JPS595151B2 - Method for producing iron oxide pigment with good dispersibility - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for producing iron oxide pigments, and an object of the present invention is to provide iron oxide pigments that have almost no agglomeration, have excellent dispersibility, and exhibit vivid colors. That is.

Hydrous ferric oxide (hereinafter α-Fe0), which is a form of iron oxide
0H) has been traditionally used as a yellow pigment, and its shape is generally needle-like or rod-like, and its size is about 0.1μ in the width direction and 1μ in length. be.

When these fine α-Fe00H particles are used as a paint, it is extremely difficult to disperse them in the step of kneading the particles into an organic solvent and resin. 10 more
In recent years, there has been an increase in demand for extremely fine α-Fe00H, which is about 1/10 the size of the above-mentioned ones, as a transparent pigment that has many uses such as various metallic coatings, coloring of plastics and building materials, and use in cosmetics. I came. Although the α-15Fe00H used for this transparent pigment is fine, its surface area is large, and the cohesive force between the particles is also very strong. Improved dispersibility is highly desired in the industry. α-Fe00H powder is generally produced by reacting an iron salt in the form of an aqueous solution 20 under oxidative conditions in the presence of an alkali or other neutralizing agent, followed by filtering and drying by heating. However, during the above heat drying process, α-F
The agglomeration of e00H particles and significant reduction in dispersibility hinders the industrial use of α-Fe00H. As a result of studying this problem, we found that the coexistence of water in the heating drying process described above is the direct cause of agglomeration between particles.
It turned out that the maintenance of this process was an important technical issue. The present invention has solved the above-mentioned problems, and the present invention has 30
According to the method, a water-containing slurry of α-Fe00H produced by wet reaction of iron salts under oxidative conditions is (a) dispersed in a hydrophilic organic solvent that is miscible with water in any proportion, and then (
b) the dispersion is immiscible with water in any proportion;
Adding water and a hydrophobic organic solvent that can form a three-component co-distillation system with the above-mentioned hydrophilic solvent, (c) by three-component azeotropic distillation of water, the hydrophilic organic solvent, and the hydrophobic organic solvent, After distilling off the water present in the system and the hydrophilic organic solvent, (d) concentrating or completely removing the remaining hydrophobic organic solvent dispersion, it is possible to obtain excellent dispersibility. As a result, iron oxide pigments can be obtained.

The α-FeOOH produced by the present invention exhibits almost no aggregation and exhibits good dispersibility in a solvent, as is clear from observation with an electron microscope. A method of dehydrating surface-adsorbed water or crystallized water of an inorganic compound by azeotropic distillation with benzene is known.

However, when the above α-FeOOH water-containing slurry is added to benzene, due to the hydrophobicity of benzene, α-FeOOH
Significant agglomeration of OH occurs, and the dispersibility of the resulting pigment is almost the same as that of the pigment obtained by heating and drying an α-FeOOH aqueous slurry. Although the details of the mechanism of the present invention are not yet clear, the hydrophilic organic solvent
Because of its hydrophilic nature, it can be mixed well with α-FeOOH water-containing slurry without causing aggregation of α-FeOOH, and it also mixes well with hydrophobic organic solvents.
The hydrophilic solvent will disperse the slurry in the hydrophobic organic solvent while maintaining its mixed and dispersed state, and as a result, the dispersibility of the slurry in the hydrophobic solvent will be improved.

Therefore, it is considered that the hydrophilic organic solvent constitutes one component of the azeotropic composition and also functions as a surfactant. The powder obtained by the present invention exhibits a bright yellow color compared to the brownish color of the powder obtained by the conventional method obtained by drying an α-FeOOH water-containing slurry with hot air. Furthermore, the results of sedimentation rate measurements and initial dispersibility measurements in linseed oil show that the powder obtained by the method of the present invention has significantly improved dispersibility in organic solvents compared to powder obtained by the conventional method. It became clear that The α-FeOOH aqueous slurry used in the present invention is not subject to any other limitations as long as it is synthesized in an aqueous solution under oxidizing conditions for iron salts.

In the present invention, the hydrophilic solvent is a solvent that can be mixed with water at an arbitrary ratio at room temperature, and includes, for example, alcohols such as acetone and nitriles.

In addition, a hydrophobic solvent is a solvent that is immiscible with water in any proportion in the temperature range from the distillation temperature under normal pressure to room temperature when water and hydrophilic solvents present in the system are removed by azeotropic distillation. For example, hydrocarbons, halogenated hydrocarbons, esters, ketones other than acetone, etc. can be used. In order to achieve the purpose of the present invention, it is necessary to use a hydrophilic organic solvent and a hydrophobic organic solvent in a combination that can form a three-component azeotropic system when water is further added to the mixture. For example, the following combinations can be mentioned: In the first step of the present invention, α-
The hydrophilic organic solvent to be mixed with the water-containing slurry of FeOOH is used in a small amount as long as α-FeOOH does not coagulate when mixed with a hydrophobic organic solvent in the subsequent process or when the mixture is subjected to azeotropic distillation. The more desirable it is.

There is no problem in using the hydrophilic organic solvent in an amount greater than the minimum amount necessary, except for the fact that economical problems such as the amount of heat required for removal and the increase in the size of the processing container arise. The amount of hydrophilic solvent that does not cause aggregation of α-FeOOH varies depending on the type of solvent and the type of hydrophobic organic solvent used in combination, so it is best to know the amount for a given solvent through preliminary experiments. . In addition, in the second step of the present invention, the hydrophobic organic solvent that is further mixed into the mixed system of the α-FeOOH water-containing slurry and the hydrophilic organic solvent is added to the water in the water-containing slurry by three-component azeotropic distillation in the subsequent step. As in the case of hydrophilic organic solvents, it is desirable to use the minimum amount necessary to completely distill off the hydrophilic organic solvent. The amount is
It can be calculated from the amounts of water and hydrophilic solvent and the azeotropic composition. In general, α-FeO according to the invention
The OH pigment is manufactured as follows. First, an α-FeOOH water-containing slurry obtained by a conventional method such as reacting an iron salt in an aqueous solution under oxidative conditions and then filtering the reaction solution is mixed with the minimum amount of hydrophilic organic compound as described above. Add to solvent and stir. After α-FeOOH is sufficiently dispersed, an appropriate amount of a desired hydrophobic organic solvent is added to the dispersion, followed by azeotropic distillation under normal pressure or reduced pressure. The required amount of the hydrophobic organic solvent may be added all at once before distillation, or a portion of the required amount may be added first, and the remaining portion may be added sequentially concurrently with distillation. It was confirmed from the distillation temperature that water and the hydrophilic organic solvent were completely distilled off. The thus obtained α-FeOOH monohydrophobic organic solvent slurry can be obtained by removing the solvent by means such as vacuum drying, spray drying, freeze drying, etc.
Give OH powder. In this case, if a hydrophobic organic solvent such as benzene, which has a freezing point near room temperature, is used, freeze-drying can be easily carried out. A pigment is obtained. If desired, a yellow iron oxide pigment organic solvent dispersion suitable for direct paint application can be obtained by concentrating the α-FeOOH-hydrophobic solvent slurry obtained using an appropriately selected hydrophobic organic solvent. can be manufactured. According to this completely wet manufacturing method, there is no need to take out the iron oxide powder, which is advantageous in terms of dust pollution countermeasures, and also has the advantage of simplifying the manufacturing process. The iron oxide pigment produced by the present invention has a clear color and has excellent initial dispersibility, so it has good dispersibility, and in the case of fine particles, it has excellent transparency, so it can be used in paints. It is particularly suitable as a pigment for metallic coatings.

It is also suitable for the production of printing inks and for transparent wood coatings. Next, the present invention will be explained in more detail using reference examples, working examples, and comparative examples.

Reference Example 1 (Production of α-FeOOH water-containing slurry) 51<g of caustic soda (NaOH) was dissolved in 50 tons of water, and separately, 60 kg of ferrous sulfate (FeSO4.7H20) was dissolved in 300 tons of water.

A caustic soda solution and a ferrous sulfate solution are mixed with stirring to precipitate a portion of Fe2+ as Fe(0H)2,
The precipitated Fe(0H)2 was then maintained under oxidative conditions for 90 minutes at a liquid temperature of 35°C with vigorous stirring to obtain α-F.
eOOH was generated. After thoroughly filtering this, it was thoroughly washed with water to obtain an α-FeOOH water-containing slurry. The obtained α-F
The eOOH particles were fine particles with a specific surface area of 90 I/7, a width direction of 0.015 μm, and a length of 0.15 μm as determined by the BET method. Example 1 5 kg of α-FeOOH water-containing slurry synthesized by the method of Reference Example 1 was dispersed in 25 tons of ethanol with stirring,
Next, 25 tons of benzene was added to the dispersion.

Distillation was carried out while adding benzene, and a ternary azeotropic mixture of water, ethanol, and benzene was distilled out at a boiling point of 64°C. When the boiling point of the three-component azeotropic distillation rose to 68°C, which is the ethanol-benzene azeotropic distillation temperature, the completion of the three-component azeotropic distillation was confirmed, τ, and the addition of benzene was stopped, and the boiling point of pure benzene was reached. Distillation was continued until the distillation temperature reached 80°C, and ethanol was completely distilled off. The obtained αFeOO
A yellow powder was obtained by drying the benzene dispersion of H at 60° C. under reduced pressure.

The amount of benzene added during distillation was 100L.
It was hot. Gas chromatogram analysis of the distillate revealed that α
It was confirmed that the water in the FeOOH water-containing slurry was completely distilled off. α-Fe thus obtained
Polish OOH powder 27 and boiled linseed oil 1W11 50 times x 2 times using a foil mala to form a paste.
The value of method A-B measured with a grind gauge according to ISK54OO was 40μ-20μ. As shown in the scanning electron micrograph of FIG. 1 (13,000x magnification), the obtained powder contained almost no aggregates and had a bright yellow color. Example 2 Instead of drying the α-FeOOH benzene dispersion under reduced pressure in Example 1, it was dried by freeze-drying to obtain a powder containing no aggregates.

Example 3 The amount of benzene added to the ethanol dispersion was 75 t,
A bright yellow powder was obtained in exactly the same manner as in Example 1, except that the amount of benzene added at the same time as the distillation was 50 tons.

Example 4 An α-FeOOH benzene dispersion prepared in exactly the same manner as in Example 3 was dried by freeze-drying.
It was dry.

Example 5 A yellow powder was obtained in the same manner as in Example 1 except that carbon tetrachloride was used instead of benzene.

Example 6 A yellow powder was obtained in exactly the same manner as in Example 1 except that allyl alcohol was used instead of ethanol.

Comparative Example 1 The α-FeOOH water-containing slurry obtained by the method of Reference Example 1 was heated and dried at 100° C. for 24 hours to obtain a brown powder.

As shown in Figure 2, a scanning electron micrograph (13,000
As a result of the measurement, it was confirmed that the powder contained block-like aggregates with a diameter of several microns. Table 1 summarizes the agglomeration state, dispersibility, color tone, and sedimentation rate in benzene of the yellow powders obtained by the methods of Comparative Example 1 and Examples 1 to 6 described above.

Next, using the α-FeOOH powder obtained in Example 1 and using a cellulose derivative as a vehicle, the pigment concentration (P.
W. C) Create a 45% Lutzker paint and apply it to a thickness of 2
The light transmittance of a coating film obtained by coating a 5μ transparent polyester film to a thickness of 40μ was measured using a photoelectric spectrophotometer (model QR-50 manufactured by Shimadzu Corporation). The results are shown in Figure 3. From this result, it was clear that the pigment obtained according to the present invention had excellent transparency.

[Brief explanation of drawings]

FIG. 1 is a scanning electron micrograph of α-FeOOH obtained by the method of the present invention, and FIG. 2 is a scanning electron micrograph of α-FeOOH obtained by the conventional method.

Claims (1)

[Claims] 1. A water-containing slurry of α-FeOOH produced by wet reaction of iron salts under oxidative conditions is (a) dispersed in a hydrophilic organic solvent that is miscible with water in any proportion, and then (b)
A hydrophobic organic solvent that is immiscible with water in any proportion but can form a three-component azeotropic distillation system with water and the above-mentioned hydrophilic solvent is added to the dispersion, and (c) water, hydrophilic organic After distilling off the water and hydrophilic organic solvent present in the system by three-component azeotropic distillation of the solvent and the hydrophobic organic solvent, (d
) A method for producing an iron oxide pigment with good dispersibility, which comprises a step of concentrating or completely removing the remaining hydrophobic organic solvent dispersion.