Coated particles, ultraviolet shielding agent, cosmetic preparation, coating material, and method for producing coated particles

Abstract

With respect to coated particles according to the present invention, at least a part of zinc oxide (ZnO) is covered with a carbonate-type layered double hydroxide (LDH) [M2+ 1-xM3+ x(OH)2](CO3)x / 2·yH2O (M2+ and M3+ are bivalent and trivalent metal ions that are capable of constituting an LDH). The coated particles are obtained by treating ZnO in the presence of hydroxide and carbonate ions of a metal capable of constituting an LDH. The coated particles are suitable for, for example, a coating material having an ultraviolet shielding function, a gas permeation suppressing function or the like in addition to an ultraviolet shielding agent and a cosmetic preparation containing the same.

Description

Coated particles, UV shielding agent, cosmetic, paint, and method for producing coated particles

[0001] The present invention relates to coated particles, ultraviolet shielding agents, cosmetics, paints, and methods for producing coated particles.

[0002] Titanium dioxide is a substance with anatase or rutile structure, and it is used as a UV shielding agent because it absorbs ultraviolet light corresponding to its band gap. Furthermore, transparency can be ensured by controlling the particle size. However, there are concerns that the photocatalytic activity of titanium dioxide may have adverse effects on the skin.

[0003] Zinc oxide (ZnO) is also expected to have UV-blocking properties. ZnO is a hexagonal wurtzite-type structured material with a band gap similar to that of titanium dioxide, thus possessing UV-blocking capabilities. Compared to titanium dioxide, it has a broader absorption range in the UVA region of 320-380 nm, and also exhibits high visible light transmittance and excellent transparency, making it a promising UV-blocking agent for use in sunscreens and cosmetics. However, its leaching into water and adverse effects on the skin remain concerns (see Patent Document 1).

[0004] Regarding elution into water, when ZnO is used in water-based cosmetics, the eluted zinc ions (Zn) may react with water-soluble polymers such as organic UV absorbers and thickeners, potentially leading to problems such as decreased cosmetic performance, discoloration, and changes in viscosity. Therefore, using ZnO in water-based cosmetics has limited the flexibility of formulation.

[0005] In particular, when carbomers such as carboxyvinyl polymers, which are commonly used as thickeners, are used in combination with ZnO, the eluted Zn and the carboxylate group (COO) of the carbomer are released. －The reaction of (the above) destroys the gel structure of carbomer, which causes the problem that the viscosity of cosmetics decreases. Therefore, in order to suppress the elution of Zn, surface-coated ZnO whose surface is coated with an inorganic compound such as silicon oxide has been proposed (see, for example, Patent Documents 2 and 3). It is reported that the silicon oxide film-coated ZnO described in Patent Document 3 can suppress the decrease in viscosity caused by carbomer when applied to aqueous materials.

[0006] Japanese Patent Application Laid-Open No. 2012-207039, Japanese Patent Application Laid-Open No. 2007-16111, WO2016 / 136797

[0007] However, silicon oxide tends to form an amorphous structure under low-temperature synthesis conditions, especially in a solution reaction field that is not in a molten state, it easily forms an aggregate of fine nanoparticles as typified by a silica gel structure. This is a problem caused by the surface energy of silicon oxide in the synthesis field, and it is difficult to form a uniform and dense film in principle. Therefore, even though it appears to cover the ZnO surface at first glance, it is a porous film at the micro level. When it comes into contact with water or a solution, dissolution occurs in the portion that comes into contact with Zn, and Zn elutes to the outside through the voids. Increasing the thickness of the silicon oxide film can substantially suppress this kinetically, but the possibility of Zn elution still cannot be ruled out. Even when carbomer is used for a thickening effect, when applied to an aqueous material, it is possible that the decrease in viscosity caused by carbomer cannot be completely suppressed. In addition, amorphous silicon oxide has increased solubility in water at pH 9 or higher, so its stability cannot be ensured in the alkaline region.

[0008] The present invention has been made in view of such problems. An object of the present invention is to provide carbonate-type LDH film-coated ZnO capable of almost completely suppressing the elution of Zn into water by coating the ZnO surface with a safe and stable carbonate-type layered double hydroxide (LDH), and an ultraviolet shielding agent and a cosmetic containing the carbonate-type LDH film-coated ZnO. Layered double hydroxide LDH has high affinity to ZnO and low surface energy, so it is less prone to nanoparticle formation and the formation of its aggregated structure (porous body) as observed with silicon oxide, and it can be expected to form a uniform and dense protective film on Zn.

[0009] As a result of extensive studies, the present inventors have found that by coating ZnO in the presence of a metal hydroxide capable of constituting LDH and carbonate ions, at least a part of ZnO can be coated with carbonate-type LDH, and the elution amount of Zn into water can be suppressed to 1 / 20 or less compared with that of untreated ZnO, and thus completed the present invention. Specifically, the present invention provides the following.

[0010] The invention according to a first aspect provides coated particles, wherein at least a part of zinc oxide (ZnO) is covered with carbonate-type layered double hydroxide (LDH) [M ２＋ １－ｘ M ３＋ ｘ (OH) ２ (CO ３ ) ｘ／２ ·yH ２ O (M ２＋ and M ３＋ are divalent and trivalent metal ions capable of constituting LDH, respectively).

[0011] The invention according to a second aspect is the invention according to the first aspect, wherein when 200 mg of the coated particles are added to 40 mL of water at 25° C. and subjected to ultrasonic dispersion for 10 minutes, the amount of zinc ions contained in the water after dispersion is 1 / 20 or less of that in the case of untreated ZnO.

[0012] According to the invention according to the first or second aspect, at least a part of ZnO is coated with carbonate-type LDH. As a result, the elution amount of Zn into water can be suppressed to 1 / 20 or less compared with that of untreated ZnO.

[0013] The invention according to a third aspect is the invention according to the first or second aspect, wherein when the coated particles are dispersed in cyclopentasiloxane to a concentration of 15% by mass to form a paste coating film having a thickness of 12 μm, the transmittance of visible light at a wavelength of 450 nm is 80% or more, and the transmittance of long-wavelength ultraviolet light (UVA) at a wavelength of 370 nm is 20% or less.

[0014] The invention according to a fourth aspect is the invention according to any one of the first to third aspects, wherein the M ２＋is one or more divalent metal ions selected from Mg, Ca, Mn, Fe, Co, Ni, Cu, and Zn, and the M ３＋ is one or more trivalent metal ions selected from Al, Cr, Mn, Fe, Co, Ni, Ga, and La.

[0015] Generally, forming a sound shell structure with different materials requires high chemical affinity between the materials, crystal lattice matching, and low surface energy in the solvent. Forming single-crystal films called epitaxy is not easy due to lattice constant mismatch. In such cases, two-dimensional nucleation occurs on the surface of ZnO, and these islands grow. If the mismatch is large, wettability is poor, and in extreme cases, droplet (sphere) precipitation occurs on the particles, resulting in a product that appears as a powdery precipitate or aggregated particle state. If the affinity is high, precipitation occurs in a way that wets the surface, so large islands grow, and ultimately polycrystalline material is formed on the particle surface. In either case, compared to silicon dioxide, LDH is more likely to form homogeneous and dense films from the viewpoints of chemical affinity, crystal mismatch, and surface energy.

[0016] According to the invention relating to the fourth feature, since the ionic radius of M does not differ significantly from the ionic radius of Zn, a mismatch in lattice constants can be prevented, and as a result, polycrystalline material can be formed on the particle surface. Even in this case, compared to silicon oxide film formation, it is less likely to result in minute nanoparticles, thus enabling the formation of a denser film.

[0017] The invention relating to the fifth feature is an ultraviolet shielding agent containing coated particles relating to any of the first to fourth features. The invention relating to the sixth feature is the invention relating to the fifth feature, further containing a carbomer such as a carboxyvinyl polymer. The invention relating to the seventh feature is a cosmetic composition containing the ultraviolet shielding agent relating to the fifth or sixth feature. The invention relating to the eighth feature provides a paint containing the ultraviolet shielding agent relating to the fifth or sixth feature.

[0018] According to the inventions relating to the fifth and sixth features, it is possible to provide an ultraviolet shielding agent that has high ultraviolet shielding ability while minimizing elution into water and impact on the skin. According to the invention relating to the seventh feature, the ultraviolet shielding agent is suitable for cosmetic use due to its high safety. According to the invention relating to the eighth feature, the ultraviolet shielding agent is suitable for paint use because elution into water is suppressed and it has a long service life.

[0019] The invention relating to the ninth feature is a dispersion or slurry containing 20% ​​by mass or more of the ultraviolet shielding agent relating to the fifth or sixth feature of the invention.

[0020] The invention relating to the tenth feature is a method for producing coated particles according to any one of the first to fourth features, comprising the step of coating ZnO in the presence of a metal hydroxide and carbonate ions capable of constituting LDH.

[0021] According to the invention relating to the tenth feature, at least a portion of the ZnO is coated with carbonate-type LDH. As a result, the amount of Zn that dissolves into water can be reduced to less than 1 / 20th compared to the case of untreated ZnO.

[0022] The invention relating to the eleventh feature is the invention relating to the tenth feature, wherein the pH during the coating treatment is 9 or higher and 12 or lower.

[0023] ZnO has high solubility in water, even dissolving at room temperature. Dissolution proceeds particularly well at low pH, but conversely, dissolution is relatively suppressed at high pH.

[0024] Furthermore, it is generally known that LDH is synthesized by a coprecipitation reaction in which a metal source is mixed while maintaining an alkaline pH of around 10 (Miyata, S., Clays Clay Miner. 28, 50-56 (1980)).

[0025] According to the invention relating to the eleventh feature, since the pH is maintained at an alkaline level, the dissolution of ZnO can be suppressed.

[0026] The invention relating to the twelfth feature is the invention relating to the tenth or eleventh feature, wherein the concentration of the raw material ZnO is 0.5 mol / L or higher.

[0027] LDH precipitation occurs in parallel through uniform nucleation in the liquid phase and precipitation on particles. However, the former is proportional to the solution space V, while the latter is proportional to the particle surface area S. Therefore, if the particle concentration is high and the raw material concentration is kept low, precipitation on particles becomes dominant.

[0028] Under conditions where the former is dominant (low particle concentration and / or high precipitate source concentration), uniform nucleation occurs. Therefore, even if it appears to be precipitated on ZnO, it is actually fine particles that have accumulated due to uniform nucleation, resulting in a powdery precipitate on the ZnO particles. In some cases, a porous material may form, in which case, although a coating structure may appear to be formed, similar to porous silicon oxide films, ZnO dissolves in water or solution upon contact, diffuses through the voids of the porous material, and as a result, elution is a concern.

[0029] Under the latter conditions (high particle concentration and low concentration of precipitation raw material), precipitation occurs on the target ZnO particles.

[0030] According to the invention relating to the twelfth feature, at least a portion of the ZnO can be reliably coated with carbonate-type LDH, and as a result, the elution of ZnO can be further suppressed.

[0031] The invention relating to the 13th feature is an invention relating to any of the 10th to 12th features, wherein the temperature during the coating process is 20°C or higher and 40°C or lower.

[0032] ZnO has high solubility in water, dissolving even at room temperature, and dissolution proceeds even further at higher temperatures.

[0033] Furthermore, LDH is generally known to be synthesized by a coprecipitation reaction in which a metal source is mixed at around 40°C (see the non-patent literature by Miyata et al. mentioned above). At higher temperatures, the crystallinity of LDH increases, causing the fine particles produced by uniform nucleation to crystallize, hindering precipitation onto ZnO particles. To form a coating structure on ZnO, temperatures around room temperature are desirable.

[0034] According to the invention relating to the 13th feature, at least a portion of the ZnO can be reliably coated with carbonate-type LDH, and as a result, the elution of ZnO can be further suppressed.

[0035] According to the present invention, a shell structure can be formed on the ZnO surface using safe and stable carbonate-type LDH.

[0036] Figure 1 shows the FT-IR spectra of ZnO used in Test Example 1 and sample A obtained from Example 1. Figure 2 shows the XRD patterns of ZnO used in Test Example 1 and samples A and B obtained from Example 1 and Comparative Example 1. Figure 3 shows the scanning electron microscope (SEM) image of ZnO used in Test Example 1. Figure 4 shows the SEM image of sample A obtained from Example 1. Figure 5 shows the SEM image of sample A obtained from Example 1 and the mapping results of the EDX analysis. Figure 6 shows the X-ray photoelectron spectroscopy (XPS) spectra of ZnO used in Test Example 1 and samples A and B obtained from Example 1 and Comparative Example 1. Figure 7 shows the ultraviolet-visible diffuse reflectance spectra of ZnO used in Test Example 1 and sample A obtained from Example 1. Figure 8 shows the results of a simple water elution test using "Pack Test Zinc" of ZnO used in Test Example 1 and sample A obtained from Example 1.

[0037] The following describes specific embodiments of the present invention in detail. However, the present invention is not limited in any way to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0038] <Method for producing coated particles> The coated particles of the present invention have at least a portion of ZnO that is [M ２＋ １－ｘ M ３＋ ｘ (OH) ２ ] (CO ３ ) ｘ／２ ・yH ２ O(M) ２＋ and M ３＋The particles are covered with divalent and trivalent metal ions capable of forming layered double hydroxides (LDHs). The coated particles are obtained by coating ZnO in the presence of LDH-forming metal hydroxides and carbonate ions.

[0039] [Coating Process] [Raw Materials] The raw materials are ZnO and divalent metal ions M capable of forming LDH. ２＋ and trivalent metal ions M ３＋ And so it is.

[0040] (ZnO) The ZnO concentration when performing the coating treatment is preferably 0.5 mol / L or higher, and more preferably 1 mol / L or higher.

[0041] LDH precipitation occurs in parallel through uniform nucleation in the liquid phase and precipitation on particles. However, the former is proportional to the solution space V, while the latter is proportional to the particle surface area S. Therefore, at high particle concentrations, precipitation on particles becomes dominant.

[0042] Under conditions where the former is dominant (low particle concentration and / or high raw material concentration), uniform nucleation occurs in the raw material to be coated. As a result, a powdery precipitate-like state forms on the ZnO particles. In some cases, a porous structure may form, in which case, although a coating structure appears to be formed at first glance, there is a concern about elution from ZnO.

[0043] Under the latter conditions (high particle concentration and low raw material concentration), precipitation occurs on the target ZnO particles.

[0044] As long as the coating material concentration remains constant, there is no particular upper limit to the ZnO concentration C. However, caution is required when precipitating while maintaining a constant coating thickness. Increasing the particle concentration increases the surface area (and thus the precipitation rate), but the increased total ZnOx coating amount leads to a larger charging M concentration, which increases the uniform nucleation rate. Under conditions where the precipitation material concentration M is relatively low, the increase in precipitation rate and uniform nucleation rate compensate for each other, and as S increases, the void V decreases, so there is no problem. However, in regions where M is high, uniform nucleation may increase rapidly, so caution is required. In that case, from the viewpoint of preventing excess ZnO from remaining, the ZnO concentration is preferably 10 mol / L or less, and more preferably 5 mol / L or less.

[0045] (Divalent metal ions M that can constitute LDH) ２＋ and trivalent metal ions M ３＋ ) M ２＋ and M ３＋ Any M can be used, but one with a lattice constant close to that of ZnO is preferable. It is also preferable that the ionic radius of M does not differ too greatly from the ionic radius of Zn (74 pm).

[0046] M ２＋ Specific examples of ions include one or more selected from Mg (72 pm), Ca (100 pm), Mn (80 pm), Fe (76 pm), Co (74 pm), Ni (69 pm), Cu (73 pm), and Zn (74 pm). Among these, M is chosen because its ionic radius is closer to that of Zn. ２＋ It is more preferable that the ion be one or more selected from Mg, Mn, Fe, Co, Ni, Cu, and Zn.

[0047] M ３＋ Specific examples of ions include one or more selected from Al (53 pm), Cr (62 pm), Mn (66 pm), Fe (64 pm), Co (63 pm), Ni (62 pm), Ga (62 pm), and La (103 pm). Among these, M is chosen because its ionic radius is closer to that of Zn and it is in a stable state. ３＋ The ion is more preferably one or more selected from Al, Cr, Fe, and Ga (62 pm).

[0048] Creating a sound shell structure for different materials is not easy due to lattice constant mismatches. In such cases, two-dimensional nucleation occurs on the surface of ZnO, and these islands grow. If the mismatch is large, wettability is poor, and in extreme cases, droplets (spheres) form on the particle, resulting in a precipitated state that looks like powder or aggregates. If the affinity is high, precipitation occurs in a way that wets the surface, so large islands are observed to grow, and eventually, polycrystalline material is formed on the particle surface.

[0049] (Carbonate ion source) The carbonate ion source is CO ３ ２－ As long as it produces ions, there are no particular restrictions, and it can be appropriately selected according to the purpose, but for example, ammonium carbonate [(NH₄] ４ ) ２ CO ３ ], sodium carbonate [Na ２ CO ３ ], sodium bicarbonate [NaHCO ３ ], carbon dioxide, urea [(NH ２ ) ２ Examples include CO.

[0050] [Solvent] The solvent is not particularly limited as long as it can dissolve the raw materials. For example, aqueous materials can be used as solvents.

[0051] Aqueous materials refer to water, polar organic solvents, or mixed solvents of water and polar organic solvents. Examples of aqueous materials include water, alcohols, carboxylic acids, ketones, ethers, esters, amides, amines, sulfur compounds, and mixtures thereof.

[0052] Examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, octanol, glycerin, and phenol.

[0053] Examples of carboxylic acids include lower carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and caproic acid.

[0054] Examples of ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0055] Examples of ethers include 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.

[0056] Examples of esters include ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and γ-butyrolactone.

[0057] Examples of amides include formamide, dimethylformamide, acetamide, dimethylacetamide, nitromethane, and acetonitrile.

[0058] Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine.

[0059] Examples of sulfur compounds include dimethyl sulfoxide.

[0060] In particular, because it is easy to handle, the water-based material preferably contains one or more selected from water, alcohols, and carboxylic acids, and more preferably water.

[0061] Furthermore, pH adjusters, oxidizing agents, and reducing agents can be added to the aqueous material to control the reaction field.

[0062] Examples of pH adjusters include hydrochloric acid, nitric acid, acetic acid, sulfuric acid, carbonic acid, or their ammonium salts as acids, and potassium hydroxide, sodium hydroxide, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, or ammonia as alkalis.

[0063] Examples of oxidizing and reducing agents include hydrogen peroxide, oxygen, nitric acid, as well as formic acid, hydrazine, hydrogen, ammonia, ethanol, and formaldehyde.

[0064] The coating process involves dispersing the raw materials in an aqueous solution. The raw materials can be charged as a powder or as a fluid. As long as they are fluid, they are not particularly limited and can include aqueous solutions, slurries, pastes, or suspensions containing the raw material components.

[0065] If it is difficult to prepare an aqueous slurry, the raw materials can be dispersed in an aqueous material such as ethanol to create a slurry.

[0066] The pH of the raw material liquid charged into the coating apparatus is preferably between 9 and 12.

[0067] ZnO has high solubility in water, even dissolving at room temperature. Dissolution proceeds even more at low pH, but is relatively suppressed at high pH.

[0068] Furthermore, it is generally known that LDH is synthesized by a coprecipitation reaction in which a metal source is mixed while maintaining an alkaline pH of about 10 (Non-Patent Literature 1).

[0069] [Coating Apparatus] The coating apparatus is not particularly limited as long as it is capable of mixing and stirring liquids, and can be selected and used from apparatus widely known to those skilled in the art in this field, for example, either a batch type apparatus or a flow type apparatus can be used.

[0070] The reaction temperature of the present invention is not particularly limited, but may be, for example, 0°C to 100°C, more generally 10°C to 60°C, and more typically 20°C to 40°C.

[0071] Furthermore, the reaction time of the present invention is not particularly limited, but may be, for example, 1 minute or more and 96 hours or less, more generally 5 minutes or more and 48 hours or less, and more typically 10 minutes or more and 24 hours or less.

[0072] The type of heating device used to heat aqueous materials is not particularly limited. Examples of heating devices include those that irradiate aqueous materials with microwaves, and those that heat aqueous materials by heat conduction from heating elements such as heaters.

[0073] Regarding particle recovery, if the powder is placed in a container, it is recovered as is. If recovery is done using a slurry, the product particles are separated from the fluid through a filter. The type of filter is not particularly limited, but an example is an in-line filter.

[0074] <Coated Particles> The coated particles obtained as a product by this method have at least a portion of ZnO containing [M ２＋ １－ｘ M ３＋ ｘ (OH) ２ ] (CO ３ ) ｘ／２ ・yH ２ O(M) ２＋ and M ３＋ It is covered with divalent and trivalent metal ions that can constitute LDH.

[0075] With the coated particles obtained as a product, the amount of Zn contained in the water after dispersing 200 mg of the coated particles in 40 mL of water at 25°C using ultrasonic technology for 10 minutes can be reduced to less than 1 / 20th of that in the case of untreated ZnO.

[0076] The coated particles can be used in ultraviolet shielding agents and cosmetics containing them, as well as in paints and other materials that have ultraviolet shielding functions, gas permeation suppression functions, etc.

[0077] The average particle size of the coated particles is not particularly limited, as long as it is within a range suitable for use as an ultraviolet shielding agent. Considering workability, the average particle size is preferably 2 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more. Furthermore, considering the ultraviolet shielding effect, the average particle size is preferably 20 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less.

[0078] Regarding the average particle diameter, if it is possible to measure the average particle diameter by laser diffraction scattering, the average particle diameter shall be the average particle diameter (Dv50) at 50% of the volume-based integrated value in the particle size distribution obtained by laser diffraction scattering. On the other hand, if it is not possible to measure the average particle diameter by laser diffraction scattering, the average particle diameter shall be the average particle diameter (Dv50) at 50% of the volume-based integrated value obtained from the equivalent diameter of a circle obtained by determining the area of ​​the particle by image analysis from an electron microscope image observed at a magnification of 70,000x using a scanning electron microscope (SEM), and obtaining the equivalent diameter of a circle equal to that area.

[0079] The smaller the average particle size of the coating particles, the more suitable it is for achieving high transparency when incorporated into cosmetics. On the other hand, the larger the average particle size of the coating particles, the higher the ultraviolet scattering intensity, allowing for shielding of ultraviolet rays up to long wavelengths. Therefore, the average particle size of the coating particles is appropriately selected according to the desired transparency and ultraviolet shielding properties of the cosmetic.

[0080] The content of ZnO particles in the coated particles is selected as needed, but is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. If the content of ZnO particles in the coated particles is too low, it may not be possible to obtain the desired UV shielding effect. In cosmetics containing such coated particles in a cosmetic raw material base, it is undesirable because a large amount of coated particles would have to be used to obtain the desired UV shielding effect.

[0081] The ZnO particle content in the coated particles is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less. If the ZnO particle content in the coated particles is too high, the proportion of ZnO particles in these coated particles may become too high. As a result, the surface of the ZnO particles may not be sufficiently covered with the carbonate-type LDH coating, which may lead to insufficient photocatalytic activity of ZnO and suppression of Zn elution, so this is undesirable.

[0082] The content of carbonate-type LDH in the coated particles is appropriately adjusted according to the average particle size of the ZnO particles. For example, for ZnO particles with an average particle size of 50 nm or less, the content of carbonate-type LDH is preferably 3% by mass or more and 45% by mass or less. For ZnO particles with an average particle size exceeding 50 nm, the content of carbonate-type LDH is preferably 1% by mass or more and 35% by mass or less.

[0083] The thickness of the carbonate-type LDH on the coated particles can be selected as needed, but is preferably 1 nm or more, more preferably 2 nm or more, and even more preferably 3 nm or more. If the thickness of the carbonate-type LDH on the coated particles is too thin, the surface of the ZnO particles cannot be sufficiently covered with the carbonate-type LDH coating, which may result in insufficient photocatalytic activity of ZnO and suppression of Zn elution, so this is undesirable.

[0084] The thickness of the carbonate-type LDH on the coated particles can be selected as needed, but is preferably 20 nm or less, more preferably 10 nm or less, and even more preferably 5 nm or less. If the thickness of the carbonate-type LDH on the coated particles is too thick, it may not be possible to obtain the desired UV shielding effect. In cosmetics containing such coated particles in a cosmetic raw material base, it is undesirable because a large amount of coated particles would have to be used to obtain the desired UV shielding effect.

[0085] <Coated Particle-Containing UV Shielding Agent> The coated particle-containing UV shielding agent of this embodiment contains the carbonate-type LDH-coated ZnO of this embodiment.

[0086] [Average Particle Diameter] In the coated particle-containing ultraviolet shielding agent of this embodiment, the average particle diameter of the carbonate-type LDH-coated ZnO can be arbitrarily selected, but it is preferably 2 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more. Furthermore, the average particle diameter is preferably 500 nm or less, and more preferably 400 nm or less.

[0087] The reason for limiting the average particle size of the carbonate-type LDH-coated ZnO to the above range is that if the average particle size is less than 2 nm, the surface energy of the carbonate-type LDH-coated ZnO is too high due to its small size, making it prone to aggregation and difficult to maintain the desired shape and size. On the other hand, if the average particle size exceeds 500 nm, the transparency of the carbonate-type LDH-coated ZnO itself tends to decrease, and when a UV shielding agent containing these coated particles is used in cosmetics, etc., there is a risk of impairing transparency in the visible light region or causing a gritty texture and worsening the user experience.

[0088] [Average Dispersion Particle Size] The average dispersion particle size of the carbonate-type LDH coating ZnO in the coated particle-containing ultraviolet shielding agent of this embodiment is preferably 10 nm or more. More preferably 20 nm or more, and even more preferably 25 nm or more. Furthermore, the average dispersion particle size is preferably 1 μm or less. More preferably 800 nm or less, and even more preferably 500 nm or less.

[0089] If the average dispersed particle size of the carbonate-type LDH-coated ZnO is less than 10 nm, the crystallinity of the carbonate-type LDH-coated ZnO will be low, which may result in insufficient UV shielding. On the other hand, if the average dispersed particle size of the carbonate-type LDH-coated ZnO exceeds 1 μm, glare, grittiness, etc. may occur, which may result in a poor tactile feel when formulated in cosmetics, and the dispersion stability may decrease, which may result in an inability to obtain a stable composition. In this invention, dispersed particle size refers to the particle size when multiple carbonate-type LDH-coated ZnO particles are dispersed together.

[0090] [Content of Carbonate-Type LDH-Coated ZnO] The content of carbonate-type LDH-coated ZnO in the coated particle-containing ultraviolet shielding agent of this embodiment can be adjusted as appropriate to obtain the desired ultraviolet shielding performance and is not particularly limited. The content is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. Also, the content is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0091] Here, it was stated that the content of carbonated LDH-coated ZnO is preferably 1% by mass or more and 80% by mass or less. The reason is that if the content of carbonated LDH-coated ZnO is less than 1% by mass, it will not be able to exhibit sufficient ultraviolet shielding function. As a result, when incorporating it into cosmetics, etc., it will be necessary to add a large amount of coated particle-containing ultraviolet shielding agent in order to exhibit the desired ultraviolet shielding function, which may increase manufacturing costs and is therefore undesirable. On the other hand, if the content of carbonated LDH-coated ZnO exceeds 80% by mass, the viscosity of the coated particle-containing ultraviolet shielding agent will increase, reducing the dispersion stability of carbonated LDH-coated ZnO, and there is a risk that carbonated LDH-coated ZnO will be more likely to settle, which is therefore undesirable.

[0092] [Solvent] The solvent used in the coated particle-containing ultraviolet shielding agent of this embodiment is not particularly limited, as long as it can disperse the above-mentioned carbonate-type LDH coating ZnO. Specifically, examples include those listed in the [Solvent] section of the [Coating Treatment Step] described above. These solvents may be used individually or as a mixture of two or more.

[0093] By dispersing the UV-blocking agent in a solvent, a dispersion or slurry containing a high concentration of the UV-blocking agent can be provided.

[0094] Furthermore, other solvents that can be used in the coated particle-containing ultraviolet shielding agent of this embodiment include 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-dimethylacetacetamide, and N-methylpyrrolidone; and linear polysiloxanes such as dimethylpolysiloxane, methylphenylpolysiloxane, and diphenylpolysiloxane.

[0095] In addition, cyclic polysiloxanes such as octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexanesiloxane; and modified polysiloxanes such as amino-modified polysiloxane, polyether-modified polysiloxane, alkyl-modified polysiloxane, and fluorine-modified polysiloxane are also suitably used. These solvents may be used individually or in mixtures of two or more.

[0096] Regarding the transmittance when coated particles are dispersed in cyclopentasiloxane to form a paste coating film with a thickness of 12 μm, with a coating particle concentration of 15% by mass, the transmittance of visible light at a wavelength of 450 nm is preferably 80% or more, and more preferably 85% or more. Furthermore, the transmittance of long-wavelength ultraviolet light (UVA) at a wavelength of 370 nm is preferably 20% or less, preferably 15% or less, and more preferably 10% or less.

[0097] The transmittance shall be determined using a UV-Vis-Near-Infrared Spectrophotometer V-770 (manufactured by JASCO Corporation).

[0098] [Additives] The UV shielding agent containing coated particles of this embodiment may contain commonly used additives such as dispersants, stabilizers, water-soluble binders, and thickeners, to the extent that it does not impair its properties.

[0099] [Dispersants] Suitable dispersants include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, silane coupling agents such as organoalkoxysilanes and organochlorosilanes, and modified silicones such as polyether-modified silicones and amino-modified silicones. The type and amount of these dispersants can be appropriately selected according to the particle size of the composite particles and the type of dispersion medium to be used. Only one of the above dispersants may be used, or two or more may be mixed and used.

[0100] [Water-soluble binder] Examples of water-soluble binders that can be used include polyvinyl alcohol (PVA), polyvinylpyrrolidone, hydroxycellulose, and polyacrylic acid.

[0101] [Thickening Agent] When the coated particle-containing UV shielding agent of this embodiment is applied to a cosmetic, any thickening agent used in cosmetics may be used, and is not particularly limited. Suitable thickening agents include, for example, natural water-soluble polymers such as gelatin, casein, collagen, hyaluronic acid, albumin, and starch; semi-synthetic polymers such as methylcellulose, ethylcellulose, methylhydroxypropylcellulose, carboxymethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose, sodium carboxymethylcellulose, and propylene glycol alginate; synthetic polymers such as polyvinyl alcohol, polyvinylpyrrolidone, carbomer (carboxyvinyl polymer), polyacrylate, and polyethylene oxide; and inorganic minerals such as bentonite, laponite, and hectorite. These thickening agents may be used individually or in combination of two or more.

[0102] Among these thickeners, synthetic polymers are preferred, and carboxyvinyl polymers (carbomers) are more preferred. Note that carboxyvinyl polymers also include those in which a part of the carboxyvinyl polymer has been modified, such as alkyl-modified carboxyvinyl polymers.

[0103] Here, when a carboxyvinyl polymer is used as a thickening agent, the content of the carboxyvinyl polymer in the coated particle-containing ultraviolet shielding agent of this embodiment is preferably 0.0001% by mass or more, and more preferably 1% by mass or less. Furthermore, the content is preferably 10% by mass or less, and more preferably 1% by mass or less.

[0104] If the carboxyvinyl polymer content in the coated particle-containing UV shielding agent of this embodiment is less than 0.0001% by mass, the thickening effect may not be obtained. On the other hand, if the carboxyvinyl polymer content exceeds 10% by mass, the viscosity of the coated particle-containing UV shielding agent becomes too high, which is undesirable from a usage standpoint.

[0105] [pH] When carboxyvinyl polymer is used as a thickening agent, the hydrogen ion concentration (pH) of the coated particle-containing UV shielding agent is preferably 5 or higher, more preferably 6 or higher, and even more preferably 7 or higher. Furthermore, the pH is preferably 11 or lower, more preferably 10 or lower, and even more preferably 9 or lower. By setting the pH of the coated particle-containing UV shielding agent of this embodiment within the above range, changes in viscosity and other properties over time can be suppressed.

[0106] [Method for producing a UV shielding agent containing coated particles] The method for producing the UV shielding agent containing coated particles in this embodiment is not particularly limited, as long as the above-mentioned carbonate-type LDH coated ZnO can be dispersed in the above-mentioned solvent.

[0107] For this type of dispersion, known dispersion methods can be used. For example, in addition to a stirrer, dispersion methods using zirconia beads such as a bead mill, ball mill, homogenizer, ultrasonic disperser, kneader, three-roll mill, and rotational / revolving mixer are preferably used.

[0108] The time required for the dispersion process should be sufficient to allow the above-mentioned carbonate-type LDH-coated ZnO to be uniformly dispersed in the above-mentioned solvent.

[0109] <Cosmetics> An example of the cosmetics of this embodiment contains the carbonate-type LDH-coated ZnO of this embodiment or the coated particle-containing ultraviolet shielding agent of this embodiment.

[0110] Another example of the cosmetic composition of this embodiment comprises a cosmetic raw material base and a carbonate-type LDH-coated ZnO or coated particle-containing ultraviolet shielding agent of this embodiment, dispersed in the cosmetic raw material base.

[0111] Here, cosmetic base ingredients refer to the various raw materials that form the main body of cosmetics, and include oily raw materials, aqueous raw materials, surfactants, powdered raw materials, etc.

[0112] Examples of oily raw materials include oils and fats, higher fatty acids, higher alcohols, and ester oils.

[0113] Examples of aqueous ingredients include purified water, alcohol, and thickeners.

[0114] Examples of powdered raw materials include colored pigments, white pigments, pearlescent agents, and extender pigments.

[0115] The cosmetic composition of this embodiment can be obtained, for example, by conventionally incorporating the carbonated LDH-coated ZnO or coated particle-containing ultraviolet shielding agent of this embodiment into a cosmetic raw material base such as lotion, cream, foundation, lipstick, blush, or eyeshadow.

[0116] Alternatively, the carbonated LDH-coated ZnO or coated particle-containing ultraviolet shielding agent of this embodiment may be blended into an oil phase or aqueous phase to form an emulsion, which may then be blended with a cosmetic raw material base.

[0117] The content of carbonated LDH-coated ZnO in cosmetics can be adjusted as appropriate according to the desired properties. For example, the lower limit of the carbonated LDH-coated ZnO content may be 0.01% by mass or more, 0.1% by mass or more, or 1% by mass or more. The upper limit of the carbonated LDH-coated ZnO content may be 50% by mass or less, 40% by mass or less, or 30% by mass or less. The upper and lower limits of the carbonated LDH-coated ZnO content in cosmetics can be arbitrarily combined.

[0118] The following provides a detailed explanation of sunscreen cosmetics.

[0119] In order to effectively block ultraviolet rays, especially long-wavelength ultraviolet rays (UVA), the content of the coated particle-containing UV shielding agent in the sunscreen cosmetic composition is preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less, in terms of the content of the carbonate-type LDH-coated ZnO contained in the coated particle-containing UV shielding agent.

[0120] Sunscreen cosmetics may, as needed, contain hydrophobic dispersion media, inorganic fine particles other than ZnO or inorganic pigments, hydrophilic dispersion media, oils and fats, surfactants, humectants, thickeners, pH adjusters, nutrients, antioxidants, fragrances, etc. Examples of hydrophobic dispersion media include 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 decamethylcyclopentasiloxane, dimethylpolysiloxane, and methylphenylpolysiloxane, higher fatty acids such as uric acid, myristic acid, palmitic acid, and stearic acid, and higher alcohols such as lauryl alcohol, cetyl alcohol, stearyl alcohol, hexyldodecanol, and isostearyl alcohol.

[0121] Examples of inorganic fine particles and inorganic pigments other than ZnO include calcium carbonate, calcium phosphate (apatite), magnesium carbonate, calcium silicate, magnesium silicate, aluminum silicate, kaolin, talc, titanium dioxide, aluminum oxide, yellow iron oxide, γ-iron oxide, cobalt titanate, cobalt violet, and silicon dioxide. Of these, titanium dioxide in particular has a higher ultraviolet shielding ability than ZnO in the mid-wavelength ultraviolet (UVB) region of 280 to 320 nm, and may be combined with ZnO in any ratio to cover the entire UVB and UVA region.

[0122] The sunscreen cosmetic may further contain at least one organic UV absorber. Examples of organic UV absorbers include benzotriazole-based UV absorbers, benzoylmethane-based UV absorbers, benzoic acid-based UV absorbers, anthranilic acid-based UV absorbers, salicylic acid-based UV absorbers, cinnamic acid-based UV absorbers, silicone-based cinnamic acid-based UV absorbers, and other organic UV absorbers.

[0123] Examples of benzotriazole-based ultraviolet absorbers include 2,2'-hydroxy-5-methylphenylbenzotriazole, 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, and 2-(2'-hydroxy-5'-methylphenylbenzotriazole).

[0124] Examples of benzoylmethane-based ultraviolet absorbers include dibenzarazine, dianisioylmethane, 4-tert-butyl-4'-methoxydibenzoylmethane, 1-(4'-isopropylphenyl)-3-phenylpropane-1,3-dione, and 5-(3,3'-dimethyl-2-norbornylidene)-3-pentan-2-one.

[0125] Examples of benzoic acid-based ultraviolet absorbers include para-aminobenzoic acid (PABA), PABA monoglycerol 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, and N,N-dimethyl PABA methyl ester.

[0126] Examples of anthranilic acid-based UV absorbers include homomenthyl-N-acetylanthranilate.

[0127] Examples of salicylic acid-based ultraviolet absorbers include amyl salicylate, menthyl salicylate, homomenthyl salicylate, octyl salicylate, phenyl salicylate, benzyl salicylate, and p-2-propanolphenyl salicylate.

[0128] Examples of cinnamic acid-based UV absorbers include octyl methoxycinnamate, di-paramethoxycinnamate-mono-2-ethylhexanoate glyceryl, octyl cinnamate, ethyl-4-isopropyl cinnamate, methyl-2,5-diisopropyl cinnamate, ethyl-2,4-diisopropyl cinnamate, methyl-2,4-diisopropyl cinnamate, propyl-p-methoxycinnamate, and isopropyl-p-methoxycinnamate. Examples include isoamyl-p-methoxycinnamate, octyl-p-methoxycinnamate (2-ethylhexyl-p-methoxycinnamate), 2-ethoxyethyl-p-methoxycinnamate, cyclohexyl-p-methoxycinnamate, ethyl-α-cyano-β-phenylcinnamate, 2-ethylhexyl-α-cyano-β-phenylcinnamate, and glyceryl mono-2-ethylhexanoyl-diparamethoxycinnamate.

[0129] Examples of silicone-based cinnamic acid UV absorbers 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, and [3-tris(trimethylsiloxy)silyl-1-methylpropyl]-3,4-dimethoxycinnamate.

[0130] Examples of organic ultraviolet absorbers other than those mentioned above include 3-(4'-methylbenzylidene)-d,l-camphor, 3-benzylidene-d,l-camphor, urocanic acid, ethyl urocanic acid, 2-phenyl-5-methylbenzoxazole, 5-(3,3'-dimethyl-2-norbornylidene)-3-pentan-2-one, silicone-modified ultraviolet absorbers, fluorine-modified ultraviolet absorbers, and the like.

[0131] According to the coated particle-containing ultraviolet shielding agent of this embodiment, because it contains the carbonate-type LDH-coated ZnO of this embodiment, even when applied to water-based materials such as water-based cosmetics, it is possible to suppress the decrease in viscosity caused by carbomer and maintain the quality stability of the water-based material.

[0132] According to the cosmetic composition of this embodiment, because it contains the coated particle-containing UV shielding agent of this embodiment, there is no decrease in viscosity caused by carbomer, and it has excellent quality stability.

[0133] <Paint> Furthermore, an example of the paint of this embodiment contains either the carbonate-type LDH coating ZnO of this embodiment or the coated particle-containing ultraviolet shielding agent of this embodiment. The dissolution of the carbonate-type LDH coating ZnO into water is suppressed, and the service life is extended. For this reason, the ultraviolet shielding agent is suitable for use in paints.

[0134] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0135] <Test Example 1> [Sample Preparation] [Example 1] (Production of Carbonate-type LDH-coated ZnO) Place 350 mg of sodium hydroxide and 1.06 g of sodium carbonate in a 50 ml vial, H ２ It was dissolved in 25 ml of O. 2 g of ZnO with a particle size of approximately 200 nm was added to this and ultrasonically dispersed for 10 minutes. Then, while stirring the resulting turbid liquid, 0.8 mol / L Al(NO) was added. ３ ) ３ 9H ２ Aqueous solution O was added dropwise at a rate of 1 to 2 drops per second. After adding until the pH reached 10, the mixture was stirred at room temperature for 16 hours. The resulting dispersion was centrifuged to collect the precipitate, and sample A (white solid, 2.29 g) was obtained by thoroughly centrifugating with water.

[0136] [Comparative Example 1] (Production of carbonate-type LDH) 700 mg of sodium hydroxide and 2.12 g of sodium carbonate were placed in a 50 ml vial, H ２ It was dissolved in 25 ml of O. 2 g of ZnO with a particle size of approximately 20 nm was added, and ultrasonic dispersion was performed for 10 minutes. Then, while stirring the resulting turbid liquid, 0.8 mol / L Al(NO) was added. ３ ) ３9H ２ Aqueous solution O was added dropwise at a rate of 1 to 2 drops per second. After adding until the pH reached 10, the mixture was stirred at room temperature for 16 hours. The resulting dispersion was centrifuged to collect the precipitate, and sample B (white solid, 3.19 g) was obtained by thoroughly centrifugating with water.

[0137] [Evaluation] Figure 1 shows the FT-IR spectra of untreated ZnO and sample A obtained from Example 1. At 800 cm⁻¹ for sample A... －１ and 1500cm －１ CO in the vicinity ３ ２－ The presence of carbonate ions is suggested by the observation of a peak that is thought to be the source of the phenomenon.

[0138] Figure 2 shows the X-ray diffraction patterns (XRD patterns) of untreated ZnO, sample A, and sample B. Compared to the original ZnO, new peaks appear in sample A at 2θ = 11.7° and 23.6°. Based on the IR spectrum, which indicates the presence of carbonate ions, the analysis revealed that zaccagnaite (chemical formula Zn4Al2(OH)), a carbonate-type LDH composed of Zn and Al, is present. 12 The peak was identified as originating from CO3・3H2O. Furthermore, in sample B, no peak originating from ZnO was observed, and only the new peak component that appeared in sample A was seen, so sample B was identified as pure zaccagnaite.

[0139] Figure 3 shows scanning electron microscope (SEM) images of untreated ZnO. Figure 3(A) is an image at a magnification of 70,000x, and Figure 3(B) is an image at a magnification of 300,000x. Overall, it was observed to have a bright contrast.

[0140] Figure 4 shows SEM images of sample A. Figure 4(A) is an image at a magnification of 70,000x, and Figure 4(B) is an image at a magnification of 500,000x. Compared to the original ZnO, a darker contrast can be observed. Furthermore, when the dark contrast areas are observed at high magnification, it can be confirmed that granular material of a few nanometers in size is attached to the surface.

[0141] Figure 5 shows the SEM image of sample A and the mapping results of energy-dispersive X-ray analysis (EDX analysis) in the same field. Al was detected in the dark contrast areas. This suggests that the dark contrast areas are where zaccagnaite is present.

[0142] Figure 6 shows the spectra obtained by X-ray photoelectron spectroscopy (XPS) of untreated ZnO, sample A, and sample B. In both sample A and sample B, peaks appear at 288.8 eV in the C1s spectrum and at 531.1 eV in the O1s spectrum. This is due to the carbonic acid (CO2) contained in zaccagnaite. ３ ２－ This peak is thought to be of origin.

[0143] In the Al2p spectrum, no peak was observed in untreated ZnO, but peaks appeared in samples A and B. This indicates that Al is present in samples A and B.

[0144] Zn2p ３／２ In the spectrum, the peak top was at 1020.8 eV for untreated ZnO, while it was slightly shifted to 1021.3 eV for sample B. This is thought to be because the environment for Zn in ZnO and Zn in Zaccagnaite are different. In sample A, the 1021.3 eV peak component, i.e., the Zn component of ZnO, is the main component, but the peak is slightly bulging towards higher energies, and the 1021.3 eV peak component, i.e., the Zn component in Zaccagnaite from sample B, is also present. Since the analysis depth of XPS is about 10 nm from the sample surface, assuming uniform modification, this suggests that the surface of ZnO is modified with Zaccagnaite on a scale of a few nanometers.

[0145] Based on simple calculations derived from weight changes before and after coating, and visual estimations from SEM observations, the thickness of the zaccagnaite is estimated to be approximately 3-4 nm.

[0146] Figure 7 shows the diffuse reflectance spectra in the ultraviolet and visible regions for sample A and the original ZnO. Compared with the original ZnO, sample A showed no significant change in absorption in the UV region below 400 nm, particularly in the UVA region between 320 and 400 nm, confirming that it maintained its ultraviolet shielding ability even after coating.

[0147] Figure 8 shows the results of a simple water elution test for sample A and the original ZnO. 200 mg each of sample A and untreated ZnO were placed in 2.5 ml of pure water and ultrasonically dispersed for 10 minutes. The dispersion was then filtered, and the zinc concentration in the filtrate was roughly estimated using "Pack Test Zinc" manufactured by Kyoritsu Chemical Research Institute Co., Ltd. As a result, the zinc ion concentration in water for untreated ZnO was estimated to be 2-5 ppm, while for sample A it was estimated to be less than 0.2 ppm.

[0148] Furthermore, for sample A, 2 g was placed in 25 ml of pure water and ultrasonically dispersed for 10 minutes. The dispersion was then centrifuged, and the zinc concentration in the supernatant was measured by atomic absorption spectrometry (detection wavelength: 213.8 nm). As a result, the zinc ion concentration in the solution was less than 0.1 ppm. In other words, it was found that protecting the ZnO surface with Zaccagnaite can prevent zinc from leaching into water.

[0149] <Test Example 2> [Sample Preparation] [Example 2] (Size Dependence of ZnO) Samples C and D were obtained using the same method as in Example 1, except that ZnO with particle sizes of approximately 20 nm and 1 μm were used.

[0150] [Comparative Example 2-1] (Time dependence of coating treatment) Al(NO ３ ) ３ 9H ２ Samples E, F, G, and H were obtained using the same method as in Example 1, except that after adding an aqueous solution of O dropwise to adjust the pH to 10, the mixture was stirred at room temperature for 10 minutes, 1 hour, 3 hours, and 4 hours.

[0151] [Comparative Example 2-2] (Coating treatment in the absence of sodium carbonate) Sample I was obtained using the same method as in Example 1, except that sodium carbonate was not added, and instead 70 mg of sodium hydroxide was added.

[0152] [Comparative Example 2-3] (Coating treatment in the absence of sodium hydroxide) Sample J was obtained using the same method as in Example 1, except that sodium hydroxide was not added.

[0153] [Evaluation] Zinc elution tests were performed on samples C and D using "Pack Test Zinc," and the amount of zinc eluted was estimated to be less than 0.2 ppm in both cases. Furthermore, 2 g of each sample C and D were placed in 25 ml of pure water, ultrasonically dispersed for 10 minutes, and the dispersion was centrifuged. The concentration of zinc in the supernatant was measured by atomic absorption spectrometry (detection wavelength: 213.8 nm). As a result, the zinc ion concentration in the solution was less than 0.1 ppm in both cases. In other words, it was found that even for ZnO of different sizes, protecting the surface with zaccagnaite can prevent zinc elution into water.

[0154] Zinc leaching tests were conducted on samples E, F, G, and H using "Pack Test Zinc." The estimated zinc leaching amounts were: sample E: 0.5 ppm, samples F and G: 0.2–0.5 ppm, and sample H: less than 0.2 ppm. In other words, it appears that a longer coating time is better to suppress zinc leaching.

[0155] A zinc elution test was performed on sample I using "Pack Test Zinc," and the amount of zinc eluted was estimated to be 2-5 ppm. In other words, it is thought that without the addition of sodium carbonate, there is insufficient carbonic acid, resulting in inadequate Zaccagnaite modification and an inability to suppress zinc elution.

[0156] A zinc elution test was performed on sample J using "Pack Test Zinc," and the amount of zinc eluted was estimated to be 2-5 ppm. This suggests that when sodium carbonate alone is used without sodium hydroxide, there is a lack of base, resulting in insufficient zaccagnaite modification.

[0157] <Test Example 3> [Water Dissolution Test] [Example 3] (pH Stability of Carbonate-Type LDH-Coated ZnO) Aqueous solutions were prepared by adjusting the pH to 3 to 12 using hydrochloric acid and sodium chloride, and a zinc dissolution test was performed on sample A at each pH using "Pack Test Zinc".

[0158] [Comparative Example 3] (Commercially available silicon dioxide coated ZnO) For comparison, a zinc elution test using "Pack Test Zinc" was also performed on commercially available silicon dioxide coated ZnO.

[0159] [Evaluation] Table 1 shows the results of "Pack Test Zinc" in Example 3 and Comparative Example 3.

[0160] For sample A, the amount of zinc eluted was estimated to be less than 0.2 ppm in the pH range of 4 to 11, confirming that zinc elution was suppressed. This is thought to be because the ZnO is coated with carbonate-type LDH, which has higher pH stability. On the other hand, for commercially available silicon dioxide-coated ZnO, the amount of zinc eluted was estimated to be 5 ppm or more, suggesting that zinc elution was not suppressed.

[0161] <Test Example 4> [Sample Preparation] [Example 4-1] (Production of carbonate-type LDH-coated ZnO using a homogenizer in the presence of a dispersant) H ２ Add 30 ml of O, add 0.2 g of Shin-Etsu Chemical Co., Ltd.'s silicone surfactant KF-6011 as a dispersant and mix well, then add 328 mg of sodium hydroxide and 530 mg of sodium carbonate and dissolve. Add 2 g of ZnO with a particle size of about 35 nm and ultrasonically disperse for 10 minutes, then mix for 10 minutes using AS ONE Corporation's homogenizer AHG-160A. After that, while stirring the resulting turbid liquid, add 0.7 mol / L of Al(NO) ３ ) ３ 9H ２ 3.6 ml of aqueous solution O was added dropwise at a rate of 1 to 2 drops per second. After addition, the mixture was stirred again in a homogenizer for 10 minutes, and then stirred at room temperature for 4 hours. The resulting dispersion was centrifuged to collect the precipitate, and sample K (white solid, 1.77 g) was obtained by thoroughly centrifugating with water.

[0162] [Example 4-2] (Production of carbonate-type LDH-coated ZnO using a wet bead mill in the presence of a dispersant) Sample L was obtained using the same method as in Example 4-1, except that the amounts of each reagent and solvent were increased by 15 times, and a wet bead mill device (Labostar Mini DMS65, using beads with a diameter of 0.1 mm) manufactured by Ashizawa Finetech Co., Ltd. was used instead of a homogenizer during stirring.

[0163] [Evaluation] Zinc leaching tests were conducted on samples K and L using "Pack Test Zinc," and the amount of zinc leached was estimated to be less than 0.2 ppm in both cases. In other words, it was found that even under conditions where a dispersant is present, protecting the ZnO surface with Zaccagnaite can prevent zinc leaching into water.

[0164] <Test Example 5> [High-Concentration Dispersion] [Example 5] (High-concentration dispersion of carbonate-type LDH-coated ZnO using a dispersant) 210 g of sample L was placed in a 500 mL beaker, 90 ml of H2O and 21 g of dispersant (isododecane) were added, and the mixture was stirred for 30 minutes using a wet bead mill. After collection, it was left to stand overnight and confirmed that there was no precipitate to obtain a high-concentration dispersed sample M.

[0165] [Evaluation] A zinc leaching test was performed on sample M using "Pack Test Zinc," and the amount of zinc leached was estimated to be less than 0.2 ppm. In other words, it was found that zinc leaching into water can be prevented even in samples dispersed at high concentrations.

[0166] <Test Example 6> [Ultraviolet-Visible Light Transmittance] [Example 6] (Transmittance measurement using a carbonate-type LDH coating containing ZnO) A coating was obtained by adding sample A to 15% by mass using cyclopentasiloxane as a dispersion medium and dispersing it with paint conditioner. The obtained coating was uniformly applied to a transparent polypropylene film to a thickness of 12 μm and air-dried, and the transmittance at each wavelength of the obtained coating was measured using a spectrophotometer (V-770, JASCO).

[0167] <Comparative Example 6-1> (Transmittance measurement using untreated ZnO-containing coating film) The transmittance was measured using the same method as in Example 6, except that untreated ZnO was used.

[0168] <Comparative Example 6-2> (Transmittance measurement using titanium dioxide-containing coating film) The transmittance was measured using the same method as in Example 6, except that commercially available titanium dioxide was used.

[0169] [Evaluation] Table 2 shows the transmittance results at 450 nm (visible light region), 370 nm (UVA region), and 300 nm (UVB region) obtained from Example 6, Comparative Example 6-1, and Comparative Example 6-2. There was no significant difference in transmittance at any wavelength between Sample A and untreated ZnO, confirming that transparency and UV shielding ability were maintained even after coating. Compared with titanium dioxide, Sample A and untreated ZnO had higher transmittance at 450 nm, indicating higher transparency. Furthermore, Sample A and untreated ZnO had lower transmittance at 370 nm, suggesting higher UV shielding ability in the UVA region. On the other hand, titanium dioxide had lower transmittance at 300 nm, suggesting that titanium dioxide had higher UV shielding ability in the UVB region.

Claims

1. Coated particles wherein at least a portion of zinc oxide (ZnO) is covered with carbonate-type layered double hydroxide (LDH) [M ２＋ １－ｘ M ３＋ ｘ (OH) ２ (CO ３ ) ｘ／２ ·yH ２ O (M ２＋ and M ３＋ are divalent and trivalent metal ions capable of constituting LDH).

2. The coated particles according to claim 1, wherein 200 mg of coated particles are placed in 40 mL of water at a temperature of 25°C and ultrasonically dispersed for 10 minutes, and the amount of zinc ions contained in the water is 1 / 20th or less of that in the case of untreated ZnO.

3. The coated particles according to claim 1, wherein when the coated particles are dispersed in cyclopentasiloxane to form a paste coating film with a thickness of 12 μm, the transmittance of visible light at a wavelength of 450 nm is 80% or more, and the transmittance of long-wavelength ultraviolet light (UVA) at a wavelength of 370 nm is 20% or less.

4. Said M ２＋ is one or more divalent metal ions selected from Mg, Ca, Mn, Fe, Co, Ni, Cu, and Zn, and the M ３＋ The coated particle according to claim 1, wherein is one or more trivalent metal ions selected from Al, Cr, Mn, Fe, Co, Ni, Ga, and La.

5. An ultraviolet shielding agent containing coated particles according to any one of claims 1 to 4.

6. The ultraviolet shielding agent according to claim 5, further containing a carbomer such as a carboxyvinyl polymer.

7. A cosmetic composition containing the ultraviolet shielding agent described in claim 5.

8. A paint containing the ultraviolet shielding agent described in claim 5.

9. A dispersion or slurry containing 20% ​​by mass or more of the ultraviolet shielding agent described in claim 5.

10. A method for producing coated particles according to any one of claims 1 to 4, comprising the step of coating ZnO in the presence of a metal hydroxide and carbonate ions capable of constituting LDH.

11. The method according to claim 10, wherein the pH of the coating treatment is 9 or higher and 12 or lower.

12. The method according to claim 10, wherein the concentration of the raw material ZnO is 0.5 mol / L or higher.

13. The method according to claim 10, wherein the temperature during the coating treatment is 20°C or higher and 40°C or lower.

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