JP5195086B2 - Developing device, image forming apparatus, and image forming method - Google Patents

Description

  The present invention is provided in an image forming apparatus such as a copying machine, a facsimile, or a printer, and develops an image carrier such as a photosensitive member with a two-component developer, an image forming apparatus having the same, and an image forming method using them. About.

  Various image forming apparatuses such as copiers, facsimile machines, printers, etc., have proposed various developing apparatuses for developing an electrostatic latent image formed on an image carrier such as a photoreceptor using a two-component developer containing toner and a carrier. (For example, see [Patent Document 1] to [Patent Document 6]). In general, the developing device carries a two-component developer and conveys the two-component developer carried with rotation to a region facing the image carrier, and the toner in the developer is transferred to the image carrier in the opposite region. A developer carrier to be supplied is provided. Such a developing apparatus is excellent in that high-quality image formation is performed over time, and is mounted in many image forming apparatuses mainly in monochrome digital copying machines and full-color copying machines that require high image quality.

In recent years, speeding up of image formation has been demanded, and along with this, the moving speed of the image carrier has been increased.
On the other hand, as exemplified below, various techniques for increasing the amount of toner supplied to the image carrier have been proposed. According to such a technique, development is possible even if the moving speed of the image carrier is increased. It is thought that ability can be secured.

A technique for increasing the rotation speed of the developer carrying member and increasing the amount of toner supplied to the image carrying member per unit time in a region facing the image carrying member.

-An image carrier is provided between the developer carrier and the image carrier by a collision member that collides with the tip of the magnetic brush on the developer carrier and separates and disperses the toner in the magnetic brush from the carrier. Technology for increasing the amount of toner supplied to the body (for example, see [Patent Document 1]).

The toner in the developer forming the magnetic brush by transporting the two-component developer to the area facing the image carrier and causing the developer to be spiked by the internal magnetic poles to form a magnetic brush. In the developer carrier for supplying the image carrier to the image carrier, the repulsive magnetic field is formed by arranging the magnetic poles of the same polarity along the rotation direction of the developer carrier in the opposite region, and the magnetic brush formation region is applied. A technique for increasing the amount of toner supplied to the image carrier by enlarging it in the rotation direction (see, for example, [Patent Document 2]).

・ Multiple developer carriers are provided along the moving direction of the image carrier, and the developer is transferred by these developer carriers to expand the development area and increase the amount of toner supplied to the image carrier. Technology (see, for example, [Patent Document 3]).

An electrode wire having a shape along the curvature of the developer carrying member, the electrode wire for forming an equipotential surface between the developer carrying member and the image carrying member, the developer carrying member and the image carrying member (See Patent Document 4), for example, in which a large number of developer carriers are juxtaposed across the entire width to increase the amount of toner supplied to the image carrier.

  However, in the technique for increasing the rotation speed of the developer carrying member, the centrifugal force acting on the carried developer may be increased and the scattering of the developer may increase. The scattered developer is a problem because it can cause contamination inside the image forming apparatus and cause a decrease in function. In addition, when the rotation speed of the developer carrier is increased, the force that the developer carried by the developer carrier rubs against the image carrier increases, and the toner supplied to the image carrier is scraped off to form. There is also a problem that the image is disturbed and an abnormal image is likely to occur.

  Further, in the technique of providing the collision member, toner scattering occurs, so that the scattered developer may cause contamination inside the image forming apparatus and cause a function deterioration, which may cause the same problem as described above. In addition to the above technique, there is a technique for increasing the toner concentration in the two-component developer as a technique for increasing the amount of toner supplied to the image carrier, but this technique also causes toner scattering. Further, the scattered developer may cause the inside of the image forming apparatus to be contaminated, resulting in a decrease in function.

  In addition, in the technology in which the repulsive magnetic field is formed to enlarge the magnetic brush forming area in the direction of rotation of the developer carrier, the magnetic force that the developer carrier carries the magnetic carrier decreases in the region where the repulsive magnetic field is formed. However, the magnetic carrier may adhere to the image bearing member to lower the quality of the formed image, and there is a problem that a suitable image formation is not always performed.

  Further, in the technique of providing a plurality of developer carriers along the moving direction of the image carrier, the developing device is increased in cost and size, and in particular, an image in which a plurality of developing devices are mounted like an image forming apparatus that performs full-color images. In the forming apparatus, the degree of increase in cost and size is large, and there is a problem that it is contrary to the recent demand for cost reduction and downsizing of the image forming apparatus. In addition, the developer is not smoothly transferred between the developer carriers, and the developer is concentrated in the gap between adjacent developer carriers and the rotation of the developer carrier is stopped. There is a problem in that the other image carrier can be rotated and the development can be hindered. Therefore, in order to smoothly transfer the developer between the developer carriers, a technique has been proposed in which the magnetic poles arranged at positions facing the adjacent developer carriers are made different from each other. In this case, the developer carriers are magnetically attracted to each other to cause bending, which increases the torque required to drive the developer carrier, leading to an increase in the size of the motor and an increase in power consumption. As a result, there is a problem that the rotation of the developer carrying member may stop and the development may be hindered.

  Further, in the technique of arranging a large number of electrode wires, there is a problem that it is difficult to position the electrode wires and the cost increases.

  By the way, in a developing device using a two-component developer, the two-component developer is carried in a fixed state on the developer carrier in a region where the developer carrier and the image carrier are opposed to each other. As a result, it is known that, of the two-component developer carried on the developer carrying member, only the surface layer portion on the image carrier side actually contributes to development (for example, [Patent Document 5]). (See Patent Document 6).

  Therefore, as exemplified below, various techniques for disturbing the two-component developer carried on the developer carrier have been proposed in order to make the two-component developer on the developer carrier side also contribute to the development. According to such a technique, it is considered that the developing capacity can be secured even if the moving speed of the image carrier is increased by increasing the amount of toner supplied to the image carrier.

The magnetic pole for causing the two-component developer to rise on the developer carrying member in the opposed region between the developer carrying member and the image carrying member is positioned and arranged in a range corresponding to the opposed region, thereby developing the developer. A technique for disturbing a two-component developer carried on a carrier (for example, see [Patent Document 5]).

In addition to the magnetic pole that causes the two-component developer to rise on the developer carrier in the opposite area between the developer carrier and the image carrier, the two-component developer carried on the developer carrier in the opposite area A technique for disturbing the two-component developer carried on the developer carrier by arranging magnetic poles that are horizontally moved along the surface of the developer carrier (see, for example, [Patent Document 6]).

Japanese Patent Application Laid-Open No. 08-044214 Japanese Patent Laid-Open No. 51-43151 JP 2004-021125 A Japanese Patent No. 3541203 JP 2003-084573 A Japanese Patent No. 3166441

  However, since the technology for disturbing the two-component developer carried on the developer carrier by the arrangement of the magnetic poles is required at a high level of magnetic pole positioning accuracy, the development performance may vary from product to product. There is a problem that the cost may increase due to a decrease in yield due to such variation. Therefore, it is desirable to propose a technique for disturbing the two-component developer carried on the developer carrying member by a method other than the method of arranging the magnetic poles.

  The present invention is provided in an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, and an image carrier such as a photosensitive member by disturbing a two-component developer carried on the developer carrier by a method other than the arrangement of magnetic poles. An object of the present invention is to provide a developing device capable of increasing the amount of toner supplied to the image forming apparatus, an image forming apparatus having the same, and an image forming method using them.

In order to achieve the above object, the invention described in claim 1 is a developer carrier that is arranged opposite to an image carrier and carries and moves a two-component developer, and this developer carrier is used as an image carrier. It is located between the developer carrying member and the image carrier in the opposed region facing each other, and is disposed at a position buried in the two-component developer carried on the developer carrier in the opposed region, possess a stirring member for stirring the contact with the two-component developer in the two-component developer carried on the developer carrying member in the region, the agitating member along the movement direction of said developer carrying member By alternately forming a high-density area with a high density of the two-component developer and a low-density area with a low density of the two-component developer between the image carrier and the developer carrier in the opposite area Agitating the supported two-component developer, the high-density region The spacing between the stirring member and the image carrier in the high-density region and in the high-density region adjacent to each other in the movement direction is the downstream side in the movement direction. In the developing device, the distance between the stirring member and the image carrier in the high-density area is equal to or greater than the distance between the stirring member and the image carrier in the upstream high-density area in the same movement direction .

According to a second aspect of the present invention, there is provided a developer carrying member that is disposed opposite to an image carrier and carries and moves a two-component developer, and the same development in a facing region where the developer carrier is opposed to the image carrier. A position between the developer carrying body and the image carrying body, and in a moving direction of the developer carrying body, a position on the upstream side and a downstream side of the position where the developer carrying body is closest to the image carrying body. And a plurality of agitating members that are arranged so as to extend in the width direction of the developer carrier and are in contact with the two-component developer carried on the developer carrier in the facing region. Of the plurality of stirring members, the distance between the stirring member disposed at the downstream position and the image carrier is the distance between the stirring member disposed at the upstream position and the image carrier. The developing device is as described above.

According to a third aspect of the present invention, there is provided the developing device according to the second aspect, wherein the stirrer includes a high-density region and a two-component high-density two-component developer between the stirring member and the image carrier along the moving direction. By alternately forming low density regions with low developer density, the two-component developer carried on the developer carrier in the facing region is agitated, and the high density region is moved in the moving direction. The spacing between the stirring member and the image carrier in the high-density region that is adjacent to each other in the moving direction is the downstream high-density region in the moving direction. The distance between the agitating member and the image carrier in is equal to or greater than the distance between the agitating member and the image carrier in the high-density area on the upstream side in the moving direction .

According to a fourth aspect of the present invention, in the developing device according to the first or third aspect , the stirring member and the image carrier in the high density region other than the high density region located on the most downstream side in the moving direction in the high density region. The distance from the body is at least two layers in the layer thickness of the two-component developer.

According to a fifth aspect of the present invention, in the developing device according to the first, third, or fourth aspect, at least one of the high-density regions is closest to the image carrier in the moving direction. It is located upstream from the position.

  According to a sixth aspect of the present invention, in the developing device according to any one of the first to fifth aspects, the stirring member is nonmagnetic.

  According to a seventh aspect of the present invention, there is provided an image forming apparatus comprising the developing device according to any one of the first to sixth aspects.

  According to an eighth aspect of the present invention, there is provided an image forming method for forming an image using the developing device according to any one of the first to sixth aspects or the image forming apparatus according to the seventh aspect.

The present invention relates to a developer carrying member that is arranged to face an image carrier and carries and moves a two-component developer, and the developer carrier in a facing region where the developer carrier is opposed to the image carrier. It is located at a position between the image carrier and a position where it is buried in the two-component developer carried on the developer carrier in the facing region, and is carried on the developer carrier in the facing region. 2 the component developer contact possess a stirring member for stirring the same two-component developer, the agitating member along the movement direction of said developer carrier, two-component development between the image carrier Agitating the two-component developer carried on the developer carrier in the opposite region by alternately forming a high-density region with a high density of the agent and a low-density region with a low density of the two-component developer And a plurality of the high-density regions are formed along the moving direction. The spacing between the stirring member and the image carrier in the high-density region and in the high-density region adjacent to each other in the movement direction is the same as that of the stirring member and the image carrier in the downstream high-density region in the movement direction. Since the developing device has a gap with the body equal to or greater than the gap between the stirring member and the image carrier in the upstream high-density area in the same moving direction, the low-density area is secured and the high-density area is passed. Since the developer is disturbed in the low density region, the toner density in the vicinity of the image carrier is increased by disturbing the two-component developer carried on the developer carrier without using the magnetic pole arrangement, and the image carrier It is possible to provide a developing device that can increase the amount of toner supplied to the body and can contribute to good image formation even when image formation is performed at high speed.

  Among the high-density areas, the distance between the stirring member and the image carrier in the high-density area other than the high-density area located on the most downstream side in the moving direction is at least two layers in the layer thickness of the two-component developer. If it is an interval, the two-component developer is allowed to pass through the interval to perform efficient development, and the developer that has passed through the high-density region is disturbed in the low-density region. Without disturbing the two-component developer carried on the developer carrying member, the toner concentration in the vicinity of the image carrying member can be increased, and the amount of toner supplied to the image carrying member can be increased. It is possible to provide a developing device that can contribute to good image formation even when image formation is performed at high speed.

  If at least one of the high-density regions is located upstream of the position where the developer carrier is closest to the image carrier in the moving direction, the high-density region is possible. As long as it is formed in or near the opposing area between the developer carrier and the image carrier and suppresses the factors that degrade the image quality due to the high density area, the developer passing through the high density area is disturbed in the low density area. As a result, the toner density in the vicinity of the image carrier is increased by disturbing the two-component developer carried on the developer carrier without using the magnetic pole arrangement, and the amount of toner supplied to the image carrier is reduced. Therefore, it is possible to provide a developing device that can contribute to good image formation even when image formation is performed at high speed.

  If the stirring member is non-magnetic, the two-component developer is prevented from staying by the stirring member, and the two-component developer carried on the developer carrier is disturbed without using the magnetic pole arrangement. Can increase the toner density in the vicinity of the image carrier, increase the amount of toner supplied to the image carrier, and can contribute to good image formation even when image formation is performed at high speed. A developing device can be provided.

  Since the present invention is in an image forming apparatus having such a developing device, the toner density in the vicinity of the image carrier is increased by disturbing the two-component developer carried on the developer carrier without using the magnetic pole arrangement. In addition, it is possible to provide an image forming apparatus that can increase the amount of toner supplied to the image carrier and can perform good image formation even when image formation is performed at high speed.

  The present invention resides in such a developing apparatus or an image forming method for forming an image using such an image forming apparatus, so that the two-component developer carried on the developer carrying member is disturbed without using the magnetic pole arrangement. As a result, the toner density in the vicinity of the image carrier can be increased, the amount of toner supplied to the image carrier can be increased, and good image formation can be performed even when image formation is performed at high speed. An image forming method can be provided.

  FIG. 1 shows an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus 100 is a multifunction peripheral of a copying machine, a printer, and a facsimile machine, and can perform full-color image formation, but other image forming apparatuses, that is, a monochrome machine, a copying machine, and a printer. It may be a single facsimile, or another multi-function machine such as a copier / printer multi-function machine. When used as a printer, the image forming apparatus 100 performs an image forming process based on an image signal corresponding to image information received from the outside. This is the same when the image forming apparatus 100 is used as a facsimile.

  The image forming apparatus 100 can form an image on a sheet-like recording medium using not only plain paper generally used for copying, but also OHP sheets, cardboard, cardboard, cardboard, and envelopes. It is. The image forming apparatus 100 is also a double-sided image forming apparatus capable of forming an image on both sides of a transfer sheet as a recording medium as a recording medium.

  The image forming apparatus 100 includes a main body 101 that occupies a central position in the vertical direction and functions as a printer unit, a reading device 21 that is positioned above the main body 101 and that reads a document, and a document on which a document is stacked and loaded. An automatic document feeder 22 which is an automatic document feeder called ADF which is sent out toward 21, and the photosensitive drums 20 </ b> Y, 20 </ b> M, 20 </ b> C, 20 </ b> BK located below the main body 101 and the transfer belt 11. A sheet feeding device 23 serving as a paper feeding device serving as a paper feeding table on which the transfer paper to be conveyed is stacked.

  The image forming apparatus 100 includes a plurality of photosensitive drums 20Y, 20M, 20C, and 20BK that can form images as images corresponding to colors separated into yellow, magenta, cyan, and black, respectively. 1 is a tandem type image forming apparatus that employs a tandem structure in which the two are arranged side by side. The photosensitive drums 20Y, 20M, 20C, and 20BK have the same diameter, and are transfer belts as intermediate transfer belts that are intermediate transfer members that are endless belts disposed almost at the center inside the main body 101 of the image forming apparatus 100. 11 are arranged at equal intervals on the outer peripheral surface side, that is, on the image forming surface side.

  The transfer belt 11 is movable in the arrow A1 direction, which is the clockwise direction in the figure, while facing the respective photosensitive drums 20Y, 20M, 20C, and 20BK. The visible image, that is, the toner image formed on each of the photoconductive drums 20Y, 20M, 20C, and 20BK is superimposed and transferred onto the transfer belt 11 that moves in the direction of the arrow A1, and is then collectively transferred onto the transfer paper. It has become. As described above, the image forming apparatus 100 employs the indirect transfer method.

  In the superimposing transfer to the transfer belt 11, the toner images formed on the photosensitive drums 20Y, 20M, 20C, and 20BK are transferred to the same position on the transfer belt 11 while the transfer belt 11 moves in the A1 direction. Thus, a primary transfer roller as a transfer charger disposed at a position facing each of the photosensitive drums 20Y, 20M, 20C, and 20BK across the transfer belt 11 and in contact with the inner peripheral surface of the transfer belt 11. By applying voltages by 12Y, 12M, 12C, and 12BK, the timing is shifted from the upstream side toward the downstream side in the A1 direction, and the transfer is performed at a position immediately below each photosensitive drum 20Y, 20M, 20C, and 20BK.

  The photosensitive drums 20Y, 20M, 20C, and 20BK are arranged in this order from the upstream side in the A1 direction. The photosensitive drums 20Y, 20M, 20C, and 20BK are provided in image stations 60Y, 60M, 60C, and 60BK, respectively, for forming yellow, magenta, cyan, and black images.

  The image forming apparatus 100 is arranged opposite to the image forming unit 60 as an image forming unit constituted by four image stations 60Y, 60M, 60C, and 60BK, and below the respective photosensitive drums 20Y, 20M, 20C, and 20BK. A transfer belt unit 10 as a belt unit, which is an intermediate transfer unit provided with the transfer belt 11, and is disposed so as to face the transfer belt 11 and is in contact with the transfer belt 11. As a secondary transfer device that includes a secondary transfer belt 5 that is a paper transport belt as a transfer member that rotates in the same direction as the transfer belt 11 and moves endlessly, and transfers the toner image on the transfer belt 11 to the transfer paper and transports it. And a secondary transfer unit 76.

  The image forming apparatus 100 also includes an optical scanning device 8 serving as an exposure device serving as an optical writing unit serving as an optical writing device serving as an optical writing device disposed above the image stations 60Y, 60M, 60C, and 60BK, and a sheet. The transfer sheet conveyed from the feeding device 23 is transferred between the transfer belt 11 and the secondary transfer belt 5 at a predetermined timing in accordance with the toner image formation timing by the image stations 60Y, 60M, 60C, and 60BK. A registration roller pair 13 that is fed out toward the printing section, and a sensor (not shown) that detects that the leading edge of the transfer paper has reached the registration roller pair 13.

  The image forming apparatus 100 also serves as a belt-fixing type fixing unit for transferring the toner image on the transfer belt 11 transferred by the secondary transfer unit 76 and fixing the toner image on the transfer paper. A fixing unit 6, a paper discharge unit that discharges the fixed transfer paper to the outside of the main body 101, and a reverse path that transports the transfer paper toward the registration roller pair 13 again. 79 and the paper discharge unit 79, when the transfer paper having an image formed on one side is conveyed to the reverse path, the transfer paper is switched back and reversed, and is again conveyed toward the registration roller pair 13. And a duplex unit 96 which is a sheet reversing device as a refeed unit.

  The image forming apparatus 100 also includes a paper discharge tray 75 as a stack unit that is disposed outside the main body 101 and stacks transfer sheets on which image formation has been performed, and a manual sheet feeding device disposed on the right side surface of the main body 101 in FIG. 33, an operation panel (not shown) that operates the image forming apparatus 100, and a control unit (not shown) as a control unit that controls the operation of the entire image forming apparatus 100.

  In addition to the transfer belt 11, the transfer belt unit 10 is driven as a primary transfer roller 12Y, 12M, 12C, 12BK and a tension roller 72, a transfer inlet roller 73, and a tension roller around which the transfer belt 11 is wound. The transfer belt 11 is sandwiched between the roller 74 and the drive roller 74, and the transfer belt 11 is moved endlessly in the A1 direction by rotating the drive roller 72 and the intermediate transfer belt cleaning device 14 for cleaning the surface of the transfer belt 11. A belt drive motor (not shown) and a transfer belt unit drive means (not shown) for displacing the transfer belt 11 and the like according to whether image formation is performed with a multicolor image of two or more colors or a monochrome image of only black, that is, a monochrome image And have.

  When the image formation is performed with two or more multi-color images, the transfer belt unit driving means places the transfer belt 11 in a state where the transfer belt 11 is stretched substantially horizontally as shown in FIG. When contact is made with 20Y, 20M, 20C, and 20BK and image formation is performed in a monochrome image, the transfer belt 11 is moved away from the photosensitive drums 20Y, 20M, and 20C so that the left side of the figure is displaced downward. It is assumed that the belt 11 is in contact with only the photosensitive drums 20BK. When the image formation is performed with a monochrome image, the operations of the image stations 60Y, 60M, and 60C are stopped, including the rotation of the photosensitive drums 20Y, 20M, and 20C.

  In addition to the secondary transfer belt 5, the secondary transfer unit 76 is a tension roller around which the secondary transfer belt 5 is wound. A transfer entrance roller 73 that is a backup roller as a counter roller that is provided and pressed via the transfer belt 11 and a power supply (not shown) that applies a secondary transfer bias having a polarity opposite to that of the toner to the driving roller 15 are provided. .

  The driving roller 15 and the transfer entrance roller 73 sandwich the transfer belt 11 and the secondary transfer belt 5 between them, and the secondary transfer belt 11 and the secondary transfer belt 5 come into contact with each other by the sandwiching. A nip is formed. In the secondary transfer nip, by applying a secondary transfer bias, a four-color toner image carried on the transfer belt 11 is electrostatically moved from the transfer belt 11 side to the drive roller 15 side as described later. A secondary transfer electric field is formed. The four-color toner image is transferred to the transfer paper conveyed between the transfer belt 11 and the secondary transfer roller 5 by the registration roller 13 by a secondary transfer electric field and nip pressure as will be described later.

  As the secondary transfer unit 76, a configuration using a transfer roller or a non-contact charger may be used, but in this case, another member for transporting the transfer paper toward the fixing device 6 is required.

  The optical scanning device 8 scans and exposes the surfaces to be scanned formed by the surfaces of the photosensitive drums 20Y, 20M, 20C, and 20BK, and forms a laser beam based on an image signal for forming an electrostatic latent image. A light source (not shown) that emits laser light (not shown), a polygon mirror (not shown) that scans the laser light emitted by the light source by its rotation, a polygon motor (not shown) that drives the polygon mirror to rotate, and a laser that is scanned by the polygon mirror It has a large number of optical elements (not shown) such as an f-θ lens (not shown) and a reflection mirror for imaging light on the photosensitive drums 20Y, 20M, 20C, and 20B and scanning.

  The fixing device 6 includes a heating roller 62 having a heat source therein, a fixing belt 64 wound around the heating roller 62, a fixing roller 65 wound around the fixing belt 64 together with the heating roller 62, and the fixing roller 65. And a pressure roller 63 that presses against the fixing belt 64 and forms a fixing nip as a fixing portion that is a pressing portion. The heating roller 62, the fixing belt 64, and the fixing roller 65 constitute a belt unit in which the fixing belt 64 moves endlessly. The fixing device 6 passes the transfer paper carrying the toner image through the fixing nip, thereby fixing the carried toner image on the surface of the transfer paper by the action of heat and pressure.

  A paper discharge unit 79 transports the fixed transfer paper transported from the fixing device 6 toward the duplex unit 96, a paper discharge roller 98 that discharges the paper to the outside of the main body 101, and a fixed transfer. There is provided a switching claw 94 for switching whether the paper is guided to the paper discharge path with the conveying roller 97 and discharged out of the main body 101 or the paper is guided to the reverse path with the paper discharge roller 98 to enter the duplex unit 96.

  The duplex unit 96 is a tray 92 on which transfer paper having an image formed on one side, which has been conveyed from the paper discharge unit 79, is temporarily stacked, a reverse roller 93 that switches back the transfer paper on the tray 92, and a reverse roller. The sheet feeding roller 95 and the like for feeding the transfer sheet switched back by 93 to the registration roller 13 are provided.

  The sheet feeding device 23 includes a paper bank 26 in which a plurality of sheet feeding cassettes 25 that can store a plurality of transfer sheets in a bundle of sheets are arranged in a vertical direction, and a plurality of transfer sheets stacked on the sheet feeding cassette 25. Among them, a feeding roller 24 as a sheet feeding roller that contacts the upper surface of the uppermost transfer sheet, a separation roller 27 that separates the transfer sheets fed by the feeding roller 24 one by one, a sheet feeding roller 24 and a separation roller And a paper feed path 29 through which the transfer paper fed by the roller 27 passes.

  The paper feed path 29 includes a transport roller 28 that transports the transfer paper fed by the paper feed roller 24 and the separation roller 27 toward the registration roller pair 13 and a registration roller 13 that is positioned at the downstream end in the transport direction of the transfer paper. The transfer paper sheet feeding device 23 transported by the transport roller 28 is provided so as to continue into the main body 101, and the transport roller 28 is also disposed in the paper feed path 29 in the main body 101.

  In the sheet feeding device 23, the feeding roller 24 is rotated in the counterclockwise direction in the drawing, and the separation roller 27 acts to guide the uppermost transfer paper into the paper feeding path 29, so that the conveying roller 28 The sheet is fed toward the registration roller pair 13 by rotation, and the transferred transfer paper is abutted against the registration roller pair 13 and stopped.

  The manual paper feed device 33 includes a manual feed tray 34 on which transfer paper is stacked, a feed roller 35 as a paper feed roller that contacts the upper surface of the uppermost transfer paper among the transfer papers stacked on the manual feed tray 34, It has a separation roller 36 for separating the transfer paper fed by the feed roller 35 one by one, and a paper sensor for detecting that the transfer paper is placed on the manual feed tray 34.

  In the manual sheet feeding device 33, the feeding roller 35 is driven to rotate in the clockwise direction in the drawing, and the separation roller 36 acts to guide the uppermost transfer sheet into the sheet feeding path 29 on the main body 101 side and to register the sheet. The transfer paper fed to the roller pair 13 is transported against the registration roller pair 13 and stopped.

The reading device 21 includes a contact glass 21a on which a document is placed, a light source (not shown) that irradiates light on the document placed on the contact glass 21a, and a first light source (not shown) that reflects light reflected from the light source. A first traveling body 21b that includes a reflector and travels in the left-right direction in FIG. 1; a second traveling body 21c that includes a second reflector (not shown) that reflects light reflected by the reflector of the first traveling body 21b; An image forming lens 21d for forming an image of light from the second traveling body 21c, a reading sensor 21e for receiving the light passing through the image forming lens 21d and reading the contents of the document are provided.
The automatic document feeder 22 is rotatable, and the contact glass 21a is exposed when the automatic document feeder 22 is rotated upward.

The operation panel is an operation display unit having a liquid crystal display, a start button that functions as a copy start switch for starting copying, and various key buttons such as a numeric keypad for inputting the number of copies. On the operation panel, it is possible to specify whether image formation is performed with a multicolor image or a monochrome image, and it is possible to set a single-sided print mode, which is a mode for forming an image only on one side of a transfer sheet. Yes. The single-sided print mode includes a direct discharge mode, a reverse discharge mode, and a reverse decal discharge mode, and one of these is selected.
The control means includes a CPU, a memory as a storage means, and the like.

  Regarding the image stations 60Y, 60C, 60M, and 60BK, the configuration will be described as a representative of the configuration of the image station 60Y including the photosensitive drum 20Y. Since the configuration of other image stations is substantially the same, in the following description, for the sake of convenience, reference numerals corresponding to the reference numerals assigned to the configuration of the image station including the photosensitive drum 20Y are used for other image stations. A detailed description will be omitted as appropriate for the station configuration, and those with Y, C, M, and K at the end of the reference numerals are used to form yellow, cyan, magenta, and black images, respectively. It is assumed that this is the configuration.

  As shown in FIG. 2, the image station 60Y including the photosensitive drum 20Y has a primary transfer roller 12Y and a cleaning member around the photosensitive drum 20Y along the rotation direction B1 that is counterclockwise in the drawing. It has a cleaning device 40Y as a means, a charging device 30Y as a charging unit as a charging means, and a developing device 50Y as a developing unit as a developing means.

  The photosensitive drum 20Y, the cleaning device 40Y, the charging device 30Y, and the developing device 50Y are integrated to form a process cartridge 95Y. The process cartridge 95Y can be pulled out of the main body 101 along a guide rail (not shown) fixed to the main body 101, can be pushed into the main body 101, and is detachably installed on the main body 101. .

  When the process cartridge 95Y is pushed into the main body 101, it is loaded and positioned at a predetermined position suitable for image formation. Making a process cartridge in this way is very preferable because it can be handled as a replacement part, so that the maintainability is remarkably improved. The process cartridges 95Y, 95M, 95C, and 95BK constitute an image forming unit.

  The process cartridge 95Y includes at least the photosensitive drum 20Y and the developing device 50Y among the photosensitive drum 20Y, the cleaning device 40Y as a drum cleaning device, the charging device 30Y as a developing device as a charging unit, and the developing device 50Y. Are units that are integrated and are detachably installed on the main body 101.

The charging device 30Y includes a voltage applying unit (not shown) that applies a bias of an alternating current component to a direct current, and at the same time as removing the surface of the photosensitive drum 20Y in a charging region facing the photosensitive drum 20Y, The polarity is uniformly charged.
In this embodiment, a non-contact type charging system is employed, but the charging system may be one using a proximity roller or a contact roller.

  A predetermined voltage suitable for primary transfer is applied to the primary transfer roller 12Y by bias applying means and bias control means having a power source (not shown). The primary transfer roller 12Y is subjected to primary transfer. It functions as a bias roller. The primary transfer roller 12Y presses the transfer belt 11 from the inner peripheral surface side to the photosensitive drum 20Y to form a primary transfer nip. A primary transfer electric field is formed in the primary transfer nip due to the influence of the primary transfer bias.

  As shown in FIG. 2, the optical scanning device 8 shown in FIG. 1 irradiates a region between the charging region and the development region D on the photosensitive drum 20Y with a laser beam L that is light-modulated according to image information. Then, the surface of the photosensitive drum 20Y charged by the charging device 30Y is exposed to form an electrostatic latent image that is visualized as a yellow toner image by the developing device 50Y.

  The cleaning device 40Y has a cleaning case 43Y having an opening at a portion facing the photoconductor drum 20Y, and scrapes off unnecessary materials such as residual toner, carrier, and paper dust on the photoconductor drum 20Y in contact with the photoconductor drum 20Y. The brush roller 45Y as a rotating brush to be cleaned and the rotating direction B1 of the photosensitive drum 20Y contact the photosensitive drum 20Y at a position downstream of the brush roller 45Y and scrape off unnecessary matter on the photosensitive drum 20Y. And a cleaning blade 41Y as a blade for cleaning.

  The cleaning device 40Y is also rotatably supported by the cleaning case 43Y. The cleaning device 40Y is scraped by the brush roller 45Y and the cleaning blade 41Y. It has a discharge screw 42Y that constitutes a part of a waste toner path (not shown) for conveyance.

  The developing device 50Y includes a developing case 55Y having an opening at a portion facing the photoreceptor drum 20Y, and a developer carrying member disposed in close proximity to the photoreceptor drum 20Y so as to face the photoreceptor drum 20Y from the opening. A developing roller 51Y as a body, and a developing blade 52Y as a doctor as an agent regulating member that regulates the developer on the developing roller 51Y to a certain height.

  The developing device 50Y is also disposed below the developing case 55Y so as to face each other, and is driven to rotate in opposite directions to stir the developer and to supply the developer to the developing roller 51Y. The first conveying screw 53Y and the second agitating screw 54Y as supply members, the partition wall 57Y provided between the first conveying screw 53Y and the second conveying screw 54Y, and the first conveying screw partitioned by the partition wall 57Y. 53Y, and a second storage chamber 59Y that constitutes a developer storage section as a developer storage device that stores the second transport screw 54Y.

  The developing device 50Y also includes a toner hopper 80Y that stores yellow toner, and a T sensor as a toner concentration measuring sensor that is provided at the bottom of the second storage chamber 59Y and serves as a toner concentration detecting unit that measures the toner concentration in the developer. And a toner concentration detection sensor 56Y as a toner concentration detection device.

  The developing device 50Y also includes a bias applying unit (not shown) that applies a developing bias of a DC component, a developing driving unit (not shown) that drives the developing roller 51Y, and the first transport screw 53Y and the second transport screw 54Y in opposite directions. (Not shown) for supplying toner to the second storage chamber 59Y from the toner hopper 80Y.

  The developing roller 51Y includes a magnet roller 81Y as a magnetic field generating unit, and a nonmagnetic developing sleeve 82Y that includes the magnet roller 81Y and is driven and moved in the C1 direction, which is the clockwise direction in the drawing, by the developing driving unit. . In this embodiment, the developing roller 51Y is described as a developer carrier, but the developing sleeve 82Y may be a developer carrier.

  Although not shown, the magnet roller 81Y has a plastic roller fixed to the developing case 55Y and a magnet block that is a plurality of magnets forming a plurality of magnetic poles embedded in the plastic roller 84Y. However, a magnetic pole having the polarity shown in FIG. 2 is formed at the position shown in FIG.

  The developing sleeve 82Y is rotatably supported by the developing case 55Y and the magnet roller 81Y. A developing bias of an appropriate size is applied between the developing sleeve 82Y and the photosensitive drum 20Y by a bias applying unit. The gap between the developing sleeve 82Y and the photosensitive drum 20Y, that is, the developing gap in the developing region D, which is a facing region where the developing sleeve 82Y and the photosensitive drum 20Y face each other, is set to be 0.3 ± 0.05 mm. Yes.

  The developing blade 52Y is formed of a SUS material. The gap between the developing sleeve 82Y and the developing blade 52Y, that is, the doctor gap, is set to be 0.5 ± 0.04 mm, so that excess developer is scraped off and an appropriate amount of developer enters the developing area D. It has become.

The developer is a powdery two-component developer containing toner and carrier.
The carrier is a magnetic carrier, and has a core material and a resin coating layer formed on the surface of the core material. The resin coating layer contains conductive particles in which a conductive coating layer comprising a tin dioxide layer and an indium oxide layer containing tin dioxide provided on the tin dioxide layer is provided on the surface of the substrate particles. .

  The toner is a magnetic toner but may be a non-magnetic toner, and is mainly composed of a binder resin, a release agent, and a colorant. The binder resin contains a hybrid resin having a vinyl polymer and a polyester polymer. The content of the hybrid resin with respect to the content of the release agent is formed to be in the range of 0.5 to 3.

  The toner concentration in the developer is controlled to be within a predetermined range of about 4 to 11% by weight based on detection by the toner concentration detection sensor 56Y and controlled by the control means described below, and the toner is mixed with the carrier. The ratio is always kept at an appropriate value, which contributes to obtaining a high quality image. The control by the control means means that when the toner density decreases as the toner is consumed by the development, and the toner density detection sensor 56Y detects that the toner density falls below the lower limit of the above-mentioned predetermined range, The toner is supplied from the hopper 80Y to the second storage chamber 59Y by the toner supply means.

  The first transport screw 53Y and the second transport screw 54Y are disposed so as to extend in the width direction of the developing roller 51Y, in other words, in the direction perpendicular to the paper surface in FIG. 2, which is the longitudinal direction of the developing roller 51Y.

  The first transport screw 53Y is rotationally driven by the transport driving means, and supplies the developer in the first storage chamber 58Y to the developing roller 51Y while transporting the developer from the back side to the front side in FIG. The developer transported to the vicinity of the end in the first storage chamber 58Y by the first transport screw 53Y enters the second storage chamber 59Y through an opening (not shown) formed in the partition wall 57Y.

  In the second storage chamber 59Y, the second transport screw 54Y is rotationally driven by the transport drive means to transport the developer sent from the first storage chamber 58Y in the opposite direction to the first transport screw 53Y. . At this time, when the toner is replenished from the toner hopper 80Y, the replenished toner is conveyed while being agitated and mixed in the developer. The developer transported to the vicinity of the end of the second storage chamber 59Y by the second transport screw 54Y returns to the first storage chamber 58Y through another opening (not shown) provided in the partition wall 57Y.

  The toner thus supplied is agitated and mixed by the first conveying screw 53Y and the second conveying screw 54Y while being agitated and conveyed with the developer, frictionally charged, and supplied and carried on the developing roller 51Y.

  The developing roller 51Y, whose developer amount is regulated by the developing blade 52Y and whose layer thickness is regulated, is developed in the developing region D by the developing blade 52Y by the developing bias by the rotation and bias applying means. The yellow toner in the developer is electrostatically transferred to the electrostatic latent image formed on the surface of the photosensitive drum 20Y, and the electrostatic latent image is visualized as a yellow toner image. It has become.

The developer that has consumed the yellow toner by the development is returned to the developing device 50Y as the developing roller 51Y rotates.
In this embodiment, the DC component developing bias is applied by the bias applying means. However, the developing bias may be an AC component, or an AC component superimposed on the DC component.

  As described above, in the developing device 50Y, the developer agitated and conveyed by the first conveying screw 53Y and the second conveying screw 54Y is pumped up by the magnetic force of the magnet roller 81Y and carried on the developing sleeve 82Y to the developing region D. The toner in the developer is electrostatically transferred and supplied to the latent image on the photosensitive drum 20Y, and development, that is, the latent image is visualized. The developer that has consumed the toner after development is released from the surface of the developing sleeve 82Y into the first storage chamber 58Y, and is stored in the first storage chamber 58Y and the second storage chamber 59Y by the first transport screw 53Y and the second transport screw 54Y. The cycle in which the developer is stirred and pumped up to the surface of the developing sleeve 82Y is repeated. The magnet block is arranged to repeat such a cycle.

  As shown in FIG. 3, in the developing region D, the two-component developer carried on the developing sleeve 82Y is in contact with the photosensitive drum 20Y. A range where the two-component developer carried on the developing sleeve 82Y is in contact with the photosensitive drum 20Y is referred to as a developing nip. As will be described later, the actual developing nip in the developing device 50Y is different from the state shown in FIG.

  When the behavior of the two-component developer in the development nip shown in FIG. 3 is observed, it is as shown in FIG. In the figure, a large white circle indicates a carrier, and a small black circle indicates toner. As shown in the figure, in the developing nip between the developing sleeve and the photosensitive member, the two-component developer is fixed on the developing sleeve, in other words, it is carried in a packed state. Of the two-component developer carried on the developing sleeve, the actual contribution to the development is only the surface layer portion on the photosensitive member side, and among the developer layers formed by the two-component developer, the photosensitive member side It has been found that only one or two layers of this contribute only to development.

  Such a phenomenon is considered to be caused by the following reason. That is, since the developer is conveyed with a speed difference with respect to the photosensitive member by the developing sleeve, the developer in the vicinity of the photosensitive member is rubbed against the photosensitive member to form a toner that is a part of the developer. It can be said that is easy to move. On the other hand, the developer that is away from the photosensitive member, that is, in the vicinity of the developing sleeve is not easily subjected to the rubbing force generated by the speed difference between the developing sleeve and the photosensitive member, and the toner that is a part of the developer is difficult to move. . Therefore, even if the same electric field is applied to all the toner in the developer, the toner in the surface layer developer only contributes to the development from the viewpoint of the mobility of the toner.

  As described above, among the developer conveyed through the development nip, only the surface layers 1 and 2 contribute to development. Therefore, if the toner density of the developer after passing through the development region is compared, the photosensitive layer The toner density differs between the developer near the body and the developer near the developing sleeve. In other words, the developer near the photoconductor is in a state where toner is consumed, so the toner concentration is lower than before development, but the developer near the developing sleeve consumes little toner, The toner density does not change, and therefore the developer has a different toner density depending on the position in the thickness direction.

  Therefore, if the developer on the developing sleeve side having a relatively high toner concentration in the development nip can be moved to the photosensitive member side, the developer having a sufficient toner concentration and a high toner concentration moves to the photosensitive member side. Development with a high developer is performed again, and the amount of toner used for development increases. That is, the development efficiency is improved.

  Therefore, in the developing device 50Y, as shown in FIG. 5, the developing device 50Y is buried in the developer carried on the developing roller 51Y in the developing region D at a position between the developing roller 51Y and the photosensitive drum 20Y in the developing region D. The developer rectifying members 86Y and 87Y as stirring members that are disposed in the developing area D and abut on the developer carried on the developing roller 51Y in the developing region D and stir the developer are directed from the upstream to the downstream in the C1 direction. Have in this order.

  Each of the developer rectifying members 86Y and 87Y is formed in a wire shape from a non-magnetic material such as a polymer resin material, and extends in a range including the arrangement range of the developing roller 51Y in the width direction of the developing roller 51Y. Both ends are fixed and stretched to the developing case 55Y. Since the developer rectifying members 86Y and 87Y are arranged by simply stretching the developer rectifying members 86Y and 87Y, respectively, the arrangement work is easily performed. Although the developer rectifying members 86Y and 87Y having a circular cross-sectional shape are shown in the drawing, the cross-sectional shape is not limited to this and may be a polygon. However, when the cross-sectional shape is circular, resistance to developer flow is less likely to occur.

  As shown in FIG. 6, an interval E1 between the developer rectifying member 86Y on the upstream side in the C1 direction and the photosensitive drum 20Y and an interval E2 between the developer rectifying member 87Y on the downstream side in the C1 direction and the photosensitive drum 20Y are as follows: The interval E2 is larger than the interval E1. The interval E1 is an interval of two or more layers in the developer layer thickness. In the drawing, an interval E3 indicates an interval at the closest position between the developing sleeve 82Y and the photosensitive drum 20Y. The interval E3 is naturally larger than the intervals E1 and E2. The developer rectifying members 86Y and 87Y are respectively disposed on the upstream side in the C1 direction and the downstream side in the C2 direction in the vicinity of the closest position between the developing sleeve 82Y and the photosensitive drum 20Y.

  With this configuration, the developer whose layer thickness is regulated by passing through the developing blade 52Y is transported to the developing region D as the developing sleeve 82Y rotates, and the interval between the photosensitive drum 20Y and the developing sleeve 82Y is set at the developing position. The arrangement of the developer rectifying member 86Y on the upstream side in the C1 direction as the developing sleeve 82Y rotates while contacting with the photosensitive drum 20Y and developing with a developing bias when the height of the developer becomes smaller than the height of the magnetic spike of the agent. It reaches the position and is further conveyed while its flow rate is regulated by the developer rectifying member 86Y. At this time, the amount of developer passing between the developer rectifying member 86Y and the photosensitive drum 20Y is determined by the interval E1.

  As described above, the interval E3 that is the interval between the developing sleeve 82Y and the photosensitive drum 20Y in the region between the developer rectifying member 86Y and the developer rectifying member 87Y in the C1 direction is wider than the interval E1. Yes. Therefore, in the region between the developer rectifying member 86Y and the developer rectifying member 87Y, a sufficient space is provided for the amount of developer that has passed between the developer rectifying member 86Y and the photosensitive drum 20Y. The developer is easy to move, and the developer is attracted to the developing sleeve 82Y side by the magnetic force of the magnet roller 81Y. Therefore, the development that has passed between the developer rectifying member 86Y and the photosensitive drum 20Y is performed. The agent leaves the photosensitive drum 20Y and moves toward the developing sleeve 82Y while being disturbed. The developer sucked by the developing sleeve 82Y is transported toward the developer rectifying member 87Y along with the momentum of the developing sleeve 82Y and the rotation of the developing sleeve 82Y.

  Since the developer conveyed toward the developer rectifying member 87Y is again restricted from moving in the C1 direction by the developer rectifying member 87Y, the developer starts to accumulate on the upstream side in the C1 direction from the developer rectifying member 87Y. The developer comes into contact with the photosensitive drum 20Y again to perform development.

  As described above, since the interval E2 is larger than the interval E1, the space between the developing sleeve 82Y and the photosensitive drum 20Y in the region between the developer rectifying member 86Y and the developer rectifying member 87Y in the C1 direction. In this case, the developer does not stay and the developer is disturbed satisfactorily. However, if the interval E2 is too large, the developer does not come into contact with the photosensitive drum 20Y in the vicinity of the developer rectifying member 87Y and the development is not performed. Therefore, the interval E2 is the developer in the vicinity of the developer rectifying member 87Y. It is determined to come into contact with the drum 20Y.

  In this way, the developer carried on the developing roller 51Y is in the vicinity of the developer rectifying member 86Y and the developer rectifying member 87Y in the course of the rotation of the developing sleeve 82Y in the C1 direction. The first development nip G1 and the second development nip G2 that are high density areas with high developer density are formed, and the low density of the developer is low between the development nips G1 and G2. A density region H is formed.

  In the development nips G1 and G2, the developer is packed or close to being packed. On the other hand, in the low density region H, the developer can move relatively freely.

  In the above description, it has been described that the developer does not come into contact with the photosensitive drum 20Y in the low density region H. However, the low density region H is developed to such an extent that the developer is disturbed and stirred as described below. As long as the density of the agent is lowered, the developer may be in contact with the photosensitive drum 20Y.

  With reference to FIG. 7, the toner concentration in the developer in the process of passing through the development nips G1 and G2 and the low density region H will be described.

  The toner density 1A of the developer before being used for development at the development nip G1 and the toner density 1B of the developer after being used for development at the development nip G1 are the toner density 1A. Lower than. At this time, the toner density 1B will be described in detail. The toner on the photosensitive member side is used for development and moves to the photosensitive member side, and the toner concentration is low, but the toner on the developing sleeve side is difficult to move. Since it is difficult to use for development, the toner density is hardly changed.

  In the low density region H, the developer is easily moved because it is released from the packing state, and until reaching the development nip G2, the developer having a relatively high toner density and the developer having a relatively low toner density are disturbed and re-applied. Stir.

  Therefore, the developer that has reached the developing nip G2 is re-stirred, and the developer having a high toner concentration and the developer having a low toner concentration are mixed and the toner concentration is made uniform. When the toner density 2A of the developer before being used for development at the development nip G2 is compared with the toner density 1B, the former is relatively higher, and therefore development is also relatively good at the development nip G2. To be done. The toner density 2B of the developer after passing through the development nip G2 is lower than the toner density 2A due to toner consumption when passing through the development nip G2.

  As a result, the total amount of toner consumption in the development nips G1 and G2 is increased compared to the toner consumption in the configuration in which the developer is maintained in the packing state in the development region D as shown in FIG. Yes. In other words, with respect to the density of the developer, the developer is stirred by alternately forming a high-density region and a low-density region, and the developer stirred by forming a plurality of high-density regions is used for development. Development efficiency is improved. In this embodiment, two high density regions are provided by providing two stirring members. However, if alternately formed with low density regions, three or more stirring members are provided to provide high density regions. Three or more may be provided. Further, as will be described later, it is possible to form a plurality of high-density regions with a single stirring member.

  Further, since the interval E1 is an interval of two or more layers in the developer layer thickness, the development at the developing nip G1 is favorably performed, and the agitation in the low density region H causes the photosensitive drum 20Y side. The toner concentration increases efficiently, and the overall toner consumption rate is improved. That is, as described above, since the toner present in about one to two layers of the layer thickness is used for development as described above, if the layer thickness at the interval E1 is about one layer, the toner supply Although the amount is reduced and the development performance is reduced, the interval E1 is set to two or more layers in the developer layer thickness, so that the toner is efficiently developed in the development nip G1, and the development is good. Done. In addition, since the toner use efficiency in the development nip G1 is high, the toner concentration in the developer near the photosensitive drum 20Y immediately after passing through the development nip G1 is greatly reduced. The increase rate of the toner concentration due to the stirring in H is high, and the developer having the increased toner concentration is subjected to development in the development nip G2, so that the overall toner consumption rate is improved and the development efficiency is increased.

  Moreover, the low density area | region H is reliably formed when the space | interval E2 is larger than the space | interval E1. That is, the amount of developer flowing into the space between the developing sleeve 82Y and the photosensitive drum 20Y in the region between the developer rectifying member 86Y and the developer rectifying member 87Y in the C1 direction, and the developer from the same space If the amount of inflow is larger than the amount of outflow, the density of the developer in such a space becomes high and the developer becomes packed, which is the same as shown in FIG. Therefore, the developer is not stirred as described above. On the other hand, the inflow amount and the outflow amount depend on the sizes of the intervals E1 and E2, respectively. The larger the interval E1, the greater the inflow amount, and the greater the interval E2, the greater the outflow amount. Then, since the interval E2 is larger than the interval E1 in the developing device 50Y, such packing does not occur and the low density region H is formed. For this reason, the above-mentioned developer is agitated well and contributes to good development.

  In this inflow amount and the outflow amount, packing occurs when the inflow amount is larger than the outflow amount. Therefore, in order to prevent packing, the interval E1 may be equal to or greater than the interval E2. In addition, when three or more high-density regions are provided as described above, among the stirring members that form the high-density regions adjacent in the C1 direction, the stirring member downstream in the same direction in order to prevent packing. And the photosensitive drum 20Y are set to be equal to or larger than the distance between the upstream stirring member and the photosensitive drum 20Y in the same direction. The same applies to the case where a plurality of high-density regions are formed by a single stirring member as will be described later.

  Here, in order to disturb the developer in the low density region H, the space between the developing sleeve 82Y and the photosensitive drum 20Y in the region between the developer rectifying member 86Y and the developer rectifying member 87Y in the C1 direction. Must be secured to a certain size. As a result of an actual experiment, it is confirmed that if the spacing between the developer rectifying members 86Y and 87Y is too narrow, the developer is not disturbed and is transported to the developer rectifying member 87Y in a packed state. As a result, it has been found that it is necessary to secure the space between the developer rectifying members 86Y and 86Y to some extent and to secure such space to some extent. On the other hand, it has also been found that it is not desirable to place the developer rectifying member 87Y too far downstream in the C1 direction from the viewpoint of carrier adhesion to the photosensitive drum 20Y. In this regard, if the developer rectifying member 86Y on the upstream side in the C1 direction is disposed on the downstream side in the C1 direction with respect to the closest position between the developing sleeve 82Y and the photosensitive drum 20Y, the developer rectifying member 87Y on the downstream side in the C1 direction further has C1. In other words, it is not preferable in view of such carrier adhesion. For this reason, the downstream rectifying member has to be disposed further downstream, and if it is disposed downstream of a certain region, there is a concern about carrier adhesion, so at least one is desirably disposed upstream. Therefore, the developer rectifying member 86Y on the upstream side in the C1 direction is disposed on the upstream side in the C1 direction from the closest position between the developing sleeve 82Y and the photosensitive drum 20Y. Even when three or more high-density areas are provided as described above, for the same reason, the stirring member constituting at least one of the high-density areas is C1 rather than the closest position between the developing sleeve 82Y and the photosensitive drum 20Y. It is desirable to arrange in the direction upstream. The same applies to the case where a plurality of high-density regions are formed by a single stirring member as will be described later.

  Further, since the developer rectifying members 86Y and 87Y are made of a non-magnetic material, a developer pool due to magnetic binding force is not formed in the vicinity of the developer rectifying members 86Y and 87Y. In this case, the flow and movement of the developer are not hindered, and as a result, the development is performed well.

  FIG. 8 shows a modification of the stirring member. The developer rectifying member 88Y shown in the figure is a member integrally including developer rectifying portions 88aY and 88bY as stirring portions corresponding to the developer rectifying members 86Y and 87Y, respectively. Are made of a non-magnetic material, and the developer rectifying portions 88aY and 88bY are spaced apart from the photosensitive drum 20Y by E1 and E2, respectively, satisfying E1 ≦ E2, and developing nips G1 and G2 having a low density. A function similar to that of the developer rectifying members 86Y and 87Y, such as forming the region H, is provided. Thus, the stirring member can take various forms, and when three or more high-density regions are formed, the developer rectifying members 86Y, 87Y, and 88Y may be used in appropriate combination.

  In the image forming apparatus 100 having such a configuration, when copying, a document is set on the automatic document feeder 22 or the automatic document feeder 22 is rotated upward to place a document on the contact glass 21a. Then, the automatic document feeder 22 is rotated downward to close and hold the document, and the start button on the operation panel is pressed. The document set on the automatic document feeder 22 is, for example, a bundle-shaped sheet document, and the document set on the contact glass 21a is, for example, a single-bound document that is bound in a main shape. When the image forming apparatus 100 is used as a printer, an image forming start operation is performed after image data to be formed is selected and input by an external input device such as a PC connected to the image forming apparatus 100.

  When copying is performed and the original is set on the automatic document feeder 22, the read original is read by the reading device 21 after the set original is fed onto the contact glass 21a. Is placed on the contact glass 21a, the document is read by the reading device 21 when the start button is pressed, and image data is generated.

  Based on the generated image data or the input image data, the image stations 60Y, 60M, 60C, and 60BK having the above-described configuration operate. In parallel with the document reading operation, each device in each of the process cartridges 95Y, 95M, 95C, and 95BK, the transfer belt unit 10, the secondary transfer unit 76, the fixing device 6 and the like start driving.

  In the image station 60Y, the surface of the photosensitive drum 20Y is uniformly charged by the charging device 30Y as it rotates in the B1 direction, and exposure scanning of the modulated and deflected laser light L from the optical scanning device 8 is performed. Thus, the electrostatic latent image corresponding to the yellow color is formed by the attenuation of the potential of the photosensitive drum 20Y in the exposure unit, that is, the irradiation unit, and the electrostatic latent image is developed with the yellow toner by the developing device 50Y. The yellow toner image obtained by the development is primarily transferred to the transfer belt 11 that moves in the A1 direction by the primary transfer electric field and nip pressure formed by the primary transfer roller 12Y, and includes toner remaining after transfer. Unnecessary substances are removed by the cleaning device 40Y, and are subjected to the next charge removal and charging by the charging device 30Y to return to the initial state.

  Similarly, the toner images of the respective colors are satisfactorily formed by good development on the other photoconductive drums 20C, 20M, and 20BK, and the formed toner images of the respective colors are A1 by the primary transfer rollers 12C, 12M, and 12BK. Primary transfer is sequentially performed at the same position on the transfer belt 11 moving in the direction. A four-color superimposed toner image constituted by toner images superimposed on the transfer belt 11, that is, a four-color toner image, is a position facing the secondary transfer roller 5 as the transfer belt 11 rotates in the A1 direction. It moves to the next transfer nip, is secondarily transferred to the transfer paper, and a full color image is carried on the transfer paper.

  The transfer paper conveyed between the transfer belt 11 and the secondary transfer roller 5 is fed out from the corresponding paper feed cassette 25 by one rotation of the sheet feeding device 23 selected by the sheet feeding device 23 and fed. Is fed from the manual feed tray 34 by the rotation of the feed roller 35 of the manual paper feed device 33, or fed from the duplex unit 96 by the paper feed roller 95. At the timing when the tip of the toner image on the transfer belt 11 faces the secondary transfer belt 5 based on the detection signal from the sensor by the registration roller pair 13. It has been sent out. Such a feed operation is started substantially simultaneously with the document reading operation described above.

  When the toner image of all colors is transferred and carried on the transfer paper, it enters the fixing device 6 and passes through the fixing portion between the fixing belt 64 and the pressure roller 63 due to the action of heat and pressure. The carried toner image is fixed, and a color image is formed on the transfer paper. The fixed transfer paper that has passed through the fixing device 6 is stacked on the paper discharge tray 75 via the paper discharge roller 98 or on the duplex unit 96 via the conveyance roller 97 according to the position of the switching claw 94. Enter to prepare for double-sided image formation. On the other hand, the transfer belt 11 that has finished the secondary transfer is cleaned by removing residual toner and the like remaining on the intermediate transfer belt cleaning device 14 to prepare for the next image formation.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  For example, the image forming apparatus is not a so-called tandem type image forming apparatus, but a so-called one-drum type image forming apparatus that sequentially forms toner images of respective colors on a single photosensitive drum and sequentially superimposes the respective color toner images to obtain a color image. The present invention can be similarly applied to an image forming apparatus. The image forming apparatus may be capable of forming only a monocolor image.

  In any type of image forming apparatus, the toner image of each color may be directly transferred onto a sheet such as the transfer sheet S without using an intermediate transfer member. In this case, the toner images on the plurality of image carriers are directly transferred to the same sheet in the process of being conveyed by the conveyance belt, for example.

The image forming apparatus may not be a copier, a printer, and a facsimile machine, but may be a single unit thereof, or may be a multi-function machine of another combination such as a copier and printer. .
The stirring member can also be used in combination with the technique described in the “Background Art” column, for example, the technique using the arrangement of magnetic poles.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

1 is a schematic front view of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic front view showing a configuration around one image carrier among a plurality of image carriers provided in the image forming apparatus shown in FIG. 1. It is a reference drawing of a development nip. It is a conceptual diagram of toner consumption in the development nip. FIG. 3 is a schematic front view showing an outline of the behavior of a stirring member provided in the developing device shown in FIG. 2 and the surrounding developer. FIG. 6 is a schematic front view showing the distance between the stirring member and the image carrier shown in FIG. 5. FIG. 6 is a conceptual diagram of toner consumption in the developing device shown in FIG. 5. It is a schematic front view which shows the modification of the stirring member shown in FIG.

Explanation of symbols

20Y, 20M, 20C, 20BK Image carrier 50Y, 50M, 50C, 50BK Developing device 51Y Developer carrier 86Y, 87Y, 88Y Stirring member 100 Image forming device C1 Direction of movement of developer carrier D Opposite area E1 Developer carrier Interval between the upstream stirring member and the image carrier in the moving direction of the body E2 Interval between the downstream stirring member and the image carrier in the moving direction of the developer carrier G1, G2 High density region H Low density region

Claims (8)

A developer carrier disposed opposite to the image carrier and carrying and moving a two-component developer;
The two-component developer carried on the developer carrying member at a position between the developer carrying member and the image carrier in a facing region where the developer carrying member faces the image carrying member. And a stirring member that agitates the two-component developer in contact with the two-component developer carried on the developer carrier in the facing region,
The agitating member alternates between a high-density region having a high density of the two-component developer and a low-density region having a low density of the two-component developer along the moving direction of the developer carrier. Forming the two-component developer carried on the developer carrying member in the facing region, and forming a plurality of the high-density regions along the moving direction,
The spacing between the stirring member and the image carrier in the high-density region and adjacent to each other in the moving direction is the distance between the stirring member and the image carrier in the high-density region downstream in the moving direction. A developing device in which the distance is equal to or greater than the distance between the agitating member and the image carrier in the upstream high-density region in the moving direction. A developer carrier disposed opposite to the image carrier and carrying and moving a two-component developer;
The developer carrier is located at a position between the developer carrier and the image carrier in a facing region where the developer carrier is opposed to the image carrier, and the developer carrier is in the moving direction of the developer carrier. It is arranged so as to extend in the width direction of the developer carrier at positions upstream and downstream of the position closest to the carrier, and the developer carrier in the opposing region. have a plurality of agitation member in contact with the supported two-component developer,
Among the plurality of stirring members, an interval between the stirring member disposed at the downstream position and the image carrier is equal to or greater than an interval between the stirring member disposed at the upstream position and the image carrier. going on the developing device. The developing device according to claim 2, wherein
The stirrer member alternately forms a high-density region having a high density of the two-component developer and a low-density region having a low density of the two-component developer along the moving direction with the image carrier. The two-component developer carried on the developer carrying member in the facing region is stirred, and a plurality of the high-density regions are formed along the moving direction.
The spacing between the stirring member and the image carrier in the high-density region and adjacent to each other in the moving direction is the distance between the stirring member and the image carrier in the high-density region downstream in the moving direction. 2. A developing device according to claim 1, wherein the distance is equal to or greater than the distance between the agitating member and the image carrier in the high-density area on the upstream side in the moving direction. The developing device according to claim 1 or 3 ,
Among the high-density areas, the distance between the stirring member and the image carrier in the high-density area other than the high-density area located on the most downstream side in the moving direction is at least two layers in the layer thickness of the two-component developer. A developing device having an interval. The developing device according to claim 1, 3 or 4 ,
At least one of the high-density areas is located upstream of the position where the developer carrier is closest to the image carrier in the moving direction. The developing device according to any one of claims 1 to 5,
The developing device, wherein the stirring member is non-magnetic.   An image forming apparatus comprising the developing device according to claim 1.   An image forming method for forming an image using the developing device according to claim 1 or the image forming device according to claim 7.

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