JP2634366B2 - Spherical magnetite particle powder, method for producing the same, and magnetic toner containing spherical magnetite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spherical magnetite particle powder, a method for producing the same, and a magnetic toner containing a spherical magnetite, and more specifically, a clear copy in conventional electrophotography, electrostatic recording, electrostatic copying machines, laser printers and the like. Saturation magnetic flux density (σs) in a low magnetic field is high, excellent in dispersibility, and used in a large amount in toner, which is required in the production of small particle size toner required to obtain images and high resolution images. The present invention also relates to a magnetite particle powder which has a good kneading state with a resin, has a uniform particle size distribution of the classified toner and can reduce the toner particle size, a method for producing the same, and a magnetic toner containing the magnetite particle powder.

[0002]

2. Description of the Related Art Production of small particle size toner necessary for obtaining a clear copied image or a high resolution image in electrophotography, electrostatic recording, electrostatic copying machine, laser printer, and the like. In the past, magnetite particle powder has been used, but generally, the particle shape of the magnetite particle powder has a disadvantage that the dispersibility is poor due to cubic, octahedral and irregular shapes. Further, since the saturation magnetic flux density (σs) in a low magnetic field is low, the magnetite particle powder must be used in a large amount in the toner. This not only makes the production of the small particle size toner more difficult, but also makes the dispersion of the magnetite particle powder in the toner difficult, so that the magnetite content in the toner is uneven. Become.

[0003] However, the substances used for the magnetic toner to obtain a clear copy image or a high resolution image are as follows.
It is necessary to have a small particle size, a narrow particle size distribution, and excellent dispersibility. Conventional cubic, octahedral, and irregular particles of magnetite particles must have a large value of the remanent magnetization (σr). Is also considered to be the cause of secondary aggregation,
This is a cause of poor dispersion in the resin. Further, if the content of the magnetite particles in the magnetic toner becomes non-uniform, the particle size distribution becomes non-uniform in the pulverizing and classifying step.

[0004] As a result, the magnetic properties in the toner become non-uniform and the particle size distribution is disturbed, which causes problems such as image density and fog, and also adversely affects the fluidity and life of the toner. Therefore, it is considered that an ideal magnetite particle powder having a high saturation magnetic flux density (σs), excellent dispersibility, and a small particle size and a spherical shape is preferable. No magnetite particle powder is provided.

Accordingly, an object of the present invention is to produce a toner having a small particle size necessary for obtaining a clear copied image or a high-resolution image in conventional electrophotography, electrostatic recording, electrostatic copying machines, laser printers and the like. High saturation magnetic flux density (σs) in a low magnetic field, excellent in dispersibility, good kneading with resin even when used in a large amount in toner, and uniform particle size distribution of toner after classification It is another object of the present invention to provide a magnetite particle powder capable of reducing the toner particle size, a method for producing the same, and a magnetic toner including the magnetite particle powder.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, the particle shape was determined depending on the type of the iron salt, the type of the base used in the present invention and the reaction conditions for the combination thereof. The magnetite particle powder is different, that is, by adjusting the amount of ferrous salt, alkali metal hydroxide and alkali metal carbonate to adjust the PH value of the reaction system and in the reaction process By reducing the tendency of the reaction system to thicken and shortening the oxidation reaction time,
It has been found that the shape and size of the magnetite particle powder can be adjusted. The present invention has been made based on the above findings, and has an average particle size of 0.08 to 0.2 μm and a specific surface area of 5 to 5.
２０20 m ² / g, containing silicon (Si) in an amount of 0.1 to 3.0 atomic% with respect to iron (Fe), and in a low magnetic field (1 K 2 O 3
e) providing a spherical magnetite particle powder characterized by having a saturation magnetic flux density (σs) of 65 emu / g or more.

Further, the present invention provides a preferable method for producing the spherical magnetite particle powder of the present invention, which comprises an alkali metal hydroxide and an alkali metal carbonate, and further comprises silicon (S).
i) with respect to the total amount of iron (Fe) added to the reaction
A mixed solution containing 3.0 atomic% contains ferrous chloride in a molar ratio of 0.1 to 0.5 with respect to all ferrous salts added to the reaction,
And ferric chloride in a molar ratio of 1.0 to ferrous chloride.
To 5.0 to produce a magnetite seed crystal, and then an amount of ferrous chloride in a molar ratio of 0.5 to 0.95 to the total ferrous salt added to the reaction. The pH value of the reaction system is adjusted to 9.0 to 12.5 by adding a solution containing
An oxidizing gas is blown while maintaining the reaction temperature at 80 to 100 ° C. to generate magnetite particles, and thereafter, filtration, washing, drying, and grinding are performed. Is what you do.

In the method for producing spherical magnetite particles according to the present invention, the PH value of the reaction system is adjusted by the molar ratio of each of ferrous salt, alkali metal hydroxide and alkali metal carbonate, and the molar ratio is Needs accuracy. That is, the molar ratio of the ferrous salt, alkali metal hydroxide and alkali metal carbonate added to the reaction was 1.
0: 0.5 to 1.5: 1.0 to 3.0, and the molar ratio of the ferrous salt and the ferric salt used in the primary reaction is 1.0: 1.0 to 5.0, respectively. It is important that the PH value of the reaction system during the reaction be kept in the range of 9.0 to 12.5, and the shape of the magnetite particle powder generated at this time is a polyhedral shape. The shape of the particle powder becomes spherical.

Hereinafter, preferred embodiments of the method for producing magnetite particles according to the present invention will be described in detail. While aerating air (oxidizing gas) at a rate of 5 to 10 L / min into a stirred oxidation reaction tank having a gas vent tube, all ferrous salts, alkali metal hydroxides and The molar ratio of the alkali metal carbonate is 1.0:
0.8 to 1.1: A mixed solution of 1.0 to 1.5 is added. Furthermore, silicon (Si) is contained in the mixed solution of the reaction tank.
To the total amount of iron (Fe) added to the reaction.
Then, the temperature of the reaction vessel is raised to 80 to 100 ° C. while stirring.

Next, as a primary reaction, ferrous chloride prepared separately is contained in a molar ratio of 0.1 to 0.5 with respect to all ferrous salts added to the reaction, and ferric chloride is converted to the above-mentioned chloride. A mixed solution containing a molar ratio of 1.0 to 5.0 with respect to ferrous iron was dropped into the above-mentioned reaction tank for about 5 to 10 minutes by using a metering pump, so that colloidal or gel-like magnetite was formed. Generate seed particles. Thereafter, the inside of the reaction tank is replaced with nitrogen from air.

At this time, the ferrous chloride used in the primary reaction has a molar ratio of 0.1 to the total ferrous salt added to the reaction in order to finally produce magnetite particles having excellent dispersibility. 1 to 0.5. When the molar ratio is less than 0.1, the formed magnetite seed particles are irregular or lumpy, and when the molar ratio is more than 0.5, the generated magnetite seed particles are large. It is not suitable for

The molar ratio of the ferrous salt and the ferric salt in the primary reaction is 1.0: 1.0 to 5.0.
However, considering the ferrite composition due to the spinel structure of magnetite, the ratio is more preferably 1.0: 1.5 to 3.0.

[0013] When the time of dropping the mixed solution for the primary reaction is less than 5 minutes, the seed crystal particles of the magnetite to be formed are necklace-shaped and largely inferior in dispersibility. The magnetite seed crystal particles become too fine and become colloidal or necklace-like, both of which are not preferred.

Next, as a secondary reaction, a solution containing ferrous chloride in a molar ratio of 0.5 to 0.95 with respect to all ferrous salts added to the reaction is placed in the above-mentioned reaction tank. In addition, the pH value of the reaction system is set to 9.0 to 12.5, and the reaction temperature is set to 80 to 1
After stirring for about 5 to 10 minutes while maintaining the temperature at 00 ° C., the inside of the reaction tank is replaced again with nitrogen as air, which is an oxidizing gas, to restart the oxidation reaction to generate magnetite particles. Thereafter, the magnetite particles are filtered, washed with water, dried and pulverized by a conventional method to obtain a magnetite particle powder as a final product.

At this time, the pH value of the reaction system is controlled to 9.0 to suppress the tendency of the reaction system to thicken in the course of the reaction.
12.5. Further, the time of the whole oxidation reaction as the secondary reaction is preferably set to 2 to 3 hours.

The rate of the oxidation reaction depends on the rate of air flow of the oxidizing gas (air). If the air flow rate is too high and the oxidation is too fast, the generated magnetite particles will be extremely fine particles. If the oxidation is too slow, the magnetite particles will be large with a polyhedral shape.

Therefore, in order to make the particle size and size of the generated magnetite particles suitable for the magnetic toner, the oxidizing gas is passed at a rate of 5 to 10 l / m 2.
It is preferably in. Air, oxygen, or the like is used as the oxidizing gas.

Next, the reactants used in the method for producing spherical magnetite particle powder of the present invention will be described in detail. Examples of the alkali metal hydroxide and alkali metal carbonate used in the present invention include, but are not particularly limited to, caustic soda and sodium carbonate. The concentration of each solution of the alkali metal hydroxide and the alkali metal carbonate is the same as that used in a usual method for producing magnetite particle powder, and is 0.5 to 1.5 mol / liter.

The silicon (Si) element used in the present invention is used in the form of a silicon (Si) compound, for example, Na ₂ Si
Examples include silicates such as O ₃ and Na ₂ SiO ₅ , hydroxides such as Si (OH) ₄ and oxides such as SiO _2, but are not particularly limited thereto.

If the amount of silicon (Si) used is less than 0.1 atomic% with respect to the total amount of iron (Fe) added to the reaction, the shape of the magnetite particle powder as a final product becomes large. If the content exceeds 3.0 atomic%, the shape of the magnetite particle powder is disturbed, which is not suitable for the purpose of the present invention.

According to the method for producing spherical magnetite particle powder of the present invention described above, the average particle size is 0.08 to 0.2 μm.
m, the specific surface area is 5 to ²⁰ m ² / g, and silicon (S
i) containing 0.1 to 3.0 atomic% with respect to iron (Fe), and a saturation magnetic flux density (σ) in a low magnetic field (1 K Oe).
A spherical magnetite particle powder having s) of 65 emu / g or more is obtained. Since the magnetite particle powder of the present invention has silicon (Si) inside and on the surface of the magnetite particle powder, it has excellent dispersibility and can be used as a resin carrier or the like.

The magnetite particles have a saturation magnetic flux density (σs) of 65 em in a low magnetic field (1 K Oe).
u / g or more, so that the conventional saturation magnetic flux density (σs) can be maintained even if the content of the magnetite particle powder in the toner is smaller than that of the usual magnetite particle powder.

The evaluation of the dispersibility of the magnetite particle powder of the present invention in a resin was performed by the following method. That is, the magnetite particle powder is melt-kneaded with two pressurized heat rollers by a conventional method, and a magnetic toner having an average particle diameter of 10 μm is obtained using a jet mill type pulverizer and a classifier.
With respect to this magnetic toner, the magnetic distribution of the magnetic toner was measured by the following brush scattering method using an improved developer box for commercially available one-component copying.

In the brush scattering method, when the number of rotations of the mag roller is variably improved and the charged amount of the magnetic toner is fixed, the number of rotations is increased to increase the number of rotations of the toner. Is a method of measuring the dispersibility of magnetite in the toner by measuring the amount of the toner and the magnetism of the toner. In other words, the brush scattering method is a measurement method using the fact that when the dispersion of the magnetite particle powder in the resin is poor, the magnetic force of each toner is different, so that the toner having a weak magnetic force is quickly blown.

As a result of evaluating the dispersibility of the magnetite particle powder of the present invention in the resin using the above-mentioned measuring method, the magnetite particle powder of the present invention has a uniform particle size distribution while exhibiting a fine particle shape. The particle shape is spherical, and silicon (Si) is retained inside and on the surface, so that the dispersibility is excellent, and the kneading state with the resin which is a necessary condition for the small particle size toner is good. The magnetic properties were also uniform. Therefore, since the content of the magnetite particle powder per manufactured toner is uniform, the image quality and resolution of the copy are improved, and a clear copy image is obtained without fear of fogging or toner scattering.

[0026]

EXAMPLES Hereinafter, the spherical magnetite particle powder of the present invention and a method for producing the same will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In addition, each reaction amount of the substance used in the following Examples 1 to 4 and Comparative Examples 1 to 4 is shown in [Table 1].

<Embodiment 1> Internal volume 5 having gas vent tube
While passing air at a rate of 10 liter / min into a 0-liter stirred oxidation reaction tank, 0.64 kg of solid caustic soda and 2.544 kg of sodium carbonate were added to 22.
Dissolved in 5 liters and 60g of silicon (Si) compound
Was dissolved and stirred, and the temperature of the reaction vessel was raised to 90 to 100 ° C. Next, as a primary reaction, a separately prepared concentration of 4
717 ml of 25 g / l ferrous chloride solution for seed crystals and 1304 ml of 510 g / l ferric chloride solution
Water was mixed with the mixed solution containing the above, and the mixed solution having a total volume of 2.5 liters was dropped into the above-mentioned reaction tank using a metering pump in about 7 minutes, and the colloidal or gel-like magnetite seeds were added. After generating the crystal grains, the inside of the reaction vessel was replaced with nitrogen from air. Next, as a secondary reaction, water was mixed with 4046 ml of a ferrous chloride solution having a concentration of 425 g / liter, and a total of 15 liters of the ferrous chloride solution was added to the reaction tank to adjust the PH value to 9. 0 to 12.5
The mixture was stirred for about 5 minutes while maintaining the reaction temperature at 80 to 100 ° C. After that, air was introduced into the reaction tank by 10 times.
Ventilation was performed at a rate of 1 liter / min, and the inside of the reaction tank was replaced with nitrogen to air to restart the oxidation reaction, thereby producing magnetite particles. The time for the entire secondary reaction at this time was about 2.5 hours.

Thereafter, the magnetite particle powder produced by the above method was filtered, washed with water, dried and pulverized by a conventional method, and the dispersibility of the generated magnetite particle powder in the resin was evaluated by a brush scattering method. The results are shown in Table 2 and the particle structure of the magnetite particles is shown in FIG. As is clear from the results in Table 2, the magnetite particles had an average particle size of 0.16 μm and a specific surface area of 1
1.1 m ² / g, containing 2.4 atomic% of silicon (Si) with respect to iron (Fe), and having a saturation magnetic flux density (σs) in a low magnetic field (1 K Oe) of 70.1 emu / g. there were. Further, as is apparent from the results of FIG. 1, the shape of the magnetite particle powder was spherical.

<Examples 2 to 4> Except that the addition amount of the silicon (Si) compound was changed, the reaction was carried out under the same reaction conditions as in Example 1, and the magnetite particle powder having a spherical shape was obtained by miniaturization. It was manufactured, and the dispersibility of the magnetite particle powder in the resin was evaluated in the same manner as in Example 1. The results are shown in [Table 2]. As is clear from the results in Table 2, the magnetite particle powders produced in the respective examples all have an average particle diameter of 0.08 to 0.2 μm.
m, a spherical shape, a specific surface area of 5 to ²⁰ m ² / g, and a saturation magnetic flux density (σ) in a low magnetic field (1 K Oe).
s) was 65 emu / g or more.

<Comparative Example 1> Dropping of a mixed solution containing a ferrous chloride solution and a ferric chloride solution was omitted, and 4760 ml of a ferrous chloride solution having a concentration of 425 g / liter was used as a secondary reaction.
The reaction was carried out under the same reaction conditions as in Example 1 except that a ferrous chloride solution having a total volume of 15 liters was added to the reaction vessel to produce magnetite particle powder. In the same manner as in Example 1, the dispersibility of the magnetite particle powder in the resin was evaluated. The results are shown in Table 2 and the particle structure of the magnetite particles is shown in FIG. Table 2
As is clear from the results, the magnetite particle powder had a low saturation magnetic flux density (σs) in a low magnetic field (1 K Oe) of 62.3 emu / g. Further, as is apparent from the results of FIG. 2, the shape of the magnetite particle powder was octahedral.

<Comparative Example 2> A magnetite particle powder was prepared by reacting under the same reaction conditions as in Example 1 except that the addition of sodium carbonate was omitted. Was evaluated for dispersibility. The results are shown in [Table 2]. As is clear from the results in Table 2,
The magnetite particle powder has an average particle diameter of 0.11 to 0.11.
0.3μm, non-uniform particle size distribution, low magnetic field (1K Oe
) Also has a saturation magnetic flux density (σs) of 61.8 emu /
g. In addition, the shape of the magnetite particle powder was irregular.

<Comparative Example 3> The addition of sodium carbonate and the replacement of the air inside the reaction tank with nitrogen during the secondary reaction were omitted, and the secondary reaction was carried out in 4760 ml of a ferrous chloride solution having a concentration of 425 g / l. Water was mixed and the reaction was carried out under the same reaction conditions as in Example 1 except that a ferrous chloride solution having a total volume of 15 liters was added to the above-mentioned reaction vessel, thereby producing magnetite particles. The dispersibility of the magnetite particle powder in the resin was evaluated in the same manner as described above. The results are shown in [Table 2]. As is clear from the results in Table 2, the magnetite particle powder has an average particle size of 0.10 to 0.3.
μm, the particle size distribution was not uniform, and the saturation magnetic flux density (σs) in a low magnetic field (1 K Oe) was as low as 60.6 emu / g. Further, the shape of the magnetite particle powder was octahedral, and some of the magnetite particles had a needle shape.

Comparative Example 4 A magnetite particle powder was produced by reacting under the same reaction conditions as in Example 1 except that the addition of the silicon (Si) compound was omitted, and the magnetite particle powder was produced in the same manner as in Example 1. Was evaluated for dispersibility in a resin. The results are shown in [Table 2]. As is clear from the results in Table 2, the magnetite particles have an average particle size of 0.10 to 0.3 μm, a nonuniform particle size distribution, and a saturation magnetic flux density (σs) in a low magnetic field (1 K Oe). 50.8
emu / g was low. The magnetite had an octahedral shape.

[0034]

[Table 1]

[Table 2]

[0035]

The spherical magnetite particle powder of the present invention, the method for producing the same, and the magnetic toner containing the spherical magnetite can be used to produce a sharp copy image or a high-resolution image in an electrophotography, electrostatic recording, electrostatic copier, laser printer, or the like. High saturation magnetic flux density (σs) in a low magnetic field, excellent in dispersibility, and kneaded with resin even when used in a large amount in toner The particle size distribution of the classified toner is uniform, and the particle size of the toner can be reduced.

[Brief description of the drawings]

FIG. 1 is an electron micrograph showing the particle structure of a magnetite particle powder produced in Example 1 of the present invention.

FIG. 2 is an electron micrograph showing the particle structure of the magnetite particle powder produced in Comparative Example 1.

 ────────────────────────────────────────────────── ─── Continuation of front page (56) References JP 5-213620 (JP, A) JP 5-286723 (JP, A) JP 3-9045 (JP, B2)

Claims (3)

(57) [Claims] An average particle size is 0.08 to 0.2 μm, a specific surface area is 5 to ²⁰ m ² / g, and silicon (Si) is contained in an amount of 0.1 to 3.0 atomic% with respect to iron (Fe). Saturated magnetic flux density (σs) at low magnetic field (1K Oe) is 65e
Spherical magnetite particle powder characterized by being at least mu / g. 2. The method for producing spherical magnetite particles according to claim 1, wherein the total amount of iron (Fe) containing an alkali metal hydroxide and an alkali metal carbonate and further adding silicon (Si) to the reaction. In a mixed solution containing 0.1 to 3.0 atomic%, ferrous chloride is contained in a molar ratio of 0.1 to 0.5 with respect to all ferrous salts added to the reaction, and ferric chloride is contained. A mixed solution containing 1.0 to 5.0 in molar ratio with respect to the ferrous chloride is added to generate a magnetite seed crystal, and then in a molar ratio of 0.1 to the total ferrous salt added to the reaction. 5
A solution containing ferrous chloride in an amount of 0.95 to 0.95 was added to adjust the pH value of the reaction system to 9.0 to 12.5, and the reaction temperature to 80
A method for producing magnetite particle powder, comprising blowing an oxidizing gas while maintaining the temperature at 〜100 ° C. to generate magnetite particles, and then performing filtration, washing with water, drying and pulverization. 3. A toner comprising the magnetite particle powder according to claim 1.