JPH11109755A - Developing device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the density of a picture by preventing fogging and carrier attraction. SOLUTION: This developing device is equipped with a developing housing 40, a rotatable developing sleeve, 50 a fixed magnet roller 51 and a regulating member 60. A 1st magnetic pole 52 is arranged at a position facing to a photoreceptor drum 6, and a 2nd magnetic pole 53 having the same polarity as the pole 52 is arranged on the upstream side of the pole 52 and on a downstream side from the member 60 near the inside surface of the roller 51, and a zero magnetic field area is substantially formed on the sleeve 50 between the poles 52 and 53. Cascade development is accelerated between the poles 52 and 53, and magnetic brush development is accelerated by the pole 53. It is good to set an angle θ1 formed by a line linking the pole 52 and the shaft of the roller 51 with a line linking the pole 53 and the shaft of the roller 51 on the cross section of the roller 51 within 45 deg. to 90 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a developing device for an image forming apparatus, and more particularly to a developing device using a developer containing a magnetic component. In the present invention, the substantially zero magnetic field region refers to a region where the magnetic force of the magnet roller for attracting the developer to the developing sleeve is lost or weakened, and the developer is separated from the developing sleeve.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine,
For example, an electrostatic latent image based on image data is formed on the photosensitive drum by a laser scan unit. A developing device is provided adjacent to the photosensitive drum, and the developing device causes toner to adhere to the electrostatic latent image on the surface of the photosensitive drum to form a visible image. The developing device has a developing sleeve arranged in contact with or in close proximity to the photosensitive drum, and a developing housing for storing a developer such as toner.

[0003] As a developing method used in such a developing device, cascade development in which a developer is applied to an electrostatic latent image on a photosensitive drum by centrifugal force of a developing sleeve, or development on the surface of a developing sleeve having a magnet inside is used. Magnetic brush development in which a magnetic brush of an agent is formed and the photosensitive drum is rubbed with the brush. JP-A-61-5017
In Japanese Patent Application Laid-Open No. 3 (1999) -1995, there is described a developing device in which a developer is applied to an electrostatic latent image by magnetic repulsion to reduce the size of the device as an improvement of cascade development.

[0004]

However, Japanese Patent Application Laid-Open No.
In the developing device using cascade development described in Japanese Patent No. 50173, a background fogging phenomenon due to excessive developer, an agent spilling out of the excessive developer outside the machine, a carrier pulling of a carrier onto a transfer sheet, and the like. Various phenomena are likely to occur, and it is difficult to obtain a sufficient density of the face image.

An object of the present invention is to prevent the above-mentioned phenomena such as fogging while using cascade development, and to provide an image having a sufficient image density in a surface portion and excellent in reproducibility of a line image and a halftone. An object of the present invention is to provide a developing device for an image forming apparatus.

[0006]

According to the present invention, there is provided a developing device for developing an electrostatic latent image formed on a photoreceptor drum. A developing housing containing a two-component developer, a cylindrical developing sleeve, a magnet roller, and a regulating member are provided. A first magnetic pole and a second magnetic pole having the same polarity are arranged inside the magnet roller. And a developing device for the image forming apparatus.

[0007] The cylindrical developing sleeve is rotatably provided in the developing housing adjacent to the photosensitive drum, and forms a toner image on the electrostatic latent image on the photosensitive drum. The magnet roller is provided along the developing sleeve and is fixed inside the developing sleeve. The regulating member is provided near the surface of the developing sleeve, and regulates the thickness of the developer layer on the developing sleeve.

The first magnetic pole is provided near the inner surface of the magnet roller and at a position facing the photosensitive drum. The second magnetic pole having the same polarity as the first magnetic pole is arranged near the inner surface of the magnet roller and upstream of the first magnetic pole and downstream of the regulating member. First magnetic pole and second magnetic pole
A substantially zero magnetic field region is formed on the developing sleeve between the magnetic pole and the cascade development near the zero magnetic field region. Further, the second magnetic pole located opposite to the photosensitive drum plays a role of promoting magnetic brush development.

In this developing device, the developer is attracted to the developing sleeve by the magnetic force of the magnet roller and is conveyed on the developing sleeve while being charged while rotating on the rotating developing sleeve. Further, the thickness of the developer layer is regulated by the regulating member, and triboelectric charging is promoted. The developer regulated to a certain thickness is separated from the developing sleeve by the centrifugal force of the developing sleeve in a zero magnetic field region between the first magnetic pole and the second magnetic pole, and falls on the photosensitive drum to perform cascade development. Will be When the developer adhered to the photosensitive drum receives the magnetic force of the second magnetic pole due to the rotation of the photosensitive drum, spikes of the developer are formed, and magnetic brush development is performed. Magnetic brush development following cascade development ensures that toner is supplied to the photoreceptor, captures excessively supplied toner and residual carrier, and prevents fogging, carrier pulling, agent dropout, etc. In addition, it is possible to provide a high-quality image having a sufficient density of a face image. It is preferable that a toner replenishing roller is rotatably provided at the preceding stage of the developing sleeve, and the developing sleeve and the toner replenishing roller are rubbed with each other.

In the developing device of the image forming apparatus,
The angle .theta.1 between the line connecting the first magnetic pole and the axis of the magnet roller and the line connecting the second magnetic pole and the axis of the magnet roller in the cross section of the magnet roller should be within a range of at least more than 45 degrees and not exceeding 90 degrees. Adjustment is preferable in the following points. That is, when the angle θ1 is adjusted to be larger than 45 °, a substantially zero magnetic field region is easily formed, and as a result, cascade development becomes easier. When the angle θ1 is adjusted so as not to exceed 90 ° and the zero magnetic field region is formed on the development region side from the top of the development sleeve, the developer is introduced into the image forming apparatus by enlarging the region that promotes cascade development. Scattering can be prevented.

Further, in the developing device of the above-mentioned image forming apparatus, in the vicinity of the inner surface of the magnet roller,
A third magnetic pole and a fourth magnetic pole having the same polarity are arranged adjacent to each other on the downstream side of the first magnetic pole, and a substantially zero magnetic field region is formed on the developing sleeve between the third magnetic pole and the fourth magnetic pole. This is preferable because the used developer is separated from the developing sleeve.

The angle .theta.2 between the line connecting the third magnetic pole and the axis of the magnet roller and the line connecting the fourth magnetic pole and the axis of the magnet roller is at least 70.degree. It is preferable to adjust the angle so as not to exceed 120 °. By making the range of the zero magnetic field region larger than the zero magnetic field region that promotes cascade development, the developer can be easily peeled off from the surface of the developing sleeve.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

<Overall Configuration> An image forming apparatus employing an embodiment of the present invention will be described with reference to FIG. In FIG. 1, a document table 2 is fixed on an upper surface of an image forming apparatus main body 1, and a document holder 3 is provided on the document table 2 so as to be openable and closable. At the lower part of the image forming apparatus main body 1, a paper feed cassette 13,
14 and 15 and a paper feed deck 16 are provided.

Inside the main body 1 of the image forming apparatus, an exposure section 4 for reading a document is provided at an upper portion thereof. The exposure unit 4 includes a light source, a mirror, a lens unit, and the like. Further, an image forming section 5 for forming a toner image of a read document is provided at a central portion of the image forming apparatus main body 1. The image forming section 5 has a photosensitive drum 6 on the surface of which a latent image is formed. Around the photosensitive drum 6, a charging device 7, a developing device 8, a transfer device 9, and a cleaning device 10 are arranged.

[0015] Paper feed cassettes 13, 14, 15, 16
Forming section 5 composed of a photosensitive drum 6 and the like
And a vertical transport path 2 for guiding the paper upward.
6 are provided. Also, on the downstream side of the image forming unit 5,
A paper discharge conveyance path 30, a fixing unit 31 for fusing and fixing the toner image on the paper, and discharge rollers 32 and 33 for discharging the paper passing through the fixing unit 31 are arranged. <Developing Apparatus> FIG. 2 is a view showing an embodiment of the developing apparatus 8 in which first and second N poles having the same polarity are attached to a built-in magnet roller, and FIG. 3 is a partially enlarged view. FIG. The developing device 8 has a developing housing 40, in which a developing sleeve 50, a magnet roller 51, a first north pole 52, a second north pole 53, a blade 60, a toner supply roller 70, and a paddle 80 are provided. . A toner cartridge 90 containing a two-component developer is mounted on the upper part of the developing housing 40 to supply the developer into the developing housing 40, and the developer is stirred by the paddle 80. The scraper 100 is provided to peel off the remaining developer used from the developing sleeve.

The developing sleeve 50 has a cylindrical shape and is disposed in the developing housing 40 adjacent to the photosensitive drum 6.
The developing housing 40 is rotatably provided between both side walls (not shown). Inside the cylindrical developing sleeve 50,
The magnet roller 51 is fixed parallel to the developing sleeve 50, and has a width at least as large as that of the developing sleeve 50.

The blade 60 is provided close to the outer surface of the developing sleeve 50 at least over the width of the developing sleeve 50, and regulates the thickness of the developer layer on the developing sleeve 50 to a certain range. The toner supply roller 70 is
The developing housing 40 is provided in the developing housing 40 so as to be in parallel with and in sliding contact with the developing sleeve 50, and is rotatably mounted between both side walls (not shown) of the developing housing 40. The scraper 100 is provided downstream of the first N-pole and in contact with the developing sleeve 50 upstream of the toner supply roller 70.

A plurality of magnets are arranged near the inner surface of the magnet roller 51. The first N pole 52 is arranged to face the photosensitive drum 6, and the second N pole 53 is
The second magnetic pole region is arranged on the developing sleeve 50 between the first north pole 52 and the second north pole 53 at a position upstream of the blade 2 and downstream of the blade 60. A line connecting the first N pole 52 and the shaft 55 of the magnet roller,
The angle θ1 formed by the line connecting the second north pole 53 and the shaft 55 of the magnet roller in the cross section of the magnet roller 51
Depends on the magnetic strength of the first N pole and the second N pole,
A range greater than 5 ° and not exceeding 90 ° is appropriate. When the angle θ1 is adjusted to the above range, the cascade development is easily performed by the zero magnetic field region, and the developer is easily prevented from being scattered in the image forming apparatus due to the enlargement of the cascade development region. In adjusting the angle θ1,
Adjusting the zero magnetic field region 54 so as to be formed on the developing sleeve side (downstream side) from the top of the developing sleeve 50 is preferable because the developer hardly scatters into the image forming apparatus by cascade development. In addition, usually, the magnet arranged inside the magnet roller 51 is used in the range of 600 to 1200 gauss. On the opposite side of the zero magnetic field region 54,
In the region between the first N pole 52 and the second N pole 53, the N pole and S
The poles are arranged alternately, and the developer rotates by itself as the developing sleeve 50 rotates.

The developing process in such a developing device will be described. The two-component developer is supplied from the toner supply roller 70 to the developing sleeve 50. The developer alternately receives the magnetic force of the opposite polarity from the magnet roller 51 while being transported by the rotating developing sleeve 50,
The developing sleeve 50 rotates in the rotation direction of the developing sleeve 50 while being attracted to the zero. Further, the thickness of the developer layer of the developer is regulated by a blade 60 within a certain range.

In the zero magnetic field region 54 formed between the first N pole 52 and the second N pole 53, the magnetic force for attracting the developer to the developing sleeve 50 disappears, or the centrifugal force of the developing sleeve 50 is reduced by the magnetic force. It is stronger than. Therefore, the developer that has entered the zero magnetic field region 54 is separated from the developing sleeve 50 by the centrifugal force of the developing sleeve 50 and falls down on the photosensitive drum 6 to perform cascade development.

The developer once attached to the photosensitive drum 6 is
Receiving the magnetic force of the first magnetic pole 52 by the rotation of the photosensitive drum,
An ear is formed between the photosensitive drum 6 and the developing sleeve 50, and magnetic brush development is performed. By this magnetic brush development, the carrier adhered on the electrostatic latent image by the cascade development is recovered, and a high-quality image having excellent reproducibility of a line image and a halftone and a high density of a surface image portion can be provided. The remaining developer including the collected carrier has a small toner content, and is thus separated from the developing sleeve by the scraper 100. <Other Embodiments> As shown in FIG. 4, a zero magnetic field region 56 is formed in a portion of the developing sleeve where the scraper 100 contacts, instead of the scraper 100 in the above-described embodiment. It can be omitted. In this case, magnetic poles of the same polarity, for example, the first south pole 57 and the second south pole 58 are arranged adjacent to each other near the inner surface of the magnet roller downstream of the first north pole 52 and upstream of the toner supply roller 70. I just need. A line connecting the first S pole 57 to the shaft 55 of the magnet roller;
The angle θ2 between the line connecting the pole 58 and the shaft 55 of the magnet roller in the cross section of the magnet roller 51 is 70
A range of {120} is appropriate. Zero magnetic field area 56
Is larger than the zero magnetic field region 54 that promotes the cascade development, so that the developer is
Easy to peel off from the surface.

Although the above embodiment has been described using a two-component developer, the developing device according to the present invention can also be used for a magnetic one-component developer. Excess developer can be prevented from spilling out of the developing machine, and a high-quality image can be provided as described above.

[0023]

The developing device of the present invention performs magnetic brush development following cascade development by arranging magnets of the same polarity adjacent to the magnet roller and forming a zero magnetic field region on the development sleeve. Even in cascade development, it is possible to stably supply a high-quality image having a sufficient density in a surface image portion and excellent in halftone and line image reproducibility.

[Brief description of the drawings]

FIG. 1 is an image forming apparatus to which an embodiment of the present invention is applied.

FIG. 2 is a diagram showing an embodiment of a developing device in which first and second N poles are attached to a magnet roller.

FIG. 3 is an enlarged view of the vicinity of a development area in FIG. 2;

FIG. 4 is a diagram showing another embodiment.

[Explanation of symbols]

 6; photoconductor drum 40; developing housing 50; developing sleeve 51; magnet roller 52; first N pole 53; second N pole 54, 56; zero magnetic field region 57; first S pole 58; Supply roller

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masanori Kawasumi 1-2-28 Tamazo, Chuo-ku, Osaka-shi Inside Mita Kogyo Co., Ltd. (72) Isao Iwakawa 1-2-28 Tamazo, Chuo-ku, Osaka-shi Mita Kogyo Co., Ltd.

Claims (4)

[Claims] 1. A developing device for developing an electrostatic latent image formed on a photosensitive drum, comprising: a developing housing containing a magnetic one-component developer or a two-component developer therein; A cylindrical developing sleeve that is rotatably provided in the developing housing adjacent to the developing housing and forms a toner image on an electrostatic latent image of the photosensitive drum; and a developing sleeve that is provided along the developing sleeve and is provided along the developing sleeve. And a regulating member provided in close proximity to the surface of the developing sleeve and regulating the thickness of the developer layer on the developing sleeve, near the inner surface of the magnet roller. A first magnetic pole disposed at a position facing the photosensitive drum, and a second magnetic pole having the same polarity as the first magnetic pole disposed upstream of the first magnetic pole and downstream of the regulating member, respectively. Forming a substantially zero field region on the developing sleeve between the first and second magnetic poles, facilitating cascade development between the first and second magnetic poles and magnetic brush development with the first magnetic pole, respectively. A developing device of the image forming apparatus. 2. An angle .theta.1 between a line connecting the first magnetic pole and the axis of the magnet roller and a line connecting the second magnetic pole and the axis of the magnet roller in a cross section of the magnet roller is at least 45. The developing device of the image forming apparatus according to claim 1, wherein the developing device does not exceed 90 °. 3. In the vicinity of the inner surface of the magnet roller, a third pole of the same polarity is further provided downstream of the first magnetic pole.
The image forming apparatus according to claim 1, wherein the magnetic pole and the fourth magnetic pole are arranged adjacent to each other, and form a substantially zero magnetic field region on the developing sleeve between the third magnetic pole and the fourth magnetic pole. Developing device. 4. An angle .theta.2 between a line connecting the third magnetic pole and the axis of the magnet roller and a line connecting the fourth magnetic pole and the axis of the magnet roller in a cross section of the magnet roller is at least 70. The developing device of the image forming apparatus according to claim 3, wherein the developing device does not exceed 120 ° and does not exceed 120 °.