JP2025031109A - Surface-modified zinc oxide, method for producing surface-modified zinc oxide, dispersion, composition, and cosmetic - Google Patents

Abstract

The present invention provides a surface-modified zinc oxide that can sufficiently suppress the generation of active oxygen and has excellent dispersibility, and a method for producing the same.
The surface-modified zinc oxide of the present invention is a surface-modified zinc oxide in which the surfaces of zinc oxide particles are treated with a surface treatment agent, and the color difference ΔE before and after a vitamin E mixing test is 5.0 or less.
A method for producing surface-modified zinc oxide includes contacting zinc oxide particles and a surface treatment agent in a container in the presence of supercritical carbon dioxide; reducing the pressure in the container to remove carbon dioxide and recover a mixture of the zinc oxide particles and the surface treatment agent; and heating the mixture to react the zinc oxide particles and the surface treatment agent.
[Selection diagram] None

Description

The present invention relates to surface-modified zinc oxide, a method for producing surface-modified zinc oxide, a dispersion, a composition, and a cosmetic.

Pigment powders used in sunscreens and the like are sometimes subjected to surface treatment to suppress the generation of active oxygen (for example, see Patent Document 1).
There are two methods for obtaining surface-treated pigment powder: a dry method and a wet method. In the dry method, the surface treatment agent and the pigment powder are directly contacted and mixed. In the wet method, the surface treatment agent is dissolved or suspended in a medium, and then mixed with the pigment powder, after which the medium is removed. After the medium is removed, pulverization is performed as necessary.

JP 2007-1867 A

However, with the dry method, it is not possible to bring the surface treatment agent into sufficient contact with the inside of the fine zinc oxide particles. In this case, untreated zinc oxide particles remain, and the generation of active oxygen cannot be sufficiently suppressed. With the wet method, the powder is prone to agglomeration when the medium is removed. It is not easy to finely grind the agglomerated powder.

The present invention aims to provide a surface-modified zinc oxide that can sufficiently suppress the generation of active oxygen and has excellent dispersibility, and a method for producing the same.

The present invention has the following aspects.
[1] Zinc oxide particles are surface-modified zinc oxide particles in which the surfaces are treated with a surface treatment agent,
A surface-modified zinc oxide having a color difference ΔE of 5 or less before and after a vitamin E mixing test.
[2] The surface-modified zinc oxide according to [1], wherein the surface treatment agent contains a silicon compound.
[3] The surface-modified zinc oxide according to [2], wherein the silicon compound is at least one selected from the group consisting of silane compounds, silicone compounds and silane coupling agents.
[4] Contacting zinc oxide particles and a surface treatment agent in a container in the presence of supercritical carbon dioxide;
Removing carbon dioxide by reducing the pressure inside the container to recover the mixture of the zinc oxide particles and the surface treatment agent; and
heating the mixture to react the zinc oxide particles and the surface treatment agent;
A method for producing surface-modified zinc oxide comprising the steps of:
[5] The method according to [4], wherein the surface treatment agent contains a silicon compound.
[6] The method according to [5], wherein the silicon compound is at least one selected from the group consisting of a silane compound, a silicone compound, and a silane coupling agent.
[7] A dispersion comprising the surface-modified zinc oxide according to any one of [1] to [3] and a dispersion medium.
[8] A composition comprising the surface-modified zinc oxide according to any one of [1] to [3], a dispersion medium, and a resin.
[9] A cosmetic comprising the surface-modified zinc oxide according to any one of [1] to [3] and a cosmetic base raw material.

The present invention provides a surface-modified zinc oxide that can sufficiently suppress the generation of active oxygen and has excellent dispersibility, as well as a method for producing the same.

<Surface modified zinc oxide>
The surface-modified zinc oxide of the present invention is a surface-modified zinc oxide in which the surfaces of zinc oxide particles are treated with a surface treatment agent. "Treated with a surface treatment agent" means that the surface treatment agent comes into contact with or bonds to the zinc oxide particles due to an interaction between the surface treatment agent and the zinc oxide particles.
The contact referred to here may be, for example, physical adsorption. The bond may be, for example, an ionic bond, a hydrogen bond, or a covalent bond. The zinc oxide particles and the surface treatment agent will be described later.

(Color difference ΔE of surface-modified zinc oxide)
The color difference ΔE of the surface-modified zinc oxide of the present invention before and after a vitamin E mixing test is 5 or less. The color difference ΔE before and after a vitamin E mixing test is the color difference in the L ^* a ^* b ^* color system chromaticity diagram of the surface-modified zinc oxide before and after mixing with vitamin E. Since the color difference ΔE is 5 or less, the generation of active oxygen is sufficiently suppressed in the surface-modified zinc oxide.

"L ^* " is a correlation amount of lightness defined in JIS Z 8781-4:2013 "Colorimetry-Part 4: CIE 1976 L*a*b* color space" (corresponding international standard ISO 11664-4:2008). Also, "a ^* " and "b ^* " are color coordinates defined in JIS Z 8781-4:2013 "Colorimetry-Part 4: CIE 1976 L*a*b* color space" (corresponding international standard ISO 11664-4:2008).
The method for measuring the color difference ΔE before and after the vitamin E mixing test is as follows.

The surface modified zinc oxide before mixing with vitamin E is subjected to measurements as follows.
A blank solution is prepared by mixing 3 g of the powder containing surface-modified zinc oxide and 5 g of cyclopentasiloxane.
Next, the quartz cell with an optical path length of 0.1 mm containing the blank solution is set in an ultraviolet-visible-near infrared spectrophotometer (manufactured by Hitachi High-Tech Science Corporation, model number: UH4150). The diffuse reflectance spectrum of the mixed solution is measured using an integrating sphere, and then _L1 ^* , _a1 ^* , and _b1 ^* of the blank solution are calculated from the measurement results.

Measurements are performed on the surface modified zinc oxide after mixing with Vitamin E as follows:
Vitamin E and cyclopentasiloxane are mixed to prepare a cyclopentasiloxane mixed solvent having a vitamin E concentration of 2% by mass.
3 g of powder containing surface-modified zinc oxide and 5 g of cyclopentasiloxane mixed solvent are mixed to prepare a sample solution containing vitamin E. The diffuse reflectance spectrum of the sample solution is measured by the above-mentioned method, and then the _L2 ^* , _a2 ^* , and _b2 ^* of the sample solution are calculated from the measurement results.

From the above results, the color difference ΔE = (( _L2 ^* - _L1 ^* ) ² + ( _a2 ^* - _a1 ^* ) ² + ( _b2 ^* - _b1 ^* ) ² ) ^1/2 is calculated, where _L1 ^* , _a1 ^* , _b1 ^* , _L2 ^* , _a2 ^* , and _b2 ^* indicate values in the L ^* a ^* b ^* color system chromaticity diagram.

It is unclear why the dispersibility of the surface-modified zinc oxide is improved by the color difference ΔE before and after the vitamin E mixing test being 5 or less. It is speculated that the reason why the color difference ΔE is small is because the generation of active oxygen is suppressed.
However, there is no method for directly measuring how the surface treatment agent modifies the surface of zinc oxide particles. Therefore, the details of the action of the surface treatment agent to modify the surface of zinc oxide particles to reduce the color difference ΔE are unclear. It is speculated that this is because the surface treatment agent is uniformly and densely present on the surface of zinc oxide particles, but it is also assumed that this alone cannot explain the phenomenon.

It is presumed that the effect of sufficiently suppressing the generation of active oxygen and improving dispersibility by making the color difference ΔE 5 or less is manifested by a complex intertwining of multiple factors. For example, one of the factors may be the manufacturing conditions in which the surface treatment agent is dissolved in supercritical carbon dioxide and then mixed with zinc oxide particles. It is presumed that the surface treatment agent has better compatibility with non-polar molecular solvents than zinc oxide particles, and therefore may contribute to improving dispersibility.
However, it is believed to be virtually impossible to directly describe or identify the characteristics of surface-modified zinc oxide based on the surface state that emerges when the surface treatment agent is dissolved in supercritical carbon dioxide beforehand and then surface-modified.

As a result of various investigations, the present inventors have focused on the color difference ΔE and found that by dissolving a surface treatment agent in supercritical carbon dioxide in advance and then performing surface treatment, the color difference ΔE can be reduced to 5 or less. Surface-modified zinc oxide with a color difference ΔE of 5 or less has excellent dispersibility and can sufficiently suppress the generation of active oxygen. When ΔE is 3 or less, no difference can be seen visually, but when ΔE is 2 or less, the surface treatment is strong and is very excellent for cosmetic applications.
From the above viewpoints, the color difference ΔE is preferably 4.5 or less, more preferably 3 or less, and even more preferably 2 or less.

Properties of Surface-Modified Zinc Oxide According to a Preferred Embodiment
The D90 of the surface-modified zinc oxide is preferably 1 μm or less, more preferably 0.5 μm or less, even more preferably 0.4 μm or less, and particularly preferably 0.3 μm or less.
Surface-modified zinc oxide having a D90 of 1 μm or less is useful for use in cosmetics. The lower limit of D90 may be 0.05 μm or 0.1 μm.
The upper and lower limits of the D90 of the surface-modified zinc oxide can be arbitrarily combined. The D90 of the surface-modified zinc oxide is the particle size when the cumulative volume percentage of the particle size distribution is 90%.

The specific surface area of the surface-modified zinc oxide is not particularly limited, but is preferably 1.5 m ² /g or more, more preferably 10.0 m ² /g or more, and even more preferably 30.0 m ² /g or more.
The specific surface area of the surface-modified zinc oxide may be, for example, 300 ^m2 /g or less, preferably 150 ^m2 /g or less, and more preferably 100 ^m2 /g or less. If necessary, the specific surface area of the surface-modified zinc oxide may be 80 ^m2 /g or less, 60 ^m2 /g or less, or 50 ^m2 /g or less. The upper and lower limit values of the specific surface area of the surface-modified zinc oxide can be combined in any manner.
If the specific surface area of the surface-modified zinc oxide is 1.5 to 300 ^{m 2} /g, light scattering and reflection of ultraviolet light are likely to occur.

The specific surface area (unit: m ² /g) of the surface-modified zinc oxide is the BET specific surface area determined by the BET method.
The specific surface area of the surface-modified zinc oxide can be measured, for example, by the BET method using a fully automatic specific surface area measuring device (product name: Macsorb HM Model-1201, manufactured by Mountec Co., Ltd.).

(Zinc oxide particles)
The specific surface area of the zinc oxide particles before being treated with the surface treatment agent is not particularly limited, but is preferably 1.5 m ² /g or more, more preferably 10.0 m ² /g or more, and even more preferably 30.0 m ² /g or more. The specific surface area is preferably 300 m ² /g or less, and more preferably 150 m ² /g or less. If necessary, the specific surface area may be 100 m ² /g or less, 80 m ² /g or less, or 50 m ² /g or less.

The specific surface area of zinc oxide particles before treatment and the specific surface area of surface-modified zinc oxide vary somewhat depending on how the surface treatment agent is attached, but do not change significantly. Therefore, in order to obtain surface-modified zinc oxide with a desired specific surface area, zinc oxide particles having the desired specific surface area can be used. Therefore, the details and preferred aspects of the specific surface area of surface-modified zinc oxide can be the same as those of the specific surface area of zinc oxide particles.

The BET average particle diameter of the zinc oxide particles before treatment with the surface treatment agent is preferably 3 to 200 nm, more preferably 5 to 100 nm, and even more preferably 10 to 100 nm. When the BET average particle diameter is equal to or greater than the lower limit of the above-mentioned numerical range, it is easy to obtain a surface-modified zinc oxide that can more sufficiently suppress the generation of active oxygen. When the BET average particle diameter is equal to or less than the upper limit of the above-mentioned numerical range, it is easy to obtain a surface-modified zinc oxide with even more excellent dispersibility.
The upper and lower limits of the BET average particle diameter of the zinc oxide particles before being treated with a surface treatment agent can be arbitrarily combined. The BET average particle diameter of the zinc oxide particles before being treated with a surface treatment agent refers to the particle diameter calculated by the formula average particle diameter (nm) = 6000/(S × density) using the specific surface area S ( ^m2 /g) measured by the BET method and the density (g/ ^cm3 ) of the zinc oxide particles.

(Surface treatment agent)
The surface treatment agent is not particularly limited as long as it is hydrolyzable. Here, "hydrolyzable" includes not only hydrolysis of alkoxy groups, but also dealkalization of metal soaps and dehydrogenation of SiH of silicone.

Examples of surface treatment agents include silicon compounds, fatty acids, fatty acid soaps, fatty acid esters, organic titanate compounds, aluminum compounds, and surfactants. One type of surface treatment agent may be used alone, or two or more types may be used in combination.

Examples of fatty acids include palmitic acid, isostearic acid, stearic acid, lauric acid, myristic acid, behenic acid, oleic acid, rosin acid, and 12-hydroxystearic acid.
Examples of fatty acid soaps include magnesium stearate, zinc stearate, aluminum stearate, calcium stearate, magnesium myristate, zinc myristate, aluminum distearate, aluminum dimyristate, and aluminum 12-hydroxystearate.
Examples of fatty acid esters include dextrin fatty acid esters, cholesterol fatty acid esters, sucrose fatty acid esters, and starch fatty acid esters.

Examples of the organic titanate compound include isopropyl triisostearoyl titanate, isopropyl dimethacryl isostearoyl titanate, isopropyl tri(dodecyl)benzenesulfonyl titanate, neopentyl(diallyl)oxy-tri(dioctyl)phosphate titanate, and neopentyl(diallyl)oxy-trineododecanoyl titanate.
Examples of the aluminum compound include organoaluminum compounds and aluminum hydroxide.
Examples of the organoaluminum compound include an aluminate coupling agent and an aluminum complex.

Examples of the silicon compound include a silane compound, a silicone compound, and a silane coupling agent.
The silicon compounds may be used alone or in combination of two or more kinds.

Examples of the silane compound include alkylsilanes and fluoroalkylsilanes.
Examples of alkylsilanes include methyltrimethoxysilane, ethyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, and octyltriethoxysilane.
Examples of fluoroalkylsilanes include trifluoromethylethyltrimethoxysilane and heptadecafluorodecyltrimethoxysilane.
As the silane compound, alkylsilanes are preferred, and octyltriethoxysilane is particularly preferred. The silane compounds may be used alone or in combination of two or more.

Examples of silicone compounds include silicone oil, methicone, dimethicone, hydrogen dimethicone, triethoxysilylethyl polydimethylsiloxyethyl dimethicone, triethoxysilylethyl polydimethylsiloxyethylhexyl dimethicone, (acrylates/tridecyl acrylate/triethoxysilylpropyl methacrylate/dimethicone methacrylate) copolymer, and triethoxycaprylylsilane.
Examples of silicone oils include methylhydrogenpolysiloxane, dimethylpolysiloxane, and methylphenylpolysiloxane.
The silicone compound may be used alone or in combination of two or more kinds. A copolymer of these silicone compounds may also be used as the silicone compound.

An example of a silane coupling agent is a silane coupling agent having an alkoxy group represented by the following formula (1):

R ¹ Si(OR ² ) ₃ ...(1)
In formula (1), R ¹ is an alkyl group having 1 to 18 carbon atoms, a fluoroalkyl group or a phenyl group, and R ² is an alkyl group having 1 to 4 carbon atoms.

The silane coupling agents may be used alone or in combination of two or more.
As the silane coupling agent, alkylalkoxysilane, allylalkoxysilane, polysiloxane having an alkyl group on the side chain, and polysiloxane having an allyl group on the side chain are preferred.

Examples of alkylalkoxysilanes include tetramethoxyorthosilane, tetraethoxyorthosilane, tetrapropoxyorthosilane, tetrabutoxyorthosilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, and diphenyldiethoxysilane.
The alkylalkoxysilanes may be used alone or in combination of two or more kinds.

As the silane coupling agent, a polymeric silane coupling agent having a siloxane skeleton as the main chain and an alkoxy group and an acrylic group in the molecular structure may be used. Examples of the polymeric silane coupling agent include dimethoxydiphenylsilane-triethoxycaprylylsilane crosspolymer, triethoxysilylethyl polydimethylsiloxyethyl dimethicone, and triethoxysilylethyl polydimethylsiloxyethylhexyl dimethicone.

As the silane coupling agent, a fluoroalkylalkoxysilane may be used. Examples of the fluoroalkylalkoxysilane include trifluoropropyltrimethoxysilane, perfluorooctyltriethoxysilane, and tridecafluorooctyltriethoxysilane.

As the silane coupling agent, a silane coupling agent having an octyl group in the molecule is preferable. A silane coupling agent that can be used with a wide range of oil phases of polarity, from natural oils and ester oils to silicone oils, is more preferable. As the silane coupling agent, at least one selected from the group consisting of n-octyltriethoxysilane, n-octyltrimethoxysilane, and dimethoxydiphenylsilane-triethoxycaprylylsilane crosspolymer is particularly preferable.

When surface-modified zinc oxide is applied to cosmetics, preferred silicon compounds are, for example, methicone, dimethicone, hydrogen dimethicone, octyltrimethoxysilane, octyltriethoxysilane, and triethoxycaprylylsilane.

<Method for producing surface-modified zinc oxide>
The surface-modified zinc oxide can be produced by a production method including the following (i), (ii) and (iii).
(i): Contacting zinc oxide particles and a surface treatment agent in a container in the presence of supercritical carbon dioxide.
(ii): Reducing the pressure inside the container to remove carbon dioxide and recover a mixture of zinc oxide particles and a surface treatment agent.
(iii): heating the mixture to cause a reaction between the zinc oxide particles and the surface treatment agent.
Here, the details and preferred embodiments of the zinc oxide particles and the surface treatment agent are the same as those described above.

Carbon dioxide has a critical temperature (Tc) of 31° C. and a critical pressure (Pc) of 7.4 MPa. Supercritical carbon dioxide refers to carbon dioxide having a pressure equal to or higher than the critical temperature (Tc) and equal to or higher than the critical pressure (Pc).
Supercritical carbon dioxide has the following characteristics: high diffusivity close to that of a gas, dissolving power close to that of a liquid, no surface tension, and instantaneous gasification. Supercritical carbon dioxide also has the property that its density changes suddenly with a slight change in pressure.
When the pressure of supercritical carbon dioxide is further increased slightly above the critical pressure (Pc) and critical temperature (Tc), the density of supercritical carbon dioxide increases rapidly. Therefore, in the region above the critical pressure, the solubility of the solute in carbon dioxide increases rapidly. Conversely, when the pressure of supercritical carbon dioxide is reduced, the solubility of the solute in carbon dioxide can be reduced rapidly. Therefore, it is possible to separate the solute from the supercritical carbon dioxide simply by reducing the pressure.

According to the production method including the above (i), (ii) and (iii), the surface treatment agent can be dissolved in supercritical carbon dioxide. By contacting zinc oxide particles with the surface treatment agent in the presence of supercritical carbon dioxide, the surface treatment agent can be uniformly and efficiently adsorbed onto the surfaces of the zinc oxide particles.
In addition, after the zinc oxide particles and the surface treatment agent are contacted, the supercritical carbon dioxide can be instantly converted to gaseous carbon dioxide by adjusting the pressure and temperature in the system. Since the gaseous carbon dioxide can be instantly removed from the system by drying, the mixture of the zinc oxide particles and the surface treatment agent can be efficiently recovered while suppressing aggregation during drying.

In the recovered mixture, composite particles are present in which the surface treatment agent is uniformly and densely adsorbed onto the surface of zinc oxide particles. Therefore, by heating the zinc oxide particles and surface treatment agent mixed in the presence of supercritical carbon dioxide, the surfaces of the zinc oxide particles can be efficiently and densely treated with the surface treatment agent. As a result, it is believed that the generation of active oxygen can be sufficiently suppressed, and surface-modified zinc oxide with excellent dispersibility can be obtained.

In (i) above, the temperature and pressure conditions in the container when the zinc oxide particles and the surface treatment agent are brought into contact with each other in the presence of supercritical carbon dioxide can be appropriately set by a person skilled in the art in consideration of the properties of supercritical carbon dioxide described above. In (ii) above, the temperature and pressure conditions in the container when carbon dioxide is removed can also be appropriately set by a person skilled in the art in consideration of the properties of supercritical carbon dioxide described above.

In (iii) above, the conditions for reacting the zinc oxide particles with the surface treatment agent are not particularly limited. They can be appropriately set by a person skilled in the art depending on the properties of the zinc oxide particles and the surface treatment agent.

The mixing ratio of zinc oxide particles and surface treatment agent during production is not particularly limited. For example, the ratio of the surface treatment agent is preferably 1 to 100 parts by mass, more preferably 2 to 50 parts by mass, and even more preferably 2 to 30 parts by mass, per 100 parts by mass of zinc oxide particles. If the ratio of the surface treatment agent is equal to or greater than the lower limit of the above numerical range, the treatment reaction is likely to proceed, and the surface of the zinc oxide particles is likely to be sufficiently modified. As a result, it is easy to obtain surface-modified zinc oxide that can further sufficiently suppress the generation of active oxygen. If the ratio of the surface treatment agent is equal to or less than the upper limit of the above numerical range, the surface treatment agent is less likely to be liberated by itself. This makes it possible to shorten the treatment time.

The mixing ratio of zinc oxide particles and surface treatment agent during production may vary slightly from the mass ratio of zinc oxide particles and chemical structures derived from the surface treatment agent in the resulting surface-modified zinc oxide powder, but does not change significantly. Therefore, in order to obtain a surface-modified zinc oxide powder with a desired mass ratio, the mixing ratio of zinc oxide particles and surface treatment agent during production may be set to a desired value. Therefore, the details and preferred aspects of the mass ratio of zinc oxide particles and chemical structures derived from the surface treatment agent in the surface-modified zinc oxide can be the same as the mixing ratio of zinc oxide particles and surface treatment agent during production.

<Applications of surface-modified zinc oxide>
The following describes some examples of uses of the surface-modified zinc oxide. The following descriptions are representative examples of uses, and are not intended to limit the scope of the invention.

(Dispersion)
The dispersion includes a surface-modified zinc oxide and a dispersion medium. The dispersion may include a paste-like dispersion having a high viscosity.
The dispersion medium is not particularly limited as long as it can disperse the surface-modified zinc oxide. For example, when the surface-modified zinc oxide is used for a cosmetic application, a dispersion medium that can be formulated in a cosmetic may be used.

Examples of the dispersion medium include chain polysiloxanes such as dimethylpolysiloxane, methylphenylpolysiloxane, and diphenylpolysiloxane;
Cyclic polysiloxanes such as octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane;
Modified polysiloxanes such as amino-modified polysiloxanes, polyether-modified polysiloxanes, alkyl-modified polysiloxanes, and fluorine-modified polysiloxanes;
Hydrocarbon oils such as liquid paraffin, squalane, isoparaffin, branched light paraffin, vaseline, ceresin, dodecane, isododecane, tridecane, tetradecane, hexadecane, isohexadecane, and octadecane;
Ester oils such as isopropyl myristate, cetyl isooctanoate, glyceryl trioctanoate, tri(caprylic/capric)glyceryl, and alkyl benzoate (C12-15);
Higher fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid;
Examples of the hydrophobic dispersion medium include higher alcohols such as lauryl alcohol, cetyl alcohol, stearyl alcohol, octyldodecanol, and isostearyl alcohol.

In addition to the hydrophobic dispersion medium, examples of the dispersion medium include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-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;
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;
Aromatic hydrocarbons such as benzene, toluene, ethylbenzene, 1-phenylpropane, isopropylbenzene, n-butylbenzene, tert-butylbenzene, sec-butylbenzene, o-, m- or p-xylene, 2-, 3- or 4-ethyltoluene;
Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone;
Amides such as dimethylformamide, N,N-dimethylacetoacetamide, and N-methylpyrrolidone; nitriles such as acetonitrile;
Natural oils such as oleic acid, jojoba oil, olive oil, coconut oil, grapeseed oil, castor oil, rice bran oil, horse oil, and mink oil.
The dispersion medium may be used alone or in combination of two or more kinds.

When surface-modified zinc oxide is used in cosmetic applications, the preferred dispersion media are linear polysiloxanes, cyclic polysiloxanes, modified polysiloxanes, hydrocarbon oils, ester oils, higher fatty acids, higher alcohols, natural oils, ethanol, and glycerin.

The dispersion may further contain commonly used additives to the extent that the properties of the dispersion are not impaired. Examples of additives include preservatives, dispersants, dispersion aids, stabilizers, water-soluble binders, thickeners, oil-soluble drugs, oil-soluble dyes, oil-soluble proteins, and UV absorbers.

The particle size (D50) when the cumulative volume percentage of the particle size distribution in the dispersion is 50% is not particularly limited, but is preferably 300 nm or less, more preferably 250 nm or less, and even more preferably 200 nm or less. The upper limit of D50 may be 150 nm or less, or 100 nm or less. The lower limit of D50 is not particularly limited, and may be, for example, 20 nm or more, 40 nm or more, or 60 nm or more. The upper and lower limits of D50 can be combined in any combination.

The particle size (D90) when the cumulative volume percentage of the particle size distribution in the dispersion is 90% is preferably 350 nm or less, more preferably 300 nm or less, and even more preferably 250 nm or less.
The lower limit of D90 is not particularly limited, and may be, for example, 60 nm or more, 80 nm or more, or 100 nm or more. The upper and lower limits of D90 can be combined in any manner.

When the D50 of the dispersion is 300 nm or less, the surface-modified zinc oxide is more likely to be uniformly distributed when a cosmetic produced using this dispersion is applied to the skin, and this is preferable because the ultraviolet ray shielding effect is improved. When the D90 of the dispersion is 350 nm or less, this is preferable because the transparency of the dispersion is high.

One example of a method for measuring the cumulative volume percentage of particle size distribution in a dispersion liquid is a method using a dynamic light scattering particle size distribution measuring device (manufactured by Microtrac Bell, model number: NANOTRAC WAVE).

The content of the surface-modified zinc oxide in the dispersion is appropriately adjusted depending on the desired properties of the dispersion.
When the dispersion is used in a cosmetic preparation, the content of the surface-modified zinc oxide in the dispersion is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.
The upper and lower limits for the content of the surface-modified zinc oxide in the dispersion may be combined in any desired manner.

When the content of surface-modified zinc oxide in the dispersion is within the above numerical range, the surface-modified zinc oxide tends to be at a sufficiently high concentration in the dispersion. This tends to improve the freedom of cosmetic formulation. In addition, the viscosity of the dispersion can be easily adjusted to a range that is easy to handle.

When the content of surface-modified zinc oxide is 37.5% by mass, the viscosity of the dispersion at 20°C is preferably 5000 mPa·s or less, more preferably 3000 mPa·s or less, and even more preferably 1000 mPa·s or less. If the viscosity is equal to or less than the upper limit, it can be said that the dispersion has excellent dispersibility. The lower limit of the viscosity of the dispersion is not particularly limited, but may be, for example, 10 mPa·s, 100 mPa·s, or 300 mPa·s.
The viscosity of the dispersion at 20° C. is measured by a tuning fork vibration viscometer (Model: SV-10, manufactured by A&D Co., Ltd.) The measured value is taken 5 minutes after the start of sample measurement.

The method for producing the dispersion is not particularly limited, and may be, for example, a method in which the surface-modified zinc oxide is mechanically dispersed in a dispersion medium using a dispersing device.
The dispersion device is not particularly limited, and examples thereof include a stirrer, a planetary mixer, a homomixer, an ultrasonic homogenizer, a sand mill, a ball mill, and a roll mill.

(Composition)
The composition includes a surface-modified zinc oxide, a dispersing medium, and a resin.
The content of the surface-modified zinc oxide in the composition is appropriately adjusted depending on the desired properties of the composition. The content of the surface-modified zinc oxide in the composition is, for example, preferably 10 to 40 mass %, more preferably 20 to 40 mass %.

When the content of surface-modified zinc oxide in the composition is within the above range, the surface-modified zinc oxide tends to be highly concentrated in the composition. As a result, the properties of the surface-modified zinc oxide can be fully obtained, and a composition in which the surface-modified zinc oxide is uniformly dispersed can be obtained.

The dispersion medium of the composition is not particularly limited as long as it is one that is generally used in industrial applications.
Examples of the dispersion medium include alcohols such as methanol, ethanol, and propanol;
Methyl acetate, ethyl acetate, toluene, methyl ethyl ketone, methyl isobutyl ketone, and the like.
The content of the dispersion medium in the composition is not particularly limited and is appropriately adjusted depending on the desired properties of the composition.

The resin is not particularly limited as long as it is one that is generally used in industrial applications, and examples of the resin include acrylic resin, epoxy resin, urethane resin, polyester resin, and silicone resin.
The content of the resin in the composition is not particularly limited and is appropriately adjusted depending on the desired properties of the composition.

The composition may contain commonly used additives to the extent that the properties of the composition are not impaired.
Examples of the additives include a polymerization initiator, a dispersant, and a preservative.

The method for producing the composition is not particularly limited. For example, the surface-modified zinc oxide, the resin and the dispersion medium are mechanically mixed in a mixing device. The composition may be prepared by mechanically mixing the above-mentioned dispersion and the resin in a mixing device.
Examples of the mixing device include a stirrer, a planetary mixer, a homomixer, and an ultrasonic homogenizer.

The use of the composition is not particularly limited. For example, a coating film can be formed by applying the composition to a plastic substrate such as a polyester film by a conventional application method such as roll coating, flow coating, spray coating, screen printing, brush coating, or immersion.

(Cosmetics)
The cosmetic contains surface-modified zinc oxide and a cosmetic base raw material. In addition to the surface-modified zinc oxide and the cosmetic base raw material, the cosmetic may further contain a dispersion medium.
A cosmetic base raw material is a raw material that can be the main component of a cosmetic product. Examples of cosmetic base raw materials include oil-based raw materials, water-based raw materials, surfactants, and powder raw materials.

Examples of oil-based raw materials include fats and oils, higher fatty acids, higher alcohols, and ester oils.
Examples of aqueous ingredients include purified water, alcohol, and thickeners.
Examples of powdered raw materials include colored pigments, white pigments, pearlescent agents, and extender pigments.

Cosmetic base raw materials may be used alone or in combination of two or more types. As cosmetic base raw materials, the use of oil-based raw materials alone, powder raw materials alone, or a combination of oil-based raw materials and powder raw materials is preferred, and the use of oil-based raw materials alone is more preferred.

In cosmetics, the surface-modified zinc oxide is preferably contained in an oil component or oil phase.
The oil component used in the oil-based cosmetic or oil phase of the emulsion is not particularly limited as long as it is one that is commonly used in cosmetics, such as silicone oil, oils and fats, higher fatty acids, higher alcohols, ester oils, and natural oils.

The content of the surface-modified zinc oxide in the cosmetic is appropriately adjusted according to the properties of the cosmetic to be produced. For example, the lower limit of the content of the surface-modified zinc oxide 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 content of the surface-modified zinc oxide may be 50% by mass or less, 40% by mass or less, or 30% by mass or less.
The upper and lower limit values for the content of the surface-modified zinc oxide in the cosmetic can be combined in any manner.

The cosmetic may be an oil-based cosmetic, or an emulsion-type cosmetic containing surface-modified zinc oxide in an oil phase, or a cosmetic in which the surface-modified zinc oxide is contained in an oil component (oil phase) during the production process or in the final form, such as a powdered solid cosmetic produced by mixing surface-modified zinc oxide with an oil and then removing the oil to form a molded product.
The emulsion-type cosmetic preparation may be an O/W type emulsion or a W/O type emulsion.

Cosmetics can be obtained by blending the surface-modified zinc oxide or the above-mentioned dispersion with a cosmetic base such as milky lotion, cream, sunscreen, foundation, lipstick, blusher, eyeshadow, or the like.
The cosmetic preparation can be obtained, for example, by blending the surface-modified zinc oxide or the above-mentioned dispersion liquid into an oil phase to form an O/W or W/O emulsion, and then blending the emulsion with the cosmetic preparation raw materials.

A sunscreen cosmetic will be described in detail below as an example of the cosmetic.
In order to effectively block ultraviolet rays, particularly long-wavelength ultraviolet rays (UVA), and obtain a good feeling of use with little powderiness or squeaking, the lower limit of the content of the surface-modified zinc oxide in the sunscreen cosmetic is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more. The upper limit of the content of the surface-modified zinc oxide in the sunscreen cosmetic may be 50% by mass or less, 40% by mass or less, or 30% by mass or less. The upper and lower limit values of the content of the surface-modified zinc oxide in the sunscreen cosmetic can be combined in any manner.

The sunscreen cosmetic may further contain, as necessary, a hydrophobic dispersion medium, inorganic fine particles or inorganic pigments other than surface-modified zinc oxide, a hydrophilic dispersion medium, oils and fats, surfactants, moisturizers, thickeners, pH adjusters, nutrients, antioxidants, fragrances, etc.

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 decamethylcyclopentasiloxane, dimethylpolysiloxane, and methylphenylpolysiloxane;
Higher fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid;
Higher alcohols such as lauryl alcohol, cetyl alcohol, stearyl alcohol, hexyldodecanol, and isostearyl alcohol.

Examples of inorganic fine particles and inorganic pigments other than surface-modified zinc oxide contained in cosmetics include calcium carbonate, calcium phosphate (apatite), magnesium carbonate, calcium silicate, magnesium silicate, aluminum silicate, kaolin, talc, titanium oxide, aluminum oxide, yellow iron oxide, gamma-iron oxide, cobalt titanate, cobalt violet, and silicon oxide.

The sunscreen cosmetic may further contain at least one organic ultraviolet absorbing agent.
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, and silicone-based cinnamic acid ultraviolet absorbers.

Examples of benzotriazole-based UV absorbers include 2,2'-hydroxy-5-methylphenylbenzotriazole, 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, and 2-(2'-hydroxy-5'-methylphenylbenzotriazole.

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

Examples of 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, and N,N-dimethyl PABA methyl ester.

An example of an anthranilic acid-based UV absorber is homomenthyl-N-acetylanthranilate.

Examples of salicylic acid-based UV absorbers include amyl salicylate, menthyl salicylate, homomenthyl salicylate, octyl salicylate, phenyl salicylate, benzyl salicylate, and p-2-propanol phenyl salicylate.

Examples of cinnamic acid-based UV absorbers include octyl methoxycinnamate (ethylhexyl methoxycinnamate), glyceryl di-paramethoxycinnamate-mono-2-ethylhexanoate, octyl cinnamate, ethyl 4-isopropyl cinnamate, methyl 2,5-diisopropyl cinnamate, ethyl 2,4-diisopropyl cinnamate, methyl 2,4-diisopropyl cinnamate, propyl p-methoxycinnamate, isopropyl p- Examples include methoxycinnamate, 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-di-para-methoxycinnamate.

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.

Other organic UV absorbers include, for example, 3-(4'-methylbenzylidene)-d,l-camphor, 3-benzylidene-d,l-camphor, urocanic acid, urocanic acid ethyl ester, 2-phenyl-5-methylbenzoxazole, 5-(3,3'-dimethyl-2-norbornylidene)-3-pentan-2-one, silicone-modified UV absorbers, and fluorine-modified UV absorbers.

The present invention will be described in more detail below using examples. However, the present invention is not limited to the description of the following examples.

<Ingredients, abbreviations>
(Zinc oxide particles)
FZO-50: Zinc oxide fine particle powder with a BET average particle size of 21 nm (manufactured by Ishihara Sangyo Kaisha).
F-1: Zinc oxide fine particle powder having a BET average particle size of 100 nm (product of Hakusui Tech Co., Ltd.).

(Surface treatment agent)
KF-9901: Hydrogen Dimethicone (Shin-Etsu Chemical Co., Ltd. product)
KF-99: Methicone (product of Shin-Etsu Chemical Co., Ltd.)
KBE-3083: Octyltriethoxysilane (product of Shin-Etsu Chemical Co., Ltd.)

Example 1
100 g of FZO-50 and 5 g of KF-9901 were mixed and placed in a pressure vessel. Carbon dioxide gas was injected into the pressure vessel, and the pressure was increased until a supercritical state was reached, and the temperature was adjusted. Thereafter, FZO-50 and KF-9901 were mixed in the presence of supercritical carbon dioxide, thereby allowing KF-9901 to be in sufficient contact with the surface of FZO-50.
Next, the pressure in the pressure-resistant container was reduced to convert the supercritical carbon dioxide into carbon dioxide gas. The carbon dioxide gas was separated to extract the powder of the mixture. The powder was then placed in an oven at 120°C for heat treatment. The heat treatment caused FZO-50 and KF-9901 to react with each other, and the surface-modified zinc oxide powder of Example 1 was obtained.

<Examples 2 to 6>
Surface-modified zinc oxide powders of each example were obtained by supercritical treatment in the same manner as in Example 1, except that the type of zinc oxide particles, the type of silicon compound in the surface treatment agent, and the mixing ratio of the surface treatment agent to the zinc oxide particles (amount of treatment agent) were changed as shown in Table 1.

<Comparative Example 1>
While FZO-50 was being stirred at high speed with a Henschel mixer, KF-9901 was added dropwise to FZO-50 so that the mixing ratio (amount of treatment agent) was 5 mass %. After stirring for 5 minutes, the powder obtained was heat-treated in an oven at 120° C. to obtain the powder of Comparative Example 1.

<Comparative Examples 2-5 and 7>
Powders of each example were obtained by dry processing in the same manner as in Comparative Example 1, except that the type of zinc oxide particles, the type of treating agent, and the amount of treating agent were changed as shown in Table 2.

<Comparative Example 6>
KF-9901 was weighed and dissolved in methyl ethyl ketone to a concentration of 5% by mass. 100 g of FZO-50 was added to 100 g of this solution, and then ultrasonic irradiation was performed for 5 minutes using an ultrasonic disperser ("UH-600S" manufactured by SMT Corporation, horn diameter 20 mm, scale 7). Next, methyl ethyl ketone was completely removed using a rotary evaporator, and the obtained powder was heat-treated in an oven at 120°C to obtain the powder of Comparative Example 6.

<Comparative Example 8>
In Comparative Example 8, the following evaluation was carried out on FZO-50 without surface treatment.

<Measurement and Evaluation>
(Color difference ΔE)
The color difference ΔE before and after the vitamin E mixing test was measured by the method described below.
The powder of each example before being mixed with vitamin E was subjected to the following measurements.
A blank solution was prepared by mixing 3 g of powder and 5 g of cyclopentasiloxane. Then, a quartz cell with an optical path length of 0.1 mm containing the blank solution was set in an ultraviolet-visible-near infrared spectrophotometer (manufactured by Hitachi High-Tech Science Corporation, model number: UH4150). After measuring the diffuse reflectance spectrum of the mixed solution using an integrating sphere, L ₁ ^* , a ₁ ^* , and b ₁ ^* of the blank solution were calculated from the measurement results.

The powder of each example after mixing with vitamin E was subjected to the following measurements.
Vitamin E and cyclopentasiloxane were mixed to prepare a cyclopentasiloxane mixed solvent having a vitamin E concentration of 2% by mass.
3 g of the powder and 5 g of the cyclopentasiloxane mixed solvent were mixed to prepare a sample solution containing vitamin E. The diffuse reflectance spectrum of the sample solution was measured by the above-mentioned method, and then the _L2 ^* , _a2 ^* , and _b2 ^* of the sample solution were calculated from the measurement results.

From the above results, the color difference ΔE=((L ₂ ^* −L ₁ ^* ) ² +(a ₂ ^* −a ₁ ^* ) ² +(b ₂ ^* −b ₁ ^* ) ² ) ^1/2 was calculated.

(Dispersibility)
30 g of powder and 50 g of cyclopentasiloxane were mixed. The viscosity of the resulting dispersion at 20° C. was measured using a tuning fork vibration viscometer (manufactured by A&D Co., Ltd., model number: SV-10). The dispersion state was measured according to the following criteria:
A: The viscosity of the dispersion is less than 1000 mPa·s. The dispersion state is good.
B: The viscosity of the dispersion is 1000 mPa·s or more and less than 5000 mPa·s. The dispersion state is somewhat poor.
C: The viscosity of the dispersion is 5000 mPa·s or more. The dispersion state is poor.

<Results>
The results of each example are shown in Tables 1 and 2.

In Examples 1 to 6, the color difference ΔE was 5 or less. Therefore, the generation of active oxygen was sufficiently suppressed. Furthermore, surface-modified zinc oxide with excellent dispersibility was obtained. In contrast, in Comparative Examples 1 to 8, the dispersibility was poor. It is considered that the generation of active oxygen cannot be sufficiently suppressed in Comparative Examples 1 to 8, in which the color difference ΔE exceeded 5.

The present invention provides a surface-modified zinc oxide that can sufficiently suppress the generation of active oxygen and has excellent dispersibility, as well as a method for producing the same.

Claims (9)

The zinc oxide particles are surface-modified zinc oxide particles in which the surfaces of the zinc oxide particles are treated with a surface treatment agent,
A surface-modified zinc oxide having a color difference ΔE of 5 or less before and after a vitamin E mixing test. The surface-modified zinc oxide of claim 1, wherein the surface treatment agent includes a silicon compound. The surface-modified zinc oxide according to claim 2, wherein the silicon compound is at least one selected from the group consisting of silane compounds, silicone compounds, and silane coupling agents. Contacting zinc oxide particles and a surface treatment agent in a container in the presence of supercritical carbon dioxide;
Removing carbon dioxide by reducing the pressure inside the container to recover the mixture of the zinc oxide particles and the surface treatment agent; and
heating the mixture to react the zinc oxide particles and the surface treatment agent;
A method for producing surface-modified zinc oxide comprising the steps of: The manufacturing method according to claim 4, wherein the surface treatment agent includes a silicon compound. The method according to claim 5, wherein the silicon compound is at least one selected from the group consisting of silane compounds, silicone compounds, and silane coupling agents. A dispersion liquid comprising the surface-modified zinc oxide according to any one of claims 1 to 3 and a dispersion medium. A composition comprising the surface-modified zinc oxide according to any one of claims 1 to 3, a dispersion medium, and a resin. A cosmetic comprising the surface-modified zinc oxide according to any one of claims 1 to 3 and a cosmetic base ingredient.