JPS6333754A - Magnetic resin carrier for electrophotography - Google Patents

Abstract

PURPOSE:To improve an image characteristic by incorporating specific flat magnetic powder consisting of iron into a resin carrier. CONSTITUTION:The flat magnetic powder consisting of the iron and having <=10mum major diameter and <=1.0mum thickness is incorporated into the carrier. The magnetic powder is the magnetic powder essentially consisting of the thinly rolled iron having the flat shape. The size of the particles thereof is <=10mum, more preferably <=5mum major diameter and the thickness thereof is <=1.0mum, more preferably <=0.5mum. The magnetic powder having >=5 (major diameter/ thickness) is more preferable. The magnetic powder having such shape has 70-14emu/g satd. magnetic flux density sigmas in at 1kOe magnetic field measured in the outside part. The content of the magnetic powder in the magnetic resin carrier is preferably 40-80wt% and the magnetic resin carrier having the grain sizes ranging 7-200mum, more particularly 7-100mum is more preferable. The carrier which has the large magnetic flux density, is free from carrier starvation and has the excellent image characteristic is thereby obtd.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides a developer with excellent image characteristics that is used in two-component and 1.5-component developers for developing electrostatic latent images in electrophotography and the like. The present invention relates to a magnetic resin carrier for electrophotography.

(Prior art and its problems) In electrophotography, the dry developer used when developing an electrostatic latent image formed on a photoreceptor by a magnetic brush method is a two-component developer consisting of toner and carrier. type is used.

Two-component developers usually consist of a mixture of toner particles with a particle size of 5 to 20 μm and magnetic carrier particles with a particle size of 40 to 150 μm. There are demands for higher image quality and longer life, and developers that satisfy these demands are being actively developed.

Regarding carriers, in order to satisfy the demands for higher image quality and longer life, there is a desire for a magnetic material that is lighter, more dense, and can form magnetic brushes with softer ears.

In recent years, in order to satisfy such demands, relatively lightweight magnetic granulated carriers made by granulating and firing metal oxide powders such as ferrite and magnetite have been used, and the particle size has also increased to higher quality. In order to achieve this, particle diameters are gradually becoming smaller (50 μm or less), but there is a problem in that it is difficult to efficiently produce magnetic granulated carriers with such small particle diameters using conventional manufacturing techniques. In addition, in order to achieve higher image quality and longer life, it is becoming common to apply a coating treatment to the carrier surface with an appropriate coating agent. Generally, a granulation phenomenon is likely to occur due to mutual adhesion of the cores due to the coating agent, and there is a problem that the product yield after coating is significantly reduced.

In order to solve these problems, after heating and kneading magnetic powder such as ferrite or magnetite and binder resin,
The use of magnetic resin carriers obtained by pulverization and classification is being considered.

However, since such magnetic resin carriers are a mixture of magnetic powder and binder resin, which is a non-magnetic substance,
Since the magnetic flux density (σS) is lower than that of a carrier containing only magnetic powder, it is easy to cause carrier formation during development (in order to prevent this, increasing the content ratio of magnetic powder in the magnetic resin carrier causes the carrier to become brittle). (The current situation is that a satisfactory magnetic resin carrier cannot necessarily be obtained using conventional magnetic powders such as ferrite and magnetite, as this results in a decrease in strength and problems with durability.)
■Magnetic powder with a large flux density (σS) is required.

Generally, in a dry type copying machine using electrophotography, the magnetic field strength of the magnet 7) used in the developing machine is around 1000 Gauss. On the other hand, in order to provide the carrier with a sufficient magnetic binding force, it is necessary that the magnetic flux density (σS) of the magnetic powder be large in an external measurement magnetic field of 1 KOe.

However, magnetite and ferrite, which are conventionally used as magnetic powder, have a magnetic flux density of 40 to 65 emu/g in an external measurement magnetic field of 1 KOe, and carbonyl iron powder has a magnetic flux density of 30 to 65 emu/g.
50 e mu/g, and 20 to 40 e mu/g for iron alloy powder whose main component is iron, which is acicular and has high holding power.
/g, it is not possible to sufficiently increase the magnetic flux density of the magnetic resin carrier using conventional magnetic powder.

In order to increase the magnetic flux density of magnetic powder, metallic iron or an iron alloy whose main component is iron has a higher saturation magnetic flux density than iron oxides such as magnetite or ferrite (metallic iron or iron alloy powder). Saturation magnetic flux density in case of: 120~2
10 emu/g, the saturation magnetic flux density of magnetite and ferrite is advantageous (near 5-90 emu/g), but as mentioned above, in the externally measured magnetic field IKOe, conventional metallic iron and iron alloys and iron oxides There is no big difference in the magnetic flux density.

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

[Means for solving problems]

As a result of extensive research to achieve the above object, the present inventors have found that the magnetic flux density (σS) of magnetic powder in an externally measured magnetic field of 1 KOe varies greatly depending on the shape of the magnetic powder. In other words, the thinner and flatter the shape of the magnetic powder, the more
We found that the magnetic flux density in an externally measured magnetic field of 1 KOe becomes thicker (and conversely, the closer to a spherical shape, the smaller the magnetic flux density becomes.The reason for this is not clear, but the magnetic flux density that affects the magnetic properties of magnetic powder It is presumed that this is related to the shape anisotropy factor among the anisotropy factors.

The present invention has been made based on the above findings, and is characterized in that it contains flat magnetic powder consisting essentially of iron and having a major axis of 10 μm or less and a thickness of 1.0 μm or less. It provides a carrier.

The electrophotographic magnetic resin carrier of the present invention will be described in detail below.

The magnetic powder used in the present invention is a magnetic powder whose main component is iron and has a thinly rolled flat shape, and the particle size is
The major diameter is 10 μm or less, preferably 5 μm or less, and the thickness is 1
．． It is preferably 0 μm or less, preferably 0°5 μm or less, and the ratio of its major axis to thickness is (major axis/thickness)≧5. Magnetic powder with such a shape can be used in externally measured magnetic field IK
The magnetic flux density (σS) at Oe is 70 to l 40 em
It has a magnetic flux density of approximately twice the magnetic flux density (40 to 65 emu/g) of conventionally commonly used magnetite.

The above-mentioned 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 resulting reduced iron powder is wet-pulverized using an attritor to obtain magnetic powder.

The above-mentioned ζn property i5) may be subjected to various surface treatments, such as formation of oxide +19 or coating with an organic compound such as a silane coupling agent.

The content of the magnetic powder in the magnetic resin carrier is from 40 to
Although 80% by weight is preferable, it may be increased or decreased depending on the required magnetic flux density.

The resins used in the present invention include polystyrene-based, styrene-containing copolymer-based, polyacrylic ester-based,
Polymethacrylic acid ester type, polyester type, polyamide type, polyvinyl acetate type, ethylene/vinyl acetate copolymer type, epoxy type, phenol type, hydrocarbon type,
Examples include petroleum-based and chlorinated paraffin-based binder resins, which can be used alone or in combination.

In addition, various additives such as a lubricant such as wax, a colloidal glue, a fluidity imparting agent such as carbon black, a charge control agent, a coloring agent, etc. may be used in combination as necessary.

The method for producing the magnetic resin carrier of the present invention itself is the same as the method for producing conventionally known hexa-propane resin carriers. That is, the magnetic resin carrier of the present invention is produced, for example, in the following manner using the above-mentioned IF agent, the above-mentioned resin, and, if necessary, the above-mentioned various additives.

The magnetic powder and the resin, as well as the various additives as necessary, are premixed, thoroughly kneaded using a heated kneader, cooled and then pulverized, and classified as necessary. ,
Further, a magnetic resin carrier is obtained by adding a lubricant, a fluidity imparting agent, etc. afterwards. Alternatively, the magnetic powder and, if necessary, the various additives mentioned above are dispersed in a resin solution, which is spray-dried in a heated air stream, and classified according to the required G4, and a lubricant and a fluidity imparting agent are added. etc., to obtain a magnetic resin carrier.

The magnetic resin carrier of the present invention has a particle size of 7 to 200 μm.
In particular, those within the range of 7 to 100 μm are preferred.

〔Example〕

EXAMPLES The present invention will be explained in more detail below by giving examples of the present invention together with comparative examples.

Example 1 Hematite for pigments (MR270E manufactured by Bengara Morishita) was placed in a reduction furnace and heated to 450°C in a hydrogen gas atmosphere.
After maintaining this temperature for 5 hours, heating was stopped and the mixture was cooled to room temperature. The obtained reduced iron powder and methanol are charged into an attritor and processed to have a maximum length of 10 μm or less and an average length of 2 μm.
A flat iron powder having a diameter of 0.3 μm and a thickness of 0.3 μm or less was obtained. The external measurement of this flat iron powder also showed that the magnetic flux density (σS) in n-field IKOe was 110 emu/g.

Next, 50% by weight of this flat iron powder and 50% by weight of the styrene/butyl methacrylate copolymer were heated and kneaded using hot rolls, cooled, and coarsely pulverized using a Wiley pulverizer.
The mixture was finely pulverized using a jet mill, and a 6N resin carrier having an average particle size of 30 μm was obtained using an air classifier. The magnetic flux density of this magnetic resin carrier at an externally measured magnetic field of 1 KOe is 47
emu/g.

Next, 1 part of 85 parts of this magnetic resin carrier and 15 parts of toner were added.
After thoroughly mixing parts by weight, an electrostatic latent image is formed on a selenium photoreceptor, and developed by a magnetic brush method using a magnetic brush developing magnet with a surface magnetic flux density of 1000 Gauss.
When transferred onto plain paper and fixed with a hot roll, a clear image was obtained.

Example 2 Cubic magnetite (BC100S manufactured by Kanto Denka Kogyo ■)
) was placed in 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. The obtained raw iron powder and methanol were charged into an attritor and treated to obtain rope-prone iron powder having a maximum major axis of 10 μm or less, an average major diameter of 1 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 IKOe was 80 emu/g.Next, 60% by weight of this flat iron powder and 40% of the styrene-butyl methacrylate copolymer were heated. The mixture was heated and kneaded using rolls, cooled, and then coarsely ground using a Wiley grinder, finely ground using a jet mill, and then used with an air classifier to obtain a magnetic resin carrier having an average particle size of 30 μm. The magnetic flux density of this magnetic resin carrier at an externally measured magnetic field of 1 KOe is 43
emu/g.

Next, 1 part of 85 parts of this magnetic resin carrier and 15 parts of toner were added.
After thoroughly mixing parts by weight, an electrostatic latent image is formed on a selenium photoreceptor, and developed by a magnetic bran method using a magnetic bran developing magnet with a surface magnetic flux density of 1000 Gauss.
When transferred onto plain paper and fixed with a hot roll, a clear image was obtained.

Example 3 The reduced iron powder and methanol obtained in Example 1 were charged into a sand grinder and processed to obtain flat iron powder with a maximum length of 10 μm or less, an average length of 1.5 μm, and a thickness of 0.2 μm or less. . The magnetic flux density of this flat iron powder in the externally measured magnetic field IKOe was 10,100 e/g.

Next, 60% by weight of this flat iron powder and 40% by weight of the styrene-butyl methacrylate copolymer were heated and kneaded using hot rolls, cooled, and coarsely pulverized using a Wiley pulverizer.
The mixture was finely pulverized using a jet mill, and a magnetic resin carrier having an average particle size of 30 μm was obtained using an air classifier. The magnetic flux density of this magnetic resin carrier in an external magnetic field of 1 KOe is 57
emu/g.

Next, 85 parts by weight of this magnetic resin carrier and 15 parts by weight of toner were added.
After thoroughly mixing the old and heavy parts, an electrostatic latent image is formed on the selenium photoreceptor H, and developed by a magnetic brush method using a magnetic brush developing magnet with a surface magnetic flux density of 1000 Gauss.
When transferred onto plain paper and fixed with a hot roll, a clear image was obtained. - Comparative Example 1 Magnetic flux density in external measurement magnetic fields IK and Oe is 62 emu
/g Cubic magnetite (Kanto Denka Kogyo!1'@
Example 1 except that 50% by weight of the flat iron powder obtained in Example 1 was used instead of 50% by weight of the flat iron powder obtained in Example 1.
A magnetic resin carrier was obtained in the same manner as above.

The magnetic flux density of this n-type resin carrier in the externally measured magnetic field IKOe was 31 emu/g.

Next, 85 parts by weight of this magnetic resin carrier and 15 parts by weight of toner were added.
After thoroughly mixing parts by weight, an electrostatic latent image is formed on a selenium photoreceptor, and developed by a magnetic brush method using a magnetic brush developing magnet with a surface magnetic flux density of 1000 Gauss.
When the image was transferred onto plain paper and fixed using a hot roll, a good image could not be obtained due to a lot of carrier removal.

Comparative Example 2 Cubic magnetite used in Comparative Example 1 (Kanto Denka Kogyo!)
1% by weight of Ikiku KBC100) 80% by weight and 20% by weight of styrene-butyl methacrylate copolymer were heated and kneaded using hot rolls, cooled, coarsely ground using a Willey grinder, and finely ground using a jet mill. A magnetic resin carrier with an average particle size of 30 μm was obtained using an air classifier. The magnetic flux density of this magnetic resin carrier in the externally measured magnetic field IKOe was 48 emu/g.

Next, 85 parts by weight of this magnetic resin carrier and 15 parts by weight of toner were added.
After thoroughly mixing parts by weight, an electrostatic latent image is formed on a selenium photoreceptor, and developed by a magnetic brush method using a magnetic brush developing magnet with a surface magnetic flux density of 1000 Gauss.
When the image was transferred onto plain paper and fixed with a hot roll, a clear image could be obtained, but it was found that the carrier particles were easily broken and fog increased over time during actual printing, and there were problems with durability.

〔Effect of the invention〕

The 'magnetic resin carrier for electrophotography of the present invention, as a magnetic powder, has a magnetic flux density (σS) in an externally measured magnetic field IKOe.
It uses large, flat, fine iron powder, and has a large single flux density, no carrier build-up, and image characteristics are not affected by external measurement + i-field 1 KOe, which could not be obtained with conventional magnetic powder. be.

Claims (2)

[Claims] (1) A magnetic resin carrier for electrophotography, characterized in that it contains flat magnetic powder substantially made of iron and having a major axis of 10 μm or less and a thickness of 1.0 μm or less. (2) Magnetic flux density (σ
The electrophotographic magnetic resin carrier according to claim 1, wherein s) is 70 to 140 emu/g.