JPH0456983B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carrier for an electrophotographic developer,
More specifically, the present invention relates to a carrier for a two-component developer in which fine magnetic powder is dispersed in a resin.

In recent years, as a carrier for two-component magnetic brush developers, instead of the conventional large diameter (80μ to 200μ) iron powder, etc., small diameter (5μ to 5μ), which is made by dispersing magnetic fine powder of 0.1μ to 1.0μ in binder resin, has been used as a carrier for two-component magnetic brush developers. 40μ) particles are now being put into practical use. This type of two-component developer has a smaller carrier particle size than conventional carriers such as iron powder, so the quality of the copied images is good, and the variation in the carrier to toner mixing ratio is less It has the advantage of wide tolerance. However, on the other hand, since the carrier is very small, it tends to adhere to the image area of the latent image formed on the photoreceptor or around the image area during development.
Particularly in cases where the amount of the carrier is too large, a portion of the adhered carrier is transferred to the paper and appears as dust around the image area, resulting in a problem of a shortage of carrier.

This problem of carrier adhesion to the photoreceptor has been analyzed since then, and basically, the balance between the electrostatic force that attracts the carrier to the photoreceptor side and the magnetic force that attracts it to the magnetic roll side is disrupted, resulting in static electricity. Adhesion to the photoreceptor occurs when the magnetic force exceeds the magnetic force. The electrostatic force is related to the amount of charge on the carrier, including the charge induced on the carrier during development, the type of photoreceptor used as the development condition, the bias voltage, etc., and the magnetic force is related to the magnetic flux of the magnetic roll. It has become clear that density and carrier magnetization are related.

Therefore, various measures can be taken to prevent carrier adhesion, but it is difficult to easily change development conditions such as the type of photoconductor, bias voltage, and magnetic flux density of the magnetic roll due to the system configuration. The amount of charge cannot be easily changed due to the overall design of the developer. Also, it was proposed to add silica to toner (Japanese Patent Application Laid-Open No. 1983-
62256), but this method cannot be expected to have much of an effect. Furthermore, there are also negative effects such as film forming due to the addition of silica.

Under such circumstances, the most effective method to prevent carrier adhesion is to increase the magnetization of the carrier. To achieve this, (1) increase the magnetization of the carrier; (2) In particular, in magnetic powder-dispersed resin carriers made by dispersing magnetic fine powder in resin, increasing the content of magnetic fine powder will (3) use magnetic fine powder with high magnetization; Three methods are possible. However, in methods (1) and (2), if the average particle size of the carrier exceeds 50μ, it loses its characteristics as a developer, and the amount of magnetic fine powder that can be mixed into the resin is limited. has its own limits, so there are limits to its effectiveness. Method (3) is considered to be promising as a countermeasure against carrier adhesion, but so far no material suitable for this purpose has been found. In other words, for the normally used magnetite, the magnetization in a magnetic field of 1K oersted is the maximum magnetization that is generally expected.
The magnetization is about 65 emu/gr, and it is impossible to obtain magnetization higher than that. If iron powder with a particle size of 0.1μ to 1.0μ is used instead of magnetite, the magnetization can be reduced to 65emu/
Although it is possible to increase the gr
It is difficult to manufacture using normal methods because it is extremely unstable and has manufacturing risks, and the manufacturing process is expected to be quite complex and expensive, so it is not practical to use this method. It's not.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic powder-dispersed resin carrier having high magnetization to prevent the carrier from adhering to a photoreceptor.

Another object of the present invention is to provide a magnetic powder-dispersed resin carrier that can be safely manufactured by a conventional manufacturing method using magnetic fine powder containing metal iron having higher magnetization than magnetite or the like.

The magnetic powder-dispersed resin carrier for electrophotographic development of the present invention, which achieves these objectives, has a surface of a metal iron core such that the polymerization ratio of metal iron and iron oxide is 25:75 to 85:15. It is made by dispersing magnetic fine powder coated with iron oxide in an insulating binder.
It is characterized by an average particle size of 10 to 35μ.

The average particle size of the magnetic fine powder is suitably 0.1 to 1.0μ. The magnetization of such magnetic fine powder is 1K
It is more than 70 emu/gr in the Oersted magnetic field, and its coercive force is 70 to 300 Oersted.
These magnetization and coercivity values are sufficient to prevent the carrier from sticking to the photoreceptor.

Examples of the insulating binder resin include homopolymers of styrene or substituted products thereof such as polystyrene, polyP-chlorostyrene, and polyvinyltoluene, styrene-P-chlorostyrene copolymers, styrene-propylene copolymers, and styrene-vinyl Toluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-methyl methacrylate copolymer, Styrenic copolymers such as styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, and styrene-isoprene copolymer; polymethyl In addition to thermoplastic resins such as methacrylate, polyvinyl chloride, polyethylene, polypropylene, thermoplastic polyester, and polyurethane, thermosetting resins such as modified acrylic resins, phenolic resins, melamine resins, and urea resins can be used.

The blending ratio of magnetic fine powder and insulating binder is
It is appropriate to use 80 to 400 parts by weight of the magnetic fine powder per 100 parts by weight of the insulating binder resin.

In addition to the above two components, the carrier of the present invention further contains coloring agents such as pigments and dyes, auxiliary agents such as resistance control agents and charge control agents, etc., and does not impede the purpose of the present invention. It may also contain other magnetic fine powders such as magnetite.

The carrier of the present invention is produced by melt-kneading, pulverizing, and classifying a mixture of the above components. The average particle size of the carrier is suitably 10-35μ, preferably 15-30μ.

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

"Parts" and "%" in each example mean "parts by weight" and "% by weight," respectively.

Example 1 Styrene-acrylic copolymer 100 parts (manufactured by Sanyo Kasei Co., Ltd., "HIMER SBM73") Magnetic fine powder 200 parts Manufactured by Dowa Iron Powder Co., Ltd., "MR-20" Metallic iron content 28.2% In a magnetic field of 1 K oersted magnetization of
70 emu/gr Coercive force 110 oersted Powder diameter 0.2 μm to 0.8 μm The mixture having the above composition was melt-kneaded in a kneader, cooled, pulverized, and classified to obtain a magnetic powder-dispersed resin carrier having an average particle size of 23 μm. The magnetization of this carrier in a 1K oersted magnetic field is 47emu/gr.
Coercive force is 110 Oersted resistance is 9×10 ¹² Ω-cm
It was hot.

Separately, 100 parts of styrene resin (manufactured by Etsuo Kagaku Co., Ltd., "Picolastik D-125"), carbon black (manufactured by Kabot Corporation, "Elftek 8")
Melt and knead 10 parts and 2 parts of dye ("Oil Black B2" manufactured by Orient Chemical Co., Ltd.) in a kneader,
After cooling, it was crushed and classified to obtain a toner with an average particle size of 12μ.

The carrier and toner obtained in this way are
A two-component developer was prepared by mixing at a ratio of 90:10, and development was carried out using an electrophotographic copying machine equipped with a magnetic brush developing device. As a result, no carrier adhesion was observed in or around the image area, and a copy image of excellent quality was obtained.

Comparative Example 1 Same as Example 1 except that the magnetic fine powder of Example 1 was replaced with magnetite (manufactured by Titan Kogyo Co., Ltd., "RB-BL", magnetization 49 emu/gr in a 1K Oersted magnetic field, coercive force 220 Oersted). A magnetic powder-dispersed resin carrier having an average particle size of 25 μm was obtained in the same manner.
The magnetization of this carrier in a magnetic field of 1 K Oersted was 33 emu/gr, the coercive force was 220 Oersted, and the resistance was 2×10 ¹³ Ω-cm.

Using this carrier, a development test was conducted in the same manner as in Example 1. As a result, the resulting image was of poor quality with carrier adhering to the periphery of the image area.

Example 2 Styrene-acrylic copolymer 100 parts ("Higher SBM" 73) Magnetic fine powder 100 parts "MR-25" manufactured by Dowa Iron Powder Co., Ltd. Metallic iron content 53% Magnetization in a 1K Oersted magnetic field
80 emu/gr Coercive force 100 oersted Powder size 0.2 μ to 0.8 μ Magnetite 100 parts (manufactured by Titan Kogyo Co., Ltd., “RB-BL”) Using a mixture with the above composition, magnetic particles with an average particle size of 24 μ were prepared in the same manner as in Example 1. A powder-dispersed resin carrier was obtained. The magnetization of this carrier in a 1K Oersted magnetic field was 43 emu/gr, the coercive force was 160 Oersted, and the resistance was 1×10 ¹³ Ω-cm.

A developer was prepared by mixing this magnetic powder dispersed resin carrier and the toner described in Example 1 at a ratio of 90:10, and development was carried out in the same manner as in Example 1 using this developer. As a result, no carrier adhesion was observed either around the image area or in the image area, and a copied image of excellent image quality was obtained.

Example 3 A magnetic powder-dispersed resin carrier with an average particle size of 29 μm was obtained in the same manner as in Example 1 except that 6 parts of carbon black (manufactured by CABOT Co., Ltd., “XC-72” was added. The resistance of this carrier was It was 5×10 ⁹ Ω-cm.

Using this carrier, a development test was conducted in the same manner as in Example 1.

As a result, no carrier adhesion was observed either around the image area or in the image area, and a copied image of excellent image quality was obtained.

Example 4 A dye (manufactured by Orient Chemical Co., Ltd.,
6 parts of "Spirit Black SB") were added, melted and kneaded in a kneader, cooled, pulverized, and classified to obtain a magnetic powder-dispersed resin carrier with an average particle size of 35 μm.

Separately, a mixture with the following composition was melt-kneaded, cooled, crushed, and classified to have an average particle size of 11.0μ.
A magnetic toner was obtained.

Styrene-acrylic copolymer 100 parts by weight (manufactured by Sanyo Kasei Co., Ltd., "Himer SBM 700") Magnetite 70 parts by weight (manufactured by Titan Kogyo Co., Ltd., "BL-100") The above carrier and magnetic toner were mixed in a ratio of 80:20. A developer was prepared using this developer, and development was carried out using an electrophotographic copying machine equipped with a magnetic brush developing device for developing a positively charged latent image.

As a result, no carrier adhesion was observed either around the image area or in the image area, and a copy image of excellent quality was obtained.

Claims (1)

[Claims] 1. The weight ratio of metallic iron and iron oxide is 25:75 to 25:75.
It is made by dispersing magnetic fine powder, which is made by coating the surface of a metal iron core with iron oxide in a ratio of 85:15, in an insulating binder, and has an average particle size of 10 to 35μ. A magnetic powder-dispersed resin carrier for electrophotographic development. 2. The carrier according to claim 1, wherein the magnetic fine powder has an average particle size of 0.1 to 1.0μ.