JP4694874B2 - Developing device, process cartridge including the same, and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile that forms an image using an electrophotographic method, and a developing device that combines development with a magnetic brush and recovery of transfer residual toner with the magnetic brush. The present invention relates to a provided process cartridge and an image forming apparatus.

  Conventionally, from the viewpoint of miniaturization of an image forming apparatus, development that combines development with a magnetic brush using a two-component developer with a carrier and toner (so-called magnetic brush method) and recovery of transfer residual toner with the magnetic brush The apparatus is used for an image forming apparatus. In general, in the magnetic brush method, development is performed by rotating the developing sleeve and fixing the magnet roller in the developing sleeve. When a space where a magnetic force is generated around a magnet provided in the magnet roller, a magnetic field is generated on the surface of the developing sleeve. The state of the magnetic field is represented by the normal direction magnetic flux density generated on the surface of the developing sleeve (hereinafter referred to as “normal direction magnetic flux density”). The developer transported to the development region is spiked along the normal direction magnetic flux density generated on the surface of the development sleeve to form a magnetic brush. The magnetic brush is conveyed in the direction in which the developing sleeve moves, and contacts the surface of the image carrier to supply toner while rubbing against the electrostatic latent image to form a visible image. However, since the conventional magnetic brush method has a low ability to collect the transfer residual toner by the magnetic brush, the rotation direction of the developing sleeve is made the same as the rotation direction of the image carrier, and the development sleeve facing the image carrier is used. It was necessary to improve the recovery capability of the transfer residual toner so that the moving direction of the developing sleeve surface and the moving direction of the image carrier surface in the gap (hereinafter referred to as “developing gap”) are reversed. Further, there is a problem that the image is deteriorated by the operation of scraping off the toner image once formed on the surface of the image carrier by the magnetic brush formed on the surface of the developing sleeve.

  As a conventional technique that has been improved in order to solve the problems of the magnetic brush method described above, the image bearing at the nip boundary with respect to the distance between the image bearing member and the developer bearing member (developing gap) in the center in the developing nip There is an example in which the ratio of the distance between the body and the developer carrying body (the gap between the nip boundaries) is 1.5 or less (see, for example, Patent Document 1). In addition, the magnetic pattern at the magnetic pole facing the developer blocking member is set so as to inhibit the developer from escaping from the developer blocking member, and the normal magnetic force is maximized in the vicinity of the position facing the developer blocking member. An example in which the tangential magnetic force is set to the minimum value and the tangential magnetic force is set to the maximum value near the position facing the layer thickness regulating member and the normal direction magnetic force is set to the minimum value. (For example, refer to Patent Document 2). Further, in the developing device in which a plurality of developer carriers rotating in the same direction as the image carrier are arranged close to each other, and the upstream developer carrier also serves as a developer layer thickness regulating member of the downstream developer carrier The image forming apparatus is characterized in that a bias of alternating current and direct current components is applied to each developer carrier during image formation, and the developer carrier is not applied with an alternating current component during non-image forming operation and has a predetermined direction opposite to that during image formation. There is an example in which an angular rotation is performed, and an idle rotation operation is performed in the same direction as the image formation after the reverse rotation (see, for example, Patent Document 3). Further, for example, a photosensitive member provided with a roller-like conductive contact provided with a surface layer made of a conductive fluorine-containing resin on the surface of the elastic rubber layer, and voltage applying means for applying a voltage to the conductive contact In the developing means, a charging disturbance means for charging the toner and the surface of the photosensitive member to the same polarity is provided by disturbing the toner remaining on the photosensitive member by non-patterning by rubbing between the toner and the conductive contact. A recording apparatus (for example, refer to Patent Document 4) that promotes the collection of residual toner, a magnetic field forming unit is provided between the transfer unit and the charging unit to form a magnetic field that promotes the rotation of the magnetic toner remaining on the surface of the photosensitive member. Thus, there is disclosed a cleanerless image forming apparatus (see, for example, Patent Document 5) that promotes the collection of residual toner in the developing unit.

JP 2001-324873 A JP 2002-182477 A JP 2003-280389 A Japanese Patent No. 3304379 JP-A-11-282253

However, any of the disclosed techniques of Patent Documents 1 to 3 is insufficient to prevent image deterioration, and the disclosed techniques of Patent Documents 4 and 5 cannot sufficiently perform cleaning by a developing device. .
The present invention further improves the above prior art, and even when the rotation direction of the developer carrier is reversed to the rotation direction of the image carrier, the recovery ability of the transfer residual toner is kept high, density unevenness, etc. An object of the present invention is to provide a developing device capable of preventing the occurrence of image defects due to the above, a process cartridge and an image forming apparatus provided with the developing device.

In order to solve the above problems, the present invention has the following features.
The developing device of the present invention includes a rotating member that holds a developer, and a developer carrier that includes a magnet inside the rotating member, and visualizes an electrostatic latent image on the image carrier. In the developing device for removing the residual toner on the image carrier, the rotation direction of the rotating member is opposite to the rotation direction of the image carrier, and at least two magnetic poles of the magnet facing the image carrier are provided. More than the pole arrangement, the normal magnetic flux density of the magnetic pole located at the upstream side in the rotation direction of the developer carrier among the magnetic poles at the position opposed to the image carrier, The normal direction magnetic flux density formed at the magnetic pole located further upstream than the magnetic pole is strengthened, and at least two or more magnetic poles at positions facing the image carrier further upstream in the rotation direction of the developer carrier. On the magnetic pole located The normal flux density formed you are, characterized by being stronger than the normal flux density formed in at least two or more magnetic poles at a position opposing the image bearing member.
By setting the strength of the magnetic flux density in the normal direction in this way, the carrier spikes formed on the surface of the developer carrier are formed so as to be inclined to the upstream side of the development gap portion in the development gap portion. Thus, the magnetic brush is brought into contact with the transfer residual toner image on the surface of the image carrier for a long distance, and the ability to scrape off the transfer residual toner is improved. In this way, by further enhancing the toner recovery capability of the developing device, the development with the magnetic brush using the two-component developer and the recovery of the transfer residual toner with the magnetic brush are performed, and the cleaning device is omitted. An apparatus can be provided.

Further, the developing device of the present invention is characterized in that the rotation direction of the developer carrier is opposite to the rotation direction in the region facing the image carrier.
By using the magnetic brush method with improved toner recovery capability without degrading the developability for developing the latent image on the image carrier, the rotation direction of the developer carrier is opposite to the rotation direction of the image carrier. Even in this case, the ability to collect the transfer residual toner can be kept high, and the occurrence of image defects due to density unevenness can be prevented.

The process cartridge of the present invention is a process cartridge that integrally supports the image carrier and the developing device and is detachable from the main body of the image forming apparatus, wherein the developing device is the above-described developing device.
The function of the process cartridge can be improved by integrally supporting the above developing device on the process cartridge.

The image forming apparatus according to the present invention includes an image carrier, a charging unit for charging the image carrier, an information writing unit for forming an electrostatic latent image on the image carrier, and an electrostatic latent image on the image carrier is visualized. And an image forming apparatus comprising: a developing device that removes residual toner on the image carrier; and a transfer unit that transfers a toner image visualized on the image carrier to recording paper. The developing device described above.
By providing the above-described developing device in the image forming apparatus, convenience such as maintenance can be improved, and the image forming apparatus can be reduced in size and cost.

The image forming apparatus of the present invention further includes the above-described process cartridge.
By providing the above-described process cartridge in the image forming apparatus, convenience such as maintenance can be improved.

  By means for solving the above-mentioned problems, the present invention can provide a developing device using a magnetic brush method in which the toner collecting ability of the developing device is improved, a process cartridge and an image forming apparatus provided with the developing device. .

  The best mode for carrying out the present invention will be described below with reference to FIGS. However, these are merely embodiments and do not limit the scope of the claims of the present invention.

FIG. 1 is a schematic view showing the vicinity of a developing unit of an image forming apparatus provided with a developing device.
The image carrier 1 on which an electrostatic latent image is formed has a charging device 2 that uniformly charges the surface of the image carrier 1 and a toner image attached to the electrostatic latent image to form a visible toner image. A developing device 3, a transfer roller 4 for transferring the toner image on the surface of the image carrier 1 to a recording paper, and a toner charge control means 5 for controlling the charge of the transfer residual toner on the surface of the image carrier 1. However, in this image forming apparatus, there is no cleaning device that cleans and removes transfer residual toner around the image carrier 1, and the developing device 3 has a cleaning function of collecting the transfer residual toner of the image carrier 1. Also serves as. The developing device 3 includes a developing sleeve 7 that holds the carrier with toner supplied to the electrostatic latent image portion on the surface of the image carrier 1, and a doctor blade that makes the carrier layer thickness adsorbed to the outer peripheral surface of the developing sleeve 7 constant. 6, a magnet roller 8 having eight magnets P1a to P1c and P2 to P6, and a conveying screw 10 that agitates a two-component developer mixed with non-magnetic toner and a magnetic carrier and conveys it to the developing sleeve 7. Yes.
P1a, P1b, and P1c are configured by magnets having a small cross section. In general, since the magnetic force becomes weaker when the cross section of the magnet is reduced, in the present embodiment, the three magnets P1a, P1b, and P1c are made of magnets made of a rare earth metal alloy having a relatively strong magnetic force. Among rare earth metal alloy magnets, a typical iron neodymium boron alloy magnet can obtain a maximum energy product of 358 [kJ / m ³ ]. Moreover, according to the iron neodymium boron alloy bonded magnet, the maximum energy product of around 80 [kJ / m ³ ] can be obtained. Generally, a ferrite magnet, a ferrite bonded magnet, or the like having a maximum energy product of around 36 [kJ / m ³ ] or around 20 [kJ / m ³ ] is used. However, if a rare earth metal alloy magnet is used as in this embodiment, a stronger magnetic force can be ensured than these. For this reason, even if a magnet having a small cross section is used, the magnetic force on the surface of the developing sleeve 7 can be sufficiently secured.
The magnet roller 8 is provided with three magnets P1a, P1b, and P1c in order to generate a magnetic field on the surface of the developing sleeve 7 and make the ears of the carrier stand along the normal direction magnetic flux density. By arranging these magnets P1a, P1b, and magnets P1c in this order from the upstream side in the surface movement direction of the developing sleeve 7, the positions of P1a, P1b, and P1c from the upstream side of the position facing the image carrier 1 are arranged. Each magnetic pole will be located side by side.
Since the carrier is made of a magnetic material such as iron powder or ferrite, the spikes stand by the normal direction magnetic flux density generated on the surface of the developing sleeve 7 and are arranged in a chain shape. The carrier generates a magnetic brush by causing the toner to generate a sufficient charge for development and adhering the toner to the carrier that is lined up in a chain shape. That is, in the development gap portion, the carrier to which the toner is attached is linked in a chain shape by a magnetic force to form a magnetic brush. The magnetic brush is conveyed in the direction in which the developing sleeve 7 moves, contacts the surface of the image carrier 1 and supplies toner while making friction with the electrostatic latent image to make a visible image. Furthermore, the transfer residual toner on the surface of the image carrier 1 can be collected while being rubbed.

FIG. 2 is a pie chart showing the distribution of normal direction magnetic flux density as a solid line.
The magnet roller 8 has eight magnets P1a to P1c and P2 to P6. When a space where a magnetic force is generated around a plurality of magnets included in the magnet roller 8, a magnetic field is generated on the surface of the developing sleeve 7. The state of the magnetic field is represented by the normal direction magnetic flux density generated on the surface of the developing sleeve. As a measurement device, an ADS Gauss meter (HGM-8300) and an ADS A1 type axial probe were used, and the results measured with these were recorded by a circular chart recorder. In the present embodiment, the normal direction magnetic flux density generated on the surface of the developing sleeve 7 by the magnetic poles of the north and south poles of the respective magnets P1a, P1b, and P1c is 100 [mT] or more and 200 [mT] or less. It is set to be.
In the present embodiment, magnets P1a, P1b, and P1c are arranged side by side from the upstream side in the rotation direction of the developing sleeve 7 at a position facing the image carrier 1, thereby setting the magnetic pole to two or more poles, Of the magnetic poles facing the image carrier 1, the P6 magnetic poles arranged further upstream than the normal direction magnetic flux density formed at the P1a magnetic poles located upstream in the rotation direction of the developing sleeve 7. The magnetic flux density in the normal direction formed in is increased. In the present embodiment, the strength of each normal direction magnetic flux density is set so that the relationship of P1b <P1a <P6 is established. By setting the strength of the magnetic flux density in the normal direction in this way, the carrier spikes formed on the surface of the developing sleeve 7 are formed so as to incline toward the upstream side of the developing gap portion in the developing gap portion. The magnetic brush is brought into contact with the toner image remaining on the surface of the image carrier 1 for a long distance, and the ability to scrape the toner remaining after transfer is improved. As a result, the toner recovery capability in the developing device 3 is dramatically improved, and the developing device 3 using the magnetic brush method in which the cleaning device is omitted in the two-component developer can be provided. Furthermore, since the contact can be made over a long distance, the developability can be improved, and a high-quality image without image fading or ground fogging can be obtained.

As an action, when the surface of the image carrier 1 is uniformly charged and an image is written in the exposure portion indicated by the arrow, the potential of the portion is lowered and an electrostatic latent image is formed. Next, due to the electrical difference between the electrostatic latent image on the surface of the image carrier 1 and the surface of the developing sleeve 7, the toner on the surface of the developing sleeve 7 moves only to the electrostatic latent image portion and is visualized. The visualized toner image is transferred onto the recording paper by the transfer roller 4. In the transfer step, the toner on the surface of the image carrier 1 is not completely transferred onto the recording paper, and the toner remains on the surface of the image carrier 1. This residual toner after transfer is charged with a potential that does not adhere to the charging roller 2 because it has the same polarity in the process of passing through the toner charge control means 5. In this state, the untransferred toner that has passed through the charging roller 2 and reached the development gap is collected by the magnetic brush that is raised on the upstream side of the development gap due to the above-described arrangement of the magnets. As a result, the toner collection capability of the developing device 3 has been dramatically improved, and the developing device 3 based on the magnetic brush method in which the cleaning device is omitted in the two-component developer can be provided.
Conventionally, the rotation direction of the developing sleeve 7 is the same as the rotation direction of the image carrier 1, and the movement direction of the surface of the development sleeve 7 and the movement direction of the surface of the image carrier 1 in the development gap are opposite. The recovery ability of the transfer residual toner was increased. However, the magnetic brush formed on the surface of the developing sleeve 7 performs an operation of scraping off the toner image once formed on the surface of the image carrier 1, so that there is a problem that the image deteriorates. Accordingly, in order to solve the above-described problems, the present invention uses the magnetic brush method in which the toner collection capability is remarkably improved, thereby reversing the rotation direction of the developing sleeve from the rotation direction of the image carrier. As a result, it is possible to prevent the occurrence of image defects due to uneven density.

FIG. 3 is a diagram illustrating a configuration of the image forming apparatus.
The image forming apparatus 100 includes an image forming unit 101, a paper feed table 200 on which the image forming unit 101 is placed, a scanner 400 mounted on the image forming apparatus main body 101, and an automatic document feeder (ADF) 300 mounted thereon.
The image forming apparatus 100 according to this embodiment includes four image forming units 50 each including an image carrier 1, a charging device 2 and a developing device 3 provided around the image carrier 1. A tandem image forming apparatus for forming an image. Above the image forming means 50, there is provided an exposure device 51 that exposes the image carrier 1 with laser light based on image information to form a latent image. Further, an intermediate transfer belt 40 made of an endless belt member is provided at a position facing each image carrier 1. In the primary transfer area, primary transfer means 92 for transferring the toner images of the respective colors formed on the image carrier 1 to the intermediate transfer belt 40 is disposed. In the secondary transfer region, the toner image is transferred from the intermediate transfer belt 40 to the transfer paper by the bias of the support roller 47. Thereafter, the toner is melted and fixed by the fixing device 55 and fixed onto the transfer paper, and is discharged onto the paper discharge tray 87 by the paper discharge roller 86. The image forming unit 50 of the present embodiment is configured as a process cartridge that integrally supports the image carrier 1, the charging device 2, and the developing device 3 , and is detachable from the image forming apparatus 100. Alternatively, only the image carrier 1 and the developing device 3 may be integrally configured to be detachable.
By configuring the image forming unit 50 as a process cartridge that is detachable from the image forming apparatus main body 100 as described above, convenience such as maintenance can be improved.

FIG. 2 is a schematic diagram illustrating the vicinity of a developing unit of an image forming apparatus including a developing device. It is a pie chart showing the distribution of normal direction magnetic flux density with a solid line. 1 is a diagram illustrating a configuration of an image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image carrier 2 Charging device 3 Developing device 4 Transfer roller 5 Toner charge control means 6 Doctor blade 7 Developing sleeve 8 Magnet roller 10 Conveying screw 40 Intermediate transfer belts 44, 45, 46, 47 Support roller 50 Image forming means 51 Exposure device 55 Fixing device 60 Document base 62 Contact glass 63 First traveling body 64 Second traveling body 65 Imaging lens 66 Reading sensor 72, 80 Paper feed roller 73 Paper bank 74 Paper feed cassette 75, 82 Separation rollers 76, 78 Paper feed path 77 Conveyance roller 79 Registration roller 81 Manual feed tray 83 Manual feed path 85 Switching claw 86 Discharge roller 87 Discharge tray 92 Primary transfer means 100 Image forming apparatus 101 Image forming section 200 Paper feed table 300 Automatic document feeder (ADF)
400 scanner

Claims (5)

A rotating member holding the developer;
A developer carrier configured to enclose a magnet inside the rotating member;
In a developing device for visualizing an electrostatic latent image on an image carrier and removing residual toner on the image carrier,
The rotation direction of the rotation member and the rotation direction of the image carrier are opposite,
The magnetic poles at positions facing the image carrier of the magnet are arranged in at least two or more poles, and the magnetic poles located at the upstream side in the rotation direction of the developer carrier among the magnetic poles at the positions facing the image carrier are formed. The normal direction magnetic flux density formed at the magnetic pole located further upstream than the magnetic pole at the opposite position is made stronger than the normal direction magnetic flux density ,
The normal direction magnetic flux density formed at the magnetic pole located at the upstream side in the rotation direction of the developer carrying member further than the at least two or more magnetic poles at the position facing the image carrying member, the position facing the image carrying member. A developing device characterized in that it is stronger than the magnetic flux density in the normal direction formed by at least two magnetic poles . The developing device according to claim 1, wherein the developing device rotates the developer carrying member in a direction opposite to a rotation direction in a region facing the image carrying member. In the process cartridge that integrally supports the image carrier and the developing device and is detachable from the image forming apparatus main body,
The developing device according to claim 1, wherein the developing device is a developing device according to claim 1. An image forming apparatus comprising the developing device according to claim 1. An image forming apparatus comprising the process cartridge according to claim 3.

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