JP2002287505A - Magnetic roller and its manufacturing method, developing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic roller realizing the reduction of cost while realizing complicated magnet constitution. SOLUTION: This magnetic roller is obtained by nearly concentrically superposing and arranging sheet type magnets 3 magnetized in different directions according to their positions in a surface direction. Thus, the magnetic roller 1 realizing the complicated magnet constitution that magnets whose magnetic field direction is different by 90 deg. are made adjacent and realizing the reduction of manufacture cost is obtained. Namely, the magnetic roller 1 is constituted by nearly concentrically superposing and arranging the sheet type magnets 3 magnetized in the different directions according to the positions in the surface direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer and a facsimile for forming an image by electrophotography or electrostatic recording, and more particularly, to a magnetic element which is one of the elements constituting the image forming apparatus. The present invention relates to a magnetic roller for forming a magnetic brush built in a brush developing device. This magnetic roller can also be applied to a cleaning roller for removing the magnetic developer remaining on the surface of the latent image carrier after the transfer of the developer.

[0002]

2. Description of the Related Art Magnetic rollers are roughly classified into rollers using sintered magnets obtained by baking and hardening a magnetic material, and rollers using bonded magnets obtained by kneading and hardening a magnetic material into a resin. The former, that is, the one using the sintered magnet can obtain a strong magnetic force, but has a problem that the cost is high due to the sintering process and the assembling process. The latter, that is, the one using a bonded magnet is easy and inexpensive to manufacture, but has the drawback that the magnetic force is weak. At present, a manufacturing method in which the material of the bonded magnet is shaped into a roller and magnetized can reduce the cost most.

On the other hand, there is a demand for a magnetic roller having a strong magnetic field due to the problem of carrier scattering. For this purpose, conventionally, a sintered magnet is embedded in a necessary portion in a bonded magnet, and further, as disclosed in, for example, Japanese Patent No. 2885136,
It has been considered to use a material having a strong magnetic force such as a rare earth element. Rare earth elements are expensive, and any of these methods will significantly increase the manufacturing cost of the magnetic roller.

[0004]

On the other hand, by using a magnet arrangement method called a Halbach arrangement, for example, by changing the arrangement of the magnets from FIG. 7 (a) to FIG. 7 (b), It is possible to configure a magnetic roller that generates a strong magnetic field at a low cost with a combination of weak but inexpensive magnets.

However, in the arrangement shown in FIG. 7 (b), it is difficult to magnetize the rollers after shaping the rollers because magnets having different directions of the magnetic field by 90 ° must be adjacent to each other. For this reason, an assembling process is further required at the time of manufacturing the roller, which causes an increase in cost.

Accordingly, an object of the present invention is to provide a magnetic roller capable of reducing costs while enabling a complicated magnet configuration.

[0007]

As a result of diligent studies by the present inventors, as shown in FIG. 1, a configuration in which sheet-like magnets magnetized in different directions depending on the position of the surface are arranged substantially concentrically and overlapped. The magnetic field direction is 9
The present inventors have found that it is possible to obtain a magnetic roller that can have a complicated magnet configuration such as adjacent magnets that are different from each other by 0 ° and that can be manufactured at low cost. That is, the present invention is a magnetic roller having a configuration in which sheet-like magnets magnetized in different directions depending on the surface direction position are arranged substantially concentrically and overlapped.

It is preferable that the sheet magnet is wound around a roller shaft. It is more effective if the sheet thickness decreases as the sheet magnet wound around the roller shaft approaches the roller circumferential end. Alternatively, a structure in which a plurality of sheet magnet cylinders having different radii are stacked is also preferable.

The sheet magnet preferably has at least a region magnetized parallel to the longitudinal direction of the sheet surface and a region magnetized in the direction of the sheet thickness depending on the magnetized state. It is also convenient that a plurality of layers of magnet sheets at the same angular position in the roller circumferential direction are magnetized in the same direction. It is even better if the magnetic material constituting the sheet magnet is composed of fine particles having magnetic anisotropy, and the direction of easy magnetization of the fine particles is the same as the direction of magnetization.

After the magnetic sheet is magnetized in different directions depending on the surface direction, the sheet-like magnet is wound around the roller shaft to manufacture the magnetic roller. At this time, by heating the sheet-shaped magnetic material / thermally crosslinkable resin composition in a magnetic field, magnetization and crosslinking are performed simultaneously, and the sheet portion other than the region being magnetized is cooled to prevent crosslinking. Is effective.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. Usually, a method of manufacturing a magnetic roller using a bonded magnet is as follows. That is, a mixture of a magnetic material powder and a resin is formed into a roller shape by injection molding or the like.
As shown schematically, a magnetic field is applied by a magnet or an electromagnet to perform magnetization. In such a method, there is no magnet assembling step or the like, so that there is an advantage that the manufacturing cost is very low. However, as in the above-described Halbach array, it is difficult to arrange magnets having different magnetic pole directions by 90 ° adjacent to each other.
You can recognize that it is very difficult just by looking at it.

The problem is to build a fine pole configuration in the very thick magnetic layer of the roller. In magnetic recording such as music tapes and magnetic disks, it is known that the upper limit of the recording density depends on the thickness of the magnetic layer. For example, the minimum period that can be magnetically recorded in the longitudinal direction is about twice the thickness of the magnetic material, and if the period is shortened, the intensity of the recording signal is significantly reduced.

Making the magnetic pole structure finer to realize the Halbach arrangement with the magnetic roller is nothing less than increasing the recording density in magnetic recording, and at least reducing the thickness of the magnetic layer at the time of magnetization. Is required.

For example, if the circumferential width of the magnetic pole oriented in the circumferential direction is set to 2 mm, the thickness of the magnetic layer is 1 mm at the maximum.
In order to obtain a magnetic pole configuration close to a rectangle, it is necessary to further reduce the thickness and to set it on the order of 0.1 mm.

However, even if a thinner magnetic pole configuration can be realized by merely reducing the thickness, the magnetic flux density becomes insufficient for the reduced thickness. Therefore, at the stage of magnetization, a thin magnetic sheet is magnetized into a sheet-like magnet, which is arranged substantially concentrically to form a magnetic roller, whereby the sheet-like magnets overlap to form a magnetic layer. The thickness can be increased, and the required magnetic flux density can be secured. In addition, with such a configuration, for example, a very strong magnet can be easily formed by aligning the magnetic poles of a plurality of layers at the same angular position in the circumferential direction of the roller, and thus the magnetic poles of the overlapping layers. can do. Further, since the magnetic pole configuration can be set for each layer, a magnetic roller having a more complicated magnetic pole configuration than in the case of a single layer can be realized.

The following two types can be considered as more specific configurations of the stacked magnetic sheets: One is a configuration in which one sheet-like magnet is wound around a roller axis. This is manufactured by magnetizing a magnetic sheet in different directions at longitudinal positions on the sheet surface, and then winding the magnet sheet around a roller shaft. At this time, since the edge of the sheet becomes a step, in order to reduce the step, it is preferable that the sheet is formed so that the sheet thickness becomes thinner toward the end of the sheet. The other is a configuration in which a plurality of sheet magnet cylinders having different radii are formed in advance, and these are stacked.

The sheet magnet can have a region magnetized in a direction perpendicular to the sheet surface and a region magnetized in a direction parallel to the sheet surface. This allows for complex magnetic pole configurations such as a Halbach array.

The magnetic sheet is composed of fine particles of a magnetic material represented by ferrite and a resin as a binder. As the magnetic material fine particles, there are a case where a magnetic isotropic material is used and a case where a magnetic anisotropic material is used. In the latter case, the direction of easy magnetization of the fine particles is desirably substantially the same as the direction of magnetization.

For this purpose, it is desirable to use a resin which can be crosslinked by heat or radiation as a binder resin, and to perform crosslinking by heat or radiation in a magnetic field. Needless to say, a magnetic field can be applied to the magnetic sheet from the previous stage to make the magnetization easy directions of the fine particles uniform.

[0020]

Embodiments of the present invention will be described below. FIG.
FIG. 2 is a schematic sectional view of a magnetic roller according to the present invention. Fig. 1 (a)
1 shows an overall sectional configuration, and FIG. 1B shows a partially enlarged configuration.

The magnetic roller 1 is made of SUS, aluminum,
A shaft core 2 made of brass, resin, ceramic or the like having a diameter of 10 mm, and a sheet-like magnet 3 made of a ferrite-based bonded magnet wound around the outer periphery like a naruto of a ramen.
It consists of. In the figure, the thickness of the sheet-like magnet 3 is emphasized, and the actual thickness of the sheet-like magnet 3 is, for example, about 0.5 mm. In addition, although a step is generated due to the end of the sheet magnet, the step at the end can also be reduced by processing the end into a tapered shape as shown in FIG.

FIG. 1B shows an enlarged view of a part of the sheet-like magnet 3, where the arrow indicates the direction of the magnetic pole. The sheet-like magnet 3 has three layers, and each layer is composed of two regions, a region 4 magnetized in a substantially radial direction of the roller and a region 5 magnetized in a substantially circumferential direction of the roller.

The magnetized area is divided into 16 in the circumferential direction, and one circumferential width is about 2 mm at the outermost circumference. These two regions are arranged in a Halbach arrangement.
Further, since the positions where the circumferential positions (roller angle positions) of the layers match each other are overlapped so that the magnetization directions are also the same, as a whole, about 1 layer equivalent to three layers of the sheet magnet 3. A Halbach array is constituted by magnets having a thickness of 0.5 mm. It goes without saying that a configuration having four or more layers can be easily manufactured.

Further, in the figure, the circumferential width of the magnetized region becomes longer toward the outer periphery, but it is possible to make the width constant between the inner periphery and the outer periphery, and to easily form a region which becomes shorter toward the outer periphery. it can. Further, as shown in FIG. 4, a non-magnetized region can be left, and a conventional magnetic roller having a 5-pole configuration or a 6-pole configuration can be manufactured.

When the magnetization is performed in a direction perpendicular to the surface of the magnetic sheet, a linear electromagnet 6 or a magnet as shown in FIG. 5 can be used. Although the electromagnets 6 are arranged above and below the magnetic sheet 9 in FIG. 5, the electromagnets 6 can be arranged only on one side. Alternatively, the electromagnet 6 may be disposed on one side, and the auxiliary magnetic pole (corresponding to the electromagnet except for the coil) may be disposed on the other side.

When magnetic particles having magnetic anisotropy are used, it is necessary to orient the magnetic particles in this magnetization step, and to crosslink and cure the sheet. In FIG. 5, the sheet is heated and thermally crosslinked by sending warm air from the periphery of the electromagnet 6 to the magnetic sheet. At this time, the cooling member 8 is brought into contact with the magnetic material sheet 9 to cool the magnetic material sheet in order to prevent a region other than the magnetized region from being crosslinked.

When magnetizing in the direction along the surface of the magnetic sheet, that is, in the longitudinal direction, a ring-shaped electromagnet 6 or a magnet as shown in FIG. 6 can be used. In the figure, when the magnetic material sheet 9 flows from right to left and the region to be magnetized comes to the electromagnet portion, the conveyance of the sheet is stopped and a magnetic field is applied. At this time, it is preferable that the gap interval can be changed so that the width of the magnetized region can be changed. In FIG. 6, a ring-shaped electromagnet 6 is provided above and below the sheet.
Are arranged, but the electromagnet 6 can be arranged only on one side.

The direction of the magnetization is not limited to the substantially longitudinal direction or the substantially radial direction with respect to the roller surface.
It is possible to magnetize in almost all directions by combining different kinds of magnetizing means.

[0029]

As described above, according to the present invention,
It is possible to obtain a magnetic roll that can cope with a more complicated magnet configuration than before and has a low cost.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a configuration of a magnetic roller according to the present invention, wherein (a) shows the entire configuration and (b) shows a partially enlarged view.

FIG. 2 is a schematic cross-sectional view showing a conventional method of magnetizing a magnetic roller with a bonded magnet.

3A and 3B are schematic diagrams illustrating an example of a form in which a sheet-like magnet is wound, wherein FIG. 3A illustrates a state without end face tapering processing, and FIG. 3B illustrates a state with end face tapering processing.

FIGS. 4A and 4B are schematic cross-sectional views of a magnetic roller configuration according to another configuration of the present invention, wherein FIG. 4A shows the entire configuration and FIG.

FIG. 5 is a schematic configuration diagram of an apparatus for magnetizing a magnetic sheet in a direction perpendicular to a longitudinal direction.

FIG. 6 is a schematic configuration diagram of an apparatus for magnetizing a magnetic sheet in a longitudinal direction.

7A and 7B are schematic cross-sectional views of a magnetic roller showing an example of a Halbach array, wherein FIG. 7A shows an array of magnets that are not a Halbach array, and FIG. 7B shows an array of magnets according to the Halbach array.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic roller 2 Shaft core 3 Sheet magnet 4 Magnet area magnetized in the perpendicular direction to the roller surface 5 Magnet area magnetized in the longitudinal direction to the roller surface 6 Electromagnet 8 Cooling member 9 Magnetic sheet

Claims (11)

[Claims] 1. A magnetic roller in which a plurality of magnetic poles are arranged in a circumferential direction, wherein sheet-like magnets magnetized in different directions depending on the surface position are arranged concentrically and overlapped. Magnetic roller. 2. The magnetic roller according to claim 1, wherein the sheet-like magnet has a structure wound around a roller shaft. 3. The magnetic roller according to claim 2, wherein the sheet thickness of the sheet-shaped magnet wound on the roller shaft decreases as it approaches the circumferential end of the roller. 4. The magnetic roller according to claim 1, wherein the magnetic roller has a structure in which a plurality of sheet magnet cylinders having different radii are stacked. 5. The sheet-like magnet is magnetized according to its magnetized state.
The magnetic roller according to any one of claims 1 to 4, further comprising at least a region magnetized in a direction parallel to the sheet surface longitudinal direction and a region magnetized in a sheet thickness direction. 6. The magnetic roller according to claim 1, wherein a plurality of layers of magnet sheets at the same angular position in the roller circumferential direction are magnetized in the same direction. 7. The magnetic material constituting the sheet magnet is made of fine particles having magnetic anisotropy, and the direction of easy magnetization of the fine particles is the same as the direction of magnetization.
The magnetic roller according to any one of claims 1 to 6, wherein 8. A developing device comprising the magnetic roller according to claim 1. 9. An image forming apparatus comprising the magnetic roller according to claim 1. 10. A method of manufacturing a magnetic roller, comprising: magnetizing a magnetic sheet in different directions depending on the surface direction, and winding the sheet magnet around a roller shaft. 11. A sheet-like magnetic material / heat-crosslinkable resin composition is heated in a magnetic field to simultaneously perform magnetization and cross-linking, and to cool and cross-link a portion of the sheet other than the region being magnetized. The method for manufacturing a magnetic roller according to claim 10, wherein the magnetic roller is prevented.