JP3006924B2 - Fine particle composite oxide brown pigment and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine particle composite oxide brown pigment and a method for producing the same. The object of the present invention is to provide a composite oxide brown pigment excellent in clarity, transparency and heat resistance. Accordingly, it is an object of the present invention to provide a particulate composite oxide brown pigment which is useful for coloring automotive paints, thin films, printing inks and the like, for example, by utilizing the properties newly developed.

[0002]

2. Description of the Related Art Composite oxide brown pigments are widely known as inorganic pigments having excellent heat resistance, and are widely used, for example, as colorants for paints and synthetic resins, and as colorants for the ceramic industry.
Among the above brown pigments are compounds consisting of oxides of zinc, iron and chromium, the structure of which is generally spinel or a mixture of spinel and iron oxide.
The production method is mainly carried out by mixing, calcination and grinding of oxides and carbonates of zinc, iron and chromium by a dry method. However, the above-mentioned dry method has a drawback that a large amount of energy is required for pulverization, and at present, fine particles of pigment cannot be obtained due to pulverization of the sintered body. In the wet method, there is a report on a zinc-iron composite oxide, but there is almost no report on a system containing chromium. Nor has it been done industrially.

[0003]

In the dry method conventionally practiced, zinc, iron and chromium oxides or carbonates are mixed, sometimes together with a mineralizer, fired at a high temperature, and then fired. This is a method of pulverizing the tied particles with a powerful pulverizer and converting it into a pigment.However, as long as each component is not fine particles, the product after firing is unlikely to become transparent fine particles. However, it also sintered during firing and required more energy for pulverization. On the other hand, a composite oxide brown pigment is expected to be obtained by the wet method. In this case, a mixed metal salt solution in which a salt of zinc, trivalent iron and trivalent chromium is dissolved is used as a precipitant such as sodium hydroxide and the like. After coprecipitation using an alkali, heating and aging, firing is considered. However, in this method, when the heating temperature is low, too fine particles are generated, and the pigment is not suitable. At a high temperature, the particle growth of iron oxide alone is intense, and it is difficult to obtain fine particles.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to meet the above-mentioned demand, and have found that after a wet precipitation reaction, 50 ° C.
The inventors have found that the desired fine particles can be obtained by air oxidation under the following conditions, and have completed the present invention. That is, the first invention of the present invention comprises an oxide of zinc, iron and chromium, and has a BET specific surface area of 50 m ² / g.
As described above, the present invention is a fine particle composite oxide brown pigment characterized by being 100 m ² / g or less, and a second invention provides a mixed solution of three components of a zinc salt, a divalent iron salt and a trivalent chromium compound. After coprecipitation of each salt using an excess alkali aqueous solution as a precipitant, air is blown at a temperature of 50 ° C. or less, and a precursor of the fine particle pigment is formed, followed by filtration, washing with water, drying and heat treatment. The method for producing a fine particle composite oxide brown pigment described above.

[0005]

According to the present invention, an oxidizing gas such as air is blown into a mixed aqueous solution of a zinc salt, a divalent iron salt and a trivalent chromium compound, after coprecipitation using a precipitant such as an alkali, and the products are compared. By heat treatment at a relatively low temperature, a fine-particle composite oxide brown pigment having a transparent and reddish brown color tone can be obtained. Next, the present invention will be described in more detail with reference to preferred embodiments.

The salts of the constituent elements used in the present invention are sulfates,
Any of the conventional nitrate, chloride, acetate, and other complex oxide brown pigments used in the production of the pigment can be used. In the above, the constituent ratio of each component is most preferably zinc: iron: chromium = 1: 1: 1 in terms of the molar ratio of the metal, and at this ratio, a transparent brown color is good. Further, according to the results of the study of the present inventors, the molar ratio of the constituent components zinc (Zn), iron (Fe) and chromium (Cr) is 0.5 to 1.5 to 1.
It was recognized that if the composition change was within the range of 0.5 and chromium 0.5 to 1.5, the transparency was not significantly affected. Also, as the iron ratio increases, the color becomes reddish, and the molar ratio becomes 1.5.
Beyond is opaque. On the other hand, as the amount of chromium increases, redness decreases and the color tends to be slightly dull.

[0007] All the metal salts of the respective constituent elements as described above are dissolved in water to form a mixed salt aqueous solution. The concentration at that time is suitably about 5 to 50% by weight as a whole in a molar ratio as described above. This mixed solution is simultaneously dropped into a precipitating medium prepared in advance using an aqueous alkaline solution such as caustic soda as a precipitant. The reaction concentration at this time is not so great as to have a particularly bad influence on the transparency, but preferably 0.05 mol / L to 0.2 mol / L in consideration of workability and the subsequent oxidation step using air or the like. Liter is appropriate, and the lower the concentration, the smaller the particles and the better the transparency. Further, if the synthesis temperature is in a range where the synthesis is performed normally, that is, in a range of 0 to 100 ° C., the effect can be sufficiently exhibited. However, when the temperature is 50 ° C. or higher, the growth of the particles tends to be large, and the transparency tends to be slightly impaired. In addition, as long as the pH at the time of synthesis at this time is on the alkaline side of 8 or more, there is no significant effect in any pH range. Excess alkali is added after precipitation. At this time, the excess amount of alkali is 1.1 to 1.1 with respect to the alkali mole number required for precipitation.
A range of 5 times, desirably around 1.1 times is the best in both color tone and transparency. When the excess amount of alkali is small, the growth of particles is suppressed and the transparency is excellent, but the color tone tends to be dull. If the amount of excess alkali is large, the particles grow violently, making it difficult to obtain fine-particle pigments, dissolving chromium in the excess alkali, causing a change in composition, and adversely affecting subsequent treatment.

After the precipitate is formed while stirring for 30 minutes to 1 hour in this way, the mixture is aged for about 5 to 20 minutes to complete the precipitation reaction. Next, an oxidizing gas such as air is blown into the coprecipitate with stirring to completely oxidize divalent iron. The amount of air at this time is 1.0 to 2.0 liter / min. Within this range there is no significant effect on quality. However, when the amount of air is small, an opaque pigment is obtained in which the growth of particles is intense. In addition, when the amount is large, the particle size is too small, the color tone is faint, and a pigment having poor dispersibility can be obtained. The temperature during oxidation is 50 ° C.
The temperature is preferably as low as 20 to 30 ° C. At a temperature higher than 50 ° C., the growth of the particles is remarkable, and it is difficult to obtain a transparent pigment.

[0009] Under the above conditions, the air blowing time ends in about 3 to 4 hours. The end of the reaction can be known by measuring the oxidation-reduction potential of the solution. That is, under the conditions, at the start of the reaction, +830 to +850 mV
At the end of the reaction drops to around +50 mV. Under these conditions, trivalent chromium is hardly oxidized to hexavalent, and very little.
Next, the obtained product is filtered, washed with water, and dried at a temperature of about 100 to 120 ° C. By subjecting the obtained dried product to a heat treatment at a temperature of 500 to 700 ° C. for 30 minutes to 1 hour in an oxidizing atmosphere, the fine particle composite oxide brown pigment of the present invention can be obtained. The fine particle composite oxide brown pigment according to the present invention thus obtained has a transparent and deep color tone as compared with the conventional dry method, and has a BET specific surface area of 50 to 100 m ² / g.
By adjusting the particle size, the particle size was adjusted, and the dispersion in the coating system was good.

[0010]

【Example】

Example 1 27.4 parts by weight of zinc chloride, 55.7 parts by weight of ferrous sulfate heptahydrate and 119 parts by weight of a 40% by weight chromium nitrate solution were weighed.
Water is added and completely dissolved to make the whole about 300 parts by weight. Next, 57 parts by weight of caustic soda is measured as a precipitant, and water is added to make about 300 parts by weight. About 1,200 parts by weight of water, which is a precipitating medium prepared in advance, is adjusted to about 25 ° C. with a gas burner or an electric heater, and the mixed salt aqueous solution and the caustic soda aqueous solution are simultaneously dropped therein,
The precipitation reaction is completed in about 30 minutes to 1 hour. At this time, care is taken so that the pH is about 10 and, when dripping of the mixed salt aqueous solution is completed, excess caustic soda aqueous solution is continuously added, followed by aging for about 20 minutes.

Next, a glass tube processed into a thin capillary is prepared, and 1.5 l / min. Blow in air at the flow rate. During this time, stirring was continued, the rotation speed of the stirring blade was adjusted to around 300 rpm, the temperature was adjusted to 25 ° C., and air blowing was continued for about 4 hours. At the beginning, the green precipitate changes to a reddish precipitate at the end. The end point of the reaction is measured using an oxidation-reduction potentiometer, and the process is terminated when a value around +850 mV changes to around +50 mV. Next, the product is taken out, washed sufficiently with decantation to remove residual salts, and filtered. Then, it is dried at a temperature of 100 to 120 ° C. for 12 hours or more. The dried product was heat-treated at 700 ° C. for 1 hour in an oxidizing atmosphere, cooled, and further heat-treated at 400 ° C. for 1 hour to obtain a fine particle composite oxide brown pigment.

The pigment thus obtained had fine particles, a BET specific surface area of 70 m ² / g, a reddish brown color and transparency, and a deep color. The fired product is then dispersed in a melamine alkyd resin (PHR30) with a paint shaker. Then, the color was applied to art paper with a black belt using a 6-mil applicator, and the color tone was observed.

EXAMPLE 2 83.5 parts by weight of ferrous sulfate heptahydrate and caustic soda 68
A pigment of the present invention was obtained in the same manner as in Example 1 except that the amount was changed to parts by weight. The pigment thus obtained had fine particles, a BET specific surface area of 65 m / g, a deep reddish brown color and transparency, as in Example 1.

Comparative Example 1 88.8 parts by weight of a commercially available needle-like hydrous ferric oxide pigment, 40.7 parts by weight of zinc oxide and 15.2 parts by weight of chromium oxide are weighed and thoroughly mixed. This was calcined at 850 ° C. for 1 hour, and pulverized according to a conventional method to obtain a pigment. The pigment obtained by the dry method obtained in this way had larger particles and was opaque than the pigment obtained in Example 1. Table 1 summarizes the above results.

Table 1Hue ¹⁾ Clarity Dispersibility Specific surface area  Conventional product Brown no good 5m^Two/ GExample 1 Brown good 70m^Two/ GExample 2 Brown Yes Good 65m^Two/ GComparative Example 1 Brown no good 4m^Two/ G

Note 1) Hue Transparency: Melamine alkyd / PHR30 The conventional products in Table 1 above are commercially available composite oxide brown pigments.

[0017]

As described above, according to the present invention, a deep reddish-brown fine-particle composite oxide brown pigment having excellent transparency can be obtained. It is used as a coloring agent for plastics and synthetic resins, as a coloring agent for ceramics, and is expected to be applied to, for example, transparent paints, transparent thin films, printing inks, cosmetics, phosphors, abrasives, etc. by utilizing its characteristics. .

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C09C 1/34 C09C 1/34 (72) Inventor Akira Nishio 4-10-22 Higashi-Oizumi, Nerima-ku, Tokyo (72) Inventor Mineki Michiyoshi Saitama 1194-58, Kamihideya, Okegawa-shi, Japan (56) References JP-A-61-48431 (JP, A) JP-A-4-224115 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) C01G 49/00-49/08 C01G 9/02 C01G 37/02

Claims (4)

(57) [Claims] (1) An oxide of zinc, iron and chromium,
A particulate composite oxide brown pigment having an ET specific surface area of 50 m ² / g or more and 100 m ² / g or less. 2. The molar ratio of zinc, iron and chromium as constituents is 0.5 to 1.5 iron and 0.5 chromium per 1 zinc.
2. The fine particle composite oxide brown pigment according to claim 1, which has a range of from 1.5 to 1.5. 3. A zinc salt, a divalent iron salt and a trivalent chromium salt.
After excessively adding an aqueous alkali solution as a precipitant to the component mixture solution to form a coprecipitate, air is blown at a temperature of 50 ° C. or less to generate a precursor of the fine particle pigment, which is filtered, washed with water and dried. , A heat-treating method for producing a fine-particle composite oxide brown pigment. 4. The process for producing a particulate composite oxide brown pigment according to claim 3, wherein the heat treatment temperature is in the range of 500 to 700 ° C.