JP6906964B2 - Image forming device - Google Patents

Description

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

Conventionally, as an image forming apparatus using an electrophotographic method, an intermediate transfer type image forming apparatus that first transfers a toner image formed on an image carrier such as a photoconductor to an intermediate transfer body and then secondarily transfers the toner image to a recording material. There is.

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

On the other hand, a configuration has been proposed in which a voltage is applied to a current supply member that contacts the outer peripheral surface of a conductive intermediate transfer member to supply a current to the primary transfer member to perform primary transfer (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 by eliminating the need for a high-voltage power supply dedicated to the primary transfer.

Japanese Unexamined Patent Publication No. 2013-231948

However, in the above-mentioned conventional configuration, when an ionic conductive intermediate transfer belt is used, if repeated image formation is performed, an appropriate transfer current may not flow in the primary transfer portion, and transfer defects may easily occur.

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

In order to alleviate such uneven distribution of ions (conductive agents), it is effective, for example, to periodically pass a current in the primary transfer member in the direction opposite to that during the primary transfer. However, when the voltage applied to the primary transfer member to pass the reverse current is a fixed value, a desired current can flow against fluctuations in the electrical resistance of the intermediate transfer belt due to environmental fluctuations and deterioration over time. Sometimes not. As a result, transfer defects due to uneven distribution of the above-mentioned ions (conductive agents) may not be sufficiently reduced.

Therefore, an object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of transfer defects due to uneven distribution of conductive agents in the intermediate transfer belt.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises an image carrier carrying 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. The primary transfer member in contact with the inner peripheral surface of the belt, the current supply member in contact with the outer peripheral surface of the intermediate transfer belt, and the current supply member facing the current supply member via the intermediate transfer belt, and the inner circumference of the intermediate transfer belt. An opposing member that is in contact with the surface and electrically connected to the primary transfer member, a first power source that applies a voltage of the first polarity to the current supply member, and the first polarity to the current supply member. A voltage maintaining means electrically connected between a second power source that applies a voltage having a second polarity opposite to that of the above, the primary transfer member, the opposing member, and the ground. The voltage maintaining means for maintaining the potential of the primary transfer member when a voltage is applied from the power source of 1 to the current supply member is electrically connected between the primary transfer member and the facing member and the ground. From the constant voltage element , which is a constant voltage element that cuts off the current between the constant voltage element and the ground when a voltage is applied from the second power source to the current supply member, and from the first power source. A voltage is applied to the current supply member to execute the primary transfer, and when the primary transfer is not performed, a voltage is applied to the current supply member from the second power source to perform the primary transfer. It has a control means for executing a recovery operation for alleviating the uneven distribution of the conductive agent in the intermediate transfer belt caused by the above, and at the time of the primary transfer, the voltage applied to the primary transfer member is determined by the voltage maintenance means. The voltage applied to the primary transfer member during the recovery operation is determined by the output of the second power source, and the control means has an absolute value for the constant voltage element during the recovery operation. The image forming apparatus is characterized in that the output of the second power source is controlled so that a voltage smaller than the breakdown voltage of the constant voltage element is applied.

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

FIG. 5 is a schematic cross-sectional view of the image forming apparatus of the first embodiment. It is a circuit block diagram about the transfer structure in Example 1. FIG. It is the schematic sectional drawing for demonstrating the cleaning operation of an intermediate transfer belt. FIG. 5 is a substantially equivalent circuit diagram relating to the transfer configuration in Examples 1 and 2. It is the schematic sectional drawing of the image forming apparatus of Example 2. FIG. It is a circuit block diagram which concerns on the transfer structure in Example 2. It is a schematic block diagram which shows the control mode of the main part of an image forming apparatus. It is a schematic cross-sectional view which shows the layer structure of an intermediate transfer belt.

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

[Example 1]
1. 1. Overall Configuration and Operation of the Image Forming Device FIG. 1 is a schematic cross-sectional view of the image forming device 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem type printer adopting an intermediate transfer method capable of forming a full-color image by using an electrophotographic method.

The image forming apparatus 100 is a first, second, third, and fourth image forming unit (station) that forms a toner image of yellow (Y), magenta (M), cyan (C), and black (K), respectively. It has Sa, Sb, Sc, and Sd. For elements having the same or corresponding functions or configurations in each image forming unit Sa, Sb, Sc, Sd, a, b, c, d at the end of the code indicating that the element is for any color is omitted. And there is a general explanation. 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.

The photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) photoconductor (electrophotographic photosensitive member) as an image carrier that supports a toner image, has a predetermined peripheral speed (process speed) in the direction of arrow R1 in the drawing. It is driven to rotate with. 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 electrode property in this embodiment) by a charging roller 2 which is a roller-type photoconductor charging member as a photoconductor charging means. Will be done. The surface of the charged photosensitive drum 1 is scanned and exposed by an exposure apparatus 3 as an exposure means according to image information, 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) by a developing device 4 as a developing means using toner as a developer, and a toner image is formed on the photosensitive drum 1. In this embodiment, toner charged to the same polarity as the charging polarity of the photosensitive drum 1 adheres to the exposed portion on the photosensitive drum 1 whose absolute potential value is lowered 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 during development, is the negative electrode property.

An intermediate transfer belt 10 which is an intermediate transfer body composed of an endless belt is arranged so as to face each photosensitive drum 1 of each image forming unit S. The intermediate transfer belt 10 is stretched over a drive roller 11, a tension roller 12, and a secondary transfer opposed roller 13 as a plurality of tension rollers (tension members) and is tensioned with a predetermined tension. The intermediate transfer belt 10 is driven by the rotation of the drive roller 11 to drive the peripheral speed of the photosensitive drum 1 in the direction of arrow R2 in the figure (the direction in which the intermediate transfer belt 10 moves in the same direction as the photosensitive drum 1 at the contact portion with the photosensitive drum 1). It rotates (circulates) at almost the same peripheral speed as. 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 as a primary transfer means is arranged corresponding to each photosensitive drum 1. In this embodiment, the primary transfer brush 14 is arranged to face the photosensitive drum 1 via the intermediate transfer belt 10. The primary transfer brush 14 is pressed toward the photosensitive drum 1 via the intermediate transfer belt 10 to form a primary transfer portion (primary transfer nip portion) T1 in which the photosensitive drum 1 and the intermediate transfer belt 10 come into contact with each other. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) on the intermediate transfer belt 10 by the action of the primary transfer brush 14 in the primary transfer unit T1. For example, at the time of forming a full-color image, the toner images of each color of yellow, magenta, cyan, and black formed on each photosensitive drum 1 are sequentially primary-transferred so as to be superimposed on the intermediate transfer belt 10. The primary transfer operation will be described in more detail later.

On the outer peripheral surface (surface) side of the intermediate transfer belt 10, a secondary transfer roller 20, which is a roller-type secondary transfer member as a secondary transfer means, is arranged at a position facing the secondary transfer opposed roller 13. There is. The secondary transfer roller 20 is pressed toward the secondary transfer opposed roller 13 via the intermediate transfer belt 10, and the secondary transfer portion (secondary transfer nip portion) in which the intermediate transfer belt 10 and the secondary transfer roller 20 come into contact with each other. ) Form T2. The toner image formed on the intermediate transfer belt 10 is transferred by the action of the secondary transfer roller 20 in the secondary transfer unit T2, such as paper sandwiched between the intermediate transfer belt 10 and the secondary transfer roller 20. It is transferred (secondary transfer) onto the 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 opposite to the normal charging polarity of the toner (positive electrode property in this embodiment) is applied from the power supply device 60 to the secondary transfer roller 20. The recording material P is stored in the storage cassette 41, is conveyed by the feeding roller 42 or the like, and is supplied to the secondary transfer unit T2 at the same timing as the toner image on the intermediate transfer belt 10.

The recording material P to which the toner image is transferred is conveyed to the fixing device 30 as a fixing means, and after the toner image is fixed (melted and fixed) by being heated and pressed by the fixing device 30, the image forming apparatus 100 It is discharged (output) to the outside of the device body.

On the other hand, the toner remaining on the surface of the photosensitive drum 1 after the primary transfer (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 by the cleaning device 5 as a cleaning means and recovered. 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 arranged 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 arranged at a position facing the secondary transfer facing roller 13 as a charging means for charging the toner on the intermediate transfer belt 10. Has been done. The charging brush 16 contacts the surface of the intermediate transfer belt 10 on the downstream side of the secondary transfer portion T2 and on the upstream side of the primary transfer portion T1 (upstream primary transfer portion T1a) in the rotation direction of the intermediate transfer belt 10. , Toner charging portion Ch is formed. The toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 10 after the secondary transfer is substantially uniformly dispersed and charged by the charging brush 16 in the toner charging portion Ch. Then, the charged secondary transfer residual toner is transferred to the photosensitive drum 1a in the primary transfer unit T1a of the first image forming unit Sa in this embodiment. The secondary transfer residual toner transferred to the photosensitive drum 1a is recovered 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 electrode property in this embodiment) is applied to the charging brush 16 from the power supply device 60. The transfer of toner from the intermediate transfer belt 10 to the photosensitive drum 1a can be performed at the same time as the primary transfer of the toner image from the photosensitive drum 1a to the intermediate transfer belt 10.

FIG. 7 is a block diagram showing a control mode of a main part of the image forming apparatus 100 of this embodiment. In this embodiment, the operation of each part of the image forming apparatus 100 is collectively controlled by a control unit (control circuit) 50 as a control means provided in the apparatus main body of the image forming apparatus 100. The control unit 50 includes a CPU 51 as an arithmetic control means, a ROM as a storage means, a memory 52 such as a RAM, and the like. Further, the control unit 50 has an environment sensor for detecting the temperature and humidity inside the device body as an environment detecting means for detecting at least one of the temperature and humidity inside or outside the device body of the image forming apparatus 100. 70 is connected. The environment sensor 70 inputs a signal corresponding to the detected temperature and humidity to the control unit 50. Further, the control unit 50 is connected to a counter 80 that counts the number of images (the number of prints) output by using the intermediate transfer belt 10 as a counting means for counting information that correlates with the usage amount of the intermediate transfer belt 10. Has been done. The counter 80 integrates and stores the number of prints each time an image is output, and the control unit 50 refers to the number of prints stored in the counter 80 as needed. Further, the control unit 50 is connected to a current detection unit (current detection circuit) 90 as a current detection means for detecting the current flowing 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 according to a program stored in the memory 52 by the CPU 51. In particular, in this embodiment, the control unit 50 controls 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 the image drawing operation and the recovery operation described later. Take control.

Here, the image forming apparatus 100 executes a job (printing operation) which is a series of operations of forming and outputting an image on a single or a plurality of recording materials P, which is started by one start instruction. A job is generally composed of a pre-processing operation, an image-creating operation, and a post-processing operation. The image forming operation generally includes forming an electrostatic latent image of an output image, forming a toner image, an image forming (printing) process of performing primary transfer or secondary transfer of a toner image, and recording when continuously outputting an image. It is configured to have a paper-to-paper 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 the preparatory operation is performed from the input of the start instruction to the start of the image-drawing operation. The post-processing operation (post-rotation process) is a period during which the organizing operation (preparation operation) is performed after the image drawing operation is completed. The non-image forming time means, in addition to the pre-processing operation and the post-processing operation, the inter-paper process, the pre-multi-rotation process which is a preparatory operation when the power of the image forming apparatus 100 is turned on or when returning from the sleep state, and the like. Is included.

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

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

In the primary transfer brush 14, the intermediate transfer belt 10 is pushed up 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 subjected to the photosensitive drum. 1 is brought into contact with a predetermined contact pressure. The primary transfer brush 14 is arranged 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. The resistivity ρ of this fiber ^{is preferably in the range of 10 to 8} Ωcm from the viewpoint of transfer efficiency. In this embodiment, the resistivity of the fiber ρ is 10 ⁶ [Omega] cm. The primary transfer brush 14 is an example of a primary transfer member that contacts the inner peripheral surface of the intermediate transfer belt 10 for primary transfer of a toner image from the photosensitive drum 1 to the intermediate transfer belt 10.

The charging brush 16 is pressed against the surface of the intermediate transfer belt 10 and is in contact with the surface. The charging brush 16 is arranged at a fixed position with respect to the intermediate transfer belt 10. Further, the charging brush 16 is arranged so as to have a predetermined penetration amount with respect to the surface of the intermediate transfer belt 10. Then, 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 charged 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, when the secondary transfer residual toner is charged, a voltage of about + 2700 V is applied to the charging brush 16 from the power supply device 60. The charging brush 16 is another example of a current supply member that comes into contact with the outer peripheral surface of the intermediate transfer belt 10.

The secondary transfer opposed roller 13 has an outer diameter of an elastic body layer having a thickness of 1.9 mm, which is composed of a hydrin rubber layer and covers the outer circumference of an aluminum core metal (core material) having an outer diameter of 26.0 mm. It is a 29.8 mm elastic roller. Secondary transfer counter roller 13, the electric resistance value in the electric resistance of the hydrin rubber layer is adjusted is a 10 ⁶ Omega, are electrically conductive. The rubber hardness of the hydrin rubber layer is 40 ° according to the JIS-A standard. The secondary transfer roller 20 and the charging brush 16 are in contact with the secondary transfer opposed roller 13 via the intermediate transfer belt 10. The secondary transfer opposing roller 13 is an example of an opposing 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. be.

3. 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 has a base layer (base material) 10A and a surface layer (surface layer, coat layer) 10B. That is, in this embodiment, the base layer 10A comes into contact with the tension member such as the secondary transfer opposing roller 13 and the primary transfer brush 14. Further, in this 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 comes into 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 ionic conductive conductive agent, and has ionic conductivity.

Examples of the base resin material of the base layer 10A include polycarbonate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polymethylpentene-1, polystyrene, polyamide, polysulfone, polyarylate, polyethylene terephthalate, polybutylene terephthalate, and 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. These can be mixed and used in two or more kinds.

Examples of the ionic conductive conductive agent for imparting conductivity to the base layer 10A include polyvalent metal salts and quaternary ammonium salts. Examples of the quaternary ammonium salt include tetraethylammonium ion, tetrapropylammonium ion, tetraisopropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, and tetrahexylammonium ion as the cation part, and the anion part includes the anion part. 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 a resin composition can be obtained by melting and blending each of the above 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 is 10 ⁹ [Omega] cm, electrically conductive.

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

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

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

The volume resistivity of the intermediate transfer belt 10 shall be measured using Mitsubishi Chemical Corporation Hiresta-UP (MCP-HT450) under the 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 sec. Can be done. The electrical resistance of the intermediate transfer belt 10 (each layer thereof) ^{is preferably about 1 × 10 7 to} 3 × 10 ¹¹ Ω · cm in terms of volume resistivity.

4. Primary transfer operation Next, the primary transfer operation in this 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 the current supply member serves as a voltage supply source for the primary transfer. That is, at the time of primary transfer, a DC voltage having a polarity opposite to the normal charging polarity of the toner (positive electrode property in this embodiment) is arranged from the power supply device 60 in contact with the intermediate transfer belt 10 in the secondary transfer roller 20. And applied to the charging brush 16. As a result, the current flowing from the secondary transfer roller 20 and the charging brush 16 arranged in contact with the intermediate transfer belt 10 to the secondary transfer opposing roller 13 via the intermediate transfer belt 10 is supplied to the primary transfer brush 14. NS. Then, the negative electrode property on the photosensitive drum 1 is determined by the current (transfer current) flowing from the intermediate transfer belt 10 to the photosensitive drum 1 based on the potential difference between the potential of the photosensitive drum 1 and the potential of the intermediate transfer belt 10 in the primary transfer unit T1. The toner is first transferred onto the intermediate transfer belt 10.

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

Further, the primary transfer brush 14, the secondary transfer opposed roller 13, and the tension roller 12 are electrically grounded (connected to the ground) via a second Zener diode 17, which 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 in the opposite direction to the first Zener diode 15. That is, the anode side of the second Zener diode 17 is connected to the first Zener diode 15, and the cathode side is 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 diode are used in order to allow a substantially uniform current to flow through the primary transfer portions T1 without being affected by the variation in the electrical resistance of the primary transfer brush 14. Resistance elements 6a to 6d are connected to 15 respectively. In this embodiment, a resistance element of 50 MΩ was used as each resistance element 6.

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

FIG. 2 is a circuit configuration diagram relating to the transfer configuration in this embodiment. The power supply device 60 has 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 of the first polarity to the current supply member, respectively. Further, the power supply device 60 has 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 supply 63 is an example of a second power supply that applies a voltage having a second polarity opposite to the first polarity to the current supply member. Further, the first bleeder resistor 64 is connected in parallel to the secondary transfer power supply 61, and the second bleeder resistor 65 is connected in parallel to the charging power supply 62. When a negative voltage is applied from the negative power supply 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, the third bleeder resistor 66 is connected in parallel to the negative power supply 63. 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. The resistance element 67 in FIG. 2 shows the electrical resistance of the secondary transfer unit T2, which is the combined resistance of the secondary transfer roller 20 and the intermediate transfer belt 10. Further, the resistance element 68 in FIG. 2 shows the electric resistance of the toner charging portion Ch, which is the combined resistance of the charging brush 16 and the intermediate transfer belt 10. Since the electrical resistance values of the secondary transfer unit T2 and the toner charging unit Ch change depending on the environment and the life state (whether the life period is the beginning or the end), the variable resistance elements 67 and 68 are shown in FIG. It is described as.

When a positive voltage equal to or higher than a predetermined value 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 point X in FIG. 2 is approximately the first Zener. It is held at + 750V, which is the breakdown voltage of the diode 15. Then, the potential of each primary transfer brush 14 is maintained at + 750 V, which is the yield voltage, and the intermediate transfer belt 10 in the portion in contact with each primary transfer brush 14, that is, the intermediate transfer belt 10 in each primary transfer unit 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 unit T1, a sufficient transfer current flows from the intermediate transfer belt 10 to each photosensitive drum 1 to stabilize the transfer current. Primary transcription 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 at the same time. Then, in this embodiment, at the time of the primary transfer, 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. Further, substantially the same positive current flows through each of the primary transfer brushes 14.

5. Cleaning operation of the intermediate transfer belt 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 of the vicinity of the secondary transfer unit T2.

In this embodiment, the toner of the toner image primaryly transferred on 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 in 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 residual secondary transfer toner remaining on the intermediate transfer belt 10 after the secondary transfer contains toner having both positive and negative polarities due to the influence of the positive voltage applied to the secondary transfer roller 20. Mixed. Further, due to the influence of the unevenness of the surface of the recording material P, the secondary transfer residual toner locally overlaps a plurality of layers and remains on the intermediate transfer belt 10 (A in FIG. 3). The secondary transfer residual toner deposited 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. It is scattered at the height of (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 controlled to a constant current with a predetermined target current (the target current is 10 μA in this embodiment). As a result, the secondary transfer residual toner on the intermediate transfer belt 10 is charged to a positive electrode property having a polarity opposite to the normal charging polarity of the toner when passing through the toner charging portion Ch. In this embodiment, the positively charged secondary transfer residual toner is transferred to the negatively charged photosensitive drum 1a in the primary transfer portion T1a of the first image forming unit Sa, and is collected by the cleaning device 5a. Will be done.

The negative electrode toner that could not be fully charged to the positive electrode by 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 described later during the post-processing operation at the end of the job. The discharged toner is transferred to the photosensitive drum 1a in the primary transfer unit T1a of the first image forming unit Sa in this embodiment by supplying a negative current to the primary transfer brush 14 as described later. , Collected by the cleaning device 5a.

6. Recovery operation By using the ion-conducting intermediate transfer belt 10 in which the main conductive agent is ion-conducting, electricity is compared with the case where the electron-conductive intermediate transfer belt 10 in which the main conductive agent is electron-conductive is used. There are advantages such as being able to keep the manufacturing tolerance of the resistor small.

However, when the ionic conductive intermediate transfer belt 10 is used, if repeated image formation is performed, an appropriate transfer current may not flow in the primary transfer unit 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 the anion and the cation responsible for the ionic conductivity receive a force by the electric field. Then, the positively charged cation moves in the direction of the electric field, and the negatively charged anion moves in the direction opposite to the electric field. During the image drawing 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, the cation moves to the outer peripheral surface side of the intermediate transfer belt 10, and the anion moves to the inner peripheral surface side of the intermediate transfer belt 10. Then, when the image forming operation is continuously performed, the cation continuously receives a force and moves to the outer peripheral surface side of the intermediate transfer belt 10, and the anion continues to the inner peripheral surface side of the intermediate transfer belt 10. Move by receiving force. When ions (conductive agents) are unevenly distributed in the intermediate transfer belt in this way, the electrical resistance of the intermediate transfer belt 10 fluctuates, an appropriate transfer current does not flow, and 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, the cations are blocked by the coat layer 10B, and the outer peripheral surface of the intermediate transfer belt 10 is blocked. Does not precipitate in. However, since the coat layer is not provided on the back surface of the intermediate transfer belt 10, in some cases, anions may precipitate on the back surface of the intermediate transfer belt 10 to form a compound and lose conductivity. Further, the compound due to the anion deposited on the back surface of the intermediate transfer belt 10 adheres to the primary transfer brush 14, and causes an increase in the electrical resistance of the primary transfer brush 14. As a result, the transfer current in the primary transfer unit T1 may be insufficient, and transfer defects may easily occur.

On the other hand, the image forming apparatus 100 of this embodiment executes the following "recovery operation" at the time of non-image forming. That is, in the recovery operation, a negative voltage, which is a voltage having the opposite polarity to that at the time of the primary transfer, is applied from the power supply device 60 to the secondary transfer roller 20 and the charging brush 16, and the direction is opposite to that at the time of the primary transfer. Supply the negative current of. As a result, the uneven distribution of ions (conductive agent) in the intermediate transfer belt 10 caused by the image-forming operation is alleviated, the electric resistance of the intermediate transfer belt 10 fluctuates, and the electric resistance of the primary transfer brush 14 increases due to the precipitation of the conductive agent. It can be suppressed. In particular, in this embodiment, the image forming apparatus 100 executes a recovery operation during each job post-processing operation (post-rotation process). However, the recovery operation may be executed for each of a plurality of jobs as long as the uneven distribution of ions (conductive agents) in the intermediate transfer belt can be sufficiently alleviated. Further, the recovery operation can be executed in a paper-to-paper process, a pre-processing operation (pre-rotation process), a pre-multi-rotation process, or the like during non-image formation.

As described above, it is effective to periodically pass a current in the primary transfer brush 14 in the direction opposite to that at the time of the primary transfer in order to alleviate the uneven distribution of ions (conductive agents) in the intermediate transfer belt 10. However, when the voltage applied to the primary transfer brush 14 for flowing the reverse current is a fixed value, a desired current is applied to fluctuations in the electrical resistance of the intermediate transfer belt 10 due to environmental fluctuations and deterioration over time. May not be able to flow. As a result, transfer defects due to uneven distribution of the above-mentioned ions (conductive agents) 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 supplied to the second Zener diode 17 so that a negative voltage whose absolute value is equal to or greater than the breakdown voltage of the second Zener diode 17 is applied. A configuration that outputs from the device 60 is conceivable. However, in such a configuration, the voltage applied to the primary transfer brush 14 during the recovery operation becomes a fixed value, the negative current cannot sufficiently flow as described above, and the ions (conductive agent) in the intermediate transfer belt 10 are formed 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. The voltage is output from the power supply device 60. In this case, when the negative voltage is output by the negative power supply 63, the second Zener diode 17 cuts off the negative current, so that the negative current does not flow to the ground. Then, 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. A substantially same negative current flows through each of the primary transfer brushes 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 blocking means for cutting off the negative current flowing to the ground when a negative voltage is applied to the primary transfer brush 14.

4 (a) and 4 (b) show substantially equivalent circuits regarding the transfer configuration during the primary transfer and the recovery operation in the image forming apparatus 100 of this embodiment, respectively. The arrow in the figure indicates 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, at the time of primary transfer, a voltage is applied from the power supply device 60 so that a positive voltage having an absolute value equal to or higher than the breakdown voltage of the first Zener diode 15 is applied to the first Zener diode 15. It 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 kept substantially constant at the yield voltage. On the other hand, as shown in FIG. 4B, during the recovery operation, the power supply device has a voltage such that 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. Output from 60, almost all negative current flows through 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 electric resistance of the intermediate transfer belt 10 due to the environmental fluctuation and the 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 controlled by a constant current 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.

Further, the output of the power supply device 60 during the recovery operation is controlled at a constant voltage with a voltage value set in advance so that a desired current flows according to fluctuations in the electrical resistance of the intermediate transfer belt 10 due to the environment or deterioration over time. You may. For example, when executing the print 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 powers the power supply during the recovery operation based on the information in which the environmental information preset and stored in the memory 52 and the recovery operation condition (voltage value at which a desired current flows) are related. The output voltage value of the device 60 can be determined. Further, for example, when the control unit 50 executes the print operation, the control unit 50 acquires the count value of the number of prints by the counter 80 at least before the start of the recovery operation. Then, the control unit 50 recovers the operation based on the information in which the count value of the counter 80 preset and stored in the memory 52 and the condition of the recovery operation (voltage value through which a desired current flows) are related. The output voltage value of the power supply device 60 at the time can be determined. 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. Effect Next, the result of verifying the effect of this example will be described. Table 1 shows the results of performing durability tests on this example and comparative examples and evaluating the increase in electrical resistance of the primary transfer unit T1.

In the durability test, when the number of prints is 0K, 25K, 50K (1K is 1000), the negative current value flowing through each primary transfer brush 14 in the recovery operation (negative current value flowing through each primary transfer brush 14a to 14d). The average value of) was examined. Further, the electric resistance value of each primary transfer unit T1 (the average value of the electric resistance values of each primary transfer unit T1a to T1d) at the time of the number of prints was examined. In addition, the primary transferability at the time of the number of prints 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) after each image formation. In this embodiment, a Zener diode having a breakdown voltage of 3000 V is used as the second Zener diode 17. Further, in this embodiment, a negative voltage whose absolute value is smaller than the breakdown voltage of the second Zener diode 17, which is set so that a desired negative current (about -13 mA) flows in advance according to the number of prints during 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 at approximately −2000 V. Then, in the comparative example, during the recovery operation, a negative voltage having an absolute value equal to or higher than the yield voltage of the second Zener diode 17 was applied from the power supply device 60 regardless of the number of prints. Except for the above points, the configuration and operation of the image forming apparatus 100 are substantially the same in this example and the comparative example.

The current flowing through each primary transfer brush 14 during the recovery operation and the electric resistance value of each primary transfer unit 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. The primary transferability was evaluated according to the following evaluation criteria by first transferring a predetermined evaluation image from the photosensitive drum 1 to the intermediate transfer belt 10 and visually observing the toner image on the intermediate transfer belt 10. When almost all the toner of the evaluation image could be primarily transferred, it was evaluated as ◯ (good). In addition, when the primary transfer of a part of the toner of the evaluation image could not be performed, the value was set to Δ (in some cases, a problematic level). In addition, when almost all the toner of the evaluation image could not be primarily transferred, it was evaluated as x (defective).

In the comparative example, a negative current of -13.5 μA could be passed at 0 K sheets (early endurance), but up to -10.2 μA at 25 K sheets and -8.5 μA at 50 K sheets (end of endurance). The negative current has decreased. Further, in the comparative example, the electric resistance of the primary transfer unit T1 increased from 83 MΩ at 0 K sheets to 117 MΩ at 25 K sheets and 148 MΩ at 50 K sheets. Further, in the comparative example, although good primary transferability was obtained at 0K sheets, the primary transferability decreased as the number of prints increased to 25K sheets and 50K sheets.

On the other hand, in this embodiment, almost a desired negative current flows from 0K sheets (early endurance) to 50K sheets (end of endurance), and the electrical resistance of the primary transfer unit T1 is 83 MΩ at 0K sheets. Even at the time of 50K sheets, it was possible to suppress the rise to 103MΩ. Further, in this example, good primary transferability was obtained from 0 K sheets to 50 K sheets.

As described above, according to the present embodiment, a desired negative current can be stably passed through the primary transfer brush 14 while suppressing the influence of fluctuations in the electrical resistance of the ionic conductive intermediate transfer belt 10. As a result, the uneven distribution of ions (conductive agent) in the intermediate transfer belt 10 caused by the image-forming operation can be sufficiently alleviated, and transfer defects due to the improper transfer current not flowing can be suppressed.

[Example 2]
Next, other examples of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of Example 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Example 1 are designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 5 is a schematic cross-sectional view of the image forming apparatus 100 in this embodiment. In this embodiment, as a current blocking means for blocking the negative current flowing to the ground when a negative voltage is applied to the primary transfer brush 14, the diode 18 which is a rectifying element is used instead of the second Zener diode 17 in the first embodiment. Is used. In this embodiment, the primary transfer brush 14, the secondary transfer opposed 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 cuts off the negative current flowing from the Zener diode 15 to the ground. That is, the anode side of the diode 18 is connected to the Zener diode 15, and the cathode side is connected to the ground.

FIG. 6 is a circuit configuration diagram relating to the transfer configuration in this embodiment. When a positive voltage equal to or higher than a predetermined value 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 point X in FIG. 6 is approximately the breakdown voltage value of the Zener diode 15. It is held at + 750V. By the action of this voltage, the primary transfer is performed in the same manner as in Example 1. On the other hand, when a negative voltage is output by the negative power supply 63, the diode 18 cuts off the negative current, so that the negative current does not flow to the ground. Then, 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. A substantially same negative current flows through each of the primary transfer brushes 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.

The substantially equivalent circuits relating to the transfer configurations during the primary transfer and the recovery operation in the image forming apparatus 100 of the present embodiment are the same as those of FIGS. 4 (a) and 4 (b) described in the first embodiment, respectively. That is, as shown in FIG. 4A, at the time of primary transfer, the power supply device 60 outputs a voltage such that a positive voltage whose absolute value is equal to or higher than 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 yield 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 the negative current flows through 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 electric resistance of the intermediate transfer belt 10 due to the environmental fluctuation and the deterioration with time, and a desired negative current can be passed through the primary transfer brush 14. In this embodiment, 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 effect as that of the first embodiment can be obtained, and cost reduction and miniaturization can be achieved by using a diode which is cheaper and smaller than the Zener diode.

[Example 3]
Next, other examples of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of Example 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Example 1 are designated by the same reference numerals and detailed description thereof will be omitted.

In this embodiment, the value of the target current during the recovery operation is changed according to the fluctuation of the electric resistance of the intermediate transfer belt 10 due to the environment and deterioration over time.

For example, when executing the print 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 in which the environmental information preset and stored in the memory 52 and the condition of the recovery operation (target current value) are related to each other. Can be done.

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 in which the temperature is higher than 25 ° C. and the relative humidity is higher than 60%. The NN environment is an environment in which the temperature is higher than 20 ° C. and 25 ° C. or lower, and the relative humidity is higher than 30% and 60% or lower. The LL environment is an environment in which the temperature is 20 ° C. or lower and the relative humidity is 30% or less. The mobility of ions in the intermediate transfer belt 10 is higher in a high temperature and high humidity environment and smaller in a low temperature and low humidity environment. Therefore, by passing a larger 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 formation operation can be alleviated more efficiently in the recovery operation for a predetermined time. There is.

In this way, 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 means. In this embodiment, the conditions for recovery operation were changed based on the temperature and relative humidity of the environment, but the mobility of ions in the intermediate transfer belt 10 may have a sufficient correlation with at least one of temperature and humidity. be. Therefore, the conditions of the recovery operation can be changed based on at least one of the temperature and humidity of the environment. Typically, the absolute value of the current supplied in the recovery operation when the temperature is lower than the first temperature is lower than the absolute value of the current supplied in the recovery operation when the temperature is the first temperature. Make it larger. Further, the absolute value of the current supplied in the recovery operation when the humidity is lower than the first humidity is larger than the absolute value of the current supplied in the recovery operation when the humidity is the first humidity. To be.

Further, for example, when the control unit 50 executes the print operation, the control unit 50 acquires the count value of the number of prints 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 in which the count value of the counter 80 preset and stored in the memory 52 and the condition of the recovery operation (target current value) are related to each other. Can be decided.

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, and the count value is divided into 0K or more and less than 10K, 10K or more and less than 25K, and 25K or more and 50K or less. The uneven distribution of ions in the intermediate transfer belt 10 tends to become more remarkable as the amount of the intermediate transfer belt 10 used increases. Therefore, by passing a larger amount of current in the recovery operation as the intermediate transfer belt 10 approaches the end of durability than the initial end of durability, the uneven distribution of ions (conductive agent) generated during the image formation operation is more efficient in the recovery operation for a predetermined time. It may be alleviated.

In this way, 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 means. In this embodiment, the recovery operation conditions are changed based on the number of prints as information that correlates with the usage amount of the intermediate transfer belt 10, but if the information correlates with the usage amount of the intermediate transfer belt 10, for example, rotation. The number of times, rotation time, etc. may be used. Typically, recovery in the case of a second usage amount larger 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 is larger than the first usage amount. Make sure that the absolute value of the current supplied during operation is larger.

The current supplied to the primary transfer brush 14 in the recovery operation may be changed based on both the environment and the amount of the intermediate transfer belt 10 used. Further, 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 recovery operation may be changed depending on the environment and the amount of the intermediate transfer belt 10 used as described above. ..

As described above, in this embodiment, the same effect as in Example 1 can be obtained, and the ions (conductive agent) in the intermediate transfer belt 10 can be more efficiently used depending on the environment and the life state of the intermediate transfer belt 10. Uneven distribution can be alleviated.

[others]
Although the present invention has been described above with reference to specific examples, the present invention is not limited to the above-mentioned examples.

In the above-described 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, in a configuration in which a cleaning member for scraping the secondary transfer residual toner from the intermediate transfer belt is provided as a cleaning means for the intermediate transfer belt and no charging member is provided, the current supply member may be only the secondary transfer member. good.

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

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

1 Photosensitive drum 10 Intermediate transfer belt 13 Secondary transfer facing roller 14 Primary transfer brush 15 Zener diode for positive voltage 16 Charging brush 17 Zener diode for negative voltage 18 Diode for negative voltage 20 Secondary transfer roller 60 Power supply

Claims (8)

An image carrier that supports a toner image and
An intermediate transfer belt with ionic conductivity and
A primary transfer member that contacts the 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 that comes into contact with the outer peripheral surface of the intermediate transfer belt, and
An opposing member that faces the current supply member via the intermediate transfer belt, contacts the inner peripheral surface of the intermediate transfer belt, and is electrically connected to the primary transfer member.
A first power source that applies a voltage of the first polarity to the current supply member, and
A second power supply that applies a voltage of a second polarity that is opposite to the first polarity to the current supply member, and
A voltage maintaining means electrically connected between the primary transfer member and the opposing member and the ground, and the primary transfer member of the primary transfer member when a voltage is applied from the first power source to the current supply member. Voltage maintenance means to maintain potential and
Wherein a constant voltage element that is electrically connected between the ground and the primary transfer member and the opposing member, and the constant voltage element when the voltage on the current supply member from the second power is applied A constant voltage element that cuts off the current between ground and
A voltage is applied to the current supply member from the first power source to execute the primary transfer, and a voltage is applied to the current supply member from the second power source when the primary transfer is not performed. A control means for executing a recovery operation for alleviating the uneven distribution of the conductive agent in the intermediate transfer belt caused by performing the primary transfer, and
Have,
At the time of the primary transfer, the voltage applied to the primary transfer member is held at a predetermined voltage by the voltage maintaining means, and at the time of the recovery operation, the voltage applied to the primary transfer member is generated by the output of the second power supply. Decided ,
The control means controls the output of the second power supply so that a voltage whose absolute value is smaller than the yield voltage of the constant voltage element is applied to the constant voltage element during the recovery operation. Forming device. The constant voltage element is the first constant voltage element.
The voltage maintaining means is a second constant voltage element, and is
The claim is characterized in that, at the time of the primary transfer, the control means controls the output of the first power supply so that a voltage whose absolute value is equal to or higher than the yield voltage of the voltage maintenance means is applied to the voltage maintenance means. Item 1. The image forming apparatus according to item 1. The image forming apparatus according to claim 1 or 2 , wherein the control means controls the output of the second power source so that a predetermined current flows through the primary transfer member during the recovery operation. The image forming apparatus according to claim 3 , further comprising an environment detecting means for detecting the environment, wherein the control means changes the predetermined current based on the detection result of the environment detecting means. 3. The third aspect of the present invention is the third aspect of the present invention, which comprises a counting means for counting information correlating with the amount of the intermediate transfer belt used, and the control means changes the predetermined current based on the counting result of the counting means. The image forming apparatus according to the description. The image forming apparatus according to any one of claims 1 to 5 , 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 a toner image is secondarily transferred from the intermediate transfer belt to a recording material. The image forming apparatus according to any one of claims 1 to 5 , wherein the image forming apparatus is a charging member that charges the toner remaining in the surface. The image forming apparatus according to any one of claims 1 to 7 , wherein the primary transfer member is a brush-shaped member.

Images