JPH0580413B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides particles having a spherical shape, a bulk density of 0.40 to 1.00 g/cm ³ , and excellent dispersibility. The present invention relates to a maghemite particle powder exhibiting a spherical shape and a method for producing the same.

The spherical maghemite particles produced according to the present invention are mainly used as a brown pigment powder for paints and as a 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, it is important to improve the dispersibility of maghemite particles in vehicles when manufacturing paints. ,More,
It is requested.

In the production of paints, whether or not the dispersibility of the pigment powder in the vehicle is good affects the work efficiency in the paint manufacturing process and is an extremely important factor that 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).

``...It is no exaggeration to say that most of the characteristics that a paint film should have are determined by the dispersibility of the pigment in the paint film if the pigments are the same. .If the dispersibility of the pigment in the coating film is good, the color tone will be clear and the coloring power will be high.
Theory teaches that the fundamental properties of pigments, such as their strength, can also be improved. 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, making it difficult to obtain a uniform toner with no manufacturing variations. Furthermore, in the case of insulating toner, it may cause a decrease in the electrical resistance of the toner.'' Furthermore, Japanese Patent Publication No. 53-21656 states, ``...By uniformly distributing iron oxide throughout the developer particles, It is stated that it is possible to obtain the appropriate magnetization required for visualizing an electrostatic latent image.

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 particles are heated and oxidized in air to form maghemite.

In producing the above magnehemite particle powder,
It is known that the particle shape of magnetite particles produced from an aqueous solution varies depending on the pH of the reaction aqueous solution.

In other words, this fact is based on the Powder Metallurgy Society of Japan's 1970 Autumn Conference Abstracts, page 122, lines 14-19: 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. The PH controls the amount of sodium hydroxide, and the acidic side (NaOH40~41g/0.3) allows for condensed hexahedral particles, while 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 “…PH10 containing Fe(OH) ₂ colloid
By maintaining the above aqueous solution at a temperature of 45°C or higher and 70°C or lower, and carrying out the oxidation reaction while the precipitated particles present in the liquid are sufficiently moved by stirring,
It is clear from the description "...producing a precipitate consisting of black ferromagnetic particles (magnetite particles) exhibiting a granular or cubic (hexahedral) shape...".

[Problem that the invention seeks to solve]

Maghemite particles with excellent dispersibility are currently most in demand, but it cannot be said that the powder particles obtained by the above-mentioned known method for producing maghemite particles have excellent dispersibility.

The present inventor focused on the shape of maghemite particles, and found that in order to obtain maghemite particles with excellent dispersibility, the particles must have a spherical shape with a large bulk density. In order to obtain particles, we considered that it is necessary for the magnetite particles, which are the starting material particles, to be spherical particles with a large bulk density.

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,
The produced magnetite particles were hexahedral or octahedral particles and had a small bulk density.

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:
Ferrous salt aqueous solution or ferrous salt and 2 such as Co ²⁺
A first step in which an alkali metal carbonate in an amount equivalent to or less than the acid radical contained in the aqueous solution is added to a mixed aqueous solution of valent metal salts, and an oxidation reaction is performed at a temperature below the boiling temperature to generate a ferromagnetic particle matrix. , ferromagnetic fine particles (MO Fe ₂ O ₃ M : Fe ⁺² or a part or all of Fe ⁺² replaced with a divalent metal such as Co ⁺² M: Fe ⁺²
In this case, the second step consists of producing magnetite.

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. It is agglomerated and has a small bulk density.
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. Since magnetite core particles are rapidly precipitated and formed, it is thought that the shape cannot be controlled sufficiently, and therefore, it is unsuitable as a starting material for spherical maghemite.

[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 and having a high bulk density at a high yield.

That is, the present invention provides maghemite particle powder having a spherical particle shape and a bulk density of 0.40 to 1.00 g/cm ³ and a 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 to Fe ²⁺ in the iron salt aqueous solution at a temperature of at least 75°C.
The ferrous hydroxide colloid is oxidized by passing oxygen-containing gas while heating in a temperature range of 100°C, and then alkali hydroxide in an amount of 1.00 equivalent or more based on Fe ²⁺ remaining in the reaction mother liquor is added to the heating. By adding under the same conditions as the oxidation conditions, spherical magnetite particles are generated. After washing with water, separating, and drying using a conventional method, the spherical magnetite particles are heated and oxidized in air at 300 to 350°C. This is a method for producing spherical maghemite particles by obtaining spherical maghemite particles.

[Effect]

First, the spherical maghemite particles according to the present invention are produced by heating and oxidizing spherical magnetite particles, which are starting raw material particles, in air at 300 to 350°C, so that there is no aggregation between the particles. Since maghemite particles having a large bulk density can be obtained, excellent filling properties and dispersibility can be obtained in the production of paints and magnetic toners.

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 temperature at which the ferrous salt aqueous solution and the alkali hydroxide are reacted is at least 75°C. If the temperature is lower than 75°C, spherical magnetite particles cannot be produced.

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.

If the temperature is less than 70°C, acicular datum particles are mixed, and even if 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.

In the present invention, the amount of alkali hydroxide added to Fe ²⁺ remaining in the reaction 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

In the present invention, the heating temperature of the starting material particles in air is 300 to 350°C.

If the temperature is less than 300°C, the oxidation reaction will not occur or it will take a long time to oxidize to maghemite particles, while if it exceeds 350°C, the maghemite particles will transform into hematite particles, which is not preferable.

〔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 shape was observed by electron microscopy.

<Production of starting material magnetite particles> Example 1 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 0.88 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.
℃ for 240 minutes at 100 air per minute.

Next, 3.78-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 was no aggregation between the particles, the particles were spherical, and the particle size was uniform.

In addition, this spherical magnetite particle powder has an average particle diameter of 0.18 μm and a bulk density of 0.54 g/
cm ³ and had extremely good dispersibility.

Example 2 Ferrous sulfate aqueous solution containing 1.5 mol/Fe ²⁺ 20
2.79-N prepared in advance in the reactor
of N in NaOH aqueous solution 20 plus (0.93 for Fe ²⁺
corresponds to equivalent amount. ), PH6.7, Fe at temperature 75℃
An aqueous ferrous salt solution containing (OH) ₂ was produced.

Temperature 75 to the ferrous salt aqueous solution containing Fe(OH) ₂ above.
℃ for 240 minutes at 100 air per minute.

Next, 3.78-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 11.8 and a temperature of 75°C. magnetite particles were produced.

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 was no aggregation between the particles, the particles were spherical, and the particle size was uniform.

In addition, this spherical magnetite particle powder has an average particle diameter of 0.11 μm and a bulk density of 0.46 g/
cm ³ and had extremely good dispersibility.

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 produced by aerating air at a rate of 100 per minute for 220 minutes at ℃.As is clear from the electron micrograph (×20000) shown in Figure 3, the obtained magnetite particles had
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:
They were irregularly shaped particles.

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 pH 11.6 and 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.

The obtained magnetite particles were irregularly shaped particles, as shown in the electron micrograph (×20000) shown in FIG.

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> Example 3 100 g of spherical magnetite particles obtained in Example 1 were oxidized by heating in air at 310°C for 60 minutes using an electric furnace to obtain maghemite particles. Ta.

As is clear from the electric micrograph (×20,000) shown in FIG. 6, the obtained maghemato particles were spherical particles with no aggregation among particles.

In addition, this spherical maghemite particle powder has an average particle diameter of 0.18 μm and a bulk density of 0.56 g/cm ³
The dispersibility was extremely good.

Example 4 100 g of the spherical magnetite particles obtained in Example 2 were heated and oxidized in air at 340° C. for 40 minutes using an electric furnace to obtain maghemite particles.

As is clear from the electric micrograph (×20,000) shown in FIG. 7, the obtained maghematode particles were spherical particles with no aggregation among particles.

In addition, the maghemite particles exhibiting this spherical shape have an average particle diameter of 0.12 μm and a bulk density of 0.48 g/cm ³
The dispersibility was extremely good.

Comparative Example 4 100 g of the magnetite particles obtained in Comparative Example 1 were heated and oxidized in air at 310° C. for 60 minutes using an electric furnace to obtain maghemite particles.

As a result of electron microscopy observation, the obtained maghemato particle powder exhibited a hexahedral shape with an average particle diameter of 0.20 μm.
The particles had a bulk density of 0.26 g/cm ³ .

Comparative Example 5 100 g of the magnetite particles obtained in Comparative Example 2 were heated and oxidized in air at 310° C. for 60 minutes using an electric furnace to obtain maghemite particles.

As a result of electron microscopic observation, the obtained maghemite particles had an amorphous shape and an average particle diameter of 0.21μ.
The particles had a bulk density of 0.35 g/cm ³ .

Comparative Example 6 100 g of the magnetite particles obtained in Comparative Example 3 were heated and oxidized in air at 310° C. for 60 minutes using an electric furnace to obtain maghemite particles.

As a result of electron microscopy observation, the obtained maghemato particle powder exhibited an amorphous shape with an average particle diameter of 0.14 μm.
The particles had a bulk density of 0.30 g/cm ³ .

〔effect〕

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

Furthermore, according to the present invention, spherical magnetite particles, which are the 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 a high yield. In addition, maghemite particles having a spherical shape can be obtained without discharging Fe ²⁺ that causes wastewater pollution.

When the spherical maghemite particles obtained according to 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. You can get better image quality.

[Brief explanation of drawings]

Figures 1 to 5 are electron micrographs (x20000) showing the particle morphology of magnetite particles.
1 and 2 show the spherical magnetite particles obtained in Example 1 and Example 2, respectively, FIG. 3 shows the hexahedral magnetite particles obtained in Comparative Example 1, and FIG. 5 shows the amorphous magnetite particles obtained in Comparative Example 2, and FIG. 5 shows the magnetite particles with insufficient sphericity obtained in Comparative Example 3. 6 and 7 are electron micrographs (×20,000) showing the particle morphology of maghemite particle powder exhibiting a spherical shape.
These are maghemite particle powders obtained in Example 3 and Example 4, respectively.

Claims (1)

[Scope of Claims] 1. Maghemite particle powder exhibiting a spherical shape and having a bulk density of 0.40 to 1.00 g/cm ³ . 2 Ferrous salt aqueous solution and the ferrous salt aqueous solution
A ferrous salt reaction aqueous solution containing ferrous hydroxide colloid obtained by reacting 0.80 to 0.99 equivalents of alkali hydroxide to Fe ²⁺ at at least 75°C
The ferrous hydroxide colloid is oxidized by passing oxygen-containing gas while heating in a temperature range of 100°C, and then alkali hydroxide in an amount of 1.00 equivalents or more based on Fe ²⁺ remaining in the reaction mother liquor is heated. By adding under the same conditions as the oxidation conditions, spherical magnetite particles are generated. After washing with water, separating, and drying using a conventional method, the spherical magnetite particles are heated and oxidized in air at 300 to 350°C. A method for producing spherical maghemite particles having a bulk density of 0.40 to 1.00 g/cm ^{3 ,} the method comprising obtaining spherical maghemite particles by doing so.