JP2019066606A - Image forming apparatus - Google Patents

Abstract

To reduce a fogging toner that transfers to an intermediate transfer body without increasing downtime required for cleaning the intermediate transfer body at non-image-formation time.SOLUTION: An image forming apparatus is provided that includes: a charging member which charges developer on an intermediate transfer body; and cleaning means which can perform a cleaning mode in which the developer remaining on the intermediate transfer body after secondarily transferred to a recording material from the intermediate transfer body is charged by the charging member and is removed from the intermediate transfer body, in the image forming apparatus, the cleaning means decreases an absolute value of voltage applied to the charging member when the cleaning mode is performed at image-formation time compared to a case when the cleaning mode is performed at non-image-formation time when an image is not formed, and sets a potential difference ΔVb between voltage applied to a developer carrier and voltage applied to a developer regulation member to be a value having the same polarity side as a normal charging polarity of the developer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus such as, for example, a copying machine or a printer, which has a function of forming an image on a recording material such as a sheet.

In recent years, colorization has progressed in image forming apparatuses such as printers, copiers and facsimiles, and an image forming apparatus of an intermediate transfer type is known as an apparatus for forming a color image. In an intermediate transfer type image forming apparatus, after transfer of a developer (toner) image from an intermediate transfer member to a recording material, transfer residual toner (secondary transfer residual toner) may remain on the intermediate transfer member. The transfer residual toner on the intermediate transfer member is removed and collected from the intermediate transfer member by the cleaning unit for the intermediate transfer member.
Patent Document 1 proposes that a charging member for charging the secondary transfer residual toner on the intermediate transfer member to a polarity reverse to the regular charging polarity of the toner is provided as a cleaning unit for the intermediate transfer member. In this case, the secondary transfer residual toner is charged to the opposite polarity to the regular charge polarity of the toner, so that the intermediate transfer member to the image carrier (photosensitive drum) in the subsequent primary transfer portion of the image forming portion. And finally collected by the cleaning blade on the photosensitive drum.
Further, as a cleaning means of an intermediate transfer member (intermediate transfer belt) in an in-line type image forming apparatus, a method as described in Patent Document 2 is also proposed. In Patent Document 2, a voltage (charging bias) applied to the charging member and a voltage (primary transfer bias) applied to the primary transfer portion are used as means for collecting the toner remaining on the intermediate transfer belt after paper jam (jam). ) Has the same polarity as the regular charge polarity of the toner.
The toner remaining on the intermediate transfer belt at the time of jamming is the toner remaining without being secondarily transferred, has a regular charging polarity of the toner, and has a larger amount than the secondary transfer residual toner at the time of image formation. . Therefore, when applying a bias of reverse polarity to the normal charging polarity of the toner to the charging member for cleaning, it is difficult to properly charge all the toner of reverse polarity and a large amount by the charging member, and a cleaning failure occurs. There is a risk of In contrast, in Patent Document 2, as a cleaning unit after jamming, a bias having the same polarity as the regular charging polarity of toner is applied to the charging member. Thus, the toner on the intermediate transfer belt passes through the charging member while maintaining the polarity, and is electrostatically moved from the photosensitive drum at the subsequent primary transfer portion to be removed from the intermediate transfer belt. .

  The cleaning means described above is a useful means not only after jamming but also as cleaning means to be executed after the density adjustment mode described below. The density adjustment mode is a mode in which a test patch is formed on the intermediate transfer member, and the density and chromaticity of the test patch are measured by an optical sensor to optimize the image forming conditions. The test patch remains on the intermediate transfer belt without being secondarily transferred. Therefore, as in the case of cleaning after jamming, the bias applied to the charging member and the bias applied to the primary transfer portion are properly removed from the intermediate transfer belt by setting the same polarity as the regular charging polarity of the toner. It is possible to

Patent No. 3267507 gazette JP, 2016-4140, A

In order to clean the toner remaining on the intermediate transfer belt during non-image formation such as after jamming or after the density adjustment mode, the voltage applied to the charging member and the voltage applied to the primary transfer portion are It was found that the following problems existed when making the same polarity.
When the toner on the intermediate transfer belt is cleaned, a small amount of “fogging developer (fogging toner)” may be transferred onto the intermediate transfer member from an image forming unit having a developing unit. The "fog toner" referred to here is a toner which is transferred to an area on the photosensitive drum where the electrostatic latent image is not formed, and has a tendency that it does not have an appropriate charge amount due to deterioration or the like. It is also a toner. Therefore, the "fog toner" may be transferred to the photosensitive drum and the intermediate transfer belt even during non-image formation and cleaning after the jam and density adjustment mode in which the electrostatic latent image is not formed. . As a means for preventing transfer of "fog toner" to the photosensitive drum at the time of cleaning after jamming or after the density adjustment mode, there is a method of mechanically separating the developing portion from the photosensitive drum at the time of cleaning. However, in an image forming apparatus that does not have a developing unit separation mechanism for the purpose of cost reduction, or in an image forming apparatus that can not perform development separation during cleaning due to other restrictions, "fog toner" transfers to the photosensitive drum and the intermediate transfer belt. You may
As described above, when the "fogging toner" is transferred to the intermediate transfer belt, the "fogging toner" can not be charged by the charging member at the time of cleaning after the jamming or after the density adjustment mode, for the reason described later. For this reason, the "fog toner" remains on the intermediate transfer belt even after the cleaning is completed. That is, the reason why the "fog toner" can not be charged after the jam or at the time of cleaning after the density adjustment mode is because a bias as high as charging the toner can not be applied to the charging member.

  Specifically, a bias of the same polarity as the residual toner (normally not transferred secondarily) is applied to the charging member at the time of cleaning after jamming or after the density adjustment mode, and electrostatic repulsive force is applied. Prevents the residual toner from adhering to the charging member. At this time, the bias applied to the charging member is a bias for passing the residual toner, and it is not necessary to apply a bias high enough to charge the toner. On the contrary, if the applied bias is too high, the residual toner is excessively charged, and the mirror force of the residual toner to the intermediate transfer belt becomes strong, the electrostatic adhesion to the belt becomes strong, and the first order There is a possibility that the movement of the residual toner to the photosensitive drum at the transfer portion may be hindered. Therefore, the absolute value of the bias applied to the charging member at the time of cleaning is set to a value lower than the absolute value of the bias applied at the time of image formation. As a result, the "fogging toner" transferred onto the intermediate transfer belt is not properly charged by the charging member and remains on the intermediate transfer belt.

However, when the amount of "fogging toner" remaining on the intermediate transfer belt is large, the "fogging toner" is charged by the charging member to the opposite polarity to the regular charging polarity of the toner at the time of image formation thereafter, and the primary transfer is performed. It may not be possible to recover everything even if it is attempted to recover in a department. In such a case, contamination (cleaning failure) caused by "fog toner" occurs on the output image. The "fog toner" is a toner with low chargeability that has not been properly charged in the developing section, and is a toner that is difficult to properly charge even with a charging member provided on the intermediate transfer belt.
In addition, the amount of “fog toner” tends to increase with the deterioration of the toner, and particularly at the end of the life of the image forming portion, the cleaning defect caused by the “fog toner” tends to occur easily.

Therefore, in order to prevent defective cleaning due to "fogging toner" remaining on the intermediate transfer belt, "fogging toner" is performed by performing the following method after cleaning after the jamming or after the density adjustment mode is completed. It is possible to recover. It rotates the belt several times while applying a bias of reverse polarity to the regular charging polarity of the toner to the charging member, charging the "fog toner" little by little, and "fog toner" at the primary transfer portion. It is a method of recovery.
However, in the above-described method, there is a concern that the time from the jam processing to the start of the next print and the time from the execution of the density adjustment mode to the start of the next print may be long.
As described above, in recent years where reduction of downtime is required, cleaning defects caused by “fog toner” at the time of cleaning after jamming and after the density adjustment mode have become major issues.

  The present invention has been made in view of the above-described circumstances, and reduces the fog toner transferred to the intermediate transfer member without increasing the downtime required for cleaning the intermediate transfer member during non-image formation. The purpose is to

In the present invention to achieve the above object,
An image carrier on which an electrostatic latent image is formed;
A developer carrier for carrying a developer for developing the electrostatic latent image formed on the image carrier;
A developer regulating member that regulates the amount of the developer on the developer carrier;
A transfer unit is provided, and the developer image developed on the image carrier is primarily transferred to the transfer unit by bringing the transfer unit and the image carrier into contact with each other, and the transfer unit and the recording material are in contact with each other. An intermediate transfer member on which the developer image is further secondarily transferred from the transfer portion to the recording material;
A charging member for charging the developer on the intermediate transfer member;
A cleaning unit capable of executing a cleaning mode in which the developer remaining on the intermediate transfer member after being secondarily transferred from the intermediate transfer member to the recording material is charged by the charging member and removed from the intermediate transfer member; ,
In an image forming apparatus having
When the cleaning unit executes the cleaning mode when forming an image without forming an image, the absolute value of the voltage applied to the charging member is different from when performing the cleaning mode when forming an image forming an image. And setting the potential difference .DELTA.Vb of the voltage applied to the developer regulating member to the voltage applied to the developer carrier to a value on the same polarity side as the regular charging polarity of the developer. It is characterized by

An image carrier on which an electrostatic latent image is formed;
A developer carrier for carrying a developer for developing the electrostatic latent image formed on the image carrier;
A developer supply member for supplying the developer to the developer carrier;
A transfer unit is provided, and the developer image developed on the image carrier is primarily transferred to the transfer unit by bringing the transfer unit and the image carrier into contact with each other, and the transfer unit and the recording material are in contact with each other. An intermediate transfer member on which the developer image is further secondarily transferred from the transfer portion to the recording material;
A charging member for charging the developer on the intermediate transfer member;
A cleaning unit capable of executing a cleaning mode in which the developer remaining on the intermediate transfer member after being secondarily transferred from the intermediate transfer member to the recording material is charged by the charging member and removed from the intermediate transfer member; ,
In an image forming apparatus having
When the cleaning unit executes the cleaning mode when forming an image without forming an image, the absolute value of the voltage applied to the charging member is different from when performing the cleaning mode when forming an image forming an image. And the potential difference .DELTA.Vs of the voltage applied to the developer supply member to the voltage applied to the developer carrier is set to a value opposite to the regular charge polarity of the developer It is characterized by

An image bearing member on which an electrostatic latent image is formed after the surface is charged;
A developer carrier for carrying a developer for developing the electrostatic latent image formed on the image carrier;
A transfer unit is provided, and the developer image developed on the image carrier is primarily transferred to the transfer unit by bringing the transfer unit and the image carrier into contact with each other, and the transfer unit and the recording material are in contact with each other. An intermediate transfer member on which the developer image is further secondarily transferred from the transfer portion to the recording material;
A transfer member for primarily transferring the developer image from the image carrier to the intermediate transfer member;
A charging member for charging the developer on the intermediate transfer member;
A cleaning unit capable of executing a cleaning mode in which the developer remaining on the intermediate transfer member after being secondarily transferred from the intermediate transfer member to the recording material is charged by the charging member and removed from the intermediate transfer member; ,
In an image forming apparatus having
When the cleaning unit executes the cleaning mode when forming an image without forming an image, the absolute value of the voltage applied to the charging member is different from when performing the cleaning mode when forming an image forming an image. Changing the absolute value of the potential difference Vback between the voltage applied to the developer carrier and the surface voltage before the electrostatic latent image is formed on the charged image carrier. It features.

  According to the present invention, in cleaning of the intermediate transfer member at the time of non-image formation, it is possible to reduce the fog toner transferred to the intermediate transfer member without increasing the down time required for the cleaning.

Schematic which shows the structure of the belt cleaning part of Example 1 FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to Embodiment 1. FIG. 1 is a schematic cross-sectional view of an image forming portion as viewed from the longitudinal direction of a photosensitive drum in Embodiment 1. Diagram for explaining a belt cleaning mechanism in the first embodiment A diagram for explaining the relationship between the developing bias and the developing blade bias in Example 1 FIG. 6 is a graph showing the measurement results of the amount of fog toner transferred onto the intermediate transfer belt of Example 1. The figure for demonstrating the modification which provided the electroconductive brush in the upstream of the charging roller. The figure for demonstrating the relationship between the developing bias of Example 3, and a toner supply bias. FIG. 16 shows the results of measurement of the amount of fog toner transferred onto the intermediate transfer belt of Example 3.

  DETAILED DESCRIPTION Exemplary embodiments of the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, etc. of the components described in this embodiment should be changed as appropriate depending on the configuration of the apparatus to which the invention is applied and various conditions, and The scope of the present invention is not intended to be limited to the following embodiments.

Example 1
The first embodiment will be described below.
(1) Image Forming Apparatus First, the overall configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG.
FIG. 2 is a schematic cross-sectional view of the image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 of the present embodiment is a full-color printer of an in-line type and an intermediate transfer type using an electrophotographic method.

The image forming apparatus 10 of this embodiment has first, second, third, and fourth image forming units (image forming stations) 1a, 1b, 1c, and 1d as a plurality of image forming units. The first, second, third and fourth image forming portions 1a, 1b, 1c and 1d are for forming an image of each color of yellow, magenta, cyan and black, respectively. The image forming units 1a, 1b, 1c, and 1d are arranged in a line at regular intervals.
In the present embodiment, the configurations of the first to fourth image forming portions 1a to 1d are substantially the same except that the color of the toner (developer) to be used is different. Therefore, in the following, suffixes a, b, c and d given to reference numerals in the drawings are omitted to indicate that the elements are provided for any color unless distinction is particularly required. Explain it.

  In the image forming unit 1, a drum-shaped electrophotographic photosensitive member (hereinafter, photosensitive drum) 2 as an image bearing member on which a toner image (developer image) is formed by an electrophotographic process means is installed. A drum charging roller 3, a developing device 4, a primary transfer roller 5, and a drum cleaning device 6 are provided around the photosensitive drum 2 as members forming an electrophotographic process unit. Further, as shown in FIG. 2, an exposure device (laser scanner device) 7 is installed below the drum charging roller 3 and the developing device 4. Here, the developing device 4 corresponds to a developing unit. Also, the primary transfer roller 5 corresponds to a transfer member. The image forming apparatus 10 further includes a control unit 11 for controlling the operation of the entire image forming apparatus.

Further, an intermediate transfer belt 20 as an endless belt-like intermediate transfer member is disposed to face all the photosensitive drums 2a to 2d of the respective image forming portions 1a to 1d. The intermediate transfer belt 20 is wound around a drive roller 21 as a plurality of support members, a cleaning opposing roller 22 and a secondary transfer opposing roller 23, and rotates in the direction of arrow R3 in FIG. On the inner peripheral surface side of the intermediate transfer belt 20, the primary transfer rollers 5 are disposed corresponding to the photosensitive drums 2 of the image forming units 1, respectively. Further, on the outer peripheral surface side of the intermediate transfer belt 20, a secondary transfer roller 24 as a secondary transfer unit is disposed at a position facing the secondary transfer opposing roller 23.
The photosensitive drum 2 in the present embodiment is a negatively chargeable OPC (organic photoconductor) photosensitive member, and has a photosensitive layer on an aluminum drum substrate. The photosensitive drum 2 is rotationally driven at a predetermined peripheral speed (surface movement speed) in the direction of arrow R1 in FIG. 2 (clockwise in FIG. 2) by a driving device (not shown). In the present embodiment, the peripheral speed of the photosensitive drum 2 corresponds to the process speed of the image forming apparatus 10.

The drum charging roller 3 is in contact with the surface (peripheral surface) of the photosensitive drum 2 with a predetermined pressing force, and a predetermined drum charging voltage (drum charging bias) from a power source (voltage application means, not shown) applying a voltage. Is applied to uniformly charge the surface of the photosensitive drum 2 to a predetermined potential. In the present embodiment, the photosensitive drum 2 is negatively charged by the drum charging roller 3.
The exposure device 7 exposes the surface of the photosensitive drum 2 to form an electrostatic latent image (electrostatic image) corresponding to the image information on the surface of the photosensitive drum 2 charged by the drum charging roller 3. That is, in the exposure device 7, a laser beam modulated corresponding to the time-series electric digital pixel signal of the image information input from the host computer (not shown) is output from the laser output unit, and this laser beam is a reflection mirror The surface of the photosensitive drum 2 is irradiated via the

The developing device 4 in this embodiment uses a contact developing method as a developing method, and has a developing roller 8 as a developer carrier. The toner carried in a thin layer on the developing roller 8 (on the developer carrying member) is rotated by the driving means (not shown) to drive the developing roller 8 to face the photosensitive drum 2 (a developing portion Transported to Then, the developing voltage (developing bias) is applied to the developing roller 8 from the power supply 90 (see FIG. 3), whereby the electrostatic latent image formed on the photosensitive drum 2 (on the image carrier) is developed as a toner image. Be done. Details of the configuration and operation of the developing device 4 will be described later. In this embodiment, an embodiment in which the electrostatic latent image is developed by the reversal development method will be described. That is, the photosensitive drum 2 is made to adhere to the uniformly charged portion of the photosensitive drum 2 on which the toner has been charged by the same polarity as the charging polarity of the photosensitive drum 2 (exposure portion). The upper electrostatic latent image is developed as a toner image. In this embodiment, the regular charge polarity of the toner is negative, and the toner forming the toner image mainly has a negative charge.
The developing devices 4a, 4b, 4c and 4d store toners of yellow, magenta, cyan and black, respectively. In the full color mode, all the developing rollers 8 of the four developing devices 4 abut on the photosensitive drum 2. In the monochrome (monochrome) mode, the developing roller 8 of the developing device 4 other than the image forming portion for forming an image is configured to be separated from the photosensitive drum 2. This is to prevent the deterioration and consumption of the developing roller 8 and the toner.

In this embodiment, as the intermediate transfer belt 20 carrying a toner image, one composed of PEN (polyethylene naphthalate) resin was used. The surface resistivity of the intermediate transfer belt 20 is 5.0 × 10 ¹¹ Ω / □, and the volume resistivity is 8.0 × 10 ¹¹ Ωcm.
In addition, in the intermediate transfer belt 20, a resin such as PVDF (vinylidene fluoride resin), ETFE (tetrafluorinated ethylene-ethylene copolymer resin), polyimide, PET (polyethylene terephthalate), polycarbonate or the like is formed into an endless belt shape Can be used. Alternatively, as the intermediate transfer belt 20, for example, a rubber base layer such as EPDM coated with a urethane resin in which a fluorine resin such as PTFE is dispersed may be coated to form an endless belt.
When the driving roller 21 is rotationally driven in the direction of arrow R2 in FIG. 2 (counterclockwise in FIG. 2), the intermediate transfer belt 20 is rotated in the direction of arrow R3 in FIG. 2 (counterclockwise in FIG. 2). Circumferential movement (rotation) is performed at approximately the same speed as the peripheral speed of 2, that is, at a predetermined process speed.

The primary transfer roller 5 is made of, for example, an elastic member such as sponge rubber. In this embodiment, as the primary transfer roller, a nickel-plated steel rod 6 mm in diameter coated with NBR hydrin rubber at a thickness of 4 mm was used. The electric resistance value of the primary transfer roller 5 is 1.0 × when the primary transfer roller 5 is pressed at a force of 9.8 N on an aluminum cylinder and 100 V is applied while being rotated at 50 mm / sec. It is 10 ⁵ Ω.
Further, the primary transfer roller 5 contacts the photosensitive drum 2 via the intermediate transfer belt 20, and a primary transfer portion (primary transfer nip portion, transfer portion) at the contact portion between the intermediate transfer belt 20 and the photosensitive drum 2. Form The primary transfer roller 5 follows the movement of the intermediate transfer belt 20 and rotates.
A power supply 40 is connected to the primary transfer roller 5, and a primary transfer voltage (primary transfer bias) is applied to the primary transfer roller 5 from the power supply 40. The power supply 40 can select and apply biases of positive and negative polarities. The toner image formed on the photosensitive drum 2 is rotated by the primary transfer roller 5 to which a primary transfer bias having a polarity reverse to the regular charge polarity (negative polarity) of the toner is applied. Transferred to the top (primary transfer).

The secondary transfer roller 24 is made of, for example, an elastic member such as sponge rubber. In this embodiment, as the secondary transfer roller, a nickel-plated steel rod 6 mm in diameter coated with NBR hydrin rubber at a thickness of 6 mm was used. The electric resistance value of the secondary transfer roller 24 is 3.0 × when the secondary transfer roller 24 is pressed at a force of 9.8 N on an aluminum cylinder and rotated at 50 mm / sec and 1000 V is applied. It is 10 ⁷ Ω.
The secondary transfer roller 24 is disposed in contact with the secondary transfer opposing roller 23 via the intermediate transfer belt 20, and a secondary transfer portion (secondary transfer nip portion, transfer portion) is formed at the contact portion thereof. There is. The secondary transfer roller 24 rotates following the movement of the intermediate transfer belt 20 or the movement of the intermediate transfer belt 20 and the recording material P. A power source 44 is connected to the secondary transfer roller 24, and a secondary transfer voltage (secondary transfer bias) is applied to the secondary transfer roller 24 from the power source 44. The power supply 44 can select and apply biases of positive and negative polarities.
The toner image formed on the intermediate transfer belt 20 is conveyed to the secondary transfer portion by the secondary transfer roller 24 to which a secondary transfer bias having a polarity reverse to the regular charging polarity of the toner is applied. It is transferred onto P (secondary transfer).

A belt cleaning unit 30 is installed on the outer peripheral side of the intermediate transfer belt 20 and on the downstream side of the secondary transfer unit in the rotational direction of the intermediate transfer belt 20 (the arrow R3 direction in FIG. . Details of the configuration and operation of the belt cleaning unit 30 will be described later.
On the upstream side of the secondary transfer portion in the conveyance direction of the recording material P, a registration roller 13, a conveyance roller 15, and a feeding roller 14 which constitute means for supplying the recording material P are provided.
Further, the fixing device 12 is disposed downstream of the secondary transfer portion in the conveyance direction of the recording material P. The fixing device 12 has a fixing roller 12A provided with a heat source, and a pressure roller 12B pressed against the fixing roller 12A.

Next, an image forming operation by the image forming apparatus 10 of the present embodiment will be described by taking a full color mode as an example.
First, toner images of respective colors are formed on the photosensitive drums 2 of the respective image forming portions 1 by an electrophotographic process. That is, when the start signal of the image forming operation is issued, each photosensitive drum 2 rotationally driven at a predetermined process speed is uniformly charged by the drum charging roller 3 respectively. Then, each exposure device 7 converts the input color separated color image signal into an optical signal at the laser output unit. Then, each exposure device 7 scans and exposes the uniformly charged photosensitive drums 2 with laser light which is a converted light signal, and forms an electrostatic latent image on each photosensitive drum 2. Then, in the first image forming unit 1a, the yellow toner is electrostatically attracted from the developing device 4a in accordance with the potential of the surface of the photosensitive drum 2a, and thus, the toner is developed as a yellow toner image.

Here, the configuration of the developing device 4 will be described in detail with reference to FIG.
FIG. 3 is a schematic cross-sectional view of the image forming unit 1 of the present embodiment as viewed from the longitudinal direction (rotational axis direction) of the photosensitive drum 2.
The developing device 4 includes a developing roller 8 as a developer carrier, a developing blade 81 as a developer regulation member, a toner supply roller 82 as a developer supply member, and a toner storage chamber 85 for storing toner T as a developer. It consists of In the present embodiment, a nonmagnetic spherical toner having a particle size of 7 μm was used as the toner T. Further, on the surface of the toner T, silica particles (externally added particles) having a particle diameter of 20 nm are added as a toner external additive. Further, as described above, the regular charging polarity of the toner T of this embodiment is negative.
The developing blade 81 is in contact with the developing roller 8 in the counter direction, and regulates the coat amount of the toner supplied by the toner supply roller 82 (regulates the layer thickness of the toner on the developing roller 8) and applies charge. The developing blade 81 is formed of a thin plate-like member, and a spring pressure of a thin plate is used to form a contact pressure, and the surface thereof is in contact with the toner and the developing roller 8.

In this embodiment, as the developing blade 81, a plate spring-like thin plate made of SUS (stainless steel) having a thickness of 0.1 mm is coated with a semiconductive resin, and the surface of the developing blade 81 is a toner and a developing roller. It comprised so that it might abut on 8. At this time, the contact pressure is generated by utilizing the spring elasticity of the thin plate. The developing blade 81 is not limited to this, and a thin metal plate such as phosphor bronze or aluminum may be used instead of SUS. Also, instead of the semiconductive resin, a semiconductive rubber may be used, or a thin metal sheet with no coating on the surface may be used.
In this embodiment, a predetermined voltage is applied to the developing blade 81 from the power supply 91. The toner on the developing roller 8 is subjected to negative charge by the discharge between the developing blade 81 and the developing roller 8 and the frictional electrification due to the friction between the developing blade 81 and the developing roller 8, and the layer thickness is regulated simultaneously.
Further, during image formation, a DC voltage (developing blade bias) is applied to the developing blade 81 from the power supply 91 so that the potential difference ΔVb of the developing blade 81 with respect to the potential of the developing roller 8 becomes −100V.

The toner supply roller 82 is disposed with a predetermined nip portion formed on the circumferential surface of the developing roller 8, and rotates in the direction of the arrow R5 in FIG. 3 (counterclockwise in FIG. 3). The toner supply roller 82 is an elastic sponge roller in which a foam is formed on the outer periphery of a conductive cored bar. The toner supply roller 82 and the developing roller 8 are in contact with each other with a predetermined amount of penetration. At this contact portion, the toner supply roller 82 and the developing roller 8 rotate so as to move in opposite directions to each other, and by this operation, the toner supply roller 82 supplies the toner to the developing roller 8 and remains as development residual toner. The toner on the developing roller 8 is peeled off. At this time, by adjusting the potential difference between the toner supply roller 82 and the developing roller 8, the amount of toner supplied to the developing roller 8 can be adjusted. In this embodiment, during image formation, a DC voltage (toner supply bias) is applied from the power supply 92 to the toner supply roller 82 so that the potential difference ΔVs of the toner supply roller 82 relative to the potential of the developing roller 8 is −50V. There is.
In the present embodiment, the developing roller 8 and the toner supply roller 82 both have an outer diameter of 20 mm, and the penetration amount of the toner supply roller 82 to the developing roller 8 is set to 1.5 mm. Further, in the toner storage chamber 85, a toner stirring member 83 is provided. The toner stirring member 83 is for stirring the toner stored in the toner storage chamber 85 and for transporting the toner toward the upper portion of the toner supply roller 82 in the direction of the arrow G in FIG.

The developing roller 8 and the photosensitive drum 2 rotate so that the respective surfaces move in the same direction (in the present embodiment, in the directions indicated by arrows R4 and R1 in FIG. 3) at the contact portions.
In this embodiment, a DC voltage (developing bias) having the same polarity as the charging polarity (negative polarity in this embodiment) of the photosensitive drum 2 is applied from the power supply 90 to the developing roller 8. In the developing portion where the developing roller 8 contacts (slidingly contacts) the photosensitive drum 2, the negatively charged toner is transferred only to the electrostatic latent image portion due to the potential difference between the developing roller 8 and the photosensitive drum 2 and electrostatic latent The image is visualized.

Return to the description of the image forming operation. Subsequently, as shown in FIG. 2, the yellow toner image developed on the photosensitive drum 2a is rotated by the primary transfer roller 5a to which the primary transfer bias is applied at the primary transfer portion. The toner image is primarily transferred onto the transfer belt 20. At this time, to the primary transfer roller 5a, a primary transfer bias having a polarity (positive in this embodiment) opposite to the regular charging polarity of the toner is applied. The intermediate transfer belt 20 to which the yellow toner image has been transferred in this manner moves to the second image forming unit 1 b side.
In the second image forming unit 1b, similarly to the first image forming unit 1a, a magenta toner image is formed on the photosensitive drum 2b. Then, the magenta toner image is primarily transferred so as to be superimposed on the yellow toner image on the intermediate transfer belt 20 at the primary transfer portion. Similarly, in the third and fourth image forming units 1c and 1d, on the yellow and magenta toner images on the intermediate transfer belt 20, the cyan and black toner images are formed in the primary transfer unit. Primary transfer is performed so as to sequentially overlap.
In this manner, on the intermediate transfer belt 20, toner images (multiple toner images) of a plurality of colors on which the toner images of the respective colors are sequentially superimposed in the respective primary transfer portions are formed.

The recording material P fed out by the feeding roller 14 is conveyed by the conveyance roller 15 and the registration roller 13 to the secondary transfer portion at the timing when the leading end of the toner image on the intermediate transfer belt 20 reaches the secondary transfer portion. Be done. Then, at the secondary transfer portion, the toner image on the intermediate transfer belt 20 is generated by the secondary transfer roller 24 to which a secondary transfer bias having a polarity (positive in this embodiment) opposite to the regular charging polarity of the toner is applied. Are collectively secondarily transferred to the recording material P.
Thereafter, the recording material P to which the toner image has been transferred is conveyed to the fixing device 12. The recording material P carrying the toner image is heated and pressurized at a fixing nip portion between the fixing roller 12A and the pressure roller 12B installed in the fixing device 12. Thus, the toner image is thermally fixed (melted and fixed) on the surface of the recording material P, and an image (full color image) is formed on the recording material P. Thereafter, the recording material P is discharged to the outside of the image forming apparatus 10, and a series of image forming operations are completed.

The toner (primary transfer residual toner) remaining on the photosensitive drum 2 after the primary transfer process is removed from the photosensitive drum 2 by the drum cleaning device 6 and collected. The drum cleaning device 6 includes: a drum cleaning blade 61 which is a plate-like member formed of an elastic body such as urethane rubber; Have.
Further, the toner (secondary transfer residual toner) remaining on the intermediate transfer belt 20 after the secondary transfer process is uniformly charged to a positive polarity by the belt cleaning unit 30, and then the photosensitive drum 2 is placed on the photosensitive The intermediate transfer belt 20 is removed and collected. This point will be described in detail below. Here, the control unit 11 can execute a cleaning mode for removing the toner remaining on the intermediate transfer belt 20 from the intermediate transfer belt 20 at the time of image formation or non-image formation. The control unit 11 capable of executing the cleaning mode corresponds to a cleaning unit. In the following description, moving the toner remaining on the intermediate transfer belt 20 from the intermediate transfer belt 20 to the photosensitive drum 2 may be referred to as reverse transfer.

(2) Belt Cleaning Mechanism at the Time of Image Formation The belt cleaning mechanism at the time of image formation in this embodiment will be described in detail with reference to FIG.
FIG. 1 is a schematic view showing the configuration of a belt cleaning unit 30 of the present embodiment. The belt cleaning unit 30 of this embodiment charges the toner remaining on the intermediate transfer belt 20 in order to remove the toner such as secondary transfer residual toner Ta remaining on the intermediate transfer belt 20 from the intermediate transfer belt 20. A charging roller 32 is provided as a charging member. The charging roller 32 is located downstream of the secondary transfer portion and upstream of the primary transfer portion in the rotational direction of the intermediate transfer belt 20.
As the charging roller 32 in the present embodiment, a nickel-plated steel rod 6 mm in diameter coated with a solid elastic body made of EPDM rubber in which carbon is dispersed is used with a thickness of 5 mm. The electric resistance value of the charging roller 32 is 5.0 × 10 ⁷ Ω when 500 V is applied while pressing the charging roller on the aluminum cylinder with a force of 9.8 N and rotating at 50 mm / sec. The charging roller 32 is in contact with the intermediate transfer belt 20 and is pressed toward the cleaning opposing roller 22 with a total pressure of 9.8N.

As shown in FIG. 1, the charging roller 32 is electrically connected to the high voltage power supply 52 through the current detecting means 72, and is configured to be able to selectively apply a positive polarity bias and a negative polarity bias. There is.
During the belt cleaning operation, the high-voltage power supply 52 outputs a positive DC voltage to the charging roller 32. The output value of the DC voltage is controlled based on the current value detected by the current detection means 72, and constant current control is performed so that the current value becomes a preset target current value. The target current value is selected so as not to charge the secondary transfer residual toner Ta excessively and not to cause a cleaning failure due to insufficient charging, and the target current value of the charging roller in this embodiment is 30 μA.
The toner on the intermediate transfer belt 20 before the secondary transfer process is negatively charged with the same polarity as the charge on the surface of the photosensitive drum 2 and is charged in a state where the variation of the charge distribution is small. On the other hand, secondary transfer residual toner Ta on the intermediate transfer belt after the secondary transfer process has a broad charge distribution and a peak on the positive polarity side, which is the reverse polarity to the regular charge polarity of the toner. Form a moved distribution. As a result, the secondary transfer residual toner Ta is in a mixed state of those negatively charged, those hardly charged, and those positively charged.

During cleaning operation, by applying a positive bias to the charging roller 32, a positive electric field is formed from the charging roller 32 toward the intermediate transfer belt 20, and secondary transfer is performed by the discharge between the charging roller 32 and the secondary transfer residual toner. The residual toner Ta is charged to the positive polarity side.
The secondary transfer residual toner Ta charged to the positive polarity by the charging roller 32 advances to the primary transfer portion of the first image forming portion 1a. The intermediate transfer belt 20 is reversely transferred from the intermediate transfer belt 20 to the photosensitive drum 2a of the first image forming unit 1a by the action of the primary transfer bias of positive polarity applied to the primary transfer roller 5a of the first image forming unit 1a. Ru. Thereafter, the toner reversely transferred to the photosensitive drum 2a is removed and collected from the photosensitive drum 2a by the drum cleaning blade 61a in the drum cleaning device 6a.
As described above, the secondary transfer residual toner Ta is uniformly positively charged by the charging roller 32 and reversely transferred to the photosensitive drum 2 at the subsequent primary transfer portion, whereby the secondary transfer residual toner Ta is intermediately transferred. It is possible to remove from the belt 20.

The method of collecting the secondary transfer residual toner Ta charged to the positive polarity by the charging roller 32 is not limited to the method of collecting using the photosensitive drum 2, and the following method may be used. . That is a method using a dedicated collection device provided on the intermediate transfer belt 20, such as a metal roller or a fur brush to which a negative bias is applied.
In addition, in order to prevent the toner from adhering to the charging roller 32 and lowering the charging performance of the toner when the cleaning is repeated, the same polarity as the regular charging polarity of the toner at the time of non-image formation (in this embodiment) Negative bias) is applied to the charging roller 32. Most of the toner adhering to the charging roller 32 has a negative polarity during cleaning, and by applying a negative bias to the charging roller 32, the toner adhering to the charging roller 32 is electrostatically transferred to the intermediate transfer belt 20. I am moving it. By regularly performing this moving step (discharging step), the toner attached to the charging roller 32 is removed, and good cleaning performance is maintained.
Further, the toner discharged onto the intermediate transfer belt 20 is reversely transferred to the photosensitive drum 2 at the primary transfer portion on the downstream side in the rotational direction of the intermediate transfer belt 20 and collected by the drum cleaning device 6. Specifically, in the image forming units 1a to 1d during the discharging process, a negative bias is applied from the power source 40 to the transfer roller 5 of at least one image forming unit, so that the discharged negative toner is applied to the photosensitive drum 2. Reverse transcription. Finally, the negative polarity toner discharged from the photosensitive drum 2 is removed by the drum cleaning blade 61 on the photosensitive drum 2.

(3) Belt cleaning mechanism after jamming or after density adjustment mode Next, in this embodiment, the belt cleaning mechanism executed after jamming or after density adjustment mode during non-image formation will be described in detail with reference to FIGS. 4A and 4B. Do.
FIG. 4A is a schematic view showing the polarity of a bias applied to the charging roller 32, the primary transfer roller 5 and the secondary transfer roller 24 during image formation. FIG. 4B is a schematic view showing the polarity of the bias applied to the charging roller 32, the primary transfer roller 5, and the secondary transfer roller 24 during the belt cleaning performed after the jamming or after the density adjustment mode.

When the secondary transfer residual toner is cleaned during image formation, as described above, a positive bias is applied to each of the charging roller 32, the primary transfer roller 5 and the secondary transfer roller 24.
On the other hand, during the belt cleaning performed after jamming or after the density adjustment mode, the following bias application is performed. That is, a negative bias is applied to the charging roller 32 and a negative bias is applied to the secondary transfer roller 24, and in the primary transfer roller 5, the first and fourth image forming portions 1 a,
In 1d, a negative bias is applied, and in the second and third image forming portions 1b and 1c, a positive bias is applied. The reason why the polarity of the bias applied to each member is the polarity shown in FIG. 4B will be described below.

The toner remaining on the intermediate transfer belt 20 at the time of jamming and the test patch in the density adjustment mode are the toner remaining on the intermediate transfer belt 20 without being secondarily transferred (hereinafter sometimes referred to as residual toner) And has a regular charge polarity (negative in this embodiment). Such residual toner is also larger in amount than secondary transfer residual toner at the time of image formation.
Therefore, even if it is intended to make the residual toner positive by applying a positive bias to the charging roller 32 as in the case of image formation, the residual toner has the opposite polarity and the large amount of toner. It is difficult to make all of them uniformly positive.

Therefore, at the time of non-image formation as described above, as shown in FIG. 4B, a negative bias of the same polarity as the residual toner is applied to the charging roller 32, and electrostatic repulsion is applied without reversing the polarity of the residual toner. The residual toner is prevented from adhering to the charging roller 32. At this time, the negative bias applied to the charging roller 32 is a bias for passing the residual toner, and it is not necessary to apply a bias high enough to charge the toner. On the other hand, if the negative bias is too high, the residual toner is excessively charged, and the mirror force of the toner to the intermediate transfer belt 20 becomes strong, the electrostatic adhesion to the belt becomes strong, and the first order There is a possibility that the reverse transfer to the photosensitive drum 2 at the transfer portion may be inhibited. Therefore, the absolute value of the negative bias applied to the charging roller 32 at the time of cleaning is set to a value lower than the absolute value of the positive bias applied at the time of image formation. In this embodiment, the bias applied to the charging roller 32 at the time of image formation (bias necessary for supplying the target current of 30 μA) is +1500 V, while the bias applied to the charging roller 32 at cleaning is set to -500 V. ing.
Similarly, a negative bias is also applied to the secondary transfer roller 24 to prevent the residual toner from adhering to the secondary transfer roller 24 by electrostatic repulsion.

  On the other hand, in the primary transfer roller 5, the polarity of the bias applied is changed for each image forming unit. A negative bias is applied to the primary transfer rollers 5a and 5d in the first and fourth image forming portions 1a and 1d, and the residual toner having passed through the secondary transfer roller 24 and the charging roller 32 is electrostatically The photosensitive drums 2 a and 2 d are reversely transferred to the photosensitive drums 2 a and 2 d and removed from the intermediate transfer belt 20. The residual toner removed from the intermediate transfer belt 20 at the primary transfer portion is reversely transferred to the photosensitive drum 2 as in the case of image formation, and then the drum cleaning blade 6 overlies the photosensitive drum 2 by the drum cleaning blade 61. It is removed and recovered. The reason why the residual toner is collected by the first and fourth image forming portions 1a and 1d is that, when the amount of residual toner is large, all the residual toner can be done at one time with only one image forming portion. It is because it is difficult to recover. Here, the case where the amount of residual toner is large means, for example, a case where a jam occurs while printing a high printing rate image. In the present embodiment, a fourth image forming portion 1 d exists downstream of the first image forming portion 1 a in the rotational direction of the intermediate transfer belt 20 with respect to the residual toner which can not be recovered by the first image forming portion 1 a. It is collected by

Further, a positive bias is applied to the primary transfer rollers 5b and 5c in the second and third image forming units 1b and 1c. Most of the toner remaining on the intermediate transfer belt 20 after the jamming or after the density adjustment mode has a negative polarity, but there is also a toner having a small but positive polarity. For example, when a jam occurs, part of the secondary transfer residual toner existing in the area where secondary transfer has already been made positive by the positive bias applied from the secondary transfer roller 24 during image formation. In order to collect such positive polarity toner during cleaning, a positive bias is applied to the primary transfer rollers 5b and 5c. By this, the positive polarity toner on the intermediate transfer belt 20 can be electrostatically transferred to the photosensitive drums 2b and 2c.
As described above, in the belt cleaning at the time of non-image formation such as after jamming and after the density adjustment mode, the negative polarity toner remaining on the intermediate transfer belt 20 is not charged to the opposite polarity by the charging roller 32, and the primary It is reversely transferred at the transfer section and collected at the image forming section.

The polarity of the bias applied to the primary transfer roller of each image forming unit is not limited to the combination shown in the present embodiment, and may be appropriately selected according to the amount of residual toner and the collection performance of the photosensitive drum. It is possible to optimize. For example, when the amount of residual toner is small, a negative bias may be applied only to the primary transfer roller 5a, and a positive bias may be applied to the primary transfer rollers 5b, 5c, and 5d. Conversely, when the amount of residual toner is large, it is preferable to apply a negative bias to the primary transfer rollers 5a, 5c and 5d and apply a positive bias only to the primary transfer roller 5b.
In addition, when the amount of residual toner to be collected by a specific image forming unit is large, there is a possibility that a collection failure (a toner slip through) in the drum cleaning blade 61 may occur. For this reason, it is preferable to distribute the collection of the residual toner among the plurality of image forming sections by adjusting the time of applying the negative bias and the application timing. Since the residual toner is collected while the negative bias is applied to the primary transfer roller, if the negative bias application time in a specific image forming portion is shortened, the amount of the residual toner collected in the image forming portion Can be reduced. For example, in the present embodiment, the amount of toner collected by the drum cleaning blades 61a and 61d by adjusting the time for applying a negative bias to the primary transfer roller 5a and the time for applying a negative bias to the primary transfer roller 5d. It is possible to adjust the As a result, it is possible to prevent a large amount of residual toner from being sent to one of the drum cleaning blades 61.

Further, as described above, the method of collecting the residual toner on the intermediate transfer belt 20 is not limited to the collection method using the image forming unit 1, and for example, a dedicated collection device provided on the intermediate transfer belt 20 May be used.
Further, although the case where the belt cleaning is performed after the jamming or after the density adjustment mode has been described in the present embodiment, the present invention is not limited thereto. The belt cleaning of this embodiment is performed at the time of non-image formation where the amount of toner remaining on the intermediate transfer belt 20 is larger than the secondary transfer residual toner at the time of image formation. Good.

(4) Setting of developing blade bias during belt cleaning after jamming and after density adjustment mode Next, setting of developing blade bias during belt cleaning after jamming and after density adjustment mode, which is a feature of this embodiment FIG. 5A 5C to describe in detail.
In this embodiment, the potential difference ΔVb of the developing blade bias with respect to the developing bias at the time of belt cleaning after jamming and after the density adjustment mode, and the value on the same polarity side as the regular charging polarity of toner with respect to the potential difference ΔVb at the time of image formation. It is characterized in that it is set to. That is, the potential difference of the voltage applied to the developing blade 81 with respect to the voltage applied to the developing roller 8 is shifted to the more negative side. In the following description, setting the value on the same polarity side as the regular charging polarity of toner with respect to the potential difference ΔVb at the time of image formation means setting the potential difference ΔVb larger on the same polarity side as the regular charging polarity of toner. There is a case to set or simply to increase (increase) the potential difference ΔVb.
The reason for increasing the potential difference ΔVb of the developing blade bias with respect to the developing bias is to reduce “fogging toner” transferred to the intermediate transfer belt after jamming or during belt cleaning after the density adjustment mode.

5A and 5B are schematic diagrams showing the relationship between the developing bias applied to the developing roller 8 and the developing blade bias applied to the developing blade 81, and FIG. 5A is a relationship during image formation, and FIG. It shows the relationship at the time of cleaning after the density adjustment mode.
An optimum value is selected as the developing bias applied to the developing roller 8 according to the degree of consumption of the developing device 4 (each member constituting the developing device 4) and the photosensitive drum 2, the use environment and the like. For example,
When the development bias is set to -350 V, the development blade bias applied to the development blade 81 during image formation is set to -450 V, and the potential difference ΔVb of the development blade bias with respect to the development bias is set to -100 V (FIG. 5A). On the other hand, at the time of cleaning after jamming or after the density adjustment mode, the developing bias is set to -350V, and the developing blade bias applied to the developing blade 81 is set to -550V. As described above, the potential difference .DELTA.Vb of the developing blade bias with respect to the developing bias is set to be -200 V, which is higher than that at the time of image formation (FIG. 5B).
In this embodiment, by increasing the potential difference of the developing blade bias to the developing bias, the negative polarity discharge from the developing blade 81 to the toner on the developing roller 8 becomes active, and the polarity of the toner on the developing roller 8 becomes more It becomes possible to shift to the negative polarity side.

FIG. 5C is a diagram schematically showing the charge distribution of the toner on the developing roller 8. The solid line A represents the charge distribution when the potential difference ΔVb of the developing blade bias with respect to the developing bias is -100 V (FIG. 5A). Shows the charge distribution when .DELTA.Vb = -200 V (FIG. 5B). Thus, the toner on the developing roller 8 can be charged more to the negative polarity side by increasing the developing blade bias to the negative polarity side with respect to the developing bias.
In FIG. 5B in which the toner on the developing roller 8 is charged to the more negative side, even if the toner is shifted to the positive side by frictional charging due to rubbing with the photosensitive drum 2, the charge distribution after frictional charging is It exists on the negative side of the charge distribution after the triboelectric charging in FIG. 5A. Therefore, the amount of “fogging toner” transferred to the photosensitive drum 2 is smaller at the time of cleaning after the jam or after the density adjustment mode (FIG. 5B) than at the time of image formation (FIG. 5A).
Further, the toner is deteriorated with the consumption of the developing device 4 to deteriorate the chargeability, and the developing blade bias is increased to the negative polarity side even for the toner which can not maintain the regular charge amount on the developing roller 8, By activating the sexual discharge, it is possible to approach the regular charge amount. Thereby, the amount of “fogging toner” transferred to the photosensitive drum 2 can be reduced.

  As described above, the amount of “fogging toner” transferred to the photosensitive drum 2 can be reduced by increasing the developing blade bias to the negative polarity side with respect to the developing bias. As a result, the amount of “fogging toner” transferred to the intermediate transfer belt 20 at the subsequent primary transfer portion can be reduced.

  Actually, in the present embodiment, when the potential difference ΔVb of the developing blade bias with respect to the developing bias is shaken, the result of measuring the amount of “fog toner” transferred onto the intermediate transfer belt 20 is shown in FIG. In FIG. 6, the horizontal axis represents the potential difference ΔVb of the developing blade bias with respect to the developing bias, and the vertical axis represents the "fog toner" remaining on the intermediate transfer belt 20 after the jam or when the cleaning after the density adjustment mode is completed. It shows the concentration.

  Here, the fogging density of the "fog toner" on the intermediate transfer belt 20 was measured by the following procedure. First, a sheet of a solid white image (image with a printing rate of 0%) is printed, and it is forcibly stopped in the middle of printing to cause a jam. After that, the jammed paper is removed, and post-jamming cleaning is performed. In the state where the cleaning after the jam is completed, the "fogging toner" present on the intermediate transfer belt 20 is attached to an adhesive tape (Scotch Mending Tape, manufactured by Sumitomo 3M Co., Ltd.). Then, the adhesive tape from which the “covering toner” has been collected is pasted on a sheet of white paper (trade name GF-C081 manufactured by Canon Inc.). Also, for comparison, an adhesive tape from which "cover toner" is not collected is also stuck on the same sheet. Then, the whiteness (reflectance D1 (%)) of the adhesive tape part from which "Fogging Toner" was collected using "REFLECTMETER MODEL TC-6DS" (manufactured by Tokyo Denshoku Co., Ltd.) and the adhesion not collecting "Fogging Toner" The whiteness (reflectance D2 (%)) of the tape portion was measured. And fog density (%) (= D2 (%)-D1 (%)) was measured from the difference.

As shown in FIG. 6, it can be seen that as the absolute value of the potential difference ΔVb of the developing blade bias with respect to the developing bias increases, the fogging density of the “fog toner” on the intermediate transfer belt 20 decreases.
From these results, it is also experimentally found that the amount of the “fog toner” transferred to the intermediate transfer belt 20 is reduced by increasing the potential difference ΔVb.

As described above, the "fogging toner" is a toner not having a proper charge amount, for example, a toner having a low negative charge amount or a polarity opposite to the regular polarity (in the present embodiment, positive polarity) Refers to a charged toner. The “fogging toner” is generated by the deterioration of the toner with the consumption of the developing device 4 to reduce the chargeability, and the inability to maintain the regular charge amount on the developing roller 8. The “fogging toner” is generated by the polarity of the toner being shifted to the positive polarity side by the frictional charge between the toner on the developing roller 8 and the photosensitive drum 2.
Such "fogging toner" has weak electrostatic repulsion with respect to the area on the photosensitive drum 2 where the electrostatic latent image is not formed, and also transfers to the area where the electrostatic latent image is not formed. Therefore, it transfers to the photosensitive drum 2 also during non-image formation and after a jam that does not form an electrostatic latent image or during cleaning after the density adjustment mode, and also to the intermediate transfer belt 20 via the primary transfer portion. It will metastasize.

Here, a method of mechanically separating the developing roller from the photosensitive drum at the time of cleaning may be mentioned as a means for preventing transfer of the "fog toner" to the photosensitive drum at the time of cleaning after jamming or after the density adjustment mode. However, in an image forming apparatus in which the developing roller separating mechanism is not provided for the purpose of cost reduction, or in an image forming apparatus in which the developing roller can not be separated at the time of cleaning due to other restrictions, “fog toner” is transferred to the photosensitive drum and the intermediate transfer belt. There is a concern that it will shift. For example, in order to reduce noise (blade noise) due to minute vibration generated by rubbing between the photosensitive drum and the drum cleaning blade, the developing roller must always be in contact with the photosensitive drum to suppress the minute vibration. There may be restrictions such as: In such a case, the developing roller can not be separated from the photosensitive drum, and there is a concern that the "fog toner" is transferred to the intermediate transfer belt at the time of cleaning.
As described above, if the "fogging toner" is transferred to the intermediate transfer belt at the time of cleaning after the jamming or after the density adjustment mode, there is a possibility that a cleaning failure caused by the "fogging toner" may occur when the image formation is performed after the cleaning. There is.

In cleaning after jamming or after the density adjustment mode, as shown in FIG. 4B, the polarity of the bias applied to the charging roller 32 is a negative bias, and a high bias that charges the residual toner is not applied. Therefore, the "fogging toner" on the intermediate transfer belt can not be charged to a uniform polarity, and the "fogging toner" maintains a charge amount lower than the regular charge amount. Therefore, it is difficult to electrostatically transfer the "fogging toner" back to the photosensitive drum at the primary transfer portion. As a result, even after cleaning, the "fogging toner" remains on the intermediate transfer belt.
Furthermore, when there is a large amount of "fogging toner" remaining on the intermediate transfer belt, even when trying to charge the "fogging toner" positively with the charging roller to which a positive bias is applied when forming an image after the cleaning, It is difficult to make the "fogging toner" uniformly positive. In the first place, “fog toner” is a toner whose chargeability has become poor due to the deterioration of the toner, and is a toner that is less likely to be charged than secondary transfer residual toner at the time of image formation, even if charging by a charging roller.
Therefore, when there is a large amount of "fogging toner" remaining, there is a possibility that the "fogging toner" may appear as a stain (cleaning failure) on the output image at the time of the next image formation.

On the other hand, in order to prevent the cleaning failure due to the "fogging toner" remaining on the intermediate transfer belt, a method of recovering the "fogging toner" as follows can be considered. That is, after the jamming and after completion of the cleaning after the density adjustment mode, the intermediate transfer belt is rotated many times while applying a positive bias to the charging roller based on constant current control, and the "fogging toner" is made slightly positive. Charged and collected at the primary transfer portion. However, in this method, there is a concern that the time from the jam processing or after the density adjustment to the start of the next image formation may be long, and the downtime may be long.

Therefore, in the present embodiment, the potential difference ΔVb of the developing blade bias with respect to the developing bias at the time of cleaning after jamming or after the density adjustment mode is set to a value larger than the potential difference ΔVb at the time of image formation. At this time, as described above, the absolute value of the negative bias applied to the charging roller 32 is set to a value lower than the absolute value of the positive bias applied at the time of image formation.
As a result, the amount of "fogging toner" transferred to the intermediate transfer belt 20 can be reduced, so that it is possible to prevent a cleaning failure caused by the "fogging toner" without increasing the downtime required for cleaning. Become.

  As shown in FIG. 6, the larger the potential difference ΔVb, the smaller the amount of “fog toner” transferred to the intermediate transfer belt. However, in the present embodiment, the potential difference ΔVb is limited to −200 V. There is. The reason is to suppress abnormal discharge from the developing blade 81 to the developing roller 8. If the potential difference ΔVb becomes excessively large, uniform discharge from the developing blade 81 to the developing roller 8 can not be maintained, and a strong discharge (abnormal discharge) may occur locally. When the abnormal discharge occurs, the charge distribution of the toner on the developing roller 8 becomes uneven, and the developing blade 81 and the developing roller 8 may be damaged. Therefore, in the present embodiment, the potential difference ΔVb is as high as possible within the range where abnormal discharge does not occur, and the potential difference ΔVb is set to −200 V. It is preferable that such a value in a range where abnormal discharge does not occur between the developing roller 8 and the developing blade 81 is predetermined.

Further, in the present embodiment, the potential difference ΔVb is set to −200 V only at the time of cleaning after jamming or after the density adjustment mode, and the potential difference ΔVb is not set to −200 V at the time of normal image formation. Explain to.
If the potential difference ΔVb is constantly set to a high value, the discharge between the developing roller 8 and the developing blade 81 is active, so for example, the semiconductive material coated on the SUS which is a component of the developing blade 81 Deterioration of the resin may be promoted. In addition, deterioration of the surface of the developing roller 8 may be promoted. Therefore, always raising the developing blade bias to the negative polarity side during image formation may reduce the durable life of the developing device 4.

In the present embodiment, therefore, it is judged that the belt cleaning property is advantageous when forming an image in which a positive bias is applied to the charging roller 32 and the secondary transfer residual toner is positively charged and collected, and the potential difference ΔVb is -100V. By setting a relatively low value, the life of the developing device 4 is extended.
On the other hand, since the belt cleaning property is disadvantageous after the jam applying a weak negative bias to the charging roller 32 or at the time of the cleaning after the density adjustment mode, the potential difference ΔVb is set as high as −200V. As a result, the amount of “fogging toner” transferred to the intermediate transfer belt 20 can be reduced, and good cleanability can be ensured.

  As described above, in this embodiment, the developing device obtains a good cleaning performance by changing the potential difference ΔVb of the developing blade bias with respect to the developing bias in accordance with the cleaning performance of the charging roller 32 on the intermediate transfer belt 20. 4 to achieve longer life.

(5) Image output experiment result Next, the result of the image output experiment in a present Example, the comparative example 1, and the comparative example 2 is demonstrated.
In the image output experiment, the potential difference ΔVb of the developing blade bias with respect to the developing bias at the time of cleaning after jamming and after the density adjustment mode is set to -200 V, -100 V and -400 V in this embodiment and comparative examples 1 and 2, respectively. The output images were compared.

As a comparison of output images, first, a sheet of a solid white image (an image with a printing rate of 0%) is printed, and it is forcibly stopped in the middle of printing to generate a jam. After that, the jammed paper is removed, and post-jamming cleaning is performed. The potential difference ΔVb of the developing blade bias with respect to the developing bias during the post-jamming cleaning is set to −100 V (Comparative Example 1), −200 V (Example), and −400 V (Comparative Example 2).
After completion of the post-jamming cleaning, solid white images were continuously fed, and the cleaning properties were compared based on whether or not stain (poor cleaning) caused by "fog toner" occurred in the solid white images.
The process speed of the image forming apparatus which carried out the output experiment is 180 mm / sec, and the throughput is 30 sheets per minute. As a sheet of paper, a Canon Inc. brand name GF-C081 was used, and a plain paper mode was selected as an image forming mode.

Table 1 shows the results of the presence or absence of the cleaning failure on the output image in the present embodiment and comparative examples 1 and 2. In Table 1, x indicates that a cleaning failure has occurred, and 〇 indicates that no cleaning failure has occurred.
In addition, in the present embodiment and Comparative Examples 1 and 2, it was also confirmed whether or not abnormal discharge occurs between the developing roller and the developing blade. With regard to the occurrence of abnormal discharge, when an image is formed at each bias setting of the present embodiment and comparative examples 1 and 2 under an environment of 0.8 atmospheric pressure, the toner layer coated on the developing roller is caused by the abnormal discharge It was judged whether or not coat unevenness occurred. In Table 1, when abnormal discharge generate | occur | produces, it is set as x, when abnormal discharge does not generate | occur | produce.

As shown in Table 1, in Comparative Example 1 in which the potential difference ΔVb of the developing blade bias with respect to the developing bias is set to a low value of −100 V, toner contamination of a level visually recognizable on the solid white image as an output image occurs. As a cleaning property, it was x. On the other hand, in the present embodiment and the comparative example 2 in which the potential difference ΔVb is -200 V or more, no toner contamination of a level visually recognizable on the solid white image which is an output image is generated. there were. Thus, by increasing the potential difference ΔVb, the cleaning property of the output image can be improved.
On the other hand, when focusing on the abnormal discharge, the abnormal discharge was not confirmed in Comparative Example 1 and the present example in which the potential difference ΔVb is −200 V or less. On the other hand, in Comparative Example 2 in which the potential difference ΔVb was −400 V, the coating unevenness due to the abnormal discharge was confirmed in the toner layer coated on the developing roller, and thus it was x. As described above, when the potential difference ΔVb is too high, abnormal discharge may occur between the developing roller and the developing blade, which may damage the developing device 4.

  From the above experimental results, it was found that it is preferable to set the value of the potential difference ΔVb at the time of cleaning after jamming or after the density adjustment mode as follows. That is, in order to improve the cleaning performance, it is preferable to set it higher than the bias at the time of image formation and to a value at which abnormal discharge does not occur. In this embodiment, the potential difference ΔVb is set to -200V. .

In the present embodiment, -200 V is set as the value of the potential difference ΔVb of the developing blade bias with respect to the developing bias. However, the optimum value of the potential difference ΔVb differs according to the specifications of the image forming apparatus, and is optimum according to the specifications of the image forming apparatus in view of the cleaning property of the charging roller, the durability of the developing device 4 and the like. It is preferable to set the potential difference ΔVb.
Further, in the present embodiment, the potential difference ΔVb is increased by increasing the developing blade bias, but this is not a limitation, and the developing bias is lowered, or both of the developing blade bias and the developing bias are changed. May correspond.
Further, in the present embodiment, the configuration in which the negative bias is applied to the charging roller at the time of cleaning after jamming or after the density adjustment mode has been described, but the present invention is not limited to this. The present invention can be suitably applied to a configuration in which only a positive bias can be applied to the charging roller due to cost reduction and the like. In such a configuration, the bias applied to the charging roller is set smaller than at the time of image formation at the time of cleaning after jamming or after the density adjustment mode, and residual toner having a regular charging polarity is less likely to adhere to the charging roller It is good to do. Then, the cleaning performance can be improved by increasing the potential difference ΔVb after the jam or at the time of cleaning after the density adjustment mode.

Further, although the charging roller 32 is used as the charging member for charging the secondary transfer residual toner on the intermediate transfer belt in this embodiment, the present invention is not limited to this. Instead of the charging roller 32, a conductive brush member or the like may be used as the charging member, or a conductive brush member or the like may be used in addition to the roller member.
FIG. 7 is a view for explaining a modification in which a conductive brush is provided on the upstream side of the charging roller 32 in the rotation direction of the intermediate transfer belt 20. As shown in FIG.
In the example of FIG. 7, the conductive brush 31 is provided on the upstream side of the charging roller 32 in the rotation direction of the intermediate transfer belt 20 to improve the cleaning performance. As the conductive brush 31, it is preferable to use nylon or the like to which conductivity has been imparted, and as shown in FIG. Preferably, the bias of can be selectively applied.

At the time of image formation, a positive bias is output from the high voltage power supply 51 to the conductive brush 31. The output value is controlled based on the current value detected by the current detection means 71, and constant current control is performed so that the current value becomes a preset target current value. By providing the conductive brush 31 on the upstream side of the charging roller 32 in the rotational direction of the intermediate transfer belt 20, the pre-charging action and the action of dispersing the toner on the intermediate transfer belt 20 with respect to the toner on the intermediate transfer belt 20 are provided. As a result, the cleaning property at the time of image formation can be improved. Therefore, the allowable amount of "fogging toner" that does not cause cleaning failure is larger in the configuration (FIG. 7) in which the conductive brush 31 is added than in the configuration (FIG. 1) having only the charging roller 32.
Therefore, the provision of the conductive brush 31 makes it possible to lower the value of the potential difference ΔVb at the time of cleaning after jamming and after the density adjustment mode, and as a result, it is possible to prolong the life of the developing device 4.

(Example 2)
Next, Example 2 will be described. The basic configuration of the image forming apparatus of this embodiment is the same as that of the first embodiment. Therefore, in the present embodiment, different components with respect to the first embodiment will be described, and the description of the same components as the first embodiment will be omitted.
In the first embodiment, the potential difference ΔVb between the developing bias and the developing blade bias at the time of cleaning after jamming or after the density adjustment mode is set to a constant value. On the other hand, in the present embodiment, the potential difference ΔVb is changed according to the degree of wear of the charging roller 32 and the degree of deterioration of the toner T in the image forming unit 1.

First, the reason for changing the potential difference ΔVb in accordance with the degree of wear of the charging roller 32 will be described. When the image forming apparatus 10 is used for a long time, the rubber itself, which is a roller member, may deteriorate due to the electrification of the charging roller 32 or the discharge to toner, or the discharge product generated at the time of toner charging may adhere to the roller surface. is there. In such a case, the charging performance of the charging roller 32, that is, the cleaning performance, gradually decreases as the number of printed sheets increases.
Therefore, in the present embodiment, in the new state where the cleaning performance is high, the potential difference ΔVb between the developing bias and the developing blade bias at the time of cleaning after jamming or after the density adjustment mode is set low, and life extension of the developing device 4 is prioritized. I am doing it. Then, when the image forming apparatus 10 is used for a long time with the cleaning performance lowered, the potential difference ΔVb is set high, and the reduction of the “fog toner” amount is prioritized.

Next, the reason why the potential difference ΔVb is changed in accordance with the degree of deterioration of the toner T in the image forming unit 1 will be described. When the use of the image forming unit 1 is repeated, the toner in the developing device 4 causes mechanical damage due to stirring, rubbing with the developing blade, etc., and electrical damage due to the action of electricity on the developing roller and charging. receive. This causes the toner to deteriorate. Specifically, if the external additive contributing to the toner chargeability is dropped off or embedded in the toner, the chargeability of the toner is lowered.
The degree of deterioration can be grasped, for example, by the rotation distance of the developing roller 8, the energization time of the developing blade 81, or the like.
Further, the deterioration of the toner T becomes more remarkable as the amount of the toner T present in the developing device 4 is smaller. This is because, in the case where the amount of toner T in the developing device 4 is small compared with the case where the amount of toner T is large, the frequency at which one toner is affected by agitation or energization relatively increases. The degree of influence can be grasped, for example, using the remaining amount of toner T present in the developing device 4 as an index.

As described above, as the deterioration of the toner T progresses, the existence probability of the toner having low chargeability increases, and as a result, the probability that “fog toner” is generated also increases.
Therefore, in the present embodiment, in the state of initial use of the image forming portion 1 in which the occurrence probability of the "fog toner" becomes relatively low, the potential difference ΔVb is set low, and the life extension of the developing device 4 is prioritized. . Then, in the long-term use state of the image forming unit 1 where the occurrence probability of the "fog toner" becomes high, the potential difference ΔVb is set high, and the "fog toner" suppression is prioritized.
As described above, in the present embodiment, the potential difference ΔVb at the time of cleaning after jamming or after the density adjustment mode is changed according to the cleaning property of the charging roller 32 and the occurrence probability of “fogging toner” in the image forming portion. . Thereby, the balance between the cleaning property and the life of the developing device 4 can be optimized.

Next, a specific control method in the present embodiment will be described.
The consumption degree Cr (%) of the charging roller 32 is determined based on the history of the number of printed sheets from the new state (0%) to the product life (100%) of the charging roller. Similarly, the deterioration degree Cp (%) of the toner T in the image forming unit 1 is determined based on the history of the number of printed sheets from the new state (0%) to the product life (100%) of the image forming unit. Here, Cp was determined in consideration of the traveling distance of the developing roller 8 and the amount of toner T in the developing device 4 as a whole. The control unit 11 that determines the consumption degree Cr (%) of the charging roller 32 and the deterioration degree Cp (%) of the toner T corresponds to calculation means.
Then, based on the determined degree of consumption Cr (%) and the degree of deterioration Cp (%), the potential difference ΔVb at the time of cleaning after jamming or after the density adjustment mode is calculated based on the following equation (1) decide.

…式（１）

... Equation (1)

In the equation (1), α and β are coefficients obtained by weighting the contribution to the cleaning performance by the deterioration degree of the charging roller and the toner, respectively, and in this embodiment, α = 2 and β = 3.
In the equation (1), when both the charging roller 32 and the image forming unit 1 are new, the potential difference ΔVb is the same −100 V as at the time of image formation, and the maximum value The value of the potential difference ΔVb gradually increases toward −200 V). For example, when the consumption degree Cr of the charging roller 32 is 50% and the deterioration degree Cp of the toner is 30%, the potential difference ΔVb is -138 V. If the developing bias is -350 V, the developing blade bias is used. Is selected -488V.

As described above, in the present embodiment, the potential difference ΔVb at the time of cleaning after the jamming or after the density adjustment mode is changed as follows according to the degree of consumption of the charging roller 32 and the degree of deterioration of the toner. That is, under the condition where the cleaning performance is severe, the potential difference ΔVb is set relatively high. By this, the "fog toner" can be reduced. The potential difference ΔVb is set relatively low under the condition that the cleaning property is advantageous. This can prolong the life of the developing device 4.
As a result, in the present embodiment, the life of the developing device 4 can be further extended as compared with the first embodiment while maintaining good cleaning performance.

The method of calculating the potential difference ΔVb in the present embodiment is not limited to the above-described method, and the influence of the degree of wear of the charging roller 32 and the degree of deterioration of the toner T on the cleaning performance and the image forming apparatus 10 It is preferable to use an optimal calculation method according to the configuration.
For example, when the influence of the degree of wear of the charging roller 32 and the degree of deterioration of the toner T are compared, if one of the degrees of influence is very large, the numerical value may be determined in consideration of only the one degree. It is possible. Further, the potential difference ΔVb may be changed based on either the degree of wear of the charging roller 32 or the degree of deterioration of the toner T.

(Example 3)
Next, Example 3 will be described. The basic configuration of the image forming apparatus of this embodiment is the same as that of the first embodiment. Therefore, in the present embodiment, different components with respect to the first embodiment will be described, and the description of the same components as the first embodiment will be omitted.
The present embodiment is characterized in that the toner supply bias applied to the toner supply roller 82 is changed as a means for reducing the "fogging toner" transferred to the intermediate transfer belt at the time of cleaning after jamming or after the density adjustment mode. .
Specifically, the potential difference ΔVs of the toner supply bias with respect to the developing bias at the time of belt cleaning after the jamming or after the density adjustment mode, the polarity side opposite to the regular charging polarity of the toner In this embodiment, it is shifted to the positive polarity side). That is, the potential difference of the voltage applied to the toner supply roller 82 to the voltage applied to the developing roller 8 is shifted to the more positive side. At this time, as in the first embodiment, the absolute value of the negative bias applied to the charging roller 32 is set to a value lower than the absolute value of the positive bias applied at the time of image formation.

The reason why the amount of “fogging toner” transferred to the intermediate transfer belt is reduced by shifting the potential difference ΔVs to the positive polarity side will be described with reference to FIGS. 8A to 8C.
8A to 8C schematically show the relationship between the developing bias applied to the developing roller 8 and the toner supply bias applied to the toner supplying roller 82, and the polarity and amount of the toner on the developing roller 8 and on the photosensitive drum 2. FIG. In the drawing, a white circle indicated by Tb indicates a toner of negative polarity, and a black circle indicated by Tc indicates a toner of positive polarity.

FIG. 8A shows the relationship during image formation, in which the developing bias is −350 V, the toner supply bias is −400 V, and the potential difference ΔVs of the toner supply bias to the developing bias is set to −50 V. ing. As described above, during the image formation, a negative electric field is formed from the toner supply roller 82 to the developing roller 8, and the negative polarity toner Tb (white circle in the figure) having regular charging polarity is positively Supply to The reason for positively supplying negative polarity toner during image formation is that, for example, when an image with a high printing rate such as a solid image (maximum density level image) is continuously printed at the time of image formation, solid tracking due to toner supply shortage This is to prevent the deterioration of the color (the stability of the density of the solid image). If the amount of toner supplied to the developing roller 8 is small, there is a concern that image defects such as white spots may occur when an image with a high printing rate is continuously printed. Therefore, during image formation, the potential difference ΔVs of the toner supply bias with respect to the developing bias is set to the negative polarity side, and the negative polarity toner is positively supplied.
However, since the amount of toner supplied to the developing roller 8 is large, the amount of toner present on the developing roller 8 is also large, and "fog toner" generated by charging to the positive polarity side by frictional charging with the photosensitive drum In the figure, the amount of black circle toner Tc also inevitably increases.

On the other hand, FIG. 8B shows the relationship between the developing bias and the toner supply bias at the time of belt cleaning after jamming and after the density adjustment mode. At the time of belt cleaning after jamming and after the density adjustment mode, the toner supply bias is -350 V, the potential difference ΔVs of the toner supply bias with respect to the developing bias is 0 V, and the positive electrode is for the potential difference ΔVs at the time of image formation (FIG. 8A). It is shifted to the sex side.
The reason for shifting the potential difference ΔVs to the positive polarity side at the time of belt cleaning after jamming and after the density adjustment mode is to reduce the amount of toner supplied to the developing roller 8. By shifting the potential difference with respect to the developing roller 8 to the positive polarity side, the negative electric field formed from the toner supply roller 82 to the developing roller 8 is weakened, and the supply amount of the negative toner is reduced. By thus reducing the amount of toner supplied to the developing roller 8, the amount of toner on the developing roller 8 decreases. Therefore, the amount of “fogging toner” generated by the toner on the developing roller 8 being charged to the positive polarity side by the frictional charging with the photosensitive drum 2 also necessarily decreases. By thus reducing the absolute number of toners on the developing roller 8, the amount of "fog toner" can be reduced.
The belt cleaning after the jamming or after the density adjustment mode is at the time of non-image formation, and there is no need to worry about the solid followability, so the potential difference ΔVs can be shifted to the positive polarity side as in this embodiment. .

  As described above, in the present embodiment, the amount of generation of “fog toner” is reduced by shifting the potential difference ΔVs between the toner supply bias to the developing bias to the positive polarity side and reducing the toner amount on the developing roller 8. Can. By reducing the amount of “fogging toner”, the “fogging toner” transferred to the intermediate transfer belt 20 is also reduced, and as a result, the cleaning performance can be improved.

Note that FIG. 8C shows the relationship when the toner supply bias is shifted further to the positive polarity side than in FIG. 8B for comparison. In the relationship of FIG. 8C, the toner supply bias is set to −250 V, and the potential difference ΔVs of the toner supply bias with respect to the developing bias is set to +100 V. The relationship of FIG.
When the potential difference ΔVs is extremely shifted to the positive polarity side, an electric field of positive polarity is formed from the toner supply roller 82 to the developing roller 8. As a result, the toner supply roller 82 electrostatically peels off the negative polarity toner from the developing roller 8, and the amount of the negative polarity toner on the developing roller 8 is further reduced. However, as shown in FIG. 8C, since the toner Tc (black circles in the figure) of positive polarity is supplied from the toner supply roller 82 to the developing roller 8, a large amount of “fogging toner” of positive polarity is present on the developing roller 8. As a result, the amount of “fog toner” transferred to the photosensitive drum 2 increases.
As described above, when the potential difference ΔVs is excessively shifted to the positive polarity side, the amount of “fog toner” transferred to the intermediate transfer belt 20 increases.

Actually, in the present embodiment, when the potential difference ΔVs of the toner supply bias with respect to the development bias is shaken, the result of measuring the amount of “fog toner” transferred onto the intermediate transfer belt 20 is shown in FIG. In FIG. 9, the abscissa represents the potential difference .DELTA.Vs of the toner supply bias with respect to the development bias, and the ordinate represents the "fog toner" remaining on the intermediate transfer belt 20 after the jam or when the cleaning after the density adjustment mode is completed. It shows the concentration.
Here, the fog density (%) (= D2 (%) − D1 (%)) of “fog toner” on the intermediate transfer belt 20 was measured by the same procedure as in Example 1.
As shown in FIG. 9, for example, when the potential difference ΔVs of the toner supply bias to the developing bias is as high as −100 V on the negative polarity side, the fogging density of “fog toner” on the intermediate transfer belt 20 is very high. . On the other hand, when the potential difference ΔVs is shifted to the positive polarity side, such as −50 V and 0 V, the fog density is gradually decreased. On the other hand, when the potential difference ΔVs is further shifted to the positive polarity side, the fog density is conversely increased at +100 V or more.

From this result, it is also experimentally found that the amount of “fogging toner” transferred to the intermediate transfer belt 20 is reduced by shifting the potential difference ΔVs to the positive polarity side. However, it is confirmed that when the potential difference ΔVs is extremely shifted to the positive side too much, the positive toner supplied from the toner supply roller 82 to the developing roller 8 increases, and as a result, the amount of “fog toner” increases. It was done.
Based on the above results, in the present embodiment, the potential difference ΔVs at the time of belt cleaning after jamming and after the density adjustment mode is set to 0 V (approximately 0 V).

  As described above, in this embodiment, the potential difference ΔVs of the toner supply bias with respect to the developing bias at the time of belt cleaning after jamming or after the density adjustment mode is properly shifted to the positive polarity side than ΔVs at the time of image formation. . This makes it possible to reduce the "fogging toner" transferred onto the intermediate transfer belt 20 and improve the cleaning performance.

(6) Image output experiment result Next, the result of the image output experiment in a present Example, the comparative example 3 and the comparative example 4 is demonstrated.
In the image output experiment, the potential difference ΔVs of the toner supply bias with respect to the developing bias at the time of cleaning after jamming and after the density adjustment mode is set to 0 V, -50 V, and +200 V in this embodiment and comparative examples 3 and 4, respectively. A comparison was made.

As a comparison of output images, first, a sheet of a solid white image (an image with a printing rate of 0%) is printed, and it is forcibly stopped in the middle of printing to generate a jam. After that, the jammed paper is removed, and post-jamming cleaning is performed. The potential difference ΔVs of the toner supply bias with respect to the developing bias during the post-jamming cleaning is set to −50 V (Comparative Example 3), 0 V (this example), and +200 V (Comparative Example 4).
After completion of the post-jamming cleaning, solid white images were continuously fed, and the cleaning properties were compared based on whether or not stain (poor cleaning) caused by "fog toner" occurred in the solid white images.
The process speed of the image forming apparatus which carried out the output experiment is 180 mm / sec, and the throughput is 30 sheets per minute. As a sheet of paper, a Canon Inc. brand name GF-C081 was used, and a plain paper mode was selected as an image forming mode.

  Table 2 shows the results of the presence or absence of cleaning failure on the output image in the present embodiment and comparative examples 3 and 4. In Table 2, x indicates that a cleaning failure has occurred, and 〇 indicates that no cleaning failure has occurred.

  As shown in Table 2, in Comparative Example 1 in which the potential difference ΔVs of the toner supply bias with respect to the developing bias is −50 V, which is the same as at the time of image formation, toner stains at a visually recognizable level occur on the solid white image which is the output image. The cleaning property was x. On the other hand, in the present example in which the potential difference ΔVs is 0 V, no toner stain of a level visually recognizable on the solid white image which is the output image occurs, and the cleaning property is 〇. On the other hand, in Comparative Example 4 in which the potential difference ΔVs is further shifted to the positive polarity side and +200 V, toner contamination of a level that can be visually confirmed is generated on the solid white image which is an output image of slight. As was x.

  From the above experimental results, it was found that it is preferable to set the value of the potential difference ΔVs at the time of cleaning after jamming or after the density adjustment mode as follows. That is, it is preferable to shift to a positive polarity side with respect to the bias at the time of image formation so that the toner supply amount to the developing roller 8 is reduced, and to set a value such that a large amount of positive polarity toner is not supplied to the developing roller 8 In the present embodiment, the potential difference ΔVs is set to 0V.

In the present embodiment, 0 V is set as the value of the potential difference ΔVs of the toner supply bias with respect to the developing bias. However, the optimum value of the potential difference ΔVs differs depending on the specifications of the image forming apparatus, and the specifications of the image forming apparatus in view of the configuration of the toner supply roller 82 and the developing roller 8 and the chargeability and charge distribution of the toner. It is preferable to set an optimal potential difference ΔVs for
Further, in the present embodiment, when the potential difference ΔVs is shifted to the positive polarity side, the toner supply bias is shifted to the positive polarity side to cope with this, but the present invention is not limited to this. That is, the development bias may be shifted to the negative polarity side, or both of the toner supply bias and the development bias may be changed.
Further, similarly to the second embodiment, also in the present embodiment, the potential difference ΔVs may be calculated based on the exhaustion degree of the charging roller 32 and the deterioration degree of the toner T. In this embodiment, when the degree of consumption of the charging roller 32 and / or the degree of deterioration of the toner T is relatively large and relatively small, the potential difference ΔVs has a polarity opposite to the normal charging polarity. It will be set to the value of the side.

(Example 4)
Next, the fourth embodiment will be described. The basic configuration of the image forming apparatus of this embodiment is the same as that of the first embodiment. Therefore, in the present embodiment, different components with respect to the first embodiment will be described, and the description of the same components as the first embodiment will be omitted.
In this embodiment, the potential difference between the surface potential (surface voltage) of the photosensitive drum 2 and the developing bias is used as a means for reducing the “fogging toner” transferred to the intermediate transfer belt 20 at the time of cleaning after jamming or after density adjustment mode. It is characterized by changing.
The reason why the “fogging toner” transferred to the intermediate transfer belt 20 can be reduced by changing the potential difference between the surface potential of the photosensitive drum 2 and the developing bias will be described in order.

  As shown in FIG. 5C, on the developing roller 8, not only the negatively charged toner having the regular charge polarity but also the toner having a small charge amount even if it is negative and the part is positively charged Toner is present. When the toner on the developing roller 8 is transferred onto the photosensitive drum 2 as a "fogging toner", the polarity of the transferred "fogging toner" is largely related to the potential difference between the surface potential of the photosensitive drum 2 and the developing bias. Here, the surface potential of the photosensitive drum 2 is, more specifically, the surface potential of the photosensitive drum 2 charged by the drum charging bias (hereinafter referred to as the dark portion potential Vd) before the electrostatic latent image is formed. In the following description, the potential difference between the dark portion potential Vd and the developing bias is referred to as a potential difference Vback.

When the potential difference Vback is small, that is, when the negative electric field formed from the photosensitive drum 2 to the developing roller 8 is weak, the Coulomb force acting on the negatively charged toner on the developing roller 8 is weakened. Therefore, among the toners charged to the negative polarity, the toner with a relatively small charge amount is also transferred to the photosensitive drum 2 as a "fogging toner". Therefore, when the potential difference Vback is small, the toner of the negative polarity transferred to the photosensitive drum 2 increases, and as a result, the polarity of the “fog toner” shifts to the negative polarity side.
On the other hand, when the potential difference Vback is large, that is, when the negative electric field formed from the photosensitive drum 2 to the developing roller 8 is strong, the coulomb force acting on the negatively charged toner on the developing roller 8 becomes stronger. The amount of negative polarity toner transferred to is reduced. However, as the Coulomb force acting on a small amount of positive polarity toner present on the developing roller 8 becomes strong, the amount of positive polarity “fogging toner” transferred to the photosensitive drum 2 increases. Therefore, when the potential difference Vback is large, the toner of positive polarity transferred to the photosensitive drum 2 increases, and as a result, the polarity of the “fog toner” shifts to the positive polarity side.
As described above, it is possible to control the polarity of the "fog toner" transferred to the photosensitive drum 2 by the magnitude of the potential difference Vback between the dark portion potential Vd and the developing bias.

Next, focusing on the primary transfer portion, the “fogging toner” transferred to the intermediate transfer belt 20 by controlling the polarity of the “fogging toner” according to the polarity of the bias applied to the primary transfer roller 5 The amount can be reduced.
For example, at the time of cleaning after jamming or after the density adjustment mode, a positive bias is applied to the primary transfer roller 5 in the second and third image forming units 1b and 1c, as shown in FIG. 4B. In this case, in the second and third image forming portions 1b and 1c, the "fogging toner" is transferred to the intermediate transfer belt 20 when the polarity of the "fogging toner" on the photosensitive drum 2 is shifted to the positive polarity side. Can reduce the amount of The reason is that since the electric field of positive polarity is formed from the primary transfer roller 5 to the photosensitive drum 2, the “fogging toner” of positive polarity is difficult to electrostatically transfer to the intermediate transfer belt 20. Therefore, in the second and third image forming portions 1b and 1c, the "fogging toner" transferred to the intermediate transfer belt 20 is increased by increasing the potential difference Vback and shifting the polarity of the "fogging toner" to the positive polarity side. It can be reduced.

  On the other hand, at the time of cleaning after jamming and after the density adjustment mode, a negative bias is applied to the primary transfer roller 5 in the first and fourth image forming portions 1a and 1d as shown in FIG. 4B. In this case, in the first and fourth image forming portions 1a and 1d, the "fogging toner" is transferred to the intermediate transfer belt 20 when the "fogging toner" on the photosensitive drum 2 is shifted to the negative polarity side. Can reduce the amount of The reason is that since the negative transfer electric field is formed from the primary transfer roller 5 to the photosensitive drum 2, it is difficult for the “fogging toner” of the negative transfer to be electrostatically transferred to the intermediate transfer belt 20. Therefore, in the first and fourth image forming units 1a and 1d, the "fogging toner" transferred to the intermediate transfer belt 20 is reduced by decreasing the potential difference Vback and shifting the polarity of the "fogging toner" to the negative side. It can be reduced.

  As described above, by changing the potential difference Vback between the dark area potential Vd of the photosensitive drum 2 and the developing bias in accordance with the polarity of the primary transfer bias of each image forming unit 1, transfer to the intermediate transfer belt 20 is performed. The "fog toner" can be reduced. As a result, it is possible to prevent a cleaning failure caused by "fog toner".

Next, a specific control method of the present embodiment will be described.
At the time of image formation, the values of the developing bias and the drum charging bias in each of the image forming portions 1 are selected in accordance with the degree of consumption of the developing device 4 and the photosensitive drum 2 and the use environment. For example, the drum charging bias is applied such that the setting of the developing bias in each image forming unit 1 is -350V and the dark portion potential Vd of the photosensitive drum 2 is -500V at the time of image formation, and the potential difference Vback at the time of image formation is set to 150V. Will be described.

In such a case, in the present embodiment, the value of the potential difference Vback at the time of cleaning after jamming and after the density adjustment mode is set to 120 V in the first and fourth image forming portions 1a and 1d, and the second and third In the image forming units 1b and 1c, the voltage is set to 180V.
In the first and fourth image forming portions 1a and 1d, the developing bias value is set to -350 V, which is the same as that at the time of image formation, and the magnitude of the drum charging bias is smaller than at the time of image formation. It is set to 470V. As a result, the potential difference Vback is set to 120 V, which is smaller than at the time of image formation. By thus reducing the potential difference Vback, it is possible to shift the polarity of the “fog toner” transferred to the photosensitive drum 2 to the negative polarity side. As a result, in the first and fourth image forming portions 1 a and 1 d applying a negative bias to the primary transfer roller 5, the amount of “fog toner” transferred to the intermediate transfer belt 20 can be reduced.

  On the other hand, in the second and third image forming portions 1b and 1c, the developing bias value is set to -350 V, which is the same as that at the time of image formation, and the magnitude of the drum charging bias is larger than at the time of image formation. Is set to -530V. By this, the potential difference Vback is set to 180 V which is larger than that at the time of image formation. By thus increasing the potential difference Vback, it is possible to shift the polarity of the “fog toner” transferred to the photosensitive drum 2 to the positive polarity side. As a result, in the second and third image forming portions 1 b and 1 c applying a positive bias to the primary transfer roller 5, the amount of “fog toner” transferred to the intermediate transfer belt 20 can be reduced.

As described above, in the present embodiment, the potential difference Vback between the dark area potential Vd of the photosensitive drum 2 and the developing bias is changed according to the polarity of the primary transfer bias of each image forming unit 1. That is, in the first and fourth image forming units 1a and 1d, a negative bias of the same polarity as that of the residual toner is applied to the charging roller 32 at the time of belt cleaning after jamming or after the density adjustment mode. , 5d, and reduce the potential difference Vback. Thereby, the residual toner on the intermediate transfer belt 20 can be suitably recovered. Further, the polarity of the "fogging toner" transferred to the photosensitive drum 2 can be shifted to the negative polarity side, and the amount of the "fogging toner" transferred to the intermediate transfer belt 20 can be reduced.
Further, in the second and third image forming portions 1b and 1c, a positive bias is applied to the primary transfer rollers 5b and 5c, so the potential difference Vback is increased. This also reduces the amount of "fogging toner" transferred to the intermediate transfer belt 20.
As described above, also in this embodiment, the “fogging toner” transferred to the intermediate transfer belt 20 can be reduced, and as a result, the cleaning failure caused by the “fogging toner” can be prevented.

In this embodiment, the potential difference Vback between the dark portion potential Vd of the photosensitive drum 2 and the developing bias at the time of cleaning after jamming or after the density adjustment mode is 120 V for the first and fourth image forming portions 1a and 1d. In the third image forming units 1b and 1c, the voltage is set to 180V. However, the present invention is not limited to this, and the value of the potential difference Vback may be appropriately set to an optimum value according to the specification of the image forming apparatus.
Also, in view of the amount of negative polarity “fogging toner” and positive polarity “fogging toner” generated in the image forming unit 1, control to take measures only for “fogging toner” of either polarity is taken. It may be done. For example, in the case where the amount of negative polarity "fogging toner" generated in the image forming unit 1 is extremely small, the following control may be performed. That is, the potential difference Vback is increased only for the second and third image forming portions 1b and 1c that apply a positive bias to the primary transfer roller 5 at the time of cleaning after jamming and after the density adjustment mode, and the first and fourth image formation The sections 1a and 1d are controls that do not change the potential difference Vback.
In the present embodiment, the potential difference Vback is changed by changing the drum charging bias. However, the present invention is not limited to this, and the developing bias may be changed, or both the drum charging bias and the developing bias may be changed. You may change the
Further, similarly to the second embodiment, also in the present embodiment, the potential difference Vback may be calculated based on the consumption degree of the charging roller 32 and the deterioration degree of the toner T. For example, in the present embodiment, in the first and fourth image forming units 1a and 1d, when the degree of wear of the charging roller 32 and / or the degree of deterioration of the toner T are relatively large or relatively small. On the other hand, the absolute value of the potential difference Vback may be reduced. On the other hand, in the second and third image forming portions 1b and 1c, when the degree of consumption of the charging roller 32 and / or the degree of deterioration of the toner T is relatively large, the potential difference Vback is larger than when the degree is relatively small. The absolute value of may be increased.

As described above in the first to fourth embodiments, the transfer to the intermediate transfer belt is performed by changing the developing blade bias, the toner supply bias, and the drum charging bias at the time of cleaning after jamming and after the density adjustment mode. It is possible to reduce toner. As a result, it is possible to prevent a cleaning failure caused by the "fog toner" without increasing the downtime required for the cleaning.
The embodiments described above are intended to illustrate the embodiments of the present invention, and combinations or various modifications may be made as much as possible without departing from the scope of the present invention. Is possible. The effects of changing the biases of the developing blade bias, the toner supply bias, and the drum charging bias described in the first to fourth embodiments are independent of one another. Therefore, the biases may be appropriately combined and changed after the jamming or at the time of cleaning after the density adjustment mode. For example, all of the developing blade bias, the toner supply bias, and the drum charging bias can be simultaneously changed. This makes it possible to significantly reduce the amount of "fog toner" transferred to the intermediate transfer belt.
In each embodiment, although the case where the regular charging polarity of the toner is negative has been described, the present invention is not limited thereto, and the present invention is preferably applied even when the regular charging polarity of the toner is positive. be able to. In each embodiment, the electrostatic latent image is developed by the reversal development method, but the present invention is not limited to this. The present invention can be suitably applied even to an image forming apparatus adopting a regular development method.

  Reference Signs List 2 photosensitive drum 4 developing device 8 developing roller 10 image forming device 11 control unit 20 intermediate transfer belt 32 charging roller 81 developing blade

Claims (16)

An image carrier on which an electrostatic latent image is formed;
A developer carrier for carrying a developer for developing the electrostatic latent image formed on the image carrier;
A developer regulating member that regulates the amount of the developer on the developer carrier;
A transfer unit is provided, and the developer image developed on the image carrier is primarily transferred to the transfer unit by bringing the transfer unit and the image carrier into contact with each other, and the transfer unit and the recording material are in contact with each other. An intermediate transfer member on which the developer image is further secondarily transferred from the transfer portion to the recording material;
A charging member for charging the developer on the intermediate transfer member;
A cleaning unit capable of executing a cleaning mode in which the developer remaining on the intermediate transfer member after being secondarily transferred from the intermediate transfer member to the recording material is charged by the charging member and removed from the intermediate transfer member; ,
In an image forming apparatus having
When the cleaning unit executes the cleaning mode when forming an image without forming an image, the absolute value of the voltage applied to the charging member is different from when performing the cleaning mode when forming an image forming an image. And setting the potential difference .DELTA.Vb of the voltage applied to the developer regulating member to the voltage applied to the developer carrier to a value on the same polarity side as the regular charging polarity of the developer. An image forming apparatus characterized by The cleaning means sets the potential difference ΔVb to a predetermined value at which abnormal discharge does not occur between the developer carrier and the developer regulating member. Image forming apparatus. It comprises calculation means for calculating the degree of wear of the charging member and / or the degree of deterioration of the developer,
The image forming apparatus according to claim 1, wherein the cleaning unit changes the potential difference ΔVb based on a calculation result by the calculation unit. When the degree of wear of the charging member calculated by the calculation means and / or the degree of deterioration of the developer is relatively large, the cleaning means compares the potential difference ΔVb with the case where it is relatively small. The image forming apparatus according to claim 3, wherein the value is set to the same value as the normal charging polarity. An image carrier on which an electrostatic latent image is formed;
A developer carrier for carrying a developer for developing the electrostatic latent image formed on the image carrier;
A developer supply member for supplying the developer to the developer carrier;
A transfer unit is provided, and the developer image developed on the image carrier is primarily transferred to the transfer unit by bringing the transfer unit and the image carrier into contact with each other, and the transfer unit and the recording material are in contact with each other. An intermediate transfer member on which the developer image is further secondarily transferred from the transfer portion to the recording material;
A charging member for charging the developer on the intermediate transfer member;
A cleaning unit capable of executing a cleaning mode in which the developer remaining on the intermediate transfer member after being secondarily transferred from the intermediate transfer member to the recording material is charged by the charging member and removed from the intermediate transfer member; ,
In an image forming apparatus having
When the cleaning unit executes the cleaning mode when forming an image without forming an image, the absolute value of the voltage applied to the charging member is different from when performing the cleaning mode when forming an image forming an image. And the potential difference .DELTA.Vs of the voltage applied to the developer supply member to the voltage applied to the developer carrier is set to a value opposite to the regular charge polarity of the developer An image forming apparatus characterized by The image forming apparatus according to claim 5, wherein the cleaning unit sets the potential difference ΔVs to approximately 0V. It comprises calculation means for calculating the degree of wear of the charging member and / or the degree of deterioration of the developer,
The image forming apparatus according to claim 5, wherein the cleaning unit changes the potential difference ΔVs based on a calculation result by the calculation unit. When the degree of wear of the charging member calculated by the calculation means and / or the degree of deterioration of the developer is relatively large, the cleaning means compares the potential difference ΔVs with the case where it is relatively small. The image forming apparatus according to claim 7, wherein the value is set to a value opposite to the normal charging polarity. An image carrier on which an electrostatic latent image is formed after the surface is charged;
A developer carrier for carrying a developer for developing the electrostatic latent image formed on the image carrier;
A transfer unit is provided, and the developer image developed on the image carrier is primarily transferred to the transfer unit by bringing the transfer unit and the image carrier into contact with each other, and the transfer unit and the recording material are in contact with each other. An intermediate transfer member on which the developer image is further secondarily transferred from the transfer portion to the recording material;
A transfer member for primarily transferring the developer image from the image carrier to the intermediate transfer member;
A charging member for charging the developer on the intermediate transfer member;
A cleaning unit capable of executing a cleaning mode in which the developer remaining on the intermediate transfer member after being secondarily transferred from the intermediate transfer member to the recording material is charged by the charging member and removed from the intermediate transfer member; ,
In an image forming apparatus having
When the cleaning unit executes the cleaning mode when forming an image without forming an image, the absolute value of the voltage applied to the charging member is different from when performing the cleaning mode when forming an image forming an image. Changing the absolute value of the potential difference Vback between the voltage applied to the developer carrier and the surface voltage before the electrostatic latent image is formed on the charged image carrier. Image forming apparatus characterized by When the cleaning unit executes the cleaning mode at the time of non-image formation, the polarity of the voltage applied to the transfer member is the same as the regular charge polarity of the developer, and the cleaning mode is performed at the time of image formation. In the case where the electrostatic latent image on the image carrier is charged, the absolute value of the voltage applied to the charging member is reduced, and the voltage applied to the developer carrier is reduced. The image forming apparatus according to claim 9, wherein an absolute value of a potential difference Vback with respect to a surface voltage before formation is reduced. When the cleaning unit executes the cleaning mode at the time of non-image formation, the polarity of the voltage applied to the transfer member is different from the regular charge polarity of the developer, and the cleaning mode is performed at the time of image formation In the case where the electrostatic latent image on the image carrier is charged, the absolute value of the voltage applied to the charging member is reduced, and the voltage applied to the developer carrier is reduced. The image forming apparatus according to claim 9, wherein an absolute value of a potential difference Vback with respect to a surface voltage before formation is increased. It comprises calculation means for calculating the degree of wear of the charging member and / or the degree of deterioration of the developer,
The image forming apparatus according to any one of claims 9 to 11, wherein the cleaning unit changes the potential difference Vback based on a calculation result by the calculation unit. The developer carrier according to any one of claims 1 to 12, wherein the developer carrier is in contact with the image carrier, and the image carrier is in contact with the intermediate transfer member. Image forming apparatus. In the cleaning mode performed at the time of image formation, the developer remaining on the intermediate transfer member without being secondarily transferred is charged by the charging member to a polarity reverse to the normal charging polarity. 14. The cleaning device according to any one of claims 1 to 13, wherein the developer on the image carrier is moved to the image carrier and cleaned when the developer is primarily transferred to the intermediate transfer member. The image forming apparatus according to claim 1. A transfer member for primary transfer of the developer image from the image carrier to the intermediate transfer member;
In the cleaning mode performed at the time of non-image formation, a voltage having the same polarity as the regular charging polarity is applied to the transfer member, and the developer remaining on the intermediate transfer member is transferred to the image bearing member The image forming apparatus according to any one of claims 1 to 8, wherein the image forming apparatus is cleaned. The image forming apparatus according to any one of claims 1 to 15, wherein the charging member comprises a roller member and / or a brush member.

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