Oil-in-water emulsion-containing sunscreen cosmetic

Abstract

This oil-in-water emulsion-containing a sunscreen cosmetic comprises: oil component-containing fine particles that include an ultraviolet scattering agent and an oil component; and an aqueous dispersion medium. The oil component-containing fine particles are dispersed in the aqueous dispersion medium. The surface of the ultraviolet scattering agent is hydrophobic. The aqueous dispersion medium contains (A) C12-24 monovalent linear aliphatic alcohol, (B) at least one emulsifier selected from the group consisting of polyglyceryl pentastearate and sodium stearoyl lactylate, and (C) sodium methyl stearoyl taurate. The total content of the linear aliphatic alcohol and the emulsifier is 1.2-5.5 mass%.

Description

Sunscreen cosmetics containing oil-in-water emulsion

[0001] The present invention relates to a sunscreen cosmetic containing an oil-in-water emulsion. More specifically, the present invention relates to a sunscreen cosmetic containing an oil-in-water emulsion that is easy to use and has excellent storage stability, and forms a coating that is excellent in water resistance and cleansability, even without using polymer particles as a raw material.

[0002] Oil-in-water emulsions are used in cosmetics applied to human skin because they provide a refreshing feel to the skin compared to water-in-oil emulsions. In recent years, an oil-in-water emulsion sunscreen cosmetic has been proposed that can achieve high UV protection power and has excellent emulsion storage stability by improving the UV protection power of the UV scattering agent, comprising (A) an acrylic copolymer having a phosphate group, (B) a hydrophobized UV scattering agent, and (C) 0.3 mass% or more of an aqueous phase thickener, with the UV scattering agent dispersed in the oil phase (see, for example, paragraphs

[0007] and

[0009] of Patent Document 1).

[0003] The oil-in-water emulsion sunscreen cosmetic composition is said to be able to improve the UV protection power of the UV scattering agent contained therein while maintaining emulsion storage stability, and therefore can be formulated with a UV absorber that is a highly polar oil (see, for example, paragraph

[0010] of Patent Document 1).The oil-in-water emulsion sunscreen cosmetic composition uses an aqueous dispersion of polyacrylic acid having phosphate groups as the acrylic copolymer (A) having phosphate groups (see, for example, paragraph

[0015] of Patent Document 1).

[0004] In recent years, it has been pointed out that plastic waste is accumulating in the ocean, where it becomes microplastics. There are concerns that the lives of marine organisms are threatened by the ingestion of microplastics, and that human health may be affected if humans ingest marine organisms that have ingested microplastics.

[0005] Therefore, in order to prevent microplastics from ending up in the ocean, it is desirable to refrain from using polymer particles in sunscreen cosmetics.

[0006] Japanese Patent Application Laid-Open No. 2021-100921

[0007] The present invention has been made in view of the above-mentioned prior art, and an object of the present invention is to provide a sunscreen cosmetic containing an oil-in-water emulsion that is excellent overall in usability, storage stability, water resistance, and cleansability, even without using polymer particles as a raw material.

[0008] The present invention provides: (1) an oil-in-water emulsion-containing sunscreen cosmetic, comprising oil-component-containing microparticles containing an ultraviolet scattering agent and an oil component, and an aqueous dispersion medium, the oil-component-containing microparticles being dispersed in the aqueous dispersion medium, wherein the ultraviolet scattering agent is an ultraviolet scattering agent having a hydrophobic surface, the aqueous dispersion medium contains (A) a monovalent linear aliphatic alcohol having 12 to 24 carbon atoms, (B) at least one emulsifier selected from the group consisting of polyglyceryl pentastearate and stearoyl lactylate sodium salt, and (C) stearoyl methyl taurine sodium salt, and the total content of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms and (B) the emulsifier is 1.2 to 5.5 mass %; (2) an oil-in-water emulsion-containing sunscreen cosmetic according to (1) above, further containing a monovalent aliphatic alcohol having 2 to 4 carbon atoms; and (3) The present invention relates to the oil-in-water emulsion-containing sunscreen cosmetic composition according to (1) or (2) above, which further contains inorganic powder.

[0009] According to the present invention, there is provided a sunscreen cosmetic containing an oil-in-water emulsion that is excellent overall in usability, storage stability, water resistance, and cleansing properties, even without using polymer particles as a raw material.

[0010] FIG. 1 is a schematic diagram illustrating a sunscreen cosmetic containing an oil-in-water emulsion of the present invention.

[0011] As described above, the oil-in-water emulsion-containing sunscreen cosmetic of the present invention is an oil-in-water emulsion-containing sunscreen cosmetic comprising oil component-containing microparticles containing an ultraviolet scattering agent and an oil component, and an aqueous dispersion medium, wherein the oil component-containing microparticles are dispersed in the aqueous dispersion medium, wherein the ultraviolet scattering agent used is an ultraviolet scattering agent having a hydrophobic surface, the aqueous dispersion medium comprises (A) a monovalent linear aliphatic alcohol having 12 to 24 carbon atoms, (B) at least one emulsifier selected from the group consisting of polyglyceryl pentastearate and stearoyl lactylate sodium salt, and (C) stearoyl methyl taurine sodium salt, and the total content of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms and (B) the emulsifier is 1.2 to 5.5 mass%.

[0012] The oil-in-water emulsion-containing sunscreen cosmetic of the present invention has the above-mentioned constitution and is therefore excellent overall in usability, storage stability, water resistance and cleansing properties, even though it does not use polymer particles as a raw material.

[0013] The oil-in-water emulsion-containing sunscreen cosmetic of the present invention (hereinafter referred to as "sunscreen cosmetic" for convenience) contains oil component-containing fine particles and an aqueous dispersion medium, as described above.

[0014] (1) Oil-Component-Containing Fine Particles The oil-component-containing fine particles contain an ultraviolet scattering agent and an oil component.

[0015] [Ultraviolet Scattering Agent] The ultraviolet scattering agent is an inorganic material having the property of scattering ultraviolet rays. The inorganic powder described below is a broad concept that includes the inorganic material having the property of scattering ultraviolet rays, whereas the ultraviolet scattering agent refers to the inorganic material among the inorganic powders that has the property of scattering ultraviolet rays.

[0016] In general, UV scattering agents have hydrophilic properties on their surfaces. Examples of UV scattering agents include metal oxide particles and metal particles. Among these, metal oxide particles are preferred from the viewpoint of obtaining a sunscreen cosmetic that is comprehensively excellent in usability, storage stability, water resistance, and cleansability, even without using polymer particles as a raw material.

[0017] Examples of metal oxides constituting the metal oxide particles include titanium oxide, titanium dioxide, zinc oxide, zirconium oxide, cerium oxide, etc., but the present invention is not limited to these examples. These metal oxides may be used alone or in combination of two or more.

[0018] Examples of the shape of the metal oxide particles include spherical, oval spherical, and irregular shapes such as crushed, but the present invention is not limited by the shape of the metal oxide particles.

[0019] The average particle size of the particles of the ultraviolet scattering agent is preferably 5 to 300 nm, more preferably 10 to 250 nm, and even more preferably 10 to 200 nm, from the viewpoint of obtaining a sunscreen cosmetic that is excellent in usability and storage stability and that forms a coating that is excellent in water resistance and cleansability.

[0020] In the present invention, the average particle size of particles means the median size determined from the volume-based particle size distribution measured by laser diffraction.

[0021] In the present invention, an ultraviolet scattering agent having a hydrophobic surface is used, thereby solving the problems that arise when conventional polymer particles are used. The ultraviolet scattering agent having a hydrophobic surface may contain an ultraviolet scattering agent that does not have a hydrophobic surface, as long as the object of the present invention is not impaired.

[0022] An ultraviolet scattering agent having a hydrophobic surface can be obtained, for example, by subjecting the surface of an ultraviolet scattering agent to a hydrophobic treatment. Methods for subjecting the surface of an ultraviolet scattering agent to a hydrophobic treatment include a method of attaching a hydrophobicity-imparting agent to the surface of the ultraviolet scattering agent (physical method) and a method of modifying the surface of the ultraviolet scattering agent so that the surface is hydrophobic (chemical method). Of these methods, the former method of attaching a hydrophobicity-imparting agent to the surface of the ultraviolet scattering agent is preferred because of its simple operation.

[0023] Examples of hydrophobicity-imparting agents used in hydrophobizing the surface of the UV scattering agent include fatty acids that impart hydrophobicity, such as stearic acid, isostearic acid, palmitic acid, lauric acid, myristic acid, oleic acid, and behenic acid; silicones such as dimethylpolysiloxane and methylphenylpolysiloxane; fluororesins such as polytetrafluoroethylene; and silane coupling agents such as methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, and p-styryltrimethoxysilane, but the present invention is not limited to these examples. These hydrophobicity-imparting agents may be used alone or in combination of two or more.

[0024] The amount of hydrophobicity-imparting agent used when subjecting the surface of the ultraviolet scattering agent to hydrophobic treatment is the amount necessary to impart hydrophobicity to the surface of the ultraviolet scattering agent, and cannot be determined in general because it differs depending on the types of ultraviolet scattering agent and hydrophobicity-imparting agent. From the viewpoint of imparting sufficient hydrophobicity to the surface of the ultraviolet scattering agent, it is desirable that preferably 90% or more, more preferably 95% or more of the surface of the ultraviolet scattering agent is covered with the hydrophobicity-imparting agent, and it is even more desirable that the entire surface of the ultraviolet scattering agent is covered with the hydrophobicity-imparting agent.

[0025] The UV scattering agent having a hydrophobic surface is readily available commercially. Examples of the UV scattering agent having a hydrophobic surface that is readily available commercially include titanium oxide particles whose surfaces have been hydrophobized with isostearic acid, manufactured by KOBO Dispatec Co., Ltd., under the trade names MHLP50TIJN and MHLP65ZISJ, but the present invention is not limited to these examples.

[0026] The content of the UV scattering agent having a hydrophobic surface in a sunscreen cosmetic varies depending on the type of UV scattering agent having a hydrophobic surface and cannot be determined in general terms, so it is preferable to adjust it appropriately depending on the type of UV scattering agent having a hydrophobic surface. From the viewpoint of adequately protecting the skin from UV rays, the content is preferably 0.5% by mass or more, more preferably 0.8% by mass or more, and from the viewpoint of improving the usability of the sunscreen cosmetic, the content is preferably 30% by mass or less, more preferably 25% by mass or less.

[0027] The ultraviolet scattering agent is usually present in a dispersed state in the oil component, but an aqueous dispersion medium may be inevitably contained.

[0028] [Oil Component] Examples of the oil component include vegetable oil, animal oil and synthetic oil. These oil components may be used alone or in combination of two or more.

[0029] Examples of vegetable oils include, but are not limited to, squalane, coconut oil, eucalyptus oil, olive oil, palm oil, macadamia nut oil, avocado oil, safflower oil, castor oil, jojoba oil, camellia oil, soybean oil, sunflower oil, etc. These vegetable oils may be used alone or in combination of two or more.

[0030] Examples of synthetic oils include ester oils, hydrocarbon oils, fats and oils, waxes, hardened oils, higher alcohol oils, silicone oils, and fluorine-based oils, but the present invention is not limited to these examples. These synthetic oils may be used alone or in combination of two or more. Among the synthetic oils, ester oils are preferred.

[0031] Examples of ester oils include triethylhexanoin, cetyl octanoate, ethyl oleate, isopropyl myristate, octyldodecyl myristate, myristyl myristate, isocetyl myristate, octyldodecyl myristate, cetyl ethylhexanoate, hexyldecyl ethylhexanoate, isostearyl neopentanoate, isodecyl neopentanoate, octyldodecyl neopentanoate, isopropyl palmitate, cetyl palmitate, ethylhexyl palmitate, methylheptyl laurate, isopropyl isostearate, hexyldecyl isostearate, isopropyl palmitate ... Examples of the ester oil include propylene glycol isostearate, isotridecyl isononanoate, isononyl isononanoate, neopentyl glycol dicaprate, neopentyl glycol diethylhexanoate, trimethylolpropane triethylhexanoate, erythrityl triethylhexanoate, pentaerythrityl tetraethylhexanoate, dipentaerythrityl hexahydroxystearate, pentaerythrityl tetraoctanoate, pentaerythrityl tetraisostearate, and diisopropyl adipate, but the present invention is not limited to these examples. These ester oils may be used alone or in combination of two or more.

[0032] Among the oil components, vegetable oils and synthetic oils are preferred from the viewpoint of improving the storage stability and usability of the sunscreen cosmetic.

[0033] The content of oil components in the sunscreen cosmetic is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of improving the usability of the sunscreen cosmetic, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, from the viewpoint of improving the usability of the sunscreen cosmetic.

[0034] [Oil-containing microparticles] Oil-containing microparticles can be prepared, for example, by mixing components such as an ultraviolet scattering agent, an oil component, an aqueous dispersion medium, and water, as described below. When the components are mixed, the ultraviolet scattering agent and the oil component have excellent affinity, so the ultraviolet scattering agent disperses in the oil component to form oil-containing microparticles. The formed oil-containing microparticles are dispersed in the aqueous dispersion medium.

[0035] The oil component-containing microparticles may be composed only of an ultraviolet scattering agent and an oil component, or may contain other components, such as components used in the aqueous dispersion medium, which may be unavoidably contained, within the scope that does not impede the objectives of the present invention.

[0036] In the oil component-containing microparticles, the mass ratio of the ultraviolet scattering agent to the oil component (ultraviolet scattering agent / oil component) is preferably 3 / 100 to 120 / 100, more preferably 30 / 100 to 90 / 100, from the viewpoints of improving the dispersibility of the ultraviolet scattering agent having a hydrophobic surface, the ultraviolet protection effect of the ultraviolet scattering agent, and the storage stability and usability of the sunscreen cosmetic.

[0037] The oil-containing microparticles are emulsion particles contained in the oil-in-water emulsion contained in the sunscreen cosmetic of the present invention. The particle size of the oil-containing microparticles cannot be determined in general because it varies depending on factors such as the type of UV scattering agent contained in the oil-containing microparticles, but from the viewpoints of dispersion stability and film smoothness, it is usually about 1 to 100 μm.

[0038] (2) Aqueous Dispersion Medium In the present invention, an aqueous dispersion medium containing (A) a monovalent linear aliphatic alcohol having 12 to 24 carbon atoms, (B) at least one emulsifier selected from the group consisting of polyglyceryl pentastearate and sodium stearoyl lactylate, and (C) sodium stearoyl methyl taurate is used. This makes it possible to use an ultraviolet scattering agent having a hydrophobic surface, thereby improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of the dried film made of the sunscreen cosmetic and the storage stability of the sunscreen cosmetic.

[0039] [(A) Monovalent Linear Aliphatic Alcohol Having 12 to 24 Carbon Atoms] In the present invention, a monovalent linear aliphatic alcohol having 12 to 24 carbon atoms is used, which can improve the adhesion of the sunscreen cosmetic to the skin.

[0040] Examples of monohydric linear aliphatic alcohols having 12 to 24 carbon atoms include cetyl alcohol (number of carbon atoms: 16), 1-heptadecanol (number of carbon atoms: 17), stearyl alcohol (number of carbon atoms: 18), nonadecyl alcohol (number of carbon atoms: 19), arachidyl alcohol (number of carbon atoms: 20), heneicosanol (number of carbon atoms: 21), and behenyl alcohol (number of carbon atoms: 22), but the present invention is not limited to these examples. These linear aliphatic alcohols may be used alone or in combination of two or more. Among the monohydric linear aliphatic alcohols having 12 to 24 carbon atoms, from the viewpoints of improving the adhesion of the sunscreen cosmetic on the skin and improving the water resistance of the dried film formed from the sunscreen cosmetic, preferred are monohydric linear aliphatic alcohols having 16 to 22 carbon atoms, and at least one selected from the group consisting of cetyl alcohol, stearyl alcohol, arachidyl alcohol, and behenyl alcohol is more preferred.

[0041] The lower limit of the content of the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms in the sunscreen cosmetic is preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and even more preferably 0.7% by mass or more, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dried film made from the sunscreen cosmetic. The upper limit of the content of the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms in the sunscreen cosmetic is preferably 2.5% by mass or less, more preferably 2.0% by mass or less, and even more preferably 1.5% by mass or less, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dried film made from the sunscreen cosmetic.

[0042] Furthermore, the content of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms in the mixture of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms, (B) the emulsifier, and (C) stearoyl methyl taurine sodium salt is preferably 30% by mass or more, more preferably 35% by mass or more, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, and is preferably 50% by mass or less, more preferably 45% by mass or less, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, as described above.

[0043] [Emulsifier (B)] In the present invention, at least one emulsifier (B) selected from the group consisting of polyglyceryl pentastearate and sodium stearoyl lactylate (hereinafter referred to as "emulsifier (B)") is used, which improves the adhesion of the sunscreen cosmetic to the skin and also improves the water resistance of the dried film made of the sunscreen cosmetic.

[0044] Polyglyceryl pentastearate is a lipophilic emulsifier, also known as polyglyceryl-10 pentastearate or decaglyceryl pentastearate.

[0045] Polyglyceryl pentastearate is commercially available. Examples of commercially available polyglyceryl pentastearate include NIKKOL Decaglyn 5-SV (HLB value: 3.5) manufactured by Nikko Chemicals Co., Ltd. and SUNSOLFT Q-185S-C (HLB value: 7.0) manufactured by Taiyo Kagaku Co., Ltd., but the present invention is not limited to these examples. There are various methods for determining the HLB (hydrophilic-lipophilic balance) value, but the Griffin method is used in the present invention. The HLB value of a nonionic surfactant according to the Griffin method can be calculated based on the formula: [HLB of nonionic surfactant] = 20 × [(molecular weight of the hydrophilic portion of the nonionic surfactant) / (molecular weight of the nonionic surfactant)].

[0046] The content of polyglyceryl pentastearate in the mixture of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms and (B) the emulsifier is preferably 25% by mass or more, more preferably 30% by mass or more, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, and is preferably 50% by mass or less, more preferably 45% by mass or less, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, as described above.

[0047] Sodium stearoyl lactylate is an ester of stearic acid and the sodium salt of the dimer of lactic acid, and is an anionic emulsifier. Sodium stearoyl lactylate is also known as sodium stearoyl lactylate. The molecular weight of sodium stearoyl lactylate is about 450.

[0048] The content of stearoyl lactylate sodium salt in the mixture of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms and (B) the emulsifier is preferably 3% by mass or more, more preferably 5% by mass or more, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, and is preferably 25% by mass or less, more preferably 20% by mass or less, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, as described above.

[0049] The emulsifier (B) may be composed of only at least one selected from the group consisting of polyglyceryl pentastearate and sodium stearoyl lactylate, or may contain other emulsifiers within a range that does not impair the object of the present invention.

[0050] In the present invention, from the viewpoint of obtaining a sunscreen cosmetic that exhibits excellent usability and storage stability even without using polymer particles as a raw material and that forms a film that is excellent in water resistance and cleansability, it is preferable to use polyglyceryl pentastearate and sodium stearoyl lactylate in combination as an emulsifier. In this case, from the viewpoint of obtaining a sunscreen cosmetic that exhibits excellent usability and storage stability even without using polymer particles as a raw material and that forms a film that is excellent in water resistance and cleansability, the mass ratio of polyglyceryl pentastearate to sodium stearoyl lactylate (polyglyceryl pentastearate / sodium stearoyl lactylate) is preferably 2 / 1 to 5 / 1, more preferably 2.5 / 1 to 4.5 / 1, and even more preferably 3 / 1 to 4 / 1.

[0051] The lower limit of the content of the emulsifier in the sunscreen cosmetic is preferably 0.6% by mass or more, more preferably 0.7% by mass or more, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic. The upper limit of the content of the emulsifier in the sunscreen cosmetic is preferably 3.0% by mass or less, more preferably 2.8% by mass or less, and even more preferably 2.6% by mass or less, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic.

[0052] Furthermore, the content of the emulsifier (B) in the mixture of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms, (B) the emulsifier, and (C) the sodium salt of stearoyl methyl taurine is preferably 30% by mass or more, more preferably 35% by mass or more, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic; and, similarly to the above, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, it is preferably 55% by mass or less, more preferably 50% by mass or less.

[0053] [(A) Monovalent Linear Aliphatic Alcohol Having 12 to 24 Carbon Atoms and (B) Emulsifier] In the present invention, (A) a monovalent linear aliphatic alcohol having 12 to 24 carbon atoms and (B) an emulsifier are used in combination, which improves the adhesion of the sunscreen cosmetic to the skin and also improves the water resistance of a dried film made of the sunscreen cosmetic.

[0054] The mass ratio of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms to (B) the emulsifier [(A) monovalent linear aliphatic alcohol having 12 to 24 carbon atoms / (B) emulsifier] is preferably 40 / 60 or more, more preferably 45 / 55 or more, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, and is preferably 60 / 40 or less, more preferably 55 / 45 or less, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, as described above.

[0055] The total content of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms and (B) the emulsifier in the sunscreen cosmetic is at least 1.2% by mass, preferably at least 1.5% by mass, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, and is at most 5.5% by mass, preferably at most 5.0% by mass, from the viewpoints of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dry film made of the sunscreen cosmetic, as described above.

[0056] [(C) Stearoylmethyl taurine sodium salt] In the present invention, (C) stearoylmethyl taurine sodium salt is used, which inhibits the oil component-containing microparticles from aggregating over time, thereby improving the storage stability of the sunscreen cosmetic.

[0057] Sodium stearoyl methyl taurine is an anionic surfactant classified as an acyl methyl taurine salt of a taurine-based surfactant. Sodium stearoyl methyl taurine is a sodium salt of a condensation product of stearic acid and N-methyl taurine, and has a molecular weight of approximately 428.

[0058] The content of stearoyl methyl taurine sodium salt in the sunscreen cosmetic is preferably 0.1% by mass or more from the viewpoint of inhibiting aggregation of oil component-containing microparticles over time and improving the storage stability of the sunscreen cosmetic, and is preferably 1% by mass or less from the viewpoint of improving the fixation of the sunscreen cosmetic on the skin and improving the water resistance of a dried film made of the sunscreen cosmetic.

[0059] (3) Other Components In the present invention, the following components can be used as other components in addition to (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms, (B) the emulsifier, and (C) the sodium salt of stearoyl methyl taurine.

[0060] [Monohydric aliphatic alcohol having 2 to 4 carbon atoms] By including an alcohol in a sunscreen cosmetic, the spreadability of the sunscreen cosmetic when applied to the skin is improved, thereby improving the usability of the sunscreen cosmetic. Therefore, it is preferable that the sunscreen cosmetic include a monohydric aliphatic alcohol having 2 to 4 carbon atoms.

[0061] The use of a monohydric aliphatic alcohol having 2 to 4 carbon atoms can accelerate the drying of the sunscreen cosmetic when applied to the skin, suppress the stickiness of the formed film, and improve the adhesion of the film to the skin. Examples of monohydric aliphatic alcohols having 2 to 4 carbon atoms include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and tert-butanol. These aliphatic alcohols can be used alone or in combination of two or more. Of these aliphatic alcohols, ethanol is preferred from the viewpoints of accelerating the drying of the sunscreen cosmetic when applied to the skin, suppressing the stickiness of the formed film, and improving the adhesion of the film to the skin.

[0062] The content of the monohydric aliphatic alcohol having 2 to 4 carbon atoms in the sunscreen cosmetic is preferably 1 to 15% by mass, from the viewpoints of accelerating the drying of the sunscreen cosmetic when applied to the skin, suppressing the stickiness of the formed film, and improving the adhesion of the film to the skin.

[0063] [Inorganic Powder] When an inorganic powder is contained in a sunscreen cosmetic, the spreadability of the sunscreen cosmetic is improved when the sunscreen cosmetic is applied to the skin, thereby improving the usability of the sunscreen cosmetic. Therefore, it is preferable that the sunscreen cosmetic contains an inorganic powder.

[0064] Examples of the shape of the inorganic powder include particles, scales, and layers. Examples of inorganic powder include mica particles, silica particles, and hydroxyapatite particles, but the present invention is not limited to these examples. These inorganic powders may be used alone or in combination of two or more types. Mica particles, silica particles, and hydroxyapatite particles are all suitable for use in sunscreen cosmetics.

[0065] Among inorganic powders, from the viewpoint of improving the usability of sunscreen cosmetics, particulate inorganic powders and scaly or layered inorganic powders with a high aspect ratio are preferred, particulate inorganic powders with an average particle size of 10 to 35 μm and scaly inorganic powders with an aspect ratio of 70 to 80 are more preferred, mica particles with an aspect ratio of 70 to 80, silica particles with an aspect ratio of 70 to 80 and hydroxyapatite particles with an aspect ratio of 70 to 80 are even more preferred, and mica particles with an aspect ratio of 70 to 80 are even more preferred.

[0066] Mica particles, silica particles, and hydroxyapatite particles are all readily available commercially. For example, commercially available mica particles include those manufactured by Yamaguchi Mica Co., Ltd., product number AB-25S (average particle size: 24 μm, aspect ratio: 70), but the present invention is not limited to these examples.

[0067] The content of inorganic powder in the sunscreen cosmetic is preferably 0.1 to 2% by mass, from the viewpoints of improving the spreadability of the sunscreen cosmetic when applied to the skin, thereby improving usability, and improving the water resistance of the dried film of the sunscreen cosmetic.

[0068] [Water-soluble components] In addition to the above-mentioned components, sunscreen cosmetics can also contain water-soluble components commonly used in cosmetics. Examples of water-soluble components include propylene glycol, dipropylene glycol, butanediol, polyethylene glycol, glycerin, diglycerin, polyglycerin, glyceryl glucoxide, phenoxyethanol, xanthan gum, guar gum, carrageenan, mucopolysaccharides, sodium chondroitin sulfate, hyaluronic acid, collagen, elastin, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, carboxyvinyl polymer, polyvinyl alcohol, polyvinylpyrrolidone, and sodium polyacrylate, but the present invention is not limited to these examples. These water-soluble components may be used alone or in combination of two or more.

[0069] The content of the water-soluble components in the sunscreen cosmetic is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, from the viewpoint of achieving the effects based on the water-soluble components and improving the usability of the sunscreen cosmetic, and is preferably 35% by mass or less, more preferably 20% by mass or less, from the viewpoint of achieving the effects based on the water-soluble components and improving the usability of the sunscreen cosmetic, as described above.

[0070] [Additives] The sunscreen cosmetic may contain additives that are generally used in oil-in-water emulsion cosmetics, within the scope that does not impair the object of the present invention.

[0071] Examples of additives include ultraviolet absorbers, chelating agents such as sodium ethylenediaminetetraacetic acid, antioxidants, vitamins, skin-beautifying ingredients, colorants, thickeners, preservatives, antioxidants, texture improvers, moisturizers, cooling agents, anti-inflammatory agents, fragrances, pH adjusters, film-forming agents, and astringents, but the present invention is not limited to these examples.

[0072] [Water] The balance of the sunscreen cosmetic ingredients is water. Water can be used as an aqueous dispersion medium. Examples of water include pure water, purified water, ion-exchanged water, and tap water, but the present invention is not limited to these examples.

[0073] The amount of water is adjusted so that each component other than water is contained in the sunscreen cosmetic at a predetermined content. The amount of water is not particularly limited, but from the viewpoint of obtaining a sunscreen cosmetic that is comprehensively excellent in usability, storage stability, water resistance, and cleansability, it is usually preferably 20 to 100 parts by mass per 100 parts by mass of the total amount of components other than water.

[0074] (4) Sunscreen Cosmetics Sunscreen cosmetics can be prepared, for example, by gradually adding ingredients other than water to water while stirring them at room temperature or, if necessary, under heating. Alternatively, sunscreen cosmetics can be prepared, for example, by mixing the ingredients to form a uniform composition, dispersing them in water, and then molding the resulting dispersion into a container of a predetermined shape. When preparing the dispersion, the ingredients may be mixed while being heated to ensure uniform dispersion. The sunscreen cosmetics of the present invention can be prepared in the manner described above.

[0075] The sunscreen cosmetic of the present invention comprises an aqueous dispersion medium and oil-component-containing microparticles that contain an ultraviolet scattering agent and an oil component, the oil-component-containing microparticles being dispersed in the aqueous dispersion medium, the ultraviolet scattering agent being an ultraviolet scattering agent having a hydrophobic surface, the aqueous dispersion medium containing (A) a monovalent linear aliphatic alcohol having 12 to 24 carbon atoms, (B) an emulsifier, and (C) stearoyl methyl taurine sodium salt, and the total content of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms and (B) the emulsifier is in a specific ratio, so that the sunscreen cosmetic has excellent usability and storage stability even without using polymer particles as a raw material, and forms a coating that is excellent in water resistance and cleansability.

[0076] Furthermore, the sunscreen cosmetic of the present invention can contain a dispersed ultraviolet scattering agent even in a composition with a low viscosity, such as an emulsion, and has a smooth texture that does not creak when applied to the skin, making it easy to use.The dried film of the sunscreen cosmetic is water-resistant and can be easily washed off with soap or the like.

[0077] The sunscreen cosmetic of the present invention exhibits such excellent effects based on the aforementioned constituent features. Although this is merely speculation, it is thought that the sunscreen cosmetic of the present invention will form the structure shown in Figure 1. Figure 1 is a schematic explanatory diagram of the sunscreen cosmetic of the present invention, created speculatively to conceptually explain the composition of the sunscreen cosmetic of the present invention.

[0078] As shown in Figure 1, the sunscreen cosmetic of the present invention contains oil component-containing microparticles 1 surrounded by a dashed line and an aqueous dispersion medium 2. The oil component-containing microparticles 1 contain an ultraviolet scattering agent (hereinafter simply referred to as "UV scattering agent") 3 having a hydrophobic surface and an oil component 4. Because the UV scattering agent 3 has excellent affinity with the oil component 4, it is dispersed in the oil component 4 and, together with the oil component 4, forms the oil component-containing microparticles 1 surrounded by the dashed line. Note that in Figure 1, the shape of the oil component-containing microparticles 1 is depicted schematically and does not necessarily represent the actual shape of the oil component-containing microparticles 1.

[0079] The aqueous dispersion medium 2 constitutes the area other than the area associated with the oil-component-containing microparticles 1. The aqueous dispersion medium 2 contains (A) a monovalent linear aliphatic alcohol having 12 to 24 carbon atoms (hereinafter simply referred to as "linear aliphatic alcohol") 5, (B) an emulsifier 6, and (C) a stearoyl methyl taurine sodium salt 7.

[0080] In the aqueous dispersion medium 2, it is presumed that a lamellar gel phase 8 is formed by the linear aliphatic alcohol 5, the emulsifier 6, and the sodium salt of stearoyl methyl taurine 7.

[0081] The membrane 9 is composed of membranes 9a and 9b. The membranes 9a and 9b are each formed of a linear aliphatic alcohol 5, an emulsifier 6, and stearoyl methyl taurine sodium salt 7. The membranes 9a and 9b are positioned opposite each other, and the hydrophobic groups of the membranes 9a and 9b are oriented so as to face each other.

[0082] The lamellar gel phase 8 has a membrane 9 and an aqueous phase 10, and the membrane 9 and the aqueous phase 10 are formed with a gap therebetween. When the lamellar gel phase 8 has a plurality of membranes 9, the aqueous phase 10 exists between each membrane 9.

[0083] Oil component-containing particles 1 indicated by dashed lines are dispersed in oil component 4 surrounded by membranes 9a and 9b.

[0084] The gel matrix 11 enclosed by the dashed line is formed by the lamellar gel phase 8, the oil component 4, and the oil component-containing microparticles 1 dispersed in the oil component 4. The gel matrix 11 is dispersed in the aqueous dispersion medium 2.

[0085] According to the sunscreen cosmetic of the present invention, a gel matrix 11 is formed and dispersed in the aqueous dispersion medium 2, and therefore the sunscreen cosmetic of the present invention has an excellent feel on the skin when used, and since the oil component-containing microparticles 1 are dispersed in the aqueous dispersion medium 2 and this dispersed state is stably maintained, the sunscreen cosmetic of the present invention also has excellent storage stability, and it is considered that the dried film formed by applying the sunscreen cosmetic of the present invention to the skin and drying it has excellent water resistance because the gel matrix 11 is formed by the oil component-containing microparticles 1 surrounded by the lamellar gel phase 8 and the membranes 9a and 9b that constitute the lamellar gel phase 8.

[0086] Furthermore, although it is generally believed that a dry film having excellent water resistance also has poor washability, the dry film formed using the sunscreen cosmetic of the present invention is surprisingly easy to wash off with soap or the like, demonstrating that the sunscreen cosmetic of the present invention also has excellent washability.

[0087] Therefore, since the sunscreen cosmetic of the present invention has the excellent properties described above, it can be suitably used as a cosmetic for human skin in the form of, for example, a cream, gel, or emulsion.

[0088] Next, the sunscreen cosmetic of the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[0089] Examples 1 to 31 and Comparative Examples 1 to 3 The components shown in the following tables (units of the amount of each component shown in the tables: mass %) were mixed under stirring at room temperature (about 23°C) to obtain a uniform composition, thereby obtaining sunscreen cosmetics.

[0090] In each example and comparative example, titanium oxide particles (secondary particle diameter: 100 to 150 nm) that had been surface-treated with isostearic acid and had a hydrophobic surface were used as the ultraviolet scattering agent A, and zinc oxide particles (secondary particle diameter: 140 to 200 nm) that had been surface-treated with isostearic acid and had a hydrophobic surface were used as the ultraviolet scattering agent B. The particle diameters of the particles were values ​​measured by laser diffraction.

[0091] Next, the sunscreen cosmetic compositions obtained above were examined for usability, water resistance, cleansing properties and storage stability according to the following methods, and the results are shown in the tables.

[0092] [Usability] Five female panelists examined the sensation of use when applying a sunscreen cosmetic taken on the fingers of one hand to the cheeks of the face, and evaluated the usability based on the following evaluation criteria.

[0093] (Evaluation criteria for usability) ◎: Five panelists rated it as having a smooth texture without any creaking ○: Four panelists rated it as having a smooth texture without any creaking △: Three panelists rated it as having a smooth texture without any creaking ×: Two or less panelists rated it as having a smooth texture without any creaking (fail)

[0094] [Water resistance] Using a measurement kit for SPF / PA value evaluation system (manufactured by Jusco Engineering Co., Ltd., product name: Sunscreen SPF / PA), a sunscreen cosmetic was applied to a cell (SPF cell) having a groove about 20 μm deep, with a film thickness of 2 μL / cm. 2 After uniformly applying the coating so that the thickness was 100 μm, the resulting coating was dried in air at room temperature (about 25° C.) for 20 minutes.

[0095] The cell on which the coating was formed as described above was placed in the integrating sphere unit of an ultraviolet-visible spectrophotometer (manufactured by Jusco Engineering Co., Ltd., product number: V-770), and the optical path length was set to 40 μm. After that, an SPF-corresponding transmittance (% T) and a PA-corresponding transmittance (% T), which are the transmittances for mid-wavelength ultraviolet radiation UVB (wavelength 290 to 320 nm) and long-wavelength ultraviolet radiation UVA (wavelength 320 to 400 nm), were calculated from the transmission spectrum of wavelengths of 290 to 400 nm using an SPF / PA value calculation program.

[0096] The cell was immersed in water at a temperature of 30° C. for 20 minutes, then removed from the water and dried in air at room temperature (approximately 25° C.) for 20 minutes. The cell was then placed in the integrating sphere unit of an ultraviolet-visible spectrophotometer (manufactured by Jusco Engineering Co., Ltd., product number: V-770) and the optical path length was set to 40 μm. Then, an SPF-corresponding transmittance (% T) and a PA-corresponding transmittance (% T), which are the transmittances for mid-wavelength ultraviolet radiation UVB (wavelengths of 290 to 320 nm) and long-wavelength ultraviolet radiation UVA (wavelengths of 320 to 400 nm), were calculated from the transmission spectrum in the wavelength range of 290 to 400 nm using an SPF / PA value calculation program.

[0097] The differences in transmittance for mid-wavelength ultraviolet rays UVB and long-wavelength ultraviolet rays UVA before immersion in water (before immersion) and after immersion in water (after immersion) (ΔSPF (%T) and ΔPA (%T)) were calculated based on the formulas: [ΔSPF (%T)] = [SPF-corresponding transmittance after immersion (%T) - SPF-corresponding transmittance before immersion (%T)] and [ΔPA (%T)] = [PA-corresponding transmittance after immersion (%T) - PA-corresponding transmittance before immersion (%T)], respectively.

[0098] For comparison, a sunscreen cosmetic (manufactured by Kao Corporation, trade name: Curel UV Cut UV Essence SPF30 / PA++) was used to determine the transmittance differences ΔSPF (% T) and ΔPA (% T) in the same manner as above, and the determined SPF (% T) and ΔPA (% T) were used as reference values. The smaller the transmittance differences ΔSPF (% T) and ΔPA (% T), the more excellent the water resistance.

[0099] (Evaluation criteria for water resistance) ◎: Both ΔSPF (% T) and ΔPA (% T) are less than half of the standard value. ○: Either ΔSPF (% T) or ΔPA (% T) is less than half of the standard value, and the other is half or more of the standard value and less than the standard value. △: Both ΔSPF (% T) and ΔPA (% T) are half or more of the standard value and less than the standard value. ×: Both ΔSPF (% T) and ΔPA (% T) are equal to or greater than the standard value (failure)

[0100] [Cleanability] 0.1 g of the sunscreen cosmetic was applied per spot to a black Bioskin plate (manufactured by Viewlux Co., Ltd.) and allowed to dry in air at room temperature (approximately 25°C) for 1 hour. The dried film formed was then observed and photographed under an optical microscope (magnification: 100x).

[0101] Next, an amino acid-based facial cleanser (manufactured by Daiichi Sankyo Healthcare Co., Ltd., product name: Minon Gentle Wash Whip) was lathered onto the formed dry film, and the resulting lather was used to gently stroke the dry film to clean it, and the facial cleanser was then rinsed off with lukewarm water at approximately 37°C.

[0102] In addition, since the amino acid-based facial cleanser is generally known as a facial cleanser with mild cleansing power, the amino acid-based facial cleanser was used to evaluate whether a facial cleanser with mild cleansing power can easily remove cosmetics adhering to the skin.

[0103] Subsequently, the sunscreen cosmetic on the Bioskin Plate was dried with a hot air dryer, and the dried film formed was observed and photographed under an optical microscope (magnification: 100 times).

[0104] By comparing photographs of the coating before and after washing, it was determined whether the cosmetics applied to the Bioskin Plate (artificial skin) could be easily washed off, and the cleansing ability was evaluated based on the following evaluation criteria.

[0105] (Criteria for evaluation of cleaning performance) ◎: Sunscreen cosmetics attached to the Bio Skin plate were completely removed. ○: Sunscreen cosmetics attached to the Bio Skin plate were almost completely removed. △: Sunscreen cosmetics attached to the Bio Skin plate were slightly remaining. ×: Sunscreen cosmetics attached to the Bio Skin plate were clearly remaining (failed).

[0106] [Storage Stability] Approximately 30 g of a sunscreen cosmetic was filled into a sealed container, and the sealed container was placed in a thermostatic bath at room temperature or 50°C. After storage for 4 weeks, the sealed container was removed from the thermostatic bath, and the surface condition of the sunscreen cosmetic in the sealed container was visually observed, and the storage stability was evaluated based on the following evaluation criteria.

[0107] (Evaluation criteria for storage stability) ⊚: No separation of the oil layer and the water layer is observed in the sunscreen cosmetic even after 4 weeks of storage, and the surface condition is very similar to that immediately after preparation. ◯: No separation of the oil layer and the water layer is observed in the sunscreen cosmetic after 4 weeks of storage, but the surface condition is different from that immediately after preparation. △: Some separation of the oil layer and the water layer is observed in the sunscreen cosmetic after 4 weeks of storage. ×: Significant separation of the oil layer and the water layer is observed in the sunscreen cosmetic after 4 weeks of storage (failure).

[0108]

[0109]

[0110]

[0111]

[0112]

[0113] The results shown in Tables 1 to 5 demonstrate that the sunscreen cosmetics obtained in each Example were excellent overall in terms of usability, storage stability, water resistance, and cleansability, even though they did not use polymer particles as a raw material. Among these, sunscreen cosmetics that were rated ○ or ⊚ for usability, storage stability, water resistance, and cleansability were found to be even more excellent overall in terms of usability, storage stability, water resistance, and cleansability.

[0114] 1. Oil component-containing microparticles 2. Aqueous dispersion medium 3. UV scattering agent 4. Oil component 5. Linear aliphatic alcohol 6. Emulsifier 7. Stearoyl methyl taurine sodium salt

Claims

1. A sunscreen cosmetic containing an oil-in-water emulsion, comprising oil-component-containing microparticles containing an ultraviolet scattering agent and an oil component, and an aqueous dispersion medium, wherein the oil-component-containing microparticles are dispersed in the aqueous dispersion medium, wherein the ultraviolet scattering agent is an ultraviolet scattering agent having a hydrophobic surface, the aqueous dispersion medium contains (A) a monovalent linear aliphatic alcohol having 12 to 24 carbon atoms, (B) at least one emulsifier selected from the group consisting of polyglyceryl pentastearate and sodium stearoyl lactylate, and (C) sodium stearoyl methyl taurine, and the total content of (A) the monovalent linear aliphatic alcohol having 12 to 24 carbon atoms and (B) the emulsifier is 1.2 to 5.5% by mass.

2. The sunscreen cosmetic composition containing the oil-in-water emulsion according to claim 1, further comprising a monohydric aliphatic alcohol having 2 to 4 carbon atoms.

3. A sunscreen cosmetic containing an oil-in-water emulsion according to claim 1 or 2, further comprising inorganic powder.

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