JPS61284773A - Fine particle reducing iron powder and its production - Google Patents

Abstract

PURPOSE:To improve picture image characteristics by using the iron powders formed an iron oxide layer on the surface thereof and having a specific particles size to the titled iron powders. CONSTITUTION:The used iron powders are powders formed the iron oxide layer on the surface thereof and having 0.1-5mum the particle size. The prescribed iron powders are produced by reducing one or >=2 kinds of the iron oxides or the iron contg. hydroxides such as a hematite, a maghematite, an akaganeite and a lepidochrocite with a reducing gas at a temp. of 300-600 deg.C, followed by cooling it. The obtd. reduced iron powders are oxidized on the surface thereof, using a gas contg. <=10vol.% an oxygen. The reduced iron powder has 0.1-5mum the particle size. The thickness of the iron oxide layer is preferable to be 0.2-10wt.% the oxygen content. Thus, the content of the magnetic material contd. in the toner is reduced, and may be relatively increased the amount of the resin.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a fine particle reduced iron powder having an iron oxide layer formed on its surface, which is suitable as a magnetic material for electrophotographic magnetic toner, and a method for producing the same. The reduced iron powder is used in an electrophotographic magnetic toner in an amount of 10 to 50% by weight.

[Prior art and problems to be solved by the invention] In the electrophotographic development method, powder made of a mixture of synthetic resin and carbon is used as toner, and this is used as a toner to develop electrophotography using a magnetic brush made of carrier iron powder. There is a two-component method in which toner is transferred to a photoreceptor, and a one-component method in which magnetic powder such as magnetite or ferrite is mixed into the toner to maintain magnetism in the toner itself and no carrier is used.

Two-component type toners usually consist of synthetic resin at 9% or more and the rest is non-magnetic colored material, so compared to -component type toners, they have a lower heat capacity and melt viscosity, and are less susceptible to heat and pressure. Because it can be completely fixed on paper, and because it does not contain magnetic materials, electrical leakage does not occur even in high humidity conditions (mainly because it has excellent image characteristics, such as no deterioration of image characteristics) However, two-component methods are currently more popular than single-component methods.

However, with the two-component method, the toner concentration in the developer has a large effect on image quality, the developer deteriorates after long-term use, so the developer needs to be replaced, and the developer circulation etc. Therefore, the developing mechanism is complicated and the device becomes large.

On the other hand, in the -component method, the toner has a synthetic resin content of 30 to 60%.
The remainder of the weight percentage is made up of magnetic powders such as magnetite and ferrite, which has the disadvantage of poor fixation to paper and poorer image characteristics than two-component methods, but the developing mechanism is simpler with this device. It is easy to adjust, and there is no need to replace the developer just by supplying additional toner. Moreover, the development unit is simple, which greatly facilitates maintenance of the device, and reduces the weight and cost of the device. It has the charm of being able to achieve this.

Therefore, in the -component method, in order to improve the image characteristics, which is the biggest drawback compared to the two-component method, special In addition, using expensive and high-grade resin,
Efforts have been made to mix resins with low molecular weight.

However, magnetic powders such as magnetite and ferrite, which are conventionally used together with the above resins as constituent components of toner, have a saturation magnetic flux density (σS) in a magnetic field of about 1.0000e.
Since the magnetic powder is about 40 to 65 emu/g, the toner must contain 40 to 70% by weight of the magnetic powder, but since this magnetic powder is hard, it easily damages the photoreceptor on the drum surface. When the content of toner is increased, black color becomes dominant, and it becomes extremely difficult to produce colored toners such as blue, red, and brown.

In particular, a high content of magnetic powder causes disadvantages such as increased fogging and poor images at high temperatures and high humidity, and difficulty in controlling toner characteristics such as adjusting the amount of charge.

In this way, the drawbacks of the -component method are due to the low resin content and high magnetic powder content in the toner. If a magnetic material with 100% of the magnetic material appears, it would be possible to reduce the content of magnetic material (magnetic powder) in the toner and relatively increase the resin content, which would improve all the drawbacks of the one-component method mentioned above. Conceivable.

However, iron powder and alloy powder have a large magnetic flux density, but 5 μm
Since it is difficult to economically produce the following fine particles, they are generally not used as magnetic materials for magnetic toners.

Therefore, an object of the present invention is to provide a novel magnetic material that is inexpensive, fine, and has a high magnetic flux density, and to provide image characteristics using the magnetic material, in order to solve the drawbacks of conventional electrophotographic magnetic toners and magnetic materials. An object of the present invention is to provide an excellent new electrophotographic magnetic toner.

[Means for solving problems]

While conducting various studies to achieve the above object, the present inventors discovered that hematite, maghematite, which has already been widely produced industrially, was used as a method for manufacturing fine magnetic materials.
We focused on a method using one or more iron oxides or iron hydrated oxides such as magnetite, oostite, bertolite, goethite, acanite, and lepidocrocite as raw materials. These iron oxides or iron hydrated oxides are inexpensive and have a particle size of 1.0 μm or less, so
If the particle size is maintained as it is, a magnetic material with a small particle size can be manufactured at low cost. For example, when hematite, magnetite, maghematite, etc. of various particle sizes are reduced with a reducing gas such as hydrogen gas, reduced iron powder having a size proportional to the particle size of the raw material can be obtained. however,
The surface activity of this reduced iron powder increases as the particle size decreases, and when the particle size of the reduced iron powder becomes smaller than 5 μm, it generates heat when exposed to the atmosphere and is oxidized until the entire surface becomes hematite. Therefore, the production of this reduced iron powder,
It is necessary to shut off the atmosphere during storage, transportation, and even the manufacturing process of magnetic toner, making it unsuitable as an industrial material from both cost and safety standpoints.

Therefore, as a result of further various studies, the present inventors found that hematite, maghematite, magnetite, oostite,
By reducing iron oxides or iron hydrated oxides such as bertolite, goethite, acaganite, and lepidocrocite, cooling them, and then gently oxidizing them, reduced iron powder with a thin iron oxide layer formed on the surface can be obtained. This reduced iron powder has a small particle size, is stable against oxidation, and has a large saturation magnetic flux density, and a magnetic toner containing 10 to 50% by weight of this reduced iron powder has good fixing properties to paper. We discovered that the images obtained were clear and had excellent image characteristics.
This led to the present invention.

That is, the present invention provides reduced iron powder for electrophotographic magnetic toner, which has an iron oxide layer formed on its surface and has a particle size of 0.1 to 5 μm.

Further, the present invention provides one or more iron oxides or iron hydrated oxides such as hematite, maghematite, magnetite, oostite, bertolite, goethite, acaganite, and lepidocrocite at a temperature of 300 to 600°C. The present invention provides a method for producing reduced iron powder, which comprises reducing the powder with a reducing gas, followed by cooling, and then oxidizing the surface with a gas having an oxygen concentration of 10% by volume or less.

First, the reduced iron powder of the present invention will be explained in detail.

The thickness of the iron oxide layer on the surface of the reduced iron powder of the present invention needs to have a thickness that does not depend on the size of the particles. Therefore, in terms of oxygen content, the smaller the particles, the higher the oxygen content. There is a tendency that it cannot be stabilized unless it is increased. That is, when the particle size is 1 to 5 μm, the total oxygen content is 0.2 to 4
Although it is stable even when the particle size is less than 1 μm, it is unstable against oxidation unless the total oxygen content is as high as 0.5 to 10% by weight.

Therefore, as a magnetic material for magnetic toner, the smaller the particle size, the better, but when the surface is stabilized, the iron oxide layer becomes relatively thicker as the particle size becomes smaller, and the characteristic of high saturation magnetic flux density diminishes. .

Taking these factors together, the reduced iron powder of the present invention has a particle size of 0.1 to 5 μm and a thickness of the iron oxide layer that preferably has an oxygen content of 0.2 to 10% by weight. It is appropriate that there be.

Incidentally, the particle size here refers to the diameter of the largest particle among about 100 particles that come into view when observed with an electron microscope.

Further, the saturation magnetic flux density (σS) of the reduced iron powder of the present invention is at least 80 emu/g at a measuring magnetic field of 1,0000 e.
It is preferable that it is above.

Next, the method for producing reduced iron powder of the present invention will be described in detail.

As raw materials for the reduced iron powder of the present invention, iron oxides or iron hydrated oxides such as hematite, maghematite, magnetite, oostite, bertolite, goethite, acaganite, and lepidocrocite are used, and these may be used alone or in combination. A mixture of more than one species may also be used.

Although it is possible to grow particles to a large size by selecting reduction conditions, large raw materials cannot be made fine, so the particle size of the raw material must be smaller than the particle size of the desired product. Regarding the reduction method and the surface oxidation method, it is important that the particles do not sinter with each other during the reduction stage, and that the inside is not oxidized during the surface oxidation stage. Any method such as a fixed bed method is possible.

The simplest and most preferable manufacturing method for the reduced iron powder of the present invention is to charge the above-mentioned iron oxide or iron hydrated oxide into a stationary or rotary furnace and dry it with hydrogen gas at a temperature of 300 to 600°C. One method is to reduce the surface for 3 hours or more, lower the temperature to about room temperature, and then flow nitrogen gas with an oxygen concentration of 10% by volume or less to gently oxidize the surface. At the reduction reaction stage, it is desirable to completely reduce the oxide, but since the purpose is to increase the saturation magnetic flux density of the reduction product, there is no practical problem even if some unreduced material remains inside. do not have.

If the reduction temperature is less than 300°C, the reduction cannot be performed sufficiently,
Moreover, if the temperature exceeds 600°C, there is a risk that the particles will sinter with each other.

In addition, the oxygen concentration of the gas used for surface oxidation was increased to 10% by volume.
If it is too high, oxidation will proceed rapidly and the inside of the particles will be oxidized.

The reduced iron powder of the present invention produced in this way has a saturation magnetic flux density of at least 80 e at a measuring magnetic field of 1.0000 e.
mu/g or higher, and exhibits a higher value than conventionally used magnetic materials such as magnetite and ferrite.

The reduced iron powder of the present invention is used by being contained in an electrophotographic magnetic toner, and the reduced iron powder is used in an electrophotographic magnetic toner.
By containing the above amount by weight, an electrophotographic magnetic toner having good fixability to paper can be obtained.

Synthetic resins that are another component of electrophotographic magnetic toner include homopolymers of styrene, vinyl, acrylic ester, methacrylic ester, polyamide, epoxy, and phenol resins. or a copolymer is used, and for electrophotographic magnetic toner,
If necessary, a charge control agent, a fluidity modifier, a coloring agent, a plasticizer, a filler, etc. may be added.

When producing an electrophotographic magnetic toner using the reduced iron powder of the present invention, the constituent materials are sufficiently kneaded using a heat kneader such as an extruder, a heat kneader, and two heat rolls, and then cooled and then milled using a hammer mill. The average lO
A method of manufacturing a magnetic toner with the size of a μ seaweed, or a method of manufacturing a magnetic toner by dispersing a magnetic material (reduced iron powder) and material (b) in a resin solution and spray-drying it in a heated air stream. etc. can be used.

〔Example〕

The present invention will be explained in more detail by giving Examples and Comparative Examples below.

Example 1 Hematite for pigments (manufactured by Morishita Bengara, ?IR-2702)
was charged into a reduction furnace, heated to 450°C in a hydrogen gas atmosphere, and held at this temperature for 5 hours, then heating was stopped and cooled to room temperature. After cooling, the gas in the furnace was replaced with nitrogen, and then nitrogen gas with an oxygen concentration of 5% by volume was introduced into the furnace for 4 hours,
After mild oxidation, the product in the furnace was taken out and crushed to obtain fine reduced iron powder with an iron oxide layer formed on the surface. This reduced iron powder has a saturation magnetic flux density of 101 emu/g.
(measured magnetic field 1.0000e), maximum particle diameter 0.8μ
m, oxygen content 3.9% by weight, oxidation start temperature 1'70°C
Met.

Next, 20 parts by weight of the above reduced iron powder, softening point 100-12
55 parts by weight of styrene-butyl methacrylate copolymer at 0°C, 20 parts by weight of polystyrene with a softening point of 125°C, and 5 parts by weight of carbon black were melt-kneaded, and after cooling to room temperature,
The powder was coarsely pulverized with a hammer mill, further finely pulverized with a jet mill, and a magnetic toner with a size of about 10 μm was obtained using an air classifier.

Using this magnetic toner, an electrostatic image is formed on a selenium photosensitive plate drum, and developed by a magnetic brush method according to a conventional method.
When the image was transferred onto plain paper and fixed, a good image was obtained.

Example 2 Cubic magnetite (Kanto Denka Kogyo type, MBC-100
) was placed in a reduction furnace, heated to 500° C. in a hydrogen gas atmosphere, and held at this temperature for 5 hours, then heating was stopped and cooled to room temperature. After cooling, the gas in the furnace is replaced with nitrogen, and then nitrogen gas with an oxygen concentration of 5% by volume is introduced into the furnace for 4 hours to gently oxidize, and then the products in the furnace are taken out and crushed to oxidize the surface. Fine reduced iron powder with an iron layer formed thereon was obtained. The characteristic of this reduced iron powder is that the saturation magnetic flux density is 82 en+u/
g (measured magnetic field 1.0000e), maximum particle diameter 1.
2μm, oxygen content 6.3% by weight, oxidation start temperature 190
It was ℃.

Next, a magnetic toner was obtained in the same manner as in Example 1 using the above reduced iron powder. This magnetic toner was placed in an electrophotographic copying machine equipped with a selenium photosensitive plate drum, and when it was transferred and fixed onto plain paper, a good image was obtained.

Example 3 Pigment-use hematite (manufactured by Bayer, 140M) and cubic magnetite (Kanto Denka Kogyo type, BC-200) were mixed at a weight ratio of 1:1, and the mixture was charged into a reduction furnace and the same procedure as in Example 1 was carried out. Fine particles of reduced iron powder with an iron oxide layer formed on the surface were obtained. This reduced iron powder had a saturation magnetic flux density of 188 emu/g (measuring magnetic field of 1.0000 e), a maximum particle diameter of 1.5 μm, an oxygen content of 0.83% by weight, and an oxidation start temperature of 170°C.

Next, a magnetic toner was obtained in the same manner as in Example 1 using the above reduced iron powder. This magnetic toner was placed in an electrophotographic copying machine equipped with a selenium photosensitive plate drum, and when it was transferred and fixed onto plain paper, a good image was obtained.

Comparative Example 1 Saturation magnetic flux density is 62 e+mu/g (measurement magnetic field 1.0
Example I except that 20 parts by weight of cubic magnetite (Kanto Denka Kogyo Department, WBC-100), which is 000e), was used instead of 20 parts by weight of the reduced iron powder obtained in Example 1.
A magnetic toner was obtained in the same manner as above. When this magnetic toner was put into an electrophotographic copying machine equipped with a selenium photosensitive drum and transferred and fixed onto plain paper, there was a lot of fogging and a good image could not be obtained.

Comparative Example 2 Saturation magnetic flux density was 62 emu/g (measured magnetic field 1, 0
Example 1 except that 50 parts by weight of cubic magnetite (000e) (Kanto Denka Kogyo Department, KBC-100) was used instead of 20 parts by weight of the reduced iron powder obtained in Example 1.
A magnetic toner was obtained in the same manner as above. When this magnetic toner was placed in an electrophotographic copying machine equipped with a selenium photosensitive plate drum and transferred and fixed onto plain paper, the image fog was improved, but the fixing performance was somewhat poor, and fogging occurred under high temperature and high humidity conditions. It came out and the image was dirty.

〔Effect of the invention〕

The reduced iron powder of the present invention is fine and has a high saturation magnetic flux density, so it is suitable as a magnetic material for electrophotographic magnetic toner. It is possible to obtain an electrophotographic magnetic toner that has good fixing properties to paper and excellent image characteristics, and can be produced economically using reduced iron powder. Effects such as being able to do this can be achieved.

Claims (4)

[Claims] (1) Reduced iron powder for electrophotographic magnetic toner, which has an iron oxide layer formed on its surface and has a particle size of 0.1 to 5 μm. (2) The reduced iron powder according to claim (1), which has an oxygen content of 0.2 to 10% by weight. (3) The saturation magnetic flux density at a measurement magnetic field of 1,000 0e is at least 80 emu/g or more (
Reduced iron powder described in section 1). (4) One or more iron oxides or iron hydrated oxides such as hematite, maghematite, magnetite, oostite, bertolite, goethite, acaganite, and lepidocrocite are reduced at a temperature of 300 to 600°C. After being reduced by a reactive gas and then cooled, the oxygen concentration is reduced to 1.
A method for producing reduced iron powder characterized by oxidizing the surface with a gas of 0% by volume or less.