JPH0522652B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention has a bulk density of 0.40 to 1.10 g/cm ³ and contains 0.1 to 5.0 at% of Si relative to Fe,
The present invention also relates to a spherical maghemite particle powder made of spherical maghemite particles that have excellent temperature stability and excellent dispersibility, and a method for producing the same.

Its main uses are brown pigment powder for paints and material powder for magnetic toners for electrostatic copying.

[Prior art]

Conventionally, maghemite particles have been widely used as a brown pigment, and from the viewpoint of improving work efficiency and improving the physical properties of paint films in the energy-saving era, improvements in the dispersibility of maghemite particles in vehicles are used in the production of paints. but,
It is increasingly requested.

In the production of paints, whether or not the dispersibility of the pigment powder in the vehicle is good is an extremely important factor that not only affects the efficiency of the paint manufacturing process but also determines the various physical properties of the paint film.

This is clear, for example, from the following statement on page 8 of the Coloring Materials Association Journal, Vol. 49, No. 1 (1976).

“...The various characteristics that a paint film should have are summarized as follows:
It seems no exaggeration to say that, for the same pigment, the dispersibility of the pigment in the coating film largely determines the dispersibility of the pigment. 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 inherent to the pigment, such as coloring power and impregnation power, will also improve. Furthermore, the gloss, sharpness, mechanical properties, and air permeability of the coating film are improved, which results in improved durability of the coating film. It can thus be understood that the dispersibility of pigments in a coating film is an extremely important factor in determining the various physical properties of the coating film. On the other hand, the spread of electrostatic copying machines has been remarkable in recent years, and along with this, research and development of magnetic toner, which is a developer, is active, and improvements in its properties are required.

For example, JP-A-54-122129 describes the following. “...Magnetic toner has a considerable amount of magnetic fine particles mixed in the toner binder, but magnetic fine particles generally have poor dispersibility in the toner binder resin.
In manufacturing, it is difficult to obtain a uniform toner without variations, and furthermore, insulating toners cause a decrease in the electrical resistance of the toner. ”Furthermore, the special public
Publication No. 21656 states that it is possible to "obtain appropriate magnetism necessary for visualization of electrostatic latent images by uniformly distributing iron oxide throughout the developer particles." There is.

Magnetic toner is produced by heating, melting, and kneading magnetic particles such as maghemite particles and resin, cooling and solidifying them, pulverizing them, and then passing them through a heated hot air stream in the form of a spray to form a spheroid. It is manufactured by Further, during development, heat fixing or pressure fixing is performed to fix the magnetic toner.

Therefore, as mentioned above, maghemite particles, which are the material powder for magnetic toner, are exposed to high temperatures during the production and development of magnetic toners, and when the brown maghemite particles reach a high temperature of about 550°C, they turn into hematite and turn reddish brown. Maghemite particles with excellent temperature stability are required because they lose their magnetism at the same time as they change color, and their saturation magnetization, for example, decreases to about 5 emu/g.

Conventionally, as a manufacturing method for maghemite particle powder, a starting material is extracted from an aqueous solution by passing an oxygen-containing gas through a reaction aqueous solution containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an alkali. A method is known in which magnetite particles are produced as particles and then the magnetite particle powder is heated in air.

It is known that the particle shape of magnetite particles produced from an aqueous solution in the production of the above-mentioned maghemite particle powder varies depending on the pH of the reaction aqueous solution.

In other words, this fact is based on the Powder Metallurgy Association 1971 Autumn Conference Lecture Summary Collection, page 112, lines 14-19: Sodium aqueous solution (40~
44g/0.3) was added, the temperature was raised to 50°C, and the temperature was maintained for 5 hours to obtain fine particles. The pH was changed to change the external shape of the particles. PH is controlled by the amount of sodium hydroxide, and condensed hexahedral particles are produced on the acidic side (NaOH40-41g/0.3), and on the alkaline side (more than 43g/0.3).
) to the octahedral particles near neutrality (NaOH42g/
0.3), polyhedral, nearly spherical particles were obtained. ” and the claims of Japanese Patent Publication No. 44-668, “…an aqueous solution containing Fe(OH) ₂ colloid with a pH of 10 or higher is maintained at a temperature of 45°C or higher and 70°C or lower,
By carrying out an oxidation reaction while the precipitate particles present in the liquid are in sufficient motion due to stirring, a precipitate consisting of black ferromagnetic particles (magnetite particles) with a granular or cubic (hexahedral) shape is produced. It is clear from the statement "...".

[Problem that the invention seeks to solve]

Maghemite particles with excellent dispersibility and temperature stability are currently in the greatest demand, but the powder particles obtained by the above-mentioned known methods for producing maghemite particles are still lacking in excellent dispersibility and temperature stability. It's hard to say that there is.

The present inventor has discovered that in order to obtain maghemite particles with excellent dispersibility, it is necessary that the particles exhibit a spherical shape with a large bulk density and have a uniform particle size. In order to obtain this, we thought that it is necessary that the magnetite particles, which are the starting material particles, have a spherical shape with a large bulk density, and that the particle size is uniform.

Furthermore, the present inventor has found that as the sphericity of maghemite particles is improved, the contact points between particles become smaller, so there is no aggregation between particles, and the bulk density increases, resulting in better dispersion. We thought that it would be necessary to improve the sphericity of the magnetite particles, which are the starting material particles.

On the other hand, as mentioned above, it is known that magnetite particles exhibiting a spherical shape are generated in aqueous solutions near neutrality, but in this case, the total amount of Fe ²⁺ in the ferrous salt aqueous solution It is difficult to convert Fe ²⁺ into magnetite particles, and unreacted Fe 2+ remains, resulting in a low yield. Furthermore, unreacted Fe ²⁺ causes wastewater pollution, so countermeasures were needed.

In order to generate magnetite particles from the total amount of Fe ²⁺ in a ferrous salt aqueous solution and increase the yield, it is necessary to react the ferrous salt aqueous solution with an alkali equivalent of 1 equivalent or more to the ferrous salt aqueous solution. In this case, it becomes an alkaline reaction aqueous solution with a pH of about 11 or higher,
Since the produced magnetite particles were hexahedral or octahedral particles, their bulk density was small.

Conventionally, as a method for producing spherical magnetite particles from the total amount of Fe ²⁺ in an aqueous ferrous salt solution, there is, for example, a method described in JP-A-49-35900.

That is, the method described in Japanese Patent Application Laid-open No. 49-35900 is as follows:
To a ferrous salt aqueous solution or a mixed aqueous solution of a ferrous salt and a water-soluble salt of a divalent metal (such as Co ⁺² ), add an alkali metal carbonate in an amount equal to or less than the acid radical contained in the aqueous solution. , a first step of performing an oxidation reaction at a temperature below the boiling temperature to generate a ferromagnetic particle matrix, and a sufficient amount so that all of the unreacted metal ions remaining in the solution are precipitated on the ferromagnetic fine particle matrix. The second step consists of producing ferromagnetic fine particles (MO Fe ₂ O ₃ M: Fe ⁺² or Co ⁺² ) by adding an alkali metal hydroxide.

However, as shown in Comparative Example 3 described later, the spherical magnetite particles obtained by the above method have insufficient sphericity, and therefore, the generated particles have an insufficient sphericity. They are intertwined with each other, have a small bulk density, and have asymmetric particle sizes. This is because the magnetite particles obtained by the method described in JP-A-49-35900 are produced by a hydrolysis reaction of iron carbonate obtained from ferrous sulfate and an alkali metal carbonate in the first step. It is thought that because the magnetite core particles were rapidly precipitated and formed, the shape could not be controlled sufficiently.

As mentioned above, there is a strong desire to establish a method for producing spherical magnetite particles with improved [-] sphericity at a high yield.

[Means for solving problems]

The present inventor has arrived at the present invention as a result of various studies on a method for producing maghemite particles exhibiting a spherical shape with improved [-] sphericity in a high yield.

That is, the present invention has a bulk density of 0.40 to 1.10 g/cm ³
A spherical maghemite particle powder comprising spherical maghemite particles containing 0.1 to 5.0 at% of Si relative to Fe and having excellent temperature stability. and 0.80 to Fe ²⁺ in the ferrous salt aqueous solution and the ferrous salt aqueous solution
In oxidizing the ferrous hydroxide colloid by passing an oxygen-containing gas through the ferrous salt reaction aqueous solution containing the ferrous hydroxide colloid obtained by reacting it with 0.99 equivalents of alkali hydroxide while heating it. , to either the alkali hydroxide or the ferrous salt reaction aqueous solution containing the ferrous hydroxide colloid, 0.1 to 5.0 atomic % of water-soluble silicate is added in terms of Si based on Fe, and then, Oxygen-containing gas is passed through while heating in the temperature range of 70 to 100°C, and then, under the same heating oxidation conditions, 1.00 equivalent or more of alkali hydroxide is added to Fe ²⁺ remaining in the reaction mother liquor. After producing spherical magnetite particles, the magnetite particles are heated in air at 300 to 400°C.
This is a method for producing maghemite particles having a spherical shape, which comprises obtaining maghemite particles having a spherical shape by heating and oxidizing the powder.

[Effect]

First, the most important point in the present invention is that the sphericity of the generated magnetite particles is improved by adding water-soluble silicate during the production of magnetite particles, which are starting material particles, and Due to the uniform particle size, there is no agglomeration between particles, and the bulk density is large. As a result, magnetite particles with excellent dispersibility can be obtained in high yield.

Although the effect of water-soluble silicate on improving the sphericity of magnetite particles in the present invention is not yet clear, the present inventor has found that the addition of water-soluble silicate allows the growth of magnetite nuclei to become dense and uniform. We believe that this is because magnetite nuclei grew isotropically as a result of this process, and then magnetite grew epitaxially on the surface of the magnetite particles, which had a spherical shape with improved sphericity.

Another important point of the present invention is that maghemite particles having a spherical shape with excellent temperature stability can be obtained.

In the case of the present invention, it is not yet clear why maghemite particles with excellent temperature stability can be obtained, but the sphericity of maghemite particles obtained by heating and oxidizing maghemite particles with improved sphericity This is thought to be due to the decrease in the surface activity of the particles due to an improvement in the surface activity, and the action of Si contained in the maghemite particles.

Conventional methods for adding water-soluble silicate to produce magnetite particles include, for example, methods described in Japanese Patent Publication No. 55-28203 and Japanese Patent Application Laid-Open No. 58-2226.

However, none of the above methods relates to magnetite particle powder exhibiting a spherical shape;
In addition, the added water-soluble silicate has the effect of suppressing particle growth during roasting when producing magnetite particles to produce magnetite sintered bodies or red iron oxide. This is completely different from the effect of the water-soluble silicate in the present invention, which is to control the particle shape of spherical magnetite particles generated in an aqueous solution.

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

As the ferrous salt aqueous solution in the present invention, ferrous sulfate, ferrous chloride, etc. are used.

As the alkali hydroxide in the present invention, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal oxides and hydroxides such as magnesium hydroxide and calcium hydroxide can be used. .

The amount of alkali hydroxide used to precipitate the ferrous hydroxide colloid in the present invention is 0.80 to 0.99 equivalent to Fe ²⁺ in the ferrous salt aqueous solution.

If it is less than 0.80 equivalent or more than 0.99 equivalent,
It is difficult to produce spherical magnetite particles.

In the present invention, the reaction temperature when oxygen-containing gas is passed through the ferrous salt reaction aqueous solution containing ferrous hydroxide colloid is 70°C to 100°C.

When the temperature is below 70°C, acicular goethite particles are mixed, and even when the temperature exceeds 100°C, spherical magnetite particles are produced, but this is not suitable for industrial use.

The oxidation means is carried out by passing an oxygen-containing gas (for example, air) into the liquid.

Water-soluble silicates used in the present invention include sodium and potassium silicates.

The amount of water-soluble silicate added is
In terms of conversion, it is 0.1 to 5.0 atomic%.

If it is less than 0.1 atomic %, it is impossible to obtain starting material particles, which are magnetite particles exhibiting a spherical shape with excellent sphericity.

When the amount exceeds 5.0 at%, the added water-soluble silicate precipitates alone and is mixed in the spherical magnetite particles.

In the present invention, the water-soluble silicate is involved in the shape of the generated spherical magnetite particles, and therefore, the timing of adding the water-soluble silicate is determined by the timing of addition of the ferrous hydroxide colloid. It is necessary that the oxygen-containing gas is passed through the ferrous salt reaction aqueous solution to generate magnetite particles, and either an alkali hydroxide or a ferrous salt reaction aqueous solution containing a ferrous hydroxide colloid is used. Can be added to crab.

When water-soluble silicate is added to a ferrous salt aqueous solution, it is precipitated as SiO ₂ at the same time as the water-soluble silicate is added, so the starting material particles, spherical magnetite particles with improved sphericity, are can't get it.

Almost all of the added water-soluble silicate was contained in the produced magnetite particles, and as shown in the Examples below, the obtained magnetite particles contained almost the same amount as the added amount.

In the present invention, the amount of alkali hydroxide added to Fe ²⁺ remaining in the mother liquor after oxidation of the ferrous hydroxide colloid is 1.00 equivalent or more.

If the amount is less than 1.00 equivalent, all Fe ²⁺ will not precipitate. 1.00
A preferable amount is an amount that takes industrial efficiency into consideration.

In the present invention, the reaction temperature and oxidation means when adding alkali hydroxide to the Fe ²⁺ remaining in the reaction mother liquor are such that oxygen-containing gas is passed through the ferrous salt reaction aqueous solution containing the ferrous hydroxide colloid. The conditions may be the same as those used when

The heating oxidation temperature of the starting material magnetite particles in air in the present invention is 300 to 400°C.

If the temperature is less than 300°C, the oxidation reaction of magnetite is slow and it takes a long time to generate magnetite.

When the temperature exceeds 400°C, the oxidation reaction of magnetite occurs rapidly, and the transformation of the produced maghemite into hematite is promoted.

〔Example〕

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

In addition, the average particle diameter in the following examples and comparative examples is determined by the BET method, and the bulk density is determined by JIS K 5101.
The particle morphology was observed using an electron microscope.

The amount of Si in the particles was measured using a Fluorescent X-ray analyzer model 3063M.
(manufactured by Rigaku Denki Kogyo) in accordance with JIS K 0119 "General Rules for Fluorescent X-ray Analysis".

<Production of starting material magnetite particles> Examples 1 to 3, Comparative Examples 1 to 3; Example 1 Ferrous sulfate aqueous solution containing 1.5 mol/Fe ²⁺ 20
2.64-N obtained by adding 18.9 g of sodium silicate (No. 3) (28.55 wt% SiO ₂ ) to the Fe prepared in the reactor in advance to contain 0.3 atomic % in terms of Si. In addition to NaOH aqueous solution 20 (corresponding to 0.95 equivalent to Fe ²⁺ ), a ferrous salt aqueous solution containing Fe(OH) ₂ was generated at pH 6.9 and temperature 90°C.

The above ferrous salt aqueous solution containing Fe(OH) ₂ was heated to a temperature of 90°C.
℃ for 240 minutes at 100 air per minute.

Next, 1.58-N NaOH aqueous solution 2 was added to the above reaction mother liquor (corresponding to 1.05 equivalents to the residual Fe ²⁺ ), and air was bubbled through at a rate of 20/min for 60 minutes at pH 11.8 and temperature 90°C. produced magnetite particles.

The generated particles are washed with water, separated, dried, and
Shattered.

As is clear from the electron micrograph (×20000) shown in Figure 1, the obtained magnetite particle powder has the following properties:
There is no aggregation between particles, and the particle size is uniform,
The particles were spherical with an average particle diameter of 0.20 μm.

In addition, as a result of fluorescent X-ray analysis, the spherical magnetite particles contained 0.29 atomic percent of Si relative to Fe, and had a bulk density of 0.57 g/cm ³ .
The dispersibility was extremely good.

Example 2 Ferrous sulfate aqueous solution containing 1.5 mol/Fe ²⁺ 20
of 2.64-N obtained by adding 190 g of sodium silicate (No. 3) (28.55 wt% SiO ₂ ) to the Fe prepared in the reactor in advance to contain 3.0 atomic % in terms of Si. In addition to NaOH aqueous solution 20 (corresponding to 0.95 equivalent to Fe ²⁺ ), a ferrous salt aqueous solution containing Fe(OH) ₂ was produced at pH 6.9 and temperature 90°C.

The above ferrous salt aqueous solution containing Fe(OH) ₂ was heated to a temperature of 90°C.
℃ for 240 minutes at 100 air per minute.

Next, 1.58-N NaOH aqueous solution 2 was added to the above reaction mother liquor (corresponding to 1.05 equivalents to the residual Fe ²⁺ ), and air was bubbled through at a rate of 20 per minute for 60 minutes at a pH of 11.4 and a temperature of 90°C. produced magnetite particles.

The generated particles are washed with water, separated, dried, and
Shattered.

As is clear from the electron micrograph (×20000) shown in Figure 2, the obtained magnetite particle powder has the following properties:
There is no aggregation between particles, and the particle size is uniform,
The particles were spherical with an average particle diameter of 0.15 μm.

Furthermore, as a result of fluorescent X-ray analysis, this spherical magnetite particle powder contained 2.96 atomic percent of Si relative to Fe, and had a bulk density of 0.59 g/cm ³ .
The dispersibility was extremely good.

Example 3 Ferrous sulfate aqueous solution containing 1.5 mol/Fe ²⁺ 20
2.64-N prepared in advance in the reactor
In addition to NaOH aqueous solution 20 (corresponds to 0.95 equivalent to Fe ²⁺ ), Fe
After producing an aqueous ferrous salt solution containing (OH) ₂ ,
Add 32.1 g of sodium silicate (No. 3) (SiO ₂ 28.55 wt%) so that it contains 0.5 atomic % based on Si in terms of Fe, and heat it to the above ferrous salt aqueous solution containing Fe(OH) ₂ at a temperature of 90 %.
℃ for 240 minutes at 100 air per minute.

Next, 1.58-N NaOH aqueous solution 2 was added to the above reaction mother liquor (corresponding to 1.05 equivalents to the residual Fe ²⁺ ), and air was bubbled through at a rate of 20/min for 60 minutes at a pH of 12.0 and a temperature of 90°C. produced magnetite particles.

The generated particles are washed with water, separated, dried, and
Shattered.

As a result of electron microscopy observation, the obtained magnetite particles had uniform particle size without agglomeration between particles, and had an average particle size.
The particles had a spherical shape of 0.19 μm.

Further, as a result of fluorescent X-ray analysis, this spherical magnetite particle powder contained 0.48 atomic % of Si relative to Fe, and had a bulk density of 0.55 g/cm ³ .
The dispersibility was extremely good.

Comparative example 1 Ferrous sulfate aqueous solution containing 1.5 mol/Fe ²⁺ 20
3.45-N prepared in advance in the reactor
In addition to NaOH aqueous solution 20 (corresponds to 1.15 equivalents to Fe ²⁺ ), Fe
An aqueous ferrous salt solution containing (OH) ₂ was produced.

The above ferrous salt aqueous solution containing Fe(OH) ₂ was heated to a temperature of 90°C.
Magnetite particles were generated by bubbling air at 100 °C per minute for 220 minutes.

As is clear from the electron micrograph (×20000) shown in Figure 3, the obtained magnetite particle powder has the following properties:
The particles were hexahedral.

This hexahedral magnetite particle powder is
The average particle diameter is 0.17μm, and the bulk density is 0.25g/
It was warm at ^cm3 .

Comparative Example 2 Ferrous sulfate aqueous solution containing 1.5 mol/Fe ²⁺ 20
1.92-N prepared in advance in the reactor
In addition to NaOH aqueous solution 20 (corresponds to 0.64 equivalent to Fe ²⁺ ), Fe
An aqueous ferrous salt solution containing (OH) ₂ was produced.

The above ferrous salt aqueous solution containing Fe(OH) ₂ was heated to a temperature of 90°C.
Magnetite particles were generated by bubbling air at 100 °C per minute for 190 minutes.

As is clear from the electron micrograph (×20000) shown in FIG. 4, the obtained magnetite particle powder has the following properties:
The particles were irregularly shaped and had asymmetric particle sizes.

This irregularly shaped magnetite particle powder had an average particle diameter of 0.19 μm and a bulk density of 0.34 g/cm ³ .

Comparative Example 3 Ferrous sulfate aqueous solution containing 1.5 mol/Fe ²⁺ 20
2.85-N prepared in advance in the reactor
In addition to Na ₂ CO ₃ aqueous solution 20 (corresponding to 0.95 equivalent to Fe ²⁺ ), at pH 6.6 and temperature 90 ° C.
A ferrous salt aqueous solution containing FeCO ₃ was produced.

A ferrous salt aqueous solution containing magnetite particles was produced by passing 100 air per minute through the ferrous salt aqueous solution containing FeCO ₃ at a temperature of 90° C. for 240 minutes.

Next, 1.58-N NaOH aqueous solution 2 was added to the ferrous salt aqueous solution containing the magnetite particles (corresponding to 1.05 equivalent to Fe ²⁺ ), and 20 air per minute was added at a pH of 11.6 and a temperature of 90°C. Aeration was performed for 60 minutes to generate magnetite particles.

The generated particles are washed with water, separated, dried, and
Shattered.

As shown in the electron micrograph (×20,000) shown in FIG. 5, the obtained magnetite particles had irregular shapes, could hardly be called spherical, and had asymmetric particle sizes.

The particle size of this magnetite particle powder is 0.12μm
The bulk density was 0.29 g/cm ³ .

<Production of spherical maghemite particles> Examples 4 to 6, Comparative Examples 4 to 6; Example 4 100 g of spherical magnetite particles obtained in Example 1 were heated in air using an electric furnace. , oxidized by heating at 370°C for 60 minutes to obtain maghemite particles.

As is clear from the electron micrograph (×20000) shown in FIG. 6, the obtained maghemite particle powder has the following characteristics.
There is no aggregation between particles, and the particle size is uniform,
The particles were spherical with an average particle diameter of 0.21 μm.

In addition, as a result of fluorescent X-ray analysis, this spherical maghemite particle powder contained ^0.30 at. It was in good condition.

The saturation magnetization σs of the particles obtained by heating 30 g of the above-mentioned spherical maghemite particles at 400° C. for 30 minutes in air was 76 emu/g, and had excellent temperature stability.

Example 5 100 g of the spherical magnetite particles obtained in Example 2 were heated and oxidized in air at 350° C. for 60 minutes using an electric furnace to obtain maghemite particles.

As is clear from the electron micrograph (×20000) shown in FIG. 7, the obtained maghemite particle powder has the following characteristics:
There is no aggregation between particles, and the particle size is uniform,
The particles were spherical with an average particle diameter of 0.15 μm.

In addition, as a result of fluorescent X-ray analysis, this spherical maghemite particle powder contained 2.98 atomic % of Si relative to Fe, and had a bulk density of 0.59 g/cm ³ , showing extremely high dispersibility. It was in good condition.

The saturation magnetization σs of the particles obtained by heating 30 g of the above-mentioned spherical maghemite particles at 400° C. for 30 minutes in air was 72 emu/g, and had excellent temperature stability.

Example 6 100 g of the spherical magnetite particles obtained in Example 3 were heated and oxidized in air at 320° C. for 60 minutes using an electric furnace to obtain maghemite particles.

As a result of electron microscopy observation, the obtained maghemite particles had a uniform particle size without any agglomeration between particles, as in Example 4, and had an average particle size.
The particles had a spherical shape of 0.20 μm.

In addition, as a result of fluorescent X-ray analysis, this spherical maghemite particle powder contained 0.50 atom% of Si relative to Fe, and had a bulk density of 0.56 g/cm ³ , showing extremely high dispersibility. It was in good condition.

The saturation magnetization σs of the particles obtained by heating 30 g of the above-mentioned spherical maghemite particles at 400° C. for 30 minutes in air was 75 emu/g, and had excellent temperature stability.

Comparative Example 4 100 g of the magnetite particles obtained in Comparative Example 1 were heated and oxidized in air at 350° C. for 60 minutes using an electric furnace to obtain maghemite particles.

As a result of electron microscopic observation, the obtained maghemite particles were found to be hexahedral particles in which the particles aggregated with each other, the particle size was asymmetric, and the average particle size was
The particles were 0.18 μm and had a bulk density of 0.25 g/cm ³ .

30g of maghemite particle powder exhibiting the above hexahedron shape
The saturation magnetization σs of the particles obtained by heating them in air at 400°C for 30 minutes was 55 emu/g.

Comparative Example 5 100 g of the magnetite particles obtained in Comparative Example 2 were oxidized by heating at 350° C. for 60 minutes in air using an electric furnace to obtain maghemite particles.

As a result of electron microscopic observation, the obtained maghemite particles were found to be amorphous particles in which the particles aggregated with each other, the particle size was asymmetric, and the average particle size was
The particles were 0.20 μm and had a bulk density of 0.35 g/cm ³ .

The saturation magnetization σs of the particles obtained by heating 30 g of the irregularly shaped maghemite particles in air at 400° C. for 30 minutes was 50 emu/g.

Comparative Example 6 100 g of the magnetite particles obtained in Comparative Example 3 were oxidized by heating at 350° C. for 30 minutes in air using an electric furnace to obtain maghemite particles.

As a result of electron microscopic observation, the obtained maghemite particles were found to be amorphous particles in which the particles aggregated with each other, the particle size was asymmetric, and the average particle size was
The particles were 0.14 μm and had a bulk density of 0.30 g/cm ³ .

The saturation magnetization σs of the particles obtained by heating 30 g of the irregularly shaped maghemite particles in air at 400° C. for 30 minutes was 52 emu/g.

〔effect〕

As shown in the previous example, the spherical maghemite particles according to the present invention have improved sphericity, so there is no aggregation between particles, and the bulk density is large. As a result, it has excellent dispersibility, so it is suitable as a brown pigment powder for paints and a material powder for magnetic toners for electrostatic copying, which are currently most in demand.

Furthermore, according to the present invention, magnetite particles with improved sphericity as a starting material can be obtained from the entire amount of Fe ²⁺ without leaving any unreacted Fe ²⁺ in the ferrous salt aqueous solution, resulting in high yield. It is possible to obtain maghemite particle powder with improved sphericity at a low rate and without discharging Fe ²⁺ that causes wastewater pollution.

When the spherical maghemite particles obtained by the present invention are used in the production of paints, they are well dispersed in the vehicle, resulting in improvements in paint film properties such as gloss, clarity, and durability. This also improves work efficiency.

When the spherical maghemite particles obtained according to the present invention are used in the production of magnetic toner, it has good dispersibility in resin, so it has appropriate magnetism and excellent image density. It is possible to obtain high image quality and has excellent temperature stability.
Discoloration and deterioration of magnetic properties do not occur during the production and development of the magnetic toner.

[Brief explanation of the drawing]

1 to 5 are electron micrographs (×
20000), and FIGS. 1 and 2 show the spherical magnetite particles obtained in Example 1 and Example 2, respectively, and FIG. 3 shows the hexahedral magnetite particles obtained in Comparative Example 1. Figure 4 shows comparative example 2.
Irregularly shaped magnetite particle powder obtained in Figure 5
is the magnetite particle powder obtained in Comparative Example 3 with insufficient sphericity. 6 and 7 are electron micrographs (×20000) showing the particle morphology (structure) of maghemite particle powder exhibiting a spherical shape.
These are maghemite particle powders obtained in Example 4 and Example 5, respectively.

Claims (1)

[Claims] 1. The bulk density is 0.40 to 1.10 g/cm ³ and Si is
Contains 0.1 to 5.0 at% of Fe, and
A spherical maghemite particle powder consisting of spherical maghemite particles characterized by excellent temperature stability. 2 Ferrous salt aqueous solution and the ferrous salt aqueous solution
A ferrous salt reaction aqueous solution containing a ferrous hydroxide colloid obtained by reacting 0.80 to 0.99 equivalents of alkali hydroxide with Fe ²⁺ is heated while passing an oxygen-containing gas through the ferrous hydroxide colloid. In oxidizing the ferrous colloid, a water-soluble silicate is added in advance to either the alkali hydroxide or the ferrous salt reaction aqueous solution containing the ferrous hydroxide colloid.
Add 0.1 to 5.0 atomic% in terms of Si, and then add 70 to 5.0 atomic%.
Oxygen-containing gas was passed through the reactor while heating in a temperature range of 100°C, and then, under the same conditions as the heating oxidation conditions, 1.00 equivalent or more of alkali hydroxide was added to Fe ²⁺ remaining in the reaction mother liquor. Magnetite particles having a spherical shape are obtained by generating spherical magnetite particles and then heating and oxidizing the magnetite particles in air at 300 to 400°C to obtain spherical maghemite particles. Powder manufacturing method.