JP3457971B2 - Magnetite particle powder, method for producing the same, and magnetic toner containing magnetite particle powder - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic material for toner used in electrophotography, electrostatic recording, etc., and particularly, it has high initial chargeability and filming (toner particles adhere to a photosensitive drum). The present invention relates to a magnetite particle powder having an preventing effect, a method for producing the same, and a magnetic toner containing the magnetite particle powder.

[0002]

2. Description of the Related Art Conventionally, as magnetic materials for toners used in electrophotography, electrostatic recording, etc., magnetic oxide particles such as magnetite or ferrite or magnetic metal particles have been used. Is used. The general manufacturing method of magnetic toner is the process of adding a dye, a pigment, a conductive material, etc. to the magnetic material of the main raw material as needed in addition to the binder resin, heating, kneading, cooling, and then pulverizing. However, at this time, the magnetic material is often exposed on the surface of the magnetic toner particles. Therefore, the triboelectrification amount of the magnetic toner particles becomes non-uniform, and the ground fogging phenomenon or the fogging phenomenon occurs, the fluidity of the toner deteriorates due to the influence of water in a high humidity environment characteristic, or the surface of the photoconductor is damaged. Problems such as occur. Further exposed magnetite,
There are drawbacks such as causing the filming phenomenon,
In order to solve these problems, attempts have been made to improve magnetic materials, but the current situation is that they are still insufficient.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks, to provide a magnetite particle powder having properties suitable for a magnetic toner and also having an effect of preventing filming, and a method for producing the same. .

[0004]

According to the present invention, magnesium oxide is contained in an amount of 0.5 to 2.5% by weight with respect to Fe in terms of Mg, and a particle-shaped projection is provided on the surface of BE.
Magnetite particles having a T specific surface area of 10 to 30 m ² / g, and a ferrous salt aqueous solution to which caustic alkali and / or alkali carbonate are added, and then a gas containing oxygen is aerated to produce magnetite. In the reaction process that produces
From the start of the oxidation reaction until the oxidation rate of the ferrous salt reaches 60%, a method for producing the magnetite particle powder, which comprises adding a magnesium compound, and a magnetic toner containing the magnetite particle powder Is.

Details of the conditions for producing the magnetite particle powder of the present invention are as follows. That is, while replacing the stirring reaction tank with N ₂ gas, an equivalent amount or more of a caustic alkali and / or alkali carbonate aqueous solution is added to an aqueous solution of a ferrous salt, ie, ferrous chloride or ferrous sulfate, and the reaction temperature is adjusted.
While maintaining the temperature at 70 to 95 ° C, a gas containing oxygen (air, etc.) was passed through the suspension of the hydrous iron solution at a rate at which the reaction was completed in 2 to 3 hours, and a separately prepared magnesium compound aqueous solution was added to ferrous iron. Until the oxidation rate of the salt reaches 60%, for example, the salt is dropped at a predetermined rate at the same time when the oxidation starts. Here, when the magnesium compound is added to the suspension of the hydrous iron solution before the start of the oxidation reaction, it becomes ferrosoferric oxide having a spinel structure of a magneteferrite composition or an iron oxide, which is a feature of the present invention. Magnetite with a hump-shaped protrusion is not possible. In the above reaction, the oxidation rate changes depending on the change in the flow rate of the oxidizing gas. If the oxidation rate is high, the particles tend to be fine, and if the oxidation rate is low, the particles become large. In the method of the present invention, the aeration rate is set to the above in order to obtain a particle size suitable for magnetic toners, but the addition method of the magnesium compound is the same even for the oxidation rate in this range.

As the caustic alkali and the alkali carbonate used in the present invention, caustic soda and sodium carbonate are generally used, and the concentration of the aqueous solution is the same as that used in the usual magnetite-forming reaction (0.1 to 0.5 mol / l). Good. As the magnesium compound used in the present invention, basic magnesium carbonate, magnesium sulfate, magnesium chloride and the like can be mentioned. These inorganic salts of gnesium may be used alone or in combination of two or more.
Particularly preferred is magnesium oxide.

The magnetite produced under these conditions is
Specifically, 50 particles measured on a scanning electron microscope have an average particle size of 0.1 to 0.3 μm, a BET specific surface area of 10 to 30 m ² / g due to nitrogen adsorption, and a measurement using a powder tester manufactured by Hosokawa Micron Co., Ltd. Apparent density of 0.5-0.8g / cm ³
And, the Mg content in magnetite is 0.5 with respect to Fe in terms of Mg.
It is a magnetite particle powder having a charge amount of +5 to 40 μc / g measured by a blow-off powder charge amount measuring device manufactured by Toshiba Chemical Co., Ltd. is there. Magnetite particle powder containing magnesium of the present invention is different from the conventional cubic or spherical, amorphous magnetite, it is fine, has a large specific surface area, and is excellent in oxidative stability, so that its own charge amount is large. , Even when used for high speed copiers, etc.
The initial charge rises quickly and is stable. Further, even if magnetite is exposed on the fractured surface of the magnetic toner generated by pulverization, and even if magnetite is attached to the surface of the toner particles, the environmental characteristics are good and the charge amount is always stable. Regarding the dispersibility, the apparent density is large, and since the particle surface has the protrusions having the shape of a tub, the secondary cohesive force is weak and the flowability is excellent. The magnetite content per toner particle is evenly distributed even when kneading Has the advantage that it is constant. In addition to the above advantages, it is also characterized by good environmental characteristics and effective filming prevention. That is, in the conventional toner, magnetite is often exposed on the surface of the toner, the electric resistance is lowered due to the influence of the humidity of the environmental conditions, and the charge amount becomes non-uniform, which is a big defect in the image. In addition, the exposure of magnetite causes problems such as damage to the surface of the photoconductor and deterioration of fluidity. Further, in order to remove the residual toner on the surface of the photoconductor, various cleaning members are brought into pressure contact with each other with an appropriate pressure to remove the residual toner, but the toner is fixed on the surface of the photoconductor drum during repeated use. However, a toner film is formed, which causes cleaning failure and causes deterioration of the electrophotographic state.Therefore, a method of intentionally adding magnetite as an external additive to the toner particle surface has been adopted. It may also be a cause of defects. On the other hand, since the magnetite of the present invention is less affected by environmental characteristics, the charge amount and fluidity are always constant,
Moreover, the surface-shaped protrusions protruding from the surface of the magnetic toner particles scrape off the toner adhered to the surface of the photoconductor without damaging the surface.

[0008]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Comparative Example 1 N ₂ gas (3 liters) was added to a stirring tank having a gas blowing pipe.
/ min) while caustic soda (0.192kg, 4.8mol)
Was dissolved in water (30 liters), added to a stirring tank and heated to 90 ° C. with stirring. Thereafter, the temperature was maintained at 90 ° C until the reaction was completed. Next, ferrous chloride aqueous solution (0.36 liter, 1.2mo
A mixed solution of (1) and water (9.64 liters) was added, the hydrous iron suspension was stirred for 30 minutes, and the substitution was continued. afterwards,
Oxidizing gas (air) was aerated (4 l / min) to start the reaction. The oxidation rate reached about 60% in 2 hours, and when the reaction was further continued, the reaction time was 2.5 hours in total and magnetite particles were generated (mol concentration of total iron was 0.3 mol / l).
did. The produced particles were filtered, washed with water, dried and pulverized by a conventional method, and the obtained magnetite particles were ordinary cubic particles. FIG. 1 is an electron micrograph showing the structure of the magnetite particles. Comparative Example 2 From the beginning of the reaction, an aqueous solution of Mg (MgCl ₂ · 6H ₂ O 4 mol% /
FeCl ₂ ) was mixed in an aqueous solution of ferrous chloride and reacted, and the reaction was carried out in the same manner as in Comparative Example 1. As a result, the generated magnetite particle powder was found to have a large amount of tub-shaped protrusions on the surface of the magnetite particles. I could not do it. FIG. 2 is an electron micrograph showing the structure of the magnetite particles.

Example 1 Up to the step before the oxidation reaction, the reaction was performed under the same conditions as in Comparative Example 1, and when the oxidation reaction was started, a separately prepared aqueous solution of Mg (MgCl ₂ .6H ₂ O 4 mol% / FeCl ₂ 1 liter) was used. ) Was added at a constant rate (8.3 ml / min, 2 hours) from the upper part of the stirring tank with a metering pump, and the reaction was continued for a total reaction time of 2.5 hours, and magnetite particles were formed. This magnetite particle powder was a particle having a hump-shaped projection on the surface of the magnetite particle. FIG. 3 is an electron micrograph showing the structure of the magnetite particles. Example 2 The total iron mol concentration of the produced magnetite particles is 0.2 mol /
The reaction was carried out in the same manner as in Example 1 except that the amount of the ferrous chloride aqueous solution to be added was changed so that it became 1. The produced magnetite particle powder was particles having a tab-shaped projection on the surface of the magnetite particles. FIG. 4 is an electron micrograph showing the structure of the magnetite particles. Examples 3 to 4 The reaction was carried out in the same manner as in Example 1 except that the amount of the ferrous chloride aqueous solution added was changed as shown in Table 1 so that the mol concentration of total iron in the generated magnetite particles was changed. went. The generated magnetite particle powders were particles each having a tsubu-shaped protrusion on the particle surface similar to those in Examples 1 and 2. Examples 5 to 6 The reaction was performed in the same manner as in Example 1 except that the concentration of the Mg aqueous solution added was changed as shown in Table 1. The generated magnetite particle powders were particles each having a tsubu-shaped protrusion on the particle surface similar to those in Examples 1 and 2. Examples 7 to 8 The type of magnesium compound or alkali to be added is
The reaction was carried out in the same manner as in Example 1 except that the changes were made as shown in Table 1. The generated magnetite particle powders were all particles having a tsubu-shaped protrusion on the particle surface as in Examples 1 and 2. Table 1 shows the reaction conditions of Comparative Examples 1 and 2 and Examples 1 to 8 and the physical properties of the produced magnetite.

[0010]

[Table 1]

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the particle structure of magnetite particles obtained in Comparative Example 1.

FIG. 2 is an electron micrograph showing a particle structure of magnetite particles obtained in Comparative Example 2.

FIG. 3 is an electron micrograph showing the particle structure of magnetite particles obtained in Example 1.

FIG. 4 is an electron micrograph showing the particle structure of magnetite particles obtained in Example 2.

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Claims (3)

(57) [Claims] 1. Magnesium oxide is contained in an amount of 0.5 to 2.5% by weight with respect to Fe in terms of Mg, and the surface of the particles has a hump-like projection and a BET specific surface area of 10 to 30 m ² / g.
Magnetite particles, characterized in that. 2. A ferrous salt aqueous solution containing caustic and / or
Alternatively, in the reaction process of adding alkali carbonate and then a gas containing oxygen to generate magnetite, a magnesium compound is added from the start of the oxidation reaction until the oxidation rate of the ferrous salt reaches 60%. The method for producing magnetite particle powder according to claim 1, wherein 3. A magnetic toner containing the magnetite particle powder according to claim 1.