JPH0638169B2 - Magnetic resin carrier for electrophotography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention has excellent image characteristics, which are used for two-component and 1.5-component developers for developing electrostatic latent images such as electrophotography. The present invention relates to a magnetic resin carrier for electrophotography.

[Conventional technology and its problems]

In the electrophotographic method, a dry developer used when developing an electrostatic latent image formed on a photoconductor by a magnetic brush method is a two-component type developer composed of a toner and a carrier.

This two-component developer is usually composed of a mixture of toner particles having a particle diameter of 5 to 20 μm and magnetic carrier particles having a particle diameter of 40 to 150 μm. In recent years, with the progress of electrophotography. Higher image quality and longer life are required, and developers that satisfy these requirements are being actively developed.

With respect to the carrier, in order to satisfy the demands for high image quality and long life, a magnetic material which is lighter in weight, more compact and has a soft brush is desired.

In recent years, in order to meet such requirements, a relatively lightweight magnetic granulation carrier obtained by granulating and firing a metal oxide powder such as ferrite or magnetite is being used, and the particle size of the carrier is improved. In order to achieve this, the particle diameter is gradually reduced (50 μm or less), but it is difficult to efficiently manufacture a magnetic granulation carrier having such a small particle diameter by the conventional manufacturing technology. In addition, in order to achieve higher image quality and longer life, it is becoming common to apply a coating treatment to the surface of the carrier with an appropriate coating agent, but when using a magnetic granulation carrier with such a small particle size as the core Generally, there is a problem that granulation development is likely to occur due to mutual adhesion of the cores by the coating agent, and the product yield after coating is significantly reduced.

In order to solve such a problem, after heating and kneading a magnetic powder such as ferrite or magnetite and a binder resin,
The use of a magnetic resin carrier obtained by crushing and classifying has been studied.

However, since such a magnetic resin carrier is a mixture of magnetic powder and a binder resin which is a non-magnetic substance,
Since the magnetic flux density (σs) is lower than that of the carrier containing only magnetic powder, carrier pulling is likely to occur during development. If the content ratio of magnetic powder in the magnetic resin carrier is increased to prevent this, the carrier becomes brittle. As a result, conventional magnetic powders such as ferrite and magnetite do not always provide a satisfactory magnetic resin carrier because the strength decreases and durability becomes a problem.
There is a demand for magnetic powder having a higher magnetic flux density (σs).

Generally, in the electrophotographic dry copying machine, the magnetic field strength of the magnet used in the developing machine is about 1000 gauss, and therefore, in general, the magnetic field strength of such a magnet is In order for the carrier to have a sufficient magnetic binding force, it is necessary that the magnetic density (σs) of the magnetic powder in the external measurement magnetic field of 1 KOe is large.

However, with magnetite and ferrite conventionally used as magnetic powder, the magnetic flux density at an external measurement magnetic field of 1 KOe is 40 to 65 emu / g, and with carbonyl iron powder it is 30 to 50 emu.
emu / g, and the needle-like iron alloy powder containing iron as a main component and having a high coercive force is 20 to 40 emu / g. Therefore, the magnetic flux density of the magnetic resin carrier cannot be sufficiently increased with the conventional magnetic powder. There wasn't.

In order to increase the magnetic flux density of magnetic powder, the saturation magnetic flux density of metallic iron or iron alloys containing iron as a main component is higher than that of iron oxides such as magnetite and ferrite (metallic iron or iron alloy powder). Saturation magnetic flux density in the case of: 120 to 210
emu / g, saturation magnetic flux density of magnetite or ferrite: 75 to 90 emu / g) is advantageous, but as described above, in the external measurement magnetic field of 1 KOe, conventional metallic iron and iron alloys and iron oxides There is no big difference in magnetic flux density.

Therefore, an object of the present invention is to solve the problems of the conventional magnetic resin carrier and provide a magnetic resin carrier for electrophotography having excellent image characteristics.

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, the magnetic flux density (σs) of the magnetic powder at an external measurement magnetic field of 1 KOe was found to be the shape of the magnetic powder. It was found that the changes greatly depend on. That is, as the shape of the magnetic powder becomes thinner and flatter,
It was found that the magnetic flux density at the externally measured magnetic field of 1 KOe increases, and conversely, the closer to a 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
The present invention provides a magnetic resin carrier for electrophotography, which comprises flat iron powder having a thickness of not more than μm and a thickness of not more than 1.0 μm.

Hereinafter, the magnetic resin carrier for electrophotography 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) has a magnetic flux density about twice as high.

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 resin carrier is 40 to 8
0 wt% is preferable, but it may be increased or decreased depending on the required magnetic flux density.

As the resin used in the present invention, polystyrene-based, copolymer system containing styrene, polyacrylic acid ester-based,
Polymethacrylate ester type, polyester type, polyamide type, polyvinyl acetate type, ethylene / vinyl acetate copolymer type, epoxy type, phenol type, hydrocarbon type,
Examples of the binder resin include petroleum-based and chlorinated paraffin-based resins, and 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 control agent, and a coloring agent can be appropriately used in combination.

The manufacturing method itself of the magnetic resin carrier of the present invention is the same as the conventionally known manufacturing method of the magnetic resin carrier. That is,
The magnetic resin carrier of the present invention is produced, for example, as follows, using the iron powder and the resin, and optionally 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 post-added to obtain a magnetic resin carrier. 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 to obtain a magnetic resin carrier.

The magnetic resin carrier of the present invention has a particle size of 7 to 200 μm.
m, particularly preferably in the range of 7 to 100 μm.

〔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.
m, and a flat iron powder having a thickness of 0.3 μm or less was obtained. The magnetic flux density (σs) of this flat iron powder in an externally measured magnetic field of 1 KOe was 110 emu / g.

Next, 50% by weight of the flat iron powder and 50% by weight of a styrene / butyl methacrylate copolymer were kneaded by heating with a hot roll, cooled, and coarsely crushed with a Wiley crusher.
The mixture was finely pulverized with a jet mill, and a magnetic resin carrier having an average particle size of 30 μm was obtained with an air classifier. The magnetic flux density of this magnetic resin carrier is 47e when the external measurement magnetic field is 1KOe.
It was mu / g.

Next, 85 parts by weight of this magnetic resin carrier and toner 15
After mixing well with 1 part by weight, an electrostatic latent image is formed on the selenium photoconductor and developed by a magnetic brush method using a magnetic brush developing magnet having a surface magnetic flux density of 1000 gauss,
When transferred onto plain paper and fixed with a heat roll, a clear image could be 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. As a result of charging the obtained reduced iron powder and methanol in an attritor, a 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 was obtained. The magnetic flux density (σs) of the flat iron powder in the externally measured magnetic field of 1 KOe was 80 emu / g.

Next, 60% by weight of the flat iron powder and 40% by weight of styrene / butyl methacrylate copolymer were kneaded by heating with a hot roll, cooled, and coarsely crushed by a Wiley crusher.
The mixture was finely pulverized with a jet mill, and a magnetic resin carrier having an average particle size of 30 μm was obtained with an air classifier. The magnetic flux density of this magnetic resin carrier at an external measurement magnetic field of 1KOe is 48e.
It was mu / g.

Next, 85 parts by weight of this magnetic resin carrier and toner 15
After mixing well with 1 part by weight, an electrostatic latent image is formed on the selenium photoconductor and developed by a magnetic brush method using a magnetic brush developing magnet having a surface magnetic flux density of 1000 gauss,
When transferred onto plain paper and fixed with a heat roll, a clear image could be 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 of this flat iron powder in an external measurement magnetic field of 1 KOe was 100 emu / g.

Next, 60% by weight of the flat iron powder and 40% by weight of styrene / butyl methacrylate copolymer were kneaded by heating with a hot roll, cooled, and coarsely crushed by a Willey crusher.
The mixture was finely pulverized with a jet mill, and a magnetic resin carrier having an average particle size of 30 μm was obtained with an air classifier. The magnetic flux density of this magnetic resin carrier is 57e when the external measurement magnetic field is 1KOe.
It was mu / g.

Next, 85 parts by weight of this magnetic resin carrier and toner 15
After mixing well with 1 part by weight, an electrostatic latent image is formed on the selenium photoconductor and developed by a magnetic brush method using a magnetic brush developing magnet having a surface magnetic flux density of 1000 gauss,
When transferred onto plain paper and fixed with a heat roll, a clear image could be obtained.

Comparative Example 1 Cubic magnetite having a magnetic flux density of 62 emu / g in an externally measured magnetic field of 1 KOe (KBC 10 manufactured by Kanto Denka Kogyo Co., Ltd.)
0) A magnetic resin carrier was obtained in the same manner as in Example 1 except that 50% by weight was used instead of 50% by weight of the flat iron powder obtained in Example 1. The magnetic flux density of this magnetic resin carrier in an externally measured magnetic field of 1 KOe was 31 emu / g.

Next, 85 parts by weight of this magnetic resin carrier and toner 15
After mixing well with 1 part by weight, an electrostatic latent image is formed on the selenium photoconductor and developed by a magnetic brush method using a magnetic brush developing magnet having a surface magnetic flux density of 1000 gauss,
When it was transferred onto plain paper and fixed with a hot roll, the carrier went up so much that a good image could not be obtained.

Comparative Example 2 Cubic magnetite used in Comparative Example 1 (Kanto Denka Kogyo)
80% by weight of KBC 100 manufactured by K.K. Co., Ltd. and 20% by weight of styrene / butyl methacrylate copolymer are kneaded by heating with a hot roll, cooled, coarsely pulverized by a Willey pulverizer, and then finely pulverized by a jet mill. , Average particle size 30μ by wind classifier
m magnetic resin carrier was obtained. The magnetic flux density of this magnetic resin carrier in the external measurement magnetic field of 1 KOe is 48 em.
It was u / g.

Next, 85 parts by weight of this magnetic resin carrier and toner 15
After mixing well with 1 part by weight, an electrostatic latent image is formed on the selenium photoconductor and developed by a magnetic brush method using a magnetic brush developing magnet having a surface magnetic flux density of 1000 gauss,
When it was transferred onto plain paper and fixed with a heat roll, a clear image could be obtained, but carrier particles were easily crushed and fog increased during actual running and it was found that there was a problem with durability.

〔The invention's effect〕

The magnetic resin carrier for electrophotography of the present invention uses, as the magnetic powder, a flat fine iron powder having a large magnetic flux density (σs) in the external measurement magnetic field of 1 KOe, which is not obtained by the conventional magnetic powder. It has a large magnetic flux density at 1 KOe, has no carrier rise and is excellent in image characteristics.

Claims (2)

[Claims] 1. A magnetic resin carrier for electrophotography, 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 resin carrier for electrophotography according to claim 1, wherein the magnetic flux density (σs) of the iron powder in an external measurement magnetic field of 1 KOe is 70 to 140 emu / g.