JP4275796B2 - Method for producing zinc oxide dispersion - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a zinc oxide dispersion having a high visible light transparency and an excellent effect of preventing ultraviolet rays.
[0002]
[Prior art]
Zinc oxide is blended in various cosmetics because it has an effect of preventing ultraviolet rays. Among these, the fine particle zinc oxide can be produced by mechanical pulverization or can be produced by a wet method such as a sol-gel method. As a wet method, colloidal particles in a hydrosol of zinc sulfate or zinc chloride prepared in an aqueous solution are lipophilically converted with an anionic surfactant, then flushed with an organic solvent, and then the organic solvent is dried and removed. There is obtained fine zinc oxide (Japanese Patent Publication No. 5-77644).
[0003]
However, the fine particle zinc oxide dispersion obtained by preparing a hydrosol in an aqueous solution is white due to aggregation of zinc oxide, and when applied to a cosmetic, it is whitish and has a transparent finish. Also, the production efficiency was very bad.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for efficiently producing a fine particle zinc oxide dispersion having a transparent appearance.
[0005]
[Means for Solving the Problems]
The inventors focused on hydrogen bonding between zinc oxides in water as a cause of the aggregation of the fine particles, and studied the preparation of fine particle zinc oxide in a dispersion system having weak hydrogen bonding properties. As a result, it has been found that if zinc oxide fine particles are prepared using a zinc salt as a raw material under methanolic or propanolic alkaline conditions, a transparent primary particle dispersion can be efficiently produced.
[0006]
In the present invention, a solution in which a zinc salt is dissolved in methanol, propanol, or a mixed solvent of two or more of methanol, ethanol, and propanol, and an alkali metal hydroxide are methanol, propanol, or methanol, ethanol, and propanol. Provided is a method for producing a zinc oxide dispersion characterized by mixing a solution dissolved in two or more of these mixed solvents, and adjusting the pH after mixing and after mixing to less than 9. .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the zinc oxide dispersion is prepared in methanol, propanol, or a mixed solution of two or more of methanol, ethanol and propanol (hereinafter sometimes simply referred to as “mixed solvent”). That is, a zinc oxide dispersion is obtained by mixing a methanol, propanol or mixed solvent solution of a zinc salt with an alkaline methanol, propanol or mixed solvent solution. Examples of the zinc salt used here include zinc chloride, zinc nitrate, zinc acetate, zinc stearate, zinc oleate, and zinc salicylate. Zinc chloride and zinc acetate are preferred, and zinc chloride is particularly effective in terms of production efficiency. To preferred. Examples of the alkali include alkali metal hydroxides, alkali metal methoxides, alkali metal ethoxides, and potassium hydroxide, sodium hydroxide, and sodium methoxide are preferable. The concentrations of zinc salt and alkali in methanol, propanol or mixed solvent are each preferably about 0.01 to 6 mol / L, particularly preferably 0.05 to 5 mol / L. The zinc concentration in the dispersion obtained by mixing a zinc salt and an alkali is preferably more than 0.1 mol / L, particularly preferably 0.2 mol / L or more, and more preferably 0.3 mol / L or more. This is because the higher the zinc concentration, the higher the productivity of the zinc oxide fine particles and the smaller the amount of methanol, propanol or mixed solvent used. Further, as the zinc concentration is higher, the absorption edge wavelength of the zinc oxide dispersion is shifted to a longer wavelength side of, for example, 330 nm or more, and a wider range of ultraviolet rays can be shielded. When a mixed solvent is used, the solvent of the zinc salt solution and the alkali solution may be different. For example, one of the zinc salt and the alkali is a methanol solution, and the other is an ethanol solution, a propanol solution, or a mixed solvent solution. May be mixed.
[0008]
The pH of the dispersion when mixing the zinc salt and the alkali is adjusted to less than 9, and the pH is preferably 8.5 or less, particularly preferably 8.2 or less. When the pH is 9 or more, zinc oxide tends to aggregate, whereas when the pH is less than 9, zinc oxide is highly dispersed, and a desired transparent primary particle dispersion can be obtained. Here, the pH of the dispersion means a value displayed on a calibrated pH meter when measured at room temperature (20 to 40 ° C.).
The equivalent ratio of zinc salt: alkali is preferably mixed in the range of 1: 0.3 to 1: 1.1, particularly 1: 0.35 to 1: 0.95, more preferably 1: 0.4 to 1: 0.9 is preferred. In the above range, the generated zinc oxide is highly dispersed, and a desired dispersion is obtained. Although the temperature at the time of mixing a zinc salt and an alkali is not specifically limited, 65 degrees C or less is preferable from the relationship of the boiling points of solvents, such as methanol, and 60 degrees C or less is especially preferable. Further, the mixing method of the zinc salt and the alkali can be either a continuous type or a batch type. By-product salt particles can be removed by ordinary filtration, centrifugation, or the like, which is preferable from the viewpoint of the stability of the zinc oxide fine particles.
[0009]
The zinc oxide fine particles in the dispersion thus obtained have a particle size of approximately 1 to 20 nm, preferably 1 to 10 nm, and an average particle size of 1 to 10 nm.
[0010]
By further adding a hydrophobic compound having a polar group to the obtained dispersion, it is possible to surface-treat the zinc oxide fine particles and stabilize the dispersion. The hydrophobic compound having a polar group used here is not particularly limited as long as it is soluble in methanol, propanol or a mixed solvent, or a solvent that can be mixed with these, fatty acids, long-chain alkyl sulfates, long-chains. Examples thereof include monoalkyl phosphates, long-chain dialkyl phosphates, acyl amino acids, alkyl amino acids, amide derivatives, amine derivatives, guanidine derivatives, alkyl betaines and the like.
The hydrophobic compound having these polar groups is preferably added in an amount of 0.01 to 1 part by weight, particularly 0.05 to 0.9 part by weight, based on 1 part by weight of zinc oxide.
[0011]
The thus added hydrophobic compound having a polar group can be adsorbed on the zinc oxide fine particles in the dispersion to form hydrophobic zinc oxide.
Subsequently, the dispersion medium is concentrated as necessary to obtain a zinc oxide dispersion containing 0.5 to 50% by weight, preferably 0.5 to 30% by weight of lipophilic fine particle zinc oxide.
[0012]
Zinc oxide dispersions obtained by the present invention are widely used in skin care products such as lotions, emulsions, creams and cosmetic oils, as well as makeup cosmetics such as foundations, powders, lipsticks, blushers, eye shadows and nail enamels. Can be blended into various cosmetics.
[0013]
【The invention's effect】
According to the present invention, by using methanol, propanol, or a mixed solvent as a dispersion medium, it is possible to efficiently produce a zinc oxide dispersion liquid that is highly transparent and excellent in the effect of preventing ultraviolet rays.
[0014]
【Example】
Example 1
20.4 g of zinc chloride was dissolved in methanol to make 100 mL (the concentration of zinc chloride used as a raw material solution was 1.5 mol / L). Subsequently, 200 mL of an alkaline solution in which 10.8 g of sodium hydroxide was mixed with methanol was dropped into the raw material liquid maintained at 30 ± 1 ° C. to obtain 300 mL of a slurry (the concentration of sodium hydroxide in the alkaline solution was 1). .35 mol / L, the equivalent ratio of zinc chloride to sodium hydroxide is 1: 0.9, and the zinc concentration after mixing is 0.5 mol / L). It was 8.2 when pH of the obtained slurry was measured with a pH meter (D-12, manufactured by Horiba Ltd.). Further, the slurry was centrifuged at 1500 G for 5 minutes with a centrifuge (HIMAC SCR20B, manufactured by Hitachi Koki Co., Ltd.) to obtain a colorless and transparent sol. When the absorption spectrum of this zinc oxide dispersion was measured with a spectrophotometer (UV 160A, manufactured by Shimadzu Corporation), the absorption edge wavelength was 330 nm. The absorption edge wavelength was determined at the intersection of the tangent and the wavelength axis at the inflection point of the curve based on the absorbance curve with respect to the wavelength.
[0015]
Example 2
16.4 g of zinc chloride was dissolved in a methanol / ethanol mixed solution (mixing ratio 1: 1) to make 100 mL (the concentration of zinc chloride used as a raw material solution is 1.2 mol / L). Subsequently, 200 mL of an alkaline solution in which 8.2 g of sodium hydroxide was mixed with a methanol / ethanol mixed solution was dropped into the raw material liquid maintained at 30 ± 1 ° C. to obtain 300 mL of a slurry (sodium hydroxide in an alkaline solution). Is 1.0 mol / L, the equivalent ratio of zinc chloride to sodium hydroxide is 1: 0.85, and the zinc concentration after mixing is 0.4 mol / L). The pH of the obtained slurry was measured in the same manner as in Example 1. As a result, it was 8.1. Further, the slurry was centrifuged in the same manner as in Example 1 to obtain a colorless and transparent sol. When the absorption spectrum of this zinc oxide dispersion was measured in the same manner as in Example 1, the absorption edge wavelength was 324 nm.
[0016]
Example 3
16.4 g of zinc chloride was dissolved in methanol to make 100 mL (the concentration of zinc chloride used as a raw material solution was 1.2 mol / L). Subsequently, 200 mL of an alkaline solution in which 8.2 g of sodium hydroxide was mixed with ethanol was added dropwise to the raw material liquid maintained at 30 ± 1 ° C. to obtain 300 mL of a slurry (the concentration of sodium hydroxide in the alkaline solution was 1). 0.0 mol / L, the equivalent ratio of zinc chloride to sodium hydroxide is 1: 0.85, and the zinc concentration after mixing is 0.4 mol / L). The pH of the obtained slurry was measured in the same manner as in Example 1. As a result, it was 7.8. Further, the slurry was centrifuged in the same manner as in Example 1 to obtain a colorless and transparent sol. When the absorption spectrum of this zinc oxide dispersion was measured in the same manner as in Example 1, the absorption edge wavelength was 324 nm.
[0017]
Example 4
6.1 g of zinc chloride was dissolved in 2-propanol to make 100 mL (the concentration of zinc chloride used as a raw material solution was 0.5 mol / L). Subsequently, 200 mL of an alkaline solution in which 2.5 g of sodium hydroxide was mixed with 2-propanol was added dropwise to the raw material liquid maintained at 30 ± 1 ° C. to obtain 300 mL of a slurry (concentration of sodium hydroxide in the alkaline solution). Is 0.3 mol / L, the equivalent ratio of zinc chloride to sodium hydroxide is 1: 0.7, and the zinc concentration after mixing is 0.15 mol / L). The pH of the obtained slurry was measured in the same manner as in Example 1. As a result, it was 7.0. Further, the slurry was centrifuged in the same manner as in Example 1 to obtain a colorless and transparent sol. When the absorption spectrum of this zinc oxide dispersion was measured in the same manner as in Example 1, the absorption edge wavelength was 320 nm.

Claims (5)

A solution in which a zinc salt is dissolved in methanol, propanol, or a mixed solvent of two or more of methanol, ethanol, and propanol, and an alkali metal hydroxide, methanol, propanol, or two of methanol, ethanol, and propanol A method for producing a zinc oxide dispersion , comprising mixing a solution dissolved in the above mixed solvent, and adjusting the pH after mixing and after mixing to less than 9. The method for producing a zinc oxide dispersion according to claim 1, wherein the zinc concentration is more than 0.1 mol / L and not more than 0.5 mol / L. The method for producing a zinc oxide dispersion according to claim 1 or 2, wherein the zinc salt is zinc chloride . The method for producing a zinc oxide dispersion according to any one of claims 1 to 3, wherein the alkali metal hydroxide is sodium hydroxide . The method for producing a zinc oxide dispersion according to any one of claims 1 to 4, wherein the salt particles produced as a by-product are removed after adjusting the pH to less than 9 during and after mixing .