JP2634366C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing spherical magnetite particles,
The saturation magnetic flux density (σs) in a low magnetic field, which is required in the production of a small particle size toner required for obtaining a clear copied image or a high-resolution image in an electrostatic recording, an electrostatic copying machine, a laser printer, or the like. ) Is excellent in dispersibility, is well kneaded with the resin even when used in a large amount in the toner, has a uniform particle size distribution of the classified toner, and can reduce the toner particle size. It relates to a manufacturing method. 2. Description of the Related Art A small particle size required for obtaining a clear copied image or a high-resolution image in an electrophotography, an electrostatic recording, an electrostatic copying machine, a laser printer or the like. In the production of toner, magnetite particle powder has been conventionally used, but generally, the particle shape of the magnetite particle powder is disadvantageous in that it has poor dispersibility due to cubic shape, octahedral shape, and irregular shape. In addition, the magnetite particle powder must be used in a large amount in toner because of its low saturation magnetic flux density (σs) in a low magnetic field. 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. However, a substance used for a magnetic toner in order to obtain a clear copy image or a high-resolution image needs to have a small particle size, a narrow particle size distribution, and excellent dispersibility. The cubic, octahedral, and irregular particles of conventional magnetite particles are considered to have a large remanent magnetization (σr) value, which is likely to cause secondary agglomeration and cause poor dispersion in the resin. It is. 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] Therefore, 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 small particle size toner necessary for obtaining a clear copied image or a high-resolution image in a conventional electrophotography, electrostatic recording, electrostatic copying machine, laser printer, or 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 method for producing magnetite particle powder that can reduce the toner particle size. Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, the type of iron salt used in the present invention, the type of base, and the reaction conditions for the combination thereof have been determined. The magnetite particle powder having a different particle shape is produced, 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 It has been found that the shape and size of the magnetite particle powder can be adjusted by reducing the tendency of the reaction system to thicken in the reaction process and shortening the oxidation reaction time. The present invention has been made based on the above findings, and has an average particle size of 0.08 to 0.2.
μm, a specific surface area of 5 to ²⁰ m ² / g, containing silicon (Si) in an amount of 0.1 to 3.0 atomic% with respect to iron (Fe), and a saturation magnetic flux density (1 K Oe) in a low magnetic field (1 K Oe).
s) is 65 emu / g or more, and a method for producing spherical magnetite particle powder. That is, the present invention provides a preferred method for producing the spherical magnetite particle powder,
Ferrous chloride is added to a mixed solution containing an alkali metal hydroxide and an alkali metal carbonate and further containing 0.1 to 3.0 atomic% of silicon (Si) based on the total iron (Fe) added to the reaction. A mixed solution containing a molar ratio of 0.1 to 0.5 with respect to all ferrous salts added to the reaction and containing a ferric chloride with a molar ratio of 1.0 to 5.0 with respect to the ferrous chloride. To form a magnetite seed crystal, and then add 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 to form a reaction system. PH of 9.0 to 12.5, and while maintaining the reaction temperature at 80 to 100 ° C,
An object of the present invention is to provide a method for producing magnetite particle powder, which comprises blowing an oxidizing gas to generate magnetite particles, and thereafter performing filtration, washing, drying, and pulverization. In the method for producing a spherical magnetite particle powder of 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 ferrous salt and ferric salt used in the primary reaction is 1.0: 1.0 to 5.0, respectively. PH of reaction system inside
It is important to keep the value 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. By further refining the shape, the shape of the magnetite particle powder becomes spherical. become. Hereinafter, preferred embodiments of the method for producing magnetite particle powder of the present invention will be described in detail. Air (oxidizing gas) is introduced into a stirring type oxidation reaction tank having a gas vent tube by 5 to 10%.
While aerating at a rate of 1 liter / min, the molar ratio of all ferrous salts, alkali metal hydroxides and alkali metal carbonates added to the reaction was 1.0: 0.8 to 1 respectively.
. 1: A mixed solution of 1.0 to 1.5 is added. Furthermore, in the mixed solution of the above-mentioned reaction tank, silicon (Si) is added to the reaction by all iron (
Fe) is added so as to contain 0.1 to 3.0 atomic% based on the amount of Fe), and the temperature of the reaction vessel is raised to 80 to 100 ° C. while stirring. [0010] 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 added 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, but more preferably 1.0: 1.5 to 3.0 in consideration of the ferrite composition due to the spinel structure of magnetite. Further, if the drop time of the mixed solution for the primary reaction is less than 5 minutes, the generated magnetite seed crystal particles are necklace-shaped and have poor dispersibility.
If the time is longer than 0 minutes, the generated magnetite seed crystal particles become too fine and become colloidal or necklace-like, and both are not preferred. [0014] Next, as a secondary reaction, a molar ratio of 0.5 to 0.5 with respect to all ferrous salts added to the reaction.
A solution containing ferrous chloride in an amount of 0.95 was added to the above reaction vessel, and the P of the reaction system was added.
The H value is set to 9.0 to 12.5, and the reaction temperature is maintained at 80 to 100 ° C. for about 5 to
After stirring for about 10 minutes, the inside of the reaction tank is replaced again with nitrogen as air, which is an oxidizing gas, and the oxidation reaction is restarted 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 set to 9.0 to 12.5 in order to suppress the tendency of the reaction system to thicken in a reaction process. 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, and the air flow rate will be reduced. 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 / min.
It is preferred that Air, oxygen, or the like is used as the oxidizing gas. Next, the reactants used in the method for producing the spherical magnetite particle powder of the present invention will be described in detail. As the alkali metal hydroxide and alkali metal carbonate used in the present invention,
Examples include caustic soda and sodium carbonate, but are not particularly limited thereto. 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, a silicate such as Na ₂ SiO ₃ or Na ₂ SiO _5, or a silicate such as Si (OH) ₄ . Examples include hydroxides and oxides such as SiO _2, but are not particularly limited thereto. If the silicon (Si) used is less than 0.1 atomic% with respect to the total iron (Fe) added to the reaction, the shape of the magnetite particle powder as the final product becomes large, If it exceeds 3.0 atomic%, the shape of the magnetite particle powder will be disturbed. 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, specific surface area of 5 to ²⁰ 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 Oe). A spherical magnetite particle powder having a saturation magnetic flux density (σs) of 65 emu / g or more is obtained. The magnetite particle powder obtained by the production method of the present invention has excellent dispersibility since silicon (Si) is present inside and on the surface of the magnetite particle powder, and can be used as a resin carrier or the like. Further, the magnetite particle powder has a saturation magnetic flux density (σs) of 65 emu / g or more in a low magnetic field (1 K Oe). Therefore, the content of the magnetite particle powder in the toner is reduced to a normal magnetite particle powder. Even if it is less, the conventional saturation magnetic flux density (σs) can be maintained. The evaluation of the dispersibility of the magnetite particle powder obtained by the production method of the present invention in a resin was performed by the following method. That is, the magnetite particle powder is melt-kneaded with a two-pressure heating roller by a conventional method, and a magnetic toner having an average particle size of 10 μm is obtained using a jet mill type pulverizer and a classifier. 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. The brush scattering method refers to a method in which the number of rotations of a mag roller is variably improved and the amount of magnetic toner charged is kept constant. By increasing the number of rotations, toner having a weak magnetic force (content of a magnetic material) 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 obtained by the production method of the present invention in a resin using the above measurement method, this magnetite particle powder has a fine particle shape, The particle size distribution is uniform, the particle shape is spherical, and silicon (Si) is retained inside and on the surface, so that it has excellent dispersibility and is a necessary condition for a small particle size toner. And the magnetic properties were 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. EXAMPLES Hereinafter, the method for producing the spherical magnetite particle powder of the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto. The reaction amounts of the substances used in Examples 1 to 4 and Comparative Examples 1 to 4 below are shown in Table 1 below.
]. <Example 1> [0027] Into a 50-liter internal stirring type oxidation reaction tank having a gas ventilation tube, 1 air was introduced.
While aerating at a rate of 0 liter / min, 0.64 kg of solid caustic soda and 2.544 kg of sodium carbonate were dissolved in 22.5 liters of water, and silicon (Si) was further added.
60 g of the compound was dissolved and the temperature of the reaction vessel was raised to 90 to 100 ° C. while stirring. Next, as a primary reaction, water was mixed with a separately prepared mixed solution containing 717 g of a ferrous chloride solution for seed crystals having a concentration of 425 g / l and 1304 ml of a ferric chloride solution having a concentration of 510 g / l, and the total amount was 2.5 g. A liter of the mixed solution was dropped into the reactor using a metering pump in about 7 minutes to generate colloidal or gel-like magnetite seed crystal particles. Was replaced with nitrogen. Next, as a secondary reaction, 4046 ml of a ferrous chloride solution having a concentration of 425 g / liter.
, And a ferrous chloride solution having a total volume of 15 liters was added to the reaction vessel to adjust the pH value to 9.0 to 12.5, while maintaining the reaction temperature at 80 to 100 ° C. Stir for about 5 minutes. Then, 10 liters / mi of air was introduced into the reactor.
Air was passed at a rate of n, 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. After that, the magnetite particle powder produced by the above-mentioned method is filtered, washed with water by a conventional method,
Drying and pulverization were performed, and the dispersibility of the magnetite particle powder generated by a brush scattering method in a resin was evaluated. 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 particle powder has an average particle size of 0.1.
16 μm, a specific surface area of 11.1 m ² / g, containing 2.4 atomic% of silicon (Si) with respect to iron (Fe), and a saturation magnetic flux density (σs) in a low magnetic field (1 K Oe).
) Was 70.1 emu / g. 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 performed 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 evident from the results in Table 2, the magnetite particle powders produced in the respective examples all have a small spherical shape with an average particle size of 0.08 to 0.2 μm,
The specific surface area was 5 to ²⁰ m ² / g, and the saturation magnetic flux density (σs) in a low magnetic field (1 K Oe) 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 water was mixed with 4760 ml of a ferrous chloride solution having a concentration of 425 g / liter as a secondary reaction. A magnetite particle powder was produced by reacting under the same reaction conditions as in Example 1 except that a ferrous chloride solution having a total volume of 15 liters was added into the reaction tank, and a magnetite particle powder was produced 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. As is evident from the results in Table 2, the magnetite particle powder has a low magnetic field (1 K Oe).
)) Was as low as 62.3 emu / g. As is clear from the results shown in FIG. 2, the shape of the magnetite particles was octahedral. Comparative Example 2 A magnetite particle powder was produced by reacting under the same reaction conditions as in Example 1 except that the addition of sodium carbonate was omitted, and the same procedure as in Example 1 was carried out. 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 size of 0.1.
The particle size distribution was 11 to 0.3 μm, the particle size distribution was non-uniform, and the saturation magnetic flux density (σs) in a low magnetic field (1 K Oe) was as low as 61.8 emu / g. In addition, the shape of the magnetite particle powder was irregular. <Comparative Example 3> Addition of sodium carbonate and replacement of the air inside the reaction tank with nitrogen during the secondary reaction were omitted, and 4760 ml of a ferrous chloride solution having a concentration of 425 g / liter was used as the secondary reaction.
The magnetite particles were produced by reacting 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. 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]. As is clear from the results in Table 2, the magnetite particle powder has an average particle size of 0.1.
The particle size distribution was 10 to 0.3 μm, the particle size distribution was uneven, 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 particle powder has an average particle size of 0.1.
The particle size distribution was 10 to 0.3 μm, the particle size distribution was nonuniform, and the saturation magnetic flux density (σs) in a low magnetic field (1 K Oe) was as low as 50.8 emu / g. In addition, the magnetite is
The shape was octahedral. [Table 1] [Table 2] The spherical magnetite particle powder obtained by the production method of the present invention can be used as a clear copy image or a high-resolution image in electrophotography, electrostatic recording, an electrostatic copying machine, a 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 a 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.

Claims (1)

Claims: 1. An average particle size of 0.08 to 0.2 μm and a specific surface area of 5 to ²⁰ m ² /
g, containing 0.1 to 3.0 atomic% of silicon (Si) with respect to iron (Fe),
A method for producing a spherical magnetite particle powder having a saturation magnetic flux density (σs) of 65 emu / g or more in a low magnetic field (1 K Oe), comprising an alkali metal hydroxide and an alkali metal carbonate, and further comprising silicon (Si) In a mixed solution containing 0.1 to 3.0 atomic% with respect to the total amount of iron (Fe) added to the reaction, and ferrous chloride in a molar ratio of 0.1 to 3.0 with respect to the total ferrous salt added to the reaction. 0.5 and a mixed solution containing ferric chloride in a molar ratio of 1.0 to 5.0 with respect to the ferrous chloride to form a magnetite seed crystal. 0.5 to 0.95 in molar ratio to ferrous salt
The pH value of the reaction system is adjusted to 9.0 to 12.5 by adding a solution containing ferrous chloride in an amount of A method for producing magnetite particle powder, which comprises producing, followed by filtration, washing, drying and grinding.