JPH0648389B2 - Manufacturing method of reduced iron powder for magnetic toner - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a fine particle reduced iron powder having an iron oxide layer formed on the surface thereof, which is suitable as a magnetic material for an electrophotographic magnetic toner. The reduced iron powder according to the production method is used by being contained in the electrophotographic magnetic toner in an amount of 10 to 50% by weight.

[Problems to be Solved by Prior Art and Invention]

The electrophotographic development method uses a powder composed of a mixture of synthetic resin and carbon as a toner, and a two-component method in which the powder is transferred to an electrophotographic photoreceptor by a magnetic brush made of iron powder carrier, and a magnetite in the toner. There is a one-component system in which magnetic powder such as ferrite is mixed and the toner itself retains magnetism without using a carrier.

The two-component toner is usually composed of 90% by weight or more of synthetic resin and the rest is composed of a non-magnetic coloring substance, and therefore has a lower heat capacity and a lower melt viscosity than the one-component toner, and the heat and pressure. Since it can be completely fixed on paper by using, and because it does not contain a magnetic material, it does not easily cause electrical leakage even in high humidity conditions and does not cause deterioration of image characteristics, mainly because it has excellent image characteristics. At present, the two-component method is more common than the one-component method.

However, in the two-component method, the toner concentration in the developer has a large influence on the image quality, the developer needs to be replaced because the developer deteriorates due to long-term use, and the developer is circulated. Therefore, there is a drawback that the developing mechanism is complicated and the apparatus becomes large.

On the other hand, in the one-component method, the toner is 30 to 60 synthetic resin.
Since the rest is made up of magnetic powder such as magnetite or ferrite in weight%, it has the disadvantage of poor fixability on paper and poorer image characteristics than the two-component system, but the device has a simple development mechanism. It is easy to adjust, does not need to replace the developer only by supplying additional toner, and the development unit is simple, so the maintenance of the device is greatly facilitated, and the weight and cost of the device are reduced. It has the appeal that

Therefore, in order to improve the image characteristics, which is the biggest drawback of the one-component method, compared to the two-component method, it is special to improve the fixability of toner to paper even with a small resin content. And use expensive and high-grade resin,
Ingenuity such as mixing a resin with a low molecular weight has been made.
However, magnetic powders such as magnetite and ferrite that are conventionally used together with the above resin as a constituent component of toner have a saturation magnetic flux density (σs) of 40 in a magnetic field of about 1,000 Oe.
Since it is about 65 emu / g, the magnetic powder must be contained in the toner in an amount of 40 to 70% by weight. However, since the magnetic powder is hard, the photoreceptor on the drum surface is easily damaged, and the magnetic powder is contained. When the amount is increased, black becomes dominant, and it becomes extremely difficult to produce colored toners such as blue, red and brown. In particular, the high content of the magnetic powder causes a drawback that the image is deteriorated due to a large amount of fogging at high temperature and high humidity, and it becomes difficult to control the toner characteristics such as adjusting the charge amount.

As described above, the drawbacks of the one-component system are that the content of the resin in the toner is small and the content of the magnetic powder is large, so that the one-component system has fine and excellent magnetic characteristics. If a magnetic material having such a material appears, the content of the magnetic material (magnetic powder) in the toner can be decreased and the resin content can be relatively increased, so that all the drawbacks of the one-component system are considered to be improved. To be

However, iron powder and alloy powder have high magnetic flux density,
Since it is difficult to economically produce the following fine particles, they are not generally 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 large magnetic flux density in order to solve the drawbacks of the conventional electrophotographic magnetic toner and magnetic material, and to provide image characteristics using the magnetic material. To provide a novel toner having excellent electrophotographic characteristics.

[Means for solving problems]

The present inventors, while conducting various studies to achieve the above object, as a method for producing a fine magnetic material, hematite, which has already been widely industrially produced, maghematite,
We focused on a method using one or more iron oxides or iron-containing hydroxides such as magnetite, wustite, belt light, goethite, acaganite and lepidocrocite as raw materials. These iron oxides or iron hydrates are inexpensive and have a particle size of 1.0 μm or less,
If the particle size is maintained as it is, a magnetic material having a small particle size can be manufactured at low cost. For example, when hematite, magnetite, maghematite or the like having various particle diameters is reduced with a reducing gas such as hydrogen gas, reduced iron powder having a size substantially proportional to the particle diameter of the raw material is obtained. However,
This reduced iron powder has a higher degree of surface activity as the particle diameter becomes smaller. When the particle diameter of the reduced iron powder becomes smaller than 5 μm, the reduced iron powder generates heat when exposed to the atmosphere and is entirely oxidized to hematite. Therefore, the production of this reduced iron powder,
It is necessary to carry out the work by shutting off the atmosphere from the storage and transportation to the manufacturing process of the magnetic toner, and it is unsuitable as an industrial material from the viewpoint of cost and safety.

Therefore, the present inventors further studied variously, hematite, maghematite, magnetite, wustite,
Reduced iron oxides or iron hydroxides such as belt light, goethite, acaganite and lepidocrocite, cooled and gently oxidized to obtain reduced iron powder with a thin iron oxide layer formed on the surface. The reduced iron powder has a small particle size, is stable against oxidation and has a large saturation magnetic flux density, and the magnetic toner containing the reduced iron powder in an amount of 10 to 50% by weight has a good fixing property on paper. Not only that, we found that the obtained image was clear and had excellent image characteristics,
The present invention has been achieved.

That is, the present invention, one or more iron oxides or iron-containing hydroxides such as hematite, maghematite, magnetite, wustite, belt light, goethite, acaganite and lepidocrocite, at a temperature of 300 to 600 ° C. After reducing with a reducing gas for 3 hours or more and then cooling, the surface is oxidized with a gas having an oxygen concentration of 10% by volume or less, the particle diameter is 0.1 to 5 μm, and the oxygen content is 0.2. -10% by weight and measuring magnetic field 1,000
Provided is a method for producing a reduced iron powder for a magnetic toner, which has a saturation magnetic flux density in Oe of at least 80 emu / g or more.

First, the reduced iron powder according to the present invention will be described in detail.

The thickness of the iron oxide layer on the surface of the reduced iron powder according to the present invention needs to have a certain thickness irrespective of the size of the particles. Therefore, in terms of oxygen content, the smaller the particles, the more oxygen. Unless the content is increased, it tends not to be stabilized. That is, when the particle size is 1 to 5 μm, the total oxygen content is 0.2 to
It is stable even at 4% by weight, but when the particle size is less than 1 μm, it is unstable to oxidation unless the total oxygen content is increased to 0.5 to 10% by weight.

Therefore, the smaller the particle diameter is, the more preferable as the magnetic material for the magnetic toner. However, when the surface is stabilized, the iron oxide layer becomes relatively thicker as the particle diameter becomes smaller, and the characteristic that the saturation magnetic flux density is large is diminished. .

Summarizing these factors, the reduced iron powder according to the present invention,
The particle diameter is 0.1 to 5 μm, and the thickness of the iron oxide layer is such that the oxygen content is 0.2 to 10% by weight.

The particle size referred to here is represented by the maximum particle size out of about 100 particles observed in an electron microscope.

Further, the saturation magnetic flux density (σs) of the reduced iron powder according to the present invention
Is at least 80 emu / g or more at a measurement magnetic field of 1,000 Oe.

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

As the raw material of the reduced iron powder of the present invention, hematite, maghematite, magnetite, wustite, iron oxide or iron hydrous oxide such as belt light, goethite, acaganite and lepidocrocite are used, and these may be used alone. It may be a mixture of two or more species.

Particles can be grown large by selecting reducing conditions, but a large raw material cannot be made fine. Therefore, the particle diameter of the raw material must be smaller than that of the desired product. Regarding the reduction method and the surface oxidation method, it is essential that the particles do not sinter each other in the reduction step and that the inside is not oxidized in the surface oxidation step, and the reaction method is a flow-down method, a fluidized bed method, a rotary method or Any method such as a fixed bed type is possible.

As the most simple and preferable method for producing the reduced iron powder of the present invention, the above iron oxide or iron hydrate is charged into a fixed or rotary furnace, and hydrogen gas is dried at a temperature of 300 to 600 ° C. A method of reducing the temperature for 3 hours or more, lowering the temperature to room temperature, and then flowing a nitrogen gas having an oxygen concentration of 10% by volume or less to gently oxidize the surface can be mentioned. At the stage of the reduction reaction, it is desirable to completely reduce the oxide, but the purpose is to increase the saturation magnetic flux density of the reduction product, so even if some unreduced substances remain inside, there is no practical problem. Absent.

If the reduction temperature is less than 300 ° C, the reduction cannot be sufficiently performed,
On the other hand, if it exceeds 600 ° C, the particles may be sintered with each other.
Also, the oxygen concentration of the gas used for surface oxidation is set to 10% by volume.
If it is over, there is a fear that the oxidation will proceed rapidly and the inside of the particles will be oxidized.

The saturated magnetic flux density of the reduced iron powder according to the present invention produced in this way is at least 80 emu / g at a measurement magnetic field of 1,000 Oe.
As described above, the value is higher than that of magnetic materials such as magnetite and ferrite that have been conventionally used.

The reduced iron powder according to the present invention is used by being contained in an electrophotographic magnetic toner.
By containing 50% by weight, an electrophotographic magnetic toner having good fixability on paper can be obtained.

The synthetic resin, which is another constituent of the electrophotographic magnetic toner, is a homopolymer of a styrene-based resin, a vinyl-based resin, an acrylic ester-based resin, a methacrylic ester-based resin, a polyamide-based resin, an epoxy-based resin, a phenol-based resin, or the like. Alternatively, a copolymer is used, and a charge control agent, a fluidity modifier, a colorant, a plasticizer, a filler and the like may be added to the electrophotographic magnetic toner, if necessary.

In the production of the electrophotographic magnetic toner using the reduced iron powder according to the present invention, the constituent materials are sufficiently kneaded using a heat kneader such as an extruder, a heat kneader, and a heat roll, and then cooled and hammer milled. The magnetic material (reduced iron powder) and other materials are dispersed in a resin solution and spray dried in a heated air stream. It is possible to use a method for producing a magnetic toner by using the above method.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 Pigment hematite (Morishita Benji, MR-270E) was placed in a reducing furnace, heated to 450 ° C. in a hydrogen gas atmosphere, kept at the temperature for 5 hours, then stopped heating and cooled to room temperature. did. 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 to gently oxidize it, and then the product in the furnace was taken out, crushed and oxidized to the surface. A fine particle reduced iron powder having an iron layer was obtained. The characteristic of this reduced iron powder is that its saturation magnetic flux density is 101 emu / g (measurement magnetic field 1,000 O
e), the maximum particle size was about 0.8 μm, the oxygen content was 3.9% by weight, and the oxidation start temperature was 170 ° C.

Next, 20 parts by weight of the reduced iron powder and a softening point of 100 to 12
55 parts by weight of styrene-butyl methacrylate copolymer at 0 ° C., 20 parts by weight of polystyrene having a softening point of 125 ° C. and 5 parts by weight of carbon black were melt-kneaded, and after cooling to room temperature,
Coarse pulverization was performed with a hammer mill, and fine pulverization was performed with a jet mill, and a magnetic toner of about 10 μm was obtained with 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 transferred and fixed on plain paper, a good image could be obtained.

Example 2 Cubic magnetite (KBC-100 manufactured by Kanto Denka Kogyo Co., Ltd.) was placed in a reduction furnace, heated to 500 ° C. in a hydrogen gas atmosphere, kept at the temperature for 5 hours, then stopped heating and cooled to room temperature. did. 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 to gently oxidize it, and then the product in the furnace was taken out, crushed and oxidized to the surface. A fine particle reduced iron powder having an iron layer was obtained. The characteristic of this reduced iron powder is that the saturation magnetic flux density is 82 emu / g (measurement magnetic field 1.0
00Oe), maximum particle size about 1.2 μm, oxygen content 6.3% by weight,
The oxidation start temperature was 190 ° C.

Then, using the above reduced iron powder, a magnetic toner was obtained in the same manner as in Example 1. When this magnetic toner was placed in an electrophotographic copying machine equipped with a selenium photosensitive plate drum and transferred and fixed on plain paper, a good image could be obtained.

Example 3 Pigment hematite (manufactured by Bayer, 140M) and cubic magnetite (manufactured by Kanto Denka Kogyo, KBC-200) were mixed at a weight ratio of 1: 1 and charged in a reducing furnace, followed by the same procedure as in Example 1. This was carried out to obtain fine reduced iron powder having an iron oxide layer formed on the surface. The characteristic of this reduced iron powder is that the saturation magnetic flux density is 188 emu.
/ G (measurement magnetic field 1,000 Oe), maximum particle diameter of about 1.5 μm, oxygen content of 0.83 wt%, oxidation start temperature 170 ° C.

Then, using the above reduced iron powder, a magnetic toner was obtained in the same manner as in Example 1. When this magnetic toner was placed in an electrophotographic copying machine equipped with a selenium photosensitive plate drum and transferred and fixed on plain paper, a good image could be obtained.

Comparative Example 1 Cubic magnetite with a saturation magnetic flux density of 62 emu / g (measurement magnetic field of 1,000 Oe) (Kanto Denka Kogyo, KBC-100) 20
A magnetic toner was obtained in the same manner as in Example 1 except that 20 parts by weight of the reduced iron powder obtained in Example 1 was used instead of 20 parts by weight. When this magnetic toner was placed in an electrophotographic copying machine equipped with a selenium photosensitive plate drum and transferred and fixed on plain paper, fogging was large and a good image could not be obtained.

Comparative Example 2 Cubic magnetite with a saturation magnetic flux density of 62 emu / g (measurement magnetic field 1,000 Oe) (Kanto Denka Kogyo, KBC-100) 50
A magnetic toner was obtained in the same manner as in Example 1 except that 20 parts by weight of the reduced iron powder obtained in Example 1 was used instead of 20 parts by weight. When this magnetic toner was placed in an electrophotographic copying machine equipped with a selenium photosensitive plate drum and transferred and fixed on plain paper, the fog of the image was improved, but the fixability was rather poor,
Further, under high temperature and high humidity conditions, fogging occurred and the image was stained.

〔The invention's effect〕

Since the reduced iron powder according to the present invention is fine and has a large saturation magnetic flux density, it is suitable as a magnetic material for an electrophotographic magnetic toner. According to the reduced iron powder according to the present invention, the magnetic material in the toner is It is possible to decrease the content and relatively increase the content of resin, and it is possible to obtain an electrophotographic magnetic toner having good fixability on paper and excellent image characteristics, and moreover, reduced iron powder is economically produced. The effect of being able to do is exhibited.

Claims (1)

[Claims] 1. One or more iron oxides or iron-containing hydroxides such as hematite, maghematite, magnetite, wustite, beltlite, goethite, acaganite and lepidocrocite at a temperature of 300 to 600 ° C. After reducing with a reducing gas for 3 hours or more, and then cooling, the surface is oxidized with a gas having an oxygen concentration of 10% by volume or less, the particle diameter is 0.1 to 5 μm, and the oxygen content is 0.2 to 10 wt% and measuring magnetic field 1,000 Oe
A method for producing reduced iron powder for magnetic toner, wherein the saturated magnetic flux density is at least 80 emu / g or more.