JP2002284527A - Method for producing fine powder of zinc oxide, fine powder of zinc oxide and resin composition containing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fine powder of zinc oxide having an excellent ultraviolet screening property, an excellent dispersibility, an excellent transparency for visible ray, a low activity for photocatalysis, and 100 nm or less of average particle diameter, and a method for producing this fine powder of zinc oxide at low cost. SOLUTION: A method for producing a fine powder of zinc oxide characterized in that a given amount of a zinc containing solution and a given amount of an alkali solution are mixed while stirring within 0.1-600 seconds so as to make pH to 11-13 at the end point of mixing, and then the fine powder of zinc oxide in the mixed solution is matured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing zinc oxide fine powder, a zinc oxide fine powder obtained by the method, and a resin composition containing the zinc oxide fine powder.

[0002]

2. Description of the Related Art Conventional methods for industrially producing zinc oxide fine powder include a dry method and a wet method. In the dry method, zinc vapor is oxidized in the gas phase to obtain zinc oxide fine powder.
In the wet method, an aqueous solution containing a zinc salt is neutralized in the aqueous solution,
There is known a method in which the generated precipitate is filtered, dried, and then heated at a high temperature to obtain zinc oxide fine powder.

[0003] However, since the zinc oxide fine powder obtained by these methods is treated at a high temperature, there is a problem that it is difficult to disperse due to a strong cohesive force, and that the photocatalytic activity is large.

Therefore, there have been reported several methods for producing zinc oxide fine powder without a step of heating at a high temperature.
1) JP-A-4-16813 discloses that an alkaline aqueous solution is dropped into an aqueous solution of a zinc salt at a temperature of 60 ° C. or more, and a zinc oxide precipitate is formed at a final pH of 9 or more to give an average particle size of 0.2 μm or less. A method for synthesizing a fine zinc oxide powder is described. 2) JP-A-9-137152 discloses that
A method containing zinc ions, containing one or more acid groups in an amount exceeding the equivalent amount in total with respect to the zinc ions, and forming a precipitate from a mother liquor having a pH of 11 or more,
Average particle size 0.1-1 μm, average particle thickness 0.01-0.
A method for synthesizing 2 μm flaky zinc oxide having an average plate ratio of 3 or more is described. 3) JP-A-2000-9551
In Japanese Patent Application Publication No. 9 (1999), after an alkaline aqueous solution is brought into contact with an acidic aqueous solution 1 containing zinc in an equivalence ratio of more than 1 and 1.5 or less, it is immediately dropped into a large amount of flowing aqueous solution. Thus, a method for continuously synthesizing a zinc oxide powder is described.

[0005]

However, in the above-mentioned method 1), the time for dropping the aqueous alkali solution into the aqueous zinc salt solution is not taken into consideration, and thus the obtained zinc oxide fine powder contains zinc hydroxide. However, there is a problem that impurities such as impurities are mixed in, and the particle size increases due to the particle growth, and the particle size varies.

In the above method 2), the resulting zinc oxide fine powder is plate-like, has a strong cohesive force, is difficult to disperse, and has an average particle size because an excessive acid group is added in the reaction step. There was a problem that it was as large as 0.1 μm or more.

In the above method 3), attention is paid only to the equivalence ratio between the acidic aqueous solution and the alkaline aqueous solution, and the pH is not taken into account. Therefore, the obtained zinc oxide fine powder contains impurities such as zinc hydroxide. Or a large particle size of 0.1 μm or more can be obtained. Further, since a large amount of water is required, large-scale equipment is required, and the production cost is increased. There was also.

An object of the present invention is to provide a zinc oxide fine powder having excellent ultraviolet shielding properties, dispersibility and visible light transmittance, a small photocatalytic activity and an average particle diameter of 100 nm or less, and inexpensively supply this zinc oxide fine powder. To provide a manufacturing method.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a gel having a high water content is formed immediately after mixing a zinc-containing solution and an alkaline aqueous solution, and zinc oxide is formed by a dehydration reaction of the gel. Was found, and as a result of investigating the formation mechanism of this zinc oxide in detail, by controlling the pH and the mixing time when mixing the zinc-containing solution and the aqueous alkali solution, the ultraviolet shielding property and dispersibility and The present inventors have found that a zinc oxide fine powder having excellent visible light transmittance, low photocatalytic activity and an average particle diameter of 100 nm or less can be obtained, and reached the present invention.

That is, a first aspect of the present invention is to stir a predetermined amount of a zinc-containing solution and a predetermined amount of an alkaline aqueous solution at a pH of 11 to 13 at the end of mixing for 0.1 to 600 seconds. The present invention provides a method for producing a zinc oxide fine powder, which comprises mixing and then aging the zinc oxide fine powder in the mixed solution. A second aspect of the present invention is to provide a zinc oxide fine powder having an average particle diameter of 100 nm or less obtained by the first production method of the present invention, and a third aspect of the present invention is the above-described zinc oxide fine powder. The gist is a resin composition containing a powder.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The zinc-containing solution used in the present invention may be any solution containing zinc ions, such as a solution of zinc metal dissolved in sulfuric acid, hydrochloric acid or nitric acid, or a solution of zinc sulfate, zinc chloride or zinc acetate in water. It may contain a water-soluble inorganic substance such as sodium chloride or potassium chloride or a water-soluble organic substance such as alcohol, fatty acid, or polymer.

The zinc concentration in the zinc-containing liquid is 0.0
1 mol / L or more and 5.0 mol / L or less, more preferably 0.1 mol / L or more,
2.0 mol / liter or less. Zinc concentration 0.01
If the amount is less than mol / liter, productivity is undesirably reduced.

The aqueous alkaline solution used in the present invention is:
Aqueous solutions such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, and aqueous solutions thereof, and aqueous solutions thereof, and water-soluble inorganic substances such as sodium chloride and potassium chloride, and water-soluble organic substances such as alcohols, fatty acids, and polymers can be used. It may be contained.

The concentration of the aqueous alkali solution is 0.01
It is preferably at least mol / l and at most 10 mol / l, more preferably at least 0.1 mol / l and at most 5 mol / l. The concentration of the aqueous alkali solution is 0.
If the amount is less than 01 mol / liter, productivity is undesirably reduced.

In the present invention, the predetermined amount of the zinc-containing liquid and the aqueous alkaline solution is such that the pH at the end of mixing the zinc-containing liquid and the aqueous alkaline solution is 11 to 13. That is, in order to determine the predetermined amounts of the zinc-containing solution and the aqueous alkali solution at the target pH at the end of the mixing, for example, the pH at the time of mixing the zinc-containing solution and the aqueous alkali solution may be measured in advance.

In the present invention, the method of mixing the zinc-containing solution with the aqueous alkali solution includes, for example, 1) a method of dropping or injecting the aqueous alkali solution into the zinc-containing solution, and 2) adding the zinc-containing solution to the aqueous alkali solution. A method of dropping or injecting with a pump, 3) a method of simultaneously dropping or injecting a zinc-containing solution and an aqueous alkali solution with a pump, or any other method may be used.

A feature of the present invention is that the time required to complete the mixing of the respective predetermined amounts of the zinc-containing solution and the aqueous alkaline solution is 0.1 to 600 seconds. This time is preferably between 1 and 300 seconds. At this time, it is preferable to sufficiently stir the mixture so as to be sufficiently mixed. In this time, the induction period until the gel formed immediately after mixing forms zinc oxide by a dehydration reaction is 0.1%.
This is derived from finding that the time is from second to 600 seconds. If the mixing time exceeds 600 seconds, the particle size increases, such as the zinc oxide fine powder generated up to that time being aggregated or growing from the surface of the zinc oxide fine powder once generated, and the dispersion of the particle size is also large. Cannot be adopted.

As a method of stirring, rotary stirring using a stirring blade or the like is performed. When the Reynolds number is used as a standard of the stirring power, stirring with a Reynolds number of 10 or more is required, and a Reynolds number of 50 is used. The above stirring is preferred. Unless stirring or stirring with a Reynolds number of less than 10 is not performed, particles of 100 nm or more are generated, which is not preferable. During mixing and subsequent ripening, the liquid temperature is 0.
The temperature may be about 100C to 100C, and preferably 10C to 90C. If the temperature is lower than 0 ° C., the cooling cost increases, and if it exceeds 100 ° C., a pressure-resistant container is required, which is not preferable.

In the present invention, when the mixing is completed, the pH of the mixture can be further adjusted to 11 to 13.
Preferably the pH is between 11.5-12.5. If the pH at the end of mixing is less than 11, impurities such as hydroxides will be mixed and the particle size will increase.
Is more than 13, rod-shaped particles of 100 nm or more are not suitable. Examples of the method for adjusting the pH include a method of adjusting the pH by adding an acidic aqueous solution or an alkaline aqueous solution after mixing.

Thereafter, stirring is continued to ripen the zinc oxide fine powder in the mixture. Stirring is necessary because aggregation of particles may occur during aging, and the aging time is preferably 600 seconds or more.

The zinc oxide fine powder in the liquid phase obtained by aging is filtered, decanted, centrifuged or the like to remove impurities such as dissolved salts in the aqueous solution and then used as it is or as a surfactant. Or a slurry to which a thixotropic agent, a dispersant, or the like is added, or as a dry powder by a method such as vacuum drying, freeze drying, spray drying, standing drying, and heat drying. By the above method,
A fine zinc oxide powder is obtained.

The zinc oxide fine powder obtained by the production method of the present invention has an average particle size of 100 nm or less, preferably has an average particle size of 1 to 70 nm, and more preferably has an average particle size of 5 to 50 nm. If the average particle size is less than 1 nm, a strong cohesive force is generated, and if the average particle size exceeds 100 nm, the transmittance of visible light decreases. Here, the average particle diameter is an average number particle diameter of 200 or more primary particles observed by a transmission electron microscope. After the zinc oxide fine powder obtained in the present invention is formed in the liquid phase, it can be heated to 60 ° C. or higher in the liquid phase or after drying to improve the crystallinity.

The zinc oxide fine powder of the present invention may be subjected to a surface treatment with sodium silicate or aluminum silicate, a coupling agent, a fatty acid, a silicone compound or the like after being formed in an aqueous solution or after being dried. In addition, since the zinc oxide fine powder obtained in the present invention has not been subjected to high-temperature treatment such as firing, it is considered that the outermost surface layer of the zinc oxide fine powder contains amorphous zinc oxide or hydroxide, and therefore, has a photocatalytic activity. And, when mixed with cosmetics, paints, resins, films, etc., it is not necessary to perform a surface treatment necessary for suppressing photocatalytic activity. A surface treatment for further suppressing the photocatalytic activity or improving the dispersibility may be performed. Further, the zinc oxide fine powder of the present invention is considered to have a high antibacterial property because the outermost surface layer is considered to be amorphous or contain a large amount of hydroxide. Therefore, the zinc oxide fine powder obtained by the present invention without surface treatment, or the zinc oxide fine powder obtained by the present invention, which has been partially surface-treated, is mixed or coated into a molded product or a paint or paste. By using the compound, an ultraviolet shielding effect and an antibacterial effect can be imparted without impairing the transparency of cosmetics, films, resins, glass, and the like.

A third aspect of the present invention is a resin composition containing the above zinc oxide fine powder. As the contained resin,
Examples include, but are not limited to, polyamide, polyester, silicone, acrylic, polystyrene, polypropylene, polyethylene, phenol, fluororesin, Teflon (registered trademark), melamine, epoxy, cellulose, polylactic acid, and the like. The zinc oxide fine powder is mixed in the resin or coated or adhered to the resin surface. The zinc oxide fine powder preferably contains 0.0001 to 50% by weight of the resin.

The resin composition of the present invention comprises a film, a fiber,
It is used for various purposes such as paints and cosmetics as sheets, particles and various molded articles. For example, in the case of a paint, it means a paint containing 0.0001 to 50% by weight of zinc oxide fine powder, and the zinc oxide fine powder is used by being dispersed in the paint. In the case of cosmetics, a fine powder of zinc oxide is used in an amount of 0.1.
Cosmetics containing 0001 to 70% by weight are used by mixing or dispersing them in powdery or liquid cosmetics. A resin composition containing the zinc oxide fine powder,
Paints and cosmetics have the property of shielding ultraviolet rays by the contained zinc oxide fine powder, and have the characteristic that the visible light shielding rate by the zinc oxide fine powder is small. Further, when the zinc oxide fine powder is not subjected to a surface treatment, or when the surface treatment is partially performed, the zinc oxide fine powder also has an antibacterial property.

[0026]

The present invention will now be described in detail with reference to the following Examples. Example 1 2 mol of 0.5 mol / l zinc chloride aqueous solution at 25 ° C. and 1 mol / l sodium hydroxide aqueous solution at 25 ° C. 05 liters were added under vigorous stirring and mixed, the mixing was stopped in 20 seconds, the pH was adjusted to 12.1, and the stirring was continued. After 10 minutes from the start of mixing, a white product was separated from the mixed solution by centrifugation, and the white product was washed with water, and then vacuum-dried at 30 ° C. for 24 hours to obtain 79.3 g of a white powder. Was done. As a result of X-ray diffraction, this white powder was found to be zinc oxide. When the zinc concentration was determined by chelate titration and converted to zinc oxide, the zinc oxide purity was 99.5%. When the particle size of 230 primary particles was measured with a transmission electron microscope, the average particle size was 32 nm.

Example 2 To 1 liter of a 0.1 mol / l aqueous solution of zinc sulfate at 40 ° C., 1.2 liter of a 0.2 mol / l aqueous sodium hydroxide solution at 40 ° C. was added under vigorous stirring and mixed.
Mixing was completed in seconds, the pH was adjusted to 11.9, and stirring was continued. After 10 minutes from the start of mixing, a white product was separated from the mixed solution by centrifugation, and the white product was washed with water, and then vacuum-dried at 30 ° C. for 24 hours to obtain 7.5 g of a white powder. Was done. As a result of X-ray diffraction, this white powder was found to be zinc oxide. When the zinc concentration was determined by chelate titration and converted to zinc oxide, the zinc oxide purity was 99.1%. When the particle size of 243 primary particles was measured with a transmission electron microscope, the average particle size was 38 nm.

Example 3 45 liters of a 1 mol / l aqueous zinc chloride solution at 30 ° C. and 48 liters of a 2 mol / l aqueous sodium hydroxide solution at 30 ° C. were simultaneously added over 100 seconds, and mixed with vigorous stirring. The pH after mixing was 12.3. Thirty minutes after the start of mixing, a white product was separated from the mixture by centrifugation, and the white product was washed with water and then heated to 105 ° C.
For 24 hours, and 3.51 kg of white powder was obtained. As a result of X-ray diffraction, this white powder was found to be zinc oxide. When the zinc concentration was determined by chelate titration and converted into zinc oxide, the zinc oxide purity was 99.
3%. The average particle size of the 223 primary particles measured by a transmission electron microscope was 28 nm.

Example 4 To 450 liters of a 1 mol / l aqueous solution of zinc chloride at 50 ° C., 480 liters of a 2 mol / l aqueous sodium hydroxide solution at 50 ° C. were simultaneously added for 200 seconds, and mixed with vigorous stirring. The pH after mixing was 12.4. After 60 minutes from the start of mixing, a white product was separated from the liquid mixture by centrifugation.
After vacuum drying at 24 ° C. for 24 hours, 34.5 kg of a white powder was obtained. As a result of X-ray diffraction, this white powder was found to be zinc oxide. When the zinc concentration was determined by chelate titration and converted to zinc oxide, the zinc oxide purity was 9
It was 9.5%. When the particle size of 243 primary particles was measured with a transmission electron microscope, the average particle size was 38 nm.

Example 5 To 10 liters of a 0.1 mol / l aqueous solution of zinc sulfate at 40 ° C., 10 liters of a 0.2 mol / l aqueous sodium hydroxide solution at 40 ° C. were added under vigorous stirring and mixed.
Mixing was completed in seconds, the pH was adjusted to 11.9, and stirring was continued. After 10 minutes from the start of mixing, a white product was separated from the mixed solution by centrifugation, and the white product was washed with water, and then vacuum-dried at 30 ° C. for 24 hours to obtain 7.0 g of a white powder. Was done. As a result of X-ray diffraction, this white powder was found to be zinc oxide. When the zinc concentration was determined by chelate titration and converted to zinc oxide, the zinc oxide purity was 98.5%. When the particle size of 211 primary particles was measured with a transmission electron microscope, the average particle size was 58 nm.

COMPARATIVE EXAMPLE 1 To 9 liters of a 0.1 mol / l aqueous solution of zinc sulfate at 40 ° C., 9 liters of a 0.2 mol / l aqueous solution of sodium hydroxide at 40 ° C. were added under strong stirring over 300 seconds and mixed. The pH was adjusted to 9.9 and stirring was continued. After 10 minutes from the start of mixing, a white product was separated from the mixture by centrifugation, and the white product was washed with water, and then vacuum-dried at 30 ° C. for 24 hours to obtain 6.8 g of a white powder. Was done. As a result of X-ray diffraction, this white powder was found to be zinc oxide. When the zinc concentration was determined by chelate titration and converted to zinc oxide, the zinc oxide purity was 93.4%. The average particle size of the 241 primary particles measured by a transmission electron microscope was 138 nm.

COMPARATIVE EXAMPLE 2 To 9 liters of a 1 mol / l aqueous solution of zinc sulfate at 40 ° C., 13 liters of a 2 mol / l aqueous sodium hydroxide solution at 40 ° C. were added under vigorous stirring for 300 seconds, and mixed. .3 and stirring was continued. After 10 minutes from the start of mixing, a white product was separated from the mixed solution by centrifugation, and the white product was washed with water, and then vacuum-dried at 30 ° C. for 24 hours to obtain 70.3 g of a white powder. Was done. As a result of X-ray diffraction, this white powder was found to be zinc oxide. When the zinc concentration was determined by chelate titration and converted to zinc oxide, the zinc oxide purity was 98.8%.
Met. When the particle size of 211 primary particles was measured with a transmission electron microscope, the average particle size was 430 nm.

Comparative Example 3 To 9 liters of a 0.1 mol / l aqueous solution of zinc sulfate at 40 ° C., 10 liters of a 0.2 mol / l aqueous sodium hydroxide solution at 40 ° C. were added over 1200 seconds with vigorous stirring and mixed. Then, the pH was adjusted to 11.9 and stirring was continued.
After 30 minutes from the start of mixing, a white product was separated from the mixture by centrifugation, and the white product was washed with water.
Vacuum drying was performed at 30 ° C. for 24 hours to obtain 7.0 g of a white powder. As a result of X-ray diffraction, this white powder was found to be zinc oxide. When the zinc concentration was determined by chelate titration and converted to zinc oxide, the zinc oxide purity was 9
It was 8.4%. The average particle size of the 219 primary particles measured by a transmission electron microscope was 142 nm.

[0034]

According to the present invention, it is possible to produce inexpensively zinc oxide fine powder having excellent ultraviolet shielding properties, dispersibility and visible light transmittance, low photocatalytic activity and an average particle diameter of 100 nm or less.

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Claims (3)

[Claims] 1. A predetermined amount of a zinc-containing solution and a predetermined amount of an aqueous alkaline solution are mixed with stirring at a time of 0.1 to 600 seconds so that the pH at the end of mixing is 11 to 13. A method for producing zinc oxide fine powder, which comprises aging the zinc oxide fine powder in the liquid. 2. A zinc oxide fine powder having an average particle diameter of 100 nm or less obtained by the production method according to claim 1. 3. A resin composition containing the zinc oxide fine powder according to claim 2.