JP3512838B2 - Method for producing flaky zinc oxide powder - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing flaky zinc oxide powder. More specifically, flaky oxidization having a narrow particle size distribution with an arbitrary average particle size and excellent in UV screening ability, which is suitable as a UV screening filler for, for example, cosmetics, resins, fibers, packaging materials, paints, etc. The present invention relates to a method for producing zinc powder.

In recent years, an increase in the amount of ultraviolet rays of sunlight reaching the surface due to ozone holes is mainly due to UVB (290 to 320).
Acute inflammation of the skin due to sunburn and snowburn caused by UV rays (nm wavelength UV) or mainly UVA (320-40)
Aging of the skin caused by repeated irradiation of (0 nm wavelength ultraviolet ray) and further increase of skin cancer such as melanoma not only adversely affect the organism, but also industrial products, clothing, food,
It is said that it causes an increase in ultraviolet deterioration even in houses, etc.
Solving this problem has become an important issue.

[0003]

2. Description of the Related Art Conventionally, organic substances and inorganic substances that absorb and scatter ultraviolet rays for the purpose of avoiding the influence of ultraviolet rays, for example, organic substances such as para-aminobenzoic acid and salicylic acid, and inorganic substances such as titanium oxide, zinc oxide and iron oxide. Coating and mixing are widely performed. However, organic substances for shielding ultraviolet rays have a problem in durability such as irritation to the skin, decomposition by light, or deterioration in performance. On the other hand, the inorganic material is excellent in stability and ultraviolet ray absorbing ability of the material itself, and among them, zinc oxide has excellent ultraviolet ray absorbing ability. By the way, zinc oxide for pigments, which is widely distributed, has a large particle size and is inferior in touch and transparency, and therefore ultrafine zinc oxide has been studied for use in cosmetics and the like. However, ultrafine zinc oxide
Although satisfactory ultraviolet ray shielding ability and transparency are satisfied, since they are fine particles, they have a large surface area and are highly active, so that they have the adverse effect of reacting with organic substances or promoting their decomposition when they come into contact with organic substances. Therefore, the development of zinc oxide, which is excellent in hiding property and transparency, and which does not have strong reactivity with organic substances, is desired.

Flake-shaped zinc oxide is considered as one of the materials satisfying the above requirements, and its manufacturing method is also known. For example, Japanese Examined Patent Publication No. 55-25133 teaches "a method for producing a basic zinc sulfate plate-like crystal body in which a crystalline body is precipitated in an acidic region by contacting and absorbing ammonia gas in an acidic aqueous solution containing zinc sulfate". For this purpose, a plate-like zinc oxide powder for white pigment is described. However, the plate-shaped zinc oxide powder obtained by the method has a maximum particle size of several hundred μm and a thickness of several μm or more.
In addition to being inferior to the touch, the concealed area per unit weight is low, and therefore the ultraviolet shielding ability is also low.

Further, Japanese Examined Patent Publications Nos. 54-19235 and 54-
No. 42960 describes "a method for producing a plate-shaped zinc hydroxide having a uniform particle size by mixing and reacting a specific zinc salt with urea under specific conditions". However, although zinc hydroxide produced by these methods shows a uniform particle size,
Since the particle size of m is 10 μm and the thickness is 10 μm, the zinc oxide obtained by firing this also has a low hiding property per unit weight.
Poor UV blocking ability. Further, JP-A 1-230431 discloses that "average particle diameter is 0.1 to 1 µm, average particle thickness is 0.01.
.About.0.2 μm, flaky zinc oxide powder having an average plate ratio of 3 or more, from an aqueous solution containing zinc having a pH of 11 or more containing an equivalent amount or more of acid groups, and optionally in the presence of a water-soluble organic substance,
"Preparation method obtained as a precipitate" is taught. However, the zinc oxide produced by this method has a defect that the average particle diameter is 0.1 to 1 μm, which is equivalent to that of visible light, and therefore the transmittance of visible light is poor due to scattering.

[0006]

Under the circumstances, the present inventors have found that the visible light transmittance and the ultraviolet ray shielding ability are
In particular, it excels in UV blocking ability in the UVA range,
As a result of earnest studies to obtain flaky zinc oxide powder having excellent hiding property, as a result of performing a neutralization reaction of a zinc salt solution in the presence of a specific substance and firing this, all of the above properties are satisfied. The inventors have found that flaky zinc oxide powder can be obtained, and completed the present invention.

[0007]

Means for Solving the Problems That is, according to the present invention, a zinc salt solution and a solution containing an ammonium ion or a compound which decomposes to generate an ammonium ion are mixed, and a flaky basic zinc salt crystal is formed by a neutralization reaction. or to deposit crystals of the flaky zinc hydroxide, filtration, and dried, in the method for producing the flaky zinc oxide powder by calcining, performs neutralization reaction in the presence of a water-soluble organic substances It is another object of the present invention to provide a method for producing flaky zinc oxide powder.

Further, in the present invention, a zinc salt solution is mixed with a solution containing ammonium ions or a compound which decomposes to generate ammonium ions, and crystals of flaky basic zinc salt or flaky zinc hydroxide are formed by a neutralization reaction. Deposit crystals,
In the method for producing a flaky zinc oxide powder by filtering, drying and firing if necessary, the neutralization reaction is carried out in an amount of 0.0001 mol to 1 mol of zinc atom in the solution and the water-soluble organic substance. Another object of the present invention is to provide a method for producing flaky zinc oxide powder, which is characterized in that it is carried out in the presence of 0.5 mol of aluminum and / or iron metal atoms.

The method of the present invention will be described in more detail below.
In the present invention, the flaky zinc oxide is in the form of plate, flakes, hexagonal plate, disc, disc, leaf, mica, foil, etc., and has an aspect ratio of 3 or more, Preferably 5-40
And the average thickness is 0.1 μm to 1 μ, and the average diameter is 1 μm to
100 μm powder is shown. The flaky zinc oxide obtained by the method of the present invention has a narrow flaky shape with an average particle size of 1 to 100 μm and a variation in particle size of 70% or less, preferably 60% or less, more preferably 50% or less. It is a zinc oxide powder. Since the shape (size) of the flakes is not constant here, the average diameter in the present invention is the average value of the values of (maximum difference diameter + minimum difference diameter) / 2 of 100 pieces. The variation of the particle size distribution is specified by (standard deviation / average particle size) × 100 (%) value of the particle size of 100 flakes. The thickness of each thin piece was the average particle thickness obtained by arithmetically averaging the thicknesses of all the thin pieces that can be read within the field of view of the scanning electron microscope.

In the method of the present invention, a solution of a zinc salt and a solution containing an ammonium ion or a compound which decomposes to generate an ammonium ion are mixed, and crystals of flaky basic zinc salt or flaky zinc hydroxide are subjected to a neutralization reaction. In the method for producing flaky zinc oxide powder by precipitating crystals of the above, filtering and drying if necessary, and then calcining, the neutralization reaction is carried out in the presence of a water-soluble organic substance. It is a thing. When carrying out this method, examples of the zinc salt solution used include organic acid salts such as zinc sulfate, zinc nitrate, zinc chloride and zinc acetate, and zinc alkoxide.

Examples of the solution containing ammonium ion or a compound that decomposes to generate ammonium ion include ammonia gas, ammonia water, aqueous urea solution, and aqueous hexamethylenetetramine solution.

In the present invention, it is essential that a water-soluble organic substance be present during the neutralization reaction of the zinc salt solution and ammonium ion or a compound that decomposes to generate ammonium ion. Crystallinity such as particle size, particle size distribution and crystal form of flaky basic zinc salt crystals or flaky zinc hydroxide obtained by carrying out the neutralization reaction in the presence of a water-soluble organic substance is possible. Becomes Water-soluble organic substances having such effects include alcohols, polyols, ketones, polyethers, esters, carboxylic acids, polycarboxylic acids, celluloses, saccharides, sulfonic acids, amino acids, amines, More specifically, aliphatic alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, etc., aliphatic polyhydric alcohols such as ethylene glycol, propanediol, butanediol, glycerin, polyethylene glycol, polypropylene glycol, phenol, catechol. , Aromatic alcohols such as cresol, alcohols having a heterocycle such as furfuryl acol, ketones such as acetone, methyl ethyl ketone, acetylacetone, ethyl ether, tetrahydrofuran, dioxane Polyoxyalkylene ethers, ethylene oxide adducts,
Ethers or polyethers such as propylene oxide adducts, esters such as ethyl acetate, ethyl acetoacetate, glycine ethyl ester, formic acid, acetic acid, propionic acid, butanoic acid, butyric acid, oxalic acid, malonic acid, citric acid, tartaric acid, glucon Acid, salicylic acid, benzoic acid, acrylic acid, maleic acid, glyceric acid, eleostearic acid,
Carboxylic acid such as polyacrylic acid, polymaleic acid, acrylic acid-maleic acid copolymer, polycarboxylic acid, or hydroxycarboxylic acid or salts thereof, carboxymethylcellulose, glucose, galactose and other monosaccharides, sucrose, lactose, amylose, chitin, cellulose Polysaccharides such as, alkylbenzene sulfonic acid, paratoluene sulfonic acid, alkyl sulfonic acid, α-olefin sulfonic acid, polyoxyethylene alkyl sulfonic acid,
Sulfonic acids such as ligninsulfonic acid and naphthalenesulfonic acid and salts thereof, amino acids such as glycine, glutamic acid, aspartic acid and alanine, hydroxyamines such as monoethanolamine, diethanolamine, triethanolamine and butanolamine, trimethylaminoethylalkylamide , Alkylpyridinium sulfate, alkyltrimethylammonium halide, alkylbetaine, alkyldiethylenetriaminoacetic acid and the like can be mentioned as examples.

Among these water-soluble organic substances, water-soluble organic substances having one or more functional groups of hydroxyl group, carboxyl group and amino group are preferable, and hydroxycarboxylic acid having hydroxyl group and carboxyl group and salts thereof are particularly preferable. preferable. These may be used alone or in combination of two or more. The water-soluble organic substance present during the neutralization reaction of the zinc salt solution and ammonium ion or a compound that decomposes to generate ammonium ion is a flaky basic zinc salt crystal or flaky zinc hydroxide surface which is precipitated by the neutralization reaction. It is believed that the particles are adsorbed on and control the growth of particles, and as a result, the crystallinity such as the crystal form, average particle size, and particle size distribution can be controlled.

The water-soluble organic matter is contained in the mother liquor (a solution containing a zinc salt solution and ammonium ions or a compound which decomposes to generate ammonium ions) in an amount of about 0.001% by weight.
It is preferable to coexist in the range of about 10% by weight, and the amount thereof is determined by the desired particle size, particle size distribution and the like.

It is essential that this water-soluble organic substance is present when the flaky basic zinc salt or flaky zinc hydroxide is deposited, and an aqueous zinc salt solution or ammonium ion or decomposes to generate ammonium ion in advance. It can be achieved by dissolving and mixing in an aqueous solution containing a compound, and then subjecting it to reaction precipitation, or by appropriately adding a separately dissolved water-soluble organic substance solution during reaction precipitation. In order to improve the mechanical strength of the flakes, 0.0001 to 0.5 mol per mol of zinc atom, preferably 0.0001 to 0.4 mol of metal atom of aluminum and / or iron per mol of zinc atom. Performing the neutralization reaction in the presence is a particularly effective method.

A method of precipitating flaky basic zinc salt crystals or flaky zinc hydroxide by a neutralization reaction by mixing a zinc salt solution with a solution containing ammonium ions or a compound which decomposes to generate ammonium ions Known methods can be applied. Stirring and temperature control during this neutralization reaction are important for obtaining good flaky basic zinc salt and zinc hydroxide. The reaction temperature varies depending on the type of ammonium ion used or the compound that decomposes to generate ammonium ion, but it can usually be carried out between about 30 ° C. and the boiling point of the solution, and about 60 to increase the reactivity and productivity. More preferred is a temperature of from 0 ° C to about 100 ° C. 10 minutes or more at the reaction temperature or lower after the reaction precipitation,
Preferably, holding for 30 minutes or more is particularly effective for improving the crystallinity, shape, surface properties and the like of the obtained flaky basic zinc or flaky zinc hydroxide.

The solution precipitated by reaction or kept at a reaction temperature or lower for a specific time is then subjected to solid-liquid separation, washed and dried. In order to obtain zinc oxide having good dispersibility, crystalline It is preferable to remove the water-soluble organic substances used for control and to remove the ions remaining in the mother liquor.For example, for washing the ions remaining in the mother liquor, the conductivity of the precipitated flaky basic zinc or flaky zinc hydroxide slurry Is recommended to be depleted of ions for up to about 1000 μs or less, more preferably about 500 μs or less.

Further, for the purpose of further improving the dispersibility, after dispersing in a water-soluble organic solvent such as tetrahydrofuran, acetone or a lower alcohol such as methanol, ethanol or isopropanol in the final stage of solid-liquid separation after washing treatment and the like,
In some cases, it is recommended to dry with a spray dryer or a drum dryer after the ultrasonic dispersion treatment.

The dried flakes are then calcined, usually in an oxygen-containing atmosphere, specifically air. The firing temperature is about 850 to about 1200 ° C and about 10
Min or more, usually 30 minutes to about 2 hours. The firing temperature and time are determined by the physical properties of the fired zinc oxide. The firing furnace may be a tubular furnace, a batch furnace such as a box furnace, a pusher furnace, a continuous kiln such as a rotary kiln tunnel furnace, a roller hearth furnace, or the like.
It is not restricted by electricity.

The flaked material after firing is, if necessary, crushed and then classified to a desired particle size to be used for general resin fillers, rubber fillers, pigments, cosmetic pigments, and further cosmetics, clothing, paints. It can be used as an ultraviolet shielding agent for various uses such as food packaging materials.

[0021]

INDUSTRIAL APPLICABILITY The flaky zinc oxide powder obtained by the method of the present invention described in detail above has a particle size variation of 70% or less, preferably 60% or less, more preferably, in a desired particle size. It has a narrow particle size distribution of 50% or less, and has no remarkable fine powder or coarse particles, so it has excellent visible light transmittance, ultraviolet ray shielding ability, hiding ability, filling ability, and reactivity with organic substances. It has the characteristic of being mild and its industrial value is enormous.

[0022]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 57.6 g of zinc sulfate heptahydrate (ZnSO ₄ .7H ₂ O / manufactured by Toho Zinc) and sodium gluconate (manufactured by Wako Pure Chemical Industries)
0.15 g was dissolved in 100 g deionized water. This solution was put into a 500 ml separable flask and heated to 90 ° C. while stirring with a magnetic stirrer to dissolve. While maintaining this solution at 90 ° C., 16.3 g of 25% ammonium water was added dropwise by a microtube pump over 15 minutes. After completion of dropping, the mixture was kept at 90 ° C. for 4 hours for aging, and then the solution was poured into about 5 liters of deionized water,
I let it stand. After standing, it was subjected to solid-liquid separation and further washed with deionized water three times, and the conductivity of the supernatant of the slurry was 75 μm.
It became s. This slurry was filtered and dried to 18.5 g.
Of white powder was obtained. When the particle size of this powder was observed with an optical microscope, the average was 4.5 μm and the variation was 40%.
The thickness was 0.2 μm as measured by a scanning electron microscope. The above-obtained powder was mixed in a muffle furnace at 900 ° C for 3
Firing was performed for 0 minutes to obtain 16.0 g of flaky zinc oxide powder.
0.18 g of the flaky zinc oxide powder obtained above was thoroughly mixed with 1.02 g of silicon oil (KS-62F / manufactured by Shin-Etsu Chemical Co., Ltd.) in an agate mortar, and this mixture was applied to a degreased polypropylene film (thickness 50 μm) by a doctor. The blade method is applied to a thickness of 10 μm, and its spectral diffusion transmittance (5
It was 12% / 370 nm and 81% / 500 nm when measured with a 0φ integrating sphere / Hitachi 330 spectrophotometer). The linear transmittance (without integrating sphere) at 380 nm was measured using the same sample, and the absorbance was 2.2.
It was 3. As a method for measuring the strength of the flakes, 0.5 g of the flaky zinc oxide powder obtained above was added to 100 ml of a 0.2% aqueous sodium hexametaphosphate homogenizer (U).
S-300T: Dispersed with an ultrasonic disperser / made by Leeds & No-Slap), and dispersed with Microtrac MKII (made by Leeds & No-Slap) for 1 minute and 10 minutes, respectively, and then the thin pieces after treatment By measuring the average particle size, the strength of the flakes was determined as (average particle size of flakes after 10 minutes dispersion treatment / average particle size of flakes after 1 minute dispersion treatment) × 100%. The result was 68%.

Example 2 In Example 1, 27.7 g of 25% ammonium water was added.
To 14 mg tartaric acid instead of sodium gluconate,
19.5 g of white powder of flaky basic zinc sulfate was obtained in the same manner except that the reaction temperature was changed to 100 ° C. When the particle size of this powder was observed with an optical microscope, the average was 8 μm, the thickness was 0.4 μm, and the variation was 38%.

Examples 3 to 5 In Example 1, instead of sodium gluconate, 0.2 g of ethylene glycol (Example 3), 0.3 g of 2,3-butanediol (Example 4), and 0.1 g of gelatin ( The water-soluble organic substance of Example 5) was added as an additive to synthesize white powder of flaky basic zinc sulfate, and the particle size was observed with an optical microscope. The average particle size of ethylene glycol was 6.1 μm. , Thickness 0.5 μm, variation 37%, mean particle size 5.8 μm, thickness 0.6 μm, variation 47% in 2,3-butanediol, mean particle size 3.1 μm, thickness 0.2 μ in gelatin
The variation was 42%.

Comparative Example 1 In Example 1, flaky basic zinc sulfate was synthesized under the same conditions except that sodium gluconate was not added, and when observed with an optical microscope, the average particle size was 6.6 μm.
m, the thickness was 0.7 μm, and the variation was 94%.

Example 6 In Example 1, aluminum sulfate hydrate (Al ₂ (S
O ₄ ) ₃・ 14-18H ₂ O / Wako Pure Chemical Industries) 0.63 g
Flake basic zinc sulfate having an average particle size of 4.1 μm, a thickness of 0.2 μm and a variation of 43% was obtained in the same manner except that was added. The zinc oxide powder obtained by baking this powder at 900 ° C. for 30 minutes has a spectral diffusion transmittance of 8% / 370 nm, 7
At 8% / 500 nm, the intensity was 75%.

Comparative Example 2 In Example 2, flaky basic zinc sulfate was synthesized under the same conditions except that tartaric acid was not added, and observed with an optical microscope. The average particle diameter was 26 μm and the thickness was 2. 5μ
The variation was 78%.

Comparative Example 3 In Example 2, flaky basic zinc sulfate was synthesized under the same conditions except that 28 g of urotropin was used instead of 25% ammonium water and sodium gluconate was not added, and an optical microscope was used. The average particle size was 5.6.
The thickness was 0.4 μm and the variation was 75%.

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Claims (5)

(57) [Claims] 1. A zinc salt solution and a solution containing an ammonium ion or a compound which decomposes to generate an ammonium ion are mixed, and flaky basic zinc salt crystals or flaky zinc hydroxide crystals are formed by a neutralization reaction. precipitation, filtration, and dried, in the method for producing the flaky zinc oxide powder by calcining, flaky zinc oxide and performing neutralization reaction in the presence of a water-soluble organic substances Powder manufacturing method. 2. The water-soluble organic substance is a hydroxyl group, a carboxyl group,
2. The method for producing flaky zinc oxide powder according to claim 1, which has one or more functional groups of amino groups. 3. The method for producing flaky zinc oxide powder according to claim 1, wherein the zinc salt solution is any one of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate and zinc carbonate. 4. The flaky zinc oxide powder according to claim 1, wherein the solution containing ammonium ions or a compound that decomposes to generate ammonium ions is an aqueous ammonia solution, an aqueous urea solution or hexamethylenetetramine. Manufacturing method. 5. The neutralization reaction is carried out in the presence of a water-soluble organic substance and 0.0001 to 0.5 mol of metal atoms of aluminum and / or iron per mol of zinc atoms in the solution. The method for producing the flaky zinc oxide powder according to claim 1.