JP2013029854A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus of an in-line system which recovers secondary transfer residual toner with a simultaneous transfer-and-recovery system, the apparatus being capable of satisfactorily recovering residual toner on an intermediate transfer body.SOLUTION: An image forming apparatus 100A is configured so that in a color mode and in a monochrome mode, an image forming part 10 for mainly recovering toner by reverse transfer among a plurality of image forming parts 10 is different and in the color mode, at least a part of the toner on an intermediate transfer body 50 electrified to a reverse polarity and reaching the primary transfer part N1a of the most upstream image forming part 10a after primary transfer in the most upstream image forming part 10a is completed is recovered by the reverse transfer at image forming parts 10 except the most upstream image forming part 10a after passing through the primary transfer part N1a of the most upstream image forming part 10a.

Description

  The present invention relates to an image forming apparatus in which a toner image formed on an image carrier is primarily transferred to an intermediate transfer member, and then this toner image is secondarily transferred to a transfer material to form a recorded image. The present invention is particularly suitable for application to an in-line image forming apparatus that forms a monochrome image or a color image on a transfer material.

  Conventionally, as an electrophotographic image forming apparatus such as a copying machine or a laser beam printer, an intermediate transfer image forming apparatus using an intermediate transfer member is known. The intermediate transfer type image forming apparatus forms a color image (multicolor image) on a transfer material by a primary transfer process and a secondary transfer process.

  That is, first, as a primary transfer step, a toner image as a transferable image formed on the surface of an electrophotographic photosensitive member (hereinafter simply referred to as “photosensitive member”) as a first image carrier is converted into a second image. Transfer (primary transfer) to an intermediate transfer member as an image carrier.

  By repeating this primary transfer process for a plurality of color toner images, a multiple toner image comprising a plurality of color toner images is formed on the surface of the intermediate transfer member.

  Subsequently, as a secondary transfer step, a multiple toner image formed of a plurality of color toners formed on the surface of the intermediate transfer member is transferred collectively onto the surface of a transfer material such as paper as a third image carrier ( Secondary transfer).

  The intermediate transfer type image forming apparatus has an advantage that it is possible to form a color image in which the misregistration of the toner images of each color, that is, so-called color misregistration is suppressed.

  In an intermediate transfer type image forming apparatus, after secondary transfer of a toner image from an intermediate transfer member to a transfer material, secondary transfer residual toner (transfer residual toner, residual toner, waste toner) is formed on the surface of the intermediate transfer member. ) Toner remains.

  Accordingly, in order to remove the transfer residual toner remaining on the surface of the intermediate transfer member, as described in Patent Document 1, the following image forming apparatus has been proposed.

  The basic structure of the image forming apparatus described in Patent Document 1 is as follows. That is, the primary transfer nip is formed by bringing the surface of the movable second image carrier (intermediate transfer member) into contact with the surface of the movable first image carrier (photosensitive member). In addition, a secondary transfer member is provided on the surface of the second image carrier so as to face the secondary transfer member. In this image forming apparatus, the toner images sequentially formed on the surface of the first image carrier are primarily transferred sequentially to the surface of the second image carrier through the primary transfer nip. Further, in this image forming apparatus, a plurality of toner images primarily transferred onto the surface of the second image carrier are transferred to the third image carrier (transfer material) by the secondary transfer member at the secondary transfer position. Secondary transfer at once.

  The image forming apparatus described in Patent Document 1 further includes a charge applying unit that applies a charge to the toner image before the secondary transfer, and a downstream of the secondary transfer position in the moving direction of the surface of the second image carrier. And charging means disposed on the upstream side of the primary transfer nip. The charging means causes the secondary transfer residual toner remaining on the surface of the second image carrier without being transferred to the third image carrier at the secondary transfer position to be the surface potential of the first image carrier. Charge to reverse polarity. That is, the secondary transfer residual toner is charged to a polarity opposite to the normal charging polarity of the toner. Then, the secondary transfer residual toner having the reverse polarity on the second image carrier is transferred back to the surface of the first image carrier through the primary transfer nip simultaneously with the primary transfer (simultaneous transfer recovery). method).

  Patent Document 2 proposes an in-line image forming apparatus having a charger (contact charging member) that charges secondary transfer residual toner to a polarity opposite to the normal charging polarity. An in-line type image forming apparatus includes an image carrier and a waste toner container that contains toner removed from the image carrier, and each forms an image with different types (colors) of toner. (Hereinafter referred to as “station”). In an in-line image forming apparatus, a large amount of secondary transfer residual toner enters a specific waste toner container, and the replacement frequency of only that cartridge increases, which is uneconomical. Therefore, in the image forming apparatus described in Patent Document 2, the capacity of the waste toner container is increased only for the cartridge in which a lot of secondary transfer residual toner is contained.

  Also, Patent Document 3 proposes a method in which in-line image forming apparatus distributes and collects toner remaining on the moving body as test toner or jammed toner, or toner remaining as a fog toner to different stations. Has been. The moving body is a transfer material carrier or an intermediate transfer body. The jam is a phenomenon that the transfer material is clogged in the image forming apparatus. The fog toner is toner that adheres to the non-image area.

Japanese Patent Laid-Open No. 9-50167 Japanese Patent Laid-Open No. 2004-21134 JP 2001-175047 A

  However, as described in Patent Document 2, the inline-type image forming apparatus having the toner charging unit that charges the secondary transfer residual toner with a polarity opposite to the normal charging polarity of the toner has the following problems. There is.

  Here, the image forming apparatus has first, second, third, and fourth stations that are stations for each color of yellow (Y), magenta (M), cyan (C), and black (K). Will be described.

  That is, in a multi-color image forming mode (hereinafter referred to as “color mode”) in which images are formed at all stations to form a multi-color image (color image), the downstream side of the toner charging unit in the rotational direction of the intermediate transfer member. Secondary transfer residual toner is collected at the first station.

  When the first to fourth stations are stations for each color of Y, M, C, and K, among the stations for each color of Y, M, and C, the secondary is placed in the waste toner container of the first station. The transfer residual toner is concentrated and collected.

  To illustrate an extreme case, in the case of a user with an extremely high M color image ratio, the secondary transfer residual toner is present in the first Y color station even though the Y color station is not used. It is collected in a concentrated manner. For this reason, when the waste toner container of the first station is full and the process means of each station is made into a cartridge, for example, the cartridge of the first station may be forced to be replaced.

  Even in a single color image forming mode (hereinafter referred to as “monochrome mode”) in which image formation is performed only by a single station (for example, for K color) to form a single color image (monochrome image), the first station Secondary transfer residual toner is collected. Therefore, a user who frequently uses the monochrome mode is forced to replace the cartridge of the first station because the waste toner container of the first station is full even though the color image is not printed. There is a case. In business use and the like, this is more likely to occur because the monochrome mode is generally used more frequently than the color mode.

  According to the invention described in Patent Document 2, the cartridge replacement interval of the collection station can be reduced by increasing the capacity of the waste toner container of the station (hereinafter referred to as “collection station”) where the secondary transfer residual toner is collected. It can be extended.

  However, the ratio of Y, M, and C colors used, and the usage ratio of the color mode and the monochrome mode differ depending on the user. Therefore, if the capacity of the waste toner container is designed assuming the worst possible case, the capacity of the waste toner container becomes very large, leading to an increase in the size of the image forming apparatus.

  Further, according to the invention described in Patent Document 3, the secondary transfer residual toner on the intermediate transfer member can be collected and distributed to different stations. In Patent Document 3, as a method of selecting a collection station, first, a method of changing the collection station to the first, second, third, and fourth stations in order is exemplified.

  However, Patent Document 3 does not specifically describe a sorting method that can be particularly suitably used for an image forming apparatus that simultaneously collects and transfers secondary residual toner at the first station.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of recovering the residual toner on the intermediate transfer member satisfactorily in an in-line image forming apparatus that recovers secondary transfer residual toner by the simultaneous transfer recovery system. That is.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises an image carrier on which a toner image is formed on the surface with toner charged to a regular charge polarity, and a container for containing the toner removed from the image carrier. A plurality of image forming units, an intermediate transfer member on which the toner on the image carrier of the plurality of image forming units is transferred, and a toner on the image carrier of the plurality of image forming units. Primary transfer means for forming an electric field at each primary transfer portion and performing primary transfer onto the intermediate transfer member, and secondary for secondary transfer of toner on the intermediate transfer member onto a transfer material at the secondary transfer portion A transfer unit and a downstream side of the secondary transfer unit in the moving direction of the surface of the intermediate transfer member and an upstream side of the primary transfer unit of the most upstream image forming unit in the moving direction among the plurality of image forming units; Side, the toner on the intermediate transfer member is Anda toner charging means for charging the opposite polarity to the polarity of,
The toner on the intermediate transfer member charged to the reverse polarity is reversely transferred from the intermediate transfer member onto the image carrier of any of the plurality of image forming units and collected in the container of the image forming unit. The reverse transfer can be performed simultaneously with the primary transfer, and a first image forming mode for forming the toner image in all of the plurality of image forming units; A second image forming mode in which the toner image is formed in a specific image forming unit among a plurality of image forming units, and the specific image forming unit is other than the most upstream image forming unit. In an image forming apparatus that is an image forming unit,
The first image forming mode and the second image forming mode are different in the image forming unit that mainly collects toner by the reverse transfer among the plurality of image forming units, and the first image forming mode. In the mode, after the primary transfer at the most upstream image forming unit is completed, at least the toner on the intermediate transfer body charged to the reverse polarity reaching the primary transfer unit of the most upstream image forming unit A part of the image forming apparatus is collected by the reverse transfer in an image forming unit other than the most upstream image forming unit after passing through the primary transfer unit of the most upstream image forming unit. is there.

  According to the present invention, the residual toner on the intermediate transfer member can be recovered well in an in-line image forming apparatus that recovers secondary transfer residual toner by the simultaneous transfer recovery method.

1 is a schematic cross-sectional configuration diagram of an embodiment of an image forming apparatus according to the present invention. FIG. 6 is a block diagram for explaining the operation of the embodiment of the image forming apparatus according to the present invention. FIG. 7 is a timing chart for explaining a secondary transfer residual toner collecting operation according to the present invention. FIG. 6 is a graph illustrating an example of a toner recovery rate. FIG. 7 is a timing chart for explaining a secondary transfer residual toner collecting operation according to the present invention. FIG. 6 is a schematic cross-sectional configuration diagram of another embodiment of an image forming apparatus according to the present invention. FIG. 7 is a schematic cross-sectional configuration diagram illustrating a state in which the intermediate transfer belt is separated from the photosensitive drums of the first to third stations in the image forming apparatus of FIG. 6.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
[Overall Configuration and Operation of Image Forming Apparatus]
(1) Overall Configuration of Image Forming Apparatus First, the overall configuration and operation of an embodiment of an image forming apparatus according to the present invention will be described.

  FIG. 1 shows a schematic cross-sectional configuration of an image forming apparatus 100A of the present embodiment. The image forming apparatus 100A of this embodiment is a laser beam printer that employs an inline method and an intermediate transfer method. As will be described in detail later, the image forming apparatus 100A according to the present exemplary embodiment collects secondary transfer residual toner by a simultaneous transfer recovery method.

  The image forming apparatus 100A includes first, second, third, and fourth stations (image forming stations) 10a, 10b, 10c, and 10d as a plurality of image forming units. The first, second, third, and fourth stations 10a, 10b, 10c, and 10d are arranged in this order from the most upstream side along the moving direction of the surface of the intermediate transfer belt 50 that can move around as an intermediate transfer member. Arranged in a row.

  In this embodiment, the first, second, third and fourth stations 10a, 10b, 10c and 10d are respectively yellow (Y), magenta (M), cyan (C) and black ( K) A station for forming a color toner image.

  In this embodiment, the basic configuration and operation of the first to fourth stations 10a to 10d are substantially the same except that the color of the toner used is different. Accordingly, in the following, when there is no particular need to distinguish, the subscripts a, b, c, and d given to the reference numerals to indicate that they are elements provided for any color will be omitted and will be comprehensively described. To do.

  The station 10 is provided with a cylindrical electrophotographic photosensitive member, that is, a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is driven to rotate in the direction indicated by the arrow R1 (counterclockwise). In this embodiment, the photosensitive drum 1 is an OPC (organic photoconductor) photosensitive drum. In other words, in this embodiment, the photosensitive drum 1 is formed by laminating a plurality of functional organic materials including a carrier generation layer that generates a charge by exposure on a metal cylinder, a charge transport layer that transports the generated charge, and the like. The outermost layer has low electrical conductivity and is almost insulative.

  Around the photosensitive drum 1, a charging roller (photosensitive member charging member) 2 is provided as a charging means for charging the photosensitive drum 1. The charging roller 2 is in contact with the photosensitive drum 1 and uniformly charges the surface of the photosensitive drum 1 because it is not driven to rotate as the photosensitive drum 1 rotates. In this embodiment, the charging polarity of the photosensitive drum 1 is negative. The charging roller 2 is applied with a DC voltage or a voltage obtained by superimposing an AC voltage on the DC voltage. Then, in the rotation direction of the photosensitive drum 1, the photosensitive drum 1 is charged by generating a discharge in a small air gap upstream and downstream of the contact nip portion between the charging roller 2 and the surface of the photosensitive drum 1.

  An exposure device 3 as an exposure unit is arranged so that the surface of the charged photosensitive drum 1 can be exposed. Examples of the exposure apparatus 3 include a scanner unit that scans laser light with a polygon mirror, or an LED array. In this embodiment, the exposure apparatus 3 is configured with a scanner unit, and a scanning beam L that is modulated based on an image signal. Is irradiated onto the photosensitive drum 1. As a result, an electrostatic image (latent image) based on the image signal is formed on the photosensitive drum 1.

  A developing device (developing unit) 4 is provided around the photosensitive drum 1 as developing means for developing the electrostatic image formed on the photosensitive drum 1. The developing device 4 includes a developing container 42 that stores a non-magnetic one-component developer as a developer, that is, toner. The developing container 42 is provided with a developing roller 41 as a developer carrying member and a developer application blade 43 as a developer regulating member.

  A cleaning device (cleaning unit) 6 for cleaning the toner on the photosensitive drum 1 is provided around the photosensitive drum 1. The cleaning device 6 includes a waste toner container 62 that is a container for storing toner removed from the photosensitive drum 1. Further, the waste toner container 62 is provided with a cleaning blade 61 as a cleaning member as a cleaning means for removing toner from the photosensitive drum 1. The cleaning blade 61 contacts the photosensitive drum 1, scrapes off the toner on the photosensitive drum 1, and collects it in the waste toner container 62.

  Further, an intermediate transfer unit (intermediate transfer device) 5 having an intermediate transfer belt 50 formed of an endless belt as an intermediate transfer member is provided so as to face the photosensitive drum 1 of each station 10. The intermediate transfer unit 5 includes a primary transfer roller as a primary transfer member (rotating member) as a primary transfer unit at a position facing the photosensitive drum 1 of each station 10 on the inner peripheral surface side of the intermediate transfer belt 50. 51 is arranged. The primary transfer roller 51 presses the intermediate transfer belt 50 toward the photosensitive drum 1 to form a nip (primary transfer nip) at the primary transfer portion N1 where the intermediate transfer belt 50 and the photosensitive drum 1 are in contact with each other. . Further, on the outer peripheral surface side of the intermediate transfer belt 50, a secondary transfer member (rotating member) as a secondary transfer unit is disposed at a position facing a secondary transfer counter roller 55 which is one of the stretching members of the intermediate transfer belt 50. ) Secondary transfer roller 52 is disposed. The secondary transfer roller 52 is pressed against the intermediate transfer belt 50 and forms a nip (secondary transfer nip) at the secondary transfer portion N2 where the secondary transfer roller 52 and the intermediate transfer belt 50 are in contact with each other. Further, in this embodiment, secondary transfer residual toner charge as a toner charging unit is disposed on the outer peripheral surface side of the intermediate transfer belt 50 at a position facing a tension roller 54 that is one of the stretching members of the intermediate transfer belt 50. A toner charging roller 58 as a member (rotating member) is disposed. The toner charging roller 58 is disposed in contact with the intermediate transfer belt 50. That is, in this embodiment, on the surface of the intermediate transfer belt 50 on the downstream side of the secondary transfer portion N2 and upstream of the primary transfer portion N1a of the first station in the moving direction of the surface of the intermediate transfer belt 50. A toner charging roller 58 that comes into contact is disposed.

  The image forming apparatus 100A further includes a fixing device 7 as a fixing unit that fixes the toner transferred to the transfer material P to the transfer material P, a transfer material supply device 8 for feeding the transfer material P for forming an image, and the like. Have.

  In this embodiment, the photosensitive drum 1, the charging roller 2, the developing device 4 and the cleaning device 6 as process means acting on the photosensitive drum 1 are the main body of the image forming apparatus (hereinafter also simply referred to as “device main body”) A. It is an integrated process cartridge 9 that can be freely attached and detached. The process cartridge is a cartridge in which a photosensitive member and at least one of a charging unit, a developing unit, and a cleaning unit as a processing unit that acts on the photosensitive unit are integrally formed into a cartridge. On the other hand, it shall be removable.

  The charging roller 2 is connected to a charging bias power source 21 that is a voltage supply means (bias output means) to the charging roller 2. The developing roller 41 is connected to a developing bias power supply 44 that is a voltage supply means (bias output means) to the developing roller 41. The primary transfer roller 51 is connected to a primary transfer bias power source 56 that is a voltage supply means (bias output means) to the primary transfer roller 51. The secondary transfer roller 52 is connected to a secondary transfer bias power source 57 that is a voltage supply means (bias output means) to the secondary transfer roller 52. Further, the toner charging roller 58 is connected to a toner charging bias power source 59 which is a voltage supply means (bias output means) to the toner charging roller 58.

  Here, the intermediate transfer belt 50 is supported by three rollers, ie, a driving roller 53, a tension roller 54, and a secondary transfer counter roller 55, as a stretching member, so that appropriate tension is maintained. Yes. By rotating the drive roller 53, the surface of the intermediate transfer belt 50 moves in the forward direction at substantially the same speed with respect to the surface of the photosensitive drum 1.

In this embodiment, as the intermediate transfer belt 50, an endless belt made of PVDF having a thickness of 100 μm and a volume resistivity of 10 ¹¹ Ωcm was used. As the driving roller 53 serving as a tension member, an aluminum cored bar having a diameter of 30 mm and covered with EPDM rubber having a resistance of 10 ⁴ Ω and a thickness of 1.0 mm in which carbon is dispersed as a conductive agent was used. Further, as the tension roller 54 as a tension member, an aluminum metal rod having a diameter of 30 mm was used. The tension applied to the intermediate transfer belt 50 at both ends in the rotation axis direction of the tension roller 54 was 19.6 N on one side and the total pressure 39.2 N.

  The intermediate transfer belt 50 rotates (circulates) in the illustrated arrow R2 direction (clockwise). The primary transfer roller 51 is disposed on the opposite side of the photosensitive drum 1 with the intermediate transfer belt 50 interposed therebetween.

  Further, on the downstream side of each primary transfer roller 51 in the rotation direction (moving direction) of the intermediate transfer belt 50, a static elimination member (static elimination needle) 11 is disposed on the inner peripheral surface side of the intermediate transfer belt 50. Yes.

  The drive roller 53, the tension roller 54, the charge removal member 11, and the secondary transfer counter roller 55 are electrically grounded.

In this embodiment, as the primary transfer roller 51, a nickel-plated steel rod having a diameter of 6 mm is coated with an NBR foamed sponge-like elastic body with a thickness of 4 mm. Resistance of the primary transfer roller 51, in the absolute water content ^{1g / m 3, 4 × 10} 8 Ω during 500V is applied, in the absolute water content 25 g / m ^3, at 500V applied 2.5 × 10 ⁷ Ω Met.

In this embodiment, the secondary transfer roller 52 is a nickel-plated steel rod having a diameter of 6 mm and an NBR foam sponge-like elastic body coated with a thickness of 5 mm. Resistance of the secondary transfer roller 52, in the absolute water content ^{1g / m 3, 4 × 10} 7 Ω at 500V application, in absolute water content 25 g / m ^3, at 500V applied 2.5 × 10 ⁶ Ω Met.

  In this embodiment, the secondary transfer roller 52 is brought into contact with the intermediate transfer belt 50 with a linear pressure of about 5 to 15 g / cm, and the moving direction of the surface of the intermediate transfer belt 50 is. It arrange | positioned so that it might rotate at a substantially equal speed in the forward direction.

In this embodiment, as the toner charging roller 58, a nickel-plated steel rod having a diameter of 6 mm and a solid elastic body in which carbon is dispersed in EPDM rubber are coated with a thickness of 5 mm. Resistance of the toner charging roller 58 is, in absolute water content ^{1g / m 3, 4 × 10} 6 Ω at 100V application, in absolute water content 25 g / m ^3, at the time of 100V is applied 2.5 × 10 ⁶ Ω there were.

  FIG. 2 is a block diagram for explaining the operation of the image forming apparatus 100A of this embodiment.

  The host computer 200 is responsible for issuing a print command and transferring the image data of the print image to the interface board 151 installed in the image forming apparatus 100A. The interface board 151 converts image data from the host computer 200 into exposure data, and issues a print command to the DC controller 150 serving as a control unit. The DC controller 150 operates with power supplied from the low-voltage power supply 152. Upon receiving a print command, the DC controller 150 starts an image forming sequence while monitoring the state of various sensors 154.

  The DC controller 150 is equipped with a CPU, memory, and the like (not shown), and performs operations programmed in advance. Specifically, operations of various driving devices 155 such as a main motor, a developing device 4 and a driving device for the photosensitive drum 1 are controlled. At the same time, the exposure apparatus 3 is controlled so that the amount of exposure light is stabilized. Further, the power control device 156 connected to the fixing device 7 is controlled to perform power control so that the temperature of the fixing device 7 is maintained at a predetermined temperature. Further, the DC controller 150 discriminates between the color mode and the monochrome mode, and controls the operation of the developing and separating device 45d for the black developing device for bringing the black developing device 4d into contact with or separating from the photosensitive drum 1d. Similarly, the DC controller 150 controls the operation of the color developing devices 45a to 45c for bringing the color developing devices 4a to 4c into contact with or separating from the photosensitive drums 1a to 1c. Further, the DC controller 150 controls the high-voltage power supply at a preprogrammed control voltage, control current, and timing while monitoring the applied voltage and current of a plurality of high-voltage power supply units provided in the high-voltage power supply 153. The plurality of high-voltage power supply units provided in the high-voltage power supply 153 includes the above-described charging bias power supply 21, development bias power supply 44, primary transfer bias power supply 56, secondary transfer vice power supply 57, and toner charging bias power supply 59.

  That is, various functional components that control image formation are connected to the high-voltage power supply 153. For example, the charging roller 2 provided in each station 10 is supplied with a high voltage from a high voltage power source 153 (charging bias power source 21), and comes into contact with or close to the photosensitive drum 1 of each station 10 so as to be in contact with the photosensitive drum 1. It plays a role of charging the surface of the film to a uniform potential. This charging potential is controlled by the DC controller 150 controlling the high voltage generated in the high voltage power supply 153 (charging bias power supply 21). Similarly, a high voltage is supplied from the high voltage power source 153 to the developing roller 41, the primary transfer roller 51, the secondary transfer roller 52, and the toner charging roller 58 provided in each station 10, and the applied voltage and applied current are DC. It is controlled by the controller 150.

(2) Image Forming Operation of Image Forming Apparatus Next, the image forming operation of the image forming apparatus 100A of the present embodiment will be described.

(2-1) Color Mode First, an image forming operation in a color mode (multicolor image forming mode) capable of forming a full color image using all of the first to fourth stations 10a to 10d will be described.

  When the image forming apparatus 100A receives a color print command from the standby state, the image forming apparatus 100A starts an image forming operation in a color mode, drives each driving device, starts an exposure device, starts a fixing device, and applies a high voltage application sequence. Start. The photosensitive drum 1, the intermediate transfer belt 50, and the like start to rotate in the directions indicated by the arrows at a predetermined process speed. In the color mode, the developing devices 4a to 4d of the first to fourth stations 10a to 10d are in contact with the photosensitive drums 1a to 1d, respectively.

  The photosensitive drum 1 is uniformly charged to a predetermined potential (−500 V in this embodiment) having a predetermined polarity (negative polarity in this embodiment) by supplying a bias to the charging roller 2 from the charging bias power supply 21. Is done. Subsequently, an electrostatic image (latent image) according to the image information is formed on the surface of the charged photosensitive drum 1 by the scanning beam L from the exposure device 3.

  The toner in the developing device 4 is charged to a predetermined polarity (negative polarity in this embodiment) by the developer application blade 43 and applied to the developing roller 41. The developing roller 41 is supplied with a bias having a predetermined potential (−300 V in this embodiment) having a predetermined polarity (negative polarity in this embodiment) from a developing bias power supply 44. As a result, when the photosensitive drum 1 rotates and the electrostatic image formed on the photosensitive drum 1 reaches a portion (developing portion) facing the developing roller 41, the electrostatic image is visualized by the negative polarity toner, A toner image of a color corresponding to each station is formed on the drum 1.

  As described above, in this embodiment, the developing device 4 applies the toner charged to the same polarity as the charged polarity of the photosensitive member to the portion (exposure portion, image portion) where the charge is attenuated by the exposure of the surface of the charged photosensitive member. The electrostatic image is developed by the reversal development method to be attached.

  In the color mode, first, a toner image of the first color (Y color in this embodiment) is formed on the photosensitive drum 1a of the first station 10a. The second to fourth stations 10b, 10c, and 10d operate in the same manner, and toner images of M, C, and K colors are formed on the photosensitive drums 1b, 1c, and 1d, respectively. At this time, an electrostatic image is formed on each of the photosensitive drums 1 a to 1 d by the exposure device 3 while delaying the writing signal from the DC controller 150 at a certain timing for each color according to the distance between the primary transfer positions. .

  Next, the primary transfer rollers 51a to 51d of the stations 10a to 10d are supplied with the reverse polarity (that is, positive polarity in the present embodiment) from the normal charging polarity of the toner from the primary transfer bias power sources 56a to 56d. A DC bias is applied.

  Through the above steps, toner images of each color Y, M, C, and K are sequentially superimposed and transferred (primary transfer) to the intermediate transfer belt 50, and a multiple image is formed on the intermediate transfer belt 50.

  The toner remaining on the photosensitive drum 1 after the primary transfer process, that is, the primary transfer residual toner is removed and collected by the cleaning device 6.

  Thereafter, the transfer material P is supplied to the secondary transfer portion N2 by the transfer material supply device 8 in accordance with the electrostatic image formation by exposure. That is, the transfer material P loaded on the transfer material cassette 81 is picked up by the transfer material supply roller 82 and conveyed to the registration roller 83 by a conveyance roller (not shown). Next, in synchronization with the toner image on the intermediate transfer belt 50, the transfer material P is a contact portion (secondary transfer portion) N2 formed by the registration roller 83 between the intermediate transfer belt 50 and the secondary transfer roller 52. It is conveyed to.

  A bias having a polarity opposite to the normal charging polarity of the toner (that is, positive polarity in this embodiment) is applied to the secondary transfer roller 52 by a secondary transfer bias power source 57. As a result, the four color multiple toner images carried on the intermediate transfer belt 50 are collectively transferred (secondary transfer) onto the transfer material P.

  On the other hand, the toner remaining on the intermediate transfer belt 50 after the secondary transfer process, that is, the secondary transfer residual toner, is charged by a toner charging roller 58 disposed in contact with the intermediate transfer belt 50. A toner charging bias power source 59 is connected to the toner charging roller 58, and a voltage obtained by superimposing a DC voltage of + 500V on an AC voltage having a frequency of 1 kHz and a peak-to-peak voltage of 1800V is applied.

  Toner having a normal charging polarity (negative polarity in this embodiment) before the secondary transfer process is usually transferred onto the transfer material P in the secondary transfer process. Therefore, the secondary transfer residual toner is often charged to a polarity opposite to the normal charging polarity (that is, positive polarity in this embodiment), that is, the polarity is reversed. However, the polarity of all secondary transfer residual toners is not reversed, and some toners are neutralized and have no charge, and some toners maintain negative polarity.

  Between the toner charging roller 58 and the intermediate transfer belt 50, discharge occurs in the minute gap portions on the upstream side and the downstream side of the contact nip portion. There is an effect of charging to the side opposite to the charging polarity (that is, positive polarity in this embodiment). In this embodiment, typically, the toner charging roller 58 charges substantially all of the secondary transfer residual toner on the intermediate transfer belt 50 to a polarity opposite to the normal charging polarity.

  The secondary transfer residual toner subjected to the charging process by the toner charging roller 58 moves to the station 10 while being on the intermediate transfer belt 50, is reversely transferred to the photosensitive drum 1, and is collected in the waste toner container 62 of the station 10. Is done. The secondary transfer residual toner collecting operation will be described in detail later.

  The transfer material P after the completion of the secondary transfer process is conveyed to the fixing device 7, undergoes a toner image fixing process, and is discharged outside the image forming apparatus 100 </ b> A as an image formed product (print, copy). When it is detected by various sensors (not shown) that the image formed material has been normally discharged to the outside of the image forming apparatus 100A, the image forming apparatus 100A stops the operation of each driving device and returns to the standby state.

(2-2) Monochrome Mode Next, an image forming operation in a monochrome mode (monochrome image forming mode) in which a monochrome image can be formed using a specific single station will be described.

  In the present embodiment, the image forming apparatus 100A has a monochrome mode in which a monochrome image can be formed as a monochrome image using only the fourth K color station 10d.

  The basic image forming operation in the monochrome mode is the same as that in the color mode described above except that there is a station that does not form a toner image. However, as will be described in detail later, the secondary transfer residual toner collecting operation is different between the color mode and the monochrome mode.

  More specifically, upon receiving a monochrome print command from the standby state, the image forming apparatus 100A starts an image forming operation in the monochrome mode, drives each driving device, starts the exposure device, and starts the fixing device. Start the high voltage application sequence.

  In the present embodiment, in the monochrome mode, the developing devices 4a to 4c of the first to third stations 10a to 10c, which are stations for the colors Y, M, and C, are kept apart from the photosensitive drums 1a to 1c, respectively. Be drunk. In the monochrome mode, the developing device 4d is brought into contact with the photosensitive drum 1d only in the fourth station 10d which is a K color station. As a result, only in the fourth station 10d, the electrostatic image drawn on the photosensitive drum 1d by the exposure device 3d becomes visible as a toner image. However, in this embodiment, the photosensitive drum rotates at all four stations.

[Recovery of secondary transfer residual toner]
(1) Outline of Secondary Transfer Residual Toner Collection Operation Next, the secondary transfer residual toner collection operation will be described.

  In general, the object of the present embodiment is to recover the residual toner on the intermediate transfer member satisfactorily in an in-line image forming apparatus that recovers secondary transfer residual toner by the simultaneous transfer recovery method. One of the more detailed purposes of this embodiment is to collect residual toner by more efficiently distributing it to a plurality of waste toner containers in an in-line type image forming apparatus that collects secondary transfer residual toner by the simultaneous transfer recovery method. It is to be. Also, one of the more detailed purposes of this embodiment is that, in the simultaneous transfer recovery type and in-line type image forming apparatus, each station is used regardless of the ratio of use of each station and the use ratio of color mode and monochrome mode. It is possible to economically use the waste toner container.

  In this embodiment, the image forming apparatus 100A reversely transfers the toner on the intermediate transfer belt 50 charged to the reverse polarity onto the photosensitive drum 1 of the plurality of stations 10 from the intermediate transfer belt 50. Ten waste toner containers are collected. Here, the reverse transfer can be performed simultaneously with the primary transfer. In addition, a color mode (first image forming mode) in which toner images are formed in all of the plurality of stations 10a to 10d, and a monochrome mode (second image) in which toner images are formed in a single specific station 10d. Forming mode). Here, the specific station 10 d that forms the toner image in the monochrome mode is a station other than the most upstream station 10 a in the moving direction of the surface of the intermediate transfer belt 50.

  In this embodiment, the station that mainly collects toner by the reverse transfer among the plurality of stations 10 differs between the color mode and the monochrome mode. In the color mode, at least a part of the toner on the intermediate transfer belt 50 charged to a reverse polarity reaching the primary transfer portion N1a of the most upstream station 10a after the primary transfer at the most upstream station 10a is completed. Is recovered as follows. That is, after passing through the primary transfer portion N1a of the most upstream station 10a, it is recovered by the reverse transfer at a station other than the most upstream station 10a.

(2) Details of Secondary Transfer Residual Toner Collection Operation (2-1) Secondary Transfer Residual Toner Collection Operation in Color Mode First, the secondary transfer residual toner collection operation in the color mode will be described.

  FIG. 3 is a timing chart for specifically explaining the operation in the color mode. The horizontal axis in FIG. 3 is time. In FIG. Mst. Cst. Kst. These lines represent the operations (specifically, bias applied to the primary transfer roller) of the primary transfer portions N1a to N1d of the first to fourth stations 10a to 10d, respectively. Also, the 2ndXfer line in FIG. 3 represents the operation of the secondary transfer portion N2 (specifically, the bias applied to the secondary transfer roller). FIG. 3 shows an example in which six images are continuously printed by one print command (one job).

  The output of the bias applied to the primary transfer roller 51a of the first station 10a is turned on sufficiently before the toner image reaches the primary transfer portion N1a (preferably before one turn of the photosensitive drum 1). . At this time, the bias applied to the primary transfer roller 51a is set to a voltage level during image formation, that is, a normal primary transfer bias (primary transfer voltage) + 500V. Similarly, also in the second to fourth stations 10b to 10d, the output of the bias applied sequentially to the primary transfer rollers 51b to 51d is turned on. At this time, the bias applied to the primary transfer rollers 51b to 51d is set to +500 V, which is a normal primary transfer bias.

  Thereafter, the toner image formed by the developing unit of the first station 10 a is primarily transferred to the intermediate transfer belt 50. Y1 in FIG. 3 represents a period during which the first toner image formed at the first station 10a is primarily transferred from the photosensitive drum 1a to the intermediate transfer belt 50. Y2, Y3, Y4, Y5, and Y6 represent periods during which the second to sixth toner images formed at the first station 10a are primarily transferred. The same applies to M1 to M6 for the second station 10b, C1 to C6 for the third station 10c, and K1 to K6 for the fourth station 10d, and the first English letter indicates the color of the station, The second number indicates how many.

  Also, the bias applied to the secondary transfer roller 52 indicated by the 2ndXfer line alternately changes the output between the Lo level and the Hi level. Lo indicates a state in which a relatively low bias (+1000 V in this embodiment) is output when the transfer material P is not in the secondary transfer portion N2. Hi indicates a state in which a relatively high bias (+1500 V in this embodiment) is output when the transfer material P is in the secondary transfer portion N2. In FIG. 3, page 1 to page 6 represent periods during which secondary transfer of the first to sixth toner images to the transfer material P is performed.

  Time t1 is the time at which primary transfer of the first toner image on the intermediate transfer belt 50 is started at the primary transfer portion N1a of the first station 10a. Between time t1 and time t2, the leading edge of the toner image moves on the intermediate transfer belt 50 to the primary transfer portion N1b of the second station 10b. At time t2, the M toner image is superimposed on the Y toner image, and primary transfer starts.

  Similarly, at times t3 and t4, the leading edge of the first toner image formed on the intermediate transfer belt 50 reaches the primary transfer portions N1c and N1d of the third and fourth stations 10c and 10d, respectively. It's time.

  t5 is the time when the toner image on the intermediate transfer belt 50 reaches the secondary transfer portion N2 and the secondary transfer of the toner image onto the transfer material P is started.

  Time t6 is the time when the secondary transfer residual toner of the first toner image reaches the primary transfer portion N1a of the first station 10a after being charged by the toner charging roller 58. That is, between the time t1 and the time t6, the intermediate transfer belt 50 rotates once. In other words, the time from time t1 to time t6 is the time required for the primary transferred toner image to circulate as secondary transfer residual toner and return to the primary transfer portion N1 of the same station. .

  WY1 in FIG. 3 indicates a period during which the secondary transfer residual toner of the first toner image passes through the primary transfer portion N1a of the first station 10a. WY2, WY3, WY4, WY5, and WY6 indicate periods during which the secondary transfer residual toner of the second to sixth toner images passes through the primary transfer portion N1a of the first station 10a. The same applies to the second station 10b and the third station 10c. The first letter W is the secondary transfer residual toner, the second letter is the station color, and the third letter is the number. Whether the toner image is the secondary transfer residual toner of the first toner image is shown.

  While the secondary transfer residual toner passes through the primary transfer portion N1, a bias having the same polarity (positive polarity in this embodiment) as that of the secondary transfer residual toner reversely charged is applied to the primary transfer portion N1. Then, the secondary transfer residual toner is reversely transferred to the photosensitive drum 1 of the station 10.

  Here, for example, during the period Y3 in FIG. 3, the secondary transfer charged to the opposite polarity to the normal polarity while the toner image formed on the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 50. The remaining toner is moved to the primary transfer portion N1. At this time, the secondary transfer residual toner on the intermediate transfer belt 50 and charged to a polarity opposite to the normal polarity and the toner on the photosensitive drum 1 and charged to the normal polarity to be primary transferred are In the nip portion between the photosensitive drum 1 and the intermediate transfer belt 50, there is almost no electrical neutralization. For this reason, for example, the toner on the photosensitive drum 1a charged to the normal polarity in the period Y3 moves to the intermediate transfer belt 50, and the toner on the intermediate transfer belt 50 charged in the reverse polarity in the period WY1 to the photosensitive drum 1a. Moving. In this way, the toner to be primarily transferred on the photosensitive drum 1 and the secondary transfer residual toner on the intermediate transfer belt 50 move independently of each other, and simultaneous transfer recovery is performed. The same applies to the period in which the other primary transfer process and the secondary transfer residual toner collecting process overlap, that is, the period Y4 and the period WY2, the period Y5 and the period WY3, and the period Y6 and the period WY4.

  In this embodiment, the primary transfer roller of the first station 10a at time t7 after the secondary transfer residual toner of the fourth toner image passes through the primary transfer portion N1a of the first station 10a. The bias applied to 51a is switched to -500V. That is, at time t7 immediately after the period WY4 has elapsed, the bias applied to the primary transfer roller 51a of the first station 10a is switched. In this embodiment, at time t7, the bias applied to the primary transfer roller 51a of the first station 10a is a bias having the same polarity as the normal charging polarity of the toner from a bias having a polarity opposite to the normal polarity of the toner. Can be switched to.

  The secondary transfer residual toner in each period of WY1, WY2, WY3, and WY4 is reversely transferred to the photosensitive drum 1a by the primary transfer portion N1a of the first station 10a, and collected in the waste toner container 62a of the first station 10a. Is done.

  The secondary transfer residual toner of the fifth and sixth toner images (that is, each period of WY5 and WY6) is hardly collected in the first station 10a, and the primary transfer portion of the first station 10a. It passes through N1a and is carried to the primary transfer portion N1b of the second station 10b.

  During the period WM5 during which the secondary transfer residual toner of the fifth toner image passes through the primary transfer portion N1b of the second station 10b, the primary transfer roller 51b of the second station 10b has a normal primary transfer roller 51b. A transfer bias (primary transfer voltage) is applied. Therefore, almost the entire amount of secondary transfer residual toner in the period WM5 is collected by the second station 10b.

  Next, the secondary transfer residual toner of the fifth toner image is applied to the primary transfer roller 51b of the second station 10b at time t9 after passing through the primary transfer portion N1b of the second station 10b. The bias is switched to -500V. That is, at time t9 immediately after the period WM5 has elapsed, the bias applied to the primary transfer roller 51b of the second station 10b is switched. In this embodiment, at time t9, the bias applied to the primary transfer roller 51b of the second station 10b is a bias having the same polarity as the normal charging polarity of the toner from a bias having a polarity opposite to the normal polarity of the toner. Can be switched to.

  The secondary transfer residual toner of the sixth toner image (that is, the period WM6) is hardly collected at the second station 10b, but passes through the primary transfer portion N1b of the second station 10b and passes through the third transfer portion N1b. It is carried to the primary transfer portion N1c of the station 10c.

  In the period WC6 during which the secondary transfer residual toner of the sixth toner image passes through the primary transfer portion N1c of the third station 10c, the primary transfer roller 51c of the third station 10c A bias for primary transfer is applied. Therefore, almost the entire amount of secondary transfer residual toner in the period WC6 is collected by the third station 10c.

  The bias applied to the primary transfer rollers 51a to 51d of the first to fourth stations 10a to 10d is turned off at t11, t12, t13, and t8, respectively. That is, in the first station 10a, the bias applied to the primary transfer roller 51a is switched at time t7 as described above, and then turned off at time t11 immediately after the period WY6 has elapsed. In the second station 10b, the bias applied to the primary transfer roller 51b is switched at time t9 as described above, and then turned off at time t12 immediately after the period WM6 has elapsed. In the third station 10c, the bias applied to the primary transfer roller 51c is not switched and is turned off at time t13 immediately after the period WC6 has elapsed. On the other hand, in this embodiment, in the color mode, substantially all secondary transfer residual toner is collected at the first to third stations 10a to 10c. For this reason, in the fourth station 10d, the bias applied to the primary transfer roller 51d is immediately after the period K6 in which the sixth K-color toner image is primarily transferred from the photosensitive drum 1d to the intermediate transfer belt 50. It is turned off at time t8.

  FIG. 4 shows the relationship between the applied voltage and the recovery rate (recovery ratio) in the primary transfer portion. The horizontal axis of FIG. 4 shows the voltage value of the bias applied to the primary transfer roller 51a of the first station 10a. The vertical axis in FIG. 4 represents the recovery rate as a percentage.

The solid line in FIG. 4 shows the recovery rate of the first station 10a when the voltage applied to the primary transfer roller 51a of the first station 10a is changed. Here, the recovery rate of the first station 10a is defined as follows. That is, in the moving direction of the surface of the intermediate transfer belt 50, the weight of the secondary transfer residual toner on the intermediate transfer belt 50 in front of the primary transfer portion N1a of the first station 10a is α. Further, let β be the weight of the secondary transfer residual toner transferred to the photosensitive drum 1a of the first station 10a after the portion on the intermediate transfer belt 50 passes through the primary transfer portion N1a of the first station 10a. At this time, the recovery rate of the first station 10a is expressed by the following equation:
(Β / α) × 100
It is a weight ratio represented by.

The broken line in FIG. 4 shows the recovery rate of the second station 10b when the voltage applied to the primary transfer roller 51a of the first station 10a is changed. Here, the recovery rate of the second station is defined as follows. That is, as described above, the weight of the secondary transfer residual toner on the intermediate transfer belt 50 in front of the primary transfer portion N1a of the first station 10a in the moving direction of the surface of the intermediate transfer belt 50 is α. Further, the weight of the secondary transfer residual toner transferred to the photosensitive drum 1b of the second station 10b after the portion on the intermediate transfer belt 50 passes through the primary transfer portion N1b of the second station 10b is represented by γ. At this time, the recovery rate of the second station 10b is expressed by the following equation:
(Γ / α) × 100
It is a weight ratio represented by.

  In this experiment, the surface potentials (charging potentials) of the photosensitive drums 1a and 1b of the first and second stations 10a and 10b were set to -500V and constant. The bias applied to the primary transfer roller 51b of the second station 10b was fixed at + 500V. Further, a voltage obtained by superimposing a DC voltage of +500 V on an AC voltage having a frequency of 1 kHz and a peak-to-peak voltage of 1800 V was applied to the toner charging roller 58.

  When the bias applied to the primary transfer roller 51a of the first station 10a is −500 V or less (for example, −800 V), the secondary transfer residual toner is not collected in the first station 10a. Then, almost all of the secondary transfer residual toner passes through the primary transfer portion N1a of the first station 10a. That is, if the bias applied to the primary transfer roller 51a is −500 V or a negative polarity side bias, the secondary transfer residual toner is not collected at the first station 10a. Then, almost all of the secondary transfer residual toner passes through the primary transfer portion N1a of the first station 10a.

  When the bias applied to the primary transfer roller 51a is higher than −500 V, which is the surface potential of the photosensitive drum 1a, positive toner is transferred from the intermediate transfer belt 50 between the primary transfer roller 51a and the photosensitive drum 1a. An electric field is generated in a direction to be moved on the photosensitive drum 1a. That is, if the bias applied to the primary transfer roller 51a is a positive polarity bias from −500 V, positive toner is transferred from the intermediate transfer belt 50 between the primary transfer member 51a and the photosensitive drum 1a. An electric field is generated in a direction to be moved on the photosensitive drum 1a. This electric field is a positive electric field from the primary transfer roller 51a to the photosensitive drum 1a. Due to this electric field, reverse transfer of the secondary transfer residual toner having the positive polarity of the polarity starts reverse transfer from the intermediate transfer belt 50 to the photosensitive drum 1a, and recovery at the first station 10a starts.

  If the bias applied to the primary transfer roller 51a of the first station 10a is -300V to -100V, some secondary transfer residual toner passes through the primary transfer portion N1a of the first station 10a. .

  Further, the sum of the recovery rate of the first station 10a and the recovery rate of the second station 10b is almost 100% regardless of the bias applied to the primary transfer roller 51a of the first station 10a. Therefore, regardless of the bias applied to the primary transfer roller 51a of the first station 10a, for example, the bias applied to the primary transfer roller 51b of the second station 10b is set to + 500V. As a result, the secondary transfer residual toner that has passed through the primary transfer portion N1a of the first station 10a is collected almost entirely by the second station 10b.

  As described above, preferably, the bias applied to the primary transfer roller is equal to the surface potential of the photosensitive drum or the potential on the regular charging polarity side of the toner with respect to the surface potential of the photosensitive drum. The secondary transfer residual toner can be prevented from being collected. In other words, the bias applied to the primary transfer roller is made equal to the surface potential of the photosensitive drum, or the voltage difference between the surface potential of the photosensitive drum and the bias applied to the primary transfer roller is made the same polarity as the toner. Thus, recovery of the secondary transfer residual toner at the station can be suppressed. Thereby, it is possible to suppress the secondary transfer residual toner from being concentrated and collected at a specific station. For this reason, it is possible to alleviate the inconvenience due to frequent replacement, which tends to be noticeable with the cartridge of the first station 10a.

  Further, for example, consider a case where the bias applied to the primary transfer roller 51a is set to -200 V and the recovery rate of the first station 10a is set to be around 50%. In this case, the ratio of the amount of secondary transfer residual toner to be collected and the amount of toner remaining after transfer includes the charge amount of the secondary transfer residual toner, the temperature and humidity of the surrounding environment where the image forming apparatus is installed, and the use of the process cartridge. It tends to change due to many factors such as history. That is, if the recovery rate of each station is adjusted by holding different biases applied to the primary transfer roller 51 for each station, the recovery rate is likely to change depending on the environment.

  On the other hand, in the vicinity of the recovery rate of 0% and near 100%, the influence of the fluctuation factors as described above on the recovery rate is small. As described above, the bias applied to the primary transfer roller is preferably equal to the surface potential of the photosensitive drum or on the normal charging polarity side of the toner with respect to the surface potential of the photosensitive drum. In other words, the voltage difference between the surface potential of the photosensitive drum and the bias applied to the primary transfer roller is substantially zero or the same polarity as the toner. As a result, the intermediate transfer region where the reverse transfer amount becomes unstable can be removed, and the secondary transfer residual toner can be passed relatively stably.

  In order to stabilize the collection rate, it is more preferable to switch the bias condition for stably collecting almost the entire amount and the bias condition for allowing almost the entire amount of secondary transfer residual toner to pass stably over time. That is, by adjusting the collection amount by controlling the ratio between the collection time and the passage time, it is possible to control the passage and collection ratio more accurately.

  In this embodiment, the secondary transfer residual toner for almost four sheets of the output image is collected in the first station 10a, one sheet is collected in the second station 10b, and one sheet is collected in the third station 10c. The And the recovery rate does not change substantially due to the fluctuation factors such as the surrounding environment as described above.

  Note that if the bias applied to the primary transfer roller is changed during the primary transfer process of the toner image, the transfer efficiency of the toner from the photosensitive drum to the intermediate transfer belt fluctuates, resulting in density unevenness or density step on the image. Or, it is not preferable because it causes a horizontal streak-like image defect. Further, if the bias applied to the primary transfer roller 51a is not changed until all the secondary transfer residual toner passes through the primary transfer portion N1a of the first station 10a, the secondary transfer residual is biased toward the first station 10a. The toner is collected. Further, when the secondary transfer residual toner passes without being collected in any of the four stations, it circulates on the intermediate transfer belt and reaches the secondary transfer roller. Therefore, the secondary transfer roller is undesirably contaminated with the secondary transfer residual toner in contact therewith, which may cause the back surface of the transfer material P to become dirty at the next printing.

  Therefore, in this embodiment, when the primary transfer of the toner image is not performed in the first station 10a and before all the secondary transfer residual toner passes through the primary transfer portion N1a of the first station 10a. The bias applied to the primary transfer roller 51a is changed. As described above, at this time, the bias applied to the primary transfer roller 51a of the first station 10a is changed in the same polarity direction as the normal charging polarity of the toner from the normal primary transfer bias (in this embodiment, Change to the negative side (that is, the direction to decrease the voltage). Further, the secondary transfer residual toner that has passed through the primary transfer portion N1a of the first station 10a is not collected on the intermediate transfer belt 50, but is collected at any station thereafter. In the present embodiment, collection is performed at the second and third stations 10b and 10c, respectively. Thereby, it is possible to suppress the collection of the secondary transfer residual toner at the first station 10a while maintaining the image quality. Therefore, it is possible to prevent the secondary transfer residual toner from being concentrated and collected at a specific station, and to mitigate the inconvenience due to frequent replacement, which tends to be noticeable with the cartridge of the first station 10a.

(2-2) Secondary Transfer Residual Toner Collection Operation in Monochrome Mode FIG. 5 is a timing chart for specifically explaining the operation in the monochrome mode. FIG. 5 shows the timing when six images are continuously printed in monochrome mode by one print command (one job). The reference numerals in FIG. 5 are basically the same as the reference numerals in FIG. Meaningful (however, times t1 to t10 indicate different times).

  In the monochrome mode, only the fourth station 10d, which is a K color station, performs image formation. In the monochrome mode, it is not necessary to superimpose toner images, and the image formation of the fourth station 10d is started without waiting until the toner image of the first station 10a reaches the fourth station 10d. For this reason, it is possible to shorten the time required to print the first sheet (the time from when the print signal is received until the transfer material P is discharged), and there is an advantage that the productivity of the image can be improved. In particular, this effect is greatest when the station that performs image formation in the monochrome mode (the station for K color in this embodiment) is the most downstream station in the movement direction of the surface of the intermediate transfer belt 50.

  At time t1, application of a bias of +500 V to the primary transfer roller 51d is started at the fourth station 10d. At the same time, in the first to third stations 10a to 10c, application of a bias of −500 V to the primary transfer rollers 51a to 51c is started.

  Thereafter, the first toner image reaches the primary transfer portion N1d on the photosensitive drum 1d of the fourth station 10d, and is primarily transferred onto the intermediate transfer belt 50 in the period K1. Similarly, in each period from K2 to K6, the second to sixth toner images are primarily transferred to the intermediate transfer belt 50 at the primary transfer portion N1d of the fourth station 10d.

  In the period WY1 during which the secondary transfer residual toner of the first toner image passes through the primary transfer portion N1a of the first station 10a, the bias applied to the primary transfer roller 51a of the first station 10a is −500V. It has become. For this reason, the secondary transfer residual toner is not collected at the first station 10a and almost the entire amount passes through the primary transfer portion N1a of the first station 10a. Similarly, in each period of WY2 to WY6, almost all of the secondary transfer residual toner passes through the primary transfer portion N1a of the first station 10a.

  A bias of −500 V is also applied to the primary transfer rollers 51b and 51c of the second and third stations 10b and 10c. For this reason, the secondary transfer residual toner of the six toner images hardly reaches the first to third stations 10a to 10d and reaches the primary transfer portion N1d of the fourth station 10d.

  On the other hand, in the fourth station 10d, the secondary transfer residual toner in each period WK1 to WK4 is transferred to the photosensitive drum 1d simultaneously with the primary transfer (periods K3 to K6) of the third to sixth toner images. Reverse transcription. In each period of WK5 and WK6, the bias applied to the primary transfer roller 51d of the fourth station 10d is maintained at +500 V, which is the same as the normal primary transfer bias, so that the secondary transfer residual toner is The image is reversely transferred to the photosensitive drum 1d. Thereby, substantially all of the secondary transfer residual toner of the six toner images is collected in the waste toner container 62d of the fourth station 10d.

  The bias applied to the primary transfer rollers 51a to 51d of the first to fourth stations 10a to 10d is turned off at t7, t8, t9, and t10, respectively. That is, in the first station 10a, the bias applied to the primary transfer roller 51a is turned off at time t7 immediately after the period WY6 has elapsed. In the second station 10b, the bias applied to the primary transfer roller 51b is turned off at time t8 immediately after the period WM6 has elapsed. In the third station 10c, the bias applied to the primary transfer roller 51c is turned off at time t9 immediately after the period WC6 has elapsed. In the fourth station 10d, the bias applied to the primary transfer roller 51d is turned off at time t10 immediately after the period WK6 has elapsed.

  Thus, in this embodiment, in the color mode, the following electric fields are generated by switching between the photosensitive drum 1 and the intermediate transfer belt 50 in the first and second stations 10a and 10b. First, the first polarity toner, which is the normal charging polarity of the toner, is moved from the photosensitive drum 1 to the intermediate transfer belt 50, and the second polarity is opposite to the first polarity. This is an electric field (first electric field) in a direction in which the toner moves from the intermediate transfer belt 50 to the photosensitive drum 1. Second, the toner having the first polarity is moved from the intermediate transfer belt 50 onto the photosensitive drum 1, and the toner having the second polarity opposite to the first polarity is transferred from the photosensitive drum 1. This is the electric field (second electric field) in the direction of movement on the intermediate transfer belt 50. The first electric field and the second electric field are opposite electric fields. The first electric field is an electric field in the same direction as at the time of primary transfer, and is an electric field in a direction in which toner charged to a polarity opposite to the normal charging polarity is reversely transferred to the photosensitive drum at the primary transfer portion. The second electric field is an electric field in a direction in which the toner charged to a polarity opposite to the normal charging polarity passes through the primary transfer portion. In particular, in this embodiment, the first electric field and the second electric field are switched by changing the polarity of the bias output from the primary transfer bias power source 56 to the primary transfer roller 51. On the other hand, in the color mode, the first electric field is generated in the third and fourth stations 10c and 10d.

  In the monochrome mode, the second electric field is generated in the first to third stations 10a to 10c. In particular, in this embodiment, this second electric field is generated by changing the polarity of the bias output from the primary transfer bias power source 56 to the primary transfer roller 51 from the polarity at the time of primary transfer in the color mode. Generate. On the other hand, in the monochrome mode, the first station generates the first electric field.

  In other words, in this embodiment, at least the primary transfer bias power sources 56a to 56c of the first to third stations 10a to 10c can generate the first electric field and the second electric field. In particular, in this embodiment, the primary transfer vice power sources 56a to 56c of at least the first to third stations 10a to 10c include switching means for switching the polarity of the bias output to the primary transfer rollers 51a to 51c. Have. In other words, in this embodiment, at least the primary transfer vice power sources 56a to 56c have the first bias output unit that outputs a bias having the same polarity as the normal charging polarity of the toner and the normal charging polarity of the toner. And a second bias output unit that outputs a bias of reverse polarity.

  Here, since the surface of the photosensitive drum is insulative, the potential is likely to fluctuate in an unstable manner upon receiving the charge of the member or toner that comes into contact. Therefore, if the photosensitive drum is in contact with the intermediate transfer belt with the charging bias and the exposure device turned off at a station where image formation is not performed, reverse transfer of toner from the intermediate transfer belt to the photosensitive drum occurs in an unstable manner. easy.

  By the way, when the photosensitive drum and the intermediate transfer belt are in contact with each other, the secondary transfer residual toner can be passed between the photosensitive drum and the intermediate transfer belt at the contact portion without being reversely transferred to the photosensitive drum. It is preferable to actively provide the following electric field. That is, an electric field in a direction in which toner charged to a polarity opposite to the normal charging polarity is moved from the surface of the photosensitive drum toward the intermediate transfer belt. In the present exemplary embodiment, it is preferable that the surface potential of the photosensitive drum be on the side opposite to the normal charging polarity of the toner with respect to the bias applied to the primary transfer roller. In other words, in this embodiment, it is preferable to make the difference between the surface potential of the photosensitive drum and the bias applied to the primary transfer roller positive.

  In order to stably maintain such an electric field, it is preferable to stably control the potential of the photosensitive drum. Specifically, the potential of the photosensitive drum can be stabilized by applying a charging voltage to the charging roller in contact with the photosensitive drum and / or exposing the photosensitive drum.

  As described above, preferably, even in a station that is not involved in image formation in the monochrome mode, the photosensitive drum is exposed by applying a charging voltage to the photosensitive drum, or in addition to or instead of the charging voltage. Accordingly, the secondary transfer residual toner can be stably passed through the primary transfer portion of the station without collecting the secondary transfer residual toner in the station.

(2-3) Effects of this embodiment As described above, according to this embodiment, the residual toner on the intermediate transfer member can be satisfactorily removed in the inline type image forming apparatus that collects the secondary transfer residual toner by the simultaneous transfer recovery method. It can be recovered. In particular, according to this embodiment, in an in-line image forming apparatus that collects secondary transfer residual toner by the simultaneous transfer recovery method, the residual toner can be more efficiently distributed to a plurality of waste toner containers. . Further, according to the present embodiment, in the simultaneous transfer recovery type and in-line type image forming apparatus, the economy of the waste toner container of each station irrespective of the use ratio of each station and the use ratio of the color mode and the monochrome mode. Can be used.

  That is, in the conventional image forming apparatus, for example, when continuous image formation is performed, a positive voltage is continuously applied to the primary transfer roller of the first station during the primary transfer process. When the secondary transfer residual toner subjected to the charging process reaches the primary transfer portion of the first station, the toner image on the photosensitive drum moves to the intermediate transfer belt, and the secondary transfer residual toner on the intermediate transfer belt is photosensitive. Reverse transfer to drum. The reversely transferred secondary transfer residual toner is stored in a waste toner container of the first station. At this time, in the color mode, almost all secondary transfer residual toners of Y, M, C, and K are collected in the waste toner container of the first station. Similarly, in the monochrome mode, almost all K-color secondary transfer residual toner is collected in the waste toner container of the first station. For this reason, if the monochrome mode is frequently used, the waste toner container of the first station becomes full even though the color image is not printed, and the cartridge of the first station, for example, the yellow cartridge is replaced. There was a case to be forced.

  On the other hand, according to the present embodiment, the stations for mainly collecting the secondary transfer residual toner are different in the color mode and the monochrome mode. As a result, the secondary transfer residual toner is prevented from being concentrated and collected in the first station, and the cartridge can be used economically.

  According to this embodiment, in the monochrome mode, the secondary transfer residual toner is collected mainly at a station (a fourth station for K color in this embodiment) that forms a toner image in the monochrome mode. Thereby, in the monochrome mode, it is possible to suppress the secondary transfer residual toner from being collected in the station that forms the toner image only in the color mode, and it is possible to economically use the cartridge that is used only in the color mode. In particular, in the monochrome mode, the secondary transfer residual toner is prevented from being concentrated and collected in the first station that forms the toner image only in the color mode, and the cartridge of the first station used only in the color mode is suppressed. Economical use is possible.

  By the way, when the toner image primarily transferred onto the intermediate transfer belt passes through the primary transfer portion of the station downstream in the rotation direction of the intermediate transfer belt, the intermediate transfer belt or the toner image and the photosensitive drum are discharged. In some cases, toner having a reversed charge polarity may be generated. Since a part of the toner is reversely transferred to the photosensitive drum, the toner amount of the toner image on the intermediate transfer belt may decrease as it proceeds to a downstream station. This phenomenon is called retransfer.

  The retransfer phenomenon can be caused not only by discharge but also by mechanical adhesion between the toner and the photosensitive drum. In the first station, since there is no station on the upstream side, the retransferred toner is hardly collected. However, in the fourth station, the retransferred toner is collected from the toner images formed in the first, second, and third stations. In other words, the station on the downstream side tends to increase the amount of collected retransferred toner.

  As described above, as a phenomenon peculiar to the in-line image forming apparatus for simultaneously transferring and collecting the secondary transfer residual toner, there is a tendency that the amount of waste toner collected in the first station and the fourth station increases. The first station is the first station on the downstream side of the toner charging roller in the rotation direction of the intermediate transfer belt (the first (upstream) station in the toner image formation order in the color mode). The fourth station is the first station upstream of the toner charging roller in the rotational direction of the intermediate transfer belt (the last (most downstream) station in the toner image formation order in the color mode).

  Therefore, it is preferable to distribute the secondary transfer residual toner to each station in order to eliminate the above-described imbalance in the amount of collected waste toner regardless of the use ratio of the color mode and the monochrome mode.

  In addition, as described above, it is preferable that the use of only the station that forms the toner image in the monochrome mode suppresses the necessity of replacing the cartridge of the station that forms the toner image only in the color mode.

  That is, in the color mode, when simultaneous transfer transfer is not performed (that is, when primary transfer is not performed), the first station and the station other than the station that forms the toner image in the monochrome mode are minimized. It is preferable to recover the next transfer residual toner. In other words, if the station that forms the toner image in the monochrome mode is the fourth station, in the color mode, the secondary transfer residual in the stations other than the first station and the fourth station when simultaneous transfer recovery is not performed. It is preferable to collect the toner.

  Furthermore, the amount of toner collected by retransfer at the time of the color mode in the second station and the third station tends to be larger in the third station for the reason described above. For this reason, in order to maintain the balance of the total waste toner amount at each station, it is more preferable that the recovery amount of the secondary transfer residual toner is larger than the recovery amount at the second station.

  According to the present embodiment, in the color mode, the secondary transfer residual toner is collected at a station other than the station that forms the toner image in the monochrome mode (the fourth station for K color in the present embodiment). As a result, in the color mode, the secondary transfer residual toner is prevented from being concentrated and collected at the station where the toner image is formed in the monochrome mode, and the cartridge used in the monochrome mode can be economically used. Further, according to the present embodiment, when primary transfer is not performed, the first station and a station other than the station that forms the toner image in the monochrome mode as much as possible (second and third stations in the present embodiment). Then, the secondary transfer residual toner is collected. As a result, the cartridge used in the color mode can be used economically.

  In this way, preferably, in the color mode, the secondary transfer residual toner is collected at a station other than the station that forms the toner image in the monochrome mode, and other than the first station except during the primary transfer. Collect at the station. As a result, it is possible to suppress the secondary transfer residual toner from being concentrated and collected at the first station and the station where the toner image is formed in the monochrome mode, and it is possible to economically use all the cartridges.

  In this embodiment, in the monochrome mode, a voltage having the same polarity as the normal charging characteristics of the toner is applied to the primary transfer roller at a station other than the station that forms the toner image in the monochrome mode. Preferably, in the monochrome mode, the bias applied to the primary transfer roller is equal to or equal to the surface potential of the photosensitive drum at a station other than the station where the toner image is formed in the monochrome mode. To the charge polarity side. In other words, in the monochrome mode, the difference between the surface potential of the photosensitive drum and the bias applied to the primary transfer roller is substantially zero or the same polarity as the toner in a station other than the station that forms the toner image in the monochrome mode. To. Thus, control is performed so that the secondary transfer residual toner is not collected at a station (first to third stations in this embodiment) that forms a toner image only in the color mode. Then, almost all the secondary transfer residual toner is collected at a station (a fourth station in this embodiment) that forms a toner image in the monochrome mode. Thus, by performing image formation in the monochrome mode, it is possible to prevent the volume of the waste toner container of the station that forms the toner image only in the color mode from being reduced. Accordingly, it is possible to suppress a problem that a waste toner container of a cartridge used only in the color mode, for example, a yellow cartridge becomes full and the cartridge is forced to be replaced in spite of using only the monochrome mode. it can.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, elements having the same functions or configurations as those of the image forming apparatus 100A according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 6 shows a schematic cross-sectional configuration of the image forming apparatus 100B of the present embodiment.

  In this embodiment, the intermediate transfer belt 50 provided in the intermediate transfer unit 5 is supported by four rollers: a driving roller 53, a tension roller 54, a secondary transfer counter roller 55, and a separation / contact control roller 12.

  In the color mode, the separation control roller 12 is in the position shown in FIG. 6, and the intermediate transfer belt 50 and the photosensitive drums 1a to 1d of the first to fourth stations 10a to 10d are moved by the primary transfer rollers 51a to 51d. The state of being pressed and in contact is maintained. In the color mode, the operation is performed according to the same timing chart as in the first embodiment.

  On the other hand, in the monochrome mode, the separation control roller 12 is at the position shown in FIG. 7, and the intermediate transfer belt 50 is separated from the photosensitive drums 1a to 1c of the first to third stations 10a to 10c, and the fourth transfer mode. The state in contact with the photosensitive drum 1d of the station 10d is maintained.

  More specifically, when the image forming apparatus 100B of this embodiment receives a print command in the monochrome mode from the standby state, the contact control roller 12 is moved from the position shown in FIG. As shown in the figure, it is retracted downward. That is, the separation control roller 12 is directed toward the inner side of the intermediate transfer belt 50 so as to release the bias of the intermediate transfer belt 50 from a position where the intermediate transfer belt 50 is biased from the inner peripheral side toward the outer peripheral side. Move. At the same time, the primary transfer rollers 51a to 51c and the charge eliminating members (charge eliminating needles) 11a to 11c of the first to third stations 10a to 10c are interlocked and retracted downward in the figure. The separation contact control roller 12 and its movable means, movable primary transfer rollers 51a to 51c, and the like are provided, and the photosensitive drums 1a to 1d and the intermediate transfer belt 50 are brought into contact with or separated from each other in the color mode and the monochrome mode. A contact / separation mechanism for changing the state is configured. By this operation, the intermediate transfer belt 50 is separated from the photosensitive drums 1a to 1c of the first to third stations 10a to 10c, and only the photosensitive drum 1d of the fourth station 10d is brought into contact with the intermediate transfer belt 50.

  In the monochrome mode, in the first to third stations 10a to 10c, the photosensitive drums 1a to 1c stop rotating, and the charging rollers 2a to 2c and the developing rollers 41a to 41c are not supplied with power and maintained at 0V. . Further, the developing rollers 41a to 41c maintain a state of being separated from the photosensitive drums 1a to 1c.

  In the monochrome mode, for example, secondary transfer residual toner generated when continuous printing is performed does not contact the photosensitive drums 1a to 1c of the first to third stations 10a to 10c. Therefore, the secondary transfer residual toner is not reversely transferred to these photosensitive drums 1a to 1c, but circulates to the primary transfer portion N1d of the fourth station 10d. The primary transfer roller 51d of the fourth station 10d is applied with + 500V that is a normal primary transfer bias until all the secondary transfer residual toner passes through the primary transfer portion N1d. As a result, substantially all of the secondary transfer residual toner is reversely transferred to the photosensitive drum 1d of the fourth station 10d and collected in the waste toner container 62d of the fourth station 10d.

  By such an operation, in the monochrome mode, more precise control is performed so that the secondary transfer residual toner is not collected at a station (a first to a third station in this embodiment) that forms a toner image only in the color mode. be able to. In addition, by collecting almost all of the secondary transfer residual toner at the station that forms the toner image in the monochrome mode, the volume of the waste toner container of the station that forms the toner image only in the color mode is prevented from decreasing in the monochrome mode. can do. This suppresses the problem that the waste toner container of a cartridge that is used only in the color mode, for example, a yellow cartridge, becomes full and the cartridge needs to be replaced despite the use of only the monochrome mode. Can do.

  In this embodiment, in the monochrome mode, the rotating operation and bias application of the photosensitive drums 1a to 1c of the first to third stations 10a to 10c are not performed. Therefore, it is possible to prevent the photosensitive drums 1a to 1c from being worn, extend the life of the cartridge used only in the color mode, and further economically use it.

  In addition, by providing a contact / separation mechanism between the photosensitive drum and the intermediate transfer belt in each station individually, the secondary transfer residual toner is alleviated from being collected in the first station 10a in the color mode. More preferred. In this case, after the primary transfer process in the first station 10a is finished in the color mode, if only the photosensitive drum 1a in the first station 10a is separated from the intermediate transfer belt 50, a part of the secondary transfer residue is left. The toner can be passed downstream. Therefore, it is possible to prevent the secondary transfer residual toner from being concentrated and collected at the first station 10a. Further, after the secondary transfer residual toner is collected at the second station 10b for a certain period of time, the photosensitive drum 1b of the second station 10b is separated from the intermediate transfer belt 50, and the secondary transfer residual toner at the third station 10c. Can be recovered. As a result, it is possible to maintain a balance in the amount of waste toner collected between the second station 10b and the third station 10c. That is, in the first embodiment, the intermediate transfer belt 50 is separated from the photosensitive drums 1a and 1b of the first and second stations 10a and 10b at the same timing as when the bias applied to the primary transfer roller is switched. Secondary transfer residual toner can be passed.

  In this case, the contact / separation mechanism between the photosensitive drum and the intermediate transfer belt requires a certain amount of time to reciprocate the contact / separation state, and is frequently switched while the secondary transfer residual toner passes. difficult. In addition, if the photosensitive drum and the intermediate transfer belt are separated from each other during the primary transfer process, the primary transfer is interrupted and an image defect occurs, which is not preferable. Therefore, after the secondary transfer residual toner is collected from the upstream station in the moving direction of the surface of the intermediate transfer belt for a certain period of time before the secondary transfer residual toner passes during a period when the primary transfer is not performed. It is preferable to sequentially separate the photosensitive drum from the intermediate transfer belt. Furthermore, if the contact and separation operation between the photosensitive drum and the intermediate transfer belt is performed during the primary transfer at another station, the image may be disturbed by the mechanical shock. For this reason, it is preferable to operate the contact / separation mechanism between the photosensitive drum and the intermediate transfer belt during a period when all the stations are not performing the primary transfer and during a period when the secondary transfer is not being performed.

  When performing the separation operation between the intermediate transfer belt and the photosensitive drum, the bias applied to all the primary transfer rollers may be maintained at the normal primary transfer bias, and may be changed before and after the separation. The application of the bias may be turned off. However, it is more preferable to perform a contact / separation operation between the intermediate transfer belt and the photosensitive drum by applying a voltage to the transfer means so that the surface potential of the photosensitive drum and the surface potential of the intermediate transfer belt are substantially the same. Thereby, when the intermediate transfer belt and the photosensitive drum are brought into contact with and separated from each other, it is possible to prevent electric discharge from being generated between the transfer unit and the photosensitive drum to create an electrical memory in the photosensitive drum. Further, in order to prevent the photosensitive drum from being rubbed and scratched, the contact speed of the intermediate transfer belt and the photosensitive drum may be changed by making the moving speed of the surface of the photosensitive drum equal to the moving speed of the intermediate transfer belt. preferable. That is, if one of the intermediate transfer belt and the photosensitive drum is stopped, the other is preferably stopped, and if one is rotating, the other is also rotated.

  As described above, according to this embodiment, the secondary transfer residual toner is concentrated and collected in the first station by changing the contact / separation state between the photosensitive drum and the intermediate transfer belt in the color mode and the monochrome mode. This can be suppressed, and the cartridge can be used economically. Further, according to this embodiment, in the monochrome mode, the photosensitive drum and the intermediate transfer belt of the station that forms the toner image are separated only in the color mode. For this reason, in the monochrome mode, it is possible to suppress the secondary transfer residual toner from being collected in a station that forms a toner image only in the color mode, and it is possible to economically use a cartridge that is used only in the color mode.

  As mentioned above, although this invention was demonstrated according to the specific Example, it should be understood that this invention is not limited to the above-mentioned embodiment.

  For example, in the first embodiment and the second embodiment, the case where a plurality of stations are arranged in the order for each of the colors Y, M, C, and K is illustrated. However, the first station is not a station for K color. If so, the present invention can be suitably used. In consideration of the productivity of the monochrome mode, the station for K color is particularly preferably the last station in the order of forming the toner images of a plurality of colors. The order is arbitrary.

  In each of the above embodiments, the waste toner container is provided in the process cartridge and is detachable from the main body of the image forming apparatus. However, at least the waste toner container is detachable from the main body of the image forming apparatus. If so, the present invention works very effectively. However, when the waste toner container is fixed to the main body of the image forming apparatus, for example, when the waste toner container is full, the toner is removed and collected from the waste toner container by a predetermined operation. Even so, the same effects as described above can be obtained by applying the present invention.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Exposure apparatus 4 Developing apparatus 5 Intermediate transfer unit 6 Cleaning apparatus 50 Intermediate transfer belt 51 Primary transfer roller 52 Secondary transfer roller 58 Toner charging roller 61 Cleaning blade 62 Waste toner container

Claims (10)

A plurality of image forming units each comprising: an image carrier on which a toner image is formed on the surface with toner charged to a regular charge polarity; and a container containing the toner removed from the image carrier; An intermediate transfer member on which the toner on the image carrier of the plurality of image forming units is transferred and an electric field are applied to the toner on the image carrier of the plurality of image forming units at each primary transfer unit. A primary transfer unit that is formed and primarily transferred onto the intermediate transfer member; a secondary transfer unit that secondarily transfers toner on the intermediate transfer member onto a transfer material at a secondary transfer portion; and the intermediate transfer member. On the intermediate transfer member on the downstream side of the secondary transfer unit in the moving direction of the surface and upstream of the primary transfer unit of the upstreammost image forming unit in the moving direction among the plurality of image forming units. The toner with a polarity opposite to the normal charging polarity. A toner charging unit configured to, the,
The toner on the intermediate transfer member charged to the reverse polarity is reversely transferred from the intermediate transfer member onto the image carrier of any of the plurality of image forming units and collected in the container of the image forming unit. The reverse transfer can be performed simultaneously with the primary transfer, and a first image forming mode for forming the toner image in all of the plurality of image forming units; A second image forming mode in which the toner image is formed in a specific image forming unit among a plurality of image forming units, and the specific image forming unit is other than the most upstream image forming unit. In an image forming apparatus that is an image forming unit,
The first image forming mode and the second image forming mode are different in the image forming unit that mainly collects toner by the reverse transfer among the plurality of image forming units, and the first image forming mode. In the mode, after the primary transfer at the most upstream image forming unit is completed, at least the toner on the intermediate transfer body charged to the reverse polarity reaching the primary transfer unit of the most upstream image forming unit A part of the image forming apparatus is collected by the reverse transfer in an image forming unit other than the most upstream image forming unit after passing through the primary transfer unit of the most upstream image forming unit.   In the first image forming mode, at least a part of the toner on the intermediate transfer member charged to the reverse polarity that has passed through the primary transfer unit of the most upstream image forming unit is the most upstream image forming unit. 2. After being passed through the primary transfer unit of at least one image forming unit other than the first image forming unit, the image is collected by the reverse transfer in another image forming unit other than the most upstream image forming unit. The image forming apparatus described.   In the first image forming mode, toner is mainly collected by the reverse transfer in an image forming unit other than the specific image forming unit that forms the toner image in the second image forming mode. The image forming apparatus according to claim 1 or 2.   In the first image forming mode, when the primary transfer is performed in the most upstream image forming unit, the intermediate transfer charged to the reverse polarity reaching the primary transfer unit of the most upstream image forming unit The image forming apparatus according to claim 1, wherein the toner on the body is collected by the reverse transfer at the most upstream image forming unit.   The toner in the second image forming mode is mainly collected by the reverse transfer in the specific image forming unit that forms the toner image in the second image forming mode. The image forming apparatus according to any one of items 4 to 4.   In the first image forming mode, when the toner on the intermediate transfer member charged with the reverse polarity is allowed to pass, the primary transfer unit generates an electric field in a direction opposite to that during the primary transfer at the primary transfer portion. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed.   A contact / separation mechanism for changing a state of contact or separation between the image carrier and the intermediate transfer member of the plurality of image forming units; and in the second image formation mode, the second image formation. The image bearing member and the intermediate transfer member of an image forming unit other than the specific image forming unit that forms the toner image in a mode are separated from each other. Image forming apparatus.   A contact / separation mechanism for changing a state of contact or separation between the image carrier and the intermediate transfer member of the plurality of image forming units; 6. The image forming apparatus according to claim 1, wherein when the toner on the intermediate transfer member is allowed to pass, the image carrier and the intermediate transfer member of the image forming unit are separated from each other. .   9. The specific image forming unit that forms the toner image in the second image forming mode is an image forming unit that is the most downstream in the moving direction of the surface of the intermediate transfer member. The image forming apparatus according to any one of the above.   The image forming apparatus according to claim 1, wherein at least the containers of the plurality of image forming units are detachable from a main body of the image forming apparatus.

Images