JP6477173B2 - Method for producing surface-coated zinc oxide particles - Google Patents

Description

The present invention relates to a method of producing surface coated zinc oxide particles.

Zinc oxide is also referred to as zinc flower and has a UV shielding property, and is widely used as a cosmetic material and the like. However, zinc oxide dissolves the emulsifying system when added to cosmetics because zinc ion elutes with time, and it also has the problem that other components are modified by the surface catalytic activity of zinc oxide. It was Therefore, for the purpose of reduction of zinc elution, suppression of catalyst activity, improvement of dispersibility and the like, zinc oxide is subjected to an inorganic treatment with an inorganic substance such as silica, titania, metal soap or the like (see, for example, Patent Documents An organic treatment with an organic substance such as silicone or fatty acid (see, for example, Patent Document 3) is performed.

JP, 2008-94917, A Japanese Patent Application Publication No. 2003-411147 JP-A-7-267894

As described above, an inorganic treatment or an organic treatment of zinc oxide is performed for the purpose of reducing the elution of zinc, suppressing the catalytic activity, improving the dispersibility, and the like. However, in the conventional treatment, there is room for improvement in these points because zinc elution is not sufficiently suppressed and the zinc oxide surface is not uniformly treated. In addition, conventional dispersions containing zinc oxide may increase in viscosity due to changes with time due to combinations of solvents, dispersants, etc. When formulated into cosmetics, they will not be well compatible with ester oil etc., cosmetics There was also a problem that Therefore, there has been a demand for zinc oxide which is stable in an organic solvent, particularly an ester solvent, and in which the elution of zinc is sufficiently suppressed, and a dispersion thereof.

In addition, cosmetic products that do not contain silicone are required in the market from the viewpoint of eliminating the need for strong cleansing and having a low environmental impact, etc. Also, they do not contain silicone as a cosmetic material (also referred to as cosmetic material). A thing, ie, a non-silicone material, was called for.

An object of the present invention is, in view of the above-mentioned present situation, to provide a manufacturing method capable of easily giving surface-coated zinc oxide particles in which zinc elution is sufficiently suppressed and compatibility with an organic solvent is good. Another object of the present invention is to provide a surface-coated zinc oxide particle obtained by this production method, and a zinc oxide particle dispersion and a cosmetic comprising the same and which are stable over time.

The present inventors variously studied zinc oxide with low zinc elution, and noted that zinc elution is sufficiently suppressed if particles in which a part or all of the surface of zinc oxide is coated with a fatty acid salt. If a slurry containing zinc oxide and a fatty acid salt and having a zinc oxide concentration in a predetermined range is aged at 85 ° C. or higher in order to obtain such surface-coated zinc oxide particles, zinc elution is significantly suppressed. Found that. In general, it is known that particles are easily aggregated when zinc oxide is used as a water slurry and the slurry is heated to a high temperature of 50 ° C. or higher. When the particles are surface-treated in this state, the particles are surface-treated And the processing was likely to be uneven. Also, if the temperature exceeds 80 ° C., the amount of liquid level evaporation water will be large, and it will be easy to form coarse aggregates with a dried slurry near the liquid surface of the reaction tank, and coarse particles will be mixed in the product, or uniform processing will be performed. It is also known to be difficult. However, contrary to such conventional technical common sense, the present inventors set the temperature of the aging step to 85 ° C. or higher, and when the concentration of zinc oxide in the slurry to be subjected to the aging step is set to a predetermined range, zinc elution is significantly suppressed. It was found that the obtained zinc oxide particles were obtained. Since the zinc oxide particles are uniformly surface-coated with a fatty acid salt, they are well compatible with the organic solvent, and are found to be in a uniformly and stably dispersed state in the organic solvent. In the present invention, the present invention has been completed.

That is, the present invention includes a slurry preparation step of preparing a slurry containing zinc oxide and a fatty acid salt and having a concentration of 110 g / L or less, and a ripening step of ripening the slurry at 85 ° C. or higher. It is a manufacturing method of surface covering zinc oxide particles.

The fatty acid salt is preferably a metal salt and / or an amine salt. This makes it possible to obtain surface-coated zinc oxide particles with less zinc elution and better compatibility with organic solvents.

The present invention is also the surface-coated zinc oxide particles obtained by the above-mentioned production method.

The present invention is also a zinc oxide particle dispersion comprising the above surface-coated zinc oxide particles, an organic solvent and a dispersant. This dispersion is in a state in which the surface-coated zinc oxide particles are uniformly and stably dispersed in an organic solvent without the viscosity increasing with time, and thus physical properties derived from the surface-coated zinc oxide particles (for example, ultraviolet light The shielding performance etc. can be exhibited stably.

The dispersant preferably contains polyhydroxystearic acid. This makes it possible to disperse the surface-coated zinc oxide particles more uniformly.

It is preferable that the said zinc oxide particle dispersion is used for a cosmetics raw material. Thereby, cosmetics excellent in ultraviolet shielding performance etc. can be given.

The present invention is also a cosmetic comprising the above-mentioned zinc oxide particle dispersion.

According to the method for producing surface-coated zinc oxide particles of the present invention, it is possible to easily provide surface-coated zinc oxide particles in which zinc elution is sufficiently suppressed and compatibility with an organic solvent is good. The surface-coated zinc oxide particles obtained by this production method are particles in which a part or the whole of the surface of zinc oxide is coated with a fatty acid salt, but they have good compatibility with organic solvents, particularly ester solvents, It is possible to give a stable dispersion over time. Such surface-coated zinc oxide particles and zinc oxide particle dispersions are particularly useful as raw materials for cosmetics, and also useful as non-silicone materials that have a good feeling of use in recent years.

FIG. 1 is a graph showing the time-dependent change in viscosity of a dispersion obtained by adding each sample powder obtained in Examples or Comparative Examples to an alcohol solution of oleic acid. FIG. 2 is a graph showing the temporal viscosity change of the dispersion containing the surface-coated zinc oxide particles, the organic solvent and the dispersant obtained in Example 1 or 2.

Hereinafter, although an example of the present invention is explained concretely, the present invention is not limited only to the following descriptions, and can be suitably changed and applied in the range which does not change the gist of the present invention.

[Method of producing surface-coated zinc oxide particles]
The production method of the present invention includes a slurry preparation step and a ripening step, but may further include one or more other steps performed in surface treatment of ordinary particles and the like. In addition, each step may be performed twice or more as necessary.

(I) Slurry preparation step The slurry preparation step is a step of preparing a slurry containing zinc oxide and a fatty acid salt and having a concentration of 110 g / L or less. The production method is not particularly limited, and it is preferable to stir the raw materials so as to be in a uniformly mixed state. The order of addition and mixing of the respective raw materials is not particularly limited, and the temperature at the time of slurry preparation is also not particularly limited. For example, from the work surface, it is preferable to prepare the slurry at 5 to 35 ° C.

The above-mentioned slurry contains zinc oxide, a fatty acid salt and a dispersion medium, but may contain other components as long as the effects of the present invention are not impaired. The other components will be described later.
Each component can be used alone or in combination of two or more.

Although the said zinc oxide is not specifically limited, For example, it is preferable that it is a particle | grain with an average primary particle diameter of 1-300 nm. Thereby, since the ultraviolet shielding property and the visible light transparency can be enhanced, the obtained surface-coated zinc oxide particles become more suitable for cosmetic material applications. The average primary particle size is more preferably 5 to 200 nm, still more preferably 10 to 100 nm, and particularly preferably 15 to 50 nm. The particle shape is not particularly limited.

In the present specification, the average particle diameter is obtained by drawing a diagonal line on an image taken with a field emission scanning electron microscope (JSM-7000F, manufactured by Nippon Denshi Co., Ltd.), and measuring the maximum inscribed circle of 100 particles on each line. Means the arithmetic mean of the diameters.
When the average primary particle size of zinc oxide in the slurry is measured, the slurry is filtered and washed with water, and then dried at 105 ° C. for 2 hours using a constant temperature drier (SONW-450 manufactured by As One Corporation). Use the particles.

The concentration of zinc oxide in the slurry is 110 g / L or less. By subjecting the slurry having a concentration of zinc oxide in this range to a ripening step at a predetermined temperature, zinc elution can be sufficiently suppressed, and surface-coated zinc oxide particles having good compatibility with an organic solvent can be obtained. Preferably it is 100 g / L or less, More preferably, it is 90 g / L or less, More preferably, it is 80 g / L or less. The lower limit of the concentration of zinc oxide is not particularly limited, but is preferably 30 g / L or more, for example, from the viewpoint of improvement of coating efficiency, production cost, and the like. More preferably, it is 40 g / L or more, more preferably 50 g / L or more.
In the present specification, the concentration of zinc oxide means the content (g) of zinc oxide relative to 1 L of dispersion medium contained in the slurry.

Although the said fatty acid salt is not specifically limited, For example, it is preferable that it is a C8-C30 fatty acid (monocarboxylic acid) salt. The lower limit of the carbon number of the fatty acid is more preferably 10 or more, still more preferably 14 or more, whereby the skin irritability of the surface-coated zinc oxide particles obtained is further reduced, and the cosmetic material is used Will be more useful. Further, in consideration of the solubility or dispersibility in the slurry, the upper limit of the carbon number is more preferably 24 or less, still more preferably 20 or less.

Specific examples of the fatty acid constituting the above-mentioned fatty acid salt include, for example, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid And saturated fatty acids such as myric acid; unsaturated fatty acids such as oleic acid, linoleic acid and linolenic acid; and the like, which further have a substituent (eg, hydroxyl group, carbonyl group, epoxy group etc.) May be Among them, saturated fatty acids are preferred.

The fatty acid salt is preferably a metal salt and / or an amine salt. This makes it possible to obtain surface-coated zinc oxide particles with less zinc elution and better compatibility with organic solvents. Among them, metal salts are preferred.

The metal constituting the metal salt is not particularly limited, but, for example, metal other than periodic table group 1 metal such as sodium, lithium, potassium, rubidium and cesium, group 2 metal such as magnesium, calcium, strontium and barium, and manganese And iron, copper, zinc, aluminum and the like, and one or more of these can be used. Among them, periodic table group 1 metals are preferable. More preferably, sodium, potassium and lithium are used. That is, the metal salt (fatty acid metal salt) is preferably a sodium salt, a potassium salt and / or a lithium salt.

The amine which comprises the said amine salt is not specifically limited, You may use any of a primary amine, a secondary amine, and a tertiary amine. In addition, it may be a polyamine having two or more amino groups in one molecule. Specifically, an alkylamine etc. are mentioned, for example.

The content of the fatty acid salt is preferably 1 to 50 parts by weight with respect to 100 parts by weight of zinc oxide in the slurry. By setting this range, it becomes possible to coat the zinc oxide surface more uniformly with the fatty acid salt. More preferably, it is 5 parts by weight or more. Further, it is more preferably 40 parts by weight or less, still more preferably 30 parts by weight or less, and particularly preferably 15 parts by weight or less.

The dispersion medium is not particularly limited, and examples thereof include water, an organic solvent, and a mixture thereof. Examples of the organic solvent include alcohols, acetone, dimethylsulfoxide, dimethylformamide, tetrahydrofuran, dioxane and the like, and as the alcohol, monohydric water-soluble alcohols such as methanol, ethanol and propanol; dihydric or more such as ethylene glycol and glycerin Water-soluble alcohol; and the like. The dispersion medium is preferably water, more preferably ion exchanged water.

It does not specifically limit as said other component, For example, a dispersing agent etc. are mentioned. Although the content of the other components is not particularly limited, for example, it is preferably 10 wt% or less in 100 wt% of the slurry.

(Ii) Aging step The aging step is a step of aging the slurry obtained in the slurry preparation step at 85 ° C. or higher. By setting the aging temperature of the slurry in which the zinc oxide concentration is within the predetermined range to 85 ° C. or more, it is possible to obtain surface-coated zinc oxide particles in which zinc elution is sufficiently suppressed and in which the compatibility with organic solvents is good. The ripening temperature is preferably 87 ° C. or more, more preferably 90 ° C. or more. The upper limit of the ripening temperature is not particularly limited, but is preferably 200 ° C. or less for the convenience of, for example, equipment. More preferably, it is 150 degrees C or less, More preferably, it is 120 degrees C or less.

In the above-mentioned ripening step, the ripening time is not particularly limited, but is preferably 1 minute or more. More preferably, it is 5 minutes or more, More preferably, it is 10 minutes or more. Although the upper limit of the ripening time is not particularly limited, for example, it is preferable to set it to 10 hours or less from the viewpoint of improving the production efficiency. More preferably, it is 5 hours or less, still more preferably 2 hours or less.
In the present specification, the ripening temperature means the maximum temperature during ripening. Further, the aging time means the holding time of the maximum temperature (aging temperature) at the time of aging, and does not include the temperature rising time until the maximum temperature is reached. The heating time is not particularly limited, but is preferably as short as possible.

Although surface-coated zinc oxide particles can be obtained through the above-described steps, the following steps may be performed as necessary.

(Iii) Neutralization Step After the above-mentioned ripening step, the slurry (also referred to as aged slurry) may be neutralized if necessary. In the neutralization step, the pH of the aged slurry is preferably adjusted to 7 to 10, more preferably 7 to 8, and further preferably 7 to 7.5.

In the neutralization step, it is preferable to use a zinc salt such as zinc chloride as a neutralizing agent. Thereby, surface-coated zinc oxide particles in which zinc elution is more sufficiently suppressed can be obtained. Moreover, you may use the acid and alkali generally used generally as a pH adjuster.
In order to carry out the neutralization reaction sufficiently, the slurry may be aged after charging the neutralizing agent. The temperature and time of the subsequent ripening step are not particularly limited.

(Iv) Washing Step Also, if necessary, the aged slurry (also including those obtained through other steps such as a neutralization step and a post aging step) may be washed. Although the washing method is not particularly limited, for example, after filtering the matured slurry, it is preferable to wash with water and / or an organic solvent until the electric conductivity of the filtrate becomes 100 μS / cm or less.

(V) Grinding Step After the above-mentioned ripening step (or after performing other steps), it is preferable to refine the particles by wet grinding or dry grinding. Among them, dry grinding is preferable. In dry grinding, high-speed rotary grinders, edge runners by the action of compression, friction, shear and the like can be used. As a high speed rotary crusher, an atomizer is mentioned, for example.

[Surface coated zinc oxide particles]
The surface-coated zinc oxide particles obtained by the production method of the present invention are in a state of being stably dispersed in an organic solvent because zinc elution is small and compatibility with the organic solvent is good. It is therefore particularly suitable for applications which are often stored or used in the form of dispersions. Among them, it is particularly suitably used as a cosmetic material.

The particle shape of the surface-coated zinc oxide particles is not particularly limited, and examples thereof include needle-like, rod-like, plate-like and spherical shapes. Moreover, it is preferable that an average particle diameter is 1 to 100 nm. Thereby, the ultraviolet shielding properties and the visible light transparency can be enhanced, and therefore, they are more suitable for cosmetic material applications. More preferably, it is 5-80 nm, More preferably, it is 10-50 nm.

[Zinc oxide particle dispersion]
The zinc oxide particle dispersion (also simply referred to as "dispersion") of the present invention comprises surface-coated zinc oxide particles obtained by the production method of the present invention, an organic solvent, and a dispersant. As described above, since the surface-coated zinc oxide particles have good compatibility with the organic solvent, the dispersion of the present invention is in a state where the surface-coated zinc oxide particles are uniformly and stably dispersed in the organic solvent. Therefore, the viscosity does not increase with time, and even if sedimentation occurs during storage or use, the particles can be easily re-dispersed by simple stirring, so various uses such as cosmetic applications etc. Useful for use.
Each component can be used alone or in combination of two or more.

The content of the surface-coated zinc oxide particles in the dispersion is, for example, preferably 10 to 80% by weight with respect to 100% by weight of the total of the surface-coated zinc oxide particles, the organic solvent and the dispersant. Thereby, the performance derived from the surface-coated zinc oxide particles can be more sufficiently exhibited, and the particles are in a more uniformly and stably dispersed state. More preferably, it is 30-70 weight%, More preferably, it is 50-60 weight%.

The organic solvent is not particularly limited, and examples thereof include ester oils such as ethylhexyl palmitate and triisodecyl isononanoate; alcohols; liquid paraffins such as hydrogenated polyisobutene; silicone oils such as decamethylcyclopentasiloxane; Among them, it is preferable to use an ester oil because the surface-coated zinc oxide particles have particularly good compatibility with the ester oil.

The content of the organic solvent in the dispersion is, for example, preferably 10 to 80% by weight with respect to 100% by weight in total of the surface-coated zinc oxide particles, the organic solvent and the dispersant. More preferably, it is 30 to 70% by weight, still more preferably 35 to 49% by weight.

The dispersant is not particularly limited, and a compound used in a common dispersion may be used, and particularly preferably polyhydroxystearic acid.

In the dispersion, the content of the dispersant is, for example, preferably 0.01 to 20 parts by weight with respect to 100 parts by weight of the surface-coated zinc oxide particles. Thereby, the surface-coated zinc oxide particles can be uniformly dispersed by the organic solvent. More preferably, it is 0.1 to 8 parts by weight, still more preferably 1 to 5 parts by weight.

The dispersion may further contain one or more other components, as necessary.

The method for producing the above dispersion is not particularly limited, and it can be produced by a common method of mixing and stirring each raw material, for example, bead mill, ball mill, high pressure homogenizer, stirring type homogenizer, ultrasonic homogenizer, wet jet It is preferable to manufacture using an apparatus such as a mill. These devices may be appropriately selected from the viewpoint of the degree of dispersion, production efficiency, and the like.

Cosmetics
The dispersion of the present invention can be used in various applications because the surface-coated zinc oxide particles are uniformly and stably dispersed in an organic solvent. Among them, they are particularly useful as cosmetic raw materials. The cosmetic to be applied is not particularly limited, and examples thereof include foundation, makeup base, sunscreen, eye shadow, blusher, mascara, lipstick, sunscreen agent and the like. Thus, a cosmetic containing the dispersion of the present invention is also one of the present invention.
In addition, since the dispersion of the present invention does not require silicone, it can also be used as a non-silicone material which has recently been attracting attention as a material for providing a cosmetic excellent in feeling in use.

The cosmetic may contain one or more other components in addition to the dispersion of the present invention, as necessary. Other components are not particularly limited, and examples thereof include any aqueous component and oil component generally used in the cosmetic field. Specifically, oils, surfactants, moisturizers, higher alcohols, sequestering agents, natural and synthetic polymers, water-soluble and oil-soluble polymers, UV screening agents, various extracts, inorganic and organic pigments, inorganic And various powders such as organic clay minerals, inorganic and organic pigments treated with metal soap or treated with silicone, colorants such as organic dyes, preservatives, antioxidants, dyes, thickeners, pH adjusters, perfumes, Cooling agents, antiperspirants, bactericidal agents, skin activators and the like can be mentioned. The content of these components is not particularly limited as long as the effects of the present invention are not impaired.

The following examples are provided to describe the present invention in detail, but the present invention is not limited to these examples. Unless otherwise noted, "%" shall mean "wt% (mass%)".

Example 1
An aqueous slurry of 80 g / L of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., FINEX-30, average particle diameter 35 nm) was prepared.
Then, add sodium stearate (manufactured by Nippon Color Industrial Co., Ltd., KS-3) to the water slurry so as to be 10% based on the weight of zinc oxide, and heat up to 90 ° C., and 2 hours after reaching 90 ° C. Aged.
An aqueous solution of zinc chloride in the same molar amount as the added sodium stearate was added to the slurry over 30 minutes, neutralized to pH 7.0-7.5, and then aged for 1 hour.
The filtrate is washed with water until the conductivity of the filtrate is 100 μS / cm or less, and the resulting cake is dried at 85 ° C. for 16 hours, and then crushed with an atomizer to obtain surface-coated zinc oxide particles (1) of the present invention Obtained.

Example 2
Surface-coated zinc oxide particles (2) of the present invention were obtained in the same manner as in Example 1 except that the ripening time after reaching 90 ° C. was 10 minutes.

Comparative Example 1
A comparative product (C1) was obtained in the same manner as Example 1, except that the zinc oxide concentration at the time of preparation of the water slurry was 140 g / L.

Comparative example 2
A comparative product (C2) was obtained in the same manner as in Example 1 except that the aging temperature after adding sodium stearate to the water slurry was set to 80 ° C.

Comparative example 3
In a high-speed stirrer, zinc oxide (FINEX-30, manufactured by Sakai Chemical Industry Co., Ltd., average particle diameter 35 nm) and methyl hydroxide polysiloxane (Shin-Etsu Chemical Co., Ltd., KF-9901) so as to be 5% with respect to zinc oxide. ) Was added and stirred for 10 minutes.
The resulting treated powder was heated in a drier at 120 ° C. for 16 hours.
The heated powder was pulverized using a jet mill to obtain a comparative product (C3).

1. Zinc elution suppression effect In order to evaluate the zinc elution suppression effect, each (sample powder) of the surface-coated zinc oxide particles obtained in the example or the comparative product obtained in the comparative example is added to an alcohol solution of oleic acid, The viscosity of this dispersion (the test solution) was measured over time. When zinc elutes with time, the viscosity of the solution increases, so the zinc elution suppression effect by the added zinc oxide can be evaluated based on the degree of the viscosity increase. Details of the test method are shown below. The results are shown in FIG. In FIG. 1, the case (blank) which did not contain sample powder was also written together for reference.
<Test method>
(1) Add oleic acid to isopropyl alcohol at 20% by weight to prepare a test solution.
(2) Take the solution into a sample tube, add 10% by weight of sample powder to the test solution, shake the sample tube, and mix the test solution with the powder.
(3) The viscosity of the test solution immediately after mixing is measured with a B-type viscometer (rotor No. 3, 12 rpm, after 1 minute). Thereafter, the sample tube is allowed to stand at room temperature (25 ° C.), and the viscosity is measured over time.

The following was confirmed from FIG.
Example 1 and Comparative Example 1 differ only in the zinc oxide concentration of the slurry subjected to the aging step, and Example 1 and Comparative Example 2 differ only in the aging temperature. In addition, Example 2 is an example in which only aging time is different from Example 1. Under these differences, when the viscosity changes of the obtained dispersions containing zinc oxide with time are compared, it can be seen from FIG. 1 that when the respective comparative products obtained in Comparative Examples 1 and 2 are used, While the viscosity of the test solution was significantly increased at the above, when the surface-coated zinc oxide particles obtained in Examples 1 and 2 were used, the viscosity was hardly increased. From this, it was found that surface-coated zinc oxide particles extremely excellent in the zinc elution suppression effect can be obtained only by subjecting a slurry having a zinc oxide concentration in a predetermined range to an aging step at a predetermined temperature.
Moreover, although the comparative example 3 is an example which performed the conventional organic treatment to zinc oxide, the viscosity of the test liquid raised significantly with time similarly to the comparative example 1 and 2. FIG. Therefore, it was found that the surface-coated zinc oxide particles obtained by the production method of the present invention are excellent in the zinc elution suppressing effect also to zinc oxide subjected to the conventional organic treatment.

2. Evaluation of familiarity with organic solvents In order to evaluate familiarity with organic solvents, the oil absorption of each of the surface-coated zinc oxide particles obtained in the examples or the comparative product obtained in the comparative examples (sample) was measured. The smaller the oil absorption value, the better the compatibility with the measurement oil (organic solvent). Details of the test method are shown below. The results are shown in Table 1.
<Test method>
(1) Precisely weigh about 0.5 g of the sample on a medicine package.
(2) Place the sample on a 10 cm ground glass portion at the center of the glass plate.
(3) Put the measurement oil into a micro buret, add 0.2 mL to the sample dropwise, and knead it with gold sliver.
(4) Then, add 1 to 2 drops of the measurement oil, and knead the whole with a gold pan each time it is added dropwise.
(5) The end point is when the whole becomes a hard putty-like mass for the first time.
(6) The oil absorption amount is calculated by the following equation.
Oil absorption (ml / 100g) = V (mL) / sample weight (g) x 100
In the formula, V represents the amount (mL) of the measured oil added dropwise.

The details of the measurement oil used are shown below.
Isopropyl myristate: manufactured by Kao Corporation, Excepearl IPM
Hydrogenated polyisobutene: manufactured by NOF Corporation, Pearl Reem 3
Triisodecyl isononanoate: manufactured by Nisshin Oillio Group, Inc., Saracos 913

From Table 1, the following was confirmed.
Comparing the oil absorption of each sample, the surface coated zinc oxide particles obtained in Examples 1 and 2 have significantly larger oil absorption relative to each of the measurement oils than the comparative products obtained in Comparative Examples 1 to 3. It is reduced (Table 1). Therefore, it has been found that the surface-coated zinc oxide particles obtained by the production method of the present invention have very good compatibility with organic solvents.

3. Evaluation of dispersion stability In order to evaluate the stability of the dispersion, the dispersion comprising the surface-coated zinc oxide particles (test powder) obtained in Example 1 or 2 and an organic solvent and a dispersant The viscosity change over time was observed. Details of the test method are shown below. The results are shown in FIG.
<Test method>
(1) In a 140 ml mayonnaise bottle, 50 g of the test powder, 4 g of polyhydroxystearate, 46 g of ethylhexyl palmitate, and 100 g of φ0.5 mm zirconia (ZrO ₂ ) beads are charged.
(2) After tightly sealing with an inner lid and dispersing with a paint shaker for 1 hour, the beads are separated to obtain an organic solvent dispersion of zinc oxide.
(3) The dispersion is placed in a sample tube, stored in a drier at 40 ° C., and the viscosity change over time (B-type viscometer: rotor No. M3, 60 rpm, 1 minute) is observed.

The following was confirmed from FIG.
The surface-coated zinc oxide particles obtained in Examples 1 and 2 are all obtained by the production method of the present invention, but according to FIG. 2, the dispersion containing any of these has a viscosity rise with time. It turns out that it hardly occurred. Therefore, it was found that the zinc oxide dispersion containing the surface-coated zinc oxide particles, the organic solvent and the dispersant obtained by the production method of the present invention is stable over time.

Claims (6)

A slurry producing step of producing a slurry containing zinc oxide and a fatty acid salt and having a concentration of 110 g / L or less of zinc oxide;
And a ripening step of ripening the slurry at 85 ° C. or more. The method for producing surface-coated zinc oxide particles according to claim 1, wherein the fatty acid salt is a metal salt and / or an amine salt. Zinc oxide comprising a step of mixing surface-coated zinc oxide particles obtained by the method for producing surface-coated zinc oxide particles according to claim 1 or 2 with an organic solvent and a dispersing agent. Method of producing a particle dispersion. The method for producing a zinc oxide particle dispersion according to claim 3 , wherein the dispersing agent comprises polyhydroxystearic acid. The said zinc oxide particle dispersion is used for a cosmetics raw material, The manufacturing method of the zinc oxide particle dispersion of Claim 3 or 4 characterized by the above-mentioned. Cosmetics manufacturing method according to claim <br/> using zinc oxide particles dispersion obtained by the production method of the zinc oxide particles dispersion according to any of claims 3-5 as a raw material.

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