JPH05121257A - Manufacture of magnet roll for magnetic brush - Google Patents

Abstract

PURPOSE:To provide a plastic magnet roll having a high magnetic flux density by injecting or extruding a mixture of magnetic material and polymer while applying a magnetic pattern for a magnetic brush roll, forming a recess in the part for the developer pole of the magnet roll, and performing anisotropic treatment. CONSTITUTION:A composition containing ferrite particles and polymer is kneaded, and it is subjected to injection molding or extrusion molding in a magnetic field to form a magnet roll 2 having an easy axis of magnetization of the ferrite particles in a given orientation. During the molding, the roll is provided with a recess 3 in its periphery while the easy axis of the magnetic material is oriented into a magnetic pattern corresponding to the repulsion pole. According to this method, a magnet roll is manufactured at lower cost with improved productivity compared with the sintered magnet roll or plastic roll.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a method of manufacturing a magnetic roll used in a magnetic brush developing device and a magnetic brush cleaning device of an electrostatic copying machine.

[0002]

2. Description of the Related Art Isotropic or anisotropic ferrite-based sintered magnets are generally used as magnetic rolls for magnetic brush development. However, this magnet has many problems as described below during roll forming. There is.

(1) It is difficult to compress a ferrite powder into a roll shape having a length larger than the diameter by a usual apparatus, and a special molding apparatus must be used. (2) The compression molded body obtained in (1) above is very liable to be chipped and fragile until firing is completed, and thus requires careful handling. (3) Since it shrinks greatly during firing and the dimensional accuracy is poor, post-processing is required to improve accuracy. (4) Since the sintered ferrite magnet itself is also hard and brittle, processing to improve the dimensional accuracy must be performed by grinding or the like, and since the cutting amount of the grinding wheel cannot be increased, productivity is poor.

On the other hand, in order to eliminate the above-mentioned drawbacks of the sintered ferrite magnet roll, it has been proposed to use a rubber magnet or a plastic magnet in which a ferrite powder is mixed with a polymer in a roll shape. There is. For example,
In JP-A-55-157218, a mixture of an oxide magnetic powder and a mixed medium and additives, if necessary, is extrusion-molded and magnetized so as to have a plurality of magnetisms extending in the axial direction during roll molding. However, it is described later about a magnet roll that is sintered and then equipped with a non-magnetic cylinder on the outer periphery.

Further, in JP-A-55-165606, a mixture of a ferromagnetic powder having magnetic anisotropy and a resin is applied in a magnetizing direction in a state where the ferromagnetic powder can move freely. Then, the ferromagnetic powder is oriented in the same direction as the magnetization direction at the same time as the magnetization, and is molded to produce a long multipole magnet roll. However, the rubber magnet roll and the plastic magnet roll produced in this manner have a lower ferrite density as compared with the ferrite magnet roll produced by the above-mentioned sintering method because of the high polymer content, and are therefore magnetically weak. Becomes
It is not suitable for magnetic brush development and has not been put to practical use as a magnetic roll for development.

On the other hand, generally, the density of a developed image in an electrophotographic apparatus or the like largely depends on the time during which the magnetic brush is in contact with the latent image carrier. Since the latent image carrier usually moves at a constant speed, it is related to the width of contact of the magnetic brush with the latent image carrier. Further, as a method of increasing the contact width of the magnetic brush with the latent image carrier, a repulsive magnetic field is generated by cutting the magnetic pole center of the magnet at the developing position or adjoining magnets of the same pole to generate a plurality of magnetic field strength distributions. It is already known that it is effective to generate.

In Japanese Unexamined Patent Publication No. 54-95243, a magnet in a developing roll constitutes a substantially integral magnetic portion which produces a magnetic field intensity distribution having a plurality of peaks at a developing position. However, this developing roll is not a magnetic roll formed by extruding a mixture obtained by adding a mixed medium to oxide magnetic powder, but a predetermined depression is formed by magnetizing a sintered magnet piece such as ferrite and magnetizing it. Although it was formed by a cutter, it requires cutting with a diamond cutter, etc., resulting in very poor productivity.

Japanese Unexamined Patent Publication No. 54-82097 discloses a developing roller composed of a magnet roller and a cylindrical sleeve of a non-magnetic material which rotates around an outer circumference of the magnet roller, and the surface of the magnet roller body on the sleeve side is It is possible to form a correction member from a composition in which magnetic particles such as Fe fine particles are mixed in a resin such as vinyl chloride resin, and to form various magnetic toner peaks such as two peaks or three peaks depending on the shape of the correction member. It is stated that it is possible. This method is only for forming a plurality of magnetic field strength distributions by a correction member having isotropic magnetism, and it is impossible to generate a strong magnetic flux by such a method.

[0009]

In the magnet roll for a magnetic brush having a repulsive magnetic pole, the contact area of the magnetic brush with the photosensitive member is increased to improve the developing efficiency, but the magnetic force is lowered in the valley portion of the repulsive magnetic pole. Therefore, it is difficult to obtain a magnet roll for a magnetic brush having a repulsive magnetic pole from a synthetic resin roll having a low magnetic flux density, because it is difficult to prevent the developer from scattering and it is difficult to obtain a ferrite-based sintered magnet with a high magnetic flux density. A magnet was used.

It is an object of the present invention to provide a magnetic brush magnet roll having a developing magnetic pole having a plurality of magnetic field strength distributions, particularly a magnetic brush having a high magnetic flux density in the developing magnetic pole portion and made of a synthetic resin magnet having a repulsive magnetic pole. To provide a magnet roll for use.

According to the present invention, a mixture containing a magnetic material and a high molecular compound is applied to a magnetic field corresponding to a magnetizing pattern for a magnetic brush roll having a repulsive magnetic field pattern formed in a concave portion to be formed in a part of its peripheral surface. While applying, by injection molding or extrusion molding into a roll while orienting the easy axis of magnetization of the magnetic material along this magnetic field, to form a plurality of magnetic poles on the peripheral surface,
According to the method for manufacturing a magnet roll for a magnetic brush, which is characterized in that the portion sandwiching the concave portion is magnetized in a repulsive magnetic field pattern, a high magnetic flux density required for a repulsive magnetic pole magnetic brush roll in a synthetic resin magnet is obtained. Was achieved.

The inventors of the present invention have already kneaded a composition composed of ferrite particles and a polymer compound uniformly and then applied a magnetic field by injection molding or extrusion molding while applying a pressure to apply an easy axis of magnetization of the ferrite particles. A method for manufacturing a magnet roll in which magnets are oriented in a certain direction has already been proposed (Japanese Patent Laid-Open No. Sho 5).
6-108207).

The present invention utilizes the above-described method for manufacturing a magnet roll, and a non-magnetic body 5 and a magnetic body 4 are alternately arranged on the inner peripheral surface of a molding machine in which a shaft is arranged as shown in FIGS. 2 and 3. And a magnetic body 4 is brought into contact with an electromagnet 6 formed by winding a coil on the outside, and one of the magnetic bodies 4 is a molding roll provided with a convex portion capable of forming a concave portion. Formed by injecting or extruding a mixture containing a magnetic material and a polymer compound into the mold while applying a magnetic field corresponding to a magnetizing pattern for a magnetic brush roll for an electrostatic copying machine from the electromagnet 6. , A magnet having an anisotropy formed by forming a recess in the portion corresponding to the developing pole of the cylindrical magnet roll [Fig. 4
See (a) and (b)]. Since the molded product thus obtained is in a magnetized state, it may be used as a magnet roll as it is,
Alternatively, it is used as a magnet roll that has been demagnetized once and then re-magnetized.

A magnetic field is applied by kneading the above-mentioned composition composed of ferrite particles and a polymer compound and then injection molding or extrusion molding while applying pressure to orient the easy axis of magnetization of the ferrite particles in a certain direction. It is also possible to obtain a high magnetic flux density by forming a recess in the portion corresponding to the developing pole of the magnet roll after forming the magnet roll, but the magnetic flux is used as the developing pole of the repulsive magnetic field magnetic brush magnet roll. Insufficient density. Further, according to the present invention, a recess is formed in a part of the peripheral surface at the time of injection molding or extrusion molding, and at the same time, the easy axis of magnetization of the magnetic material is oriented in a magnetic field pattern corresponding to the repulsive magnetic pole. Since it is not necessary to remove the magnetic material in the valley portion of the recessed portion, the amount of the magnetic material around the recessed portion can be made denser by that amount, and the recessed portion is formed,
It is considered that since the easy axis of magnetization is oriented, the lines of magnetic force are further concentrated in the regions adjacent to the magnetizing heads on both sides of the recess, and a higher magnetic flux density can be obtained.

The composition of the magnet roll of the present invention comprises 70 to 95% by weight of magnetic material particles having a large magnetic anisotropy constant such as ferrite powder or rare earth magnet powder containing at least one of barium, strontium and lead, polyethylene, Polystyrene, chlorinated polyethylene, polyamide,
5 to 30% by weight of a polymer compound composed of a high-fluidity thermoplastic resin such as polypropylene, 0 to 10% by weight of a solid plasticizer and / or a liquid plasticizer, 0 to 3% by weight of a lubricant, and, if necessary, other Composed of additives. After kneading and blending these compositions with a roll, a kneader, a Banbury, etc., a high magnetic flux can be obtained by injection molding or extrusion molding the above compositions in a magnetic field corresponding to a magnetizing pattern for a magnetic brush roll for electrostatic copying. A resin magnet roll having a high density can be obtained.

The lines of magnetic force by the magnetic field in the magnetized state of the magnetic roll according to the present invention and the state of orientation of the magnetic particles oriented along it are as shown by the broken line in FIG. 5 (a), and the magnetic flux density distribution of this magnet roll is It is as shown in FIG. As can be seen from FIG. 5 (a), in the magnet roll of the present invention, the recessed notch 3 is already formed when the magnetic particles are oriented during molding.
5 is formed, the lines of magnetic force generated by the magnetizing head 8 and the magnetizing heads 9 and 10 having opposite magnetic poles facing the magnetizing head 8 are shown in FIG.
As indicated by the broken line in (a), the lines of magnetic force are further concentrated in a region where the magnetizing head and the magnetic roll are not close to each other, and the magnetic flux density is increased, and the magnetic particles are oriented along the broken line. A magnet is formed.

On the other hand, in the magnetized state, the orientation state of the magnetic particles by the magnetic field of the conventional magnetic roll having no recess 3 is shown in FIG.
As shown in (a), the lines of magnetic force are spread in the region D which becomes the recess 3 after molding, so that the magnetic roll is not concentrated on both ends of the recess as in the magnetic roll of the present invention. The magnetic flux density distribution of is shown in Fig. 6 (b).
As can be seen from FIG. 5 (b) and FIG. 6 (b), the magnetic flux density of the magnetic roll of the present invention shows a higher value than that of the conventional magnetic roll in which the recesses are cut out after molding.

[0018]

The magnetic roll of the present invention thus obtained has the following effects. (1) It has excellent productivity because it can be magnetized and oriented during roll forming. In particular, since it can be manufactured as an integral molding by injection molding or extrusion molding, it is excellent in mass productivity and can be manufactured at an extremely low cost as compared with the manufacturing method of a sintered magnetic roll or a conventional resin magnet roll. (2) Compared with the anisotropic magnet roll in which the easy axis of magnetization is oriented in the radial direction, the easy axis of magnetization is oriented in the same direction as the magnetic flux lines passing through the magnet, and therefore has excellent magnetic characteristics. Further, since the repulsive magnetic field is formed in the state where the concave portion is formed, the repulsive magnetic field having a higher magnetic flux density can be formed. (3) Since it is flexible, it is resistant to cracking and chipping and has shock resistance. (4) Since it is molded using a mold, it has high dimensional accuracy and does not require post-processing. (5) Since the density is lower than that of the sintered magnet, the weight can be reduced. (6) Plastic magnets and rubber magnets have less demagnetization than sintered ferrite magnets.

[Brief description of drawings]

FIG. 1 shows a ferrite-based sintered magnet conventionally used as a developing magnetic pole.

FIG. 2 is a plan cross-sectional view of a mold for manufacturing an integrally molded magnet roll having a recess.

FIG. 3 is a vertical cross-sectional view of the manufacturing mold, and reference numeral 2 denotes a magnet roll mold (vacant space).

4A and 4B are cross-sectional views of an example of a magnet roll of the present invention.

5 (a) and 5 (b) are diagrams showing an orientation state of magnetic particles and a magnetic flux density distribution by a magnetic field of a magnet roll of the present invention.

6 (a) and 6 (b) are diagrams showing a magnetic particle orientation state and a magnetic flux density distribution of a conventional magnetic roll having no recess.

[Explanation of symbols]

 1 Shaft 2 Magnet Roll 3 Recess 4 Magnetic Material 5 Non-Magnetic Material 6 Electromagnet 7 Coil 8, 9, 10 Magnetizing Head

Front page continuation (72) Inventor Kiyoshi Miyashita 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Zero Tux Co., Ltd.Ebina Plant (72) Inventor Yasuo Koseki 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Zero Tux Co., Ltd.Ebina Plant

Claims (1)

[Claims] 1. A magnetic field is applied to a mixture containing a magnetic material and a polymer compound in accordance with a magnetizing pattern for a magnetic brush roll having a repulsive magnetic field pattern formed in a concave portion to be formed on a part of its peripheral surface. , Forming a plurality of magnetized magnetic poles on the peripheral surface while orienting the easy axis of magnetization of the magnetic material along the magnetic field to form a plurality of magnetized magnetic poles on the peripheral surface, and magnetizing the portion sandwiching the concave portion to a repulsive magnetic field pattern. A method for manufacturing a magnet roll for a magnetic brush, characterized in that