JPH0624985B2 - Spherical maghemite particle powder and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has a Si content of 0.1 to 5.0 atom% with respect to Fe, a particle surface coated with a saturated fatty acid, and an electric resistance of The present invention relates to a spherical maghemite particle powder composed of spherical maghemite particles having a temperature of 10 ¹³ to 10 ¹⁵ Ωcm and excellent in temperature stability, and a method for producing the same.

Its main application is powder particles of material for insulating magnetic toner for electrostatic copying.

[Conventional technology]

In recent years, electrostatic copying machines have been remarkably popularized, and along with this, research and development of magnetic toners, which are developers, have been brisk, and improvements in their characteristics are required.

A developer used for an electrostatic copying machine is composed of a toner that is an ink component and a carrier that conveys the toner. In this type of commonly used developer, a toner and a carrier are mixed. There are two-component type developers and one-component type developers having a carrier function.

The two-component type developer supplies toner to a latent image by using iron powder having a certain particle size, glass beads or the like as a carrier.

On the other hand, a one-component developer is called a magnetic toner, and because the toner itself has magnetic sensitivity, it is carried and developed by the toner itself without using a carrier. It is a powder of constant particle size dispersed in.

The one-component type developer is roughly classified into conductive magnetic toner and insulating magnetic toner, and the latter is widely used because it can be copied on plain paper.

The insulating magnetic toner is described in, for example, Journal of Electrostatic Society Vol. 7, No. 4
No. (1983), page 238, "... (2) Insulating magnetic toner: Incorporate magnetic powder in resin to set specific resistance of 10 ¹³ Ωcm or more." But
It is necessary to be 10 ¹³ Ωcm or more, but for that purpose,
It is strongly demanded that the magnetic particle powder dispersed in the resin has as high an electric resistance as possible and is stable for a long period of time.

That is, although the resin itself is a high insulator showing about 10 ¹⁵ Ωcm, the electric resistance of the magnetic particle powder contained in the resin in a large amount (30 to 60% by weight) is as low as about 10 ⁷ Ωcm, so that it can be obtained. This is because the electric resistance of magnetic toner is generally lower than that of resin.

Further, since the magnetic toner is exposed to a high temperature at the time of manufacturing and developing, the magnetic particle powder as the material powder for the magnetic toner is
There is a strong demand for excellent temperature stability.

That is, the magnetic toner is obtained by heating, melting and kneading a magnetic particle powder such as maghemite particles and a resin, cooling and solidifying the resin, pulverizing the powder, and passing it in a spray form in a heated hot air stream to obtain a spheroidizing treatment. Is manufactured by performing. Also,
At the time of development, heat fixing or pressure fixing is performed to fix the magnetic toner.

Conventionally, granular or cubic maghemite particles, which generally show a dark brown color, have been widely used as the magnetic particle powder for sepia magnetic toner, and the maghemite particles are generally obtained by the reaction of an aqueous ferrous salt solution and an aqueous alkaline solution. By passing an oxygen-containing gas such as air into the suspension containing ferrous hydroxide colloid, magnetite particles as starting material particles are generated from the aqueous solution, and then the magnetite particle powder is heated in air. Manufactured by oxidation.

[Problems to be solved by the invention]

Maghemite particle powder having high electric resistance and stable for a long period of time, and moreover, excellent temperature stability is currently most demanded, but the electric resistance of the maghemite particle powder obtained by the above-mentioned known method is as described above. As I did
It is as low as about 10 ⁷ Ωcm, and it is hard to say that it has excellent temperature stability. That is, the sepia-colored maghemite particle powder obtained by the known method becomes hematite at a high temperature of about 550 ° C. and becomes reddish brown and loses magnetism at the same time. For example, the saturation magnetization decreases to about 5 emu / g. .

As mentioned above, it has a high electric resistance and is stable for a long period of time.
Moreover, there is a strong demand for establishment of a method for producing magnetite particle powder having excellent temperature stability.

[Means for solving problems]

The present inventor has reached the present invention as a result of various studies on a method for producing a maghemite particle powder having high electric resistance, stability over a long period of time, and excellent temperature stability.

That is, the present invention, the Si content is 0.1 to 5.0 atom% with respect to Fe, the particle surface is coated with a saturated fatty acid, and the electrical resistance is 10 ¹³ to 10 ¹⁵ Ωcm, and the temperature 0.80 to 0.99 for spherical maghemite particles powder and ferrous salt aqueous solution and ferrous salt aqueous solution having spherical shape consisting of spherical maghemite particles characterized by excellent stability In oxidizing the ferrous hydroxide colloid by ventilating an oxygen-containing gas while heating an aqueous ferrous salt reaction solution containing a ferrous hydroxide colloid obtained by reacting with an equivalent amount of alkali hydroxide, A water-soluble silicate in advance of 0.1 to 5.0 atomic% in terms of Si of Fe is added to either the aqueous solution of the ferrous salt containing the alkali hydroxide or the ferrous hydroxide colloid, and then 70 to 100 ° C. Oxygen-containing gas while heating in the temperature range of After aeration, a spherical shape was obtained by adding 1.00 equivalent or more of alkali hydroxide to the ferrous salt remaining in the reaction mother liquor after oxidation of the ferrous hydroxide colloid under the same heating and oxidation conditions. Presented Si
Magnetite particles containing Si are generated, and then the spherical magnetite particles containing Si are heated to 300 nm in air.
Obtaining spherical Si-containing maghemite particles by heating and oxidizing at ~ 400 ℃, the spherical Si-containing maghemite particles by stirring and mixing the spherical Si-containing maghemite particles A method for producing a spherical maghemite particle powder composed of spherical maghemite particles by coating the surface of the contained maghemite particles with a saturated fatty acid.

[Work]

First, the most important point in the present invention is 0.80 to the ferrous salt solution in the ferrous salt aqueous solution and the ferrous salt aqueous solution as the treated maghemite particles in the treatment with the saturated fatty acid.
In oxidizing the hydroxide colloid by aeration of an oxygen-containing gas while heating an aqueous ferrous salt reaction solution containing a ferrous hydroxide colloid obtained by reacting with 0.99 equivalents of alkali hydroxide, the water A water-soluble silicate is added in advance to an alkali oxide or an aqueous solution of a ferrous salt containing the ferrous hydroxide colloid in an amount of 0.1 to 5.0 atomic% in terms of Si, and then at a temperature of 70 to 100%. After aeration with an oxygen-containing gas while heating in a range, 1.00 equivalent or more of water relative to the ferrous salt remaining in the reaction mother liquor after oxidation of the ferrous hydroxide colloid under the same conditions as the heating and oxidizing conditions. Spherical Si-containing magnetite particles were generated by adding alkali oxide, and the spherical shape obtained by heating and oxidizing the spherical Si-containing magnetite particles in air at 300 to 400 ° C was measured. Presented Si In that using maghemite particles containing.

In the present invention, the reason why the electrical resistance is high and stable over a long period of time is not yet clear, but the present inventors have improved the sphericity of the spherical Si-containing maghemite particles used as the particles to be treated. It is considered that the saturated fatty acid is strongly oriented and adsorbed on the particle surface of the maghemite particles in a uniform and dense state from the particle surface to the outside by the saturated fatty acid.

Further, in the present invention, the reason why the maghemite particles having excellent temperature stability are obtained is not yet clear, but the present inventor has found that the spherical shape of the maghemite particles exhibiting a spherical shape improves the particle It is considered that the surface activity was reduced and the action of Si contained in the maghemite particles.

Conventionally, various attempts have been made to coat the magnetic particle powder with a fatty acid or a salt thereof, for example, JP-A-58-14773, JP-A-61-53654, JP-A-54-139544. There are methods described in JP-A-56-64348 and JP-A-56-129857, but in each case, magnetic particles having sufficiently high electric resistance and stable for a long time have not been obtained yet.

Conventionally, as a method for obtaining spherical magnetite particles, for example, there is a method described in JP-A-49-35900 and JP-A-60-71529, in the production of magnetite particles, water-soluble silicate. Examples of the method of adding the compound include those described in JP-B-55-28203 and JP-A-58-2226. However, there is no description of treating maghemite particles obtained by heating and oxidizing these magnetite particles with a fatty acid, and in fact, as shown in Comparative Examples described later, the electric resistance is low, and the temperature is low. It is hard to say that it has excellent stability.

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

The ferrous salt aqueous solution in the present invention, ferrous sulfate,
Ferrous chloride or the like is used.

The alkali hydroxide in the present invention is sodium hydroxide,
Alkali metal hydroxides such as potassium hydroxide and alkaline earth metal 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 the amount of Fe in the ferrous salt aqueous solution.
It is 0.80 to 0.99 equivalents to ²⁺ .

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

The reaction temperature when the oxygen-containing gas is passed through the ferrous iron reaction aqueous solution containing the ferrous hydroxide colloid in the present invention is 70 ° C to
It is 100 ° C.

If the temperature is lower than 70 ° C, needle-shaped goethite particles are mixed, and even if the temperature exceeds 100 ° C, spherical magnetite particles are formed, but this is not industrial.

The oxidizing means is performed 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 0.1 in terms of Si with respect to Fe.
~ 5.0 atomic%.

If the amount is less than 0.1 atomic%, it is impossible to obtain the magnetite particle powder having a spherical shape excellent in sphericity, which is the object of the present invention.

If it exceeds 5.0 atomic%, the added water-soluble silicate is precipitated alone and mixed in the spherical magnetite particles.

The water-soluble silicate in the present invention is involved in the shape of the spherical magnetite particles to be formed, and therefore, the timing of adding the water-soluble silicate is the ferrous iron containing the ferrous hydroxide colloid. It is necessary to ventilate an oxygen-containing gas into the salt reaction aqueous solution to generate magnetite particles, and add it to either an alkali hydroxide or a ferrous salt reaction aqueous solution containing a ferrous hydroxide colloid. can do.

When the water-soluble silicate is added to the aqueous solution of ferrous salt, magnetite particles with improved sphericity cannot be obtained because the water-soluble silicate is added and simultaneously precipitated as SiO ₂ .

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

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

If it is less than 1.00 equivalent, the total amount of Fe ²⁺ does not precipitate. A preferable amount is 1.00 equivalent or more in consideration of industrial properties.

The reaction temperature and oxidizing means when adding an alkali hydroxide to Fe ²⁺ remaining in the reaction mother liquor in the present invention, oxygen-containing gas is passed through the ferrous salt reaction aqueous solution containing the above-mentioned ferrous hydroxide colloid. It may be the same as the condition for performing.

The thermal oxidation temperature of maghemite particles in the present invention is 300
~ 400 ° C.

When the temperature is lower than 300 ° C, the oxidation reaction of maghemite particles is slow and it takes a long time to generate maghemite particles.

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

As the type of fatty acid in the present invention, a saturated fatty acid can be used, and a linear saturated fatty acid is particularly preferable,
Specifically, lauric acid, myristic acid, palmitic acid,
Stearic acid or the like can be used.

The amount of the saturated fatty acid is at least the amount necessary for forming a monolayer film of the saturated fatty acid on the particle surface of the maghemite particles as the particles to be treated.

That is, the amount (W) of saturated fatty acid required to form a monolayer film can be calculated by the following equation.

Where M: molecular weight of saturated fatty acid (g) S: specific surface area of BET method due to N ₂ adsorption of treated particles magnetite particles (cm ² / g) A: adsorption occupied cross-sectional area of saturated fatty acid (Å ² ) amount of saturated fatty acid However, if the amount is less than that required for forming a monolayer film, maghemite particles having high electric resistance cannot be obtained. If it is at least an amount necessary to form a monolayer film, it is possible to achieve the object of the present invention, but it is meaningless to add more than necessary, and excess saturated fatty acid that is not adsorbed on the particle surface of maghemite particles Since a large amount is present, the charging characteristics of the magnetic toner obtained by using the maghemite particles are affected. Considering the insulating property and stability of the obtained maghemite particles coated with saturated fatty acid, the upper limit thereof is twice as much as the amount necessary for forming the monolayer film.

The stirring mixing of the spherical Si-containing maghemite particles and the saturated fatty acid in the present invention is performed by heating the dried spherical Si-containing maghemite particles and the saturated fatty acid to a temperature equal to or higher than the melting point of the saturated fatty acid. However, it is preferably performed in an inert gas atmosphere.

〔Example〕

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

The average particle size in the following examples and comparative examples is B
The bulk density was measured by the ET method by the method described in JIS K 5101, and the particle morphology was observed by an electron microscope.

The amount of Si in the particles can be determined by performing a fluorescent X-ray analysis according to JIS K 0119 "General rules for fluorescent X-ray analysis" using "Fluorescent X-ray analyzer 3063M type" (manufactured by Rigaku Denki Kogyo). It was measured.

The electrical resistance was obtained by using maghemite particles that had been left overnight under the conditions of a temperature of 20 ° C. and a humidity of 65%, and the maghemite particles were provided between a pair of electrodes having a diameter of 1.8 cm so that the filling rate was 2 to 2.5 g / cm ^2.
After pinching at a constant distance of 0.2 cm, apply a voltage of 25 V
It was applied to 0 V and measured with a high resistance meter 4329 A (manufactured by Yokogawa Hulet Packard). Stability of electrical resistance is 20
It is shown by the value of electric resistance when left for 10 days under conditions of ℃ and humidity of 65%.

The temperature stability was indicated by the saturation magnetization σs value of the particle powder obtained by heating maghemite particles in air at a temperature of 400 ° C for 30 minutes. The lower the saturation magnetization σ s value, the more transformed the maghemite particles.

<Production of Magnetite Particle Powder> Examples 1 to 10, Comparative Examples 1 to 4; Example 1 Ferrous sulfate aqueous solution 20 containing Fe ²⁺ 1. mol / into Fe prepared in advance in the reactor. On the other hand, 0.3 in terms of Si
Sodium silicate (No. 3) (Si ₂ 28.55wt%)
%) 2.64-N NaOH aqueous solution obtained by adding 18.9 g 20
In addition to (corresponding to 0.95 equivalent to Fe ²⁺ ), pH 6.9,
The ferrous salt aqueous solution containing Fe (OH) ₂ was produced at a temperature of 90 ℃.

The ferrous salt aqueous solution containing Fe (OH) ₂ was aerated at 100 ° C. for 240 minutes at a temperature of 90 ° C. to generate a ferrous salt aqueous solution containing magnetite particles.

Then, to the ferrous salt aqueous solution containing the magnetite particles
Two 1.58-N NaOH aqueous solutions were added (corresponding to 1.05 equivalent to Fe ²⁺ ), 20 air per minute was aerated at pH 11.8 and a temperature of 90 ° C. for 60 minutes to generate magnetite particles.

The produced particles were washed with water, separated, dried and pulverized by a conventional method.

As can be seen from the electron micrograph (× 20000) shown in FIG. 1, the obtained magneteacit particle powder was spherical particles having no entanglement between particles and an average particle diameter of 0.20 μm.

Further, the spherical magnetite particle powder was found to contain 0.29 atomic% of Si with respect to Fe as a result of fluorescent X-ray analysis, and had a bulk density of 0.57 g / cm ³ and an oil absorption amount of 17 ml / 100.
The g and L values were 34.8.

Examples 2 to 10 Type of ferrous salt aqueous solution, concentration and usage amount, type of alkali hydroxide, concentration and usage amount, water-soluble silicic acid in the production of ferrous salt reaction aqueous solution containing ferrous hydroxide colloid Magnetite particle powder was obtained in the same manner as in Example 1 except that the type of salt, the amount and timing of addition, the type and amount of alkali hydroxide used for precipitation of residual Fe ²⁺ , and the reaction temperature in each step were variously changed. It was

Table 1 shows the main production conditions and various characteristics of the generated magnetite particle powder at this time.

The magnetite particle powders obtained in Examples 2 to 10 were spherical particles with no entanglement among the particles as a result of observation with an electric microscope.

An electron micrograph (× 20000) of the magnetite particle powder obtained in Example 3 is shown in FIG.

Comparative Example 1 An aqueous solution of ferrous sulfate 20 containing Fe ²⁺ 1.5 mol / was prepared in advance in a reactor, and an aqueous solution of 3.45-N NaOH 20 was prepared.
In addition to (corresponding to 1.15 equivalent to Fe ²⁺ ), pH 12.8
A ferrous salt aqueous solution containing Fe (OH) ₂ was produced at a temperature of 90 ° C.

The above ferrous salt aqueous solution containing Fe (OH) ₂ was aerated with 100 air / minute for 220 minutes at a temperature of 90 ° C. to produce magnetite particles. The obtained magnetite particle powder is an electron micrograph ( As is clear from (20000), the particles were hexahedral particles.

This hexahedral magnetite particle powder has an average particle size of 0.17 μm, a bulk density of 0.25 g / cm ³ , and an oil absorption of 29.
The L value was 40.1.

Comparative Example 2 An aqueous solution of ferrous sulfate 20 containing Fe ²⁺ 1.5 mol / was prepared in advance in a reactor and used as an aqueous solution of 1.92-N NaOH 20.
In addition to (corresponding to 0.64 equivalent to Fe ²⁺ ), pH 4.8,
The ferrous salt aqueous solution containing Fe (OH) ₂ was produced at a temperature of 90 ° C.

Magnetite particles were produced by passing 100 air per minute for 190 minutes at a temperature of 90 ° C. through the ferrous salt aqueous solution containing Fe (OH) ₂ .

The obtained magnetite particles were amorphous particles, as is clear from the electron micrograph (× 20000) shown in FIG.

This amorphous magnetite particle powder has an average particle size of 0.
19 μm, bulk density 0.34 g / cm ³ , oil absorption 27 ml / 1
It was 00g and L value was 39.0.

Comparative Example 3 A ferrous sulfate aqueous solution 20 containing Fe ²⁺ 1.5 mol / was prepared in advance in a reactor, and a 2.85-N Na ₂ CO ₃ aqueous solution 20 was prepared.
In addition to (equal to 0.95 equivalent to Fe ²⁺ ), pH 6.
6. A ferrous salt aqueous solution containing FeCO ₃ was produced at a temperature of 90 ° C.

The ferrous salt aqueous solution containing FeCO ₃ was aerated at 100 ° C./min for 240 minutes at a temperature of 90 ° C. to produce a ferrous salt aqueous solution containing magnetite particles.

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

The produced particles were washed with water, separated, dried and pulverized by a conventional method.

As shown in the electron micrograph (× 20000) shown in FIG. 5, the obtained magnetite particle powder was indefinite and hardly spherical.

The particle size of this magnetite particle powder is 0.12 μm,
Bulk density 0.29 g / cm ³ , oil absorption 23 ml / 100 g, L value 38.4
Met.

Comparative Example 4 Magnetite particles were produced in the same manner as in Example 1 except that the water-soluble silicate was not added.

The obtained magnetite particles had a particle size of 0.19 μm, a bulk density of 0.52 g / cm ³ , an oil absorption of 19 ml / 100 g, and an L value.
It was 36.0.

<Production of Maghemite Particle Powder> Examples 11 to 20 and Comparative Examples 5 to 8; Example 11 100 g of spherical magnetite particles obtained in Example 1
Was heated and oxidized in an electric furnace at 370 ° C. for 60 minutes in air to obtain maghemite particles.

As is apparent from the electron micrograph (× 20,000) shown in FIG. 6, the obtained maghemite particle powder had a uniform particle size without aggregation between particles and had an average particle size of 0.21.
The particles had a spherical shape of μm.

Also, this spherical maghemite particle powder is fluorescent X
As a result of the line analysis, it contained 0.30 atomic% of Si with respect to Fe, had a bulk density of 0.58 g / cm ³ , and had an electric resistance of 5.3 × 1
It was 0 ⁷ Ωcm.

40 g of the above-mentioned spherical maghemite particle powder in air 40
Saturation magnetization σs of particle powder obtained by heating at 0 ° C for 30 minutes
Was 76 emu / g, which was excellent in temperature stability.

Examples 12 to 20 Maghemite particles were obtained in the same manner as in Example 11 except that the type of magnetite particles and the heating and oxidation temperature were variously changed.

Table 2 shows the main manufacturing conditions and various characteristics at this time.

As a result of electron microscopic observation, the maghemite particles obtained in Examples 12 to 20 were all spherical particles without entanglement between the particles.

An electron micrograph (× 20,000) of the maghemite particle powder obtained in Example 13 is shown in FIG. 7.

Comparative Example 5 100 g of the magnetite particles obtained in Comparative Example 1 were heated and oxidized in an electric furnace at 350 ° C. for 60 minutes in air to obtain maghemite particles.

As a result of electron microscopic observation, the obtained maghemite particle powder was a hexahedral particle in which the particles were aggregated with each other, the particle size was asymmetric, the average particle size was 0.18 μm, and the bulk density was 0.25.
The particles were g / cm ³ and the electrical resistance was 4.2 × 10 ⁷ Ωcm.

30g of the above-mentioned hexahedral maghemite particle powder in air
Saturation magnetization σ of particle powder obtained by heating at 400 ℃ for 30 minutes
The s was 55 emu / g.

Comparative Example 6 Maghemite particles were obtained by thermally oxidizing 100 g of the magnetite particles obtained in Comparative Example 2 in an electric furnace at 350 ° C. for 60 minutes in air.

As a result of electron microscopic observation, the obtained maghemite particle powder was an amorphous particle in which the particles were aggregated with each other, the particle size was asymmetric, the average particle diameter was 0.20 μm, and the bulk density was 0.35.
The particles were g / cm ³ and the electric resistance was 6.2 × 10 ⁷ Ωcm.

30g of the above-mentioned irregular-shaped maghemite particle powder in air at 400 ℃
The saturation magnetization σs of the particle powder obtained by heating for 30 minutes at 50 is
It was emu / g.

Comparative Example 7 Maghemite particles were obtained by thermally oxidizing 100 g of the magnetite particles obtained in Comparative Example 3 in an electric furnace in air at 350 ° C. for 60 minutes.

As a result of electron microscopic observation, the obtained maghemite particle powder was an amorphous particle in which the particles were aggregated with each other, the particle size was asymmetric, the average particle diameter was 0.14 μm, and the bulk density was 0.30.
The particles were g / cm ³ and the electrical resistance was 4.2 × 10 ⁷ Ωcm.

30 g of the above-mentioned irregular-shaped maghemite particle powder in air at 400 ° C
The saturation magnetization σs of the particle powder obtained by heating for 30 minutes at
It was emu / g.

Comparative Example 8 100 g of magnetite particles obtained in Comparative Example 4 were heated and oxidized in an electric furnace at 350 ° C. for 30 minutes in air to obtain maghemite particles.

The obtained maghemite particle powder has an average particle diameter of 0.20μ.
m, the bulk density is 0.53 g / cm ³ , and the electric resistance is 6.5 × 10.
The particles were ⁷ Ωcm.

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

<Coating Treatment of Maghemite Particles with Fatty Acids> Examples 21 to 30 and Comparative Examples 9 to 12; Example 21 The spherical Si-containing maghemite particles of Example 11 were used, and the maghemite particles 2000 g and stearic acid 27.8 were used.
and g (corresponding to 1.2 times the equivalent amount of the monolayer coating) were stirred and mixed at a temperature of 120 ° C. for 30 minutes under a N ₂ gas flow.

The electrical resistance of the obtained spherical maghemite particles containing Si coated with stearic acid was as high as 1.2 × 10 ¹⁵ Ωcm, and the electrical resistance after standing for 10 days was 1.3 × 10 ¹⁵
It was as stable as Ωcm. The saturation magnetization σs of the particle powder obtained by heating 30 g of the maghemite particles in air at 400 ° C. for 30 minutes was 76 emu / g.

Examples 22 to 30 and Comparative Examples 9 to 12 Maghemite particles coated with a fatty acid were obtained in the same manner as in Example 21 except that the type of maghemite particles, the type and amount of fatty acid, and the heating temperature were variously changed. Table 3 shows the main manufacturing conditions and various characteristics at this time.

(Effect) The spherical Si-containing maghemite particle powder according to the present invention has high electric resistance, is stable for a long period of time, and is excellent in temperature stability. It is suitable as a material particle powder for magnetic toner for electrostatic copying.

In the production of the magnetic toner, when the spherical Si-containing maghemite particles obtained by the present invention are used, it is possible to obtain an insulating magnetic toner having a high electric resistance and stable for a long period of time. Because it has excellent temperature stability,
It does not cause discoloration or deterioration of magnetic properties during the production or development of the magnetic toner.

[Brief description of drawings]

1 to 5 are electron micrographs (× 20,000) showing the particle morphology (structure) of magnetite particle powder, and FIGS. 1 and 2 show the spherical shapes obtained in Example 1 and Example 3, respectively. The magnetite particle powder exhibited, FIG. 3 shows the hexahedral magnetite particle powder obtained in Comparative Example 1,
FIG. 4 shows the amorphous magnetite particle powder obtained in Comparative Example 2, and FIG. 5 shows the insufficiently spherical magnetite particle powder obtained in Comparative Example 3. 6 and 7 are electron micrographs (× 2) showing the particle morphology (structure) of the spherical maghemite particle powder.
6) and FIG. 7 are the maghemite particle powders obtained in Example 11 and Example 13, respectively.

Claims (2)

[Claims] 1. A Si content of 0.1 to 5.0 atomic% with respect to Fe, a particle surface of which is coated with a saturated fatty acid, and
A spherical maghemite particle powder comprising spherical maghemite particles having an electric resistance of 10 ¹³ to 10 ¹⁵ Ωcm and having excellent temperature stability. 2. A ferrous hydroxide colloid obtained by reacting a ferrous salt aqueous solution with 0.80 to 0.99 equivalents of alkali hydroxide to the ferrous salt in the ferrous salt aqueous solution. When oxidizing the ferrous hydroxide colloid by passing an oxygen-containing gas while heating the ferrous salt reaction aqueous solution, either the alkali hydroxide or the ferrous salt aqueous solution containing the ferrous hydroxide colloid is used. In advance, water-soluble silicate was added to Fe in an amount of 0.1 to 5.0 atomic% in terms of Si, and then 70 to 100
After passing an oxygen-containing gas while heating in the temperature range of ℃, the ferrous hydroxide colloid under the same conditions as the heating and oxidizing conditions, with respect to the ferrous salt remaining in the reaction mother liquor after oxidation 1.
Spherical Si-containing magnetite particles are generated by adding 00 equivalents or more of alkali hydroxide, and then the spherical Si-containing magnetite particles are heated and oxidized in air at 300 to 400 ° C. Obtaining a spherical Si-containing maghemite particles by, the particle surface of the spherical Si-containing maghemite particles by stirring and mixing the spherical Si-containing maghemite particles and saturated fatty acid A method for producing a spherical maghemite particle powder, which comprises spherical maghemite particles, characterized in that is coated with a saturated fatty acid.