alumina seed particles as raw material powder, drying the resulting mixture at 30°C or higher and 150°C or lower to obtain a dry powder with a moisture content of 3% by mass or higher and 55% by mass or lower, firing the dry powder to obtain an α-alumina coarse powder, and then sieving the α-alumina coarse powder.

[0031] The α-alumina precursor is a compound that can be converted to α-alumina by calcination, and examples thereof include aluminum alkoxides such as aluminum isopropoxide, aluminum ethoxide, aluminum s-butoxide, and aluminum t-butoxide, and transition aluminas such as aluminum hydroxide, γ-alumina, δ-alumina, and θ-alumina.

[0032] The aluminum hydroxide can be obtained, for example, by hydrolyzing a hydrolyzable aluminum compound. Examples of the hydrolyzable aluminum compound include aluminum alkoxide and aluminum chloride, and aluminum alkoxide is preferred because aluminum hydroxide with a high purity of 99.99% by mass or more can be easily obtained. The aluminum hydroxide is not particularly limited, but it is desirable to use one with high purity and a crystal system belonging to boehmite.

[0033] The α-alumina seed particles preferably have a median particle size of 0.1 to 1.0 μm, more preferably 0.1 to 0.4 μm. For example, high-purity α-alumina particles with a purity of 99.99% by mass or more can be pulverized to obtain the α-alumina seed particles. As the pulverization method, from the viewpoint of uniformly mixing with the α-alumina precursor in a subsequent step, a method of wet pulverization in which a solvent is added and pulverized in a slurry state using a pulverizing device such as a ball mill or a media stirring mill is preferable. As the solvent, water is usually used, and a dispersant may be added to pulverize the α-alumina seed particles to obtain a pulverized α-alumina seed particles having a media stirring mill or the like, in order ...

[0034] When aluminum hydroxide is used as the α-alumina precursor, the amount of α-alumina seed particles added relative to the aluminum hydroxide is preferably 0.1 to 10 parts by weight, and more preferably 0.3 to 7 parts by weight, when the weight of the calcined α-alumina powder is taken as 100 parts by weight. If the amount added is less than 0.1 part by weight, it is difficult to obtain α-alumina powder, while if the amount added exceeds 10 parts by weight, the physical properties of the obtained α-alumina powder do not change and the amount added increases unnecessarily, which is not preferable.

[0035] The α-alumina seed particle slurry obtained by the pulverization preferably has a water content of 50 to 120 parts by weight relative to 100 parts by weight of aluminum hydroxide. By making the water content 50 parts by weight or more, the fluidity of the mixture can be increased, and the α-alumina seed particles and aluminum hydroxide can be mixed sufficiently. On the other hand, by making the water content 120 parts by weight or less, it is possible to prevent the mixture from becoming a slurry, and to prevent the particle size of the granulated particles from becoming excessively large. In addition, it is possible to reduce the energy required for drying. The water content is more preferably 60 to 90 parts by weight.

[0036] As a method for obtaining a mixture by mixing and granulating the α-alumina seed particle slurry and the α-alumina precursor, a method such as stirring, ball milling, ultrasonic dispersion, etc. can be adopted. When aluminum hydroxide particles are used as the α-alumina precursor, it is preferable to use a blade type mixer, since it is possible to mix the α-alumina seed particles uniformly while applying shear force. As an example of such a mixer, the mixer used in the examples can be mentioned. As a granulation method for obtaining the above mixture, in addition to the above, a method of forming with a jet mill to obtain rounded alumina particles, a dish type granulation method, or a method of obtaining granular products by spray drying can be mentioned.

[0037] The mixture obtained by the mixing and granulation is dried to remove water. The temperature and drying time during drying may be adjusted so that the moisture content of the dried powder is 3% by mass or more and 55% by mass or less. From the viewpoint of preventing particles from colliding with each other and breaking to generate particles with low circularity, the moisture content of the dried powder is preferably 30% by mass or more and 45% by mass or less.

[0038] The drying temperature may be 30° C. or higher and 150° C. or lower. From the viewpoint of preventing particles from colliding with each other and breaking to generate particles with low circularity, the drying temperature is preferably 35° C. or higher and 120° C. or lower. From the viewpoint of improving the light bulk density, it is desirable to carry out fluidized drying using a fluidized bed dryer.

[0039] By calcining the dry powder having the moisture content, it is possible to obtain a spherical α-alumina coarse powder in which the generation of fragmentary fine particles with low circularity is suppressed. The calcination temperature is preferably 1200° C. or higher and 1500° C. or lower, more preferably 1250° C. or higher and 1450° C. or lower, from the viewpoint of sufficiently advancing the transition of aluminum hydroxide to a gelatinized form and easily obtaining a high-purity α-alumina coarse powder.

[0040] The rate of temperature rise to the calcination temperature may be, for example, 30°C / hour to 500°C / hour. The calcination holding time may be a time sufficient for the α-alumina precursor to be converted to α-alumina to obtain α-alumina. The rate of temperature rise varies depending on the type of aluminum compound used, the ratio of the amount of α-alumina precursor to the α-alumina seed particles used, the type of calcination furnace, the calcination temperature, the calcination atmosphere, etc., but is, for example, 30 minutes or more and 24 hours or less, preferably 1 hour or more and 10 hours or less.

[0041] The firing atmosphere may be air, or may be in an inert gas such as nitrogen gas or argon gas, or may be in a humid atmosphere with a high partial pressure of water vapor.

[0042] For the calcination, a typical calcination furnace such as a tubular electric furnace, a box-type electric furnace, a tunnel furnace, a far-infrared furnace, a microwave heating furnace, a shaft furnace, a reverberatory furnace, a rotary furnace, a roller hearth furnace, etc. may be used. The mixture may be calcined in a batch or continuous manner. In addition, the mixture may be calcined in a static or fluidized manner.

[0043] The resulting coarse α-alumina powder usually has a wide distribution of particle sizes, and therefore, for example, by sieving it, α-alumina powder having a desired particle size distribution can be obtained.

[0044] Incidentally, a flame fusion method can be mentioned as a method for producing spherical alumina having a high circularity and close to a perfect circle, but the spherical alumina particles close to a perfect circle tend to have point contact with each other, making it difficult to obtain high thermal conductivity. In this embodiment, from the viewpoint that it is preferable to obtain a powder that is spherical but has a lower circularity than a perfect circle as the α-alumina raw material particles, it is preferable to produce the α-alumina raw material particles by the above-mentioned method rather than the flame fusion method.

[0045] The above method has been described as a method for producing alumina powder, but for example, instead of water as the solvent used in the above production method, a binder containing one or more of resin, wax, plasticizer, oil, surfactant, varnish, etc., and an organic solvent may be used to granulate the powder, and then degrease and sinter the resulting powder. This makes it possible to produce ceramic powders with low water resistance, such as magnesia and nitride ceramics.

[0046] For example, alumina powder as the ceramic powder according to this embodiment may be formed only from alumina raw material particles produced by the above-mentioned method, or may be obtained by mixing alumina raw material particles produced by the above-mentioned method with alumina raw material particles produced by another method within a range that satisfies the circularity of the ceramic powder according to this embodiment.

[0047] [Resin composition] By using the ceramic powder according to this embodiment as, for example, a filler for a resin composition, a resin composition (composite) with high thermal conductivity can be obtained. The resin composition may contain ceramic powder other than that of this embodiment in addition to the ceramic powder and resin according to this embodiment. For example, as shown in the preparation of the resin composition in the examples described later, in order to realize high filling, the resin composition may contain, in addition to the alumina powder and resin according to this embodiment, alumina medium particles with a particle size of several microns to several tens of microns and alumina small particles with a particle size of several hundred nm as a filler alumina powder other than the ceramic powder according to this embodiment.

[0048] In order to obtain a resin composition exhibiting excellent thermal conductivity, the ratio (mixing ratio) of the ceramic powder according to this embodiment contained in the resin composition is preferably 40 volume % or more, more preferably 50 volume % or more. On the other hand, from the viewpoint of ensuring the flexibility characteristic of resin, the ratio of the ceramic powder is preferably 75 volume % or less, more preferably 73 volume % or less.

[0049] From the viewpoint of increasing the filling rate of ceramics in the resin composition to ensure higher thermal conductivity, it is preferable that the total amount of the ceramic powder according to this embodiment and, for example, alumina powder for filling other than the ceramic powder according to this embodiment in the resin composition is 45 volume % or more and 90 volume % or less.

[0050] The resin used in the resin composition can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. The resins may be used alone or in combination of two or more.

[0051] Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers; fluorine-based polymers such as polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, polyvinyl acetal, polyvinylidene fluoride, and polytetrafluoroethylene; polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene copolymer (ABS) resins, polyphenylene-ether copolymers (PPE) resins, modified PPE resins, aliphatic polyamides, aromatic polyamides, polyimides, polyamideimides, polymethacrylic acid, polymethacrylic acid esters such as polymethacrylic acid methyl ester, polyacrylic acids, polycarbonates, polyphenylene sulfide, polysulfones, polyether sulfones, polyether nitriles, polyether ketones, polyketones, liquid crystal polymers, silicone resins, and ionomers.

[0052] Examples of the thermoplastic elastomer include a styrene-butadiene block copolymer or a hydrogenated product thereof, a styrene-isoprene block copolymer or a hydrogenated product thereof, a styrene-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, a vinyl chloride-based thermoplastic elastomer, a polyester-based thermoplastic elastomer, a polyurethane-based thermoplastic elastomer, and a polyamide-based thermoplastic elastomer.

[0053] Examples of the thermosetting resin include crosslinked rubber, epoxy resin, phenol resin, polyimide resin, unsaturated polyester resin, diallyl phthalate resin, etc. Specific examples of the crosslinked rubber include natural rubber, acrylic rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene copolymer rubber, chlorinated polyethylene rubber, chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluororubber, urethane rubber, and silicone rubber.

[0054] From the viewpoint of processability and properties, polyolefin resins, acrylic resins, polyimide resins, polyamide resins, polyamideimide resins, epoxy resins, phenol resins, and silicone resins are preferably used.

[0055] Furthermore, these resin compositions may contain, as necessary, any one or more of known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weather resistance agents, anti-blocking agents, antistatic agents, leveling agents, and release agents, within the scope of the invention.

[0056] A method for producing the resin composition will be described. The resin composition can be obtained by mixing the ceramic powder according to this embodiment with a resin using a commonly used known method. For example, when the resin is liquid (such as liquid epoxy resin), the liquid resin, ceramic powder, and a curing agent are mixed, and then cured with heat or ultraviolet light to obtain a resin composition. Known curing agents, mixing methods, and curing methods can be used. On the other hand, when the resin is solid (such as polyolefin resin or acrylic resin), the ceramic powder and resin are mixed, and then kneaded by a known method such as melt kneading to obtain the desired resin composition.

[0057] Aspects of the resin composition according to this embodiment include a compound obtained by compounding raw materials containing ceramic particles and a resin, a mixture obtained by mixing raw materials containing ceramic particles and a resin, a molded product obtained by molding the mixture, and a cured product (molded body) obtained by curing the mixture or the molded product. EXAMPLES

[0058] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the above and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

[0059] [Preparation of alumina raw material particles] The following alumina raw material particles 1 to 3 were prepared as the alumina raw material particles. Alumina raw material particles 1 and 2 were obtained by firing a mixture of α-alumina precursor and α-alumina seed particles to obtain α-alumina coarse powder, and then sieving the obtained α-alumina coarse powder.

[0060] (Alumina raw material particles 1) High-purity α-alumina (product name AKP-53, manufactured by Sumitomo Chemical Co., Ltd.) was pulverized in a wet ball mill to obtain α-alumina seed particles, the average particle size of which was 0.25 μm.

[0061] The α-alumina seed particles were mixed with pure water to prepare an α-alumina seed particle slurry containing the α-alumina seed particles at a solid content of 20 parts by weight. Meanwhile, high-purity aluminum hydroxide obtained by hydrolysis of aluminum alkoxide was prepared as an α-alumina precursor.

[0062] The high-purity aluminum hydroxide and the α-alumina seed slurry were mixed and granulated in a blade mixer having stirring blades with a multi-stage cross-shaped decomposition structure rotating at high speed on the inner surface to obtain a mixture. The amount of α-alumina seed particles contained in the α-alumina seed particle slurry added during mixing was 1.7 parts by weight when the weight of the α-alumina powder after firing was taken as 100 parts by weight. The amount of water in the α-alumina seed particle slurry was 73 parts by weight relative to 100 parts by weight of aluminum hydroxide.

[0063] The mixture obtained by the mixing was dried in a fluidized bed dryer at 90°C for 10 minutes to obtain an α-alumina precursor powder containing alumina seeds as a dry powder. The moisture content of the obtained dry powder was 38 mass%. Next, the α-alumina precursor powder containing alumina seeds (dry powder) was fired at a firing temperature of 1340°C for 4 hours with a heating rate of 100°C / hour to obtain an α-alumina coarse powder. The powder was then sieved to obtain alumina raw material particles 1 having a D50 of 160 μm and showing the cumulative circularity distribution shown in FIG. 1. An example of an SEM photograph of the alumina raw material particles 1 is shown in FIG. 2.

[0064] (Alumina raw material particles 2) High-purity α-alumina (product name AKP-53, manufactured by Sumitomo Chemical Co., Ltd.) was pulverized in a wet ball mill to obtain α-alumina seed particles, the average particle size of which was 0.25 μm.

[0065] The α-alumina seed particles were mixed with pure water to prepare an α-alumina seed particle slurry containing the α-alumina seed particles at a solid content of 20 parts by weight. Meanwhile, high-purity aluminum hydroxide obtained by hydrolysis of aluminum alkoxide was prepared as an α-alumina precursor.

[0066] The high-purity aluminum hydroxide and the α-alumina seed slurry were mixed in a blender-type mixer having stirring blades with a multi-stage cross-shaped decomposition structure rotating at high speed on the inner surface. The amount of α-alumina contained in the α-alumina seed particle slurry added during mixing was 1.7 parts by weight when the weight of the α-alumina powder after firing was taken as 100 parts by weight. The amount of water in the α-alumina seed particle slurry was 149 parts by weight relative to 100 parts by weight of aluminum hydroxide.

[0067] The mixed powder obtained by the above mixing was dried in a fluidized bed dryer at 200°C for 40 minutes to obtain an α-alumina precursor powder containing alumina seeds as a dry powder. The moisture content of the obtained dry powder was 5 mass% or less. Next, the α-alumina precursor powder containing alumina seeds (dry powder) was fired at a firing temperature of 1340°C for 4 hours with a heating rate of 100°C / hour to obtain an α-alumina coarse powder. The powder was then sieved to obtain alumina raw material particles 2 having a D50 of 150 μm and showing the cumulative circularity distribution shown in FIG. 1. An example of an SEM photograph of the alumina raw material particles 2 is shown in FIG. 3.

[0068] (Alumina raw material particles 3) Commercially available spherical alumina powder (particle size D50 of 200 μm) was used.

[0069] [Preparation of alumina powder] The alumina raw material particles 1 to 3 prepared as described above were blended in the ratios (volume ratios) shown in Table 1 for Examples 1 to 3 and Comparative Examples 1 to 3, respectively, and mixed uniformly using a rotation-revolution mixer (ARV-310) manufactured by Thinky Corporation to obtain an alumina powder as a ceramic powder. Note that the alumina raw material particles 1 to 3 are all α-alumina particles, and the alumina powders of Examples 1 to 3 and Comparative Examples 1 to 3 obtained by using these as they are or blending multiple types also consisted of the α-alumina phase.

[0070] The circularity and particle size of the resulting alumina powder were determined as follows.

[0071] [Circularity of alumina powder] The circularity of the alumina powder of each of the examples and comparative examples shown in Table 1 was calculated and evaluated by the following procedure.

[0072] SEM images of each alumina powder were obtained as follows. The alumina powder was fixed on carbon tape. The SEM images were obtained by acquiring images at a predetermined accelerating voltage using a scanning electron microscope (Hitachi High-Technologies Corporation, product number: S-4800).

[0073] The acquired SEM images were automatically binarized using image processing software (e.g., the free software ImageJ (https: / / fiji.sc / )) by selecting the analysis area. In the processed images, the area of ​​the particle surrounded by the outline ("area" in the following formula (3)) and the perimeter of the particle ("perimeter" in the following formula (3)) were calculated. The circularity of a single particle was then calculated using the following formula (3). Circularity of one particle = 4 × π × area / (perimeter 2 ) · · · (3)

[0074] From the above measurement and calculation results, a cumulative circularity distribution based on the number was created, and from the smallest circularity, i.e., from the low circularity side, C10, which is the cumulative 10% circularity, C50, which is the cumulative 50% circularity, and C90, which is the cumulative 90% circularity, were calculated.

[0075] Furthermore, the span value was calculated from the following formula (2) using the values ​​of the cumulative 10% circularity C10, the cumulative 50% circularity C50, and the cumulative 90% circularity C90. Span value = (C90 - C10) / C50 (2)

[0076] [Particle size of alumina powder] The D50 of the alumina powder was measured by the laser diffraction method using a Microtrack MT3300EXII laser particle size distribution measuring device manufactured by Microtrack Bell Co., Ltd., to measure the particle size distribution of the alumina powder and obtain the particle diameter D50 equivalent to the cumulative percentage of 50% on a volume basis. The measurement sample was prepared by adding the powder to be measured to a 0.2% by mass aqueous solution of sodium hexametaphosphate so that the laser scattering intensity was appropriate, and dispersing the powder for 5 minutes with the built-in ultrasonic of 40 W. The refractive index of alumina was set to 1.76.

[0077] [Table 1]

[0078] [Measurement of Viscosity of Resin Composition] (Preparation of resin composition for viscosity measurement) First, a resin composition for viscosity measurement was prepared. The alumina powder shown in Table 1, AA-5 (particle size 5 μm) manufactured by Sumitomo Chemical Co., Ltd., and AA-04 (particle size 0.4 μm) manufactured by Sumitomo Chemical Co., Ltd. were mixed to a ratio (mass ratio) of 6:3:1. The above AA-5 and AA-04 are alumina powders for filling other than the alumina powder according to this embodiment, and are medium alumina particles and small alumina particles used to achieve high filling in anticipation of practical use. In this example, the same type and amount of medium alumina particles and small alumina particles are used in all examples, so the difference in viscosity between the examples can be said to be due to the difference in the alumina powders shown in Table 1.

[0079] Resin 1 (53-type epoxy base resin (manufactured by Sankei Co., Ltd.)) was prepared as the resin. The resins were mixed to the mixing ratio (mass ratio of alumina powder group to resin 1) shown in Table 2, and mixed and kneaded using a centrifugal mixer (ARV-310) manufactured by Thinky Corporation to obtain a resin composition for viscosity measurement.

[0080] (Measurement of Viscosity of Resin Composition for Viscosity Measurement) The viscosity of the obtained resin composition for viscosity measurement was measured using a dynamic viscoelasticity measuring device ("Rheosol-G3000" manufactured by UBM). Parallel plates with a diameter of 40 mm were used, and the gap was 1 mm and the shear rate was 1 s -1 The measurements were made at 25°C. Viscosities below 500 Pa s were evaluated as having low viscosity and good fluidity (○), while viscosities of 500 Pa s or more were evaluated as having high viscosity and poor fluidity (×). The results are shown in Table 2.

[0081] [Table 2]

[0082] [Measurement of thermal conductivity of resin composition] (Preparation of resin composition for thermal conductivity measurement) First, a resin composition for measuring thermal conductivity was prepared. The alumina powder shown in Table 1, AA-5 (particle size 5 μm) manufactured by Sumitomo Chemical Co., Ltd., and AA-04 (particle size 0.4 μm) manufactured by Sumitomo Chemical Co., Ltd. were mixed to a ratio (mass ratio) of 6:3:1. The above AA-5 and AA-04 are alumina powders for filling other than the alumina powder according to this embodiment, and are alumina medium particles and alumina small particles used to achieve high filling in anticipation of practical use. In this example, the same type and amount of alumina medium particles and alumina small particles are used in all examples, so the difference in thermal conductivity between each example can be said to be due to the difference in alumina powder shown in Table 1.

[0083] Resin 1 (53-type epoxy base resin (manufactured by Sankei Co., Ltd.)) and resin 2 (53-type epoxy hardener (manufactured by Sankei Co., Ltd.)) were prepared as the resins. They were then mixed and kneaded to obtain the blending ratios shown in Table 3 (mass ratios of alumina powder group, resin 1, and resin 2) using a centrifugal mixer (ARV-310) manufactured by Thinky Corporation, to obtain a resin composition for measuring thermal conductivity.

[0084] (Measurement of thermal conductivity of resin composition) The obtained resin composition for thermal conductivity measurement was put into a mold with a diameter of 20 mm in an amount of 5 g, molded under a pressure of 30 MPa, and left at room temperature for 24 hours to harden the resin. The hardened molded body was then processed into a size of 10 mm square x 2 mm thick, and the surface was polished to obtain a test piece. The thermal conductivity of this test piece in the thickness direction was measured by the laser flash method using a xenon flash analyzer (NETZSCH, LFA467). The measurement was performed under the conditions of air and 25°C. Then, a test piece with a thermal conductivity of 4.3 W / (m·K) or more was evaluated as having high thermal conductivity, and a test piece with a thermal conductivity of less than 4.3 W / (m·K) was evaluated as having low thermal conductivity. The results are shown in Table 3.

[0085] [Table 3]

[0086] As can be seen from Tables 1 to 3, the alumina powders of Examples 1 to 3, which are ceramic particles according to this embodiment, have a cumulative circularity distribution within a specified range, and therefore have high fluidity when mixed with resin, and the resin composition obtained by mixing with resin exhibits high thermal conductivity.

[0087] In contrast, the cumulative 10% circularity C10 was high in Comparative Examples 1 and 2, and the resin compositions obtained by mixing with the resin had low thermal conductivity. In addition, the cumulative 50% circularity C50 in Comparative Example 3 was low, resulting in poor fluidity.

Claims

1. The cumulative circularity C50 of 50% from the low circularity side of the cumulative circularity distribution based on the number is 0.83 or more, A ceramic powder having a cumulative circularity C10 of less than 0.81 for 10% of the particles from the low circularity side of a cumulative circularity distribution based on the number of particles.

2. 2. The ceramic powder according to claim 1, wherein the cumulative 50% particle size D50 from the fine particle side of the cumulative particle size distribution on a volume basis is 70 to 250 μm.

3. A cumulative circularity C90 of 90% from the low circularity side of the cumulative circularity distribution based on the number of particles; The ceramic powder according to claim 1, wherein the circularity C10 and the circularity C50 satisfy the following formula (1). (C90-C10) / C50≧0.11...(1)

4. The ceramic powder according to any one of claims 1 to 3, which is an alumina powder containing 90% or more of an α-alumina phase.

5. A resin composition comprising the ceramic powder according to claim 4.

6. The method for producing a ceramic powder according to claim 4, Mixing and granulating the raw material powders by wet granulation to obtain a mixture; drying the mixture at 30° C. or more and 150° C. or less to obtain a dry powder having a moisture content of 3% by mass or more and 55% by mass or less; and firing the dried powder.

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