JP2003167446A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the soiling of the edge of transfer material by electrostatically transferring leaked toner which is leaked from the vicinities of both ends of the aperture part of a developing device and adheres to a carrying belt through a photoreceptor drum from the carrying belt to the photoreceptor drum. <P>SOLUTION: The toner is stuck to an electrostatic latent image formed on the photoreceptor drum by the developing device so as to develop the latent image as a toner image, and the toner image is transferred to transfer material carried on the surface of the carrying belt 11 rotating in a direction shown by an arrow R11. The transfer material is sucked to the surface of the belt 11 by a suction roller 22. When a distance between both ends in the longitudinal direction of the aperture part of the developing device is defined as developing aperture length C, the effective surface length B of the roller 22 is set to B>C. Thus, the toner leaked from the end and adhering to the surface of the belt 11 is electrified by the roller 22 so as to be reversely transferred to the surface of the photoreceptor drum from the belt 11 by the transfer roller. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer and a facsimile.

[0002]

2. Description of the Related Art Conventionally, various methods such as an electrophotographic method, a thermal transfer method, and an inkjet method have been adopted as an image forming apparatus. Among these, the image forming apparatus using the electrophotographic method is superior to the others in terms of high speed, high image quality, and quietness.

In recent years, a color image forming apparatus using an electrophotographic system has become widespread, and this color image forming apparatus is also divided into various systems. For example, in addition to the multiple transfer system and the intermediate transfer system, a multiple development system in which color images are superposed on the surface of the photoconductor and then collectively transferred to form an image, or an image forming means (process station) of a plurality of different colors is provided. There is an in-line method in which the toner is transferred to a transfer material (for example, paper or a transparent film) that is carried by a carrier. In the color image forming apparatus as described above, a belt is often used as an intermediate transfer body or a transport body.

FIG. 10 shows an example of a schematic configuration of an electrophotographic image forming apparatus using a conveyor belt as a conveyor. The image forming apparatus shown in the figure has a rotatable drum-shaped electrophotographic photosensitive member as an image bearing member, that is, photosensitive drums 1a, 1b, 1c and 1d. Photosensitive drum 1
The surfaces of a, 1b, 1c, 1d are uniformly charged by charging devices (primary charging devices) 2a, 2b, 2c, 2d, and then exposed by an exposure device 3 such as an LED or a laser scanner.
Exposure according to image information is performed by a, 3b, 3c, and 3d, whereby an electrostatic latent image is formed. After that, the electrostatic latent image is developed as a toner image with toner electrostatically attached by the developing devices 4a, 4b, 4c, 4d. The toner images on these photosensitive drums are transferred to the photosensitive drums 1a, 1b, 1 by a conveyor belt (transfer material conveying member) 11.
The transfer rollers (transfer members) 12a, 12b, 12 are transferred onto the transfer material that has been conveyed to the transfer position opposite to c and 1d.
It is electrostatically transferred by c and 12d.

The unfixed toner image transferred onto the transfer material in this way is fixed on the transfer material by being heated and pressed by the fixing device 19. As a result, a permanent image is formed.

On the other hand, the toner (residual toner) remaining on the surface of the photosensitive drum after the transfer of the toner image is removed by the cleaning devices (cleaning blades) 6a, 6b, 6c, 6d and collected in the waste toner container. The photosensitive drums 1a, 1b, 1c, whose surfaces are thus cleaned,
1d is repeatedly used for image formation.

In the case of the above-mentioned electrophotographic image forming apparatus, if toner adheres to the conveyor belt 11, it causes a defective image. Therefore, it is necessary to provide a toner removing unit for removing the toner adhering to the conveyor belt 11. As the toner removing means, directly on the conveyor belt 11,
There is a method of attaching the transport belt cleaning member 14c. A member such as a blade or a brush is generally used as the transport belt cleaning member 14c. Such a conveyor belt cleaning member 14c is formed on the conveyor belt 11.
If there is a blade etc., the conveyor belt 11
During the rotation, the toner that has been cleaned and removed at all times is collected in the waste toner container for the conveyor belt.
Therefore, a defective image due to defective cleaning is unlikely to occur.

As another method for cleaning the conveyor belt 11, transfer rollers 12a, 12b, 12c,
A positive bias or a negative bias is applied to 12d to electrostatically reverse transfer the toner on the conveyor belt 11 onto the photosensitive drum, which is in contact with the photosensitive drums 1a, 1b, 1c and 1d. Cleaning devices 6a, 6 for photosensitive drums
There is an electrostatic cleaning method in which the toner is removed by b, 6c and 6d and is collected in a waste toner container. According to this method, members such as the above-mentioned blades and brushes are not necessary as the conveyor belt cleaning member, and the waste toner container dedicated to the conveyor belt is not necessary, so that the configuration can be simplified, and It leads to cost reduction.

The reference numerals not described in FIG. 10 will be described later in the embodiments.

[0010]

The above-mentioned transport belt 11 is to be solved.
One of the factors that the toner adheres to the developing devices 4a, 4
There is a toner leakage from the ends of b, 4c and 4d. Each of the developing devices 4a, 4b, 4c, and 4d has a developing container that contains a developer.
A rectangular opening (window portion) that is long in the axial direction of the photosensitive drum is formed at a position facing the surfaces a, 1b, 1c, and 1d. A developing roller is disposed in this opening, and the developing roller causes the photosensitive drums 1a, 1b, 1
Toner is attached to the electrostatic latent images on c and 1d and developed as a toner image. The above-mentioned toner leakage at the end portion is a phenomenon in which toner leaks out from the vicinity of both end portions in the longitudinal direction of the opening portion. Although the amount of the toner that causes the edge toner leakage (hereinafter appropriately referred to as “edge leakage toner”) is very small, it accumulates on the conveyor belt 11 via the photosensitive drums 1a, 1b, 1c, and 1d. As shown in FIG. 11, near the both ends of the conveyor belt 11 in the width direction, band-shaped end toner stains G are formed along the rotation direction of the conveyor belt 11 (direction of arrow R11). Then, when the edge toner stain G becomes thicker, both end portions in the width direction of the transfer material are soiled, that is, so-called dust stain occurs.

FIG. 11 is a view of the conveyor belt 11, the suction roller (leakage toner charging member) 22 and the like as viewed from the left side in FIG. The drive roller 13 in FIG.
1 is for rotating in the direction of arrow R11, and the suction roller 22 transfers the transfer material P, which has been transported from inside the paper feed cassette 17, onto the transport belt 11 (front surface), as shown in FIG. To be adsorbed on. As shown in FIG. 11, the sheet passing width (length in the width direction) of the transfer material P is A, the suction roller effective surface length (leakage toner charging member effective surface length: length of the contact portion between the suction roller 22 and the transport belt 11). Is B, and the developing opening length (the length of the opening of the developing container in the longitudinal direction, that is, the distance between the two ends of the opening of the developing device in the longitudinal direction) is C. Conventionally, B <A <C. Each dimension is set as follows. Further, as shown in FIG. 12, the suction roller 22 may have tapered portions 22a at both ends, but in this case as well, it is set so that B <A <C. That is, the developing opening length C is set to be the longest. The above-mentioned toner stain G on the end portion is caused by the conveyor belt 11.
Occurs in the vicinity of both ends in the width direction, that is, in the portions corresponding to the vicinity of both ends of the development opening length C of the conveyor belt 11, along the rotation direction of the conveyor belt 11. Then, as described above, when the end portion toner stain G grows and becomes thick, the above-described dust stain occurs at both end portions of the transfer material P in the sheet passing width direction.

When the conveyor belt 11 is provided with a conveyor belt cleaning member such as a cleaning blade, such dust can be always cleaned while the conveyor belt 11 is rotating. There is nothing to do.

However, in the method in which the toner on the conveying belt 11 is reversely transferred to the photosensitive drums 1a, 1b, 1c and 1d and is collected in the waste toner containers of the cleaning devices 6a, 6b, 6c and 6d for the photosensitive drums. Since the cleaning sequence needs to be provided separately from the image forming sequence, the cleaning of the conveyor belt 11 is not always performed. Cleaning of the transport belt 11 is performed, for example, when the power is turned on, when a jam occurs, or after a certain number of images are formed (after printing). For this reason, when the toner that has leaked from the end portion of the toner before the cleaning is accumulated on the transport belt 11 and the end portion of the toner is contaminated, the image defect such as the above-described dust stain is caused. . Further, the polarity of the toner that causes the toner leakage at the end portions is unstable, and becomes nearly non-polar over time, so that the toner on the conveyor belt 11 is transferred to the photosensitive drums 1a, 1b, 1c, 1d. It is difficult to collect by an electrostatic cleaning method in which reverse transfer is performed on the.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to satisfactorily remove the unnecessary toner on the conveying belt and prevent the image stain caused by the unnecessary toner. The purpose is to provide a device.

[0015]

The invention according to claim 1 is
A photoreceptor having a movable surface, a charging device for charging the photoreceptor surface, an exposure device for exposing the photoreceptor surface after charging to form an electrostatic latent image, and a toner for the electrostatic latent image. A developing device for adhering and developing as a toner image, a transfer material carrying member carrying and carrying a transfer material on which the toner image is transferred, and a toner image on the photoconductor on the transfer material carried by the transfer material carrying member. And a cleaning device that cleans the surface of the photoconductor after the toner image is transferred, and the unnecessary toner adhering to the transfer material conveying member is electrostatically reverse-transferred to the photoconductor to transfer the toner. In an image forming apparatus that removes by a cleaning device, toner that leaks from the vicinity of both ends in the longitudinal direction of the opening of the developing device facing the photoconductor and adheres to the transfer material conveying member through the photoconductor is the end part. Leakage When the toner is used as a toner, a leaking toner charging member is provided on the upstream side of the photosensitive member along the moving direction of the transfer material transporting member so as to come into contact with the transfer material transporting member. The charging member is brought into contact with the transfer material conveying member in a region including a region of the end leakage toner along a direction intersecting a moving direction of the transfer material conveying member, and at the same time, the end leakage toner is removed. It is characterized in that the transfer material is charged to a polarity reversely transferred from the transfer material conveying member to the photoconductor.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, an area where the charging device charges the surface of the photoconductor is an effective surface length of the charging device, and the leakage toner charging member is the transfer material. When the area in contact with the conveying member is the leaky toner charging member effective surface length and the area where the cleaning device cleans the photosensitive member surface is the cleaning member effective surface length, these charging device effective surface length and leaking toner charging member effective surface length The surface length and the effective surface length of the cleaning member are
It is characterized in that it is set longer than the distance between both ends of the opening of the developing device in the longitudinal direction.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the leakage toner charging member is an attraction member for attracting the transfer material to the transfer material conveying member. And

According to a fourth aspect of the present invention, a photosensitive member having a movable surface, a charging device for charging the surface of the photosensitive member, and an exposure for exposing the surface of the photosensitive member after charging to form an electrostatic latent image. A device, a developing device for adhering toner to the electrostatic latent image to develop it as a toner image, an intermediate transfer member on which the toner image is transferred, and a toner image on the photoconductor is transferred to the intermediate transfer member. The intermediate transfer member includes a first transfer device, a second transfer device for transferring the toner image on the intermediate transfer member to a transfer material, and a cleaning device for cleaning the surface of the photosensitive member after the toner image transfer. In an image forming apparatus in which unnecessary toner adhering to the surface of the developing device is electrostatically reverse-transferred to the photoconductor and removed by the cleaning device, leakage from the vicinity of both longitudinal ends of the opening of the developing device facing the photoconductor. Out the photosensitivity When the toner adhering to the intermediate transfer body through the end transfer toner is an end leak toner, the toner is arranged so as to contact the intermediate transfer body on the upstream side of the photosensitive body along the moving direction of the intermediate transfer body. A leakage toner charging member provided, the leakage toner charging member abutting the intermediate transfer member in a region including a region of the end leakage toner along a direction intersecting a moving direction of the intermediate transfer member. While being in contact with each other, the toner leaking from the end portion is charged to have a polarity reversely transferred from the intermediate transfer member to the photosensitive member.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, an area where the charging device charges the surface of the photoconductor is an effective surface length of the charging device, and the leaking toner charging member is the intermediate transfer. When the area in contact with the body is the leaky toner charging member effective surface length and the area where the cleaning device cleans the photosensitive member surface is the cleaning member effective surface length, the charging device effective surface length and the leakage toner charging member effective surface are The length and the effective surface length of the cleaning member are set to be longer than the distance between both ends in the longitudinal direction of the opening of the developing device.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. The same reference numerals in the drawings denote the same configurations or operations, and repeated description thereof will be omitted as appropriate.

<First Embodiment> [Overall of Image Forming Apparatus] FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in the figure is an electrophotographic four-color full-color laser printer having four image forming stations (image forming sections), and the figure is a longitudinal sectional view showing the schematic configuration thereof. Further, FIG. 2 shows a vertical sectional view of the process cartridge. The image forming apparatus according to the present invention may be an electrophotographic laser printer, an electrophotographic copying machine, a facsimile, or an electrostatic recording printer, a copying machine, a facsimile, or the like. It may be.

The laser printer (hereinafter referred to as "image forming apparatus") shown in FIG. 1 has four image forming stations (from below) along the conveyance direction of the transfer material P inside the image forming apparatus main body 100. Image forming unit) Sa, Sb, Sc,
It is equipped with Sd. In this order, cyan, yellow, magenta, and black toner images are formed. These image forming stations Sa, Sb, Sc, Sd are
Process cartridges 7a, 7b, 7c, 7d, respectively
Is provided, and each process cartridge 7a, 7a
b, 7c and 7d, drum-shaped electrophotographic photosensitive members (hereinafter referred to as "photosensitive drums") 1a and 1 as image bearing members.
b, 1c, 1d are arranged. In the following description, a, b, c, and d will be omitted and the generic names such as “image forming station S”, “process cartridge P”, and “photosensitive drum 1” will be used unless it is necessary to distinguish colors. I will write.
This point also applies to other members.

FIG. 2 shows a cyan process cartridge 7
The enlarged longitudinal cross-sectional view of a is shown. Note that the other three-color process cartridges 7b, 7c, and 7d are similar in configuration and operation to the cyan process cartridge 7a, and therefore description thereof will be appropriately omitted.

The photosensitive drums 1a, 1b, 1c, 1d are rotationally driven counterclockwise in FIG. 1 by driving means (not shown). Around the photosensitive drums 1a, 1b, 1c, 1d, charging devices (primary charging devices) 2a, 2b, 2c, 2d and exposure devices 3a, 3 are arranged substantially in order along the rotation direction.
b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers (transfer member, transfer device) 12a, 12b, 12
c, 12d, cleaning devices 6a, 6b, 6c, 6d
Etc. are provided.

The charging devices 2a, 2b, 2c and 2d are for uniformly charging the surfaces of the photosensitive drums 1a, 1b, 1c and 1d. Exposure device (scanner unit) 3a, 3b,
3c and 3d are photosensitive drums 1a, 1b, 1c, and
The surface 1d is irradiated with a laser beam based on image information to form an electrostatic latent image. Developing devices 4a, 4b,
The toners 4c and 4d attach toners to the electrostatic latent images formed by the exposure devices 3a, 3b, 3c and 3d to develop them as toner images. Transfer rollers 12a, 12b, 12c, 1
2d transfers the toner image formed on the photosensitive drums 1a, 1b, 1c, 1d onto the transfer material P. The cleaning devices 6a, 6b, 6c, 6d remove the toner (residual toner) remaining on the surfaces of the photosensitive drums 1a, 1b, 1c, 1d after the transfer.

Here, as shown in FIGS. 1 and 2, the photosensitive drums 1a, 1b, 1c and 1d and the charging devices 2a, 2b and 2 are used.
c, 2d, the developing devices 4a, 4b, 4c, 4d, and the cleaning devices 6a, 6b, 6c, 6d are integrally made into a cartridge to form process cartridges 7a, 7b, 7
c and 7d. These process cartridges 7a, 7b, 7c, 7d are further divided into a photosensitive drum unit 50a and a developing unit 45a, as shown in the cyan process cartridge 7a in FIG. The former photosensitive drum unit 50a is equivalent to the photosensitive drum 1
a is a unit having a charging device 2a and a cleaning device 6a, while the developing unit 45a is a unit having a developing device 4a (see FIG. 1).

The photosensitive drum 1 will be described in detail below.

The photosensitive drum 1 is constituted by coating an organic optical semiconductor layer (OPC photosensitive layer) on the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm, for example. The photosensitive drum 1 is
Both ends thereof are rotatably supported by a support member (not shown), and the driving force from a drive motor (not shown) is transmitted to one end of the support member to rotate counterclockwise in FIG. Driven.

The charging device 2 has a charging roller (conductive roller) formed in a roller shape and a charging bias applying power source (not shown). The charging device 2 brings the charging roller into contact with the surface of the photosensitive drum 1 and applies a charging bias to the charging roller by the above-mentioned charging bias applying power source so that the surface of the photosensitive drum 1 has a predetermined polarity.
It is to be uniformly (uniformly) charged to the electric potential. In the present embodiment, the surfaces of the photosensitive drums 1a, 1b, 1c, 1d are
The charging devices 2a, 2b, 2c, 2d are uniformly charged in a negative polarity.

The exposure devices 3a, 3b, 3c and 3d are shown in FIG.
The image light corresponding to the image signal is arranged on the left side of the respective photosensitive drums 1a, 1b, 1c, 1d in the inside, and the image light corresponding to the image signal is emitted by the scanner motor (not shown).
Polygon mirrors 9a, 9b, 9 rotated at high speed by
It is irradiated to c and 9d. Polygon mirrors 9a, 9b, 9
The image light reflected by c and 9d is formed by the imaging lens 10
The electrostatic latent images are formed by selectively exposing the charged surfaces of the photosensitive drums 1a, 1b, 1c and 1d via a, 10b, 10c and 10d. In the present embodiment, the charge in the portion irradiated with the image light is removed to form an electrostatic latent image.

Each of the developing devices 4a, 4b, 4c and 4d has a toner container containing toner of each color of cyan, yellow, magenta and black. As shown in the cyan toner container 41a in FIG. 2, the developing device 4a feeds the toner in the toner container 41a to the toner supply roller 43a by the feeding mechanism 42a, and rotates in the clockwise direction (arrow Z direction) in the figure. A toner supply roller 43a,
The developing blade 4 pressed against the outer peripheral surface of the developing roller 40a.
4a and the developing roller 40 that rotates in the Y direction.
The toner is applied to the outer peripheral surface of a and an electric charge is applied to the applied toner. An electrostatic latent image on the photosensitive drum 1a is applied by applying a developing bias from a developing bias applying power source (not shown) to the developing roller 40a facing and in contact with the photosensitive drum 1a on which the electrostatic latent image is formed. The toner of negative polarity is attached to and developed as a toner image. The developing devices 4b, 4c and 4d for the other colors have the same configuration and operation as the above-described cyan developing device 4a.

Process cartridges 7a, 7 in FIG.
The transfer device 5 is disposed to the right of b, 7c, and 7d. The transfer device 5 includes photosensitive drums 1a, 1b, 1c, 1d.
It has a conveyor belt (electrostatic transfer belt as a transfer material conveying member) 11 that circulates (rotates) so as to face and contact with. The conveyor belt 11 is 10 ⁸ to 10 ¹³ Ω · c.
It is composed of a film-like member having a volume resistivity value of m and a thickness of 50 to 300 μm. In the present embodiment, the conveyor belt 11 is made of PVdF (polyvinylidene fluoride). The conveyor belt 11 is stretched over four rollers 13, 14, 15, 16 arranged in parallel with each other, and is arranged in the vertical direction as a whole. The conveyor belt 11 includes the roller 13 and the roller 1 in FIG.
In the portion located between the outer peripheral surface and the outer peripheral surface 4, the transfer material P is rotated while being electrostatically attracted to the outer peripheral surface. As a result, the transfer material P
Are sequentially conveyed to the above-mentioned photosensitive drums 1a, 1b, 1c and 1d at the transfer positions, respectively, and
The toner images on a, 1b, 1c and 1d are sequentially transferred by transfer rollers 12a, 12b, 12c and 12d described below.

The photosensitive drum 1 is provided inside the conveyor belt 11.
Four transfer rollers 12a, 12b, 12c and 12d are arranged at positions corresponding to a, 1b, 1c and 1d, respectively. These transfer rollers 12a, 12b, 12c,
12d is in contact with the back side of the conveyor belt 11,
The conveyor belt 11 is sandwiched between the photosensitive drums 1a, 1b, 1c and 1d. As a result, the first, second, third and fourth transfer portions (transfer nip portion) are provided between the photosensitive drums 1a, 1b, 1c and 1d and the conveyor belt 11.
Is formed. In the present embodiment, the transfer rollers 12a, 12a are driven by a transfer bias applying power source (not shown).
A positive transfer bias is applied to b, 12c, and 12d, whereby the negative toner images of the respective colors on the photosensitive drums 1a, 1b, 1c, and 1d are transferred onto the transfer material P at the first to fourth transfer portions. It is designed to be transferred in sequence.

The residual toner remaining on the photosensitive drums 1a, 1b, 1c and 1d without being transferred to the transfer material P at the time of transferring the toner image is removed by the cleaning devices 6a, 6b, 6c and 6d. As shown in FIG. 2, the cyan cleaning device 6a has a cleaning blade 60a that is in contact with the surface of the photosensitive drum 1a to remove the residual toner on the surface of the photosensitive drum 1a. Cleaning blade 60
The residual toner removed from the surface of the photosensitive drum 1a by a is sequentially sent to the waste toner chamber 53a provided behind the cleaning frame 51a by the toner sending mechanism 52a.

At the bottom of the image forming apparatus main body 100, a detachable paper feed cassette 17 is arranged. A plurality of transfer materials P (for example, plain paper, envelope, transparent film) are stored in the paper feed cassette 17 in a stacked state. The transfer material P in the paper feed cassette 17 is separated and fed one by one by the drive rotation of the paper feed roller 18 (half-moon roller) at the time of image formation, and is temporarily stopped by abutting the leading end thereof against the registration roller pair 19. Form a loop. afterwards,
Rotation of the conveyor belt 11 and the photosensitive drums 1a, 1b, 1
In synchronization with the image writing start positions on c and 1d, the image is supplied to the conveyor belt 11 by the registration roller pair 19. The transfer material P supplied toward the conveyor belt 11 is a suction roller (leakage toner charging member) as a suction member arranged further upstream than the most upstream photosensitive drum 1a.
It is adsorbed on the surface of the conveyor belt 11 by 22.

A fixing device 20 is disposed further downstream (upper) of the most downstream image forming station Sd. The fixing device 20 fixes the toner images of a plurality of colors transferred to the transfer material P, and includes a rotating fixing roller (heating roller) 23 and a pressing roller which is pressed against the fixing roller 23 to apply heat and pressure to the transfer material P. And a pressure roller 24. That is, the transfer material P on which the toner images of the respective colors on the photosensitive drums 1a, 1b, 1c, 1d are transferred so as to be sequentially superposed on each other.
Is heated and pressed while being nipped and conveyed by the fixing roller 23 and the pressure roller 24 when passing through the fixing device 20, and the toner images of a plurality of colors are fixed on the surface.

The image forming operation in the above-mentioned image forming apparatus is as follows. Process cartridges 7a, 7
Photosensitive drums 1a, 1b, 1c, 1d in b, 7c, 7d
Is rotated counterclockwise according to the image forming timing, and is uniformly charged by the charging devices 2a, 2b, 2c, 2d. Charged photosensitive drums 1a, 1b, 1c, 1
The exposure device 3a, 3b, 3c, 3d exposes d according to the image signal (image information) to form an electrostatic latent image. The part that is not exposed at this time is the dark part (high potential part)
And its potential (dark part potential) is VD. On the other hand, the exposed portion becomes a bright portion (low potential portion), and the potential (bright portion potential) is VL. Developing devices 4a, 4b, 4c, 4d
Attaches toner to the bright portion of the electrostatic latent image described above, and causes cyan, respectively, on the photosensitive drums 1a, 1b, 1c, 1d.
It forms yellow, magenta, and black toner images.

On the other hand, from the paper feed cassette 17 to the paper feed roller 1
8, the transfer material P supplied to the conveyor belt 11 by the registration roller pair 19 and the like is attracted to the suction roller 22 and the conveyor belt 1.
1 is pressed against the surface (peripheral surface) of the conveyor belt 11 so as to be sandwiched between them, and a voltage is applied between the conveyor belt 11 and the suction roller 22, so that the surface of the conveyor belt 11 is electrostatically adsorbed. It At this time, the suction roller 2
A positive voltage is applied from the 2 side, and the roller (adsorption facing roller) 14 is grounded. The roller 14 is formed longer than the suction roller 22 in the longitudinal direction. This allows
The transfer material P is stably adsorbed by the transfer belt 11 and is transferred to the fourth transfer section on the most downstream side.

The transfer material P adsorbed on the surface of the conveyor belt 11 in this manner is sequentially conveyed to the first to fourth transfer portions of each color by the rotation of the conveyor belt 11 in the direction of arrow R11.
Photosensitive drums 1a, 1b, 1c, 1d and transfer roller 12
By the electric field (transfer electric field) formed between the photosensitive drums 1a, 1b, 1c, and 12d.
The toner images of c and 1d are sequentially transferred.

The transfer material P on which the four color toner images have been transferred is
The roller (belt driving roller) 13 is curvature-separated from the conveyor belt 11 by the curvature and is carried into the fixing device 20.
The transfer material P is heated and pressed by the transfer roller 23 and the pressure roller 24 in the fixing device 20, and the toner images of four colors are fixed on the surface. The transfer material P after the toner image is fixed is
The pair of paper discharge rollers 25 discharges the image surface downward onto a paper discharge tray 26 formed on the upper surface of the image forming apparatus main body 100. On the other hand, the residual toner remaining on the surface of the photosensitive drums 1a, 1b, 1c, 1d after fixing the toner image is removed by the cleaning devices 6a, 6b, 6c, 6d, and is used for the next image formation. As described above, the four-color full-color image formation is completed.

[Cleaning of Conveyor Belt] The conveyor belt 11 is used for image formation after a feeding jam of the transfer material P during image formation or after intentionally transferring a toner image for density detection onto the conveyor belt. It is necessary to remove unnecessary toner on the conveyor belt 11 in order to prevent defects.

A method of removing toner when toner adheres to the conveyor belt 11 will be described. In the present embodiment, a conveyor belt cleaning member (for example, a cleaning blade) dedicated to the conveyor belt 11 is not provided. The toner adhering to the conveyor belt 11 is transferred to the photosensitive drums 1a, 1
Reverse transfer onto b, 1c, and 1d, and recovery is performed using the cleaning devices 6a, 6b, 6c, and 6d in the photosensitive drum unit.

First, in the first transfer portion of the image forming station Sa, an electric field having a polarity opposite to that of the electric field at the time of normal transfer (when the toner image on the photosensitive drum 1a is transferred onto the transfer material P) is generated. Thus, the transfer bias and the surface potential of the photosensitive drum 1a are adjusted. The electric field adjusted in this way is hereinafter referred to as "transfer reverse electric field". For example, the photosensitive drum 1
The surface a has a dark portion potential VD, and a negative bias having an absolute value larger than VD is used as the transfer bias.
applied to a. Hereinafter, the negative transfer bias will be referred to as a transfer reverse bias. Since the transfer reverse electric field is formed in the first transfer portion, the normally charged (negative polarity) toner is reversely transferred to the photosensitive drum 1a, and the waste toner chamber 53a is discharged by the cleaning device 6a for the photosensitive drum.
Will be collected. In the configuration of the present embodiment, when the dark potential VD on the surface of the photosensitive drum 1a is set to -700V, a transfer reverse bias of about -1.5 kV is applied.

Next, in the second transfer portion of the image forming station Sb, the transfer bias and the surface potential of the photosensitive drum 1b are adjusted so that an electric field having the same polarity as the electric field at the time of transferring the toner image is generated. The electric field adjusted in this way is hereinafter referred to as a "transfer positive electric field". In order to realize this, the surface of the photosensitive drum 1b is set to the dark part potential VD potential and a bias having an absolute positive polarity is applied as the transfer bias. In the second transfer portion, by forming a transfer positive electric field, the toner whose polarity is reversed (positive charge) is reversely transferred to the photosensitive drum 1b, and discharge is caused between the photosensitive drum 1b and the transport belt 11. As a result, the toner is recharged to the negative polarity. For example, in this embodiment, the surface potential VD of the photosensitive drum 1 is set to −700 V, and about +1.0 kV is applied as the second transfer bias.

Next, in the third transfer portion, a transfer reverse electric field similar to that in the first transfer portion was formed. Its purpose and effect are the same as those of the first transfer portion.

Next, in the fourth transfer portion, a transfer positive electric field similar to that in the second transfer portion was formed. In the fourth transfer section,
By completely reversely transferring the positively charged toner to the photosensitive drum 1, the removal of the toner on the conveyor belt 11 is completed.

Further, when the transport belt 11 is cleaned, that is, the toner on the transport belt 11 is removed from the photosensitive drum 1.
When reverse transfer is performed on the a, 1b, 1c, and 1d, the moving speed (rotating speed) of the transport belt 11 is significantly positive or negative relative to the rotating speed of the photosensitive drums 1a, 1b, 1c, and 1d. By providing the speed difference, the toner on the conveyor belt 11 is also collected by the photosensitive drums 1a, 1b, 1c, 1d. In the present embodiment, the moving speed of the conveyor belt 11 is set to about 50% faster than the rotating speed of the photosensitive drums 1a, 1b, 1c, 1d.

For cleaning the conveyor belt 1, for example,
After the toner image for detection is intentionally formed on the conveyor belt 11 for the purpose of density control, registration (registration) control, or the like, or due to a feeding jam of the transfer material P at the time of image formation, the toner is inevitably conveyed. This is executed during the recovery operation of the image forming apparatus main body 100 after the toner is transferred onto the belt 11.

[Countermeasures for Toner Leakage at Edge] As described above,
One of the causes of the toner adhering to the conveyor belt 11 is the toner leakage from the end portion of the developing device and the toner leakage from the end portion. This toner leakage at the end portion is caused by the developing devices 4a, 4b, 4
Toner leaking from the edges of c and 4d (edge leak toner)
However, it is attached in a belt shape to the end portion of the conveyor belt 11 in the width direction via the photosensitive drums 1a, 1b, 1c and 1d.
For example, uncharged toner is likely to accumulate at the longitudinal ends of the openings of the developing devices 4a, 4b, 4c, 4d, and such toners may not be charged in the developing devices 4a, 4b, 4c, 4d leak from the photosensitive drum 1a,
1b, 1c, 1d, and the photosensitive drums 1a, 1
Transfer from b, 1c and 1d to the conveyor belt 11 and adhere. The amount of leakage of the end leakage toner is very small, and the position where the toner adheres is outside the sheet passing width (sheet passing area) A as is clear from FIGS. No image defect occurs in the image forming operation. However, as shown in FIG. 11 of the conventional example, when image formation is continued, the toner is gradually accumulated, and the edge toner stain G grows thick as shown by the diagonal lines. In such a state, the edge toner stain G is present up to the sheet passing width A. Then, when the transfer material P is passed, the toner that causes the edge toner stain G adheres to the left and right ends of the transfer material P,
An image defect due to smudges occurs.

In the present embodiment, the suction roller 22 is used as a toner charging roller in consideration of the occurrence of such image defects. Therefore, as shown in FIG. 3, the suction roller effective surface length B is made longer than the developing opening length C. In other words, the suction roller 22 moves in the rotation direction of the conveyor belt 11 (movement direction: arrow R11 direction).
In the area including the area of the toner leaked at the end portion along the direction intersecting with, the conveyor belt 11 is contacted. Further, as shown in FIG. 5, the photosensitive drums 1a,
Charging devices 2a, 2b, 2 contacting 1b, 1c, 1d
Effective surface length in the longitudinal direction of c and 2d (effective surface length of the charging device)
D, and effective surface length in the longitudinal direction of the cleaning blades of the cleaning devices 6a, 6b, 6c, 6d (cleaning blade effective surface length: cleaning member effective surface length) E
Is the development opening length (length in the longitudinal direction of the opening of the developing container, that is, the distance between both ends in the longitudinal direction of the opening of the developing device).
It is longer than C. According to the present embodiment, the toner leaked at the end portion can be charged by the suction roller 22, so that the toner is discharged from the photosensitive drums 1a, 1b, 1c, 1d.
Reverse transfer to the cleaning device 6a, 6b, 6
It is possible to collect them in the waste toner chamber 53a of c and 6d.

As shown in FIG. 4, the transfer material P
The suction roller 2 in order to attract the toner to the surface of the conveyor belt 11.
A positive voltage is applied from 2. At this time, if the end leakage toner adheres to the non-sheet passing portion, the suction roller 2
By the positive bias applied to 2, the end leakage toner having unstable electric charge is positively charged. The edge leakage toner is conveyed to the first transfer portion of the cyan image forming station Sa while being positively charged. In the first transfer portion, in order to transfer the toner on the photosensitive drum 1a to the transfer material P, the photosensitive drum 1a is negatively charged,
A positive transfer bias is applied to the transfer roller 12a. Here, as shown in FIG. 5, the effective surface length D of the charging device is longer than the development opening length C, so that the surface of the photosensitive drum at the portion where the end leakage toner is also negatively charged. Therefore, the toner on the photosensitive drum 1a is transferred to the transfer material P.
Simultaneously with the operation of transferring the toner onto the photosensitive drum 1a, the end leakage toner charged to the positive polarity is reversely transferred onto the photosensitive drum 1a. Then, the cleaning blade 6 is carried to the cleaning device 6a.
0a scrapes the photosensitive drum 1a and collects it in the waste toner chamber 53a. Since the cleaning blade effective surface length E is also longer than the developing opening length C, it is possible to scrape off the end leak toner from the photosensitive drum 1a. Since such a cleaning operation is performed for each image forming operation, the toner leaked at the edge does not accumulate and the toner stain at the edge becomes thick in a band shape. Therefore, it is possible to collect the end leak toner in the cleaning device 6a via the photosensitive drum 1a before an image defect such as dust stain occurs. The same applies to the other image forming stations Sb, Sc, Sd.

The image forming apparatus of this embodiment is, for example,
In the case of an A4 / letter size compatible image forming apparatus, as shown in FIG.
(Toner charging roller length) B is 226 mm, charging device effective surface length D is 232 mm, cleaning blade effective surface length E is 232 mm, and developing opening length C is 220 mm. That is, all of the suction roller effective surface length B, the charging device effective surface length D, and the cleaning blade effective surface length E can cover the outside of the developing opening length C. The transfer rollers 12a, 12b, 12c, 12
Although d has an effective surface length of 222 mm in the longitudinal direction, it can be shorter than this as long as it is within a range in which the electric field can pass through the conveyor belt 11.

Conventionally, as shown in FIG. 11, for example, when the effective surface length B of the suction roller is 215 mm, the toner on the end portion outside the 215 mm stains the photosensitive drum 1.
Since it was not possible to perform reverse transfer to a, 1b, 1c, and 1d, the transfer material P had an image defect due to dust stains. On the other hand, in the present embodiment, as shown in FIG. 3, by increasing the effective surface length B of the suction roller to 226 mm, the end leak toner is removed from the photosensitive drums 1a, 1b, 1c, and.
It is possible to reverse transfer onto 1d, and it is possible to satisfactorily remove the toner leaked at the end portion on the conveyor belt 11 which causes a defective image.

As described above, by making all of the suction roller effective surface length B, the charging device effective surface length D and the cleaning blade effective surface length E longer than the developing opening length C, the transfer material P is obtained.
It was possible to prevent image defects such as dust stains on the edges.

In this embodiment, the end roller leaked toner on the conveyor belt 11 is recharged by using the suction roller 22 and reversely transferred onto the photosensitive drums 1a, 1b, 1c and 1d, whereby the conveyor belt 11 The upper end leak toner is removed.

<Second Embodiment> A second embodiment will be described. The basic structure of the image forming apparatus is the same as that of the above-described first embodiment, and thus the description thereof is omitted.

The image forming apparatus described in this embodiment is
The image forming apparatus is compatible with A3 size and is capable of printing up to a size slightly larger than A3 size (A3 size).

In the present embodiment, the suction roller 22 having the tapered portions 22a at both longitudinal ends is used. As shown in FIG. 6, in the present embodiment, the suction roller effective surface length B corresponding to the length of the suction roller 22 excluding the tapered portion 22a is 319 mm, and the charging device effective surface length D (see FIG. 5) is 324 mm, the effective surface length E of the cleaning blade is 323 mm, and the developing opening length C is 317 mm.

Conventionally, as shown in FIG. 12, the attraction roller effective surface length B is 308 mm, and a taper portion 22a having a gentle taper portion 22a is used outside the effective surface length. The pass width of the transfer material P normally used is 297 for A3 size paper.
mm, and the leisure paper is 279 mm, and if the suction roller effective surface length B is 308 mm, there is a sufficient margin, and no image defect due to toner leakage at the end portion occurred. However, A3 novisize (for example, 31
In the case of (2 mm) paper passing, there is a possibility that an image defect due to dust stain due to edge leakage toner may occur, so it has been considered to clean the conveyor belt 11.
However, it is difficult to remove the end leak toner adhering to the portion corresponding to the tapered portion 22a located outside the effective surface length B of the suction roller. In this state, 31
When 2 mm paper was passed, toner adhered to the image surface, resulting in an image defect. Therefore, in this embodiment, as shown in FIG. 6, by setting the suction roller effective surface length B to 319 mm, it is possible to always clean the toner leaked at the end portion and prevent the image defect. Further, the number of times of cleaning the conveyor belt 11 can be reduced. The transfer rollers 12a, 12b, 12c, 12d used had an effective surface length in the longitudinal direction of 319 mm.

<Third Embodiment> FIGS. 7, 8, and 9 show a third embodiment. 7 is a vertical cross-sectional view showing a schematic configuration of the image forming apparatus according to the present embodiment, and FIG.
1 and the like viewed from the left side in FIG. 7, and FIG. 9 is a partially enlarged view of FIG. 7. The present embodiment is different from the above-described first embodiment in that a dedicated toner charging unit is provided in order to charge the end leak toner on the conveyor belt 11, and the other points are the same. It should be noted that description of similar parts is omitted.

In the first embodiment, the conveyor belt 11 is used.
Although the suction roller 22 was also used as the toner charging means for charging the edge leakage toner adhering to the toner, in the present embodiment, a dedicated member is provided as the toner charging means. In this embodiment, the effective surface length B of the suction roller is 21.
It is 5 mm, which is shorter than the developing opening length C of 220 mm.
Therefore, in the present embodiment, the dedicated end leak toner charging roller 29 is provided for charging the end leak toner. The end leakage toner charging roller 29 is arranged so as to contact the surface of the conveyance belt 11 at a position on the conveyance belt 11 where the end leakage toner can be charged, as shown in FIG. As described above, the end leak toner can be removed by disposing not only the suction roller 22 but also another member as long as the end leak toner on the transport belt 11 can be charged. Is possible. Note that, as shown in FIG. 8, in the present embodiment, the end leakage toner charging roller 29 is divided into two, but instead of this, it is formed continuously. May be

In the above embodiments, the case where the end leak toner adhering to the belt-shaped conveyor belt 11 for conveying the transfer material P adsorbed on the surface is removed has been described as an example, but the present invention is not limited to this. However, the present invention can be applied not only to the case where the member that conveys the transfer material P is a drum-shaped conveyance drum. Further, the present invention can be applied to an image forming apparatus having an intermediate transfer body (for example, an intermediate transfer belt or an intermediate transfer drum) instead of the transfer belt or the transfer drum that transfers the transfer material P. That is, it has an intermediate transfer member on which the toner images of a plurality of colors sequentially formed on the photosensitive drum are transferred so as to be sequentially overlapped, and thereafter, the toner images of a plurality of colors on the intermediate transfer member are collectively transferred to the transfer material P. The present invention can also be applied to an image forming apparatus of the type that transfers the image. In addition, the first embodiment described above
3 to 3, the image formation having four photosensitive drums has been described as an example, but the present invention can also be applied to an image forming apparatus of a system in which toner images of different colors are sequentially formed on one photosensitive drum.

In the above, an example in which the present invention is applied to an electrophotographic image forming apparatus has been described, but the present invention is not limited to an electrophotographic image forming apparatus, but an image forming apparatus of another type, for example, a static image forming apparatus. It can also be applied to an electrographic image forming apparatus. However, in this case, if a toner image carrier is used instead of the photosensitive drum, and an electrostatic latent image is directly formed on the toner image carrier to develop the electrostatic latent image. Good.

[0064]

As described above, according to the present invention,
Since the leakage toner charging member is in contact with the transfer material conveying member in a region including the region of the end leakage toner along the direction intersecting the moving direction of the transfer material conveying member, By applying a bias to reverse transfer of the end leakage toner adhering to the transfer material conveying member to the photoconductor, the end leakage toner can be reversely transferred to clean the transfer material conveying member well. . This prevents the transfer material from becoming dirty. Note that the end leakage toner that is reversely transferred to the photoconductor can be removed from the photoconductor by, for example, a photoconductor cleaning device.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is an enlarged view of the cyan process cartridge in FIG.

FIG. 3 is a diagram of a transport belt and the like as viewed from the left side in FIG. 1, and is a diagram for comparing an effective surface length B of a suction roller and a development opening length C.

FIG. 4 is an enlarged vertical sectional view of a cyan process cartridge, a conveyor belt, a suction roller and the like according to the first embodiment.

FIG. 5 is an effective surface length B of the suction roller according to the first embodiment,
Charging device effective surface length D, cleaning blade effective surface length E
FIG. 6 is a diagram for comparing a development opening length C with the above.

FIG. 6 is a schematic diagram showing a suction roller effective surface length B in the second embodiment.
FIG. 6 is a diagram comparing a development opening length C with a development opening length C;

FIG. 7 is a vertical sectional view showing a schematic configuration of an image forming apparatus according to a third embodiment.

FIG. 8 is an effective surface length B of the suction roller according to the third embodiment.
FIG. 6 is a diagram comparing a developing opening length C with an effective surface length of a toner leakage roller for charging an end leakage toner.

FIG. 9 is an enlarged vertical sectional view of a cyan process cartridge, a conveyor belt, a suction roller, an end leakage toner charging roller and the like according to a third embodiment.

FIG. 10 is a vertical sectional view showing a schematic configuration of a conventional image forming apparatus.

FIG. 11 is a conventional paper passing width A and a suction roller effective surface length B.
FIG. 6 is a diagram for comparing a development opening length C with the above.

FIG. 12 is a diagram comparing a conventional sheet passing width A, a suction roller effective surface length B, and a developing opening length C in the case where the suction roller has a taper portion at the end.

[Explanation of symbols]

1a, 1b, 1c, 1d photoconductor (photosensitive drum) 2a, 2b, 2c, 2d charging device 3a, 3b, 3c, 3d exposure device 4a, 4b, 4c, 4d developing device 6a, 6b, 6c, 6d cleaning device 7a , 7b, 7c, 7d Process cartridge 11 Transfer material conveying member (conveying belt) 12a, 12b, 12c, 12d Transfer device (transfer roller) 22 Leakage toner charging member (adsorption member, adsorption roller) 100 Image forming apparatus main body A Paper passing width B Leakage Toner Charging Member Effective Surface Length (Suction Roller Effective Surface Length) C Distance Between Both Ends of Developing Device Opening in Longitudinal Direction (Development Opening Length) D Charging Device Effective Surface Length E Cleaning Member Effective Surface Length (Cleaning Blade Effective surface length) P Transfer material Sa, Sb, Sc, Sd Image forming station

Continued front page    F-term (reference) 2H077 AC04 AD06 AD13 AD17 BA08                       EA15 GA13                 2H134 GA01 GA06 GA08 GA10 GB02                       HA01 HA13 HD01 HF16 KF03                       KG04 KH07 KJ02                 2H200 FA19 GA12 GA23 GA34 GA47                       GB12 GB25 HA02 HB12 HB22                       HB45 JA02 JA28 JA29 JB06                       JB10 JB26 JB42 JB45 JB46                       JC02 JC03 JC12 JC18 LB03                       LB08 LB15 LB18 LB38 LB39                       MA04 MB01 MB04 NA02 NA09                       PA05 PA11 PA23

Claims (5)

[Claims] 1. A photoconductor having a movable surface, a charging device for charging the photoconductor surface, an exposure device for exposing the photoconductor surface after charging to form an electrostatic latent image, and the electrostatic device. A developing device that attaches toner to the latent image to develop it as a toner image, a transfer material conveying member that carries and conveys a transfer material onto which the toner image is transferred, and the transfer material carried by the transfer material conveying member is exposed to the photosensitive material. A transfer device for transferring the toner image on the body,
A cleaning device for cleaning the surface of the photoconductor after the transfer of the toner image, and image formation in which unnecessary toner adhering to the transfer material conveying member is electrostatically reverse-transferred to the photoconductor and removed by the cleaning device. In the apparatus, when the toner leaking from the vicinity of both ends in the longitudinal direction of the opening of the developing device facing the photoconductor and adhering to the transfer material conveying member via the photoconductor is the end leak toner, An upstream side of the photoconductor along the moving direction of the transfer material transporting member is provided with a leaking toner charging member disposed so as to contact the transfer material transporting member, wherein the leaking toner charging member is the transfer toner. The end portion leaks while being in contact with the transfer material conveying member in a region including a region of the end portion leakage toner along a direction intersecting the moving direction of the material conveying member. To charge the toner from the transfer material transporting member to a polarity which is reverse-transcribed into the photosensitive member, an image forming apparatus characterized by. 2. An effective surface length of the charging device is an area where the charging device charges the surface of the photoconductor, and an effective surface length of the toner charging member is a surface where the leakage toner charging member contacts the transfer material conveying member, and the cleaning. When the area where the apparatus cleans the surface of the photoconductor is the effective surface length of the cleaning member, the effective surface length of the charging device, the leakage toner effective surface length of the charging member, and the effective surface length of the cleaning member are the opening of the developing device. The image forming apparatus according to claim 1, wherein the image forming apparatus is set to be longer than a distance between both ends in the longitudinal direction. 3. The image forming apparatus according to claim 2, wherein the leakage toner charging member is an adsorption member for adsorbing the transfer material to the transfer material conveying member. 4. A photosensitive member having a movable surface, a charging device for charging the photosensitive member surface, an exposure device for exposing the charged photosensitive member surface to form an electrostatic latent image, and the electrostatic device. A developing device that attaches toner to the latent image and develops it as a toner image, an intermediate transfer member to which the toner image is transferred, and a first transfer device that transfers the toner image on the photosensitive member to the intermediate transfer member. A second transfer device for transferring the toner image on the intermediate transfer member to a transfer material, and a cleaning device for cleaning the surface of the photosensitive member after the toner image transfer, and unnecessary toner adhering to the intermediate transfer member. In an image forming apparatus that electrostatically reverse-transfers to the photosensitive member and is removed by the cleaning device, leaking from the vicinity of both longitudinal end portions of the opening of the developing device facing the photosensitive member to remove the photosensitive member. Through the intermediate transfer When the toner adhering to the body is the end portion leakage toner, the leakage toner charging is arranged so as to contact the intermediate transfer body on the upstream side of the photosensitive body along the moving direction of the intermediate transfer body. The leakage toner charging member is abutted on the intermediate transfer member in a region including a region of the end leakage toner along a direction intersecting a moving direction of the intermediate transfer member, and An image forming apparatus, wherein the end leakage toner is charged to a polarity that is reversely transferred from the intermediate transfer member to the photosensitive member. 5. An effective surface length of the charging device is an area where the charging device charges the surface of the photosensitive member, and an effective surface length of the toner charging member is a surface where the leaking toner charging member contacts the intermediate transfer member. When the area for cleaning the surface of the photoconductor is the effective surface length of the cleaning member, the effective surface length of the charging device, the effective surface length of the leaking toner charging member and the effective surface length of the cleaning member are the effective surface length of the developing device. The image forming apparatus according to claim 4, wherein the image forming apparatus is set to be longer than a distance between both ends in the longitudinal direction.