JP6580207B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer.

  Conventionally, an electrophotographic color image forming apparatus has a configuration in which a toner image is sequentially transferred from an image forming portion of each color to an intermediate transfer member, and further, the toner image is collectively transferred from the intermediate transfer member to a transfer material. It has been.

  In such an image forming apparatus, each color image forming section has a drum-shaped photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. The toner image formed on the photosensitive drum of each image forming unit applies a voltage from a primary transfer power source to a primary transfer member provided opposite to the photosensitive drum via an intermediate transfer member such as an intermediate transfer belt. Thus, primary transfer is performed on the intermediate transfer member. Each color toner image primarily transferred from the image forming portion of each color to the intermediate transfer member is applied with a voltage from the secondary transfer power source to the secondary transfer member in the secondary transfer portion, thereby causing the paper or OHP from the intermediate transfer member. Secondary transfer is performed collectively on a transfer material such as a sheet. The toner images of the respective colors transferred to the transfer material are then fixed on the transfer material by fixing means.

  Japanese Patent Application Laid-Open No. 2004-228561 has a configuration in which the intermediate transfer member is cleaned by electrostatically collecting toner (transfer residual toner) remaining on the intermediate transfer member after secondary transfer of the toner image onto the transfer material with a photosensitive drum. It is disclosed. In this configuration, the transfer residual toner is charged when passing through a position where the charging member disposed downstream of the secondary transfer member with respect to the moving direction of the intermediate transfer member contacts the intermediate transfer member. Thereafter, the intermediate transfer member moves together with the intermediate transfer member, and at the position where the photosensitive drum and the intermediate transfer member come into contact with each other, the reverse transfer is performed from the intermediate transfer member to the photosensitive drum due to the potential difference between the photosensitive drum and the intermediate transfer member. The untransferred toner that has moved to the photosensitive drum is collected by a cleaning unit provided on the photosensitive drum and removed from the photosensitive drum.

JP 2009-205012 A

  However, in the configuration of Patent Document 1, when the transfer residual toner is charged by the charging member, the intermediate transfer member is also charged at the same time, so that the potential of the intermediate transfer member gradually increases. As the potential of the intermediate transfer member increases, when the potential difference formed between the photosensitive drum and the intermediate transfer member is insufficient, the position where a part of the transfer residual toner comes into contact with the photosensitive drum and the intermediate transfer member is changed. There is a possibility that cleaning failure may occur due to slipping through.

  For example, in a mode in which there are a plurality of photosensitive drums in contact with the intermediate transfer body, even if the transfer residual toner cannot be completely collected by the upstream photosensitive drum in the moving direction of the intermediate transfer body, it can be collected by the downstream photosensitive drum. Is possible. On the other hand, in a mode in which there is only one photosensitive drum in contact with the intermediate transfer member, if the transfer residual toner passes through the position where the photosensitive drum and the intermediate transfer member contact each other, a cleaning failure occurs.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to ensure good cleaning performance in an image forming apparatus that collects toner remaining on an intermediate transfer member with an image carrier, regardless of the number of image carriers that are in contact with the intermediate transfer member. And

The present invention provides a first image carrier that carries a toner image, a second image carrier that carries a toner image, and is carried on at least one of the first image carrier and the second image carrier. A movable intermediate transfer body on which the toner image is primarily transferred, a transfer member that is in contact with an inner peripheral surface of the intermediate transfer body and is disposed at a position corresponding to the first image carrier, and the transfer A power source for applying a voltage to the member and a moving direction of the intermediate transfer member, the secondary transfer unit being disposed downstream of a secondary transfer unit for secondary transfer of a toner image from the intermediate transfer member to a transfer material; Charging means for charging the toner that has passed through, and the charging means is charged to the reverse polarity in a state where a voltage having a polarity opposite to the normal charging polarity of the toner is applied to the transfer member from the power source. the toner from the intermediate transfer member, said first image carrier And an image forming apparatus capable of executing a recovery operation to move at least one of said second image bearing member, the pre-Symbol first image bearing member and said second image bearing member of the intermediate transfer body When the collecting operation is executed in the first mode in contact, a first voltage is applied from the power source to the transfer member to bring the first image carrier into contact with the intermediate transfer member. when performing the recovery operation in the second mode in which is separated the previous SL second image carrier from the intermediate transfer member, is larger in absolute value than the first voltage to the transfer member from said power supply A second voltage is applied.

  According to the present invention, in an image forming apparatus that collects toner remaining on an intermediate transfer member with an image carrier, it is possible to ensure good cleaning performance regardless of the number of image carriers that are in contact with the intermediate transfer member. It is.

1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus in Embodiment 1. FIG. 1 is a block diagram in Embodiment 1. FIG. FIG. 2 is a schematic diagram illustrating a configuration of a charging unit in the first embodiment. FIG. 3 is a schematic diagram for explaining a contact state or a separation state between an image carrier and an intermediate transfer member when a monochrome mode is executed in Embodiment 1. FIG. 6 is a measurement result of a surface potential of an intermediate transfer body according to the number of transfer materials after passing 150,000 sheets in a comparative example. FIG. 6 is a schematic diagram illustrating a path of a current flowing from the charging unit and the primary transfer member to the intermediate transfer member in the full color mode according to the first exemplary embodiment. FIG. 6 is a measurement result of a surface potential of an intermediate transfer member according to the number of transfer materials after passing 150,000 sheets in the monochrome mode of Example 1. FIG. 6 is a measurement result of the surface potential of the intermediate transfer body according to the number of transfer materials after passing 200,000 sheets with respect to the configuration of Example 1. FIG. 6 is a measurement result of a surface potential of an intermediate transfer body according to the number of transfer materials after passing 200,000 sheets in the monochrome mode of Example 2. FIG.

  The preferred embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following examples should be changed as appropriate according to the configuration of the apparatus to which the invention is applied and various conditions. The present invention is not intended to be limited to the following examples.

Example 1
[Configuration of Image Forming Apparatus]
FIG. 1 is a schematic cross-sectional view of an image forming apparatus 10 in this embodiment. FIG. 2 is a block diagram of a control system of the image forming apparatus 10 of the present embodiment. As shown in FIG. 2, the image forming apparatus 10 is connected to a personal computer 200 which is a host device. An operation start command and an image signal from the personal computer 200 are transmitted to a controller 110 as a control unit, and the controller 110 controls various units, whereby image formation is executed in the image forming apparatus 10.

  An image forming apparatus 10 according to the present exemplary embodiment is an intermediate transfer type color image forming apparatus using an electrophotographic system, and includes a first, second, third, and fourth image forming units as a plurality of image forming units. 1a, 1b, 1c, 1d. The first, second, third, and fourth image forming units 1a, 1b, 1c, and 1d are for forming yellow, magenta, cyan, and black color images, respectively. As shown in FIG. 1, these four image forming units 1a, 1b, 1c, and 1d are arranged in a line at a constant interval.

  In the present embodiment, the configurations of the first to fourth image forming units 1a to 1d are substantially the same except that the color of the toner used is different. Therefore, unless otherwise distinguished, the description will be made comprehensively by omitting the suffixes a, b, c, and d given to the reference numerals to indicate the elements provided for any color.

  As shown in FIG. 1, the image forming unit 1 includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive member) that can rotate in the direction of the arrow R1 and serves as a first image carrier on which a toner image is formed. (Referred to as drum) 2 is installed. Around the photosensitive drum 2, a drum charging roller 3 as a means for charging the photosensitive drum 2, a developing means 4, and a cleaning means 6 are installed. An exposure unit 7 (laser scanner) is disposed downstream of the drum charging roller 3 and upstream of the developing unit 4 with respect to the rotation direction of the photosensitive drum 2.

  Further, an intermediate transfer belt 20 that is an endless belt-like intermediate transfer member is disposed so as to face the photosensitive drum 2 of each image forming unit 1. The intermediate transfer belt 20 is stretched around a driving roller 21, a stretching roller 22, and a counter roller 23 as a plurality of support members, and can be moved in the illustrated arrow R3 direction by the driving roller 21 rotating in the illustrated arrow R2 direction. is there. The driving roller 21, the stretching roller 22, and the opposing roller 23 are connected to ground.

  On the inner peripheral surface of the intermediate transfer belt 20, primary transfer rollers 5 a to 5 d as primary transfer members are arranged corresponding to the respective photosensitive drums 2 of the respective image forming units 1. Further, a secondary transfer roller 24 as a secondary transfer member is disposed on the outer peripheral surface side of the intermediate transfer belt 20 so as to face the counter roller 23.

  The photosensitive drum 2 in this embodiment is a negatively chargeable OPC (organic photoconductor) photosensitive member, and has a photosensitive layer on an aluminum drum base. The photosensitive drum 2 is rotationally driven at a predetermined peripheral speed (surface movement speed) in a direction indicated by an arrow R1 (clockwise) by a driving device (not shown). In this embodiment, the peripheral speed of the photosensitive drum 2 corresponds to the process speed of the image forming apparatus 10.

  Each of the developing units 4a, 4b, 4c, and 4d stores yellow, magenta, cyan, and black toners. In the full color image forming mode (hereinafter referred to as the full color mode) as the first mode, as shown in FIG. 1, the four photosensitive drums 2 are in contact with the intermediate transfer belt 20, and the developing rollers 8 of the four developing units 4 are used. Abuts against each photosensitive drum 2. A mono-color image forming mode (hereinafter referred to as a monochrome mode) as the second mode will be described later.

In this embodiment, as the intermediate transfer belt 20, an intermediate transfer belt made of polyethylene naphthalate resin (PEN) was used. The initial surface resistivity of the intermediate transfer belt 20 is 5.0 × 10 ¹¹ Ω / □, and the volume resistivity is 8.0 × 10 ¹¹ Ωcm.

  In addition, as the intermediate transfer belt 20, resins such as vinylidene fluoride resin (PVDF), tetrafluoroethylene-ethylene copolymer resin (ETFE), polyimide resin, polyethylene terephthalate (PET), and polycarbonate can be used. Alternatively, for example, the surface of a rubber base layer composed of ethylene propylene diene rubber (EPDM) is coated with a urethane rubber dispersed with a fluorine resin such as polytetrafluoroethylene (PTFE) to form an endless belt. Can be used.

The primary transfer roller 5 is made of an elastic member such as sponge rubber. In this embodiment, the primary transfer roller 5 is a nickel-plated steel rod with a diameter of 6 mm and coated with NBR hydrin rubber with a thickness of 4 mm. The electrical resistance value of the primary transfer roller 5 is obtained when a voltage of 100 [V] is applied while the primary transfer roller 5 is pressed on an aluminum cylinder with a force of 9.8 N and rotated at 50 mm / sec. 1.0 × 10 ⁵ Ω.

  The primary transfer roller 5 is disposed at a position facing the photosensitive drum 2 via the intermediate transfer belt 20, and presses the intermediate transfer belt 20 against the photosensitive drum 2 to form the primary transfer portion N1. To do. The primary transfer roller 5 rotates following the movement of the intermediate transfer belt 20. A primary transfer power supply 40 is connected to the primary transfer roller 5, and the primary transfer power supply 40 can apply a positive or negative voltage to the primary transfer roller 5.

The secondary transfer roller 24 is made of an elastic member such as sponge rubber, for example. In this embodiment, a secondary transfer roller was used in which a nickel-plated steel rod having a diameter of 6 mm was coated with NBR hydrin rubber with a thickness of 6 mm. The electrical resistance value of the secondary transfer roller 24 is 3.0 × 10 when 1000 V is applied while the secondary transfer roller is pressed on the aluminum cylinder with a force of 9.8 N and rotated at 50 mm / sec. ⁷ Ω.

  The secondary transfer roller 24 abuts on the intermediate transfer belt 20 at a position facing the counter roller 23 to form a secondary transfer portion N2. A secondary transfer power supply 44 is connected to the secondary transfer roller 24, and the secondary transfer power supply 44 can apply a positive or negative voltage to the secondary transfer roller 24.

  A charging unit 30 for charging the toner remaining on the intermediate transfer belt 20 is provided on the downstream side of the secondary transfer portion N2 with respect to the moving direction of the intermediate transfer belt 20. Details of the configuration and operation of the charging means 30 will be described later.

  With respect to the transfer direction of the transfer material P, a registration roller 13 as a transfer means for transferring the transfer material P is disposed upstream of the secondary transfer portion N2. Further, on the downstream side of the secondary transfer portion N2 with respect to the conveyance direction of the transfer material P, a fixing roller 12A provided with a heat source and a pressure roller 12B that contacts the fixing roller 12A with a predetermined pressure are provided. A fixing unit 12 is provided.

[Image forming operation]
Next, an image forming operation in the image forming apparatus 10 will be described with reference to FIG.

  First, when an image forming operation start signal is issued, the photosensitive drum 2 is driven to rotate in the direction of the arrow R1 in the drawing at a predetermined peripheral speed, and the drum charging roller 3 is charged during the rotation process, thereby causing a uniform potential on the surface. Formed. The drum charging roller 3 is in contact with the photosensitive drum 2 with a predetermined contact pressure, and uniformly charges the surface of the photosensitive drum 2 to a predetermined potential by applying a predetermined voltage from a charging power source (not shown). To do. In this embodiment, the photosensitive drum 2 is charged negatively by the drum charging roller 3.

  The exposure unit 7 exposes the surface of the photosensitive drum 2 to form an electrostatic latent image corresponding to image information on the surface of the photosensitive drum 2 charged by the drum charging roller 3. That is, the exposure unit 7 outputs laser light modulated in accordance with the time series electric digital pixel signal of the image information input from the personal computer 200 from the laser output unit. Then, the laser beam is irradiated onto the surface of the photosensitive drum 2 through the reflection mirror, whereby an electrostatic latent image is formed on the surface of the photosensitive drum 2.

  The developing means 4 uses a contact developing method as a developing method, and has a developing roller 8 as a developer carrying member that contacts the photosensitive drum 2. The developing roller 8 is rotationally driven by a driving unit (not shown), and the toner carried in a thin layer on the developing roller 8 is conveyed to a developing unit where the photosensitive drum 2 and the developing roller 8 are in contact with each other. The electrostatic latent image formed on the photosensitive drum 2 is developed as a toner image by applying a voltage to the developing roller 8 from a developing power source (not shown).

  The electrostatic latent image formed on the photosensitive drum 2 is developed by a reversal development method. That is, an electrostatic latent image is obtained by attaching toner charged to the same polarity as the charged polarity of the photosensitive drum 2 (negative polarity in this embodiment) to the exposed portion of the photosensitive drum 2 exposed by the exposure means 7. Is developed as a toner image. Here, the normal charging polarity of the toner stored in the developing unit 4 is negative.

  In this embodiment, the contact development method is used. However, the present invention is not limited to this, and a non-contact development method may be used. In this embodiment, the electrostatic latent image is developed using the reversal development method. However, the present invention is not limited to this, and the electrostatic latent image is formed by toner charged to a polarity opposite to the charged polarity of the photosensitive drum 2. The present invention can also be applied to an image forming apparatus that performs normal development.

  The toner image developed on the photosensitive drum 2 is applied with a positive voltage having a polarity opposite to the normal charging polarity of the toner from the primary transfer power supply 40 to the primary transfer roller 5 in the primary transfer portion N1. Thus, the primary transfer is performed from the photosensitive drum 2 to the intermediate transfer belt 20. In this manner, in each primary transfer portion N1, the toner images of each color are sequentially superimposed and primarily transferred onto the intermediate transfer belt 20, and a multiple toner image composed of a plurality of color toner images is formed on the intermediate transfer belt 20. Is done.

  The registration roller 13 conveys the transfer material P to the secondary transfer portion N2 in accordance with the timing at which the tips of the toner images of the plurality of colors primarily transferred to the intermediate transfer belt 20 reach the secondary transfer portion N2. Then, by applying a positive voltage having a polarity opposite to the normal charging polarity of the toner from the secondary transfer power supply 44 to the secondary transfer roller 24, the transfer material is transferred from the intermediate transfer belt 20 to the transfer material at the secondary transfer portion N2. A plurality of color toner images are collectively transferred to P in P.

  Thereafter, the transfer material P on which the toner images of a plurality of colors are secondarily transferred is conveyed to the fixing unit 12 and heated and pressed by the fixing roller 12A and the pressure roller 12B, whereby the toners of the plurality of colors are melted and mixed. To the transfer material P. Then, the transfer material P on which the toner images of a plurality of colors are fixed is discharged to the outside of the image forming apparatus 10, and a series of image forming operations is completed.

  The toner remaining on the photosensitive drum 2 after the primary transfer is removed from the photosensitive drum 2 by a cleaning blade 61 as an abutting member formed of an elastic body such as urethane rubber, and cleaning means 6 as a collecting means for collecting the toner. To be recovered.

  In addition, toner that is not secondarily transferred to the transfer material P and remains on the intermediate transfer belt 20 (hereinafter referred to as transfer residual toner) moves with the intermediate transfer belt 20 and is charged by the charging unit 30. Thereafter, the transfer residual toner moves together with the intermediate transfer belt 20 and electrostatically transfers from the intermediate transfer belt 20 to the photosensitive drum 2 due to a potential difference between the photosensitive drum 2 and the intermediate transfer belt 20 when passing through the primary transfer portion N1. And is collected by the cleaning means 6.

[Collecting residual toner]
The operation of collecting the transfer residual toner in this embodiment will be described in detail with reference to FIG. FIG. 3 is a schematic diagram illustrating the configuration of the charging unit 30 in the present embodiment.

  As shown in FIG. 3, the charging unit 30 includes a conductive brush 31 and a conductive roller 32. The conductive brush 31 and the conductive roller 32 are disposed downstream of the secondary transfer portion N2 and upstream of the primary transfer portion N1a with respect to the moving direction of the intermediate transfer belt 20. The conductive roller 32 is disposed between the conductive brush 31 and the primary transfer portion N1a. The conductive brush 31 and the conductive roller 32 are in contact with the intermediate transfer belt 20.

The conductive brush 31 is a brush member using nylon imparting conductivity to a material, and has a fineness of 7 dtex, a pile length of 5 mm, and a brush width of 5 mm. The electric resistance value of the conductive brush 31 is 1.0 when a voltage of 500 [V] is applied while the conductive brush 31 is pressed against the aluminum cylinder with a force of 9.8 N and rotated at 50 mm / sec. × 10 ⁶ Ω.

As the conductive roller 32 (roller member), a nickel-plated steel rod having a diameter of 6 mm covered with a solid elastic body made of EPDM in which carbon is dispersed with a thickness of 5 mm was used. The electric resistance value of the conductive roller 32 is 5.0 when a voltage of 500 [V] is applied with the conductive roller 32 pressed against the aluminum cylinder with a force of 9.8 N and rotated at 50 mm / sec. × 10 ⁷ Ω. The conductive roller 32 is pressed toward the stretching roller 22 via the intermediate transfer belt 20 with a total pressure of 9.8 N.

  As shown in FIG. 3, the conductive brush 31 is electrically connected to the charging power source 51 via the current detection means 71, and the charging power source 51 applies a positive or negative voltage to the conductive brush 31. It is possible. Similarly, the conductive roller 32 is also electrically connected to the charging power source 52 via the current detection means 72, and the charging power source 52 can apply a positive or negative voltage to the conductive roller 32. is there.

  When the transfer residual toner collecting operation is executed, positive voltage is applied to the conductive brush 31 and the conductive roller 32 from the charging power source 51 and the charging power source 52, respectively. Based on the current detected by the current detection means 71 and the current detection means 72, the output value of the voltage output from the charging power supply 51 and the charging power supply 52 becomes a target current value preset by the controller 110 as the control means. Control (constant current control). The target current value is appropriately set according to the design and environment of the image forming apparatus 10 so that the transfer residual toner is not excessively charged and a cleaning failure due to insufficient charging of the transfer residual toner does not occur. In this embodiment, the target current value of the conductive brush 31 is set to 20 μA, and the target current value of the conductive roller 32 is set to 30 μA.

<Collecting operation of transfer residual toner in full color mode>
When the transfer residual toner collecting operation is executed in the full color mode, the transfer residual toner on the intermediate transfer belt 20 is charged to the positive polarity by the charging unit 30. At this time, by applying a positive voltage from the charging power supply 51 to the conductive brush 31, a part of the transfer residual toner charged negatively adheres to the conductive brush 31 electrostatically. As a result, the amount of toner passing through the position where the conductive roller 32 and the intermediate transfer belt 20 are in contact during the collecting operation can be reduced.

  The transfer residual toner charged to the positive polarity by the charging unit 30 reaches the primary transfer portion N1a of the image forming portion 1a arranged at the most upstream position with the movement of the intermediate transfer belt 20. At this time, by applying a positive voltage to the primary transfer roller 5a, the transfer residual toner charged to the positive polarity is electrostatically moved from the intermediate transfer belt 20 to the photosensitive drum 2a. Thereafter, the untransferred toner that has moved to the photosensitive drum 2a moves as the photosensitive drum 2a rotates, and is collected by the cleaning means 6a by the cleaning blade 61a.

  In the full color mode, the transfer residual toner collecting operation is executed in this way. In the present exemplary embodiment, the configuration in which the transfer residual toner is collected by the photosensitive drum 2a disposed on the most upstream side with respect to the moving direction of the intermediate transfer belt 20 has been described. However, the present invention is not limited thereto, and it is also possible to collect the transfer residual toner on a photosensitive drum other than the photosensitive drum 2a by controlling the direction of the electric field formed in each primary transfer portion N1. For example, the direction of the electric field formed in the primary transfer portion N1 is controlled by controlling the polarity and output value of the voltage applied to the primary transfer roller 5 from the drum charging roller 3, the exposure means 7, and the primary transfer power supply 40. It is possible to control.

<Recovery operation of transfer residual toner in monochrome mode>
FIG. 4 is a schematic diagram for explaining a contact state between each photosensitive drum 2 and the intermediate transfer belt 20 when the monochrome mode in the present embodiment is executed. As shown in FIG. 4, in the monochrome mode, the developing unit 4d has a black color when the photosensitive drum 2d and the intermediate transfer belt 20 are brought into contact with each other and the other photosensitive drums 2a to 2c are separated from the intermediate transfer belt 20. Image formation is performed only by the image forming unit 1d containing toner. At this time, the developing rollers 8a to 8c of the image forming units 1a to 1c that do not perform image formation are separated from the photosensitive drums 2a to 2c. As described above, in the image forming units 1a to 1c that do not perform image formation, the photosensitive drums 2a to 2c and the developing rollers 8a to 8c are separated from each other, thereby suppressing deterioration and wear of each member due to contact rotation and voltage application. It is possible.

  Regarding the mechanism for bringing the photosensitive drum 2 and the intermediate transfer belt 20 into contact with or separating from each other, for example, a configuration in which the primary transfer roller 5 is pressed toward the photosensitive drum 2 via the intermediate transfer belt 20 by an urging means such as a spring. Can be considered. In such a configuration, the primary transfer roller 5 and the intermediate transfer belt 20 can be separated from the photosensitive drum 2 by releasing the biased state by the spring.

  When the transfer residual toner recovery operation is executed in the monochrome mode, the transfer residual toner is first charged to the positive polarity by the charging unit 30 as in the recovery operation in the full color mode. The untransferred toner is a position where the intermediate transfer belt 20 and the image forming units 1a to 1c, in which the primary transfer units N1a to N1c are eliminated by a separation mechanism (not shown) as the intermediate transfer belt 20 moves. And reaches the primary transfer portion N1d.

  At this time, by applying a positive voltage from the primary transfer power supply 40d to the primary transfer roller 5d, the transfer residual toner charged positively is electrostatically moved from the intermediate transfer belt 20 to the photosensitive drum 2d. . Thereafter, the untransferred toner moved to the photosensitive drum 2d moves as the photosensitive drum 2d rotates, and is collected by the cleaning unit 6d by the cleaning blade 61d. In the monochrome mode, the transfer residual toner collecting operation is performed as described above.

[Recovery operation of transfer residual toner in comparative example]
Hereinafter, the control of the recovery operation of the transfer residual toner and the result of the image output experiment in the comparative example of the present embodiment will be described. The image output experiment is performed using a test for confirming the durability of each member when the transfer material P is continuously passed (hereinafter referred to as a paper passing durability test). Image evaluation was performed in each monochrome mode. Details of the paper passing durability test and the image evaluation method will be described below.

  In the paper passing durability test, GFC-081 (manufactured by Canon Marketing Japan) was used as the transfer material P in a temperature 15 ° C. and humidity 10% environment, and an image with an image ratio of 25% for each color of cyan, magenta, yellow, and black was used. The operation of continuously forming the two transfer materials P was repeated. The plain paper mode is used as the image forming mode, the process speed of the image forming apparatus 10 is 180 mm / sec, and the throughput is 30 sheets per minute.

  Further, in the same environment as the test environment, an evaluation image was formed at the start of the paper passing durability test and every 50000 durable paper passing, and image evaluation was performed. As an evaluation image in the full-color mode, GFC-081 (manufactured by Canon Marketing Japan) is used as the transfer material P, and the primary colors of cyan, magenta, yellow and black and the secondary colors of red, blue and green are as follows. Created an image. More specifically, a maximum density level image (solid image), an image ratio 50% image (halftone image), and a character thin line image were taken as one set, and a total of 63 sets were output for each of the aforementioned colors.

  As an evaluation image in the monochrome mode, the same transfer material P as that in the full color mode is used. For the black color, a maximum density level image (solid image), an image with an image ratio of 50% (halftone image), and a character thin line image are used. A total of 63 sheets of 21 sets were output as one set.

  Then, the evaluation image thus formed was evaluated by confirming whether or not an image defect due to a cleaning defect occurred. Specifically, the formed evaluation image was evaluated by observing whether an image of one turn before the intermediate transfer belt 20 at the position corresponding to the secondary transfer portion N2 is generated during the secondary transfer. As evaluation criteria, a case where no cleaning failure occurred was indicated as ◯, a case where the cleaning failure occurred was indicated as ×, and a case where a slight image failure was observed was indicated as Δ.

  Table 1 shows the output value of the primary transfer power source 40 at the time of image evaluation, the target current value of the conductive brush 31, and the target current of the conductive roller 32 every time 50,000 sheets are passed in the full color mode paper passing durability test of the comparative example. It is the table | surface which described the value and the result of the image evaluation for every 10 sheets. Note that the target current value of the conductive brush 31 is a value detected by the current detection means 71, and the target current value of the conductive roller 32 is a value detected by the current detection means 72. As shown in Table 1, the output value (first voltage) of the initial primary transfer power supply 40 in the full color mode of the comparative example is 1400 [V], the target current of the conductive brush 31 is 20 μA, and the conductive roller 32. The target current is 30 μA.

  The primary transfer roller 5 and the intermediate transfer belt 20 tend to increase in electrical resistance as the number of sheets of the transfer material P increases. Therefore, if the same voltage as the initial voltage is continuously output from the primary transfer power supply 40 when the sheet passing durability test is performed, the intermediate transfer belt 20 and the photosensitive drum 2 in the primary transfer portion N1 according to the increase in the number of sheets to be passed. When the potential difference between them becomes small, the primary transfer property changes. For this reason, in the paper passing durability test, as shown in Table 1, the output value from the primary transfer power supply 40 is increased according to the number of sheets to ensure a certain primary transfer property.

  According to the results shown in Table 1, in the full color mode of the comparative example, no image defect was observed in the evaluation image even when 150,000 sheets were passed, and no cleaning defect occurred.

  Table 2 shows the output value of the primary transfer power supply 40 at the time of image evaluation, the target current value of the conductive brush 31, and the target current of the conductive roller 32 every time 50,000 sheets are passed in the monochrome mode paper endurance test of the comparative example. It is the table | surface which described the value and the result of the image evaluation for every 10 sheets. As shown in Table 2, the voltage output value of the primary transfer power supply 40d and the target current values of the conductive brush 31 and the conductive roller 32 were set to the same values as in the full color mode. In the monochrome mode, since the image is formed only by the image forming unit 1d, no voltage is output from the primary transfer power sources 40a to 40c.

  According to the results shown in Table 2, in the monochrome mode of the comparative example, an image defect due to a cleaning defect was observed from the evaluation image when 100,000 sheets were passed.

  When there are a plurality of photosensitive drums 2 in contact with the intermediate transfer belt 20 as in the full color mode, the photosensitive drums on the downstream side can be collected even if the transfer residual toner cannot be collected by the upstream photosensitive drum 2a in the moving direction of the intermediate transfer belt 20. The drums 2b to 2d can be collected. On the other hand, in the monochrome mode in which only one photosensitive drum 2d is in contact with the intermediate transfer belt 20, when the transfer residual toner passes through the primary transfer portion N1d, a member for collecting the transfer residual toner is provided further downstream. Since this is not done, cleaning failure occurs.

  Further, as the number of sheets passed increases, it is considered that an image defect due to a cleaning defect occurs in the monochrome mode as compared with the full color mode as described below.

  FIG. 5 shows the measurement of the surface potential of the intermediate transfer belt 20 according to the number of sheets of the transfer material P forming the evaluation image when image evaluation is performed after 150,000 sheets have been passed by the sheet passing durability test. It is a result. The surface potential of the intermediate transfer belt 20 during the passage of the transfer material P forming the evaluation image was measured using a surface potential measuring device (MODEL 344, manufactured by Trek Japan Co., Ltd.). More specifically, a surface potential measurement probe (MODEL555P-4, manufactured by Trek Japan Co., Ltd.) was installed at a position about 10 mm directly above the stretching roller 22 and the signal was output to a surface potential measuring device.

  As shown in FIG. 5, in the full color mode, an increase in the surface potential of the intermediate transfer belt 20 is suppressed, whereas in the monochrome mode, the surface potential of the intermediate transfer belt 20 is about 240 [V] when 60 sheets are passed. ] Up to This indicates that in the full color mode, the increase in the surface potential of the intermediate transfer belt 20 when the transfer residual toner is charged positively by the charging unit 30 is alleviated by passing through the primary transfer portion N1. ing.

FIG. 6 is a schematic diagram for explaining a path of a current flowing from the charging unit 30 and the primary transfer roller 5 to the intermediate transfer belt 20 in the full color mode. As shown in FIG. 6, a positive voltage is applied to the charging unit 30 from the charging power source 51 and the charging power source 52, and the charging unit 30 is located at a position where the charging unit 30 contacts the intermediate transfer belt 20. A current I ₃₁ and a current I ₃₂ flow from the outer peripheral surface side toward the inner peripheral surface side. On the other hand, in the primary transfer portion N1a, a positive voltage is applied from the primary transfer power supply 40a to the primary transfer roller 5a, and a negative potential is formed on the photosensitive drum 2a. A current I _5a flows from the inner peripheral surface side of the transfer belt 20 toward the outer peripheral surface side.

In the full-color mode, in other image forming unit 1 b to 1 d, a current corresponding to the current I _5a in the image forming unit 1a flows. That is, the charging unit 30 that contacts the outer peripheral surface side of the intermediate transfer belt 20 and the primary transfer roller 5 that contacts the inner peripheral surface side of the intermediate transfer belt 20 alleviate the surface potential formed on the intermediate transfer belt 20. There is a relationship.

  In the monochrome mode, the photosensitive drum 2d and the primary transfer roller 5d are in contact with the intermediate transfer belt 20 to form the primary transfer portion N1d, and the primary transfer portions N1a to N1c are formed in the other image forming portions 1a to 1c. Not. Therefore, compared to the full-color mode configuration, the increase in the surface potential of the intermediate transfer belt 20 due to the charging of the charging unit 30 is difficult to suppress. As a result, the surface potential increases every time the intermediate transfer belt 20 circulates, and the potential difference necessary to move the transfer residual toner from the intermediate transfer belt 20 to the photosensitive drum 2d cannot be secured at the primary transfer portion N1d. This causes defective cleaning.

  In particular, after the number of sheets of the transfer material P passing through the secondary transfer portion exceeds a predetermined number (late end of life), in other words, in a state where the electrical resistance of the intermediate transfer belt 20 is increased due to the deterioration of energization, Due to the above-mentioned causes, cleaning failure tends to occur. This is because the charge accumulation in the intermediate transfer belt 20 is difficult to be eliminated in the end of durability.

[Collecting operation of transfer residual toner in this embodiment]
Next, with reference to Table 3 and FIG. 7, the operation of collecting the transfer residual toner in the monochrome mode in this embodiment will be described. Note that the transfer operation and control of the transfer residual toner in the full color mode in this embodiment are the same as those in the comparative example, and thus the description thereof is omitted.

  Table 3 shows the output value of the primary transfer power supply 40 at the time of image evaluation, the target current value of the conductive brush 31, and the target of the conductive roller 32 every time 50,000 sheets are passed in the monochrome mode paper endurance test of this embodiment. It is the table | surface which described the electric current value and the result of the image evaluation for every 10 sheets. As shown in Table 3, in this embodiment, the voltage output value (second voltage) of the primary transfer power supply 40d in the monochrome mode is the output value (first voltage) of the primary transfer power supply 40 in the full color mode. Value). Specifically, the output value is 700 [V] larger than the output value in the full color mode. As a result, in the configuration of this example, no image defect due to the cleaning defect was observed. Note that the target current values of the conductive brush 31 and the conductive roller 32 were set to the same values as in the full color mode.

  Here, as the second voltage, the larger the absolute value with respect to the first voltage, the easier the rise in the surface potential of the intermediate transfer belt 20 is mitigated. However, if the value is too large, the potential difference at the primary transfer portion N1d becomes too large, causing abnormal discharge, which may cause unevenness in the surface potential of the photosensitive drum 2d after passing through the primary transfer portion N1d. There is. Then, in the subsequent rotation process of the photosensitive drum 2a, when the unevenness of the surface potential of the photosensitive drum 2d is not eliminated by the charging by the drum charging roller 3, the developability also becomes uneven, resulting in the image density unevenness. Defects will occur.

  Therefore, it is desirable to set the second voltage within a range in which abnormal discharge does not occur in the primary transfer portion N1d. This voltage setting range is appropriately set according to the impedance in the primary transfer portion N1d such as the electrical resistance value of the intermediate transfer belt 20 and the electrical resistance value of the primary transfer roller 5d. In the configuration of this embodiment, if the difference between the absolute value of the second voltage and the absolute value of the first voltage is less than 1500 [V], it is possible to suppress the occurrence of image defects due to the abnormal discharge described above. It is. However, in order to further suppress the occurrence of abnormal discharge in the primary transfer portion N1d in the configuration of the present embodiment, the difference between the absolute value of the second voltage and the absolute value of the first voltage is less than 800 [V]. It is more desirable to set to.

  Further, if the absolute value of the second voltage is larger than the absolute value of the first voltage, an effect of reducing the increase in the surface potential of the intermediate transfer belt 20 can be obtained. However, the surface potential of the intermediate transfer belt 20 increases when the difference between the absolute value of the second voltage and the absolute value of the first voltage is too small depending on the impedance of the primary transfer portion N1d and the configuration of the image forming apparatus. There is a possibility that sufficient relaxation effect cannot be obtained. In the configuration of the image forming apparatus of the present embodiment, the second voltage is set so that the difference between the absolute value of the second voltage and the absolute value of the first voltage is 30 [V] or more. desirable.

  In this embodiment, the voltage of the primary transfer power supply 40 is controlled by constant voltage control, but the voltage may be controlled by constant current control. When the constant current control is used, the target current value in the monochrome mode is set higher than the target current value in the full color mode. At this time, in the configuration of the image forming apparatus according to the present exemplary embodiment, the target current value in the monochrome mode is preferably set so that the voltage value is less than “voltage in full color mode + 1500 V”. In the configuration of the image forming apparatus according to the present exemplary embodiment, the target current value in the monochrome mode is preferably set to be in a range of “voltage in full color mode + 30 V” or more.

  FIG. 7 shows the intermediate transfer belt 20 according to the number of sheets of the transfer material P forming the evaluation image in the monochrome mode when image evaluation is performed after 150,000 sheets have been passed by the sheet passing durability test. It is a measurement result of surface potential. As shown in FIG. 5, in the measurement result in the comparative example, the surface potential of the intermediate transfer belt 20 was increased to about 240 [V], whereas as shown in FIG. [V] is suppressed. This is because, by increasing the voltage applied from the primary transfer power supply 40d to the primary transfer roller 5d, relaxation of the surface potential of the intermediate transfer belt 20 formed by being charged by the charging means 30 is promoted. It is. As shown in FIG. 7, the value of the surface potential of the intermediate transfer belt 20 is almost saturated when 60 sheets of the transfer material P are passed.

  As described above, according to the present embodiment, it is possible to suppress the occurrence of cleaning failure by increasing the value of the voltage applied to the primary transfer roller 5 in the monochrome mode with respect to the full color mode. It is.

  In the present embodiment, a description has been given of the configuration in which the value of the voltage applied to the primary transfer roller 5 is increased in the monochrome mode with respect to the full color mode, regardless of the number of sheets to be passed, when the transfer residual toner collecting operation is performed. However, it is not limited to this. At the end of the endurance when the number of transfer materials P to which the toner image is secondarily transferred in the secondary transfer portion N2 exceeds a predetermined number and the electrical resistance of the intermediate transfer belt 20 increases, the primary color in the monochrome mode with respect to the full color mode. The value of the voltage applied to the transfer roller 5 may be increased.

  In the monochrome mode, the photosensitive drums 2a to 2c are not separated from the intermediate transfer belt 20, and a positive voltage is applied to the primary transfer rollers 5a to 5c from the primary transfer power sources 40a to 40c, thereby causing poor cleaning. A method for suppressing the occurrence is conceivable. However, in such a configuration, there is a possibility that the consumption of the image forming units 1 a to 1 c that are not used for image formation may be promoted, which may hinder the life of the image forming apparatus 10. Further, in such a configuration, the transfer residual toner moves to the photosensitive drum 2a instead of the photosensitive drum 2d and is collected by the cleaning unit 6a, so that it is difficult to sort and collect the transfer residual toner. As a result, the cleaning means 6a may be increased in size to secure a capacity for accommodating the transfer residual toner.

  In the present embodiment, the output value of the primary transfer power supply 40 in the full color mode is a common value in each of the image forming units 1a to 1d. However, the value is not limited to this, and a different value is used in each of the image forming units 1a to 1d. May be set. In this case, the voltage (second voltage) applied to the primary transfer roller 5d in the monochrome mode may be set as follows. That is, in the full color mode, the absolute value is larger than the voltage (first voltage) applied to any of the primary transfer rollers 5a to 5d in order to move the transfer residual toner to any of the photosensitive drums 2a to 2d. Set it. For example, when a voltage of 1400 [V] is applied to the primary transfer roller 5a to collect the transfer residual toner on the photosensitive drum 2a in the full color mode, the absolute value is larger than 1400 [V] in the monochrome mode. A voltage may be applied to the primary transfer roller 5d.

  In this embodiment, the configuration using the two members of the conductive brush 31 and the conductive roller 32 as the charging means 30 for the transfer residual toner has been described. However, the present invention is not limited to this. The structure which performs this may be sufficient and you may provide three or more charging means. Further, the charging unit 30 is not limited to the contact type charging unit, and a non-contact type charging unit may be used.

  Further, in this embodiment, the primary transfer roller 5 having an elastic member such as sponge rubber is used as the primary transfer member. However, the primary transfer member is not limited thereto, and a transfer brush, a transfer sheet, a metal roller, or the like is used as the primary transfer member. May be used. In addition, the primary transfer member may be arranged offset at a position shifted upstream or downstream from the primary transfer portion N1 with respect to the moving direction of the intermediate transfer belt 20.

  The collecting operation of the transfer residual toner in the present embodiment may be performed simultaneously with the image forming operation in each image forming unit 1 or may be performed at the time of the post-rotation operation after the end of the image forming operation. By applying a positive voltage from the primary transfer power source 40 to the primary transfer roller 5, the toner image charged negatively from the photosensitive drum 2 to the intermediate transfer belt 20 is primarily transferred from the intermediate transfer belt 20. The transfer residual toner charged positively on the photosensitive drum 2 can be moved.

  In this embodiment, the four primary transfer power sources 40a to 40d are connected to the four primary transfer rollers 5a to 5d, respectively. However, the present invention is not limited to this, and some primary transfer power sources are shared. It may be a configuration. For example, a common primary transfer power source may be connected to the primary transfer rollers 5a to 5c, and one primary transfer power source may be connected to the primary transfer roller 5d. By reducing the number of primary transfer power sources 40 that are charging power sources, the cost can be reduced and the size of the image forming apparatus 10 can be reduced.

(Example 2)
In the first embodiment, the voltage output value from the primary transfer power supply 40 in the monochrome mode (second mode) is changed with respect to the output value from the primary transfer power supply 40 in the full color mode (first mode). The configuration has been described. In contrast, in the second embodiment, a configuration in which the target current value of the charging unit 30 is changed while increasing the output value of the primary transfer power supply 40 will be described. In the second embodiment, portions common to the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  Table 4 shows the output value of the primary transfer power source 40, the target current value of the conductive brush 31 and the target current value of the conductive roller 32 when the paper passing durability test is performed up to 200000 sheets in the full color mode of this embodiment. It is the table | surface which described the result of the image evaluation for every 10 sheets. As shown in Table 4, in the full-color mode configuration, no cleaning failure occurred even when a paper passing durability test of 200000 sheets was performed.

  Table 5 shows the results of performing a 200,000 sheet passing durability test and image evaluation in the monochrome mode in a state where the output value of the voltage applied from the primary transfer power supply 40d to the primary transfer roller 5d is larger than that in the full color mode. It is. At this time, the output value (second voltage) of the voltage at the primary transfer power supply 40d is 700 [V] larger than the output value (first voltage) of the primary transfer power supply 40 in the full color mode. . Further, the target current value of the conductive brush 31 in the monochrome mode and the target current value of the conductive roller 32 are set to the same values as the respective target current values in the full color mode.

  As shown in Table 5, the same results as in Example 1 were obtained up to 150,000 sheets, but in the image evaluation after passing 200000 sheets, a cleaning failure occurred.

  FIG. 8 shows the measurement of the surface potential of the intermediate transfer belt 20 according to the number of sheets of the transfer material P that forms the evaluation image when image evaluation is performed after passing 200,000 sheets in the sheet passing durability test. It is a result. As shown in FIG. 8, in the full color mode, an increase in the surface potential of the intermediate transfer belt 20 is suppressed, but in the monochrome mode, the surface potential of the intermediate transfer belt 20 increases to about 180 [V] when 60 sheets are passed. did. This is because the electrical resistance of the intermediate transfer belt 20 further increases due to an increase in the number of sheets passed, and the charge accumulated in the intermediate transfer belt 20 becomes difficult to be relaxed.

  Table 6 shows the output value of the primary transfer power supply 40 at the time of image evaluation, the target current value of the conductive brush 31, and the target of the conductive roller 32 every time 50,000 sheets are passed in the monochrome mode paper passing durability test of this embodiment. It is the table | surface which described the electric current value and the result of the image evaluation for every 10 sheets. As shown in Table 6, in this embodiment, the target current values of the conductive brush 31 and the conductive roller 32 were set to 5 μA and 15 μA, respectively, in the endurance period when the number of sheets passed increased. Thus, even after 200000 sheets have been passed, no image defect due to a cleaning defect was observed during image evaluation.

  FIG. 9 shows an intermediate transfer according to the number of sheets of the transfer material P on which an evaluation image is formed when image evaluation is performed after passing 200,000 sheets by the sheet passing durability test in the monochrome mode of this embodiment. It is a measurement result of the surface potential of the belt 20. In the result of FIG. 9 in which the values of the target current values of the conductive brush 31 and the conductive roller 32 are changed with respect to the result of FIG. 8, the increase in the surface potential of the intermediate transfer belt 20 is suppressed to about 80 [V]. Yes.

  The rise in the surface potential of the intermediate transfer belt 20 depends on the current flowing from the charging unit 30 and the primary transfer roller 5 to the intermediate transfer belt 20. Therefore, an increase in the surface potential of the intermediate transfer belt 20 can be suppressed by reducing the target current value flowing from the charging unit 30 toward the intermediate transfer belt 20.

  Lowering the target current value of the charging means 30 also reduces the ability to charge the transfer residual toner, but the toner image primarily transferred to the intermediate transfer belt 20 in the monochrome mode is a multi-color toner as in the full color mode. Is not a superimposed toner image. Accordingly, the amount of transfer residual toner is small compared to the full color mode, and the transfer residual toner can be charged even if the target current value of the charging means 30 is lowered.

  In the present embodiment, the configuration in which the target current values of both the conductive brush 31 and the conductive roller 32 are reduced has been described. However, the present invention is not limited to this, and any one of the charging means 30 may be decreased. .

[Modification]
In the present embodiment, the configuration in which the target current value of the charging unit 30 is changed in the endurance period when the electrical resistance of the intermediate transfer belt 20 increases has been described. However, the present invention is not limited to this, and when performing the operation of collecting the residual toner in the monochrome mode, the target current value of the charging unit 30 is always set to a value lower than the target current value in the full color mode regardless of the number of sheets to be passed. May be. By setting in this way, the value of the voltage output from the charging power source 51 and the charging power source 52 can be set low, and the conduction deterioration of the conductive brush 31 and the conductive roller 32 can be suppressed.

2 Photosensitive drum 5 Primary transfer roller 20 Intermediate transfer belt 24 Secondary transfer roller 30 Charging means 40 Primary transfer power supply

Claims (19)

A first image carrier that carries a toner image, a second image carrier that carries a toner image, and a toner image carried on at least one of the first image carrier and the second image carrier A transferable intermediate transfer member to which the image is primarily transferred, a transfer member that is in contact with an inner peripheral surface of the intermediate transfer member and is disposed at a position corresponding to the first image carrier, and a voltage applied to the transfer member. With respect to the power supply to be applied and the moving direction of the intermediate transfer body, the toner is disposed downstream of the secondary transfer section that secondary-transfers the toner image from the intermediate transfer body to the transfer material, and has passed through the secondary transfer section. and a charging means for charging the, while the application of a reverse polarity voltage and the charging polarity of the normal toner on the transfer member from said power supply, a toner charged to the opposite polarity by the charging unit, the from the intermediate transfer member, said first image bearing member and said In the image forming apparatus capable of executing a recovery operation to move at least one of the two of the image bearing member, so the pre-Symbol first image bearing member and said second image bearing member for abutting on the intermediate transfer body and when executing the recovery operation in the first mode, the first voltage is applied to the transfer member from said power source, the pre-SL is brought into contact with the first image carrier to said intermediate transfer member 2 of the image bearing member when performing the recovery operation in the second mode in which is separated from the intermediate transfer member, the absolute value is larger second than the first voltage to the transfer member from said power supply An image forming apparatus characterized by applying a voltage. A charging power source for charging the toner that has passed through the secondary transfer portion to the reverse polarity by applying a voltage of the reverse polarity to the charging unit;
In the second mode, the charging power source has a value of current flowing from the charging unit to the intermediate transfer member in the second mode from a value of current flowing from the charging unit to the intermediate transfer member in the first mode. 2. The image forming apparatus according to claim 1, wherein the voltage having the reverse polarity is applied to the charging unit so that the absolute value becomes a small value. After the number of transfer materials onto which the toner image is secondarily transferred in the secondary transfer portion exceeds a predetermined number,
In the second mode, the charging power source has a value of current flowing from the charging unit to the intermediate transfer member in the second mode from a value of current flowing from the charging unit to the intermediate transfer member in the first mode. 3. The image forming apparatus according to claim 2, wherein the voltage having the reverse polarity is applied to the charging unit so that the absolute value becomes a small value.   A current detection unit configured to detect a value of a current flowing through the charging unit when a voltage is applied from the charging power source to the charging unit; and a current detected by the current detection unit is set to a predetermined current value. The image forming apparatus according to claim 2, wherein the reverse polarity voltage is applied from the charging power source to the charging unit. If the number of the transfer material is secondarily transfers the toner image at the secondary transfer portion to perform the recovery operation in the second mode after exceeding the predetermined number, the power supply to the transfer member The image forming apparatus according to claim 1, wherein the second voltage is applied. The transfer member is a first transfer member, the power source is a first power source, and a second transfer is arranged at a position corresponding to the second image carrier in contact with the inner peripheral surface of the intermediate transfer member. A member and a second power source for applying a voltage to the second image carrier,
Regarding the moving direction of the intermediate transfer member, the second image carrier is provided upstream of the first image carrier and downstream of the secondary transfer unit.
In the first mode, the first voltage is applied from the first power source and the second power source to the first transfer member, and the reverse polarity is applied from the second power source to the second transfer member. by applying a voltage, while the primary transfer of the toner image on the intermediate transfer member from the first image bearing member and said second image bearing member, the intermediate transfer body before Symbol second image bearing The image forming apparatus according to claim 1, wherein the collecting operation is performed at a position where the body abuts. With respect to the rotation direction of the second image carrier, the second image carrier is provided on the downstream side of the primary transfer portion where the second image carrier and the intermediate transfer member abut, and after passing through the primary transfer portion, A recovery means for recovering the toner remaining on the image carrier 2;
The collecting unit has a contact member that contacts the second image carrier and collects toner remaining on the second image carrier to the collecting unit;
When executing the collecting operation in the first mode, the collecting unit collects the toner charged to the reverse polarity by the charging unit and moved from the intermediate transfer member to the second image carrier. The image forming apparatus according to claim 6. The reverse polarity of the voltage applied to the prior SL second or power et before Symbol second transfer member is different from the first voltage applied to the first transfer member from said first power supply The image forming apparatus according to claim 6 , wherein the voltage is a value voltage . A third image carrier provided upstream of the first image carrier and downstream of the second image carrier with respect to the moving direction of the intermediate transfer member; and A third transfer member that contacts an inner peripheral surface and is disposed at a position corresponding to the third image carrier.
9. The image forming apparatus according to claim 6, wherein the second image carrier is an image carrier that is provided on the most upstream side in the moving direction of the intermediate transfer member. The image forming apparatus according to claim 9, wherein a voltage is applied to the third transfer member from the second power source. The image forming apparatus according to claim 9, further comprising a third power source that applies a voltage to the third transfer member. By applying the second voltage the to the power supply or al before Symbol transfer member in said second mode, at a position where the intermediate transfer member and the first image bearing member abuts, the first image bearing wherein the body intermediate transfer member the image forming apparatus according to any one of claims 1 to 5, characterized in that to perform said recovery operation while the primary transfer of the toner image on the. With respect to the rotational direction of said first image bearing member, the intermediate transfer member and the first image bearing member is disposed downstream of the primary transfer portion abutting said after passing through the primary transfer portion first A recovery means for recovering the toner remaining on the image carrier of 1 ;
It said recovery means includes a contact member for recovering toner remaining in contact with the first image carrier to said first image carrier to the recovery means,
When performing the recovery operation in the second mode, being charged by said charging means to said opposite polarity, you collected by the toner is moved to the first image carrier from the intermediate transfer member the collecting means the image forming apparatus according to claim 12, wherein the this. Said first image bearing member, an image forming apparatus according to any one of claims 1 to 13, characterized in that an image bearing member for bearing a toner image of black. The intermediate transfer member is further provided with a second transfer member that is disposed at a position corresponding to the second image carrier and in contact with the inner peripheral surface of the intermediate transfer member. by contact with or spaced the second transfer member with respect to the second image bearing member via, be pre-SL and the second image bearing member and said intermediate transfer member contact with or separated from the image forming apparatus according to any one of claims 1 to 1 4, characterized in that possible is. It said charging means is a roller member having conductivity, wherein the roller member is an image forming apparatus according to any one of claims 1 to 1 5, characterized in that in contact with the intermediate transfer member. It said charging means is a brush member having conductivity, wherein the brush member, the image forming apparatus according to any one of claims 1 to 1 5, characterized in that in contact with the intermediate transfer member. The charging unit is a conductive roller member, and a conductive brush member disposed upstream of the roller member with respect to the moving direction of the intermediate transfer member. The roller member and the brush member are the image forming apparatus according to any one of claims 1 to 1 5, characterized in that in contact with the intermediate transfer member. The transfer member is a metal roller, wherein with respect to the moving direction of the intermediate transfer member, prior Symbol metal roller shifted to the upstream side or downstream side of a position where the front Symbol first image bearing member and said intermediate transfer member is in contact the image forming apparatus according to any one of claims 1 to 1 8, characterized in that arranged in position.

Images