Silicon-oxide-coated zinc oxide particle, dispersion, cosmetic, and method for producing silicon-oxide-coated zinc oxide particle

Abstract

Provided is a silicon-oxide-coated zinc oxide particle comprising a zinc oxide particle and a silicon oxide film that coats the surface of the zinc oxide particle. The thickness of the silicon oxide film is 0.1 nm to 10 nm.

Description

Silicon oxide-coated zinc oxide particles, dispersion, cosmetic, and method for producing silicon oxide-coated zinc oxide particles

[0001] The present invention relates to silicon oxide-coated zinc oxide particles, a dispersion containing the same, a cosmetic composition, and a method for producing the silicon oxide-coated zinc oxide particles. This application claims priority to Japanese Patent Application No. 2024-053465 filed on March 28, 2024, and Japanese Patent Application No. 2024-142998 filed on August 23, 2024, the contents of which are incorporated herein by reference.

[0002] Ultraviolet rays are said to be a cause of not only suntans and sunburns, but also aging and skin cancer. Therefore, ultraviolet screening agents are widely used in the field of cosmetics. Examples of ultraviolet screening agents include organic ultraviolet absorbers such as benzophenone-based, methoxycinnamic acid-based, and dibenzoylmethane-based agents, and inorganic ultraviolet scattering agents such as zinc oxide particles and titanium oxide particles. Zinc oxide particles have photocatalytic activity. For the purpose of suppressing the photocatalytic activity of zinc oxide particles, surface-coated zinc oxide particles, in which the surfaces of zinc oxide particles are coated with a low-activity substance such as silicon oxide or aluminum oxide, are used (see, for example, Patent Documents 1 and 2).

[0003] Water-based cosmetics are less sticky than oil-based cosmetics and offer a lighter feel when used, making them popular in various cosmetic applications, such as sunscreens, emulsions, and creams. However, the use of zinc oxide particles in water-based cosmetics poses challenges unique to water-based cosmetics. Because zinc oxide particles are an oxide of an amphoteric metal, they not only readily dissolve in acids and alkalis, but also dissolve in trace amounts in water, releasing zinc ions. Water-based cosmetics contain organic UV absorbers, water-soluble polymers, and the like. Therefore, when zinc ions are released from zinc oxide particles contained in water-based cosmetics, they react with the organic UV absorbers, water-soluble polymers, and the like, resulting in problems such as reduced cosmetic performance, discoloration, and increased or decreased viscosity. In particular, when zinc oxide particles are used in combination with carbomers, such as carboxyvinyl polymers, which are commonly used as thickeners, the zinc ions eluted from the zinc oxide particles react with the carboxylate groups (COO-) of the carbomer, destroying the gel structure of the carbomer and reducing viscosity. Therefore, in order to suppress the elution of zinc ions, silicon oxide-coated zinc oxide particles have been proposed, in which the surfaces of zinc oxide particles are coated with dense silicon oxide (see, for example, Patent Document 3).

[0004] However, in Patent Document 3, sodium silicate is used to form a dense silicon oxide film, and therefore when sodium silicate is blended into an aqueous cosmetic, there is a problem in that the hydrogen ion exponent (pH) changes, resulting in poor quality stability.

[0005] Therefore, Patent Document 4 proposes zinc oxide particles coated with silicon oxide, in which Na contained in the silicon oxide coating is replaced with at least one element selected from the group consisting of Mg, Ca, and Ba, thereby suppressing the elution of zinc ions and suppressing fluctuations in the hydrogen ion exponent (pH).

[0006] Japanese Patent Application Laid-Open No. 3-183620 Japanese Patent Application Laid-Open No. 11-256133 International Publication No. 2014 / 171322 International Publication No. 2015 / 072499

[0007] In the silicon oxide-coated zinc oxide particles of Patent Documents 3 and 4, a dense silicon oxide coating is formed using sodium silicate and an alkoxysilane to suppress the elution of zinc ions. As a result, the silicon oxide coating is thick. A thick silicon oxide coating reduces the UV-shielding ability of the silicon oxide-coated zinc oxide particles per unit amount. Therefore, in order for a cosmetic to achieve UV-shielding performance, a certain amount or more of silicon oxide-coated zinc oxide particles must be blended into the cosmetic.

[0008] The present invention has been made in view of the above circumstances, and aims to provide silicon oxide-coated zinc oxide particles that suppress the elution of zinc ions and have excellent ultraviolet shielding properties, as well as a dispersion and cosmetic containing the same, and a method for producing the silicon oxide-coated zinc oxide particles.

[0009] The present invention has the following aspects: [1] Silicon oxide-coated zinc oxide particles, comprising zinc oxide particles and a silicon oxide coating coating the surfaces of the zinc oxide particles, wherein the thickness of the silicon oxide coating is 0.1 nm to 10 nm. [2] The silicon oxide-coated zinc oxide particles according to [1], wherein the silicon oxide-coated zinc oxide particles are mixed with pure water to prepare a mixed liquid, and when the silicon oxide-coated zinc oxide particles are mixed so that the silicon oxide content relative to the total mass of the mixed liquid is 10 mass%, the pH of the mixed liquid is 7.0 to 8.4. [3] The silicon oxide-coated zinc oxide particles according to [1] or [2], wherein the difference between the pH of the first mixed solution obtained by mixing the zinc oxide particles before coating with pure water to prepare a first dispersion, and the pH of the second mixed solution obtained by mixing the silicon oxide-coated zinc oxide particles after coating with pure water to prepare a second mixed solution ... ２ / g or more 65m ２ / g or less. [6] Silicon oxide-coated zinc oxide particles according to any one of [1] to [3], having a zinc elution rate of 0.8 mg / L or less. [7] Silicon oxide-coated zinc oxide particles according to any one of [1] to [5], having a sodium content of 10 ppm or less. [8] A dispersion comprising the silicon oxide-coated zinc oxide particles according to any one of [1] to [7] and a dispersion medium. [9] A cosmetic comprising at least one of the silicon oxide-coated zinc oxide particles according to any one of [1] to [7] and the dispersion according to [8].

[10] A method for producing silicon oxide-coated zinc oxide particles according to any one of [1] to [7], comprising: a hydrolysis step of mixing an alkoxysilane, water, and an organic solvent to obtain a hydrolyzed liquid; a mixing step of mixing the hydrolyzed liquid with zinc oxide particles to obtain a mixture; and a heat treatment step of heat-treating the mixture to obtain silicon oxide-coated zinc oxide particles, wherein in the hydrolysis step, the molar ratio of the water to the alkoxysilane is 0.1 or more and 2 or less; in the hydrolysis step, the content of the organic solvent with respect to the total mass of the hydrolyzed liquid is 0.1 mass% or more; and in the mixing step, the mass ratio of the alkoxysilane to the zinc oxide particles is 0.1 or more and 1.5 or less, calculated as oxide.

[0010] According to the present invention, it is possible to provide silicon oxide-coated zinc oxide particles that suppress zinc ion elution and have excellent ultraviolet shielding properties, a method for producing the same, and a dispersion and cosmetic preparation containing the silicon oxide-coated zinc oxide particles.

[0011] 1 is a transmission electron microscope (TEM) image of the silicon oxide-coated zinc oxide particles obtained in Example 1 of the present invention. It is a diagram showing the integrated transmittance of the dispersions (measurement samples) obtained in Examples 1, 2, and 3 of the present invention and Comparative Example 2.

[0012] Preferred embodiments of the silicon oxide-coated zinc oxide particles, dispersion, cosmetic, and method for producing silicon oxide-coated zinc oxide particles of the present invention are described below. Note that these embodiments are specifically described to provide a better understanding of the gist of the invention, and do not limit the present invention unless otherwise specified. The present invention allows for changes, omissions, substitutions, additions, etc. to be made to the numerical values, amounts, materials, types, time, temperature, order, etc., within the scope of the gist.

[0013] [Silicon oxide-coated zinc oxide particles] The silicon oxide-coated zinc oxide particles of this embodiment comprise zinc oxide particles and a silicon oxide coating coating the surfaces of the zinc oxide particles, and the thickness of the silicon oxide coating is 0.1 nm to 10 nm. The silicon oxide-coated zinc oxide particles of this embodiment are preferably prepared by mixing the silicon oxide-coated zinc oxide particles with pure water to prepare a mixed solution, and the pH of the mixed solution is preferably 7.0 to 8.4 when the silicon oxide content of the mixed solution is 10 mass% relative to the total mass of the mixed solution. The silicon oxide-coated zinc oxide particles of this embodiment preferably have a pH difference of ±0.5 or less between the pH of the first mixed solution obtained by mixing the zinc oxide particles before coating with pure water to form a first mixed solution, and the pH of the second mixed solution obtained by mixing the silicon oxide-coated zinc oxide particles after coating with pure water to form a second ..., and the pH of the second mixed solution obtained by mixing the silicon oxide-coated zinc oxide particles after coating with pure water, and the pH of the second mixed solution obtained by mixing the silicon oxide-coated zinc oxide particles after coating with pure water, and the pH of the second mixed solution obtained by mixing the silicon oxide-coated zinc oxide particles after coating with pure water, and the pH of the second mixed solution obtained by mixing the silicon oxide-coated zinc oxide particles after coating with pure water, and the silicon oxide-coated zinc oxide particles after coating with pure water, and the silicon oxide-coated zinc oxide particles after coating with pure water, and the silicon oxide-coated zinc oxide particles after coating with pure water, and the silicon oxide-coated zinc oxide particles after coating with pure water, and the silicon oxide-coated zinc oxide particles ２ / g or more 65m ２ / g or less. The zinc elution rate of the silicon oxide-coated zinc oxide particles of this embodiment is preferably 0.8 mg / L or less. The silicon oxide-coated zinc oxide particles of this embodiment are preferably such that the entire surface of the zinc oxide particles is coated with silicon oxide. In other words, the silicon oxide-coated zinc oxide particles of this embodiment are preferably such that the zinc oxide particles are not exposed on the surface. The silicon oxide-coated zinc oxide particles of this embodiment preferably have a sodium content of 10 ppm or less. When the silicon oxide-coated zinc oxide particles of this embodiment are mixed with water to a concentration of 10% by mass to prepare a mixed solution, the mixed solution preferably has a conductivity of 60 μS / cm or less after standing at 60°C for 24 hours. It is also preferable that the conductivity is 50 μS / cm or less or 25 μS / cm or less. It is also preferable that the difference in conductivity between after 1 hour and after standing for 24 hours is, for example, 40 μS / cm or less or 30 μS / cm or less. The conductivity can be measured, for example, using the method described in the Examples. The silicon oxide-coated zinc oxide particles of this embodiment preferably have a color difference ΔE before and after 360 hours of irradiation with simulated sunlight of no more than 8, more preferably no more than 7, and even more preferably no more than 5. The color difference can be measured, for example, using the method described in the examples.

[0014] The silicon oxide-coated zinc oxide particles of this embodiment are preferably those in which the entire surfaces of the zinc oxide particles are coated with a silicon oxide film having a thickness of 0.1 nm to 10 nm by using the manufacturing method described below, without using sodium silicate. That is, the entire surfaces of the zinc oxide particles can be thinly coated with only alkoxysilane. Therefore, the silicon oxide-coated zinc oxide particles of this embodiment are inhibited from eluting zinc ions from the zinc oxide particles, and have excellent ultraviolet shielding properties.

[0015] (Thickness of silicon oxide coating) The thickness of the silicon oxide coating is 0.1 nm or more and 10 nm or less, preferably 0.3 nm or more and 8 nm or less, and more preferably 0.5 nm or more and 7 nm or less. It may be 0.7 nm or more and 5 nm or less, or 1.0 nm or more and 3.0 nm or less. When the thickness of the silicon oxide coating is within the above range, elution of zinc ions from the zinc oxide particles can be suppressed, and the ultraviolet-shielding ability of the silicon oxide-coated zinc oxide particles can be improved.

[0016] The silicon oxide-coated zinc oxide particles of this embodiment can thinly coat the entire surface of the zinc oxide particles with only alkoxysilane, without using sodium-containing sodium silicate, and therefore can maintain a pH near neutral when mixed with pure water. That is, conventional silicon oxide-coated zinc oxide particles using sodium silicate have residual Na and other elements in the silicon oxide coating, which causes Na ions to elute when mixed with pure water, causing pH fluctuations. However, the silicon oxide-coated zinc oxide particles of this embodiment can suppress zinc ion elute without adding extra ions to the zinc oxide particles before surface treatment, thereby maintaining a pH near neutral. Furthermore, the pH fluctuation when mixed with pure water is small before and after surface treatment. Such silicon oxide-coated zinc oxide particles are inhibited from reacting with other ingredients when incorporated into cosmetics, thereby improving formulation stability and quality stability. The silicon oxide-coated zinc oxide particles of this embodiment preferably do not contain alkali metals such as Na or alkaline earth metals such as Mg, Ca, Ba in the silicon oxide coating, i.e., Na, Mg, Ca, and Ba are preferably below the detection limit when the particles are analyzed with an ICP optical emission spectrometer.

[0017] (Method for Measuring Silicon Oxide Coating Thickness) The thickness of the silicon oxide coating can be measured using, for example, images observed with a transmission electron microscope (TEM). The silicon oxide coating preferably covers the entire surface of the zinc oxide particles without exposing the surface of the zinc oxide particles. When zinc oxide particles are aggregated, the silicon oxide coating preferably covers the entire surface of the aggregated particles without exposing the surface of the aggregated particles. That is, the silicon oxide coating of this embodiment only needs to cover the surface of the zinc oxide particles to an extent that it can prevent the zinc oxide particles from reacting with other components contained in the cosmetic. The thickness of the silicon oxide coating is preferably 0.1 nm to 10 nm at all locations, but may be outside this range at some locations as long as the effects of the present invention are not impaired. Alternatively, the thickness of the silicon oxide coating of this embodiment may be measured at five locations in a TEM image observing the thickness of the silicon oxide coating, and the arithmetic average value of the measured values ​​may be used. The five measurement locations preferably include one thick location, one thin location, and three intermediate thickness locations.

[0018] (Silicon oxide content) The silicon oxide content relative to the total mass (100 mass%) of the silicon oxide-coated zinc oxide particles is preferably 0.05 mass% or more and 23 mass% or less, more preferably 0.1 mass% or more and 21 mass% or less, even more preferably 0.5 mass% or more and 15 mass% or less, particularly preferably 1 mass% or more and 10 mass% or less, and even more preferably 1 mass% or more and 5 mass% or less. It may be 2 mass% or more and 13 mass% or less, or 3 mass% or more and 7 mass% or less, for example. When the silicon oxide content is within the above range, the surface of the zinc oxide particles can be coated with a silicon oxide coating having a thickness of 0.1 nm or more and 10 nm or less. The silicon oxide content in the silicon oxide-coated zinc oxide particles can be measured, for example, by the following measurement method.

[0019] (Method for Measuring Silicon Oxide Content) 0.2 g of the silicon oxide-coated zinc oxide particles was placed in a platinum crucible, and the temperature was gradually increased to 700°C in an electric furnace to incinerate the silicon oxide-coated zinc oxide particles. 2 g of lithium tetraborate was added to the incinerated sample, and the sample was melted by heating to 925°C in an electric furnace. The melted sample was then placed in a 100 mL tall beaker along with the platinum crucible. 70 mL of warm water and 8 mL of nitric acid were then added to the tall beaker, and the contents of the tall beaker were heated and stirred with a hot stirrer to dissolve the sample and obtain a solution. This solution was transferred to a 200 mL measuring flask and adjusted to a constant volume, and this was used as the test solution. A Y standard solution was added to this test solution as an internal standard substance to achieve a Y concentration of 1000 ppm. A calibration curve was created using elemental standard solutions of known concentrations. The elemental standard solution used to create the calibration curve also contained Y as an internal standard substance, lithium tetraborate, and nitric acid, so that the concentrations were the same as those of the test solution. The test solution is analyzed by an ICP emission spectrometer, the Si content is determined by a calibration curve method, and the silicon oxide content is calculated.

[0020] (Specific Surface Area of ​​Zinc Oxide Particles Coated with Silicon Oxide) The specific surface area of ​​the zinc oxide particles coated with silicon oxide of this embodiment can be selected arbitrarily. ２ / g or more, and 2.5m ２ / g or more is more preferable, and 4m ２ The specific surface area of ​​the silicon oxide-coated zinc oxide particles is preferably 65 m / g or more. ２ / g or less, and ２ / g or less, and ２ If necessary, the specific surface area of ​​the silicon oxide-coated zinc oxide particles is 45 m / g or less. ２ / g or less, ２ / g or less, ２ The upper and lower limits of the specific surface area of ​​the silicon oxide-coated zinc oxide particles can be arbitrarily combined. ２ / g or more 65m ２If the viscosity is 1 / g or less, the transparency and ultraviolet shielding properties will be excellent when blended into a cosmetic.

[0021] When it is desired to increase the transparency when blended in a cosmetic, the specific surface area of ​​the silicon oxide coated zinc oxide particles is set to 8 m ２ / g or more, and ２ / g or more is more preferable, and 20m ２ For example, the specific surface area of ​​the silicon oxide coated zinc oxide particles is 20 m / g or more. ２ / g or more 65m ２ / g or less, and ２ / g or more 60m ２ / g or less is more preferable, and 20m ２ / g or more 55m ２ It is more preferable that the specific surface area of ​​the silicon oxide-coated zinc oxide particles is 20 m / g or less. ２ / g or more 30m ２ / g or less, 20m ２ / g or more 38m ２ / g or less, 20m ２ / g or more 50m ２ / g or less. When the specific surface area of ​​the silicon oxide-coated zinc oxide particles is equal to or greater than the above lower limit, a cosmetic having excellent transparency can be obtained when the silicon oxide-coated zinc oxide particles are blended into a cosmetic. On the other hand, when the specific surface area of ​​the silicon oxide-coated zinc oxide particles is equal to or less than the above upper limit, the surface energy of the particles is not too high, and the silicon oxide-coated zinc oxide particles can be blended into a cosmetic with little energy.

[0022] On the other hand, when it is desired to enhance the ultraviolet ray shielding property in the UVA region when blended in a cosmetic, the specific surface area of ​​the silicon oxide coated zinc oxide particles is 20 m ２ / g, and preferably less than 15m ２ / g or less is more preferable, and ２ For example, the specific surface area of ​​the silicon oxide coated zinc oxide particles is 1.5 m / g or less. ２ / g or more 20m ２ / g, and preferably less than 1.5m ２ / g or more 15m ２ / g, more preferably less than 1.5m ２ / g or more 8m ２ / g. When the specific surface area of ​​the silicon oxide-coated zinc oxide particles is equal to or greater than the above lower limit, a cosmetic having transparency can be obtained when the silicon oxide-coated zinc oxide particles are blended into a cosmetic. On the other hand, when the specific surface area of ​​the silicon oxide-coated zinc oxide particles is less than the above upper limit, the surface energy of the particles is not too large, so that the silicon oxide-coated zinc oxide particles can be blended into a cosmetic with little energy, and a cosmetic having excellent ultraviolet ray shielding properties in the UVA region can be obtained.

[0023] (Method for measuring specific surface area) The specific surface area (unit: m) of the silicon oxide-coated zinc oxide particles was measured. ２ / g) refers to the BET specific surface area determined by the BET method. Examples of a method for measuring the specific surface area of ​​silicon oxide-coated zinc oxide particles include the BET method using a fully automatic specific surface area measuring device (for example, Macsorb HM Model-1201, product name, manufactured by Mountech Co., Ltd.).

[0024] (Na Content) The silicon oxide-coated zinc oxide particles of this embodiment preferably do not use sodium silicate as a material for forming the silicon oxide film. That is, the sodium (Na) content in the silicon oxide-coated zinc oxide particles of this embodiment is preferably 500 ppm or less, more preferably 200 ppm or less, even more preferably 150 ppm or less, even more preferably 90 ppm or less, even more preferably 30 ppm or less, particularly preferably 10 ppm or less, and most preferably an amount below the detection limit (less than 10 ppm). When the Na content in the silicon oxide-coated zinc oxide particles is within the above range, when the silicon oxide-coated zinc oxide particles are blended into an aqueous cosmetic, fluctuations in the pH and viscosity of the aqueous cosmetic can be preferably suppressed.

[0025] (Method for Measuring Na Content) The Na content in the silicon oxide-coated zinc oxide particles can be measured, for example, by ICP atomic emission spectroscopy (ICP-AES). Specifically, the Na content can be measured, for example, as follows. A measurement solution to be measured by ICP atomic emission spectroscopy is prepared in the following manner. 0.02 g of a sample (silicon oxide-coated zinc oxide particles) and an alkaline flux (lithium tetraborate) are added to a platinum crucible, and the mixture is heated and melted in a melting apparatus, for example, a high-frequency melting apparatus (TK-4100, manufactured by Tokyo Scientific Co., Ltd.). After allowing to cool, hydrochloric acid is added to dissolve the mixture, and the volume is adjusted to 100 mL to prepare a measurement solution. This measurement solution is analyzed using an ICP optical emission spectrometer, for example an ICP optical emission spectrometer (Shimadzu Corporation, ICPE-9820), under conditions of RF power 1.2 kW, plasma gas 14 L / min, auxiliary gas 1.2 L / min, and carrier gas 0.70 L / min, in qualitative / semi-quantitative mode using a single-point calibration method, with observations made in the axial direction. This method allows the Na content in the silicon oxide-coated zinc oxide particles to be measured. The alkaline flux may be lithium metaborate, or both lithium metaborate and lithium tetraborate may be used.

[0026] (Viscosity of aqueous cosmetic) When mixed with an aqueous cosmetic, the silicon oxide-coated zinc oxide particles of this embodiment preferably do not change the viscosity of the aqueous cosmetic. Specifically, when the silicon oxide-coated zinc oxide particles of this embodiment are mixed with an aqueous cosmetic, the change in viscosity of the aqueous cosmetic (B / A), measured using the measurement method described below, is preferably 0.5 or more and 1 or less, and more preferably 0.6 or more and 1 or less. If the change in viscosity is within the above range, changes in the properties of the cosmetic can be suppressed when mixed with an aqueous cosmetic.

[0027] (Method for measuring changes in viscosity of aqueous cosmetics) 1.5 g of a carbomer such as a carboxyvinyl polymer, for example, Carbomer Ultrez 10 (manufactured by Lubrizol Advanced Materials), 985 g of pure water, and 6.2 g of 10% aqueous sodium hydroxide solution are mixed to prepare a carbomer gel. The viscosity value A of the prepared carbomer gel immediately after preparation and 24 hours later is measured using a viscometer, for example, a BII-type viscometer (manufactured by Toki Sangyo Co., Ltd.), at 20°C and 30 rpm. 95 g of the immediately prepared carbomer gel and 5 g of the silicon oxide-coated zinc oxide particles of this embodiment are gently mixed, for example, with a dropper, so as not to destroy the structure of the carbomer gel. Next, the viscosity value B of the carbomer gel immediately after mixing and 24 hours later is measured using the viscometer at 20°C and 30 rpm. The obtained viscosity value B is divided by the value A to calculate B / A.

[0028] (UV-Shielding Property (Difference in Integrated Transmittance)) The silicon oxide-coated zinc oxide particles of this embodiment preferably have high UV-shielding property. Specifically, the difference between the integrated transmittance at a wavelength of 550 nm and the integrated transmittance at a wavelength of 360 nm, measured by the following measurement method ((integral transmittance at a wavelength of 550 nm) - (integral transmittance at a wavelength of 360 nm)), is preferably 35% or more, more preferably 40% or more, and even more preferably 50% or more. It is also preferably 60% or more or 70% or more. A high integrated transmittance at a wavelength of 550 nm results in high transparency. A low integrated transmittance at a wavelength of 360 nm results in high UV-shielding property. Therefore, the larger the difference between the integrated transmittance at a wavelength of 550 nm and the integrated transmittance at a wavelength of 360 nm, the higher the transparency and the UV-shielding property. Note that the integrated transmittance means the transmittance measured using an integrating sphere.

[0029] (Method for Measuring Integrated Transmittance) 1 part by mass of the silicon oxide-coated zinc oxide particles of this embodiment is mixed with 99 parts by mass of pure water to obtain a first mixture, and ultrasonic waves are applied to this first mixture for 10 minutes, for example, in the explosive cleaning mode (superimposed 24 kHz and 31 kHz) of a tabletop ultrasonic cleaner (manufactured by Honda Electronics Co., Ltd., model number: Dual Frequency Explosive Cleaning W-113MK2). 0.02 parts by mass of the ultrasonically treated first mixture is mixed with 99.98 parts by mass of pure water to obtain a second mixture, and the transmittance of this second mixture at wavelengths of 300 nm to 800 nm is measured using an integrating sphere, for example, a spectrophotometer (manufactured by Jasco, V-770). From the measured transmittance, the difference between the integrated transmittance at a wavelength of 550 nm and the integrated transmittance at a wavelength of 360 nm is calculated.

[0030] (Zinc elution rate) The zinc elution rate of the silicon oxide-coated zinc oxide particles of this embodiment is preferably 0.8 mg / L or less, more preferably 0.7 mg / L or less, and even more preferably 0.6 mg / L or less. The zinc elution rate can be measured, for example, by the following measurement method.

[0031] (Method for Measuring Zinc Leaching Rate) 10 kg of pure water, 0.657 g of sodium bicarbonate, 0.0575 g of potassium chloride, 2.94 g of calcium chloride dihydrate, and 1.23 g of magnesium sulfate heptahydrate are mixed to obtain a first mixture. This first mixture is stirred at 200 rpm for 30 minutes to prepare an eluate. 1000 g of this eluate is mixed with 0.1 g of the silicon oxide-coated zinc oxide particles of this embodiment to obtain a second mixture. This second mixture is stirred at room temperature (25°C) at 200 rpm with a stirring blade for 24 hours. Next, the stirred second mixture is filtered through a filter with a pore size smaller than the particles, for example, a filter (manufactured by Advantec Co., Ltd., polyethersulfone, pore size 0.2 μm).

[0032] Add 40 mL of the resulting filtrate, 1 mL of concentrated nitric acid, and 50 μL of yttrium standard solution (internal standard) to a volumetric flask, and then add ultrapure water to a final volume of 50 mL to prepare a test solution. A calibration curve is created using an elemental standard solution of known concentration (approximately 40 mL of ultrapure water, 1 mL of concentrated nitric acid, 250 μL of zinc standard solution, 50 μL of yttrium standard solution, and add ultrapure water to a final volume of 50 mL). The test solution is measured using an ICP optical emission spectrometer, for example, an ICP optical emission spectrometer (trade name: ICP-AES 700-ES, manufactured by Varian), to determine the amount of zinc contained in the test solution, i.e., the amount of zinc eluted into the eluate.

[0033] (Zinc Oxide Particles) The specific surface area of ​​the zinc oxide particles (before being coated with silicon oxide) in this embodiment can be selected arbitrarily, but is preferably 1.5 m ２ / g or more, and 2.5m ２ / g or more is more preferable, and 4m ２ It is more preferable that the specific surface area of ​​the zinc oxide particles is 8 m / g or more. ２ / g or more, and ２ The specific surface area of ​​the zinc oxide particles may be 65 m / g or more. ２ / g or less, and ２ / g or less. If necessary, the specific surface area of ​​the zinc oxide particles is 50 m ２ / g or less, ２ / g or less, ２ / g or less, and ２ / g or less, ２ / g or less. The specific surface area of ​​zinc oxide particles before being coated with silicon oxide and the specific surface area of ​​zinc oxide particles coated with silicon oxide vary somewhat depending on the method of coating with silicon oxide, but do not change significantly. Therefore, in order to obtain zinc oxide particles coated with silicon oxide with a desired specific surface area, zinc oxide particles having a desired specific surface area can be used. That is, the zinc oxide particles coated with silicon oxide of this embodiment can preferably have the same value and range as the preferred specific surface area value and range of the zinc oxide particles described above.

[0034] [Method for Producing Silicon Oxide-Coated Zinc Oxide Particles] The method for producing silicon oxide-coated zinc oxide particles of this embodiment is the same as the method for producing silicon oxide-coated zinc oxide particles of the above embodiment, but includes a hydrolysis step of mixing an alkoxysilane, water, and an organic solvent to obtain a hydrolyzed solution, a mixing step of mixing the hydrolyzed solution with zinc oxide particles to obtain a mixture, and a heat treatment step of heat-treating the mixture to obtain silicon oxide-coated zinc oxide particles. In the hydrolysis step, the molar ratio of water to alkoxysilane is 0.1 to 2, the content of the organic solvent relative to the total mass of the hydrolyzed solution is 0.1 mass% or more, and the mass ratio of alkoxysilane to zinc oxide particles is 0.1 to 1.5, calculated as oxide, in the mixing step. In the hydrolysis step, the water includes the amount of water adsorbed on the zinc oxide particles. Therefore, if the molar ratio of water to alkoxysilane is 0.1 or more due to the water adsorbed on the zinc oxide particles alone, it is not necessary to add water. The hydrolysis step and the mixing step may be performed separately or simultaneously. That is, the mixture may be obtained by mixing an alkoxysilane, water, an organic solvent, and zinc oxide particles. When the hydrolysis step and the mixing step are performed simultaneously, water or an organic solvent does not need to be added.

[0035] The silicon oxide-coated zinc oxide particles of this embodiment are obtained by mixing zinc oxide particles with a hydrolyzed solution of an alkoxysilane in a mass ratio of the alkoxysilane to the zinc oxide particles of 0.1 or more and 1.5 or less in terms of oxide, followed by heat treatment. ２The mass ratio is defined as the ratio of alkoxysilane to zinc oxide particles (ZnO). In the method for producing silicon oxide-coated zinc oxide particles of this embodiment, a hydrolysis solution in a state where the hydrolysis solution has been hydrolyzed to a certain extent is mixed with zinc oxide particles so that the amount of alkoxysilane exceeds the amount of silicon oxide required for the intended film thickness. Subsequently, heat treatment is performed, thereby enabling the entire surface of the zinc oxide particles to be coated solely with alkoxysilane, which can form a dense silicon oxide coating. In other words, in the past, the entire surface of zinc oxide particles could not be uniformly coated with alkoxysilane unless a silicon oxide coating was formed using a material containing an alkali metal, such as sodium silicate. However, the present inventors have found that the above-mentioned production method allows the formation of a uniform silicon oxide coating on the surface of zinc oxide particles using only alkoxysilane. The production method of this embodiment allows production without using a material containing an alkali metal. The silicon oxide-coated zinc oxide particles obtained by this production method have zinc oxide particles uniformly coated with a silicon oxide coating, thereby suppressing zinc elution. Furthermore, since the silicon oxide coating is thin, at 1 nm to 10 nm, the amount of zinc oxide in the silicon oxide-coated zinc oxide particles increases relatively, resulting in excellent ultraviolet blocking properties. Each step is explained below.

[0036] In the hydrolysis step of the present embodiment, a hydrolyzed solution is obtained by mixing an alkoxysilane, water, and an organic solvent. The molar ratio of the water to the alkoxysilane is 0.1 to 2, and the content of the organic solvent relative to the total mass of the hydrolyzed solution is 0.1 mass% or more.

[0037] The alkoxysilane is not particularly limited as long as it can form a dense silicon oxide coating on the surface of zinc oxide particles, but tetraalkoxysilane is preferred. The alkoxysilane may be a monomer or an oligomer of 10 or less. From the viewpoint of preventing the hydrolysis process of the alkoxysilane from proceeding too far, the alkoxysilane is preferably a monomer. This tetraalkoxysilane is represented by the following general formula (1): Si(OR) ４(1) Here, OR is an alkoxyl group (RO group), and these four alkoxyl groups (RO groups) may all be the same, or some or all may be different. These alkoxyl groups preferably have 1 to 8 carbon atoms.

[0038] Examples of such tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetraisopropoxysilane, tetra-n-butoxysilane, tetraisobutoxysilane, tetra-sec-butoxysilane, tetra-t-butoxysilane, tetraphenoxysilane, monoethoxytrimethoxysilane, monobutoxytrimethoxysilane, monopentoxytrimethoxysilane, monohexoxytrimethoxysilane, dimethoxydiethoxysilane, and dimethoxydibutoxysilane. Among these, tetramethoxysilane and tetraethoxysilane are preferred because they have a high Si content, are easy to control the concentration when dispersed in a solvent, and have high hydrolysis and condensation reactivity. These tetraalkoxysilanes may be used alone or in combination of two or more.

[0039] The above-mentioned tetraalkoxysilane oligomers having a molecular weight of 10 or less can be obtained by adding water to one or more tetraalkoxysilane monomers as described above and subjecting them to a certain degree of hydrolysis and condensation. Such tetraalkoxysilane oligomers are commercially available as MKC Silicate MS51 (manufactured by Mitsubishi Chemical Corporation), Methyl Silicate 51 (average tetramer, manufactured by Coalcoat Co.), Methyl Silicate 53A (average heptamer, manufactured by Coalcoat Co.), Ethyl Silicate 40 (average pentamer, manufactured by Coalcoat Co.), Ethyl Silicate 48 (average decamer, manufactured by Coalcoat Co.), etc.

[0040] The alkoxysilane is preferably contained in the hydrolyzed liquid in an amount of 70% by mass to 90% by mass. By containing the alkoxysilane in this range, the hydrolyzed liquid containing a high concentration of alkoxysilane can be mixed with the zinc oxide particles in the mixing step. That is, the coating reaction can proceed in a state where excess alkoxysilane is present on the surfaces of the zinc oxide particles.

[0041] The water may be added in an amount necessary to hydrolyze the alkoxysilane to a certain extent, and the molar ratio of the water to the alkoxysilane is 0.1 or more and 2 or less. By having the molar ratio of the water to the alkoxysilane in the above range, the alkoxysilane can be hydrolyzed appropriately. The molar ratio may be 0.3 or more and 1.5 or 0.5 or more and 1.0 or less, as necessary.

[0042] The organic solvent is mixed to adjust the concentration of alkoxysilane in the hydrolysis solution. Therefore, the organic solvent is not particularly limited, as long as it can be mixed with the hydrolysis solution and does not excessively inhibit or excessively promote the hydrolysis reaction. From the viewpoint of reacting alkoxysilane at a high concentration, it is preferable that the amount of organic solvent added is small or zero. Suitable examples of such organic solvents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and octanol; esters such as ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and γ-butyrolactone; and ethers such as diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether. Suitable organic solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; and amides such as dimethylformamide, N,N-dimethylacetoacetamide, and N-methylpyrrolidone. These solvents may be used alone or in combination of two or more. Alcohols are preferred because of their ease of handling.

[0043] The content of the organic solvent relative to the total mass of the hydrolyzed liquid is preferably 0.1% by mass to 25% by mass, more preferably 0.5% by mass to 23% by mass, even more preferably 1% by mass to 20% by mass, and particularly preferably 5% by mass to 10% by mass. By having the content of the organic solvent within this range, the content of the alkoxysilane relative to the total mass of the hydrolyzed liquid can be made sufficient.

[0044] The hydrolysis solution may contain a catalyst or general additive that promotes the hydrolysis reaction or polycondensation reaction, provided that the purpose of the present invention is not impaired. Known acid catalysts or basic catalysts can be used as the catalyst. Examples of the acid catalyst include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; and organic acids such as formic acid, acetic acid, oxalic acid, lactic acid, and tartaric acid. Among these, inorganic acids, particularly hydrochloric acid, are preferred. The acid catalysts may be used alone or in combination of two or more. Examples of the basic catalyst include sodium hydroxide, potassium hydroxide, lithium hydroxide, cerium hydroxide, barium hydroxide, calcium hydroxide, pyridine, pyrrole, piperazine, pyrrolidine, piperidine, picoline, ammonia, methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, monoethanolamine, diethanolamine, dimethylmonoethanolamine, monomethyldiethanolamine, triethanolamine, diazabicyclooctane, diazabicyclononane, diazabicycloundecene, urea, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, and choline. Among these, ammonia, organic amines, and ammonium hydroxides are preferably used. These basic catalysts may be used alone or in combination of two or more. These catalysts may be either acid catalysts or basic catalysts, but acid catalysts, which are catalysts for electrophilic reactions, are preferably used. From the viewpoint of suppressing pH fluctuations, it is preferable that the silicon oxide-coated zinc oxide particles do not contain impurities. Therefore, catalysts and general additives do not need to be used in the hydrolysis process, etc. Alternatively, when catalysts and general additives are used, a washing process may be appropriately performed after the heat treatment process or the crushing process, which will be described later.

[0045] In the hydrolysis step, the temperature at which the alkoxysilane, water, and organic solvent are mixed is preferably 0° C. to 60° C., more preferably 20° C. to 40° C., and even more preferably 20° C. to 38° C. In the hydrolysis step, the time for mixing the alkoxysilane, water, and organic solvent is not particularly limited as long as the above components are mixed, and may be, for example, 1 minute to 24 hours.

[0046] (Mixing Step) In the mixing step of this embodiment, the hydrolysis solution and the zinc oxide particles are mixed so that the mass ratio of the alkoxysilane to the zinc oxide particles is 0.1 or more and 1.5 or less, calculated as oxide. The mass ratio of the alkoxysilane to the zinc oxide particles is preferably 0.2 or more and 1.3 or less, and more preferably 0.2 or more and 1.1 or less, calculated as oxide. By mixing the alkoxysilane and the zinc oxide particles in the above ratio, a silicon oxide coating having a thickness of 1 nm to 10 nm can be formed on the entire surface of the zinc oxide particles.

[0047] In the mixing step, the temperature at which the alkoxysilane and the zinc oxide particles are mixed is preferably 0°C to 60°C, more preferably 20°C to 40°C, and even more preferably 20°C to 38°C, from the viewpoint of preventing the hydrolysis reaction or condensation polymerization reaction from proceeding too far. The time for mixing the alkoxysilane and the zinc oxide particles in the mixing step is not particularly limited as long as the hydrolysis solution and the zinc oxide particles are mixed, and may be, for example, 1 minute to 24 hours. Any mixing device may be selected.

[0048] After the mixing, the resulting mixture may be subjected to solid-liquid separation by atmospheric filtration, reduced pressure filtration, pressure filtration, centrifugation, or the like to obtain a solid mixture.

[0049] (Heat Treatment Step) In the heat treatment step of this embodiment, the mixture obtained in the mixing step is heat-treated to promote the condensation reaction of the alkoxysilane, thereby forming a silicon oxide coating on the surface of the zinc oxide particles.

[0050] The temperature at which the mixture obtained in the mixing step is heat-treated (heat treatment temperature) is not particularly limited, as long as a silicon oxide coating dense enough to suppress zinc elution is formed on the surface of the zinc oxide particles. For example, the temperature may be 200°C or higher and 550°C or lower, 250°C or higher and 500°C or lower, or 300°C or higher and 500°C or lower. It may also be 230°C or higher and 480°C or lower, or 350°C or higher and 430°C or lower. The heat treatment temperature within the above range promotes densification of the silicon oxide coating, while suppressing coarsening of the zinc oxide particles and aggregation of the silicon oxide-coated zinc oxide particles. The time for which the mixture obtained in the mixing step is heat-treated (heat treatment time) may be, for example, 30 minutes or higher and 5 hours or lower. The heat treatment time within the above range allows a silicon oxide coating to be formed on the surface of the zinc oxide particles, and aggregation of the silicon oxide-coated zinc oxide particles to be suppressed.

[0051] (Crushing step) The silicon oxide-coated zinc oxide particles after the heat treatment may be crushed using a crusher. Any crusher can be selected, and examples thereof include an atomizer, a hammer mill, a jet mill, an impeller mill, and a pin mill. The crushing step can, for example, suppress the rough feeling of the silicon oxide-coated zinc oxide particles when blended into a cosmetic. In other words, the feel when the silicon oxide-coated zinc oxide particles are used in a cosmetic can be improved.

[0052] The silicon oxide-coated zinc oxide particles of this embodiment are obtained by the above-mentioned crushing step.

[0053] [Dispersion] The dispersion of the present embodiment contains the silicon oxide-coated zinc oxide particles of the present embodiment and a dispersion medium. Examples of the dispersion of the present embodiment also include a paste-like dispersion with high viscosity.

[0054] The content of the silicon oxide-coated zinc oxide particles relative to the total mass of the dispersion of this embodiment is not particularly limited and can be selected as desired, but is, for example, preferably 10% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 85% by mass or less, and even more preferably 30% by mass or more and 80% by mass or less. If the content of the silicon oxide-coated zinc oxide particles in the dispersion is within the above range, the desirable properties of the silicon oxide-coated zinc oxide particles can be obtained, and an increase in the viscosity of the dispersion over time can be suppressed.

[0055] The dispersion medium is appropriately selected depending on the application of the dispersion liquid. Suitable dispersion media are exemplified below, but the dispersion medium in this embodiment is not limited to these. The following dispersion media may be used alone or in combination from the examples below. Examples of dispersion media include alcohols such as water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, octanol, and glycerin; esters such as ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and γ-butyrolactone; and ethers such as diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether; and these are preferably used. These dispersion media may be used alone or in combination of two or more.

[0056] Other suitable dispersion media include, for example, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; cyclic hydrocarbons such as cyclohexane; amides such as dimethylformamide, N,N-dimethylacetoacetamide, and N-methylpyrrolidone; and chain polysiloxanes such as dimethylpolysiloxane, methylphenylpolysiloxane, and diphenylpolysiloxane. These dispersion media may be used alone or in combination of two or more.

[0057] Further, other suitable dispersion media include cyclic polysiloxanes such as octamethylcyclotetrasiloxane, cyclopentasiloxane, and dodecamethylcyclohexasiloxane; and modified polysiloxanes such as amino-modified polysiloxane, polyether-modified polysiloxane, alkyl-modified polysiloxane, and fluorine-modified polysiloxane. These dispersion media may be used alone or in combination of two or more.

[0058] Other dispersion media different from those mentioned above also include hydrophobic dispersion media such as hydrocarbon oils such as liquid paraffin, squalane, isoparaffin, branched-chain light paraffin, petrolatum, and ceresin, ester oils such as isopropyl myristate, cetyl isooctanoate, and glyceryl trioctanoate, silicone oils such as cyclopentasiloxane, dimethylpolysiloxane, and methylphenylpolysiloxane, higher fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid, and higher alcohols such as lauryl alcohol, cetyl alcohol, stearyl alcohol, hexyldodecanol, and isostearyl alcohol. These dispersion media may be used alone or in combination of two or more.

[0059] The dispersion of this embodiment may contain commonly used additives to the extent that the properties of the dispersion are not impaired. Examples of additives include dispersants, surfactants, stabilizers, water-soluble binders, thickeners, oil-soluble preservatives, UV absorbers, oil-soluble drugs, oil-soluble dyes, oil-soluble proteins, vegetable oils, and animal oils. These additives may be contained in any amount selected.

[0060] The dispersion of this embodiment can be an aqueous dispersion containing the silicon oxide-coated zinc oxide particles of this embodiment and an aqueous dispersion containing water.The aqueous dispersion of this embodiment may contain additives generally used in aqueous cosmetics, such as surfactants, dispersants, stabilizers, water-soluble binders, thickeners, alcohols, chelating agents, and solvents, as necessary.For example, as a pH stabilizer, ethylenediaminetetraacetic acid (EDTA) may be contained in an amount of 0.01% by mass or more and 1.0% by mass or less relative to the total mass of the aqueous dispersion.In addition, the aqueous dispersion of this embodiment may contain a nonionic surfactant.

[0061] The method for producing the dispersion of this embodiment is not particularly limited, but examples thereof include a method in which the silicon oxide-coated zinc oxide particles of this embodiment and a dispersion medium are mechanically dispersed using a known dispersion device, such as a stirrer, a planetary mixer, a homomixer, an ultrasonic homogenizer, a sand mill, a ball mill, or a roll mill.

[0062] The dispersion of this embodiment can be preferably used in aqueous cosmetics as well as paints having ultraviolet blocking properties, gas permeation inhibiting properties, and the like.

[0063] [Composition] The composition of the present embodiment contains the silicon oxide-coated zinc oxide particles of the present embodiment and a resin. Alternatively, the composition of the present embodiment contains the dispersion of the present embodiment and a resin.

[0064] The content of the silicon oxide-coated zinc oxide particles relative to the total mass of the composition of this embodiment may be appropriately adjusted according to the desired properties. The content of the silicon oxide-coated zinc oxide particles may be selected arbitrarily, but is preferably, for example, 10% by mass or more and 40% by mass or less, more preferably 15% by mass or more and 35% by mass or less, and even more preferably 20% by mass or more and 30% by mass or less. By having the content of the silicon oxide-coated zinc oxide particles relative to the total mass of the composition within the above range, the properties of the silicon oxide-coated zinc oxide particles can be obtained, and the increase in viscosity of the paint over time can be suppressed.

[0065] The resin is not particularly limited as long as it is one that is commonly used in industrial applications, and examples thereof include acrylic resin, epoxy resin, urethane resin, polyester resin, silicone resin, water-soluble polymer, etc. The content of the resin in the composition of the present embodiment is not particularly limited and is adjusted appropriately depending on the properties of the intended composition.

[0066] The composition of the present embodiment may contain commonly used additives, such as a polymerization initiator, a dispersant, and a preservative, as long as the additives do not impair the properties of the composition.

[0067] The composition of the present embodiment can be an aqueous composition containing at least one of the silicon oxide-coated zinc oxide particles of the present embodiment and the aqueous dispersion of the present embodiment, and a water-soluble polymer.

[0068] The water-soluble polymer is preferably a water-soluble vinyl polymer. The water-soluble vinyl polymer is not particularly limited as long as it is one that can be used in cosmetics, as described below, and examples thereof include carboxyvinyl polymers, alkyl-modified carboxyvinyl polymers, and alkyl acrylate / methacrylic acid / polyoxyethylene copolymers. These water-soluble vinyl polymers may be used alone or in combination of two or more.

[0069] Examples of carboxyvinyl polymers include those known under the trade names Carbopol® 940, Carbopol® 941, Carbopol® 980, Carbopol® 981, and Carbopol® Ultrez 10 (all manufactured by Lubrizol Advanced Materials).

[0070] Examples of alkyl-modified carboxyvinyl polymers include those known under the trade names Carbopol (registered trademark) 1342, PEMULEN (registered trademark) TR-1, and PEMULEN (registered trademark) TR-2 (all manufactured by Lubrizol Advanced Materials).

[0071] Examples of alkyl acrylate / methacrylic acid / polyoxyethylene copolymers include (acrylates / steareth-20 methacrylate) copolymer, (acrylates / beheneth-25 methacrylate) copolymer, and (acrylates / steareth-20 methacrylate) crosspolymer. Furthermore, commercially available products of Rohm & Haas Co., Inc., such as Accurylin (registered trademark) 22, Accurylin (registered trademark) 28, and Accurylin (registered trademark) 88, may also be used as alkyl acrylate / methacrylic acid / polyoxyethylene copolymers.

[0072] In the aqueous composition of this embodiment, the content of the water-soluble vinyl polymer relative to 100 parts by mass of the silicon oxide-coated zinc oxide particles can be selected as desired, but is preferably from 0.02 to 6.0 parts by mass, more preferably from 0.05 to 5.0 parts by mass, and even more preferably from 0.1 to 4.5 parts by mass. If the content of the water-soluble vinyl polymer relative to 100 parts by mass of the silicon oxide-coated zinc oxide particles is from 0.02 to 6.0 parts by mass, the effect of improving the UV blocking ability is likely to be obtained even when the composition is applied to an aqueous cosmetic composition, which is preferable.

[0073] Furthermore, in the aqueous composition of the present embodiment, the content of the water-soluble vinyl polymer is preferably 0.02% by mass or more and 6.0% by mass or less, more preferably 0.05% by mass or more and 5.0% by mass or less, and even more preferably 0.1% by mass or more and 4.5% by mass or less.

[0074] In the aqueous composition of this embodiment, the aqueous dispersion of this embodiment preferably contains silicon oxide-coated zinc oxide particles in an amount of 1% by mass or more and 80% by mass or less, more preferably 5% by mass or more and 70% by mass or less, even more preferably 10% by mass or more and 70% by mass or less, and even more preferably 20% by mass or more and 65% by mass or less.

[0075] The aqueous composition of this embodiment preferably contains an alcohol in order to improve the dispersibility of the water-soluble vinyl polymer and the silicon oxide-coated zinc oxide particles in water.

[0076] In the aqueous composition of this embodiment, the content of alcohols relative to 100 parts by mass of silicon oxide-coated zinc oxide particles is preferably 10 parts by mass or more and 100 parts by mass or less, and more preferably 20 parts by mass or more and 50 parts by mass or less. If the content of alcohols relative to 100 parts by mass of silicon oxide-coated zinc oxide particles is 10 parts by mass or more, the dispersibility of the silicon oxide-coated zinc oxide particles can be further improved. On the other hand, if the content of alcohols relative to 100 parts by mass of silicon oxide-coated zinc oxide particles is 100 parts by mass or less, stickiness and deterioration of the feel can be suppressed when an aqueous composition containing silicon oxide-coated zinc oxide particles is incorporated into a cosmetic.

[0077] The content of alcohols relative to the total mass of the aqueous composition of this embodiment is preferably 0.1% by mass to 30% by mass, more preferably 0.3% by mass to 25% by mass, and even more preferably 0.5% by mass to 20% by mass, and may be 1.0% by mass to 15% by mass, or 5% by mass to 10% by mass, for example.

[0078] The alcohol is not particularly limited as long as it can be used in cosmetics, and examples of the alcohol that can be used include monohydric alcohols or polyhydric alcohols having 1 to 6 carbon atoms, such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, octanol, glycerin, 1,3-butylene glycol, propylene glycol, sorbitol, etc. Among these alcohols, glycerin is preferred because it is widely used in cosmetics to improve the feel of cosmetics and to provide moisturizing effects.

[0079] The aqueous composition of the present embodiment may contain additives generally used in aqueous cosmetics, such as dispersants, stabilizers, water-soluble binders, thickeners, alcohols, chelating agents, and solvents, as needed.

[0080] In the aqueous composition of this embodiment, the content of water, including the water contained in the aqueous dispersion, relative to the total mass of the aqueous composition is preferably 10% by mass or more and 99% by mass or less, more preferably 20% by mass or more and 95% by mass or less, and even more preferably 40% by mass or more and 94% by mass or less. Note that in the aqueous composition of this embodiment, the total content of each component is 100% by mass, and the total content of each component will not exceed 100% by mass.

[0081] The method for producing the composition of the present embodiment is not particularly limited, but examples thereof include a method in which the silicon oxide-coated zinc oxide particles of the present embodiment and a resin are mechanically mixed using a known mixing device. Also, examples thereof include a method in which the dispersion and a resin are mechanically mixed using a known mixing device. Examples of mixing devices include a stirrer, a planetary mixer, a homomixer, and an ultrasonic homogenizer.

[0082] A coating film can be formed by applying the composition of the present embodiment to a plastic substrate such as a polyester film by a common coating method such as roll coating, flow coating, spray coating, screen printing, brush coating, dipping, etc. These coating films can be used as ultraviolet screening films or gas barrier films.

[0083] [Cosmetics] A cosmetic according to one embodiment of the present invention contains at least one selected from the group consisting of the silicon oxide-coated zinc oxide particles of this embodiment, the dispersion of this embodiment, and the composition of this embodiment. Another embodiment of the present invention contains a base and, dispersed in the base, at least one selected from the group consisting of the silicon oxide-coated zinc oxide particles of this embodiment, the dispersion of this embodiment, and the composition of this embodiment. The cosmetic according to this embodiment can be obtained, for example, by blending at least one selected from the group consisting of the silicon oxide-coated zinc oxide particles of this embodiment, the dispersion of this embodiment, and the composition of this embodiment into a base such as a lotion, cream, foundation, lipstick, blusher, or eye shadow in a conventional manner. The cosmetic according to this embodiment may also be obtained by blending the silicon oxide-coated zinc oxide particles of this embodiment into an oil phase or an aqueous phase to form an O / W or W / O emulsion, and then blending the emulsion with a base.

[0084] The base is not particularly limited as long as it can be used as a base for cosmetics. The base refers to raw materials that are the main components of cosmetics. Examples of the base include oil-based raw materials, aqueous raw materials, surfactants, powder raw materials, etc. The oil-based raw materials can be selected arbitrarily, and examples thereof include fats and oils, higher fatty acids, higher alcohols, ester oils, etc.

[0085] The aqueous raw material can be selected arbitrarily, and examples thereof include purified water, alcohol, thickeners, etc. The powder raw material can be selected arbitrarily, and examples thereof include colored pigments, white pigments, pearlescent agents, extender pigments, etc.

[0086] The sunscreen cosmetic will be specifically described below.

[0087] The content of the silicon oxide-coated zinc oxide particles relative to the total mass of the sunscreen cosmetic can be selected as desired, but in order to effectively block ultraviolet rays, particularly long-wavelength ultraviolet rays (UVA), it is preferably from 1% by mass to 30% by mass, more preferably from 3% by mass to 20% by mass, and even more preferably from 5% by mass to 15% by mass.

[0088] The sunscreen cosmetic may contain, as necessary, a hydrophobic dispersion medium, inorganic fine particles or inorganic pigments other than the silicon oxide-coated zinc oxide particles, a hydrophobic dispersion medium, a hydrophilic dispersion medium, oils and fats, surfactants, moisturizers, thickeners, pH adjusters, nutrients, antioxidants, fragrances, preservatives, dispersants, antifoaming agents, colorants, cosmetic ingredients, polymeric substances, biologically derived ingredients, plant-derived ingredients, antibacterial agents, bactericides, antifungal agents, aqueous ingredients, oily ingredients, vitamins, emulsifiers, stabilizers, solubilizers, pearlescent agents, refatting substances, and the like. Examples of hydrophobic dispersion media include hydrocarbon oils such as liquid paraffin, squalane, isoparaffin, branched light paraffin, petrolatum, and ceresin; ester oils such as isopropyl myristate, cetyl isooctanoate, and glyceryl trioctanoate; silicone oils such as cyclopentasiloxane, dimethylpolysiloxane, and methylphenylpolysiloxane; higher fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid; and higher alcohols such as lauryl alcohol, cetyl alcohol, stearyl alcohol, hexyldodecanol, and isostearyl alcohol.

[0089] Examples of inorganic fine particles and inorganic pigments other than the silicon oxide-coated zinc oxide particles include calcium carbonate, calcium phosphate (apatite), magnesium carbonate, calcium silicate, magnesium silicate, aluminum silicate, kaolin, talc, titanium oxide, aluminum oxide, yellow iron oxide, γ-iron oxide, cobalt titanate, cobalt violet, and silicon oxide.

[0090] The sunscreen cosmetic may further contain at least one organic ultraviolet absorber. The content of the organic ultraviolet absorber may be adjusted as appropriate to obtain the desired ultraviolet shielding properties. For organic ultraviolet absorbers whose amount that can be incorporated into sunscreen cosmetics is regulated, the upper limit may be adjusted as appropriate in accordance with the regulations of each country. For example, the content of the organic ultraviolet absorber relative to the total mass of the sunscreen cosmetic may be 20% by mass or less, 15% by mass or less, 12% by mass or less, 10% by mass or less, 9% by mass or less, 8% by mass or less, 6% by mass or less, 4% by mass or less, or 3% by mass or less.

[0091] Examples of organic ultraviolet absorbers include benzotriazole-based ultraviolet absorbers, benzoylmethane-based ultraviolet absorbers, benzoic acid-based ultraviolet absorbers, anthranilic acid-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, cinnamic acid-based ultraviolet absorbers, silicone-based ultraviolet absorbers, triazine-based ultraviolet absorbers, imidazole-based ultraviolet absorbers, camphor-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, and other organic ultraviolet absorbers.

[0092] Examples of the benzotriazole-based ultraviolet absorbers include 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, etc. Examples of the benzoylmethane-based ultraviolet absorbers include dibenzalazine, dianisoylmethane, 4-tert-butyl-4'-methoxydibenzoylmethane, 1-(4'-isopropylphenyl)-3-phenylpropane-1,3-dione, 5-(3,3'-dimethyl-2-norbornylidene)-3-pentan-2-one, etc.

[0093] Examples of the benzoic acid-based UV absorbers include para-aminobenzoic acid (PABA), PABA monoglycerin ester, N,N-dipropoxy PABA ethyl ester, N,N-diethoxy PABA ethyl ester, N,N-dimethyl PABA ethyl ester, N,N-dimethyl PABA butyl ester, N,N-dimethyl PABA methyl ester, dimethyl PABA ethylhexyl, and dimethyl PABA amyl. Examples of the anthranilic acid-based UV absorbers include homomenthyl-N-acetylanthranilate. Examples of the salicylic acid-based UV absorbers include amyl salicylate, menthyl salicylate, homomenthyl salicylate, octyl salicylate, phenyl salicylate, benzyl salicylate, p-2-propanol phenyl salicylate, and ethylhexyl salicylate.

[0094] Examples of the cinnamic acid-based ultraviolet absorber include octyl methoxycinnamate, glyceryl di-paramethoxycinnamate-mono-2-ethylhexanoate, octyl cinnamate, ethyl-4-isopropyl cinnamate, methyl diisopropyl cinnamate, ethyl-2,4-diisopropyl cinnamate, methyl-2,4-diisopropyl cinnamate, propyl-p-methoxycinnamate, isopropyl-p-methoxycinnamate, isoamyl-p-methoxycinnamate, and octyl-p-methoxycinnamate. cinnamate (2-ethylhexyl-p-methoxycinnamate), 2-ethoxyethyl-p-methoxycinnamate, cyclohexyl-p-methoxycinnamate, ethyl-α-cyano-β-phenylcinnamate, 2-ethylhexyl-α-cyano-β-phenylcinnamate, glyceryl mono-2-ethylhexanoyl-di-paramethoxycinnamate, ferulic acid, cinoxate, methylbis(trimethylsiloxy)silylisopentyl trimethoxycinnamate, and isopropyl paramethoxycinnamate.

[0095] Examples of the silicone-based ultraviolet absorber include [3-bis(trimethylsiloxy)methylsilyl-1-methylpropyl]-3,4,5-trimethoxycinnamate, [3-bis(trimethylsiloxy)methylsilyl-3-methylpropyl]-3,4,5-trimethoxycinnamate, [3-bis(trimethylsiloxy)methylsilylpropyl]-3,4,5-trimethoxycinnamate, [3-bis(trimethylsiloxy)methylsilylbutyl]-3,4,5-trimethoxycinnamate, [3-tris(trimethylsiloxy)silylbutyl]-3,4,5-trimethoxycinnamate, [3-tris(trimethylsiloxy)silyl-1-methylpropyl]-3,4-dimethoxycinnamate, polysilicone-15, and drometrizole trisiloxane.

[0096] Examples of the triazine-based ultraviolet absorbers include bisethylhexyloxyphenol methoxyphenyl triazine, ethylhexyl triazone, methylene bisbenzotriazolyl tetramethyl butyl phenol, trisbiphenyl triazine, diethylhexyl butamido triazone, etc. Examples of the imidazole-based ultraviolet absorbers include phenyl dibenzimidazole tetrasulfonic acid disodium, phenylbenzimidazole sulfonic acid, dimethoxybenzylidene dioxoimidazolidine ethylhexyl propionate, etc.

[0097] Examples of the camphor-based ultraviolet absorbers include 3-(4'-methylbenzylidene)-d,l-camphor, 3-benzylidene-d,l-camphor, terephthalylidene dicamphorsulfonic acid, camphor benzalkonium methosulfate, benzylidene camphorsulfonic acid, polyacrylamidomethyl benzylidene camphor, etc. Examples of the benzophenone-based ultraviolet absorbers include oxybenzone-1, oxybenzone-2, oxybenzone-3, oxybenzone-4, oxybenzone-5, oxybenzone-6, oxybenzone-7, oxybenzone-8, oxybenzone-9, 4-(2-β-glucopyranosyloxy)propoxy-2-hydroxybenzophenone, etc.

[0098] Examples of organic ultraviolet absorbers other than those mentioned above include urocanic acid, urocanic acid ethyl ester, 2-phenyl-5-methylbenzoxazole, 5-(3,3'-dimethyl-2-norbornylidene)-3-pentan-2-one, diethylaminohydroxybenzoylhexyl benzoate, octocrylene, silicone-modified ultraviolet absorbers, and fluorine-modified ultraviolet absorbers.

[0099] The cosmetic of the present embodiment contains at least one selected from the group consisting of the silicon oxide-coated zinc oxide particles of the present embodiment, the dispersion of the present embodiment, and the composition of the present embodiment, and therefore, zinc elution is suppressed, making it possible to obtain a cosmetic that has excellent UV-shielding properties.

[0100] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0101] [Example 1] (Hydrolysis step) 86.5 parts by mass of tetraethoxysilane (manufactured by Kanto Chemical Co., Inc.), 7.5 parts by mass of water, and 6.0 parts by mass of isopropyl alcohol were mixed and stirred at room temperature for 5 minutes to obtain a hydrolyzed liquid. The molar ratio of tetraethoxysilane to water was 1:1. The obtained hydrolyzed liquid contained 6% by mass of isopropyl alcohol, an organic solvent.

[0102] (Mixing step) 79.9 parts by mass of the obtained hydrolyzed liquid and zinc oxide particles (manufactured by Sumitomo Osaka Cement Co., Ltd., BET specific surface area 40 m ２ That is, the mass ratio of tetraethoxysilane to zinc oxide particles was 1 (SiO ２ :ZnO=1:1).

[0103] (Heat Treatment Step) The resulting mixture was subjected to solid-liquid separation, and the recovered solid portion (silicon oxide-coated zinc oxide particles) was dried at 80° C. for 1 hour. Then, the solid portion was heat-treated at 500° C. for 3 hours. The heat-treated silicon oxide-coated zinc oxide particles were then crushed in a mortar to obtain silicon oxide-coated zinc oxide particles of Example 1.

[0104] (Evaluation of Silicon Oxide Content) 0.2 g of the silicon oxide-coated zinc oxide particles of Example 1 was placed in a platinum crucible, and the temperature was gradually increased to 700°C in an electric furnace to incinerate the zinc oxide particles. 2 g of lithium tetraborate was added to the incinerated sample, which was then heated to 925°C in an electric furnace to melt. The molten sample, including the platinum crucible, was then placed in a 100 mL tall beaker. 70 mL of warm water and 8 mL of nitric acid were then added to the tall beaker, and the mixture was heated and stirred with a hot stirrer to dissolve the sample. This solution was transferred to a 200 mL measuring flask and adjusted to a constant volume, and this was used as a test solution. A Y standard solution was added to this test solution as an internal standard substance to achieve a Y concentration of 1000 ppm. A calibration curve was prepared using elemental standard solutions of known concentrations. The elemental standard solutions used to prepare the calibration curve also contained Y as an internal standard substance, lithium tetraborate, and nitric acid, so that their concentrations were the same as those of the test solution. The test solution was measured using an ICP emission spectrometer, the Si content was quantified using a calibration curve method, and the silicon oxide content was calculated. ２ The content was 20.6 mass %. The results are shown in Table 1.

[0105] (Evaluation of Zinc Leaching Rate) 10 kg of pure water, 0.657 g of sodium bicarbonate, 0.0575 g of potassium chloride, 2.94 g of calcium chloride dihydrate, and 1.23 g of magnesium sulfate heptahydrate were mixed. This mixture was stirred at 200 rpm for 30 minutes to prepare an eluate. 1000 g of this eluate was mixed with 0.1 g of the silicon oxide-coated zinc oxide particles of Example 1. This mixture was stirred at room temperature (25°C) at 200 rpm with a stirring blade for 24 hours. Next, the stirred mixture was filtered through a filter (manufactured by Advantec Co., Ltd., polyethersulfone, pore size 0.2 μm).

[0106] To a volumetric flask, 40 mL of the resulting filtrate, 1 mL of concentrated nitric acid, and 50 μL of yttrium standard solution (internal standard substance) were added, and the mixture was adjusted to 50 mL with ultrapure water to prepare a test solution. A calibration curve was prepared using an analytical device described below, using elemental standard solutions of known concentrations (approximately 40 mL of ultrapure water, 1 mL of concentrated nitric acid, 250 μL of zinc standard solution, 50 μL of yttrium standard solution, and ultrapure water to a final volume of 50 mL). The test solution was measured using an ICP atomic emission spectrometer (product name: ICP-AES 700-ES, manufactured by Varian) to determine the amount of zinc contained in the eluate of Example 1. The zinc elution rate from the silicon oxide-coated zinc oxide particles of Example 1 was 0.48 mg / L. The results are shown in Table 1.

[0107] (Evaluation of Silicon Oxide Coating Thickness) The silicon oxide-coated zinc oxide particles of Example 1 were observed with a transmission electron microscope (TEM) to measure the thickness of the silicon oxide coating. As a result, it was confirmed that the silicon oxide coating of the silicon oxide-coated zinc oxide particles of Example 1 was 1 nm to 5 nm thick, and that the silicon oxide coating coated the zinc oxide particles with a substantially uniform thickness, without exposing the surface of the zinc oxide particles. A TEM image of the silicon oxide-coated zinc oxide particles of Example 1 is shown in Figure 1.

[0108] (Evaluation of sodium content) Using the ICP atomic emission spectroscopy described above in (Method for measuring Na content), the amount of sodium (Na) contained in the silicon oxide-coated zinc oxide particles of Example 1 was measured. As a result, sodium was not detected, being below the detection limit (10 ppm). The results are shown in Table 1.

[0109] (Evaluation of Viscosity Change) Carbomer Ultrez 10 (Lubrizol Advanced Materials) 1.5 g, pure water 985 g, and 10% sodium hydroxide aqueous solution 6.2 g were mixed to prepare a carbomer gel. The viscosity A of the obtained carbomer gel was measured immediately after preparation and 24 hours later using a BII type viscometer (Toki Sangyo Co., Ltd.) at 20 ° C. and 30 rpm.

[0110] 95 g of the resulting carbomer gel and 5 g of the silicon oxide-coated zinc oxide particles of Example 1 were gently mixed with a dropper, taking care not to destroy the structure of the carbomer gel. The viscosity B was measured 24 hours after mixing at 20°C and 30 rpm using the BII type viscometer. The resulting B / A ratio was 0.68. The results are shown in Table 1.

[0111] (pH Evaluation) 10 parts by mass of the silicon oxide-coated zinc oxide particles of Example 1 and 90 parts by mass of pure water were mixed, and ultrasonic waves were applied to this mixture for 10 minutes using a tabletop ultrasonic cleaner (manufactured by Honda Electronics Co., Ltd., model number: Dual Frequency Explosive Cleaning W-113MK2) in explosive cleaning mode (superimposed 24 kHz and 31 kHz). The pH of this mixture was measured using a pH meter (manufactured by HORIBA Co., Ltd., model number: LAQUAact pH meter D-71) 5 days after storage at room temperature from the time of preparation, and the pH was found to be 7.5. The pH of this mixture was measured 15 days after storage at room temperature, and the pH was found to be 7.6. The pH of the zinc oxide particles before surface treatment was measured, and the pH after 5 days was found to be 7.7. The results are shown in Table 1.

[0112] (Evaluation of Electrical Conductivity) Ultrasonic waves were applied for 10 minutes to a mixture obtained by mixing 10 parts by mass of silicon oxide-coated zinc oxide particles and 90 parts by mass of pure water, and the mixture was allowed to stand at 60°C for a predetermined time. The electrical conductivity of the mixture was measured using a conductivity meter. Specifically, 10 parts by mass of the silicon oxide-coated zinc oxide particles of Example 1 and 90 parts by mass of pure water were mixed, and ultrasonic waves were applied to this mixture for 10 minutes using the explosive cleaning mode (superimposed 24 kHz and 31 kHz) of a tabletop ultrasonic cleaner (manufactured by Honda Electronics Co., Ltd., model number: Dual Frequency Explosive Cleaning W-113MK2). This mixture was allowed to stand at 60°C. The electrical conductivity of the mixture was measured 1 hour and 24 hours after standing at 60°C by inserting a conductivity meter (trade name: ES-12, manufactured by Horiba, Ltd.) into the mixture. As a result, the conductivity was 14 μS / cm after 1 hour and 19 μS / cm after 24 hours after being left standing at 60° C. The results are shown in Table 1.

[0113] (Evaluation of UV-shielding property (transmittance)) One part by mass of the silicon oxide-coated zinc oxide particles of Example 1 was mixed with 99 parts by mass of pure water to obtain a first mixed solution, and ultrasonic waves were applied to this first mixed solution for 10 minutes using a desktop ultrasonic cleaner (manufactured by Honda Electronics Co., Ltd., model number: Dual Frequency Explosive Cleaning W-113MK2) in explosive cleaning mode (superimposed 24 kHz and 31 kHz). 0.02 parts by mass of the ultrasonically treated first mixed solution was mixed with 99.98 parts by mass of pure water to obtain a second mixed solution, and the transmittance of this second mixed solution at wavelengths of 300 nm to 800 nm was measured using an integrating sphere on a spectrophotometer (V-770). As a result, the difference between the integrated transmittance at a wavelength of 550 nm and the integrated transmittance at a wavelength of 360 nm ((integrated transmittance at a wavelength of 550 nm) - (integrated transmittance at a wavelength of 360 nm)) was 41.5%. The measurement results are shown in Table 1 and FIG.

[0114] [Example 2] Silicon oxide-coated zinc oxide particles of Example 2 were obtained in the same manner as in Example 1, except that 45.4 parts by mass of zinc oxide particles and 54.6 parts by mass of the hydrolyzed liquid were mixed in the mixing step of Example 1. That is, in the mixing step of Example 2, the mass ratio of tetraethoxysilane to zinc oxide particles was 0.3 (SiO ２ The pH was 7.5 after 5 days and 7.6 after 15 days (ZnO = 0.3:1). The results of evaluation in the same manner as in Example 1 are shown in Table 1 and Figure 2. Measurements in the same manner as in Example 1 showed that the pH was 7.5 after 5 days and 7.6 after 15 days. TEM images confirmed that the silicon oxide coating of the silicon oxide-coated zinc oxide particles of Example 2 had a thickness of 1 nm to 2 nm, and that the silicon oxide coating coated the zinc oxide particles with a substantially uniform thickness, leaving the surface of the zinc oxide particles unexposed.

[0115] (Evaluation of photocatalytic activity) A mixture obtained by mixing 3 g of zinc oxide particles coated with silicon oxide and 3 g of 1,3-butanediol was irradiated with a xenon lamp for 360 hours. １ ＊ , a １ ＊ , b １ ＊ and L after irradiation ２ ＊ , a ２ ＊ , b ２＊ were measured using a spectrophotometer, and the color difference ΔE was calculated using the following formula (1). Specifically, 3 g of the silicon oxide-coated zinc oxide particles of Example 2 and 3 g of 1,3-butanediol were mixed in a 30 mL transparent screw tube. After mixing, the bottom surface of the screw tube was used as the measurement surface, and the L ＊ a ＊ b ＊ In the color system chromaticity diagram, L １ ＊ , a １ ＊ , b １ ＊ Next, the bottom surface of the screw tube was irradiated with simulated sunlight for 360 hours using a xenon lamp in a small light irradiation tester (manufactured by Iwasaki Electric Co., Ltd., model number: EYE SUN-CUBE Xenon). 360 hours of irradiation with simulated sunlight corresponds to 18 hours of irradiation with sunlight. The bottom surface of the screw tube after irradiation was used as the measurement surface, and the L after exposure was measured. ＊ a ＊ b ＊ In the color system chromaticity diagram, L ２ ＊ , a ２ ＊ , b ２ ＊ The color difference ΔE was calculated using the following formula (1): Color difference ΔE=((L ２ ＊ -L １ ＊ ) ２ + (a ２ ＊ -a １ ＊ ) ２ +(b ２ ＊ -b １ ＊ ) ２ ) １／２ ... (1) As a result, ΔE was 6.3. The same evaluation was performed on zinc oxide particles before surface treatment, i.e., particles with a specific surface area of ​​40 m ２ / g of zinc oxide particles. As a result, ΔE was 14.8. From this result, it was confirmed that the photocatalytic activity of the surface-treated zinc oxide particles of Example 2 was suppressed by being coated with silicon oxide.

[0116] [Example 3] In the mixing step of Example 1, a mixture having a BET specific surface area of ​​5 m ２ The silicon oxide-coated zinc oxide particles of Example 3 were obtained in the same manner as in Example 1, except that 55.6 parts by mass of zinc oxide particles having a SiO 2 content of 1 / g were mixed with 44.4 parts by mass of the hydrolysis solution. That is, in the mixing step of Example 3, the mass ratio of tetraethoxysilane to the zinc oxide particles was 0.2 (SiO 2 ) in terms of oxide. ２ The pH was 7.5 after 5 days and 7.6 after 15 days. TEM images confirmed that the silicon oxide coating of the silicon oxide-coated zinc oxide particles of Example 3 was 1 nm to 2 nm thick, and that the silicon oxide coating coated the zinc oxide particles with a substantially uniform thickness, without exposing the surface of the zinc oxide particles. The results of measurements similar to those of Example 1 are shown in Table 1 and FIG. 2.

[0117] The photocatalytic activity of the zinc oxide particles coated with silicon oxide in Example 3 was measured in the same manner as in Example 2, and the result was ΔE=2.3. ２ The photocatalytic activity of the zinc oxide particles at 1000 nm / g was evaluated, and the result was ΔE=3.8. This result confirmed that the photocatalytic activity of the surface-treated zinc oxide particles of Example 3 was suppressed by being coated with silicon oxide.

[0118] Comparative Example 1 Zinc oxide particles (manufactured by Sumitomo Osaka Cement Co., Ltd., BET specific surface area 40 m ２ / g) and water were mixed, followed by ultrasonic dispersion to prepare a zinc oxide aqueous suspension with a zinc oxide content of 10% by mass. Next, an aqueous sodium silicate solution was added to this zinc oxide aqueous suspension so that the content, calculated as silicon oxide, was 21% by mass relative to the zinc oxide particles in the zinc oxide aqueous suspension, and the mixture was vigorously stirred. Next, 1N hydrochloric acid was added to this suspension, the pH of the mixture was adjusted to 7.0, and the mixture was allowed to stand for 2 hours. As a result, silicon oxide gradually precipitated on the surfaces of the zinc oxide particles, forming a coating. Next, the suspension was filtered, and the resulting solid was washed with water and further heated and dried at 105°C in a dryer. Next, the mixture was heat-treated at 500°C for 2 hours to obtain silicon oxide-coated zinc oxide particles of Comparative Example 1. The silicon oxide-coated zinc oxide particles of Comparative Example 1 were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0119] [Comparative Example 2] Zinc oxide particles (manufactured by Sumitomo Osaka Cement Co., Ltd., BET specific surface area 40 m ２ The zinc oxide particles were mixed with water (20% by mass of zinc oxide particles) and ultrasonically dispersed to prepare a suspension containing 20% ​​by mass of zinc oxide particles. This suspension was then added to an aqueous sodium silicate solution containing 5% by mass of silicon oxide based on the mass of the zinc oxide particles in the suspension, and the mixture was vigorously stirred to obtain a mixed solution.

[0120] Next, this mixed solution was heated to 60°C, and dilute hydrochloric acid was gradually added to this mixed solution to adjust the pH to 6.5 to 7. Thereafter, the mixed solution was left to stand for 2 hours, and the solid matter obtained was separated into solid and liquid, and washed with water. This solid matter was dried at 150°C and further subjected to heat treatment (calcination) at 500°C to produce silicon oxide-coated zinc oxide particles X.

[0121] Next, these silicon oxide-coated zinc oxide particles X were mixed with methanol, and the mixture was ultrasonically dispersed to prepare a mixed solution containing 10 mass% silicon oxide-coated zinc oxide particles X. Next, methyl silicate 51 (manufactured by Colcoat Co., Ltd.), methanol, and water were mixed so that the content, calculated as silicon oxide, of the zinc oxide particles in the mixed solution was 30 mass%. Then, 1N hydrochloric acid was added to this mixed solution. The content of silicon oxide-coated zinc oxide particles X in this mixed solution was 5 mass%, and the molar ratio of methyl silicate 51 to pure water and hydrochloric acid was 1:10:0.1.

[0122] Next, this mixed solution was heated to 60°C and maintained at this temperature for 3 hours to allow the reaction to occur. After the reaction, solid-liquid separation was performed by centrifugation, and the resulting solid reaction product was dried at 120°C and then heat-treated at 500°C for 2 hours to obtain silicon oxide-coated zinc oxide particles of Comparative Example 2. The silicon oxide-coated zinc oxide particles of Comparative Example 2 were evaluated in the same manner as in Example 1. The results are shown in Table 1 and Figure 2. Note that the silicon oxide coating was thick in the silicon oxide-coated zinc oxide particles of Comparative Example 2. Measurements were performed in the same manner as in Example 1, and the pH was 9.8 after 5 days and 9.4 after 15 days. The results are shown in Table 1.

[0123]

[0124] In Table 1, a blank (-) indicates that no measurement was performed. As shown in Table 1, when Examples 1 and 2 were compared with Comparative Example 2, the zinc elution rate and viscosity change in Examples 1 and 2 were comparable to or slightly inferior to those in Comparative Example 2, despite the silica coating thickness being thinner than that in Comparative Example 2. Furthermore, a comparison of Example 2 with Comparative Example 2 confirmed that a thinner silica coating increases the content of zinc oxide particles per unit volume in the silicon oxide-coated zinc oxide particles, thereby increasing the difference in integrated transmittance and improving UV screening properties. Furthermore, the results of Examples 2 and 3, in which ΔE was small, confirmed that the photocatalytic activity of the silicon oxide-coated zinc oxide particles of this embodiment was suppressed. Furthermore, a comparison of Examples 1 to 3 with Comparative Examples 1 and 2 confirmed that the low sodium content maintained the pH near neutral, reduced the electrical conductivity, reduced the rate of change in electrical conductivity, and suppressed viscosity change.

[0125] The present invention can provide silicon oxide-coated zinc oxide particles that are inhibited from eluting zinc ions and have excellent ultraviolet shielding properties. The silicon oxide-coated zinc oxide particles of the present invention are of great industrial value when used in aqueous materials because they are inhibited from eluting zinc and have excellent ultraviolet shielding properties.

Claims

1. Silicon oxide-coated zinc oxide particles comprising zinc oxide particles and a silicon oxide coating covering the surfaces of the zinc oxide particles, wherein the thickness of the silicon oxide coating is 0.1 nm or more and 10 nm or less.

2. The silicon oxide-coated zinc oxide particles according to claim 1, wherein the silicon oxide-coated zinc oxide particles are mixed with pure water to form a mixed solution, and when mixed so that the content of the silicon oxide-coated zinc oxide particles relative to the total mass of the mixed solution is 10 mass%, the pH of the mixed solution is 7.0 or more and 8.4 or less.

3. The silicon oxide-coated zinc oxide particles according to claim 1 or 2, wherein the difference between the pH of the first mixed solution obtained by mixing the zinc oxide particles before coating with pure water to form a first mixed solution so that the content of the zinc oxide particles relative to the total mass of the first mixed solution is 10% by mass and the pH of the second mixed solution obtained by mixing the silicon oxide-coated zinc oxide particles after coating with pure water to form a second mixed solution so that the content of the silicon oxide-coated zinc oxide particles relative to the total mass of the second mixed solution is 10% by mass is ±0.5 or less.

4. Silicon oxide-coated zinc oxide particles according to any one of claims 1 to 3, wherein the silicon oxide content is 0.05% by mass or more and 23% by mass or less.

5. The specific surface area of ​​the zinc oxide particles is 1.5 m ２ / g or more 65m ２ The silicon oxide-coated zinc oxide particles according to any one of claims 1 to 4, wherein the surface area of ​​the silicon oxide-coated zinc oxide particles is 1 / g or less.

6. The silicon oxide coated zinc oxide particles according to any one of claims 1 to 5, wherein the zinc elution rate is 0.8 mg / L or less.

7. The silicon oxide-coated zinc oxide particles according to any one of claims 1 to 6, having a sodium content of 10 ppm or less.

8. A dispersion comprising the silicon oxide-coated zinc oxide particles according to any one of claims 1 to 7 and a dispersion medium.

9. A cosmetic comprising at least one of the silicon oxide-coated zinc oxide particles according to any one of claims 1 to 7 and the dispersion according to claim 8.

10. A method for producing silicon oxide-coated zinc oxide particles according to any one of claims 1 to 7, comprising: a hydrolysis step of mixing an alkoxysilane, water, and an organic solvent to obtain a hydrolyzed liquid; a mixing step of mixing the hydrolyzed liquid with zinc oxide particles to obtain a mixture; and a heat treatment step of heat-treating the mixture to obtain silicon oxide-coated zinc oxide particles, wherein in the hydrolysis step, the molar ratio of the water to the alkoxysilane is 0.1 or more and 2 or less; in the hydrolysis step, the content of the organic solvent relative to the total mass of the hydrolyzed liquid is 0.1 mass% or more; and in the mixing step, the mass ratio of the alkoxysilane to the zinc oxide particles, calculated as oxide, is 0.1 or more and 1.5 or less.

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