Zinc oxide powder, method for producing same, and surface-treated zinc oxide powder and composition containing same

Abstract

This zinc oxide powder is characterized in that when 5 g of the zinc oxide powder are added to 70g of ion exchange water and stirred, the concentration of zinc ions released in the water is 0.2 ppm or less. Thus, provided are: a zinc oxide powder and a surface-treated zinc oxide powder for which the concentration of zinc ions released in water is reduced to a specific level or less; and a composition that can reduce the environmental load and has excellent stability over time.

Description

Zinc oxide powder, its manufacturing method, surface-treated zinc oxide powder, and composition containing the same

[0001] The present invention relates to a zinc oxide powder and a method for producing the same, as well as a surface-treated zinc oxide powder and a composition containing the same.

[0002] Zinc oxide is environmentally toxic because it releases zinc ions into water, and it is generally known that when zinc oxide is used in aqueous cosmetics, the released zinc ions act on anionic aqueous thickeners, significantly impairing the stability of the cosmetics. One example of anionic aqueous thickeners is carbomer, a carboxyvinyl polymer. However, when used in combination with zinc oxide, the zinc ions released from the zinc oxide reduce the viscosity of the carbomer.

[0003] Patent Document 1 describes a silicon oxide-coated zinc oxide comprising zinc oxide particles and a silicon oxide coating on the surfaces of the zinc oxide particles, characterized in that the suspension water conductivity is 120 μS / cm or less. According to this document, since the suspension water conductivity is 120 μS / cm or less, even when the zinc oxide is applied to aqueous materials such as aqueous cosmetics, it is possible to suppress the decrease in viscosity caused by carbomer and maintain the quality stability of the aqueous material. However, there has been a demand for further suppression of zinc ion elution from zinc oxide.

[0004] WO2016 / 136797

[0005] The present invention has been made to solve the above-mentioned problems, and aims to provide a zinc oxide powder and a surface-treated zinc oxide powder in which the concentration of zinc ions eluted in water is reduced to a certain level or less, and also to provide a composition which can reduce the environmental load and has excellent stability over time.

[0006] The above problem is solved by providing a zinc oxide powder characterized in that when 5 g of the zinc oxide powder is added to 70 g of ion-exchanged water and the mixture is stirred, the concentration of zinc ions dissolved in the water is 0.2 ppm or less.

[0007] At this time, the BET specific surface area is 0.5 to 100 m ２ / g, and CO ２ -CO measured by TPD ２ Ratio of desorption amount to BET specific surface area (CO ２ Desorption amount / BET specific surface area) is 1.4 μmol / m ２ It is preferable that the above is true.

[0008] The above-mentioned problems can also be solved by providing a method for producing zinc oxide powder, which includes: a first neutralization step of adding at least one alkali source selected from the group consisting of sodium carbonate, potassium carbonate, lithium carbonate, ammonium carbonate, sodium hydrogencarbonate, and ammonium bicarbonate to at least one zinc source selected from the group consisting of zinc chloride, zinc sulfate, zinc acetate, and zinc nitrate so that the molar ratio (alkali source / zinc source) is less than 1, and mixing them; a second neutralization step of adding the alkali source to the zinc source so that the total molar ratio (alkali source / zinc source) is 1.05 to 5, and mixing them; a filtration and washing step; and a calcination step at 200 to 1000°C.

[0009] Furthermore, the above-mentioned problem can also be solved by providing a surface-treated zinc oxide powder obtained by surface-treating zinc oxide powder, characterized in that when 5 g of the surface-treated zinc oxide powder is added to 70 g of ion-exchanged water and the mixture is stirred, the concentration of zinc ions dissolved in the water is 0.2 ppm or less.

[0010] In this case, a preferred embodiment is a surface-treated zinc oxide powder obtained by treating the surface of the zinc oxide powder with at least one surface treatment agent selected from the group consisting of silicone oil, fatty acid, alkylsilane, and hydrated silica, and the BET specific surface area of ​​the surface-treated zinc oxide powder is 0.5 to 70 m ２ / g, and CO ２ -CO measured by TPD ２ Ratio of desorption amount to BET specific surface area (CO ２ Desorption amount / BET specific surface area) is 0.2 μmol / m ２ The above is preferable, and a composition containing the surface-treated zinc oxide powder is a preferable embodiment.

[0011] It is preferable that the composition further contains an aqueous thickener, and that the aqueous thickener has at least one selected from the group consisting of a sulfonic acid group, a carboxyl group, and salts thereof. It is preferable that the aqueous thickener is at least one copolymer selected from the group consisting of (sodium acrylate / sodium acryloyldimethyltaurate) copolymer, (hydroxyethyl acrylate / sodium acryloyldimethyltaurate) copolymer, (ammonium acryloyldimethyltaurate / vinylpyrrolidone) copolymer, (dimethylacrylamide / sodium acryloyldimethyltaurate) crosspolymer, carboxyvinyl polymer, xanthan gum, and carrageenan. A cosmetic composition containing the composition is a preferable embodiment, and a coating composition containing the composition is also a preferable embodiment.

[0012] The present invention provides a zinc oxide powder and a surface-treated zinc oxide powder in which the concentration of zinc ions eluted in water is reduced to a certain level or less, thereby reducing the environmental load and providing a cosmetic composition or a coating composition that is stable over time.

[0013] The zinc oxide powder of the present invention is characterized in that when 5 g of the zinc oxide powder is added to 70 g of ion-exchanged water and the mixture is stirred, the concentration of zinc ions dissolved in the water (hereinafter, sometimes abbreviated as "zinc ion elution amount") is 0.2 ppm or less. Also, the surface-treated zinc oxide powder of the present invention is a surface-treated zinc oxide powder obtained by surface-treating zinc oxide powder, and is characterized in that when 5 g of the surface-treated zinc oxide powder is added to 70 g of ion-exchanged water and the mixture is stirred, the concentration of zinc ions dissolved in the water (hereinafter, sometimes abbreviated as "zinc ion elution amount") is 0.2 ppm or less.

[0014] In the present invention, the stirring is performed by shaking and mixing with a paint conditioner for 1 hour at 25° C. In the present invention, the amount of zinc ions eluted is determined by centrifuging the solution after the stirring, filtering the supernatant through filter paper (5C) and a membrane filter (mesh opening: 0.45 μm), and quantifying the obtained test solution with an ICP emission spectrometer.

[0015] The zinc oxide powder and surface-treated zinc oxide powder of the present invention have a zinc ion elution amount of 0.2 ppm or less. As can be seen from a comparison between the Examples and Comparative Examples described below, the zinc oxide powders and surface-treated zinc oxide powders obtained in the Examples had a zinc ion elution amount of 0.001 to 0.06 ppm, while the zinc oxide powders and surface-treated zinc oxide powders obtained in the Comparative Examples had a zinc ion elution amount of 2 to 12 ppm, indicating that the zinc ion elution amounts of the Examples were significantly reduced compared to the Comparative Examples. Compositions containing a combination of carbomer and surface-treated zinc oxide powder were prepared and their stability over one month was evaluated. As a result, it was revealed that the compositions using the surface-treated zinc oxide powder obtained in the Examples had small viscosity and pH change rates, effectively suppressed pH fluctuations and viscosity reduction, and exhibited excellent stability over time. Therefore, there is great significance in adopting the zinc oxide powder and surface-treated zinc oxide powder of the present invention, which have a zinc ion elution amount reduced to a certain level or less.

[0016] If the amount of zinc ions eluted from the zinc oxide powder and surface-treated zinc oxide powder of the present invention exceeds 0.2 ppm, the reduction in environmental load will be insufficient, and the stability over time will also be insufficient when a composition is prepared using a carbomer in combination with the surface-treated zinc oxide powder. The amount of zinc ions eluted is preferably 0.1 ppm or less, more preferably 0.05 ppm or less, even more preferably 0.01 ppm or less, and particularly preferably 0.005 ppm or less. On the other hand, the amount of zinc ions eluted is usually 0.00001 ppm or more.

[0017] In the zinc oxide powder of the present invention, the BET specific surface area is 0.5 to 100 m ２ / g. It is preferable that the BET specific surface area is 0.5 m ２ If the BET specific surface area is less than 3 m / g, the dispersibility of the zinc oxide powder when applied to cosmetics may be significantly reduced. ２ / g or more is more preferable, and 5m ２ / g or more, and more preferably 10m ２ / g or more is particularly preferred, and 15m ２ On the other hand, it is most preferable that the BET specific surface area is 100 m / g or more.２ If the BET specific surface area is more than 90 m / g, the ultraviolet ray shielding effect may be significantly reduced when the zinc oxide powder is applied to cosmetics. ２ / g or less is more preferable, and ２ / g or less is more preferable, and 70m ２ / g or less. ２ / g) is calculated by the BET method using a fully automatic specific surface area measuring device.

[0018] The zinc oxide powder of the present invention is ２ -CO measured by TPD ２ The amount of CO desorption is preferably 15 to 200 μmol / g. The present inventors have confirmed that the amount of CO desorption is correlated with the BET specific surface area. ２ -CO measured by TPD ２ Ratio of desorption amount to BET specific surface area (CO ２ Desorption amount / BET specific surface area) is 1.4 μmol / m ２ In a preferred embodiment, the ratio (CO ２ Desorption amount / BET specific surface area) is 1.4 μmol / m ２ If the amount of zinc ions eluted is less than 1.6 μmol / m, it becomes difficult to reduce the amount of zinc ions eluted. ２ More preferably, it is 1.8 μmol / m or more. ２ More preferably, it is 2.0 μmol / m or more. ２ On the other hand, it is particularly preferable that the ratio (CO ２ The desorption amount / BET specific surface area) is 10 μmol / m ２ It is preferable that:

[0019] The surface-treated zinc oxide powder of the present invention is obtained by surface-treating zinc oxide powder, and a preferred embodiment is that the zinc oxide powder is surface-treated with at least one surface-treating agent selected from the group consisting of silicone oil, fatty acid, alkylsilane, and hydrous silica. In the present invention, "surface-treated zinc oxide powder" means that the surface of the zinc oxide powder is present to the extent that the surface-treating agent is coated on the zinc oxide surface, and it does not matter if there are some uncoated areas.

[0020] Suitable silicone oils include methicone, dimethylpolysiloxane (dimethicone), methylphenylpolysiloxane, methylhydrogenpolysiloxane (hydrogendimethicone), trimethylsiloxysilicate, triethoxysilylethylpolydimethylsiloxyethylhexyldimethicone, etc. Suitable fatty acids include stearic acid, isostearic acid, lauric acid, myristic acid, palmitic acid, behenic acid, etc. As alkylsilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, triethoxycaprylylsilane, tetramethoxysilane, tetraethoxysilane, phenyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltriethoxysilane (triethoxycaprylylsilane), decyltrimethoxysilane, etc. are preferably used.As hydrated silica, hydrolyzates of tetramethoxysilane, tetraethoxysilane, etc.; methylsilicate oligomer, ethylsilicate oligomer, etc. are preferably used.These surface treatment agents may be used alone or in combination of two or more.

[0021] In the surface-treated zinc oxide powder of the present invention, the BET specific surface area is 0.5 to 70 m ２ / g. It is preferable that the BET specific surface area is 0.5 m ２ If the BET specific surface area is less than 3 m / g, the dispersibility of the zinc oxide powder when applied to cosmetics may be significantly reduced. ２ / g or more is more preferable, and 5m ２ / g or more, and ２ On the other hand, it is particularly preferable that the BET specific surface area is 70 m ２ If the BET specific surface area is more than 60 m / g, the ultraviolet ray shielding effect may be significantly reduced when the zinc oxide powder is applied to cosmetics. ２ / g or less is more preferable, and 50m ２ / g or less. ２ / g) is calculated by the BET method using a fully automatic specific surface area measuring device.

[0022] In the surface-treated zinc oxide powder of the present invention, CO ２ -CO measured by TPD ２ The amount of CO desorption is preferably 4.0 to 50 μmol / g. The present inventors have confirmed that the value of the peak area is correlated with the BET specific surface area. ２ -CO measured by TPD ２ Ratio of desorption amount to BET specific surface area (CO ２ Desorption amount / BET specific surface area) is 0.2 μmol / m ２ In a preferred embodiment, the ratio (CO ２ Desorption amount / BET specific surface area) is 0.2 μmol / m ２ If the concentration is less than 0.3 μmol / m, it becomes difficult to reduce the amount of zinc ions eluted. ２ More preferably, it is 0.4 μmol / m or more. ２ More preferably, it is 0.5 μmol / m or more. ２ On the other hand, it is particularly preferable that the ratio (CO ２ The desorption amount / BET specific surface area was 2.0 μmol / m ２ It is preferable that:

[0023] The production method of the present invention is not particularly limited. The zinc oxide powder of the present invention can be suitably produced by carrying out a first neutralization step in which at least one alkali source selected from the group consisting of sodium carbonate, potassium carbonate, lithium carbonate, ammonium carbonate, sodium hydrogencarbonate, and ammonium bicarbonate is added to and mixed with at least one zinc source selected from the group consisting of zinc chloride, zinc sulfate, zinc acetate, and zinc nitrate so that the molar ratio (alkali source / zinc source) is less than 1, a second neutralization step in which the alkali source is added and mixed so that the total molar ratio (alkali source / zinc source) is 1.05 to 5, a filtration step, a washing step, and a calcination step at 200 to 1,000° C. Then, the zinc oxide powder is surface-treated to produce the surface-treated zinc oxide powder of the present invention.

[0024] As is clear from a comparison between the Examples and Comparative Examples described below, the zinc oxide powders and surface-treated zinc oxide powders obtained in the Examples had zinc ion elution amounts of 0.001 to 0.06 ppm, confirming that the amount of zinc ion elution was significantly reduced. On the other hand, in Comparative Examples 1 to 5, in which the second neutralization step was not performed, the amount of zinc ion elution was 9 to 12 ppm, and in Comparative Examples 6 to 9, in which the second neutralization step was not performed and the molar ratio (alkali source / zinc source) in the first neutralization step was 1.1 to 2, the amount of zinc ion elution was 8 to 9 ppm, confirming that the reduction in the amount of zinc ion elution was insufficient. Therefore, in the production method of the present invention, it is a preferred embodiment to employ both the first and second neutralization steps.

[0025] In the first neutralization step, a method is preferably employed in which the alkali source is added to the zinc source so that the molar ratio (alkali source / zinc source) is less than 1, and then mixed. The zinc source and the alkali source are preferably both added as aqueous solutions and then mixed. The time and method for adding the alkali source to the zinc source and mixing are not particularly limited, and the alkali source may be added all at once and mixed, or may be added and mixed while being added over an addition time set to 10 seconds to 30 minutes, or the zinc source and the alkali source may be added simultaneously to a reaction vessel and mixed. The reaction temperature in the first neutralization step is not particularly limited, but is preferably 5 to 80°C.

[0026] In the first neutralization step, if the molar ratio (alkali source / zinc source) is 1 or more, there is a risk that a zinc oxide powder in which the amount of zinc ions eluted is insufficiently reduced may be obtained. Therefore, the molar ratio (alkali source / zinc source) is more preferably 0.98 or less, further preferably 0.96 or less, particularly preferably 0.94 or less, and most preferably 0.92 or less. On the other hand, the molar ratio (alkali source / zinc source) is preferably 0.6 or more.

[0027] In a preferred embodiment, after the first neutralization step, a second neutralization step is performed in which the alkali source is added and mixed so that the total molar ratio (alkali source / zinc source) is 1.05 to 5. The alkali source is preferably added and mixed as an aqueous solution. In a preferred embodiment, in the second neutralization step, the alkali source is not added all at once, but is gradually added over a period of 30 seconds to 60 minutes while being mixed so that the total molar ratio (alkali source / zinc source) is 1.05 to 5. The time period for the gradual addition is more preferably 2 to 45 minutes, even more preferably 3 to 40 minutes, and particularly preferably 5 to 35 minutes. The product of the first neutralization step and the alkali source may be added to a reaction vessel and mixed simultaneously. The reaction temperature in the second neutralization step is not particularly limited, but is preferably 5 to 80°C.

[0028] The total molar ratio (alkali source / zinc source) in the second neutralization step refers to the molar ratio of the alkali sources added in the first and second neutralization steps to the zinc source in the first neutralization step. In the second neutralization step, if the total molar ratio (alkali source / zinc source) is less than 1.05, the resulting zinc oxide powder may not sufficiently reduce the amount of zinc ions eluted. Therefore, the total molar ratio (alkali source / zinc source) is more preferably 1.06 or more, and even more preferably 1.08 or more. On the other hand, if the total molar ratio (alkali source / zinc source) exceeds 5, the ultraviolet blocking effect of the zinc oxide powder when applied to cosmetics may be significantly reduced. Therefore, the total molar ratio (alkali source / zinc source) is more preferably 4 or less, even more preferably 3.5 or less, particularly preferably 3 or less, and most preferably 2.5 or less. After the first neutralization step, filtration and washing steps, followed by a drying step, may be carried out.

[0029] In a preferred embodiment, a filtration and washing step is carried out after the second neutralization step. By carrying out the filtration and washing step, it is possible to remove impurities such as unreacted substances. As the filtration and washing method, a known method is adopted. Among them, a washing method using water is preferably adopted, and washing with water until the electrical conductivity becomes 500 μS / cm or less is a preferred embodiment, and washing until the electrical conductivity becomes 300 μS / cm or less is a more preferred embodiment.

[0030] A preferred embodiment is to carry out a drying step after the filtration and washing steps. This has the advantage of improving the quality stability of the resulting zinc oxide powder, such as the specific surface area. The drying step is not particularly limited, but it is preferable to carry out a drying step using at least one method selected from the group consisting of air drying, air flash drying, spray drying, drum drying, and vacuum drying after obtaining a cake by filtration and washing. The drying temperature is preferably 80 to 150°C. The drying time is preferably 30 minutes to 48 hours.

[0031] Next, in a preferred embodiment, a calcination step is carried out at 200 to 1000° C. If the calcination temperature is less than 200° C., the purity of zinc oxide in the zinc oxide powder may be significantly reduced, so the calcination temperature is more preferably 220° C. or higher, even more preferably 240° C. or higher, and particularly preferably 300° C. or higher. On the other hand, if the calcination temperature exceeds 1000° C., the specific surface area may be reduced, so the calcination temperature is more preferably 950° C. or lower, even more preferably 900° C. or lower, and particularly preferably 880° C. or lower.

[0032] The firing time in the firing step is preferably 30 minutes to 48 hours. If the firing time is less than 1 hour, unreacted raw materials may remain, and the zinc oxide powder of the present invention may not be obtained. The firing time is more preferably 1 hour or more, and even more preferably 2 hours or more. On the other hand, if the firing time exceeds 48 hours, productivity may decrease. The firing time is more preferably 24 hours or less, even more preferably 15 hours or less, and particularly preferably 8 hours or less.

[0033] Although the zinc oxide powder of the present invention can be suitably obtained by carrying out the calcination step, a preferred embodiment is to carry out a pulverization step after the calcination step. This has the advantage of suppressing the inclusion of coarse particles and producing a zinc oxide powder with good quality stability, and also has the advantage of producing a uniform surface-treated zinc oxide powder when the zinc oxide powder is surface-treated. As a pulverization method, a method of pulverization using a known pulverizer or the like is adopted. The pulverizer is not particularly limited, and a pin mill, ball mill, jet mill, mortar and pestle mill, ultracentrifugal pulverizer, etc. can be used.

[0034] The zinc oxide powder of the present invention can be surface-treated to obtain a surface-treated zinc oxide powder. A method for producing the surface-treated zinc oxide powder involves mixing the zinc oxide powder with the surface treatment agent. The surface treatment can be carried out by dry mixing, or by wet mixing using a dispersion solvent. The dispersion solvent preferably includes alcohols such as methanol, ethanol, and isopropanol, or toluene. For the surface treatment, the surface treatment agent is preferably blended in an amount of 0.5 to 20 parts by mass, and more preferably 1 to 15 parts by mass, per 100 parts by mass of the zinc oxide powder. Subsequently, the surface-treated zinc oxide powder of the present invention can be obtained by optionally performing a drying step or a pulverization step.

[0035] The surface-treated zinc oxide powder of the present invention can be blended with various components and used as a composition. The composition can be suitably used as a powder composition, an aqueous composition, an oil-based composition, or an emulsion composition (oil-in-water type (O / W type) or water-in-oil type (W / O type). Among these, a cosmetic composition containing the surface-treated zinc oxide powder or a coating composition containing the surface-treated zinc oxide powder is a more preferred embodiment. The cosmetic composition containing the surface-treated zinc oxide powder of the present invention is preferably in the form of a powder composition, an oil-based composition, or an emulsion composition (oil-in-water type (O / W type) or water-in-oil type (W / O type)). When the cosmetic composition containing the surface-treated zinc oxide powder of the present invention is in the form of an emulsion composition (oil-in-water type (O / W type) or water-in-oil type (W / O type)), the emulsion composition may be prepared by blending the surface-treated zinc oxide powder of the present invention with an aqueous phase or an oil phase containing various cosmetic ingredients, or the emulsion may be prepared by mixing the aqueous phase and the oil phase and blending the surface-treated zinc oxide powder of the present invention into the emulsion. The amount of the surface-treated zinc oxide powder in the composition is preferably 5 to 30 mass %.

[0036] The various components to be blended into the cosmetic composition are not particularly limited, and may include, for example, water; polyhydric alcohols; aqueous thickeners; ester oils; fats and oils; hydrocarbon oils; silicone oils; and the like. Suitable polyhydric alcohols include glycerin, 1,3-butylene glycol, propylene glycol, and polyethylene glycol. Suitable aqueous thickeners include those having at least one selected from the group consisting of sulfonic acid groups, carboxyl groups, and salts thereof. Suitable aqueous thickeners include at least one copolymer selected from the group consisting of sodium acrylate / sodium acryloyldimethyltaurate copolymer, hydroxyethyl acrylate / sodium acryloyldimethyltaurate copolymer, ammonium acryloyldimethyltaurate / vinylpyrrolidone copolymer, dimethylacrylamide / sodium acryloyldimethyltaurate crosspolymer, carboxyvinyl polymer, xanthan gum, and carrageenan. Among these, carboxyvinyl polymers are particularly suitable as aqueous thickeners. Examples of ester oils include isopropyl myristate, cetyl isooctanoate, glyceryl trioctanoate, isononyl isononanoate, and ethylhexyl methoxycinnamate. Examples of fats and oils include camellia oil, evening primrose oil, macadamia nut oil, olive oil, rapeseed oil, corn oil, and sesame oil. Examples of hydrocarbon oils include liquid paraffin, squalane, isoparaffin, branched-chain light paraffin, petrolatum, and ceresin. Examples of silicone oils include dimethicone, methylphenylpolysiloxane, decamethylcyclopentasiloxane, caprylyl methicone, and methyl trimethicone. If necessary, surfactants, moisturizers, pH adjusters, nutrients, antioxidants, and fragrances may also be included.

[0037] As will be seen from a comparison between the Examples and Comparative Examples described below, compositions containing a combination of carbomer and surface-treated zinc oxide powder were prepared and their stability over time was evaluated for one month. As a result, the compositions containing the surface-treated zinc oxide powder of the present invention had small viscosity and pH change rates, effectively suppressed pH fluctuations and viscosity reductions, and exhibited excellent stability over time. Therefore, they can be suitably used as cosmetics. In particular, they can be suitably used as cosmetics for sunscreens, emulsions, creams, foundations, lipsticks, and eye shadows, and are even more suitably used as cosmetics for sunscreens and foundations.

[0038] The present invention will be explained in more detail below using examples.

[0039] [Preparation of Zinc Oxide Powder and Surface-Treated Zinc Oxide Powder] Example 1 434 g of a 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and then 195 g of a 10 wt % aqueous sodium carbonate solution was slowly added over 10 minutes to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 250°C for 10 hours. The obtained powder was pulverized using a pin mill to produce the zinc oxide powder of Example 1.

[0040] Example 2: 434 g of 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and then 195 g of a 10 wt % aqueous sodium carbonate solution was slowly added over 10 minutes to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 380°C for 3 hours. The obtained powder was pulverized in a pin mill to produce the zinc oxide powder of Example 2.

[0041] Example 3: 434 g of 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and then 195 g of a 10 wt % aqueous sodium carbonate solution was slowly added over 10 minutes to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The obtained powder was pulverized in a pin mill to produce the zinc oxide powder of Example 3.

[0042] Example 4: 434 g of 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and then 195 g of a 10 wt % aqueous sodium carbonate solution was slowly added over 10 minutes to obtain a white slurry. The resulting slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The resulting cake was dried at 130°C for 12 hours and then calcined at 600°C for 3 hours. The resulting powder was pulverized in a pin mill to produce the zinc oxide powder of Example 4.

[0043] Example 5: 434 g of 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and then 195 g of a 10 wt % aqueous sodium carbonate solution was slowly added over 10 minutes to obtain a white slurry. The resulting slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The resulting cake was dried at 130°C for 12 hours and then calcined at 850°C for 3 hours. The resulting powder was pulverized in a pin mill to produce the zinc oxide powder of Example 5.

[0044] Example 6: 566 g of 10 wt % aqueous potassium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), followed by the slow addition of 254 g of a 10 wt % aqueous potassium carbonate solution over 10 minutes to obtain a white slurry. The resulting slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The resulting cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The resulting powder was pulverized in a pin mill to produce the zinc oxide powder of Example 6.

[0045] Example 7: 434 g of 10 wt % aqueous sodium carbonate solution was added to 263 g of a 28 wt % aqueous zinc sulfate solution prepared using zinc sulfate heptahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.), followed by the slow addition of 195 g of a 10 wt % aqueous sodium carbonate solution over 10 minutes to obtain a white slurry. The resulting slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The resulting cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The resulting powder was pulverized in a pin mill to produce the zinc oxide powder of Example 7.

[0046] Example 8: 434 g of 10 wt % aqueous sodium carbonate solution was added to 279 g of a 30 wt % aqueous zinc acetate solution prepared using zinc acetate dihydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), followed by the slow addition of 195 g of a 10 wt % aqueous sodium carbonate solution over 10 minutes to obtain a white slurry. The resulting slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The resulting cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The resulting powder was pulverized in a pin mill to produce the zinc oxide powder of Example 8.

[0047] Example 9: 434 g of 10 wt % aqueous sodium carbonate solution was added to 288 g of a 30 wt % aqueous zinc nitrate solution prepared using zinc nitrate hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), followed by the slow addition of 195 g of a 10 wt % aqueous sodium carbonate solution over 10 minutes to obtain a white slurry. The resulting slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The resulting cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The resulting powder was pulverized in a pin mill to produce the zinc oxide powder of Example 9.

[0048] Example 10: 434 g of 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), followed by the slow addition of 97 g of a 10 wt % aqueous sodium carbonate solution over 10 minutes to obtain a white slurry. The resulting slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The resulting cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The resulting powder was pulverized in a pin mill to produce the zinc oxide powder of Example 10.

[0049] Example 11: 434 g of 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and then 338 g of a 10 wt % aqueous sodium carbonate solution was slowly added over 10 minutes to obtain a white slurry. The resulting slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The resulting cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The resulting powder was pulverized in a pin mill to produce the zinc oxide powder of Example 11.

[0050] Example 12: 434 g of 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and then 531 g of a 10 wt % aqueous sodium carbonate solution was slowly added over 10 minutes to obtain a white slurry. The resulting slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The resulting cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The resulting powder was pulverized in a pin mill to produce the zinc oxide powder of Example 12.

[0051] 100 g of the zinc oxide powder prepared in Example 3 and 3.5 g of isostearic acid (Isostearic Acid EX, manufactured by High Alcohol Co., Ltd.) were mixed and stirred for 20 minutes in a bench blender. The powder obtained after the treatment was dried at 100°C for 2 hours and pulverized in a pin mill to prepare the surface-treated zinc oxide powder of Example 13.

[0052] Example 14 100 g of the zinc oxide powder prepared in Example 3 and 3.5 g of stearic acid (Kao Corporation: purified stearic acid 450V) were mixed and stirred for 20 minutes in a bench blender while heating at 80° C. After the treatment, the resulting powder was dried at 80° C. for 2 hours and pulverized in a pin mill to prepare the surface-treated zinc oxide powder of Example 14.

[0053] Example 15 100 g of the zinc oxide powder prepared in Example 3 and 3.5 g of dimethicone (KF-96-1000cs, manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed and stirred for 20 minutes in a bench blender. The powder obtained after the treatment was dried at 170°C for 2 hours and pulverized in a pin mill to prepare the surface-treated zinc oxide powder of Example 15.

[0054] Example 16 100 g of the zinc oxide powder prepared in Example 3 and 3.5 g of hydrogen dimethicone (KF-9901, manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed and stirred for 20 minutes in a bench blender. The powder obtained after the treatment was dried at 170°C for 2 hours and pulverized in a pin mill to prepare the surface-treated zinc oxide powder of Example 16.

[0055] Example 17 100 g of the zinc oxide powder prepared in Example 3 and 3.5 g of triethoxycaprylylsilane (SILQUEST A-137, manufactured by Momentive Performance Materials Japan, LLC) were mixed and stirred for 20 minutes in a bench blender. The powder obtained after the treatment was dried at 170°C for 2 hours and pulverized in a pin mill to prepare the surface-treated zinc oxide powder of Example 17.

[0056] Example 18 100 g of the zinc oxide powder produced in Example 3 and 4.1 g of methyl silicate oligomer (MKC Silicate MS51 manufactured by Mitsubishi Chemical Corporation) were mixed and stirred for 20 minutes in a bench blender while heating at 120°C. Subsequently, 2.1 g of hydrogen dimethicone (KF-9901 manufactured by Shin-Etsu Chemical Co., Ltd.) and 1.1 g of triethoxysilylethyl polydimethylsiloxyethylhexyl dimethicone (KF-9909 manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed and stirred for 20 minutes in a bench blender. After the treatment, the resulting powder was dried at 170°C for 2 hours and pulverized in a pin mill to produce the surface-treated zinc oxide powder of Example 18.

[0057] Example 19 100 g of the zinc oxide powder prepared in Example 2 and 8.5 g of triethoxycaprylylsilane (SILQUEST A-137, manufactured by Momentive Performance Materials Japan, LLC) were mixed and stirred for 20 minutes in a bench blender. The powder obtained after the treatment was dried at 170°C for 2 hours and pulverized in a pin mill to prepare the surface-treated zinc oxide powder of Example 19.

[0058] Comparative Example 1 434 g of a 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 250°C for 10 hours. The obtained powder was pulverized using a pin mill to produce the zinc oxide powder of Comparative Example 1.

[0059] Comparative Example 2 434 g of a 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 380°C for 3 hours. The obtained powder was pulverized using a pin mill to produce the zinc oxide powder of Comparative Example 2.

[0060] Comparative Example 3 434 g of a 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The obtained powder was pulverized using a pin mill to produce the zinc oxide powder of Comparative Example 3.

[0061] Comparative Example 4 434 g of a 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 550°C for 3 hours. The obtained powder was pulverized using a pin mill to produce the zinc oxide powder of Comparative Example 4.

[0062] Comparative Example 5: 434 g of a 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 650°C for 3 hours. The obtained powder was pulverized using a pin mill to produce the zinc oxide powder of Comparative Example 5.

[0063] Comparative Example 6 531 g of 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The obtained powder was pulverized using a pin mill to produce the zinc oxide powder of Comparative Example 6.

[0064] Comparative Example 7: 627 g of a 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The obtained powder was pulverized using a pin mill to produce the zinc oxide powder of Comparative Example 7.

[0065] Comparative Example 8 772 g of a 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The obtained powder was pulverized using a pin mill to produce the zinc oxide powder of Comparative Example 8.

[0066] Comparative Example 9: 965 g of a 10 wt % aqueous sodium carbonate solution was added to 132 g of a 47 wt % aqueous zinc chloride solution prepared using zinc chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a white slurry. The obtained slurry was filtered and washed with ion-exchanged water until the EC of the filtrate reached 150 μS / cm or less. The obtained cake was dried at 130°C for 12 hours and then calcined at 480°C for 3 hours. The obtained powder was pulverized using a pin mill to produce the zinc oxide powder of Comparative Example 9.

[0067] 100 g of the zinc oxide powder prepared in Comparative Example 3 and 3.5 g of isostearic acid (Isostearic Acid EX, manufactured by High Alcohol Co., Ltd.) were mixed and stirred for 20 minutes using a bench blender. The powder obtained after the treatment was placed in a dryer, dried at 100°C for 2 hours, and pulverized using a pin mill to prepare the surface-treated zinc oxide powder of Comparative Example 10.

[0068] Comparative Example 11 100 g of the zinc oxide powder prepared in Comparative Example 3 and 3.5 g of dimethicone (KF-96-1000cs, manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed and stirred for 20 minutes using a bench blender. After the treatment, the resulting powder was placed in a dryer, dried at 170°C for 2 hours, and pulverized using a pin mill to prepare the surface-treated zinc oxide powder of Comparative Example 11.

[0069] Comparative Example 12 100 g of the zinc oxide powder prepared in Comparative Example 3 and 3.5 g of triethoxycaprylylsilane (SILQUEST A-137, manufactured by Momentive Performance Materials Japan, LLC) were mixed and stirred for 20 minutes in a bench blender. The powder obtained after the treatment was placed in a dryer, dried at 170°C for 2 hours, and pulverized in a pin mill to prepare the surface-treated zinc oxide powder of Comparative Example 12.

[0070] Comparative Example 13 100 g of the zinc oxide powder prepared in Comparative Example 2 and 8.5 g of triethoxycaprylylsilane (SILQUEST A-137, manufactured by Momentive Performance Materials Japan, LLC) were mixed and stirred for 20 minutes in a bench blender. The powder obtained after the treatment was placed in a dryer, dried at 170°C for 2 hours, and pulverized in a pin mill to prepare the surface-treated zinc oxide powder of Comparative Example 13.

[0071] (1) Measurement of BET Specific Surface Area The specific surface area of ​​the zinc oxide powders or surface-treated zinc oxide powders obtained in the Examples and Comparative Examples was measured by the BET method using a fully automatic specific surface area measuring device (Macsorb HM model-1208, manufactured by Mountec Co., Ltd.). The degassing step was carried out under the conditions of 150°C and 20 minutes.

[0072] (2) Measurement of TPD-MS The solid basicity of the zinc oxide powder or surface-treated zinc oxide powder obtained in the examples and comparative examples was measured using a catalyst analyzer (MicrotrackBell, BELCAT-B) by CO ２ The adsorbed moisture was determined by TPD measurement. First, 0.20 g of the zinc oxide powder or surface-treated zinc oxide powder obtained in the Examples and Comparative Examples was weighed and filled into a quartz cell. Next, the temperature was raised to 400°C in He over 40 minutes, held at that temperature for 1 hour, and then lowered to 100°C in He over 10 minutes to remove the adsorbed moisture. Furthermore, CO ２ CO was measured by passing the gas through the reactor at a flow rate of 20 mL / min for 30 minutes. ２ After the adsorption of CO, the gas was switched to He, and while flowing at a flow rate of 30 mL / min, the temperature was increased to 500°C at a rate of 10°C / min. ２ At this time, the CO concentration detected (each concentration 5%) ２ A calibration curve was created using the / He balance gas as the standard gas, and CO ２ The amount of CO released was measured, and the peak area of ​​the spectrum was counted. ２ The peak detection of CO in the mass spectrum ２ (m / e=44) fragment.

[0073] (3) Measurement of Zinc Ion Elution Amount 5.0 g of the zinc oxide powder or surface-treated zinc oxide powder obtained in the Examples and Comparative Examples and 70 g of ion-exchanged water at 25°C were weighed into a sealed container (Nikko Hansen, J Bottle, round, wide-mouth, 100 mL) and mixed by shaking for 1 hour in a paint conditioner (Red Devil, Paint Conditioner 1400). After shaking, the solution was centrifuged, and the supernatant was filtered through filter paper (Advantec Toyo Co., Ltd., No. 5C) and then through a membrane filter (Advantec Toyo Co., Ltd., 0.45 μm mesh) to obtain a test solution. The amount of zinc ion elution from the test solution was quantified using an ICP-OES (SPECTRO Analytical Instruments, ARCOS). For quantification, a calibration curve was established using a general-purpose mixed standard solution (manufactured by SPEX, XSTC-22).

[0074] [Preparation of Composition] Preparation Example 1 The oil phase components in Table 1 were accurately weighed and stirred in a disper mixer until the surface-treated zinc oxide powder of Example 13 was uniformly blended. The water phase components in Table 1 were accurately weighed and stirred in a disper mixer while heating at 80°C. After the PEG-100 hydrogenated castor oil was completely dissolved, the oil phase components were added and stirring was continued until the mixture was uniform, thereby preparing the oil-in-water emulsion composition of Preparation Example 1.

[0075]

[0076] Preparation Example 2 An oil-in-water emulsion composition of Preparation Example 2 was prepared in the same manner as in Preparation Example 1, except that the surface-treated zinc oxide powder of Example 17 was used instead of the surface-treated zinc oxide powder of Example 13.

[0077] Preparation Example 3 An oil-in-water emulsion composition of Preparation Example 3 was prepared in the same manner as in Preparation Example 1, except that the surface-treated zinc oxide powder of Example 18 was used instead of the surface-treated zinc oxide powder of Example 13.

[0078] Preparation Example 4 An oil-in-water emulsion composition of Preparation Example 4 was prepared in the same manner as in Preparation Example 1, except that the surface-treated zinc oxide powder of Example 19 was used instead of the surface-treated zinc oxide powder of Example 13.

[0079] Preparation Example 5 The oil phase components in Table 2 were accurately weighed and stirred in a Disper mixer until the surface-treated zinc oxide powder of Example 19 was uniformly incorporated. The water phase components in Table 2 were accurately weighed and stirred in a Disper mixer while heating at 80°C. After the PEG-100 hydrogenated castor oil was completely dissolved, the oil phase components were added and stirring was continued until the mixture was uniform, thereby preparing the oil-in-water emulsion composition of Preparation Example 5.

[0080]

[0081] Preparation Example 6 The oil phase components in Table 3 were accurately weighed and stirred in a Disper mixer until the surface-treated zinc oxide powder of Example 19 and the stearic acid-treated titanium oxide were uniformly mixed. The water phase components in Table 3 were accurately weighed and stirred in a Disper mixer while heating at 80°C. After the PEG-100 hydrogenated castor oil was completely dissolved, the oil phase components were added and stirring was continued until the mixture was uniform, thereby preparing the oil-in-water emulsion composition of Preparation Example 6.

[0082]

[0083] Preparation Example 7 The aqueous phase components in Table 4 were accurately weighed and stirred until uniform. The oil phase components were accurately weighed and stirred in a disper mixer until the surface-treated zinc oxide powder of Example 19 and the stearic acid-treated titanium oxide were uniformly mixed. While stirring the oil phase with a disper mixer, the aqueous phase was added, and stirring was maintained until uniform, thereby preparing the water-in-oil emulsion composition of Preparation Example 7.

[0084]

[0085] Comparative Preparation Example 1 An oil-in-water emulsion composition of Comparative Preparation Example 1 was prepared in the same manner as Preparation Example 1, except that the surface-treated zinc oxide powder of Comparative Example 6 was used instead of the surface-treated zinc oxide powder of Example 13.

[0086] Comparative Preparation Example 2 An oil-in-water emulsion composition of Comparative Preparation Example 2 was prepared in the same manner as in Preparation Example 1, except that the surface-treated zinc oxide powder of Comparative Example 8 was used instead of the surface-treated zinc oxide powder of Example 13.

[0087] Comparative Preparation Example 3 An oil-in-water emulsion composition of Comparative Preparation Example 3 was prepared in the same manner as in Preparation Example 1, except that the surface-treated zinc oxide powder of Comparative Example 12 was used instead of the surface-treated zinc oxide powder of Example 13.

[0088] Comparative Preparation Example 4 A water-in-oil emulsion composition of Comparative Preparation Example 4 was prepared in the same manner as in Preparation Example 7, except that the surface-treated zinc oxide powder of Comparative Example 12 was used instead of the surface-treated zinc oxide powder of Example 19.

[0089] (4) Viscosity Measurement The oil-in-water emulsion compositions obtained in the Preparation Examples and Comparative Preparation Examples were filled into 30 mL screw vials, and the viscosity was recorded 1 minute after the start of measurement at 12 rpm using a B-type viscometer (TVB-10, manufactured by Toki Sangyo Co., Ltd.) while the vials were left to stand.

[0090] (5) Measurement of pH The oil-in-water emulsion compositions obtained in Preparation Examples and Comparative Preparation Examples were filled into 30 mL screw vials, and the pH was recorded 5 minutes after the start of measurement using a pH meter (manufactured by HORIBA, D-51S) calibrated with calibration solutions of pH 4, 7, and 9.

[0091] (6) Rate of change after one month at 50°C The viscosity and pH of the oil-in-water emulsion compositions obtained in the Preparation Examples and Comparative Preparation Examples were measured immediately after preparation and after one month of storage in a thermostatic bath maintained at 50°C, and the rate of change in viscosity and pH at 25°C were calculated using the following formula. The oil-in-water emulsion compositions stored at 50°C were immersed in water at 25°C for 3 hours, and the viscosity and pH were measured after confirming that the temperature had reached 25°C. Rate of change in viscosity = [(viscosity at 25°C after one month at 50°C) - (viscosity at 25°C immediately after preparation)] / (viscosity at 25°C immediately after preparation) Rate of change in pH = [(pH at 25°C after one month at 50°C) - (pH at 25°C immediately after preparation)] / (pH at 25°C immediately after preparation)

[0092] (7) Measurement of the amount of zinc ions eluted from water-in-oil emulsion compositions. The water-in-oil emulsion compositions obtained in Preparation Examples and Comparative Preparation Examples were coated on a PMMA plate (HelioScreen, HERIOPLATE HD6) at a concentration of 1.3 mg / cm in accordance with ISO 24443. ２ The PMMA plate was coated with the water-in-oil emulsion composition and allowed to dry in the dark at 25°C for 30 minutes. Then, 300 g of ion-exchanged water was weighed into a 500 mL beaker (HARIO, B-500 SCI). While stirring with a stirrer and a stirring bar, the PMMA plate coated with the water-in-oil emulsion composition was immersed in the ion-exchanged water so that the entire surface was immersed. After 24 hours, the ion-exchanged water was filtered through a membrane filter (ADVANTEC, 0.25 μm mesh), and the amount of zinc ions eluted was quantified using an ICP-OES (SPECTRO Analytical Instruments GmbH, ARCOS). A calibration curve was established using a general-purpose mixed standard solution (SPEX, XSTC-22) for quantification.

[0093]

[0094]

[0095]

Claims

1. A zinc oxide powder characterized in that when 5 g of the zinc oxide powder is added to 70 g of ion-exchanged water and stirred, the concentration of zinc ions dissolved in the water is 0.2 ppm or less.

2. BET specific surface area: 0.5 to 100 m ２ 2. The zinc oxide powder according to claim 1, wherein the ZnO content is 1 / g.

3. CO ２ -CO measured by TPD ２ Ratio of desorption amount to BET specific surface area (CO ２ Desorption amount / BET specific surface area) is 1.4 μmol / m ２ The zinc oxide powder according to claim 1 or 2.

4. 3. A method for producing zinc oxide powder according to claim 1, comprising: a first neutralization step of adding at least one alkali source selected from the group consisting of sodium carbonate, potassium carbonate, lithium carbonate, ammonium carbonate, sodium hydrogencarbonate, and ammonium bicarbonate to at least one zinc source selected from the group consisting of zinc chloride, zinc sulfate, zinc acetate, and zinc nitrate so that the molar ratio (alkali source / zinc source) is less than 1, and mixing the resulting mixture; a second neutralization step of adding the alkali source to the resulting mixture so that the total molar ratio (alkali source / zinc source) is 1.05 to 5, and mixing the resulting mixture; a filtration and washing step; and a calcination step at 200 to 1,000°C.

5. A surface-treated zinc oxide powder obtained by surface-treating zinc oxide powder, characterized in that when 5 g of the surface-treated zinc oxide powder is added to 70 g of ion-exchanged water and stirred, the concentration of zinc ions dissolved in the water is 0.2 ppm or less.

6. 6. The surface-treated zinc oxide powder according to claim 5, wherein the zinc oxide powder is surface-treated with at least one surface treatment agent selected from the group consisting of silicone oil, fatty acid, alkylsilane, and hydrated silica.

7. BET specific surface area: 0.5 to 70 m ２ The surface-treated zinc oxide powder according to claim 5 or 6, wherein the surface-treated zinc oxide powder has a molecular weight of 1.001 or more and a molecular weight of 1.001 or more.

8. CO ２ -CO measured by TPD ２ Ratio of desorption amount to BET specific surface area (CO ２ Desorption amount / BET specific surface area) is 0.2 μmol / m ２ The surface-treated zinc oxide powder according to claim 5 or 6.

9. A composition comprising the surface-treated zinc oxide powder according to claim 5 or 6.

10. The composition of claim 9 further comprising an aqueous thickener.

11. The composition according to claim 10, wherein the aqueous thickener has at least one selected from the group consisting of a sulfonic acid group, a carboxyl group, and salts thereof.

12. 12. The composition of claim 11, wherein the aqueous thickener is at least one copolymer selected from the group consisting of sodium acrylate / sodium acryloyldimethyltaurate copolymer, hydroxyethyl acrylate / sodium acryloyldimethyltaurate copolymer, ammonium acryloyldimethyltaurate / vinylpyrrolidone copolymer, dimethylacrylamide / sodium acryloyldimethyltaurate crosspolymer, carboxyvinyl polymer, xanthan gum, and carrageenan.

13. A cosmetic composition comprising the composition according to claim 9.

14. A coating composition comprising the composition of claim 9.