JP6659124B2 - Image forming device - Google Patents

Description

  The present invention relates to an electrophotographic or electrostatic recording type image forming apparatus.

  2. Description of the Related Art Conventionally, as an image forming apparatus such as a laser beam printer, an in-line color 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 photosensitive drum as an image carrier is uniformly charged by a charging unit, a toner image is developed by a developing unit on an electrostatic latent image created on the photosensitive drum by an exposure unit, and an intermediate transfer member is developed. First transfer. Thereafter, the same primary transfer is repeated for a plurality of colors to form a full-color toner image on the intermediate transfer member. Subsequently, the full-color toner image is secondarily transferred to a recording material, and the fixing device fixes the full-color toner image to the recording material. Here, so-called one-component contact development is used as the developing means. At the time of image formation, a developing roller as a developer carrier is brought into contact with the photosensitive drum to develop an electrostatic latent image on the photosensitive drum. During non-image formation, the developing roller is separated from the photosensitive drum.

  By the way, toner remaining on the intermediate transfer body without being transferred to the transfer material in the secondary transfer step (transfer residual toner) needs to be removed 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 body is charged by the toner charging means to the polarity opposite to the normal charge state of the toner, 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 cleaning means such as a cleaning blade. Further, Patent Document 2 proposes a method using a conductive brush member and a conductive roller member as a method of collecting transfer residual toner (hereinafter, secondary transfer residual toner) on an intermediate transfer member. Specifically, by applying a DC voltage to the brush member, the secondary transfer residual toner on the intermediate transfer member is mechanically dispersed, primary recovered, and charged.

  With the configuration as in Patent Document 2, collection can be performed simultaneously with the primary transfer of the next page, and continuous image formation can be performed 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, the primary collected toner accumulated on the brush member is discharged onto the intermediate transfer member. 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 non-image forming state in order to maintain the toner charging performance of the brush member. Then, the toner accumulated in the brush member is discharged. Since such recovery of the secondary transfer residual toner on the last page and recovery of the discharged toner from the brush member are performed during non-image formation, the photosensitive drum and the developing roller are separated from each other.

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

However, in the case of the configuration described below, vertical black stripes may occur due to defective cleaning of the photosensitive drum. As a specific configuration, an intermediate transfer member cleaning blade as an intermediate transfer member cleaning member is added to the configuration of Patent Document 2 after the secondary transfer process.
Further, it is provided between the toner charging brush members. In addition, a drive source for driving the intermediate transfer member and the photosensitive drum is common. In such a configuration, when the toner is discharged from the brush member to the intermediate transfer body, reaches the intermediate transfer body cleaning blade by driving the intermediate transfer body, and performs the operation of collecting the toner, the photosensitive drum is also continuously driven for a long time. become. At this time, since the intermediate transfer member and the photosensitive drum are controlled to be separated from each other, no toner is collected from the intermediate transfer member to the photosensitive drum, but the toner on the photosensitive drum cannot be cleaned, and a cleaning failure occurs. . When such a cleaning failure occurs, the toner that has passed through the cleaning blade appears as a vertical black streak image as it is, or the charging roller becomes dirty with toner and a charging failure occurs and is developed by the developing unit to form a vertical stripe image. Or

  This phenomenon is caused by the fact that the developing roller is separated from the photosensitive drum during non-image formation, so that a toner external additive (particles added as auxiliary particles or externally added particles to the toner particles) is transferred from the developing roller to the photosensitive drum. ) Is lost. When the supply of the toner external additive to the cleaning blade edge portion is stopped, the toner external additive layer (hereinafter, referred to as a blocking layer) formed on the cleaning blade edge portion and serving as a barrier disappears, and cleaning failure occurs. More likely to occur.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide a technique capable of reducing occurrence of image defects due to shortage of externally added particles at a contact portion between an image carrier and a cleaning member.

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,
A rotatable image carrier that carries a developer image in which an electrostatic image has been developed by contact with the developer carrier,
A cleaning member for cleaning the surface of the image carrier by contact with the image carrier;
An intermediate transfer member for supporting the developer image transferred from the image carrier,
The same drive source that drives the image carrier and the intermediate transfer member ,
An image forming apparatus in which the first operation of slidingly contacting the cleaning member is performed in a state where the image carrier is separated from both the intermediate transfer body and the developer carrier,
A second operation of temporarily contacting the developer carrier with the image carrier during the execution of the first operation and supplying the externally added particles to a contact portion of the cleaning member with the image carrier. Can be executed.
Further, in order to achieve the above object, the image forming apparatus of the present invention,
A developer carrying member carrying a developer to which externally added particles are added,
A rotatable image carrier on which an electrostatic latent image formed on the surface is developed by sliding contact with the developer carrier,
A first cleaning member for cleaning the surface of the image carrier by sliding contact with the image carrier;
An intermediate transfer member onto which a developer image developed on the surface of the image carrier is transferred by sliding contact with the image carrier;
A brush member that is in sliding contact with the intermediate transfer body and charges residual toner on the surface of the intermediate transfer body;
A second cleaning member that slides on the intermediate transfer member to clean the surface of the image carrier;
The same drive source that drives the image carrier and the intermediate transfer member ,
The developer carrier and the image carrier, the intermediate transfer body and the image carrier are configured to be separable, respectively ,
Before SL during non-image formation is not performed development of an electrostatic latent image in a state where said intermediate transfer member and then separating the said image bearing member, the residual toner which the brush member is held on the surface of the intermediate transfer body An image forming apparatus capable of performing a cleaning operation of discharging and removing the surface from the surface of the intermediate transfer member by the second cleaning member;
During the execution of the cleaning operation,
A first period for separating the image carrier and the developer carrier,
A second period in which the image carrier and the developer carrier are brought into contact with each other;
It is characterized by having.
Further, in order to achieve the above object, the image forming apparatus of the present invention,
A developer carrying member carrying a developer to which externally added particles are added,
A rotatable image carrier that carries a developer image in which an electrostatic image has been developed by contact with the developer carrier,
A cleaning member for cleaning the surface of the image carrier by contact with the image carrier;
An intermediate transfer member for supporting the developer image transferred from the image carrier,
The same drive source that drives the image carrier and the intermediate transfer member ,
An image forming apparatus in which the first operation of slidingly contacting the cleaning member is performed in a state where the image carrier is separated from both the intermediate transfer body and the developer carrier,
A second operation of temporarily contacting the developer carrier with the image carrier during the execution of the first operation and supplying the developer to a contact portion of the cleaning member with the image carrier. It is configured to be executable.

  According to the present invention, it is possible to reduce the occurrence of image defects due to a shortage of externally added particles at the contact portion between the image carrier and the cleaning member.

Explanatory diagram of an image forming apparatus according to an embodiment. Explanatory drawing of a process cartridge in an embodiment. Explanatory drawing of the process cartridge when the developing roller is separated in the embodiment. Explanatory drawing of the developing roller contact / separation timing of the embodiment and the comparative example Enlarged view of the cleaning blade edge portion in the embodiment

  Embodiments for carrying out the present invention will be illustratively 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.

(Example)
In the embodiment of the present invention, when the toner attached to the toner charging brush 11 is discharged during non-image formation, the development roller 17K is brought into contact with the photosensitive drum 1K to prevent the generation of a vertical black streak image due to a cleaning failure. It is characterized by. At this time, the toner discharged from the toner charging brush 11 is not collected on the photosensitive drum 1 because the intermediate transfer belt 5 and the photosensitive drum 1 are separated from each other. The toner discharged from the toner charging brush 11 is collected by driving the intermediate transfer belt 5 to reach the intermediate transfer belt cleaning blade 22.

(1) Outline of Configuration and Operation of Image Forming Apparatus With reference to FIG. 1, an overall configuration of an electrophotographic image forming apparatus (image forming apparatus) according to an embodiment of 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 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 in a direction intersecting the vertical direction. 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 reference numerals to indicate that the elements are provided for any of the colors are omitted. explain.

  That is, in the present embodiment, the image forming apparatus 100 includes four drum-type electrophotographic photosensitive members, that is, the photosensitive drums 1 arranged in parallel in a direction intersecting the vertical direction, as a plurality of image carriers. The photosensitive drum 1 is rotationally driven by a driving unit (a driving motor 30 as a driving source) in a direction indicated by an arrow A (clockwise). Around the photosensitive drum 1, a charging roller 2 as a charging unit for uniformly charging the surface of the photosensitive drum 1, and irradiates a laser based on image information to form an electrostatic image (electrostatic latent image) on the photosensitive drum 1. A scanner unit (exposure device) 3 is disposed as an exposure unit for forming the image. 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 the transfer. A cleaning blade 6 is disposed as cleaning means for performing cleaning. Further, an intermediate transfer belt 5 as an intermediate transfer body 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 this 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 integrated as a process cartridge 7. The process cartridge 7 is detachable from the apparatus main body of the image forming apparatus 100. Here, the apparatus main body refers to a component of the configuration of the image forming apparatus 100 excluding a configuration detachable as the process cartridge 7. In the present embodiment, the process cartridges 7 for each color all have the same shape, and yellow (Y), magenta (M), cyan (C), and blank (K ) 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 indicated by arrow B (counterclockwise). 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 as primary transfer means are arranged side by side so as to face the respective photosensitive drums 1. 5, a primary transfer nip N1 is formed. Then, a bias having a polarity opposite to the normal charge polarity of the toner is applied to the primary transfer roller 8 from a primary transfer bias power supply (not shown). Thus, the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 5 at each primary transfer nip N1. A secondary transfer roller 9 as a secondary transfer means is disposed at a position facing the secondary transfer opposing roller 52 on the outer peripheral surface side of the intermediate transfer belt 5, and the intermediate transfer belt 5 and the secondary transfer roller 9 The secondary transfer nip N2 is formed at the contact portion of the second transfer roller. Then, a bias having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 9 from a secondary transfer bias power supply (not shown). As a result, the toner image on the intermediate transfer belt 5 is transferred to the recording material 12 at the secondary transfer nip N2.

During image formation, first, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, an electrostatic image (electrostatic latent 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 (developer image) 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. Thereafter, 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 first collected by the intermediate transfer body cleaning blade 22. If there is any toner that cannot be collected, the toner charging brush 11 applies a charge having a polarity opposite to the normal charge polarity of the toner. The secondary transfer residual toner charged by the toner charging brush 11 is reversely transferred to the photosensitive drum 1Y of the first image forming unit in the next primary transfer step, and is collected by the cleaning blade 6.

[Process cartridge]
With reference to FIG. 2, an 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 as viewed from the longitudinal direction (the 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 (first unit) including the photosensitive drum 1 and the like, and a developing unit 4 (second unit) including a developing roller 17 (developer carrier) 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 mounted on 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 30 as a driving unit (driving source) to the photosensitive 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. In the photoconductor unit 13, the cleaning member 6 and the charging roller 2 are arranged so as to be in contact with the peripheral surface of the photoconductor 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, whereby 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 the charge on the surface by the carrier from the carrier generating 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, a developing blade 19, a toner supply roller 18, a toner 15, and a toner storage chamber 16 for storing the toner. Toner 15 (developer)
Used a non-magnetic spherical toner which is negatively charged as a regular polarity and has a particle diameter of 7 μm. On the surface of the toner 15, silica particles (externally added particles) having a particle diameter of 20 nm are added as a toner external additive.

  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. The surface of the developing blade 19 comes 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 to be charged, 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 opposing portions (contact portions). . In the present embodiment, the toner charged negatively due to frictional charging with respect to a predetermined DC bias applied to the developing roller 17 contacts the photosensitive drum 1 (sliding contact) in the developing section where the toner is charged. Then, the electrostatic latent image is visualized by transferring only to the light potential portion.

  The toner supply roller 18 is provided with a predetermined nip formed on the peripheral surface of the developing roller 17 and rotates in the direction indicated by 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 penetration. 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 part of the toner supply roller 18 in the direction of arrow G in the drawing. 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 abutting on the photosensitive drum 1, the toner is transferred only to the bright section potential section from the potential difference, so that the electrostatic latent image is transferred. Visualize the image.

[Developing roller contact / separation mechanism]
FIG. 3 is a schematic sectional view of the process cartridge 7 of the present embodiment, and shows a state in which the developing roller 17 is separated from the photosensitive drum 1. The developing roller 17 is configured to be capable of coming into contact with and separating from the photosensitive drum 1. The developing roller 17 is in contact with the photosensitive drum 1 during image formation, and is separated as shown in FIG. I have. Here, the time of image formation is when a developer image is formed by transferring the developer from the developing roller 17 according to the electrostatic latent image formed on the photosensitive drum 1. The non-image formation 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). 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. Even when the developer image is not formed in the provided period, it is also at the 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 pressurizing 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 rotational position of the cam 23 to push and rotate the developing unit 4 from the bottom. In addition, various operations of each configuration in the image forming apparatus 1 are controlled by a control unit (CPU) provided in the apparatus main body controlling a power source such as a motor.

  The contact / separation mechanism for enabling the separation between the developing roller 17 and the photosensitive drum 1 is not limited to the above-described one using the cam and the spring member. There is no problem with what you have.

[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. Further, 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]
As the primary transfer roller 8, 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. 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 member configured so that nylon fibers having a conductivity of 10 ⁶ to 10 ⁹ Ωcm is substantially dense is fixedly disposed. In the present embodiment, the tip position of the toner charging brush 11 is set so 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. Further, 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 collecting method]
The secondary transfer residual toner collecting method (fourth operation) as a cleaning operation performed during printing will be described in detail. After the secondary transfer process, the secondary transfer residual toner on the intermediate transfer belt 5 is first collected by the intermediate transfer member cleaning blade 22 (second cleaning member). Here, for the toner that cannot be recovered, a polarity opposite to the normal charging polarity of the toner, that is, a positive bias of +1.5 kV in this embodiment is applied to the toner charging brush 11. As a result, the toner not collected by the intermediate transfer body cleaning blade is charged to a positive polarity when passing through the toner charging brush 11. 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 toner to which the positive charge has been applied by the toner charging brush 11 is reversely transferred to the photosensitive drum 1Y of the first image forming unit during the primary transfer step, and is collected by the cleaning blade 6 (first cleaning member). .

Here, the reason why the secondary transfer residual toner passes through the intermediate transfer belt cleaning blade 22 is that the surface properties of the intermediate transfer belt (surface unevenness and friction coefficient) are not stable as compared with the photosensitive drum surface. . If a part of the surface of the intermediate transfer belt is uneven, the edge of the intermediate transfer body cleaning blade 22 is chipped, and cleaning failure easily occurs. If the coefficient of friction of the surface of the intermediate transfer belt is not stable, the way in which the edge of the cleaning blade is caught is not stable, and the pressure applied to the intermediate transfer belt 5 also fluctuates. In particular, in a low-temperature environment where the rubber elastic modulus of the cleaning blade decreases, cleaning failure of the intermediate transfer belt may occur.

[Toner charging brush discharging process]
The discharging process (third operation) from the toner charging brush 11 as the cleaning operation 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. Therefore, 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. In the present embodiment, the same polarity as the normal charging polarity of the toner, that is, a negative bias of −1.5 kV is applied to the toner charging brush 11 in the post-rotation step during non-image formation, The negative toner is discharged onto the intermediate transfer belt 5. The intermediate transfer belt 5 and the photosensitive drum 1 are configured to be separable. At this time, the intermediate transfer belt 5 and the photosensitive drum 1 are separated from each other, and the discharged toner is not collected on the photosensitive drum 1. Instead, the toner discharged from the toner charging brush 11 is recovered by reaching the intermediate transfer belt cleaning blade 22 by driving the intermediate transfer belt 5.

  In the present embodiment, the motor for driving the intermediate transfer belt 5 and the photosensitive drum 1K of the fourth image forming unit is common (drive motor 30). The photosensitive drum 1K of the fourth image forming section is also driven at the same time. In the present embodiment, during the discharging process, the photosensitive drum 1 and the secondary transfer roller 9 are separated from the intermediate transfer belt 5, and the photosensitive drums 1Y, 1M, and 1C are controlled to stop. However, the photosensitive drum 1K is driven because the intermediate transfer belt 5 and the drive motor are common as described above. Therefore, the photosensitive drum 1K continues to be driven for about one rotation of the intermediate transfer belt 5 when the discharged toner is collected. In the present embodiment, the ejection process is performed during post-rotation, but a period in which the ejection process is performed separately from printing may be provided. In this embodiment, this step is periodically performed every time 100 images are printed.

(3) Description of Features of the Present Embodiment In the present embodiment, the first operation of separating the developing roller 17 from the photosensitive drum 1 during the discharging process from the toner charging brush 11 performed during non-image formation described above (at this time, the photosensitive drum 1 is also separated from the intermediate transfer belt 5.), a second operation of temporarily bringing the developing roller 17 into contact with the photosensitive drum 1 can be executed. The cleaning performance was compared when the discharge process was actually performed.
In the present embodiment, as the first operation, the operation of separating the photosensitive drum 1 from the intermediate transfer belt 5 and the developing roller 17 at the time of the discharging process from the toner charging brush 11 is described. Not done. In other words, even when the discharging operation from the toner charging brush 11 is not performed, the operation of driving the photosensitive drum 1 while the photosensitive drum 1 is separated from both the intermediate transfer belt 5 and the developing roller 11 is performed. One operation can be performed. The present invention relates to a state at a contact portion where a cleaning blade contacts a photosensitive drum. Then, in various operations, there is a state where the photosensitive drum is separated from the developing roller or the intermediate transfer belt and no material is supplied to the contact portion. Therefore, in the present invention, the externally added particles are supplied to the contact portion by temporarily contacting the developing roller.
The operation of temporarily contacting the developing roller with the photosensitive drum is referred to as the second operation. More specifically, the operation is preferably performed prior to the image forming operation. More preferably, during the post-rotation after the image forming period, the photosensitive drum and the developing roller are brought into contact with each other after a predetermined time has elapsed from the start of the post-rotation. Here, the state in which the photosensitive drum and the developing roller are in contact with each other during post-rotation is not a contact state formed by the state in which the developing roller and the photosensitive drum are in contact with each other during image formation and continuing during post-rotation. . That is, the state in which the photosensitive drum and the developing roller are in contact with each other during post-rotation is a contact state formed by once separating from the contact state during image formation and then making contact again. In the present embodiment, the contact is made immediately after the start of the post-rotation, but the contact is separated at one end and comes into contact again in the second operation. Of course, the present invention is not limited to this, and may be separated at the start of post-rotation.

  FIG. 4 is a timing chart of the rotation and stop of the photosensitive drum 1K, the timing of applying a positive or negative bias to the toner charging brush 11, and the timing of contact and separation of the developing roller 17K in the comparative example and the embodiment. As shown in FIG. 4, the timing of rotating and stopping the photosensitive drum 1K is compared with the timing of changing the bias applied to the toner charging brush 11 from +1.5 kV to -1.5 kV in the discharging process of the toner charging brush 11 in the post-rotation. The same applies to the examples and the embodiments. However, the contact / separation state between the developing roller 17K and the photosensitive drum 1K during the discharging process of the toner charging brush 11 is different. In the comparative example, immediately after the completion of the image formation, the developing roller 17K and the photosensitive drum 1K are separated from each other, and the printing is completed in that state. On the other hand, in the embodiment, the developing roller 17K is temporarily separated immediately after the image formation is completed (first period a), but the developing roller 17K is brought into contact with the photosensitive drum 1K immediately before the discharging step of the toner charging brush 11 ( Second period b). Then, control is performed such that the photosensitive drum 1K is separated immediately before stopping (first period a).

  As a common condition, an image obtained by printing 100 horizontal line images with a printing rate of 5% for each color continuously, then performing a discharging process from the toner charging brush 11, and immediately after printing a yellow halftone image with a printing rate of 25%. Defective (vertical black stripes) were confirmed. The image forming apparatus 100 was installed in a low-temperature and low-humidity environment (temperature: 15 ° C./humidity: 10%), which is severe against poor cleaning.

Table 1 Results of cleaning failure in the discharge recovery process

  As shown in Table 1, in the comparative example, vertical black stripes were generated due to defective cleaning. However, in the configuration of the example, no defective cleaning occurred. The cleaning failure of the comparative example is caused by toner accumulated on the edge of the cleaning blade slipping through the cleaning blade. In this embodiment, since the motor for driving the intermediate transfer belt 5 and the photosensitive drum 1K of the fourth image forming unit is common, the photosensitive drum 1K is also driven during the discharging process until the discharged toner is collected by the intermediate transfer belt cleaning blade. are doing. If there is no supply of the external additive to the cleaning blade edge for a long time as described above, the blocking layer is lost and cleaning failure is likely to occur. Further, if the toner charged to the positive polarity exists at the edge of the cleaning blade, the toner enters the blocking layer in a state where the electrostatic adhesion to the surface of the photosensitive drum 1 having the negative polarity is increased. Is easy to break.

At this time, by bringing the developing roller 17 into contact with the photosensitive drum 1, the external additive is directly transferred to the photosensitive drum 1 from the fog toner transferred to the photosensitive drum 1 and the toner coated on the developing roller 17. Is supplied to the edge of the cleaning blade 6. The external additive also moves to the photosensitive drum 1 from the fog toner that has moved to the photosensitive drum 1 from the developing roller 17 and is supplied to the edge of the cleaning blade 6. The supplied external additive forms a blocking layer serving as a barrier layer at the edge of the cleaning blade, and improves the cleaning performance.

  A mechanism for improving the cleaning performance will be described with reference to an enlarged view of the cleaning blade edge portion in FIG. The cleaning blade 6 is a blade member extending in a counter direction with respect to the rotation direction of the photosensitive drum 1. As shown in FIG. 5, the cleaning blade 6 abuts in the counter direction with respect to the rotation direction of the photosensitive drum 1, that is, is a tip portion extending in the direction opposite to the moving direction of the photosensitive drum 1 relative to the cleaning blade 6. The edge portion e contacts the surface of the photosensitive drum 1. Therefore, the edge e of the cleaning blade 6 is wound in the moving direction of the photosensitive drum 1 as the photosensitive drum 1 rotates. The toner external additive that has migrated to the photosensitive drum 1 accumulates in the portion (contact portion) of the wedge that is entangled, and forms a layer (hereinafter, referred to as a blocking layer 21). If the toner is to be cleaned without the blocking layer 21, which is a layer of the externally added particles, the toner tends to sneak in from the wedge portion in which the edge is caught, and cleaning failure is likely to occur. When the blocking layer 21 exists at the edge of the cleaning blade as shown in FIG. 5, 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 of about 20 nm, a constant amount of the external additive is always removed from the edge of the cleaning blade. Therefore, when the developing roller 17 is separated from the photosensitive drum 1 and the supply of the external additive to the cleaning edge portion is stopped, the blocking layer 21 gradually disappears, and the cleaning performance is reduced. The longer the contact time of the developing roller 17K with the photosensitive drum 1K, the more the blocking layer can be formed. (That is, the second operation of bringing the developing roller into contact with the photosensitive drum is an operation of forming a layer (blocking layer) of the externally added particles.) In this embodiment, the blocking of the photosensitive drum 1K is caused by the long-time rotation of the photosensitive drum 1K. In order to prevent disappearance of the developing roller 17K, the developing roller 17K was controlled to be in contact from the start of the discharging process to immediately before the stop of the photosensitive drum 1K was stopped.

  As described above, by using the configuration of the present embodiment, even if the cleaning blade of the photosensitive drum lacks the blocking layer at the time of non-image formation and the cleaning performance is deteriorated, the generation of the vertical black stripe image due to the cleaning failure is prevented. Can be prevented. Further, the drive source of the intermediate transfer belt 5 and the photosensitive drum 1K is common (the photosensitive drum 1K and the intermediate transfer belt 5 are simultaneously driven by the drive motor 30 as the same drive source). Costs can be reduced.

  In this embodiment, only the developing roller 17K is brought into contact with the photosensitive drum 1K at the time of the discharging step, but the timing of the contact and the image forming section are not limited to this. In other words, when the driving time of the photosensitive drum 1 becomes longer and a cleaning failure may occur, such as in the toner density adjustment step or the color misregistration correction step, the timing may be other than the discharge step. 1 may be abutted. Further, the image forming unit is not limited to performing the contact operation only with the photosensitive drum having the same driving source as the intermediate transfer belt 5, and in the image forming unit in which the toner is collected from the intermediate transfer belt 5 as described above, the cleaning failure may occur. Since this may occur, the contact operation may be performed during non-image formation.

  Further, even in an image forming apparatus in which the intermediate transfer belt cleaning blade 22 is omitted from the configuration of the present embodiment, the operation of bringing the developing roller 17 into contact with the photosensitive drum 1 during non-image formation, which is a feature of the present embodiment, is performed. You may. That is, the present embodiment can be applied to an image forming apparatus in which the toner remaining on the intermediate transfer belt 5 is charged by the toner charging brush 11 and transferred to the photosensitive drum 1. Specifically, when the photosensitive drum 1 is rotated for a long time during non-image formation and the blocking layer is insufficient, the development roller 17 is brought into contact with the photosensitive drum 1 to prevent the occurrence of a vertical black stripe image due to defective cleaning. it can.

In addition, a temperature sensor (temperature detecting unit) for detecting the installation temperature of the image forming apparatus is provided in the apparatus main body, and the image forming apparatus 100 controls the contact between the developing roller 17 and the photosensitive drum 1 according to the present embodiment. It may be performed only when the temperature lower than or equal to is detected. Insufficient cleaning is more likely to occur in a low-temperature environment where the rubber elasticity of the cleaning blade decreases and the ability to follow the photosensitive drum decreases. Therefore, by performing the control of this embodiment only when, for example, a temperature of 20 ° C. or lower is detected, excessive deterioration of members such as the developing roller 17 and toner due to rotation of the developing roller can be prevented.

  Reference Signs List 1: photosensitive drum (image carrier), 5: intermediate transfer belt (intermediate transfer member), 6: cleaning blade (cleaning member), 11: toner charging brush (brush member), 15: toner (developer), 17 ... Developing roller (developer carrier), 21: blocking layer (layer of externally added particles), 22: intermediate transfer member cleaning blade (second cleaning member), 100: image forming apparatus

Claims (11)

A developer carrying member carrying a developer to which externally added particles are added,
A rotatable image carrier that carries a developer image in which an electrostatic image has been developed by contact with the developer carrier,
A cleaning member for cleaning the surface of the image carrier by contact with the image carrier;
An intermediate transfer member for supporting the developer image transferred from the image carrier,
The same drive source that drives the image carrier and the intermediate transfer member ,
An image forming apparatus in which the first operation of slidingly contacting the cleaning member is performed in a state where the image carrier is separated from both the intermediate transfer body and the developer carrier,
A second operation of temporarily contacting the developer carrier with the image carrier during the execution of the first operation and supplying the externally added particles to a contact portion of the cleaning member with the image carrier. An image forming apparatus characterized by being able to execute.   The image forming apparatus according to claim 1, wherein the second operation is an operation of forming a layer of the externally added particles on the contact portion.   3. The image forming apparatus according to claim 1, wherein the cleaning member is a blade member having a tip end extending in a direction opposite to a moving direction of the image carrier with respect to the cleaning member and abutting on a surface of the image carrier. An image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the first operation is performed during non-image formation in which the electrostatic image is not developed. A brush member that is in sliding contact with the intermediate transfer member,
A second cleaning member that is in sliding contact with the intermediate transfer member;
In a state where the intermediate transfer member and the image carrier are separated from each other, the remaining toner held by the brush member is discharged onto the surface of the intermediate transfer member, and the second cleaning member removes the remaining toner from the surface of the intermediate transfer member. A third operation of removing is executable;
Claims 1-4 noise, wherein the first operation is executed during execution of the third operation
The image forming apparatus according to item 1 Zureka. In a state where the developer carrier and the image carrier are separated from each other, the remaining toner on the surface of the intermediate transfer body is transferred to the image carrier, and is removed from the surface of the image carrier by the cleaning member. the image forming apparatus according to have Zureka one of claims 1-5, characterized in that 4 operation available. It further includes a temperature detector,
The second operation, the image forming apparatus according to any one of claims 1 to 6, the temperature of the temperature detecting portion is detected, characterized in that it is executed when a predetermined temperature or less. At least the developer carrier, the image carrier, and the cleaning member are integrated as a cartridge, and are configured to be detachable from an apparatus main body of the image forming apparatus. Item 8. The image forming apparatus according to any one of Items 1 to 7. The cartridge is
A first unit including the image carrier and the cleaning member;
A second unit including the developer carrier,
Has,
The image forming apparatus according to claim 8, wherein the first unit and the second unit are configured to be separable so that the image carrier and the developer carrier are separated from each other. A developer carrying member carrying a developer to which externally added particles are added,
A rotatable image carrier on which an electrostatic latent image formed on the surface is developed by sliding contact with the developer carrier,
A first cleaning member for cleaning the surface of the image carrier by sliding contact with the image carrier;
An intermediate transfer member onto which a developer image developed on the surface of the image carrier is transferred by sliding contact with the image carrier;
A brush member that is in sliding contact with the intermediate transfer body and charges residual toner on the surface of the intermediate transfer body;
A second cleaning member that slides on the intermediate transfer member to clean the surface of the image carrier;
The same drive source for driving the image carrier and the intermediate transfer member,
With
The developer carrier and the image carrier, the intermediate transfer body and the image carrier are configured to be separable, respectively ,
Before SL during non-image formation is not performed development of an electrostatic latent image in a state where said intermediate transfer member and then separating the said image bearing member, the residual toner which the brush member is held on the surface of the intermediate transfer body An image forming apparatus capable of performing a cleaning operation of discharging and removing the surface from the surface of the intermediate transfer member by the second cleaning member;
During the execution of the cleaning operation,
A first period for separating the image carrier and the developer carrier,
A second period in which the image carrier and the developer carrier are brought into contact with each other;
An image forming apparatus comprising: A developer carrying member carrying a developer to which externally added particles are added,
A rotatable image carrier that carries a developer image in which an electrostatic image has been developed by contact with the developer carrier,
A cleaning member for cleaning the surface of the image carrier by contact with the image carrier;
An intermediate transfer member for supporting the developer image transferred from the image carrier,
The same drive source that drives the image carrier and the intermediate transfer member ,
An image forming apparatus in which the first operation of slidingly contacting the cleaning member is performed in a state where the image carrier is separated from both the intermediate transfer body and the developer carrier,
A second operation of temporarily contacting the developer carrier with the image carrier during the execution of the first operation and supplying the developer to a contact portion of the cleaning member with the image carrier. An image forming apparatus configured to be executable.

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