JPH0638164B2 - Magnetic toner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a one-component developer for developing an electrostatic latent image such as electrophotography, that is, a magnetic toner. It has excellent fixability and weather resistance, and is also suitable for color development.

[Conventional technology and its problems]

As a developer used for developing an electrostatic latent image, a two-component developer composed of two components of a toner and a carrier and a one-component developer composed of only a magnetic toner are used.

In the case of a two-component developer, the toner is usually composed of a synthetic resin and a small amount of a non-magnetic substance, and has a lower heat capacity and melt viscosity than a one-component developer, At present, two-component developers are generally used because they have good fixability and excellent high-humidity environment characteristics because they do not contain a magnetic material.

However, in order to maintain a good image, the two-component developer needs to keep the compounding ratio of the carrier and the toner constant, but this control mechanism is complicated and there is a drawback that the device becomes large, Further, since the developer is deteriorated due to the spent toner on the surface of the carrier when used for a long time, the dry copying machine using the two-component developer requires a complicated work of replacing the developer. It has drawbacks.

On the other hand, the one-component developer (magnetic toner) contains 40 parts of magnetic powder.
It is composed of a synthetic resin containing 70% by weight to 70% by weight, and as described above, it has the drawback of being inferior in high humidity environment characteristics and fixability as compared with the toner of the two-component developer, but the developing device and mechanism are simple. In addition, since there is no need to replace the developer, the dry copying machine using the one-component developer has advantages that the device can be made compact, lightweight and cost-effective.

Examples of the magnetic powder used in the magnetic toner include magnetite, ferrite, iron powder, and the like, but at present, a satisfactory magnetic toner is not always obtained with these conventional magnetic powders. That is, in order to improve the high humidity environment characteristics and the fixability of the magnetic toner, it is necessary that the content of the magnetic powder in the magnetic toner is small. Generally, the strength of the magnetic field of the magnet used in the developing machine of the dry copying machine is around 1000 gauss, and in order to reduce the content of magnetic powder in the magnetic toner, the magnetic flux density (σs) at the external measurement magnetic field of 1 KOe It is necessary to use high magnetic powder. However, it is conventionally used as a magnetic powder. The magnetic flux density of magnetite and ferrite is 40 to 65 emu / g,
Carbonyl iron powder has a magnetic flux density of 30 to 50 emu / g, and acicular iron alloy having iron with a high coercive force has a magnetic flux density of 20 to 40 emu / g. It is not possible to reduce its content in the toner. For example, in the case of using magnetite, its content in the magnetic toner reaches 40 to 70% by weight, which causes problems in high-humidity environment characteristics and fixability, and further, in magnetite itself. Since the color is black, it is not suitable for color development.

Therefore, an object of the present invention is to solve the above-mentioned problems in the conventional magnetic toner, and to have excellent fixability and high humidity environment characteristics,
Another object is to provide a magnetic toner suitable for color development.

[Means for solving problems]

The present inventor has conducted extensive studies in order to achieve the above-mentioned object, and as a result, the magnetic flux density (σ
It was found that s) greatly changes depending on the shape of the magnetic powder. That is, it has been found that the thinner and flatter the shape of the magnetic powder, the larger the magnetic flux density in the external measurement magnetic field of 1 KOe, and conversely, the closer it is to the spherical shape, the smaller the magnetic flux density. The reason for this is not clear, but it is presumed that it may be related to the shape anisotropy factor among the magnetic anisotropy factors that affect the magnetic properties of the magnetic powder.

The present invention has been made on the basis of the above findings and has a long diameter of 10
A magnetic toner comprising flat iron powder having a thickness of not more than μm and a thickness of not more than 1.0 μm.

Hereinafter, the magnetic toner of the present invention will be described in detail.

The magnetic powder used in the present invention is a thin rolled iron powder having a flat shape, and the particle size is 10 μm or less in major axis,
It is preferably 5 μm or less and 1.0 μm or less in thickness, preferably 0.5 μm or less, and the ratio of major axis to thickness is (major axis / thickness) ≧ 5. The iron powder having such a shape has a magnetic flux density (σs) of 70 to 140 emu / g in an externally measured magnetic field of 1 KOe, and a magnetic flux density (40 to 65 emu) of conventionally used magnetite.
/ G), the magnetic flux density is about double.

The iron powder is produced, for example, by the following method.

Iron oxides such as hematite and magnetite are reduced with a reducing gas such as hydrogen gas, and the obtained reduced iron powder is wet-milled with an attritor to obtain iron powder.

The iron powder may be subjected to various surface treatments such as oxide film formation and coating with an organic compound such as a silane coupling agent.

The content of the iron powder in the magnetic toner is 10 to 40% by weight.
However, it may be increased or decreased according to the required magnetic flux density.

The iron powder used in the present invention is gray because it is substantially composed of iron, and since the content in the magnetic toner is small, it is also suitable for a magnetic toner for color development. .

As the resin used in the present invention, polystyrene-based, copolymer system containing styrene, polyacrylic acid ester-based,
Examples of binder resins such as polymethacrylic acid ester type, polyester type, polyamide type, polyvinyl acetate type, ethylene-vinyl acetate copolymer type, epoxy type, phenol type, hydrocarbon type, petroleum type, chlorinated paraffin type, etc. These can be used alone or in combination.

If necessary, various additives such as a lubricant such as wax, a fluidity-imparting agent such as colloidal silica and carbon black, a charge adjusting agent, and a coloring agent can be appropriately used in combination.

The method itself for producing the magnetic toner of the present invention is the same as the conventionally known method for producing magnetic toner. That is, the magnetic toner of the present invention is produced, for example, as follows, using the iron powder, the resin, and, if necessary, the various additives described above.

The iron powder and the resin, further preliminarily mixed with the various additives as necessary, after sufficiently kneading using a heating kneader, cooled and pulverized, if necessary, classified, Further, a lubricant, a fluidity imparting agent and the like are added later to obtain a magnetic toner. Alternatively, the iron powder and, if necessary, the various additives described above are dispersed in a resin solution, spray-dried in a heated air stream, and if necessary, classified, a lubricant, a fluidity imparting agent, etc. Is added later to obtain a magnetic toner.

The average particle size of the magnetic toner of the present invention is 10 to 20 μm.
It is preferably m.

〔Example〕

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

Example 1 Pigment hematite (Morishita Benji MR270E) was placed in a reducing furnace, heated to 450 ° C. in a hydrogen gas atmosphere, held at the temperature for 5 hours, then stopped heating and cooled to room temperature. The obtained reduced iron powder and methanol were placed in an attritor and treated, and the maximum major axis was 10 μm or less and the average major axis was 2 μm.
A flat iron powder having a thickness of m and a thickness of 0.3 μm or less was obtained. This flat iron powder has a magnetic flux density (σ
s) was 110 emu / g.

Next, 20 parts by weight of this flat iron powder, 75 parts by weight of styrene / butyl methacrylate copolymer, and 5 parts by weight of carbon broWe were melted and kneaded by a hot roll, cooled, and coarsely crushed by a Wiley crusher. A fine powder was pulverized with a jet mill, and a magnetic toner having an average particle size of 12 μm was obtained with an air classifier.

Using this magnetic toner, an electrostatic image was formed on a selenium photosensitive plate drum in an environment of 20 ° C. and 60% RH, developed by a magnetic brush method, transferred onto plain paper, and fixed with a heat roll. It was possible to obtain a clear image with excellent properties. Further, when an image was similarly printed in a high humidity environment of 30 ° C. and 85% RH, a good image excellent in fixing property was obtained.

Example 2 Cubic magnetite (KBC 100S manufactured by Kanto Denka Co., Ltd.)
Was charged in a reducing furnace, heated to 450 ° C. in a hydrogen gas atmosphere, and kept at that temperature for 5 hours, then stopped heating and cooled to room temperature. The obtained reduced iron powder and methanol were charged into an attritor and treated to obtain flat iron powder having a maximum major axis of 10 μm or less and an average major axis of 1 μm and a thickness of 0.2 μm or less. The magnetic flux density (σs) of the flat iron powder in the externally measured magnetic field of 1 KOe was 80 emu / g.

Then, using this flat iron powder, a magnetic toner having an average particle size of 12 μm was obtained in the same manner as in Example 1.

Using this magnetic toner, an electrostatic image was formed on a selenium photosensitive plate drum in an environment of 20 ° C. and 60% RH, developed by a magnetic brush method, transferred onto plain paper, and fixed with a heat roll. It was possible to obtain a clear image with excellent properties. Further, when an image was similarly printed in a high humidity environment of 30 ° C. and 85% RH, a good image excellent in fixing property was obtained.

Example 3 The reduced iron powder obtained in Example 1 and methanol were charged into a sand grinder and treated to obtain a flat iron powder having a maximum major axis of 10 μm or less, an average major axis of 1.5 μm, and a thickness of 0.2 μm or less. . The magnetic flux density (σs) of this flat iron powder in the externally measured magnetic field of 1 KOe was 100 emu / g.

Then, using this flat iron powder, a magnetic toner having an average particle size of 12 μm was obtained in the same manner as in Example 1.

Using this magnetic toner, an electrostatic image was formed on a selenium photosensitive plate drum in an environment of 20 ° C. and 60% RH, developed by a magnetic brush method, transferred onto plain paper, and fixed with a heat roll. It was possible to obtain a clear image with excellent properties. Further, when an image was similarly printed in a high humidity environment of 30 ° C. and 85% RH, a good image excellent in fixing property was obtained.

Example 4 20 parts by weight of the flat iron powder obtained in Example 1, 50 parts by weight of polyethylene wax, 25 parts by weight of ethylene / vinyl acetate copolymer, and 5 parts by weight of carbon black were kneaded with a hot roll, and after cooling. After roughly pulverizing with a Willey pulverizer, finely pulverizing with a jet mill, a magnetic toner having an average particle size of 13 μm was obtained with an air classifier.

Using this magnetic toner, an electrostatic image was formed on a drain of a selenium photosensitive plate in an environment of 20 ° C. and 60% RH, developed by a magnetic brush method, transferred onto plain paper, and fixed by a pressure fixing roll. A clear image having excellent fixability could be obtained. Further, when an image was similarly printed in a high humidity environment of 30 ° C. and 85% RH, a good image excellent in fixing property was obtained.

Comparative Example 1 The magnetic flux density (σs) in the externally measured magnetic field of 1 KOe was 62 e.
cubic magnetite with mu / g (Kanto Denka Kogyo Co., Ltd.)
KBC 100) 25 parts by weight of the flat iron powder 2 obtained in Example 1
A magnetic toner was obtained in the same manner as in Example 1 except that 0 part by weight was used instead.

An electrostatic image was formed on a selenium photosensitive plate drum using this magnetic toner, and was developed by a magnetic brush method in accordance with a usual method. As a result, a sufficient magnetic brush was not formed, development failure occurred, and it was transferred onto plain paper. After fixing with a hot roll, the fixability was good, but fogging was large and a good image could not be obtained.

Comparative Example 2 The magnetic flux density (σs) in the external measurement magnetic field of 1 KOe is 62 e.
cubic magnetite with mu / g (Kanto Denka Kogyo Co., Ltd.)
KBC 100) 50 parts by weight of flat iron powder 2 obtained in Example 1
A magnetic toner was obtained in the same manner as in Example 1 except that 0 part by weight was used instead.

An electrostatic image is formed on a selenium photosensitive plate drum using this magnetic toner, developed by a magnetic brush method according to a conventional method in an environment of 20 ° C. and 60% RH, transferred onto plain paper, and fixed by a heat fixing roll. I got a clear image,
When the image was similarly printed in a high humidity environment of 30 ° C. and 80% RH, the fogging was large and the image density was unclear, resulting in an unclear image.

〔The invention's effect〕

The magnetic toner of the present invention is used as a magnetic powder in the external measurement magnetic field 1
Since the flat fine particles having a large magnetic flux density (σs) in KOe are used, the magnetic powder content in the toner is small, and the resin content can be relatively increased, so that the fixability on paper is improved. It can be used as a magnetic toner for electrophotography, which has good image characteristics and excellent high-humidity environment characteristics. Further, since the magnetic powder has a gray color and its content can be reduced, A vivid color can be easily achieved, and it is also excellent as a magnetic toner for color.

Claims (2)

[Claims] 1. A magnetic toner comprising flat iron powder having a major axis of 10 μm or less and a thickness of 1.0 μm or less. 2. The magnetic toner according to claim 1, wherein the magnetic flux density (σs) of the iron powder in an externally measured magnetic field of 1 KOe is 70 to 140 emu / g.