Cosmetic composition and application method

Abstract

To provide a cosmetic composition having a soft focus effect.SOLUTION: A cosmetic composition contains alumina particles each having a card-house structure that is formed from three or more sheets of tabular alumina, with the sheets of tabular alumina fixed to each other, the alumina particles having an average particle size of 3 μm or more and 1000 μm or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to cosmetic compositions and application methods. This application claims priority to U.S. provisional application US62 / 912,656, filed October 9, 2019, the contents of which are incorporated herein by reference. [Background technology]

[0002] Cosmetic compositions for skin care or makeup generally contain fillers made of at least one of organic compounds and inorganic compounds. Examples of fillers include polymethylmethacrylate methylmethacrylate crosslinked polymers, mica, nylon particles, unfilled or filled melamine resins, talc, SiO2, kaolin, oxides or hydroxides of aluminum, magnesium, calcium, and zinc, BiOcl, barium sulfate, calcium sulfate, alkaline earth basic carbonates (calcium carbonate, magnesium carbonate, etc.), etc. These may be used alone or in combination in the cosmetic composition.

[0003] On the other hand, cosmetic compositions are desired to have the effect of hiding skin defects such as pores, scars, and fine wrinkles. A soft focus effect is known as an effect of hiding these skin defects. The soft focus effect is an effect of using light diffusing particles to scatter light on the skin surface and make the shadow of the skin less visible, thereby making the skin defects less noticeable. Examples of light diffusing particles that can achieve the soft focus effect include boron nitride particles, nylon particles, flaky or plate-like alumina particles coated with polymers or other materials, and spherical silica particles.

[0004] Patent Document 1 discloses a soft focus cosmetic composition containing 3 mass % or more of alumina particles (fumed alumina particles) consisting of substantially spherical primary particles fused or primary aggregated into relatively large, irregularly formed primary aggregate particles, relative to the total mass of the composition. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2007-507550 Summary of the Invention [Problem to be solved by the invention]

[0006] However, there continues to be a need for additional compositions to achieve a soft focus effect in cosmetic compositions.

[0007] The present invention has been made in consideration of the above circumstances, and provides a cosmetic composition having a soft focus effect and a method for applying the cosmetic composition to the skin. [Means for solving the problem]

[0008] That is, the present invention includes the following aspects. (1) A cosmetic composition comprising alumina particles having an average particle diameter of 3 μm or more and 1,000 μm or less, the alumina particles being formed of three or more sheets of tabular alumina and having a house-of-cards structure in which the tabular alumina particles are fixed together. (2) The cosmetic composition according to (1), wherein the alumina particles contain silicon and / or germanium. (3) The cosmetic composition according to (1) or (2), wherein the alumina particles contain molybdenum. (4) The cosmetic composition according to (3), wherein the molybdenum content relative to 100% by mass of the alumina particles is 10% by mass or less, calculated as molybdenum trioxide. (5) The cosmetic composition according to any one of (1) to (4), wherein the alumina particles have an oil absorption of 0.6 g or more and 5.0 g or less per 1 g of solid content. (6) The cosmetic composition according to any one of (1) to (5), which is for skin care or makeup. (7) The cosmetic composition according to any one of (1) to (6), further comprising a colorant. (8) The cosmetic composition according to any one of (1) to (7), which is a cosmetic selected from the group consisting of foundation, concealer, makeup base, eye shadow, eyeliner, mascara, blusher, lipstick, nail enamel, body cosmetics, and sunscreen. (9) A method for applying the cosmetic composition according to any one of (1) to (8) to skin. Effect of the Invention

[0009] According to the cosmetic composition of the present invention, a cosmetic composition having a soft focus effect can be provided. The application method of the present invention is a method using the cosmetic composition, and can hide skin defects with a soft focus effect. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of an alumina particle having a house-of-card structure according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing another example of the configuration of an alumina particle having a house-of-card structure according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a cosmetic composition and an application method according to one embodiment of the present invention will be described in detail.

[0012] <Cosmetic Composition> A cosmetic composition according to one embodiment of the present invention (hereinafter, may be referred to as "the cosmetic composition of the present embodiment") contains alumina particles. The alumina particles are formed of three or more alumina plates, have a card-house structure in which the alumina plates are fixed together, and have an average particle size of 3 μm or more and 1000 μm or less.

[0013] The alumina particles contained in the cosmetic composition of this embodiment have a larger specific surface area than spherical alumina particles of the same shape, and have a card-house structure in which tabular alumina particles are fixed, so that light is easily scattered. Therefore, the cosmetic composition of this embodiment can exhibit a soft focus effect. Next, each of the components contained in the cosmetic composition of this embodiment will be described in detail below.

[0014] [Alumina particles with a house-of-cards structure] The alumina particles having a house-of-cards structure are formed by three or more sheets of flat alumina, and have a house-of-cards structure in which the flat alumina are fixed to each other. Hereinafter, the alumina particles having a house-of-cards structure may be simply abbreviated as alumina particles. The flat plate shape may be, for example, a three-dimensional hexahedral plate shape, and the shape of the two-dimensional projection plane may be a typical quadrangle with four corners (quadrangle plate shape), or the shape of the two-dimensional projection plane may be a polygon with five or more corners (hereinafter, the latter may be referred to as polygonal plate shape). The alumina particles of the embodiment may contain potassium. The alumina particles of the embodiment may contain one or more selected from the group consisting of mullite and germanium compounds. The alumina particles have a house-of-cards structure, and therefore have an internal structure derived from the flat alumina constituting the house-of-cards structure, and have a higher specific surface area than spherical alumina particles of the same particle diameter, resulting in a high oil absorption amount, easy light scattering, and an effective soft focus effect.

[0015] The morphology of the alumina particles can be confirmed by a scanning electron microscope (SEM). The card house structure refers to a structure in which, for example, plate-like particles are arranged in a complex manner without being oriented. In this specification, the card house structure refers to a structure formed by three or more plate-like alumina sheets, which are fixed to each other (see, for example, FIG. 1), and may refer to a structure in which, for example, three or more plate-like alumina sheets are intersected and assembled at two or more points, and the intersecting faces of the plate-like alumina sheets may be arranged in a disordered manner (see FIG. 2). The intersecting position may be any position on the plate-like alumina sheets. The disordered arrangement refers to a state in which the directions in which the faces intersect with each other are not limited in any direction of the X-axis, Y-axis, or Z-axis, and the angles at which the faces intersect with each other may be any angle. Details of the plate-like alumina sheets will be described later.

[0016] Although it varies depending on the required average particle size of the alumina particles, when used in a cosmetic composition, the number of tabular alumina particles contained in one alumina particle is, for example, preferably 3 to 10,000, more preferably 10 to 5,000, and even more preferably 15 to 3,000, from the viewpoints of both performance and ease of production.

[0017] The intersection of the plate-like alumina occurs when three or more plates of plate-like alumina adhere to each other through some kind of interaction, for example, by bonding together during the crystallization process during the firing process. As a result, it may appear to be a crisscross pattern. The plate-like alumina adheres firmly to each other, which increases the strength of the house-of-cards structure.

[0018] In addition, an intersection means that two or more faces meet at one point, and there are no restrictions on the position, diameter, area, etc. of the intersection. In addition, the number of directions of the faces starting from the intersection point can be three, four or more.

[0019] The major axis, minor axis and thickness of the flat alumina itself contained in the card house structure may be any size, and the card house structure may include flat alumina of a plurality of sizes.

[0020] As described above, the tabular alumina may be tetragonal or polygonal. A single alumina particle may contain either tetragonal or polygonal alumina or both, and there is no limitation on the ratio.

[0021] In addition to the house-of-cards structure, the alumina particles may contain particles of an approximately X-shape (sometimes called twin crystal alumina particles; see FIG. 1) in which two sheets of flat alumina intersect, an approximately T-shape, an approximately L-shape, or a single sheet of flat alumina. In order to obtain excellent fluidity, the content ratio of these is preferably low, and the content ratio of alumina particles having a house-of-cards structure formed by three or more sheets of flat alumina and in which the flat alumina are fixed to each other is preferably 80% or more by weight or number. More preferably, it is 90% or more, and even more preferably, it is 95% or more. The content ratio of twin crystals or a single sheet of flat alumina can be easily adjusted by a general classification operation such as sieve classification or air classification.

[0022] Due to their unique structure, alumina particles having a house-of-cards structure have very high crushing strength and do not easily collapse even when external stress is applied. As a result, when incorporated into a cosmetic composition, they are less likely to break and can maintain a good texture. Therefore, the inherent functions of the alumina particles can be fully brought out, and even if they are mixed with plate-like alumina particles, the plate-like alumina particles, which tend to be oriented in the longitudinal direction, can be made to exist in random directions. As a result, excellent mechanical strength, soft focus effect, etc. can be expressed not only in the longitudinal direction but also in the thickness direction.

[0023] Due to their unique structure, alumina particles have excellent flowability as a powder, and it is possible to increase the discharge rate of feeders used for mechanical transport such as hoppers and feeders for industrial product applications. Alumina particles have voids inside due to their unique structure, so their bulk density is not significantly different from that of plate-like alumina particles, but compared to plate-like alumina particles, they have a higher sphericity and, as mentioned above, a higher crushing strength and are less likely to break, so it is presumed that they have a greater effect on ease of transport due to the rolling of the alumina particles.

[0024] The alumina particles have a house-of-cards structure. The house-of-cards structure is as described above. The alumina particles preferably have a flat alumina plate shape having a polygonal shape with more than 4 sides, and at least a part of adjacent alumina particles are in contact with each other, and more preferably have a flat alumina plate shape having a polygonal shape with more than 5 sides, and at least a part of adjacent alumina particles are in contact with each other.

[0025] [Crystal form / α crystallinity] The alumina particles are aluminum oxide, and the crystal form is not particularly limited. For example, the alumina may be transition alumina having various crystal forms such as γ, δ, θ, κ, etc., or may contain alumina hydrate in transition alumina. However, it is preferable that the a-crystal form is basically the α-crystal form because it has superior mechanical strength.

[0026] The α-crystallization rate of the alumina particles can be determined by XRD measurement. For example, using a wide-angle X-ray diffraction (XRD) device (Ultima IV, manufactured by Rigaku Corporation) described later, the prepared sample is placed on a holder for a measurement sample, and measurement is performed under conditions of Cu / Kα radiation, 40 kV / 40 mA, a scan speed of 2 degrees / min, and a scan range of 10 to 70°, and the α-crystallinity is calculated from the intensity ratio of the α-alumina peak to the baseline. The α-crystallinity rate varies depending on the firing conditions and the raw materials used, and from the viewpoint of improving the crushing strength and fluidity of the alumina particles, the α-crystallinity rate is preferably 90% or more, and more preferably 95% or more. The sample to be measured may be alumina particles or tabular alumina obtained by breaking down into a card house structure by some mechanical processing.

[0027] [Average particle size] The average particle size of the alumina particles having a house-of-cards structure may be any size within the range in which the structure can be formed, but in terms of excellent fluidity and improved soft focus effect, the average particle size is 3 μm or more, preferably 10 μm or more. On the other hand, if the size is too large, the house-of-cards structure may be exposed in the cosmetic composition, causing deterioration of the texture and reduced adhesion to the skin, so the average particle size is 1000 μm or less, preferably 300 μm or less, and more preferably 100 μm or less. An example of the range of the above numerical value is 3 μm or more and 300 μm or less, and may be 10 μm or more and 100 μm or less. In this specification, the "average particle size of alumina particles" refers to the volume-based median diameter D from the volume-based cumulative particle size distribution measured by a laser diffraction dry particle size distribution analyzer. 50 The value calculated as follows.

[0028] [Maximum particle size] In addition, the maximum particle diameter of the alumina particles based on volume (hereinafter in this specification, may be simply referred to as "maximum particle diameter") is not particularly limited, but is usually 3000 μm or less, preferably 1000 μm or less, and more preferably 500 μm or less.

[0029] If the maximum particle size of the alumina particles is larger than the above upper limit, the alumina particles may protrude from the surface onto which the cosmetic composition is applied, which may cause deterioration of the texture and decrease in adhesion to the skin, which is undesirable.

[0030] The average particle size and maximum particle size of the alumina particles referred to here are values ​​determined by a dry method in which the alumina particles themselves, which are formed of three or more sheets of flat alumina and have a card-house structure in which the flat alumina sheets are adhered to each other, are measured using a laser diffraction particle size distribution analyzer. The average particle size and maximum particle size can also be estimated by a wet method, for example, by dispersing the alumina particles in an appropriate solvent, specifically, by measuring a sample prepared by dispersing the alumina particles in a pure water medium containing sodium hexametaphosphate or the like as a dispersion stabilizer using a laser diffraction / scattering particle size distribution measuring device.

[0031] [Aspect ratio of plate-shaped alumina] The tabular alumina is preferably polygonal and has an aspect ratio, which is the ratio of particle diameter to thickness, of 2 to 500. An aspect ratio of 2 or more is advantageous for forming a house-of-cards structure while maintaining the properties specific to tabular alumina, and an aspect ratio of 500 or less is preferable because it allows easy adjustment of the average particle diameter of alumina particles and prevents deterioration of texture, deterioration of adhesion to skin, and deterioration of mechanical strength due to exposure of the house-of-cards structure in cosmetic compositions. More preferably, the aspect ratio is 5 to 300, even more preferably 7 to 100, and particularly preferably 10 to 50. An aspect ratio of 10 to 100 provides alumina particles having a house-of-cards structure with excellent thermal properties and optical properties including brightness of tabular alumina, and high fluidity and soft focus effect, which is preferable in terms of practicality.

[0032] In this specification, the thickness of the tabular alumina is determined by measuring the thickness of 10 pieces using a scanning electron microscope (SEM) and then averaging the measured thickness.

[0033] The particle size of the tabular alumina refers to the arithmetic mean value of the longest distance between two points on the contour line of the plate, and this value is measured using a scanning electron microscope (SEM).

[0034] The value of the long diameter of the tabular alumina means a value calculated by measuring the long diameter of any 100 tabular alumina particles from an image obtained by a scanning electron microscope (SEM). The long diameter of the tabular alumina can be measured, for example, by observing the alumina particles with an SEM and measuring the maximum length of the tabular alumina located at the center of the alumina particles. Alternatively, the maximum length of a single piece obtained by performing an air classification operation on the alumina particles can be measured with an SEM. Alternatively, a method can be used in which, under conditions that do not destroy the tabular alumina itself, a card house structure is broken down by some kind of mechanical processing to obtain a single piece, and the maximum length is measured with an SEM.

[0035] Furthermore, since the alumina particles having a house-of-cards structure preferably have an average particle diameter of, for example, 3 μm to 1000 μm, the tabular alumina constituting the alumina particles preferably has a thickness of, for example, 0.01 μm to 5 μm, a major axis of 0.1 μm to 500 μm, and an aspect ratio, which is the ratio of the major axis to the thickness, of 2 to 500. In particular, when the alumina particles are used as a cosmetic composition, it is more preferable that the thickness of the tabular alumina is 0.03 μm to 3 μm, the major axis of 0.5 μm to 100 μm, and the aspect ratio of 5 to 300, because of good usability. Even more preferably, the thickness of the tabular alumina is 0.1 μm to 3 μm, the major axis of 1 μm to 30 μm, and the aspect ratio of 10 to 100.

[0036] [Silicon-Germanium] In addition, the alumina particles having a card house structure preferably contain silicon (one or more selected from the group consisting of silicon atom and inorganic silicon compound) and one or more selected from the group consisting of germanium (one or more selected from the group consisting of germanium atom and inorganic germanium compound), and among them, it is preferable that one or more selected from the group consisting of silicon and germanium are contained on the surface of the tabular alumina.In particular, it is preferable that the alumina particles are contained locally on the surface in a smaller amount than that the alumina particles are contained inside, for example, in order to effectively improve affinity with a binder.

[0037] The silicon and germanium may be derived from the silicon, silicon compound, and germanium compound used as a shape control agent in the method for producing alumina particles described below.

[0038] The silicon contained in the alumina particles may be silicon alone or silicon in a silicon compound. The tabular alumina particles according to the embodiment may contain at least one selected from the group consisting of mullite, Si, SiO2, SiO, and aluminum silicate produced by reacting with alumina as silicon or a silicon compound, and may contain the above-mentioned substance in the surface layer. Mullite will be described later.

[0039] The amount of one or more elements selected from the group consisting of silicon and germanium unevenly distributed on the surface of tabular alumina containing one or more elements selected from the group consisting of silicon and germanium can be measured, for example, by analysis using an X-ray fluorescence analyzer (XRF) and analysis using X-ray photoelectron spectroscopy (XPS).

[0040] Generally, X-ray fluorescence spectroscopy (XRF) is a method for quantitatively analyzing the bulk composition of a material by detecting fluorescent X-rays generated by X-ray irradiation and measuring the wavelength and intensity. Generally, X-ray photoelectron spectroscopy (XPS) is a method for analyzing the elemental composition of a sample surface by irradiating the sample surface with X-rays and measuring the kinetic energy of photoelectrons emitted from the sample surface. The presence of one or more elements selected from the group consisting of silicon and germanium on the surface and its vicinity of the tabular alumina can be estimated from whether the [Si] / [Al]% (surface) or [Ge] / [Al]% (surface) obtained by the XPS analysis shows a larger value than the [Si] / [Al]% (bulk, molar ratio) or [Ge] / [Al]% (bulk, molar ratio) obtained by the XRF analysis of the product. This is because the surface of the tabular alumina obtained by blending one or more selected from the group consisting of silicon and germanium means that the amount of one or more selected from the group consisting of silicon and germanium is greater than that of the innermost part of the tabular alumina. The XRF analysis as described above can be performed using Primus IV manufactured by Rigaku Corporation. The XPS analysis can be performed using Quantera SXM manufactured by ULVAC-PHI, Inc.

[0041] The alumina particles preferably contain one or more selected from the group consisting of silicon atoms and inorganic silicon compounds locally on the surface of the tabular alumina constituting the alumina particles.In XPS analysis, the molar ratio of Si to Al, [Si] / [Al], is preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.1 or more. The upper limit of the molar ratio [Si] / [Al] in the XPS analysis is not particularly limited, but may be 0.5 or less, 0.4 or less, or 0.3 or less.

[0042] The alumina particles preferably have a molar ratio of Si to Al [Si] / [Al] obtained by XPS analysis of 0.001 or more and 0.5 or less, more preferably 0.01 or more and 0.4 or less, even more preferably 0.02 or more and 0.3 or less, and particularly preferably 0.1 or more and 0.3 or less. When the molar ratio of Si to Al obtained by XPS analysis is within the above range, alumina particles having a card house structure formed by tabular alumina can be easily obtained, and the obtained alumina particles exhibit excellent fluidity and crushing strength, and can improve the soft focus effect, which is preferable. In addition, for example, the adhesion to the skin can be improved.

[0043] By having a large amount of one or more selected from the group consisting of silicon atoms and inorganic silicon compounds on the surface of the tabular alumina, not only can the surface properties of the alumina particles made of the tabular alumina be made more hydrophobic than when they are not present, but also it is possible to improve the adhesion to the skin when used as a cosmetic composition. Furthermore, the one or more selected from the group consisting of silicon atoms and silicon compounds present on the surface of the alumina particles serve as reaction sites to contribute to reactions with various coupling agents including organic silane compounds, and it is also possible to easily adjust the surface condition of the alumina surface.

[0044] When the amount of Si on the surface of alumina particles is analyzed using the above-mentioned X-ray photoelectron spectroscopy (XPS) device, the sample is pressed and fixed onto double-sided tape, and composition analysis can be performed under the following conditions. X-ray source: Monochromatic AlKα, beam diameter 100μmφ, output 25W Measurement: Area measurement (1000 μm square), n=3 Charge correction: C1s=284.8eV

[0045] When the alumina particles further contain silicon, Si is detected by XRF analysis. In the alumina particles according to the embodiment, the molar ratio [Si] / [Al] of Si to Al obtained by XRF analysis is preferably 0.0003 or more and 0.1 or less, more preferably 0.0005 or more and 0.08 or less, more preferably 0.005 or more and 0.05 or less, and even more preferably 0.005 or more and 0.01 or less.

[0046] When the molar ratio [Si] / [Al] obtained by the XRF analysis is within the above range, alumina particles having a house-of-cards structure formed from tabular alumina can be easily obtained, and the obtained alumina particles exhibit excellent fluidity and crushing strength, thereby improving the soft focus effect, which is preferable.

[0047] The alumina particles contain silicon corresponding to the silicon or silicon compound used in the manufacturing method thereof. The silicon content relative to 100% by mass of the alumina particles obtained by XRF analysis is preferably 0.01% by mass to 8% by mass, more preferably 0.1% by mass to 5% by mass, even more preferably 0.5% by mass to 4% by mass, and particularly preferably 0.5% by mass to 2% by mass, calculated as silicon dioxide (SiO2). By having the silicon content within the above range, alumina particles having a house-of-cards structure formed by tabular alumina can be easily obtained, and the obtained alumina particles exhibit excellent fluidity and crushing strength, and are preferable because they can improve the soft focus effect.

[0048] The XRF analysis should be carried out under the same measurement conditions as those described in the Examples below, or under compatible conditions that give the same measurement results.

[0049] (germanium) The alumina particles may contain germanium. Also, the alumina particles may contain germanium in a surface layer. Although it depends on the raw material used, the alumina particles are germanium or germanium compounds such as Ge, GeO2, GeO, GeCl2, GeBr4, GeI4, GeS2, AlGe, GeTe, GeTe 3、 It may contain at least one selected from the group consisting of compounds such as As2, GeSe, GeS3As, SiGe, Li2Ge, FeGe, SrGe, GaGe, and oxides thereof, and the above substance may be contained in the surface layer. In addition, the "germanium or germanium compound" contained in the alumina particles according to the embodiment and the "raw germanium compound" used as a shape control agent of the raw material may be the same type of germanium compound.

[0050] The alumina particles according to the embodiment may contain germanium or a germanium compound in the surface layer of the tabular alumina constituting the alumina particles. By containing germanium or a germanium compound in the surface layer, for example, when blended in a cosmetic composition, a cosmetic composition having high adhesion to the skin and an even better soft focus effect can be provided. In addition, by containing germanium or a germanium compound with low Mohs hardness in the surface layer of the alumina particles, the texture can be made better.

[0051] Germanium or a germanium compound is contained in the surface layer of the tabular alumina, thereby exhibiting a remarkable soft focus effect and texture improvement effect. Here, the "surface layer" refers to within 10 nm from the surface of the tabular alumina particle according to the embodiment. This distance corresponds to the detection depth of XPS. The surface layer containing germanium is a very thin layer of within 10 nm, and in the case of germanium dioxide, for example, if the germanium dioxide structure on the surface and interface has many defects, it will have better compatibility with resin, and will exhibit a more remarkable soft focus effect than germanium dioxide with no or few structural defects. The alumina particles preferably have germanium or a germanium compound unevenly distributed in the surface layer of the tabular alumina. Here, "distributed unevenly in the surface layer" refers to a state in which the mass of germanium or a germanium compound per unit volume in the surface layer is greater than the mass of germanium or a germanium compound per unit volume in the other part of the surface layer. The uneven distribution of germanium or a germanium compound in the surface layer can be determined by comparing the results of the surface analysis by XPS and the overall analysis by XRF. By distributing germanium or a germanium compound unevenly in the surface layer, it is possible to exhibit excellent soft focus effect and texture improvement effect based on germanium or a germanium compound at a similar level with a smaller amount than when germanium or a germanium compound is present not only in the surface layer but also in the other part of the surface layer (inner layer).

[0052] The germanium content relative to 100% by mass of the alumina particles obtained by XRF analysis, calculated as germanium dioxide (GeO2), is preferably 0.01% by mass or more and 8% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less, and even more preferably 0.5% by mass or more and 4% by mass or less.

[0053] (Mullite) The alumina particles according to the embodiment may contain mullite in the surface layer of the tabular alumina constituting the alumina particles. By containing mullite in the surface layer, for example, when blended in a cosmetic composition, a cosmetic composition having high adhesion to the skin and an even more excellent soft focus effect can be provided. In addition, by containing mullite with a low Mohs hardness in the surface layer of the alumina particles, the texture can be made better.

[0054] Mullite, when contained in the surface layer of the tabular alumina, exerts a remarkable soft focus effect and texture improvement effect. The "mullite" that may be contained in the surface layer of the alumina particles is a composite oxide of Al and Si. X S Y O zHowever, there is no particular limit to the values ​​of x, y, and z. A more preferable range is Al2Si1O5 to Al6Si2O 13 For example, Al 2.85 SiO 6.3 , Al3SiO 6.5 , Al 3.67 SiO 7.5 , Al4Si1O8, or Al6Si2O 13 The tabular alumina particles contain Al 2.85 SiO 6.3 , Al3SiO 6.5 , Al 3.67 SiO 7.5 , Al4Si1O8, and Al6Si2O 13 The surface layer may contain at least one compound selected from the group consisting of. Here, the "surface layer" refers to within 10 nm from the surface of the tabular alumina. This distance corresponds to the detection depth of XPS. This mullite surface layer is a very thin layer of 10 nm or less, and if there are many defects in the mullite crystals on the surface and interface, the compatibility with the resin becomes even better, and compared to mullite with no or few crystal defects, the soft focus effect and texture improvement effect can be more significantly exhibited. The alumina particles preferably have mullite unevenly distributed in the surface layer of the tabular alumina. Here, "distributed unevenly in the surface layer" refers to a state in which the mass of mullite per unit volume in the surface layer is greater than the mass of mullite per unit volume in the other parts of the surface layer. The uneven distribution of mullite in the surface layer can be determined by comparing the results of surface analysis by XPS and overall analysis by XRF. By distributing mullite unevenly in the surface layer, it is possible to exhibit excellent soft focus effect and texture improvement effect based on mullite at the same level with a smaller amount than when mullite is present not only in the surface layer but also in the other parts of the surface layer (inner layer).

[0055] Moreover, the mullite of the surface layer may form a mullite layer, or may be in a state where mullite and alumina are mixed. The interface between the mullite and alumina of the surface layer may be in a state where the mullite and alumina are in physical contact with each other, or the mullite and alumina may form chemical bonds such as Si-O-Al. Compared to the combination of alumina and SiO2, the combination of alumina and mullite as essential components can bond alumina and mullite more firmly and make them less likely to peel off, from the viewpoint of the high similarity of the constituent atomic composition and the ease of forming chemical bonds such as Si-O-Al based on the flux method when the flux method is adopted. For this reason, if the amount of Si is at the same level, the combination of alumina and mullite as essential components is more preferable because it can exert a soft focus effect and a texture improvement effect for a longer period of time. The technical effects of a combination containing alumina and mullite as essential components can be expected from either alumina and mullite alone or alumina, mullite and silica, but if anything, the combination of the former two will provide a higher level of technical effect.

[0056] The presence or absence of mullite on the surface of alumina particles can be analyzed using a wide-angle X-ray diffraction (XRD) device such as Ultima IV manufactured by Rigaku Corporation. For example, a sample is placed on a measurement sample holder with a depth of 0.5 mm, and filled flat with a constant load. The sample is then set in the wide-angle X-ray diffraction (XRD) apparatus described above, and measurements are performed under the following conditions: Cu / Kα radiation, 40 kV / 40 mA, a scan speed of 2 degrees / min, and a scan range of 10 to 70 degrees. The presence or absence of mullite can be determined by the following formula, where the peak height of mullite observed at 2θ=26.2±0.2 degrees is A, the peak height of the (104) α-alumina plane observed at 2θ=35.1±0.2 degrees is B, and the baseline value at 2θ=30±0.2 degrees is C. The value of R may be, for example, 0.02 or more, 0.02 or more and 0.3 or less, 0.05 or more and 0.2 or less, or 0.1 or more and less than 0.12.

[0057] R = (AC) / (BC)

[0058] (R: Ratio of mullite peak height A to α-alumina (104) plane peak height B)

[0059] [molybdenum] The alumina particles having a house-of-card structure may contain molybdenum.

[0060] The molybdenum may be derived from a molybdenum compound used as a fluxing agent in the method for producing alumina particles described below.

[0061] Molybdenum has catalytic and optical properties, and by using molybdenum, alumina particles with excellent flowability can be produced in a production method as described below.

[0062] The molybdenum is not particularly limited, and in addition to molybdenum metal, it includes molybdenum oxide, partially reduced molybdenum compounds, molybdates, etc. The molybdenum may be contained in the tabular alumina particles in any of the polymorphs that the molybdenum compound can take, or in combination, and may be contained in the tabular alumina particles as α-MoO3, β-MoO3, MoO2, MoO, a molybdenum cluster structure, etc.

[0063] The form in which molybdenum is contained is not particularly limited, and may be contained in a form in which it is adhered to the surface of the tabular alumina of an alumina particle having a house-of-card structure, or may be contained in a form in which it is substituted for part of the aluminum in the crystal structure of the alumina, or may be a combination of these.

[0064] The molybdenum content relative to 100% by mass of the alumina particles, as calculated in molybdenum trioxide (MoO3) obtained by XRF analysis, is preferably 10% by mass or less, and by adjusting the firing temperature, firing time, and flux conditions, it is preferably 0.001% by mass or more and 8% by mass or less, more preferably 0.01% by mass or more and 8% by mass or less, and even more preferably 0.1% by mass or more and 5% by mass or less. A molybdenum content of 10% by mass or less is preferable because it improves the α single crystal quality of alumina.

[0065] The XRF analysis should be carried out under the same measurement conditions as those described in the Examples below, or under compatible conditions that give the same measurement results.

[0066] The amount of Mo on the surface of the alumina particles can be analyzed using the above-mentioned X-ray photoelectron spectroscopy (XPS) device. For example, the composition analysis can be performed using the above-mentioned X-ray photoelectron spectroscopy (XPS) apparatus under the following conditions, with the sample being press-fixed onto double-sided tape: When the [Mo] / [Al] (molar ratio) determined from the XPS analysis results is taken as the amount of Mo on the surface of the house-of-card-type alumina particles, the amount of Mo is preferably 0.0005 or more.

[0067] (conditions) X-ray source: Monochromatic AlKα, beam diameter 100μmφ, output 25W Measurement: Area measurement (1000 μm square), n=3 Charge correction: C1s=284.8eV

[0068] [potassium] The alumina particles having a house-of-card structure may contain potassium.

[0069] The potassium may be derived from potassium that can be used as a fluxing agent in the method for producing alumina particles described below. By utilizing potassium, alumina particles having excellent fluidity can be produced with high efficiency in the method for producing alumina particles described below.

[0070] The potassium is not particularly limited, but includes potassium metal, potassium oxide, partially reduced potassium compounds, and the like.

[0071] The form in which potassium is contained is not particularly limited, and may be contained in a form in which it is adhered to the surface of the tabular alumina of alumina particles having a house-of-card structure, or may be contained in a form in which it is substituted for part of the aluminum in the crystal structure of the alumina, or may be a combination of these.

[0072] The potassium content relative to 100% by mass of the alumina particles, as calculated by XRF analysis, is preferably 0.05% by mass or more, more preferably 0.05 to 5% by mass, even more preferably 0.1 to 3% by mass, and particularly preferably 0.1 to 1% by mass. Alumina particles having a potassium content within the above range are preferred because they have a house-of-cards structure and have suitable values ​​for the average particle size, etc. Also preferred are those having excellent fluidity and capable of improving the soft focus effect.

[0073] The XRF analysis should be carried out under the same measurement conditions as those described in the Examples below, or under compatible conditions that give the same measurement results.

[0074] (Inevitable impurities) The alumina particles may contain unavoidable impurities.

[0075] Inevitable impurities are impurities that originate from metal compounds used in production, are present in raw materials, or are inevitably mixed into alumina particles during the production process. Although they are not actually required, they are present in trace amounts and do not affect the properties of the alumina particles.

[0076] The inevitable impurities are not particularly limited, but include magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, sodium, etc. These inevitable impurities may be contained alone or in combination of two or more kinds.

[0077] The content of unavoidable impurities in the alumina particles is preferably 10,000 ppm or less, more preferably 1,000 ppm or less, and further preferably 10 to 500 ppm, based on the mass of the alumina particles.

[0078] (other atoms) The other atoms refer to those that are intentionally added to the alumina particles for the purpose of imparting soft focus effect, mechanical strength, and electrical or magnetic functions, within the scope of not impairing the effects of the present invention.

[0079] The other atoms are not particularly limited, but include zinc, manganese, calcium, strontium, yttrium, etc. These other atoms may be used alone or in combination of two or more.

[0080] The content of other atoms in the alumina particles is preferably 5 mass % or less, and more preferably 2 mass % or less, based on the mass of the alumina particles.

[0081] [Organic compounds] In one embodiment, the alumina particles may contain an organic compound. The organic compound is present on the surface of the alumina particles and has a function of adjusting the surface properties of the alumina particles. For example, alumina particles containing an organic compound on the surface improve adhesion to the skin, and therefore the function of the alumina particles can be maximized in a cosmetic composition.

[0082] Organic compounds include, but are not limited to, organosilanes, alkylphosphonic acids, and polymers.

[0083] Examples of the organic silane include alkyltrimethoxysilanes or alkyltrichlorosilanes having an alkyl group having 1 to 22 carbon atoms, such as methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, pentyltrimethoxysilane, and hexyltrimethoxysilane; 3,3,3-trifluoropropyltrimethoxysilane, tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilanes; phenyltrimethoxysilane, phenyltriethoxysilane, p-chloromethylphenyltrimethoxysilane, and p-chloromethylphenyltriethoxysilanes.

[0084] Examples of the phosphonic acid include methylphosphonic acid, ethylphosphonic acid, propylphosphonic acid, butylphosphonic acid, pentylphosphonic acid, hexylphosphonic acid, heptylphosphonic acid, octylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, octadecylphosphonic acid, 2-ethylhexylphosphonic acid, cyclohexylmethylphosphonic acid, cyclohexylethylphosphonic acid, benzylphosphonic acid, phenylphosphonic acid, and dodecylbenzenephosphonic acid.

[0085] As the polymer, for example, poly(meth)acrylates can be suitably used.Specific examples include polymethyl(meth)acrylate, polyethyl(meth)acrylate, polybutyl(meth)acrylate, polybenzyl(meth)acrylate, polycyclohexyl(meth)acrylate, polyt-butyl(meth)acrylate, polyglycidyl(meth)acrylate, polypentafluoropropyl(meth)acrylate, etc., and also include general-purpose polymers such as polystyrene, polyvinyl chloride, polyvinyl acetate, epoxy resin, polyester, polyimide, polycarbonate, etc.

[0086] The organic compound may be contained alone or in combination of two or more kinds.

[0087] The form in which the organic compound is contained is not particularly limited, and the organic compound may be bonded to the alumina via a covalent bond, or may coat the alumina.

[0088] The content of the organic compound is preferably 20% by mass or less, more preferably 10 to 0.01% by mass, based on the mass of the alumina particles. When the content of the organic compound is 20% by mass or less, it is preferable because the physical properties derived from the alumina particles can be easily expressed.

[0089] [Crushing strength] Alumina particles preferably have a higher crushing strength because their inherent fluidity is lost if the card-house structure is destroyed by mechanical dispersion by compression, shear, etc. The crushing strength differs depending on the intersection position, number, area, thickness and aspect ratio of the tabular alumina, etc., and the crushing strength required for various applications differs, so from the viewpoint of practicality, the crushing strength is preferably 1 MPa to 100 MPa, more preferably 20 MPa to 100 MPa, and even more preferably 50 MPa to 100 MPa. The crushing strength of alumina particles can be measured using, for example, a microparticle crushing force measuring device NS-A100 manufactured by Nanoseeds Co., Ltd., or an MCT-510 manufactured by Shimadzu Corporation. The difference between the peak value at the time of crushing and the baseline (when no force is applied) is defined as the crushing force F [N], and the crushing strength S [Pa] is the average value of 10 values ​​calculated using the following formula.

[0090] S = 2.8F / (π D 2 )

[0091] In the above formula, F is the crushing force [N] and D is the particle diameter [m].

[0092] As described above, the alumina particles are formed of three or more flat alumina sheets and have a card house structure in which the alumina particles are fixed together. The present inventors have found that alumina particles containing at least one selected from the group consisting of silicon atoms and inorganic silicon compounds in a moderate amount have a higher crushing strength than those not containing these. The crushing strength also varies depending on the content of at least one selected from the group consisting of silicon atoms and inorganic silicon compounds, and the more the content is appropriately increased, the higher the fluidity and crushing strength of the particles can be. In addition, for example, the crushing strength can be increased by adopting specific manufacturing conditions as the manufacturing method. The crushing strength can also be adjusted arbitrarily in terms of manufacturing conditions, and as an example, the crushing strength of the alumina particles can be increased by increasing the firing temperature.

[0093] [Powder fluidity] The powder of alumina particles according to the embodiment has excellent flowability as a powder compared with plate-like alumina particles and twin crystal alumina particles, because the alumina itself constituting the powder has a unique structure and preferably has a specific average particle diameter, but in order to further improve the flowability, it is preferable that the shape of the maximum surrounding surface on a volume basis when the alumina particles forming a card house structure of one unit are surrounded so as to include all the plate-like alumina constituting the particle is spherical or approximately spherical. Furthermore, if necessary, a lubricant, fine silica particles, etc. may be added arbitrarily to further improve the flowability.

[0094] The flowability of the powder of the card-house structured alumina particles can be determined, for example, by measuring the angle of repose according to JIS R9301-2-2. The value of the angle of repose is preferably 50° or less, since problems such as hopper bridges, feed necks, non-uniform supply, and reduced discharge rate are unlikely to occur during mechanical transport using a feeder, hopper, etc. More preferably, it is 40° or less.

[0095] The alumina particles may be formed of three or more flat alumina sheets, have a card-house structure in which the flat alumina sheets are fixed to each other, and have an average particle size of 1 to 1000 μm. More preferably, the alumina particles have an internal structure in which the three or more flat alumina sheets are intersected and assembled at two or more points as a card-house structure fixed to each other, and the intersecting flat plates are randomly arranged in the plane direction.

[0096] Conventionally known twin crystal alumina particles have a structure with prominent corners due to their shape, and are less likely to roll than the alumina particles according to the embodiment, so that they do not have sufficient fluidity as a filler. In addition, even if the alumina particles have the same house-of-cards structure as the alumina particles according to the embodiment, those with a moderately large average particle size have better fluidity. The alumina particles according to the embodiment exhibit particularly excellent fluidity due to the synergistic effect of the house-of-cards structure and the preferred average particle size.

[0097] [pH at isoelectric point] The pH of the isoelectric point of the alumina particles is, for example, in the range of 2 to 8, preferably in the range of 2.5 to 7, and more preferably in the range of 3 to 6. Alumina particles having an isoelectric point within the above range have a high electrostatic repulsive force, and can enhance the dispersion stability when blended into the above-mentioned dispersion medium, and can be easily modified by surface treatment such as a coupling treatment agent for further improving performance.

[0098] The pH value of the isoelectric point is obtained by measuring the zeta potential with a zeta potential measuring device (Malvern Instruments, Zetasizer Nano ZSP) by stirring 20 mg of sample and 10 mL of 10 mM KCl aqueous solution for 3 minutes in stirring / degassing mode with a foam remover (Thinky Corporation, ARE-310), leaving it to stand for 5 minutes, and using the supernatant as the measurement sample. 0.1 N HCl is added to the sample with an automatic titration device, and the zeta potential is measured in the range up to pH = 2 (applied voltage 100 V, Monomodl mode), and the pH at the isoelectric point where the potential becomes zero is evaluated.

[0099] [Specific surface area] The specific surface area of ​​alumina particles is usually 50 to 0.001 m 2 / g, but preferably in the range of 10m 2 / g~0.01m 2 / g, more preferably 5.0m 2 / g~1m 2 Within the above range, the number of tabular alumina particles forming the card house structure is appropriate, the oil absorption is large, the cosmetic lasts longer, and the cosmetic tends to be less likely to come off. Furthermore, there is no significant increase in viscosity when made into a slurry, and the processability is excellent.

[0100] The specific surface area can be measured by JIS Z 8830: BET one-point method (adsorption gas: nitrogen) or the like.

[0101] [Porosity] The alumina particles are formed of three or more flat alumina sheets, and have a card house structure in which the flat alumina sheets are fixed to each other, so that the alumina particles have voids. When the ratio of voids is large, the shape tends to be uniform and the fluidity tends to be improved, so the void ratio is preferably 10% by volume or more. More preferably, it is 30% by volume or more. Furthermore, when the ratio of voids is large, the crushing strength of the powder decreases, so the void ratio is preferably 90% by volume or less. More preferably, it is 70% by volume or less. When the void ratio is within this range, the bulk density is appropriate, the fluidity is not impaired, and the handleability is also good. This void ratio can be determined by measurements such as gas adsorption method and mercury porosimetry according to JIS Z 8831.

[0102] Conveniently, the porosity can be estimated by mixing alumina particles with a liquid curable compound such as an epoxy compound or a (meth)acrylic monomer, curing the mixture, and then cutting and polishing the cross section and observing it with an SEM.

[0103] [Oil absorption of alumina particles] The oil absorption per 1 g of solid content of the alumina particles is preferably 0.6 g to 5.0 g, more preferably 0.8 g to 4.5 g, and even more preferably 1.0 g to 4.0 g. The alumina particles used in the cosmetic composition of this embodiment have a card house structure, and therefore have a larger surface area than conventional alumina particles, so that the oil absorption can be set to the above range. In addition, by setting the oil absorption within the above range, the cosmetic composition of this embodiment tends to have a longer makeup life and be less likely to come off. The oil absorption can be measured using the method shown in the examples described below.

[0104] [Alumina particle content] The content of alumina particles in the cosmetic composition of this embodiment can be from 0.01% by mass to 95% by mass, from 0.1% by mass to 50% by mass, or from 1% by mass to 10% by mass, relative to the total mass of the composition.

[0105] <Method of manufacturing alumina particles> Next, the method for producing alumina particles according to the embodiment will be described in detail, but the method for producing alumina particles according to the embodiment is not limited to the method for producing alumina particles described below.

[0106] The average particle size, fluidity, specific surface area, mechanical strength, porosity, thickness and aspect ratio of the tabular alumina particles can be adjusted by the manufacturing method described later in detail. For example, when the flux method is adopted as the manufacturing method, the average particle size can be adjusted by the molybdenum compound (preferably further potassium compound) as the flux agent, the aluminum compound type, the average particle size of the aluminum compound, the purity of the aluminum compound, the use ratio of at least one shape control agent selected from silicon, silicon compounds and germanium compounds, the type of other shape control agents, the use ratio with other shape control agents, the existence state of one or more shape control agents selected from the group consisting of silicon, silicon compounds and germanium compounds and the aluminum compound, the existence state of other shape control agents and the aluminum compound, etc.

[0107] The alumina particles may be obtained based on any manufacturing method as long as they can have a card house structure. However, it is not preferable to obtain alumina having a unique structure, such as a card house structure, by post-treatment using alumina of an existing structure, since the manufacturing process is multi-staged and the productivity is poor. For example, it is preferable from the viewpoint of productivity to adopt a manufacturing method of alumina particles that can selectively form a card house structure as a structure from an existing alumina raw material, can easily contain molybdenum therein, and can also easily contain potassium, silicon, germanium, etc., and can satisfy all of these at once.

[0108] That is, in obtaining alumina particles, it is preferable to obtain them by calcining an aluminum compound in the presence of a molybdenum compound, at least one shape control agent selected from silicon, a silicon compound, and a germanium compound, and, if necessary, other shape control agents, in terms of superior fluidity, dispersibility, and productivity. In addition, since almost all of the alumina particles produced can have a card house structure and thus have superior productivity, it is preferable to obtain the alumina particles by calcining an aluminum compound in the presence of a molybdenum compound, a potassium compound, at least one shape control agent selected from silicon, a silicon compound and a germanium compound, and, if necessary, other shape control agents.

[0109] More specifically, a preferred method for producing alumina particles includes a step (calcination step) of calcining an aluminum compound in the presence of a molybdenum compound and at least one shape control agent selected from silicon, a silicon compound, and a germanium compound. The calcination step may be a step of calcining a mixture obtained in a step (mixing step) of obtaining a mixture to be calcined. The mixture preferably further contains a potassium compound. The mixture preferably further contains a metal compound described below. The metal compound is preferably an yttrium compound.

[0110] When organic compounds are used as the molybdenum compound or silicon compound, the organic components are burned off by firing. That is, alumina particles can be obtained more easily by incorporating molybdenum into alumina particles when the molybdenum compound reacts with an aluminum compound at high temperature to form aluminum molybdate, and the aluminum molybdate is further decomposed into alumina and molybdenum oxide at a higher temperature. Molybdenum oxide sublimes, but it can be recovered and reused. Hereinafter, this manufacturing method is called the flux method. This flux method will be described in detail later.

[0111] The shape control agent plays an important role in the growth of plate-like crystals. In the commonly used flux method using a molybdenum compound, molybdenum oxide reacts with an aluminum compound to form aluminum molybdate, and then the change in chemical potential during the decomposition of this aluminum molybdate serves as the driving force for crystallization, forming hexagonal bipyramidal polyhedral particles with developed idiomorphic faces (113). In the manufacturing method of the embodiment, the shape control agent is localized near the particle surface during the α-alumina growth process, significantly inhibiting the growth of the idiomorphic faces (113), resulting in relatively fast growth of the crystal orientation in the face direction, and the (001) or (006) face growing, which is believed to form a plate-like morphology. By using a molybdenum compound as a flux agent, alumina particles made of tabular alumina containing molybdenum with a high α-crystallization rate, particularly an α-crystallization rate of 90% or more, can be more easily formed.

[0112] It should be noted that the above mechanism is merely speculation, and even if the effects of the present invention are obtained through a mechanism different from the above mechanism, this is still within the technical scope of the present invention.

[0113] By utilizing a molybdenum compound, the alumina particles have a high α-crystal ratio and are idiomorphic, so that excellent dispersibility in the matrix, mechanical strength, and luster can be achieved.

[0114] In addition, the alumina particles obtained by the above-mentioned production method have excellent dispersibility because the isoelectric point of the zeta potential is shifted to the acidic side compared to ordinary alumina due to the inclusion of molybdenum in the particles. Furthermore, the properties of the molybdenum contained in the alumina particles may be utilized to apply the alumina particles to cosmetic compositions.

[0115] [Method of manufacturing alumina particles using the flux method] The method for producing the alumina particles is not particularly limited, but from the viewpoint of being able to suitably control alumina having a high α crystallization rate at a relatively low temperature, a production method using a flux method utilizing a molybdenum compound can be preferably applied.

[0116] More specifically, a preferred method for producing alumina particles includes a step of calcining an aluminum compound in the presence of a molybdenum compound, at least one shape control agent selected from the group consisting of silicon, silicon compounds and germanium compounds, and, if necessary, other shape control agents.

[0117] The present inventors have newly discovered that when employing a manufacturing method in which a molybdenum compound is used as a flux agent in combination with a shape control agent, and these are mixed with an aluminum compound and fired in a flux method, the size of the raw aluminum compound, the amount of molybdenum compound used (and the amount of potassium compound used when a potassium compound is used as a flux agent), and the amount of shape control agent used are important factors in selectively producing alumina particles.

[0118] In the flux method, it is also preferable to use a molybdenum compound and a potassium compound as fluxing agents. The compound containing molybdenum and potassium as a fluxing agent can be produced, for example, in the firing process using a molybdenum compound and a potassium compound, which are cheaper and easier to obtain, as raw materials. Here, the case where a molybdenum compound and a potassium compound are used as fluxing agents will be described as an example, combining the case where a molybdenum compound and a potassium compound are used as fluxing agents and the case where a compound containing molybdenum and potassium is used as fluxing agents.

[0119] In a method for producing alumina particles, in which a molybdenum compound is used as an essential fluxing agent, a shape control agent is used in combination, and these are mixed with an aluminum compound and fired, compared to a case in which only a molybdenum compound such as molybdenum trioxide is used, when a molybdenum compound and a potassium compound are used as fluxing agents, or when a compound containing molybdenum and potassium is used as a fluxing agent, the firing step is carried out in the presence of a compound containing molybdenum and potassium, which is difficult to vaporize, so that the fluxing agent is not released outside the system and deterioration of the firing work environment is reduced, and further, since the compound containing molybdenum and potassium contained in the mixture of alumina particles and fluxing agent particles generated in the cooling step is often highly water-soluble, it becomes possible to remove more molybdenum from alumina more easily. By using a molybdenum compound and a potassium compound as a fluxing agent, or by using a compound containing molybdenum and potassium as a fluxing agent, and by including the cooling step, it is possible to obtain alumina particles having a house-of-cards structure without the need for strong crushing, and furthermore, the yield of alumina particles having a house-of-cards structure can be made very high. This is believed to be because, with such a configuration, the fluxing agent occupies the spaces between the alumina particles having a house-of-cards structure, so to speak, the fluxing agent acts as a spacer, preventing the particles from fusing together, and the fluxing agent can be easily removed in a post-treatment step. From the viewpoint of preventing the fusion of particles, the amount of flux agent used (the amount of molybdenum compound and potassium compound when the total amount of raw materials converted into oxides is taken as 100 mass%) is preferably 2 mass% or more in terms of Mo2K2O7.

[0120] [Mixing process] The mixing step is a step of mixing raw materials such as an aluminum compound, a molybdenum compound, a shape control agent, etc. to obtain a mixture. The mixture may further contain a potassium compound. The contents of the mixture will be described below.

[0121] (Aluminum Compounds) The raw aluminum compound is a raw material for the above-mentioned alumina particles, and is not particularly limited as long as it becomes alumina by heat treatment. For example, aluminum chloride, aluminum sulfate, basic aluminum acetate, aluminum hydroxide, boehmite, pseudo-boehmite, transition alumina (γ-alumina, δ-alumina, θ-alumina, etc.), α-alumina, mixed alumina having two or more crystal phases, etc. can be used, and one or more types selected from the group consisting of aluminum hydroxide and transition alumina are preferable.

[0122] The aluminum compound may be composed of only an aluminum compound, or may be a complex of an aluminum compound and an organic compound. For example, an organic / inorganic complex obtained by modifying an aluminum compound with an organic silane compound, an aluminum compound complex adsorbing a polymer, etc. may be suitably used. Since the organic components of the organic compound are burned off by firing, when using these complexes, the content of the organic compound is not particularly limited, but from the viewpoint of efficiently producing alumina particles having a house-of-cards structure, the content is preferably 60% by mass or less, more preferably 30% by mass or less.

[0123] The specific surface area of ​​the aluminum compound is not particularly limited. Since the molybdenum compound of the fluxing agent acts effectively, it is preferable that the specific surface area is large, but by adjusting the firing conditions and the amount of the molybdenum compound used, any specific surface area can be used as the raw material.

[0124] According to the flux method described below, the shape of the alumina particles reflects the shape of the raw material aluminum compound. Any shape such as a sphere, an amorphous shape, an aspected structure (wire, fiber, ribbon, tube, etc.), or a sheet can be used, but from the viewpoint of improving the flowability of the powder, it is preferable to use a spherical aluminum compound because the resulting alumina particles are closer to a sphere.

[0125] In the method for producing alumina particles from an aluminum compound, the average particle size of the alumina particles also basically reflects the particle size of the aluminum compound as a raw material.

[0126] According to the flux method described below, in the firing process, it is assumed that the plate-like alumina crystals are formed mainly in the raw aluminum compound particles, and that the intersection and adhesion of three or more adjacent plate-like alumina sheets progresses, resulting in a house-of-cards structure. Therefore, it is assumed that the average particle size of the obtained alumina particles having a house-of-cards structure mainly reflects the average particle size of the raw aluminum particles.

[0127] Therefore, when an aluminum compound having a smaller average particle diameter is used as a raw material, alumina particles having a smaller average particle diameter are more likely to be obtained, and when an aluminum compound having a larger average particle diameter is used, alumina particles having a larger average particle diameter are more likely to be obtained.

[0128] Since the alumina particles preferably have an average particle size of 3 μm or more and 1000 μm or less, it is preferable to use an aluminum compound having an average particle size that is the same or approximately the same as that of the alumina particles having a specific average particle size to be generated, within the above range.

[0129] The alumina particles having a house-of-cards structure can be obtained by forming tabular alumina in a method for producing alumina particles, the method including a step of calcining an aluminum compound in the presence of a molybdenum compound, one or more shape control agents selected from the group consisting of silicon, silicon compounds, and germanium compounds, and other shape control agents as necessary, and by bringing three or more of the tabular alumina into contact with each other's crystal faces at multiple locations at the same time as the formation, intersecting and fixing the alumina particles. The fixing makes the house-of-cards structure not easily broken (unraveled) by external stress such as pressure, and provides a fixed state. For example, the flux conditions when the tabular alumina is formed affect the crushing strength of the alumina particles having the obtained house-of-cards structure.

[0130] The smaller the amount of the molybdenum compound, the faster and more frequently three or more plates of alumina are fixed to an aluminum compound particle, and therefore a strong house-of-cards structure with high crushing strength can be obtained.

[0131] According to the findings of the present inventors focusing on the flux method, specifically, for example, when 1) an aluminum compound having an average particle size of 2 μm or more, particularly 4 μm or more, corresponding to the particle size of the desired alumina particles is used as the raw material aluminum compound, 2) the amount of the molybdenum compound as the fluxing agent is 0.005 to 0.236 mol of molybdenum metal in the molybdenum compound per 1 mol of aluminum metal in the aluminum compound, and 3) the amount of the silicon compound as the shape control agent is 0.003 to 0.09 mol of silicon metal in the silicon compound per 1 mol of aluminum metal in the aluminum compound, it is preferable because alumina particles having a card-house structure with higher fluidity and higher crushing strength can be obtained.

[0132] In the flux method, a method for producing alumina particles in which a molybdenum compound and a potassium compound are used as fluxing agents and silicon or a silicon compound are used in combination as a shape control agent, which are mixed with an aluminum compound and fired, is preferable because it is possible to selectively produce alumina particles that are formed from three or more tabular alumina sheets within a specific average particle size range and have a card house structure in which the tabular alumina sheets are adhered to each other by 1) using a raw aluminum compound having a specific average particle size, 2) limiting the amount of the molybdenum compound and the potassium compound used to a specific range, and 3) limiting the amount of the silicon or a silicon compound used to a specific range.

[0133] Furthermore, the average particle size and shape of the alumina particles having a house-of-card structure can be adjusted as desired by the crushing step and classification step described below.

[0134] (Molybdenum Compounds) As described later, the molybdenum compound functions as a fluxing agent in the growth of α-crystals of alumina. The molybdenum compound is not particularly limited, but may be, for example, molybdenum oxide, molybdenum metal bonded with oxygen to form an acid radical anion (MoO x n- ) is included.

[0135] The acid radical anion (MoO x n- ) is not particularly limited, but may be, for example, molybdic acid, sodium molybdate, potassium molybdate, lithium molybdate, HPMo 12 O 40 , H3SiMo 12 O 40 , NH4Mo7O 12 , molybdenum disulfide, etc.

[0136] The molybdenum compound may also contain sodium or silicon, in which case the molybdenum compound containing sodium or silicon acts as both a flux agent and a shape control agent.

[0137] Among the above molybdenum compounds, it is preferable to use molybdenum oxide from the viewpoint of cost. The above molybdenum compounds may be used alone or in combination of two or more kinds.

[0138] In addition, potassium molybdate (K2Mo n O 3n+1 (n=1 to 3) contains potassium and therefore may also function as a potassium compound, which will be described later. In the manufacturing method of the embodiment, using potassium molybdate as a fluxing agent is synonymous with using a molybdenum compound and a potassium compound as fluxing agents.

[0139] The amount of the molybdenum compound used is not particularly limited, but is preferably 0.005 to 0.236 mol, more preferably 0.007 to 0.09 mol, and even more preferably 0.01 to 0.04 mol, as molybdenum metal of the molybdenum compound, relative to 1 mol of aluminum metal of the aluminum compound. When the amount of the molybdenum compound used is within the above range, it is preferable because alumina particles having a house-of-cards structure made of tabular alumina having a high aspect ratio and excellent dispersibility are easily obtained. In addition, when a molybdenum compound is used as a fluxing agent when the flux method is adopted, the alumina particles contain molybdenum, and this evidence can be used to identify the manufacturing method by which the unknown alumina particles were manufactured.

[0140] When the molybdenum compound and the potassium compound are used as fluxing agents, the amount of the molybdenum compound is not particularly limited, but the molar ratio of the molybdenum element of the molybdenum compound to the aluminum element of the aluminum compound (molybdenum element / aluminum element) is preferably 0.01 to 3.0, more preferably 0.1 to 1.0, and even more preferably 0.30 to 0.70 for good productivity and favorable crystal growth. When the amount of the molybdenum compound is within the above range, it is preferable because it is easy to obtain alumina particles having a card house structure made of tabular alumina having a high aspect ratio and excellent dispersibility.

[0141] (Potassium compounds) When a molybdenum compound and a potassium compound are used as a fluxing agent, the potassium compound is not particularly limited, but includes potassium chloride, potassium chlorite, potassium chlorate, potassium sulfate, potassium hydrogen sulfate, potassium sulfite, potassium hydrogen sulfite, potassium nitrate, potassium carbonate, potassium hydrogen carbonate, potassium acetate, potassium oxide, potassium bromide, potassium bromate, potassium hydroxide, potassium silicate, potassium phosphate, potassium hydrogen phosphate, potassium sulfide, potassium hydrogen sulfide, potassium molybdate, potassium tungstate, etc. In this case, the potassium compound includes isomers, as in the case of the molybdenum compound. Among these, it is preferable to use potassium carbonate, potassium hydrogen carbonate, potassium oxide, potassium hydroxide, potassium chloride, potassium sulfate, or potassium molybdate, and it is more preferable to use potassium carbonate, potassium hydrogen carbonate, potassium chloride, potassium sulfate, or potassium molybdate.

[0142] The potassium compounds described above may be used alone or in combination of two or more kinds.

[0143] In addition, as described above, potassium molybdate contains molybdenum, and therefore can also function as the molybdenum compound described above. In the manufacturing method of the embodiment, the use of potassium molybdate as a fluxing agent is synonymous with the use of a molybdenum compound and a potassium compound as fluxing agents.

[0144] As the potassium compound used when the raw materials are charged or generated in a reaction during the temperature rise process during calcination, a water-soluble potassium compound, for example, potassium molybdate, does not vaporize even in the calcination temperature range and can be easily recovered by washing after calcination. This reduces the amount of molybdenum compounds released outside the calcination furnace, and also enables a significant reduction in production costs.

[0145] When a molybdenum compound and a potassium compound are used as fluxing agents, the molar ratio of the molybdenum element of the molybdenum compound to the potassium element of the potassium compound (molybdenum element / potassium element) is preferably 5 or less, more preferably 0.01 to 3, and even more preferably 0.5 to 1.5, in order to further reduce production costs. When the molar ratio (molybdenum element / potassium element) is within the above range, alumina particles having a preferred particle size can be obtained.

[0146] (Silicon or silicon compounds) In the method for producing alumina particles, it is preferable to use silicon or a silicon compound as a shape control agent, since the resulting alumina particles have better fluidity, etc. Silicon or a silicon compound plays an important role in the growth of tabular crystals of alumina by firing an alumina compound in the presence of a molybdenum compound.

[0147] Silicon in silicon compounds selectively adsorbs to the

[0113] plane of the α crystal of alumina, suppressing the selective adsorption of the fluxing agent molybdenum oxide to the

[0113] plane, thereby forming a plate-like morphology with a close-packed hexagonal lattice crystal structure with a developed (001) or (006) plane, which is the most thermodynamically stable. It is presumed that the greater the amount of silicon, the more favorable the formation of the crystals in the (001) or (006) plane will be, resulting in a thinner plate-like alumina.

[0148] In addition, silicon, when present in a sufficient amount to be selectively adsorbed on the

[0113] plane of the alumina α crystal, can suppress the selective adsorption of molybdenum oxide on the

[0113] plane, and form a plate-like shape having a thermodynamically most stable close-packed hexagonal lattice crystal structure with a developed (001) or (006) plane. It is presumed that the greater the amount of silicon, the more likely the intersections of the plate-like alumina will have the thermodynamically most stable close-packed hexagonal lattice crystal structure, as well as other portions, and can be firmly fixed. In other words, the more the amount of silicon is appropriately increased, the more the crushing strength of the resulting alumina particles having a house-of-cards structure is improved.

[0149] The type of silicon or silicon compound is not particularly limited, and any known silicon compound, including silicon atoms, can be used. Specific examples of these include metal silicon (silicon atoms), organic silane compounds, silicone resins, silica (SiO2) fine particles, artificially synthesized silicon compounds such as silica gel, mesoporous silica, SiC, and mullite; and natural silicon compounds such as biosilica. Among these, it is preferable to use organic silane compounds, silicone resins, and silica fine particles from the viewpoint of forming a more uniform composite or mixture with an aluminum compound. The above-mentioned materials may be used alone or in combination of two or more.

[0150] In the case where the silicon compound is an organic silicon compound, the organic components are burned off by firing, and the silicon atoms or inorganic silicon compounds are contained in the alumina particles. In the case where the silicon compound is an inorganic silicon compound, the silicon atoms or inorganic silicon compounds that do not decompose at high temperatures during firing are left as they are and are contained locally on the surface of the tabular alumina. From the above viewpoint, it is preferable to use one or more selected from the group consisting of silicon atoms and inorganic silicon compounds, which can increase the content of silicon atoms with a smaller amount of the same molecular weight.

[0151] The shape of the silicon or silicon compound is not particularly limited, and for example, a sphere, an amorphous shape, an aspected structure (wire, fiber, ribbon, tube, etc.), a sheet, etc. can be suitably used.

[0152] The amount of silicon or silicon compound used is not particularly limited, but it is preferable to use a sufficient amount to selectively adsorb onto the

[0113] face of the α crystal of alumina, and the amount of silicon metal in the silicon compound is preferably 0.003 to 0.09 mol, more preferably 0.005 to 0.04 mol, and even more preferably 0.007 to 0.03 mol, per mol of aluminum metal in the aluminum compound used as the raw material. When a molybdenum compound and a potassium compound are used as a fluxing agent, the addition rate of the silicon compound to the aluminum compound is preferably 0.01 to 10 mass%, more preferably 0.03 to 7 mass%, and further preferably 0.03 to 3 mass%. When the amount of silicon compound is within the above range, the aspect ratio of the tabular alumina is high and alumina particles with excellent dispersibility are easily obtained, which is preferable. When the amount of silicon compound is insufficient, the adsorption of the fluxing agent molybdenum oxide to the

[0113] face is often not sufficiently suppressed, and the aspect ratio of the tabular alumina tends to be small and the tabular alumina tends to be non-uniform. Furthermore, when the amount of silicon compound is insufficient, the alumina particles produced tend to be polyhedral alumina, not a house of cards structure, which is undesirable. When the amount of silicon compound is too large, the excess silicon becomes an oxide by itself, and also contains heterogeneous crystals other than alumina, such as 3Al2O3·2SiO2, which is undesirable.

[0153] As described above, silicon or a silicon compound may be added to the aluminum compound as desired, but may also be contained in the aluminum compound as an impurity.

[0154] In the above-mentioned production method, the method of adding silicon or a silicon compound is not particularly limited, and a dry blend method in which the silicon or silicon compound is directly added and mixed as a powder, a mixing method using a mixer, or a method in which the silicon or silicon compound is dispersed in a solvent, monomer, or the like in advance and then added may be used.

[0155] By passing through the process of calcining an aluminum compound in the presence of a molybdenum compound and a silicon compound, it is possible to easily obtain alumina particles having a card house structure, in which one or more selected from the group consisting of silicon atoms and inorganic silicon compounds are unevenly distributed on the surface and its vicinity of the tabular alumina. According to the findings of the present inventors, the use of a silicon compound during charging is an important factor for easily obtaining a card house structure, while the presence of one or more selected from the group consisting of silicon atoms and inorganic silicon compounds unevenly distributed on the surface and its vicinity of the alumina particles produced by calcination brings about a large change in the surface state of alumina, which is originally poor in active sites, and not only maximizes the excellent properties of alumina itself, but also becomes an important factor that enables the provision of a better surface state by integration with a surface treatment agent through reaction starting from the active sites.

[0156] (Germanium compounds) A germanium compound may be used as a shape control agent in combination with silicon or a silicon compound, or in place of silicon or a silicon compound. The germanium compound plays an important role in the growth of tabular crystals of alumina by firing an alumina compound in the presence of a molybdenum compound.

[0157] The raw germanium compound used as the shape control agent is not particularly limited, and known compounds can be used. Specific examples of the raw germanium compound include germanium metal, germanium dioxide, germanium monoxide, germanium tetrachloride, and organic germanium compounds having Ge-C bonds. The raw germanium compound may be used alone or in combination of two or more. In addition, it may be used in combination with other shape control agents as long as it does not impair the effects of the present invention.

[0158] The shape of the raw material germanium compound is not particularly limited, and for example, a sphere, an amorphous shape, an aspected structure (wire, fiber, ribbon, tube, etc.), a sheet, etc. can be suitably used.

[0159] The amount of the germanium compound used is not particularly limited, but is preferably 0.002 to 0.09 mol, more preferably 0.004 to 0.04 mol, and even more preferably 0.005 to 0.03 mol, of germanium metal in the germanium compound relative to 1 mol of aluminum metal in the raw aluminum compound.

[0160] (Other shape control agents) In the alumina particles, other shape control agents than those mentioned above may be used as necessary, so long as they do not inhibit the formation of tabular alumina by at least one shape control agent selected from silicon, silicon compounds, and germanium compounds, in order to adjust the fluidity, dispersibility, mechanical strength, average particle size, aspect ratio of the tabular alumina, etc. The other shape control agents, like these, contribute to the growth of plate-like crystals of alumina by firing the alumina compound in the presence of a molybdenum compound.

[0161] The state of the other shape control agent is not particularly limited as long as it can contact the aluminum compound. For example, a physical mixture of the shape control agent and the aluminum compound, or a complex in which the shape control agent is uniformly or locally present on the surface or inside of the aluminum compound can be suitably used.

[0162] Further, other shape control agents may be added to the aluminum compound as desired, but may also be contained in the aluminum compound as impurities.

[0163] There are no particular limitations on the method of adding other shape control agents, and they may be added as powders by a dry blending method, mixed using a mixer, or dispersed in a solvent, monomer, or the like beforehand.

[0164] The type of other shape control agent is not particularly limited as long as it can suppress the selective adsorption of molybdenum oxide to the

[0113] face of α-alumina during high-temperature firing in the presence of a molybdenum compound and form a plate-like shape, as with at least one shape control agent selected from silicon, silicon compounds, and germanium compounds. It is preferable to use a metal compound other than a molybdenum compound and an aluminum compound, in order to obtain a higher aspect ratio of the plate-like alumina, a better fluidity and dispersibility of the alumina particles, and a better productivity. Alternatively, it is more preferable to use one or more selected from the group consisting of sodium atoms and sodium compounds.

[0165] The one or more selected from the group consisting of sodium atoms and sodium compounds are not particularly limited, and known compounds can be used. Specific examples of these include sodium carbonate, sodium molybdenum, sodium oxide, sodium sulfate, sodium hydroxide, sodium nitrate, sodium chloride, metallic sodium, etc. Among these, it is preferable to use sodium carbonate, sodium molybdate, sodium oxide, and sodium sulfate from the viewpoint of industrially easy availability and ease of handling. Incidentally, sodium or a compound containing a sodium atom may be used alone or in combination of two or more.

[0166] The shape of the one or more selected from the group consisting of sodium atoms and sodium compounds is not particularly limited, and for example, a sphere, an amorphous shape, an aspected structure (wire, fiber, ribbon, tube, etc.), a sheet, etc. can be suitably used.

[0167] The amount of one or more selected from the group consisting of sodium atoms and sodium compounds is not particularly limited, but is preferably 0.0001 to 2 moles, and more preferably 0.001 to 1 mole, of sodium metal relative to 1 mole of aluminum metal in the aluminum compound. When the amount of one or more selected from the group consisting of sodium atoms and sodium compounds is within the above range, alumina particles having a high aspect ratio and excellent dispersibility are easily obtained, which is preferable.

[0168] (metal compound) The metal compound can have a function of promoting the crystal growth of alumina, as described below. The metal compound can be used during firing as desired. Note that the metal compound has a function of promoting the crystal growth of α-alumina, and is therefore not essential for the production of alumina particles.

[0169] The metal compound is not particularly limited, but preferably contains at least one selected from the group consisting of Group II metal compounds and Group III metal compounds.

[0170] Examples of the Group II metal compound include magnesium compounds, calcium compounds, strontium compounds, and barium compounds.

[0171] Examples of the Group III metal compound include a scandium compound, an yttrium compound, a lanthanum compound, and a cerium compound.

[0172] The above-mentioned metal compounds refer to oxides, hydroxides, carbonates, and chlorides of metal elements. For example, yttrium compounds include yttrium oxide (Y2O3), yttrium hydroxide, and yttrium carbonate. Of these, the metal compounds are preferably oxides of metal elements. These metal compounds include isomers.

[0173] Among these, the metal compounds of the third periodic elements, the metal compounds of the fourth periodic elements, the metal compounds of the fifth periodic elements, and the metal compounds of the sixth periodic elements are preferred, the metal compounds of the fourth periodic elements and the metal compounds of the fifth periodic elements are more preferred, and the metal compounds of the fifth periodic elements are even more preferred. Specifically, it is preferred to use magnesium compounds, calcium compounds, yttrium compounds, and lanthanum compounds, it is more preferred to use magnesium compounds, calcium compounds, and yttrium compounds, and it is particularly preferred to use yttrium compounds.

[0174] The addition rate of the metal compound is preferably 0.02 to 20 mass% based on the mass equivalent of aluminum atoms in the aluminum compound, and more preferably 0.1 to 20 mass%. When the addition rate of the metal compound is 0.02 mass% or more, the crystal growth of α-alumina containing molybdenum can proceed favorably, which is preferable. On the other hand, when the addition rate of the metal compound is 20 mass% or less, alumina particles having a low content of impurities derived from the metal compound can be obtained, which is preferable.

[0175] (yttrium) When an aluminum compound is calcined in the presence of an yttrium compound as a metal compound, crystal growth proceeds more favorably in the calcination process, and α-alumina and a water-soluble yttrium compound are produced. At this time, the water-soluble yttrium compound is likely to be localized on the surface of the α-alumina particles, so that if necessary, the yttrium compound can be removed from the alumina particles by washing with water, alkaline water, or a liquid obtained by warming these.

[0176] When a molybdenum compound is used as a fluxing agent, the amounts of the aluminum compound, molybdenum compound, and shape control agent used are not particularly limited. Examples of the amount of the compound containing molybdenum element may include converting the compound into molybdenum trioxide (MoO3) as an oxide and firing the following mixture of 1) or 2) when the total amount of the raw materials converted into an oxide is taken as 100 mass%. 1-1) An aluminum compound containing 80 mass% or more of aluminum element calculated as Al2O3, A molybdenum compound having 1.0 mass% or more in terms of MoO3; A silicon compound containing 0.4 mass% or more of silicon or silicon element in terms of SiO2; A mixture of the above. 1-2) An aluminum compound containing 80 mass% or more of aluminum element calculated as Al2O3, A molybdenum compound having 1.0 mass% or more in terms of MoO3; A germanium compound having a GeO2 content of 0.4% or more by mass, A mixture of the above.

[0177] By using the mixture of 1-1) or 1-2) above, alumina particles having a house-of-cards structure can be produced more efficiently. A common phenomenon that occurs when the mixture of 1-1) or 1-2) above is fired is that the crystal growth proceeds while at least a part of the original shape of the aluminum compound used as the raw material is retained at the beginning of the crystal growth. As a result, plate-like alumina is formed from each part of the raw aluminum compound as the starting point, and a house-of-cards structure is formed by three or more plate-like alumina sheets that are fixed together.

[0178] In the above 1-1), a silicon compound containing 0.4 mass% or more of silicon, calculated as SiO2, or silicon element is used, and by using a relatively large proportion of this compound, it is believed that deformation of the raw aluminum compound is suppressed and the shape of the aluminum compound used as the raw material can be maintained. In the above 1-2), a germanium compound of 0.4 mass% or less calculated as GeO2 is used. By using a relatively large proportion of this germanium compound, it is believed that deformation of the raw material aluminum compound is suppressed and the shape of the raw material aluminum compound can be maintained.

[0179] In the above 1-1), in order to more easily produce alumina particles having a house-of-cards structure and excellent fluidity, it is preferable that the blending amounts of each raw material in the mixture, when the total amount of raw materials calculated as oxide is 100 mass%, be as follows. In the above 1-1), when the total amount of the raw materials calculated as oxides is taken as 100 mass%, the blending amount of the aluminum compound, calculated as Al2O3, is preferably 80 mass% or more, more preferably 85 mass% or more and 99 mass% or less, and even more preferably 85 mass% or more and 95 mass% or less. In the above 1-1), when the total amount of the raw materials calculated as oxides is taken as 100 mass%, the molybdenum compound is preferably 1.0 mass% or more, more preferably 2.0 mass% or more and 15 mass% or less, and even more preferably 4.0 mass% or more and 10 mass% or less, calculated as MoO3. In the above 1-1), when the total amount of the raw materials calculated as oxides is taken as 100 mass%, the amount of silicon or a silicon compound containing elemental silicon is preferably 0.4 mass% or more, more preferably 0.4 mass% or more and 5.0 mass% or less, and even more preferably 0.5 mass% or more and 2.0 mass% or less, calculated as SiO2.

[0180] In the above 1-2), in order to more easily produce alumina particles having a house-of-cards structure and excellent fluidity, it is preferable that the blending amounts of each raw material in the mixture, when the total amount of raw materials calculated as oxide is 100 mass%, be as follows. In the above 1-2), when the total amount of the raw materials calculated as oxides is taken as 100 mass%, the blending amount of the aluminum compound, calculated as Al2O3, is preferably 80 mass% or more, more preferably 85 mass% or more and 99 mass% or less, and even more preferably 85 mass% or more and 95 mass% or less. In the above 1-2), when the total amount of the raw materials calculated as oxides is taken as 100 mass%, the blending amount of the molybdenum compound calculated as MoO3 is preferably 1.0 mass% or more, more preferably 2.0 mass% or more and 15 mass% or less, and even more preferably 4.0 mass% or more and 10 mass% or less. In the above 1-2), when the total amount of raw materials calculated as oxides is taken as 100 mass%, the amount of germanium compound, calculated as GeO2, is preferably 0.4 mass% or more, more preferably 0.4 mass% or more and 5.0 mass% or less, and even more preferably 0.5 mass% or more and 2.0 mass% or less.

[0181] When a molybdenum compound and a potassium compound are used as fluxing agents, the amounts of the aluminum compound, molybdenum compound, potassium compound, and shape control agent used are not particularly limited. Examples of the amount of the compound containing molybdenum and potassium, or the molybdenum compound containing molybdenum and the potassium compound containing potassium, converted into oxide form as potassium molybdate (Mo2K2O7) and the total amount of the raw materials converted into oxide form is taken as 100 mass%, include firing the following mixture of 1) or 2): 2-1) An aluminum compound containing 10 mass% or more of aluminum element calculated as Al2O3, 50% by mass or more of the molybdenum compound and the potassium compound calculated as Mo2K2O7; A silicon compound containing 0.3 mass% or more of silicon or silicon element in terms of SiO2; A mixture of the above. 2-2) An aluminum compound containing 50 mass% or more of aluminum element calculated as Al2O3, 30% by mass or less of the molybdenum compound and the potassium compound calculated as Mo2K2O7; A silicon compound containing 0.01 mass% or more of silicon or silicon element in terms of SiO2; A mixture of the above.

[0182] By using the mixture of 2-1) or 2-2) above, alumina particles having a house-of-cards structure can be produced more efficiently. A common phenomenon that occurs when the mixture of 2-1) or 2-2) above is fired is that the crystal growth proceeds while at least a part of the original shape of the aluminum compound used as the raw material is retained at the beginning of the crystal growth. As a result, plate-like alumina is formed from each part of the raw aluminum compound as the starting point, and a card house structure is formed by three or more plate-like alumina sheets that are fixed to each other.

[0183] In the above 2-1), a silicon compound containing 0.3 mass% or more of silicon element calculated as SiO2 is used, and it is believed that by using a relatively large proportion of this compound, deformation of the raw aluminum compound is suppressed and the shape of the aluminum compound used as the raw material can be maintained. In the above 2-2), the molybdenum compound and the potassium compound are used in an amount of 30 mass% or less calculated as Mo2K2O7. By using a relatively small proportion of these compounds, it is believed that deformation of the raw aluminum compound is suppressed and the shape of the aluminum compound used as the raw material can be maintained.

[0184] In the above 2-1), in order to more easily produce alumina particles having a house-of-cards structure and excellent fluidity, it is preferable that the blending amounts of each raw material in the mixture, when the total amount of raw materials calculated as oxide is 100 mass%, be as follows. In the above 2-1), when the total amount of the raw materials calculated as oxides is taken as 100 mass%, the blending amount of the aluminum compound, calculated as Al2O3, is preferably 10 mass% or more, more preferably 10 mass% or more and 70 mass% or less, even more preferably 20 mass% or more and 45 mass% or less, and particularly preferably 25 mass% or more and 40 mass% or less. In the above 2-1), when the total amount of the raw materials calculated as oxides is taken as 100 mass%, the blending amount of the molybdenum compound and the potassium compound, calculated as Mo2K2O7, is preferably 50 mass% or more, more preferably 50 mass% or more and 80 mass% or less, even more preferably 55 mass% or more and 75 mass% or less, and even more preferably 60 mass% or more and 70 mass% or less. In the above 2-1), when the total amount of raw materials calculated as oxides is taken as 100 mass%, the amount of silicon or silicon compound containing elemental silicon, calculated as SiO2, is preferably 0.3 mass% or more, more preferably 0.3 mass% or more and 5 mass% or less, and even more preferably 0.4 mass% or more and 3 mass% or less.

[0185] In the above 2-2), in order to more easily produce alumina particles having a house-of-cards structure and excellent fluidity, it is preferable that the blending amounts of each raw material in the mixture, when the total amount of raw materials calculated as oxide is 100 mass%, be as follows. In the above 2-2), when the total amount of the raw materials calculated as oxides is taken as 100 mass%, the blending amount of the aluminum compound, calculated as Al2O3, is preferably 50 mass% or more, more preferably 50 mass% or more and 96 mass% or less, even more preferably 60 mass% or more and 95 mass% or less, and particularly preferably 70 mass% or more and 90 mass% or less. In the above 2-2), when the total amount of the raw materials calculated as oxides is taken as 100 mass%, the blending amount of the molybdenum compound and the potassium compound calculated as Mo2K2O7 is preferably 30 mass% or less, more preferably 2 mass% or more and 30 mass% or less, even more preferably 3 mass% or more and 25 mass% or less, and particularly preferably 4 mass% or more and 10 mass% or less. In the above 2-2), when the total amount of the raw materials calculated as oxides is taken as 100 mass%, the amount of silicon or silicon compound containing elemental silicon, calculated as SiO2, is preferably 0.01 mass% or more, more preferably 0.01 mass% or more and 5 mass% or less, even more preferably 0.05 mass% or more and 3 mass% or less, and particularly preferably 0.15 mass% or more and 3 mass% or less.

[0186] When the mixture further contains the above-mentioned yttrium compound, the amount of the yttrium compound used is not particularly limited, but preferably, when the total amount of the raw material calculated as oxide is 100 mass%, 5 mass% or less of the yttrium compound calculated as Y2O3 can be mixed. More preferably, when the total amount of the raw material calculated as oxide is 100 mass%, 0.01 mass% or more and 3 mass% or less of the yttrium compound calculated as Y2O3 can be mixed. In order to more suitably proceed with crystal growth, more preferably, when the total amount of the raw material calculated as oxide is 100 mass%, 0.1 mass% or more and 1 mass% or less of the yttrium compound calculated as Y2O3 can be mixed.

[0187] When a molybdenum compound and a potassium compound are used as a fluxing agent, alumina particles having a card house structure in which one or more selected from the group consisting of silicon and germanium are unevenly distributed on the surface and its vicinity of tabular alumina can be easily obtained by carrying out a process of calcining an aluminum compound in the presence of a molybdenum compound and a potassium compound and at least one shape control agent selected from silicon, a silicon compound and a germanium compound. According to the findings of the present inventors, the use of at least one shape control agent selected from silicon, a silicon compound and a germanium compound during the preparation is an important factor for easily obtaining a card house structure, while the presence of one or more selected from the group consisting of silicon and germanium unevenly distributed on the surface and its vicinity of the alumina particles produced by calcination brings about a large change in the surface state of alumina, which is originally poor in active sites, and not only maximizes the excellent properties of alumina itself, but also becomes an important factor that enables the provision of a better surface state by integration with a surface treatment agent through reaction starting from the active sites.

[0188] [Firing process] The calcination step is preferably a step of calcining an aluminum compound in the presence of a molybdenum compound, at least one shape control agent selected from silicon, a silicon compound, and a germanium compound, and optionally other shape control agents. The calcination step may be a step of calcining the mixture obtained in the mixing step.

[0189] Alumina particles can be obtained, for example, by firing an aluminum compound in the presence of a molybdenum compound and a shape control agent. As mentioned above, this manufacturing method is called a flux method. Based on the flux method, it is estimated that the formation of plate-like alumina and the formation of a card house structure due to the adhesion of three or more plates of the plate-like alumina proceed in parallel.

[0190] The flux method is classified as a solution method. More specifically, the flux method is a crystal growth method that utilizes the fact that the crystal-flux two-component phase diagram shows a eutectic type. The mechanism of the flux method is assumed to be as follows. That is, when a mixture of a solute and flux is heated, the solute and flux become liquid phase. At this time, since the flux is a flux, in other words, since the solute-flux two-component phase diagram shows a eutectic type, the solute melts at a temperature lower than its melting point and forms a liquid phase. If the flux is evaporated in this state, the concentration of the flux decreases, in other words, the effect of the flux in lowering the melting point of the solute is reduced, and the evaporation of the flux becomes the driving force to cause crystal growth of the solute (flux evaporation method). It is also a preferable method to grow crystals in a flux agent in the liquid phase, and the solute and flux can also cause crystal growth of the solute by cooling the liquid phase (slow cooling method).

[0191] The flux method has the advantages of being able to grow crystals at temperatures much lower than the melting point, being able to precisely control the crystal structure, and being able to form idiomorphic crystals.

[0192] In the production of alumina particles by the flux method using a molybdenum compound as a flux, the mechanism is not necessarily clear, but it is presumed to be due to the following mechanism, for example. That is, when an aluminum compound is fired in the presence of a molybdenum compound, aluminum molybdate is first formed. At this time, as can be understood from the above explanation, the aluminum molybdate grows alumina crystals at a temperature lower than the melting point of alumina. Then, for example, by evaporating the flux, the aluminum molybdate decomposes and the crystals grow, thereby obtaining alumina particles. That is, the molybdenum compound functions as a flux, and alumina particles are produced via an intermediate called aluminum molybdate.

[0193] Here, when a potassium compound and a shape control agent are used in combination in the flux method, it becomes possible to produce alumina particles having a card house structure formed by three or more plate-like alumina with high efficiency. More specifically, when a molybdenum compound and a potassium compound are used in combination, the molybdenum compound and the potassium compound react to form potassium molybdate. At the same time, the molybdenum compound reacts with an aluminum compound to form aluminum molybdate. Then, for example, aluminum molybdate is decomposed in the presence of potassium molybdate, and crystals grow in the presence of a shape control agent, thereby obtaining alumina particles having a card house structure formed by three or more plate-like alumina. That is, when alumina particles are produced via an intermediate called aluminum molybdate, if potassium molybdate is present, alumina particles having a card house structure formed by three or more plate-like alumina can be obtained.

[0194] As mentioned above, potassium or a potassium compound, such as potassium molybdate, acts as a fluxing agent.

[0195] It should be noted that the above mechanism is merely speculation, and even if the effects of the present invention are obtained through a mechanism different from the above mechanism, this is still within the technical scope of the present invention.

[0196] The structure of the potassium molybdate is not particularly limited, but usually contains a molybdenum atom, a potassium atom, and an oxygen atom. The structural formula is preferably KMo n O 3n+1 In this case, n is not particularly limited, but is preferably in the range of 1 to 3, since the alumina particle growth promotion functions effectively. Potassium molybdate may contain other atoms, and examples of the other atoms include sodium, magnesium, silicon, etc.

[0197] In one embodiment of the present invention, the above-mentioned calcination may be carried out in the presence of a metal compound. That is, the above-mentioned metal compound may be used in combination with a molybdenum compound and a potassium compound in the calcination. This allows the production of alumina particles with better fluidity. Although the mechanism is not necessarily clear, it is presumed to be due to, for example, the following mechanism. That is, the presence of a metal compound during the crystal growth of alumina particles prevents or suppresses the excessive formation of alumina crystal nuclei and / or promotes the diffusion of aluminum compounds necessary for the crystal growth of alumina, in other words, prevents the excessive generation of crystal nuclei and / or increases the diffusion rate of aluminum compounds, which enables more precise control of the crystal growth direction of alumina, facilitates shape control such as reflecting the shape of the precursor, and is believed to result in alumina particles with higher fluidity. Note that the above mechanism is merely presumed, and even if the effects of the present invention are obtained by a mechanism different from the above mechanism, it is within the technical scope of the present invention.

[0198] The calcination method is not particularly limited, and can be performed by a known, commonly used method. When the calcination temperature exceeds 700°C, the aluminum compound reacts with the molybdenum compound to form aluminum molybdate. Furthermore, when the calcination temperature reaches 900°C or higher, the aluminum molybdate decomposes and forms tabular alumina due to the action of the shape control agent. Furthermore, the tabular alumina can be obtained by incorporating molybdenum into aluminum oxide particles when the aluminum molybdate decomposes to form alumina and molybdenum oxide.

[0199] In addition, the state of the aluminum compound, the shape control agent, the molybdenum compound, and the potassium compound during firing is not particularly limited, and it is sufficient that the molybdenum compound, the potassium compound, and the shape control agent are present in such a close proximity that they can act on the aluminum compound. Specifically, they may be simply mixed by mixing the powders of the molybdenum compound, the shape control agent, and the aluminum compound, mechanically mixed using a grinder, or mixed using a mortar, or may be mixed in a dry or wet state.

[0200] There is no particular limitation on the firing temperature conditions, and the firing temperature is appropriately determined depending on the target average particle size, fluidity, dispersibility, aspect ratio of the tabular alumina, etc. Usually, the firing temperature is sufficient as long as the maximum temperature is 900°C or higher, which is the decomposition temperature of aluminum molybdate (Al2(MoO4)3).

[0201] Generally, to control the shape of α-alumina obtained after firing, it is necessary to perform firing at high temperatures of over 2000°C, which is close to the melting point of α-alumina. However, there are significant challenges to be overcome in terms of the burden on the firing furnace and fuel costs in order to utilize this method industrially.

[0202] The above-described preferred method for producing alumina particles can be carried out at high temperatures exceeding 2000°C, but even at temperatures of 1600°C or less, which are significantly lower than the melting point of α-alumina, alumina particles made of tabular alumina with a high α-crystallization rate and a high aspect ratio can be formed.

[0203] According to the preferred manufacturing method as described above, even when the maximum firing temperature is 900°C to 1600°C, alumina particles having a high aspect ratio of tabular alumina and an α-crystallization rate of 90% or more can be formed simply, efficiently, and at low cost. It is more preferable to fire at a maximum temperature of 920 to 1500°C, and most preferable to fire at a maximum temperature in the range of 950 to 1400°C.

[0204] As the firing temperature increases, the α-crystallization at the intersections of the tabular alumina particles improves as well as at other locations, resulting in alumina particles having a card-house structure with excellent mechanical strength.

[0205] Regarding the firing time, it is preferable to raise the temperature to the predetermined maximum temperature in a range of 15 minutes to 10 hours, and to hold the firing temperature for 5 minutes to 30 hours. In order to efficiently form tabular alumina, it is more preferable to hold the firing temperature for about 10 minutes to 15 hours.

[0206] The longer the holding time at the maximum firing temperature, the more the α-crystallization at the intersections of the tabular alumina improves, just like at other locations, resulting in alumina particles having a card-house structure with excellent crushing strength.

[0207] The firing atmosphere is not particularly limited as long as the effects of the present invention can be obtained. For example, an oxygen-containing atmosphere such as air or oxygen, or an inert atmosphere such as nitrogen or argon is preferable, and an air atmosphere is more preferable when cost is taken into consideration.

[0208] The calcination apparatus is not necessarily limited, and a so-called calcination furnace can be used. The calcination furnace is preferably made of a material that does not react with the sublimated molybdenum oxide, and it is preferable to use a highly airtight calcination furnace so as to efficiently utilize the molybdenum oxide. Examples of calcination furnaces that can be used in this case include a tunnel furnace, a roller hearth furnace, a rotary kiln, and a muffle furnace.

[0209] In the above-mentioned preferred manufacturing method, alumina particles having a house of card structure can be selectively obtained, and a powder containing the alumina particles at a ratio of 60% or more of the total based on the number of particles can be easily obtained. By selecting more suitable conditions from the above-mentioned manufacturing method, it is possible to more easily obtain a powder containing alumina particles having a house of card structure in which the three or more flat alumina particles are crossed and assembled at two or more points, and the surface direction of the crossed flat plates is in a disordered state, at a ratio of 80% or more of the total based on the number of particles.

[0210] [Cooling process] When a molybdenum compound and a potassium compound are used as fluxing agents, the method for producing alumina particles may include a cooling step. The cooling step is a step of cooling the alumina crystal-grown in the firing step. More specifically, the cooling step may be a step of cooling a composition containing the alumina obtained by the firing step and the fluxing agent in a liquid phase.

[0211] The cooling rate is not particularly limited, but is preferably 1 to 1000°C / hour, more preferably 5 to 500°C / hour, and even more preferably 50 to 100°C / hour. A cooling rate of 1°C / hour or more is preferable because the manufacturing time can be shortened. On the other hand, a cooling rate of 1000°C / hour or less is preferable because the firing container is less likely to crack due to heat shock and can be used for a long time.

[0212] The cooling method is not particularly limited, and may be natural cooling or a cooling device may be used.

[0213] [Post-processing process] The method for producing alumina particles according to the embodiment may include a post-treatment step. The post-treatment step is a post-treatment step for alumina particles having a house-of-cards structure, and is a step for removing a fluxing agent. The post-treatment step may be performed after the above-mentioned firing step, after the above-mentioned cooling step, or after the firing step and the cooling step. In addition, the post-treatment step may be repeated two or more times as necessary.

[0214] Post-treatment methods include washing and high temperature treatment, which may be performed in combination.

[0215] The washing method is not particularly limited, but the metal oxide can be removed by washing with water, an aqueous ammonia solution, an aqueous sodium hydroxide solution, or an acidic aqueous solution.

[0216] In this case, the molybdenum content can be controlled by appropriately changing the concentrations and amounts of water, ammonia aqueous solution, sodium hydroxide aqueous solution, and acidic aqueous solution used, as well as the cleaning locations and cleaning times.

[0217] Moreover, examples of the high-temperature treatment method include a method in which the temperature is raised to the sublimation point or boiling point of the flux or higher.

[0218] [Crushing process] In the fired product, the alumina particles may aggregate and may not satisfy the particle size range suitable for the embodiment, so the alumina particles may be pulverized as necessary to satisfy the particle size range suitable for the embodiment.

[0219] The method for pulverizing the fired product is not particularly limited, and any conventionally known pulverizing method such as a ball mill, a jaw crusher, a jet mill, a disk mill, a spectromill, a grinder, or a mixer mill can be used.

[0220] [Classification process] The alumina particles are preferably subjected to classification treatment in order to adjust the average particle size and improve the flowability of the powder, or to suppress an increase in viscosity when mixed with a binder for forming a matrix.

[0221] The classification may be either wet or dry, but from the viewpoint of productivity, dry classification is preferred. Dry classification includes classification by sieving, as well as wind classification, which classifies based on the difference between centrifugal force and fluid drag, but from the viewpoint of classification accuracy, wind classification is preferred, and can be performed using a classifier such as an air classifier utilizing the Coanda effect, a swirling air classifier, a forced vortex centrifugal classifier, or a semi-free vortex centrifugal classifier.

[0222] The above-mentioned pulverization process and classification process can be carried out at any necessary stage, including before or after the organic compound layer forming process described later. By selecting whether or not to perform pulverization or classification and the conditions thereof, for example, the average particle size of the obtained alumina particles can be adjusted. The average particle size of the alumina particles is closely related to the angle of repose, and even if the above-mentioned manufacturing method and manufacturing conditions of the alumina particles themselves are not sufficient to adjust the average particle size of the alumina particles, the fluidity of the alumina particles can be adjusted by changing the average particle size of the alumina particles (indirectly changing the angle of repose) by selecting the conditions such as classification.

[0223] Specifically, for example, when alumina particles having a house-of-cards structure and a desired average particle size are not available, alumina particles having a larger average particle size can be classified, etc., to obtain alumina particles having a smaller average particle size and a house-of-cards structure that has better fluidity than known alumina particles having the same average particle size.

[0224] [Organic compound layer formation process] In one embodiment, the above-mentioned method for producing alumina particles may further include an organic compound layer forming step of forming an organic compound layer on the surface of the tabular alumina. The organic compound layer forming step is carried out, if necessary, at a temperature at which the organic compound does not decompose, usually after the firing step or after the post-treatment step.

[0225] The method for forming an organic compound layer on the surface of the tabular alumina of the alumina particles is not particularly limited, and any known method can be appropriately adopted. For example, a method of contacting a solution or dispersion containing an organic compound with alumina particles containing molybdenum and drying the resulting mixture can be mentioned.

[0226] The organic compound that can be used to form the organic compound layer includes, for example, an organic silane compound.

[0227] (Organosilane Compounds) When the alumina particles having a card house structure contain one or more selected from the group consisting of silicon atoms and inorganic silicon compounds, the above-mentioned surface modification effect can be expected compared to the case where the alumina particles do not contain the silicon atoms and inorganic silicon compounds, but the alumina particles containing one or more selected from the group consisting of silicon atoms and inorganic silicon compounds can also be used after being reacted with an organic silane compound.Compared to the alumina particles containing one or more selected from the group consisting of silicon atoms and inorganic silicon compounds and having a card house structure, the alumina particles having a card house structure, which is a reaction product of the silicon atoms and inorganic silicon compounds and the organic silane compound, can have better affinity with the matrix based on the reaction between the silicon atoms and inorganic silicon compounds that are localized on the surface of the tabular alumina particles that constitute the alumina particles and the organic silane compound, and are preferable.

[0228] Examples of the organic silane compound include alkyltrimethoxysilanes or alkyltrichlorosilanes having an alkyl group with 1 to 22 carbon atoms, such as methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, pentyltrimethoxysilane, and hexyltrimethoxysilane; 3,3,3-trifluoropropyltrimethoxysilane, tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilanes; phenyltrimethoxysilane, phenyltriethoxysilane, p-chloromethylphenyltrimethoxysilane, p-chloromethylphenyltriethoxysilanes; and γ-glycidoxypropyltrimethoxysilane. Examples of the organic silane include epoxy silanes such as γ-glycidoxypropyltriethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, amino silanes such as γ-aminopropyltriethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, γ-aminopropyltrimethoxysilane, and γ-ureidopropyltriethoxysilane, mercapto silanes such as 3-mercaptopropyltrimethoxysilane, p-styryltrimethoxysilane, vinyltrichlorosilane, vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloxypropyltrimethoxysilane, and further include epoxy, amino, and vinyl polymer-type silanes. The organic silane compounds may be contained alone or in combination of two or more.

[0229] The organic silane compound may be bonded by a covalent bond to at least a part or all of one or more selected from the group consisting of silicon atoms and inorganic silicon compounds on the surface of the tabular alumina of the alumina particles, and may cover not only a part of but the entire alumina with the reactant. The method of providing the alumina surface may be attachment by immersion or chemical vapor deposition (CVD).

[0230] The amount of the organic silane compound used is preferably 20 mass% or less, more preferably 10 to 0.01 mass%, based on silicon atoms, relative to the mass of silicon atoms or inorganic silicon compounds contained on the surface of the tabular alumina of the alumina particles. When the amount of the organic silane compound used is 20 mass% or less, it is preferable because the physical properties derived from the alumina particles can be easily expressed.

[0231] The reaction between the alumina particles containing one or more selected from the group consisting of silicon atoms and inorganic silicon compounds and the organic silane compound can be carried out by a known and commonly used method for surface modification of fillers, and for example, a spray method using a fluid nozzle, a dry method using stirring with shear force, a ball mill, a mixer, etc., or a wet method using a water-based or organic solvent-based system can be adopted. It is desirable to carry out the treatment using shear force to such an extent that the alumina particles used in the embodiment are not destroyed.

[0232] The system temperature in the dry method or the drying temperature after the treatment in the wet method is appropriately determined according to the type of the organosilane compound within a range in which the compound does not thermally decompose. For example, when treating with the above-mentioned organosilane compound, a temperature of 80 to 150°C is preferable.

[0233] [Post-processing process] In the method for producing alumina particles, as long as the effect is not impaired, any step may be added during the production of the alumina particles, or a post-treatment step may be added to arbitrarily adjust the particle size, shape, etc. For example, a granulation step such as rolling granulation or compression granulation, or granulation by a spray-drying method using a binding agent as a binder may be mentioned, and the alumina particles can be easily obtained using commercially available equipment.

[0234] <Other ingredients> In addition to the alumina particles, the cosmetic composition of the present embodiment may contain various components acceptable for cosmetics, such as active ingredients, colorants, carriers, thickeners, surfactants, binders, preservatives, polymers, fragrances, astringents, essential oils, anti-caking agents, defoamers, buffers, fillers, denaturants, pH adjusters, propellants, reducing agents, isolating agents, cosmetic biocides, preservatives, etc.

[0235] [Active ingredient] Examples of active ingredients include, but are not limited to, UV protection agents, moisturizers, anti-aging active ingredients, vitamins, self-tanning agents, bisabolol, lactoperoxidase (LPO), ectoine and its derivatives, emblica, allantoin, bioflavonoids and its derivatives, plant extracts, lipoic acid, retinoxytrimethylsilane, dehydroepiandrosterone (DHEA), ceramides and pseudoceramides, creatine, resveratrol, hyaluronic acid, and the like.

[0236] Examples of UV protection agents include 2-ethylhexyl-p-methoxycinnamate, butyl methoxydibenzoyl-methane, 2-hydroxy-4-toxybenzo-phenone, 2-phenylbenzimidazole-5-sulfonic acid, octyldimethyl-p-aminobenzoic acid, octocrylene, 2-ethylhexyl N,N-dimethyl-p-aminobenzoate, p-aminobenzoic acid, 2-phenylbenzimidazole-5-sulfonic acid, octocrylene, oxybenzone, homomenthyl salicylate, octyl salicylate, 4,4-methoxy-t-butyldibenzoylmethane, 4-isopropyldibenzoylmethane, 3-benzylidene camphor, 3-(4-methylbenzylidene) camphor, etc. These UV protection agents can be selected to provide the desired sun protection factor (SPF). SPF is a commonly used measure of the photoprotection of a sunscreen against erythema.

[0237] The moisturizer is generally a polyhydric alcohol. Examples of the polyhydric alcohol include glycerol, propylene glycol, dipropylene glycol, polypropylene glycol, polyethylene glycol, sorbitol, hydroxypropyl sorbitol, hexylene glycol, 1,3-butylene glycol, isoprene glycol, 1,2,6-hexanetriol, ethoxylated glycerol, and propoxylated glycerol. The content of the moisturizer can be 0.5% by mass or more and 50% by mass or less, and preferably 1% by mass or more and 15% by mass or less, based on the total mass of the composition.

[0238] The vitamins may be water-soluble or water-insoluble. Examples of water-soluble vitamins include niacinamide, vitamin B2, vitamin B6, vitamin C, and biotin. Examples of water-insoluble vitamins include vitamin A (retinol), vitamin A palmitate, ascorbyl tetraisopalmitate, vitamin E (tocopherol), vitamin E acetate, and DL-panthenol. The content of the vitamins can be 0.001% by mass or more and 10% by mass or less, preferably 0.01% by mass or more and 1% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass or less, based on the total mass of the composition.

[0239] Self-tanning agents include, for example, dihydroxyacetone (DHA), erythrulose, among others.

[0240] The plant extract may be water-soluble or water-insoluble and may be carried in a hydrophilic or hydrophobic solvent. Examples of the plant extract include extracts of green tea, chamomile, rose, licorice, aloe vera, grape seed, Satsuma mandarin, lemon, lemongrass, willow bark, sage, thyme, and rosemary.

[0241] Examples of ceramides include ceramide 1, ceramide 3, ceramide 3B, ceramide 6, and the like.

[0242] [Coloring agent] As the colorant, other pigments other than the above-mentioned plate-like alumina particles can also be used. Examples of other pigments include various pigments such as coloring pigments and extender pigments. As the color pigment, a conventionally known pigment can be appropriately used according to the desired hue and performance, for example, organic pigments such as azo, benzimidazolone, isoindolinone-isoindoline, phthalocyanine, quinacridone, dioxazine, diketopyrrolopyrrole, quinophthalone, perylene-perinone, thioindigo, anthraquinone, and threne, and inorganic pigments such as iron oxide, carbon black, titanium oxide, and zinc sulfide can be used. In addition, effect pigments including multi-layer pigments or interference pigments can also be used as the colorant, and specific examples include pearlescent pigments. Pearlescent pigments are, for example, pigments based on phyllosilicates, such as natural or synthetic mica, talc, sericite, kaolin, or other silicate materials in the form of flakes, transparent or translucent materials. Pearlescent pigments are coated with colored or colorless metal oxides, such as TiO2, titanium suboxide, titanium oxynitride, Fe2O3, Fe3O4, FeOOH, SnO2, Cr2O3, ZnO, CuO, NiO and other metal oxides, alone or as mixtures, in single layers or in successive layers. The pearlescent pigment may further have a layer of Berlin blue or carmine red on the surface.

[0243] Multilayer pigments are based on a transparent, colored or colorless matrix in flake form, consisting of mica (synthetic or natural), SiO2 flakes, glass flakes, Al2O3 flakes, polymer flakes, and generally have a thickness of 0.3 to 5 μm, preferably 0.4 to 2.0 μm. The size of the width and depth is usually 1 to 250 μm, preferably 2 to 100 μm, more preferably 5 to 40 μm. Multilayer pigments consist of a matrix (substrate) coated with metal oxides (at least two). The coating of the substrate flakes, mica, SiO2 flakes, glass flakes, Al2O3 flakes in multiple layers is preferably carried out in such a way that a layer structure consisting of alternating high and low refractive index layers is formed. Multilayer pigments preferably contain 2, 3, 4, 5, 6 or 7 layers, more preferably 3, 4 or 5 layers. Suitable high refractive index metal oxides include, for example, titanium dioxide, zirconium oxide, zinc oxide, iron oxide, iron / titanium oxide (iron titanate), chromium oxide, etc., among which TiO2 or Fe2O3 is preferred. Low refractive index oxides used are SiO2 and Al2O3. In addition, in multi-layer pigments, MgF2 or organic polymers (e.g., acrylic polymers) can be used depending on the purpose. Note that "coating" here means that the substrate is completely covered with one or more layers.

[0244] The interference pigments are preferably pigments based on natural and synthetic mica, glass flakes, SiO2 flakes, Al2O3 flakes, coated with colored or colorless metal oxides, such as TiO2, titanium suboxides, titanium oxynitrides, Fe2O3, Fe3O4, SnO2, Cr2O3, ZnO, CuO, NiO and other metal oxides, alone or as mixtures, in a single layer or in successive layers.

[0245] Suitable flake-form colorants are especially pearlescent pigments, in particular pigments based on natural or synthetic mica, SiO2 flakes, Fe2O3 flakes, glass flakes or Al2O3 flakes, which are only coated with a metal oxide layer, metal-effect pigments (Al flakes, bronzes), optically variable pigments (OVP), liquid crystal polymer pigments (LCP) or holographic pigments.

[0246] Examples of spherical colorants include TiO2, colored SiO2, CaSO4, iron oxide, chromium oxide, carbon black, organic color pigments, etc. Examples of organic color pigments that are spherical colorants include anthraquinone pigments, quinacridone pigments, diketopyrrolopyrrole pigments, phthalocyanine pigments, azo pigments, and isoindoline pigments.

[0247] Examples of needle-shaped pigments include BiOCl, colored glass fiber, α-FeOOH, organic color pigments, etc. Examples of organic color pigments that are needle-shaped pigments include azo pigments, β-phthalocyanine CI Blue 15.3, Cromophtal Yellow 8GN (Ciba-Geigy), Irgalith Blue PD 56 (Ciba-Geigy), azomethine / copper complex CI Yellow 129, Irgazine Yellow 5GT (Ciba-Geigy), etc.

[0248] Suitable inorganic color pigments and dyes can be natural or synthetic and include, for example, chromium oxide and ultramarine.

[0249] [Carrier] Examples of the carrier include water, skin emollients, fatty acids, and fatty alcohols. These carriers may be used alone or in combination of two or more. The carrier may be aqueous, anhydrous, or an emulsion.

[0250] Emollients include, for example, silicone oils, natural or synthetic esters, hydrocarbons, etc. Silicone oils are classified into volatile and non-volatile varieties. In this context, "volatile" refers to materials that have a measurable vapor pressure at ambient temperature. Volatile silicone oils are selected from cyclic (cyclomethicone) or linear polydimethylsiloxanes having 3 to 9 silicon atoms, preferably 4 or 5 silicon atoms. Non-volatile silicone oils include, for example, polyalkylsiloxanes (e.g., polydimethylsiloxane, etc.), polyalkylarylsiloxanes, polyethersiloxane copolymers, emulsifying and non-emulsifying silicone elastomers, silicone waxes, etc. Emulsifying and non-emulsifying silicone elastomers include, for example, dimethicone / vinyl dimethicone crosspolymers, etc.

[0251] Examples of esters include the following: (a) Alkyl esters of saturated fatty acids having 10 to 24 carbon atoms, such as behenyl neopentanoate, isononyl isonanonoate, isopropyl myristate, octyl stearate, and the like; (b) ether-esters, such as fatty acid esters of ethoxylated saturated fatty alcohols; (c) Polyhydric alcohol esters. Examples of polyhydric alcohol esters include ethylene glycol mono- and di-fatty acid esters, diethylene glycol mono- and di-fatty acid esters, polyethylene glycol (200-6000) mono- and di-fatty acid esters, propylene glycol mono- and di-fatty acid esters, polypropylene glycol 2000 monostearate, ethoxylated propylene glycol monostearate, glyceryl mono- and di-fatty acid esters, polyglycerol poly-fatty esters, ethoxylated glyceryl mono-stearate, 1,3-butylene glycol monostearate, 1,3-butylene glycol distearate, polyoxyethylene polyol fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, pentaerythritol, trimethylolpropane, and neopentyl glycol esters of alcohols having 1 to 30 carbon atoms; (d) wax esters such as beeswax, spermaceti and tribehenin wax; (e) Sugar esters of fatty acids such as sucrose polybehenate and sucrose polycottonseedate.

[0252] Natural esters are based on mono-, di-, and triglycerides. Examples of glycerides include sunflower seed oil, cottonseed oil, borage oil, borage seed oil, primrose oil, castor oil, hydrogenated castor oil, rice bran oil, soybean oil, olive oil, safflower oil, shea butter, jojoba oil, etc. Examples of animal-derived esters include lanolin oil and lanolin derivatives, etc.

[0253] Examples of hydrocarbons include petrolatum, mineral oil, isoparaffins having 11 to 13 carbon atoms, polybutene, isohexadecane, and the like.

[0254] The fatty acid is a fatty acid having 10 to 30 carbon atoms, and specific examples thereof include pelargonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, linoleic acid, linolenic acid, hydroxystearic acid, and behenic acid.

[0255] The fatty alcohol is an fatty alcohol having 10 to 30 carbon atoms, and specific examples thereof include stearyl alcohol, lauryl alcohol, myristyl alcohol, oleyl alcohol, cetyl alcohol, and the like.

[0256] The content of the carrier can be from 1% by mass to 99.9% by mass, preferably from 70% by mass to 95% by mass, and more preferably from 80% by mass to 90% by mass, based on the total mass of the composition.

[0257] [Thickener] Thickeners include, for example, crosslinked acrylates, hydrophobically modified acrylates, polyacrylamides, acryloylmethylpropanesulfonic acid / salt polymers and copolymers, cellulose derivatives, natural gums, etc. Cellulose derivatives include, for example, sodium carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, ethylcellulose, hydroxymethylcellulose, etc. Natural gums include, for example, guar, xanthan, sclerotium, carrageenan, pectin, etc. Minerals, especially clays such as bentonite and hectorite, fumed silica, calcium carbonate, silicates (e.g., magnesium aluminum silicate) can also be used as thickeners.

[0258] The content of the thickener can be from 0.0001% by mass to 10% by mass, preferably from 0.001% by mass to 1% by mass, and more preferably from 0.01% by mass to 0.5% by mass, relative to the total mass of the composition.

[0259] [Surfactants] The surfactant may be anionic, nonionic, cationic, or amphoteric.

[0260] Examples of anionic surfactants include soap, alkyl ether sulfates, alkyl ether sulfonates, alkyl sulfates, alkyl sulfonates, alkyl benzene sulfonates, alkyl sulfosuccinates, dialkyl sulfosuccinates, acyl isethionates having 8 to 20 carbon atoms, alkyl ether phosphates having 8 to 20 carbon atoms, sarcosinates having 8 to 20 carbon atoms, acyl lactylates having 8 to 20 carbon atoms, sulfoacetates, and the like.

[0261] Examples of nonionic surfactants include surfactants having an aliphatic alcohol or acid hydrophobic group having from 10 to 20 carbon atoms condensed with from 2 to 100 moles of ethylene oxide or propylene oxide per mole of hydrophobic group, alkylphenols having from 2 to 10 carbon atoms condensed with from 2 to 20 moles of alkylene oxide, mono- and di-fatty acid esters of ethylene glycol, fatty acid monoglycerides, sorbitan, mono- and di-fatty acids having from 8 to 20 carbon atoms, polyoxyethylene sorbitan, alkyl polyglycosides, sugar fatty amides (e.g., methylglyconamide), trialkylamine oxides, and the like.

[0262] Examples of amphoteric surfactants include cocoamidopropyl betaine, trialkyl betaines having 12 to 20 carbon atoms, sodium lauroamphoacetate, and sodium laurodiamphoetate.

[0263] The content of the surfactant can be from 0.1 to 30% by mass, preferably from 0.1 to 15% by mass, and more preferably from 0.5 to 2% by mass, relative to the total mass of the composition.

[0264] [Binding agent] The binder may be in powder form or liquid form.

[0265] Powder binders include, for example, sodium stearyl fumarate, zinc stearate, magnesium stearate, calcium stearate, and the like. Examples of liquid binders include silicone oils and mineral oils. Examples of silicone oils include methylphenylpolysiloxane and polydimethylsiloxane. Mineral oils are liquid mixtures of hydrocarbons obtained from petroleum. Examples of hydrocarbons include paraffin oil, mineral oil, dodecane, isododecane, hexadecane, isohexadecane, eicosane, isoeicosane, tridecane, tetradecane, polybutene, and polyisobutene.

[0266] Other useful binders include, for example, tridecyl isononanoate, isostearyl isostearate, isocetyl isostearate, isopropyl isostearate, and isodecyl isononanoate. isonoanoate), cetyl octanoate, isononyl isononanoate, diisopropyl myristate, diisostearyl malate, isocetyl myristate, isotridecyl myristate, isopropyl myristate, isostearyl palmitate, isocetyl palmitate, isodecyl palmitate, isopropyl palmitate, octyl palmitate, caprylic / capric triglyceride, glyceryl tri-2-ethylhexanoate, neopentyl glycol di(2-ethylhexanoate), diisopropyl dimerate, tocopherol, tocopheryl acetate, avocado oil, camellia oil, turtle oil, macadamia nut oil, corn oil, mink oil, olive oil, rapeseed oil, egg yolk oil, sesame oil, persic oil, malt oil, sasanqua oil oil), castor oil, linseed oil, safflower oil, cottonseed oil, perillic oil, soybean oil, peanut oil, tea seed oil, kaya oil, rice bran oil, China tung oil, Japanese tung oil, jojoba oil, rice germ oil, glycerol trioctanate, glycerol triisopalmitate, trimethylolpropane triisostearate, isopropyl myristate, glycerol tri-2-ethylhexanoate, pentaerythritol tetra-2-ethylhexanoate, lanolin, lanolin liquid, paraffin liquid, squalane, petrolatum, cholesteryl derivatives (cholesteryl 12-hydroxystearate, cholesteryl macadamiate, cholesteryl stearate, etc.), succinic acid copolymers (PPG-7 succinic acid polypropylene glycol oligoester (35P.O.), etc.).

[0267] <Usage> The cosmetic composition of the present embodiment may be in the form of, for example, a solution, suspension, emulsion, paste, ointment, gel, cream, powder, stick, mousse, aerosol spray, non-aerosol spray, or a formulation applied to fabric (such as nonwoven fabric).

[0268] The cosmetic composition of the present embodiment can be formulated as a skin care product or a makeup product.

[0269] Examples of skin care products include, but are not limited to, lotions, day creams, night creams, face masks, cleansing products, facial cleansers, hair styling products, hair masks, hair rinses, hair shampoos, shower gels, shower oils, bath oils, body cosmetics, sunscreens, and the like. Examples of makeup products include, but are not limited to, foundation, concealer, makeup base, eye shadow, eye liner, mascara, blusher, lipstick, nail enamel, and the like.

[0270] <How to use> The cosmetic composition of the present embodiment is used by applying it to the skin. That is, in one embodiment, the present invention provides an application method including applying the cosmetic composition to the skin. According to the application method of the present embodiment, skin defects can be concealed by a soft focus effect.

[0271] As described above, the cosmetic composition of the present embodiment is useful for concealing skin defects such as wrinkles, scars, and pores. That is, in one embodiment, the present invention can be rephrased as a method for concealing skin defects, which includes applying the cosmetic composition to the skin. By applying the cosmetic composition to the skin, the skin defects can be made less visible to an observer by scattering reflected light from the skin. EXAMPLES

[0272] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0273] <Synthesis of alumina particles> [Synthesis Example 1] Synthesis of alumina particles ex1 A mixture was obtained by mixing 144.8 g of aluminum hydroxide (manufactured by Nippon Light Metals Co., Ltd., average particle size 40 μm), 0.95 g of silicon dioxide (manufactured by Kanto Chemical Co., Ltd., special grade), and 5 g of molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd.) in a mortar. The resulting mixture was placed in a crucible and fired at 1100°C for 10 hours in a ceramic electric furnace. After cooling, the crucible was removed, and 105.0 g of a light blue powder was obtained. The resulting powder was crushed in the mortar until it passed through a 106 μm sieve. Next, 100 g of the obtained light blue powder was dispersed in 150 mL of 0.5% ammonia water, and the dispersion solution was stirred at room temperature (25°C to 30°C) for 0.5 hours, after which the ammonia water was removed by filtration, and the molybdenum remaining on the particle surface was removed by washing with water and drying, to obtain 98 g of powder. Then, fine particles were classified and removed using an air classifier (Hyplec Classifier HPC-ZERO type manufactured by Powder Systems Co., Ltd.) utilizing the Coanda effect, to obtain 65 g of alumina particle powder. In addition, the zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 5.3. The obtained powder was confirmed by SEM observation to be an alumina particle having a card house structure formed by three or more flat alumina sheets and fixed together. The average particle size of the obtained powder was measured to be 35 μm. It was also confirmed that the flat alumina itself constituting the card house structure had a polygonal plate shape, a thickness of 400 nm, an average particle size of 8 μm, and an aspect ratio of 20. Furthermore, when XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, and no alumina crystal peak other than the α crystal structure was observed. The α conversion rate was 99% or more (almost 100%). Furthermore, the results of X-ray fluorescence quantitative analysis (XRF) showed that the obtained particles contained 0.71 mass% silicon in terms of silicon dioxide, 0.76 mass% molybdenum in terms of molybdenum trioxide, and the molar ratio of Si to Al [Si] / [Al] was 0.007. In addition, the powder obtained was analyzed by X-ray photoelectron spectroscopy (XPS), and the surface composition [Si] / [Al] of the tabular alumina of the alumina particles was found to be 0.24, which was significantly higher than the [Si] / [Al]% value of the bulk composition determined by X-ray fluorescence quantitative analysis, confirming that one or more types selected from the group consisting of silicon atoms and inorganic silicon compounds were unevenly distributed on the surface of the tabular alumina. In addition, the formation of a mullite layer on the surface of the tabular alumina was confirmed by XRD measurement. The specific surface area of ​​the resulting powder was measured and found to be 1.4 (m 2 / g) and the angle of repose was found to be 33°. Furthermore, the crushing strength of the obtained powder was calculated using a microparticle crushing strength measuring device NS-A100 manufactured by Nano Seeds Corporation, and was found to be 28 MPa.

[0274] <Evaluation of alumina particles obtained in synthesis examples and commercially available spherical alumina particles> [Analysis of the shape of alumina particles using a scanning electron microscope] The alumina particles obtained in the above synthesis example and commercially available spherical alumina particles (DAS-30, manufactured by Denka Co., Ltd.) were used as samples, which were fixed to a sample support with double-sided tape and observed with a surface observation device (VE-9800, manufactured by Keyence Co., Ltd.) to confirm the presence or absence of the card house structure of the alumina particles.

[0275] [Measurement of the longest diameter L of the alumina plate] The long diameter L of the tabular alumina was calculated as the arithmetic mean value of the maximum distance between two points on the outline of the plate for any 100 tabular alumina particles located at the center of the alumina particle, measured using a scanning electron microscope (SEM).

[0276] [Measurement of thickness D of plate-shaped alumina] The thickness of 10 pieces was measured using a scanning electron microscope (SEM), and the average value was used as the thickness D (μm).

[0277] [Aspect ratio L / D of plate-shaped alumina] The aspect ratio was calculated using the following formula.

[0278] (Aspect ratio) = (long diameter L of the alumina plate / thickness D of the alumina plate)

[0279] [Measuring the average particle size of alumina particles by particle size distribution measurement] The prepared sample was measured using a laser diffraction type dry particle size distribution analyzer (HELOS (H3355) & RODOS, manufactured by Japan Laser Corporation) under conditions of a dispersion pressure of 0.3 MPa and a suction pressure of 90 hPa. From the cumulative particle size distribution based on the volume, D 50 (μm) was determined and this was taken as the average particle size of the alumina particles.

[0280] [Measurement of angle of repose] 300 g of a sample was prepared, and the angle of repose of the sample was measured according to a method in accordance with JIS R9301-2-2.

[0281] [Measurement of specific surface area] The prepared samples were pretreated at 300° C. for 3 hours, and the specific surface area of ​​the pretreated samples was measured using a TriStar 3000 manufactured by Micromeritics.

[0282] [XRD peak intensity ratio - analysis of the presence or absence of mullite] The prepared sample was placed on a measurement sample holder with a depth of 0.5 mm and filled flat with a constant load. It was then set in a wide-angle X-ray diffraction (XRD) device (Ultima IV, Rigaku Corporation) and measurements were performed under the following conditions: Cu / Kα radiation, 40 kV / 40 mA, scan speed of 2 degrees / min, and scan range of 10 to 70 degrees. The peak height of mullite observed at 2θ = 26.2 ± 0.2 degrees was designated as A, the peak height of the (104) α-alumina plane observed at 2θ = 35.1 ± 0.2 degrees was designated as B, and the baseline value at 2θ = 30 ± 0.2 degrees was designated as C. The presence or absence of mullite was determined using the following formula. A value of 0.02 or more was judged to be "present" in mullite, and a value of less than 0.02 was judged to be "absent" in mullite.

[0283] Ratio of the mullite peak height to the (104) peak height of α-alumina =(AC) / (BC)

[0284] [Si content in the surface layer of plate-shaped alumina] Using an X-ray photoelectron spectroscopy (XPS) device, Quantera SXM (ULVAC-PHI, Inc.), the prepared sample was press-fixed onto double-sided tape and subjected to composition analysis under the following conditions.

[0285] (Measurement conditions) X-ray source: Monochromatic AlKα, beam diameter 100μmφ, output 25W Measurement: Area measurement (1000μm square), n=3 Charge correction: C1s=284.8eV

[0286] The [Si] / [Al] ratio determined from the results of XPS analysis was taken as the amount of Si in the surface layer of the tabular alumina particles.

[0287] [Analysis of Alpha Conversion Rate] The prepared sample was placed on a measurement sample holder with a depth of 0.5 mm, and packed flat with a constant load. It was then set in a wide-angle X-ray diffractometer (Ultima IV, Rigaku Corporation) and measurements were performed under the conditions of Cu / Kα radiation, 40 kV / 40 mA, scan speed of 2 degrees / min, and a scan range of 10 to 70 degrees. The α conversion rate was calculated from the ratio of the strongest peak heights of α-alumina and transition alumina.

[0288] [Analysis of the amount of Si contained in alumina particles] Using an X-ray fluorescence (XRF) analyzer Primus IV (Rigaku Corporation), approximately 70 mg of the prepared sample was placed on filter paper, covered with PP film, and subjected to composition analysis. The [Si] / [Al] ratio obtained from the XRF analysis was taken as the amount of Si in the alumina particles. The amount of silicon determined from the results of XRF analysis was calculated in terms of silicon dioxide (mass %) relative to 100 mass % of the alumina particles.

[0289] [Analysis of Mo content in alumina] Using a Primus IV X-ray fluorescence analyzer (Rigaku Corporation), approximately 70 mg of the prepared sample was placed on filter paper, covered with PP film, and subjected to composition analysis. The amount of molybdenum determined from the results of XRF analysis was calculated in terms of molybdenum trioxide (mass %) relative to 100 mass % of the alumina particles.

[0290] [Measurement of crushing strength] The crushing strength was measured using a microparticle crushing force measuring device, NS-A100, manufactured by Nanoseeds Co., Ltd. The difference between the peak value at the time of crushing and the baseline (when no force is applied) was taken as the crushing force F [N], and the crushing strength S [Pa] was taken as the average value of 10 values ​​calculated using the following formula.

[0291] S=2.8F / (π D2)

[0292] In the above formula, F is the crushing force [N] and D is the particle diameter [m].

[0293] [Measurement of isoelectric point] Zeta potential measurements were performed using a zeta potential measuring device (Malvern, Zetasizer Nano ZSP). 20 mg of sample and 10 mL of 10 mM KCl aqueous solution were mixed for 3 minutes in the mixing / degassing mode using a foam remover (Thinky, ARE-310), and the supernatant was left to stand for 5 minutes to be used as the measurement sample. Using an automatic titration device, 0.1 N HCl was added to the sample, and the zeta potential was measured in the range up to pH = 2 (applied voltage 100 V, Monomodl mode), and the pH of the isoelectric point where the potential becomes zero was evaluated.

[0294] [Oil absorption amount] 1 g of alumina particles was placed on a glass surface, and castor oil (Sigma Aldrich, 18722) was added dropwise onto the alumina particles and worked into the alumina particles with a spatula. The amount of castor oil required to saturate the alumina particles was recorded. This procedure was repeated a total of three times for each sample, and the average amount of castor oil recorded was used.

[0295] The composition of the raw material compounds calculated as oxides (total is 100 mass%) and the evaluation results of each alumina particle obtained in the synthesis examples are shown in the following Table 1. In addition, in Table 1, "ND" is an abbreviation for not detected, which indicates that it was not detected.

[0296] [Table 1]

[0297] <Preparation of foundation> [Example 1] A foundation having the composition shown in Table 2 was prepared. Specifically, talc, iron oxide, and titanium dioxide were weighed and placed in a large mixing cup manufactured by Hauschild, and mixed in a centrifugal mixer (FlackTek Inc., SpeedMixer DAC 105 FVZ-K) at 2000 rpm for 60 seconds. Next, mica, alumina particles, and sodium stearate were added to the mixing cup, and mixed in a centrifugal mixer at 2000 rpm for 60 seconds. Next, hydrogenated polyisobutene (trade name "Sophim MC30") was added to the mixing cup, and mixed in a centrifugal mixer at 2000 rpm for 60 seconds. Next, tri(caprylic / capric acid)glyceryl (trade name "Crodamol GTCC") was added to the mixing cup, and mixed in a centrifugal mixer at 2000 rpm for 60 seconds. Trisiloxane dimethicone (trade name "KF 90 20cts") was then added to the mixing cup and mixed with a centrifugal mixer at 2000 rpm for 60 seconds.

[0298] [Table 2]

[0299] A 4 g sample was then weighed out from the resulting mixture using an analytical balance. The 4 g sample was then pressed into a compression molding machine (Carver Model CS / N41000-208) while gradually increasing the pressure to 5 tons and holding the pressure for 20 seconds to produce a foundation.

[0300] [Comparative Example 1] A foundation was prepared in the same manner as in Example 1, except that DAS-30 was used instead of ex1 as the alumina particles.

[0301] <Foundation evaluation> [Measurement of lightness, saturation and hue] The lightness, chroma and hue of the prepared foundation were measured using a spectrophotometer (Datacolor SF600 PLUS) and a multi-angle colorimeter (BYK Mac I Cat. No.: 7030). The results are shown in Table 3.

[0302] [Table 3]

[0303] From Table 3, it was confirmed that the lightness, chroma, and hue of the foundation of Example 1 were comparable to those of the foundation of Comparative Example 1. In addition, it was inferred that the alumina particles used in the foundation of Example 1 have a card house structure, and thus tend to scatter light and have a soft focus effect. From Table 1, it was inferred that the alumina particles used in the foundation of Example 1 have a larger specific surface area than the alumina particles used in the foundation of Comparative Example 1, and therefore have a higher oil absorption, better makeup retention, and are less likely to come off.

[0304] The configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited to each embodiment, but is limited only by the scope of the claims. [Industrial Applicability]

[0305] According to the cosmetic composition of this embodiment, a cosmetic composition having a soft focus effect can be provided.

Claims

1. A cosmetic composition comprising alumina particles having an average particle diameter of 3 μm or more and 1000 μm or less, the alumina particles being formed of three or more sheets of tabular alumina, the alumina particles having a card house structure in which the tabular alumina particles are fixed together.

2. The cosmetic composition according to claim 1 , wherein the alumina particles contain silicon and / or germanium.

3. The cosmetic composition according to claim 1 or 2, wherein the alumina particles contain molybdenum.

4. 4. The cosmetic composition according to claim 3, wherein the molybdenum content is 10% by mass or less, calculated as molybdenum trioxide, relative to 100% by mass of the alumina particles.

5. The cosmetic composition according to any one of claims 1 to 4, wherein the alumina particles have an oil absorption of 0.6 g or more and 5.0 g or less per 1 g of solid content.

6. The cosmetic composition according to any one of claims 1 to 5, which is for skin care or makeup.

7. The cosmetic composition according to any one of claims 1 to 6, further comprising a colorant.

8. The cosmetic composition according to any one of claims 1 to 7, which is a cosmetic selected from the group consisting of foundation, concealer, makeup base, eye shadow, eyeliner, mascara, blusher, lipstick, nail enamel, body cosmetics, and sunscreen.

9. A method of application, comprising applying the cosmetic composition according to any one of claims 1 to 8 to skin.

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