JP3232843B2 - Method for producing aging-resistant pigment powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the aging of a resin, for example, a resin containing chlorine, which is caused by the influence of heat applied during molding or light upon exposure to the outdoors when colored with iron oxide particles. The present invention relates to a method for producing an aging-resistant pigment powder capable of minimizing the phenomenon.

[0002]

2. Description of the Related Art In recent years, with the improvement of life and culture, not only the improvement of functional quality of products but also the appearance characteristics from sensory and hobby aspects have been demanded. There is a strong demand for kneading a colored pigment and a resin in the production of a resin molded product, and mixing and dispersing the colored pigment in a vehicle in the production of a paint.

However, a molded product obtained by kneading a color pigment with a resin is liable to undergo aging of the resin due to the effect of heat applied during molding and light during outdoor exposure, etc. due to the color pigment. Is widely known.

A typical example of a chlorine-containing resin, for example, a polyvinyl chloride resin as a chlorine-containing thermoplastic resin, is described below.

[0005] Even when the polyvinyl chloride resin is not colored using goethite particle powder, hematite particle powder, or the like, the polyvinyl chloride resin can be heated by a heat treatment applied during molding.
In addition, when exposed outdoors after being commercialized, the resin decomposes and degrades due to sunlight, causing an aging phenomenon.

The cause of such an aging phenomenon is that polyvinyl chloride resin is heated to 100 to 200 by the action of heat or light.
At a temperature of ° C., a part of the chlorine bond is decomposed to generate hydrogen chloride to form a polyene structure having a double bond, and the generated HCl acts on the resin itself secondarily, and the polymer C By breaking the -C bond or causing cross-linking in a chain.

In order to suppress the above-mentioned aging phenomenon, polyvinyl chloride resin powder for thermoforming materials is usually provided with a neutralizing agent for neutralizing hydrogen chloride generated by decomposition such as a lead compound or metallic soap, an organic tin compound, or the like. It is known to add a resin stabilizer having an effect of suppressing the formation of a double bond such as an epoxy compound.

As is well known, goethite particle powder and hematite particle powder have an action of accelerating the dehydrochlorination reaction due to Fe as a constituent element, and therefore, when mixed as a coloring agent in a polyvinyl chloride resin. In this case, the aging phenomenon of the resin is remarkably enhanced.

On the other hand, when a color pigment is mixed and dispersed in a vehicle to form a paint, the dispersibility of the color pigment is important. For example, "‥‥ Elucidation of dispersion and agglomeration and applied technology" (1992), pages 210 to 211, published by Technosystem Co., Ltd. "‥‥ Pigment dispersion means adding pigment powder to a liquid vehicle and adding fine particles. Means the process of distributing the whole vehicle, and it is easy to understand if it is divided into the following three processes (1).
Wetting of pigment particles (2) Refinement of aggregated particles (3) Stabilization of dispersion, but these processes often proceed simultaneously. These three processes are generally referred to as pigment dispersibility, but each process largely depends on the properties of the pigment surface. Therefore, understanding and controlling the properties of the pigment surface is the most important matter in selecting a pigment for formulation or producing a pigment. ‥‥ ”.

Regarding the improvement of the surface of the color pigment particles, see, for example, “Elucidation of Dispersion and Aggregation and Applied Technology,”
On pages 15 to 216, "‥‥ The surface of a pigment is coated with another substance to change various properties, and many kinds of pigments are treated. Among them, titanium dioxide is produced by using alumina, silica, or a hydrate thereof. The surface coating changes the properties of the pigment surface such as acidity, basicity, and electric charge depending on the amount and process of the treatment, and the dispersibility is also remarkably improved. It is.

[0011] Even in iron oxide pigments such as goethite and hematite, aging of the resin is suppressed, and
In order to improve dispersibility, the particle surface is coated with various inorganic compounds.

As a method of coating the particle surface of the iron oxide pigment with an inorganic compound, JP-B-54-7292 and JP-B-54-7292 in which the particle surface is coated with an Al compound or a Si compound.
No. 7295, JP-A-49-99647, JP-A-51-47923, JP-A-51-66320
JP, JP-A-53-36538 and JP-A-Hei.
Each method described in 1270 gazette is mentioned.

[0013]

The iron oxide particle powder which can minimize the aging phenomenon of the resin and has excellent dispersibility is the most demanded at present. Iron oxide pigments whose particle surface is coated with an Al compound or a Si compound by the described method,
As shown in the following comparative examples, it is hard to say that the aging phenomenon of the resin can be sufficiently suppressed, and the dispersibility is still insufficient.

Regarding dispersibility, see “Elucidation of Dispersion and Aggregation and Applied Techniques”, pp. 94-96, “‥‥ Most natural and synthetic polymers adsorb to the surface of colloid particles to form a thick adsorption layer. It has a significant effect on the stability of the dispersion system because it forms: (1) the molecular weight (M) of the polymer and the saturation adsorption (As)
In general, the following relationship holds. As = K ₁ M
^a (Applicant: Note: a in the formula is α).
₁ , α is a constant peculiar to the system, particularly α is called a molecular weight dependent parameter, and varies from 0 to 1 depending on the structure of the adsorption layer. When ‥‥ α = 1, the polymer is adsorbed at the molecular end, and As is proportional to the molecular weight (M). In this system, the polymer forms the thickest adsorbed layer on the particle surface,
It shows a strong steric repulsion effect and contributes more effectively to the stability of the dispersion system. As described in “‥‥”, it can be represented by a molecular weight-dependent parameter α (hereinafter, referred to as α).

When the particle surface is coated with an Al compound or a Si compound according to the iron oxide pigments obtained so far, in particular, as disclosed in the above-mentioned publications,
α was about 0.40 to 0.45, and it was found that α was about 0.28 to 0.34 although these coating treatments were not performed.

Therefore, the present invention has a technical problem to obtain an iron oxide pigment which can minimize the aging phenomenon of the resin and has an α of more than 0.50 and excellent dispersibility. I do.

[0017]

The above technical object can be achieved by the present invention as described below.

That is, the present invention provides an aqueous suspension containing goethite particles or hematite particles by adding an aqueous alkaline solution to adjust the pH value of the suspension to 10 or more,
l or an aqueous solution containing Si or Al and Si is added, and while stirring, the pH value of this solution is rapidly adjusted to near neutral to obtain Al or Si or a hydroxide of Al and Si.
After ultra- precipitating the ultrafine particles , the particles in the liquid are separated by filtration together with the hydroxide ultrafine particles to separate the particles from the hydroxide ultrafine particles.
After obtaining a mixture consisting of water and water, the mixture is washed with water and dried, and the mixture is washed with an edge runner at 30 to 60K.
The molecular weight-dependent parameter α value consists in fixing the oxide ultrafine particles or hydroxide ultrafine Al or Si or Al and Si on the surface of the particles by the compacting pulverized at a linear load of g / cm is 0 .50 or more
A method for producing an aging-resistant pigment powder, and adding an aqueous alkali solution to an aqueous suspension containing the particles to adjust the pH value of the suspension to 1
From the operation of 0 or more to the operation of compacting and pulverizing the mixture by an edge runner, at least twice or more, Al or Si or oxide ultrafine particles or hydroxide containing Al and Si on the surface of the particles. This is a method for producing an aging-resistant pigment powder by fixing ultrafine particles .

Next, various conditions for implementing the present invention will be described.

As the iron oxide pigment in the present invention, goethite particle powder or hematite particle powder is used, and the particle shape thereof is substantially acicular, plate-like and cubic, spherical, octahedral, polyhedral, amorphous and the like. Any of so-called granular shapes having a square shape may be used, and the surface state may be smooth or uneven.

The particle size of the goethite particle powder or hematite particle powder in the present invention is not particularly limited. In the case of acicular particles, the major axis diameter is 0.1 to 10%.
0 μm, in the case of plate-like particles, the plate surface diameter is 0.05 to 50 μ
m, and the particle size of the granular particles is 0.01 to 50 μm.

In the present invention, an aqueous alkali solution is added to an aqueous suspension containing goethite particles or hematite particles to adjust the pH value of the suspension to 10 or more, and then the Al or S
The aqueous solution containing i or Al and Si is added
This is to sufficiently and uniformly mix the particles by utilizing the electric repulsion between the particles in the aqueous suspension.

As the alkaline aqueous solution for adjusting the pH value to 10 or more, an aqueous solution of sodium hydroxide, potassium hydroxide, aqueous ammonia or the like can be used.

As the aqueous solution containing Al, an aqueous solution of an alkali aluminate such as sodium aluminate or potassium aluminate, or an aluminum salt such as aluminum sulfate, aluminum chloride or aluminum nitrate can be used.

The amount of the compound containing Al is 0.01 to 20.0% by weight in terms of Al based on the goethite particle powder or the hematite particle powder. If the amount is less than 0.01% by weight, the effects of the present invention cannot be obtained. When the content exceeds 20.0% by weight, the effects aimed at by the present invention can be obtained, but when it exceeds 20.0% by weight, the effect saturates and is not industrial. In consideration of the dispersibility, aging resistance and productivity of the target substance, the content is preferably 0.05 to 10.0% by weight.

As the aqueous solution containing Si, an aqueous solution of sodium silicate, potassium silicate, colloidal silica, No. 3 water glass or the like can be used.

The amount of the compound containing Si is determined based on the amount of SiO ₂ relative to the goethite particle powder or the hematite particle powder.
It is 0.01 to 20.0% by weight in conversion. If the amount is less than 0.01% by weight, the effects of the present invention cannot be obtained. 20.
If the amount exceeds 0% by weight, the desired effect of the present invention can be obtained, but if it exceeds 0% by weight, the effect is saturated, and it is not industrial. In consideration of the dispersibility, aging resistance and productivity of the target substance, the content is preferably 0.05 to 10.0% by weight.

In the present invention, when an aqueous mixed solution containing Al and Si is added, 0.01 to 20.0% by weight of the total amount in terms of Al and SiO _{2 based on} the goethite particle powder or the hematite particle powder, Preferably 0.05 to
10.0% by weight.

From the operation of adding an aqueous alkali solution to an aqueous suspension containing goethite particles or hematite particles to adjust the pH of the suspension to 10 or more, to the operation of compacting and pulverizing the mixture with an edge runner. Is repeated at least twice or more, the amount of addition of the compound containing Al or Si may be determined in consideration of the total amount of the respective addition amounts, and is preferably 0.05 to 10.0% by weight. It is.

The reason why the compound of Al or Si is used as an aqueous solution in the present invention is to sufficiently and uniformly mix in a suspension containing goethite particles or hematite particles having a pH value of 10 or more. Or a compound of Si as a crystal salt and sufficiently dissolved in the suspension.
They can be mixed.

In the present invention, the suspension containing goethite particles or hematite particles having a pH value of 10 or more
And an aqueous solution containing a compound of Si is added, and the pH is rapidly raised to around neutral (pH 6.5 to 8.0) while stirring the suspension.
By adjusting to 5), almost the total amount of Al and Si is rapidly precipitated as hydroxide ultrafine particles to obtain a mixture of goethite particles or hematite particles and hydroxide ultrafine particles .

[0032] The time for quick settling is in the range of 1 to 10 minutes. If the time exceeds 10 minutes, a hydroxide of Al or Si may be formed in a layer on the particle surface of the goethite particles or hematite particles. Therefore, after quick settling, it is quickly separated by filtration. It may be less than 1 minute, but it takes about 1 minute when it is precipitated as Al or Si hydroxide and sufficiently mixed.

As the acid for adjusting the pH, sulfuric acid, hydrochloric acid, acetic acid, nitric acid, carbon dioxide gas and the like can be used.

In the present invention, in addition to Al and Si, Zn, Co, Ni, V, Mg, Ca, Sr, Ba,
Bi, P, Zr, Ti, Hf, Mo, Sn, Sb, A
Compounds selected from g, Pd, Cu, Fe and the like can also be added, and water-soluble salts such as sulfate, chloride, nitrate and acetate of each element can be used.

These compounds may be appropriately combined and added in accordance with the purpose of addition and the properties of the element. The amount of the compound added is 0% in terms of each element relative to the goethite particle powder or the hematite particle powder. 0.01 to 20.0% by weight. If the amount is less than 0.01% by weight, the effects of the present invention cannot be obtained. When the content exceeds 20.0% by weight, the effects aimed at by the present invention can be obtained, but when it exceeds 20.0% by weight, the effect saturates and is not industrial. Dispersibility of the target substance,
When considering aging resistance and productivity, 0.05 to 10.
0% by weight is preferred.

In addition, it is desirable to carry out the following operation for Ca, Sr, and Ba among the above-mentioned compounds which may be eluted by washing after precipitation of almost the entire amount as hydroxide ultrafine particles . When Ca is neutralized with the above-mentioned acid other than carbon dioxide gas, the pH is adjusted and then a slight amount of carbon dioxide gas is blown in to bubble Ca ions into CaCO 2.
_{As 3} it can be made difficult to elute. When Sr is also neutralized with the above-mentioned acid other than carbon dioxide, it is possible to make it difficult to elute Sr ions as SrCO ₃ by bubbling by blowing a little carbon dioxide after adjusting the pH. Ba is desirably neutralized with sulfuric acid. When neutralized with the above-mentioned acids other than sulfuric acid, it is preferable that the pH is adjusted and sulfuric acid is used again to make it difficult to elute as BaSO ₄ .

In the present invention, a method of filtering, washing, and drying a mixture composed of goethite particles or hematite particles and hydroxide ultrafine particles may be performed according to a conventional method.

Since the above-mentioned mixture is present by interaction, filtration, washing and drying can be carried out as usual, and the workability is not particularly deteriorated.

As the edge runner used in the compaction pulverization treatment in the present invention, "Sandmill" manufactured by Matsumoto Cast Iron Works, "Mix Muller" manufactured by Shinto Kogyo Co., Ltd., or the like can be used.

The line weight of the edge runner is 15 to 80 K
a g / cm, more preferably 30~60 K g / cm
It is. In the case of less than 15 K g / cm, since shear force by the grinding is too weak, mechano-chemical effect can not be obtained.
When exceeding 80 K g / cm, the shear force by trituration is too strong, it may destroy the particles themselves.
The processing time is 15 to 120 minutes, preferably 30 to 60 minutes.

In the present invention, the operation until the mixture of goethite particles or hematite particles and hydroxide ultrafine particles is subjected to consolidation and pulverization treatment by an edge runner may be repeated at least twice, preferably 2 to 5 times. . If the number of times exceeds 5, the effect can be obtained, but the effect tends to be saturated, and it is not industrial.

[0042]

The operation of the present invention having the above-described configuration is as follows.

First, regarding the dispersibility, the reason why α of the iron oxide pigment whose particle surface is coated with an Al compound or a Si compound by the methods described in the above-mentioned publications is as low as about 0.40 to 0.45 is as follows. In order to coat the Si compound or Al compound on the particle surface, the hydroxide of the compound was precipitated over a relatively long time and uniformly coated, so that when dispersed in a polymer resin, It was thought that the adsorption point of the polymer was small.

It should be noted that the fact that deposition is performed over a relatively long period of time and uniform coating is performed is described in, for example, Japanese Patent Publication No.
JP-A-7292 describes "{Slowly add. Stirring was continued for about 30 minutes after the addition was completed""and the above-mentioned JP-A-51-47923 and JP-A-51-66320. The purpose of the present invention is to cover the surface of the iron oxide particles over a relatively long period of time as described in each example of the publication of “{stirred for 1 hour after neutralization}”.

Therefore, the present inventor studied a method of increasing the thickness of the polymer adsorption layer by increasing the number of polymer adsorption points on the surface of goethite particles or hematite particles as much as possible.

As a result, in the present invention, Al or S
Considering that ultra-fine particles of i or Al and Si oxides or hydroxides should be chemically adsorbed on the surfaces of goethite particles or hematite particles as much as possible, and a suspension containing these particles is considered. Ultrafine particles of Al or Si or hydroxides of Al and Si are uniformly precipitated and mixed therein, and the surface of the particles is Al or Si or oxides of Al and Si due to the mechanochemical effect of consolidating the mixture. Alternatively, since the ultrafine particles of hydroxide could be firmly fixed, α was 0.5
It could be increased to 0 or more. This is thought to be the result of increasing the number of polymer adsorption points on the particle surface.

Accordingly, α of each of the acicular goethite particles, the acicular hematite particles, the granular hematite particles, and the plate-like hematite particles in the present invention was about 0.50 to 0.70. is there.

An anti-aging pigment having α of 0.50 or more in which Al or Si or oxide ultrafine particles or hydroxide ultrafine particles containing Al and Si is fixed to the surface of the goethite particles or hematite particles according to the present invention. The powder has excellent dispersibility when used as a paint, and also has excellent surface smoothness when used as a coating film. Further, when the resin composition is used, the resin composition is excellent in dispersibility, so that a resin composition which is extremely uniform and has no color unevenness can be obtained.

Next, the aging resistance will be described. In the case of using the aging-resistant pigment powder according to the present invention to prepare a paint,
As described above, not only the dispersibility has been improved, but also a coating film produced by applying the coating material after forming the coating material does not show discoloration of the coating film due to aging of the resin even under a bad environment.

Further, even when a kneaded product with a resin is prepared and molded to form a sheet, the dispersibility is improved, a sheet without color unevenness is obtained, and the sheet can be used in a poor environment. No discoloration of the sheet due to aging was observed.

The aging-resistant pigment powder according to the present invention is excellent in aging resistance, as shown in the examples below, because the surface of goethite particles or hematite particles
Or because Si or Al and ultrafine particles of oxides or hydroxides of Si and Al are tightly fixed, the catalytic action on the aging of the resin having goethite particles or hematite particles is attenuated and the aging of the resin is suppressed, In addition, because it is highly dispersed and compounded in the resin, it has an excellent light and heat blocking effect, so the effect of light and heat on the resin was sufficiently suppressed. thinking.

As a method of coating the particle surface with various organic compounds disclosed in JP-A-3-221965, a method in which an organic compound having a hydrophobic group is kneaded using a wheel-type kneader or a grinder is used. , The effect of the present invention cannot be obtained.

Further, depending on the method of mixing ferric oxide powder or yellow iron oxide powder and aluminum hydroxide powder disclosed in the above-mentioned JP-A-51-47923 and JP-A-51-66320. However, the effects of the present invention cannot be obtained.

[0054]

Next, the present invention will be described with reference to examples and comparative examples.

The amounts of the respective elements of the compounds such as Al, Si, Zr and Zn fixed to the goethite particles or the hematite particles were measured by X-ray fluorescence analysis.

In the evaluation of dispersibility in the present invention, the above As
= K ₁ M ^a (Applicant: Note: a in the formula is α.)
The value of α is calculated based on the value of α for different molecular weights.
Inder (urethane tree with number average molecular weight M = 15000)
Fat, 28000 urethane resin, 42,000 urethane
(Resin) , the saturated adsorption amount (As) of each binder to the goethite particle powder or the hematite particle powder is measured by a conventional method, and the obtained As and M are plotted in a log-log table to form a linear relationship. Was obtained, and the value of α was determined from the slope of the straight line.

The surface smoothness of the coating film was determined by applying a coating prepared in the following manner in the usual manner to a cast-coated paper (manufactured by Sanyo Kokusaku Pulp Co., Ltd.) and applying the coating film to a gloss meter UGV-5.
This is a value obtained by using D (manufactured by Suga Test Instruments) as a relative value of gloss at an incident angle of 60 ° based on a value of 90.6% of a standard glossy plate.

Aging-resistant pigment powder 10 parts by weight Clear lacquer (manufactured by Kansai Paint Co., Ltd.) 16 parts by weight Varnish (manufactured by Dainippon Ink and Chemicals, Inc.) 50 parts by weight Solvent (thinner: manufactured by Kansai Paint Co., Ltd.) 6 parts by weight

With respect to aging resistance (weather resistance), the following amounts were kneaded by a conventional method to prepare a colored plastic sheet having a thickness of 1 mm, and the colored plastic sheet was cut into a size of 1.5 cm square. Then, it was left for 90 minutes at 150 ° C. under normal pressure. The degree of blackening of the sheet after 90 minutes was visually determined. As a criterion, A: no blackening was observed. B: Blackening is observed at the four corner edges of the sheet piece. C: Blackening occurred around the sheet piece. D: Blackening is observed on the entire surface of the sheet piece. Of the four-step evaluation.

Aging-resistant pigment powder 10 parts by weight Hard vinyl chloride resin (manufactured by Dainippon Ink and Chemicals, Inc.) 300 parts by weight Calcium stearate (manufactured by Yoneyama Pharmaceutical Co., Ltd.) 1 part by weight

<Surface Treatment of Particle Powder> Examples 1 to 8, Comparative Examples 1 to 6;

[0062] Using the granular hematite particles of Example 1 the particle size 0.17 .mu.m, after the powder 6 K g were mixed and stirred in water, 0.1 mol / l
Was added until the pH value reached 11.5. After stirring and mixing the mixed suspension, 0.5 mol
4444 ml (corresponding to 1.0 wt% in terms of Al with respect to hematite particle powder) of 1 / l sodium aluminate aqueous solution was added, followed by stirring and mixing. Next, a 1.0 mol / l HCl aqueous solution was added to the suspension while stirring to adjust the pH to 7.0. The required time at that time was 3 minutes. Immediately, the particles were separated by filtration, washed with water and dried by a conventional method to obtain granular hematite particles. The resulting granular hematite particles 5 K g edge runner "MPUV-2 Model"
((Stock) Matsumoto casting Iron Works, Ltd.) to be turned on line load 60 K g
/ Cm for 30 minutes. The particle size of the obtained granular hematite particles is 0.17 μm, and α
Was 0.57.

[0063] Furthermore, after mixing and stirring the water again and the resulting granular hematite particles 4.5 K g, 0.1 mol
Was added to adjust the pH to 11.0. Next, 156 g of No. 3 water glass solution (corresponding to 1.0 wt% in terms of SiO ₂ with respect to the hematite particle powder) was added thereto, followed by stirring and mixing to obtain a suspension. Then, the suspension was stirred and stirred with an aqueous 1.0 mol / l HCl solution.
H was adjusted to 7.0. The required time at that time was 5 minutes. Immediately, the particles were separated by filtration, washed with water and dried by a conventional method to obtain granular hematite particles. The resulting granular hematite particles 4 K g edge runner "MPUV-2 Model" (Co.
Was performed compaction milled for 30 minutes in Matsumoto linear load 45 was poured into the cast Ironworks) K g / cm. The particle size of the obtained granular hematite particles is 0.17 μm, and α is 0.6
It was one. The glossiness of the coating film is 88.0%,
The test result of aging resistance was A.

Examples 2 to 8, Comparative Examples 1 to 6 Except that the type of the particle powder, the type and amount of the compound to be added, the time required for addition and stirring, the linear load and time of the consolidation treatment, and the number of treatments were variously changed. In the same manner as in Example 1, an aging-resistant pigment powder was obtained.

Tables 1 to 4 show the main production conditions and the properties of the obtained aging-resistant pigment powder in each Example.

[0066]

[Table 1]

[0067]

[Table 2]

[0068]

[Table 3]

[0069]

[Table 4]

[0070]

The aging-resistant pigment powder according to the present invention has ultra-fine particles of Al or Si or oxides or hydroxides of Al and Si tightly adhered to the surfaces of goethite particles or hematite particles. The resin aging phenomenon caused by the catalytic action of the goethite particles or hematite particles on the resin aging can be suppressed to a minimum, and α is as large as 0.50 or more, which is excellent in dispersibility.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-116504 (JP, A) JP-A-7-192248 (JP, A) JP-A-7-50206 (JP, A) JP-A-7- 86016 (JP, A) JP-A-53-36538 (JP, A) JP-A-63-194728 (JP, A) JP-A-63-64920 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C09C 1/00-3/12

Claims (2)

(57) [Claims] 1. An aqueous alkali solution is added to an aqueous suspension containing goethite particles or hematite particles, and
H value is set to 10 or more, Al or Si or an aqueous solution containing Al and Si is added to the suspension, and while stirring,
The pH value of this solution was rapidly adjusted to near neutral to adjust the pH of Al or S
After the hydroxide ultrafine particles i or Al and Si is Haya沈, yield a mixture of the particles of the liquid was filtered off with a hydroxide ultrafine particles consisting of the particles and hydroxide ultrafine particles, the mixture After washing and drying, the mixture is subjected to a consolidation pulverization treatment with a line load of 30 to 60 Kg / cm by an edge runner so that Al or Si or ultrafine particles of Al and Si oxides are formed on the surface of the particles. or Yi molecular weight, characterized in that to fix the hydroxide ultrafine particles
A method for producing an aging-resistant pigment powder having a storage parameter α value of 0.50 or more . 2. An aqueous alkali solution is added to an aqueous suspension containing goethite particles or hematite particles, and
H value is set to 10 or more, Al or Si or an aqueous solution containing Al and Si is added to the suspension, and while stirring,
The pH value of this solution was rapidly adjusted to near neutral to adjust the pH of Al or S
After the hydroxide ultrafine particles i or Al and Si is Haya沈, yield a mixture of the particles of the liquid was filtered off with a hydroxide ultrafine particles consisting of the particles and hydroxide ultrafine particles, the mixture Is washed and dried, and then the mixture is subjected to a compaction pulverization treatment with a line load of 30 to 60 Kg / cm by an edge runner to produce an aging-resistant pigment powder. The operation of adding an alkaline aqueous solution to the suspension to adjust the pH value of the suspension to 10 or more to the operation of compacting and pulverizing the mixture with an edge runner is repeated at least twice or more so that the surface of the particles is Al or Si or Al and S
A method for producing an aging-resistant pigment powder, comprising fixing ultrafine oxide particles or hydroxide ultrafine particles containing i.