JP2013246370A - Image forming apparatus - Google Patents

Abstract

In an image forming apparatus having a plurality of image forming units, residual toner on an intermediate transfer member is dispersed and collected in each image forming unit.
The residual toner on the intermediate transfer belt 50 is charged to a polarity opposite to the normal charging polarity of the toner by a toner charging roller 58 to be moved to the photosensitive drum 1 to be a waste toner container corresponding to the photosensitive drum 1. In the image forming apparatus that can be collected in 62, a plurality of photosensitive drums 1 and the intermediate transfer belt 50 are provided with a separation control roller 12 that can contact and separate the plurality of photosensitive drums 1, and the residual toner charged by the toner charging roller 58 When the photosensitive drum 1 is moved to the intermediate transfer belt 50 and recovered from the intermediate transfer belt 50, the contact / separation state between the plurality of photosensitive drums 1 and the intermediate transfer belt 50 is switched by the separation / contact control roller 12, thereby the intermediate transfer belt 50. The photosensitive drum 1 to which the residual toner moves is changed.
[Selection] Figure 3

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer having a function of forming an image on a recording material such as a sheet.

Conventionally, as an electrophotographic image forming apparatus such as a copying machine or a laser beam printer, an image forming apparatus using an intermediate transfer member is known. The intermediate transfer type image forming apparatus forms a color image or the like on a recording material by a primary transfer process and a secondary transfer process. Also, in order to increase the speed, an image called an inline type in which a plurality of photoconductors (image carriers) are stacked and stacked, and a toner image is sequentially formed on each photoconductor and is transferred onto an intermediate transfer body in a multiple transfer manner. There is a forming device.
In the image forming apparatus having the above configuration, first, as a primary transfer step, a toner image as a transferable image formed on the surface of the photosensitive member is transferred (primary transfer) to the intermediate transfer member. By repeating this process for a plurality of color toner images, a multiple toner image composed of 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 collectively transferred (secondary transfer) onto the surface of a recording material such as paper.

In an intermediate transfer type image forming apparatus, after secondary transfer of a toner image from an intermediate transfer member to a recording material, secondary transfer residual toner (residual toner, transfer residual toner, waste toner) is formed on the surface of the intermediate transfer member. ) Remains. Therefore, an image forming apparatus as disclosed in Patent Document 1 has been proposed in order to remove secondary transfer residual toner remaining on the surface of the intermediate transfer member.
Patent Document 1 discloses an inline image forming apparatus having a toner charging member that charges secondary transfer residual toner with a polarity opposite to a normal charging polarity. By this charging member, the secondary transfer residual toner is charged to a polarity opposite to the normal charging polarity, that is, a polarity opposite to the surface potential of the photoconductor, and is moved simultaneously with the primary transfer and returned to the surface of the photoconductor. The in-line type image forming apparatus includes a waste toner container for storing toner removed from the photoreceptor for each image forming unit (station) that forms toner images of different colors.

Japanese Patent Laid-Open No. 2004-21134

However, there is a concern that the following problems may occur in the image forming apparatus described in Patent Document 1. Here, it is assumed that the image forming apparatus has first, second, third, and fourth stations that are stations for yellow (Y), magenta (M), cyan (C), and black (K) colors. To do.
That is, when a printing operation is performed by the image forming apparatus, the secondary transfer residual toner is a first portion located immediately downstream of the toner charging member and at the most upstream portion in all stations in the moving direction of the intermediate transfer member. Collected centrally at the station. Accordingly, the waste toner container of the first station has a larger amount of waste toner accumulated than the containers of other stations, and the cartridge replacement frequency of the first station when the process means of each station is made into a cartridge. Will rise more than others. Although it is possible to extend the cartridge replacement interval by increasing the capacity of the waste toner container of the first station, the size of the cartridge and the size of the image forming apparatus are increased.

On the other hand, by providing a contact / separation mechanism between the intermediate transfer member and the photosensitive member, it is possible to suppress the secondary transfer residual toner from being concentrated and collected in the first station. Usually, a full color image forming apparatus is provided with a single color image forming mode (monochrome mode) in addition to a multicolor image forming mode (color mode). Here, the color mode is a mode in which a full color image is obtained by forming a toner image at all stations. The monochrome mode is a mode in which a monochrome image is obtained by forming a toner image only at the K color station.
In such an image forming apparatus, the following functions are provided in order to prevent the Y, M, and C color photoconductors that are not originally required to be worn in the monochrome mode. Some are provided. That is, the intermediate transfer member is separated from the photosensitive member in the Y, M, and C color stations, and the operation of the photosensitive member is stopped.
If such a function for separating the intermediate transfer member from the photosensitive member is used in the Y, M, and C color stations, the intermediate transfer member is formed after the primary transfer process of the first to third stations is completed in the color mode. Can be separated from the photoconductors of the first to third stations. As a result, a part of the secondary transfer residual toner can be transported to the fourth station and collected through the second and third stations.
However, even if the secondary transfer residual toner can be suppressed from being concentrated and collected in the first station, the secondary transfer residual toner cannot be collected in the second and third stations. Therefore, the collection amount at the fourth station increases, and the cartridge replacement frequency at the fourth station increases.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to disperse and collect residual toner on an intermediate transfer member in each image forming unit in an image forming apparatus having a plurality of image forming units. And

In order to achieve the above object, the present invention provides:
A rotatable endless intermediate transfer member;
An image forming unit arranged in parallel along the rotation direction of the intermediate transfer member, an image carrier on which a toner image is formed, and a container for collecting the toner removed from the image carrier Two or more image forming units each having;
Have
The toner image formed on each image carrier is primarily transferred to the intermediate transfer member at each primary transfer portion formed between each image carrier and the intermediate transfer member, and then the intermediate transfer is performed. An image forming apparatus in which a secondary transfer portion on a body is secondarily transferred collectively to a recording material and an image is formed on the recording material,
In the rotational direction of the intermediate transfer member, the intermediate transfer member is provided downstream of the secondary transfer unit and upstream of the primary transfer unit of the most upstream image carrier among all the image carriers. A charging member for charging the residual toner on the toner to a polarity opposite to the normal charging polarity of the toner;
In the image forming apparatus in which the residual toner on the intermediate transfer member is charged to the reverse polarity by the charging member and can be moved to the image carrier and collected in the container corresponding to the image carrier.
A contact / separation means capable of contacting and separating the plurality of image carriers and the intermediate transfer member;
When the residual toner charged by the charging member is moved to the plurality of image carriers and collected from the intermediate transfer member, the contact and separation means contacts the plurality of image carriers and the intermediate transfer member. The image carrier on which the residual toner moves from the intermediate transfer member is changed by switching the contact / separation state.

According to the present invention, in an image forming apparatus having a plurality of image forming units, the residual toner on the intermediate transfer member can be dispersed and collected in each image forming unit.

Sectional drawing which shows schematic structure of the image forming apparatus of Example 1. FIG. FIG. 3 is a block diagram for explaining the operation of the image forming apparatus according to the first embodiment. FIG. 1 is a schematic cross-sectional view showing a separated state in the image forming apparatus shown in FIG. The figure which shows the timing chart explaining the operation | movement at the time of the color mode of Example 1. FIG. The figure which shows the timing chart explaining the operation | movement at the time of the color mode of the comparison structure 1. The figure which shows the timing chart explaining the operation | movement at the time of the color mode of the comparison structure 2. The figure which shows the timing chart explaining the operation | movement at the time of the color mode of Example 2. FIG. Sectional drawing which shows schematic structure of the image forming apparatus of Example 3. FIG.

  DETAILED DESCRIPTION Exemplary embodiments for carrying out 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 this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

<Overall Configuration and Operation of Image Forming Apparatus>
(1) Overall Configuration of Image Forming Apparatus First, the overall configuration of the image forming apparatus of Embodiment 1 will be described.
FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus 100 according to the present exemplary embodiment. The image forming apparatus 100 according to the present exemplary embodiment is a laser beam printer that employs an inline method or an intermediate transfer method.
The image forming apparatus 100 includes first, second, third, and fourth stations (image forming stations) 10a, 10b, 10c, and 10d as image forming units. The first, second, third, and fourth stations 10a, 10b, 10c, and 10d are located along the moving direction of the surface of the intermediate transfer belt 50 that can move around (the rotation direction and the rotation direction of the intermediate transfer belt 50). They are arranged (in parallel) in this order from the upstream side. Here, the intermediate transfer belt 50 is formed of an endless belt, and corresponds to a rotatable endless intermediate transfer member. The first station 10a is the most upstream station in the moving direction of the surface of the intermediate transfer belt 50 among all the stations. The fourth station 10d is the most downstream station in the moving direction of the surface of the intermediate transfer belt 50 among all the stations.
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). This is a station for toner image formation. In this embodiment, the basic configuration and operation of the first to fourth stations 10a to 10d are the same except that the color of the toner used is different. Accordingly, in the following description, when there is no need for distinction, the subscripts a, b, c, and d given to the reference numerals in order to represent elements provided for any color will be omitted.

Each station 10 is provided with a cylindrical electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 shown in FIG. 1 (counterclockwise in FIG. 1). In this embodiment, the photosensitive drum 1 is an OPC (organic photoconductor) photosensitive drum.
In each station 10, around the photosensitive drum 1, there are a charging roller 2 as a charging unit, an exposure device 3 as an exposure unit, a developing device (developing unit) 4 as a developing unit, and a cleaning device (cleaning unit) 6. Is provided. Here, the charging roller 2 is for charging the photosensitive drum 1. The exposure device 3 is for exposing the surface of the charged photosensitive drum 1. The developing device 4 is for developing an electrostatic image formed on the photosensitive drum 1. The cleaning device 6 is for cleaning the toner on 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 while being 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. The photosensitive drum 1 is charged by the occurrence of discharge at the contact nip between the charging roller 2 and the surface of the photosensitive drum 1 in the rotation direction of the photosensitive drum 1.
The exposure device 3 is a scanner unit that scans laser light with a polygon mirror, and irradiates the photosensitive drum 1 with a scanning beam L that is modulated based on an image signal. As a result, an electrostatic image (electrostatic latent image) based on the image signal is formed on the photosensitive drum 1.

The developing device 4 includes a developing container 42 that stores a non-magnetic one-component developer (hereinafter, toner) as a developer. 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.
The cleaning device 6 has a waste toner container 62 as a container for containing (collecting) toner removed from the photosensitive drum 1 (on the image carrier). The waste toner container 62 is provided with a cleaning blade 61 as a cleaning member as a cleaning unit 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 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. .
On the outer peripheral surface side of the intermediate transfer belt 50, a secondary transfer member (rotating member) as a secondary transfer unit is provided at a position facing a secondary transfer counter roller 55 that is one of the stretching members of the intermediate transfer belt 50. A certain 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, a secondary transfer residual toner charging member 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 that is a (rotating member) is disposed. The toner charging roller 58 is disposed in contact with the intermediate transfer belt 50. In other words, in this embodiment, the surface of the intermediate transfer belt 50 is positioned on the surface of the intermediate transfer belt 50 downstream of the secondary transfer portion N2 and upstream of the primary transfer portion N1a of the first station 10a 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 100 further includes a fixing device 7 as fixing means for fixing the toner transferred to the recording material P to the recording material P, a recording material supply device 8 for feeding the recording material P for forming an image, and the like. Have.

In this embodiment, the photosensitive drum 1, the charging roller 2 as a process unit acting on the photosensitive drum 1, the developing device 4, and the cleaning device 6 are an integrated process cartridge 9 that is detachable from the apparatus main body of the image forming apparatus 100. Is configured. Here, the process cartridge is an apparatus main body of an image forming apparatus in which a photosensitive drum and at least one of charging means, developing means, and cleaning means as process means acting on the photosensitive drum are integrally formed into a cartridge. This means that it can be attached to and detached from.

The charging roller 2 is connected to a charging voltage power source 21 as a voltage supply unit to the charging roller 2. The developing roller 41 is connected to a developing voltage power supply 44 as a voltage supply unit to the developing roller 41. The primary transfer roller 51 is connected to a primary transfer voltage power source 56 as voltage supply means (electric field forming means for forming an electric field in the primary transfer portion N1) to the primary transfer roller 51. The secondary transfer roller 52 is connected to a secondary transfer voltage power source 57 as a voltage supply unit to the secondary transfer roller 52. The toner charging roller 58 is connected to a toner charging voltage power source 59 as voltage supply means to the toner charging roller 58.
Here, the intermediate transfer belt 50 provided in the intermediate transfer unit 5 is supported (stretched) by four rollers: a drive roller 53, a tension roller 54, a secondary transfer counter roller 55, and a separation / contact control roller 12. Appropriate tension is to be maintained. When the driving roller 53 is driven to rotate, 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, an endless belt made of PVdF (polyvinylidene fluoride) having a thickness of 100 μm and a volume resistivity of 10 ¹¹ Ωcm was used as the intermediate transfer belt 50. As the driving roller 53 serving as a tension member, an aluminum cored bar having a diameter of 30 mm and coated with EPDM rubber having a resistance of 10 ⁴ Ω dispersed with carbon as a conductive agent and a thickness of 1.0 mm was used. 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 direction of the arrow R2 shown in FIG. 1 (clockwise in FIG. 1). The primary transfer roller 51 is disposed on the opposite side of the photosensitive drum 1 with the intermediate transfer belt 50 interposed therebetween. On the downstream side of each primary transfer roller 51 in the rotation direction (movement direction) of the intermediate transfer belt 50, a static elimination member (static elimination needle) 11 located on the inner peripheral surface side of the intermediate transfer belt 50 is disposed. Here, 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.
As the secondary transfer roller 52, a nickel-plated steel rod having a diameter of 6 mm and an NBR foamed sponge-like elastic body coated with a thickness of 5 mm was used. 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.
Here, in the present 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 with respect to the moving direction of the surface of the intermediate transfer belt 50. And arranged to rotate at a substantially constant 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 100 of this embodiment.
The host computer 200 issues a print command, and prints image data of the print image.
It plays the role of transferring to the interface board 151 installed in 00. 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 operation of the developing / separating devices 45a to 45c for the color developing device for bringing the color developing devices 4a to 4c into contact with or separating from the photosensitive drums 1a to 1c is controlled.
Further, the DC controller 150 controls the operation of the movable means to move the separation control roller 12 so that the intermediate transfer belt 50 contacts the photosensitive drums 1a to 1c of the first to third stations 10a to 10c. Alternatively, control to separate them is performed. As described above, among all the stations, the photosensitive drums 1a to 1c of the first to third stations 10a to 10c except the fourth station 10d which is the most downstream in the moving direction of the surface of the intermediate transfer belt 50, and the intermediate transfer belt. 50 is provided so as to be able to contact and separate. Here, the movable means and the separation / contact control roller 12 correspond to contact / separation means. The photosensitive drums 1a to 1c correspond to a plurality of image carriers including the most upstream image carrier (corresponding to the photosensitive drum 1a) among all the image carriers (corresponding to the photosensitive drum 1). The primary transfer portion N1 is formed by the contact between the intermediate transfer belt 50 and the photosensitive drum 1, but in this embodiment, even when the intermediate transfer belt 50 and the photosensitive drum 1 are separated from each other, the primary transfer portion N1 is photosensitive. The primary transfer portion N1 (on the intermediate transfer belt 50) corresponding to the drum 1 will be described.

FIG. 3 is a schematic cross-sectional view showing a state in which the intermediate transfer belt 50 is separated from the photosensitive drums 1a to 1c of the first to third stations 10a to 10c in the image forming apparatus 100 of the present embodiment shown in FIG.
In FIG. 1, the separation control roller 12 is in a position to urge the intermediate transfer belt 50 from the inner peripheral side toward the outer peripheral side, and the intermediate transfer belt 50 and the photosensitive drums of the first to fourth stations 10a to 10d. The state which 1a-1d contact | abutted all is shown.
On the other hand, FIG. 3 shows a state in which the separation control roller 12 is retracted toward the inner side of the intermediate transfer belt 50 so as to release the urging of the intermediate transfer belt 50. At this time, the primary transfer rollers 51a to 51c and the charge removing members (charge eliminating needles) 11a to 11c of the first to third stations 10a to 10c are also retracted downward in the drawing.
Thus, the intermediate transfer belt 50 is integrally 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 in contact with the intermediate transfer belt 50. Become. This state is the home position of the image forming apparatus 100 in the standby state.

The DC controller 150 controls the high-voltage power supply with 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 voltage power supply 21, development voltage power supply 44, primary transfer voltage power supply 56, secondary transfer voltage power supply 57, and toner charging voltage 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 voltage 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. The charging potential is controlled by the DC controller 150 controlling the high voltage generated in the high voltage power supply 153 (charging voltage power supply 21).
Similarly, 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 are supplied with a high voltage from a high voltage power supply 153, and the applied voltage is applied by a DC controller 150. Be controlled. In this embodiment, the primary transfer voltage power source 56 is a single unit that supplies a common primary transfer voltage to the primary transfer rollers 51a, 51b, 51c, and 51d of each station.

(2) Image Forming Operation Next, the image forming operation of the image forming apparatus 100 of this embodiment will be described.
(2-1) Color Mode First, an image in a color mode (multicolor image forming mode, first image forming mode) capable of forming a full color image using all of the first to fourth stations 10a to 10d. The forming operation will be described.

  When the image forming apparatus 100 receives a print command for color printing from a standby state, the image forming apparatus 100 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 rotating in the direction of the arrow shown in FIG. 1 at a predetermined process speed. Here, 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. That is, when the separation control roller 12 moves from the position shown in FIG. 3 to the position shown in FIG. 1, the intermediate transfer belt 50 and the photosensitive drums 1a to 1d of the first to fourth stations 10a to 10d are all in contact. .

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 voltage from the charging voltage power supply 21 to the charging roller 2. 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 voltage having a predetermined potential (−300 V in this embodiment) having a predetermined polarity (negative polarity in this embodiment) from the developing voltage 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 the present embodiment, the developing device 4 is configured such that the toner charged to the same polarity as the charging polarity of the photosensitive drum 1 is a portion where the charge is attenuated by exposure of the surface of the charged photosensitive drum 1 (exposure portion, image portion). The electrostatic image is developed by a reversal development method that adheres to ().

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. In the second to fourth stations 10b, 10c, and 10d, toner images of M, C, and K colors are formed on the photosensitive drums 1b, 1c, and 1d, respectively, by the same operation. At this time, the DC controller 150 delays the writing signal from the DC controller 150 at a constant timing for each color according to the distance between the primary transfer positions, and the exposure device 3 outputs the electrostatic image to each of the photosensitive drums 1 a to 1. Form on 1d. Next, the primary transfer rollers 51a to 51d of the stations 10a to 10d are supplied with DC voltages from the primary transfer voltage power sources 56a to 56d having a polarity opposite to the normal charging polarity of the toner (positive in this embodiment). Is applied.
Through the above steps, the toner images of the respective colors Y, M, C, and K are transferred onto the intermediate transfer belt 50 so as to sequentially overlap (primary transfer), 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 recording material P is supplied to the secondary transfer portion N2 by the recording material supply device 8 in accordance with the electrostatic image formation by exposure. That is, the recording material P loaded in the recording material cassette 81 is picked up by the recording material supply roller 82 and conveyed to the registration roller 83 by a conveyance roller (not shown). Next, the recording material P is synchronized with the toner image on the intermediate transfer belt 50, and 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 voltage having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the secondary transfer roller 52 by a secondary transfer voltage 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 recording material P in the secondary transfer portion N2.

  On the other hand, the toner (residual toner) remaining on the intermediate transfer belt 50 (intermediate transfer member) after the secondary transfer process is finished, that is, the secondary transfer residual toner is disposed in contact with the intermediate transfer belt 50. The toner charging roller 58 is charged. A toner charging voltage 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 recording 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 (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.
Discharge occurs between the toner charging roller 58 and the intermediate transfer belt 50, and the secondary transfer residual toner on the intermediate transfer belt 50 is set to the opposite polarity (positive polarity in this embodiment) to the normal charging polarity. Has the effect of charging. In this embodiment, typically, the toner charging roller 58 charges substantially all the secondary transfer residual toner on the intermediate transfer belt 50 to a polarity opposite to the normal charging polarity of the toner.

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, moves to the photosensitive drum 1 at the primary transfer portion N1, and is discarded from the station 10. The toner is collected in the toner container 62. Here, the secondary transfer residual toner (residual toner) that has been subjected to the charging process moves from the intermediate transfer belt 50 to the photosensitive drum 1 may be referred to as reverse transfer in the following description. The secondary transfer residual toner collecting operation will be described in detail later.
The recording material P after the completion of the secondary transfer process is conveyed to the fixing device 7, receives a toner image fixing process, and is discharged to the outside of the image forming apparatus 100 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 100, the image forming apparatus 100 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, second 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 100 has a monochrome mode in which a monochrome image can be formed using only the fourth station 10d for K color.
More specifically, when the image forming apparatus 100 receives a monochrome print command from the standby state, the image forming apparatus 100 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 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. The developing devices 4a to 4c are kept apart from the photosensitive drums 1a to 1c, respectively. The developing device 4d is brought into contact with the photosensitive drum 1d only at the fourth station 10d which is a K color station.
Thereby, only at the fourth station 10d, the electrostatic image formed on the photosensitive drum 1d by the exposure device 3d becomes visible as a toner image.
The separation / contact control roller 12 does not move in the position shown in FIG. 3 and maintains the state where only the photosensitive drum 1d of the fourth station 10d is in contact with the intermediate transfer belt 50.
Other basic image forming operations are the same as those in the color mode described above except that the toner image is formed and the secondary transfer residual toner is collected only in the fourth station 10d for K color.

<Secondary transfer residual toner collection operation>
(1) Outline of Secondary Transfer Residual Toner Collection Operation Next, the secondary transfer residual toner collection operation, which is a characteristic operation of the image forming apparatus 100 of this embodiment, will be described.
In this embodiment, the residual toner on the intermediate transfer belt 50 charged to the reverse polarity is reversely transferred from the intermediate transfer belt 50 onto at least one of the photosensitive drums 1 of all the stations 10, and the waste toner in the station 10 is transferred. The container 62 is configured to be recoverable. Here, the reverse transfer can be performed simultaneously with the primary transfer.
In the color mode, after the primary transfer at the most upstream station 10a is completed, at least a part of the toner on the intermediate transfer belt 50 charged to the reverse polarity reaching the primary transfer portion N1a of the most upstream station 10a. Is recovered as follows. That is, after passing through the primary transfer portion N1a of the most upstream station 10a, it is recovered by reverse transfer at a station other than the most upstream station 10a (other than the image carrier). This is executed by moving the separation control roller 12 and controlling the intermediate transfer belt 50 to contact or separate from the photosensitive drums 1a to 1c of the first to third stations 10a to 10c. In this embodiment, as described above, the contact / separation state between the photosensitive drums 1a to 1c and the intermediate transfer belt 50 is switched by the contact / separation means (separation / contact control roller 12). The photosensitive drum 1 to which the transfer residual toner moves is changed.

(2) Details of Secondary Transfer Residual Toner Collection Operation Next, the secondary transfer residual toner collection operation in the color mode will be described.
FIG. 4 is a timing chart for explaining the operation in the color mode of this embodiment. The horizontal axis is time. On the lines “Yst.”, “Mst.”, “Cst.”, “Kst.”, Toner is present in the primary transfer portions N1a to N1d of the first to fourth stations 10a to 10d, respectively. Represents. Further, on the lines of “Y to Cst. Contact” and “Y to Cst. Separation”, the contact between the intermediate transfer belt 50 and the photosensitive drums 1 a to 1 c in the first to third stations 10 a to 10 c respectively. The separated state is shown. On the lines of “T1 voltage ON” and “T1 voltage OFF”, primary transfer voltages (voltages commonly applied to the respective primary transfer rollers) are represented. On the “2ndXfer” line, the operation of the secondary transfer portion N2 (voltage applied to the secondary transfer roller) is shown.

The operation when six images are continuously printed by one print command (one job) will be described with reference to FIG.
When receiving a color print command from the standby state of the image forming apparatus, the separation control roller 12 moves from the position shown in FIG. 3 to the position shown in FIG. 1, and the intermediate transfer belt 50 and the first to third stations 10a. 10 c of photosensitive drums 1 a to 1 c are brought into contact with each other. 4 shows a state change from “Y to Cst. Separation” to “Y to Cst. Contact”.

Next, the primary transfer voltage applied to the primary transfer rollers 51a to 51d of the stations 10a to 10d is turned on. The voltage value at this time is + 500V. FIG. 4 shows a state change from “T1 voltage OFF” to “T1 voltage ON”.
Thereafter, the toner image formed at the developing unit of the first station 10 a is primarily transferred to the intermediate transfer belt 50.

  In FIG. 4, Y1 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 respectively 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. That is, the first alphabetic character indicates the color of the station where the toner image is formed, and the second number indicates the number of sheets.

  Further, the secondary transfer roller voltage indicated by the 2ndXfer line in FIG. 4 is configured so that the output can be alternately changed between the Lo level and the Hi level. In FIG. 4, Lo indicates a state in which a relatively low voltage (+1000 V) is output when the recording material P is not in the secondary transfer portion N2. In FIG. 4, Hi indicates a state in which a relatively high voltage (+1500 V) is output when the recording material P is in the secondary transfer portion N2. In FIG. 4, pages 1 to 6 represent periods during which secondary transfer of the first to sixth toner images to the recording material P is performed.

4 is a 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. From time t1 to 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, primary transfer starts so that the M toner image overlaps the Y toner image.
Similarly, times t3 and t4 are times when 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 is.

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 recording 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 indicates a period during which the secondary transfer residual toner of the first toner image reaches the primary transfer portion N1a of the first station 10a, is reversely transferred onto the photosensitive drum 1, and is collected. In WY2, WY3, WY4, and WY5, the secondary transfer residual toner of the second to fifth toner images reaches the primary transfer portion N1a of the first station 10a, and is reversely transferred onto the photosensitive drum 1 and collected. Shows the period. In addition, the description is the same for the other, the first letter W is the secondary transfer residual toner, the second letter is the color of the station where the toner image is formed, the third letter The numbers indicate the number of sheets of toner image secondary transfer residual toner. Further, the secondary transfer residual toner reversely transferred and collected on each photosensitive drum 1 is collected in each of the waste toner containers 62a to 62d.

  While the secondary transfer residual toner passes through the primary transfer portion N1, a voltage of the same polarity (positive polarity in this embodiment) as 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. 4, during the primary transfer of the toner image formed on the photosensitive drum 1 to the intermediate transfer belt 50, the secondary transfer charged to a polarity opposite to the normal polarity. 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. As described above, 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 from each other, and in the period in which the period Y3 and the period WY1 overlap, the transfer is performed. Simultaneous collection 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.

Then, at the time t7 when the step of primary transfer of the sixth (last page) toner image on the photosensitive drum 1c to the intermediate transfer belt 50 at the primary transfer portion N1c of the third station 10c is completed, as follows. Operation (control) is performed. That is, a separation operation is performed in which the contact state between the intermediate transfer belt 50 and the photosensitive drums 1a to 1c in the first to third stations 10a to 10c is simultaneously switched to the separation state.
Note that the control for moving the separation / contact control roller 12 for this operation assumes 0.5 seconds as the time required for the separation / contact control roller 12 to move from the contacted position to the separated position. Actually, the control unit starts from a timing that is 0.5 seconds earlier than time t7. The time t7 is the time when six images are continuously printed with one print command (one job) in the present embodiment. The timing (time, time) for performing the separation operation is as follows. It can be said as follows. That is, the most downstream photosensitive drum 1c among the photosensitive drums that can be brought into contact with and separated from the intermediate transfer belt 50 when there is no subsequent recording material on which the image is continuously formed with respect to the recording material on which the image is formed. Is the timing when the primary transfer of the toner image to the intermediate transfer belt 50 is completed.

  By the above control, the secondary transfer residual toner of the fifth toner image is reversely transferred and collected on the photosensitive drum 1a by the primary transfer portion N1a of the first station 10a before time t7 (WY5), and time t7. Thereafter, the portion of the toner in the rear direction in the conveyance direction passes through the primary transfer portion N1a. The toner further passes through the primary transfer portion N1b and the primary transfer portion N1c, and reaches the primary transfer portion N1d of the fourth station 10d at time t8. Then, the positive T1 voltage is reversely transferred to the photosensitive drum 1d and collected. This period is indicated as WK5 in FIG. Here, the toner conveyance direction is the same as the movement direction of the surface of the intermediate transfer belt 50.

Next, the secondary transfer residual toner of the sixth toner image also passes through the primary transfer portions N1a, N1b, and N1c while the intermediate transfer belt 50 and the photosensitive drums 1a to 1c are separated from each other, and passes through the fourth transfer station 10d. It is conveyed to the primary transfer portion N1d. The portion near the front end of the toner in the transport direction is collected on the photosensitive drum 1d by applying a positive voltage to the primary transfer portion N1d. This period is indicated as WK6 in FIG.

Here, in the image forming apparatus according to the present exemplary embodiment, at the time t9, the trailing end (upstream end) of the sixth toner image in the secondary transfer residual toner in the transport direction passes the primary transfer portion N1a of the first station 10a. When it is time to pass (timing A), the following operation is performed. That is, a contact operation is performed in which the contact state between the intermediate transfer belt 50 and the photosensitive drums 1a to 1c in the first to third stations 10a to 10c is switched to the contact state again.
In addition, here, in the case where six images are continuously printed with one print command (one job), the second transfer of the sixth toner image is performed as the timing (time and time) for performing the contact operation. The position of the remaining toner was used. In other words, the secondary transfer residual toner is subjected to secondary transfer on the recording material when there is no subsequent recording material on which the image is continuously formed on the recording material on which the image is formed. Thus, the residual toner remains on the intermediate transfer belt 50.
Note that the control for moving the separation / contact control roller 12 for this operation also assumes 0.5 seconds as the time required for the separation / contact control roller 12 to move from the separated position to the contact position. Actually, the control unit starts from a timing that is 0.5 seconds earlier than time t9.

At this time, the secondary transfer residual toner of the sixth toner image is the photosensitive drum 1b of the second station 10b near the rear end in the transport direction and the photosensitive drum 1c of the third station 10c near the center in the transport direction. In addition, they are reversely transferred and recovered by applying a positive voltage. This period is shown as WC6 and WM6 in FIG.
After the collection of the secondary transfer residual toner is completed in the periods WC6 and WM6, the voltage applied to the primary transfer rollers 51a to 51d is turned off.
Next, the separation control roller 12 moves from the position shown in FIG. 1 to the position shown in FIG. 3, and the intermediate transfer belt 50 and the photosensitive drums 1a to 1c of the first to third stations 10a to 10c are separated. .

In this embodiment, by continuously printing six images as described above, the secondary transfer residual toner is collected in each station as follows. That is, about 4.3 sheets of secondary transfer residual toner of the output image is in the first station 10a, about 0.4 sheets are in the second station 10b, about 0.4 sheets are in the third station 10c, About 0.9 sheets were collected at the fourth station 10d.
Note that when the monochrome mode printing is performed by the image forming apparatus of the present embodiment, the separation control roller 12 does not move as shown in FIG. 3 throughout the printing operation, and the photosensitive drum 1d of the fourth station 10d. Only the contact with the intermediate transfer belt 50 is maintained. Accordingly, in the monochrome mode, all secondary transfer residual toner is collected by the photosensitive drum 1d of the fourth station 10d.

(3) Effects of this embodiment As described above, in this embodiment, a means (mechanism) is provided that enables the intermediate transfer belt to be brought into and out of contact with the photosensitive drums of a plurality of stations including the most upstream station. ing. In this embodiment, after the completion of full color printing, the intermediate transfer belt 50 and the photosensitive drum 1 are once separated and then brought into contact again to reversely transfer the secondary transfer residual toner to the separated photosensitive drum. It is characterized in that it performs control of recovery.
As a result, the secondary transfer residual toner on the intermediate transfer belt 50 can be well dispersed and collected in waste toner containers respectively provided at a plurality of stations.
In this embodiment, the timing of performing the contact operation is set to the above timing A, so that the secondary transfer residual toner of the sixth toner image can be prevented from being collected by the first station 10a.
The timing A is preferably the timing before the secondary transfer residual toner of the sixth toner image reaches the primary transfer portion N1d of the fourth station 10d. That is, the timing A may be set so that the secondary transfer residual toner of the sixth toner image is collected at the second and third stations 10b and 10c as much as possible. As a result, the secondary transfer residual toner of the sixth toner image can be suppressed from being collected at the fourth station 10d (so as not to be collected too much at the fourth station 10d). Thereby, the secondary transfer residual toner on the intermediate transfer belt 50 can be more favorably distributed and collected in a plurality of stations, and the cartridge replacement frequency of the fourth station 10d can be suppressed.
In the case where the image forming apparatus has a mechanism capable of bringing the intermediate transfer belt into and out of contact with the photosensitive drum at each of the Y, M, and C stations in order to perform monochrome printing as in this embodiment, the mechanism is used. The control of the present invention can be performed without introducing a new mechanism. On the other hand, even when the image forming apparatus is not provided with the above mechanism, a dedicated mechanism for performing the control of the present invention may be introduced.

(4) Comparative configuration (4-1) Comparative configuration 1
The secondary transfer residual toner collecting operation in the color mode of the image forming apparatus having the comparative configuration 1 will be described below.
FIG. 5 is a timing chart for explaining the operation in the color mode of the image forming apparatus of the comparative configuration 1. Each symbol shown in FIG. 5 is the same as the symbol described in FIG.

In the first embodiment, at the time when the step of primary transfer of the sixth (last page) toner image on the photosensitive drum 1c onto the intermediate transfer belt 50 at the primary transfer portion N1c of the third station 10c is completed. Control was performed. That is, the control for switching the contact state between the intermediate transfer belt 50 and the photosensitive drums 1a to 1c in the first to third stations 10a to 10c to the separated state is performed.
On the other hand, in this image forming apparatus, as in the first embodiment, control is performed to switch the contact state between the intermediate transfer belt 50 and the photosensitive drums 1a to 1c in the first to third stations 10a to 10c to the separated state. Not done.
Accordingly, the secondary transfer residual toner of the fifth toner image and the secondary transfer residual toner of the sixth toner image are all collected on the photosensitive drum 1a by the primary transfer portion N1a of the first station 10a.
In this configuration, when six images are printed, the secondary transfer residual toner for all pages of the output image is intensively collected in the first station 10a.

(4-2) Comparative configuration 2
The secondary transfer residual toner collecting operation in the color mode of the image forming apparatus having the comparative configuration 2 will be described below.
FIG. 6 is a timing chart for explaining the operation in the color mode of the image forming apparatus of the comparative configuration 2. Each symbol shown in FIG. 6 is the same as the symbol described in FIG.

In this image forming apparatus, as in the first embodiment, the step of primary transfer of the sixth (last page) toner image on the photosensitive drum 1c onto the intermediate transfer belt 50 at the primary transfer portion N1c of the third station 10c. At the time when is completed, the following control is performed. That is, control is performed to switch the contact state between the intermediate transfer belt 50 and the photosensitive drums 1a to 1c in the first to third stations 10a to 10c to the separated state.
However, after that, the intermediate transfer belt 50 and the photosensitive drum 1 are transferred at the time when the trailing end of the secondary transfer residual toner of the sixth toner image passes through the primary transfer portion N1a of the first station 10a.
Control which switches the contact state of a-1c into the state of contact again is not performed.
Accordingly, a part of the secondary transfer residual toner of the fifth toner image and the secondary transfer residual toner of the sixth toner image are collected on the photosensitive drum 1d by the primary transfer portion N1d of the fourth station 10d. Is done. However, they are not collected on the photosensitive drum 1b by the primary transfer portion N1b of the second station 10b or on the photosensitive drum 1c by the primary transfer portion N1c of the third station 10c.

In this configuration, when six images are printed, about 4.3 secondary transfer residual toner of the output image is collected in the first station 10a, and about 1.7 sheets are collected in the fourth station 10d. Is done. However, the secondary transfer residual toner is not collected at the second and third stations.
As described above, in the image forming apparatuses of the comparative configuration 1 and the comparative configuration 2, the secondary transfer residual toner cannot be well dispersed and collected in a plurality of waste toner containers.

Example 2 will be described below. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the first embodiment, and the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
In this embodiment, the control related to the secondary transfer residual toner collecting operation is different from that in the first embodiment.

In the image forming apparatus according to the first exemplary embodiment, the primary transfer voltage is turned on when the contact state between the intermediate transfer belt 50 and the photosensitive drums 1a to 1c in the first to third stations 10a to 10c is switched to the separated state. The state remained. On the other hand, in the image forming apparatus of the present embodiment, the control is performed in a state where the primary transfer voltage is turned off (the electric field of the primary transfer portion N1 is removed).
Accordingly, the following effects can be obtained in addition to the same effects as those of the first embodiment in which the secondary transfer residual toner can be efficiently dispersed and recovered in a plurality of waste toner containers. That is, it is possible to satisfactorily suppress banding (band-like density unevenness) image defects that occur on the halftone image at the timing when the contact state between the intermediate transfer belt 50 and the photosensitive drums 1a to 1c is switched to the separated state.

FIG. 7 is a timing chart for explaining the operation in the color mode of the image forming apparatus of this embodiment. Each reference numeral shown in FIG. 7 is the same as the reference numeral described in FIG. 4 of the first embodiment, and the description thereof is omitted. Further, the control up to time t6 in the image forming apparatus of the present embodiment is the same as that in the first embodiment (FIG. 4).
In the image forming apparatus of the present embodiment, the process of primary transfer of the sixth (last page) toner image on the photosensitive drum 1d onto the intermediate transfer belt 50 at the primary transfer portion N1d of the fourth station 10d is completed. At time t7, the primary transfer voltage is turned off.
Thereafter, a time interval of 0.1 seconds, which is a time required for the primary transfer voltage to fall, is set, and the contact state between the intermediate transfer belt 50 and the photosensitive drums 1a to 1c in the first to third stations 10a to 10c is Switch to the separated state.
The control for moving the separation control roller 12 for this operation is the same as in the first embodiment, and is started as follows. That is, the time required for the separation control roller 12 to move from the contact state position to the separation state position is assumed to be 0.5 seconds. It starts from a retroactive timing.

By the above control, the secondary transfer residual toner of the fifth toner image is collected on the photosensitive drum 1a by the primary transfer unit N1a of the first station 10a before time t8 (WY5), and after the time t8, the same toner. The portion near the rear end in the transport direction passes through the primary transfer portion N1a.
The toner further passes through the primary transfer portion N1b and the primary transfer portion N1c, and travels toward the primary transfer portion N1d of the fourth station 10d. Assuming the time required for the primary transfer voltage to rise 0.1 seconds with respect to time t10 when the toner reaches the primary transfer portion N1d of the fourth station 10d, 0.1 seconds with respect to time t10. The primary transfer voltage is turned on again at time t9 that is back by that time. Then, the positive T1 voltage is reversely transferred to the photosensitive drum 1d and collected. This period is indicated as WK5 in FIG.

  Next, the secondary transfer residual toner of the sixth toner image also passes through the primary transfer portions N1a, N1b, and N1c while the intermediate transfer belt 50 and the photosensitive drums 1a to 1c are separated, and the fourth station 10d. To the primary transfer portion N1d. A portion near the front end of the toner in the transport direction is collected on the photosensitive drum 1d by a positive voltage. This period is indicated as WK6 in FIG.

Here, in the image forming apparatus of the present embodiment, at time t11, as in the first embodiment, the final transfer end of the secondary transfer residual toner of the sixth toner image is the primary transfer portion N1a of the first station 10a. When it is time to pass through, the following operation is performed. That is, a contact operation is performed in which the contact state between the intermediate transfer belt 50 and the photosensitive drums 1a to 1c in the first to third stations 10a to 10c is switched to the contact state again.
The control for moving the separation / contact control roller 12 for this operation also assumes 0.5 second as the time required for the separation / contact control roller 12 to move from the separated position to the contact position. Actually, the control means starts from a timing that is 0.5 seconds earlier than time t11.

At this time, the secondary transfer residual toner of the sixth toner image is the photosensitive drum 1b of the second station 10b near the rear end in the transport direction and the photosensitive drum 1c of the third station 10c near the center in the transport direction. In addition, they are reversely transferred and collected by the positive voltage respectively. This period is shown as WC6 and WM6 in FIG.
After the collection of the periods WC6 and WM6 is completed, the voltage applied to the primary transfer rollers 51a to 51d is turned off. Next, the separation control roller 12 moves from the position shown in FIG. 1 to the position shown in FIG. 3, and the intermediate transfer belt 50 and the photosensitive drums 1a to 1c of the first to third stations 10a to 10c are separated. .

In this embodiment, by continuously printing six images as described above, the secondary transfer residual toner is collected in each station as follows. That is, about 4.8 sheets of secondary transfer residual toner of the output image is in the first station 10a, about 0.4 sheets are in the second station 10b, about 0.4 sheets are in the third station 10c, About 0.4 sheets were collected at the fourth station 10d.
In the image forming apparatus of the present embodiment as well, as in the first embodiment, the primary transfer voltage power source 56 applies a common primary transfer voltage to the primary transfer rollers 51a, 51b, 51c, and 51d of each station. To supply. Therefore, the timing (t7) for stopping the application of the primary transfer voltage must be after the primary transfer of the fourth station is completed. Therefore, compared with the first embodiment, the recovery amount of the first station is increased, and the recovery amount of the fourth station is decreased.

Here, the reason why the occurrence of banding image defects can be suppressed by the above control will be described below.
When printing is performed by the image forming apparatus of the present embodiment, both frictional force and electrostatic attraction force are generated between the intermediate transfer belt 50 and the photosensitive drum 1. That is, since the intermediate transfer belt 50 and the photosensitive drum 1 are in physical contact, a frictional force is generated between the intermediate transfer belt 50 and the photosensitive drum 1, and the voltage applied to the primary transfer roller 51 is electrostatically generated in the primary transfer portion N1. Adsorption force is generated.
Usually, the intermediate transfer belt 50 travels at a constant speed in the rotational direction by the driving force of the driving roller 53. At that time, the intermediate transfer belt 50 travels in a state where it receives a binding force from the photosensitive drum 1 due to the influence of the frictional force and the adsorption force. On the other hand, in the secondary transfer portion N2, the recording material P is conveyed by receiving a driving force from the registration roller 83. The speed of the intermediate transfer belt 50 and the speed of the recording material P in the secondary transfer portion N2 are set to be substantially constant.

When the intermediate transfer belt 50 and the photosensitive drum 1 are separated from each other in this state, the force acting between the two, that is, the frictional force and the adsorption force disappears instantaneously. At this time, a sudden speed change occurs in a portion of the intermediate transfer belt 50 interposed in the primary transfer portion N1. This speed change is propagated in the rotation direction of the intermediate transfer belt 50, and the speed change is also caused in a portion of the intermediate transfer belt 50 interposed in the secondary transfer portion N2. If the secondary transfer process is performed in the secondary transfer portion N2 at this timing, there is a concern that a mismatch may occur between the speed of the intermediate transfer belt 50 and the speed of the recording material P.
Due to this speed mismatch, banding image defects may occur on the toner image transferred from the intermediate transfer belt 50 onto the recording material. When such an image defect occurs, the text image does not stand out, but the visibility on the halftone image is high, and the full color image quality such as graphics and photographic images is impaired.

  On the other hand, if the intermediate transfer belt 50 and the photosensitive drum 1 are separated from each other after the application of the primary transfer voltage is stopped as in the control of this embodiment, the above-described intermediate transfer belt 50 can be separated. Speed fluctuation is suppressed. That is, by stopping the application of the primary transfer voltage, first, the adsorption force is reduced, and then the intermediate transfer belt 50 and the photosensitive drum 1 are separated to eliminate the friction force with a time lag. be able to. Accordingly, the forces of the two are eliminated sequentially in steps, and the restraining force received by the intermediate transfer belt 50 from the photosensitive drum 1 can be released in stages, and a sudden speed change occurs in the intermediate transfer belt 50. This can be suppressed. Therefore, the occurrence of mismatch between the speed of the recording material P and the speed of the intermediate transfer belt 50 at the secondary transfer portion N2 is suppressed, and the occurrence of banding image defects is prevented well.

In this embodiment, the operation for separating the intermediate transfer belt 50 and the photosensitive drum 1 is performed after the application of the primary transfer voltage is stopped, while the operation for bringing the intermediate transfer belt 50 and the photosensitive drum 1 into contact is performed. The control performed after the application of the next transfer voltage has been described.
However, even when the intermediate transfer belt 50 and the photosensitive drum 1 are brought into contact with each other, in the case where the secondary transfer process is performed in the secondary transfer portion N2, the operation of bringing the intermediate transfer belt 50 and the photosensitive drum 1 into contact is performed. After that, it is desirable to start application of the primary transfer voltage.
The following applies to this case. This is because, for example, the image forming apparatus has a relatively long distance from the fourth station 10d to the secondary transfer portion N2 and a relatively short distance from the secondary transfer portion N2 to the first station 10a. This is a case where control is applied. Further, for example, the control is performed to reduce the toner collection amount at the fourth station 10d and increase the collection amounts at the second and third stations 10b and 10c.

That is, the frictional force is generated first by bringing the intermediate transfer belt 50 and the photosensitive drum 1 into contact with each other, and then the suction force is generated with a time lag by starting the application of the primary transfer voltage. be able to. Accordingly, both forces are sequentially generated in steps, and the restraining force that the intermediate transfer belt 50 receives from the photosensitive drum 1 can be generated in a stepwise manner, and a sudden speed change occurs in the intermediate transfer belt 50. Can be suppressed.
Therefore, the occurrence of mismatch between the speed of the recording material P and the speed of the intermediate transfer belt in the secondary transfer portion N2 is suppressed, and the occurrence of banding image defects is prevented well. However, in the image forming apparatus of the present embodiment, since the secondary transfer process for all pages is completed at the timing of the contact, this control need not be applied.
Here, in this embodiment, when performing the separation operation, the primary transfer voltage is turned off (the electric field of the primary transfer portion N1 is removed). However, the present invention is not limited to this. is not. That is, the separation operation may be performed in a state where the primary transfer voltage is controlled so that the electric field strength of the primary transfer portion N1 is reduced.

Example 3 will be described below. The basic configuration and operation of the image forming apparatus according to the present embodiment are the same as those of the first and second embodiments. The same components as those of the first and second embodiments are denoted by the same reference numerals, and the description thereof will be omitted. Omitted.
In the present embodiment, a part of the configuration of the image forming apparatus is different from those in the first and second embodiments.

FIG. 8 is a cross-sectional view illustrating a schematic configuration of the image forming apparatus 100 according to the present exemplary embodiment.
In the image forming apparatus (FIG. 1) described in the first embodiment, the driving roller 53 drives the intermediate transfer belt 50, and the secondary transfer counter roller 55 stretches (supports) the intermediate transfer belt 50 at the secondary transfer portion N2. It was configured as a stretch roller.
On the other hand, in the image forming apparatus 100 of this embodiment, as shown in FIG. 8, the secondary transfer counter roller 551 transmits a driving force for rotating the intermediate transfer belt 50 to the intermediate transfer belt 50. Also serves as a role. The stretching roller 531 is one of a plurality of rollers that stretch the intermediate transfer belt 50.
Thereby, in addition to the effect that the secondary transfer residual toner can be well dispersed and collected in a plurality of waste toner containers, the following effects can be obtained. That is, even in a case where printing is performed on a recording material with high surface smoothness such as gloss paper, a banding image defect generated on the halftone image at the timing of switching the contact state between the intermediate transfer belt 50 and the photosensitive drums 1a to 1c to the separated state. Can be suppressed satisfactorily.

The timing chart for explaining the operation in the color mode of the image forming apparatus of the present embodiment is the same as FIG. 7 described in the second embodiment. Also in the image forming apparatus of the present embodiment, since the intermediate transfer belt 50 and the photosensitive drum 1 are separated after the application of the primary transfer voltage is stopped, the speed fluctuation of the intermediate transfer belt 50 is suppressed.
However, when printing full-color images such as graphics and photographic images on recording materials with high surface smoothness such as gloss paper, the above-mentioned intermediate It is desirable to further suppress the speed fluctuation of the transfer belt 50. This is because the toner image that is secondarily transferred from the intermediate transfer belt 50 onto the recording material having high surface smoothness has high reproducibility of the toner image including the halftone image. This is because the visibility as a banding image defect is increased. Therefore, not only the effect of suppressing the speed fluctuation obtained by performing the control of the second embodiment but also means for obtaining a further effect is required.

In order to solve such a problem, in the image forming apparatus 100 according to the present exemplary embodiment, the secondary transfer counter roller 551 also serves as a roller that drives the intermediate transfer belt 50.
In this image forming apparatus, the intermediate transfer belt 50 is driven by the secondary transfer counter roller 551 disposed on the back side of the intermediate transfer belt, and the speed of the portion interposed in the secondary transfer portion N2 of the intermediate transfer belt 50 is 2 It is directly determined by the rotation speed of the next transfer counter roller 551.
Therefore, when the intermediate transfer belt 50 and the photosensitive drum 1 are separated from each other at the primary transfer portion N1, a sudden speed change occurs in a portion of the intermediate transfer belt 50 that is interposed in the primary transfer portion N1. However, this speed change does not propagate to the second transfer portion N2. That is, even if a sudden speed change occurs in the portion of the intermediate transfer belt 50 that is interposed in the primary transfer portion N1, the speed of the portion of the intermediate transfer belt 50 that is interposed in the secondary transfer portion N2 is affected. do not do.
Therefore, even when printing full-color images such as graphics and photographic images on recording materials with high surface smoothness such as glossy paper, the manifestation of banding image defects that occur on halftone images is more effectively suppressed. The

As described above, the image forming apparatus to which the present invention is applied has been described according to specific examples, but the present invention is not limited to the above-described embodiments.
For example, in the first to third embodiments, the case where a plurality of stations are arranged in the order for each color of Y, M, C, and K is illustrated. However, if the photosensitive drum 1 and the intermediate transfer belt 50 can be brought into contact with and separated from each other at the first station, the present invention can be suitably used even in the order of other colors. However, in consideration of the productivity of the monochrome mode, the station for K color is often arranged at the last station in the order of forming the toner images of a plurality of colors. In this case, the toner images formed by the first to third stations The order of colors is arbitrary.
In the first to third embodiments, the time at which the intermediate transfer belt 50 and the photosensitive drums 1a to 1c are separated from each other and the time at which the intermediate transfer belt 50 and the photosensitive drums 1a to 1c come into contact again can be appropriately adjusted. There is room. For example, the amount of secondary transfer residual toner collected in the second and third stations is reduced by slightly delaying the re-contact time from the timing described in the first embodiment, and the secondary transfer residual toner collected in the fourth station. The amount can be increased. As described above, in consideration of the capacity of the waste toner container for each station, the assumed usage of the image forming apparatus (presumed deviation in the printing rate of each color, etc.), the secondary transfer residual toner for each station is appropriately selected. It is possible to finely adjust the distribution of the collection amount.
In the first to third embodiments, the case where the photosensitive drums 1 and the intermediate transfer belt 50 in the first to third stations among the four stations can be brought into contact with and separated from each other has been described. However, the present invention is not limited to this. The photosensitive drum 1d of the fourth station and the intermediate transfer belt 50 may also be provided so as to be able to contact and separate. In other words, the photosensitive drums 1 and the intermediate transfer belt 50 of a plurality of stations including the most upstream station among all the stations may be provided so as to be in contact with and separated from each other.

  DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 10 ... Station (image formation station), 12 ... Separation / contact control roller, 50 ... Intermediate transfer belt, 58 ... Toner charging roller, 62 ... Waste toner container, 100 ... Image forming apparatus, 150 ... DC controller, N1 ... primary transfer portion, N2 ... secondary transfer portion, P ... recording material

Claims (10)

A rotatable endless intermediate transfer member;
An image forming unit arranged in parallel along the rotation direction of the intermediate transfer member, an image carrier on which a toner image is formed, and a container for collecting the toner removed from the image carrier Two or more image forming units each having;
Have
The toner image formed on each image carrier is primarily transferred to the intermediate transfer member at each primary transfer portion formed between each image carrier and the intermediate transfer member, and then the intermediate transfer is performed. An image forming apparatus in which a secondary transfer portion on a body is secondarily transferred collectively to a recording material and an image is formed on the recording material,
In the rotational direction of the intermediate transfer member, the intermediate transfer member is provided downstream of the secondary transfer unit and upstream of the primary transfer unit of the most upstream image carrier among all the image carriers. A charging member for charging the residual toner on the toner to a polarity opposite to the normal charging polarity of the toner;
In the image forming apparatus in which the residual toner on the intermediate transfer member is charged to the reverse polarity by the charging member and can be moved to the image carrier and collected in the container corresponding to the image carrier.
A contact / separation means capable of contacting and separating the plurality of image carriers and the intermediate transfer member;
When the residual toner charged by the charging member is moved to the plurality of image carriers and collected from the intermediate transfer member, the contact and separation means contacts the plurality of image carriers and the intermediate transfer member. An image forming apparatus, wherein the image bearing member on which residual toner moves from the intermediate transfer member is changed by switching the contact / separation state. When the residual toner charged by the charging member is moved to the plurality of image carriers and collected from the intermediate transfer member, a separation operation for separating the plurality of image carriers from the intermediate transfer member is performed. By letting the contact and separation means do it,
The residual toner charged to the reverse polarity by the charging member passes through a primary transfer portion corresponding to the most upstream image carrier;
after that,
By causing the abutting / separating means to abut the abutting operation of abutting the plurality of image carriers in the separated state with the intermediate transfer member,
The residual toner is moved to an image carrier other than the most upstream image carrier among the plurality of image carriers that have been separated, and is collected in the container corresponding to the image carrier.
The image forming apparatus according to claim 1, further comprising a control unit that controls the contact / separation unit.   The contact / separation means is configured to be able to contact and separate the intermediate transfer member and the image carrier excluding the image carrier at the most downstream in the rotation direction among all the image carriers. The image forming apparatus according to claim 2.   The control means is a case where there is no subsequent recording material on which an image is continuously formed with respect to a recording material on which an image is formed, and an image carrier that is capable of contacting and separating from the intermediate transfer member. 3. The separation operation is performed by the contact / separation unit when primary transfer of a toner image from the image carrier on the most downstream side in the rotation direction to the intermediate transfer member is completed. Or the image forming apparatus according to 3. The control means includes
When there is no subsequent recording material on which continuous image formation is performed with respect to the recording material on which image formation is performed, the residual remaining on the intermediate transfer member by performing secondary transfer on the recording material Among the toners, the toner at the upstream end in the rotational direction charged to the reverse polarity by the charging member is
After passing the primary transfer portion corresponding to the most upstream image carrier,
The image forming apparatus according to claim 2, wherein the contact operation is performed by the contact / separation unit. In order to primarily transfer the toner image formed on the image carrier onto the intermediate transfer member, an electric field is formed in the primary transfer portion,
The control means includes
When the separation operation is performed by the contact / separation means,
6. The plurality of image bearing members and the intermediate transfer member are separated from each other after the electric field of each primary transfer portion is removed or the strength of the electric field is reduced. 2. The image forming apparatus according to item 1. The control means includes
When the contact operation is performed by the contact and separation means,
The image forming apparatus according to claim 6, wherein an electric field is formed in each primary transfer portion after the plurality of image carriers in the separated state and the intermediate transfer member are brought into contact with each other. The control means performs control to form an electric field in each primary transfer portion after the plurality of image carriers in the separated state and the intermediate transfer body are brought into contact with each other.
8. The image forming apparatus according to claim 7, wherein when the contact operation by the contact / separation unit is performed, secondary transfer is performed on the recording material in the secondary transfer unit.   9. The image forming apparatus according to claim 6, wherein one electric field forming unit is provided to form an electric field in each primary transfer portion. The intermediate transfer member is a belt;
The driving roller for transmitting a driving force for rotating the belt to the belt, wherein the driving roller supports the belt by the secondary transfer unit. The image forming apparatus described in the item.

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