JPH04338781A - Developing device - Google Patents

Abstract

PURPOSE:To increase the amt. of the developers to be held on magnetic pole on an upstream side regardless of the kinds of the developers by providing the same pole parts in a part facing a photosensitive body. CONSTITUTION:The two magnetic poles N1, N2 of the same polarity are provided adjacent in the region of a magnet body 2 in the region opposite to the photosensitive body. Of the two magnetic poles N1, N2, the 1st magnetic pole N1 on the upstream side in the rotating direction of a sleeve is set at the magnetic force higher than the magnetic force of the 2nd magnetic pole N2 on the downstream side so that the developers held on the 1st magnetic pole N1 are brought into contact with the photosensitive body 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a printer, or a facsimile, and particularly to the structure of a developing roller facing a photoreceptor.

0002

2. Description of the Related Art Conventionally, a developing device equipped with a developing roller shown in FIG. 5 has been proposed. In this developing device, a developing roller 1 facing a photoreceptor 10 is composed of a cylindrical magnet body 2 fixed in a non-rotating state and a sleeve 3 wrapped around the magnet body 2. A plurality of magnetic poles S1, N1, N2, S2 extending in the axial direction are provided on the outer periphery of the magnet body 2.
, . . . are magnetized, and adjacent magnetic poles N1 and N2 of the same polarity are arranged on the opposing portion of the photoreceptor 10.

[0003] In the developing device, a two-component developer consisting of toner and carrier is held on the outer periphery of the sleeve 3 by the magnetic force of the magnet body 2 . This developer is conveyed in the direction of arrow a as the sleeve 3 rotates, and after the amount of conveyance is regulated to a constant by the opposing part of the blade 4 that faces the sleeve 3 with a small gap in between, it is conveyed to the opposing part of the magnetic poles N1 and N2. be done. At the opposing portions of magnetic poles N1 and N2, the developer is exposed to magnetic fields H1,
A magnetic brush is formed along the magnetic field line of H2, and the magnetic field H1,
Due to the influence of the repulsive magnetic field H0 formed during H2, the developer forms a pool at the opposing portion of the magnetic pole N1, where it is disturbed in a three-dimensional direction. Therefore, when the developer comes into contact with the electrostatic latent image on the photoreceptor 10 moving from the direction of arrow b,
Toner is supplied from the developer in the pooled portion to this electrostatic latent image to form a toner image.

0004

[Problems to be Solved by the Invention] However, in the above-mentioned developing device, depending on the type of developer used, the magnetic pole N1
There was a problem in that a sufficiently large developer reservoir could not be formed in the opposing portion. In addition, in the developing device, the magnetic poles N1 and N2 are formed by directly magnetizing the magnet body 2. Therefore, in the case of a small-diameter developing roller, it is necessary to set these magnetic poles close to each other to a high magnetic force. It was almost impossible to create a magnetic force difference. To explain specifically, in a magnet body with a diameter of about 20 to 30 mm, the magnetic pole N
When the central angle α between the magnetic pole N1 and the magnetic pole N2 was set to 30°, the magnetic poles N1 and N2 could only be magnetized to about 700 to 800 Gauss. Therefore, the restraint force of the developer is weak around the magnetic poles N1 and N2, resulting in a problem in that the carrier detaches from the sleeve and adheres to the photoreceptor 10, resulting in poor image quality.

[0005]

[Means for Solving the Problems] Therefore, the present invention has been made to solve the above-mentioned problems. Two magnetic poles of the same polarity are provided adjacently in the area of the magnet body facing the photoreceptor, and the two magnetic poles are As for the magnetic poles, a first magnetic pole on the upstream side in the rotational direction of the sleeve is set to have a higher magnetic force than a second magnetic pole on the downstream side, and the developer held by the first magnetic pole is brought into contact with the photoreceptor. Further, at least one of the two magnetic poles is formed by magnetizing a separate magnetic body embedded in the magnet body.

[0006]

[Operation] In the developing device having the above structure, the developer held by the first magnetic pole comes into contact with the photoreceptor to perform development. The developer here forms a pool under the influence of the repulsive magnetic field existing between the magnetic poles, and the developer is disturbed in three dimensions within this pool. Furthermore, by setting the first magnetic pole to have a higher magnetic force than the second magnetic pole, the developer pool becomes larger regardless of the type of developer, the developer contacts the photoreceptor with better efficiency, and the electrostatic latent image is Developed in a high density state. Furthermore, since the developer is held by the first magnetic pole with high magnetic force, the carrier does not separate from the developer and adhere to the photoreceptor. If at least one of the first magnetic pole and the second magnetic pole is formed as an embedded magnet, a necessary difference in magnetic force between the two magnetic poles can be ensured even if the magnet body has a small diameter.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. (1) First Example In the developing roller 1 of this example shown in FIG.
A magnet 6 with a magnetic pole N1 magnetized is embedded in the. Here, the magnet body 2 is an isotropic oxide magnetic body, and the magnetic poles S1, N
2, S2, .
The magnetic force of the magnetic pole S2 is set to 600 Gauss, and the magnetic force of the magnetic pole S2 is set to 800 Gauss. On the other hand, the embedded magnet 6 is made of an anisotropic oxide or rare earth magnetic material, and the magnetic force of the magnetic pole N1 is 1200
It is set to ~1500 Gauss. As a result, the magnetic flux in the area of the developing roller 1 facing the photoreceptor is distributed as shown by the dotted line in FIG. Other configurations are shown in Figure 5.
The developing device is the same as the conventional developing device shown in FIG.

In the developing device, as shown in FIG. 2, the developer conveyed to the photoreceptor facing portion forms a pool at the portion facing the magnetic pole N1, and comes into contact with the photoreceptor 10 while being disturbed in three-dimensional directions. do. In addition, since the magnetic pole N1 is set to have a higher magnetic force than the magnetic pole N2, the amount of developer accumulated is large.
Since the contact width of the developer with respect to the photoreceptor 10 is wide, the electrostatic latent image is efficiently developed. On the other hand, since the magnetic force of the magnetic pole N1 is set to a high magnetic force, the carrier does not separate from the developer and adhere to the photoreceptor 10.

Next, the developer moves to a portion facing the magnetic pole N2. Here, if the magnetic force in the intermediate region between the magnetic poles N1 and N2 is set to 50 to 90% of that of the magnetic pole N1, a magnetic brush is also formed in that region. Therefore, development may be performed by bringing the magnetic brush in this intermediate region into contact with the photoreceptor. In this case, the magnetic brush in the intermediate region is softer than the magnetic brush in the opposing portion of the magnetic pole N1, and its contact force with respect to the photoreceptor is smaller, so the toner image formed in the opposing portion of the magnetic pole N1 is disturbed by the magnetic brush at the edge of separation. Without a problem,
No blurred pattern or the like will appear on the finally created image.

On the other hand, when the intermediate region is brought into a non-magnetic state, the developer that has passed through the portion facing the magnetic pole N1 flies and moves to the portion facing the magnetic pole N2. Therefore, development may be performed by bringing this flying developer into contact with the photoreceptor. In this case, so-called cascade or powder cloud type development is performed.

In the above embodiment, only the magnetic pole N1 on the upstream side in the rotational direction of the sleeve was formed in the embedded magnet 6, but instead of the magnetic pole N1, a magnetic material was embedded at the position of the magnetic pole N2, and this magnetic material A magnetic pole N2 may also be formed.

(2) Second Embodiment FIG. 3 shows a developing device of a second embodiment. In this example,
A groove 5 is formed in a portion of the magnet 2 facing the photoreceptor. Further, a groove 6a is formed in the embedded magnet 6 along the axial direction, and magnetic poles N1 and N2 are magnetized at both ends sandwiching the groove 6a. It is embedded in the groove 5. Here, the magnetic forces of the magnetic poles N1 and N2 are respectively similar to the above embodiment, and the magnetic force of the magnetic pole N1 is 1200
~1500 Gauss, and magnetic pole N2 is set to 700~1000 Gauss. Therefore, like the developing device of the first embodiment, the developing device of this embodiment can efficiently develop an electrostatic latent image and also prevent carrier adhesion to the photoreceptor 10. The difference in magnetic force between the magnetic poles N1 and N2 can be determined by changing the size of the magnetized portions that sandwich the groove 6a, or by changing the size of the magnetized portions that sandwich the groove 6a, or by changing the size of the photoreceptor facing region 6b of the portion where the magnetic pole N2 is magnetized, as shown in FIG.
It was secured by partially removing it.

[0013]

As is clear from the above description, the present invention provides two magnetic poles of the same polarity adjacent to each other in the area facing the photoconductor, and the first magnetic pole on the upstream side in the direction of rotation of the sleeve is the first magnetic pole. The magnetic force is set higher than that of the second magnetic pole on the downstream side, and the developer held by the first magnetic pole is brought into contact with the photoreceptor. Therefore, regardless of the type of developer, a large developer pool is formed in the opposing portion of the first magnetic pole, and efficient development is always performed. In addition, the carrier does not separate from the developer held by the first magnetic pole of ferromagnetic force and adhere to the photoreceptor, making it possible to obtain high-quality images without carrier adhesion.

Furthermore, by forming at least one of the first magnetic pole and the second magnetic pole as a separate magnetic material, sufficient magnetic force can be maintained between the first magnetic pole and the second magnetic pole even in the case of a small-diameter developing roller. The difference can be secured.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a developing device according to a first embodiment.

FIG. 2 is a partially enlarged sectional view of the developing device of the first embodiment.

FIG. 3 is a partial cross-sectional view of a developing device according to a second embodiment.

FIG. 4 is a partially enlarged sectional view of the developing device of the second embodiment.

FIG. 5 is a partial cross-sectional view of a conventional developing device.

[Explanation of symbols]

1...Developing roller 2...Magnet 3
...Sleeve 5...Groove 6...Embedded magnet 10...Photoreceptor N1...Upstream magnetic pole (first magnetic pole) N2...Downstream magnetic pole (second magnetic pole)

Claims (2)

[Claims] 1. A developing device in which a magnet body fixed in a non-rotating state is covered with a sleeve, and development is performed by bringing the developer held on the outer periphery of the sleeve into contact with a photoreceptor based on the rotation of the sleeve, wherein the magnet body is Two magnetic poles of the same polarity are provided adjacently in a region of the body facing the photoconductor, and the first magnetic pole on the upstream side in the rotational direction of the sleeve is set to have a higher magnetic force than the second magnetic pole on the downstream side. A developing device characterized in that a developer held by one magnetic pole is brought into contact with a photoreceptor. 2. The developing device according to claim 1, wherein at least one of the two magnetic poles is formed by magnetizing a separate magnetic body embedded in the magnet body.