Pickering emulsified sunscreen agent

Abstract

To provide a sunscreen agent which has sufficiently high ultraviolet protection effect, can achieve emulsion stability, comfortable use feeling and water resistance at a higher level with good balance, and furthermore can achieve a lower cost.SOLUTION: Provided is an oil-in-water type Pickering emulsified sunscreen agent in which ultraviolet ray absorber is Pickering emulsified into an oil-in-water type by using smectite as an emulsifier, a content of the ultraviolet ray absorber is 5.0 mass% or more, a value of a ratio of the content of the ultraviolet ray absorber to a content of the smectite is 15 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to Pickering emulsion sunscreens. [Background technology]

[0002] In order to protect the skin from exposure to ultraviolet rays and to suppress photoaging, which causes melanin production and blemishes and wrinkles, sunscreen cosmetics (sunscreens) containing ultraviolet protection agents (ultraviolet absorbing agents, ultraviolet scattering agents) have been developed and are widely distributed on the market. Since such sunscreens are used in various situations in daily life, they are required to have both ultraviolet protection effects and functionality such as a fresh and refreshing feel on the skin (usage) and water resistance (durability). Sunscreens are generally in the form of water-in-oil emulsions when water resistance is important, and in the form of oil-in-water emulsions when a fresh and refreshing feel is important.

[0003] On the other hand, development is also underway for water-in-oil sunscreens that have a fresh and refreshing feel when used, and for oil-in-water sunscreens that have excellent water resistance. For example, Patent Document 1 discloses a sunscreen cosmetic that contains a UV protection agent, a volatile oil, cetyl dimethicone copolyol, an (acrylates / stearyl acrylate / dimethicone methacrylate) polymer, and an organically modified clay mineral, and describes that the cosmetic has excellent water resistance and emulsion stability, is also excellent in feel when used (not sticky or oily), and is unlikely to cast white even when exposed to sweat or water. In the cosmetic, the cetyl dimethicone copolyol, which is a surfactant, acts as an emulsifier, and the organically modified clay mineral functions as an emulsifier. Patent Document 2 discloses an oil-in-water Pickering emulsion that contains a light-shielding powder and is stabilized by an emulsifying powder whose surface is charged. In the Pickering emulsion, silica powder (partially hydrophobized silica) is exemplified as the emulsified powder, and it is described that the resulting Pickering emulsion has excellent resistance to aqueous solutions containing ions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-88346 A [Patent Document 2] JP 2020-50627 A Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, water-in-oil and oil-in-water sunscreens have been developed that maintain UV protection while providing a fresh, refreshing feel and water resistance (durability). However, the inventors have found that when emulsions are formed using surfactants as emulsifiers as described in Patent Document 1, there are limitations to the improvement of UV protection and functionality (such as not being able to incorporate a high amount of UV protection agent and limitations to improving water resistance). In addition, when a Pickering emulsion is formed using silica powder as in Patent Document 2, the silica powder must be subjected to surface treatment or pretreatment to provide stability, which increases costs.

[0006] The present invention aims to provide a sunscreen agent which has a sufficiently high ultraviolet protection effect, and which can achieve a high level of emulsion stability, comfortable feel in use, and water resistance in a well-balanced manner, while also realizing cost reduction. [Means for solving the problem]

[0007] As a result of intensive research, the present inventors have found that an oil-in-water sunscreen obtained by using smectite, a layered silicate mineral, as an emulsified powder (emulsifier) ​​and an ultraviolet absorber as an emulsified dispersion material, and by enveloping oil droplets of the ultraviolet absorber with the smectite to effect Pickering emulsification, exhibits high emulsion stability even without pretreatment of the emulsified powder, and also has excellent ultraviolet protection effect, water resistance, and a comfortable feel on the skin. The present invention was completed through further research based on these findings.

[0008] The above-mentioned object of the present invention has been achieved by the following means. [1] The oil-in-water Pickering emulsion sunscreen comprises an ultraviolet absorbing agent that is Pickering emulsified into an oil-in-water type using smectite as an emulsifier, the content of the ultraviolet absorbing agent being 5.0 mass% or more, and the ratio of the content of the ultraviolet absorbing agent to the content of the smectite being 15 or less. [2] The sunscreen according to [1] above, wherein the ratio of the content of the ultraviolet absorber to the content of the smectite is 3 or more. [3] The sunscreen according to [1] or [2] above, wherein the smectite is a synthetic smectite. [4] The sunscreen according to any one of [1] to [3] above, wherein the sunscreen contains an ultraviolet scattering agent. [5] A dry powder obtained by drying the sunscreen agent according to any one of [1] to [4] above. Effect of the Invention

[0009] The oil-in-water Pickering emulsion sunscreen of the present invention can reduce production costs, has a sufficiently high ultraviolet protection effect, and achieves a balanced, high level of emulsion stability, water resistance, and comfortable skin feel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, preferred embodiments of the present invention will be described in detail, but the present invention is not limited to these embodiments except as specified in the present invention.

[0011] [Sunscreen] A preferred embodiment of the oil-in-water Pickering emulsion sunscreen agent according to the present invention (hereinafter also simply referred to as the "agent of the present invention") will be described. The agent of the present invention is an oil-in-water Pickering emulsion sunscreen agent containing at least smectite and an ultraviolet absorber. In the agent of the present invention, the ultraviolet absorber constitutes the oil phase and also constitutes the dispersed phase.

[0012] In a preferred embodiment of the agent of the present invention, the smectite particles act as an emulsifier, covering oil droplets containing an ultraviolet absorbing agent to form a structure in which the oil droplets are emulsified and dispersed in water (emulsification can be achieved by disposing the smectite particles at the interface between the water phase and the oil phase). The agent of the present invention may contain an ultraviolet scattering agent such as titanium oxide or zinc oxide. In addition, these ultraviolet scattering agents may or may not be hydrophobized. Usually, the ultraviolet scattering agent is present in a scattered state in the oil droplets.

[0013] The agent of the present invention exhibits a high ultraviolet protection effect while achieving a well-balanced high level of emulsion stability, skin feel (usage sensation) and water resistance. The ultraviolet protection effect is generally evaluated using SPF (Sun Protection Factor) or PA (Protection grade of UVA) as an index. In particular, the agent of the present invention exhibits a higher SPF value than a sunscreen agent having the same amount of ultraviolet absorber as the agent of the present invention (a sunscreen agent not emulsified with smectite through Pickering) due to the synergistic effect of smectite and ultraviolet absorber. The higher the SPF value, the higher the ultraviolet shielding effect. Specifically, the SPF value (initial SPF value) of the agent of the present invention can be 30 or more, 40 or more, or 50 or more. The SPF value can be calculated by measuring the transmittance of the absorption spectrum (wavelength=nm) using an SPF analyzer (UV-2000S manufactured by Labsphere), for example, by the method described in the Examples.

[0014] The characteristic features of the agent of the present invention will be described below.

[0015] <Smectite> In the agent of the present invention, the smectite is used as an emulsified powder (emulsifier) ​​for Pickering emulsification. By using smectite as the emulsified powder, the thixotropy due to the plate-like crystal structure of the smectite is expressed, and high emulsion stability can be imparted to the resulting Pickering emulsion. In addition, the emulsion has high thermal stability, and furthermore, the emulsified powder after drying can be redispersed again in an aqueous medium. In addition, smectite does not require surface treatment for use as an emulsified powder or pretreatment for imparting stability, and the manufacturing cost of the agent of the present invention can be reduced. In the agent of the present invention, the type of smectite is not particularly limited and can be appropriately selected according to the purpose. In addition, natural smectite or synthetic smectite can be used, and it is preferable to use synthetic smectite from the viewpoint of low impurity content. Synthetic smectite can be produced by a conventional method. In addition, it may be unmodified or modified. The smectite is preferably one or more selected from montmorillonite, beidellite, nontronite, saponite, hectorite, sauconite, and stevensite, and more preferably one or more selected from montmorillonite, beidellite, saponite, hectorite, and stevensite. Commercially available smectite products include, for example, Kunipia-F (purified montmorillonite), Sumecton-SA (synthetic saponite), Sumecton-ST (synthetic stevensite), and Sumecton-SWN (synthetic hectorite) (all manufactured by Kunimine Kogyo Co., Ltd.).

[0016] The smectite generally has a charge density of 0.4 to 1.2, and the aspect ratio (circle equivalent diameter in a planar direction / thickness) of the smectite particles in AFM (Atomic Force Microscope) observation is preferably about 20 to 1000, more preferably 20 to 700, and even more preferably 25 to 400. When the smectite has such a charge density range and aspect ratio range, the layers are more easily peeled off in water, and the smectite can act more effectively as an emulsified powder (emulsifier). In addition, since the layer surface of the smectite is hydrophobic and the smectite is a plate-like crystal, it is easy to wrap oily components such as oil droplets, and has excellent emulsification performance. Furthermore, by having such a large aspect ratio, the transparency and adhesion of the agent of the present invention when applied can be further improved. The approximate aspect ratios of the above commercially available smectites are as shown in Table 1 below.

[0017] [Table 1]

[0018] The interlayer cation species of the smectite is not particularly limited, but is preferably a sodium ion or a lithium ion, and more preferably a sodium ion. By using the sodium ion or the lithium ion as the interlayer cation, for example, when the smectite is dispersed in an aqueous medium, it is possible to impart excellent swelling properties and dispersion stability. The cation exchange capacity (CEC) of the smectite is preferably 15 meq (milliequivalent) / 100 g or more, more preferably 20 meq / 100 g or more, and even more preferably 30 meq / 100 g or more. The cation exchange capacity of the smectite usable in the present invention is usually 250 meq / 100 g or less, and preferably 120 meq / 100 g or less.

[0019] The particle size of the smectite is not particularly limited and can be appropriately set. For example, the particle size (primary particle size) of the smectite can be 20 to 500 nm, 30 to 400 nm, 40 to 380 nm, or 50 to 370 nm. In the present invention, the "particle size" of the smectite is a volume-based median size. This particle size can be determined, for example, by a laser diffraction / scattering method or a dynamic light scattering method (DLS).

[0020] In the agent of the present invention, the content of the smectite is not particularly limited, and can be appropriately set according to the amount of the ultraviolet absorber contained in the agent of the present invention. From the viewpoints of water resistance, skin feel, emulsion stability, etc., the content is preferably 0.34 mass% or more, more preferably 1.0 mass% or more, even more preferably 1.5 mass% or more, and even more preferably 2.0 mass% or more. In addition, from the viewpoint of rheological properties, the content is preferably 8.0 mass% or less, more preferably 5.0 mass% or less, even more preferably 4.0 mass% or less, and even more preferably 3.0 mass% or less.

[0021] <Ultraviolet absorbing agent> The agent of the present invention contains an ultraviolet absorbing agent as an ultraviolet protection agent. The type of the ultraviolet absorbing agent is not particularly limited as long as it is an ultraviolet absorbing agent that can constitute the oil phase in the agent of the present invention. For example, one or more of ethylhexyl methoxycinnamate, diethylamino hydroxybenzoyl hexyl benzoate, bisethylhexyloxyphenol methoxyphenyl triazine, t-butyl methoxydibenzoylmethane, homomenthyl salicylate, 2-cyano-3,3 diphenylprop-2-enoic acid 2-ethylhexyl ester (octocrylene), octyl salicylate, cinoxate, and dimethicodiethyl benzalmalonate can be used. In addition, examples of commercially available ultraviolet absorbing agents include Uvinul (registered trademark) MC80, Uvinul (registered trademark) A Plus Granular, Tinosorb (registered trademark) S (trade names, all manufactured by BASF Japan), PARSOL (registered trademark) 340, and PARSOL (registered trademark) 1789 (trade names, all manufactured by DSM). The ultraviolet absorbent constitutes the oil phase (dispersed phase) in the agent of the present invention. The ultraviolet absorbent may constitute the oil phase as a compound itself, or may constitute the oil phase as an oily composition in which the compound is mixed with an oily component such as fat or oil.

[0022] In the agent of the present invention, the content of the ultraviolet absorber is 5.0% by mass or more as described above. Since the agent of the present invention is Pickering emulsified with smectite as described above, the content of the ultraviolet absorber contained in the agent can be increased while maintaining emulsion stability compared to oil-in-water sunscreens using general surfactants. From the viewpoint of exerting a stronger ultraviolet protection effect, the content is preferably 8.0% by mass or more, more preferably 10.0% by mass or more, and even more preferably 15.0% by mass or more. In addition, from the viewpoint of emulsion stability, the content is preferably 50.0% by mass or less, more preferably 40.0% by mass or less, and even more preferably 30.0% by mass or less.

[0023] (Smectite and UV absorber content) In the agent of the present invention, the respective contents of the smectite and the ultraviolet absorber are controlled so that the ratio of the content of the ultraviolet absorber to the content of the smectite (content of ultraviolet absorber / content of smectite) is 15 or less, as described above. The value of this ratio is preferably 12 or less, and more preferably 10 or less. Moreover, the value of this ratio is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more.

[0024] (Contains UV scattering agent) The agent of the present invention may further contain an ultraviolet scattering agent as an ultraviolet protection agent. Examples of ultraviolet scattering agents include inorganic powders and white pigments that function as ultraviolet protection agents by physically reflecting and scattering ultraviolet rays, such as titanium oxide, zinc oxide, and iron oxide. The content of the ultraviolet scattering agent in the agent of the present invention is not particularly limited and can be appropriately set so as to further improve the ultraviolet protection effect of the agent of the present invention, and can be, for example, 0.5 to 20 mass%, or may be 1 to 15 mass%, 1.5 to 10 mass%, or may be 2 to 5 mass%.

[0025] <Aqueous medium> The agent of the present invention is an oil-in-water Pickering emulsion. That is, the agent of the present invention contains an aqueous medium constituting an aqueous phase (continuous phase). The aqueous medium contains water and may further contain a water-soluble organic solvent as necessary. It is preferable that the aqueous medium is 50% by mass or more of water. There is no particular limitation on the type of the water-soluble organic solvent, and it is appropriately selected according to the purpose. For example, alcohols such as ethanol, propanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butylene glycol, pentamethylene glycol, hexylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, glycerin, diglycerin, and polyglycerin can be mentioned, and one or more of these can be used. In addition, from the viewpoint of being able to uniformly disperse smectite, having high dispersion stability, and being easy to handle, it is preferable that the aqueous medium is water. There is no particular limitation on the grade of the water, and in addition to ordinary tap water, purified water from which ion components in water such as distilled water and ion-exchanged water can be removed can also be used. In particular, water from which ions have been removed is preferred, and specifically, water with an ionic conductivity of 10 μS / m or less (preferably 5 μS / m or less, and more preferably 2 μS / m or less) is more preferred. Furthermore, the aqueous medium may contain other components as appropriate, so long as the smectite can be uniformly dispersed therein and the effects of the present invention are not impaired. For example, the aqueous medium may contain a dispersant, an antifoaming agent, a wetting agent, a thickener, etc.

[0026] The content of the aqueous medium in the agent of the present invention is preferably 45% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and even more preferably 70% by mass or more. The content is preferably 94% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. The entire remainder except for the smectite and the ultraviolet absorbing agent may be the aqueous medium.

[0027] <Other ingredients> The agent of the present invention may contain optional components (other components) other than the above components. Examples of other components include liquid oils, water-soluble polymers, oil-soluble polymers, solid oils such as waxes, lower alcohols, moisturizing components, surfactants, powder components, preservatives, medicines, etc. The other components may constitute the oil phase (dispersed phase) or the water phase (continuous phase) in the agent of the present invention.

[0028] Examples of the liquid oil include silicone oil, hydrocarbon oil, vegetable oil, ester oil, and high molecular weight polyoxyalkylene glycol. Specific examples include silicone oils such as dimethicone, diphenyl dimethicone, and cyclopentasiloxane; liquid oils such as linseed oil, camellia oil, macadamia nut oil, corn oil, olive oil, avocado oil, camellia oil, castor oil, safflower oil, apricot kernel oil, cinnamon oil, jojoba oil, grape oil, almond oil, rapeseed oil, sesame oil, sunflower oil, wheat germ oil, rice germ oil, rice bran oil, cottonseed oil, soybean oil, peanut oil, tea seed oil, evening primrose oil, egg yolk oil, liver oil, triglycerin, glyceryl trioctanoate, and glyceryl triisopalmitate; octanoic acid esters such as cetyl octanoate, and isooctanoic acid esters such as glyceryl tri-2-ethylhexanoate and pentaerythritol tetra-2-ethylhexanoate. ester oils such as ethylhexyl laurate, lauric acid esters such as isopropyl myristate, octyldodecyl myristate, and the like, myristate esters such as isopropyl myristate, octyldodecyl myristate, and the like, palmitic acid esters such as octyl palmitate, stearic acid esters such as isocetyl stearate, isostearic acid esters such as isopropyl isostearate, isopalmitic acid esters such as octyl isopalmitate, and the like, oleic acid esters such as isodecyl oleate, adipic acid diesters such as diisopropyl adipate, sebacic acid diesters such as diethyl sebacate, and diisostearyl malate; hydrocarbon oils such as liquid paraffin and squalane; polyoxybutylene polyoxypropylene glycol, and the like.

[0029] Examples of the water-soluble polymer include homopolymers and copolymers of 2-acrylamido-2-methylpropanesulfonic acid (hereinafter abbreviated as "AMPS"). Examples of the copolymer include copolymers made of comonomers such as vinylpyrrolidone, acrylic acid amide, sodium acrylate, and hydroxyethyl acrylate. That is, examples include AMPS homopolymer, vinylpyrrolidone / AMPS copolymer, dimethylacrylamide / AMPS copolymer, acrylic acid amide / AMPS copolymer, and sodium acrylate / AMPS copolymer. Further examples include carboxyvinyl polymer, ammonium polyacrylate, sodium polyacrylate, sodium acrylate / alkyl acrylate / sodium methacrylate / alkyl methacrylate copolymer, carrageenan, pectin, mannan, curdlan, chondroitin sulfate, starch, glycogen, gum arabic, sodium hyaluronate, tragacanth gum, xanthan gum, mucoitin sulfate, hydroxyethyl guar gum, carboxymethyl guar gum, guar gum, dextran, keratosulfuric acid, locust bean gum, succinoglucan, chitin, chitosan, carboxymethyl chitin, agar, and the like.

[0030] Examples of oil-soluble polymers include trimethylsiloxysilicate, alkyl-modified silicone, polyamide-modified silicone, dimethicone crosspolymer, (dimethicone / vinyl dimethicone) crosspolymer, polymethylsilsesquioxane, and the like.

[0031] Examples of waxes include beeswax, candelilla wax, carnauba wax, lanolin, liquid lanolin, jojoba wax, and the like.

[0032] Examples of the lower alcohol include alcohols having 1 to 5 carbon atoms, such as ethanol and isopropanol.

[0033] Examples of moisturizing components include polyhydric alcohols such as ethylene glycol, propylene glycol, 1,3-butylene glycol, dipropylene glycol, and polybutylene glycol.

[0034] Examples of the surfactant include anionic, cationic, nonionic, or amphoteric surfactants, as well as silicone-based and hydrocarbon-based surfactants.

[0035] Examples of the powder component include nylon, acrylic polymer spherical powder, silica powder, silicone powder, and the like.

[0036] Examples of drugs include salts of L-ascorbic acid and its derivatives, glycyrrhizinic acid and its derivatives such as dipotassium glycyrrhizinate and monoammonium glycyrrhizinate, glycyrrhetinic acid and its derivatives such as stearyl glycyrrhetinate, allantoin, salts of tranexamic acid and its derivatives, salts of alkoxysalicylic acid and its derivatives, salts of glutathione and its derivatives, allantoin, azulene, and the like.

[0037] Examples of ingredients other than those mentioned above include sugars such as trehalose and erythritol, polysaccharides such as hyaluronic acid and acetylated hyaluronic acid, amino acids such as serine, glycine, hydroxyproline, glutamic acid, and alanine, and extracts such as silk extract, chlorella extract, hydrolyzed pearl protein, cornflower extract, Chinese tea extract, yeast extract, inositol, licorice extract, Sanguisorba officinalis extract, rose extract, and Coix seed extract.

[0038] The agent of the present invention can also be made into a dry powder by reducing the content of the aqueous medium by drying or the like. That is, another embodiment of the present invention is a dry powder obtained by drying the sunscreen agent of the present invention (oil-in-water Pickering emulsion sunscreen agent). The dry powder obtained by drying the agent of the present invention can exhibit a high ultraviolet protection effect even in a dry state. The drying process is not particularly limited, and for example, a conventional drying process such as a heating process or a freeze-drying process can be applied, or natural drying may be used. In addition, a pulverization process may be applied after drying, if necessary. The content of the aqueous medium (preferably water) in the dry powder is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. In the present invention, it is practically difficult to directly and appropriately specify the technical features of the dry powder by its structure, composition, and properties. Therefore, in the present invention, in order to clarify the invention by clearly indicating the difference from the prior art, the manufacturing method (process) is specified in the invention of the dry powder.

[0039] <Usage form> The agent of the present invention can be appropriately used in any form within the range that does not impair the effects of the present invention. For example, it can be used in the form of gel, cream, spray, stick, balm, etc. It can also be used by being blended with cosmetics such as foundation and emulsion. In particular, the agent of the present invention has the characteristic that it exhibits fluidity at high shear and gels when left to stand due to the thixotropy and dispersion stability of smectite. Therefore, even though it is a gel that shows high stability, it can be sprayed by spraying, and it can be an agent with excellent applicability with little dripping. The yield value of the agent of the present invention is preferably 4 to 100 Pa, more preferably 10 to 100 Pa. The yield value can be measured using a viscosity / viscoelasticity measuring device (e.g., HAAKE MARS, model: III, manufactured by Thermo Fisher Scientific) or a rotational viscometer (e.g., FANN VISCOMETER, model: 35SA, manufactured by FANN Instrument). When measuring the yield value using the above viscosity / viscoelasticity measuring device, the measurement can be performed based on the measurement procedure recommended by the measurement manufacturer. For example, the temperature of the measurement section is set to 23 degrees, and the stress change is measured while changing the rotation speed from 1 to 1000 rpm. Using the Casson formula (Formula 1 below), the coefficient of determination of the fitted curve is R 2 The yield value can be calculated by curve fitting in the range of ≧0.9.

[0040] TIFF2025023593000002.tif59170

[0041] [Sunscreen manufacturing method] In the agent of the present invention, when the ultraviolet absorbent is emulsified and dispersed in the aqueous medium, the smectite, which is a water-swellable clay mineral, is made to coexist and is homogenized by high shear treatment, so that the ultraviolet absorbent and the smectite are integrated and the smectite acts as an emulsifier, thereby obtaining an emulsion (oil-in-water Pickering emulsion sunscreen agent) with excellent emulsion stability. As the high shear treatment, wet high pressure treatment, bead mill treatment, etc. can be adopted, and wet high pressure treatment is preferred.

[0042] The wet high-pressure treatment is a method in which pressure energy is converted into kinetic energy to generate a jet flow, and the jet flow is homogenized by the shear force generated in the jet flow, and the oil is emulsified and dispersed in an aqueous medium to generate an emulsion. By adopting the wet high-pressure treatment, it is believed that the strong shear force caused by the jet flow generated by high pressure cuts open the layers of the smectite, which makes the interaction between the ultraviolet absorber and the smectite more efficient, so that the smectite acts like an emulsifier, and a stable emulsion can be obtained. The wet high-pressure treatment itself is known, and for example, Patent Publication No. 5791142, Patent Publication No. 5972434, JP 2021-115539, etc. can be referred to. Commercially available wet high-pressure treatment devices include, for example, NEW BERYU MINI (manufactured by Biryu Co., Ltd.), Starburst (manufactured by Sugino Machine Co., Ltd.), Nanovater System (manufactured by Yoshida Kikai Kogyo Co., Ltd.), Nanomaker (manufactured by Advanced Nano Technology Co., Ltd.), and G-smasher (manufactured by RIX Co., Ltd.). EXAMPLES

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0044] Details of the various raw materials used in the following Examples and Comparative Examples are as follows. (Smectite) Sumecton-SA: Trade name, synthetic saponite, manufactured by Kunimine Kogyo Co., Ltd., particle size: 100 nm Kunipia-F: Product name, natural montmorillonite, manufactured by Kunimine Kogyo Co., Ltd., particle size: 500 nm (Silica fine particles) AEROSIL® 200: Trade name, hydrophilic fumed silica, manufactured by EVONIK (UV absorber) Uvinul® MC80: Trade name, ethylhexyl methoxycinnamate, manufactured by BASF Japan Ltd. Uvinul® A Plus Granular: Product name, diethylaminohydroxybenzoyl hexyl benzoate, manufactured by BASF Japan Ltd. Tinosorb(R) S: Trade name, bis-ethylhexyloxyphenol methoxyphenyl triazine, manufactured by BASF Japan Ltd. PARSOL® 340: Trade name, octocrylene, manufactured by DSM PARSOL (registered trademark) 1789: Trade name, t-butyl methoxydibenzoylmethane, manufactured by DSM (emulsifier) Rheodor TW-O120V: Trade name, polyoxyethylene sorbitan monooleate, manufactured by Kao Corporation

[0045] Example 1 2.0 parts by mass of Sumecton-SA was added to 88 parts by mass of purified water, and mixed for 10 minutes at 1000 rpm using a stirrer (model number: PM-202, manufactured by AS ONE Corporation) equipped with a dispersing blade. 7 parts by mass of Uvinul MC80, 2 parts by mass of Uvinul A Plus Granular, and 1 part by mass of Tinosorb S were further added thereto, and mixed for 10 minutes at 1000 rpm. The resulting mixture was homogenized using a wet high-pressure processor (manufactured by Biryu Co., Ltd., NEW BERYU MINI) to obtain a Pickering-emulsified sunscreen (oil-in-water emulsion).

[0046] (Examples 2 to 13) The sunscreen agents of Examples 2 to 13 were obtained in the same manner as in Example 1, except that the types and amounts of smectite and ultraviolet absorber (simply referred to as "absorber" in the table) used were as shown in Table 2 below.

[0047] Example 14 2.0 parts by mass of Sumecton-SA was added to 88 parts by mass of purified water, and mixed for 10 minutes at 1000 rpm using a mixer equipped with a dispersing blade (model number: PM-202, manufactured by AS ONE Corporation). 7 parts by mass of Uvinul MC80, 2 parts by mass of Uvinul A Plus Granular, and 1 part by mass of Tinosorb S were further added thereto, and mixed for 10 minutes at 100 rpm. The resulting mixture was dispersed and homogenized by applying high shear force at 7000 rpm for 1 minute using a homogenizer (f model, manufactured by Tokushu Kika Kogyo Co., Ltd.), to obtain the sunscreen agent of Example 14.

[0048] (Comparative Examples 1 and 2) Sunscreen agents of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the types and amounts of smectite and ultraviolet absorbing agent used were as shown in Table 2 below.

[0049] Comparative Example 3 The sunscreen agent of Comparative Example 3 was obtained in the same manner as in Example 14 above, except that an emulsifier shown in Table 2 below was used instead of smectite, and homogenization was performed using a homogenizer in the same manner as in Example 14 above.

[0050] Comparative Example 4 A sunscreen agent of Comparative Example 4 was obtained in the same manner as in Example 1 above, except that silica fine particles shown in Table 2 below were used instead of smectite and the blending amount was as shown in Table 2 below.

[0051] The physical properties and the like of each of the obtained sunscreen agents of Examples 1 to 14 and Comparative Examples 1 to 4 were evaluated by the following tests. The results are also shown in Table 2 below.

[0052] <Initial SPF value> Each sunscreen agent (sample) of Examples 1 to 14 and Comparative Examples 1 to 4 was uniformly applied to a PMMA (polymethyl methacrylate) plate (manufactured by Labsphere, HELIOPLATE HD 6) at 1.33 mg / cm 2 so as to be uniform, and left standing at room temperature for 15 minutes to air-dry naturally. Thereafter, for each PMMA plate coated with the sample, the SPF value was measured using an SPF analyzer (manufactured by Labsphere, UV-2000 S). The measured SPF value (initial SPF value) was evaluated according to the following evaluation criteria. - Evaluation criteria - ◎: The SPF value was 50 or more. 〇: The SPF value was 30 or more and less than 50. △: The SPF value was 15 or more and less than 30. ×: The SPF value was less than 15.

[0053] <Water resistance> Each of the above PMMA plates on which the initial SPF value was measured was completely submerged in the four corners of a square vat filled with tap water at room temperature (manufactured by AS ONE; UK 18-8 square vat, 12 pieces) with the coated surface facing up. A propeller (4-blade propeller (manufactured by AS ONE; stirring blade (made of SUS304))) was placed at the center of the vat, and a three-one motor (manufactured by Shinto Kagaku; HEIDON three-one motor BL600) was installed so that the rotation speed was 95 to 100 rpm and stirred for 20 minutes. The tap water was exchanged, and the same operation was repeated twice. Then, each PMMA plate was pulled out of the vat, left standing at room temperature for 30 minutes to air-dry naturally. Thereafter, in the same manner as above, the SPF value (SPF value after immersion treatment) of each PMMA plate after the immersion treatment was measured using an SPF analyzer. From the obtained SPF value after the immersion treatment and the above initial SPF value, the water resistance was calculated by the following (Equation 2) and judged according to the following evaluation criteria. For Comparative Examples 2 and 3 in which the initial SPF value was less than 15, the calculation of the water resistance was not performed. Water resistance (%) = 100 × (SPF value after immersion treatment) / (Initial SPF value) ··· (Equation 2) -Evaluation criteria- ⊚: Water resistance was 45% or more. ◯: Water resistance was 35% or more and less than 45%. △: Water resistance was 10% or more and less than 35%. ×: Water resistance was less than 10%.

[0054] <Roughness> The skin feel (usage sensation) when each sunscreen was applied was evaluated by the following method. Each sunscreen agent (sample) of Examples 1 to 14 and Comparative Examples 1 to 4 was applied to artificial leather (Suplare, manufactured by Idemitsu Technofine) at a concentration of 1.33 mg / cm 2 The average coefficient of friction (MIU) and its average deviation (MMD) were measured using a friction tester (Kato Tech; KES-SE, measurement conditions: friction element 10 mm square silicon sensor, SENS H, SPEED 1 mm / sec, static load 25 g). Evaluation was performed according to the following evaluation criteria, using [(MMD / MIU) x 100] as an index. The value obtained by [(MMD / MIU) x 100] indicates that the smaller the value, the less roughness in terms of slipperiness and the better the skin feel. -Evaluation criteria- ◎: [(MMD / MIU) × 100] was less than 1.00. 〇: [(MMD / MIU) × 100] was greater than or equal to 1.00 and less than 1.25. △: [(MMD / MIU) × 100] was 1.25 or greater but less than 1.50. ×: [(MMD / MIU) × 100] was 1.50 or more.

[0055] <Emulsification stability> Each sunscreen agent of Examples 1 to 14 and Comparative Examples 1 to 4 was stored at room temperature (25°C) and the emulsified state was visually observed and evaluated according to the following evaluation criteria. In Table 2 below, "Pickering" in the section on emulsion form means a Pickering emulsion state, and "surfactant" means an emulsion state in which a surfactant is used as an emulsifier. -Evaluation criteria- ⊚: No phase separation was observed after 14 days of storage, and the emulsion state was maintained. ◯: Phase separation was observed after 7 days but before 14 days of storage. △: Phase separation was observed after 1 day but before 7 days of storage. ×: Phase separation was observed within 1 day of storage, or the emulsified state could not be maintained before storage.

[0056] <Overall rating> Based on the results of the above four evaluation items, evaluation was performed according to the following evaluation criteria. -Evaluation criteria- ◎: All four items were rated 〇 or ◎. ◯: One of the four items was rated △, and all others were rated ◯ or ◎. △: One of the four items was rated ×, and the rest were rated △, ◯, or ◎. ×: Two or more of the four items were rated ×.

[0057] [Table 2-1]

[0058] [Table 2-2]

[0059] The sunscreen of Comparative Example 1, in which the ratio of the content of the ultraviolet absorber to the content of the smectite is higher than the range specified in the present invention, was particularly poor in stability. The sunscreen of Comparative Example 2, in which the content of the ultraviolet absorber is lower than the range specified in the present invention, had a low initial SPF value and was also poor in stability. The sunscreen of Comparative Example 3, in which a surfactant was used as an emulsifier, had a low initial SPF value and was also rough. The sunscreen of Comparative Example 4, in which silica fine particles were used as the emulsifying powder instead of smectite, was also rough. In contrast, the sunscreens of Examples 1 to 14, which satisfied all of the configurations specified in the present invention, were clearly superior overall to the comparative examples in terms of initial SPF value, water resistance, skin feel, and emulsion stability.

Claims

1. An oil-in-water Pickering emulsion sunscreen, comprising an ultraviolet absorbing agent that is Pickering emulsified into an oil-in-water type using smectite as an emulsifier, the content of the ultraviolet absorbing agent being 5.0 mass% or more, and the ratio of the content of the ultraviolet absorbing agent to the content of the smectite being 15 or less.

2. 2. The sunscreen according to claim 1, wherein the ratio of the content of said ultraviolet absorbing agent to the content of said smectite is 3 or more.

3. 2. The sunscreen of claim 1, wherein the smectite is a synthetic smectite.

4. The sunscreen according to claim 1 , wherein the sunscreen comprises an ultraviolet ray scattering agent.

5. A dry powder obtained by drying the sunscreen agent according to any one of claims 1 to 4.

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