Powder cosmetic and method for producing powder cosmetic

Abstract

Provided is a powder cosmetic comprising azelaic acid particles, said powder cosmetic being characterized in that the shape of the azelaic acid particles is spherical or plate-like.

Description

Powder cosmetics and method for producing powder cosmetics

[0001] The present invention relates to a powder cosmetic and a method for producing the powder cosmetic. More specifically, the present invention relates to a powder cosmetic containing azelaic acid particles and a method for producing the powder cosmetic.

[0002] Azelaic acid is a saturated dicarboxylic acid and a white, finely powdered substance. Azelaic acid has the effects of suppressing excessive sebum secretion and anti-inflammatory effects, and is known to function as an active ingredient in the treatment of acne. In addition, azelaic acid is known to inhibit melanocyte activity, activate skin metabolism, and have antioxidant properties, making it an active ingredient in the treatment of skin pigmentation.

[0003] Therefore, compositions containing azelaic acid are used as external preparations to be applied to the skin.For example, Patent Document 1 discloses an acne treatment agent containing azelaic acid in a pharmaceutically acceptable carrier, the carrier being selected from cream, ointment, and lotion forms.In addition, Patent Document 2 discloses an external skin preparation containing azelaic acid, a liquid oil having a polar group in the molecule, water, and an emulsion-stabilizing component, and emulsified by dispersing at least the liquid oil in water.

[0004] Japanese Patent Publication No. 57-134416 Japanese Patent Publication No. 2015-078167

[0005] As shown in Patent Documents 1 and 2, when a composition containing azelaic acid is prepared and used as a product (such as a therapeutic agent or topical agent), azelaic acid is generally dispersed in various bases containing oil and / or water. Here, it is understood that the various efficacy effects of azelaic acid are exerted by contact with or penetration into the skin. As described in Patent Documents 1 and 2, products that use a base containing oil and / or water and contain azelaic acid in a dispersed state have the problem that, from the viewpoint of the contact efficiency of azelaic acid coming into direct contact with the skin, the various efficacy effects of azelaic acid cannot be exerted quickly or sufficiently during use.

[0006] Furthermore, azelaic acid is not limited to treating affected skin areas; it also has beneficial effects for making skin appear more beautiful (e.g., whitening effects), making it highly useful as a cosmetic ingredient. In particular, the use of azelaic acid in powder cosmetics, whose main constituent is powder, is expected to improve the contact efficiency of azelaic acid with the skin, thereby enabling the beneficial effects of azelaic acid as a cosmetic ingredient to be more effectively exerted. Azelaic acid is known to be a substance that is highly safe for the human body, and compositions containing azelaic acid as an active ingredient must contain a relatively high proportion (approximately 5 to 20% by mass) of azelaic acid. Therefore, when azelaic acid is incorporated into powder cosmetics, there are concerns that it may have a negative impact on the finish upon use. Specifically, there are concerns that it may produce a whitish finish that disrupts the uniformity of skin tone, or a powdery finish that is noticeable, resulting in an overall unnatural finish.

[0007] Therefore, an object of the present invention is to provide a powder cosmetic that can fully exhibit the various efficacy effects of azelaic acid without impairing the finish when applied to the skin, and a method for producing the powder cosmetic.

[0008] The present inventors conducted extensive research into the above-mentioned problems and discovered that the problems could be solved by controlling the particle shape of azelaic acid to be incorporated into a powder cosmetic, leading to the completion of the present invention. That is, the present invention encompasses the subject matter of the powder cosmetic and the method for producing the powder cosmetic described in the following sections.

[0009] Item 1. A powder cosmetic containing azelaic acid particles, characterized in that the azelaic acid particles are spherical or plate-shaped.

[0010] Item 2. The powder cosmetic according to Item 1, wherein the azelaic acid particles include particles having a median diameter of 10 μm or more.

[0011] Item 3. The powder cosmetic according to Item 1 or 2, characterized in that it contains 5% by mass or more of the azelaic acid particles.

[0012] Item 4. A method for producing a powder cosmetic, comprising a step of adding azelaic acid particles, wherein the azelaic acid particles are spherical or plate-like in shape. Item 5. Use of spherical or plate-like azelaic acid particles in the production of a powder cosmetic. Item 6. Spherical or plate-like azelaic acid particles having a median diameter of 10 μm or more as measured using a particle size distribution measuring device based on the laser diffraction scattering method.

[0013] According to the present invention, it is possible to provide a powder cosmetic that can fully exert the various efficacy effects of azelaic acid without impairing the finish when applied to the skin, and a method for producing the powder cosmetic.

[0014] 1A is an SEM image of commercially available azelaic acid at a magnification of 500x; FIG. 1B is an SEM image of the azelaic acid in FIG. 1A at a magnification of 1000x; FIG. 2A is an SEM image of azelaic acid particles prepared by a spray drying method and incorporated into a powder cosmetic according to an embodiment of the present invention at a magnification of 50x; FIG. 2B is an SEM image of azelaic acid particles in FIG. 2A at a magnification of 400x; FIG. 3A is an SEM image of azelaic acid particles prepared by a vacuum drying method and incorporated into a powder cosmetic according to an embodiment of the present invention at a magnification of 50x; and FIG. 3B is an SEM image of azelaic acid particles in FIG. 3A at a magnification of 300x.

[0015] In this specification, the singular form includes both the singular and the plural, unless otherwise specified in the specification or clearly contradictory in context. In this specification, the terms "comprise" and "include" are concepts that encompass "consist essentially of" and "consist only of." Below, embodiments of the powder cosmetic and the method for producing the powder cosmetic according to the present invention will be described, including the best mode.

[0016] [Powder Cosmetic] The powder cosmetic of the present invention is a powder cosmetic containing azelaic acid particles, and the azelaic acid particles have either a spherical or plate-like shape.

[0017] <Azelaic Acid Particles> The azelaic acid particles of the present invention refer to a substance obtained by granulating or granulating azelaic acid.

[0018] First, azelaic acid will be described. Azelaic acid (chemical formula C ９ H １６ O ４ ) is a saturated dicarboxylic acid and is a substance consisting of a white fine powder. Although the main industrial method for producing azelaic acid is a method of ozonolysis of oleic acid, the method for producing azelaic acid itself, which is the raw material for the azelaic acid particles of the present invention, is not particularly limited, and a commercially available product of azelaic acid may also be used.

[0019] Figures 1A and 1B are scanning electron microscope (SEM) images of commercially available azelaic acid. Figure 1A is at a magnification of 500x, and Figure 1B is at a magnification of 1000x. The SEM images in Figures 1A and 1B were obtained by using "Azelaic Acid" manufactured by CORUM Corporation as azelaic acid and a "TM4000Plus" scanning electron microscope manufactured by Hitachi High-Technologies Corporation at an accelerating voltage of 15 kV. Figures 1A and 1B show that commercially available azelaic acid contains needle-shaped, rod-shaped, spindle-shaped, and amorphous crystal structures, primarily consisting of a fine powder of crystals having a needle-shaped structure with a length of approximately 1 to 30 μm and a width of 10 μm or less. Hereinafter, the needle-shaped, rod-shaped, spindle-shaped, and amorphous crystal structures of azelaic acid are collectively referred to as "structures such as needle-shaped structures." The particle size distribution of the azelaic acid crystals at this time was measured in a dry state using a particle size distribution measuring device ("PSA1190" manufactured by Anton Paar) based on a laser diffraction scattering method, and the median diameter (D50) was found to be approximately 5.4 μm.

[0020] The morphology of the azelaic acid incorporated into the powder cosmetic of the present invention was conceived by the present inventors based on the finding that azelaic acid is a fine crystalline powder having a structure such as a needle-like structure, as shown in Figures 1A and 1B. That is, when using azelaic acid as an active ingredient in a powder cosmetic, the present inventors discovered that there is a correlation between the deterioration of the finish when the powder cosmetic is applied to the skin and the azelaic acid being a fine powder and having a structure such as a needle-like structure, and thus arrived at the configuration of the powder cosmetic of the present invention.

[0021] The azelaic acid particles incorporated into the powder cosmetic of the present invention are spherical or plate-like in shape. In the present invention, particles having a "spherical" shape are those having a substantially circular cross-sectional periphery. They may be hollow particles with an internal cavity, or solid particles without an internal cavity. In the present invention, particles having a "plate-like" shape are those having a thin, flat shape, such as a plate-like or scale-like shape. The azelaic acid particles incorporated into the powder cosmetic of the present invention may be primarily spherical or plate-like in shape. For example, they may be a mixture of spherical and plate-like shapes, or may be either spherical or plate-like. Compared to azelaic acid that is a fine powder and has a needle-like structure, spherical azelaic acid particles are expected to provide improved slipperiness on the skin surface and soft-focus effects by approaching skin grooves and pores, while plate-like azelaic acid particles can improve adhesion to the skin by approaching skin ridges and reduce the appearance of a white cast. Furthermore, when spherical and plate-shaped azelaic acid particles coexist, the respective effects are exerted. That is, it is possible to exert one or more of the efficacy effects of azelaic acid selected from the sebum-suppressing effect, anti-inflammatory effect, whitening effect, acne improvement effect, melanocyte activity suppression, skin metabolism activation, antioxidant effect, and skin pigmentation suppression without impairing the finish when using the powder cosmetic. The results of an evaluation of the finish when applied to the skin using the azelaic acid particles of an embodiment of the present invention will be described later as an example.

[0022] The azelaic acid particles of the present invention may be spherical or plate-shaped, and the particle size is not particularly limited. For example, they may be of a raw material size commonly used in powder cosmetics (median diameter D50 of approximately 5 μm to 20 μm), or may be larger than the fine powder of azelaic acid shown in FIGS. 1A and 1B. The particle size of the azelaic acid particles of the present invention is preferably 10 μm or more, more preferably 25 μm or more, as determined, for example, by a median diameter (D50) measurement using a particle size distribution analyzer based on laser diffraction scattering. While there is no particular upper limit to the particle size of the azelaic acid particles, the median diameter (D50) is preferably 300 μm or less, more preferably 150 μm or less. By ensuring that the median diameter of the azelaic acid particles falls within the above range, the azelaic acid particles can be trapped in the skin grooves and remain there when applied to the skin, thereby achieving the effect of easily maintaining a state of adhesion without peeling off from the skin surface. This makes it possible to fully exert the various efficacy effects of azelaic acid while providing an excellent finish when applied to the skin.

[0023] In addition, the means for adjusting the particle size of the azelaic acid particles in the present invention is not particularly limited.For example, it can be selected the preparation conditions (solvent, processing time, processing temperature, etc.) when preparing azelaic acid particles from raw material azelaic acid, or the prepared azelaic acid particles can be subjected to crushing treatment and classification treatment such as sieving.Therefore, those skilled in the art can obtain azelaic acid particles that meet desired size with ordinary skills.

[0024] In addition, the means for confirming (measuring) the particle size of the azelaic acid particles in the present invention is not particularly limited, and known measuring devices and measuring means can be used.For example, measurements using a particle size distribution measuring device or measurements using analysis (calculation) results based on image data can be mentioned.More specifically, in addition to the median diameter obtained using a particle size distribution measuring device based on laser diffraction scattering, the particle size of the azelaic acid particles in the present invention can also be the average value of the particle sizes (diameters, or a combination of the longest diameter and the shortest diameter) of multiple particles (for example, 20 particles) randomly selected from an SEM image of the azelaic acid particles.

[0025] <Preparation method of azelaic acid particles> The azelaic acid particles in the present invention can be prepared by granulating the raw material, which is azelaic acid that is a fine powder and has a needle-like structure or the like.The method for preparing spherical or plate-shaped azelaic acid particles is not particularly limited, but can be generally known granulation methods, such as spray drying, vacuum drying, spray freeze drying (SFD), crystallization (recrystallization) and the like.In particular, spray drying is preferably used to prepare spherical azelaic acid particles, and vacuum drying is preferably used to prepare plate-shaped azelaic acid particles.

[0026] As an example of preparing azelaic acid particles, when a spray drying method is used, the following method can be used, for example. First, azelaic acid is dissolved or uniformly dispersed in a dispersion solvent made of an alcohol such as ethanol to prepare a solution or slurry of azelaic acid. When preparing the solution or slurry of azelaic acid, an excipient or the like may be added as needed. The excipient is a substance that does not have physiological activity, and examples thereof include starch, dextrin, lactose, maltose, glucose, maltitol, sorbitol, and crystalline cellulose. The addition of the excipient can adjust the shape of the particles.

[0027] Next, the azelaic acid solution or slurry is supplied in an atomized state into a drying chamber into which hot air is supplied. This instantly evaporates the solvent, yielding azelaic acid particles. Since the azelaic acid solution or slurry is supplied as atomized droplets, the droplets are sphericalized by surface tension and become particles. In addition, in the spray drying method, the size of the resulting particles can be controlled by selecting and / or adjusting the atomization means (disk type, nozzle type, etc.).

[0028] As another example of preparing azelaic acid particles, when a vacuum drying method is used, the following method can be used. First, azelaic acid is dissolved or uniformly dispersed in a dispersion solvent consisting of an alcohol such as ethanol to prepare a solution or slurry of azelaic acid. Next, the azelaic acid solution or slurry is placed in a pallet, and the liquid content is reduced by suction drying or the like, followed by drying treatment using a vacuum dryer. This causes azelaic acid to aggregate and become granulated, thereby obtaining azelaic acid particles. Alternatively, water can be added to the prepared azelaic acid solution or slurry to cause crystallization, followed by drying treatment using a vacuum dryer. In addition, in the vacuum drying method, the particle size obtained can be controlled by selecting and / or adjusting the drying conditions (temperature, drying time, etc.) and the azelaic acid content in the azelaic acid solution or slurry treated in the vacuum dryer.

[0029] The amount of azelaic acid in the azelaic acid particles is not particularly limited, but is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more, for example, approximately 100% by mass. In the powder cosmetic of the present invention, the amount of azelaic acid particles is not particularly limited, but is preferably 0.001 to 100.0% by mass. The lower limit is more preferably 0.1% by mass or more, even more preferably 1.0% by mass or more, and particularly preferably 5.0% by mass or more. The upper limit is more preferably 50.0% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20.0% by mass or less. By being within the above range, the various efficacy and effects of azelaic acid, such as sebum suppression effect, anti-inflammatory effect, and whitening effect, can be fully exhibited. Furthermore, from the viewpoint of achieving both sufficient utilization of the various efficacy effects of azelaic acid when incorporated into a powder cosmetic and achieving an excellent finish feeling when applied to the skin, it is particularly preferable that the amount of azelaic acid particles incorporated is 5.0% by mass or more.

[0030] <Other Components> Depending on the intended use, the powder cosmetic of the present invention may contain one or more other components commonly used in general cosmetics, such as inorganic pigments, polymer powders, oily raw materials, surfactants, moisturizers, thickeners, polymers, UV protection agents, antioxidants, antioxidant aids, sequestering agents, metallic soaps such as magnesium stearate, whitening agents, anti-wrinkle agents, agents for improving rough skin, anti-acne agents, deodorizing agents, refreshing agents, astringents, antibacterial agents, organic pigments, natural colorants, fragrances, vitamins, and emollients.

[0031] Examples of inorganic pigments include extender pigments, coloring pigments, and white pigments. Extender pigments are used to maintain the product's formulation, thereby adjusting the product's usability (spreadability, adhesion), gloss, etc. Specific examples include mica, sericite, talc, kaolin, synthetic phlogopite, calcium carbonate, magnesium carbonate, silicic anhydride, aluminum oxide, and barium sulfate. Coloring pigments adjust the color tone of the product, and specific examples include red iron oxide, yellow iron oxide, black iron oxide, chromium oxide, ultramarine, Prussian blue, and carbon black. White pigments not only adjust the color tone of the product, but also adjust the hiding power, and specific examples include titanium dioxide and zinc oxide.

[0032] Specific examples of polymer powders include polyethylene powder, polymethyl methacrylate powder, polyethylene terephthalate-polymethyl methacrylate laminate powder, nylon powder, polyurethane powder, and silicone powder.

[0033] Examples of oily raw materials include fats and oils, waxes, hydrocarbons, higher fatty acids, higher alcohols, esters, and silicone oils. More specifically, examples of fats and oils include olive oil, camellia oil, macadamia nut oil, and castor oil; examples of waxes include carnauba wax, candelilla wax, jojoba oil, beeswax, and lanolin; examples of hydrocarbons include liquid paraffin, paraffin, petrolatum, ceresin, microcrystalline wax, and squalane; examples of higher fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, and isostearic acid; examples of higher alcohols include cetyl alcohol, stearyl alcohol, isostearyl alcohol, and 2-octyldodecanol; examples of esters include isopropyl myristate, 2-octyldodecyl myristate, cetyl 2-ethylhexanoate, and diisostearyl malate; and examples of silicone oils include methylpolysiloxane, methylphenylpolysiloxane, decamethylcyclopentasiloxane, and highly polymerized methylpolysiloxane.

[0034] Examples of surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. More specifically, examples of anionic surfactants include higher fatty acid soaps, alkyl sulfate ester salts, polyoxyalkyl ether sulfate salts, acyl N-methyl taurine salts, alkyl ether phosphate ester salts, and N-acyl amino acid salts. Examples of cationic surfactants include alkyl trimethyl ammonium chloride, dialkyl dimethyl ammonium chloride, and benzalkonium chloride. Examples of amphoteric surfactants include alkyl dimethyl amino acetate betaine, alkyl amidopropyl dimethyl amino acetate betaine, and 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine. Examples of nonionic surfactants include polyoxyethylene surfactants, polyhydric alcohol esters, and ethylene oxide-propylene oxide block copolymers.

[0035] Examples of moisturizing agents include glycerin, propylene glycol, dipropylene glycol, 1,3-butylene glycol, polyethylene glycol, sorbitol, sodium lactate, sodium 2-pyrrolidone-5-carboxylate, sodium hyaluronate, and ceramides (pseudoceramide, human ceramide, natural human ceramide).

[0036] Examples of thickeners include quince seed gum, xanthan gum, sodium carboxymethylcellulose, and carboxyvinyl polymer.

[0037] Examples of the polymer include polyvinyl alcohol, polyvinylpyrrolidone, nitrocellulose, and polymeric silicone.

[0038] Examples of ultraviolet protection agents include ultraviolet absorbers such as benzophenone derivatives, para-aminobenzoic acid derivatives, methoxycinnamic acid derivatives, and salicylic acid derivatives, and ultraviolet scattering agents such as fine particle titanium oxide, fine particle zinc oxide, and fine particle iron oxide.

[0039] Examples of antioxidants include tocopherol, BHT, gallic acid esters, etc. Examples of antioxidant aids include phosphoric acid, citric acid, ascorbic acid, maleic acid, malonic acid, succinic acid, fumaric acid, cephalin, hexametaphosphate, phytic acid, ethylenediaminetetraacetic acid (EDTA), etc.

[0040] Examples of sequestering agents include sodium ethylenediaminetetraacetate, phosphoric acid, citric acid, ascorbic acid, succinic acid, gluconic acid, sodium polyphosphate, and sodium metaphosphate.

[0041] Examples of whitening agents include vitamin C, arbutin, kojic acid, ellagic acid, and rucinol.

[0042] Examples of anti-wrinkle agents include retinoids (vitamin A), α-hydroxy acids, various peptides, amino acids, and the like.

[0043] Examples of the skin roughness improving agent include anti-inflammatory agents such as β-glycyrrhetinic acid, glycyrrhizinic acid derivatives, allantoin, azulene, and hydrocortisone, and protease inhibitors.

[0044] Examples of anti-acne medications include sebum-suppressing ingredients such as estradiol, estrone, ethinylestradiol, and vitamin B6; keratin-exfoliating and / or dissolving ingredients such as sulfur, salicylic acid, and resorcinol; bactericidal ingredients such as benzalkonium chloride, benzethonium chloride, halocarban, and 2,4,4-trichloro-2-hydroxyphenol; and anti-inflammatory ingredients such as glycyrrhizic acid and glycyrrhetinic acid.

[0045] Examples of deodorant agents include antiperspirant ingredients such as chlorohydroxyaluminum, aluminum chloride, allantoin chlorohydroxyaluminum, zinc oxide, zinc paraphenolsulfonate, and silver-containing zeolite; bactericidal ingredients such as benzalkonium chloride, isopropylmethylphenol, benzethonium chloride, halocarban, and chlorhexidine hydrochloride; deodorizing ingredients such as polyphenol-based persimmon tannin and tea catechin; and antioxidant ingredients such as thiotaurine, hypotaurine, and tocopherol.

[0046] Examples of the cooling agent include menthol and camphor.

[0047] Examples of astringents include zinc oxide, zinc sulfate, allantoin hydroxyaluminum, aluminum chloride, zinc sulfophenolate, tannic acid, citric acid, and lactic acid.

[0048] Examples of antibacterial agents include benzoic acid and its salts, salicylic acid and its salts, phenol, sorbic acid and its salts, dehydroacetic acid and its salts, paraben, chlorcresol, hexachlorophene, resorcinol, isopropylmethylphenol, orthophenylphenol, benzalkonium chloride, chlorhexidine hydrochloride, chlorhexidine gluconate, alkylisoquinolinium bromide, trichlorocarbanilide, halocarban, photosensitizer No. 201, phenoxyethanol, triclosan, methylchloroisothiazolinone-methylisothiazolinone solution, bisabolol, alkyldiaminoethylglycine hydrochloride, trichloro-salicylanilide, tribromo-salicylanilide, mercury-based compounds, formalin, white lime, bithionol, boric acid-borax, dichlorophen, hexachlorophene, and halogenated salicylanilide.

[0049] Other components may also be included that can impart particularly beneficial functions to powder cosmetics, such as components containing growth factors and / or cytokines that inhibit skin aging and damage and activate the production of skin tissue (e.g., human stem cell culture medium (supernatant)), and components that promote collagen production (exosomes, hydroxyapatite, etc.).

[0050] <Form and Shape of Powder Cosmetic> The powder cosmetic of the present invention may be in any form, powdered or solid, as long as the azelaic acid particles are blended while maintaining their original shape. More specifically, examples include loose powders and pressed powders. Furthermore, the product form of the powder cosmetic of the present invention is not particularly limited, and examples include foundations, control colors, base powders, and finishing powders (face powders). The foundations, control colors, and base powders may be in the form of pressed powders, and the finishing powders (face powders) may be in the form of loose powders or pressed powders. The powder cosmetic of the present invention is preferably in a form and product shape suitable for direct application to the skin. In other words, the powder cosmetic of the present invention is preferably in a form and product shape suitable for application to the skin before applying other cosmetics or after washing or face washing. This allows the beneficial effects of the azelaic acid contained in the powder cosmetic of the present invention as a cosmetic ingredient to be more effectively exerted.

[0051] [Method for producing powder cosmetics] The powder cosmetic of the present invention can be produced by filling a mixture (cosmetic composition) obtained by mixing azelaic acid particles and other ingredients by a conventional method into a container or by molding. For example, a mixture (cosmetic composition) consisting of azelaic acid particles and other ingredients mixed by a conventional method can be filled directly into a container and provided as a loose powder. Another example is to fill the cosmetic composition into a container and then provide it as a pressed powder using equipment commonly used in the production of powder cosmetics, such as a press or dryer.

[0052] The present invention will be specifically described below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0053] [Preparation of Azelaic Acid Particles] First, a method for preparing azelaic acid particles by spray drying will be described. Azelaic acid ("Azelaic Acid" manufactured by Corum; azelaic acid in Figures 1A and 1B) was dissolved in ethanol to prepare an azelaic acid solution. Next, this solution was spray-dried using a spray dryer to obtain azelaic acid particles. Figures 2A and 2B show SEM images of the obtained azelaic acid particles, acquired under the same observation conditions as those in Figures 1A and 1B. Note that Figure 2A was observed at a magnification of 50x, and Figure 2B was observed at a magnification of 400x. Figures 2A and 2B show that, compared to the raw azelaic acid (see Figures 1A and 1B), azelaic acid aggregates or granulates, resulting in spherical azelaic acid particles or plate-like (or scale-like) azelaic acid particles. 2A and 2B, it can be seen that azelaic acid particles having a particle diameter or long side length of about 50 μm to 150 μm are obtained.

[0054] Next, a method for preparing azelaic acid particles by vacuum drying will be described. Azelaic acid ("Azelaic Acid" manufactured by Corum; azelaic acid in Figures 1A and 1B) was dissolved in ethanol, and then water was added to cause crystallization, preparing a 70% by mass azelaic acid solution. This solution was then placed on a stainless steel pallet, and after reducing the water content by suction drying, it was dried in a vacuum dryer for 12 hours to obtain azelaic acid particles. SEM images of the obtained azelaic acid particles, taken under the same observation conditions as those in Figures 1A and 1B, are shown in Figures 3A and 3B. Note that Figure 3A was taken at a magnification of 50x, and Figure 3B was taken at a magnification of 300x. Figures 3A and 3B reveal that, compared to the raw azelaic acid (see Figures 1A and 1B), aggregation or granulation of the azelaic acid occurred, resulting in primarily plate-like azelaic acid particles. 3A and 3B show that azelaic acid particles having a long side length of 50 μm or more (mainly about 200 μm to 300 μm) can be obtained. The particle size distribution of the azelaic acid particles obtained was measured in a dry state using a particle size distribution analyzer ("PSA1190" manufactured by Anton Paar) based on a laser diffraction scattering method, and the median diameter (D50) was found to be about 51.5 μm.

[0055] [Evaluation of Azelaic Acid Particles] The obtained azelaic acid particles were evaluated for finish when applied to the skin. As an example, evaluation was carried out using plate-shaped azelaic acid particles obtained by a vacuum drying method (see FIG. 3). As a comparative example, azelaic acid before being made into a plate shape (the raw azelaic acid; see FIG. 1) was also similarly evaluated.

[0056] The evaluation method will be explained. Fifteen panelists were asked to apply each of the Examples and Comparative Examples to a part of the skin (inside the forearm), and a visual evaluation test was conducted from the viewpoints of "high adhesion to the skin," "powderyness of the finished product," "white cast feeling upon application," and "transparency of the finished product." The evaluation test was conducted by performing a relative evaluation of the Examples with the Comparative Example set as "0 (standard)." The evaluation criteria and evaluation results for each viewpoint are as follows:

[0057] (High Adhesion to Skin) The high adhesion to skin when the Examples were applied was visually evaluated relative to the Comparative Example. The evaluation criteria are as follows: 2: Very high (adhesion to skin compared to the Comparative Example) 1: High 0: Neither high nor low (same as the Comparative Example) -1: Low -2: Very low

[0058] Based on the above evaluation criteria, the evaluation test was conducted for each panelist, and the average of the obtained evaluation results was 1.13. In other words, it was found that the Example (azelaic acid particles having a specific shape) exhibited higher adhesion to the skin than the Comparative Example.

[0059] (Powderiness of finish) The powderiness of the finish when the Examples were applied was visually evaluated relative to that of the Comparative Example. The evaluation criteria are as follows: 2: Not powdery at all (compared to the Comparative Example) 1: Not powdery 0: Neither (same as the Comparative Example) -1: Powdery -2: Very powdery

[0060] Based on the above evaluation criteria, the evaluation test was carried out for each panelist, and the average of the obtained evaluation results was 1.93. In other words, it was found that the Examples did not exhibit a powdery finish compared to the Comparative Examples, and an excellent finish feeling was obtained.

[0061] (Feeling of white cast upon application) When the Examples were applied, the feeling of white cast against the skin color was visually evaluated relative to the feeling of white cast of the Comparative Example. The evaluation criteria were as follows: 2: No white cast at all (compared to the Comparative Example) 1: No white cast 0: Neither (same as the Comparative Example) -1: White cast -2: Very white cast

[0062] Based on the above evaluation criteria, an evaluation test was conducted for each panelist, and the average of the obtained evaluation results was 2.00. In other words, it was found that the Examples did not give off any white cast feeling when applied to the skin, as compared with the Comparative Examples, and an excellent finish feeling was obtained.

[0063] (Transparency of Finish) The transparency of the finish after application of the Examples was visually evaluated relative to the Comparative Example. The evaluation criteria are as follows: 2: Very transparent (compared to the Comparative Example) 1: Transparent 0: Neither transparent nor transparent (similar to the Comparative Example) -1: Not transparent -2: Not transparent at all Based on the above evaluation criteria, an evaluation test was conducted for each panelist, and the obtained evaluation results were averaged to obtain a score of 2.00. In other words, it was found that the Examples showed higher transparency in the finish after application to the skin than the Comparative Example, and an excellent finish feeling was obtained.

[0064]

[0046] From the above evaluation results, it can be seen that the azelaic acid particles having a specific shape in the Examples are capable of improving adhesion to the skin and reducing the feeling of white cast when applied to the skin, compared to the azelaic acid particles having a needle-like structure or the like in the Comparative Examples, and do not impair the finish upon use, even when used in a high blending amount (usage amount) as an active ingredient in a powder cosmetic. Furthermore, the azelaic acid particles in the Examples maintain the purity (99.9%±0.1%) and properties of azelaic acid, and therefore are able to fully exert the efficacy and effects of azelaic acid.

[0065] [Formulation Examples] Examples of formulations for the powder cosmetic of the present invention are shown below, however, the technical scope of the present invention is not limited to these formulation examples.

[0066] Formulation Example 1 A face powder was prepared according to the following formulation: Component name Amount (mass %) Azelaic acid particles 20.00 Talc 50.00 Sericite 20.00 Silica 5.00 Zinc myristate 5.00

[0067] (Formulation Example 2) A closed patch test was conducted on 20 subjects using five test products: (1) petrolatum and 20% azelaic acid particles obtained by vacuum drying (azelaic acid produced in Taiwan), (2) petrolatum and 20% azelaic acid particles obtained by vacuum drying (azelaic acid produced in Japan), (3) talc and 20% azelaic acid obtained by vacuum drying (azelaic acid produced in Japan), (4) saline, and (5) white petrolatum. The test products were tested in accordance with Section 3, "Human Patch Tests," in Chapter 1, "Skin Irritation Tests," of "Skin Irritation and Sensitization Testing Methods, and Skin Property Measurement and Evaluation." Specifically, a skin test patch tape filled with the test product was applied to the application site on the subject's body, and the skin test patch tape was peeled off and removed after 24 hours. Sixty minutes after peeling and 24 hours after peeling, the doctor evaluated the test products according to the evaluation criteria in Table 1, and classified the test products based on the scores in Table 2.

[0068] *Skin irritation index = (total score of the most severe reaction 60 minutes or 24 hours after peeling of the test product / number of subjects) x 100 As a result, all 20 subjects were "negative (-)" for the five test products 60 minutes and 24 hours after peeling, confirming that all products were safe.

[0069] The powder cosmetic and the method for producing the powder cosmetic of the present invention can be used to provide a powder cosmetic that can utilize the various efficacy and effects of azelaic acid without impairing the finish when used.

Claims

1. A powder cosmetic containing azelaic acid particles, characterized in that the azelaic acid particles are spherical or plate-like in shape.

2. The powder cosmetic according to claim 1, wherein the azelaic acid particles include those having a median diameter of 10 μm or more.

3. The powder cosmetic according to claim 1 or 2, characterized in that it contains 5% by mass or more of the azelaic acid particles.

4. A method for producing a powder cosmetic, comprising the step of adding azelaic acid particles, wherein the azelaic acid particles are spherical or plate-like.

5. Use of spherical or plate-shaped azelaic acid particles in the production of powder cosmetics.

6. Spherical or plate-like azelaic acid particles having a median diameter of 10 μm or more as measured using a particle size distribution measuring device based on a laser diffraction scattering method.

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