JPH07187673A - Production of plate like basic zinc salt crystal - Google Patents

Abstract

PURPOSE:To arbitrarily produce a starting material of a leaf plate like zinc oxide powder excellent in the transmittance of visible light and UV shielding capability or a zinc oxide powder having orientation property which requires thickness relatively or a plate like basic zinc salt crystal which is suitable to the starting material of a plate like fluorescent body and other industrial use, etc., and has a desired grain size. CONSTITUTION:An acidic zinc salt soln. is dropped to an aqueous ammonia or ammonium carbonate soln. or these mixture while controlling pH within a range of 9.5-6.0 to form slurry. As the second stage, this slurry is heat-treated within the range of more than 50 deg.C to less than b.p. of this soln.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a basic zinc salt crystal having a plate-like particle form, and particularly to a plate-like form used for cosmetics and white pigments as a wide range of UV shielding agents and masking agents. The present invention relates to a method for producing a plate-like basic zinc salt crystal, which is a starting material for zinc oxide and a starting material for a plate-like zinc sulfide powder as an optical material.

[0002]

2. Description of the Related Art As a prior art relating to a method for producing a plate-shaped crystal body of a zinc compound, for example, JP-A-53-8269 is known.
No. 8, Japanese Patent Publication No. 54-40478, Japanese Patent Publication No. 55
No. 25133 and Japanese Patent Publication No. 54-19237.

In Japanese Patent Laid-Open No. 53-82698, an alkali is added to an acidic zinc salt solution to start the precipitation of crystals from the acidic region, and the acidic region, for example, pH 4.0 to 6.5.
"A method for producing a zinc hydroxide plate-like crystal body" is disclosed in which the precipitation of the crystal body is completed under the condition of the range.

Further, in Japanese Patent Publication No. 54-40478, a mixed solution of zinc sulfate and urea is heated in the range of 50 to 100 ° C. and crystallized in an acidic region, for example, in the range of pH 4.0 to 6.5. "A method for producing a zinc hydroxide plate crystal body" for precipitating a body is disclosed.

In Japanese Patent Publication No. 55-25133,
"Method for producing basic zinc sulfate plate crystal" in which a mixed solution of zinc sulfate and zinc nitrate is caused to contact with ammonia gas to adsorb the ammonia gas to precipitate crystal under conditions of acidic region, for example, pH 4.0 to 6.5 Is disclosed.

Further, in Japanese Patent Publication No. 54-19237,
While maintaining the acidic zinc salt solution containing sulfate ions at a temperature of 50 ° C. or higher, ammonium crystals or an aqueous solution of a compound that generates ammonium ions is added dropwise to precipitate crystals. Method ”is disclosed.

In each of the above-mentioned prior arts, when a plate crystal of a subsalt compound is produced, only pyramidal or acicular crystals are obtained by precipitation from an alkaline region, or Zn (NO ₃ ) Plate-like crystals can be obtained by hydrolyzing ₂ with a weak alkali. The crystals thus obtained form agglomerates of very small flakes with a size of 1 μm or less. It teaches that it requires delicate control and cannot find an industrial application.

The specification of Japanese Patent Publication No. 54-40478 teaches that plate crystals cannot be obtained when a salt other than SO ₄ is used.

Further, the specification of Japanese Patent Publication No. 55-25133 teaches that when ammonia water is added to the starting solution, the reaction is too fast to obtain a desired particle size.

When a plate-like crystal body of a zinc compound is produced as described above, it is difficult to obtain a plate-like crystal by the method of precipitating a basic zinc salt from the alkali side, and Zn (N
By the method of hydrolyzing O ₃ ) ₂ with a weak alkali and the method of using aqueous ammonia, only fine particles of 1 μm or less can be obtained. For this reason, in the case of producing a plate-shaped crystal body of a zinc compound, conventionally, the precipitation was limited to the acidic region.

Among the above-mentioned prior arts, Japanese Patent Publication No. 54-1
Japanese Patent No. 9237 discloses a method of controlling the particle size of crystals to be precipitated by adjusting the dropping rate and temperature when dropping an aqueous solution of ammonium ions or a compound that generates ammonium ions. The other prior art is a manufacturing method mainly for obtaining raw materials as optical materials such as oriented zinc oxide powder and plate-like phosphors having a particle size of 100 μm and a thickness of 10 μm. When it is used as a zinc oxide in cosmetics by baking it, the visible light transmittance is low, the transparency is low, and the tactile sensation to the skin is poor, so that its use is limited.

[0012] In recent years, an increase in the amount of sunlight ultraviolet rays reaching the ground due to the ozone hole not only adversely affects living things such as aging of the skin and increase of skin cancer, but also promotes an increase in ultraviolet deterioration of industrial products, foods, etc. Solving this problem has become an important issue.

[0013]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a raw material for flaky zinc oxide powder which is excellent in visible light transmittance and ultraviolet shielding ability, or an oriented zinc oxide powder which requires a relatively large thickness. It is an object of the present invention to provide a method for arbitrarily producing a plate-like basic zinc salt crystal having a desired particle size suitable for a plate-like phosphor and other raw materials for industrial use.

[0014]

The present invention comprises an acidic zinc salt in an aqueous ammonia or ammonium carbonate solution or mixture thereof while controlling the pH to be in the range of 9.5 to 6.0. The first step of dropping the solution to form a slurry and the slurry obtained in the first step are 50
The method for producing a plate-shaped basic zinc salt crystal body is characterized by comprising a second step of heat treatment within a range of not lower than 0 ° C and not higher than the boiling point temperature of the solution.

Further, the present invention is characterized in that the pH range of the first step is 8.5 to 6.5.

Furthermore, the present invention is characterized in that the first step is carried out at a temperature of 50 ° C. or lower.

Furthermore, the present invention is characterized in that the heat treatment of the second step is performed at a temperature of 70 ° C. or higher.

Furthermore, the present invention is characterized in that the solution containing the acidic zinc salt used in the first step is a solution of zinc sulfate, zinc chloride, zinc nitrate or zinc acetate or a mixture of two or more thereof. To do.

Further, in the present invention, the solution containing the acidic zinc salt used in the first step contains not only zinc salt but also aluminum salt or iron salt in an amount of 0.5 mol or less of aluminum atom or iron atom per 1 mol of zinc atom. It is characterized by containing at a ratio of.

[0020]

According to the present invention, as a first step, a solution containing an acidic zinc salt is added dropwise to an ammonium solution such as aqueous ammonia or an ammonium carbonate solution or a mixture thereof to react the solution with a pH of 9.5.
Control within the range of to 6.0. Then, as the second step,
The slurry obtained in the first step is subjected to heat treatment within the range of 50 ° C to the boiling temperature of the solution.

When the pH exceeds 9.5 in the first step, the crystals are not grown by the heat treatment in the second step, and fine crystals of 1 μm or less can be obtained only in the state of agglomeration. Further, as the pH is lowered, large-sized crystals are obtained, but as the pH is lowered from around pH 6, the probability that large-sized crystals and agglomerated crystals of several μm or less coexist increases. In the second step, the crystals obtained at the temperature lower than 50 ° C. after the completion of the dropping are in a state in which small flakes having a diameter of 1 μm or less excessively form aggregates.

According to the invention, the pH of the first step is
By setting the control range of 8.5 to 6.5, a decrease in yield can be suppressed.

Further, according to the present invention, by controlling the temperature in the first step to 50 ° C. or lower, the rate at which agglomeration is released in the heat treatment in the second step is increased.

Further, according to the present invention, the degree of crystal growth is promoted by performing the heat treatment in the second step at a temperature of 70 ° C. or higher.

Further, according to the present invention, not only the shape of the precipitated crystal but also the particle size can be controlled by variously changing the acidic zinc solution used in the first step.

Further, according to the present invention, by adding an aluminum salt or an iron salt to the acidic zinc solution used in the first step, the mechanical strength is excellent and it is possible to prevent the flakes from being substantially destroyed. Is possible and is preferable depending on the application.

[0027]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

In the examples, the average particle size of the plate-shaped zinc oxide powder is determined by a laser diffraction particle size distribution measuring device (SALD
-1100 / manufactured by Shimadzu Corporation), and the thickness was measured with an electron microscope (manufactured by JEOL Ltd.).

Example 1 In the first step, 140 ml of 5 mol / L ammonia water (25 ° C.) was put into a flask equipped with a reflux condenser, and 710 ml of 0.75 mol / L zinc sulfate solution (25 ° C.) was gradually added. However, white turbidity started at a pH of about 11. After the addition was completed, stirring was continued for about 0.5 hour, and the pH was measured and found to be 6.6. Then, in a second step, the precipitate-containing slurry was heated and aged at 95 ° C. for 3 hours under normal pressure to obtain a hexagonal plate-shaped basic zinc sulfate crystal. Table 1 shows the particle size of the present crystal obtained by separating the solution after the precipitation treatment by a treatment such as filtration and washing.

Example 2 As the first step, 140 ml of 5 mol / L ammonia water (25 ° C.) was placed in a flask equipped with a reflux condenser.
Is charged, and 590 ml of 0.75 mol / L zinc sulfate and A
After gradually adding a mixed solution of 8.0 g of aluminum sulfate (8.0%) as l ₂ O ₃ (25 ° C.), the mixture was further stirred for about 0.5 hour and the pH was measured and found to be 7.0. Thereafter, the second step was treated in the same manner as in Example 1 to obtain a hexagonal plate-shaped basic zinc sulfate crystal. Table 1 shows the particle size of the present crystal obtained by treating in the same manner as in Example 1.

Example 3 As a second step, the slurry obtained in the same manner as in Example 2 in the first step was transferred to a glass autoclave and heat-treated at 150 ° C. for 3 hours to give a hexagonal plate-like basicity. A zinc sulfate crystal was obtained. Table 1 shows the particle size of the present crystal obtained by treating in the same manner as in Example 1.

Example 4 As the first step, 140 ml (25 ml) of 10 mol / L ammonia water was added to a flask equipped with a reflux condenser.
(45 ° C.) was added, and a mixed solution of 445 ml of a 1.5 mol / L zinc sulfate solution and 1.6 g of ferric sulfate of 15.6% as Fe ₂ O ₃ (25 ° C.) was gradually added. The cloudiness started at about 11. After the addition was completed, the mixture was further stirred for about 0.5 hour, and the pH was measured and found to be 7.9. Next, in the second step, the precipitate-containing slurry was heat-aged at 60 ° C. for 5 hours under normal pressure to obtain a hexagonal plate-shaped basic zinc sulfate crystal. Table 1 shows the particle size of the present crystal obtained by the same treatment as in Example 1.

Example 5 A plate obtained in the same manner as in Example 4 except that a slurry obtained by reacting a mixed solution of zinc sulfate and ferric sulfate with ammonia water was heated and aged at 95 ° C. for 3 hours under normal pressure. Table 1 shows the particle size of the basic zinc sulfate crystals.

Example 6 As the first step, 140 ml (25 ° C.) of 10 mol / L ammonia water was placed in a flask equipped with a reflux condenser.
Is charged and 340 ml of 1.5 mol / L zinc sulfate and Al ₂
As O ₃ , a mixed solution of 2% of 8.0% aluminum sulfate (25 ° C.) was gradually added, and the mixture was further stirred for about 1 hour to pH.
Was measured to be 9.1. Hereinafter, Table 1 shows the particle size of the plate-like basic zinc sulfate crystals obtained by treating the second step in the same manner as in Example 1.

Example 7 As the first step, 140 ml (10 ml) of 5.0 mol / L ammonia water was added to a flask equipped with a reflux condenser.
(° C.) Was added, and a mixed solution (10 ° C.) of 0.75 mol / L zinc sulfate 840 ml and Al ₂ O ₃ 8.0% aluminum sulfate 1 g was gradually added, and the mixture was further stirred for about 1 hour. Then, in the second step, the mixture was heated and aged at 90 ° C. for 1 hour under normal pressure, the slurry was cooled to room temperature, and the pH was measured. Therefore, 80 ml of the same aqueous ammonia was added to the slurry, the pH was adjusted to 7.8, and the mixture was newly aged under heating at 90 ° C. for 3 hours to obtain hexagonal plate-shaped basic zinc sulfate crystals. Table 1 shows the particle size of the present crystal obtained by treating in the same manner as in Example 1.

Example 8 As the first step, 140 ml (25 ml) of 6.5 mol / L ammonia water was added to a flask equipped with a reflux condenser.
℃) and 2.0 mol / L zinc nitrate solution 220 ml
(25 ° C) is gradually added, and the mixture is stirred for about 1 hour and then pH adjusted.
Was measured to be 6.7. Then, as a second step, the precipitate-containing slurry was heated and aged at 60 ° C. for 3 hours under normal pressure to obtain a plate-shaped basic zinc nitrate crystal in the form of a square or a diamond. Table 1 shows the particle size of the present crystal obtained by treating in the same manner as in Example 1.

Example 9 As the first step, 276 m of a 1.37 mol / L ammonium carbonate solution was added to a flask equipped with a reflux condenser.
1 (20 ° C.) was added, 200 ml (20 ° C.) of 3.14 mol / L zinc sulfate solution was gradually added, and the mixture was further stirred for about 1 hour and the pH was measured and found to be 6.4. Then
As the second step, the precipitate-containing slurry was heated and aged at 80 ° C. for 3 hours under normal pressure to obtain triangular, hexagonal, and elliptical plate-shaped basic zinc sulfate crystals. Table 1 shows the particle size of the present crystal obtained by treating in the same manner as in Example 1.

[0038]

[Table 1]

Comparative Example 1 As a first step, a mixed solution of zinc sulfate and aluminum sulfate (25 ° C.) was added to aqueous ammonia (25 ° C.), and after the reaction,
In the second step, the same treatment as in Example 4 was carried out except that the mixture was not heat-aged and stirred for 5 hours, but fine particles were densely aggregated and the shape could not be discriminated.

Comparative Example 2 When the same treatment as in Example 4 was carried out except that the heat aging in the second step was carried out at 45 ° C. for 3 hours, crystals were slightly grown but densely aggregated.

Comparative Example 3 As the first step, 140 ml (25 ° C.) of 10 mol / L ammonia water was placed in a flask equipped with a reflux condenser.
And 1.5 mol / L zinc sulfate solution 2 with stirring
A mixed solution of 80 ml and 1 g of 8.0% aluminum sulfate as Al ₂ O ₃ (25 ° C.) was gradually added, and the mixture was further stirred for about 0.5 hour and the pH was measured and found to be 9.8. Hereinafter, as a second step, the same treatment as in Example 1 was carried out to obtain plate-shaped zinc oxide, and fine particles were densely aggregated, and the shape could not be discriminated.

Reference Example The flaky plate-like basic zinc salt crystals obtained in Examples 2, 4, 5, 6 were calcined in an oxidizing atmosphere at 900 ° C. for 0.5 hours to obtain a plate-like zinc oxide having a linear transmittance of 380 nm. And the absorbance at 600 nm are shown in Table 2.

[0043]

[Table 2]

Here, the measurement of the absorbance by the linear transmittance is
0.18 g of plate-shaped zinc oxide was added to silicon oil (KS-62
F / Shin-Etsu Chemical Co., Ltd.) (1.02 g) was mixed well in an agate mortar, and this mixture was defatted polypropylene film (thickness 5).
0 μm) was applied to a thickness of 25 μm by the doctor blade method, and the absorbance was measured using a self-recording spectrophotometer (manufactured by Shimadzu Corporation).

In Table 2, 380 nm represents the ultraviolet region and 600 nm represents the visible light region. 380n
In the column of m, the ultraviolet ray shielding property is shown.
The absorbance at 0 nm represents the level of transparency which is a problem when used as a cosmetic or the like.

[0046]

As described above, according to the present invention, in the process of dropping an acidic zinc salt solution into an ammonia solution,
Since the temperature is controlled to 9.5 to 6.0, the heat treatment in the second step does not cause crystals to grow and does not show a state in which fine crystals of 1 μm or less are aggregated. It is less likely that aggregated crystals of several μm or less are mixed.

Further, according to the present invention, in the step of adding the acidic zinc solution to the ammonia solution in the first step, the pH is controlled within the range of 8.5 to 6.5, so that the amount of zinc dissolved in the mother liquor is controlled. It is possible to prevent a decrease in yield caused by the increase.

Further, according to the present invention, in the step of dropping the acidic zinc solution into the ammonia solution in the first step, the temperature is controlled to be 50 ° C. or lower, so that the rate at which the aggregation is released during the heat treatment in the second step is fast. Become.

Further, according to the present invention, since the heat treatment in the second step is carried out under the temperature condition of 70 ° C. or higher, the degree of crystal growth of the precipitated crystal can be promoted.

Further, according to the present invention, by changing the kind of the acidic zinc solution used in the first step, not only the shape of the precipitated crystal but also the particle size can be controlled.

Claims (6)

[Claims] 1. A solution containing an acidic zinc salt is added dropwise to an aqueous ammonia solution or an ammonium carbonate solution or a mixture thereof while controlling the pH to be in the range of 9.5 to 6.0 to form a slurry. And a second step in which the slurry obtained in the first step is subjected to heat treatment within a range of 50 ° C. or higher and the boiling point temperature of the solution or lower, and a plate-like basic zinc salt crystal body. Manufacturing method. 2. The pH range of the first step is 8.5 to
It is 6.5, The manufacturing method of the plate-like basic zinc salt crystal body of Claim 1 characterized by the above-mentioned. 3. The method for producing a plate-like basic zinc salt crystal body according to claim 1, wherein the first step is carried out at a temperature of 50 ° C. or lower. 4. The method for producing a plate-like basic zinc salt crystal body according to claim 1, wherein the heat treatment in the second step is carried out at a temperature of 70 ° C. or higher. 5. The solution containing an acidic zinc salt used in the first step is a solution of zinc sulfate, zinc chloride, zinc nitrate or zinc acetate, or a mixture of two or more thereof. 1. The method for producing a plate-like basic zinc salt crystal body according to 1. 6. The solution containing an acidic zinc salt used in the first step comprises an aluminum salt or an iron salt in an amount of 0.1 mol.
The content of 5 mol or less is contained.
A method for producing the plate-shaped basic zinc salt crystal body described.