Alumina particle, and slurry composition and resin composite composition containing same

Abstract

Provided are: new alumina particles, particularly alumina particles in which the ratio (α / β) of the peak area α of a 4-coordinated Al to the peak area β of a 6-coordinated Al as measured by 27Al solid NMR falls within a specific range; and a slurry composition and a resin composite composition containing the alumina particles.　The present invention pertains to: alumina particles in which the ratio (α / β) of the peak area α of a 4-coordinated Al to the peak area β of a 6-coordinated Al as measured by 27Al solid NMR is at least 0.20; and a slurry composition and a resin composite composition that contain the alumina particles.

Description

Alumina particles, and slurry composition and resin composite composition containing the same

[0001] The present invention relates to alumina particles, in particular ２７ The present invention relates to alumina particles in which the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al measured by Al solid-state NMR is within a specific range, as well as a slurry composition and a resin composite composition containing the alumina particles.

[0002] Alumina is an oxide of aluminum and has a wide range of uses. Examples of uses include the production of aluminum in molten salt electrolysis and its addition to ceramic materials such as pottery. It is also widely used in fields requiring high strength, toughness, and thermal shock resistance, such as abrasives and sand-spreading equipment, catalyst carriers for automobile exhaust gas purification catalysts, and dental treatments (restoratives and prosthetics such as inlays and crowns). It is also used as an abrasive for industrial sandblasting. It is also used in medical applications and as a material in cosmetic compositions.

[0003] According to Non-Patent Document 1, alumina is blended as a material in cosmetic compositions for the purposes of imparting gloss or modifying surfaces, and is widely used in makeup products, nail products, makeup base products, concealer products, and the like.

[0004] Patent Document 1 is a document relating to a cosmetic composition, and discloses that the composition contains highly crystalline plate-like alumina particles to achieve a soft focus effect and good brightness. The soft focus effect is defined as the effect of using light-diffusing particles such as alumina to scatter light on the skin surface, making skin shadows less visible and thereby making skin imperfections less noticeable.

[0005] Patent Document 2, also a document related to cosmetic compositions, discloses a soft-focus cosmetic composition containing about 3 wt % or more of fumed alumina particles to enhance the soft-focus effect. Fumed alumina particles are defined as a form of alumina consisting of substantially spherical primary particles, which are fused or aggregated to form relatively large, irregularly shaped agglomerates.

[0006] JP 2021-59531 A JP 2007-507550 A

[0007] Cosmetic Ingredients Journal, Cosmetic Ingredients Online, Basic Information, Purpose, and Safety of Alumina, [online], Published: November 4, 2022, Retrieved: September 11, 2023, Internet, (https: / / cosmetic-ingredients.org / pearlizing-agents / 86 / )

[0008] As described above, alumina particles are widely used in makeup products and the like (Non-Patent Document 1), and it is known that highly crystalline plate-like alumina particles or fumed alumina particles (agglomerated particles) are used to achieve a soft focus effect (Patent Documents 1 and 2).

[0009] However, there continues to be a demand for additional compositions to enhance the soft focus effect in cosmetics. Note that one embodiment of the present invention is not limited to cosmetic applications, but can be applied to a wide range of applications related to design and visibility.

[0010] The present inventors have conducted detailed studies on alumina particles, ２７ We have found that Al solid-state NMR can analyze the local structure around aluminum atoms, and that the presence of tetra- and / or hexa-coordinated aluminum in alumina changes the crystallinity of alumina depending on the ratio (abundance ratio) of these two elements, affecting the diffuse reflectance (or light scattering effect). While not wishing to be bound by a particular theory, it is believed that as the abundance ratio of tetra-coordinated aluminum to hexa-coordinated aluminum increases, the alumina's crystal structure becomes more easily disrupted, enhancing the light scattering effect. Unless otherwise specified, aluminum is synonymous with Al and may also be referred to as Al.

[0011] The present invention is intended to solve the above-mentioned problems based on the above findings, and the gist of the present invention is as follows, as set forth in the claims. [1] ２７Alumina particles characterized in that the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al measured by Al solid-state NMR is 0.20 or more. [2] Alumina particles according to [1], having a lightness (L*) of 94.5% or more as measured by a whiteness meter. [3] Alumina particles according to [1] or [2], having a diffuse reflectance of 90.0% or more as measured by an ultraviolet-visible-near-infrared spectrophotometer. [4] Alumina particles according to any one of [1] to [3], having a lightness (L*) of 95.0% or more as measured by a whiteness meter. [5] Alumina particles according to any one of [1] to [4], having a chroma (C*) of 0.50% or less as measured by a whiteness meter. [6] Alumina particles according to any one of [1] to [5], having a circularity of 0.85 or more. [7] Alumina particles according to any one of [1] to [6], having an average particle size of 0.5 to 10.0 μm. [8] A slurry composition comprising the alumina particles according to any one of [1] to [7]. [9] The slurry composition according to [8], further comprising at least one inorganic filler selected from amorphous spherical alumina particles, non-spherical alumina particles, silica particles, titania particles, magnesia particles, aluminum nitride particles, boron nitride particles, barium titanate particles, calcium titanate particles, carbon fiber, talc, mica, kaolin, calcium oxide, zinc oxide, barium sulfate, calcium sulfate, and alkaline earth basic carbonates (e.g., calcium carbonate, magnesium carbonate).

[10] A resin composite composition comprising the alumina particles according to any one of [1] to [7].

[11] The resin composite composition according to

[10] , further comprising at least one inorganic filler selected from amorphous spherical alumina particles, non-spherical alumina particles, silica particles, titania particles, magnesia particles, aluminum nitride particles, boron nitride particles, barium titanate particles, calcium titanate particles, carbon fiber, talc, mica, kaolin, calcium oxide, zinc oxide, barium sulfate, calcium sulfate, and alkaline earth basic carbonates (calcium carbonate, magnesium carbonate, etc.).

[0012] ２７ ​Alumina particles having a ratio (α / β) of the peak area α of tetrahedral Al to the peak area β of hexahedral Al measured by Al solid-state NMR within a specific range can achieve a certain level of diffuse reflectance or higher, thereby achieving an excellent soft focus effect. Furthermore, the alumina particles can achieve a certain level of whiteness or higher, thereby achieving excellent brilliance. Furthermore, the alumina particles may be spherical, and can have low abrasion or high lubricity (fluidity), thereby achieving an excellent feel (texture) when used. The above-mentioned effects are extremely useful when the alumina particles are used in cosmetic compositions.

[0013] ( ２７ The ratio (α / β) of the peak area α of tetrahedral Al to the peak area β of hexahedral Al measured by Al solid-state NMR is 0.20 or more. The alumina particles provided by one embodiment of the present invention include: ２７ The compound is characterized in that the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al measured by solid-state Al NMR is 0.20 or more.

[0014] ２７ Measuring alumina particles using solid-state Al NMR allows for analysis of the local structure around aluminum (Al) atoms. Specifically, the coordination number of aluminum present in alumina can be measured. Through this analysis, the inventors discovered that in alumina, in addition to hexacoordinated Al, which has a stable electronic structure, tetracoordinated Al is present, and that the crystal structure of alumina changes depending on the abundance ratio (the ratio of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al (α / β)), affecting the diffuse reflectance (or light scattering effect). While not wishing to be bound by a particular theory, it is believed that as the ratio of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al (α / β) increases, the crystal structure of alumina becomes more likely to become disordered, resulting in an enhanced light scattering effect.

[0015] ​Alumina can be crystalline, and typical crystalline phases include the α-phase, θ-phase, δ-phase, η-phase, γ-phase, and ρ-phase. The α-phase is composed exclusively of hexacoordinated Al and has a trigonal crystalline structure. θ-alumina and δ-alumina contain tetracoordinated Al in addition to hexacoordinated Al, and have monoclinic and orthorhombic crystalline structures, respectively. As will be described in detail later, by increasing the proportion of tetracoordinated Al in alumina through processes such as rapid cooling and controlling the ratio of the tetracoordinated Al peak area α to the hexacoordinated Al peak area β (α / β) to 0.20 or greater, crystalline structures containing tetracoordinated Al, such as the θ-, δ-, η-, γ-, and ρ-phases, are mixed in addition to the α-phase. This results in a complex crystalline structure of the alumina as a whole, including multiple crystalline phases, such as the θ-, δ-, η-, γ-, and ρ-phases, in addition to the trigonal α-phase, improving the diffuse reflectance (or light scattering effect) of alumina. Generally, the larger the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al, the more complex the crystal structure becomes, resulting in improved diffuse reflectance (or light scattering effect). Therefore, the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al may be adjusted depending on the desired diffuse reflectance (or light scattering effect). However, if the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al becomes too large, the diffuse reflectance (or light scattering effect) may actually decrease. Therefore, the upper limit of the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al may be set to 0.55.

[0016] Generally, crystal information such as the proportion of crystalline phases present in inorganic materials is evaluated based on the results of XRD analysis, etc. However, when evaluating the crystallinity of alumina particles, particularly the diffuse reflectance (or light scattering effect), more accurate analytical results can be obtained than with conventional XRD analysis by using the ratio (α / β) of the peak area α of tetrahedral Al to the peak area β of hexahedral Al as an index.

[0017] [ ２７ Measurement of the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al by Al solid-state NMR] ２７The ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al in Al solid-state NMR is measured by the following procedure.

[0018] Using a JEOL RESONANCE JNM-ECA400R / S1 type device (static magnetic field strength 9.4 T), ２７ Each sample is packed into a φ 3.2 mm solid-state NMR sample tube, and a spectrum is acquired by single-pulse measurement at 23° C. under magic angle spinning conditions at 20 kHz.

[0019] 1M AlCl ３ When the aqueous solution peak is taken as 0 ppm, the peak detected between -30 and 30 ppm is presumed to be the peak of hexacoordinated aluminum, and the peak detected between 40 and 100 ppm is presumed to be the peak of tetracoordinated aluminum. The coordination number ratio (the ratio of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al (α / β)) is calculated from the ratio of the integral values ​​of the respective peaks.

[0020] The conditions for single pulse measurement are as follows: Pulse delay time: 50 seconds; Pulse width: 30-degree pulse of hexacoordinated aluminum; Number of integrations: 8 times

[0021] [Controlling the Ratio (α / β) of the Peak Area α of Tetracoordinated Al to the Peak Area β of Hexacoordinated Al in Alumina] The ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al in alumina can be adjusted by adjusting the production conditions of the alumina. As will be described in detail later, alumina particles can be produced based on a thermal spraying method in which alumina particle raw materials (e.g., alumina, boehmite, or aluminum hydroxide) are introduced into a flame, melted, and then cooled. Generally, the crystalline morphology of alumina changes depending on the cooling conditions. Specifically, the higher the cooling rate, i.e., the more rapid the cooling, the larger the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al. Therefore, by maintaining a temperature difference between the flame temperature (melting region) and the furnace temperature (cooling region) at a certain level or greater, a desired ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al can be obtained.

[0022] In the thermal spraying method, the circularity, bulk density, etc. of the obtained alumina particles can be adjusted by adjusting the amount of raw material fed to the flame per hour and the type of fuel gas. In addition, the particle size of the alumina particles after thermal spraying can be adjusted by adjusting the particle size of the raw material used.

[0023] (Lightness (L*) measured with a whiteness meter is 94.5% or more) The alumina particles according to one embodiment of the present invention preferably have a lightness (L*) measured with a whiteness meter of 94.5% or more. In one embodiment of the present invention, the alumina particles may have a lightness (L*) measured with a whiteness meter of 95.0% or more. Furthermore, since alumina single crystals are inherently colorless and transparent, the chroma of alumina is generally low. Therefore, in one embodiment of the present invention, the alumina particles may have a chroma (C*) measured with a whiteness meter of 0.50% or less.

[0024] Here, the lightness (L*) value and chroma (C*) value are determined in accordance with JIS Z8729. The L* value and C* value are indices used to represent the color of an object to be measured according to the L*a*b* color system (CIE 1976). In this color system, the L* value represents lightness, the C* value represents chroma, and the chromaticity indicating hue and chroma is calculated using the a* value and the b* value according to the formula (a ２ +b ２ ) １／２ It is expressed as:

[0025] The a* and b* values ​​are called chromaticness indices and represent the direction of color. The a* value is based on 0, and a negative value indicates an increase in greenness in the hue of the substance being measured, and a positive value indicates an increase in redness. The b* value is based on 0, and a negative value indicates an increase in blueness in the hue of the substance being measured, and a positive value indicates an increase in yellowness. When both the a* and b* values ​​are 0, the result is an achromatic color with no hue. The C* value represents saturation and is calculated using the formula (a ２ +b ２ ) １／２ It is expressed as:

[0026] The lightness L* value indicates that the whiteness of the hue of the measured substance increases as the value increases, and the blackness increases as the value decreases. The saturation C* value indicates that the color of the measured substance is more vivid as the value increases. On the other hand, a small C* value indicates that the measured substance is close to an achromatic color with no color tint.

[0027] The alumina particles according to one embodiment of the present invention preferably have a lightness (L*) of 94.5% or more. By incorporating alumina particles with high lightness (L*) into a cosmetic composition, a cosmetic composition with high whiteness and excellent brilliance can be obtained. Generally, the higher the lightness (L*), the higher the whiteness and brilliance, and thus the more preferable. The upper limit of the lightness (L*) may be 98.0%. Meanwhile, the lower limit of the lightness (L*) may be 95.0%. Furthermore, the alumina particles according to one embodiment of the present invention may also have a chroma (C*) of 0.50% or less. Since the chroma (C*) is low, the effect of not interfering with the color of the color pigment contained in the cosmetic composition is also obtained. In this respect, the lower the chroma (C*), the more preferable. The lower limit of the chroma (C*) may be 0%.

[0028] [Measurement method of lightness (L*) and chroma (C*)] Lightness (L*) and chroma (C*) are measured using a whiteness meter (Nippon Denshoku, NW-12). * value, b * The value was measured, and the chroma (C*) was ２ +b ２ ) １／２ Calculated as follows.

[0029] (Diffuse reflectance of 90.0% or more measured with an ultraviolet-visible-near-infrared spectrophotometer) The alumina particles according to one embodiment of the present invention have a ratio (α / β) of the peak area α of tetrahedral Al to the peak area β of hexahedral Al within a specific range, and the alumina has a complex crystal structure, which results in improved diffuse reflectance (or light scattering effect). Furthermore, the alumina particles according to one embodiment of the present invention may have a lightness (L*) within a specific range measured with a whiteness meter, which is considered to have high whiteness and contribute to improved diffuse reflectance (or light scattering effect). Therefore, in one embodiment of the present invention, the alumina particles may have a diffuse reflectance of 90.0% or more measured with an ultraviolet-visible-near-infrared spectrophotometer.

[0030] Diffuse reflectance is the proportion of light diffusely reflected as scattered light relative to incident light of a specific wavelength, and is the proportion of reflected light that includes specularly reflected components. Therefore, diffuse reflectance can be considered a parameter that affects the visual sense and the color actually detected by a detector. By incorporating alumina particles with high diffuse reflectance into a cosmetic composition, light on the skin surface can be scattered, making skin shadows less visible, thereby enhancing the effect of making skin imperfections less noticeable, i.e., the so-called soft focus effect. The alumina particles according to one embodiment of the present invention have a diffuse reflectance of 90.0% or more, and can achieve an excellent soft focus effect. Generally, the higher the diffuse reflectance, the higher the soft focus effect, which is preferable. The upper limit of the diffuse reflectance may be 96.0%.

[0031] [Method for Measuring Diffuse Reflectance] The reflectance is the diffuse reflectance including the specular reflectance according to JIS Z8722:2009, and the reflected light of the alumina particles is measured using an integrating sphere. More specifically, the reflectance of the alumina particles is measured using an ultraviolet-visible-near-infrared spectrophotometer (Shimadzu Corporation, ultraviolet-visible-near-infrared spectrophotometer, SolidSpec-3700) using an integrating sphere, including the reflected light of the alumina particles and the specular reflected light. The average reflectance at measurement points from 400 nm to 700 nm in wavelength is calculated.

[0032] The alumina particles according to one embodiment of the present invention can be produced by a thermal spraying method, which allows the shape of the resulting alumina particles to be adjusted by adjusting the amount of raw material fed to the flame per unit time and the type of fuel gas, thereby producing spherical alumina particles.

[0033] "Spherical" refers not only to particles whose shape is completely spherical, but also to particles whose shape is roughly spherical. Specifically, whether a particle is spherical or not is determined by the following procedure. First, the particle is photographed as a two-dimensional image. Focusing on the shape of the two-dimensional image (i.e., circular or roughly circular), the circularity (perimeter of the equivalent circle / perimeter of the projected image of the particle) is measured. The circularity of 50 or more particles is measured and the average value is calculated. Particles whose average circularity value is 0.85 or more are considered to be spherical.

[0034] The spherical alumina particles have a circularity of 0.85 or more. The higher the circularity of the spherical particles, the lower the abrasion or the higher the lubricity (fluidity) of a composition containing the alumina particles, typically a cosmetic composition, and the like, and ultimately the better the feel (texture) of the composition when used. The circularity may be 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, 0.94 or more, or 0.95 or more. Theoretically, the upper limit of the circularity is 1.0, but from the viewpoint of production control, it may be 0.98 or less, or 0.97 or less.

[0035] [Method for Measuring Circularity] Circularity can be measured using an electron microscope or optical microscope and image analysis software or equipment. For example, images taken with an electron microscope are analyzed using Mac-View manufactured by Mountech Co., Ltd., or an automated flow particle image imaging analyzer such as FPIA manufactured by Sysmex Corporation. After obtaining a two-dimensional image of the particle using these methods, the circularity of the two-dimensional image (perimeter of the equivalent circle / perimeter of the projected image of the particle) is measured. The circularity of 50 or more particles is measured, and the average value is taken as the circularity of the particle.

[0036] (Average particle size: 0.5 to 10.0 μm) The alumina particles according to one embodiment of the present invention have an average particle size of 0.5 to 10.0 μm. An average particle size of less than 0.5 μm is undesirable because the particles tend to aggregate more, which can reduce the lubricity (fluidity) of a composition containing the alumina particles, typically a cosmetic composition. An average particle size of more than 10.0 μm can reduce the miscibility with other components in a composition containing the alumina particles, typically a cosmetic composition. The average particle size of the alumina particles can be adjusted appropriately depending on the intended use and properties of the composition containing them. Therefore, the lower limit of the average particle size may be 1.0 μm or 3.0 μm. The upper limit of the average particle size may be 7.0 μm or 5.0 μm. The alumina particles according to one embodiment of the present invention can be produced by a thermal spraying method. In the thermal spraying method, the particle size of the alumina particles after thermal spraying can be adjusted by adjusting the particle size of the raw material used.

[0037] Here, the average particle size refers to the average particle size (D50), and means the median diameter D50 at 50% cumulative volume in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. The laser diffraction / scattering particle size distribution measurement method is a method in which a dispersion in which spherical alumina particles are dispersed is irradiated with laser light, and the particle size distribution is determined from the intensity distribution pattern of the diffracted / scattered light emitted from the dispersion. In one embodiment of the present invention, a laser diffraction / scattering particle size distribution measurement device "Mastersizer 3000" (manufactured by Malvern) is used. The average particle size of the raw material alumina particles can also be determined in a similar manner.

[0038] (Slurry composition containing alumina particles) One embodiment of the present invention provides a slurry composition containing alumina particles. A slurry composition can be obtained using a composition containing alumina particles and a dispersion medium. The slurry composition can be used in the resin composite composition, cosmetic composition, etc. described below. The slurry composition, particularly the cosmetic composition, according to one embodiment of the present invention can achieve an excellent soft focus effect due to the diffuse reflectance of the contained alumina particles. Furthermore, the slurry composition, particularly the cosmetic composition, can achieve excellent brilliance due to the whiteness of the alumina particles. Furthermore, when the alumina particles are spherical, it is possible to reduce abrasion or increase lubricity (fluidity), thereby achieving an excellent feel (texture) when used. Furthermore, a resin composite composition with excellent fluidity can be obtained.

[0039] The dispersion medium in the slurry composition can be water or a known organic solvent, and can be adjusted appropriately depending on the application of the slurry composition. Multiple dispersion mediums may be used in combination. Typically, the dispersion medium is a liquid, and examples thereof include water and organic solvents. Examples of organic solvents include alkane solvents such as hexane, heptane, octane, and decane; alcohol solvents such as methanol, ethanol, and propanol; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; and aromatic solvents such as benzene, toluene, ethylbenzene, and xylene. Ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone are preferred.

[0040] When producing the slurry composition, for example, in addition to the alumina particles and the dispersion medium, known dispersants, pigments, fragrances, preservatives, purified water, surfactants, etc. may be blended as needed, and then compounded by a known method such as kneading.

[0041] The dispersant in the slurry composition may be water or a known organic solvent, and may be appropriately adjusted depending on the intended use of the slurry composition. A plurality of dispersants may be used in combination.

[0042] Examples of dispersants include dispersants containing at least one selected from nonionic dispersants and cationic dispersants. The nonionic dispersants are not particularly limited, and known dispersants can be used. Examples include polymeric compounds having a polyoxyethylene chain. Examples of polymeric compounds having a polyoxyethylene chain include alkyl polyoxyethylene ethers, alkyl polyoxyethylene-polyoxypropylene ethers, alkyl polyoxypropylene-polyoxyethylene ethers, polyoxyethylene-polyoxypropylene ethers (polyoxyethylene oxypropylene block copolymers), fatty acid polyoxyethylene esters, fatty acid polyoxyethylene sorbitan esters, fatty acid polyoxyethylene sorbitol esters, polyoxyethylene sorbitan monoalkyl ethers, polyoxyethylene alkyl ether sulfate esters, polyoxyethylene castor oil (hydrogenated castor oil), and acetylene glycol ethylene oxide adducts. Examples of alkyl polyoxyethylene ethers include polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octyl ether, polyoxyethylene cetyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, etc. Examples of fatty acid polyoxyethylene sorbitan esters include polyoxyethylene sorbitan monolaurate, etc.

[0043] The cationic dispersant is not particularly limited, and known dispersants can be used. Examples include alkylamine salts, acylamine salts, quaternary ammonium salts, ammonium salts having an amide bond, an ester bond, or an ether bond, imidazoline, imidazolium salts, and amine derivatives. The cationic dispersant may be a low-molecular-weight compound or a high-molecular-weight compound, but high-molecular-weight compounds are preferred from the viewpoint of the dispersibility of alumina particles. Examples of such high-molecular-weight dispersants include polyethyleneimine, aminoalkyl (meth)acrylate copolymers, polyvinylimidazoline, polyvinylpyridine derivatives, polyoxyethylene alkylamines, and polyoxyethylene alkylamides. Examples of polyvinylpyridine derivatives include copolymers of vinylpyridine and (meth)acrylic acid, and copolymers of vinylpyridine, (meth)acrylic acid, and an oxyethylene group-containing polymer compound. Examples of copolymers of vinylpyridine, (meth)acrylic acid, and an oxyethylene group-containing polymer compound include copolymers of vinylpyridine, (meth)acrylic acid, and polyoxyethylene. Of these, amine-type high-molecular-weight dispersants are preferred from the viewpoint of the dispersibility of alumina particles.

[0044] The dispersant may be a known surface treatment agent. The inclusion of a surface treatment agent improves the dispersibility of alumina particles in a slurry composition with a dispersion medium, the dispersibility or affinity with a resin in a resin composite composition, and the dispersibility of alumina particles in a cosmetic composition. Examples of the surface treatment agent include compounds having at least one functional group selected from alkyl groups such as methyl, ethyl, propyl, and butyl; alkenyl groups such as vinyl, ethenyl, and propenyl; phenyl, amino, phenylamino, acrylic, methacrylic, epoxy, and styryl groups; silane coupling agents; and silazanes. Silane coupling agents having SiH, SiOH, or SiOR (where R is a hydrocarbon group) and silazanes such as hexamethylenedisilazane are preferred. Examples of silane coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane. Examples of alkoxysilane compounds include hexyltrimethoxysilane, octyltriethoxysilane, and phenyltriethoxysilane. Examples of silazane compounds include hexamethyldisilazane and trimethylsilane. From the viewpoint of excellent reactivity, silazane compounds are more preferred. Hexamethyldisilazane and trimethylsilane are more preferred.

[0045] The content of alumina particles in the slurry composition (when an "inorganic filler" or "other filler" described below is contained, the combined content of these) can be adjusted appropriately depending on the application of the slurry composition. Typically, from the viewpoint of exhibiting the effects of the alumina particles of one embodiment of the present invention, it is 50 to 95 wt %. A more preferred lower limit is 55 wt %, more preferably 60 wt %, more preferably 65 wt %, and more preferably 70 wt %. A more preferred upper limit is 93 wt %, more preferably 90 wt %, and more preferably 85 wt %.

[0046] (Inorganic Filler) When producing the slurry composition and the resin composite composition described below, other inorganic fillers may be blended in addition to the alumina particles of one embodiment of the present invention. Examples of the inorganic filler include amorphous spherical alumina particles, non-spherical alumina particles, silica particles (amorphous spherical silica particles, crystalline spherical silica particles, crushed silica particles (amorphous or crystalline), etc.), titania particles, magnesia particles, aluminum nitride particles, boron nitride particles, barium titanate particles, calcium titanate particles, carbon fiber, talc, mica, kaolin, calcium oxide, zinc oxide, barium sulfate, calcium sulfate, and alkaline earth basic carbonates (calcium carbonate, magnesium carbonate, etc.). The blending ratio of the inorganic filler can be adjusted appropriately depending on the application of the slurry composition or resin composite composition. Typically, from the viewpoint of exhibiting the effects of the alumina particles of one embodiment of the present invention, the blending ratio (weight of alumina particles):(weight of other inorganic filler) may be 5:95 to 90:10.

[0047] Furthermore, when used as a cosmetic composition, organic fillers such as polymethyl methacrylate methyl methacrylate crosslinked polymers, nylon particles, and melamine resins, as well as hydroxides of aluminum, magnesium, calcium, and zinc (collectively referred to as "other fillers") may be blended in place of or in combination with the inorganic fillers. The blending ratio of the other fillers can be adjusted appropriately depending on the intended use of the slurry composition or resin composite composition. Typically, from the viewpoint of exerting the effects of the alumina particles of one embodiment of the present invention, the blending ratio of (alumina particle weight):(other filler weight) may be 5:95 to 90:10.

[0048] (Other Components) When used as a cosmetic composition, in addition to the inorganic filler, various components generally contained in cosmetics may be contained, such as, but not limited to, colorants, carriers (base materials), surfactants, active ingredients, thickeners, solidifying agents, binders, propellants, moisturizers, and antioxidants.

[0049] <Colorant> As the colorant, color pigments and extender pigments other than the above-mentioned alumina particles can also be used. As the colorant, conventionally known pigments can be used appropriately according to the desired hue. Examples thereof include inorganic pigments such as titanium oxide, chromium oxide, iron oxide, yellow lead, zinc yellow, ultramarine blue, Prussian blue, and carbon black, and organic pigments such as isoindolinone, isoindoline, azomethine, anthraquinone, anthrone, xanthene, diketopyrrolopyrrole, perylene, quinacridone, indigoid, dioxazine, phthalocyanine, and azo pigments.

[0050] <Carrier> Examples of carriers include water, aliphatic alcohols, hydrocarbons, higher fatty acids, oils and fats, esters, and silicone oils. These may be used alone or in combination of two or more. The base material may be aqueous, oil-based, or an emulsion. Examples of hydrocarbons include chain saturated hydrocarbons having 15 or more carbon atoms. Examples include petrolatum, paraffin, and isoeicosane. Examples of higher fatty acids include saturated fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, and behenic acid, and unsaturated fatty acids such as palmitoleic acid, oleic acid, elaidic acid, ricinoleic acid, linoleic acid, γ-linolenic acid, and α-linolenic acid. Examples of silicone oils include linear silicones such as dimethicone and trisiloxane, cyclic silicone oils such as cyclopentasiloxane, cyclohexasiloxane and cyclomethicone, phenyl-substituted silicone oils such as diphenyldimethicone, phenyltrimethicone and diphenylsiloxyphenyltrimethicone, alkyl-modified silicone oils such as stearyldimethicone, cetyldimethicone and caprylylmethicone, and amino-modified silicone oils such as amodimethicone, aminopropyldimethicone, bisaminopropyldimethicone and biscetearylamodimethicone.

[0051] <Surfactant> The surfactant may be amphoteric, nonionic, anionic, or cationic.

[0052] <Active Ingredients> Examples of active ingredients include UV blocking agents, moisturizing agents, anti-aging active ingredients, vitamins, and self-tanning agents.

[0053] (Resin composite composition containing alumina particles) According to one embodiment of the present invention, a resin composite composition containing alumina particles is provided. The resin composite composition can be obtained using a composition containing alumina particles and a resin.

[0054] For example, alumina particles can be used to obtain resin composite compositions, such as not only cosmetic compositions but also semiconductor encapsulants (particularly solid encapsulants) and interlayer insulating films. Furthermore, by curing these resin composite compositions, resin composites such as encapsulants (cured products) and semiconductor package substrates can be obtained. The alumina particles according to one embodiment of the present invention can be used to obtain resin composite compositions with excellent visibility in applications other than cosmetic compositions, such as semiconductor encapsulants, interlayer insulating films, heat dissipation sheets, and heat dissipation greases, and can therefore be used favorably.

[0055] When producing the resin composite composition, for example, in addition to the alumina particles and resin, a curing agent, a curing accelerator, a flame retardant, a silane coupling agent, etc. are blended as needed, and the resulting mixture is composited by a known method such as kneading, etc. Then, the resulting mixture is molded into pellets, films, etc. depending on the intended use.

[0056] Furthermore, when producing the resin composite composition, in addition to the alumina particles and resin, the aforementioned inorganic filler may be blended. Examples of inorganic fillers blended into the resin composite composition (or slurry composition) include amorphous spherical alumina particles, non-spherical alumina particles, silica particles (amorphous spherical silica particles, crystalline spherical silica particles, crushed silica particles (amorphous or crystalline), etc.), titania particles, magnesia particles, aluminum nitride particles, boron nitride particles, barium titanate particles, calcium titanate particles, and carbon fibers. The blending ratio of the inorganic fillers can be adjusted appropriately depending on the application of the resin composite composition. However, from the viewpoint of exhibiting the effects of the spherical alumina particles of one embodiment of the present invention, it is preferable that the blending ratio of the spherical alumina particles to the other inorganic fillers is 95:5 to 60:40.

[0057] Furthermore, when the resin composite composition is cured to produce a resin composite, for example, the resin composite composition is heated to melt it, processed into a shape according to the intended use, and then heated to a temperature higher than that used for melting to completely cure it. In this case, a known method such as a transfer molding method can be used.

[0058] For example, when producing a cosmetic composition, known resins can be used in the resin composite composition, but examples include melamine resins and silicone resins. Furthermore, when producing semiconductor-related materials such as packaging substrates and interlayer insulating films, known resins can be used in the resin composite composition, but epoxy resins are preferred. The epoxy resin is not particularly limited, but examples include bisphenol A epoxy resins, bisphenol F epoxy resins, biphenyl epoxy resins, phenol novolac epoxy resins, cresol novolac epoxy resins, naphthalene epoxy resins, and phenoxy epoxy resins. One of these resins can be used alone, or two or more resins with different molecular weights can be used in combination. Among these, epoxy resins having two or more epoxy groups per molecule are preferred from the standpoints of curability, heat resistance, and the like. Specific examples include biphenyl-type epoxy resins, phenol novolac-type epoxy resins, orthocresol novolac-type epoxy resins, epoxidized novolac resins of phenols and aldehydes, glycidyl ethers of bisphenol A, bisphenol F, bisphenol S, etc., glycidyl ester acid epoxy resins obtained by reacting polybasic acids such as phthalic acid or dimer acid with epochlorohydrin, linear aliphatic epoxy resins, alicyclic epoxy resins, heterocyclic epoxy resins, alkyl-modified polyfunctional epoxy resins, β-naphthol novolac-type epoxy resins, 1,6-dihydroxynaphthalene-type epoxy resins, 2,7-dihydroxynaphthalene-type epoxy resins, bishydroxybiphenyl-type epoxy resins, and epoxy resins into which halogens such as bromine have been introduced to impart flame retardancy. Among these epoxy resins having two or more epoxy groups per molecule, bisphenol A-type epoxy resins are particularly preferred.

[0059] Furthermore, resins other than epoxy resins can also be used as resin composite compositions for applications other than semiconductor encapsulation composite materials, such as prepregs for printed circuit boards and various engineering plastics. Specific examples of resins that can be used in addition to epoxy resins include silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyamides such as polyimides, polyamideimides, and polyetherimides; polyesters such as polybutylene terephthalate and polyethylene terephthalate; polyphenylene sulfide, aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins.

[0060] The curing agent used in the resin composite composition may be any known curing agent for curing the resin, such as a phenol-based curing agent, such as a phenol novolac resin, an alkylphenol novolac resin, or a polyvinylphenol, which may be used alone or in combination.

[0061] The amount of the phenolic curing agent blended is preferably such that the equivalent ratio to the epoxy resin (phenolic hydroxyl group equivalent / epoxy group equivalent) is 0.1 or more and less than 1.0, thereby eliminating any unreacted phenolic curing agent from remaining and improving moisture absorption and heat resistance.

[0062] In one embodiment of the present invention, the amount of spherical alumina particles added to the resin composite composition is preferably large from the viewpoints of heat resistance and thermal expansion coefficient. Typically, the amount is 70% by mass to 95% by mass, preferably 80% by mass to 95% by mass, and more preferably 85% by mass to 95% by mass. This is because if the amount of spherical alumina particles is too small, it is difficult to achieve effects such as improving the strength of the sealing material and suppressing thermal expansion. Conversely, if the amount is too large, segregation due to aggregation of the spherical alumina particles is likely to occur in the composite material regardless of the surface treatment of the spherical alumina particles, and the viscosity of the composite material becomes too high, making it difficult to use as a sealing material. When the aforementioned "other filler" is used in combination, the preferred amount added to the resin composite composition is the total amount of the spherical alumina particles and the "other filler."

[0063] In addition to the resin, known additives such as a silane coupling agent, a curing agent, a colorant, and a hardening retarder can be used.

[0064] As for the silane coupling agent, any known coupling agent may be used, but those having an epoxy-based functional group are preferred.

[0065] Furthermore, the composite resin composition can be used to obtain a heat-dissipating sheet, a heat-dissipating grease, and the like.

[0066] When obtaining the heat dissipation sheet, alumina particles, resin, and additives are appropriately blended and compounded by a known method such as kneading, etc. The obtained composite is molded into a sheet by a known method.

[0067] For example, when producing a heat dissipation sheet, known resins can be used in the resin composite composition, including silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyamides such as polyimides, polyamideimides, and polyetherimides; polyesters such as polybutylene terephthalate and polyethylene terephthalate; polyphenylene sulfide, aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins. Among these, silicone resins are preferred. The silicone resin is not particularly limited, but examples include peroxide-curable, addition-curable, condensation-curable, and ultraviolet-curable resins.

[0068] In addition to the resin, known additives such as a silane coupling agent, a curing agent, a colorant, and a hardening retarder can be used.

[0069] When preparing the thermally conductive grease, the spherical alumina particles, resin, and additives are appropriately blended and compounded by a known method such as kneading. The resin used in the thermally conductive grease is also called the base oil.

[0070] For example, when producing a thermally conductive grease, known resins can be used in the resin composite composition, and specific examples include silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyamides such as polyimide, polyamideimide, and polyetherimide; polyesters such as polybutylene terephthalate and polyethylene terephthalate; polyphenylene sulfide, aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins, mineral oils, synthetic hydrocarbon oils, ester oils, polyglycol oils, silicone oils, and fluorine oils.

[0071] In addition to the resin, known additives such as a silane coupling agent, a colorant, a thickener, etc. Known thickeners that can be used include calcium soap, lithium soap, aluminum soap, calcium complex, aluminum complex, lithium complex, barium complex, bentonite, urea, PTFE, sodium terephthalamate, silica gel, and organic bentonite.

[0072] [Method for Producing Alumina Particles] The alumina particles according to one embodiment of the present invention are not particularly limited in the production method, and can be produced by the following production method. This production method is a method that can suitably produce the above-mentioned alumina particles, and can include the following steps: (1) a step of producing alumina particles by introducing at least one of alumina, boehmite, aluminum hydroxide, etc. into a flame to melt the melt, and then cooling the melt; and (2) a step of classifying the alumina particles using a sieve or the like after the step of producing the alumina particles.

[0073] The step (1) of producing alumina particles is a step of introducing raw materials for alumina particles (hereinafter simply referred to as "raw materials") into a flame, melting them, and then cooling them. These raw materials can be introduced into the flame in a state suspended in a carrier gas. Examples of the carrier gas that can be used include air, oxygen, and propane gas.

[0074] The flame is preferably formed in a heat-resistant furnace. The flame is formed in the upper part of the heat-resistant furnace, the raw material is fed into the flame, and the molten alumina particles are collected from the bottom of the heat-resistant furnace as they settle due to gravity. By preventing the raw material from forming a flame in the lower part of the heat-resistant furnace, the alumina particles that settle to the bottom are cooled and spheroidized.

[0075] The region in the upper part of the heat-resistant furnace where the raw material is supplied and melted by the flame is called the melting region, and the region in the lower part of the heat-resistant furnace where the molten alumina particles are cooled is called the cooling region.

[0076] The flame formation method is not particularly limited, but may be such that a fuel (known fuel such as propane, LPG, LNG, hydrogen, or ammonia) and a combustion supporting gas (air or oxygen) are supplied to the melting zone via a burner, a mixture of fuel and combustion supporting gas is supplied to the melting zone via a burner, or a mixture of raw material, fuel, and combustion supporting gas is supplied to the melting zone via a burner to form a flame. In particular, from the viewpoint of increasing the maximum flame temperature and widening the temperature gradient within the heat-resistant furnace, a flame formation method in which a mixture of fuel and combustion supporting gas or a mixture of raw material, fuel, and combustion supporting gas is supplied to the melting zone is preferred.

[0077] When molten alumina is rapidly cooled in the cooling region, Al atoms with a tetrahedral structure, which are electronically unstable compared to hexahedral structures, tend to be produced, resulting in the formation of crystalline phases containing tetrahedral Al, such as the θ, δ, η, γ, and ρ phases.On the other hand, when the cooling rate is slow, the formation of electronically stable hexahedral Al is promoted.

[0078] One method for controlling the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al is to maintain a certain temperature difference between the melting zone and the cooling zone. By maintaining a temperature difference of, for example, 1500°C or higher, preferably 1600°C or higher, more preferably 1800°C or higher, and even more preferably 2000°C or higher, the cooling rate increases in the cooling step after melting. As a result, the ratio of tetracoordinated Al increases. On the other hand, when the cooling rate is slow, the ratio of electronically stable hexacoordinated Al increases. The temperature difference between the melting zone and the cooling zone can be appropriately adjusted depending on the particle size and composition of the desired spherical alumina particles. The temperature of the melting zone can be adjusted by the flame temperature.

[0079] Furthermore, if sufficient heat can be applied to the raw material particles in the melting region to melt them, the amount of irregularly shaped particles that do not become spherical can be reduced. This allows the bulk density of the alumina particles to be adjusted. Furthermore, the circularity and bulk density can be adjusted by adjusting the amount of material fed to the flame per unit time and the type of fuel gas. Furthermore, the particle size of the alumina particles after thermal spraying can be adjusted by adjusting the particle size of the raw material powder used.

[0080] The raw material of the alumina particles may be at least one of alumina, boehmite, aluminum hydroxide, etc. When these raw materials are introduced into the flame, the alumina remains as alumina, and the boehmite or aluminum hydroxide undergoes an oxidation or dehydration reaction to form alumina.

[0081] A refrigerant may be used in the cooling region. Although the refrigerant is not particularly limited, distilled water or ion-exchanged water that does not contain air or impurities such as sodium ions or chlorine ions is preferable from the viewpoint of not reducing the purity of the alumina particles.

[0082] In the classification step (2), the alumina particles obtained in the alumina particle production step can be suitably classified using a sieve or the like with a predetermined mesh size. If necessary, pre-treatment or post-treatment such as separation into coarse particles and fine particles using a cyclone or the like may be added. This step allows the desired particle size, particle size distribution, specific surface area, and bulk density to be obtained.

[0083] An embodiment of the present invention will be described through the following examples and comparative examples, but the embodiment of the present invention should not be construed as being limited to the following examples.

[0084] Alumina particles were produced by thermal spraying, that is, by introducing an alumina particle raw material into a flame formed by LPG and oxygen. The average particle size of the alumina particles was adjusted by controlling the particle size of the introduced alumina particle raw material, and spherical alumina particles having the physical properties shown in Table 1 were produced by adjusting the flame formation conditions, raw material particle size, raw material supply amount, classification conditions, etc. The physical properties of the obtained alumina particles are shown in Table 1.

[0085]

[0086] The methods for measuring the various physical properties are described below.

[0087] [Average particle size] The average particle size (D50) was measured using a laser diffraction / scattering particle size distribution measuring device "Mastersizer 3000" (manufactured by Malvern).

[0088] [ ２７Measurement of the ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al by Al solid-state NMR] ２７ The ratio (α / β) of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al in solid-state Al NMR was measured by the following procedure. ２７ Al NMR analysis was performed. Each sample was packed into a φ3.2 mm solid-state NMR sample tube, and the tube was rotated at 20 kHz under magic angle spinning conditions at 23°C to obtain a spectrum by single pulse measurement. The measurement conditions were as follows: Pulse delay time: 50 seconds; Pulse width: 30-degree pulse of hexacoordinated aluminum; Number of accumulations: 8 times.

[0089] 1M AlCl ３ When the aqueous solution peak was taken as 0 ppm, the peak detected between -30 and 30 ppm was assumed to be the peak of hexacoordinated aluminum, and the peak detected between 40 and 100 ppm was assumed to be the peak of tetracoordinated aluminum. The coordination number ratio (the ratio of the peak area α of tetracoordinated Al to the peak area β of hexacoordinated Al (α / β)) was calculated from the ratio of the integral values ​​of the respective peaks.

[0090] [Method for Measuring Diffuse Reflectance] Reflectance is the diffuse reflectance including specular reflectance according to JIS Z8722:2009, and the reflected light of the alumina particles was measured using an integrating sphere. Specifically, the reflectance of the alumina particles was measured using an ultraviolet-visible-near-infrared spectrophotometer (Shimadzu Corporation, ultraviolet-visible-near-infrared spectrophotometer, SolidSpec-3700) including the reflected light of the alumina particles and specular reflected light using an integrating sphere. The average reflectance at measurement points from wavelengths of 400 nm to 700 nm was calculated. More specifically, 15 g of sample was weighed and placed in a 60 mm diameter quartz glass cell. The glass cell was tapped 20 times to fill the powder into the cell, and the reflectance was measured. The diffuse reflectance was calculated from the average value of the relative reflectance relative to a Spectralon white standard reflector (99%).

[0091] [Measurement method of lightness (L*) and chroma (C*)] Lightness (L*) and chroma (C*) were measured using a whiteness meter (Nippon Denshoku Industries, NW-12). * value, b * The value was measured, and the chroma (C*) was ２ +b ２ ) １／２ The calculation was carried out in accordance with JIS Z8722:2009. 15 g of the sample was weighed and placed in a φ100 mm round cell as a measurement container. The cell was tapped 20 times to fill the powder in the cell. The cell was set in a whiteness meter, and the lightness (L*) value, a* value, and b* value of the powder were measured, and c* was calculated from the a* value and b* value.

[0092] [Circularity] The circularity of the present examples and comparative examples was measured using images taken with a field-emission scanning electron microscope and image analysis software, Mac-View Version 5, manufactured by Mountec Co., Ltd. Because particles with an average particle size of 5 μm or less tend to aggregate, electron microscope images were taken by dispersing particles in ethanol, dripping the dispersion onto a flat carbon surface, and allowing it to dry naturally. For the analysis in Mac-View, the image taken with the electron microscope was loaded, regions not recognized as particles were designated using the base setting tool, and particles were selected using the automatic capture tool. The automatic capture conditions were as follows: acquisition mode "spherical," detection sensitivity "40 [minimum]," edge correction "10%," detection accuracy "standard (0.7)," and "particle smoothing." The circularity of 50 or more particles selected under these conditions was analyzed, and the average value was used as the circularity of the powder.

[0093] It was confirmed that alumina particles within the scope of one embodiment of the present invention can achieve a good diffuse reflectance of 90.0% or more. It was also confirmed that alumina particles within the scope of one embodiment of the present invention can achieve a good whiteness, with a lightness (L*) of 95% or more or a chroma (C*) of 0.50% or less. It was also confirmed that alumina particles within the scope of one embodiment of the present invention are spherical, with a circularity of 0.85 or more. It was also confirmed that alumina particles within the scope of one embodiment of the present invention can have an average particle size of 0.5 to 10.0 μm. Furthermore, as shown in Examples 7 and 8 below, it was confirmed that a resin composite composition containing alumina particles within the scope of one embodiment of the present invention can be obtained, and that various inorganic fillers can be blended into the resin composition.

[0094] Example 7: The alumina particles obtained in Example 1 and aluminum nitride particles (D50 = 30 μm) were mixed in a ratio of 90:10 (alumina particle weight:aluminum nitride particle weight) to prepare alumina particle mixture A. Furthermore, alumina particle mixture A was mixed with Dow Toray's silicone resin CY52-276A liquid so that the amount of alumina particle mixture A in the resin composite composition was 90% by mass. The mixture was then vacuum-kneaded using a Thinky vacuum kneader called "Awatori Rentaro" to obtain a resin composite composition. The kneading conditions were 15 seconds of pre-kneading and 90 seconds of vacuum kneading. 10 g of the resulting resin composite composition was placed on a smooth-surfaced iron plate. The iron plate was tilted 60° from the horizontal to check the flowability of the resin composite composition. After 5 hours of tilting, the resin composite composition flowed for more than 15 cm, confirming its good fluidity.

[0095] Example 8: Alumina particle mixture B was prepared by mixing the alumina particles obtained in Example 2 with boron nitride particles (D50 = 20 μm) in a ratio of 90:10 (alumina particle weight:boron nitride particle weight). Furthermore, alumina particle mixture B was mixed with Dow Toray's silicone resin CY52-276A liquid so that the amount of alumina particle mixture B in the resin composite composition was 90% by mass. The mixture was then vacuum-kneaded using a Thinky vacuum kneader called "Awatori Rentaro" to obtain a resin composite composition. Kneading conditions included 15 seconds of pre-kneading and 90 seconds of vacuum kneading. 10 g of the resulting resin composite composition was placed on a smooth-surfaced iron plate. The iron plate was tilted 60° from the horizontal to check the flowability of the resin composite composition. After 5 hours of tilting, the resin composite composition had flowed for more than 15 cm, confirming its good fluidity.

[0096] The alumina particles of one embodiment of the present invention have good diffuse reflectance and can also have good whiteness, spherical shape, and particle size. The alumina particles can be used in various applications, such as cosmetic compositions. One embodiment of the present invention also provides a resin composite composition containing the alumina particles, which can provide effects such as an excellent soft focus effect depending on the properties of the alumina particles (good diffuse reflectance, etc.).

Claims

1. ２７ 1. An alumina particle characterized in that the ratio (α / β) of a peak area α of tetracoordinated Al to a peak area β of hexacoordinated Al measured by Al solid-state NMR is 0.20 or more.

2. Alumina particles according to claim 1, having a brightness (L*) of 94.5% or more as measured by a whiteness meter.

3. Alumina particles according to claim 1, having a diffuse reflectance of 90.0% or more as measured by an ultraviolet-visible-near infrared spectrophotometer.

4. Alumina particles according to claim 1, which have a brightness (L*) of 95.0% or more as measured by a whiteness meter.

5. Alumina particles according to claim 1, having a chroma (C*) of 0.50% or less as measured by a whiteness meter.

6. Alumina particles according to claim 1, having a circularity of 0.85 or more.

7. The alumina particles according to claim 1, having an average particle size of 0.5 to 10.0 um.

8. A slurry composition comprising the alumina particles according to any one of claims 1 to 7.

9. The slurry composition according to claim 8, further comprising at least one inorganic filler selected from the group consisting of amorphous spherical alumina particles, non-spherical alumina particles, silica particles, titania particles, magnesia particles, aluminum nitride particles, boron nitride particles, barium titanate particles, calcium titanate particles, carbon fiber, talc, mica, kaolin, calcium oxide, zinc oxide, barium sulfate, calcium sulfate, and alkaline earth basic carbonates (calcium carbonate, magnesium carbonate).

10. A resin composite composition comprising the alumina particles according to any one of claims 1 to 7.

11. The resin composite composition according to claim 10, further comprising at least one inorganic filler selected from the group consisting of amorphous spherical alumina particles, non-spherical alumina particles, silica particles, titania particles, magnesia particles, aluminum nitride particles, boron nitride particles, barium titanate particles, calcium titanate particles, carbon fiber, talc, mica, kaolin, calcium oxide, zinc oxide, barium sulfate, calcium sulfate, and alkaline earth basic carbonates (calcium carbonate, magnesium carbonate).

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