JPH05105453A - Iron-based magnetic powder and its production - Google Patents

Abstract

PURPOSE:To produce iron-based magnetic powder having high saturation magnetic flux density in a low magnetic field and suitable for use as magnetic powder for a magnetic toner. CONSTITUTION:Cubic, spherical or polyhedral particles of iron oxide, magnetite or iron oxide hydrate are reduced at 500-700 deg.C in reducing gas and the resulting metallic iron particles are oxidized at 350-500 deg.C in oxygen-contg. gas to form ferric oxide in the surface layers of the iron particles. Magnetite layers are then formed in the surface layers of the iron particles by re-reduction in reducing gas at 300-450 deg.C and the iron particles are further treated with an inert gas accompanied by steam to produce iron-based magnetic powder whose saturation magnetic flux density is >=38 emu/g in a low magnetic field having 0.5kOe and >=65 emu/g in a low magnetic field having 1.0kOe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic particle powder containing iron as a main component and having a high saturation magnetic flux density in a low magnetic field and a method for producing the same. The magnetic particle powder of the present invention is a one-component system or 1. It is particularly useful as a magnetic material used for a five-component developer or magnetic toner.

[0002]

2. Description of the Related Art The main raw materials of a magnetic toner in a developing system using a one-component type or a 1.5-component type developer or a capsule toner are usually magnetic powder and a binder resin. In addition to these, dyes, pigments, conductive materials and the like are used as additives as required. Iron oxide powder or ferrite powder has been conventionally used as the magnetic powder for the magnetic toner.
The demand for higher speed, higher image quality and higher resolution has increased,
Magnetite powder has been used. The reason why magnetite powder is used is that its saturation magnetization is high and its coercive force is low, but current magnetite powder has not yet fully met the demands for higher speed and higher image quality. ..

For example, an important requirement for magnetic powder for magnetic toner is that the saturation magnetic flux density at a measuring magnetic field of 1 KOe is as high as possible. The reason for this is that the brushing as a magnetic brush can be improved and enhanced.
However, the current magnetite powder has a saturated magnetic flux density
The measured magnetic field is about 34 e.mu/g at 0.5 KOe, and the measured magnetic field is about 60 e.mu/g at 1.0 KOe, which is not sufficiently high.

Further, it is necessary to increase the apparent density and increase the charge amount by reducing the diameter of the magnetic toner in order to improve the quality and speed of the image. That is, the average particle size of the magnetic toner at present is 11 to 12 μ, but in order to further improve the resolution, the target is to set the average particle size of the magnetic toner to 8 μ for the time being, further to 5 to 6 μ. Has been done.

However, the conventional magnetic powder has a low saturation magnetic flux density in a low magnetic field. Therefore, when a toner is made of resin to obtain a magnetic toner having an ideal saturation magnetic flux density, the particle size of the magnetic powder is reduced. Must be increased, which inevitably increases the particle size of the magnetic toner. Therefore, an object of the present invention is to provide a magnetic particle powder containing iron as a main component, which has a high saturation magnetic flux density in a low magnetic field and is suitable as a magnetic powder for a magnetic toner, and a method for producing the same.

[0006]

According to the present invention, the saturation magnetic flux density in a low magnetic field is 38 e.mu at a measurement magnetic field of 0.5 KOe.
/ G or more and 65e.mu/g at a measuring magnetic field of 1.0KOe
The above object has been achieved by providing the magnetic particle powder containing iron as the main component. The present invention also provides, as a method for producing the magnetic particle powder of the present invention, cubic, spherical or polyhedral iron oxide particles, magnetite particles or hydrous iron oxide particles in a reducing gas at 500 to 70.
After reducing at a temperature of 0 ° C. to form metallic iron particles, it is oxidized at 350 to 500 ° C. in a gas containing oxygen to form ferric oxide in the metallic iron particle surface layer, and then at 300 to 450 ° C.
Is reduced in a reducing gas to form a magnetite layer on the surface layer of the metallic iron particles, and further treated with an inert gas accompanied by water vapor, which has a high saturation magnetic flux density in a low magnetic field. The present invention provides a method for producing magnetic particle powder as a component.

The magnetic particle powder of the present invention and the method for producing the same will be described in detail below. Since the magnetic particle powder containing iron as a main component of the present invention has a high saturation magnetic flux density in a low magnetic field, the average particle diameter thereof can be set to about 0.1 to 6 μ, which sufficiently meets the requirement for toner size reduction. In addition, the amount of kneading as a magnetic toner can be reduced, and the time to familiarize with the magnetic field is shortened, so that it is possible to sufficiently meet the demand for higher speed.

Further, by using the magnetic particle powder of the present invention, the particle size of the magnetic toner can be reduced, so that the apparent density is increased, frictional charging due to friction between the toners is increased, and the charging property is stable. Therefore, the resolution is high. The magnetic particle powder containing iron as a main component of the present invention is manufactured as follows. Cubic, spherical or polyhedral iron oxide particles, magnetite particles or hydrous iron oxide particles are used as raw materials, and the raw materials are first mixed in a reducing gas such as hydrogen at 50
The reduction is carried out at a temperature of 0 to 700 ° C. By this reduction, the main component of the iron oxide particles, the magnetite particles or the iron oxide hydroxide particles is made to be metallic iron. Reduce temperature to 500-70
By setting the temperature to 0 ° C., the individual iron particles produced become in a sintered state and the density increases. This reduction temperature is 500
If the temperature is lower than ℃, the reduction rate is slow, and the iron particles are not sufficiently sintered, and if the temperature is higher than 700 ° C, the particles are sintered with each other.

Next, the metal iron particles are oxidized in a gas containing oxygen, for example, in air at 350 to 500 ° C. to form ferric oxide on the surface layer of the metal iron particles. Further, this is re-reduced in a reducing gas such as hydrogen at 300 to 450 ° C. to form a magnetite layer on the surface layer of the metallic iron particles. The reason for limiting the re-reduction temperature to 300 to 450 ° C is
This is because the reduction does not proceed sufficiently at a temperature lower than 300 ° C and the blackness of the magnetic powder becomes insufficient, and when the temperature exceeds 450 ° C, the magnetite layer is not formed and metallic iron is generated.

Through the above steps, iron having a saturation magnetic flux density in a low magnetic field of 38 e.mu/g or more at a measurement magnetic field of 0.5 KOe and 65 e.mu/g or more at a measurement magnetic field of 1.0 KOe is used as a main component. Although magnetic powder can be produced, the magnetic powder is treated with an inert gas accompanied by water vapor in order to impart resistance to oxidation and humidity. As an example of this treatment, nitrogen is used as an inert gas, the nitrogen gas is heated to about 300 ° C., and this gas is passed through water to entrain water vapor, and then the gas is magnetized in a reactor. A method of forming an extremely thin oxide film on the surface of the magnetic powder by bringing it into contact with the powder can be mentioned. In this case, if the amount of water vapor in the inert gas is not sufficient, a stable film cannot be formed, so the temperature of the inert gas must be at least 100 ° C. The contact time between the magnetic powder and the inert gas is 30
About 30 minutes is preferable, and if it exceeds 30 minutes, the oxide film becomes too thick, and the magnetic properties may deteriorate.

[0011]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples. Example 1 20 g of polyhedral magnetite powder having an average particle size of 0.3 μ was placed in a reduction reactor, and 1 liter / 600 liters was added to the reactor at 600 ° C.
A min of hydrogen was flowed for 60 minutes to reduce the magnetite powder. After that, nitrogen gas was charged at a rate of 1 ml / min and cooled to 400 ° C., then air was flowed at a rate of 1 ml / min to carry out an oxidation reaction for 30 minutes, and further reduced at 380 ° C. in a hydrogen stream to reduce iron. The main component was magnetic powder. Next, after bubbling a 1 liter / min nitrogen stream heated to 300 ° C. into water at 20 ° C., the mixture was put into the reactor with water vapor entrained therein, and the magnetic powder was mixed with 30
Stabilization was performed for a minute. The obtained magnetic particle powder containing iron as a main component has a particle size of 0.5 to 1 μm, and the saturation magnetic flux density in a low magnetic field is 39 e.mu at a measurement magnetic field of 0.5 KOe.
/ G, and 70 e.mu/g at a measurement magnetic field of 1.0 KOe.

Example 2 20 g of spherical magnetite powder having an average particle size of 0.3 μ was placed in a reduction reactor, and the reactor was heated at 500 ° C. to 1 liter / mi.
n of hydrogen was flowed for 60 minutes to reduce the magnetite powder. After that, nitrogen gas was charged at a rate of 1 ml / min and cooled to 400 ° C., then air was flowed at a rate of 1 ml / min to carry out an oxidation reaction for 30 minutes, and further reduced at 380 ° C. in a hydrogen stream to reduce iron. The main component was magnetic powder. Then, a 1 liter / min nitrogen stream heated to 300 ° C. was bubbled into water at 20 ° C., and then the magnetic powder was put into the reactor with water vapor entrained therein and the magnetic powder was stabilized for 30 minutes. The obtained magnetic particle powder containing iron as the main component has an average particle diameter of 0.5 μ and a saturation magnetic flux density in a low magnetic field of 38 e.mu/g at a measurement magnetic field of 0.5 KOe.
Moreover, it was 68 e.mu/g at a measured magnetic field of 1.0 KOe.

Example 3 20 g of polyhedral magnetite powder having an average particle diameter of 0.3 μ was placed in a reduction reactor, and 1 liter / 600 liters was added to the reactor.
A min of hydrogen was flowed for 60 minutes to reduce the magnetite powder. After that, nitrogen gas was charged at a rate of 1 ml / min and cooled to 380 ° C., then air was flowed at a rate of 1 ml / min to carry out an oxidation reaction for 60 minutes, and further reduced at 380 ° C. in a hydrogen stream to reduce iron. The main component was magnetic powder. Next, after bubbling a 1 liter / min nitrogen stream heated to 300 ° C. into water at 20 ° C., the mixture was put into the reactor with water vapor entrained therein, and the magnetic powder was mixed with 30
Stabilization was performed for a minute. The obtained magnetic particle powder containing iron as the main component has an average particle diameter of 0.8 μ and a saturation magnetic flux density in a low magnetic field of 38 e.mu at a measurement magnetic field of 0.5 KOe.
/ G, and 66 e.mu/g at a measuring magnetic field of 1.0 KOe.

Example 4 20 g of polyhedral magnetite powder having an average particle size of 0.3 μ was placed in a reduction reactor, and 1 liter / 600 liters was added to the reactor at 600 ° C.
A min of hydrogen was flowed for 60 minutes to reduce the magnetite powder. After that, nitrogen gas was charged at a rate of 1 ml / min and cooled to 380 ° C., then air was flowed at a rate of 2 ml / min for 30 minutes to carry out an oxidation reaction, and further reduced in a hydrogen stream at 380 ° C. Magnetic powder was used as the component.
Next, a 1 liter / min nitrogen stream heated to 300 ° C. was bubbled into water at 20 ° C., and then the magnetic powder was put into the reactor while being accompanied by steam, and the magnetic powder was stabilized for 30 minutes. The obtained iron-based magnetic particle powder has an average particle diameter of 0.5 μ and a saturation magnetic flux density in a low magnetic field of 39 e.mu/in a measured magnetic field of 0.5 KOe.
g and 68 e.mu/g at a measuring magnetic field of 1.0 KOe.

Comparative Example 1 20 g of octahedral magnetite powder having an average particle size of 0.3 μ was put in a reactor, and the reactor was heated at 600 ° C. to 1 liter / min.
The air was flowed for 60 minutes to carry out the oxidation reaction, then nitrogen gas was charged at a rate of 1 ml / min to cool to 380 ° C., and then reduced in a hydrogen flow of 1 ml / min for 60 minutes. Next, after bubbling a 1 ml / min nitrogen stream heated to 300 ° C. into water at 20 ° C., the mixture was put into the reactor with water vapor entrained therein and stabilized for 30 minutes. The obtained magnetic powder had a saturation magnetic flux density in a low magnetic field of 32 e.mu/g at a measurement magnetic field of 0.5 KOe and 56 e.mu/g at a measurement magnetic field of 1.0 KOe.

Comparative Example 2 20 g of octahedral magnetite powder having an average particle size of 0.3 μ was placed in a reactor, and the reactor was heated at 600 ° C. to 1 liter / min.
Flushed with nitrogen for 60 minutes. Then, 1 ml of nitrogen gas /
Charge at a speed of min and cool to 400 ° C, then add air to 1
Flow at a speed of ml / min to carry out oxidation reaction for 30 minutes,
Further reduction was carried out at 380 ° C. in a hydrogen stream. Then 30
A nitrogen stream of 1 liter / min heated to 0 ° C is applied to 20 ° C.
After bubbling in water, the water was entrained in the reactor with water vapor entrained therein and stabilized for 30 minutes. The obtained magnetic powder has a saturation magnetic flux density in a low magnetic field of 37 e.mu/g at a measurement magnetic field of 0.5 KOe and a measurement magnetic field of 1.0 K.
It was 62 e.mu/g in Oe.

[0017]

INDUSTRIAL APPLICABILITY The magnetic particle powder containing iron as a main component of the present invention has a high saturation magnetic flux density in a low magnetic field and is particularly useful as a magnetic powder for magnetic toner. Further, according to the method for producing the magnetic particle powder of the present invention, the magnetic particle powder of the present invention can be obtained.

Claims (2)

[Claims] 1. A magnetic particle containing iron as a main component, which has a saturation magnetic flux density of 38 e.mu/g or more at a measuring magnetic field of 0.5 KOe and 65 e.mu/g or more at a measuring magnetic field of 1.0 KOe. Powder. 2. Cubic, spherical or polyhedral iron oxide particles, magnetite particles or hydrous iron oxide particles are reduced in a reducing gas at a temperature of 500 to 700 ° C. to form metallic iron particles, and then oxygen. In a gas containing at least 350 to 500 ° C. to form ferric oxide on the metallic iron particle surface layer, and then re-reduced in a reducing gas at 300 to 450 ° C. to make the metallic iron particle surface layer magnetite. A method for producing magnetic particle powder containing iron as a main component, which has a high saturation magnetic flux density in a low magnetic field, characterized by forming a layer and further treating it with an inert gas accompanied by water vapor.