JPH0446019A - Production of yellow iron hydroxide pigment - Google Patents

Abstract

PURPOSE:To improve brightness in yellow color by blowing O2-contg. gas into a suspension in which precipitate of iron hydroxide (II) is dispersed to obtain geothite-type iron hydroxide seed crystal, and then oxidizing iron (II) ions with air in this suspension. CONSTITUTION:A suspension containing <=0.3mol/l iron hydroxide (II) prepared by adding an aq. soln. of alkali metal of >=8wt.% concn. to an aq. soln. containing iron (II) ion is stirred to disperse the iron hydroxide (II) precipitate. Then this dispersion liquid is maintained at 20 - 50 deg.C, into which O2-contg. gas is introduced for 5 - 20 hours to obtain a suspension containing geothite-type iron hydroxide seed crystal. Then iron ion (II) soln. is added to this seed crystal suspension and heated at 60 - 90 deg.C so that the seed crystal grows at the rate of <7X10<-5>mol/m<2>/hr per unit surface area of the seed crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a yellow hydrated iron oxide pigment that has excellent yellow color clarity.

BACKGROUND ART Inorganic pigments have traditionally been used as outdoor paints such as construction machinery and architectural paints and traffic paints such as road signs because of their excellent weather resistance and light resistance.

Among these, yellow pigments include lead chromate (yellow), cadmium sulfide, and zinc chromate (zinc yellow) in addition to hydrated iron oxide, but while these have excellent yellow color clarity, they are harmful to health due to heavy metals. Its use is restricted due to concerns about disability.

The yellow hydrated iron oxide pigment does not contain harmful ingredients and is weather resistant.
Although it is a compound with excellent light resistance, conventional yellow hydrated iron oxide pigments were not as good as other inorganic pigments such as lead chromate (yellow lead) in terms of yellow color clarity.

Therefore, it is desired to improve the yellow color sharpness of yellow hydrated iron oxide pigments, and the present invention provides a yellow hydrated iron oxide pigment with excellent yellow color sharpness by controlling the growth rate of seed crystals. It is intended to.

[Conventional technology]

Hitherto, hydrated iron oxide pigments have been mainly produced by a so-called wet process in which ferrous salts are oxidized in an aqueous solution.

(Japanese Patent Publication No. 27-786, U.S. Patent No. 2.939.
(No. 767, U.S. Pat. No. 2,388,659) This wet process uses ferrous sulfate and ferrous chloride as starting materials and neutralizes them with alkalis such as sodium hydroxide and ammonia. Step (1) of obtaining a precipitate of ferrous hydroxide, Fe”+ 2.NaOH-4Fe(OH)z + 2.
Na' ------- (1) Fine particles of hydrated iron oxide (goethite) are obtained by air oxidizing the precipitate of ferrous hydroxide produced.
Step (2) of obtaining seed crystals (hereinafter referred to as seed crystals), 44e(OH)2+ 02 →4・FeOOH+ 2・
HtO --- (2) Step of air oxidizing ferrous ions using the obtained seed crystals as nuclei to grow goethite particles (3)
The process consists of steps (4) and (4)' in which hydrogen ions generated at this time are neutralized with alkaline earth metal iron.

4 ・Fe" + Oz + 6 ・HtO→
4 ・Fe0OH+ 8 ・H= (3)H”
+OH-→H! O------(4)2・H"+
Fe −Fe” + Hz −−−−−−−(
4) Methods for obtaining yellow hydrated iron oxide pigments using ferrous sulfate as a raw material are broadly divided into two methods: a method in which hydrogen ions liberated during the growth process are neutralized with metallic iron, and a method in which they are neutralized with an alkali. .

In the method of neutralization with metallic iron, the metallic iron is dissolved in the liberated sulfuric acid and reused as ferrous sulfate. Although the ferrous sulfate is used efficiently, it is difficult to control the reaction rate, and the amount of oil absorbed, color, etc. However, there is a problem in that it is difficult to control the properties of pigments. Also,
The resulting pigment contains many polycrystalline particles, and the carbon contained in the metal iron mixes into the pigment, making it difficult to improve yellow color clarity.

On the other hand, the method of neutralizing the acid liberated during the growth process with an alkali (alkaline method) has poor utilization efficiency of ferrous sulfate, but it is relatively easy to control the reaction rate and pigment particle size, so it is stable. It has the characteristic that it is easy to obtain pigment properties. but,
Many factors can be selected as reaction conditions, such as starting raw materials, impurities in raw materials, type of neutralizing agent, concentration of ferrous sulfate, concentration of neutralizing agent, and reaction temperature. Iron oxide pigments have not yet been obtained.

Until now, efforts have been made to optimize the particle size of pigment particles and to narrow the particle size distribution within the optimum particle size range in order to obtain a hydrated iron oxide pigment with excellent yellow color clarity. (Koroku et al., Industrial Chemistry Magazine, Vo 1.66 (4) + p412-
416 (1963)) To improve the particle size distribution and crystallinity of pigment particles, for example, wet-synthesized hydrated iron oxide pigments are hydrothermally treated in an alkaline solution at 100 to 250°C. Method (Japanese Unexamined Patent Publications No. 51-115698, No. 63-64923), a part of the ferrous sulfate solution is partially neutralized with caustic soda or ammonia, and the generated ferrous hydroxide is neutralized under acidic conditions. A method of obtaining a yellow hydrated iron oxide pigment by air oxidation (JP-A-53-73497, JP-A-62-128929) has been proposed.

However, the method of hydrothermally treating a wet-synthesized hydrated iron oxide pigment in an alkaline solution at 100 to 250°C improves yellow color clarity, but requires treatment in an expensive autoclave and also uses a large amount of alkali. Therefore, it is not industrially practical.

In the method of partially neutralizing ferrous sulfate with caustic soda or ammonia and air-oxidizing the generated ferrous hydroxide under acidic conditions to obtain a yellow hydrated iron oxide pigment, seed crystals with a narrow particle size distribution are obtained. On the other hand, a method for producing a yellow hydrated iron oxide pigment with excellent yellow color clarity has not yet been disclosed due to the generation of branched particles due to twin crystals and the generation of a large amount of polycrystalline particles.

[Problem to be solved by the invention]

The purpose of the present invention is to provide a yellow hydrated iron oxide pigment with excellent yellow color clarity.In order to improve the yellow color clarity of the pigment, it is necessary to improve the filling properties of pigment particles in the coating film. To achieve this, it is ideal to control the average particle diameter of pigment particles within an optimal range, narrow the particle size distribution, and make monodisperse, single-crystal particles free from twins. There is.

However, with conventional manufacturing methods, it is difficult to sufficiently suppress the generation of twinned particles and agglomerated particles even when the average particle size is optimized, and a yellow hydrated iron oxide pigment with excellent yellow color clarity is synthesized. I haven't reached the point yet.

[Means to solve the problem]

Therefore, in order to synthesize such a yellow hydrated iron oxide pigment with excellent yellow color clarity, the present inventors have focused on optimizing the particle size,
Based on the idea that in addition to controlling particle size distribution, it is necessary to suppress the generation of twinned particles and secondary nucleation, we have developed pigment synthesis conditions, pigment aggregation, twinned particle generation, and secondary nucleation. We examined the relationship with frequency, etc.

As a result, the inventors discovered that by controlling the growth rate of seed crystals, it is possible to synthesize a pigment with significantly improved yellow color clarity, leading to the completion of the present invention.

That is, in the present invention, a suspension containing a ferrous hydroxide precipitate is stirred in a non-oxidizing atmosphere, and after the ferrous hydroxide precipitate is dispersed, an oxygen-containing gas is blown into the goethite type hydrated iron oxide. A method for producing a yellow hydrated iron oxide pigment in which a seed crystal suspension of (α-FeOOH) is prepared, and ferrous ions are air-oxidized in the presence of the seed crystal to grow the seed crystal. The speed is 7x10-'mol/m''/h per surface area of the seed crystal.
The present invention provides a method for producing a yellow hydrated iron oxide pigment characterized in that the pigment content is less than or equal to r.

The present invention will be explained in more detail below.

Seed crystals with excellent dispersibility can be obtained by adding an aqueous alkali metal hydroxide solution, such as an aqueous sodium hydroxide solution, with a concentration of 8 wt% or less to an aqueous solution containing ferrous ions, such as ferrous sulfate. A suspension containing 0.3 mol/j' or less of ferrous oxide is prepared, and the suspension is stirred in a non-oxidizing atmosphere to disperse the ferrous hydroxide precipitate. 50
It is obtained by aerating an oxygen-containing gas for 5 to 20 hours while maintaining the temperature at 'C.

Here, the BET specific surface area of the seed crystal is determined by the synthesis temperature of the seed crystal and the oxidation rate of the ferrous hydroxide precipitate, and can be controlled by the stirring conditions of the suspension, the synthesis temperature, and the air blowing rate. be.

In addition, the seed crystals are grown at 60-90°C, and the growth rate is 7 x 10-'mol/m per unit surface area of the seed crystals! /hr
The following is desirable. More preferably 5x10
-'mol/m'/hr or less. Here, the surface area of the seed crystal means the BET specific surface area of the dry powder of the seed crystal.

If the growth rate is 7×10 −'mol//hr or more, it is not preferable because the yellow color sharpness decreases.

Such a growth rate is determined by adjusting the stirring speed and air blowing so that the dissolution rate of oxygen into the seed crystal slurry is 7 x 10-'mol/m''/hr or less per total solid surface area of the seed crystals contained in the seed crystal slurry. This is achieved by setting the amount.

Hereinafter, the present invention will be explained in more detail with reference to Examples.
These are for the purpose of illustrating the invention and are not intended to limit the invention.

To evaluate the pigment, 1 g of the pigment sample was kneaded with 0.9 g of linseed oil to make a uniform paste-like pigment dispersion, and then diluted with 6 times the amount (by weight) of clear lacquer and applied to art paper. The color was measured using a color difference meter after drying.

In addition, there is a CIELAB unit as a quantitative expression of color.
Hue is expressed by three color values: L"a" and b8.

Here, the L1 value indicates brightness, the a1 value indicates redness, and the b1 value indicates yellowness. do.

Therefore, it is desirable that the yellow hydrated iron oxide has a high b″ value.It is also preferable to have a high L8 value from the viewpoint of brightness because it improves the brightness.

Example 1 Ferrous sulfate (FeSO4-7H!O) (manufactured by Wako Pure Chemical Industries (II), reagent grade 1) was dissolved in ion-exchanged water and 18.
A 2 wt % solution was prepared. In addition, sodium hydroxide (Na
OH) (Wako Pure Chemical Industries (refined, grade 1 reagent) was dissolved in ion-exchanged water to make a 5.0 wt% solution.

18. 19.6 kg of 2 wt% ferrous sulfate solution was added to 301
The mixture was filled into a stainless steel reaction tank and heated to 30°C. After the liquid temperature stabilizes, 5.0 wt% sodium hydroxide solution 7.8k
g was added from the top of the reaction tank with stirring to obtain a suspension of the neutralized product.

Nitrogen was bubbled through the suspension at a rate of 5 to 10 β/min, and a diameter of 15
After stirring for 2 hours at 25 rpm using a 0I1m stirring blade to sufficiently disperse the precipitate, nitrogen was added at 410cc/m.
The seed crystals with a BET specific surface area of 54 m'/g were oxidized for 9.3 hours by switching to air at
27.2 kg of seed crystal slurry containing g was obtained.

A separable flask was filled with 1000 g of the seed crystal slurry and 330 g of a 18.2 wt% ferrous sulfate solution.
After heating to 0℃, 2.5x1 per solid surface area of seed crystal
Seed crystal growth was performed at a growth rate of 0-11 mol/m'/hr.

Sulfuric acid liberated due to oxidation of ferrous sulfate was neutralized with an 11 wt% aqueous sodium hydroxide solution, and seed crystals were grown for 47 hours while maintaining the pH at 3.6.

After the growth, the pigment slurry was filtered, washed, and dried at 70°C for a day and night to obtain a yellow hydrated iron oxide pigment.

1 g of the hydrated iron oxide pigment and 0.9 g of boiled linseed oil were mixed using a two-bar mala (Yasuda Seiki Co., Ltd.) at 150 pounds (6
50 lines were connected with a load of 8 kg). By repeating this operation three times, a uniform paste-like pigment dispersion was prepared. The resulting paste-like kneaded material was diluted with 6 times the amount (weight) of nitrocellulose clear lacquer (Kansai Paint ■No. 26), and applied to 6 ml of double-sided art paper using a Baker-type film ab licator (Tenyu Kizai Co., Ltd.). The sample was coated to a thickness of 1,000 ml and dried at room temperature for 12 hours to prepare a sample for color value evaluation.

The color values were quantified using a Macbeth MS-2020 Plus type colorimetric spectrophotometer and compared in units of C and AB.

Table 1 shows the evaluation results of color value.

Example 2 In the same manner as in Example 1, 820 g of 18.2 wt% ferrous sulfate solution was filled into a separable flask, and heated in a hot water tank for 3
The temperature was 0°C. After the liquid temperature became stable, 365 g of 5.0 wt % sodium hydroxide solution was added from the top of the separable flask to obtain a suspension of the neutralized product.

Nitrogen was bubbled through the suspension at a rate of 500 cc/min.
After stirring for 2 hours at 550 rpm using a stirring blade of mm to sufficiently disperse the precipitate, the nitrogen was changed to air at 30 cc/min, and the suspension was oxidized for 4.8 hours to determine the BET specific surface area. 1150 g of seed crystal slurry containing 19 g of 59 m2/g seed crystals was obtained.

A separable flask was filled with 450 g of the seed crystal slurry and 750 g of a 18.2 wt% ferrous sulfate solution.
2.6X1 per solid surface area of seed crystal after heating to °C
Seed crystal growth was performed at a growth rate of 0-'mol/m2/hr.

The sulfuric acid liberated due to the oxidation of ferrous sulfate was neutralized with an 11 wt % aqueous sodium hydroxide solution, and seed crystals were grown for 69 hours while maintaining the pH at 3.6.

After the growth, the pigment slurry was filtered, washed, and dried at 70° C. for a day and night to obtain a yellow hydrated iron oxide pigment.

The obtained yellow hydrated iron oxide pigment was evaluated for color value in the same manner as in Example 1. Table 1 shows the evaluation results of color value.

Comparative Example 1 In the same manner as in Example 1, 820 g of 18.2 wt% ferrous sulfate solution was filled into a separable flask, and heated in a hot water tank for 30 minutes.
The temperature was 0°C. After the liquid temperature became stable, 365 g of 5.0 wt % sodium hydroxide solution was added from the top of the separable flask to obtain a suspension of the neutralized product.

Nitrogen was bubbled through the suspension at a rate of 500 cc/min.
Stir at 550 rpm for 2 hours using mrn stirring blade,
After sufficiently dispersing the precipitate, nitrogen was supplied at 30cc/min.
By switching to air and oxidizing the suspension for 4.1 hours, 1150 g of a seed crystal slurry containing 19 g of seed crystals with a BET specific surface area of 67 m''/H was obtained.

A separable flask was filled with 225 g of the seed crystal slurry and 975 g of 18.2 wt% ferrous sulfate solution, and
After the temperature was raised to °C, air was aerated, and the seed crystals were grown at a growth rate of 8.2 x 10''mol/m''/hr per solid surface area of the seed crystals.

The sulfuric acid liberated due to the oxidation of ferrous sulfate was neutralized with an 11 wt % aqueous sodium hydroxide solution, and seed crystals were grown for 61 hours while maintaining the pH at 3.6.

After the growth, the pigment slurry was filtered, washed, and dried at 70°C for a day and night to obtain a yellow hydrated iron oxide pigment.

The obtained yellow hydrated iron oxide pigment was evaluated for color value in the same manner as in Example 1. Table 1 shows the evaluation results of color value.

Table 1 Growth rate Color Phase xl, o-5mol/m2/hr L ” a ”
b ”Example 1 2.5 60 18
54 Example 2 2.6 60 18
55 Comparative Example 1 8.2 '58 19
50 [Effects of the Invention] According to the present invention, it is possible to obtain a yellow hydrated iron oxide pigment with excellent yellow color clarity, which cannot be obtained with conventional yellow hydrated iron oxide pigments.

Claims (1)

[Claims] The suspension containing the ferrous hydroxide precipitate is stirred in a non-oxidizing atmosphere, and after the ferrous hydroxide precipitate is dispersed, an oxygen-containing gas is blown into it to form a goethite-type hydrated iron oxide (α-FeOO).
H) In the method for producing a yellow hydrated iron oxide pigment, the seed crystal suspension is prepared and ferrous ions are air-oxidized in the presence of the seed crystal to grow the seed crystal. A method for producing a yellow hydrated iron oxide pigment, which is carried out at a rate of 7x10^-^5 mol/m^2/hr or less per surface area.