JPS61111925A - Production of granular goethite particle powder - Google Patents

Abstract

PURPOSE:To obtain the titled particle powder, by reacting an aqueous solution of a ferrous salt with an aqueous solution of an alkali, adding a goethite seed crystal to the resultant suspension containing ferrous hydroxide, and passing an oxygen-containing gas through the suspension under specific condition. CONSTITUTION:An aqueous solution of a ferrous salt is made to react with an aqueous solution of an alkali, and the obtained suspension containing ferrous hydroxide and having >=11pH is oxidized by passing an oxygen-containing gas through the suspension to obtain the objective goethite particle. The process is carried out as follows. A fusiform goethite particle (preferably having an aspect ratio of <=4:1 and containing 0.1-20atom% Si based on Fe) is added as a seed crystal in the suspension containing ferrous hydroxide in an amount of preferably 30-90wt% based on the produced particles, and an oxygen- containing gas is passed through the suspension at a rate to effect the oxidization of the ferrous hydroxide at a rate of 1X10<-8>-1X10<-4>mol/l. The seed crystal is grown by this process to obtain the titled powder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The object of the present invention is to obtain a rice-grain-like goethite particle powder in which dendritic particles are not mixed at all and the particle size is uniform.

Note that, unlike the spindle-shaped type in which both ends of the long axis form an acute angle, the rice grain shape is different from the spindle shape in which both ends of the long axis form an acute angle, as seen in the electron micrograph in the example below. It is not sharp and has a rounded overall shape, in other words, it has an elliptical shape, literally resembling the shape of a rice grain after milling.

Its main use is as a starting material powder for producing yellow pigment powder for paints and magnetic iron oxide particle powder for magnetic recording.

[Prior art]

Goethite particles are widely used as yellow pigments, and from the viewpoint of improving work efficiency and improving the physical properties of paint films in the era of energy conservation, it is necessary to improve the dispersibility of goethite particles in vehicles when manufacturing paints. but,
It is increasingly requested.

When manufacturing paints, whether or not the pigment powder is dispersed well into the vehicle is an important factor that not only affects the work efficiency in the paint manufacturing process but also determines the various physical properties of the paint film. becomes.

This can be seen, for example, in the Journal of the Coloring Materials Association, Vol. 49, No. 1 (197
This is clear from the following statement on page 8 of 6th year).

``...It is no exaggeration to say that the various properties that a paint film should have are largely determined by the dispersibility of the pigment in the paint film in the case of ftR materials. Theory teaches that if the dispersibility of the pigment in the coating film is good, the color tone will be clear and the fundamental properties of the pigment, such as coloring power and impregnation power, will also improve. The gloss, sharpness, mechanical properties, and air resistance of the coating film are improved, which improves the durability of the coating film.In this way, the dispersibility of pigments in the coating film is improved. It can be understood that this is an extremely important factor that determines the various physical properties of the film.'' In order to improve the dispersibility of pigment powder in the vehicle,
It is known that the particle size of the pigment powder is uniform, and in terms of shape, it is preferable to have a grain-like shape rather than a needle-like shape. This fact is explained, for example, in JP-A No. 58-49693, which states, "It affects the strength etc.",
``The ideal pigment is a powder with a narrow particle size distribution.Furthermore, it is desired that the pigment has a small axial ratio of acicular particles, has good dispersibility, and has low oil absorption.''
and “Rice grain-shaped yellow iron oxide (goethite) is
Compared to needle-shaped ones of the same color, it has lower oil absorption and bulk.
It is easy to disperse and has a low viscosity when dispersed. It is clear from the statement ``.

On the other hand, goethite particles are also widely and generally used as a starting material powder for magnetic iron oxide particles for magnetic recording.

In recent years, as magnetic recording and reproducing equipment has become smaller and lighter, there has been an increasing need for higher performance magnetic recording media such as magnetic tapes and magnetic disks. That is, improvements in various properties such as high density recording properties, high output properties, high sensitivity properties, and frequency properties are required.

Output characteristics of magnetic recording media such as magnetic tapes and magnetic disks,
The intensity characteristic depends on the residual magnetic flux density Br, and the residual magnetic flux density Br depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property.

In order to improve the dispersibility in the vehicle, the orientation and filling properties in the coating film, the magnetic particles to be dispersed in the vehicle must not contain dendritic particles, and
It is required that the particle size be uniform.

Furthermore, regarding the shape of the magnetic particles that are dispersed into the vehicle, it is known that a grain-like shape rather than a needle-like shape can improve the filling property in the coating film. This fact is clear from the fact that, for example, in Japanese Patent Publication No. 47-40758, "In Fig. 1 j, the packing density is larger than that of the song!
The horizontal axis shows the blending ratio of magnetic materials in the binder (vehicle) in weight%.
And the packing density (gr/cc) is plotted on the vertical axis.
In the figure, curved green A indicates the case where needle-shaped magnetic iron oxide particles are dispersed in the vehicle, and curve B indicates the case where rice grain-shaped magnetic iron oxide particles are dispersed in the vehicle.

Currently, acicular magnetite particles or acicular maghemite particles are used as magnetic recording materials. These reactions are generally carried out by air oxidation of a colloidal aqueous solution containing ferrous hydroxide particles obtained by reacting a ferrous salt aqueous solution with an alkali and having a pH of ti or higher.
It is called.

) are reduced to acicular magnetite particles in a reducing gas such as hydrogen at 300 to 400°C, or are then oxidized in air at 200 to 300°C to form acicular maghemite particles. It is obtained by doing.

As mentioned above, grain-like magnetic particle powder with uniform particle size and no dendritic particles is currently in the greatest demand, and in order to obtain magnetic particle powder with such characteristics, The goethite particles, which are the starting materials, are grain-like and do not contain dendritic particles, and
It is necessary that the particle size is uniform.

Conventionally, the most typical known method for producing acicular goethite particles in an alkaline region with a pH of 11 or higher is a solution containing ferrous hydroxide particles obtained by adding an equivalent or more aqueous alkaline solution to a ferrous salt solution. Acicular goethite particles are obtained by performing an oxidation reaction at a temperature above puu and below 80°C.

[Problem that the invention seeks to solve]

There is currently a demand for grain-like goethite particles that do not contain dendritic particles and have a uniform particle size, but the goethite particles obtained by the above-mentioned known method are as follows: Due to the goethite production mechanism described in detail, dendritic particles are mixed, and in terms of particle size,
It is difficult to say that the particles had a uniform particle size.

The reason for the formation of goethite particles in which dendritic particles are mixed and the particle size is asymmetric will be discussed below.

Generally, goethite particles are produced through two steps: generation of goethite nuclei and growth of the goethite nuclei.

Goethite nuclei are generated by the reaction between ferrous hydroxide particles obtained by reacting a ferrous salt aqueous solution and an alkaline aqueous solution with dissolved oxygen, but according to the above-mentioned public and known method,
Because the contact reaction between ferrous hydroxide particles and dissolved oxygen is partial and non-uniform, the generation of goethite nuclei and the growth of cough goethite nuclei occur at the same time. Since new nuclei are generated in
It is thought that the particle size becomes asymmetric.

In this way, acicular magfutite particles or acicular maghemite particles obtained by reducing and oxidizing goethite particles in which dendritic particles are mixed and the particle size is asymmetric also contain dendritic particles, Moreover, the particle size becomes asymmetric.

When a magnetic recording medium is manufactured using such magnetic particle powder, the dispersibility in the vehicle, the orientation and filling properties in the coating film are poor, and the residual magnetic flux density is therefore reduced. .

Conventionally, various methods have been attempted to obtain goethite particles with less dendritic particles.

For example, Japanese Patent Publication No. 51-86795 and Japanese Patent Publication No. 55
There is a method described in Japanese Patent No.-23215. Japanese Patent Application Publication No. 1973-
The method described in Japanese Patent Publication No. 86795 is to obtain acicular goethite particles by oxidizing ferrous hydroxide particles at a low rate, and the method described in Japanese Patent Publication No. 55-23215 is to obtain acicular goethite particles by oxidizing ferrous hydroxide particles at a low rate. Particles in a strong alkali i8 at a temperature of 20°C or higher and 40°C or lower? (Acicular goethite particles are obtained by air oxidation in l.

However, each method attempts to suppress the generation of dendritic particles as much as possible, and cannot completely eliminate the generation of dendritic particles.

In fact, Japanese Patent Application Laid-Open No. 51-86795 states, ``The present invention oxidizes a gel-like white precipitate of Fe(OH)z at a low rate to produce α-FeO.OH with less side 1 (dendritic particles).
(Goethite) is characterized by the creation of...
Japanese Patent Publication No. 55-23215 states, ``The present invention relates to a method for producing acicular goethite crystals with less branching (dendritic particles).''
It is stated that.

As is clear from the above, when goethite is produced by a known method, due to its production mechanism, dendritic particles are essentially mixed and the particle size is asymmetric.
There is a strong demand for establishing a method for producing goethite particles that are completely free of dendritic particles and have uniform particle sizes.

Furthermore, according to the known method, the obtained goethite particles have an acicular shape, and there is a strong desire to establish a method for producing rice-grain-like goethite particles.

Conventionally, the method of obtaining rice granular goethite particles is as follows:
For example, there are methods described in the above-mentioned Japanese Patent Publication No. 47-40758 and the above-mentioned Japanese Patent Application Laid-open No. 58-49693.

Is the method described in Japanese Patent Publication No. 47-40758 a goethite particle production reaction? 8I &, citric acid, tartaric acid,
Oxycarboxylic acids such as malic acid and oxymalonic acid,
One or more of these alkali salts are added.

Japanese Unexamined Patent Publication No. 58-. The method described in Publication No. 49693 is 30
A ferric salt aqueous solution is added and mixed into an alkaline aqueous solution at a temperature below ℃ to prepare ferric hydroxide.
It involves hydrothermal treatment and requires special equipment such as an autoclave.

[Means for solving problems]

The present inventor has found that dendritic particles are not mixed at all, and
As a result of various studies on how to obtain rice-grain-like goethite particles with uniform particle size, a suspension containing ferrous hydroxide with a pH higher than 100 ml was obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution. In the method for producing goethite particles by oxidizing the particles by passing an oxygen-containing gas through the particles, After spindle-shaped goethite particles are present as seed crystals in the IA solution, the ferrous hydroxide is 1.0X10-" to 1.OX10-' per minute.
It is said that when oxygen-containing gas is aerated so as to oxidize at a ratio of mol/1, it is possible to obtain rice grain-like goethite particles in which all dendritic particles are not mixed and the particle size is uniform. I gained completely new knowledge.

That is, the present invention produces goethite by passing an oxygen-containing gas through a suspension containing all 11 or more ferrous hydroxides obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution. In the method for producing particles, after spindle-shaped goethite particles are present as seed crystals in the suspension containing the ferrous hydroxide, the ferrous hydroxide is absorbed at a rate of 1.0×10− per minute. @~1. OX 10-'mol/1
This is a method for producing rice-grain-like goethite particles, which comprises producing rice-grain-shaped goethite particles by growing the seed crystal particles by passing an oxygen-containing gas so that they are oxidized at a ratio of .

[For production]

First, the goethite particles according to the present invention are rice-grain-like particles with no dendritic particles mixed therein and uniform particle size. It has the characteristic that no particles are generated at all.

In the case of the present invention, the present inventor has explained why it is possible to generate goethite particles with no dendritic particles mixed at all and whose particle size is uniform. When spindle-shaped goethite particles are present, the spindle-shaped goethite particles themselves do not contain any dendritic particles and are uniform in particle size. It is believed that this is because the epitaxial growth occurs with the core forming the nucleus.

Furthermore, in the case of the present invention, unlike in known methods, the generation of goethite nuclei and the growth of the nuclei do not occur simultaneously, and the seed crystal particles become goethite nuclei and only the goethite growth reaction occurs. I think it is 1.5 that occurs.

Furthermore, in the case of the present invention, the present inventor has investigated why the particle shape of the generated goethite particles is rice grain-like by controlling the growth reaction rate of the seed crystal particles by adjusting the oxidation rate of ferrous hydroxide. It is believed that this is because by suppressing the growth reaction, the growth reaction can be caused while maintaining the particle morphology of the spindle-shaped goethite particles that are the seed crystal particles.

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

As the ferrous salt aqueous solution in the present invention, ferrous sulfate aqueous/8 liquid, ferrous chloride aqueous solution, etc. can be used.

As the alkaline aqueous solution in the present invention, sodium hydroxide, potassium hydroxide, etc. can be used.

The spindle-shaped goethite particles of the present invention can be 4+H-treated by the following method.

Goethite particles exhibiting a spindle shape can be obtained by oxidizing an aqueous solution containing FeCO obtained by reacting an aqueous ferrous salt solution with an alkali carbonate by passing an oxygen-containing gas through the aqueous solution containing FeCO. . In this case, the axial ratio (long axis: short axis) of the spindle-shaped goethite particles obtained is 6.1 to 7:
It is about 1.

As described above, the present invention causes epitaxial growth using spindle-shaped goethite particles as seed crystal particles while maintaining the particle morphology of the nuclide crystal. Axial ratio (long axis:
The shape of the rice grain-like goethite particles produced differs depending on the short axis).

[! 11, because the larger the axial ratio (long axis: short axis) of spindle-shaped goethite particles, the larger the axial ratio (long axis: short axis) of the rice grain-like goethite particles that are produced tends to be. , goethite particles exhibiting a spindle shape with an axial ratio that matches the axial ratio of the target goethite particles may be selected.

In recent years, in order to achieve high-density recording, a method has been proposed in which the medium has an isotropic direction of easy magnetization in a magnetic recording medium.

In order to make the medium have an isotropic direction of easy magnetization in the magnetic recording medium, it is necessary to orient the magnetic iron oxide particles three-dimensionally and randomly in the coating film. For such magnetic iron oxide particles, it is effective that the axial ratio (major axis; short axis) is as small as possible. When the axial ratio is large, it is easy to line up in the longitudinal direction in the magnetic recording medium (,
Random orientation is difficult.

The present inventor has been involved in the production and development of goethite particles for many years, and in the process, he developed a technology to obtain goethite particle powder exhibiting a spindle shape with a small axial ratio (major axis: short axis). has already been established (Special application 1982-2)
No. 00621).

That is, goethite particles exhibiting a spindle shape with a small axis ratio (major axis: minor axis) are obtained by aerating a ferrous salt aqueous solution, an alkali carbonate, and an oxygen-containing gas in the method for producing spindle-shaped goethite particles described above. FeC0z before oxidation reaction
It can be obtained by adding 0.1 to 20 atomic % of water-soluble silicate in terms of S + based on Fe to any aqueous solution containing Fe.

In this case, as the amount of Si added increases, the axis ratio (major axis: short axis) of the spindle-shaped goethite particles produced tends to decrease, and when Si is added in an amount of 0.1% or less, can make the axial ratio of the produced goethite particles 4:1 or less, and when it is added in an amount of 0.3% or more, the axial ratio of the produced goethite particles can be made 2=1 or less.

If the present invention is carried out using the thus obtained spindle-shaped goethite particles with a small axial ratio as seed crystal particles,
It is possible to obtain rice-grain-like goethite particles that have a small axial ratio and are completely free of dendritic particles.

The abundance of spindle-shaped goethite particles, which are seed crystal particles in the present invention, is 30 to 30% of the generated goethite particles.
It is 90% by weight.

If the amount is less than 30% by weight, new goethite core particles are generated simultaneously with the epitaxial growth of the seed crystal particles, making it impossible to obtain the rice grain-like goethite particles that are the object of the present invention.

If it is more than 90% serious, f! The epitaxial growth of the Li crystal grains is insufficient, making it impossible to obtain the rice-grain-like goethite grains that are the object of the present invention.

The goethite particles exhibiting a spindle shape in the present invention must be present before the growth reaction of seed crystal particles occurs, and a ferrous salt aqueous solution, an alkaline aqueous solution, or an oxygen-containing gas is aerated therein. It can be present anywhere in the suspension containing ferrous hydroxide before carrying out the oxidation reaction.

The oxidation rate of ferrous hydroxide in the present invention is at a rate of 1.0 X 10-@ to 1.0 X 10-' moles/1 per minute.

If it is less than 1, OX 10-'' mole/1, granular magnetite particles will be mixed in the rice granular goethite particles.

1, OX 10-'mol/7! In the above case, strip-shaped goethite particles are produced, and it is impossible to obtain the rice-grain-shaped goethite particles that are the object of the present invention.

〔Example〕

Next, the present invention will be explained with reference to Examples and Comparative Examples.

In addition, the axial ratio (long axis short axis) and long axis of the particles in the following Examples and Comparative Examples are both shown as average values of numerical values measured from electron micrographs.

The amounts of Si, Co and Ni in the particles were measured using a Fluorescent X-ray analyzer 3063 M type J (Rigaku Denki Kogyo model).
It was measured by performing fluorescence X-ray analysis in accordance with the "General Rules for Fluorescence X-ray Analysis" of the former IS 19.

Example 1 Ferrous sulfate aqueous solution 2 containing Fe” 0.10 real
51 was added to a 5,2-N Na0II aqueous solution 251 previously prepared in a reactor, and ferrous hydroxide particles were generated at pi 13.3 and a temperature of 45°C.

Goethite particles exhibiting a spindle shape with a long axis of 0.1 μm and an axial ratio (long axis/short axis) of 4:1 as shown in the electron micrograph (X 20000) in Figure 1 were added to the aqueous solution containing the ferrous hydroxide particles. After adding 1632 g (corresponding to 88% of the produced rice granular goethite) and stirring and mixing, the mixture was heated to a temperature of 5.
The goethite growth reaction was carried out at 5° C. by blowing 11 air per minute for 28 hours (the oxidation rate of ferrous hydroxide corresponds to 3×10 −mmol/1 per minute).

The end point of the oxidation reaction was determined at 9% of the blue coloring reaction of Fe'' using a red blood salt solution after a portion of the reaction solution was taken out and acidified with hydrochloric acid.

The generated particles were washed with water, separated, dried, and pulverized using conventional methods. As is clear from the electron micrograph (X 50000) in FIG. 2, the obtained goethite particles have a long axis of 0.10
μm, rice grain-like particles with an axial ratio (major axis: short axis) of 3.1,
There were no dendritic particles mixed in at all, and the particle size was uniform.

Examples 2 to 13 Types, amounts, and timing of addition of spindle-shaped goethite particles, temperature during goethite growth reaction, type and concentration of ferrous salt aqueous solution, type and concentration of alkaline aqueous solution, ferrous hydroxide The goethite growth reaction was carried out in the same manner as in Example 1, except that the oxidation rate was varied.

Table 1 shows the main manufacturing conditions and characteristics at this time.

As a result of electron microscopy observation, the obtained goethite particles were all grain-like particles with no dendritic particles mixed therein, and the particle size was uniform.

A particle size distribution diagram of the goethite particles obtained in Example 6 is shown in FIG.

Comparative Example I An aqueous ferrous sulfate solution containing 0.60 mol/j! of ferrous sulfate/l!25ffi was prepared and added to 251 of a 5,2-N aqueous NaOH solution provided in a reactor at a pH of 1.
3.3. Ferrous hydroxide particles were generated at a temperature of 45°C.

A goethite production reaction was carried out by passing air through the aqueous solution containing the ferrous hydroxide particles at a rate of 150 l/min for 12 hours at a temperature of 55°C.

At the end of the oxidation reaction, a portion of the reaction solution is extracted, adjusted to acidic with hydrochloric acid, and then treated with a red blood salt solution to remove Fe''.

Judgment was made based on the presence or absence of a blue color reaction.

The generated particles were crushed by washing with water, door to door, drying, and pulverization using conventional methods.

As is clear from the electron micrograph (x 20000) shown in FIG. 5, the obtained acicular goethite particles have a long axis of 0.
．． The 7μ-1 axis ratio (long axis: short axis) was 10:1, dendritic particles were mixed, and the particle size was asymmetric. FIG. 6 shows a particle size distribution diagram of this particle powder.

Comparative Example 2 A particle production reaction was carried out in the same manner as in Example 1, except that the oxidation rate of ferrous hydroxide was 5XIO-t mol/1 per minute.

The obtained particle powder is shown in the electron micrograph (x
20000), rice granules and granular particles were mixed together. Moreover, as a result of XvA diffraction, this particle powder was a mixed particle of goethite and magnetite.

Comparative Example 3 The oxidation rate of ferrous hydroxide was 2.5X per minute, 10-
The growth reaction of goethite particles was carried out in the same manner as in Example 6 except that the ratio was mol/1.

The scented goethite particle powder is an electronic type 1i shown in FIG.
iI! As is clear from the mirror photo (x 50,000), it was a short-term condition.

〔effect〕

According to the method for producing goethite particles according to the present invention, as shown in the above-mentioned example, goethite particles having a rice grain shape with no dendritic particles mixed therein and uniform particle size are produced. Obtainable.

When the rice grain-like goethite particles powder described above is used in the production of paint, it is well dispersed in the vehicle, making it possible to improve paint film properties such as gloss, clarity, and durability. , work efficiency will also improve.

In addition, using the rice granular goethite particle powder as a starting material,
Magnetite particle powder and maghemite particle powder obtained by thermal reduction or further oxidation are also magnetic iron oxide particle powders that do not contain any dendritic particles and have a uniform particle size and have a rice grain shape. Therefore, it is suitable as a magnetic material for magnetic recording, which is currently most in demand.

In particular, the magnetic iron oxide particles obtained by heating or further oxidizing the rice granular goethite particles with a small axial ratio (long axis: short axis) according to the present invention as a starting material also have a small axial ratio (major axis: short axis). Since the long axis: short axis) is small, when dispersed in a magnetic recording medium, it is easy to orient it three-dimensionally at random, making it suitable as a magnetic material for high-density recording. In addition, when this magnetite particle powder or maghemite particle powder is used in the production of magnetic paint,
It has good dispersibility in a vehicle, excellent orientation and filling properties in a coating film, and a desirable magnetic recording medium can be obtained.

The effects of the present invention described above are due to the addition of Co, Mg, ^1. Cr.

F of Zns N+-, Ti, Mn, Sn, Pb, etc.
It also works effectively when metals other than e are added.

[Brief explanation of the drawing]

1, 2, 5, 7, and 8 are electron micrographs showing the particle structure of the powder particles, and FIG. 1 shows the spindle-shaped seed crystal particles used in Example 1. Electron micrograph of goethite particles powder (x 20,000)
, FIG. 2 is an electron micrograph (X5QOOO) of the rice grain-like goethite particles obtained in Example 1, and FIG. 5 is an electron micrograph (X5QOOO) of the acicular goethite particles obtained in Comparative Example 1.
20000), FIG. 7 is an electron micrograph (X2QOOO) of the particles obtained in Comparative Example 2, and FIG. 8 is an electron micrograph (X2QOOO) of the particles obtained in Comparative Example 3.
Electron micrograph of the rectangular goethite particles obtained in (x
50,000). 3, 4, and 6 all show the particle size distribution of goethite particles. FIG. 3 shows the rice-grain-like goethite particles obtained in Example 1, and FIG. 4 shows the rice-grain-like goethite particles obtained in Example 6. Powder 2 FIG. 6 shows the acicular goethite particle powder obtained in Comparative Example 1.

Claims (3)

[Claims] (1) Goethite particles are produced by passing an oxygen-containing gas through a suspension containing ferrous hydroxide with a pH of 11 or more obtained by reacting an aqueous ferrous salt solution and an aqueous alkaline solution to oxidize it. In the method, after spindle-shaped goethite particles are present as seed crystals in the suspension containing the ferrous hydroxide, the ferrous hydroxide is absorbed at a rate of 1.0×1 per minute.
By aerating an oxygen-containing gas so that the seed crystal particles are oxidized at a rate of 0^-^8 to 1.0 x 10^-^4 mol/l and growing the seed crystal particles, goethite having a rice grain shape is produced. A method for producing rice granular goethite particle powder, which is characterized by producing particles. (2) The method for producing rice grain-like goethite particles according to claim 1, wherein the amount of spindle-shaped goethite particles is 30 to 90% by weight based on the produced rice grain-like goethite particles. (3) The seed crystal grain has an axial ratio (long axis: short axis) of 4:1 or less, and contains 0.1 to 20.0 at% of Si to Fe.
The method for producing rice-grain-like goethite particles according to claim 1 or 2, which contains goethite particles exhibiting a spindle shape.