JPH02283771A - Particulate cobalt blue pigment and preparation thereof - Google Patents

Abstract

PURPOSE:To prepare a particulate cobalt blue pigment having a large specific surface area, an excellent dispersibility, transparency, etc., and a bright red tone by dissolving an aluminum salt, a cobalt salt, and urea in water, heating the solution to coprecipitate hydroxides of aluminum and cobalt, separating the coprecipitate by filtration, and washing and baking the coprecipitate. CONSTITUTION:An aluminum salt (e.g. aluminum nitrate), a cobalt salt (e.g. cobalt nitrate), and urea are dissolved in water. The aq. soln. is heated to pref. 70 deg.C or higher to coprecipitate hydroxides of aluminum and cobalt. The coprecipitate is separated by filtration, washed with water, and baked to give a particulate cobalt blue pigment having a BET specific surface area of 40m<2>/g or higher. The use of urea as the precipitant causes a homogeneous coprecipitation of hydroxides of aluminum and cobalt, making the dehydration easy, and thus a cobalt blue pigment having a bright red tone is obtd. even by baking at a relatively low temp.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fine particle cobalt blue pigment and a method for producing the same. This invention relates to a blue pigment and a method for producing the same.

(Prior art and its problems) Cobalt blue pigments are widely known as inorganic pigments with excellent heat resistance, and are widely used, for example, as colorants for paints and synthetic resins, phosphors, and even colorants for ceramics. has been done.

The cobalt blue pigment is an oxide of aluminum, and may also contain metal oxides of metals such as chromium and magnesium, if necessary.

The above-mentioned cobalt blue pigment is mainly produced by a dry method or a wet method, but it is difficult to obtain fine particle type pigments from these methods, and conventional pigments generally have a BET specific surface area of 20 n1''/g or less. were the majority.

For example, in the dry method, cobalt oxide and aluminum oxide are mixed and flux is used to crush the mixture in a crusher to form a pigment, but this method has the disadvantage of requiring a large amount of energy for crushing, and the resulting pigment has a dull color. appears and clear color tones cannot be obtained. Furthermore, since the sintered body is pulverized, fine particles cannot be obtained.

On the other hand, the wet method is a method in which a mixed solution of aluminum salt and cobalt salt is neutralized with an alkali to co-precipitate both as hydroxide, and this is fired to develop color, but the precipitated hydroxide particles The diameter is extremely small, and because the aluminum hydroxide forms a gel-like precipitate, the water content of the coprecipitate is high, and it takes a lot of energy to dry it. The particles agglomerate into hard particles, and when fired, they become even harder particles. Therefore, pulverizing these hard particles is more efficient than in the dry method.

Furthermore, there is a problem in that the pigments obtained by either method have a greenish color tone and cannot be used in applications that require transparency and a reddish color tone.

Therefore, an object of the present invention is to provide a fine particle type cobalt blue pigment having a transparent and bright reddish color tone, which has been difficult to obtain in the past.

(Means for Solving the Problems) As a result of intensive research to achieve the above object, the present inventors found that, in order to achieve the above-mentioned object, co-precipitation of aluminum hydroxide and cobalt hydroxide,
The present invention was completed by discovering that the above object can be easily achieved by using a specific precipitant.

That is, the present invention has a specific surface area of 40rrI according to the BET method.
A fine particle type cobalt blue type pigment characterized by a particle size of 100% or more than This is a method for producing a fine particle type cobalt blue pigment, which is characterized by co-precipitating a co-precipitate with a hydroxide, filtering the coprecipitate, washing with water, and then firing.

(Function) By using urea as a precipitant for hydroxide, co-precipitation of aluminum hydroxide and cobalt hydroxide is carried out uniformly, and dehydration of the coprecipitate is easy, and compared to It has a bright red color even when fired at a low temperature, and its BET specific surface area is 4.
A fine particle cobalt blue pigment having a particle size of 0rn'/g or more can be obtained, and since the cobalt blue pigment is a soft particle, it can be easily crushed.

Therefore, the cobalt blue pigment according to the present invention can be used in conventional paints, colorants for synthetic resins, phosphors, and colorants for ceramics, as well as cosmetics, printing inks, abrasives, ceramic thin films, transparent It is expected to be applied to adhesive paints, catalyst carriers that take advantage of their high surface area, etc.

(Preferred Embodiments) Next, the present invention will be described in more detail by citing preferred embodiments.

The aluminum salts and cobalt salts used in the present invention include any salts used in the production of conventional cobalt blue pigments, such as aluminum or cobalt sulfates, nitrates, carbonates, chlorides, and acetates. It can be used.

In addition to the above-mentioned essential components, small amounts of other metal salts such as chromium and magnesium can also be used together, and in particular, the color tone can be improved by using a small amount of chromium salt (0.3 mol or less per 1 mol of aluminum). Thick (can be changed to a greenish color).

In the above, the amounts of aluminum salt and cobalt salt used are:
A suitable molar ratio of Co/Ag is in the range of about 1/2 to 175.

Aluminum salts, cobalt salts, or other metal salts as described above are dissolved in water to form a mixed salt aqueous solution, the concentration of which is generally about 0.1-0.
The concentration is preferably +M/12 (based on aluminum nitrate); if the concentration is less than this range, the resulting pigment will lack transparency and the production efficiency will also decrease. On the other hand, if the above range is exceeded, the resulting pigment becomes too fine and aggregates, resulting in completely poor dispersibility.

Urea is used as a precipitating agent to precipitate the mixed hydroxide from the mixed salt solution.

According to detailed research by the present inventor, dissolving urea in the mixed salt aqueous solution does not cause any particular change at a temperature around room temperature, but when the temperature is raised while stirring, for example, 60°C or higher. , preferably at a temperature of 70°C or higher, aluminum hydroxide and cobalt hydroxide precipitate uniformly, and the precipitate particles have a certain size, unlike those obtained by conventional alkaline precipitation methods. have.

Furthermore, according to the present invention, in the above hydroxide coprecipitation step, by allowing sulfate ions to coexist in the system, secondary aggregation of the coprecipitated hydroxide is increased, and particles of the coprecipitate are By increasing the diameter, it is easy to dehydrate and dry, and it is also possible to obtain a fine particle pigment with a BET specific surface area of 40 rn''/g or more, which is soft enough that the particles do not aggregate easily during firing, and hardly requires pulverization after firing. I found it.

In addition, when hydroxide is precipitated, the hydroxide begins to precipitate from a state in which all components are uniformly dissolved, so the precipitate is a sufficiently uniform mixture, and there is no need to use any flux during firing. Met.

As the amount of sulfate ion used increases, a coprecipitate with a larger particle size can be obtained, but the preferred ratio is 0.0 as the aqueous solution concentration.
It is about 5 to 0.2M/12.

Urea, which is a precipitant as mentioned above, has a
A usage ratio of approximately 1.0 to 3.0 mol per equivalent of metal is suitable; if the usage ratio is less than the above range, precipitation of the metal hydroxide will be insufficient; on the other hand, if the usage ratio exceeds the above range, In this case, unnecessary urea is used, which is uneconomical.

In the method of the present invention as described above, each component is dissolved in water, and after the dissolution is completed, the whole is stirred at a temperature of 60°C or higher, preferably 70 to 100°C, for about 3 to 24 hours to oxidize the hydroxide. Co-precipitation of the substance is completed. Completion of coprecipitation of hydroxide can be accomplished by filtering a portion of the reaction solution, adding an alkali to the filtrate, and confirming that the filtrate is not colored.

Next, by filtering the precipitated coprecipitate, the water content becomes about 40 to 80%, and this is heated to about 70 to 120°C.
It is dried at a temperature of about 900℃ in an oxidizing atmosphere.
Color is developed by firing at a temperature of from 1,300° C. for about 30 to 90 hours, and the fine particle cobalt blue pigment of the present invention is obtained.

The firing temperature in the conventional method is required to be about 1,000 to 1,200°C for boat fishing, but in the method of the present invention, sufficient firing can be performed at the following temperatures, for example, 900°C or higher. I can do it.

In addition, the obtained cobalt blue pigment is a clear reddish blue product with no dullness, whereas conventional cobalt blue pigments have a dull greenish blue color, and the particles are very small. Because it is soft, it cannot be used with paints, synthetic resins,
It shows very good dispersibility in other coloring materials.

The BET specific surface area of these pigments is 40 ni'/g or more, and the particularly preferable specific surface area range is 45 to 100 r.
n"/g. On the other hand, the BET specific surface area of pigments obtained by conventional methods was at most 20 g/g.

(Effects) According to the present invention as described above, by using urea as a precipitant for hydroxide, co-precipitation of aluminum hydroxide and cobalt hydroxide is carried out uniformly, and the coprecipitate is It is easy to dehydrate, and even when fired at a relatively low temperature, a clear, reddish, and vivid fine particle type cobalt blue pigment can be obtained, and since the cobalt blue pigment is a soft particle, it can be easily pulverized.

Example 1 48.3 parts of aluminum nitrate nonahydrate, 15 parts of cobalt nitrate hexahydrate, and 60 parts of urea were added to a separable flask equipped with a condenser, and then 7.1 parts of sodium sulfate was added, and water was added to bring the total volume to 500 parts. Department. Stir well to completely dissolve each component, then raise the temperature while stirring. temperature is 10
Once the temperature reaches 0°C, keep it constant and leave it as is. After a while, a precipitate will start to separate out. After that, heating and stirring were continued, and after about 17 hours, in order to check whether the reaction had finished, take a portion of the slurry, remove the filtrate with a filter paper, and drop one drop of it into a dilute caustic soda solution. If the liquid is clear, the reaction has finished, so take it out and wash it thoroughly with water to wash away any remaining salt. This material is dried at a temperature of 120° C. for 12 hours or more.

The dried coprecipitate is then calcined at 1,000° C. for 1 hour in an oxidizing atmosphere. Thereafter, the fired product was dispersed in melamine alkyd resin (PHR401 varnish) using a paint shaker to form a paint, and its color tone was observed.

The pigment thus obtained was completely free of dullness and had a clear, clear blue color when compared to conventional products, and had a reddish tinge compared to those obtained by the dry method. FIG. 1 shows an electron micrograph (magnification: 30,000 times) of the cobalt blue pigment of the present invention, which has good dispersibility. still,
For comparison, an electron micrograph of a commercially available pigment at the same magnification is shown in FIG.

Example 2 48.3 parts of aluminum nitrate nonahydrate, 12.3 parts of cobalt chloride hexahydrate, 60 parts of urea and 7.1 parts of sodium sulfate are mixed with water to make a total of 500 parts.

Synthesis is then carried out in the same manner as in Example 1.

The pigment thus obtained was transparent and had a bright reddish blue color as in Example 1, had no dullness, was soft, and had good dispersibility.

Comparative Example 1 48.3 parts of aluminum nitrate nonahydrate and 15 parts of cobalt nitrate hexahydrate were dissolved in 200 parts of water, and separately 19 parts of caustic soda was dissolved.
．． Weigh out 6 parts and similarly dissolve in 200 parts of water. Take 200 parts of water in a beaker and simultaneously drop the prepared salt solution and caustic soda solution into this water while stirring with a motor at room temperature. At this time, the pH is adjusted appropriately to about 9 to 10.

After the dropping is completed, the slurry is aged at room temperature for 1 hour, then filtered and washed with water, and dried at 120° C. for 12 hours or more. At this point, the dried coprecipitate shrinks and becomes sticky.

The body was fired at 1,200° C. for 1 hour in an oxidizing atmosphere.

The pigment thus obtained had a reddish blue color, but the particles were very rough (even when crushed with a crusher, they were rough and had very poor dispersibility).

Comparative Example 2 11.3 parts of aluminum oxide and 4.1 parts of cobalt oxide were thoroughly ground and mixed with an emulsifier, and this was mixed to 1.2 parts.
It is baked in an oxidizing atmosphere at 00° C. for 1 hour.

The pigment thus obtained could be loosened by crushing it lightly with an emulsifier (it was soft, but the color tone was a little dull, greenish and lacked brightness).

When the characteristics of each of the pigments obtained as described above were investigated, the results shown in Table 1 below were obtained.

(Margin below) 1; flea 0 Observation after coating with melamine alkyd resin.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph at a magnification of 30,000 times showing the particle structure of the pigment of the present invention, and FIG. 2 is an electron micrograph at a magnification of 30,000 times showing the particle structure of a commercially available pigment. Patent applicant Dainichiseika Kagyo Co., Ltd. (1 other person)

Claims (7)

[Claims] (1) A fine particle type cobalt blue pigment characterized by having a specific surface area of 40 m^2/g or more as measured by the BET method. (2) Dissolving an aluminum salt, a cobalt salt, and urea in water to form a mixed solution, and heating this to co-precipitate aluminum hydroxide and cobalt hydroxide,
A method for producing a fine particle type cobalt blue pigment, which comprises filtering the coprecipitate, washing it with water, and then firing it. (3) The method for producing a cobalt blue pigment according to claim 2, which comprises heating to 70°C or higher. (4) The method for producing a cobalt blue pigment according to claim 2, wherein sulfate ions are coexisting in the mixed solution. (5) The method for producing a cobalt blue pigment according to claim 2, wherein the firing temperature is 900°C or higher. (6) The concentration of the salt mixed solution is 0.1 to 0.5 M/l (
The method for producing a cobalt blue pigment according to claim 2, which is based on aluminum nitrate. (7) The method for producing a cobalt blue pigment according to claim 2, in which 0.3 mol or less of a chromium salt is coexisting per 1 mol of the aluminum salt.