JP2880409B2 - Method for reducing hexavalent chromium elution from chromium-containing composite oxide pigments - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pigment treatment method for reducing hexavalent chromium eluting from composite oxide pigment particles containing chromium as a component.

[0002]

2. Description of the Related Art In a composite oxide pigment containing chromium as a component, chromium is basically composed of Cr ₂ O ₃ .
It exists in a valence state and forms a solid solution with other components.
The amount of hexavalent chromium eluted from this pigment also varies considerably depending on the content of chromium in the pigment, the type of coexisting substance, calcination conditions, washing conditions, and the like. For example, as the composite oxide pigment containing chromium, composition CuO-Cr ₂ O ₃ -M
n ₂ O ₃ based black pigments, CoO-Al ₂ O ₃ -Cr
₂ O ₃ -based green pigment, composition Fe ₂ O ₃ -Cr ₂ O ₃
—ZnO-based brown pigment, composition TiO ₂ —Sb ₂ O ₅ —
There are Cr ₂ O ₃ -based yellow pigments, which usually have an eluted hexavalent chromium of approximately 2 to 300 μg / lg of pigment.

Generally, in order to reduce the amount of hexavalent chromium eluted from a composite oxide pigment containing chromium as a component, the pigment is sufficiently washed with water or treated with a reducing agent such as sodium thiosulfate. Alternatively, a method of insolubilizing lead chromate or zinc chromate is used.
Also, a method in which lead chromate pigment particles, which are not composite oxide pigments, are coated with dense amorphous silica and an antimony compound is deposited on the coating to minimize elution of hexavalent chromium. Is disclosed in Japanese Patent Application Laid-Open No. 4-1273. However, to produce a dense amorphous silica film in this method, the slurry of the pigment is
It is necessary to add an aqueous solution of alkali silicate to the solution while maintaining the temperature at a temperature of not less than ℃ and the pH at a constant condition of 9.5 to 10.5. If the temperature and the pH are not kept constant, the formation of the silica film on the surface of the pigment will not be constant, resulting in a difference in the properties of the pigment. Further, it is necessary to use a large amount of silica as SiO _{2 at} 10% by weight or more based on the pigment.

[0004]

SUMMARY OF THE INVENTION The present inventors have conducted intensive studies to reduce the amount of hexavalent chromium eluted from the chromium-containing composite oxide pigment, and as a result, have found that the surface of the composite oxide pigment particles containing chromium as a constituent component is reduced. With hydrated silica and a substance having a reducing ability, the amount of hydrated silica can be reduced, and the elution of hexavalent chromium can be easily reduced to a very small amount by treatment under mild conditions of room temperature and a wide range of pH conditions. And found that the present invention was completed.

[0005]

According to the present invention, in a slurry of a composite oxide pigment containing chromium as a component, the pigment is brought into contact with hydrated silica and a substance having a reducing ability,
A method for reducing the elution of hexavalent chromium of a chromium-containing composite oxide pigment, which comprises treating the pigment with these substances, is provided.

[0006]

When the composite oxide pigment containing chromium as a component is treated only with hydrous silica or when treated only with a substance having a reducing ability, 6
It is not enough to suppress the elution of valent chromium. However, by treating the pigment with hydrated silica and a substance having a reducing ability and treating it under mild conditions, the elution amount of hexavalent chromium from this pigment can be suppressed to an extremely small amount.

[0007]

Next, the present invention will be described in detail with reference to preferred embodiments. The pigment used in the present invention is a composite oxide pigment containing chromium in a composition component, and is a composite oxide pigment composed of an oxide of chromium and an oxide of one or more other metals, The above CuO-Cr
₂ O ₃ -Mn ₂ O ₃ based black pigment, CoO-Al ₂ O
₃ -Cr ₂ O ₃ based green pigments, Fe ₂ O ₃ -Cr ₂ O
₃ -ZnO-based brown pigment, TiO ₂ -Sb ₂ O ₅ -C
and r ₂ O ₃ yellow pigments.

The hydrous silica used in the present invention is a hydrolysis product of an alkali silicate and / or a silica sol, and any silica sol that can deposit SiO ₂ on the surface of a pigment can be used. For example, sodium silicate, potassium silicate and the like can be used, and preferably a No. 3 sodium silicate solution.

Examples of the substance having a reducing ability include cerium compounds such as cerium nitrate, antimony compounds such as antimony trichloride and antimony oxide, iron compounds such as iron (II) sulfate, tin compounds such as tin (II) chloride, and the like. Manganese compounds such as manganese (II) nitrate, sodium thiosulfate,
It is a substance having a reducing effect, such as sodium hydrogen sulfate and sodium nitrite, which is not particularly limited as long as it does not react with the pigment component and does not significantly deteriorate the properties of the pigment. Preferably, a water-soluble substance such as a cerium salt, an antimony salt, an iron salt, a tin salt, and a manganese salt is used, and the use of a substance which can be precipitated on the pigment surface by the treatment is more effective.

The appropriate amount of hydrated silica is 0.1 to 10% by weight as SiO _{2 based} on the pigment to be treated, and the appropriate amount of the substance having a reducing ability is 0.01 to 10% by weight. In any case, if the surface treatment is performed in an amount of 10% by weight or more, the properties as a pigment are undesirably affected. Further, even if used more, the effect of reducing the eluted hexavalent chromium converges. The preferred amount of hydrated silica is
It is 0.5 to 7% by weight, and the amount of the substance having a reducing ability is 0.1 to 5% by weight.

In the method of the present invention, hydrated silica and a substance having a reducing ability are added to a pigment slurry obtained by dispersing a composite oxide pigment containing chromium as a composition component in water, and the pigment is brought into contact with the pigment. And depositing silica and the substance on the surface of the pigment. The slurry of the pigment,
It is desirable that the pigment be subjected to a dispersion treatment in advance so as to be as close to the primary particles as possible, and then treated by adding hydrated silica and a substance having a reducing ability. For the dispersion treatment of the pigment, for example, a disperser generally used for dispersing a pigment, such as a homomixer, a sand mill, or a colloid mill, is used. The concentration of the pigment slurry is usually from 50 to 400 g / l, preferably from 100 to 200 g / l.

An aqueous solution of, for example, an alkali silicate and a substance having a reducing ability is added to the pigment slurry. These aqueous solutions may be prepared by first adding an aqueous solution of an alkali silicate and then adding an aqueous solution of a substance having a reducing ability, or both aqueous solutions at the same time. When these aqueous solutions are added to the pigment slurry, it is not necessary to particularly heat the pigment slurry before and after the addition, and room temperature is sufficient. When the aqueous alkali silicate solution is added first, the pH of the pigment slurry does not need to be adjusted to a specific range. When the aqueous solution having a reducing ability is added next, the pH of the pigment slurry is adjusted to 7.0. It is preferable to add the aqueous solution of the substance while maintaining the concentration at 〜10.5. Outside this range, it is difficult to reduce the amount of hexavalent chromium eluted from the pigment. When both aqueous solutions are simultaneously added to the pigment slurry, it is preferable to add them while adjusting the pH of the pigment slurry to the above range.

As described above, an aqueous solution of an alkali silicate and a substance having a reducing ability is added to a pigment slurry, and if necessary, the mixture is aged for 0.5 to several hours to form hydrated silica and a precipitate from the substance on the pigment surface. The hydrated silica is deposited in a state where it is adhered or stabilized by reducing chromium, and these can sufficiently cover the pigment surface. In this way, a composite oxide pigment containing chromium as a constituent component in which the elution amount of hexavalent chromium is reduced to a very small amount is obtained.

[0014]

Next, the present invention will be described more specifically with reference to examples and comparative examples. Unless otherwise specified, parts and percentages in Examples and Comparative Examples are based on weight. In addition, 6 from pigment
The elution amount of chromium (VI) is determined by measuring the concentration of hexavalent chromium in an aqueous solution obtained by boiling and leaching the pigment according to JIS K 5101-1991 by diphenylcarbazide absorption spectrophotometry (JIS K
0102).

Example 1 Water was added to 3.1 parts of cerium nitrate and completely dissolved to prepare an aqueous solution having a total of 100 parts. Further, the composition CuO
-Cr ₂ O ₃ and -Mn ₂ O ₃ composite oxide black pigment powder 100.0 parts about 500 parts total by adding water to which was peptized about 30 minutes to 1 hour toward homomixer pigment A slurry was obtained. While peptizing the pigment slurry, an aqueous solution of sodium silicate No. 3 (SiO ₂ content: 29.0)
%) Was added at room temperature. Next, this pigment slurry is transferred to a beaker, and the above-mentioned cerium nitrate aqueous solution is gradually dropped into this pigment slurry while adjusting the pH with 5% sulfuric acid so that the pH of the pigment slurry becomes approximately 9, while sufficiently stirring. did.

After completion of the dropwise addition, the mixture is aged at room temperature for about 30 minutes.
The pigment treated by decantation is taken out, washed thoroughly with water to remove residual salts, and then filtered by a conventional method.
After drying and pulverizing steps, 102.4 parts of a pigment having hydrated silica and cerium hydroxide deposited on the surface of the pigment were obtained. 5 g of the obtained pigment is weighed to the order of 0.1 g in an Erlenmeyer flask, 100 ml of purified water is added, the mixture is boiled for about 5 minutes, and then boiled for 5 minutes. After boiling, the mixture was cooled in a water bath (ice water) for 30 minutes.
After shaking for 5 minutes, the mixture was allowed to stand for 5 minutes, and the eluted hexavalent chromium was measured using the filtrate of the supernatant. As a result, the untreated pigment had an eluted Cr ⁶⁺ of 2.24 ppm, whereas the treated pigment had an eluted Cr ⁶⁺ of 0.22 ppm.

Example 2 0.5 part of antimony oxide was completely dissolved in concentrated hydrochloric acid, and this was added to a saturated aqueous solution obtained by completely dissolving 30 parts of sodium chloride in 100 parts of water. Composition CuO-Cr ₂ O ₃ -Mn ₂
The whole is about 500 parts water was added to the composite oxide black pigment powder 100.0 parts of O _3, which was prepared pigment slurry was peptized about 30 minutes to 1 hour toward a homomixer. No. 3 sodium silicate solution 3.4 was added to this pigment slurry.
The portion was added while peptizing at room temperature.

Next, the above-mentioned saturated aqueous solution of antimony oxide is gradually dropped into this pigment slurry with stirring at room temperature, and during this, the pH is adjusted with a 5% aqueous sodium carbonate solution so that the pH of the pigment slurry becomes approximately 9. It was adjusted. Thereafter, in the same manner as in Example 1, 101.5 parts of a pigment whose surface was treated with a hydrated precipitate of hydrous silica and hydrolyzed antimony was obtained. The eluted Cr ⁶⁺ concentration of the treated pigment was 0.19 ppm with respect to 2.24 ppm of the untreated pigment.

Example 3 Water was added to 0.7 parts of sodium thiosulfate to completely dissolve the solution, thereby preparing an aqueous solution having a total of 100 parts. Further, the composition Cu
And _{O-Cr 2 O 3 -Mn 2} O 3 composite oxide black pigment powder 100.0 to about 500 parts of the whole by adding water to the parts,
This was peptized in a homomixer for about 30 minutes to 1 hour to obtain a pigment slurry. 3.4 parts of No. 3 sodium silicate solution was added to this pigment slurry at room temperature while peptizing,
Further, the above-mentioned aqueous solution of sodium thiosulfate was gradually added dropwise to this pigment slurry at room temperature. During that time, the pH was adjusted using 5% sulfuric acid so that the pH of the pigment slurry was approximately 9. Thereafter, in the same manner as in Example 1, 101.0 parts of a pigment whose surface was treated with hydrous silica was obtained. The result of measuring the eluted Cr ⁶⁺ concentration of this treated pigment was 0.49 ppm with respect to 2.24 ppm of the untreated pigment.

Example 4 0.5 part of antimony oxide was completely dissolved in concentrated hydrochloric acid, and this was added to a saturated aqueous solution obtained by completely dissolving 30 parts of sodium chloride in 100 parts of water. Further, the composition CuO—Cr ₂ O ₃ −
Water was added to 100.0 parts of the Mn ₂ O ₃ composite oxide green pigment powder to make the whole about 500 parts, and this was peptized with a homomixer for about 30 minutes to 1 hour to prepare a pigment slurry. Next, the pigment slurry was transferred to a beaker, and the above-mentioned aqueous solution of antimony oxide and the aqueous solution of sodium silicate were gradually dropped simultaneously with sufficient stirring.
During this time, adjust the pH of the pigment slurry to about 9
The pH was adjusted using an aqueous solution of sodium carbonate (%). Thereafter, in the same manner as in Example 1, the pigment 10 was treated with a hydrate precipitate of hydrous silica and hydrolyzed antimony.
1.5 parts were obtained. The eluted Cr ⁶⁺ concentration of this pigment was 0.18 ppm with respect to 28.0 ppm of the untreated product.

Example 5 Water was added to 3.1 parts of cerium nitrate and completely dissolved to prepare an aqueous solution having a total of 100 parts. The composition Fe ₂
O ₃ -Cr ₂ O ₃ as a whole about 500 parts by adding composite oxide brown pigment powder 100.0 parts of water -ZnO, which about 30 minutes to 1 hour toward homomixer peptized with pigment slurry Got Lee. To this pigment slurry, 3.4 parts of a No. 3 sodium silicate solution was added at room temperature while peptizing. Next, the pigment slurry was transferred to a beaker, and the cerium nitrate aqueous solution was added to the pigment slurry while stirring.
The solution was gradually added dropwise while adjusting the pH using 5% sulfuric acid so that H became about 9. Thereafter, in the same manner as in Example 1, 102.4 parts of a pigment whose surface was treated with hydroxide precipitation of hydrated silica and cerium was obtained. Cr ⁶⁺ eluted from this pigment
The concentration was 0.20 with respect to 1.9 ppm of the untreated pigment.
ppm.

Example 6 Water was added to 3.1 parts of cerium nitrate and completely dissolved to prepare an aqueous solution having a total of 100 parts. The composition TiO
And _{2 -Sb 2 O 5 -Cr 2 O} 3 composite oxide yellow pigment powder 100.0 to about 500 parts of the whole by adding water to the parts,
This was pulverized in a homomixer for about 30 minutes to 1 hour to obtain a pigment slurry. To this pigment slurry, 3.4 parts of an aqueous solution of sodium silicate No. 3 was added at room temperature while peptizing. Next, the pigment slurry was transferred to a beaker, and the above-mentioned cerium nitrate aqueous solution was added thereto while stirring sufficiently.
The pH was gradually dropped while adjusting the pH with 5% sulfuric acid so that H became 9. Thereafter, in the same manner as in Example 1, the pigment 1 whose surface was treated with hydroxide precipitation of hydrous silica and cerium 1
22.4 parts were obtained. As a result of measuring the eluted Cr ⁶⁺ concentration of this pigment, the untreated pigment was compared with 2.6 ppm and 0.1 ppm.
It was 9 ppm.

COMPARATIVE EXAMPLE 1 Water was added to 100.0 parts of a composite oxide black pigment powder having a composition of CuO--Cr ₂ O ₃ --Mn ₂ O ₃ to add about 500 parts.
The mixture was pulverized in a homomixer for about 30 minutes to 1 hour to prepare a pigment slurry. To this pigment slurry, 3.4 parts of No. 3 sodium silicate solution was added at room temperature while peptizing. Next, the pigment slurry was transferred to a beaker, and 5% sulfuric acid was gradually dropped into the beaker while adjusting the pH so that the pH became approximately 9, with sufficient stirring, and only hydrous silica was deposited on the pigment surface. Then, a treated pigment was obtained in the same manner as in Example 1. Elution Cr ⁶⁺ of the obtained treated pigment
Although the concentration is 1.47 ppm, which is improved as compared with the untreated pigment, the elution amount of hexavalent chromium is clearly larger as compared with the treated pigment of Example 1.

Comparative Example 2 0.5 parts of antimony oxide was completely dissolved in concentrated hydrochloric acid, and this was added to a saturated aqueous solution obtained by completely dissolving 30 parts of sodium chloride in 100 parts of water. Further, the composition CuO—Cr ₂ O ₃ −
Water was added to 100.0 parts of the Mn ₂ O ₃ composite oxide black pigment powder to make the whole about 500 parts, and this was peptized for about 30 minutes to 1 hour with a homomixer. To the obtained pigment slurry, the above-mentioned salt-saturated aqueous solution of antimony oxide was gradually dropped at room temperature, and only the hydrolyzed antimony hydrate was deposited on the surface of the pigment, and the treated pigment was treated in the same manner as in Example 1. I got The elution Cr ⁶⁺ concentration of this treated pigment is 1.0
ppm, which is an improvement over the untreated pigment, but the amount of hexavalent chromium eluted is clearly larger than that of the treated pigment of Example 2.

Comparative Example 3 Water was added to 3.1 parts of cerium nitrate and completely dissolved to prepare an aqueous solution having a total of 100 parts. Composition CuO-Cr ₂
O ₃ composite oxide black pigment powder 10 of -Mn ₂ O ₃
Water was added to 0.0 parts to make the whole about 500 parts, which was peptized in a homomixer for about 30 minutes to 1 hour. Next, the pigment slurry was transferred to a beaker, and while sufficiently stirring, the above cerium nitrate aqueous solution was gradually added dropwise while adjusting the pH so that the pH became about 9, and cerium hydroxide was added to the pigment surface. A treated pigment obtained by depositing only the product was obtained. The eluted Cr ⁶⁺ concentration of this treated pigment is 2.1 ppm
In comparison with the treated pigment of Example 1, the amount of hexavalent chromium eluted was clearly larger. Table 1 summarizes the treatment results of the above chromium-containing composite oxide black pigment powder.

[0026]

[Table 1]

[0027]

According to the method of the present invention, a precipitate of hydrated silica and a substance having a reducing ability is deposited on the surface of chromium-containing composite oxide pigment particles by using a small amount of these and treating at ordinary temperature.
By a simple treatment, the pigment can be adhered, and elution of hexavalent chromium from the obtained pigment can be suppressed to a very small amount.

────────────────────────────────────────────────── (5) References JP-A-48-75629 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C09C 1/00-3/12 C01G 37 / 00-37/033

Claims (6)

(57) [Claims] In a slurry of a composite oxide pigment containing chromium as a component, the pigment is brought into contact with hydrated silica and a substance having a reducing ability, and the pigment is treated with these substances. A method for reducing hexavalent chromium elution of a chromium-containing composite oxide pigment. 2. The method according to claim 1, wherein the hydrated silica is SiO 2
_{2. The} method for reducing hexavalent chromium elution of a chromium-containing composite oxide pigment according to claim 1, wherein 0.1 to 10% by weight and a substance having a reducing ability are used in 0.01 to 10% by weight as ₂ . 3. The method for reducing hexavalent chromium elution of a chromium-containing composite oxide pigment according to claim 1, wherein the pigment is brought into contact with hydrated silica and a substance having a reducing ability at room temperature. 4. A pigment slurry having a reducing ability as a p
The method for reducing hexavalent chromium elution of a chromium-containing composite oxide pigment according to claim 1, wherein H is added while maintaining H at 7.0 to 10.5. 5. The method according to claim 1, wherein the hydrous silica is a hydrolysis product of alkali silicate and / or silica sol. 6. The substance having a reducing ability is at least one substance selected from cerium compounds, antimony compounds, iron compounds, tin compounds, manganese compounds, sodium thiosulfate, sodium hydrogen sulfate and sodium nitrite. 2. A method for reducing hexavalent chromium elution of the chromium-containing composite oxide pigment according to 1.