JP2020003718A - Image formation apparatus - Google Patents

Abstract

To provide an image formation apparatus capable of suppressing or preventing a cleaning defect of a photosensitive drum even when toner having a high electric charge amount is reversely transferred from an intermediate transfer body.SOLUTION: An image formation apparatus comprises a holding device which collects a remaining developer remaining on an intermediate transfer belt and temporarily holds it, and a cleaning member which removes toner carried on a photosensitive drum, and moves the toner that the holding device holds to the intermediate transfer belt to discharge it. The image formation apparatus supplies toner from a developing roller to the cleaning member before toner reversely transferred from the intermediate transfer belt is supplied to the cleaning member.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus employing an intermediate transfer method in which a toner image formed on an image carrier is transferred to an intermediate transfer member, and then the toner image is transferred to a transfer material.

  2. Description of the Related Art Conventionally, as an image forming apparatus such as a laser beam printer, an in-line color type image forming apparatus having a configuration in which a plurality of image carriers are arranged in the rotation direction of an intermediate transfer body has been known.

  In this image forming apparatus, a toner image is developed on an electrostatic latent image formed on a photosensitive drum as an image carrier by a developing unit, and primary-transferred to an intermediate transfer body. Thereafter, by repeating the same primary transfer for a plurality of colors, a full-color toner image is formed on the intermediate transfer member. Subsequently, the full-color toner image is secondarily transferred to a recording material, and the fixing device permanently fixes the full-color toner image on the recording material. At this time, it is necessary to remove the toner (transfer residual toner) remaining on the intermediate transfer body without being transferred onto the transfer material in the secondary transfer step from the intermediate transfer body.

  Patent Document 1 proposes a so-called simultaneous transfer recovery method as a method for removing transfer residual toner from an intermediate transfer member. That is, the transfer residual toner on the intermediate transfer member is charged to a polarity opposite to the normal charge state of the toner by the toner charging means, so that it is reversely transferred to the photosensitive drum at the next primary transfer step. The toner reversely transferred to the photosensitive drum is removed by a cleaning means such as a cleaning blade.

  Further, Patent Document 2 discloses a conductive brush as a collection method that uniformly disperses transfer residual toner (hereinafter, secondary transfer residual toner) on an intermediate transfer member and prevents image defects by performing uniform charging. A method using a member and a conductive roller member has been proposed. Specifically, by applying a DC voltage to the brush member disposed on the upstream side, the secondary transfer residual toner on the intermediate transfer body is mechanically dispersed, primary recovered and charged, and disposed downstream. The secondary transfer residual toner that has passed through the brush member is charged by the roller member.

  By adopting the configuration as in Patent Document 2, it is possible to collect at the same time as the primary transfer of the next page, and it is possible to form a continuous image without reducing the printing speed. The secondary transfer residual toner on the last page of a series of continuous prints is collected by the cleaning blade of the photosensitive drum during non-image formation. Subsequently, by applying positive and negative voltages alternately to the brush member and the roller, the primary collected toner accumulated in the brush member is discharged onto the intermediate transfer member. The toner discharged onto the intermediate transfer member is reversely transferred to the photosensitive drum and collected in a primary transfer step. Further, when the primary collection toner in the brush member becomes large, for example, when the number of continuous prints is large, the printing is temporarily interrupted to maintain the toner charging performance of the brush member, and the non-image forming state is set. Then, the toner accumulated in the brush member is discharged, and the toner is reversely transferred to the photosensitive drum and collected in a primary transfer process.

JP-A-9-50167 JP 2009-205012 A

  However, in the above configuration, the toner reversely transferred from the intermediate transfer member to the photosensitive drum may not be completely cleaned by the cleaning blade of the photosensitive drum, and vertical streaks may occur on the image.

  This phenomenon occurs because the charge amount of the toner reversely transferred from the intermediate transfer member to the photosensitive drum is larger than usual. At the edge of the cleaning blade of the photosensitive drum, a layer of toner external additives (externally added particles added as auxiliary particles to the toner particles) that has migrated from the toner to the photosensitive drum is formed. It plays a role (hereinafter referred to as a blocking layer). However, if the amount of charge of the toner entering the blocking layer is larger than usual, the toner entering the blocking layer has a large adhesive force to the photosensitive drum. (Toner slip-through) occurs. For this reason, vertical stripes have occurred on the image. This problem is remarkable especially when the amount of the toner to be reversely transferred is large. In addition, the phenomenon that the reversely transferred toner cannot be completely cleaned by the cleaning blade of the photosensitive drum may occur even when a large amount of toner enters the cleaning blade even if the charge amount is not so much higher than usual.

  That is, there is a demand for an image forming apparatus capable of suppressing or preventing defective cleaning of the photosensitive drum even when the toner discharged from the intermediate transfer member is reversely transferred.

In order to achieve the above object, an image forming apparatus according to the present invention includes:
A developer carrying member carrying a developer to which externally added particles are added,
An image carrier on which a developer from the developer carrier is developed;
An intermediate transfer member,
A transfer member for applying a transfer bias for transferring a developer image developed on the image carrier to the intermediate transfer member,
After the developer image transferred to the intermediate transfer member is transferred to a recording material, a holding device that collects and temporarily holds the remaining developer remaining on the intermediate transfer member,
A cleaning member that comes into contact with the image carrier and removes a developer carried on the image carrier.
An image forming apparatus capable of performing an operation of moving a first developer held by the holding device to the intermediate transfer body and performing reverse transfer from the intermediate transfer body to the image carrier.
Before the reverse-transferred developer is supplied to the cleaning member, the developer carrier is attached to the image carrier so that the developer is supplied from the developer carrier to the cleaning member. An image forming apparatus comprising:

  According to the present invention, it is possible to provide an image forming apparatus capable of suppressing or preventing defective cleaning of a photosensitive drum even when toner discharged from an intermediate transfer member is reversely transferred.

Sectional view of an image forming apparatus according to an embodiment Sectional view of a process cartridge in an embodiment Sectional view of the process cartridge when the developing roller is separated in the embodiment. 1 is a block diagram illustrating a power supply configuration of an image forming apparatus according to an embodiment. Control block diagram in the embodiment Timing chart of the discharging process in the first image forming unit in Example 1, Comparative Example 1, and Comparative Example 2 Sectional view of the image forming apparatus for describing a bias application timing of the toner charging brush 11, the primary transfer roller 8Y, and the developing roller 17Y in the first embodiment. Timing chart of the discharging process in the second image forming unit in Example 1, Comparative Example 1, and Comparative Example 2 Enlarged view for explaining the relationship between the cleaning blade edge and the blocking layer Explanatory drawing of bias application by a toner charging brush in a discharge process of Example 2 and Comparative Example 2.

  Embodiments for carrying out the present invention will be exemplarily described in detail below based on embodiments with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment should be appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions. That is, the scope of the present invention is not intended to be limited to the following embodiments.

  In this embodiment, the image forming apparatus is capable of discharging toner, discharges toner from a toner charging brush attached to the intermediate transfer member during non-image formation, and immediately before collecting the toner on the photosensitive drum, transfers the toner from the developing roller to the photosensitive drum. It is characterized by sending toner. In this way, by forming the blocking layer on the edge portion of the cleaning blade and then collecting the toner discharged from the toner charging brush on the photosensitive drum, it is possible to prevent the occurrence of cleaning failure.

(1) Outline of Configuration and Operation of Image Forming Apparatus First, the overall configuration of an electrophotographic image forming apparatus (image forming apparatus) according to the present invention will be described. FIG. 1 is a schematic sectional view of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 of the present embodiment is a full-color laser printer employing an in-line system and an intermediate transfer system. The image forming apparatus 100 can form a full-color image on a recording material (for example, recording paper) according to the image information. The image information is input to the image forming apparatus main body from an image reading apparatus connected to the image forming apparatus main body or a host device such as a personal computer communicably connected to the image forming apparatus main body.

  The image forming apparatus 100 includes, as a plurality of image forming units, first, second, and third images for forming images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. , Fourth image forming units SY, SM, SC, and SK. In this embodiment, the first to fourth image forming units SY, SM, SC, and SK are arranged in a line along the intermediate transfer belt. Note that the image forming section S includes the primary transfer roller 8 and the process cartridge 7.

  In the present embodiment, the configurations and operations of the first to fourth image forming units are substantially the same except that the colors of the images to be formed are different. Therefore, in the following, unless it is particularly necessary to distinguish them, the suffixes Y, M, C, and K given to the symbols to indicate that they are elements provided for any color are omitted, and explain.

  In the present embodiment, the image forming apparatus 100 has four photosensitive drums 1 along the intermediate transfer belt as a plurality of image carriers. The photosensitive drum 1 is driven to rotate in a direction indicated by an arrow A (clockwise) by a driving unit (drive source) (not shown). A charging roller 2 (charging member) as charging means for uniformly charging the surface of the photosensitive drum 1 is arranged around the photosensitive drum 1. Further, a scanner unit (exposure device) 3 as exposure means for irradiating a laser based on image information to form an electrostatic image (electrostatic latent image) on the photosensitive drum 1 is arranged. A developing unit (developing device) 4 as a developing means for developing the electrostatic image as a toner image around the photosensitive drum 1, and removes toner (transfer residual toner) remaining on the surface of the photosensitive drum 1 after transfer. A cleaning blade 6 is disposed as cleaning means for performing cleaning. The cleaning blade 6 is in contact with the surface of the photoreceptor, and the contact portion is a contact portion. Further, an intermediate transfer belt 5 as an intermediate transfer member for transferring the toner image on the photosensitive drum 1 to the recording material 12 is disposed opposite to the four photosensitive drums 1.

  In the present embodiment, the photosensitive drum 1 and the charging roller 2, the developing unit 4, and the cleaning blade 6 as process means acting on the photosensitive drum 1 are integrally formed as a cartridge to form a process cartridge 7. . Each process cartridge 7 corresponds to each image forming unit. The process cartridge 7 is detachable from the image forming apparatus 100. In the present embodiment, the process cartridges 7 for each color all have the same shape, and the process cartridges 7 for each color contain yellow (Y), magenta (M), cyan (C), and blank (K), respectively. ) Are stored.

  The intermediate transfer belt 5 formed of an endless belt as an intermediate transfer member contacts all the photosensitive drums 1 and rotates in the direction of arrow B (counterclockwise) in the figure. The intermediate transfer belt 5 is stretched around a drive roller 51, a secondary transfer opposing roller 52, and a driven roller 53 as a plurality of support members. On the inner peripheral surface side of the intermediate transfer belt 5, four primary transfer rollers 8 (transfer members 8) as primary transfer means are arranged in parallel to face the respective photosensitive drums 1. Then, a bias having a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer roller 8 from a primary transfer bias power supply (not shown). As a result, the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 5. A secondary transfer roller 9 as a secondary transfer unit is disposed at a position facing the secondary transfer opposing roller 52 on the outer peripheral surface side of the intermediate transfer belt 5. Then, a bias having a polarity opposite to the normal charge polarity of the toner is applied to the secondary transfer roller 9 from a secondary transfer bias power supply (not shown). Thus, the toner image on the intermediate transfer belt 5 is transferred to the recording material 12.

  During image formation, first, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, an electrostatic image according to the image information is formed on the photosensitive drum 1 by a laser beam corresponding to the image information emitted from the scanner unit 3. Next, the electrostatic image is developed as a toner image on the image carrier (on the photosensitive drum) by the developing unit 4 and transferred (primary transfer) onto the intermediate transfer belt 5 by the action of the primary transfer roller 8.

  For example, when a full-color image is formed, the above-described process is sequentially performed in the first to fourth image forming units SY, SM, SC, and SK, and the toner images of the respective colors are then superimposed on the intermediate transfer belt 5. You. After that, the four-color toner image on the intermediate transfer belt 5 is secondarily transferred onto the recording material 12 at a time. Further, in the fixing device 10, the toner image is fixed by applying heat and pressure to the recording material 12. The primary transfer residual toner remaining on the photosensitive drum 1 after the primary transfer step is removed and collected by the cleaning blade 6.

  The secondary transfer residual toner remaining on the intermediate transfer belt 5 after the secondary transfer step is charged by the toner charging brush 11 with the normal charge polarity of the toner (the charge polarity of the developer when developing the electrostatic latent image). And a charge having a polarity opposite to that of. In addition, even with the discharge charging roller 54 (power supply 40R), a charge having a polarity opposite to the normal charging polarity is provided. The secondary transfer residual toner charged by the toner charging brush 11 and the discharging charging roller 54 is reversely transferred to the photosensitive drum 1 </ b> Y of the first image forming unit in the next primary transfer process. Collected. Note that the function of applying charge to the toner may be performed only by the toner charging brush 11.

[Process cartridge]
Next, the overall configuration of the process cartridge 7 mounted on the image forming apparatus 100 of the present embodiment will be described. FIG. 2 is a schematic cross-sectional view of the process cartridge 7 of the present embodiment viewed from a longitudinal direction (a rotation axis direction) of the photosensitive drum 1. In the present embodiment, the configuration and operation of the process cartridge 7 for each color are the same except for the type (color) of the developer contained.

  The process cartridge 7 includes a photosensitive unit 13 including the photosensitive drum 1 and the like, and a developing unit 4 including a developing roller 17 and the like.

  The photoconductor unit 13 has a cleaning frame 14 as a frame that supports various elements in the photoconductor unit 13. A photosensitive drum is rotatably attached to the cleaning frame 14 via a bearing (not shown). The photosensitive drum 1 is driven to rotate in a direction indicated by an arrow A (clockwise) in accordance with an image forming operation by transmitting a driving force of a driving motor as a driving unit (driving source) to the photoconductor unit 13. The photoreceptor drum 1, which is the center of the image forming process, uses an organic photoreceptor in which an undercoat layer, a carrier generation layer, and a carrier transport layer, which are functional films, are sequentially coated on the outer peripheral surface of an aluminum cylinder.

  The photosensitive member unit 13 is provided with a cleaning member 6 and a charging roller 2 so as to be in contact with the peripheral surface of the photosensitive drum 1. The transfer residual toner removed from the surface of the photosensitive drum 1 by the cleaning member 6 is dropped and stored in the cleaning frame 14.

  The charging roller 2 serving as a charging unit is driven to rotate by bringing a roller portion made of conductive rubber into pressure contact with the photosensitive drum 1. Here, a predetermined DC voltage is applied to the core of the charging roller 2 as a charging step with respect to the photosensitive drum 1 so that a uniform dark portion potential (Vd) is applied to the surface of the photosensitive drum 1. It is formed. The spot pattern of the laser light emitted according to the image data by the laser light from the scanner unit 3 exposes the photosensitive drum, and the exposed portion loses surface charges by carriers from the carrier generation layer. And the potential drops. As a result, an electrostatic latent image is formed on the photosensitive drum 1 in which the exposed portion has a predetermined bright portion potential (Vl) and the unexposed portion has a predetermined dark portion potential (Vd).

  On the other hand, the developing unit 4 includes a developing roller 17 (developer carrier), a developing blade 19, a toner supply roller 18, a toner 15, and a toner storage chamber 16 for storing the toner. As the toner 15, a non-magnetic spherical toner charged to a negative polarity as a regular polarity and having a particle diameter of 7 μm was used. On the surface of the toner 15, silica particles having a particle diameter of 20 nm are added as toner external additives (externally added particles).

  The developing blade 19 is in contact with the developing roller by a counter, and regulates a coating amount of the toner supplied by the toner supplying roller and gives a charge. The developing blade 19 is made of a thin plate-like member, and generates a contact pressure by utilizing the elasticity of the thin plate, and the surface thereof is brought into contact with the toner and the developing roller 17. The toner is frictionally charged by the rubbing between the developing blade 19 and the developing roller 17 and is given an electric charge, and at the same time, the layer thickness is regulated. In the present embodiment, a predetermined voltage is applied to the developing blade 19 from a blade bias power supply (not shown) to stabilize the toner coat.

  The developing roller 17 and the photosensitive drum 1 rotate so that their surfaces move in the same direction (arrows A and D, which are directions from bottom to top in this embodiment) at the opposing portion (contact portion). . In the present embodiment, the toner charged negatively by the frictional charging with respect to a predetermined DC bias applied to the developing roller 17 in the developing unit that comes into contact with the photoconductor drum 1 derives from the potential difference, And the electrostatic latent image is visualized.

  The toner supply roller 18 is provided with a predetermined nip formed on the peripheral surface of the developing roller 17 and rotates in a direction indicated by an arrow E (counterclockwise). The toner supply roller 18 is an elastic sponge roller in which a foam is formed on the outer periphery of a conductive cored bar. The toner supply roller 18 and the developing roller 17 are in contact with a predetermined amount of intrusion. The contact portions rotate so as to move in opposite directions, and by this operation, toner is supplied to the developing roller by the toner supply roller 18 and the toner on the developing roller remaining as the development residue is removed.

  A toner stirring member 20 is provided in the toner storage chamber 16. The toner stirring member 20 stirs the toner stored in the toner storage chamber 16 and also conveys the toner toward the upper portion of the toner supply roller 18 in the direction of arrow G in FIG. In this embodiment, both the developing roller 17 and the toner supply roller 18 have an outer diameter of φ20, and the amount of the toner supply roller 18 entering the development roller 17 is set to 1.5 mm. In the present embodiment, a predetermined DC bias applied to the developing roller 17 is applied, and in the developing section in contact with the photosensitive drum 1, the toner is transferred only to the light-potential portion from the potential difference, so that the electrostatic latent image is transferred. Visualize the image.

[Developing roller contact / separation mechanism]
The developing roller 17 is configured to be able to come into contact with and separate from the photosensitive drum 1, and to be in contact with the photosensitive drum 1 during image formation, and to be separated as shown in FIG. I have. Here, the time of image formation is a time of forming a developer image by transferring the developer from the developing roller 17 according to the electrostatic latent image formed on the photosensitive drum 1. The non-image forming time is when the above-described developer image is not formed. For example, after the developer image is formed on the photosensitive drum 1 and before the photosensitive drum 1 stops (hereinafter referred to as post-rotation), or after the next printing is started and the photosensitive drum 1 starts rotating, the developer This is before image formation to start image formation (hereinafter referred to as pre-rotation). The post-rotation is a period from the end of the formation of the toner image on the photosensitive drum 1 to the stop of the photosensitive drum 1. Is performed. The pre-rotation is a period from when the photosensitive drum 1 starts rotating to before a toner image is formed on the photosensitive drum 1, and a rising operation of each bias, preparation heating of the fixing device 10, and the like are performed. s In addition, special operations such as a period corresponding to a period between recording materials when a plurality of recording materials 12 are conveyed during continuous printing, an operation performed when adjusting image density, and an operation of discharging toner attached to a toner charging brush are performed. Also, when a developer image is not formed in the period provided in the above, it is also a time of non-image formation.

  As a specific contact / separation mechanism, a cam 23 provided in the image forming apparatus 1 and capable of controlling the rotational position, and a spring provided in the process cartridge 7 and pressing the developing roller 17 and the photosensitive drum 1 so as to contact each other. This is performed by a member (not shown). In the developing roller contact state, the cam 23 is controlled to a position where the developing unit 4 is not pressed, and is brought into contact with the pressing force of the spring member of the process cartridge 7. Further, the developing roller separation state is performed by controlling the rotation position of the cam 23 to push and rotate the developing unit 4 from the bottom.

  The contact / separation mechanism is not limited to the one using the cam and the spring member described above, and any mechanism using only the cam may be used as long as it can control the contact / separation.

[Intermediate transfer belt]
As the intermediate transfer belt 5, a polyvinylidene fluoride film having a thickness of 100 μm and a volume reduction efficiency adjusted to 10 ¹¹ Ωcm was used. The intermediate transfer belt 5 is stretched around three axes of a driving roller 51, a secondary transfer facing roller 52, and a driven roller 53.

[Primary transfer roller]
An elastic roller having a volume resistivity of 10 ⁵ to 10 ⁹ Ωcm and a rubber hardness of 30 ° (Asker C hardness meter) was used as the primary transfer roller 8. The primary transfer roller 8 is pressed against the photosensitive drum 1 via the intermediate transfer belt 5 at a total pressure of about 9.8N. The primary transfer roller 8 rotates following the rotation of the intermediate transfer belt 5. Further, a voltage of -2.0 to 3.5 kV can be applied to the primary transfer roller 8 from a primary transfer power supply (not shown).

[Toner charging brush]
As the toner charging brush 11, a brush configured so that nylon fibers having a conductivity of 10 ⁶ to 10 ⁹ Ωcm is substantially dense is fixedly disposed. In this embodiment, the tip position of the toner charging brush 11 is set such that the amount of penetration into the surface of the intermediate transfer belt 5 is 1.0 mm. As described above, the toner charging brush 11 located on the upstream side in the moving direction of the surface of the intermediate transfer belt 5 rubs the surface of the intermediate transfer belt 5 as the intermediate transfer belt 5 moves. The toner charging brush 11 is disposed downstream of the secondary transfer unit and upstream of the first image forming unit in the moving direction of the intermediate transfer belt 5. A voltage of -2.0 to +2.0 kV can be applied to the toner charging brush 11 from a high-voltage power supply (not shown) as a toner charging brush voltage supply unit.

(2) Description of operation at the time of collecting secondary transfer residual toner [Secondary transfer residual toner collection method]
A method of collecting the secondary transfer residual toner during printing will be described in detail.

  The secondary transfer residual toner remains on the intermediate transfer belt 5 after the secondary transfer process. Therefore, a bias of +1 kV having a polarity opposite to the normal charging polarity of the toner, that is, a positive polarity in this embodiment, is applied to the toner charging brush 11. As a result, when the secondary transfer residual toner passes through the toner charging brush 11, it is charged to a positive polarity. At this time, the negative polarity toner that has not been completely charged to the positive polarity is partially held by the toner charging brush 11. Then, the secondary transfer residual toner to which the positive charge has been applied by the toner charging brush 11 is reversely transferred to the photosensitive drum 1 </ b> Y of the first image forming unit during the primary transfer step, and is collected by the cleaning blade 6. Further, control is performed so that the secondary transfer residue of the last page of the continuous print is collected on the photosensitive drum 1Y of the first image forming apparatus during non-image formation.

[Toner charging brush discharging process]
The discharging process from the toner charging brush 11 will be described in detail.

  As described above, the negative polarity toner that has not been completely charged to the positive polarity by the toner charging brush 11 is temporarily held by the toner charging brush 11. That is, the toner charging brush 11 also functions as a holding device that collects and holds the residual developer remaining on the intermediate transfer body after the secondary transfer. Then, when the image formation is repeatedly performed, the toner accumulates on the toner charging brush 11, the electric resistance increases, and the charging performance of the toner charging brush 11 decreases. Therefore, a step of discharging the toner held by the toner charging brush 11 to the intermediate transfer belt 5 is required. The discharge process of the present embodiment is performed with a period during which post-rotation and a discharge process different from those during image formation are performed.

  In this step, the toner to be discharged has a negative polarity and the same polarity as the toner at the time of development, so that the toner cannot be transferred to the photosensitive drum 1 in the primary transfer portion during image formation. Therefore, during non-image formation, the toner is charged to the toner charging brush 11 with the same polarity as the normal charging polarity of the toner, that is, a bias of +1 kV of the positive polarity in this embodiment is applied with a bias of -1 kV of the negative polarity to perform intermediate transfer. The toner is discharged onto the belt 5. Further, a bias of each polarity is alternately applied 10 times every 0.2 seconds. The toner is discharged 10 times when a bias of -1 kV is applied. The toner accumulated on the toner charging brush 11 in this process is discharged onto the intermediate transfer belt 5.

  Here, the reason for applying the positive bias and the negative bias alternately will be described. Generally, the toner charged between the brush hairs of the toner charging brush 11 is clogged. Then, it is difficult to discharge the clogged toner only by applying a reverse polarity bias. Therefore, a high-voltage positive bias and a negative bias are alternately applied to the toner charging brush 11, and the toner charging brush 11 is mechanically vibrated by an electrostatic force, thereby discharging the clogged toner. This is the reason for applying the positive bias and the negative bias alternately.

  Next, a method of collecting the discharged toner from the toner charging brush on the photosensitive drum 1 will be described. Since a positive polarity bias is applied to the toner charging brush during image formation, basically, negative polarity toner is accumulated. However, some of the toner includes positive toner, and in this embodiment, the positive and negative discharge toners are distributed to and collected from the first to fourth image forming units. . Specifically, a bias of -1.5 kV having the same polarity as the normal charge polarity of the toner is applied to the primary transfer roller in the first and fourth image forming units, and the first and fourth image forming units apply the bias. A bias of +1.5 kV having a polarity opposite to the normal charge polarity of the toner is applied. As a result, the negative polarity toner discharged from the toner charging brush 11 is reversely transferred to the photosensitive drums 1Y and 1K and collected. Further, the positive polarity toner discharged from the toner charging brush 11 is reversely transferred to the photosensitive drums 1M and 1C and collected. The toner that has been reverse-transferred onto the photosensitive drum 1 is collected by the cleaning blade 6.

  After all the discharged toner has been collected by the cleaning blade 6 by the above-described steps, if there is further image formation, the image formation is performed again from the previous rotation. If there is no next image formation, the process ends.

  Note that this discharge step is performed periodically for a predetermined number of sheets, post-rotation, or during a discharge step period different from that during image formation. Further, the control is performed so that the frequency of the discharge process is increased as the printing rate of the printed image is increased. This is because when the printing rate of the printed image increases, the amount of the secondary transfer residual toner also increases, so that the amount of toner accumulated on the toner charging brush 11 increases. In the ejection process of this embodiment, every 300 sheets when the average printing rate is 2% or less, every 200 sheets when 2 to 5%, every 100 sheets when 5 to 10%, and every 10 to 20%. Is carried out every 50 sheets, and when it is larger than 20%, every 25 sheets. As a result, while the performance of the toner charging brush 11 is maintained, the printing operation is prevented from being stopped as much as possible so as not to excessively enter the discharging step.

[Power supply block diagram]
FIG. 4 is a block diagram of a power supply configuration of the image forming apparatus 100. Various process means are given the same reference numerals as in FIG. The power supply 30 applies a primary transfer bias to the primary transfer roller 8. A power supply is configured to apply a primary transfer bias of a positive polarity and a negative polarity to the primary transfer roller 8Y and the primary transfer roller 8K.

  The toner charging brush 11 and the discharging charging roller are provided with a power supply capable of applying a positive and a negative bias. The toner charging brush 11 applies a positive / negative bias from the power supplies 40B and 41B at the time of discharging at T4 in FIGS. The discharging charging roller applies a DC negative bias from the power supply 41R at the time of discharging at T4 in FIGS. This is to remove the negative developer adhered to the surface and to prevent the negative toner supplied at the time of discharging from the toner charging brush 11 from adhering. The charging roller 2, the primary transfer roller 8, and the developing roller 17 are provided with independent power supplies. In some cases, some power supplies may be shared. These power supplies are controlled based on an instruction from the control unit 101 described later, and the bias application in the timing charts of FIGS.

[Control block diagram]
A control block diagram of the image forming apparatus 100 will be described with reference to FIG. The control unit 101 includes a CPU (central processing unit) 501 as a central element for performing arithmetic processing, a memory 502 such as a ROM and a RAM as storage means, and an input / output interface 503 for inputting and outputting information to and from peripheral devices. Have. The RAM stores sensor detection results, calculation results, and the like, and the ROM stores control programs, previously obtained data tables, and the like. The control unit 101 is a control unit that comprehensively controls the operation of the image forming apparatus 100, and each control target in the image forming apparatus 100 is connected via an input / output I / F 503. The control unit 101 controls the transmission and reception of various electrical information signals, the timing of driving, and the like, and controls the processing of a timing chart to be described later.

  The driving unit 511 indicates various motors and driving gears. The driving unit 511 is a power source and a power mechanism for rotationally driving various rotating members included in the developing unit 4, the photoconductor unit 13, and the scanner unit 3, and operates based on a control signal from the control unit 101. The high-voltage power supply 512 is a power supply that collectively refers to power supplies that apply a high voltage to the charging roller 2, the developing roller 17, the primary transfer roller 8, the secondary transfer roller 9, the fixing device 34, and the like. The control unit 101 is connected to an environment sensor 102 such as a temperature. The control unit 101 can obtain information on the temperature and the amount of moisture in the air / humidity based on a detection signal from the environment sensor 102. it can.

(3) Description of Toner Discharge Sequence In this embodiment, immediately before the above-described discharge process from the toner charging brush 11 performed at the time of non-image formation, a protective developer image is formed on the photosensitive drum 1 from the developing roller 17 to form a blocking layer. Is supplied.

  FIG. 6 shows the rotation and stop of the photosensitive drum 1 in the first image forming section, the timing of applying a positive or negative bias to the toner charging brush 11 and the primary transfer roller 8, and the laser for purging the toner from the developing roller 17. 4 shows a timing chart of light emission. The timing for starting the rotation of the photosensitive drum 1 and the timing for changing the bias applied to the toner charging brush 11 and the primary transfer roller 8 during the discharging step of the toner charging brush 11 are described in Comparative Example 1, Comparative Example 2, and Example 1. The same is true. However, laser emission for forming a toner image (hereinafter, referred to as a protective developer image) to be supplied from the developing roller 17 to the cleaning blade 7 of the photosensitive drum 1 was performed in Example 1 and Comparative Example 2. This was not performed in Comparative Example 1. The difference between Example 1 and Comparative Example 2 is that the image pattern of the protective developer image is different. In the discharging step, the bias applied to the developing roller 17 and the charging roller 2 is the same as that in image formation. The developing roller 17 and the photosensitive drum 1 are kept in contact with each other from the time of image formation. Hereinafter, the timing of the protective developer images of Example 1 and Comparative Example 2 will be described in detail.

  First, the first image forming unit will be described with reference to FIG. At timing T1, the control unit 101 controls the driving unit 511 to start (ON) the rotation of various rotating bodies. Next, the control unit 101 controls the high-voltage power supply unit 512 at timing T2 to turn on the toner charging brush 11 and turn on the primary transfer roller 8 at timing T3 in preparation for image formation. Although not shown, various biases have been started to be applied from a high-voltage power supply corresponding to the charging roller 2, the developing roller 17, the toner supply roller 18, the secondary transfer roller 9, and the fixing device 10.

  Then, after the image forming operation is completed, the discharging process is started. It should be noted that the state after the image forming operation is completed corresponds to a state between page images (a so-called sheet interval) or a time of post-rotation described above.

  Then, at timing T4, the control unit 101 controls the high voltage power supply unit 511 to alternately apply a bias of ± 1 kV to the toner charging brush. More specifically, the toner is discharged by alternately changing +1 kV to -1 kV ten times every 0.2 seconds. As a result, the discharged developer (first developer) from the toner charging brush 11 is moved to the intermediate transfer belt.

  Then, at timing T5, the control unit 101 controls the scanner unit 3 to cause the scanner unit 3 to emit laser light of the protective developer image. By this laser emission, an electrostatic latent image for a protective developer image is formed on the photosensitive drum. Then, before the reverse-transferred developer is supplied to the cleaning blade 6, the developer (second developer) from the developing roller 17 (developer carrier) is supplied to the cleaning blade 6 to the photosensitive drum. You. In addition, the protective developer image in this embodiment has a solid black horizontal line image of one dot width (about 0.042 mm) and a blank space of one dot width over the entire image forming area in the rotation axis direction of the photosensitive drum 1. The image is a so-called one-dot-one-space image that is alternately repeated. In Comparative Example 1, the developing roller 17 and the photosensitive drum 1 are only in contact with each other without the protective developer image in the discharging process.

  Then, at timing T6, the control unit 101 controls the high-voltage power supply unit 512 to apply a negative bias to the primary transfer roller 8Y. In FIG. 6, when the protective developer image formed at the timing T5 passes through the transfer portion formed by the primary transfer roller 8Y and the intermediate transfer belt 5, it has a negative polarity (regularity of the developer). (The same polarity as the charging polarity) is applied, but the present invention is not limited to this. It has been confirmed that even when the transfer bias applied to the primary transfer roller 8Y is turned off or the transfer bias has a small positive value, a certain amount of developer for protection is supplied to the cleaning blade. .

  Here, the relationship between the timings T4 to T6 will be described with reference to FIG. As shown in FIG. 7, in the first embodiment and the comparative example 2, on the photosensitive drum 1Y, the toner based on the developer image for protection comes upstream from the head of the toner discharged from the toner charging brush 11. It is characterized by: The process speed (rotational speed of the photosensitive drum 1 and the intermediate transfer belt 5) of the first embodiment is 200 mm / s. Regarding the positional relationship between the members, the distance L1 from the toner charging brush 11 to the position where the photosensitive drum 1Y of the first image forming unit and the intermediate transfer belt 5 are in contact is 150 mm. The distance L2 from the laser irradiation position on the photosensitive drum 1Y by the scanner unit to the position where the photosensitive drum 1Y and the intermediate transfer belt 5 are in contact is 50 mm. With this configuration, in the first exemplary embodiment, when the timing at which the discharge bias (−1 kV) is started to be applied from the toner charging brush 11 is used as a reference, the toner discharged from the toner charging brush 11 is separated from the photosensitive drum 1Y by 0.75 seconds. The intermediate transfer belt 5 reaches a position where it contacts. In order to supply the protective developer image to the cleaning blade 6 before that, laser emission for the protective developer image is performed 0.4 seconds after the discharge bias of the toner charging brush 11 is applied. After 0.65 seconds, the developed developer image for protection reaches the position (contact portion) where the photosensitive drum 1Y and the intermediate transfer belt 5 are in contact with each other. Further, in order to collect (reverse transfer) the negatively discharged toner from the toner charging brush 11 to the photosensitive drum 1 and to prevent the negatively charged toner of the protective developer image from being transferred to the intermediate transfer belt 5, A negative bias is applied to the next transfer roller 8Y. As a specific example, the bias of the primary transfer roller 8Y is set to -1.5 kV 0.5 seconds after the application of the discharge bias of the toner charging brush 11 (T6). By performing the above-described control, the first image forming unit supplies the toner of the protective developer image before the toner discharged from the toner charging brush 11 is collected by the cleaning blade 6Y. As a result, the toner discharged from the toner charging brush is collected by the photosensitive drum after the blocking layer is formed on the edge portion of the cleaning blade, and the occurrence of cleaning failure at the time of discharging can be prevented. Note that the number of seconds after the application of the discharge bias of the toner charging brush 11 to perform laser emission of the protective developer image is appropriately determined by the distance L2 and the diameter of the photosensitive drum 1.

  Next, the timing of forming the developer image for protection in the second image forming section will be described. The second image forming unit is disposed downstream of the first image forming unit.

  The second image forming section collects mainly positive toner, which has not been collected in the first image forming section, out of the toner discharged from the toner charging brush 11. At this time, similarly to the first image forming unit, the protective developer image comes on the photosensitive drum 1M as the second image carrier, upstream of the head of the toner discharged from the toner charging brush 11. To do. The developer image for protection is supplied from a developing roller 17M as a second developer carrier. Note that the developer image for protection is a negative toner, and it is desired to collect the positively discharged toner from the toner charging brush 11. Therefore, the bias applied to the primary transfer roller 8 </ b> M (second transfer member) is the first. It is different from that of the image forming unit.

  Hereinafter, description will be made with reference to FIG. First, the processes at timings T1 to T4 are the same as those in the first image forming unit, and thus detailed description thereof is omitted. In the second image forming unit, a distance L12 from the toner charging brush 11 to a position where the photosensitive drum 1M of the second image forming unit contacts the intermediate transfer belt (second transfer unit) is 250 mm. 100 mm longer than L1. Under the control of the control unit 101, the toner discharged from the toner charging brush 11 at the timing T4 reaches a position (transfer nip) where the photosensitive drum 1M and the intermediate transfer belt 5 come into contact after 1.25 seconds. Further, the protective developer image (fourth developer) emits laser light 0.8 seconds after (T15) based on the application of the discharge bias of the toner charging brush 11, and 1.05 second after exposure of the photosensitive drum. 1M is brought to a position where the intermediate transfer belt 5 contacts. At this time, in order to prevent the negative toner of the protective developer image from being transferred to the intermediate transfer belt 5, the bias of the primary transfer roller 8M is set 0.95 seconds after the application of the discharge bias of the toner charging brush 11 (T16). -1.5 kV. Thereafter, in order to collect the positively-discharged toner from the toner charging brush 11 onto the photosensitive drum 1M, the bias of the primary transfer roller 8M is increased by +1.5 kV after 1.15 seconds (T17) from the application of the discharging bias of the toner charging brush 11 (T17). I have to. Note that T15 to T17 may be set at the same timing as T4 to T6 in the first embodiment. Part of the protective developer image (second developer) of the first image forming unit is transferred to the second transfer unit formed by the primary transfer roller 8M and the intermediate transfer belt 5 by the non-reverse transfer. The arrival timing is defined as a first timing. On the other hand, if the timing at which the protective developer image (fourth developer) of the second image forming unit reaches the previous second transfer unit is the second timing, the first timing is the second timing. The timing is different. If the timings match, the untransferred toner having a higher density reaches the secondary transfer portion, causing a problem of contamination of the secondary transfer portion.

  In the third image forming unit, similarly to the above-described second image forming unit, control is performed such that the protective developer image is collected by the cleaning blade 6K before the toner discharged from the toner charging brush 11 is collected. In the fourth image forming section, similarly to the above-described first image forming section, control is performed such that the protective developer image is collected by the cleaning blade 6K before the toner discharged from the toner charging brush 11 is collected.

  Hereinafter, comparison of the cleaning performance when the discharging process was actually performed under the conditions of Example 1 and Comparative Examples 1 and 2 was performed. This will be described below. As a common condition, a horizontal line image having a printing rate of 1% for each color was used as a durable image and printed up to 4000 sheets. A halftone image of each color having a printing rate of 25% was printed as an evaluation image of the cleaning property every 2000 continuous printings on the way, and image defects (vertical stripes) were confirmed. The image forming apparatus 100 was installed at a temperature of 23 ° C./50% humidity.

  In Comparative Example 2, the developing roller 17 and the photosensitive drum 1 are in contact with each other in the discharging process, and a 1-dot horizontal line is purged as a protective developer image for a total of 30 dots. Further, in the first embodiment, as described above, in a state where the developing roller 17 and the photosensitive drum 1 are in contact with each other in the discharging process, a one-dot horizontal line is purged as a protective developer image by a total of 40 dots.

  As shown in Table 1, in Comparative Example 1, vertical streaks occurred due to poor cleaning, and in Comparative Example 2, slight vertical streaks occurred. However, in the configuration of Example 1, no cleaning failure occurred. This is because an external additive (externally added particles) is transferred to the photosensitive drum 1 by supplying a protective developer image, and a blocking layer serving as a barrier layer is formed at an edge portion of the cleaning blade 6. This is because the performance is improved.

  A mechanism for improving the cleaning performance will be described with reference to an enlarged view of the cleaning blade edge portion in FIG. As shown in FIG. 9, the cleaning blade 6 is in contact with the photosensitive drum 1 in the counter direction with respect to the rotation direction, and the cleaning blade edge is entangled with the rotation of the photosensitive drum 1. The toner external additive transferred to the photosensitive drum 1 accumulates in the portion of the wedge that has been caught, forming a layer (hereinafter, referred to as a blocking layer 21). If the toner is to be cleaned without the blocking layer 21, the toner tends to sneak in from the wedge portion in which the edge is entangled, and cleaning failure easily occurs. When the blocking layer 21 exists at the edge (contact portion) of the cleaning blade as shown in FIG. 9, the above-described toner does not sneak in and the cleaning performance is improved. On the other hand, since the blocking layer 21 is formed of a toner external additive having a thickness of about 20 nm, a constant amount of the external additive always comes off the cleaning blade edge portion and disappears. Further, the toner discharged from the toner charging brush 11 in the discharging step is given a toner charge by the bias of the toner charging brush 11, and has a value of −65 to −100 μC / g. On the other hand, the charge of the toner held on the developing roller 17 is about −30 μC / g. As the toner charge increases, the adhesive force with the photosensitive drum 1 increases, so that the toner enters the blocking layer 21 with the rotation of the photosensitive drum 1 and easily breaks the blocking layer 21. Therefore, the toner discharged from the toner charging brush 11 tends to cause a cleaning failure, so that a sufficient blocking layer 21 is required before the discharged toner is collected. Therefore, in this embodiment, a protective developer image is formed on the photosensitive drum 1 in order to form a sufficient blocking layer 21 immediately before collecting the discharged toner. From Table 1, it can be seen that the amount of the protective developer image necessary for preventing the cleaning failure due to the recovery of the discharged toner is slightly less than the 30-dot horizontal line, and requires the 40-dot horizontal line.

  As described above, the use of the configuration of the present embodiment can prevent the generation of a vertical stripe image due to defective cleaning even when toner is collected from the toner charging brush 11.

  This embodiment is characterized in that the bias to the negative polarity applied to the toner charging brush 11 in the discharging process is increased stepwise instead of a constant value, compared to the first embodiment. Other configurations are the same as in the first embodiment. By setting the bias as in the present embodiment, it is possible to reduce the amount of toner discharged from the toner charging brush 11 at one time, and it is possible to prevent the generation of a vertical stripe image due to defective cleaning.

  The bias applied to the toner charging brush 11 in the discharging step will be described by comparing Comparative Example 2 and Example 2 with reference to FIG. In FIG. 10, the discharge amount from the toner charging brush 11 is indicated by a vertical bar, and the longer the length in the vertical direction, the larger the discharge amount. First, in Comparative Example 2, toner is discharged by alternately varying the bias applied to the toner charging brush 11 from +1 kV to -1 kV every 0.2 seconds. In such a discharging method, the toner discharging amount is discharged toward the leading end side as shown in FIG.

  On the other hand, in the second embodiment, the bias applied to the toner charging brush 11 is changed every 0.2 seconds as in the second comparative example. However, as shown in FIG. 10, the bias to be varied is increased stepwise from +1 kV to +900 V at the first time and from +1 kV to +800 V at the second time, and is varied from +1 kV to -1 kV at the 20th time. By gradually increasing the increase / decrease range, the amount of toner discharged at one time can be suppressed to small amounts as shown in FIG. However, in order to maintain the performance of the toner charging brush 11, the total amount of the toner to be discharged is desired to be equal to that of the comparative example 2 in the second embodiment. The developing roller 17 and the photosensitive drum 1 are kept in contact with each other from the time of image formation.

  A negatively charged toner is held at the tip of the toner charging brush 11 by applying a positive bias of +1 kV. In Example 2 of FIG. 10, in the initial stage, the increase and decrease of the bias value are repeated within the range of the positive bias. However, the weak bias application of the positive polarity gradually weakens the bias at the tip of the charging brush. The toner accumulated by the force is discharged. When the positive bias is further weakened, the toner accumulated with a strong force at the tip of the charging brush is also discharged. Then, when the increase / decrease range of the bias application is further increased and the positive bias and the negative bias are applied alternately, the clogged toner in the toner charging brush 11 described in the first embodiment is discharged. In this way, by gradually increasing the increase / decrease width of the applied bias of the toner charging brush 11, it is possible to realize the leveling of the toner discharge. When the leveling is performed, the effect of reducing the toner discharge amount per unit area and increasing the reverse transfer efficiency can be obtained. Further, even when the cleaning ability of the cleaning blade 6 is deteriorated, a large amount of toner is not supplied to the cleaning blade 6 at one time, so that the occurrence of a cleaning failure can be prevented.

  The cleaning performance was compared when the discharging process was actually performed. As a common condition, a horizontal line image of a printing rate of 1% for each color was used as a durable image and printed up to 4000 sheets. A halftone image of each color having a printing rate of 25% was printed as an evaluation image of the cleaning property every 2000 continuous printings on the way, and image defects (vertical stripes) were confirmed. The image forming apparatus 100 was installed at a temperature of 23 ° C./50% humidity. In each of the comparative example 2 and the example 2, a 30-dot horizontal line was used as the protective developer image in the discharging process.

  As shown in Table 2, in Comparative Example 2, slight vertical stripes were generated due to defective cleaning. However, in the configuration of Example 2, no defective cleaning occurred even when the protective developer image was a horizontal line of 30 dots. . The reason for no occurrence of cleaning failure in the configuration of the second embodiment is that the amount of toner expelled from the toner charging brush 11 at one time is reduced, so that the blocking layer 21 is not destroyed at a stroke, and the toner is less likely to slip through. This is because the.

  As described above, by using the configuration of the present embodiment, it is possible to prevent the generation of the vertical stripe image due to the cleaning failure even with the 30-dot horizontal line in which the amount of the protective developer image is smaller than the 40-dot horizontal line of the first embodiment. it can. Therefore, excessive toner consumption by the protective developer image can be suppressed.

  Further, the control for performing the stepwise bias fluctuation of the toner charging brush 11 as in the present embodiment may be performed only when the environment sensor 102 detects a temperature lower than a predetermined temperature. The poor cleaning is more likely to occur in a low-temperature environment where the rubber elasticity of the cleaning blade 6 decreases and the followability to the photosensitive drum decreases. Therefore, by performing the control of this embodiment only when, for example, 25 ° C. or less is detected, it is possible to prevent the occurrence of cleaning failure without increasing the number of times of bias fluctuation more than necessary.

  In the first and second embodiments, in the toner discharge sequence in FIGS. 6 and 8, for example, the toner supplied with the negative charge supplied from the toner charging brush 11 is used in the first and fourth image forming units, while the positive charge is applied. The toner to which the charge was applied was collected in the second and third image forming units. However, it is not limited to this. For example, the toner to which the positive charge is applied in the first and fourth image forming units and the toner to which the negative charge is applied in the second and third image forming units may be collected. It is optional which toner (developer) of which polarity is collected at which image forming unit.

[Other Examples]
In the first to third embodiments, the amount of the protective developer image is the same in the first to fourth image forming units, but may be reduced toward the downstream image forming unit. This is because the recovery amount of the toner discharged from the toner charging brush 11 decreases toward the downstream-side image forming portion, so that the cleaning failure hardly occurs. Therefore, the amount of the developer image for protection in the downstream image forming unit may be reduced. That is, the amount of the protective developer supplied by the second image forming unit is at least better than the amount of the protective developer supplied by the first image forming unit.

  Further, in the present embodiment, the developer image for protection was performed immediately before the toner was collected from the toner charging brush 11, but in addition to this, the developer discharged from the toner charging brush (first developer) May be performed immediately after the recovery of the wastewater. Although the cleaning failure did not occur due to the toner collection from the toner charging brush 11, the blocking layer 21 may be reduced and the cleaning failure may occur thereafter. Immediately after the toner is collected from the toner charging brush 11, a protective developer image (third developer) is supplied to compensate for the blocking layer 21 in the same manner as in T5 in FIG. 6 and T15 in FIG. .

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Scanner unit 4 Developing unit 5 Intermediate transfer belt 6 Cleaning blade 7 Process cartridge 8 Primary transfer roller 9 Secondary transfer roller 10 Fixing device 11 Toner charging brush 12 Recording material 13 Photoconductor unit 14 Cleaning frame REFERENCE SIGNS LIST 15 toner 16 toner storage chamber 17 developing roller 18 toner supply roller 19 developing blade 20 toner stirring member 21 blocking layer 23 cam 51 drive roller 52 secondary transfer facing roller 53 driven roller 100 image forming apparatus

Claims (13)

A developer carrying member carrying a developer to which externally added particles are added,
An image carrier on which a developer from the developer carrier is developed;
An intermediate transfer member,
A transfer member for applying a transfer bias for transferring a developer image developed on the image carrier to the intermediate transfer member,
After the developer image transferred to the intermediate transfer member is transferred to a recording material, a holding device that collects and temporarily holds the remaining developer remaining on the intermediate transfer member,
A cleaning member that comes into contact with the image carrier and removes a developer carried on the image carrier.
An image forming apparatus capable of performing an operation of moving a first developer held by the holding device to the intermediate transfer body and performing reverse transfer from the intermediate transfer body to the image carrier.
Before the reverse-transferred developer is supplied to the cleaning member, the developer carrier is attached to the image carrier so that the developer is supplied to the cleaning member from the developer carrier. An image forming apparatus comprising:   When the second developer passes through a transfer portion formed by the transfer member and the intermediate transfer body, the transfer member does not apply a bias, or has the same polarity as the normal charging polarity of the developer. The image forming apparatus according to claim 1, wherein a bias or a bias having a reverse polarity is applied.   Before the developer moved from the holding device to the intermediate transfer member reaches the transfer portion, the second developer passes through the transfer portion and moves to a contact portion of the cleaning member with the image carrier. The image forming apparatus according to claim 1, wherein the externally added particles are supplied. The holding device includes a charging member,
4. The image forming apparatus according to claim 1, wherein the charging member charges the developer carried on the intermediate transfer member by applying a bias having a polarity opposite to a polarity of the developer when developing the electrostatic latent image. 4. The image forming apparatus according to any one of 3.   The image forming apparatus according to claim 4, wherein the charging member applies a negative bias and a positive bias alternately and discharges the developer held in the holding device to the intermediate transfer member.   6. The image forming apparatus according to claim 4, wherein the charging member applies a bias while alternately increasing or decreasing the applied bias, and further gradually increases the increase or decrease. Further equipped with an environmental sensor,
When the temperature detected by the environment sensor corresponds to a predetermined temperature or less, the charging member applies a bias while alternately increasing and decreasing the applied bias, and further gradually increases the increase / decrease range. The image forming apparatus according to claim 6, wherein:   After the reversely transferred developer is removed by the cleaning member, the developer carrier again supplies the third developer to the image carrier, and the second developer supplies the third developer to the transfer member. 8. The transfer member according to claim 1, wherein the transfer member applies a bias opposite to the transfer bias when passing through a transfer portion formed by the transfer member and the intermediate transfer member. The image forming apparatus as described in the above. A second developer carrier that carries a developer to which externally added particles are added;
A second image carrier on which a developer from the second developer carrier is developed;
A second transfer member for applying a transfer bias for transferring a developer image developed on the second image carrier to the intermediate transfer member;
A second cleaning member that comes into contact with the second image carrier and removes the developer carried on the second image carrier.
Before the developer reversely transferred by the second transfer member is supplied to the second cleaning member, the developer from the second developer carrier is supplied to the second cleaning member. The image forming apparatus according to claim 1, wherein the second developer carrier supplies a fourth developer to the second image carrier.   When the fourth developer passes through a second transfer portion formed by the second transfer member and the intermediate transfer member, the second transfer member does not apply a bias, or A bias having the same polarity or a reverse polarity as the normal charging polarity of the developer is applied, and thereafter, the second transfer member applies a bias having the same polarity as the normal charging polarity of the developer. The image forming apparatus according to claim 9.   10. The apparatus according to claim 9, wherein the second cleaning member is disposed downstream of the first cleaning member, and the amount of the fourth developer is smaller than the amount of the second developer. An image forming apparatus according to claim 1.   The timing at which a part of the second developer reaches a second transfer portion formed by the second transfer member and the intermediate transfer member, and the timing at which the fourth developer transfers the second transfer member The image forming apparatus according to claim 9, wherein a timing at which the image forming apparatus reaches the image forming unit is different.   13. The externally added particle layer is formed on the contact portion by supplying the externally added particles to a contact portion where the cleaning member contacts the image carrier. The image forming apparatus according to claim 1.

Images