JP2018120142A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of transfer failure due to the eccentric location of a conductive agent in an intermediate transfer belt.SOLUTION: The image formation device comprises: voltage maintenance means 15 electrically connected between a primary transfer member 14 and a counter member 13, and ground, the voltage maintenance means 15 maintaining the potential of the primary transfer member 14 when a voltage is applied from a first power supply to a current supply member 20; current shutoff means 17 for shutting a current off between the primary transfer member 14 and counter member 13 and ground when a voltage is applied from a second power supply to the current supply member; and control means for causing a voltage to be applied from the first power supply to the current supply member 20 to execute primary transfer, and causing restore operation for easing the eccentric location of the conductive agent in an intermediate transfer belt 10 arising from the primary transfer performed, to be executed when primary transfer is not executed. The voltage applied to the primary transfer member 14 is maintained at a prescribed voltage by the voltage maintenance means 15 at the time of primary transfer and determined by output of the second power supply at the time of restore operation.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile apparatus using an electrophotographic system or an electrostatic recording system.

  2. Description of the Related Art Conventionally, as an image forming apparatus using an electrophotographic system, an intermediate transfer type image forming apparatus that primarily transfers a toner image formed on an image carrier such as a photoconductor to an intermediate transfer body and then secondary-transfers the recording material. There is.

  In the intermediate transfer type image forming apparatus, for the primary transfer of the toner image from the image carrier to the intermediate transfer member, a voltage is applied to the primary transfer member disposed at the opposite portion of the image carrier via the intermediate transfer member. Often done in Further, secondary transfer of a toner image from an intermediate transfer member to a recording material is often performed by applying a voltage to a secondary transfer member disposed in contact with the intermediate transfer member.

  On the other hand, a configuration has been proposed in which primary transfer is performed by supplying a current to a primary transfer member by applying a voltage to a current supply member that is in contact with the outer peripheral surface of the intermediate transfer member having conductivity (Patent Document 1). . According to this configuration, for example, by using the secondary transfer member as the current supply member, it is possible to reduce the cost and size of the image forming apparatus without using a high-voltage power source dedicated to primary transfer.

JP2013-231948A

  However, in the above conventional configuration, when an ion conductive intermediate transfer belt is used, if an image is repeatedly formed, an appropriate transfer current may not flow in the primary transfer portion and transfer defects may easily occur.

  That is, when image formation is continuously performed, ions having ion conductivity in the intermediate transfer belt are affected by an electric field, and ions are unevenly distributed in the intermediate transfer belt. If ions are unevenly distributed in the intermediate transfer belt, an appropriate transfer current does not flow, and a transfer defect is likely to occur.

  In order to alleviate such uneven distribution of ions (conductive agent), for example, it is effective to periodically pass a current in the reverse direction to the primary transfer member to the primary transfer member. However, if the voltage applied to the primary transfer member is a fixed value in order to flow the reverse current, the desired current can be flowed against fluctuations in the electrical resistance of the intermediate transfer belt due to environmental fluctuations and deterioration over time. There may not be. As a result, the transfer failure due to the uneven distribution of the ions (conductive agent) may not be sufficiently reduced.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of transfer failure due to uneven distribution of a conductive agent in an intermediate transfer belt.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image carrier that carries a toner image, an intermediate transfer belt having ionic conductivity, and the intermediate transfer for primary transfer of a toner image from the image carrier to the intermediate transfer belt. A primary transfer member in contact with the inner peripheral surface of the belt; a current supply member in contact with the outer peripheral surface of the intermediate transfer belt; and the current supply member opposed to the intermediate transfer belt through the intermediate transfer belt. An opposing member that is in contact with the surface and is electrically connected to the primary transfer member; a first power source that applies a voltage of a first polarity to the current supply member; and a first polarity that is applied to the current supply member. And a voltage maintaining means electrically connected between the primary power supply member and the opposing member and the ground, the second power supply applying a second polarity voltage opposite in polarity to the first power supply, 1 to the current supply member Voltage maintaining means for maintaining the potential of the primary transfer member when a voltage is applied, and current interrupting means electrically connected between the primary transfer member and the opposing member and the ground, A current interrupting means for interrupting a current between the current interrupting means and the ground when a voltage is applied from the power source to the current supplying member, and a voltage is applied from the first power source to the current supplying member. Conduction in the intermediate transfer belt caused by performing the primary transfer by applying a voltage from the second power source to the current supply member when the primary transfer is performed and the primary transfer is not performed. Control means for executing a recovery operation for alleviating uneven distribution of the agent, and during the primary transfer, the voltage applied to the primary transfer member is held at a predetermined voltage by the voltage maintaining means, and the recovery operation , The voltage applied to the primary transfer member is an image forming apparatus, characterized in that it is determined by the output of said second power supply.

  According to the present invention, it is possible to suppress the occurrence of transfer failure due to the uneven distribution of the conductive agent in the intermediate transfer belt.

1 is a schematic sectional view of an image forming apparatus according to Embodiment 1. FIG. 2 is a circuit configuration diagram relating to a transfer configuration in Embodiment 1. FIG. FIG. 6 is a schematic cross-sectional view for explaining a cleaning operation of the intermediate transfer belt. FIG. 3 is a substantially equivalent circuit diagram regarding a transfer configuration in Examples 1 and 2; 6 is a schematic cross-sectional view of an image forming apparatus according to Embodiment 2. FIG. 6 is a circuit configuration diagram relating to a transfer configuration in Embodiment 2. FIG. 3 is a schematic block diagram illustrating a control mode of a main part of the image forming apparatus. FIG. FIG. 3 is a schematic cross-sectional view illustrating a layer configuration of an intermediate transfer belt.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

[Example 1]
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic sectional view of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type printer that employs an intermediate transfer method that can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units (stations) that form yellow (Y), magenta (M), cyan (C), and black (K) toner images, respectively. It has Sa, Sb, Sc, Sd. For the elements having the same or corresponding functions or configurations in each of the image forming units Sa, Sb, Sc, Sd, a, b, c, d at the end of the reference numerals indicating that they are elements for any color are omitted. And may be described in a comprehensive manner. In this embodiment, the image forming unit S includes a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a primary transfer brush 14, and a cleaning device 5 which will be described later.

  A photosensitive drum 1 which is a rotatable drum type (cylindrical) photosensitive member (electrophotographic photosensitive member) as an image bearing member for carrying a toner image has a predetermined peripheral speed (process speed) in the direction of arrow R1 in the figure. Is driven to rotate. In this embodiment, the peripheral speed of the photosensitive drum 1 is 100 mm / sec. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 2 which is a roller-type photosensitive member charging member as a photosensitive member charging means. Is done. The surface of the charged photosensitive drum 1 is scanned and exposed in accordance with image information by an exposure device 3 as an exposure unit, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) using a toner as a developer by a developing device 4 as a developing unit, and a toner image is formed on the photosensitive drum 1. In this embodiment, the toner charged to the same polarity as the charged polarity of the photosensitive drum 1 adheres to the exposed portion on the photosensitive drum 1 where the absolute value of the potential is reduced by being exposed after being uniformly charged. . In this embodiment, the normal charging polarity of the toner, which is the charging polarity of the toner at the time of development, is negative.

  Opposite to the respective photosensitive drums 1 of the respective image forming units S, an intermediate transfer belt 10 that is an intermediate transfer member constituted by an endless belt is disposed. The intermediate transfer belt 10 is stretched around a driving roller 11, a tension roller 12, and a secondary transfer counter roller 13 as a plurality of stretching rollers (stretching members) and is stretched with a predetermined tension. The intermediate transfer belt 10 is driven to rotate by the driving roller 11, so that the peripheral speed of the photosensitive drum 1 is increased in the direction of arrow R <b> 2 in the drawing (the direction of movement in the same direction as the photosensitive drum 1 at the contact portion with the photosensitive drum 1). And rotate (circulate) at approximately the same peripheral speed. On the inner peripheral surface (back surface) side of the intermediate transfer belt 10, a primary transfer brush 14, which is a brush-like primary transfer member serving as a primary transfer unit, is disposed corresponding to each photosensitive drum 1. In this embodiment, the primary transfer brush 14 is disposed to face the photosensitive drum 1 with the intermediate transfer belt 10 interposed therebetween. The primary transfer brush 14 is pressed toward the photosensitive drum 1 through the intermediate transfer belt 10 to form a primary transfer portion (primary transfer nip portion) T1 where the photosensitive drum 1 and the intermediate transfer belt 10 are in contact with each other. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 10 by the action of the primary transfer brush 14 in the primary transfer portion T1. For example, during the formation of a full-color image, yellow, magenta, cyan, and black toner images formed on the respective photosensitive drums 1 are sequentially primary-transferred so as to be superimposed on the intermediate transfer belt 10. The primary transfer operation will be described in detail later.

  On the outer peripheral surface (front surface) side of the intermediate transfer belt 10, a secondary transfer roller 20 that is a roller-type secondary transfer member as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 13. Yes. The secondary transfer roller 20 is pressed toward the secondary transfer counter roller 13 via the intermediate transfer belt 10, and a secondary transfer portion (secondary transfer nip portion) where the intermediate transfer belt 10 and the secondary transfer roller 20 come into contact with each other. ) T2 is formed. The toner image formed on the intermediate transfer belt 10 is conveyed between the intermediate transfer belt 10 and the secondary transfer roller 20 by the action of the secondary transfer roller 20 in the secondary transfer portion T2. Transfer (secondary transfer) is performed on a recording material (transfer material, sheet) P. A power supply device 60 is connected to the secondary transfer roller 20. At the time of secondary transfer, a DC voltage having a polarity (positive in this embodiment) opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 20 from the power supply device 60. The recording material P is stored in a storage cassette 41, conveyed by a feeding roller 42, etc., and supplied to the secondary transfer portion T2 in timing with the toner image on the intermediate transfer belt 10.

  The recording material P to which the toner image has been transferred is conveyed to a fixing device 30 as a fixing unit, and is heated and pressed by the fixing device 30 to fix (melt and fix) the toner image, and then the image forming apparatus 100. It is discharged (output) to the outside of the main body.

  On the other hand, toner (primary transfer residual toner) remaining on the surface of the photosensitive drum 1 after the primary transfer is removed from the surface of the photosensitive drum 1 and collected by a cleaning device 5 as a cleaning unit. The cleaning device 5 scrapes and collects the primary transfer residual toner from the surface of the rotating photosensitive drum 1 by a cleaning blade as a cleaning member disposed in contact with the surface of the photosensitive drum 1.

  Further, on the outer peripheral surface side of the intermediate transfer belt 10, a charging brush 16, which is a brush-like charging member, is disposed as a charging unit that charges the toner on the intermediate transfer belt 10 at a position facing the secondary transfer counter roller 13. Has been. The charging brush 16 contacts the surface of the intermediate transfer belt 10 downstream of the secondary transfer portion T2 in the rotation direction of the intermediate transfer belt 10 and upstream of the primary transfer portion T1 (the most upstream primary transfer portion T1a). The toner charging portion Ch is formed. The toner remaining on the surface of the intermediate transfer belt 10 after the secondary transfer (secondary transfer residual toner) is scattered substantially uniformly and charged by the charging brush 16 in the toner charging portion Ch. The charged secondary transfer residual toner is transferred to the photosensitive drum 1a in the primary transfer portion T1a of the first image forming portion Sa in this embodiment. The secondary transfer residual toner transferred to the photosensitive drum 1a is collected by the cleaning device 5a. A power supply device 60 is connected to the charging brush 16. When charging the secondary transfer residual toner, a DC voltage having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the charging brush 16 from the power supply device 60. The transfer of the toner from the intermediate transfer belt 10 to the photosensitive drum 1a can be performed simultaneously with the primary transfer of the toner image from the photosensitive drum 1a to the intermediate transfer belt 10.

  FIG. 7 is a block diagram illustrating a control mode of a main part of the image forming apparatus 100 according to the present exemplary embodiment. In the present embodiment, the operation of each unit of the image forming apparatus 100 is comprehensively controlled by a control unit (control circuit) 50 serving as a control unit provided in the apparatus main body of the image forming apparatus 100. The control unit 50 includes a CPU 51 as arithmetic control means, a memory 52 such as ROM and RAM as storage means, and the like. In addition, the control unit 50 includes an environmental sensor that detects temperature and humidity in the apparatus main body as an environment detection unit that detects at least one of temperature and humidity inside or outside the apparatus main body of the image forming apparatus 100. 70 is connected. The environmental sensor 70 inputs a signal corresponding to the detected temperature and humidity to the control unit 50. The control unit 50 is connected to a counter 80 that counts the number of images (number of prints) output using the intermediate transfer belt 10 as a counting unit that counts information correlated with the usage amount of the intermediate transfer belt 10. Has been. The counter 80 accumulates and stores the number of prints every time an image is output, and the control unit 50 refers to the number of prints stored in the counter 80 as necessary. The control unit 50 is connected to a current detection unit (current detection circuit) 90 as a current detection unit that detects a current that flows when a voltage is applied from the power supply device 60 to the secondary transfer roller 20 and the charging brush 16. ing. The current detection unit 90 may be built in the power supply device 60.

  The control unit 50 controls the operation of each unit of the image forming apparatus 100 in accordance with a program stored in the memory 52 by the CPU 51. In particular, in this embodiment, the control unit 50 controls the ON / OFF switching and output of the power supply device 60 to change the direction of the current supplied to the primary transfer brush 14 in an image forming operation and a recovery operation described later. Take control.

  Here, the image forming apparatus 100 executes a job (printing operation), which is a series of operations for forming and outputting an image on one or a plurality of recording materials P, which is started by one start instruction. A job generally includes a pre-processing operation, an image forming operation, and a post-processing operation. In general, the image forming operation includes the formation of an electrostatic latent image of an output image, the formation of a toner image, an image formation (printing) process in which primary transfer and secondary transfer of the toner image are performed, and recording in a case where images are output continuously. It is configured to have an inter-sheet process corresponding to a period between the material P and the recording material P. The pre-processing operation (pre-rotation process) is a period during which a preparatory operation is performed from when the start instruction is input until the image forming operation is started. The post-processing operation (post-rotation process) is a period during which the organizing operation (preparation operation) after the image forming operation is completed. In the non-image forming period, in addition to the pre-processing operation and the post-processing operation, the above-described inter-sheet process, the pre-multi-rotation process which is a preparatory operation when the image forming apparatus 100 is turned on or returned from the sleep state, etc. Is included.

2. Configuration around the intermediate transfer belt The intermediate transfer belt 10 is an endless belt formed using a resin material to which conductivity is added by adding a conductive agent. The intermediate transfer belt 10 is supported by three axes of a driving roller 11, a tension roller 12 and a secondary transfer counter roller 13, and a tension of a total pressure of 60 N is applied by the tension roller 12.

The secondary transfer roller 20 has an outer diameter in which the outer periphery of a metal core (core material) made of a nickel-plated steel rod having an outer diameter of 8 mm is covered with an elastic layer made of a foamed sponge and having a thickness of 5 mm. Is an elastic roller of 18 mm. The foamed sponge body is made of a material mainly composed of NBR and epichlorohydrin rubber, the volume resistivity is adjusted to 10 ⁸ Ω · cm, and the secondary transfer roller 20 has conductivity. The secondary transfer roller 20 is brought into contact with the intermediate transfer belt 10 with a pressing force of 50 N, and is driven to rotate as the intermediate transfer belt 10 moves. In this embodiment, a voltage of about +2500 V is applied from the power supply device 60 to the secondary transfer roller 20 during the secondary transfer. The secondary transfer roller 20 is an example of a current supply member that contacts the outer peripheral surface of the intermediate transfer belt 10.

The primary transfer brush 14 pushes up the intermediate transfer belt 10 toward the photosensitive drum 1 by applying a pressing force by a pressing spring (not shown) as an urging means, and the outer peripheral surface of the intermediate transfer belt 10 is exposed to the photosensitive drum. 1 with a predetermined contact pressure. The primary transfer brush 14 is disposed at a fixed position with respect to the intermediate transfer belt 10 and rubs the back surface of the intermediate transfer belt 10 as the intermediate transfer belt 10 moves. The primary transfer brush 14 is composed of a conductive brush having a brush portion formed of conductive fibers. As the brush fibers constituting the brush portion of the primary transfer brush 14, conductive fibers made of nylon, polyester or the like in which carbon powder is dispersed are used. In this embodiment, the brush portion of the primary transfer brush 14 is composed of conductive fibers in which carbon powder is dispersed in nylon. It is preferable from the viewpoint of transfer efficiency that the resistivity ρ of the fiber is in the range of 10 to 10 ⁸ Ωcm. In this example, the resistivity ρ of this fiber is 10 ⁶ Ωcm. The primary transfer brush 14 is an example of a primary transfer member that comes into contact with the inner peripheral surface of the intermediate transfer belt 10 for primarily transferring a toner image from the photosensitive drum 1 to the intermediate transfer belt 10.

  The charging brush 16 is pressed against and brought into contact with the surface of the intermediate transfer belt 10. The charging brush 16 is disposed at a fixed position with respect to the intermediate transfer belt 10. Further, the charging brush 16 is disposed so as to have a predetermined penetration amount with respect to the surface of the intermediate transfer belt 10. The charging brush 16 rubs the surface of the intermediate transfer belt 10 as the intermediate transfer belt 10 moves. The charging brush 16 has the same configuration as the primary transfer brush 14. That is, the charging brush 16 is composed of a conductive brush having a brush portion formed of conductive fibers. As the brush fibers constituting the brush portion of the charging brush 16, conductive fibers made of nylon, polyester or the like in which carbon powder is dispersed are used. In this embodiment, the brush portion of the charging brush 16 is composed of conductive fibers in which carbon powder is dispersed in nylon. In this embodiment, a voltage of about +2700 V is applied to the charging brush 16 from the power supply device 60 when the secondary transfer residual toner is charged. The charging brush 16 is another example of a current supply member that contacts the outer peripheral surface of the intermediate transfer belt 10.

The secondary transfer counter roller 13 has an outer diameter of an outer diameter of a core metal (core material) made of aluminum having an outer diameter of 26.0 mm and covered with an elastic layer made of a hydrin rubber layer and having a thickness of 1.9 mm. It is a 29.8 mm elastic roller. The secondary transfer counter roller 13 has an electrical resistance value of 10 ⁶ Ω by adjusting the electrical resistance of the hydrin rubber layer, and has electrical conductivity. The rubber hardness of the hydrin rubber layer is 40 ° according to JIS-A standards. A secondary transfer roller 20 and a charging brush 16 are in contact with the secondary transfer counter roller 13 via the intermediate transfer belt 10. The secondary transfer counter roller 13 is an example of a counter member that faces the current supply member via the intermediate transfer belt 10, contacts the inner peripheral surface of the intermediate transfer belt 10, and is electrically connected to the primary transfer brush 14. is there.

3. Configuration of Intermediate Transfer Belt FIG. 8 is a schematic cross-sectional view of the intermediate transfer belt 10 in this embodiment. In this embodiment, the intermediate transfer belt 10 includes a base layer (base material) 10A and a surface layer (surface layer, coat layer) 10B. That is, in this embodiment, the base layer 10 </ b> A is in contact with the stretching member such as the secondary transfer counter roller 13 and the primary transfer brush 14. In the present embodiment, the surface layer 10B provided on the outer peripheral surface side of the intermediate transfer belt 10 with respect to the base layer 10A is in contact with the secondary transfer roller 20 and the charging brush 16. In this embodiment, the base layer 10A has a thickness of 65 μm, contains an ion conductive agent, and has ion conductivity.

  Examples of the base resin material for the base layer 10A include polycarbonate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polymethylpentene-1, polystyrene, polyamide, polysulfone, polyarylate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, Examples thereof include thermoplastic resins such as polybutylene naphthalate, polyphenylene sulfide, polyether sulfone, polyether nitrile, thermoplastic polyimide, polyether ether ketone, thermotropic liquid crystal polymer, and polyamic acid. Two or more of these can be mixed and used.

  Examples of the ion conductive conductive agent for imparting conductivity to the base layer 10A include polyvalent metal salts and quaternary ammonium salts. Quaternary ammonium salts include tetraethylammonium ion, tetrapropylammonium ion, tetraisopropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, tetrahexylammonium ion, etc. Examples thereof include fluoroalkyl sulfate ions, fluoroalkyl sulfite ions, and fluoroalkyl borate ions having 1 to 10 carbon atoms in halogen ions and fluoroalkyl groups.

The base layer 10A as the resin composition can be obtained by melt-blending the above-described material components, and then appropriately selecting and using a molding method such as inflation molding, cylindrical extrusion molding, or injection stretch blow molding. In this embodiment, the base layer 10A has a volume resistivity of 10 ⁹ Ωcm and has conductivity.

  In the present embodiment, the surface layer 10B has a thickness of 2 μm, contains an electronic conductive agent, and has electronic conductivity. That is, in this embodiment, the surface layer 10B does not have ionic conductivity.

The surface layer 10B can be provided by applying dip coating, spray coating, roll coating, spin coating or the like to the base layer 10A. Examples of the base material for the surface layer 10B include curable resins such as melamine resin, urethane resin, alkyd resin, and acrylic resin. The surface layer 10B has high airtightness, a volume resistivity of 10 ¹¹ Ωcm, and has conductivity.

  In this embodiment, the base layer 10A is formed of a material mainly composed of polyethylene naphthalate containing an ionic conductive agent. In the present embodiment, the surface layer 10B is particularly formed of a material mainly composed of an acrylic resin containing an electronic conductive agent.

The volume resistivity of the intermediate transfer belt 10 is measured using Mitsubishi Chemical Corporation Hiresta-UP (MCP-HT450) under conditions of an indoor temperature of 23 ° C., an indoor humidity of 50%, an applied voltage of 100 V, and a measurement time of 10 seconds. Can do. The electric resistance of the intermediate transfer belt 10 (each layer thereof) is preferably about 1 × 10 ^{7 to} 3 × 10 ¹¹ Ω · cm in volume resistivity.

4). Primary transfer operation Next, the primary transfer operation in the present embodiment will be further described.

  With reference to FIG. 1, in this embodiment, the voltage supplied to the secondary transfer roller 20 and the charging brush 16 as current supply members is a voltage supply source for primary transfer. That is, at the time of primary transfer, the secondary transfer roller 20 is arranged so that a DC voltage having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) from the power supply device 60 is in contact with the intermediate transfer belt 10. And applied to the charging brush 16. As a result, a current that flows from the secondary transfer roller 20 and the charging brush 16 disposed in contact with the intermediate transfer belt 10 to the secondary transfer counter roller 13 via the intermediate transfer belt 10 is supplied to the primary transfer brush 14. The Then, a negative polarity on the photosensitive drum 1 is generated by a current (transfer current) flowing from the intermediate transfer belt 10 to the photosensitive drum 1 based on a potential difference between the potential of the photosensitive drum 1 and the potential of the intermediate transfer belt 10 in the primary transfer portion T1. The toner is primarily transferred onto the intermediate transfer belt 10.

  Here, in the present exemplary embodiment, the image forming apparatus 100 is provided with a voltage maintaining unit in order to maintain the potential of the primary transfer brush 14 at the time of primary transfer at a predetermined potential. That is, in the present embodiment, the primary transfer brush 14, the secondary transfer counter roller 13 and the tension roller 12 are electrically connected so that their potentials are substantially equal. The primary transfer brush 14, the secondary transfer counter roller 13 and the tension roller 12 are electrically grounded (connected to the ground) via a first Zener diode 15 which is a constant voltage element as a common voltage maintaining unit. ing. In the present embodiment, as the first Zener diode 15, a Zener diode having a breakdown voltage (Zener voltage) of 750V is used. The first Zener diode 15 maintains the potential of the primary transfer brush 14 at a predetermined positive potential between the primary transfer brush 14, the secondary transfer counter roller 13 and the tension roller 12 and the ground (ground potential). Connected in the direction. That is, the first Zener diode 15 has the cathode side connected to the primary transfer brush 14, the secondary transfer counter roller 13 and the tension roller 12, and the anode side connected to the ground.

  The primary transfer brush 14, the secondary transfer counter roller 13, and the tension roller 12 are electrically grounded (connected to the ground) via a second Zener diode 17 that is a common constant voltage element. The second Zener diode 17 is connected in series between the first Zener diode 15 and the ground (ground potential) so as to be opposite to the first Zener diode 15. In other words, the second Zener diode 17 has the anode side connected to the first Zener diode 15 and the cathode side connected to the ground. The operation of the second Zener diode 17 will be described later.

  Further, in this embodiment, the primary transfer brushes 14a to 14d and the first Zener diodes are used in order to flow a substantially uniform current to each primary transfer portion T1 without being affected by variations in the electrical resistance of the primary transfer brush 14. The resistor elements 6a to 6d are connected to the terminal 15, respectively. In this embodiment, a 50 MΩ resistive element was used as each resistive element 6.

  In this embodiment, the drive roller 11 is configured to be electrically floated.

  FIG. 2 is a circuit configuration diagram relating to the transfer configuration in this embodiment. The power supply device 60 includes a secondary transfer power supply 61 and a charging power supply 62 which are positive power supplies (high voltage power supply circuits) that output positive voltage (positive voltage) applied to the secondary transfer roller 20 and the charging brush 16, respectively. . The secondary transfer power supply 61 and the charging power supply 62 are examples of a first power supply that applies a voltage having a first polarity to the current supply member. Further, the power supply device 60 includes a negative power supply (high voltage power supply circuit) 63 that outputs a negative voltage (negative voltage) applied to the secondary transfer roller 20 and the charging brush 16. The negative power source 63 is an example of a second power source that applies a voltage having a second polarity that is opposite to the first polarity to the current supply member. A first bleeder resistor 64 is connected in parallel to the secondary transfer power supply 61, and a second bleeder resistor 65 is connected in parallel to the charging power supply 62. When a negative voltage is applied from the negative power source 63 to the secondary transfer roller 20 and the charging brush 16, a current flows through the first and second bleeder resistors 64 and 65. On the other hand, a third bleeder resistor 66 is connected to the negative power source 63 in parallel. When a positive voltage is applied from the secondary transfer power supply 61 and the charging power supply 62 to the secondary transfer roller 20 and the charging brush 16, a current flows through the third bleeder resistor 66. A resistance element 67 in FIG. 2 indicates the electrical resistance of the secondary transfer portion T2, and is a combined resistance of the secondary transfer roller 20 and the intermediate transfer belt 10. A resistance element 68 in FIG. 2 indicates the electric resistance of the toner charging portion Ch, and is a combined resistance of the charging brush 16 and the intermediate transfer belt 10. Since the electrical resistance values of the secondary transfer portion T2 and the toner charging portion Ch both vary depending on the environment and the life state (whether it is the beginning or end of the life period), the variable resistance elements 67 and 68 in FIG. It is described as.

  When a positive voltage of a predetermined value or more is output from the secondary transfer power supply 61 and the charging power supply 62, a positive current flows through the first Zener diode 15, and the voltage with respect to the ground at the point X in FIG. The breakdown voltage of the diode 15 is maintained at + 750V. Then, the potential of each primary transfer brush 14 is maintained at +750 V, which is the breakdown voltage, and the intermediate transfer belt 10 in contact with each primary transfer brush 14, that is, the intermediate transfer belt 10 in each primary transfer portion T1. The surface potential is maintained at approximately + 750V. As a result, due to the potential difference between the intermediate transfer belt 10 and the photosensitive drum 1 in each primary transfer portion T1, a transfer current sufficient for primary transfer from the intermediate transfer belt 10 to each photosensitive drum 1 flows and is stable. Primary transfer is performed. In this embodiment, the primary transfer, the secondary transfer, the charging of the secondary transfer residual toner, and the transfer of the secondary transfer residual toner to the photosensitive drum 1 can be performed simultaneously. In this embodiment, a voltage of about +2500 V is applied to the secondary transfer roller 20 from the power supply device 60 and a voltage of about +2700 V is applied to the charging brush 16 from the power supply device 60 during the primary transfer. In addition, substantially the same positive current flows through each primary transfer brush 14.

5. Next, the cleaning operation of the intermediate transfer belt 10 in this embodiment will be further described. FIG. 3 is a schematic cross-sectional view in the vicinity of the secondary transfer portion T2.

  In this embodiment, the toner of the toner image primarily transferred onto the intermediate transfer belt 10 is negatively charged. This toner image is secondarily transferred to the recording material P by the secondary transfer roller 20 to which a positive voltage is applied. At this time, a part of the toner image on the intermediate transfer belt 10 remains on the intermediate transfer belt 10 without being secondarily transferred to the recording material P.

  As shown in FIG. 3, the secondary transfer residual toner remaining on the intermediate transfer belt 10 after the secondary transfer includes toners having both positive and negative polarities due to the positive voltage applied to the secondary transfer roller 20. Mixed. Further, under the influence of the irregularities on the surface of the recording material P, the secondary transfer residual toner locally overlaps with a plurality of layers and remains on the intermediate transfer belt 10 (A in FIG. 3). The secondary transfer residual toner accumulated in a plurality of layers on the intermediate transfer belt 10 is mechanically substantially one layer due to the relative speed between the intermediate transfer belt 10 and the charging brush 16 when passing through the toner charging portion Ch. (B in FIG. 3). Further, when the secondary transfer residual toner passes through the toner charging portion Ch, a positive voltage is applied to the charging brush 16 from the power supply device 60. In this embodiment, the positive voltage applied to the charging brush 16 is constant-current controlled with a predetermined target current (in this embodiment, the target current is 10 μA). As a result, the secondary transfer residual toner on the intermediate transfer belt 10 is charged to a positive polarity having a polarity opposite to the normal charging polarity of the toner when passing through the toner charging portion Ch. In this embodiment, the secondary transfer residual toner charged to the positive polarity is transferred to the negatively charged photosensitive drum 1a in the primary transfer portion T1a of the first image forming portion Sa, and is collected by the cleaning device 5a. Is done.

  Note that the negative polarity toner that has not been fully charged in the toner charging portion Ch is temporarily collected by the charging brush 16. The toner temporarily collected by the charging brush 16 is discharged to the intermediate transfer belt 10 by applying a negative voltage to the charging brush 16 as will be described later during a post-processing operation when the job is finished. The discharged toner is transferred to the photosensitive drum 1a in the primary transfer portion T1a of the first image forming portion Sa in this embodiment because a negative current is supplied to the primary transfer brush 14 as will be described later. It is collected by the cleaning device 5a.

6). Recovery operation By using the ionic conductive intermediate transfer belt 10 whose main conductive agent is ionic conductive, compared with the case where the electronic conductive intermediate transfer belt 10 whose main conductive agent is electronic conductive is used. There is an advantage that the manufacturing tolerance of the resistor can be kept small.

  However, when the ion-conductive intermediate transfer belt 10 is used, if an image is formed repeatedly, an appropriate transfer current may not flow in the primary transfer portion T1, and transfer defects may easily occur. That is, when an electric current is passed through the ionic conductive intermediate transfer belt 10, an electric field is generated in the intermediate transfer belt 10, and anions and cations responsible for ionic conductivity are subjected to force by the electric field. Then, positively charged cations move in the direction of the electric field, and negatively charged anions move in the direction opposite to the electric field. During an image forming operation, a positive voltage is applied from the power supply device 60 to the secondary transfer roller 20 and the charging brush 16, so that a positive current flows from the primary transfer brush 14 to the photosensitive drum 1 via the intermediate transfer belt 10. As a result, cations move to the outer peripheral surface side of the intermediate transfer belt 10 and anions move to the inner peripheral surface side of the intermediate transfer belt 10. When the image forming operation is continuously performed, the cation continues to move to the outer peripheral surface side of the intermediate transfer belt 10 by receiving a force, and the anion continues to the inner peripheral surface side of the intermediate transfer belt 10. And move with power. When the ions (conductive agent) are unevenly distributed in the intermediate transfer belt in this way, the electrical resistance of the intermediate transfer belt 10 fluctuates, and an appropriate transfer current does not flow, so that transfer defects are likely to occur. In particular, in this embodiment, since the surface layer of the intermediate transfer belt 10 is provided with a highly airtight coat layer 10B made of acrylic or the like, cations are dammed by the coat layer 10B, and the outer peripheral surface of the intermediate transfer belt 10 Does not precipitate. However, since the back surface of the intermediate transfer belt 10 is not provided with a coat layer, in some cases, anions may precipitate on the back surface of the intermediate transfer belt 10 to form a compound and lose conductivity. In addition, an anion compound deposited on the back surface of the intermediate transfer belt 10 adheres to the primary transfer brush 14 and causes an increase in electrical resistance of the primary transfer brush 14. As a result, the transfer current at the primary transfer portion T1 may be insufficient, and transfer defects may easily occur.

  In contrast, the image forming apparatus 100 according to the present exemplary embodiment performs the following “recovery operation” during non-image formation. That is, in the recovery operation, a negative voltage having a polarity opposite to that at the time of primary transfer is applied from the power supply device 60 to the secondary transfer roller 20 and the charging brush 16, and the direction opposite to that at the time of primary transfer is applied to the primary transfer brush 14. Supply negative current. As a result, the uneven distribution of ions (conductive agent) of the intermediate transfer belt 10 caused by the image forming operation is alleviated, and the electrical resistance of the primary transfer brush 14 is increased due to fluctuations in the electrical resistance of the intermediate transfer belt 10 and precipitation of the conductive agent. Can be suppressed. In particular, in this embodiment, the image forming apparatus 100 executes a recovery operation at the time of the post-processing operation (post-rotation process) of each job. However, the recovery operation may be executed for each of a plurality of jobs as long as the uneven distribution of ions (conductive agent) in the intermediate transfer belt can be sufficiently mitigated. In addition, the recovery operation can be executed in the inter-sheet process, the pre-processing operation (pre-rotation process), the pre-multi-rotation process, etc., during non-image formation.

  As described above, it is effective to periodically flow a current in the direction opposite to that at the time of primary transfer to the primary transfer brush 14 in order to alleviate the uneven distribution of ions (conductive agent) in the intermediate transfer belt 10. However, when the voltage applied to the primary transfer brush 14 in order to cause the reverse current to flow is a fixed value, a desired current against the fluctuations in the electrical resistance of the intermediate transfer belt 10 due to environmental fluctuations or deterioration over time. May not be able to flow. As a result, the transfer failure due to the uneven distribution of the ions (conductive agent) may not be sufficiently reduced.

  That is, for example, even when a negative current is supplied to the primary transfer brush 14, a voltage is applied to the second Zener diode 17 so that a negative voltage whose absolute value is greater than or equal to the breakdown voltage of the second Zener diode 17 is applied. A configuration for outputting from the device 60 is conceivable. However, in such a configuration, the voltage applied to the primary transfer brush 14 at the time of the recovery operation becomes a fixed value, so that a negative current cannot sufficiently flow as described above, and the ions (conductive agent) in the intermediate transfer belt 10 are not recovered by the recovery operation. ) May not be sufficiently suppressed.

  Therefore, in this embodiment, when a negative current is supplied to the primary transfer brush 14, a negative voltage whose absolute value is smaller than the breakdown voltage of the second Zener diode 17 is applied to the second Zener diode 17. In this configuration, a large voltage is output from the power supply device 60. In this case, when a negative voltage is output from the negative power source 63, the second Zener diode 17 cuts off the negative current, so that the negative current does not flow to the ground. The total value of the current values flowing through the secondary transfer roller 20 and the charging brush 16 and the total value of the current values flowing through the primary transfer brushes 14a to 14d are substantially equal. Note that substantially the same negative current flows through each primary transfer brush 14. In this way, almost all the current that flows when the negative voltage is output from the power supply device 60 is supplied to the primary transfer brush 14. In this case, the voltage applied to the primary transfer brush 14 can be determined by the output of the negative power supply 63. That is, in this embodiment, the second Zener diode 17 functions as a current interrupting unit that interrupts a negative current flowing to the ground when a negative voltage is applied to the primary transfer brush 14.

  FIGS. 4A and 4B respectively show substantial equivalent circuits relating to the transfer configuration during the primary transfer and the recovery operation in the image forming apparatus 100 of the present embodiment. The arrow in the figure represents the direction of the positive current (the direction of the negative current is opposite to the arrow in the figure). As shown in FIG. 4A, during the primary transfer, a voltage is applied from the power supply device 60 so that a positive voltage whose absolute value is greater than or equal to the breakdown voltage of the first Zener diode 15 is applied to the first Zener diode 15. Is output. Therefore, a positive current flows to the ground through the first Zener diode 15, and the potential of the primary transfer brush 14 is held substantially constant at the breakdown voltage. On the other hand, as shown in FIG. 4B, during the recovery operation, a voltage that causes a negative voltage whose absolute value is smaller than the breakdown voltage of the second Zener diode 17 is applied to the second Zener diode 17. 60, almost all of the negative current flows to the primary transfer brush 14. As a result, the output of the power supply device 60 can be adjusted according to the fluctuation of the electrical resistance of the intermediate transfer belt 10 due to environmental fluctuations or deterioration with time, and a desired negative current can be passed through the primary transfer brush 14.

  Typically, the output of the power supply device 60 during the recovery operation can be constant-current controlled with a predetermined target current set in advance. That is, the control unit 50 can adjust the output voltage value of the power supply device 60 during the recovery operation so that the current value detected by the current detection unit 90 approaches the target current value.

  The output of the power supply device 60 during the recovery operation is constant voltage controlled with a voltage value that is set in advance so that a desired current flows in accordance with fluctuations in the electrical resistance of the intermediate transfer belt 10 due to the environment and deterioration with time. May be. For example, when executing the printing operation, the control unit 50 acquires the detection result of the environment sensor 70 at least before the start of the recovery operation. Then, the control unit 50 determines the power supply during the recovery operation based on information relating the environment information set in advance and stored in the memory 52 to the recovery operation condition (the voltage value at which a desired current flows). The output voltage value of the device 60 can be determined. Further, for example, when executing the printing operation, the control unit 50 acquires the count value of the number of printed sheets by the counter 80 at least before the start of the recovery operation. Then, the control unit 50 performs the recovery operation based on information in which the count value of the counter 80 set in advance and stored in the memory 52 is associated with the recovery operation condition (voltage value through which a desired current flows). The output voltage value of the power supply device 60 at the time can be determined. Note that the output voltage value of the power supply device 60 during the recovery operation may be set so that a desired current flows based on both the environmental information and the usage amount information of the intermediate transfer belt 10.

7). Effects Next, the results of verifying the effects of the present embodiment will be described. Table 1 shows the results of evaluating the increase in the electrical resistance of the primary transfer portion T1 by performing a durability test on this example and the comparative example.

  In the durability test, when the number of printed sheets is 0K, 25K, or 50K (1K is 1000 sheets), the negative current value that flows to each primary transfer brush 14 in the recovery operation (the negative current value that flows to each primary transfer brush 14a to 14d). Average value). Further, the electrical resistance value of each primary transfer portion T1 (the average value of the electrical resistance values of the primary transfer portions T1a to T1d) at the time of printing was examined. Further, the primary transferability at the time of the number of printed sheets was examined.

  During the durability test, a recovery operation was performed in which a negative voltage was applied from the power supply device 60 for a predetermined time (5 seconds) every time after one image was formed. In this embodiment, a Zener diode having a breakdown voltage of 3000 V is used as the second Zener diode 17. In this embodiment, a negative voltage smaller than the breakdown voltage of the second Zener diode 17 is set so that a desired negative current (about -13 mA) flows in advance according to the number of prints in the recovery operation. Was applied from the power supply device 60. On the other hand, in the comparative example, a Zener diode having a breakdown voltage of 2000 V was used as the second Zener diode 17. That is, in the comparative example, the voltage applied to the primary transfer brush 14 during the recovery operation is fixed to approximately −2000V. In the comparative example, during the recovery operation, a negative voltage whose absolute value is equal to or higher than the breakdown voltage of the second Zener diode 17 is applied from the power supply device 60 regardless of the number of printed sheets. Except for the above points, the configuration and operation of the image forming apparatus 100 are substantially the same between the present embodiment and the comparative example.

  The current flowing through each primary transfer brush 14 during the recovery operation and the electrical resistance value of each primary transfer portion T1 were obtained from the output voltage value of the power supply device 60 during the recovery operation and the current value flowing at that time. Primary transferability was evaluated according to the following evaluation criteria by first transferring a predetermined image for evaluation from the photosensitive drum 1 to the intermediate transfer belt 10 and visually observing the toner image on the intermediate transfer belt 10. In the case where almost all of the toner of the image for evaluation was primary transferred, it was marked as “Good”. In addition, when the toner of a part of the image for evaluation could not be primarily transferred, it was set as Δ (level causing a problem in some cases). In addition, when almost all the toner of the evaluation image could not be transferred to the primary image, x (defect) was assigned.

  In the comparative example, a negative current of -13.5 μA was able to flow at 0K sheets (durability initial stage), but up to −10.2 μA at 25K sheets, and to −8.5 μA at 50K sheets (end of durability period). Negative current decreased. In the comparative example, the electrical resistance of the primary transfer portion T1 increased to 117 MΩ at 25K sheets and to 148 MΩ at 50K sheets, compared to 83 MΩ at 0K sheets. In the comparative example, good primary transferability was obtained at 0K sheets, but the primary transferability decreased as the number of printed sheets increased at 25K sheets and 50K sheets.

  On the other hand, in this embodiment, almost a desired negative current flows from 0K sheets (end of durability) to 50K sheets (end of durability), and the electrical resistance of the primary transfer portion T1 is 83 MΩ for 0K sheets. Even with 50K sheets, it was possible to suppress the increase to 103MΩ. In this example, good primary transferability was obtained from 0K sheets to 50K sheets.

  As described above, according to this embodiment, it is possible to stably flow a desired negative current to the primary transfer brush 14 while suppressing the influence of fluctuations in the electrical resistance of the ion conductive intermediate transfer belt 10. Thereby, the uneven distribution of ions (conductive agent) of the intermediate transfer belt 10 caused by the image forming operation can be sufficiently relaxed, and transfer defects due to the fact that an appropriate transfer current does not flow can be suppressed.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus according to the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 5 is a schematic cross-sectional view of the image forming apparatus 100 in the present embodiment. In this embodiment, a diode 18 which is a rectifying element is used instead of the second Zener diode 17 in Embodiment 1 as a current blocking means for blocking a negative current flowing to the ground when a negative voltage is applied to the primary transfer brush 14. Is used. In this embodiment, the primary transfer brush 14, the secondary transfer counter roller 13 and the tension roller 12 are electrically grounded (connected to the ground) via a diode 18 which is a common rectifying element. The diode 18 is connected in series between the Zener diode 15 and the ground (ground potential) in a direction that blocks a negative current flowing from the Zener diode 15 to the ground. That is, the diode 18 has an anode side connected to the Zener diode 15 and a cathode side connected to the ground.

  FIG. 6 is a circuit configuration diagram relating to the transfer configuration in this embodiment. When a positive voltage of a predetermined value or more is output from the secondary transfer power supply 61 and the charging power supply 62, a positive current flows through the Zener diode 15, and the voltage with respect to the ground at the point X in FIG. Is held at + 750V. By the action of this voltage, the primary transfer is performed as in the first embodiment. On the other hand, when a negative voltage is output from the negative power source 63, the diode 18 blocks the negative current, so that the negative current does not flow to the ground. The total value of the current values flowing through the secondary transfer roller 20 and the charging brush 16 and the total value of the current values flowing through the primary transfer brushes 14a to 14d are substantially equal. Note that substantially the same negative current flows through each primary transfer brush 14. In this way, almost all the current that flows when the negative voltage is output from the power supply device 60 is supplied to the primary transfer brush 14. In this case, the voltage applied to the primary transfer brush 14 can be determined by the output of the negative power supply 63.

  In the image forming apparatus 100 of the present embodiment, the substantially equivalent circuit regarding the transfer configuration at the time of the primary transfer and the recovery operation is the same as that shown in FIGS. 4A and 4B described in the first embodiment. That is, as shown in FIG. 4A, during primary transfer, a voltage is applied from the power supply device 60 such that a positive voltage whose absolute value is greater than or equal to the breakdown voltage of the Zener diode 15 is applied to the Zener diode 15. Therefore, a positive current flows through the Zener diode 15 to the ground, and the potential of the primary transfer brush 14 is kept substantially constant at the breakdown voltage. On the other hand, as shown in FIG. 4B, when a negative voltage is output from the power supply device 60 during the recovery operation, almost all of the negative current flows to the primary transfer brush 14. As a result, the output of the power supply device 60 can be adjusted according to the fluctuation of the electrical resistance of the intermediate transfer belt 10 due to environmental fluctuations or deterioration with time, and a desired negative current can be passed through the primary transfer brush 14. In this example, a diode having a withstand voltage of 3000 V was used as the diode 18.

  As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained, and the cost and size can be reduced by using a diode that is cheaper and smaller than a Zener diode.

[Example 3]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus according to the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, the value of the target current during the recovery operation is changed in accordance with the fluctuation of the electrical resistance of the intermediate transfer belt 10 due to the environment and aging deterioration.

  For example, when executing the printing operation, the control unit 50 acquires the detection result of the environment sensor 70 at least before the start of the recovery operation. Then, the control unit 50 determines the target current in the recovery operation based on the information that is set in advance and stored in the memory 52 and related to the recovery operation condition (target current value). Can do.

  Table 2 shows an example of the target current during the recovery operation according to the environmental information. In this embodiment, the HH environment is an environment having a temperature higher than 25 ° C. and a relative humidity higher than 60%. The NN environment is an environment where the temperature is higher than 20 ° C. and lower than or equal to 25 ° C., and the relative humidity is higher than 30% and lower than or equal to 60%. The LL environment is an environment having a temperature of 20 ° C. or lower and a relative humidity of 30% or lower. The ion mobility in the intermediate transfer belt 10 is larger in a high temperature and high humidity environment, and is smaller in a low temperature and low humidity environment. Therefore, by flowing more current in the recovery operation in the low temperature and low humidity environment than in the high temperature and high humidity environment, the uneven distribution of ions (conductive agent) generated during the image forming operation can be more efficiently mitigated by the recovery operation for a predetermined time. There is.

  In this manner, the control unit 50 can change the current supplied to the primary transfer brush 14 in the recovery operation based on the detection result of the environment detection unit. In this embodiment, the conditions for the recovery operation are changed based on the environmental temperature and relative humidity. However, the ion mobility in the intermediate transfer belt 10 may have a sufficient correlation with at least one of temperature and humidity. is there. Therefore, the conditions for the recovery operation can be changed based on at least one of the environmental temperature and humidity. Typically, the absolute value of the current supplied in the recovery operation in the case of the second temperature lower than the first temperature is smaller than the absolute value of the current supplied in the recovery operation in the case where the temperature is the first temperature. Try to be bigger. Further, the absolute value of the current supplied in the recovery operation in the case of the second humidity lower than the first humidity is larger than the absolute value of the current supplied in the recovery operation in the case where the humidity is the first humidity. To be.

  Further, for example, when executing the printing operation, the control unit 50 acquires the count value of the number of printed sheets by the counter 80 at least before the start of the recovery operation. Then, the control unit 50 sets the target current in the recovery operation based on the information related to the count value of the counter 80 that is set in advance and stored in the memory 52 and the recovery operation condition (target current value). Can be determined.

  Table 3 shows an example of the target current during the recovery operation according to the cant value of the counter 80. In this embodiment, the set life of the intermediate transfer belt 10 is 50K sheets, and the count value is classified into 0K or more and less than 10K sheets, 10K or more and less than 25K sheets, and 25K or more and 50K sheets or less. The uneven distribution of ions in the intermediate transfer belt 10 tends to become more prominent as the amount of use of the intermediate transfer belt 10 increases. Therefore, by flowing more current in the recovery operation closer to the end of durability than the initial durability of the intermediate transfer belt 10, the uneven distribution of ions (conductive agent) generated during the image forming operation is more efficient in the recovery operation for a predetermined time. Can be relaxed.

  As described above, the control unit 50 can change the current supplied to the primary transfer brush 14 in the recovery operation based on the counting result of the counting unit. In this embodiment, the recovery operation condition is changed based on the number of prints as information correlating with the amount of use of the intermediate transfer belt 10, but if the information correlates with the amount of use of the intermediate transfer belt 10, for example, rotation The number of times, rotation time, etc. may be used. Typically, the recovery in the case of the second usage amount larger than the first usage amount than the absolute value of the current supplied in the recovery operation when the usage amount of the intermediate transfer belt 10 is the first usage amount. The absolute value of the current supplied in the operation is made larger.

  The current supplied to the primary transfer brush 14 in the recovery operation may be changed based on both the environment and the usage amount of the intermediate transfer belt 10. Although the configuration of the first embodiment has been described here as an example, in the configuration of the second embodiment, the target current value at the time of the recovery operation may be changed depending on the environment and the amount of use of the intermediate transfer belt 10 as described above. .

  As described above, in this embodiment, the same effects as those of the first embodiment can be obtained, and ions (conductive agent) in the intermediate transfer belt 10 can be more efficiently converted according to the environment and the life state of the intermediate transfer belt 10. Uneven distribution can be mitigated.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  In the above embodiment, the secondary transfer member and the charging member are used as the current supply member, but the present invention is not limited to this. For example, a cleaning member for scraping off secondary transfer residual toner from the intermediate transfer belt is provided as a cleaning unit for the intermediate transfer belt, and in a configuration in which no charging member is provided, the current supply member may be the secondary transfer member alone. Good.

  Further, in the above-described embodiment, the secondary transfer member and the charging member as the current supply member are disposed to face the common facing member via the intermediate transfer belt, but each face the separate facing member. May be arranged.

  In the above embodiment, the primary transfer member is a brush-like member. However, for example, a roller-like member such as a metal roller or a roller having a conductive elastic layer, or a sheet made of conductive plastic. It may be in any form such as a shaped member.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 10 Intermediate transfer belt 13 Secondary transfer counter roller 14 Primary transfer brush 15 Positive voltage Zener diode 16 Charging brush 17 Negative voltage Zener diode 18 Negative voltage diode 20 Secondary transfer roller 60 Power supply device

Claims (10)

An image carrier for carrying a toner image;
An intermediate transfer belt having ionic conductivity;
A primary transfer member in contact with an inner peripheral surface of the intermediate transfer belt for primary transfer of a toner image from the image carrier to the intermediate transfer belt;
A current supply member in contact with the outer peripheral surface of the intermediate transfer belt;
An opposing member that faces the current supply member via the intermediate transfer belt, contacts an inner peripheral surface of the intermediate transfer belt, and is electrically connected to the primary transfer member;
A first power source for applying a voltage of a first polarity to the current supply member;
A second power source that applies a voltage of a second polarity that is opposite to the first polarity to the current supply member;
Voltage maintaining means electrically connected between the primary transfer member and the opposing member and ground, and when the voltage is applied from the first power source to the current supply member, the primary transfer member Voltage maintaining means for maintaining the potential;
Current interrupting means electrically connected between the primary transfer member and the opposing member and ground, and when the voltage is applied from the second power source to the current supply member, Current interrupting means for interrupting current between the ground and
A voltage is applied from the first power source to the current supply member to perform the primary transfer, and when the primary transfer is not performed, a voltage is applied from the second power source to the current supply member, Control means for executing a recovery operation to alleviate the uneven distribution of the conductive agent in the intermediate transfer belt caused by performing the primary transfer;
Have
During the primary transfer, the voltage applied to the primary transfer member is held at a predetermined voltage by the voltage maintaining means, and during the recovery operation, the voltage applied to the primary transfer member is determined by the output of the second power source. An image forming apparatus characterized by being determined.   The voltage maintaining unit is a constant voltage element, and the control unit is configured to apply the first power source so that a voltage having an absolute value equal to or higher than a breakdown voltage of the voltage maintaining unit is applied to the voltage maintaining unit during the primary transfer. The image forming apparatus according to claim 1, wherein an output of the image forming apparatus is controlled.   The current interrupting means is a constant voltage element, and the control means is configured to apply the second power source so that a voltage whose absolute value is smaller than the breakdown voltage of the current interrupting means is applied to the current interrupting means during the recovery operation. The image forming apparatus according to claim 1, wherein an output of the image forming apparatus is controlled.   The image forming apparatus according to claim 1, wherein the current interrupting unit is a rectifying element.   5. The control unit according to claim 1, wherein the control unit controls an output of the second power supply so that a predetermined current flows through the primary transfer member during the recovery operation. 6. Image forming apparatus.   The image forming apparatus according to claim 5, further comprising an environment detection unit configured to detect an environment, wherein the control unit changes the predetermined current based on a detection result of the environment detection unit.   6. The apparatus according to claim 5, further comprising a counting unit that counts information correlated with a usage amount of the intermediate transfer belt, wherein the control unit changes the predetermined current based on a counting result of the counting unit. The image forming apparatus described.   The image forming apparatus according to claim 1, wherein the current supply member is a secondary transfer member for secondary transfer of a toner image from the intermediate transfer belt to a recording material. .   The current supply member includes a secondary transfer member for secondary transfer of a toner image from the intermediate transfer belt to a recording material, and the intermediate transfer belt when the toner image is secondarily transferred from the intermediate transfer belt to the recording material. The image forming apparatus according to claim 1, wherein the image forming apparatus is a charging member that charges toner remaining on the toner.   The image forming apparatus according to claim 1, wherein the primary transfer member is a brush-like member.

Images