JP2012113109A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover a deteriorated carrier with a simple configuration.SOLUTION: An image forming apparatus includes a photoreceptor, an exposure part, a developing device, an intermediate transfer body 5, first and second transfer devices 71 to 74 and 8, a cleaning device 10, and a controller 34 executing first and second modes. When a two-component developer containing a toner and a carrier is used in the developing device, the controller executes a step for forming an electrostatic latent image on the photoreceptor by the exposure part, developing the electrostatic latent image into a toner image by the developing device, transferring the toner image to a first area of the intermediate transfer body by the first transfer device, transferring the transferred toner image to a recording medium by the second transfer device, and then, recovering the toner remaining on the intermediate transfer body by the cleaning device, in the first mode, and a step for making the deteriorated carrier of the developing device electrostatically adhere onto the photoreceptor, transferring the adhered deteriorated carrier to a second area of the intermediate transfer body by the first transfer device, and then, recovering the deteriorated carrier by the cleaning device, in the second mode.

Description

  The present invention relates to an electrophotographic image forming apparatus using a two-component developer.

An image forming apparatus using an electrophotographic method generally forms an image on a transfer material through steps of charging, exposure, development, transfer, peeling, cleaning, static elimination, and fixing.
In the image forming step, for example, the surface of the photoconductor to be rotated is uniformly charged by a charging device, and the surface of the photoconductor charged by the exposure device is irradiated with laser light to form an electrostatic latent image.

  Subsequently, the electrostatic latent image on the photoconductor is developed by the developing device to form a toner image on the surface of the photoconductor. Next, the toner image on the photosensitive member is transferred onto the transfer material by the transfer device, and then the toner image is fixed on the transfer material by being heated by the fixing device. Further, the transfer residual toner remaining on the surface of the photoreceptor is removed by a cleaning device and collected in a predetermined collection unit. In addition, the remaining charge is removed from the surface of the photoreceptor after the cleaning by a static eliminator in order to prepare for the next image formation.

As the developer for developing the electrostatic latent image on the photoreceptor, a one-component developer composed of only toner or a two-component developer composed of toner and carrier is generally used.
Since the one-component developer does not use a carrier, a stirring mechanism or the like for uniformly mixing the toner and the carrier is not required unlike the two-component developer. Therefore, there is an advantage that the developing device is simplified. However, there are drawbacks such as the toner charge amount being difficult to stabilize.

  Since the two-component developer requires a stirring mechanism for uniformly mixing the toner and the carrier, there is a disadvantage that the developing device becomes complicated. However, it has excellent charging stability and compatibility with high-speed machines. Therefore, it is often used in high-speed image forming apparatuses and color image forming apparatuses.

  In recent years, a trickle method has been adopted in which toner containing carrier is replenished to improve maintainability and prevent deterioration in image quality, and the developer is gradually replaced with a new one by discharging the developer. Has been. However, since the replacement of the developer is performed regardless of the deterioration level of the carrier, there is a lot of waste.

On the other hand, a method is known in which the carrier in the developer is transferred onto the photosensitive member by controlling the charging bias and the developing bias and collected by the cleaning means for the photosensitive member.
Further, it is also known that the intermediate transfer member is transferred to the intermediate transfer member and then recovered by the intermediate transfer member cleaning means, and the cleaning means is made of a magnetic brush cleaning system so as to prevent scratches on the intermediate transfer member. (For example, refer to Patent Document 1).

JP 2007-79440 A

  When the deteriorated carrier on the photosensitive member or intermediate transfer member is collected by the cleaning means, there is a problem that the photosensitive member or the intermediate transfer member is scratched by rubbing, thereby causing streaks on the image. The method of using magnetic brush cleaning to prevent scratches is effective for carrier recovery, but normal blade cleaning is more suitable for toner recovery, so there is a problem that two cleanings are required. is there.

  The present invention includes a photosensitive member, an exposure unit, a developing device, an intermediate transfer member, first and second transfer devices, a cleaning device, and a control device that executes first and second modes, and When a two-component developer containing toner and carrier is used in the apparatus, the control device causes the exposure unit to form an electrostatic latent image on the photoreceptor in the first mode, and the developing device converts the electrostatic latent image into toner. The image is developed, the toner image is transferred to the first area of the intermediate transfer member by the first transfer device, the transferred toner image is transferred to the recording medium by the second transfer device, and the residual toner on the intermediate transfer member is cleaned. The recovery process is executed by the apparatus, and in the second mode, the deteriorated carrier of the developing device is electrostatically attached onto the photosensitive member, and the attached deteriorated carrier is transferred to the second region of the intermediate transfer member by the first transfer device. Then move There is provided an image forming apparatus for executing the step of recovering the cleaning device degradation carriers.

  According to the present invention, since the deteriorated carrier is collected using the second region that is not used for image formation of the intermediate transfer member, the first region used for image formation of the intermediate transfer member is not damaged. Therefore, the carrier and the toner can be collected by the same blade cleaning device.

1 is an explanatory diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a configuration explanatory diagram illustrating a main part of the image forming apparatus in FIG. 1. FIG. 2 is a block diagram illustrating a control system of the image forming apparatus in FIG. 1.

The present invention will be described below with reference to embodiments shown in the drawings.
FIG. 1 is an explanatory diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a configuration explanatory view showing the main part of FIG.

  As shown in FIG. 1, the image forming apparatus 100 is a tandem color image forming apparatus including four image forming units 1 to 4. The image forming unit 1 is a unit that forms a black toner image, the image forming unit 2 is a unit that forms a cyan toner image, the image forming unit 3 is a unit that forms a magenta toner image, and the image forming unit 4 is A unit for forming a yellow toner image.

  Above these four image forming units 1 to 4, an intermediate transfer belt (endless belt) 5 as an intermediate transfer member is disposed. The intermediate transfer belt 5 is stretched around two support rolls 6 and 6 a and is configured to rotate in the direction indicated by the arrow R. The support roll 6a is a drive roll, and the support roll 6 is a driven roll.

  As a material for the intermediate transfer belt 5, polyimide (PI), polycarbonate (PC), polyvinylidene fluoride (PVDF), urethane rubber, nylon, or polyamideimide (PAI) is used. In the carrier recovery area of the intermediate transfer belt 5 described later, the amount of conductive carbon contained to increase the resistance is reduced or the material is changed.

For this reason, there is a difference in color between the carrier recovery area and the image forming area of the intermediate transfer belt 5, and therefore each area can be identified by an optical sensor. Therefore, an area detection sensor 41 is provided outside the intermediate transfer belt 5.
The four image forming units 1 to 4 are sequentially arranged along the rotation direction R of the intermediate transfer belt 5.

Inside the intermediate transfer belt 5, primary transfer rollers 71 to 74 for transferring the single color toner images formed by the image forming units 1 to 4 onto the intermediate transfer belt 5 are provided to the image forming units 1 to 4. Each is provided so as to face each other. The single color toner images formed by the image forming units 1 to 4 are transferred so as to be superimposed on the intermediate transfer belt 5 to form one color toner image.
A secondary transfer roller 8 for transferring the color toner image formed on the intermediate transfer belt 5 onto a sheet (recording medium) is disposed to face the support roll 6a.

  A belt cleaning unit 10 for cleaning the surface of the intermediate transfer belt 5 after the transfer is opposed to the support roll 6 on the downstream side in the rotational direction R of the intermediate transfer belt 5 with respect to the secondary transfer roller 8. Is provided. The belt cleaning unit 10 includes a belt cleaning brush 11 disposed in contact with the intermediate transfer belt 5 and a belt cleaning blade 12. The belt cleaning blade 12 is disposed downstream of the belt cleaning brush 11 in the rotational direction R of the intermediate transfer belt 5.

  Further, below the four image forming units 1 to 4, a tray 14 for storing paper is disposed. The paper in the tray 14 is conveyed to a secondary transfer position where the secondary transfer roller 8 faces the intermediate transfer belt 5 by a plurality of paper feed rollers 13. An arrow P indicates the conveyance direction of the sheet from the tray 14 to the secondary transfer roller 8.

  A fixing unit 15 for fixing the color toner image transferred onto the paper on the paper is provided downstream of the secondary transfer roller 8 in the paper conveyance direction. Further, downstream of the fixing unit 15 in the transport direction P, a paper discharge roller 13 a that discharges the paper on which the color toner image has been fixed by the fixing unit 15 from the image forming apparatus 100 is provided. In addition, a control device 34 that controls these devices is provided in the upper portion of the image forming apparatus 100.

  FIG. 2 shows the configuration of only the image forming unit 1 shown in FIG. The configurations of the image forming unit 2, the image forming unit 3, and the image forming unit 4 are substantially the same as the configuration of the image forming unit 1, and thus description of these configurations is omitted.

  As shown in FIG. 2, there are a charging device 17 for charging the photosensitive drum 16, an exposure device 18 for forming an electrostatic latent image on the photosensitive drum 16, and a photosensitive drum 16 around the photosensitive drum 16. A developing device 19 that develops and visualizes an electrostatic latent image into a toner image, a fog density sensor 26, a cleaning device 20 that removes a residue including toner remaining on the photosensitive drum 16, and a residual charge on the photosensitive drum The static elimination lamp 25 that removes is arranged in this order along the rotation direction Rd of the photosensitive drum 16.

  The charging device 17 includes a scorotron charging device, and includes a sawtooth electrode (discharge electrode) 17a and a control grid 17b that controls the amount of corona ions that reach the surface of the photosensitive drum 16 from the sawtooth electrode 17a. . A high voltage power source (not shown) that outputs a high voltage of -2 kV is connected to the saw-tooth electrode 17a.

  The control grid 17b includes a high voltage power source 32 having a high voltage transformer (TH) and a low voltage power source 33 having a constant voltage power source and a low voltage transformer (TL) via a changeover switch 31. It is connected. In this embodiment, the output voltage of the low voltage power supply 33 is about 600V, and the output voltage of the high voltage power supply 32 is about 750V. However, the polarity of the voltage is negative. The changeover switch 31 is switched by the control device 34 (FIGS. 1 and 3).

  The exposure device 18 is composed of, for example, a laser exposure device, performs exposure by laser scanning according to an input image signal, and changes the surface potential of the photosensitive drum 16 charged by the charging device 17, thereby changing the image information. A corresponding electrostatic latent image is formed. As the exposure device 18, an LED array device or the like can also be used.

  The developing device 19 contains therein a developing roller 24 that contains a two-component developer composed of a carrier and toner (in this embodiment, uses negatively charged toner) and supplies the two-component developer to the surface of the photosensitive drum 16. I have. The two-component developer contains a magnetic carrier and toner, and develops the electrostatic latent image formed on the photosensitive drum 16 by a two-component reversal development method.

  The fog density sensor 26 is a sensor for measuring the toner adhesion amount on the non-image portion on the surface of the photosensitive drum 16, and is composed of a photosensor including a light emitting element and a light receiving element, and outputs a measurement result to the control device 34. A developing bias power source 35 applies a developing bias voltage to the developing roller 24.

  FIG. 3 is a block diagram illustrating the periphery of control of the image forming apparatus 100. As shown in the figure, the control device 34 receives outputs from the operation unit 40, the area detection sensor 41, and the fog density sensor 26, and the exposure device 18, the developing device 19, and the image forming units 1 to 4 are provided. Development bias power supply 35, photosensitive drum 16, changeover switch 31 and static elimination lamp 25, bias power supplies 71a to 74a for primary transfer rollers 71 to 74, bias power supply 8a for secondary transfer roller 8, and support roll for intermediate transfer belt 5 6a, the paper feed roller 13, the paper discharge roller 13a, and the fixing unit 15 are driven and controlled.

The operation unit 40 includes a keyboard and a touch panel for inputting and setting image forming conditions, deteriorated carrier recovery conditions, and the like. The control device 34 includes a microcomputer composed of a CPU, a ROM, and a RAM.
The area detection sensor 41 is provided in the vicinity of the upper side of the intermediate transfer belt 5 (FIG. 1) as described above, and identifies the image forming area and the deteriorated carrier recovery area of the intermediate transfer belt 5.

  In such a configuration, when in the first mode (image forming mode), the control device 34 performs a normal image forming operation as follows. First, as shown in FIG. 2, the photosensitive drum 16 is rotationally driven by a drum motor (not shown), the changeover switch 31 is switched to the low voltage power supply 33 side, and −600 V is applied to the grid 17 b. The surface is charged to a uniform potential of −600 V by the charging device 17.

  Next, the surface of the photosensitive drum 16 is irradiated with laser light from the exposure device 18 to form an electrostatic latent image. The electrostatic latent image is formed on the photosensitive drum 16 by an aluminum base tube (not shown) that forms the base of the photosensitive drum 16 connected to the ground from the drum flange via the drum shaft. This is performed by lowering the potential of the exposed portion as compared to the unexposed portion.

  The formed electrostatic latent image is developed with the charged toner supplied from the developing device 19 and becomes a toner image. At this time, a developing bias voltage from a developing bias power source 35 is applied to the developing roller 24 of the developing device 19 in order to supply toner to the surface of the photosensitive drum 16.

  The toner image developed by the developing device 19 is primarily transferred to the first area (image forming area) on the intermediate transfer belt 5 detected by the area detection sensor 41. The toner remaining on the surface of the photoconductive drum 16 after the transfer is collected by the cleaning device 20, while the charge remaining on the surface of the photoconductive drum 16 is removed by the charge eliminating lamp 25.

  As shown in FIG. 1, the single color toner images formed by the image forming units 1 to 4 are sequentially transferred onto the intermediate transfer belt 5 so that a color toner image is formed on the intermediate transfer belt 5. The The color toner image on the intermediate transfer belt 5 is secondarily transferred to the paper conveyed by the paper feed roller 13 at the secondary transfer position, and then fixed on the paper by the fixing unit 15.

  The paper on which the color image is fixed is discharged from the image forming apparatus 100 by the paper discharge roller 13a. On the other hand, after the secondary transfer, the toner remaining on the intermediate transfer belt 5 without being transferred to the paper is collected by the belt cleaning unit 10.

  Next, when the control device 34 is in the second mode (degraded carrier recovery mode), the changeover switch 31 shown in FIG. 2 is switched to the high voltage power supply 32 side, and −750 V is applied to the control grid 17b, and the photosensitive drum. 16 is uniformly charged to a potential of -750V.

  A developing bias voltage (-750 V) higher than the developing bias voltage (-600 V) applied in the developing operation during normal image formation is applied to the developing roller 24, and the photosensitive drum 16 and the developing roller 24 are driven for a predetermined time. Is done. As a result, the deteriorated carrier in the two-component developer moves from the developing roller 24 onto the photosensitive drum 16 and adheres.

  Therefore, the support roll 6 a is driven to rotate the intermediate transfer belt 5, and the area detection sensor 41 detects the second area (deteriorated carrier recovery area) on the intermediate transfer belt 5. When the control device 34 receives the output of the area detection sensor 41 and sequentially applies a bias voltage of −3500 V to the primary transfer rollers 71 to 74 in synchronization with the rotation of the intermediate transfer belt 5, the rotating intermediate transfer rotates. The carrier is transferred (transferred) from the photosensitive drums 16 of the image forming units 1 to 4 to the second region on the belt 5 so as to overlap. Next, the deteriorated carrier on the intermediate transfer belt 5 is collected by the belt cleaning unit 10.

Note that the control device 34 switches the bias potential of each part as shown in Table 1 in the normal image forming mode (first mode) and the deteriorated carrier recovery mode (second mode).

The control device 34 executes the second mode in consideration of the following conditions.
(1) Since the deterioration of the carrier greatly depends on the stirring time in the developing device 19, the time when the accumulated rotation time of the developing roller 24 reaches a predetermined time is set as the execution condition of the second mode.
(2) Although it is almost unnecessary to discharge the deteriorated carrier at the initial stage when the developer is supplied to the developing device 19, it is effective to increase the discharging operation after the accumulated rotation time reaches a certain level. 1 time after ³ times, 50 × 10 ^{3 to} 100 × 10 ³ times, once every 25 × 10 ³ times, 100 × 10 ³ to 200 × 10 ³ times, once every 20 × 10 ³ times, 200 × After 10 ³ times, the execution interval is gradually narrowed, such as once every 15 × 10 ³ times.
(3) Since the carrier deterioration varies depending on the use environment, the execution interval is adjusted according to the information of the fog density sensor 26.
Based on such conditions, the control device 34 executes the second mode outside the normal image forming operation period (first mode period).

In the second mode, the reason why only the deteriorated carrier moves from the developing device 19 to the photosensitive drum 16 is as follows.
At the time of recovering the deteriorated carrier, a potential difference of −750 − (− 450) = − 300V is generated between the photosensitive drum 16 and the developing roller 24. Since the negatively charged toner receives a force in the direction of the developing roller 24 on the plus side, it does not move to the photosensitive roller 24.

  The carrier is held on the developing roller 24 by the magnetic force of the developing roller 24. Since the photosensitive drum 16 side is minus 300 V and the potential is low, the positively charged carrier is electrically pulled to the photosensitive drum 16 side. Magnetically retained on the developing roller. However, the deteriorated carrier has a high resistance and is highly charged on the plus side, so that the electric force is won and moves to the photosensitive drum 16 side. At this time, the charging device 17 charges the surface of the photosensitive drum 16 to -750 V with a grid potential of -750 V (the exposure device 18 does not expose).

The reason why the resistance of the carrier recovery area of the intermediate transfer belt 5 is made higher than that of the other areas is as follows.
The potential of the primary transfer roller when recovering the deteriorated carrier is -3500V.
In this potential setting, the voltage between the photosensitive drum 16 and the primary transfer rollers 71 to 74 is −3500 − (− 750) = − 2750V. During normal image formation, +1500 − (− 600) = 2100V, so a voltage higher by 650V is applied.

  Therefore, if the resistance of the intermediate transfer belt 5 is too low, the insulation is insufficient, and the voltage between the primary transfer rollers 71 to 74 and the photosensitive drum 16 cannot be maintained, and the movement of the deteriorated carrier may be hindered. . The reason why the voltage at the time of collecting the deteriorated carrier is set high is to move the deteriorated carrier to the intermediate transfer belt 5 more reliably, and it is not necessary to consider the image quality as at the time of toner transfer. Because.

1-4 Image forming unit 5 Intermediate transfer belt 6a, 6b Support roll 8 Secondary transfer roller 10 Belt cleaning unit 11 Belt cleaning brush 12 Belt cleaning blade 13 Paper feed roller 13a Paper discharge roller 14 Tray 15 Fixing unit 16 Photosensitive drum 17 Charging device 17a Saw-tooth electrode 17b Control grid 18 Exposure device 19 Development device 20 Cleaning device 24 Development roller 25 Static elimination lamp 26 Fog density sensor 31 Changeover switch 32 High voltage power source 33 Low voltage power source 34 Control device 35 Development bias power source 40 Operation unit 41 Area detection sensors 71 to 74 Primary transfer roller 100 Image forming apparatus R Rotation direction

Claims (3)

  A photosensitive member, an exposure unit, a developing device, an intermediate transfer member, first and second transfer devices, a cleaning device, and a control device that executes the first and second modes. When a two-component developer including a carrier is used, in the first mode, the control device forms an electrostatic latent image on the photosensitive member by the exposure unit, and develops the electrostatic latent image into a toner image by the developing device. The toner image is transferred to the first region of the intermediate transfer member by the first transfer device, the transferred toner image is transferred to the recording medium by the second transfer device, and the residual toner on the intermediate transfer member is collected by the cleaning device. In the second mode, after the process is executed, the deteriorated carrier of the developing device is electrostatically attached onto the photosensitive member, and the attached deteriorated carrier is transferred to the second region of the intermediate transfer member by the first transfer device. Relocated degradation cartridge Image forming apparatus for performing the step of recovering the A cleaning apparatus.   The image forming apparatus according to claim 1, wherein the intermediate transfer member has an electric resistance value higher in the second area than in the first area.   The photoconductor is composed of n (n ≧ 2) photoconductor drums, the first transfer device is composed of n transfer rollers, and the control device synchronizes the operations of the n photoconductor drums and the n transfer rollers. The image forming apparatus according to claim 1, further comprising a function of transferring the deteriorated carrier over the second region of the intermediate transfer member.

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