Oil-based emulsions in water

Abstract

To provide an oil-in-water emulsion composition that has superior emulsion stability and UV protection effect and serves as sunscreen cosmetics, without substantially using a surfactant as an emulsifier.SOLUTION: An oil-in-water emulsion composition includes the following components (a) and (b): (a) particles composed of polymers that include a hydrophobic part with a cationic group, including a hydrophobic monomer unit, and a hydrophilic part including at least a hydrophilic monomer unit represented by formula (I); and (b) hydrophobically treated microparticle metal oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an oil-in-water emulsion composition having excellent usability. [Background technology]

[0002] Generally, sunscreen cosmetics contain fine metal oxide powders to achieve a high SPF (Sun Protection Factor). It is widely known that these fine metal oxide particles have a strong UV-blocking effect. Because the amount of fine metal oxide particles (e.g., titanium dioxide, zinc oxide, cerium oxide) used in sunscreen cosmetics tends to be relatively large, two or more types of fine metal oxide particles are sometimes used in combination, such as titanium dioxide and zinc oxide, or, depending on the product, organic UV absorbers may also be used.

[0003] When incorporating such fine metal oxide particles into sunscreen cosmetics in the form of oil-in-water emulsions, hydrophobized fine metal oxide particles are often used to improve dispersibility in the oil phase. Simultaneously, attempts have been made to enhance the dispersibility of the hydrophobized fine metal oxide particles using surfactants. However, if a large amount of surfactant is used in an oil-in-water emulsion, it can cause problems such as stickiness and irritation when applied directly to the human body, such as the skin. Furthermore, many consumers are concerned about the effects of surfactants that can be absorbed by the human body. For this reason, it is desirable to minimize the amount of surfactant used in oil-in-water emulsions used as sunscreen cosmetics.

[0004] Against this backdrop, attempts are being made to utilize additives with emulsifying properties other than surfactants in oil-in-water emulsion compositions. One such attempt that is attracting attention is an oil-in-water emulsion composition in which solid particles are present near the interface between the oil phase and the aqueous phase.

[0005] Figure 1 is a schematic comparison of an emulsion containing a surfactant and an oil-in-water emulsion composition (hereinafter also referred to as "oil-in-water emulsion composition emulsified by solid particles"), which is emulsified by placing solid particles near the interface between the oil phase and the aqueous phase. Although the present invention is not bound by any theory, oil-in-water emulsion compositions emulsified by solid particles are generally sometimes called Pickering emulsions, and it is presumed that mineral particles or amphiphilic organic particles are present at the interface of aqueous or oily droplets, and the structure of the droplets is stabilized.

[0006] As mentioned above, there has been a certain degree of demand for emulsified compositions that do not use surfactants. An example of an oil-in-water emulsion composition used as a sunscreen cosmetic that substantially does not contain surfactants as emulsifiers is disclosed in Patent Document 1, for example, an oil-in-water emulsion composition characterized by containing light-shielding powder and being stabilized by an emulsion powder whose surface is charged. According to the oil-in-water emulsion composition described in Patent Document 1, it is said to have excellent resistance to aqueous solutions containing ions, and that the light-shielding effect is maintained or improved after contact with the aqueous solution. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-50627 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, sunscreen cosmetics that are oil-in-water type emulsion compositions, such as the oil-in-water type emulsion composition described in Patent Document 1, are difficult to highly formulate fine particle metal oxides that are light-blocking powders, and also avoid the use of surfactants. Therefore, it has been pointed out that the dispersibility of the fine particle metal oxides is poor, and as a result, the ultraviolet ray shielding effect is not sufficient. Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide an oil-in-water type emulsion composition that is excellent in usability, has good emulsion stability, and further has an excellent ultraviolet ray shielding effect.

Means for Solving the Problems

[0009] The inventors of the present invention conducted intensive research in view of the above problems. As a result, it was found that the above problems can be solved by using particles containing a polymer having a hydrophobic part containing a hydrophobic monomer unit and having a cationic group, and a hydrophilic part containing a predetermined hydrophilic monomer unit, and the present invention was completed.

[0010] That is, the present invention provides the following.

[0011] A first aspect of the present invention is an oil-in-water type emulsion composition containing the following components (a) and (b); (a) Particles containing a polymer having a hydrophobic part containing a hydrophobic monomer unit and having a cationic group, and a hydrophilic part containing at least a hydrophilic monomer unit represented by the following formula (I), (b) Hydrophobically treated fine particle metal oxide.

Chemical formula

[0012] A second aspect of the present invention is the oil-in-water type emulsion composition according to the first aspect, wherein the content of the hydrophobically treated fine particle metal oxide in the oil-in-water type emulsion composition is 1% by mass or more and 30% by mass or less.

[0013] A third aspect of the present invention is the oil-in-water emulsion composition according to the first or second aspect, wherein the oil-in-water emulsion composition substantially does not contain a surfactant as an emulsifier.

[0014] A fourth aspect of the present invention is an oil-in-water emulsion composition according to any one of the first to third aspects, wherein the cationic group is derived from a cationic radical polymerization initiator.

[0015] A fifth aspect of the present invention is that the cationic radical polymerization initiator is 2,2'-[diazen-1,2-diylbis(propane-2,2-diyl)]bis(1,3-dimethyl-4,5-dihydro-1H-imidazole-3-ium)=ditrifluoromethanesulfonate (ADIP), 2,2'-[diazen-1,2-diylbis(propane-2,2-diyl)]bis(1,3-dimethyl-4,5-dihydro-1H-imidazole-3-ium)=dichloro The oil-in-water emulsion composition is one or more selected from the group consisting of 2,2'-azobis(2-methylpropionamidine)dihydrochloride (V-50), 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane] (VA-061), as described in any of the first to fifth embodiments above.

[0016] A sixth aspect of the present invention is an oil-in-water emulsion composition according to any one of the first to fifth aspects, wherein the hydrophilic portion further comprises monomer units represented by the following formula (II), and the ratio (degree of saponification) of the number of monomer units represented by the following formula (I) to the total number of monomer units represented by the following formula (II) is 70% or more and 99% or less. [ka]

[0017] According to the present invention, it is possible to provide an oil-in-water emulsion composition for use as a sunscreen cosmetic that exhibits excellent emulsification stability and UV shielding effect without substantially using surfactants as emulsifiers. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic comparison diagram of emulsions using surfactants and emulsions using solid particles. [Figure 2] This graph shows the SPF for Experimental Examples 1 to 3 and Comparative Experimental Examples 1 to 3. [Figure 3] This graph shows the comparison results of water resistance in Experimental Example 1 and Comparative Experimental Example 2. [Modes for carrying out the invention]

[0019] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. Note that the embodiments described below are for illustrative purposes only, and the following description in these embodiments should not be construed as limiting the language of the claims.

[0020] <Oil-in-water emulsion composition> The oil-in-water emulsion composition of this embodiment comprises (a) particles containing a polymer having a hydrophobic portion having a cationic group and a hydrophilic portion containing at least a predetermined hydrophilic monomer unit, and (b) hydrophobically treated fine metal oxide particles. The oil-in-water emulsion composition of this embodiment is excellent in terms of feel and emulsification stability, and can be used as a sunscreen cosmetic for general purposes. Furthermore, because the hydrophobically treated fine metal oxide particles are sufficiently dispersed, it also has excellent UV shielding effect. In addition, the oil-in-water emulsion composition of this embodiment has excellent water resistance of the film formed thereon, making it easy to maintain a high SPF even after a bath. Moreover, from the viewpoint of having a good feel after application, it is preferable that the oil-in-water emulsion composition of this embodiment substantially does not contain surfactants as emulsifiers. In particular, since sunscreen cosmetics tend to be applied to a wide area of ​​skin, the feel after application can be extremely important. Note that "substantially not contained" means, for example, that the content in the oil-in-water emulsion composition of this embodiment is less than 1% by mass.

[0021] Furthermore, the oil-in-water emulsion composition of this embodiment can be prepared without using equipment that generates strong external forces industrially, such as ultrasonic devices or homogenizers, and heat treatment for stabilizing the dispersion state is not necessarily required. Therefore, this embodiment can also contribute to reducing the environmental burden during the preparation of the oil-in-water emulsion composition. However, the present invention also includes oil-in-water emulsion compositions prepared using ultrasonic devices, homogenizers, etc., within its scope of rights.

[0022] [(a) Particle] The oil-in-water emulsion composition of this embodiment contains particles comprising a polymer having hydrophobic monomer units, a hydrophobic portion having a cationic group, and a hydrophilic portion containing predetermined hydrophilic monomer units. The particle content in the oil-in-water emulsion composition of this embodiment is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.5% by mass or more and 4.0% by mass or less. By having a particle content within the above range, the oil-in-water emulsion composition of this embodiment achieves emulsion stability even without substantially using surfactants.

[0023] (Hydrophobic part) As described above, the hydrophobic portion contains hydrophobic monomer units, and examples of these "hydrophobic monomer units" include monomer units obtained from monomers having an ethylenically unsaturated double bond. Here, examples of monomers having an ethylenically unsaturated double bond include polymerizable monomers that have a carbon-carbon double bond in their molecule, and more specifically, (meth)acrylic acid monomer units and styrene monomer units.

[0024] Here, examples of (meth)acrylic acid monomer units include monomer units derived from alkyl (meth)acrylate having an alkyl ester group having 1 to 6 carbon atoms. Examples of alkyl ester groups having 1 to 6 carbon atoms include methyl ester group, ethyl ester group, n-propyl ester group, n-butyl ester group, n-pentyl ester group, and n-hexyl ester group. These alkyl ester groups may, if necessary, have one or more hydrogen atoms of the alkyl group constituting the alkyl ester group substituted with a hydroxyl group. From the viewpoint of ensuring sufficient storage stability of the particles, alkyl ester groups having 1 to 4 carbon atoms are more preferable.

[0025] Preferably, methyl methacrylate (MMA), butyl methacrylate (BMA), or 2-hydroxyethyl methacrylate (HEMA) are used as such alkyl (meth)acrylates, with methyl methacrylate being more preferable. When these monomers are used, the storage stability of the resulting particles is improved, and the emulsifying ability of the particles is also enhanced.

[0026] Furthermore, if the (meth)acrylic acid monomer unit has an acidic group such as a carboxyl group, the carboxyl group may be in the form of a salt, for example, a sodium salt or a potassium salt.

[0027] Examples of styrene-based monomer units include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylstyrene, isobutylstyrene, t-butylstyrene, o-bromostyrene, m-bromostyrene, p-bromostyrene, o-chlorostyrene, m-chlorostyrene, and p-chlorostyrene. Among these, styrene is preferred from the viewpoint of ensuring sufficient storage stability and emulsifying ability of the resulting particles.

[0028] When preparing a hydrophobic moiety containing hydrophobic monomer units and having a cationic group using the monomers described above, it is generally possible to radically polymerize the monomers.

[0029] (cationic group) The cationic groups in the hydrophobic portions of the particles contained in the oil-in-water emulsion composition of this embodiment are generally assumed to be cationic groups derived from a cationic radical polymerization initiator. However, they are not limited to cationic groups derived from a cationic radical polymerization initiator, and cationic groups derived from any compound or polymerization unit that can introduce any cationic group at the terminal or in the hydrophobic portion can be mentioned. Specific examples of such cationic groups include primary amino groups, secondary amino groups, tertiary amino groups, quaternary ammonium groups, imidazole groups, imidazolium groups, pyridyl groups, pyridinium groups, piperidyl groups, piperidinium groups, pyrrolidinyl groups, pyrrolidinium groups, phosphonium groups, and the like. However, in this embodiment, it is particularly preferable to use a cationic radical polymerization initiator as the polymerization initiator to polymerize the hydrophobic monomer, thereby adopting the cationic group introduced at the terminal of the hydrophobic portion as the cationic group. By using a cationic radical polymerization initiator, the terminal structure derived from the cationic radical polymerization initiator can be covalently bonded to the monomer units at the ends of the hydrophobic portion. In this embodiment, the core portion includes a hydrophobic portion, and cationic groups are arranged on or near the surface of the core portion, which can result in particles with excellent emulsifying ability.

[0030] (Cationic radical polymerization initiator) In this embodiment, cationic radical polymerization initiators that balance safety after polymerization with reactivity as radical polymerization initiators can generally be used, but more specifically, 2,2'-[diazene-1,2-diylbis(propane-2,2-diyl)]bis(1,3-dimethyl-4,5-dihydro-1H-imidazole-3-ium)=ditrifluoromethanesulfonate (ADIP), 2,2'-[diazene-1,2-diylbis(propane-2,2-diyl)]bis(1,3-dimethyl-4,5-dihydro-1 It is preferable to use one or more selected from the group consisting of H-imidazole-3-ium) dichloride (ADIP-Cl), 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane] (VA-061, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Using these cationic radical polymerization initiators results in better emulsification ability of the resulting particles.

[0031] In addition, examples of the radical polymerization initiator that can be used in the present embodiment include, for example, a cationic radical polymerization initiator represented by the general formula (III). For further details regarding the following cationic radical polymerization initiator, for example, refer to Japanese Patent Application Laid-Open No. 2017-051113. The content of this document is incorporated herein by reference. Specific examples of the cationic radical polymerization initiator represented by the general formula (III) include the above-mentioned ADIP and ADIP-Cl. By using ADIP or ADIP-Cl, particles contained in the oil-in-water type emulsion composition of the present embodiment can be prepared under milder reaction conditions, and it is also possible to suppress a decrease in the storage stability of the particles due to damage such as heating during the preparation of the particles. Further, by using ADIP or ADIP-Cl, as described above, particles contained in the oil-in-water type emulsion composition of the present embodiment can be prepared under milder reaction conditions, and thus it can contribute to the environmental load during synthesis.

Chemical formula

[0032] The term "counter anion" in the cationic radical polymerization initiator of formula (III) above is not particularly limited as long as it is an anion that is commonly used as a counter anion for organic compounds in the field of organic chemistry, and includes, for example, halide anions (chloride ion, bromide ion, fluoride ion, iodide ion), conjugate bases of organic acids (e.g., acetate ion, citrate ion, trifluoroacetate ion), nitrate ion, sulfate ion, carbonate ion, etc. Preferred counter anions in this embodiment include, for example, trifluoromethanesulfonate ion (triflate), chloride ion, nitrate ion, etc. Among these, chloride ion, acetate ion, and citrate ion are preferred, and chloride ion is more preferred, from the viewpoint of significantly improving the storage stability of the oil-in-water emulsion composition of this embodiment, increasing the yield of particles when preparing the particles contained in the oil-in-water emulsion composition of this embodiment, and improving manufacturing costs.

[0033] (Hydrophilic part) The hydrophilic portion of the particles contained in the oil-in-water emulsion composition of this embodiment more specifically includes a hydrophilic monomer unit represented by the following formula (I). [ka]

[0034] The hydrophilic monomer unit represented by formula (I) above is not particularly limited, but can generally be obtained by polymerizing vinyl acetate by a radical polymerization reaction and hydrolyzing (saponifying) the acetate ester group. Therefore, in this embodiment, although the hydrophilic portion always contains the hydrophilic monomer unit represented by formula (I) above, not all monomer units of the hydrophilic portion are limited to those represented by formula (I) above. More specifically, the hydrophilic portion comprises a monomer unit represented by the following formula (II) and a monomer unit represented by the following formula (I), derived from vinyl acetate. The ratio of the hydroxyl groups (sometimes simply referred to as "saponification degree" in this invention) to the total number of acetate groups in the monomer unit represented by the following formula (II) and the hydroxyl groups in the monomer unit represented by the following formula (I) is preferably 70% to 99%, more preferably 75% to 98%, and even more preferably 78% to 96%, from the viewpoint of improving the storage stability and emulsifying ability of the particles themselves and ensuring good emulsification stability of the oil-in-water emulsion composition formed using these particles. By adjusting this "saponification degree," the degree of hydrophilicity in the hydrophilic portion of the particles is adjusted. Therefore, it is preferable to adjust the "saponification degree" appropriately according to the intended use of the oil-in-water emulsion composition of this embodiment. [ka]

[0035] (The core of the particle) The particles contained in the oil-in-water emulsion composition of this embodiment have organic groups exposed on at least their surface, but their core may consist only of organic groups, or is not limited to consisting only of such organic groups, and may also contain inorganic materials. When the core of the particles contained in the oil-in-water emulsion composition of this embodiment contains inorganic materials, one example is to bond or associate a polymer containing hydrophobic monomer units to the surface of the inorganic substance in the core.

[0036] (Cross-linkable monomer) As organic monomer units constituting the core, crosslinkable monomer units may be used. In such embodiments, crosslinkable monomers may be partially used as one of the monomers that prepare the particles contained in the oil-in-water emulsion composition of this embodiment. Specific examples of such crosslinkable monomers include monomers containing two or more ethylenically unsaturated double bonds in the molecule, which are commonly used as crosslinking agents. However, in this embodiment, it is not necessary to use such crosslinkable monomers. If they are used, from the viewpoint of ensuring sufficient storage stability of the particles, their content can be set in a range of typically 0.1% to 20%, preferably 3% to 10%, and more preferably 5%, on a molar basis, relative to the monomers constituting the hydrophobic portion and the monomers constituting the hydrophilic portion, respectively. Specific examples of such crosslinkable monomers include N,N'-methylenebisacrylamide, N,N'-ethylenebisacrylamide, N,N'-methylenebismethacrylamide, N,N'-ethylenebismethacrylamide, ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, and divinylbenzene.

[0037] (Combinations of hydrophobic and hydrophilic parts) The above particles include a polymer having a hydrophobic portion and a hydrophilic portion. In the above particles, from the viewpoint of improving the emulsifying ability of the particles, it is preferable that the surface of the core portion of the particles is hydrophobic, and that part or all of it is directly or indirectly coated with a hydrophilic monomer or its polymer. More specifically, the hydrophobic monomer unit and the hydrophilic monomer unit may be bonded by covalent bonds ("directly coated"), or the hydrophobic monomer unit and the hydrophilic monomer unit may be bonded by intermolecular forces ("indirectly coated").

[0038] Furthermore, when hydrophobic monomer units and hydrophilic monomer units are covalently bonded, the polymer formed by the covalent bond between them may be a block copolymer or a graft copolymer. However, in particular, a graft copolymer is preferable because it provides better storage stability for the particles.

[0039] Furthermore, when hydrophobic monomer units and hydrophilic monomer units are bonded by intermolecular forces, it is preferable that the bonding by intermolecular forces is brought about by heat treatment, from the viewpoint of improving the storage stability of the particles and the emulsifying ability of the particles. Examples of heat treatment in this case include heat treatment at a temperature of 20°C to 100°C, more specifically, at a temperature of 30°C to 80°C for 30 minutes to 480 minutes.

[0040] Furthermore, the above-mentioned particles are not limited to particles in which hydrophobic monomer units and hydrophilic monomer units are bonded only by covalent bonds or only by intermolecular forces. Some hydrophobic monomer units may be bonded to hydrophilic monomer units by covalent bonds, while the remaining hydrophobic monomer units are bonded to hydrophilic monomer units by intermolecular forces. From the viewpoint of ensuring good emulsifying ability of the particles, the proportion of hydrophobic monomer units bonded to hydrophilic monomer units is preferably 10% to 90%, more preferably 30% to 70%, and even more preferably 40% to 60% of the total hydrophobic monomer units bonded to hydrophilic monomer units.

[0041] In the embodiments described above, from the viewpoint of improving the emulsification stability and degree of emulsification of the oil-in-water emulsion composition of this embodiment, the ratio of hydrophobic and hydrophilic portions is preferably such that the amount of the hydrophilic portion is 1 to 6 parts by mass, and more preferably 3 to 4 parts by mass, relative to 100 parts by mass of the hydrophobic portion.

[0042] (Cumulant average diameter) The average cumulant diameter of the above-mentioned particles is calculated by measuring the intensity of scattered light from particles undergoing Brownian motion in the dispersion medium in a dispersion containing the particles, and observing the temporal variation of that intensity (dynamic light scattering method). In this embodiment, the average cumulant diameter of the particles is preferably 100 nm to 500 nm, and more preferably 150 nm to 450 nm, from the viewpoint of improving the storage stability of the particles, improving the emulsifying ability of the particles, and improving the emulsification stability of the emulsified composition.

[0043] [(b) Hydrophobized metal oxide fine particles] The oil-in-water emulsion composition of this embodiment contains hydrophobically treated fine metal oxide particles. These hydrophobically treated fine metal oxide particles are added for the purpose of scattering or shielding ultraviolet rays, and their surfaces are made hydrophobically treated by surface treatment (coating) with fatty acids, silicones, etc. Examples of metal oxides that can be used for the hydrophobically treated fine metal oxide particles include titanium dioxide, zinc oxide, cerium oxide, zirconium oxide, etc., but among these, titanium dioxide and zinc oxide are particularly preferred. The type of hydrophobizing agent is not limited, but examples include fatty acids, higher fatty acids, higher alcohols, hydrocarbons, triglycerides, esters, silicone oils, silicone resins, fluorine compounds, acyl amino acids, etc. In the oil-in-water emulsion composition of this embodiment, the hydrophobically treated fine metal oxide particles may be a commercially available paste-type product in which the metal oxide is stably formed into lower-order particles in a volatile silicone substrate. Examples of commercially available paste-type products include "FLT-01" (titanium dioxide, aluminum hydroxide, hydrated silica, dimethicone, hydrogen dimethicone, trimethylsiloxysilicate, cyclopentasiloxane) from Teika Co., Ltd., "SA-UT-A40 / D5 (50%) MiBrid Dispersion" (titanium dioxide, aluminum hydroxide, stearic acid, dimethicone, cyclopentasiloxane) from Miyoshi Chemicals Co., Ltd., "MiyoSCREEN UT-01 / D5" (titanium dioxide, aluminum hydroxide, stearic acid, dimethicone, cyclopentasiloxane) from Miyoshi Chemicals Co., Ltd., and "MiyoSCREEN UZ-01 / D5" (zinc oxide, dimethicone, methicone, myristic acid, cyclopentasiloxane) from Miyoshi Chemicals Co., Ltd. The content of hydrophobically treated fine metal oxide particles in the oil-in-water emulsion composition of this embodiment is preferably 1% to 30% by mass, and more preferably 5% to 25% by mass, depending on the target SPF value. By having a hydrophobically treated fine metal oxide particle content within the above range, the oil-in-water emulsion composition of this embodiment can be configured as a sunscreen cosmetic having a suitable SPF.

[0044] [(c) Oils] The oil-in-water emulsion composition of this embodiment contains an oil. The oil content in the oil-in-water emulsion composition of this embodiment is preferably 35% to 70% by mass, more preferably 40% to 65% by mass, and even more preferably 45% to 60% by mass. By keeping the oil content within the above range, it is possible to maintain sufficient emulsion stability while also providing a good feel for the oil-in-water emulsion composition. The oil is not particularly limited in terms of properties or type, as long as it is commonly used in cosmetics, etc., but from the viewpoint of emulsion stability and usability, it is preferable that it be one or more selected from hydrocarbon oils, silicone oils, and ester oils.

[0045] [Other additives] The oil-in-water emulsion composition of this embodiment may contain, as an optional component, various additives commonly used for the intended use, in addition to various active ingredients (for example, cosmetic active ingredients; such as whitening agents, cell activators, anti-inflammatory agents, blood circulation promoters, skin astringents, and anti-seborrheic agents) which may be added as needed depending on the intended use of the composition, to the extent that they do not impair the objective of the present invention. Examples of such additives include antioxidants, rust inhibitors, gelling agents, dispersants, thickeners, alcohols, ethers, pH adjusters, stabilizers, bactericides, fungicides, preservatives, colorants, chelating agents, humectants, pearlescent agents, fragrances, and UV absorbers.

[0046] <Method for manufacturing particles> The method for producing the particles used in the oil-in-water emulsion composition of this embodiment is not particularly limited, and includes methods such as polymerizing the hydrophobic monomer and the hydrophilic monomer separately or sequentially (i.e., polymerizing the hydrophilic monomer separately from the hydrophobic monomer; or polymerizing the hydrophilic monomer after the polymerization of the hydrophobic monomer is complete) to form particles. The method for producing the particles is not particularly limited, but for example, it may have the particle formation step shown below and may include a modification step or other steps.

[0047] [(1) Particulate process] The above particle formation process is not particularly limited, but examples include emulsion polymerization, suspension polymerization, dispersion polymerization, etc., which involve polymerizing monomer components such as hydrophobic monomers while forming particles. It is preferable that the polymerization reaction is carried out in the presence of an emulsifier. Alternatively, the above particle formation process may involve polymerizing the monomer components by solution polymerization, etc., and then forming the resulting reaction product into particles by phase inversion emulsification, suspension polymerization, etc.

[0048] However, from the viewpoint of reducing the complexity of manufacturing, a process of atomizing monomer components while polymerizing them is preferred, with emulsion polymerization, suspension polymerization, or dispersion polymerization being more preferred, and emulsion polymerization being even more preferred. Furthermore, among emulsion polymerization methods, it is preferable to adopt a soap-free emulsion polymerization method from the viewpoint that impurities such as emulsifiers do not mix into the surface of the hydrophobic core and do not affect subsequent modification steps described below. The specific method for implementing this soap-free emulsion polymerization method is not particularly limited and can be carried out by known methods. For example, it can be carried out by emulsion polymerization of monomer components in the presence of a polymerization initiator without using emulsifiers such as surfactants, polymer emulsifiers, or reactive surfactants.

[0049] The solvent used in the particle formation process is not particularly limited, but examples include aqueous media. The aqueous media used in the particle formation process may contain water or alcohol from the viewpoint of improving the storage stability of the particles. The reaction temperature when carrying out the particle formation process is preferably set to a temperature below the boiling point of the solvent.

[0050] [(2) Modification process] In the above modification step, for example, part or all of the surface of the hydrophobic portion is directly or indirectly coated with a hydrophilic monomer or a polymer of the hydrophilic monomer. Alternatively, in the above modification step, for example, polymerized hydrophobic monomer and polymerized hydrophilic monomer are bonded or associated.

[0051] Examples of directly coating the surface of the hydrophobic portion with the hydrophilic monomer, etc. include a method of covalently bonding hydrophobic monomer units present on the surface of the hydrophobic portion with the hydrophilic monomer units, more specifically, a method of covalently bonding atomic groups derived from a polymer of the hydrophilic monomer to atomic groups derived from hydrophobic monomer units present on the surface of the core portion, or a method of covalently bonding vinyl acetate, which is a hydrophilic monomer, to atomic groups derived from hydrophobic monomer units present on the surface of the core portion, further polymerizing vinyl acetate, and then saponifying the polyvinyl acetate portion by ester hydrolysis to form a hydrophilic portion. However, from the viewpoint of improving emulsification ability, it is preferable to adopt a method of covalently bonding a polymer containing the hydrophilic monomer units to atomic groups derived from hydrophobic monomer units present on the surface of the core portion as a method of directly coating the surface of the hydrophobic portion with the hydrophilic monomer, etc., and it is more preferable that the polymer containing the hydrophilic monomer units is polyvinyl alcohol, and it is even more preferable that the covalent bond is a carbon-carbon covalent bond formed by a radical reaction using a radical polymerization initiator.

[0052] One way in which the surface of the hydrophobic portion is indirectly coated with the hydrophilic monomer, etc., is to cause the atomic groups contained in the hydrophobic monomer units present on the surface of the core portion (hydrophobic portion) to interact with the atomic groups contained in the hydrophilic monomer units by intermolecular forces, electrochemical interactions, etc. In this case, since the hydrophobic portion and the hydrophilic portion will interact as a result, any functional groups or atomic groups may be introduced into the hydrophobic portion and / or the hydrophilic portion to facilitate the interaction between the two. As a method for causing the atomic groups contained in the hydrophobic monomer units present on the surface of the hydrophobic portion and the atomic groups contained in the hydrophilic monomer units to interact by intermolecular forces, electrochemical interactions, etc., it is preferable to (1) add a polymer containing the hydrophilic monomer units to the particles obtained in the particle formation step, and introduce any functional groups or atomic groups as necessary, while appropriately setting the temperature, pressure, concentration conditions of the mixture, etc., and it is more preferable to heat, pressurize, or concentrate the mixture.

[0053] [Other processes] The above-described method for producing particles may include other steps in addition to (1) particle formation and (2) modification. The "other steps" to be added are not particularly limited, but include washing, concentration, and drying steps. For example, the washing, concentration, and drying steps may be incorporated into at least one of the steps of (1) particle formation and (2) modification, or they may be independent of the steps of (1) particle formation and (2) modification (temporarily or spatially).

[0054] The above particle manufacturing method preferably includes a washing step in order to reduce the irritancy of the composition containing the resulting particles. The medium used in the washing step is not particularly limited, and an aqueous medium can be used. For example, if the reaction solvent used in the particle formation step is an aqueous medium, the washing step can be carried out by repeating the operation of settling the particles by centrifugation, removing the supernatant, and then adding the aqueous medium to redisperse them. Alternatively, if the reaction solvent used in the particle formation step is an organic solvent, the washing step may be carried out by mixing an aqueous medium to which a salt such as brine has been added with the reaction solvent, stirring, and separating the aqueous phase from the organic phase using a separatory funnel or the like. By including a washing step in the above particle manufacturing method, the amount of unreacted radical polymerization initiators, their decomposition products, and unreacted monomers remaining in the medium can be reduced (for example, their concentrations can be reduced to less than 100 ppm).

[0055] The above-mentioned method for producing particles preferably includes a concentration step to increase the concentration of particles in the composition, from the viewpoint of fully exhibiting the emulsifying ability of the particles. Although not particularly limited, this concentration step may be carried out by centrifugation to settle the particles, removing the supernatant, and then redispersing by adding a medium in a quantity smaller than the mass and / or volume of the removed supernatant, or by drying the particles into a powder and then redispersing by adding a medium in a quantity smaller than the mass and / or volume of the medium removed by drying.

[0056] Furthermore, the method for producing the particles preferably includes a drying step to bring the particles into a powder state. This drying step can be carried out by evaporating and drying the medium containing the particles. The specific methods used in the drying step are not particularly limited and include hot air drying, infrared drying, fluidized bed drying, spray drying, freeze drying, reduced pressure drying, and vacuum drying.

[0057] The above-described method for producing particles may consist of only one particle formation step, but it may also be a multi-step method that includes other steps in addition to the particle formation step.

[0058] If the method for producing the above-mentioned particles consists of only one particle formation step, it is preferable to configure the surface of the core portion of the particles to be hydrophobic by appropriately modifying the hydrophobic portion during the particle formation step, and to directly or indirectly coat a part or all of the surface of the core portion with a hydrophilic monomer or the like.

[0059] When the above-mentioned particle manufacturing method is a multi-step method including a particle formation step, it is preferable to use a two-step method including (1) a particle formation step and (2) a modification step, from the viewpoint of improving the storage stability of the particles and ensuring sufficient emulsifying ability by the particles. Furthermore, when the above-mentioned particle manufacturing method is a multi-step method including a particle formation step, it may also be a three-step or more method including one or more other steps, but the order of each step is not important, and each step may be repeated multiple times. When the above-mentioned particle manufacturing method is a two-step or more method including (1) a particle formation step and (2) a modification step, it is preferable to form a hydrophobic part (core part) in the (1) particle formation step, and to directly or indirectly coat a part or all of the surface of the hydrophobic part (core part) with a hydrophilic monomer or the like in the (2) modification step.

[0060] More specific methods for producing the particles are disclosed in detail in the following examples.

[0061] <Method for producing oil-in-water emulsion composition> In the production of the oil-in-water emulsion composition of this embodiment, the oil phase component and the aqueous phase component are mixed and dissolved separately, and then emulsified and mixed while stirring using a stirring and mixing device such as a homomixer. For more specific details on the production method, please refer to the description in the examples. [Examples]

[0062] The present invention will be described in detail below with reference to examples. The following examples are provided for illustrative purposes only, and the content of the present invention is not limited in any way to these examples.

[0063] <Production Example 1; Synthesis of PMMA-PVA Dispersion 1> 42 g of methyl methacrylate (MMA) was added to a 300 mL baffled separable flask, and 166 g of argon-purified water (purified with Elix Essential UV [Merck Millipore]; hereinafter sometimes simply referred to as "Elix water"; the resistivity of Elix water is 5 MΩ·cm or higher) was added. The mixture was heated to 80°C while stirring at 450 rpm using a sealed stirrer (UZ-SM1, Nakamura Scientific Instruments Co., Ltd.) and a mantle heater. As a cationic radical polymerization initiator, 0.36 g of ADIP (hereinafter referred to as ADIP-Cl), whose counteranion is a chloride ion, was dissolved in 2 g of Elix water and the entire amount was added. After stirring for 6 hours, a PMMA dispersion was obtained.

[0064] In a 300 mL baffled separable flask, the above PMMA dispersion was added to a final solid content mass of 30 g. Then, 15 g of polyvinyl alcohol (saponification degree: 86% to 89%, degree of polymerization: 500) was added, and Elix water was added to bring the total mass to 198 g. The solution was then heated to 60°C while stirring at a stirring speed of 450 rpm. Next, 0.20 g of ADIP-Cl was dissolved in 2 g of Elix water and the entire amount was added. The mixture was stirred at 60°C and a stirring speed of 450 rpm for 3 hours to obtain PMMA-PVA dispersion 1.

[0065] <Experimental Example 1: Preparation of Oil-in-Water Emulsion Composition> According to the formulations shown in Table 1A (values ​​are in mass%), PMMA-PVA dispersion 1, Elix water, and 1,3-butylene glycol (BG) were uniformly mixed as aqueous components to obtain an aqueous phase composition. Separately, according to the formulations shown in Table 1A, hydrophobic treated fine particle titanium dioxide dispersion (product name: MiyoSCREEN UT-01 / D5, manufactured by Miyoshi Chemical Co., Ltd.) and cyclopentasiloxane (product name: KF-995, manufactured by Shin-Etsu Chemical Co., Ltd.) were uniformly mixed to obtain an oil phase composition. Subsequently, the oil phase composition was added to the aqueous phase composition and stirred at room temperature in a homomixer at 4,500 rpm for 1 minute. Observation of the properties and appearance 1 minute after the end of stirring confirmed that no phase separation was observed and that emulsification had occurred.

[0066] <Comparative Experiment Examples 1 and 2> As shown in Table 1B, oil-in-water emulsion compositions for Comparative Experimental Example 1 or 2 were prepared in the same manner as in Experimental Example 1, except that the PMMA-PVA dispersion 1 was replaced with 0.5% by mass or 1.0% by mass of polyvinyl alcohol (product name: Gosenol EG-05C, saponification degree 86.5% to 89.0%, manufactured by Mitsubishi Chemical Corporation), and the amount of Elix water added was 19.5% by mass or 19.0% by mass, respectively.

[0067] <Experimental Examples 2 and 3, and Comparative Experimental Example 3> Except for changing the amounts of each component as shown in Table 1C, oil-in-water emulsion compositions for Experimental Examples 2 and 3, and Comparative Experimental Example 3 were prepared in the same manner as in Experimental Example 1.

[0068] <Comparative Experiment Examples 4 to 6> As shown in Table 1D, the oil-in-water emulsion compositions for comparative experimental examples 4 to 6 were prepared in the same manner as in experimental examples 1 to 3, except that 1.0% by mass of silylated silica (AEROSIL VPNX200, manufactured by Nippon Aerosil Co., Ltd.) was used instead of PMMA-PVA dispersion 1, and the amount of Elix water added was 19.0% by mass for each.

[0069] <Rating> The oil-in-water emulsion compositions prepared in Experimental Examples 1 to 3 and Comparative Experimental Examples 1 to 6 were evaluated for initial viscosity, viscosity over time, emulsifying properties, emulsion stability, usability, and SPF using the following methods.

[0070] [Initial viscosity and viscosity over time] The obtained oil-in-water emulsion composition was filled into transparent, lightweight 6K glass bottles and stored at 25°C or 50°C. The viscosity on the day of purchase and the following day (25°C only), as well as the viscosity after one week and two weeks, was measured using a B-type viscometer (No. 4 rotor, 12 rpm, 30 seconds, 25°C). The units in the table are mPas.

[0071] [Emulsifying property] The miscibility of the oil and water in the obtained oil-in-water emulsion composition was visually evaluated according to the following criteria. ○; Well emulsified △; There is some oily residue on the surface or a few oil droplets are floating on it. ×; Complete separation or obvious oil droplets present.

[0072] [Emulsification stability] To confirm the emulsion stability of the obtained oil-in-water emulsion composition over time, it was stored at room temperature for two months and at 50°C for one month, and changes in appearance were judged according to the following criteria. In the evaluation criteria below, "separation" refers to the state in which the oil in the emulsion layer has separated after standing. "Solidification" refers to the state in which part or all of the emulsion layer has solidified after standing and has lost its fluidity. Samples that received an "X" for emulsion performance were not evaluated. (Evaluation Criteria) ○: No problem (no separation or solidification) △: Very slight separation or a slight decrease in fluidity and a tendency towards solidification are observed. ×: Either obvious separation or obvious solidification occurs.

[0073] [Usability] Five trained expert panelists applied 0.5g each of the experimental and comparative oil-in-water emulsion compositions to the inner side of their forearms and evaluated the feel of the product after application based on the following criteria. The panelists made their decisions regarding the feel of the product through consensus. Products that received a negative evaluation for emulsification were not evaluated. (Evaluation Criteria) ○; It is not sticky and has a smooth texture. △: Slightly sticky ×; sticky

[0074] [SPF] To confirm the UV shielding effect of the obtained oil-in-water emulsion composition, SPF measurements were performed using an SPF Analyzer UV-2000S (Labsphere) in accordance with ISO 24443. The results are shown in Tables 1A to 1D and Figure 2. Evaluators with an "X" rating for emulsification were not evaluated.

[0075] [Table 1A] [Table 1B] [Table 1C] [Table 1D]

[0076] As is clear from the descriptions in Tables 1A to 1D and Figure 2, the oil-in-water emulsion compositions prepared in Experimental Examples 1 to 3 showed good emulsification properties, emulsion stability, and sensory evaluation, and also exhibited good SPF values ​​of 35 or higher. In contrast, Comparative Experimental Examples 1 and 2 clearly had inferior SPF values ​​compared to Experimental Example 1, and their SPF values ​​were below 35, failing to meet the desired standards. Therefore, it was confirmed that the oil-in-water emulsion compositions prepared in Experimental Examples 1 to 3 exhibited excellent emulsion stability, UV shielding effect, and superior usability without substantially using surfactants as emulsifiers.

[0077] [water resistance] The water resistance of the oil-in-water emulsion compositions prepared in Experimental Example 1 and Comparative Experimental Example 2 was evaluated. Water resistance was assessed by determining the SPF value before the water bath (SPFi), leaving the sample in the water bath for 30 minutes after SPFi measurement, drying the sample, and then measuring the SPF value after the water bath (SPFa / SPFi). A t-test was used to evaluate the statistical significance of the difference. The significance level was set at p<0.01. As shown in Table 2 and Figure 3, Experimental Example 1 demonstrated a higher SPF value retention rate and superior water resistance compared to Comparative Experimental Example 2. While the present invention is not bound by any theory, the good water resistance obtained in the oil-in-water emulsion composition of Experimental Example 1 may be due to the use of solid particles instead of surfactants in the oil-in-water emulsion composition of Example 1.

[0078] [Table 2]

Claims

1. Oil-in-water emulsion composition comprising the components (a) and (b) below; (a) Particles comprising a polymer having a hydrophobic portion having a cationic group containing hydrophobic monomer units, and a hydrophilic portion containing at least a hydrophilic monomer unit represented by the following formula (I), (b) Hydrophobized fine metal oxide particles. 【Chemistry 1】

2. The oil-in-water emulsion composition according to claim 1, wherein the content of the hydrophobized fine metal oxide particles in the oil-in-water emulsion composition is 1% by mass or more and 30% by mass or less.

3. The oil-in-water emulsion composition according to claim 1 or 2, wherein the content of a surfactant as an emulsifier in the oil-in-water emulsion composition is less than 1% by mass.

4. The oil-in-water emulsion composition according to claim 1 or 2, wherein the cationic group is derived from a cationic radical polymerization initiator.

5. The cationic radical polymerization initiator is 2,2'-[diazen-1,2-diylbis(propane-2,2-diyl)]bis(1,3-dimethyl-4,5-dihydro-1H-imidazole-3-ium)=ditrifluoromethanesulfonate (ADIP), 2,2'-[diazen-1,2-diylbis(propane-2,2-diyl)]bis(1,3-dimethyl-4,5-dihydro-1H-imidazole-3-ium)=di The oil-in-water emulsion composition according to claim 4, comprising one or more selected from the group consisting of chloride (ADIP-Cl), 2,2'-azobis(2-methylpropionamidine)dihydrochloride (V-50), 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane] (VA-061).

6. The oil-in-water emulsion composition according to claim 1 or 2, wherein the hydrophilic portion further comprises monomer units represented by the following formula (II), and the ratio of the number of monomer units represented by formula (I) to the total number of monomer units represented by the following formula (II) (degree of saponification) is 70% or more and 99% or less. 【Chemistry 2】

Images