JPH0696454B2 - Method for producing cobalt bull-based pigment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a cobalt blue pigment, and more specifically, a cobalt blue pigment having a reddish tone and good dispersibility. Regarding the method.

(Prior Art) Cobalt blue pigments are widely known as inorganic pigments having excellent heat resistance, and are widely used, for example, as coloring agents for paints and synthetic resins, phosphors, and coloring agents for ceramics.

The cobalt blue pigment is a spinel type compound mainly composed of an oxide of aluminum and an oxide of cobalt,
If necessary, oxides of other metals such as chromium and magnesium may also be included.

The cobalt blue pigment is manufactured mainly by a dry method and a wet method.

(Problems to be Solved by the Invention) In the dry method, cobalt oxide and aluminum oxide are mixed, a flux is allowed to coexist, the mixture is burned at a high temperature, and then the sintered particles are pulverized by a powerful pulverizer to be pigmented. However, there is a problem in that a large amount of energy is required for pulverization, and a dull color appears in the obtained pigment, and a clear color tone cannot be obtained.

On the other hand, the wet method is a method in which a mixed solution of an aluminum salt and a cobalt salt is neutralized with an alkali to coprecipitate both as hydroxides, and the mixture is baked to develop color. There is a problem that the water content of the coprecipitate is high due to the extremely small diameter and the aluminum hydroxide forms a gel-like precipitate, and it requires a large amount of energy for drying. There is a problem that it is difficult to pulverize the particles because the particles aggregate to form a hard lump, and when fired, the particles become harder.

Furthermore, there is a problem that the pigment obtained by any of the methods has a greenish color tone and cannot be used in applications requiring a reddish color tone.

Therefore, there is a demand for a cobalt blue pigment that requires less energy consumption such as firing, drying, and crushing, and that has a clear and reddish and vivid color tone.

(Means for Solving Problems) As a result of earnest research to meet the above-mentioned demand, the present inventors have
The present invention has been completed by finding that the above demand can be met by using a specific precipitating agent for coprecipitation of aluminum hydroxide and cobalt hydroxide.

That is, the present invention dissolves an aluminum salt, a cobalt salt and urea in water to form a mixed solution, and heats the mixed solution to coprecipitate a hydroxide of aluminum and a hydroxide of cobalt to form a coprecipitate. A method for producing a cobalt blue pigment, which comprises firing after filtration and washing with water.

(Function) By using urea as a precipitant for hydroxide, coprecipitation of aluminum hydroxide and cobalt hydroxide is uniformly performed, and coprecipitate is easily dehydrated, and relatively Even when fired at a low temperature, a reddish and clear cobalt blue pigment can be obtained, and since the cobalt blue pigment is soft particles, it can be easily pulverized.

(Preferred Embodiment) Next, the present invention will be described in more detail with reference to preferred embodiments of the present invention.

The aluminum salt and cobalt salt used in the present invention may be any of the salts used in the production of conventional cobalt blue pigments such as aluminum or cobalt sulfate, nitrate, chloride and acetate. In addition to the above essential components, a small amount of other metal salts such as chromium and magnesium can be used in combination. Particularly, a pigment obtained by using a small amount of 0.3 mol or less of chromium salt per 1 mol of aluminum. Can have an excellent green color.

In the above, the amount of the aluminum salt and the amount of the cobalt salt used is appropriately in the range of Co / Al = 1/2 to 1/5 in molar ratio.

The aluminum salt, cobalt salt or other metal salt as described above is dissolved in water to form a mixed salt aqueous solution, and the concentration thereof is about 20% by weight or less (based on aluminum nitrate) as a whole in a molar ratio within the above range. It is good to set the concentration to a level.

Urea is used as the precipitant used to precipitate the mixed hydroxide from the mixed salt solution.

According to a detailed study by the present inventor, by dissolving urea in the mixed salt aqueous solution, no particular change occurs at a temperature near room temperature, but when the temperature is raised while stirring, for example, 60 ° C. or higher. When heated to a temperature of preferably 70 ° C. or higher, aluminum hydroxide and cobalt hydroxide are uniformly precipitated, and the particles of the precipitate have a certain size unlike the conventional alkaline precipitation method. It has a soft cobalt blue pigment that is very easy to dehydrate due to filtration, etc., and that the dehydrated product does not agglomerate hard at the time of drying, and that it does not need to be pulverized even if it is subsequently subjected to a firing treatment. Has been found to be easily obtained.

Further, when the hydroxide is deposited, the precipitation of the hydroxide starts from the state where all the components are uniformly dissolved, so the deposit is a sufficiently uniform mixture, and it is not necessary to use any flux at the time of firing. there were.

Urea, which is a precipitating agent as described above, is
A use ratio of about 1.0 to 2.0 moles per equivalent of metal salt is preferable, and if the use mole ratio is less than the above range, the precipitation of the metal hydroxide will be insufficient, while if it exceeds the above range, it is not necessary. It is uneconomical to use urea.

Further, according to the present invention, in the above hydroxide coprecipitation step, by coexisting sulfate ions in the system, it is possible to control the particle size of the hydroxide to be coprecipitated, and to control the particle size of the coprecipitate. It has been found that a larger product can be easily dehydrated and dried, and particles do not aggregate even during firing, so that a soft product can be obtained which requires almost no pulverization after firing.

A coprecipitate having a larger particle size can be obtained as the amount of sulfate ion used is increased, but the preferable ratio is 0.05M / as an aqueous solution concentration.
It is about 1 to 0.2 M / l.

In the method of the present invention as described above, each component is dissolved in water, and when the dissolution is completed, the whole is stirred at 60 ° C. or higher, preferably
Coprecipitation of the hydroxide is completed by stirring at a temperature of 70 to 100 ° C. for about 3 to 10 hours. Completion of the hydroxide coprecipitation can be accomplished by filtering a portion of the reaction solution and adding an alkali to the solution to ensure that the solution is not colored.

Next, the coprecipitate that has precipitated is filtered to reduce the water content.
40 to 60%, dried at a temperature of about 100 to 120 ° C, and dried in an oxidizing atmosphere at about 900 to 1,200 ° C
The color is developed by baking at a temperature of about 30 to 90 minutes to obtain the cobalt blue pigment of the present invention.

The firing temperature in the conventional method is generally 1,000 to 1,200 ° C.
The degree is required, but in the method of the present invention, a temperature below that,
For example, sufficient firing can be performed even at a temperature of 900 ° C to 1,200 ° C.

In addition, the obtained cobalt blue pigment is a product with a clear reddish blue color without dullness, whereas the conventional cobalt blue pigment has a dull greenish blue color, and the particles are very soft. Therefore, it exhibits extremely excellent dispersibility in paints, synthetic resins, and other materials to be colored.

(Effects) According to the present invention as described above, by using urea as a precipitant for hydroxide, coprecipitation of aluminum hydroxide and cobalt hydroxide is performed uniformly, and dehydration of the coprecipitate is performed. It is easy to obtain a cobalt blue pigment having a clear reddish color even when fired at a relatively low temperature. Since the cobalt blue pigment is soft particles, pulverization is easy.

Example 1 41.4 parts of aluminum nitrate nonahydrate and cobalt nitrate hexahydrate 16
To 60 parts of urea, 5.5 parts of sodium sulfate is added, and dissolved water is added to make 600 parts in total. After stirring well to dissolve each component completely, cover the watch glass to prevent water from splashing and raise the temperature while stirring with a magnetic stirrer. When the temperature reaches 80 ℃, keep it constant and leave it as it is. After a while, a precipitate begins to precipitate.

When the reaction is about to finish, in order to confirm that the precipitation is completely finished, a part of the slurry is taken, scraped with a filter paper to remove the filtrate, and dropped into a thin caustic soda solution. If the liquid is clear, it is finished, so take it out, wash it thoroughly with water, and wash away the residual salt. This is dried at a temperature of 120 ° C. for 12 hours or more.

Then, the dried coprecipitate is calcined at 900 ° C. for 1 hour in an oxidizing atmosphere.

The pigment thus obtained had a clear blue color with no dullness and a clear color tone, and was reddish as compared with that of the dry method. The dispersibility was also excellent.

Example 2 Aluminum nitrate nonahydrate 41.4 parts, cobalt chloride hexahydrate 9.
1 part, 60 parts of urea and 5.5 parts of sodium sulfate are added, and dissolved water is further added to make 600 parts in total.

Then, the synthesis is carried out in the same manner as in Example 1.

The pigment thus obtained had a reddish blue color similar to that in Example 1, was soft with no dullness, and was excellent in dispersibility.

Comparative Example 1 Aluminum nitrate nonahydrate 41.4 parts and cobalt nitrate hexahydrate 16
Parts and 200 parts of dissolved water, 17.6 parts of caustic soda is separately weighed, and similarly dissolved in 200 parts of dissolved water. 200 parts of precipitation water is placed in one beaker, and the prepared salt solution and caustic soda solution are simultaneously dropped into the precipitation water while stirring with a motor at room temperature. At this time, the pH is appropriately adjusted so as to be about 9 to 10.

When the addition is complete, the slurry is aged for 1 hour at room temperature, then filtered and rinsed and dried at 120 ° C. for 12 hours or more. The dried coprecipitate contracts at this point to become a tick.

Next, this is baked at 1,200 ° C. for 1 hour in an oxidizing atmosphere.

The pigment thus obtained is reddish blue,
The particles were very hard, and they were gritty even when crushed by a crusher, and the dispersibility was very poor.

Comparative Example 2 11.3 parts of aluminum oxide and 4.1 parts of cobalt oxide were well ground and mixed with a dairy bee, and the mixture was baked at 1,200 ° C. for 1 hour in an oxidizing atmosphere.

The pigment thus obtained could be loosened by crushing it lightly with a dairy bee, but the color tone was slightly dull, greenish, and had a dull color.

Claims (5)

[Claims] 1. An aluminum salt, a cobalt salt, and urea are dissolved in water to form a mixed solution, which is heated to coprecipitate an aluminum hydroxide and a cobalt hydroxide, and a coprecipitate is filtered. A method for producing a cobalt blue pigment, which comprises firing after washing with water and washing with water. 2. The method for producing a cobalt blue pigment according to claim 1, wherein the heating is heating at 70 ° C. or higher. 3. The method for producing a cobalt blue pigment according to claim 1, wherein sulfuric acid ions are allowed to coexist in the mixed solution. 4. The method for producing a cobalt blue pigment according to claim 1, wherein the firing temperature is 900 ° C. or higher. 5. The method for producing a cobalt blue pigment according to claim 1, wherein 0.3 mol or less of a chromium salt coexists with 1 mol of an aluminum salt.