Image forming device

Abstract

To provide an image forming apparatus that can suppress defective electrification caused by toner moving from a transfer member to a photoreceptor during an operation to clean the transfer member.SOLUTION: An image forming apparatus 100 has a photoreceptor 1, an electrifying member 2, an electrostatic image forming unit 4, a developing device 3, a transfer member 5, a transfer power supply E3, a brush member 10, a brush power supply E4, and a control unit 150 that can execute an operation to clean the transfer member 5. The control unit 150 controls the cleaning operation to have a first operation to form a potential difference at which toner electrified to have a normal polarity between the transfer member 5 and the photoreceptor 1 moves from the transfer member 5 toward the photoreceptor 1, and a second operation to form a potential difference at which toner electrified to have a normal polarity between the brush member 10 and the photoreceptor 1 moves from the photoreceptor 1 toward the brush member 10.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, such as a printer, a copying machine, or a facsimile machine, that uses an electrophotographic method. [Background technology]

[0002] In an electrophotographic image forming apparatus, the surface of a rotatable photoconductor such as a photoconductor drum is uniformly charged, and the charged surface of the photoconductor is exposed to light according to image information, forming an electrostatic image on the photoconductor. The electrostatic image on the photoconductor is then developed by supplying toner, forming a toner image on the photoconductor. The toner image on the photoconductor is then transferred onto a recording material such as paper. The toner image on the photoconductor is transferred onto a recording material passing through the transfer section by applying a voltage to a transfer member that contacts the surface of the photoconductor to form a transfer section. In addition, the toner remaining on the photoconductor after transfer (transfer residual toner) is removed from the photoconductor and collected.

[0003] As a charging method for charging the surface of a photoconductor, there is a method in which a charging member such as a conductive charging roller is brought into contact with the surface of the photoconductor and a voltage is applied to the charging member to charge the surface. This method is widely used from the viewpoints of environmental friendliness (low ozone generation), space efficiency, charging stability, etc. However, in this method, when a large amount of transfer residual toner is present locally on the photoconductor, the transfer residual toner may adhere to the charging member, resulting in uneven charging of the surface of the photoconductor. Therefore, a means for dispersing the transfer residual toner on the photoconductor may be provided so that a large amount of transfer residual toner is not present locally on the photoconductor.

[0004] Patent document 1 discloses a configuration in which a brush member is arranged as a scattering member that contacts the surface of the photosensitive member downstream of a transfer unit and upstream of a charging unit in the rotation direction of the photosensitive member to scatter residual toner on the photosensitive member. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-14982 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, by providing a brush member that contacts the surface of the photosensitive body downstream of the transfer unit and upstream of the charging unit in the rotational direction of the photosensitive body, it is possible to prevent residual toner from adhering unevenly to the charging member during image formation, resulting in uneven charging of the surface of the photosensitive body.

[0007] However, even in such a configuration, when a cleaning operation of the transfer member is performed to move the toner adhering to the transfer member from the transfer member to the photosensitive member during non-image formation, the toner that has moved from the transfer member to the photosensitive member may adhere unevenly to the charging member.

[0008] The toner that moves from the transfer member to the photoconductor during the cleaning operation of the transfer member is mainly charged to the normal polarity, which is the charging polarity of the toner during development. This is because a voltage of the opposite polarity to the normal polarity of the toner is applied to the transfer member during image formation, so that the toner on the photoconductor that is charged to the normal polarity is electrostatically attracted to the transfer member. During image formation, "fogging" may occur, in which toner adheres to the non-image area (non-exposed area) on the photoconductor, and of the toner that has caused this fogging, mainly the toner that is charged to the normal polarity adheres to and accumulates on the transfer member between sheets of paper or during pre-rotation.

[0009] In addition, impurities (foreign matter) other than toner, such as fibers and dust from paper powder, which is mainly used as a recording material, also adhere to the transfer member. The toner accumulated on the transfer member is mixed with impurities such as paper powder, and is transferred from the transfer member to the photoconductor in an aggregated state or in a state that easily aggregates during the cleaning operation of the transfer member. If the mixture of toner and impurities such as paper powder passes through the brush member without being dispersed by the brush member, it may be physically rubbed off from the photoconductor by the charging member and adhere unevenly to the charging member. This may cause localized charging failure of the photoconductor, resulting in image defects such as uneven density.

[0010] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS An object of the present invention is to provide an image forming apparatus capable of suppressing poor charging caused by toner that has moved from a transfer member to a photoconductor during a cleaning operation of the transfer member. [Means for solving the problem]

[0011] The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention has a rotatable photoconductor, a charging member that contacts the surface of the photoconductor to form a charging section and charges the surface of the photoconductor at the charging section, an electrostatic image forming section that forms an electrostatic image on the photoconductor charged by the charging member, a developing device that supplies toner charged to a normal polarity to the electrostatic image and forms a toner image on the photoconductor, a transfer member that contacts the surface of the photoconductor to form a transfer section and transfers the toner image on the photoconductor to a recording material passing through the transfer section, a transfer power source that applies a transfer voltage to the transfer member, a brush member that contacts the surface of the photoconductor downstream of the transfer section and upstream of the charging section in the rotation direction of the photoconductor to form a contact section, a brush power source that applies a brush voltage to the brush member, and a control unit that is capable of performing a cleaning operation to move the toner attached to the transfer member from the transfer member to the surface of the photoconductor when the recording material is not in the transfer section, and the control unit This is performed after performing an image forming operation in which a potential difference is formed between the transfer member and the photoconductor such that the toner charged to the normal polarity moves from the photoconductor toward the transfer member, and a potential difference is formed between the brush member and the photoconductor such that the toner charged to the normal polarity moves from the brush member toward the photoconductor. The cleaning operation is performed by removing the toner charged to the normal polarity between the transfer member and the photoconductor. photoreceptor From the above Transfer materialpotential difference that moves toward and a potential difference between the transfer member and the photoconductor such that the toner charged to the normal polarity moves from the transfer member toward the photoconductor. and a first operation in which the normal polarity is formed between the brush member and the photoconductor. Reverse polarity The charged toner Brush material From the above photoreceptor A second operation in which a potential difference is formed such that the ,of In the first operation, the transfer power supply is controlled to apply a voltage to the transfer member. a first transfer voltage having the normal polarity and a second transfer voltage having an absolute value larger than that of the first transfer voltage and having the normal polarity; and in the second operation, the brush voltage having the normal polarity is applied to the brush member by the brush power source. The image forming apparatus is characterized in that the voltage Vcc is applied to the image forming device. Effect of the Invention

[0012] According to the present invention, it is possible to suppress poor charging caused by toner that has moved from the transfer member to the photoconductor during a cleaning operation of the transfer member. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] FIG. 2 is a schematic diagram of a brush member (fixed brush). [Diagram 3] FIG. 2 is a schematic block diagram showing a control mode of the image forming apparatus. [Figure 4] 5A and 5B are schematic diagrams illustrating the state around the photosensitive drum during a cleaning operation. [Diagram 5] FIG. 11 is a timing chart of an example of a cleaning operation. [Figure 6] FIG. 4 is a schematic diagram showing a state around the photosensitive drum during a cleaning operation. [Figure 7] 5A and 5B are schematic diagrams illustrating the state of the periphery of the photosensitive drum and the brush member during a cleaning operation. [Figure 8] 5A and 5B are schematic diagrams illustrating the state of the periphery of the photosensitive drum and the brush member during a cleaning operation. [Figure 9] FIG. 4 is a schematic diagram showing a state around the photosensitive drum during a cleaning operation. [Figure 10] FIG. 11 is a schematic cross-sectional view of another example of an image forming apparatus. [Figure 11] FIG. 2 is a schematic cross-sectional view of a brush member (brush roller). [Figure 12] FIG. 11 is a timing chart of another example of the cleaning operation. [Figure 13] FIG. 4 is a schematic diagram showing a state around the photosensitive drum during a cleaning operation. [Figure 14] FIG. 4 is a schematic diagram showing a state around the photosensitive drum during a cleaning operation. [Figure 15] 5A and 5B are schematic diagrams illustrating the state of the periphery of the photosensitive drum and the brush member during a cleaning operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0015] [Example 1] <Image forming device> 1 is a schematic cross-sectional view of an image forming apparatus 100 according to this embodiment. The image forming apparatus 100 according to this embodiment is a monochrome laser beam printer that employs a cleanerless system and a contact charging system.

[0016] The image forming apparatus 100 has a photosensitive drum 1, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as an image carrier. When an image output operation is started, the photosensitive drum 1 is rotated in the direction of arrow R1 (clockwise direction) in the figure by a drive motor (main motor) serving as a drive means (not shown). In this embodiment, the outer diameter of the photosensitive drum 1 is 24 mm, and the peripheral speed (movement speed of the surface) is 140 mm / sec.

[0017] 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 the charging roller 2, which is a rotatable roller-type charging member serving as a charging means. The charging roller 2 is an elastic roller having a conductive elastic layer provided around a core metal. The charging roller 2 contacts the surface of the photosensitive drum 1 to form a charging portion (charging position) Pa for charging the surface of the photosensitive drum 1. In this embodiment, the charging roller 2 is rotated in the direction of the arrow R2 in the figure (counterclockwise direction) so that the photosensitive drum 1 and the charging roller 2 move in the forward direction at the contact portion between the photosensitive drum 1 and the charging roller 2. Note that a drive motor as a driving means (not shown) for driving the charging roller 2 may be a main motor common to the driving means for the photosensitive drum 1. During charging, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power source E1 (FIG. 3) serving as a charging voltage application means. In this embodiment, during charging, a negative DC voltage is applied to the charging roller 2 as the charging voltage. In this embodiment, the charging voltage is, for example, -1300 V. As a result, in this embodiment, the surface of the photosensitive drum 1 is uniformly charged to a dark potential Vd of -700 V. More specifically, the charging roller 2 charges the surface of the photosensitive drum 1 by discharge occurring in at least one of the minute gaps between the charging roller 2 and the photosensitive drum 1 formed on the upstream side and downstream side of the contact portion with the photosensitive drum 1 in the rotation direction of the photosensitive drum 1. However, in this embodiment, the contact portion between the charging roller 2 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is assumed to be the charging portion Pa.

[0018] The surface of the photosensitive drum 1 that has been charged is scanned and exposed by an exposure device (a laser exposure unit in this embodiment) 4 as an exposure means (electrostatic image forming section), and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. The exposure device 4 repeats exposure of the photosensitive drum 1 in the main scanning direction (rotation axis direction) with a laser beam L modulated according to image data, in the sub-scanning direction (direction of movement of the surface), to form an electrostatic image on the photosensitive drum 1. In this embodiment, the absolute value of the dark area potential Vd of the surface of the photosensitive drum 1 that has been uniformly charged and formed is reduced by exposure by the exposure device 4, and becomes a light area potential Vl of -100V. Here, the position on the photosensitive drum 1 that is exposed by the exposure device 4 in the rotation direction of the photosensitive drum 1 is the exposure area (exposure position) Pb.

[0019] The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by the developing device 3 as a developing means, which supplies the toner t as a developer, and a toner image (developer image) is formed on the photosensitive drum 1. In this embodiment, the toner is a spherical non-magnetic toner (spherical toner) which is a non-magnetic one-component developer having an average particle size of 6.4 μm and an average circularity of 0.98. The toner used in this embodiment preferably has a high average circularity, and more specifically, the average circularity is preferably 0.96 or more. The closer the average circularity is to 1.00, the closer the toner is to a sphere. In other words, the toner used in this embodiment preferably has an average circularity of 0.96 or more and 1.00 or less. The average circularity is used as a simple method for quantitatively expressing the shape of a particle. Here, the average circularity is calculated as follows.

[0020] First, the particle shape is measured using a flow type particle image analyzer FPIA-2100 manufactured by Toa Medical Electronics Co., Ltd., and the circularity is calculated according to the following formula 1.

[0021]

number

[0022] Furthermore, as shown in the following formula 2, the average circularity is defined as the sum of the circularities of all the measured particles divided by the total number of particles.

[0023]

number

[0024] The developing device 3 includes a developing roller 31 as a developer carrier, a toner supply roller 32 as a developer supplying means, a developer storage chamber 33 that stores toner t, an agitating member 35 as an agitating means, and a developing blade 34 as a developer regulating means. The toner stored in the developer storage chamber 33 is agitated by the agitating member 35 and supplied to the surface of the developing roller 31 by the toner supply roller 32. The toner supplied to the surface of the developing roller 31 is uniformly thinned by passing through a contact portion with the developing blade 34, and is negatively charged by frictional charging. The developing roller 31 contacts the surface of the photosensitive drum 1 to form a developing portion (developing position) Pc that supplies toner to the electrostatic image on the photosensitive drum 1. Here, the contact portion between the developing roller 31 and the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1 is the developing portion Pc. In this embodiment, the developing roller 31 is rotated in the direction of the arrow R3 in the figure (counterclockwise direction) so that the photosensitive drum 1 and the developing roller 31 move forward at the contact portion between the photosensitive drum 1 and the developing roller 31. A drive motor as a drive means (not shown) for driving the developing roller 31 may be a main motor common to the drive means for the photosensitive drum 1. The toner carried on the developing roller 31 moves from the developing roller 31 to the photosensitive drum 1 in the developing portion Pc according to the electrostatic image. During development, a predetermined developing voltage (developing bias) is applied to the developing roller 31 by a developing power source E2 (FIG. 3) as a developing voltage application means. In this embodiment, during development, a negative DC voltage is applied to the developing roller 31 as the developing voltage. In this embodiment, toner charged to the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the exposed portion (image portion) on the photosensitive drum 1, the absolute value of the potential of which has been reduced by being exposed after being uniformly charged (reverse development). In this embodiment, the normal charging polarity of the toner during development ("normal polarity") is negative. Note that, although a one-component non-magnetic contact development method is adopted in this embodiment, the present invention is not limited to this embodiment, and a two-component non-magnetic contact development method, a non-contact development method, a magnetic development method, etc. may be adopted.The two-component non-magnetic contact development method uses a two-component developer containing a non-magnetic toner and a magnetic carrier as a developer, and develops by bringing the developer (magnetic brush) carried on a developer carrier into contact with a photoconductor. The non-contact development method is a method of developing by scattering toner from a developer carrier arranged opposite the photoconductor in a non-contact manner onto the photoconductor. The magnetic development method is a method of developing by carrying magnetic toner by magnetic force on a developer carrier that contains a magnet as a magnetic field generating means and is arranged opposite the photoconductor in contact or non-contact manner.

[0025] Opposing the photosensitive drum 1, a transfer roller 5, which is a rotatable roller-type transfer member serving as a transfer means, is disposed. The transfer roller 5 contacts the photosensitive drum 1 to form a transfer portion (transfer position, transfer nip) Pd that transfers a toner image from the photosensitive drum 1 to the recording material S. Here, the contact portion between the transfer roller 5 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is the transfer portion Pd. In this embodiment, the transfer roller 5 is an elastic roller with an outer diameter of 12 mm and a hardness of 30° (Asker-C, 500 gf load) in which an elastic layer made of conductive NBR (nitrile butadiene rubber)-hydrin-based sponge rubber is formed around a core metal. The transfer roller 5 is pressed against the photosensitive drum 1 with a predetermined pressure. In synchronization with the toner image on the photosensitive drum 1, a sheet-like recording material (sheet, transfer material, recording medium) S such as paper or plastic film is transported to the transfer portion Pd from a cassette 6 or the like serving as a recording material storage portion by a transport roller 8 or the like serving as a transport means. Then, the toner image formed on the photosensitive drum 1 is transferred by the action of the transfer roller 5 at the transfer portion Pd onto the recording material S, which is sandwiched between the photosensitive drum 1 and the transfer roller 5 and conveyed to pass through the transfer portion Pd. During the transfer, a predetermined transfer voltage (transfer bias) is applied to the transfer roller 5 by a transfer power source E3 (FIG. 3) as a transfer voltage application means. In this embodiment, during the transfer, a DC voltage of a polarity opposite to the normal polarity of the toner (positive polarity in this embodiment) is applied as the transfer voltage to the transfer roller 5. In this embodiment, the transfer voltage during the transfer (transfer HIGH, described later) is +1000V, for example. Then, the toner image is electrostatically transferred from the photosensitive drum 1 to the recording material S by the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1.

[0026] The recording material S onto which the toner image has been transferred is sent to a fixing device 9 as a fixing means. The fixing device 9 applies heat and pressure to the recording material S carrying the unfixed toner image, thereby fixing (melting and bonding) the toner image to the recording material S. The recording material S onto which the toner image has been fixed is discharged (output) to the outside of the image forming apparatus 100.

[0027] On the other hand, toner (transfer residual toner) remaining on the photosensitive drum 1 without being transferred to the recording material S during transfer is collected by the developing device 3 as described later.

[0028] <Brush parts> Next, the brush member 10 used to collect the residual toner in this embodiment will be described.

[0029] 1, in this embodiment, the image forming apparatus 100 has a brush member 10 that contacts the surface of the photosensitive drum 1 downstream of a transfer portion Pd and upstream of a charging portion Pa in relation to the rotation direction of the photosensitive drum 1 to form a brush contact portion (brush contact position) Pe. Here, the contact portion between the brush member 10 and the photosensitive drum 1 in relation to the rotation direction of the photosensitive drum 1 is considered to be the brush contact portion (toner scattering portion) Pe.

[0030] Fig. 2(a) is a schematic diagram of the brush member 10 in a standalone state, as viewed along its longitudinal direction (substantially parallel to the direction of the rotation axis of the photosensitive drum 1). Fig. 2(b) is a schematic diagram of the brush member 10 in contact with the photosensitive drum 1, as viewed along its longitudinal direction.

[0031] In this embodiment, the brush member 10 has a brush portion formed of a fixed conductive fixed brush 11. The brush member 10 is disposed so that its longitudinal direction is substantially parallel to the rotation axis direction of the photosensitive drum 1. In this embodiment, the fixed brush 11 is formed by weaving conductive threads 11a formed of nylon fibers mixed with a conductive material into a base fabric 11b formed of synthetic fibers containing carbon as a conductive agent. Note that the conductive threads 11a may be made of rayon, acrylic, polyester, or the like, in addition to nylon.

[0032] As shown in FIG. 2(a), when the brush member 10 is in a single state, that is, when no external force is applied to bend the conductive thread 11a, the distance to the tip of the conductive thread 11a exposed from the base fabric 11b is defined as L1. In this embodiment, L1 is 6.5 mm. The brush member 10 is arranged such that the base fabric 11b is fixed to a support member (not shown) installed at a predetermined position of the image forming apparatus 100 by a fixing means such as double-sided tape, and the tip of the conductive thread 11a penetrates into the photosensitive drum 1. In this embodiment, the clearance between the support member and the photosensitive drum 1 is fixed. And, the shortest distance from the base fabric 11b of the brush member 10 fixed to the support member to the photosensitive drum 1 is defined as L2. In this embodiment, the difference between L2 and L1 is defined as the penetration amount of the brush member 10 into the photosensitive drum 1. In this embodiment, the penetration amount of the brush member 10 into the photosensitive drum 1 is 1 mm. In this embodiment, as shown in FIG. 2(a), when the brush member 10 is in a stand-alone state, the length L3 of the brush member 10 in the circumferential direction of the photosensitive drum 1 (hereinafter referred to as the "short direction") is 5 mm. In this embodiment, the length of the brush member 10 in the longitudinal direction is 216 mm. This allows the brush member 10 to come into contact with the entire image forming area (area where a toner image can be formed) on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. In this embodiment, the conductive threads 11a have a thickness of 2 denier and a density of 280 kF / inch. 2 It is.

[0033] The length of the brush member 10 in the short direction is preferably 3 mm or more from the viewpoint of long life. The length of the brush member 10 in the long direction can be changed appropriately according to the maximum paper passing width of the image forming apparatus 100 (the maximum length of the image forming area in the direction of the rotation axis of the photosensitive drum 1). The thickness and density of the conductive threads 11a are 1 to 6 denier and 150 to 350 kF / inch, respectively, from the viewpoint of paper dust collection. 2 It is preferable that:

[0034] Further, a brush power supply E4 (FIG. 3) serving as a brush voltage application means is connected to the brush member 10. During image formation, a predetermined brush voltage (brush bias) is applied to the brush member 10 by the brush power supply E4. In this embodiment, during image formation, a negative polarity DC voltage is applied to the brush member 10 as a brush voltage. In this embodiment, the brush voltage during image formation (brush HIGH_1, described later) is, for example, −300 V.

[0035] <Recovery of residual toner after transfer> Next, the recovery of transfer residual toner during image formation in this embodiment will be described.

[0036] Most of the transfer residual toner is positively charged toner, but negatively charged toner is also mixed in. During image formation, the surface of the photosensitive drum 1 is charged to a dark potential Vd of -700V. The image area on the photosensitive drum 1 is exposed by the exposure device 4 to a light potential Vl of -100V. In addition, the non-image area on the photosensitive drum 1 also becomes approximately -100V by passing through the transfer portion Pd due to discharge between the transfer roller 5, to which a transfer voltage of +1000V is applied, and the photosensitive drum 1. Therefore, the surface potential of the photosensitive drum 1 that reaches the brush contact portion Pe during image formation is approximately -100V. The positively charged toner among the transfer residual toner is electrostatically attracted to the brush member 10 at the brush contact portion Pe due to the potential difference between the brush voltage (-300V) and the surface potential of the photosensitive drum 1 (approximately -100V), and is primarily collected by the brush member 10. On the other hand, the negatively charged toner among the residual toner particles passes through the brush contact portion Pe while being electrostatically attracted to the photosensitive drum 1 due to the potential difference between the brush voltage (-300 V) and the surface potential of the photosensitive drum 1 (approximately -100 V) at the brush contact portion Pe.

[0037] In this embodiment, the image forming apparatus 100 has a pre-exposure device 7 as a discharging means for discharging the photosensitive drum 1 downstream of the brush contact portion Pe and upstream of the charging portion Pa in the rotation direction of the photosensitive drum 1. The pre-exposure device 7 optically discharges the surface potential of the photosensitive drum 1 before it enters the charging portion Pa in order to generate a stable discharge at the charging portion Pa. Discharging includes removing (attenuating) at least a part of the charge. Here, the position exposed (discharged) by the pre-exposure device 7 in the rotation direction of the photosensitive drum 1 is the discharging portion Pf. The toner that has passed through the brush contact portion Pe passes through the discharging portion Pf and is stably charged to a negative polarity by uniform discharge at the charging portion Pa.

[0038] The negative toner that has passed through the charging section Pa is sent to the developing section Pc as the photosensitive drum 1 rotates. In the non-image area (non-exposed area), the negative toner sent to the developing section Pc moves to the developing roller 31 due to the potential difference between the dark area potential (Vd) of the surface of the photosensitive drum 1 and the developing bias (Vdc), and is then collected by the developing device 3. On the other hand, in the image area (exposed area), the negative toner sent to the developing section Pc does not move to the developing roller 31 due to the potential difference between the light area potential (Vl) of the surface of the photosensitive drum 1 and the developing bias (Vdc). This toner is sent as it is to the transfer section Pd as the photosensitive drum 1 rotates as the toner of the image area, and is transferred to the recording material S. The developing bias (Vdc) is set to a potential between the dark area potential Vd and the light area potential Vl.

[0039] <Image output operation> In this embodiment, the image forming apparatus 100 executes an image output operation (job), which is a series of operations for forming an image on a single or multiple recording materials S, in response to a single start instruction from an external device (not shown) such as a personal computer. A job generally includes an image forming process (printing process), a pre-rotation process, a paper-interval process in the case of forming an image on multiple recording materials S, and a post-rotation process. The image forming process is a period during which an electrostatic image is actually formed on the photosensitive drum 1, the electrostatic image is developed (a toner image is formed), the toner image is transferred, the toner image is fixed, and the image forming time refers to this period. More specifically, the timing during image formation differs depending on the positions at which the electrostatic image is formed, the toner image is formed, the toner image is transferred, the toner image is fixed, and the like. The pre-rotation process is a period during which a preparatory operation is performed before the image forming process. The paper-interval process is a period corresponding to the interval between recording materials S when the image forming process is performed continuously on multiple recording materials S (during continuous image formation). The post-rotation process is a period during which an arranging operation (preparatory operation) is performed after the image forming process. The non-image forming time is a period other than the image forming time, and includes the above-mentioned pre-rotation process, inter-sheet process, post-rotation process, and further the pre-multiple-rotation process which is a preparatory operation when the image forming apparatus 100 is turned on or when returning from a sleep state. In this embodiment, at a predetermined timing during the non-image forming time, a cleaning operation of the transfer roller 5, which will be described later, is executed to move toner and the like adhering to the transfer roller 5 from the transfer roller 5 to the photosensitive drum 1 and clean the transfer roller 5.

[0040] <Control mode> 3 is a schematic block diagram showing the control mode of the main parts of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 is provided with a control unit 150. The control unit 150 has a CPU 151 as an arithmetic control means which is a central element for performing arithmetic processing, a memory (storage element) 152 such as a ROM or RAM as a storage means, an input / output unit (not shown) for controlling the transmission and reception of signals between various elements connected to the control unit 150, and the like. The RAM stores the detection results of the sensors, the arithmetic results, and the like, and the ROM stores a control program, a data table obtained in advance, and the like.

[0041] The control unit 150 is a control unit that comprehensively controls the operation of the image forming apparatus 100. The control unit 150 controls the transmission and reception of various electrical information signals, drive timing, and the like, to execute a predetermined image formation sequence. The control unit 150 is connected to each unit of the image forming apparatus 100. For example, in relation to this embodiment, the control unit 150 is connected to a charging power source E1, a developing power source E2, a transfer power source E3, a brush power source E4, and the like. The control unit 150 controls the ON / OFF and output values ​​of these various power sources E1, E2, E3, and E4, and executes a cleaning operation of the transfer roller 5, which will be described later.

[0042] <Transfer roller cleaning operation> Next, the cleaning operation (cleaning mode) of the transfer roller 5 in this embodiment will be described.

[0043] In the image forming apparatus 100, toner adheres to the non-image area (non-exposed area) on the photosensitive drum 1, resulting in "fogging." The toner that has caused this fogging adheres to the transfer roller 5, for example, during the inter-paper step or pre-rotation step. During the inter-paper step or pre-rotation step, the same transfer voltage of positive polarity, which is the opposite polarity to the normal polarity of the toner, as during image formation, is applied to the transfer roller 5. Therefore, the toner that has caused the fogging and is charged to the negative polarity, which is the normal polarity, mainly adheres to and accumulates on the transfer roller 5. On the other hand, the toner that has caused the fogging and is charged to the positive polarity, which is the opposite polarity to the normal polarity, does not adhere to the transfer roller 5 and remains on the photosensitive drum 1, and is primarily collected by the brush member 10, similar to the transfer residual toner.

[0044] 4 is a schematic diagram showing the state around the photosensitive drum 1 in the inter-sheet step when a job of continuous image formation is performed in which images are continuously formed on a plurality of recording materials S. As shown in FIG. 4, negative toner t and impurities D such as paper powder are attached to the transfer roller 5, and positive toner is attached to the brush member 10. If toner adheres to and accumulates on the transfer roller 5, it can cause back stains on the recording material S. Therefore, in this embodiment, the image forming apparatus 100 performs a cleaning operation of the transfer roller 5 to move the toner attached to the transfer roller 5 from the transfer roller 5 to the photosensitive drum 1 in the post-rotation step as a non-image forming time.

[0045] As described above, impurities (foreign matter) D other than toner, such as fibers and dust from paper powder mainly used as the recording material S, also adhere to the transfer roller 5. The toner accumulated on the transfer roller 5 mixes with impurities D such as paper powder, and moves from the transfer roller 5 to the photosensitive drum 1 in an aggregated state or in a state that easily aggregates during the cleaning operation of the transfer roller 5. If the mixture of toner and impurities D such as paper powder passes through the brush member 10 without being dispersed by the brush member 10, it may adhere unevenly to the charging roller 2 by being physically scraped off from the photosensitive drum 1 by the charging roller 2. This may cause localized charging failure of the photosensitive drum 1, resulting in image defects such as uneven density.

[0046] Therefore, in this embodiment, during the cleaning operation of the transfer roller 5, a mixture of the negative toner transferred from the transfer roller 5 to the photosensitive drum 1 and impurities D such as paper powder is primarily collected by the brush member 10, and a period is provided for separating the negative toner from the impurities D such as paper powder. Then, after that, the negative toner, separated from the impurities D such as paper powder and sufficiently dispersed, is discharged from the brush member 10 onto the photosensitive drum 1, passed through the charging section Pa, and collected by the developing device 3. This will be described in more detail below.

[0047] Fig. 5 is a timing chart of the cleaning operation of the transfer roller 5 executed in the post-rotation process in this embodiment. In this embodiment, the cleaning operation of the transfer roller 5 is executed by the control unit 150 controlling the operation of each unit of the image forming apparatus 100 according to the timing chart of Fig. 5. For convenience, the voltage applied to the transfer roller 5 by the transfer power source E3 at times other than during transfer may also be referred to as the "transfer voltage".

[0048] Timing T1: Timing T1 is the timing when the image forming process ends and the post-rotation process starts. At timing T1, the transfer voltage is switched from the transfer HIGH (+1000V) during image formation to the transfer LOW (-1000V). Here, in this embodiment, the transfer voltage is switched to the transfer LOW (-1000V) at timing T1, but the present invention is not limited to this embodiment. The voltage value of this transfer voltage may be a voltage value that forms an electric field that electrostatically attracts the negative toner to the photosensitive drum 1. More specifically, the voltage value of this transfer voltage may be a voltage value that is higher on the negative polarity side than the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (-700V)) and does not cause discharge between the transfer roller 5 and the photosensitive drum 1. In this embodiment, the voltage value of this transfer voltage is a voltage value that has the same polarity as the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (-700V)) and has an absolute value larger than that of the surface potential of the photosensitive drum 1. In order to sufficiently attract the negative toner to the photosensitive drum 1, the potential difference between this transfer voltage and the surface potential of the photosensitive drum 1 is preferably 200V or more. In this embodiment, the discharge start voltage (discharge threshold) between the transfer roller 5 and the photosensitive drum 1 is about 600V. The surface potential of the photosensitive drum 1 at the transfer portion Pd at this timing is the dark potential Vd (-700V). Therefore, after timing T1, the negative toner accumulated on the transfer roller 5 moves to the photosensitive drum 1 together with impurities D such as paper powder due to the potential difference between the transfer LOW (-1000V) and the surface potential (-700V) of the photosensitive drum 1.

[0049] Meanwhile, the brush voltage remains the same as during image formation, brush HIGH_1 (-300 V). Also, the surface potential of the photosensitive drum 1 at the brush contact portion Pe at this timing is about -100 V, which is the area that received transfer HIGH (+1000 V) during image formation at the transfer portion Pd. Therefore, the positive toner that was primarily collected by the brush member 10 during image formation remains on the brush member 10 without being expelled from the brush member 10 to the photosensitive drum 1.

[0050] FIG. 6 is a schematic diagram showing the state around the photosensitive drum 1 after timing T1. In FIG. 6, area A of the photosensitive drum 1 indicates the area of ​​the photosensitive drum 1 that has received the transfer voltage at the transfer portion Pd after the transfer voltage has been switched from transfer HIGH (+1000V) to transfer LOW (-1000V). In other words, FIG. 6 shows the state around the photosensitive drum 1 before area A of the photosensitive drum 1 that has received the transfer LOW (-1000V) at the transfer portion Pd reaches the brush contact portion Pe. As shown in FIG. 6, the negative toner t and impurities D such as paper powder that have been accumulated on the transfer roller 5 move to the photosensitive drum 1. On the other hand, the positive toner t is retained on the brush member 10.

[0051] Timing T2: At timing T2, the area A of the photosensitive drum 1 that has received the transfer LOW (-1000V) at the transfer portion Pd reaches the brush contact portion Pe. At timing T2, the brush voltage is switched from brush HIGH_1 (-300V) to brush HIGH_2 (-200V). The surface potential of the photosensitive drum 1 at the brush contact portion Pe at this timing is the dark potential Vd (-700V). Therefore, the negative toner that has moved from the transfer roller 5 to the photosensitive drum 1 and the impurities D such as paper powder are both temporarily collected by the brush member 10. In addition, the positive toner that has been retained on the brush member 10 is discharged from the brush member 10 to the photosensitive drum 1. Here, in this embodiment, the brush voltage is switched to brush HIGH_2 (-200V) at timing T2, but the present invention is not limited to such an embodiment. The voltage value of the brush voltage may be a voltage value that forms an electric field in which the negative toner is electrostatically attracted to the brush member 10 and the positive toner is electrostatically attracted to the photosensitive drum 1. More specifically, the voltage value of the brush voltage may be a voltage value that is higher on the positive polarity side than the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (-700V)) and does not cause discharge between the brush member 10 and the photosensitive drum 1. Therefore, if the above can be satisfied, the brush voltage does not need to be changed at timing T2. In this embodiment, the brush voltage is changed to increase the potential difference in consideration of the separability of the negative toner and the impurities D such as paper powder. In this embodiment, the voltage value of the brush voltage is a voltage value that has the same polarity as the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (-700V)) and has a smaller absolute value than the surface potential of the photosensitive drum 1. In order to ensure that negative toner is sufficiently attracted to the brush member 10 and positive toner is sufficiently attracted to the photosensitive drum 1, it is preferable that the potential difference between the brush voltage and the surface potential of the photosensitive drum 1 is 200V or more. In this embodiment, the discharge start voltage (discharge threshold) between the brush member 10 and the photosensitive drum 1 is about 600V.

[0052] 7A is a schematic diagram showing the state around the photosensitive drum 1 after timing T2. The positive toner t discharged from the brush member 10 onto the photosensitive drum 1 is photo-discharged at the discharge section Pf, and then is charged to a negative polarity by uniform discharge at the charging section Pa and collected by the developing roller 31. Meanwhile, the negative toner t and impurities D such as paper powder primarily collected by the brush member 10 are electrostatically attracted to the brush member 10 by the potential difference between the brush HIGH_2 (-200V) and the surface potential of the photosensitive drum 1 (-700V), and are rubbed against the photosensitive drum 1.

[0053] FIG. 7(b) is a schematic diagram showing the state inside the brush member 10 at this time. In the brush member 10, negative toner t and impurities D such as paper powder that have moved from the transfer roller 5 to the photosensitive drum 1 are mixed with positive toner t that has been retained in the brush member 10 until then. Here, impurities D such as paper fibers and dust tend to be physically entangled by the conductive threads 11a of the brush member 10 more easily than toner. In particular, in this embodiment, spherical toner is used as the toner. Impurities D such as paper fibers and dust are not spherical in shape, so they are easily physically entangled by the conductive threads 11a. On the other hand, spherical toner is not easily physically entangled by the conductive threads 11a because of its spherical shape, and is easily moved in the gaps of the conductive threads 11a. Furthermore, the toner and impurities D such as paper powder are separated within the brush member 10 by the electric field formed between the brush HIGH_2 (-200V) and the surface potential (-700V) of the photosensitive drum 1, and by the friction caused by the rotation of the photosensitive drum 1. At this time, even toner that does not have a sufficient charge can acquire a negative charge by the friction with the photosensitive drum 1. Furthermore, even after the positive toner that had been staying within the brush member 10 is expelled onto the photosensitive drum 1, the negative toner can maintain a state in which it is less likely to coagulate and is more likely to move within the brush member 10 due to the electric field and the friction.

[0054] In this way, the toner that has moved from the transfer roller 5 to the photosensitive drum 1 and impurities D such as paper powder are both primarily collected by the brush member 10, and the toner and impurities D such as paper powder can be separated by the electric field and friction between the brush member 10 and the photosensitive drum 1.

[0055] Timing T3: Timing T3 is a timing when a predetermined time has elapsed from timing T2 when the area A of the photosensitive drum 1 that has received the transfer LOW (-1000V) at the transfer portion Pd reaches the brush contact portion Pe. At timing T3, the transfer voltage is switched from the transfer LOW (-1000V) to the transfer HIGH (+1000V). In this embodiment, timing T3 can be set as follows. First, it is desired to secure a sufficient time for the negative toner accumulated on the transfer roller 5 during image formation to move to the photosensitive drum 1. It is also desired to secure a sufficient time for the positive toner that has been retained on the brush member 10 to be discharged to the photosensitive drum 1. It is also desired that when the area of ​​the photosensitive drum 1 that has received the transfer HIGH (+1000V) at the transfer portion Pd reaches the brush contact portion Pe, the negative toner in the brush member 10 is sufficiently separated from the impurities D by the electric field and rubbing at the brush contact portion Pe. In this embodiment, the timing T3 is set to be about 1.0 s after the timing T2, taking into consideration the time to expel the positive toner that has stayed on the brush member 10 and the time to separate the negative toner in the brush member 10 from impurities D such as paper dust. The surface potential of the photosensitive drum 1 that has received the transfer HIGH (+1000V) at the transfer portion Pd becomes about -100V. Here, in this embodiment, the transfer voltage is switched to the same transfer HIGH (+1000V) as during image formation at the timing T3, but the present invention is not limited to such an embodiment. The voltage value of this transfer voltage may be any voltage that can make the surface potential of the photosensitive drum 1 higher on the positive polarity side than the brush voltage. More specifically, the voltage value of this transfer voltage may be any voltage value that is higher on the positive polarity side than the surface potential of the photosensitive drum 1 (in this embodiment, the dark area potential Vd (-700V)) and that generates a discharge between the transfer roller 5 and the photosensitive drum 1. For example, it may be switched to a voltage value different from that during image formation, such as transfer HIGH_2 (+1500V). In this embodiment, the voltage value of this transfer voltage has a polarity opposite to that of the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (−700 V)), and has an absolute value greater than that of the surface potential of the photosensitive drum 1 .

[0056] FIG. 8(a) is a schematic diagram showing the state around the photosensitive drum 1 after timing T3. In FIG. 8(a), the area B of the photosensitive drum 1 indicates the area of ​​the photosensitive drum 1 that has received the transfer voltage at the transfer portion Pd after the transfer voltage has been switched from the transfer LOW_2 (-1000V) to the transfer HIGH (+1000V). That is, FIG. 8(a) shows the state around the photosensitive drum 1 before the area B of the photosensitive drum 1 that has received the transfer HIGH (+1000V) at the transfer portion Pd reaches the brush contact portion Pe. As shown in FIG. 8(a), the negative toner and impurities D such as paper powder that have accumulated on the transfer roller 5 have finished moving to the photosensitive drum 1. In addition, the positive toner that has stayed on the brush member 10 has been expelled onto the photosensitive drum 1.

[0057] 8(b) is a schematic diagram showing the state inside the brush member 10 at this time. The negative toner t that has moved from the transfer roller 5 to the photosensitive drum 1 is primarily collected inside the brush member 10. At this time, the negative toner maintains a state in which it is difficult to aggregate and easy to move inside the brush member 10 due to the electric field and friction described above.

[0058] Timing T4: At timing T4, the area B of the photosensitive drum 1 that has received the transfer HIGH (+1000V) at the transfer portion Pd reaches the brush contact portion Pe. At timing T4, the brush voltage is switched from brush HIGH_2 (-200V) to brush HIGH_1 (-300V). At this timing, the surface potential of the photosensitive drum 1 at the brush contact portion Pe is about -100V. Therefore, the negative toner that has been primarily collected by the brush member 10 is discharged from the brush member 10 to the photosensitive drum 1. Meanwhile, the impurities D such as paper powder that are physically entangled by the brush member 10 remain on the brush member 10. Here, in this embodiment, the brush voltage is switched to brush HIGH_1 (-300V) at timing T4, but the present invention is not limited to this embodiment. The voltage value of this brush voltage may be any voltage value that forms an electric field that electrostatically attracts the negative toner that has been primarily collected by the brush member 10 to the photosensitive drum 1. More specifically, the voltage value of this brush voltage may be a voltage value that is negatively higher than the surface potential of the photosensitive drum 1 (approximately -100V in this embodiment) (typically, no discharge occurs between the brush member 10 and the photosensitive drum 1). In this embodiment, the voltage value of this brush voltage is a voltage value that has the same polarity as the surface potential of the photosensitive drum 1 (approximately -100V in this embodiment) and a larger absolute value than the surface potential of the photosensitive drum 1. Note that in order to ensure that negative toner is sufficiently attracted to the photosensitive drum 1, it is preferable that the potential difference between this brush voltage and the surface potential of the photosensitive drum 1 is 200V or more.

[0059] 9 is a schematic diagram showing the state around the photosensitive drum 1 after timing T4. As shown in FIG. 9, the negative toner t discharged from the brush member 10 onto the photosensitive drum 1 passes through the charging section Pa and is collected by the developing roller 31 in a state where the toner particles are not aggregated and are separated from impurities D such as paper powder.

[0060] Timing T5: Timing T5 is a timing when a predetermined time has elapsed from timing T4 when area B of the photosensitive drum 1 that has received transfer HIGH (+1000V) at the transfer portion Pd reaches the brush contact portion Pe. Timing T5 is set to be a timing after substantially all of the negative toner discharged from the brush member 10 onto the photosensitive drum 1 has been collected by the developing roller 31. At timing T5, the various power sources E1 to E4 and drive sources (not shown) such as the main motor (driving motor for the photosensitive drum) and the scanner motor (driving motor for the rotating mirror of the exposure device 4) are turned off, and the post-rotation process ends.

[0061] In this embodiment, the main motor, the transfer voltage, the brush voltage, etc. are turned off at the same timing, but the present invention is not limited to this. For example, the timing may be shifted appropriately depending on the inertia of the motor and the fall time of various voltages.

[0062] <Action and effect> As described above, in this embodiment, the image forming apparatus 100 includes a rotatable photoconductor 1, a charging member 2 that contacts the surface of the photoconductor 1 to form a charging portion Pa and charges the surface of the photoconductor 1 at the charging portion Pa, an electrostatic image forming unit 4 that forms an electrostatic image on the photoconductor charged by the charging member 2, a developing device 3 that supplies toner charged to a normal polarity to the electrostatic image and forms a toner image on the photoconductor 1, and a transfer portion Pd that contacts the surface of the photoconductor 1 to form a transfer portion Pd. The control unit 150 includes a transfer member 5 for transferring a toner image on the photoreceptor 1, a transfer power source E3 for applying a voltage to the transfer member 5, a brush member 10 that contacts the surface of the photoreceptor 1 downstream of the transfer portion Pd and upstream of the charging portion Pa in the rotation direction of the photoreceptor 1 to form a contact portion Pe, a brush power source E4 for applying a voltage to the brush member 10, and a control unit 150 capable of performing a cleaning operation for moving the toner attached to the transfer member 5 from the transfer member 5 to the surface of the photoreceptor 1 when the recording material S is not in the transfer portion Pd. In this embodiment, the control unit 150 controls the cleaning operation to include a first operation (cleaning operation) (T1 to T3) in which a potential difference is formed between the transfer member 5 and the photoreceptor 1 such that the toner charged to the normal polarity moves from the transfer member 5 toward the photoreceptor 1, and a second operation (recovery operation) (T2 to T4) in which a potential difference is formed between the brush member 10 and the photoreceptor 1 such that the toner charged to the normal polarity moves from the photoreceptor 1 toward the brush member 10. In this embodiment, the control unit 150 controls the voltage applied to the transfer member 5 by the transfer power supply E3 in the cleaning operation. Also, in this embodiment, the control unit 150 controls the voltage applied to the brush member 10 by the brush power supply E4 in the cleaning operation.

[0063] Particularly, in this embodiment, the control unit 150 controls the transfer power source E3 to apply to the transfer member 5 a voltage (transfer LOW) that is higher on the normal polarity side of the toner than the potential of the surface of the photoconductor 1 that is charged by the charging member 2 and reaches the transfer portion Pd, and does not cause discharge between the transfer member 5 and the photoconductor 1. In addition, in this embodiment, the control unit 150 controls the brush power source E4 to apply to the brush member 10 a voltage (brush HIGH_2) that is higher on the reverse polarity side of the normal polarity of the toner than the potential of the surface of the photoconductor 1 that passes through the transfer portion Pd and reaches the contact portion Pe, and does not cause discharge between the brush member 10 and the photoconductor 1. In addition, in this embodiment, the control unit 150 controls the second operation to continue for a predetermined time from the time when the tip in the rotation direction of the surface of the photoconductor 1 that passes through the transfer portion Pd in ​​the first operation reaches the contact portion Pd. Here, since it is preferable that the time required for separating the toner of normal polarity in the brush member 10 from impurities D such as paper powder is 500 ms or more, the predetermined time is preferably 500 ms or more, and is typically about 1.0 s. Note that the predetermined time is often sufficient at 3.0 s or less, and is typically 1.5 s or less. In other words, the predetermined time can be about the time it takes for the photoconductor 1 to make 1 to 3 revolutions, typically 2 revolutions. In this embodiment, the control unit 150 also performs a third operation (discharging operation) after the second operation is completed, in which a potential difference is formed between the brush member 10 and the photoconductor 1 such that the toner charged to the normal polarity moves from the brush member 10 toward the photoconductor 1. , discharging period) (T4 to T5). In this embodiment, the control unit 150 controls the brush power source E4 to apply to the brush member 10 a voltage (brush HIGH_1) that is higher on the normal polarity side of the toner than the potential of the surface of the photoconductor 1 that passes through the transfer portion Pd and reaches the contact portion Pe after the first operation is completed, and that is higher on the normal polarity side of the toner than the potential of the surface of the photoconductor 1 that is charged by the charging member 2 and reaches the transfer portion Pd, and that is higher on the reverse polarity side of the normal polarity ...

[0064] In this embodiment, the brush member 10 has a fixed conductive brush portion 11. In this embodiment, when the toner remaining on the surface of the photoconductor 1 after the toner image is transferred from the photoconductor 1 to the recording material S at the transfer portion Pd passes through the contact portion Pe, a voltage (brush HIGH_1) having the same polarity as the normal polarity of the toner is applied to the brush member 10 by the brush power source E4. This voltage (brush HIGH_1) is typically a voltage that does not cause discharge between the brush member 10 and the photoconductor 1. In this embodiment, the toner remaining on the surface of the photoconductor 1 after the toner image is transferred from the photoconductor 1 to the recording material S at the transfer portion Pd is collected by the developing device 3. In this embodiment, the toner has an average circularity of 0.96 or more.

[0065] In this manner, in this embodiment, during the cleaning operation of the transfer roller 5, the negative toner transferred from the transfer roller 5 to the photosensitive drum 1 is primarily collected by the brush member 10. Then, this negative toner is discharged from the brush member 10 onto the photosensitive drum 1 in a state in which it is separated from impurities D such as paper powder by the electric field and friction between the brush member 10 and the photosensitive drum 1 at the brush contact portion Pe. This makes it possible to prevent the toner from coagulating and adhering unevenly to the charging roller 2, and to prevent the occurrence of image defects such as uneven density due to localized charging defects.

[0066] [Example 2] Next, another embodiment 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 embodiment 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 embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0067] FIG. 10 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment. FIG. 11 is a schematic cross-sectional view showing the state of the brush member 10 alone in this embodiment. In this embodiment, the brush member 10 has a brush portion formed of a conductive brush roller 12, which is a rotatable rotating body. In this embodiment, the brush roller 12 is formed by winding a base cloth 12b into which conductive threads 12a are woven, around a core metal 12c. The base cloth 12b is adhered to the core metal 12c by a conductive adhesive as a fixing means. In addition, the core metal 12c is supported by a conductive bearing (not shown), and a brush voltage is applied to the brush roller 12 from a brush power source E4 via this conductive bearing. The base cloth 12b is formed of synthetic fiber containing carbon as a conductive agent, and the conductive threads 12a are formed of nylon fiber mixed with a conductive material.

[0068] 11, when the brush roller 12 is in a standalone state, the distance to the tip of the conductive thread 12a exposed from the base fabric 12b is designated as L4. In this embodiment, L4 is 3 mm. Similarly to the conductive thread 11a of the fixed brush 11 in the first embodiment, the conductive thread 12a of the brush roller 12 in this embodiment has a thickness of 2 denier and a density of 280 kF / inch. 2In this embodiment, the length (outer diameter) of the brush roller 12 in the circumferential direction ("short side direction") of the photosensitive drum 1 is about 11 mm, and the diameter of the core 12c is 5 mm. The conductive thread 12a may be made of rayon, acrylic, polyester, or the like, in addition to nylon. In this embodiment, the clearance between the core 12c and the photosensitive drum 1 is fixed. The difference between the shortest distance from the base fabric 12b fixed to the core 12c to the photosensitive drum 1 and the above L4 is defined as the penetration amount of the conductive thread 12a into the photosensitive drum 1. In this embodiment, the penetration amount of the conductive thread 12a into the photosensitive drum 1 is 1 mm. In this embodiment, the brush roller 12 rotates following the rotation of the photosensitive drum 1.

[0069] The cleaning operation of the transfer roller 5 in this embodiment is the same as that in the first embodiment, and is executed according to the timing chart of FIG.

[0070] In this embodiment, similarly to the first embodiment, during the cleaning operation of the transfer roller 5, the negative toner transferred from the transfer roller 5 to the photosensitive drum 1 is primarily collected by the brush roller 12 constituting the brush member 10. Then, this negative toner is discharged from the brush roller 12 to the photosensitive drum 1 in a state in which it is separated from impurities D such as paper powder by the electric field and friction between the brush roller 12 and the photosensitive drum 1 at the brush contact portion Pe. This makes it possible to prevent the toner from coagulating and adhering unevenly to the charging roller 2, and to prevent the occurrence of image defects such as uneven density due to localized charging defects.

[0071] In this embodiment, the brush member 10 is configured as a rotatable brush roller 12, so that the contact position of the conductive threads 12a with the photosensitive drum 1 changes. Therefore, the residual toner is easily scattered when passing through the brush contact portion Pe. On the other hand, the toner that has moved from the transfer roller 5 to the photosensitive drum 1 can be primarily collected by the brush roller 12 by forming a potential difference between the brush voltage and the surface potential of the photosensitive drum 1.

[0072] In this embodiment, the brush member 10 rotates in accordance with the rotation of the photosensitive drum 1, but the present invention is not limited to this embodiment. For example, in order to improve the scraping performance of impurities D such as paper powder on the photosensitive drum 1, the brush member 10 may be rotationally driven to provide a circumferential speed difference with respect to the photosensitive drum 1, or may be rotationally driven in a counter direction with respect to the photosensitive drum 1. Also, the brush member 10 may be rotationally driven without providing a circumferential speed with respect to the photosensitive drum 1. In other words, the brush member 10 may have a rotatable conductive brush portion 12. The brush portion 12 may be configured to rotate in accordance with the rotation of the photosensitive drum 1, or to be rotationally driven so that the photosensitive drum 1 and the brush portion 12 move in the forward direction at the brush contact portion Pe with or without a speed difference with respect to the circumferential speed of the photosensitive drum 1, or to be rotationally driven so that the photosensitive drum 1 and the brush portion 12 move in the reverse direction at the brush contact portion Pe.

[0073] [Example 3] Next, another embodiment 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 embodiment 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 embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0074] In this embodiment, during the cleaning operation of the transfer roller 5, a period is provided in which the positive toner remaining on the brush member 10 is expelled from the brush member 10 to the photosensitive drum 1 before the negative toner that has moved from the transfer roller 5 to the photosensitive drum 1 reaches the brush contact part Pe. This will be described in more detail below.

[0075] <Transfer roller cleaning operation> Fig. 12 is a timing chart of the cleaning operation of the transfer roller 5 executed in the post-rotation process in this embodiment. In this embodiment, the cleaning operation of the transfer roller 5 is executed by the control unit 150 controlling the operation of each unit of the image forming apparatus 100 according to the timing chart of Fig. 12. For convenience, the voltage applied to the transfer roller 5 by the transfer power source E3 at times other than during transfer may also be referred to as the "transfer voltage".

[0076] Timing T1: Timing T1 is the timing when the image forming process ends and the post-rotation process starts. At timing T1, the transfer voltage is switched from the transfer HIGH (+1000V) during image formation to the transfer LOW_1 (-200V). Here, in this embodiment, the transfer voltage is switched to the transfer LOW_1 (-200V) at timing T1, but the present invention is not limited to such an embodiment. The voltage value of this transfer voltage may be a voltage value that forms an electric field in which the negative toner is electrostatically attracted to the transfer roller 5. More specifically, the voltage value of this transfer voltage may be a voltage value that is higher on the positive polarity side than the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (-700V)) and does not cause discharge between the transfer roller 5 and the photosensitive drum 1. In this embodiment, the voltage value of this transfer voltage is a voltage value that has the same polarity as the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (-700V)) and is smaller in absolute value than the surface potential of the photosensitive drum 1. In order to sufficiently attract the negative toner to the transfer roller 5, it is preferable that the potential difference between this transfer voltage and the surface potential of the photosensitive drum 1 is 200V or more. In this embodiment, the discharge start voltage (discharge threshold) between the transfer roller 5 and the photosensitive drum 1 is about 600V. The surface potential of the photosensitive drum 1 at the transfer portion Pd at this timing is the dark potential Vd (-700V). Therefore, due to the potential difference between the transfer LOW_1 (-200V) and the surface potential of the photosensitive drum 1 (-700V), the negative toner accumulated on the transfer roller 5 maintains a state of being electrostatically attracted to the transfer roller 5 together with impurities D such as paper powder.

[0077] Meanwhile, the brush voltage remains the same as during image formation, brush HIGH_1 (-300 V). Also, the surface potential of the photosensitive drum 1 at the brush contact portion Pe at this timing is about -100 V, which is the area that received transfer HIGH (+1000 V) during image formation at the transfer portion Pd. Therefore, the positive toner that was primarily collected by the brush member 10 during image formation remains on the brush member 10 without being expelled from the brush member 10 to the photosensitive drum 1.

[0078] Timing T2: Timing T2 is the timing when the area of ​​the photosensitive drum 1 (area of ​​dark potential Vd (-700V)) that has received transfer LOW_1 (-200V) at the transfer portion Pd reaches the brush contact portion Pe. At this timing, the brush voltage is brush HIGH_1 (-300V) unchanged from when the image was formed. Therefore, after timing T2, the positive toner that had been staying on the brush member 10 is discharged to the photosensitive drum 1 due to the potential difference between the brush HIGH_1 (-300V) and the surface potential (-700V) of the photosensitive drum 1. Here, in this embodiment, the brush voltage is maintained at brush HIGH_1 (-300V) at timing T2, but the present invention is not limited to this embodiment. The voltage value of this brush voltage may be any voltage value that forms an electric field that electrostatically attracts the positive toner to the photosensitive drum 1. More specifically, the voltage value of this brush voltage should be higher on the positive polarity side than the surface potential of the photosensitive drum 1 (dark potential Vd (-700V) in this embodiment) and should be a voltage value at which no discharge occurs between the brush member 10 and the photosensitive drum 1. Therefore, if the above can be satisfied, the brush voltage may be changed at timing T2. In this embodiment, the voltage value of this brush voltage is a voltage value that has the same polarity as the surface potential of the photosensitive drum 1 (dark potential Vd (-700V) in this embodiment) and is smaller in absolute value than the surface potential of the photosensitive drum 1. In order to ensure that the positive toner is sufficiently attracted to the photosensitive drum 1, it is preferable that the potential difference between this brush voltage and the surface potential of the photosensitive drum 1 is 200V or more. In this embodiment, the discharge start voltage (discharge threshold) between the brush member 10 and the photosensitive drum 1 is about 600V.

[0079] 13 is a schematic diagram showing the state around the photosensitive drum 1 when the positive toner t is discharged from the brush member 10 onto the photosensitive drum 1 after timing T2. As shown in FIG. 13, the positive toner that has been retained on the brush member 10 is discharged onto the photosensitive drum 1. The positive toner discharged from the brush member 10 has the surface potential of the photosensitive drum 1 optically discharged at the discharge section Pf, is then charged to a negative polarity by uniform discharge at the charging section Pa, and is collected by the developing roller 31. Meanwhile, the transfer roller 5 is maintained in a state in which the negative toner t and impurities D such as paper powder are accumulated.

[0080] Timing T3: Timing T3 is a timing when a predetermined time has elapsed from timing T2 when the area of ​​the photosensitive drum 1 (area of ​​dark potential Vd (-700V)) receiving transfer LOW_1 (-200V) at the transfer portion Pd reaches the brush contact portion Pe. At timing T3, the transfer voltage is switched from transfer LOW_1 (-200V) to transfer LOW_2 (-1000V). Timing T3 can be set as follows. That is, it is desired to secure a time for the positive polarity toner that has been staying on the brush member 10 to be sufficiently discharged to the photosensitive drum 1. In this embodiment, timing T3 is set after half a rotation of the photosensitive drum 1 (about 300 ms) has elapsed from timing T2. Here, in this embodiment, the transfer voltage is switched to transfer LOW_2 (-1000V) at timing T3, but the present invention is not limited to such an embodiment. The voltage value of this transfer voltage may be any voltage value that forms an electric field that electrostatically attracts the negative polarity toner to the photosensitive drum 1. More specifically, the transfer voltage value may be a voltage value that is higher on the negative polarity side than the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential (-700V)) and does not cause discharge between the transfer roller 5 and the photosensitive drum 1. In this embodiment, the voltage value of the transfer voltage is a voltage value that has the same polarity as the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (-700V)) and has a larger absolute value than the surface potential of the photosensitive drum 1. In order to sufficiently attract the negative toner to the photosensitive drum 1, it is preferable that the potential difference between the transfer voltage and the surface potential of the photosensitive drum 1 is 200V or more. The surface potential of the photosensitive drum 1 at the transfer portion Pd at this timing is the dark potential Vd (-700V). Therefore, after timing T3, the negative toner accumulated on the transfer roller 5 moves to the photosensitive drum 1 together with impurities D such as paper powder due to the potential difference between the transfer LOW_2 (-1000V) and the surface potential (-700V) of the photosensitive drum 1.

[0081] 14 is a schematic diagram showing the state around the photosensitive drum 1 when the negative toner t and impurities D such as paper powder are moving from the transfer roller 5 after timing T3. As shown in FIG. 14, the negative toner t and impurities D such as paper powder that have accumulated on the transfer roller 5 move to the photosensitive drum 1. In addition, the positive toner t that has been remaining on the brush member 10 has been discharged onto the photosensitive drum 1.

[0082] Timing T4: At timing T4, the area of ​​the photosensitive drum 1 receiving the transfer LOW_2 (-1000V) at the transfer portion Pd reaches the brush contact portion Pe. At timing T4, the brush voltage is switched from the brush HIGH_1 (-300V) to the brush HIGH_2 (-200V). The surface potential of the photosensitive drum 1 at the brush contact portion Pe at this timing is the dark potential Vd (-700V). Therefore, the negative toner and impurities D such as paper powder that have moved from the transfer roller 5 to the photosensitive drum 1 are both primarily collected by the brush member 10. In this embodiment, since there is substantially no positive toner in the brush member 10 at this timing, the negative toner and the positive toner do not coexist in the brush member 10. This makes it possible to suppress the charge robbing and aggregation caused by the positive toner and the negative toner, and the resulting retention of the toner in the brush member 10. Here, in this embodiment, the brush voltage is switched to brush HIGH_2 (-200V) at timing T4, but the present invention is not limited to this embodiment. The voltage value of this brush voltage may be a voltage value that forms an electric field that attracts negative toner to the brush member 10. More specifically, the voltage value of this brush voltage may be a voltage value that is higher on the positive polarity side than the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (-700V)) and does not cause discharge between the brush member 10 and the photosensitive drum 1. Therefore, if the above can be satisfied, the brush voltage does not need to be changed at timing T4. In this embodiment, the brush voltage is changed to increase the potential difference in consideration of the separability of the negative toner and the impurities D such as paper powder. In this embodiment, the voltage value of this brush voltage is a voltage value that has the same polarity as the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (-700V)) and has a smaller absolute value than the surface potential of the photosensitive drum 1. In order to ensure that the negative toner is sufficiently attracted to the brush member 10, it is preferable that the potential difference between the brush voltage and the surface potential of the photosensitive drum 1 is 200V or more.

[0083] 15A is a schematic diagram showing the state around the photosensitive drum 1 after timing T4. The negative toner t and impurities D such as paper powder that have been primarily collected by the brush member 10 are electrostatically attracted to the brush member 10 by the potential difference between the brush HIGH_2 (−200 V) and the surface potential of the photosensitive drum 1 (−700 V), and are rubbed against the photosensitive drum 1.

[0084] 15(b) is a schematic diagram showing the state inside the brush member 10 at this time. Inside the brush member 10, there are essentially only the negative toner t that has moved from the transfer roller 5 to the photosensitive drum 1 and impurities D such as paper powder, and there is no positive toner that has been staying inside the brush member 10. Then, the toner and the impurities D such as paper powder are separated inside the brush member 10 by the electric field and friction at the brush contact part Pe. At this time, even toner that does not have a sufficient charge can have a negative charge due to the friction with the photosensitive drum 1. Furthermore, the negative toner can maintain a state in which it is less likely to coagulate and is more likely to move inside the brush member 10 due to the electric field and friction.

[0085] Timing T5: Timing T5 is a timing when a predetermined time has elapsed from timing T4 when the area of ​​the photosensitive drum 1 receiving the transfer LOW_2 (-1000V) at the transfer portion Pd reaches the brush contact portion Pe. At timing T5, the transfer voltage is switched from the transfer LOW_2 (-1000V) to the transfer HIGH (+1000V). In this embodiment, the positive toner that has been staying on the brush member 10 is discharged to the photosensitive drum 1 at the time of timing T3. Therefore, in this embodiment, timing T5 can be set as follows. First, it is desired to secure enough time for the negative toner that has been accumulated on the transfer roller 5 to move to the photosensitive drum 1. In addition, when the area of ​​the photosensitive drum 1 receiving the transfer HIGH (+1000V) at the transfer portion Pd reaches the brush contact portion Pe, it is desired that the negative toner in the brush member 10 is sufficiently separated from the impurities D by the electric field and rubbing at the brush contact portion Pe. In this embodiment, the timing T5 is set to about 700 ms after the timing T3, taking into consideration the time required to separate the negative toner in the brush member 10 from the impurities D such as paper powder. The time required to separate the negative toner in the brush member 10 from the impurities D such as paper powder is preferably 500 ms or more. In this embodiment, the timing T5 is set to about 700 ms after the timing T3, taking into consideration the time required to switch the transfer voltage. The surface potential of the photosensitive drum 1 that has received the transfer HIGH (+1000V) at the transfer portion Pd becomes about -100V. Here, in this embodiment, the transfer voltage is switched to the same transfer HIGH (+1000V) as that during image formation at the timing T5, but the present invention is not limited to this embodiment. The voltage value of this transfer voltage may be set to be higher than the brush voltage so that the surface potential of the photosensitive drum 1 is higher on the positive polarity side. More specifically, the voltage value of this transfer voltage may be a voltage value that is positively higher than the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (-700V)) and generates a discharge between the transfer roller 5 and the photosensitive drum 1. For example, it may be switched to a voltage value different from that during image formation, such as transfer HIGH_2 (+1500V).In this embodiment, the voltage value of this transfer voltage has a polarity opposite to that of the surface potential of the photosensitive drum 1 (in this embodiment, the dark potential Vd (−700 V)), and has an absolute value greater than that of the surface potential of the photosensitive drum 1 .

[0086] The conditions around the photosensitive drum 1 and inside the brush member 10 after timing T5 are the same as those shown in Figures 8(a) and (b) described in the first embodiment. However, in this embodiment, there is substantially no toner (particularly positive toner) between the brush contact portion Pe and the developing portion Pc in Figure 8(a). Even in this embodiment, the negative toner t in the brush member 10 maintains a state in which it is difficult to aggregate and easy to move within the brush member 10 due to the electric field and friction described above.

[0087] Timing T6: At timing T6, the area of ​​the photosensitive drum 1 receiving the transfer HIGH (+1000V) at the transfer portion Pd reaches the brush contact portion Pe. At timing T6, the brush voltage is switched from brush HIGH_2 (-200V) to brush HIGH_1 (-300V). At this timing, the surface potential of the photosensitive drum 1 at the brush contact portion Pe is about -100V. Therefore, the negative toner that was primarily collected by the brush member 10 is discharged from the brush member 10 to the photosensitive drum 1. Meanwhile, the impurities D such as paper powder that are physically entangled by the brush member 10 remain on the brush member 10. Here, in this embodiment, the brush voltage is switched to brush HIGH_1 (-300V) at timing T6, but the present invention is not limited to this embodiment. The voltage value of this brush voltage may be any voltage value that forms an electric field that electrostatically attracts the negative toner that was primarily collected by the brush member 10 to the photosensitive drum 1. More specifically, the voltage value of this brush voltage may be a voltage value that is negatively higher than the surface potential of the photosensitive drum 1 (approximately -100V in this embodiment) (typically, no discharge occurs between the brush member 10 and the photosensitive drum 1). In this embodiment, the voltage value of this brush voltage is a voltage value that has the same polarity as the surface potential of the photosensitive drum 1 (approximately -100V in this embodiment) and a larger absolute value than the surface potential of the photosensitive drum 1. Note that in order to ensure that negative toner is sufficiently attracted to the photosensitive drum 1, it is preferable that the potential difference between this brush voltage and the surface potential of the photosensitive drum 1 is 200V or more.

[0088] 9A and 9B described in Example 1. In this example, the negative toner t discharged from the brush member 10 onto the photosensitive drum 1 does not aggregate with other toner particles and is separated from impurities D such as paper powder. The toner t passes through the charging section Pa and is collected by the developing roller 31.

[0089] Timing T7: Timing T7 is the timing when a predetermined time has elapsed from timing T6 when the area of ​​the photosensitive drum 1 that has received transfer HIGH (+1000V) at the transfer portion Pd reaches the brush contact portion Pe. Timing T7 is set to be the timing after substantially all of the negative toner discharged from the brush member 10 onto the photosensitive drum 1 has been collected by the developing roller 31. At timing T7, the various power sources E1 to E4 and drive sources (not shown) such as the main motor (driving motor for the photosensitive drum) and the scanner motor (driving motor for the rotating mirror of the exposure device 4) are turned off, and the post-rotation process ends.

[0090] In this embodiment, the main motor, the transfer voltage, the brush voltage, etc. are turned off at the same timing, but the present invention is not limited to this. For example, the timing may be shifted appropriately depending on the inertia of the motor and the fall time of various voltages.

[0091] <Action and effect> As described above, in this embodiment, the control unit 150 performs a fourth operation (pre-recovery discharging operation) in which a potential difference is formed between the brush member 10 and the photoconductor 1 such that the toner charged with a polarity opposite to the normal polarity moves from the brush member 10 toward the photoconductor 1 before the tip of the surface of the photoconductor 1 passing through the transfer portion Pd in ​​the cleaning operation, in terms of the rotation direction of the photoconductor 1, reaches the contact portion Pe. , Pre-recovery discharge period ) (T2 to T4). In this embodiment, the control unit 150 controls in the fourth operation so that a voltage (brush HIGH_1) which is a high voltage on the opposite polarity side to the normal polarity of the toner with respect to the potential of the surface of the photoconductor 1 which has been charged by the charging member 2 and then passed through the transfer portion Pd and reached the contact portion Pe in a state in which no discharge occurs between the transfer member 5 and the photoconductor 1, and which does not cause discharge between the brush member 10 and the photoconductor 1, is applied to the brush member 10 by the brush power supply E4.

[0092] In this manner, in this embodiment, similarly to the first embodiment, the negative toner transferred from the transfer roller 5 to the photosensitive drum 1 during the cleaning operation of the transfer roller 5 is primarily collected by the brush member 10. Then, this negative toner is discharged from the brush member 10 to the photosensitive drum 1 in a state in which it is separated from impurities D such as paper powder by the electric field and friction between the brush member 10 and the photosensitive drum 1 at the brush contact portion Pe. This makes it possible to prevent the toner from coagulating and adhering unevenly to the charging roller 2, and to prevent the occurrence of image defects such as uneven density due to localized charging defects.

[0093] In this embodiment, before the negative toner that has moved from the transfer roller 5 to the photosensitive drum 1 reaches the brush contact portion Pe, the positive toner that has accumulated on the brush member 10 is expelled onto the photosensitive drum 1. This makes it possible to suppress the charge robbery and aggregation between the positive toner and the negative toner, as well as the resulting accumulation of toner on the brush member 10.

[0094] As in the second embodiment, a brush member 10 formed of a brush roller 12 may be used in this embodiment.

[0095] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments.

[0096] In the above embodiment, the surface potential of the photosensitive drum is controlled by changing the transfer voltage and the brush voltage, but the present invention is not limited to such an embodiment. For example, the transfer voltage and the brush voltage may be changed while the photosensitive drum is electrically grounded and the surface potential is set to ground (0 V). In addition, the potential relationship between the transfer roller and the photosensitive drum, or between the brush member and the photosensitive drum, may be controlled by applying a voltage directly to the photosensitive drum.

[0097] In the above embodiment, the present invention is applied to a DC charging type image forming apparatus, but the present invention is not limited to this embodiment. The present invention can also be applied to an AC charging type image forming apparatus that uses an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed as a charging voltage.

[0098] In the above embodiment, the developing voltage has been described as being only a DC component, but the developing voltage may be an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed.

[0099] In the above embodiment, the brush voltage has been described as being only a DC component, but the brush voltage may be an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed.

[0100] In the above embodiment, the pre-exposure device as the charge removing means is configured to irradiate the photosensitive drum with charge removing light in the charge removing section, but the present invention is not limited to such an embodiment. For example, the photosensitive drum may be charged by contacting the bristles of a brush member made of conductive fibers such as a fur brush with the photosensitive drum. In addition, since the charge removing means is provided for the purpose of leveling out the charging unevenness by charge removal, for example, when using a charging means with sufficiently small charging unevenness, the charge removing means may not be provided.

[0101] In the above embodiment, the cleaning operation of the transfer roller is described as being performed in the post-rotation process when no image is being formed, but the present invention is not limited to this aspect. The cleaning operation of the transfer roller can be performed at any timing when no image is being formed. For example, in the above embodiment, when the number of image output sheets in a certain job becomes equal to or exceeds a predetermined threshold, the cleaning operation of the transfer roller is performed in the post-rotation process after all image formation of the job is completed. In contrast, when the number of image output sheets during a job becomes equal to or exceeds a predetermined threshold, the cleaning operation of the transfer roller can be performed by extending the paper interval, for example.

[0102] In the above embodiment, the toner is used as the developer, which is a non-magnetic one-component developer. However, the developer may be, for example, a magnetic one-component developer.

[0103] In the above embodiment, the present invention is applied to a "cleanerless" configuration that does not have a dedicated cleaning means for cleaning the photosensitive drum, but the present invention is not limited to such an embodiment. For example, the present invention can be applied to a "blade cleaning" configuration in which a cleaning blade that contacts the photosensitive drum downstream of the brush contact portion and upstream of the charging portion in the rotation direction of the photosensitive drum is used as a cleaning means. In the blade cleaning configuration, it is also desirable to prevent the toner that has moved from the transfer member to the photosensitive drum during the cleaning operation from reaching the cleaning portion in an aggregated state together with impurities such as paper powder. If such a mixture of toner and impurities reaches the cleaning portion, it may be caught in the cleaning portion, causing the toner to slip through, and the toner may adhere unevenly to the charging member, resulting in localized charging unevenness of the photosensitive drum. Therefore, it is effective to apply the present invention to the blade cleaning configuration as well. However, it can be said that the present invention is particularly effective in the cleanerless configuration in which the toner is directly sent from the brush contact portion to the charging portion.

[0104] In the above embodiment, the photoconductor is a rotatable drum type, but may be a rotatable rotating body such as a rotatable endless belt. In the above embodiment, the transfer member is a rotatable roller type member, but is not limited to this. For example, it may be a pad-shaped member, a sheet-shaped member, a brush-shaped member (such as a fixed brush or a rotatable brush roller), a rotatable endless belt (a pressing member that contacts the photoconductor via the belt may be provided), etc. Typically, the transfer member is a rotatable rotating body. In the above embodiment, the charging member is a rotatable roller type member, but may be a brush-shaped member (such as a rotatable brush roller), a rotatable endless belt, etc. [Explanation of symbols]

[0105] 1 Photosensitive drum 2. Charge roller 3. Developing device 4. Exposure equipment 5 Transfer roller 7 Pre-exposure device 10 Brush member 11 Fixed Brush 12 Brush roller

Claims

1. A rotatable photoreceptor; a charging member that contacts the surface of the photoconductor to form a charging portion and charges the surface of the photoconductor at the charging portion; an electrostatic image forming section for forming an electrostatic image on the photoconductor which has been charged by the charging member; a developing device that supplies toner charged to a normal polarity to the electrostatic image to form a toner image on the photoconductor; a transfer member that contacts the surface of the photoreceptor to form a transfer portion and transfers the toner image on the photoreceptor to a recording material passing through the transfer portion; a transfer power source that applies a transfer voltage to the transfer member; a brush member that contacts the surface of the photoconductor and forms a contact portion downstream of the transfer portion and upstream of the charging portion in the rotation direction of the photoconductor; a brush power supply that applies a brush voltage to the brush member; a control unit capable of executing a cleaning operation for moving the toner adhering to the transfer member from the transfer member to the surface of the photoconductor when the recording material is not present in the transfer portion; having The control unit is the cleaning operation, which is executed after executing an image forming operation in which a potential difference is formed between the transfer member and the photoconductor such that the toner charged to the normal polarity moves from the photoconductor toward the transfer member, and a potential difference is formed between the brush member and the photoconductor such that the toner charged to the normal polarity moves from the brush member toward the photoconductor, includes a first operation in which a potential difference is formed between the transfer member and the photoconductor such that the toner charged to the normal polarity moves from the photoconductor toward the transfer member, and a potential difference is formed between the transfer member and the photoconductor such that the toner charged to the normal polarity moves from the transfer member toward the photoconductor, and a second operation in which a potential difference is formed between the brush member and the photoconductor such that the toner charged to the normal polarity moves from the transfer member toward the photoconductor, an image forming apparatus characterized in that, in the first operation, the transfer power supply applies to the transfer member a first transfer voltage having the normal polarity and a second transfer voltage having an absolute value larger than that of the first transfer voltage and the normal polarity, and, in the second operation, the brush power supply applies to the brush member the brush voltage having the normal polarity.

2. 2. The image forming apparatus according to claim 1, wherein the first transfer voltage is a transfer voltage that is higher on the opposite polarity side than the potential of the surface of the photosensitive member that is charged by the charging member and reaches the transfer section, and is a transfer voltage that does not cause discharge between the transfer member and the photosensitive member.

3. The image forming apparatus according to claim 1 or 2, characterized in that, in the second operation, the control unit controls the brush voltage to be applied to the brush member by the brush power supply, the brush voltage being higher on the opposite polarity side than the potential of the surface of the photosensitive body that passes through the transfer section and reaches the contact section, and the brush voltage not generating a discharge between the brush member and the photosensitive body.

4. The image forming apparatus according to any one of claims 1 to 3, characterized in that the control unit controls so that after the second operation is completed, a discharge period is provided in which a potential difference is formed between the brush member and the photosensitive body such that the toner charged to the normal polarity moves from the brush member toward the photosensitive body.

5. The image forming apparatus according to any one of claims 1 to 4, characterized in that the control unit controls the cleaning operation so as to have a pre-recovery discharge period in which a potential difference is formed between the brush member and the photosensitive body such that the toner charged with the opposite polarity moves from the brush member toward the photosensitive body before the tip, in the rotational direction, of the surface of the photosensitive body passing through the transfer unit reaches the contact unit during the cleaning operation.

6. The image forming apparatus according to claim 5, characterized in that, during the pre-recovery discharge period, the control unit controls the brush member to be applied by the brush power supply with the brush voltage, which is higher in the opposite polarity side than the potential of the surface of the photosensitive body that passes through the transfer section and reaches the contact section after being charged by the charging member without generating any discharge between the transfer member and the photosensitive body, and which does not generate any discharge between the brush member and the photosensitive body.

7. 7. The image forming apparatus according to claim 1, wherein the brush member has a fixed conductive brush portion.

8. The brush member has a rotatable conductive brush portion, The image forming apparatus according to any one of claims 1 to 6, characterized in that the brush portion rotates in conjunction with the rotation of the photosensitive body, is rotationally driven so that the photosensitive body and the brush portion move in a forward direction at the contact portion with or without a speed difference relative to the peripheral speed of the photosensitive body, or is rotationally driven so that the photosensitive body and the brush portion move in a reverse direction at the contact portion.

9. 9. An image forming apparatus according to claim 1, wherein when the toner remaining on the surface of the photoconductor passes through the contact portion after the toner image is transferred from the photoconductor to the recording material in the transfer portion, the brush voltage of the normal polarity is applied to the brush member by the brush power supply.

10. 10. The image forming apparatus according to claim 1, wherein the toner remaining on the surface of the photoconductor after the toner image is transferred from the photoconductor to the recording material in the transfer section is collected by the developing device.

11. 11. The image forming apparatus according to claim 1, wherein the toner has an average circularity of 0.96 or more.

12. 12. The image forming apparatus according to claim 1, wherein the toner is a one-component developer.

13. The brush member has threads, and the density of the threads is 150 to 350 kF / inch. ２ 13. The image forming apparatus according to claim 1, wherein

Images