Image forming apparatus and method for recovering transfer residual toner

Abstract

To provide an image forming apparatus that can prevent re-transfer caused because developing means cannot recover a transfer residual toner, and can prevent an abnormal image caused by the re-transfer.SOLUTION: An image forming apparatus has an image carrier, an electrifying member, electrification voltage application means, exposure means, developing means, transfer means, and a control unit. The control unit controls a recovery operation to cause the developing means to recover a transfer residual toner that remains on the image carrier after the transfer. The recovery operation is performed in an image non-forming period (exposure OFF), and has discharge processing of discharging electricity between the electrifying member and the image carrier to electrify the transfer residual toner, and recovery processing of recovering the electrified transfer residual toner with the developing means. The control unit controls the electrification voltage application means so that, in the discharge processing, the absolute value of voltage to be applied to the electrifying member becomes larger than the absolute value of the surface potential of the image carrier before passing through an electrification position (a position where the electrifying member and the image carrier face each other), equal to or more than the absolute value of break-down voltage, and smaller than the absolute value of voltage to be applied to the electrifying member in an image forming period (exposure ON).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and a method for recovering transfer residual toner. [Background technology]

[0002] In an electrophotographic image forming apparatus, a photosensitive member (image carrier) is charged by a charging member such as a charging roller, toner is supplied to the photosensitive member by a developing means, and the toner on the photosensitive member is transferred to a recording medium or an intermediate transfer member.

[0003] In the prior art, for example, toner adhering to a photosensitive member is removed by a cleaning means such as a cleaning blade. In recent years, from the viewpoint of miniaturization of the device, a so-called cleanerless system has been proposed, which does not include a cleaning means dedicated to cleaning the photosensitive member.

[0004] In a known cleaner-less image forming apparatus, residual toner remaining on the photosensitive drum after transfer is collected by a developing unit. In such a cleaner-less image forming apparatus, residual toner is collected by the developing unit and reused, thereby reducing waste toner. This simplifies user maintenance and eliminates the need for a waste toner container, thereby reducing waste.

[0005] For example, the following methods are known for cleanerless image forming apparatuses. One method is to recover residual toner by increasing the voltage (charging bias) applied to the charging member to widen the range of the background potential (the potential difference between the potential of the charging member and the potential of the photosensitive member). Another method is to use the potential difference between the charging bias and the surface potential of the photosensitive member to expel toner adhering to the charging member onto the photosensitive member and recover it with a developing means.

[0006] Patent Document 1 discloses a cleanerless system that uses a contact charging roller, which is an example of a charging member, for the purpose of recovering residual toner from the charging roller using a developing unit. Patent Document 2 discloses a cleanerless image forming apparatus in which the developing unit recovers residual toner from the charging roller, and discloses that the volume average particle size and content of external additives contained in the toner are specified. According to Patent Document 2, the occurrence of abnormal images can be suppressed for a long period of time.

[0007] In Patent Documents 1 and 2, a cleaning operation to reduce toner adhering to the charging member is performed when no image formation is taking place, and the voltage applied to the charging roller is switched during the cleaning operation. As in Patent Documents 1 and 2, conventional techniques are known in which the voltage applied to the charging roller is switched when cleaning the charging roller (when toner is moving from the charging roller to the photosensitive member). Summary of the Invention [Problem to be solved by the invention]

[0008] In conventional cleanerless configurations, residual toner is collected using the potential difference of the background, and it was thought that the greater the potential difference of the background, the more residual toner could be collected. If the charging bias is set high to increase the background potential, the residual toner becomes excessively negatively charged due to the pre-charge discharge performed to collect the residual toner. In this case, the electrostatic attraction force between the residual toner and the photosensitive member becomes strong, and the toner cannot be collected by the developing means, resulting in re-transfer.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that can suppress retransfer, which occurs when transfer residual toner cannot be collected by a developing means, and can suppress abnormal images caused by retransfer. [Means for solving the problem]

[0010] In order to solve the above problems, the image forming apparatus of the present invention comprises: an image carrier; a charging member for charging the image bearing member; a charging voltage applying means for applying a voltage to the charging member; an exposure unit that exposes the charged image carrier to light to form a latent image on the surface of the image carrier; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer means for transferring the toner image onto a transfer target; a control unit that controls a recovery operation for recovering residual toner remaining on the image carrier after transfer into the developing unit, The recovery operation is an operation performed during non-image formation, i.e., a period when the exposure unit is not performing exposure, and includes a discharge process for charging the transfer residual toner by discharging between the charging member and the image carrier, and a recovery process for recovering the charged transfer residual toner by the developing unit, The control unit controls the charging voltage application unit so that the absolute value of the voltage applied to the charging member in the discharge process is greater than the absolute value of the surface potential of the image carrier before the charging member passes through a charging position where the charging member and the image carrier face each other, is equal to or greater than the absolute value of a discharge start voltage, and is smaller than the absolute value of the voltage applied to the charging member during image formation, which is a period during which the exposure unit is performing exposure. It is characterized by: [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an image forming apparatus that can suppress retransfer, which occurs when the transfer residual toner cannot be collected by the developing means, and can suppress abnormal images caused by retransfer. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating an embodiment of an image forming apparatus of the present invention. [Figure 2] 1A and 1B are block diagrams illustrating an example of the hardware configuration of a control unit. [Figure 3] FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 4] FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 5A] FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 5B] FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 6] This is the result of an evaluation of retransfer using development unit B (M / A small). [Figure 7] This is the result of evaluating retransfer using development unit A (large M / A). [Figure 8] FIG. 10 is a diagram showing an example of the relationship between the background potential and the toner charge amount after passing through the charging circuit when retransfer is evaluated in the development unit A (large M / A). [Figure 9] FIG. 10 is a diagram showing an example of the relationship between the voltage applied to the charging member and the amount of charge on the toner after passing through the charging member. [Figure 10] 10 is a timing chart for explaining an example of an image formation time and a non-image formation time. [Figure 11] 10 is a timing chart for explaining an example of adjusting the voltage applied to the charging member when shutting down the apparatus. [Figure 12] FIG. 10 is a schematic diagram for explaining an example of a third embodiment. [Figure 13] FIG. 10 is a schematic diagram for explaining an example of a fourth embodiment. [Figure 14] FIG. 10 is a schematic diagram for explaining an example of a fifth embodiment. [Figure 15] FIG. 10 is a schematic diagram for explaining an example of a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] The image forming apparatus and the method for recovering residual toner according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following embodiments, and other modifications, additions, corrections, deletions, and other changes can be made within the scope of what a person skilled in the art can conceive. Any embodiment is within the scope of the present invention as long as it achieves the functions and effects of the present invention.

[0014] (First embodiment) The image forming apparatus of this embodiment includes: an image carrier; a charging member for charging the image bearing member; a charging voltage applying means for applying a voltage to the charging member; an exposure unit that exposes the charged image carrier to light to form a latent image on the surface of the image carrier; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer means for transferring the toner image onto a transfer target; a control unit that controls a recovery operation for recovering residual toner remaining on the image carrier after transfer into the developing unit, The recovery operation is an operation performed during non-image formation, i.e., a period when the exposure unit is not performing exposure, and includes a discharge process for charging the transfer residual toner by discharging between the charging member and the image carrier, and a recovery process for recovering the charged transfer residual toner by the developing unit, The control unit controls the charging voltage application unit so that the absolute value of the voltage applied to the charging member in the discharge process is greater than the absolute value of the surface potential of the image carrier before the charging member passes through a charging position where the charging member and the image carrier face each other, is equal to or greater than the absolute value of a discharge start voltage, and is smaller than the absolute value of the voltage applied to the charging member during image formation, which is a period during which the exposure unit is performing exposure. It is characterized by:

[0015] The image forming apparatus may be called an electrophotographic apparatus, a printing apparatus, a printer, etc. The image forming apparatus of the present invention may be a cleanerless image forming apparatus. The cleanerless system may be called a cleanerless system, a cleanerless imaging system, etc.

[0016] The method for recovering residual toner after transfer according to this embodiment includes the steps of: an image carrier; a charging member for charging the image bearing member; an exposure unit that exposes the charged image carrier to light to form a latent image on the surface of the image carrier; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer unit that transfers the toner image onto a transfer receiving member, and a method for recovering transfer residual toner by the developing unit, the method being performed by an image forming apparatus having the transfer unit and recovering transfer residual toner remaining on the image carrier after transfer, the method comprising: During a non-image formation period in which the exposure means is not performing exposure, a discharging step is performed in which discharge is caused between the charging member and the image carrier to charge the transfer residual toner, and a recovery step is performed in which the charged transfer residual toner is recovered by the developing means, In the discharging step, the absolute value of the voltage applied to the charging member is greater than the absolute value of the surface potential of the image carrier before the charging member passes through a charging position where the charging member and the image carrier face each other, and is equal to or greater than the absolute value of a discharge start voltage, and is smaller than the absolute value of the voltage applied to the charging member during image formation, which is a period during which the exposure means is performing exposure. It is characterized by:

[0017] In this embodiment, when recovering transfer residual toner during non-image formation, the charging bias (voltage applied to the charging member) is switched to be lower than the charging bias during image formation. This reduces the amount of negative charge on the transfer residual toner and reduces the electrostatic adhesion force between the transfer residual toner and the photosensitive member. This makes it easier for the developing unit to recover the transfer residual toner, and prevents abnormal images caused by re-transfer due to the transfer residual toner not being able to be recovered by the developing unit.

[0018] In this embodiment, a period when the exposure unit is not performing exposure is defined as a non-image forming period, and a period when the exposure unit is performing exposure is defined as an image forming period. During non-image formation, toner is not supplied to the photosensitive member, so the period during which the exposure unit does not expose the photosensitive member and the development unit does not supply toner to the photosensitive member may be referred to as the non-image formation period.Furthermore, during image formation, toner is supplied to the photosensitive member, so the period during which the exposure unit exposes the photosensitive member and the development unit supplies toner to the photosensitive member may be referred to as the image formation period.

[0019] In this embodiment, the position where the charging member and the image carrier face each other is also referred to as the charging position. When the charging member is in contact with the image carrier, the charging position may also be referred to as a charging nip or the like. The image carrier is charged by the charging member at or near the charging position. The discharge process is carried out at or near the charging position. On the photosensitive member, the portion before passing through the charging position is also referred to as the portion before passing through the charging position.

[0020] The discharge treatment may also be referred to as pre-charging discharge. In the discharge treatment, a discharge is generated between the charging member and the image carrier to charge the transfer residual toner. By performing the discharge treatment, for example, a negative charge is injected into the transfer residual toner on the photosensitive member that passes through a position facing the charging member, and the transfer residual toner can be collected by the developing means.

[0021] The recovery operation is an operation performed during non-image formation, i.e., a period when the exposure unit is not performing exposure, and includes a discharge process for charging the transfer residual toner by discharging between the charging member and the image carrier, and a recovery process for recovering the charged transfer residual toner by the developing unit.

[0022] In this embodiment, the charging voltage application means is controlled so that the absolute value of the voltage applied to the charging member during the discharge process is greater than the absolute value of the surface potential of the image carrier before it passes through the charging position, is equal to or greater than the absolute value of the discharge start voltage, and is smaller than the absolute value of the voltage applied to the charging member during image formation.

[0023] The discharge process (pre-charge discharge) can be performed by setting the absolute value of the voltage applied to the charging member in the discharge process to be greater than the absolute value of the surface potential of the image carrier before it passes the charging position and equal to or greater than the absolute value of the discharge start voltage. If this relationship is not satisfied, the discharge process (pre-charge discharge) cannot be performed, the transfer residual toner cannot be charged, and the transfer residual toner cannot be collected effectively.

[0024] Furthermore, since the absolute value of the voltage applied to the charging member during the discharge process is smaller than the absolute value of the voltage applied to the charging member during image formation, the adhesion force of the transfer residual toner to the photosensitive member is prevented from becoming excessively strong when the transfer residual toner is collected by the developing means, and the transfer residual toner can be collected well.

[0025] In a comparative example not included in the present invention, in order to recover the transfer residual toner transferred from the charging member onto the photosensitive member using the developing means, the applied voltage is switched to the voltage used during image formation, and the transferred transfer residual toner is negatively charged by pre-charging discharge. In this comparative example, the transfer residual toner is charged using the voltage used during image formation, so the transfer residual toner becomes excessively negatively charged. As a result, the electrostatic adhesion force (which may also be referred to as electrostatic adsorption force) between the transfer residual toner and the photosensitive member becomes strong, preventing recovery by the developing means and resulting in re-transfer.

[0026] For example, in Patent Document 1, the voltage Vc applied to the charging roller is switched between image formation and non-image formation (Vc=-1400V during image formation, and Vc=0V after image formation is completed). Patent Document 1 also discloses that the relationship between the photosensitive member surface potential before passing the charging roller and the voltage applied to the charging roller during non-image formation is such that the voltage applied to the charging roller is less than the photosensitive member surface potential before passing the charging roller, and the potential difference is equal to or greater than the discharge start voltage Vth.

[0027] In conventional cleanerless configurations, residual toner is collected using the potential difference of the background, and it was thought that the larger the potential difference of the background, the more residual toner could be collected. However, if the charging bias is set high to increase the background potential, the residual toner becomes excessively negatively charged due to pre-charging discharge. In this case, the electrostatic attraction force between the residual toner and the photosensitive drum becomes strong, and the residual toner cannot be developed and collected, resulting in re-transfer.

[0028] Next, a cleanerless image forming apparatus used in the present invention will be described with reference to the drawings. In the following description, a charging roller is used as an example of a charging member. The developing means has, for example, a developing roller, and the following description will be made using the developing roller. A photosensitive body or a photosensitive drum is used as an example of an image carrier. Although paper or recording paper is used as an example of a transfer medium, other intermediate transfer bodies (e.g., intermediate transfer belts) can also be used as the transfer medium.

[0029] 1 is a schematic diagram showing an example of an image forming apparatus according to the present invention. As shown in the figure, a printer as an example of an image forming apparatus according to the present embodiment includes a paper feed unit 4, a pair of registration rollers 6, a photosensitive drum 10 as an image carrier, a transfer roller 62, a fixing device 12, etc.

[0030] The image forming apparatus also includes a charging power supply 21 for supplying a bias voltage required for image formation, a developing power supply 22, a cleaning power supply 23, a transfer power supply 24, and the like, and the outputs of these power supplies are controlled by a control unit 25.

[0031] The charging power supply 21 is an example of a charging voltage application means, and applies a voltage to the charging roller 160. The charging roller 160 is an example of a charging member. The voltage applied to the charging roller 160 may be referred to as a charging bias voltage or the like. The developing power supply 22 is an example of a developing voltage application means and applies a voltage to the developing means. The developing device 61 is an example of a developing means and has, for example, a developing roller 72. Although the developing power supply 22 is described as applying a voltage to the developing means, the developing power supply 22 may also apply a voltage to the developing roller 72. The voltage applied to the developing roller 72 may be referred to as a developing bias voltage or the like. The transfer power supply 24 is an example of a transfer voltage application means, and applies a voltage to the transfer roller 62. The transfer roller 62 is an example of a transfer member, and a voltage is applied to the transfer roller 62 to perform transfer. The voltage applied to the transfer roller 62 may be referred to as a transfer bias voltage or the like.

[0032] The paper feed means 4 includes a paper feed tray 14 in which sheets of paper P serving as recording paper are stored in a stacked state, and a paper feed roller 15 that separates and feeds the recording paper 105 stored in the paper feed tray 14 one sheet at a time, starting from the top one. Recording paper is an example of a transfer object, and may also be called a recording medium, recording material, medium, etc.

[0033] The recording paper 105 sent out by the paper feed roller 15 is stopped temporarily by the pair of registration rollers 6, and after any misalignment has been corrected, it is sent to the transfer location N3 by the pair of registration rollers 6 at a timing synchronized with the rotation of the photosensitive drum 10, that is, at a timing when the leading edge of the toner image formed on the photosensitive drum 10 coincides with a predetermined position of the leading edge of the paper Pa in the transport direction.

[0034] Around the photosensitive drum 10, in the rotational direction indicated by the arrow, there are arranged a charging roller 160 as charging means, a developing device 61 equipped with a developing roller 72, and a transfer roller 62. Of these, the charging roller 160 and the developing roller 72 are provided in contact with the photosensitive drum 10. In addition, a collecting brush 161 (which may also be called a brush roller, cleaning brush, cleaning member, etc.) is provided in contact with the charging roller 160. The collecting brush 161 is an example of collecting means.

[0035] The charging roller 160 may or may not be in contact with the photosensitive drum 10. The charging roller 160 is preferably provided so as to be in contact with the photosensitive drum 10. In this case, the discharge process (pre-charging discharge) can be stably and easily performed.

[0036] Between the charging roller 160 and the developing device 61, the exposure means 5 irradiates the surface of the photosensitive drum 10 with exposure light Lb, causing it to be scanned.

[0037] When the photosensitive drum 10 begins to rotate, a charging bias voltage is applied to the charging roller 160 from the charging power supply 21, uniformly charging the photosensitive surface in the charging region N1. Based on image information, the exposure means 5 irradiates the surface of the photosensitive drum 10 with exposure light Lb, and an electrostatic latent image is formed by discharging the portion of the photosensitive surface corresponding to the image to be created. This electrostatic latent image moves to the development region N2 as the photosensitive drum 10 rotates, and at this time a development bias voltage is applied from the development power supply 22 to the development roller 72 provided in the development device 61.

[0038] In development area N2, the negatively charged toner held on the development roller is supplied from development roller 72 to photosensitive drum 10 in accordance with the potential difference between the potential of the exposed area and the development bias voltage, forming a toner image on photosensitive drum 10. The toner image formed on photosensitive drum 10 moves to transfer area N3 at a predetermined timing. At this time, a transfer bias voltage is applied to transfer roller 62 from transfer power supply 24, and the toner image is transferred onto recording paper 105 that has entered transfer area N3.

[0039] The recording paper 105 carrying the toner image is transported toward the fixing device 12, where it is fixed, and then discharged and stacked on a paper output tray. Residual toner that was not transferred to the recording paper 105 in the transfer area N3 and remains on the photosensitive drum 10 reaches the charging area N1 as the photosensitive drum 10 rotates. In the charging area N1, the residual toner is charged to a negative polarity by a minute discharge of the charging bias voltage applied to the charging roller 160, and is returned to the development area N2.

[0040] In the developing area N2, the residual toner moves onto the developing roller 72 and is collected into the developing device 61 in accordance with the potential difference between the potential of the non-exposed portion, ie, the portion not exposed by the exposure means 5, and the developing bias voltage.

[0041] In the charging region N1, it is difficult to charge the residual toner completely to a negative polarity, and positive toner ends up adhering to the charging roller 160. For this reason, it is preferable to use a recovery brush 161 to scrape off dirt from the charging roller 160. A cleaning bias voltage is applied to the recovery brush 161 from the cleaning power supply 23, and the positive toner adhering to the charging roller 160 is cleaned by the potential difference and mechanical scraping. By using the recovery brush 161, the charging roller 160 can be made even cleaner.

[0042] FIG. 2A is a block diagram illustrating the hardware configuration of the control unit 25 in this embodiment. The control unit 25 includes, for example, a CPU, which is a central element for performing calculations, and memories such as ROM and RAM, which are memory elements (storage units). The RAM stores sensor detection results and calculation results, and the ROM stores control programs and pre-calculated data tables. The control unit 25 controls, for example, the charging power supply 21, the developing power supply 22, the cleaning power supply 23, and the transfer power supply 24. The control unit 25 controls the ON / OFF and output value of each power supply. The control unit 25 controls the exposure unit 5. The control unit 25 controls the static elimination lamp 64 (static elimination unit), for example, to eliminate static electricity from the photosensitive drum 10 during pre-charging discharge.

[0043] FIG. 2B is a block diagram showing an example of the hardware configuration of the control unit 25.

[0044] The control unit 25 includes a CPU (Central Processing Unit) 110, a RAM (Random Access Memory) 111, a ROM (Read Only Memory) 112, and a storage unit 113, which are connected via a bus 117.

[0045] The CPU 110 is a computing unit that controls the overall operation of the image forming apparatus 100. The RAM 111 is a volatile storage medium that allows high-speed reading and writing of information. When the CPU 110 processes information, the RAM 111 is used as a working area for the CPU 110. The ROM 112 is a read-only nonvolatile storage medium that stores programs such as firmware.

[0046] The storage unit 113 is a non-volatile storage medium that can read and write information, and stores an OS (Operating System), various control programs, application programs, etc. The storage unit 113 is, for example, an SSD (Solid State Drive) or an HDD (Hard Disk Drive).

[0047] In the image forming apparatus of this embodiment, residual toner remaining on the image carrier is collected by a developing unit. The image forming apparatus of this embodiment is configured without using a cleaning unit (e.g., a cleaning blade) for cleaning the image carrier (also called an electrostatic latent image carrier, photosensitive member, etc.). This has the advantage of allowing for a more compact apparatus.

[0048] Hereinafter, a system that does not use a cleaning device for cleaning the image carrier may also be referred to as a cleanerless system. However, a system that includes a device for cleaning the charging member or a device for cleaning the intermediate transfer belt may also be included in the cleanerless system. Furthermore, a system that includes a device for temporarily collecting residual toner remaining on the image carrier is also included in the cleanerless system.

[0049] The basic configuration and operation of a cleanerless image forming apparatus will be explained with reference to FIG. 3 is a diagram illustrating an example of a process for forming an image. As the charging member, for example, a charging roller can be used, and the following description will be given taking the charging roller as an example.

[0050] First, the charging roller 160 uniformly charges the photosensitive drum 10, which serves as an image carrier. The charging roller 160 in this example is disposed so as to contact the photosensitive drum 10, and applies, for example, a DC voltage to the photosensitive drum 10. Charging in this example is performed using a contact DC charging method. The exposure device 121 exposes the photosensitive drum 10 to exposure light L to form an electrostatic latent image on the photosensitive drum 10. The exposure device 121 is not particularly limited, but an LED, for example, is used.

[0051] The developing roller 72 is an example of a developer carrier provided in the developing device 61. A developing bias is applied to the developing roller 72 by an application means, and the developing roller 72 supplies the toner 200 to the photosensitive drum 10. As a result, a toner image (also referred to as a visible image) is formed on the photosensitive drum 10. The developing device 61 may have, for example, an agitating roller 73, which agitates the toner within the developing device 61. The rotation direction of the agitating roller 73 can be selected appropriately, and the agitating roller 73 may or may not be in contact with the developing roller 72. The transfer roller 62 transfers the toner image on the photosensitive drum 10 onto the recording paper 105 . The static elimination lamp 64 eliminates the potential of the photosensitive drum 10. For example, static elimination is performed by irradiating the photosensitive drum with static elimination light QL.

[0052] The above-described configuration is the basic configuration of a cleanerless image forming apparatus, which does not include a cleaning device such as a cleaning brush for cleaning the photosensitive drum 10 after the transfer process.

[0053] 3, for example, −300 V is applied to the developing roller 72, and −1250 V is applied to the charging roller 160. For example, when the photosensitive drum 10 is neutralized, the surface becomes approximately −50 V, and when the photosensitive drum 10 is charged, the surface becomes approximately −500 V. The image forming apparatus of this embodiment may be provided with a collection brush 161 (collection means) that collects toner on the charging roller 160. In the example shown in Fig. 3, the collection brush 161 is not provided, and is therefore indicated by a dashed line in the drawing.

[0054] Here, an example of the flow of toner will be described in the example shown in Fig. 3. For the sake of explanation, the reference symbols of toner in the figure are changed depending on the position and state of the toner. The developing roller 72 carries toner 200, and the toner 200 carried by the developing roller 72 is supplied to the photosensitive drum 10. The toner supplied to the photosensitive drum 10 forms a toner image (visible image) in accordance with the electrostatic latent image (toner 201). The toner 201 on the photosensitive drum 10 is transferred to the recording paper 105. The toner 202 transferred to the recording paper 105 is fixed to the recording paper 105 in a later process.

[0055] Toner that is not transferred in the transfer process remains on the photosensitive drum 10 as transfer residual toner 203. After the charge removal process, the transfer residual toner 203 adheres to the charging roller 160 at (or near) the contact point between the photosensitive drum 10 and the charging roller 160. Among the transfer residual toner 203, there is also toner 206 that does not adhere to the charging roller 160, and this toner 206 remains on the photosensitive drum 10. This toner 206 is collected by the developing roller 72.

[0056] Next, an example of a method for collecting residual toner after transfer in a cleaner-less image forming apparatus will be described with reference to FIGS. 4, 5A, and 5B. Figure 4 is a schematic diagram for explaining the state after Figure 3, and is a diagram that schematically shows the state during printing. "During printing" here means the state in which the device is operating, and includes not only the process of transferring toner to recording paper, but also the process of preparing to transfer toner to recording paper. Figure 4 is a diagram that explains the process that is performed between transfer to the previous recording paper and transfer to the next recording paper.

[0057] As explained in FIG. 3, toner that is not transferred in the transfer process remains on the photosensitive drum 10 as transfer residual toner 203. In FIG. 4, transfer residual toner 203 is shown remaining on the photosensitive drum 10 downstream of the transfer roller 62. After transfer to the previous recording paper 105, the surface of the photosensitive drum 10 is neutralized by the neutralization lamp 64. This increases the potential difference between the charging roller 160 and the photosensitive drum 10, causing discharge between the charging roller 160 and the photosensitive drum 10 before charging. The discharge is shown schematically in the figure.

[0058] Due to the discharge before charging, the transfer residual toner 203 is negatively charged (not shown in FIG. 4). Due to the discharge before charging, some of the transfer residual toner 203 is negatively charged, while some remains slightly positively charged. The transfer residual toner 203 that remains slightly positively charged adheres to the charging roller 160 at (or near) the point where the charging roller 160 and the photosensitive drum 10 come into contact. The toner that adheres to the charging roller 160 is shown as toner 204.

[0059] The arrow a in the figure schematically illustrates the transfer residual toner 203 on the photosensitive drum 10 adhering to the charging roller 160. The adhesion of the transfer residual toner 203 on the photosensitive drum 10 to the charging roller 160 may also be referred to as movement or the like.

[0060] The image forming apparatus of this example has a collection brush 161 that collects toner adhering to the charging roller 160. Positive toner 204 adhering to the charging roller 160 is collected by the collection brush 161. Arrow b in the figure schematically illustrates the toner 204 on the charging roller 160 being collected by the collection brush 161. The collection of toner 204 on the charging roller 160 by the collection brush 161 may also be referred to as movement, etc. A collection bias is applied to the collection brush 161. The value of the collection bias is not particularly limited and can be selected as appropriate.

[0061] Of the transfer residual toner 203 on the photosensitive drum 10, negatively charged toner does not adhere to the charging roller 160 and remains on the photosensitive drum 10. This toner is illustrated as toner 206. Note that both the toner 203 and the toner 206 are transfer residual toner.

[0062] Toner 206 remaining on the photosensitive drum 10 is collected by the developing roller 72. The toner collected by the developing roller 72 is illustrated as toner 208. The act of being collected by the developing roller 72 may also be referred to as "moving." The toner 206 passing between the photosensitive drum 10 and the developing roller 72 moves toward the developing roller 72 due to the potential difference between the photosensitive drum 10 and the developing roller 72. The arrow c in the figure schematically illustrates the toner 206 on the photosensitive drum 10 being collected by the developing roller 72.

[0063] To recover the toner with the developing roller 72 as described above, for example, the potential of each component can be adjusted. One example is to set the surface of the photosensitive drum 10 after neutralization to -50 V, the charging roller 160 to -1250 V, the recovery brush 161 to -1300 V, the surface of the photosensitive drum 10 after charging to -500 V, and the developing roller 72 to -300 V. While the potentials are shown in FIG. 4 as an example, they are not limited to this.

[0064] In the image forming apparatus of the present invention, it is preferable to have the collection brush 161, but the collection brush 161 is not essential. If the image forming apparatus does not have a collection means (for example, the collection brush 161) for collecting toner present on the charging roller 160, it is preferable to adjust the potential so as to reduce the amount of toner that moves to the charging roller 160.

[0065] Next, an example of the movement of toner when the device is shut down and toner recovery will be described with reference to Figures 5A and 5B. As explained in Figure 4, the positive residual toner 203 (as well as toner 206) that did not become negative during discharge before charging adheres to the charging roller 160 and is recovered by the recovery brush 161. Since this recovery is repeated during printing, positively charged toner 207 accumulates on the recovery brush 161.

[0066] When the device is shut down, the potential difference between the collection brush 161 and the charging roller 160 is adjusted to move a small amount of positively charged toner 207 toward the charging roller 160. This is indicated by the arrow d in the figure.

[0067] The toner 205 that has moved to the charging roller 160 moves to the photosensitive drum 10 due to the potential difference between the charging roller 160 and the photosensitive drum 10. This is indicated by the arrow e in the figure. This moved toner is indicated as toner 209 in the figure. Note that when the device is shut down, the photosensitive drum 10 is not neutralized by the neutralization lamp 64, and the potential difference between the charging roller 160 and the photosensitive drum 10 is adjusted taking this into consideration.

[0068] The positively charged toner 209 on the photosensitive drum 10 is not collected by the developing roller 72, but passes through the developing roller 72. The toner 209 then passes through the transfer roller 62. In this way, when the device is shut down, the positively charged toner 209 remains on the photosensitive drum 10.

[0069] 4, 5A, and 5B, toner particles 203, 206, and 209 are shown on the photosensitive drum 10. All of these are considered to be transfer residual toner. Toner particle 209 is transfer residual toner particle 203 that has been collected by collection brush 161 and then moved back onto the photosensitive drum 10, and this toner may also be included in the transfer residual toner.

[0070] To move the toner as shown in the example of Fig. 5A, for example, the potential of each component can be adjusted. For example, the potential of the collection brush 161 can be set to -150V, the potential of the charging roller 160 to -350V, the potential of the surface of the photosensitive drum 10 to 500V, and the potential of the developing roller 72 to +250V. While Fig. 5A illustrates the potentials as an example, the present invention is not limited to this.

[0071] Next, the recovery of toner from the photosensitive drum 10 during device shutdown will be described with reference to FIG. 5B. FIG. 5B is a continuation of FIG. 5A. As shown, the photosensitive drum 10 is neutralized by the neutralization lamp 64 at a predetermined timing. By performing neutralization, the potential difference between the charging roller 160 and the photosensitive drum 10 increases, causing discharge between the charging roller 160 and the photosensitive drum 10. The figure shows the discharge diagrammatically. Note that the neutralization shown is not for image formation, but for toner recovery.

[0072] Due to the above-described discharge, the toner 209 becomes negatively charged. As in Fig. 4, the toner 209 that is not negatively charged and remains positively charged adheres to the charging roller 160 and is collected by the collection brush 161 (arrows g and h in the figure).

[0073] The toner 209, which has been negatively charged by the above-described discharge, does not move to the charging roller 160 but remains on the photosensitive drum 10. The negatively charged toner 209 is then collected by the developing roller 72 to which a developing bias is applied (arrow i in the figure). The toner collected by the developing roller 72 is shown as toner 208 in the figure.

[0074] To move the toner as shown in the example of Fig. 5B, for example, the potential of each component can be adjusted. For example, the potential of the collection brush 161 can be set to -1300V, the potential of the charging roller 160 can be set to -1250V, the surface of the photosensitive drum 10 after static elimination can be set to -50V, the potential of the surface of the photosensitive drum 10 can be set to 500V, and the potential of the developing roller 72 can be set to -300V. While Fig. 5B illustrates the potentials as an example, the present invention is not limited to this.

[0075] The static elimination lamp 64 is an example of a static eliminator. The static eliminator may also be called static eliminator.

[0076] A detailed example of this embodiment will be described below. As explained above, the main points of the cleanerless configuration of this embodiment will be explained again.

[0077] (1) The static elimination lamp 64 (QL) eliminates the surface potential of the photosensitive drum 10 before it passes the charging roller 160. As a result, the potential difference between the applied voltage of the charging roller 160 and the surface potential on the photosensitive drum 10 increases, causing a discharge (pre-charging discharge) at the charging position.

[0078] (2) The transfer residual toner is negatively charged by the pre-charge discharge in (1) and passes between the charging roller 160 and the photosensitive drum 10. When the charging roller 160 and the photosensitive drum 10 are in contact with each other, the transfer residual toner passes through the charging nip.

[0079] (3) The negatively charged residual toner is collected by the developing roller 72 due to the potential difference between the applied voltage to the developing roller 72 and the surface potential on the photosensitive member (background potential).

[0080] The above is the mechanism for recovering residual transfer toner by the developing means in a cleanerless configuration. However, residual transfer toner that has not been negatively charged by the pre-charge discharge in (2) adheres to the charging roller 160 due to the potential difference between the applied voltage of the charging roller 160 and the surface potential of the photosensitive drum 10 or due to physical contact. As a result, the charging roller 160 becomes soiled with residual transfer toner with each printing, resulting in poor charging.

[0081] In response to this, there is a method in which the toner adhering to the charging roller is expelled onto the photosensitive member after printing is completed (at shutdown), and then collected again by the developing means. Regarding collection by the developing means at device shutdown, in addition to the explanation given in Figures 5A and 5B above, the main points will be explained again.

[0082] (1) By turning off the static elimination lamp 64 (QL), the surface potential on the photosensitive drum 10 before passing through the charging position remains the same as the surface potential after passing through the transfer position. (2) When the surface potential on the photosensitive drum 10 in (1) passes in front of the static eliminator (QL), the voltage applied to the charging roller 160 is switched as follows: In other words, the voltage applied to the charging roller 160 is switched from the voltage applied during image formation so that the absolute value of the voltage applied to the charging roller 160 is less than the absolute value of the surface potential on the photosensitive drum 10 before passing through the static eliminator (QL). (3) At the same time as (2), the voltage applied to the developing roller 72 is switched from negative to positive. (4) Due to the potential difference between the charging roller 160 and the photosensitive drum 10 in (2), the positive residual toner adhering to the charging roller 160 moves onto the photosensitive drum. (5) When the positive residual toner that has moved onto the photosensitive drum 10 passes the transfer roller 62, the discharge lamp 64 (QL) is turned on. (6) After the positive residual toner that has been transferred to the photosensitive drum 10 has passed the charge removal lamp 64 (QL), the voltage applied to the charging roller 160 is switched to the voltage applied during image formation. (7) Due to the pre-charge discharge, the positive residual toner is negatively charged and passes through the nip between the charging roller 160 and the photosensitive drum 10. At the timings (8) and (7), the voltage applied to the developing roller 72 is switched from positive to negative. (9) The negatively charged residual toner is collected in the developing device by the potential of the developing roller 72 and the photosensitive member.

[0083] The above is an example of a method for controlling the charge polarity of the toner and recovering the toner by moving it in an electric field in each process. The background to the invention will now be described. The inventors used the cleanerless system shown in FIG. 1 to evaluate image retransfer by changing the applied voltage Vc of the charging roller, the surface potential on the photosensitive member after passing the charging roller, and the background potential.

[0084] The voltage Vc [V] applied to the charging roller is, for example, a voltage applied by the charging power source 21. The surface potential [V] on the photoconductor after passing the charging roller is the surface potential on the photoconductor after passing the position facing the charging roller (charging position). The surface potential on the photoconductor after passing the charging roller is sometimes expressed as Vd [V]. The background potential is the absolute value of the difference between the applied voltage Vb [V] of the developing roller and the surface potential Vd [V] on the photosensitive member after it has passed the charging roller.

[0085] The evaluation results are shown in Figures 6 and 7. Figure 6 shows the results when evaluation was performed using development unit B, which has a small M / A ratio. Figure 7 shows the results when evaluation was performed using development unit A, which has a large M / A ratio. A development unit is an example of a developing means. M / A refers to the amount of toner per unit area on the development roller, M refers to the amount of toner (mg), and A refers to the area.

[0086] 6 and 7 are diagrams for explaining test examples for deriving the requirements of the present invention, and are examples in which the same voltage is applied to the charging roller during image formation and non-image formation. The example shown in Fig. 6 is an example where developing unit B is used and the voltage applied to the charging roller during image formation and non-image formation is -1250 V. The example shown in Fig. 6 is a reference example 1 where the voltage applied to the charging roller during image formation and non-image formation is the same, and is not included in the present invention. The example shown in Fig. 7 is an example where developing unit A is used and the voltage applied to the charging roller during image formation and non-image formation is -1250 V. The example shown in FIG. 7 is Reference Example 2, which is not included in the present invention, in which the voltage applied to the charging roller during image formation is the same as that during non-image formation.

[0087] An evaluation chart was created by varying Vd, Vc, Vb, and the background potential, and the results were ranked from 1 to 5. Rank 5 indicates a good result and is considered to be acceptable. The evaluation criteria for ranks 1 to 5 are shown in the figure. Blank spaces in the figure indicate that no evaluation has been performed, but are considered to be acceptable.

[0088] The areas indicated by bold black frames in Figures 6 and 7 indicate the set values of the applied voltage Vc of the charging roller and the background potential (|Vd-Vb|) during image formation. In the areas indicated by bold black frames, the background potential is 300 V, Vc is -1250 V, and Vd is -600 V. The reason for using these values is to ensure both a solid density on the image and suppress background scumming (fogging) on the image.

[0089] In the evaluation results in Figure 6, the re-transfer rank for the setting values in the bold black frame was 5, which is a satisfactory result. In the evaluation results in Figure 7, the re-transfer rank for the setting values in the bold black frame was 3, which means re-transfer occurred on the image.

[0090] Considering the differences between Figures 6 and 7, the developing unit A used in the evaluation of Figure 7 has a larger amount of toner adhering to the developing roller than the developing unit B used in the evaluation of Figure 6. When a large amount of toner adheres to the developing roller, the charge per toner particle decreases, and therefore, when the same background potential is set, the amount of toner adhering to the photoconductor increases. The transfer amount (toner amount) of toner transferred to paper is roughly constant relative to the transfer bias. Therefore, the more toner adheres to the photoconductor, the more residual toner there will be. Therefore, it can be said that the developing unit A used in the evaluation of Figure 7 is more likely to produce residual toner than the developing unit B used in the evaluation of Figure 6.

[0091] If pre-charge discharge is performed when there is a large amount of residual toner, the residual toner will become excessively negatively charged. Through extensive research, the inventors have found that re-transfer occurs when the residual toner becomes excessively negatively charged. The results are shown in Figure 8.

[0092] Figure 8 plots the ranks of the evaluation results of Figure 7 using development unit A, with the horizontal axis representing the background potential and the vertical axis representing the toner charge amount [-μC / g] after passing through the charging device. As shown in the figure, ranks 1 to 5 are plotted as ×, ▲, △ (light gray), △ (white), and ○, respectively. Rank 5 indicates that no problem results were obtained.

[0093] The vertical axis represents the toner charge amount [-μC / g], with the downward movement in the graph indicating a greater negative charge. As shown in the figure, the greater the negative charge, the lower the rank, resulting in retransfer. For example, when the background potential is 100 V, the toner is ranked 5 (○) around -13 μC / g, but is ranked 2 (▲) around -18 μC / g, and is ranked 1 (×) around -21 μC / g and -26 μC / g. The straight lines in the graph represent the boundaries between rank 5 and ranks 1 to 4 as an approximation.

[0094] In the figure, rank 4 (△) is plotted when the skin potential is 200V, but this is the evaluation result after repeated trials. Repeated trials can sometimes result in a lower rank.

[0095] The reason why the transfer residual toner cannot be collected by the developing means when it becomes excessively negatively charged is thought to be, for example, as follows: When the transfer residual toner becomes excessively negatively charged, the electrostatic adhesion force between the transfer residual toner and the photosensitive member becomes strong, and the potential difference of the background potential is not strong enough to remove the electrostatic adhesion force, so that the toner cannot be collected by the developing means.

[0096] Looking at the results in Figure 8, for example, when the background potential is 300V and the toner charge amount after passing through the charger is around -35μC / g, the retransfer rank is 2 (▲), and retransfer occurs on the image. In contrast, when the background potential is 300V and the toner charge amount after passing through the charger is around -30μC / g, the retransfer rank is 5 (○), and retransfer does not occur on the image. From the results in Figure 8, it can be seen that in order to solve the conventional problem, the absolute value of the toner charge amount after passing through the charger should be kept below a certain value relative to the background potential.

[0097] In the above evaluation, the toner charge amount was measured using a suction-type toner charge amount measuring device as follows: Toner was sucked from the nozzle part by a pump, and the charge amount of the toner collected in a Faraday cage equipped with a filter inside the nozzle was measured.

[0098] The amount of charge on the toner after passing through the charge roller is determined by the potential difference between the voltage applied to the charge roller where pre-charge discharge occurs and the surface potential of the photoconductor before passing through the charge roller. For example, in the configuration of this embodiment shown in FIG. 3, a static elimination lamp 64 is used, and the surface potential of the photoconductor before passing through the charge roller is neutralized. The surface potential of the photoconductor before passing through the charge roller can be selected as appropriate, for example, to about -100 V, or, as shown in FIG. 4, to be -50 V. Taking this into consideration, the potential difference between the voltage applied to the charge roller where pre-charge discharge occurs and the surface potential of the photoconductor before passing through the charge roller can be changed by changing the voltage Vc applied to the charge roller.

[0099] Furthermore, to generate pre-charging discharge, the potential difference between the applied voltage Vc of the charging roller and the surface potential of the photosensitive member before passing through the charging roller must be equal to or greater than the discharge initiation voltage. Therefore, for example, the absolute value of the applied voltage Vc of the charging roller should be 800 V or greater, and the absolute value of the discharge initiation voltage should be 700 V or greater.

[0100] Furthermore, if the absolute value of the voltage Vc applied to the charging roller during image formation is greater than 1350 V, thin lines may become thin and dots may be missing. For this reason, the absolute value of the voltage Vc applied to the charging roller is preferably 800 V or more and 1350 V or less.

[0101] Figure 9 shows the results of examining the relationship between the toner charge amount after passing through the charging device and the voltage Vc applied to the charging roller. Figure 9 is a diagram showing an example of the relationship between the toner charge amount after passing through the charging device [-μC / g] on the vertical axis and the voltage Vc applied to the charging roller [-V] on the horizontal axis. As shown in the figure, there is a proportional relationship between the voltage Vc applied to the charging roller (charging member) and the toner charge amount after passing through the charging device. The dashed line in the figure is an approximation.

[0102] Without the static elimination lamp 64, the surface potential of the photosensitive member before passing through the charging roller is affected by the applied voltage of the transfer roller 62. Therefore, without the static elimination lamp 64, it is appropriate to control the amount of toner charge after passing through the charging roller by adjusting both the applied voltage Vc of the charging roller and the applied voltage of the transfer roller 62. To prevent retransfer from occurring, the amount of toner charge must be reduced by -10 μC / g or more compared to the amount of toner charge after passing through the charging roller when the voltage applied to the charging roller during image formation is used.

[0103] Therefore, referring to Figure 9, when the development roller is used to collect the residual toner after transfer during non-image formation, the applied voltage Vc (absolute value) of the charging roller during non-image formation should be 150 V lower than the applied voltage Vc (absolute value) of the charging roller during image formation.

[0104] To add a bit more about just lowering the voltage by 150V, we believe that lowering the voltage by 150V will be effective in preventing retransfer based on the following (1) to (3). (1) From Figure 7, it can be seen that there is an effect on re-transfer when the applied voltage Vc of the charging roller is -1150V (background potential: 300V). As shown in the figure, when Vc is -1150V and the background potential is 300V, the rank is 5. (2) In FIG. 8, when the background potential is 300 V, it can be seen that if the charge amount (absolute value) of the residual toner after passing through the charging roller is 30 μC / g or less, it is effective against retransfer. (3) In Figure 9, when the applied voltage to the charging roller is -1150V, the toner charge amount (absolute value) after passing through the charging roller varies, with the upper plot exceeding 30 μC / g. In contrast, when the applied voltage to the charging roller is -1100V in the same figure, the toner charge amount (absolute value) after passing through the charging roller also varies, but even though there is variation, the upper plot remains below 30 μC / g. In other words, there is a risk that the results in Figure 7 will change from 5 to 4 if the number of trials is increased.

[0105] Due to these factors (1) to (3), it is believed that when images are not being formed, lowering the applied voltage Vc of the charging roller to -1100 V is effective against retransfer. Furthermore, since the applied voltage during image formation is -1250 V (as mentioned above, FIG. 7 shows an example in which the applied voltage during image formation is -1250 V), 1250 V - 1100 V = 150 V, so it is believed that a reduction of 150 V is sufficient.

[0106] Therefore, the image forming apparatus of this embodiment is provided with a charging roller for charging the photosensitive member, and has a cleaner-less configuration in which the transfer residual toner is collected into the developing device via the developing roller, and is configured as follows. The absolute value of the applied voltage Vc of the charging roller is greater than the absolute value of the surface potential of the photosensitive member before passing through the charging roller, and the absolute value of the potential difference between the applied voltage Vc of the charging roller and the surface potential of the photosensitive member before passing through the charging roller is equal to or greater than the absolute value of the discharge start voltage.Furthermore, the absolute value of the applied voltage Vc of the charging roller is set to be smaller than the absolute value of the voltage applied to the charging roller during image formation.

[0107] The condition in the first paragraph, i.e., the absolute value of the applied voltage Vc of the charging roller is greater than the absolute value of the surface potential of the photosensitive member before the charging roller passes, and the absolute value of the potential difference between the applied voltage Vc of the charging roller and the surface potential of the photosensitive member before the charging roller passes is equal to or greater than the absolute value of the discharge start voltage, refers to the pre-charging discharge process. In other words, the charging roller is in a state of discharging to the photosensitive member. This is expressed as the content of voltage control.

[0108] In this way, it is preferable that the control section controls the charging voltage application member so that the absolute value of the voltage applied to the charging roller when no image is formed is lower than the absolute value of the voltage applied to the charging roller when an image is formed. By lowering the voltage applied to the charging roller when the developing roller 72 collects the toner, excessive negative charging of the residual toner can be suppressed, and the electrostatic attraction force between the residual toner and the photosensitive member can be weakened. As a result, the potential difference between the voltage applied to the developing roller and the surface potential on the photosensitive member makes it easier for the developing means to collect the toner.

[0109] This embodiment will be described again. In the discharge process, the absolute value of the voltage applied to the charging member is set to be larger than the absolute value of the surface potential of the image carrier before it passes through the charging position where the charging member and the image carrier face each other, and is equal to or larger than the absolute value of the discharge start voltage, and smaller than the absolute value of the voltage applied to the charging member during image formation, which is the period when the exposure means is performing exposure. By performing such control, the evaluation results of the example shown in FIG. 6 (Reference Example 1) and the example shown in FIG. 7 (Reference Example 2) are improved. For example, for comparison with Reference Example 1, if development unit B is used and the applied voltage to the charge roller during image formation is set to -1250 V and the applied voltage to the charge roller during non-image formation is set to -1100 V, the results of ranks 1 and 4 (fail) shown in FIG. 6 can be changed to rank 5 (pass). Furthermore, for comparison with Reference Example 2, if development unit A is used and the applied voltage to the charge roller during image formation is set to -1250 V and the applied voltage to the charge roller during non-image formation is set to -1100 V, the results of ranks 1 and 3 (fail) shown in FIG. 7 can be changed to rank 5 (pass).

[0110] Next, an example of a method for switching the voltage applied to the charging roller during image formation and non-image formation will be described with reference to Fig. 10. Fig. 10 is an example of a sequence diagram during continuous printing.

[0111] At timing t1 when the image formation of the first sheet is completed, (a) the exposure is switched from ON to OFF. At this timing, (b) the applied voltage to the charging roller is switched from -1250V to -1100V. After the switch, the photoconductor is rotated one or two times, so that the residual toner after transfer is collected by the developing roller without remaining on the photoconductor.

[0112] In the figure, the period from t1 to t2 is represented by D1. D1 is preferably, for example, one or two revolutions of the photosensitive drum. In this case, it is possible to prevent the recovery operation period from becoming too long. The number of revolutions of the photosensitive drum is preferably determined based on the length of the paper gap, the printing rate, etc.

[0113] In this example, at timing t2 when the time required for the photosensitive member to make one or two revolutions has elapsed, (b) the voltage applied to the charging roller is returned from -1100V to -1250V.

[0114] Timing t3 indicates the stage when the voltage applied to the charging roller has been switched and all other printing-related modules have completed their preparations for printing. In this example, at timing t3, the transport of the paper waiting at the register (for example, the pair of register rollers 6) is resumed.

[0115] D2 in the figure represents the difference between the transport distance of the paper from the resist to the transfer position and the rotation distance of the photosensitive drum surface from the exposure position to the transfer position. D2 is the distance (time) obtained by subtracting the rotation distance of the photosensitive drum surface from the exposure position to the transfer position from the transport distance of the paper from the resist to the transfer position. Exposure is turned on at timing t4 taking this D2 into consideration.

[0116] Timing t4 is the timing when (a) exposure is switched ON after D2 has elapsed since transport began at timing t3. By switching exposure ON, image formation for the second sheet is carried out. The period from timing t2 to t4 can also be said to be a preparation period for the next image formation.

[0117] The figure shows periods during which images are formed and periods during which images are not formed. In this example, the period before t1 and the period after t4 are periods during which images are formed. In addition, the period from t1 to t4 is periods during which images are not formed.

[0118] Image formation corresponds to developing on a photosensitive drum. Development on the photosensitive drum is switched on and off by turning exposure on and off. When exposure is turned off, image formation (development) stops, and at that time, the residual toner is collected by the developing roller. During the period from t1 to t2, pre-charge discharge and development collection are performed, so during this period, the absolute value of the voltage applied to the (b) charging roller is reduced to weaken the adhesion of the residual toner to the photosensitive drum after passing through the charging roller. In this example, at t1, the voltage applied to the (b) charging roller is changed from -1250V to -1100V, reducing the absolute value of the applied voltage. This prevents the residual toner on the photosensitive drum from becoming excessively negatively charged after passing through the charging roller, making it easier for the toner to be collected by the developing roller.

[0119] In Figure 10, the collection operation corresponds to, for example, the period from t1 to t2. In this example, the collection operation is an operation performed during non-image formation (the period from t1 to t4). In this example, the discharge process is performed from t1 to t2, and the collection process is performed from t1 to t2. However, the collection operation, discharge process, and collection process may be extended to the period from t1 to t4.

[0120] 10 shows an example of voltage control for pre-charge discharge in the process of recovering residual toner by the developing means, but in this embodiment, such voltage control may also be performed during other processes. For example, similarly, control may be performed to make the voltage applied to the charging roller smaller than the voltage applied to the charging roller during image formation (development) during discharge for toner recovery performed when shutting down the device.

[0121] Fig. 11 is an example of a sequence diagram for explaining this example. Fig. 11 is an example of a sequence diagram when shutting down the device. For convenience of explanation, the process is shown as starting from timing t4.

[0122] Even when the device is shut down, the voltage applied to the (b) charging roller is controlled so that its absolute value is lower than the voltage applied to the (b) charging roller during image formation (development). In this example, voltage control is performed to set the voltage applied to the (b) charging roller to -950 V during the period from timing t12 to t15. This prevents the residual toner on the photosensitive member after passing through the charging roller from being excessively negatively charged, and allows the toner to be efficiently collected by the developing roller.

[0123] Next, other preferable examples of this embodiment will be described. It is preferable that the control unit controls the charging voltage application means so that the difference between the absolute value of the voltage applied to the charging member during image formation and the absolute value of the voltage applied to the charging member during non-image formation is 150 V or more. In this way, by controlling the applied voltage during image formation and non-image formation, it is possible to ensure both image density and suppress retransfer. Therefore, a stable cleanerless image forming apparatus can be achieved. The reason why 150V or more is preferable is due to the reasons explained in Figures 7 to 9 and (1) to (3) above.

[0124] The transfer means in this embodiment is disposed in contact with the image carrier and includes a transfer member (e.g., transfer roller 62) that transfers the toner image to a transferee that passes through the contact area with the image carrier. A voltage is applied to the transfer member to perform the transfer, and it is preferable that the absolute value of the current that flows through the transfer member due to the voltage application to the transfer member is 10 μA or more.

[0125] The current flowing through the transfer roller 62 is determined by measuring the current flowing between the transfer power supply 24 and the transfer roller 62 when a transfer bias voltage is applied. The current flowing through the transfer roller 62 may be the current flowing between the image carrier and the transferred material when a transfer bias voltage is applied. The current flowing between the image carrier and the transferred material is determined by measuring the current flowing between the transfer power supply 24 and the transfer roller 62 when a transfer bias voltage is applied.

[0126] By setting the current to 10 μA or more, the amount of charge on the residual toner after it has passed through the transfer area can be kept low. As a result, the amount of charge on the residual toner after it has passed through the transfer area does not become excessive, and the electrostatic adhesion force is suppressed. This makes it possible to further prevent retransfer. A voltage is applied to the transfer member by, for example, a transfer voltage applying means (for example, a transfer power supply 24).

[0127] The image forming apparatus of this embodiment preferably has a cleaning mode as in the following example. The charging member is a charging roller that contacts the surface of the image bearing member. The charging member has a cleaning mode in which toner adhering to the charging roller is transferred to the surface of the image bearing member. The cleaning mode is performed during non-image formation.

[0128] In this way, by performing the cleaning mode during non-image formation, the toner adhering to the charging roller can be effectively collected by the developing means. The cleaning mode in this example can be explained, for example, by the explanation of Figure 5A (arrow e).

[0129] The image forming apparatus of this embodiment preferably has a cleaning member and a cleaning mode as in the following example. The charging member is a charging roller that contacts the surface of the image carrier. The charging member has a cleaning member that contacts the surface of the charging member. The cleaning mode transfers toner adhering to the cleaning member to the charging member, and transfers toner that has transferred to the charging roller to the surface of the image carrier. The cleaning mode is performed during non-image formation.

[0130] In this way, by providing a cleaning member, the charging member can be made cleaner. Furthermore, by performing the cleaning mode when no image is being formed, the toner adhering to the charging roller can be efficiently collected by the developing means. An example of the cleaning member is the collection brush 161. The cleaning mode can be explained, for example, by referring to the explanation of FIG. 5A (arrows d and e).

[0131] (Second embodiment) Next, another embodiment of the present invention will be described, and a description of the same matters as those in the above embodiment will be omitted. In this embodiment, the voltage of the charging roller (charging member) is controlled based on the absolute humidity determined from the temperature and humidity. That is, in this embodiment, the control unit controls the voltage to be applied to the charging member based on the absolute humidity inside or outside the image forming apparatus, and such control is performed during image formation and / or non-image formation.

[0132] The control can be performed, for example, as follows: A memory (storage unit) is used for image formation, and multiple settings for the voltage applied to the charging roller are stored in advance. The voltage applied to the charging roller is selected from the various settings according to the absolute humidity, and the settings are changed accordingly.

[0133] The absolute humidity is calculated based on the output of a sensor that detects the temperature and humidity inside or outside the image forming apparatus. The calculated absolute humidity is compared with a threshold value pre-stored in the memory of the image forming apparatus. If the absolute humidity is below the threshold, the applied voltage is switched to a value lower than the applied voltage value selected when the threshold is not exceeded.

[0134] For example, when the absolute humidity is low, the toner becomes more easily charged, so the voltage applied to the charging roller during image formation is set high to ensure density, and in the recovery process, the voltage applied to the charging roller during pre-charge discharge is lowered so that the transfer residual toner does not become highly charged. According to this embodiment, when performing the discharge process (pre-charge discharge), the transfer residual toner can be stably charged to an appropriate amount without being affected by changes in absolute humidity.

[0135] (Third embodiment) Next, another embodiment of the present invention will be described, and a description of the same matters as those in the above embodiment will be omitted. This embodiment uses a peeling roller. In this embodiment, the peeling roller reduces the adhesion of toner that has strongly adhered (fixed) to the photosensitive member. This allows the developing unit to effectively collect the residual toner after transfer. In addition, this embodiment can suppress filming on the photosensitive member.

[0136] 12 is a schematic diagram illustrating an example of an image forming apparatus according to the present embodiment, and is a diagram similar to FIG. 1. In this example, the peeling roller 165 is disposed in contact with the photosensitive drum 10. In addition, the peeling roller 165 in this example is disposed downstream of the transfer roller 62 and upstream of the charging roller 160 in the rotation direction of the photosensitive drum 10. The peeling roller 165 is made of, for example, a silicone resin sponge.

[0137] In the present invention, it is possible to configure the device without using the static elimination lamp 64 (static elimination means), and this example is an example in which a static elimination lamp is not used.

[0138] In this example, the residual toner can be peeled off from the photosensitive drum 10 by, for example, using the difference in peripheral speed between the peeling roller 165 and the photosensitive drum 10. The peeling roller 165 rubs against the surface of the photosensitive drum 10, thereby peeling off the residual toner from the surface of the photosensitive drum 10. Furthermore, a negative voltage is applied to the peeling roller 165 in this example. It is preferable that a voltage (negative) smaller in absolute value than the voltage applied to the charging roller 160 during pre-charge discharge in the present invention is applied to the peeling roller 165.

[0139] By applying a voltage to the peeling roller 165 in this manner, the transfer residual toner peeled off by the peeling roller 165 is charged by the peeling roller 165 and re-adheres to the surface of the photosensitive drum 10. Then, the transfer residual toner, which has been negatively charged by the discharge process (pre-charge discharge) by the charging roller 160, is collected by the developing roller 72. The transfer residual toner is peeled off from the photosensitive drum 10 by the peeling roller 165 and re-adheres to the photosensitive drum 10 with weak adhesive force, making it easier for the developing roller 72 to collect the transfer residual toner. This makes it possible to suppress filming on the photosensitive drum 10.

[0140] In this way, in this example, the adhesive force of toner that has strongly adhered (fixed) to the photosensitive drum 10 is reduced by the peeling roller 165. The present invention has a concept of reducing the adhesive force between the transfer residual toner and the surface of the photosensitive drum 10, and this example can be said to be an example that was studied based on this concept. In this example, the peeling roller 165 can reduce the adhesive force between the transfer residual toner and the surface of the photosensitive drum 10, making it easier to collect the transfer residual toner with the developing roller 72.

[0141] This embodiment will be described again. In this embodiment, a peeling roller is provided downstream of the position where the transfer means performs transfer in the rotation direction of the image carrier, and upstream of the charging position, and the peeling roller rotates in contact with the image carrier, peeling off the residual toner adhering to the surface of the image carrier by the difference in peripheral speed with the image carrier. By arranging the peeling roller in this manner, the adhesive force of the residual toner before pre-charge discharge can be reduced, and the residual toner can be easily peeled off by utilizing the difference in peripheral speed.

[0142] In the present embodiment, it is preferable that a voltage smaller in absolute value than the voltage applied to the charging member in the discharge treatment is applied to the peeling roller. In this case, the adhesive force of the transfer residual toner that has re-adhered to the photosensitive drum 10 can be reduced.

[0143] (Fourth embodiment) Next, another embodiment of the present invention will be described, and a description of the same matters as those in the above embodiment will be omitted. In this embodiment, the charging member is of a non-contact charging type, and a temporary cleaning roller is provided on the photosensitive drum. The cleanerless system uses a developing roller to collect toner, and even if a temporary cleaning roller is used in addition to the development roller, it is still considered a cleanerless system.

[0144] Fig. 13 is a schematic diagram for explaining an example of an image forming apparatus according to this embodiment, and is a diagram similar to Fig. 1. In this example, a scorotron charger is used as the charging member. This charging member is shown as charger 163 in the drawing. As shown in the drawing, charger 163 is of a non-contact charging type.

[0145] Furthermore, a temporary cleaning roller 166 is provided downstream of the transfer roller 62 and upstream of the charger 163 in the rotation direction of the photosensitive drum 10. The temporary cleaning roller 166 is, for example, a brush roller.

[0146] A voltage, for example, a negative voltage, is applied to the temporary cleaning roller 166 by the cleaning power supply 23. In this case, the positively polarized transfer residual toner is temporarily stored on the temporary cleaning roller 166. "Stored" here means that the positively polarized transfer residual toner moves toward the temporary cleaning roller 166 and is held by the temporary cleaning roller 166. The transfer residual toner temporarily stored on the temporary cleaning roller 166 is toner charged with a polarity opposite to the normal charge. The normal charge is, for example, a negative polarity, and the toner charged with a polarity opposite to the normal charge is, for example, the positively polarized transfer residual toner as described above.

[0147] On the other hand, the negatively charged residual toner passes through the temporary cleaning roller 166 , is injected with negative charges by the discharge process (pre-charge discharge) by the charging roller 160 , and is then collected by the developing roller 72 .

[0148] In this example, when a job is completed, a positive voltage is applied to the temporary cleaning roller 166. As a result, the potential difference between the temporary cleaning roller 166 and the photosensitive drum 10 causes the positively charged residual toner stored on the temporary cleaning roller 166 to move to the photosensitive drum 10. This movement is also called expulsion. The transferred residual toner is injected with a negative charge by a discharge process (pre-charge discharge) using the charger 163, and is then collected by the developing roller 72. This allows the temporary cleaning roller 166 to be kept clean.

[0149] Furthermore, in this example, the temporary cleaning roller 166 is disposed upstream of the charger 163 in the rotation direction of the photosensitive drum 10. Therefore, the transfer residual toner that has moved from the temporary cleaning roller 166 to the photosensitive drum 10 is immediately injected with a negative charge by the charger 163. In other words, the transfer residual toner that has moved from the temporary cleaning roller 166 to the photosensitive drum 10 is injected with a negative charge by pre-charge discharge immediately after movement, so the distance that the photosensitive drum 10 must rotate before the negative charge is injected into the transfer residual toner by pre-charge discharge can be shortened.

[0150] In this example, the distance that the photosensitive drum 10 must rotate before negative charge is injected into the residual toner by pre-charge discharge can be made shorter than in the above embodiment (the embodiment using the collection brush 161). This makes it possible to slow down deterioration of the photosensitive drum 10 and extend the life of the photosensitive drum 10.

[0151] In the case of the configuration using the collection brush 161, the transfer residual toner held on the collection brush 161 moves from the collection brush 161 to the charging roller 160, passes the positions of the development roller 72 and the transfer roller 62, and then undergoes pre-charge discharge. Therefore, in this embodiment, the distance over which the photosensitive drum 10 rotates until the accumulated transfer residual toner undergoes pre-charge discharge can be shortened compared to the configuration using the collection brush 161. In the description here, the transfer residual toner temporarily accumulated on the cleaning roller 166 or the transfer residual toner accumulated on the collection brush 161 is referred to as accumulated transfer residual toner.

[0152] This embodiment will be described again. The charging member in this embodiment is a non-contact charging member that does not come into contact with the image carrier, and is located downstream of the position where the transfer means performs transfer in the rotation direction of the image carrier, and has a temporary collection means upstream of the charging position, and the temporary collection means temporarily collects transfer residual toner that is charged with a polarity opposite to the normal charge on the surface of the image carrier (for example, positive). The temporary collecting means is, for example, a temporary cleaning roller 166. By using a non-contact charging member, it is possible to prevent transfer residual toner from moving to the charging member and causing charging failure. By using the temporary collection means arranged as described above, it is possible to temporarily store transfer residual toner on the image carrier. Furthermore, when a non-contact charging member and temporary collection means are used, a collection means (e.g., collection brush 161) is not required, and the number of parts can be reduced.

[0153] In addition, the image forming apparatus of this embodiment has a cleaning voltage application means (e.g., cleaning power supply 23) that applies voltage to the temporary collection means, and the control unit controls the cleaning voltage application means at the end of image formation to move the transfer residual toner collected by the temporary collection means to the image carrier. By doing so, the transfer residual toner collected in the temporary collection means and discharged onto the image carrier can be subjected to pre-charge discharge immediately after being discharged, thereby reducing the distance the image carrier must rotate. This can extend the life of the image carrier. Furthermore, by moving the transfer residual toner collected in the temporary collection means back onto the image carrier, the temporary collection means can be kept clean over time.

[0154] (Fifth embodiment) Next, another embodiment of the present invention will be described, and a description of the same matters as those in the above embodiment will be omitted. This embodiment is an example in which a transfer belt is used to transport a recording medium, and this embodiment is also an example in which a temporary collection means, a belt cleaning mechanism, and a waste toner storage unit are used. This embodiment uses a direct transfer method, in which a toner image is transferred to a recording medium. The following explanation is an example in which a color machine is configured.

[0155] In the fourth embodiment, the toner discharged from the temporary collection means (for example, the temporary cleaning roller 166) is negatively charged and collected by the developing roller 72. In this embodiment, the toner discharged from the temporary collection means moves to the transfer belt, is collected by the belt cleaning mechanism, and is stored in the waste toner storage section.

[0156] FIG. 14 is a schematic diagram illustrating an example of an image forming apparatus according to this embodiment. The image forming apparatus according to this embodiment is an example of a color machine configuration in which photosensitive units for yellow, magenta, cyan, and black are arranged in tandem. Photosensitive units 172Y, 172M, 172C, and 172K corresponding to the respective colors are provided. The selection of colors and the arrangement of the photosensitive units are not limited to the illustrated example and can be modified as appropriate. When describing each photosensitive unit without distinction, they may be referred to as photosensitive unit 172.

[0157] The photosensitive unit 172 has a photosensitive drum 10 as an image carrier, a charger 163 as a charging member, a temporary cleaning roller 166 as a temporary collection means, and a developing roller 72 as a developer carrier of the developing device. These are provided corresponding to yellow, magenta, cyan, and black, respectively. Only the photosensitive unit 172Y is shown with the reference numerals such as photosensitive drum 10, and the reference numerals are omitted for the photosensitive units 172M, 172C, and 172K.

[0158] Although the exposure means 5 are illustrated as Y, M, C, and K corresponding to yellow, magenta, cyan, and black, respectively, the present invention is not limited to this. A common exposure means 5 may also be used.

[0159] A transfer roller 62 is disposed opposite each photosensitive drum 10. The transfer rollers 62 are labeled Y, M, C, and K, corresponding to yellow, magenta, cyan, and black. The recording paper 105 is transported by a transfer belt 180 and passes between the photosensitive drum 10 and the transfer rollers 62, whereupon the yellow, magenta, cyan, and black toner images are transferred onto the recording paper 105. The transfer belt 180 is rotated by, for example, a transport roller 181.

[0160] In this example, as in the fourth embodiment, a charger 163, which is a non-contact charging type charging member, is used. Also, as in the fourth embodiment, a temporary cleaning roller 166 is used. Although the cleaning power supply 23 is not shown in the figure, a voltage is applied to the temporary cleaning roller 166 by the cleaning power supply 23.

[0161] The image forming apparatus of this embodiment has a belt cleaning mechanism 185 for the transfer belt 180. The belt cleaning mechanism 185 in this embodiment has a cleaning roller 182, a collection roller 183, and a cleaning blade 184. The cleaning roller 182 cleans the toner on the transfer belt 180. The collection roller 183 collects the toner that has moved to the cleaning roller 182. The cleaning blade 184 cleans the toner that has moved to the collection roller 183.

[0162] The image forming apparatus of this embodiment also includes a waste toner container 186. The toner that has moved to the collection roller 183 is scraped off by a cleaning blade 184 and collected in the waste toner container 186.

[0163] An example of the operation in this embodiment will be described. When the job is completed, a positive voltage is applied to the temporary cleaning roller 166. Due to the potential difference between the temporary cleaning roller 166 and the photosensitive drum 10, the positive residual toner temporarily stored on the temporary cleaning roller 166 moves to the photosensitive drum 10. At this time, the development roller 72 is separated from the photosensitive drum 10. As a result, the toner discharged from the temporary cleaning roller 166 onto the photosensitive drum 10 passes through the development roller 72 (development area) and moves to the transfer area. At this time, by controlling the voltage of the transfer roller 62, the toner on the photosensitive drum 10 moves to the transfer belt 180. The toner that has moved to the transfer belt 180 is then collected by the belt cleaning mechanism 185 (cleaning roller 182, collection roller 183, cleaning blade 184) and stored in the waste toner container 186.

[0164] The voltage of the transfer roller 62 can be controlled by the control unit 25 controlling the transfer power supply 24. The voltage of the temporary cleaning roller 166 can be controlled by the control unit 25 controlling the cleaning power supply 23.

[0165] In this embodiment, when image formation is completed, that is, when a job is completed, the toner is collected by the belt cleaning mechanism 185 as described above and stored in the waste toner container 186. Although not explained here, in this embodiment as well, the normally charged toner (negative toner) is collected by the development roller during the exposure OFF period (when no image is being formed) as described in the above embodiment, and this embodiment is also included in the present invention.

[0166] In this manner, in this embodiment, the transfer residual toner that is temporarily stored on the temporary cleaning roller 166 and that has moved to the transfer belt 180 is collected from the transfer belt 180 in the waste toner container 186. This prevents transfer residual toner of other colors from mixing with the developing means, thereby making it possible to suppress color abnormalities that may occur due to transfer residual toner of other colors mixing with the developing means.

[0167] This embodiment will be described again. In this embodiment, the transfer means includes a transfer roller facing the image carrier and a transfer belt sandwiched between the transfer roller and the image carrier. The image forming apparatus also includes a belt cleaning mechanism that collects toner adhering to the transfer belt from the transfer belt, and a waste toner storage unit that stores the toner collected by the belt cleaning mechanism. In this embodiment, the control unit also moves the residual toner collected by the temporary collection means to the image carrier, the transfer belt, the belt cleaning mechanism, and the waste toner storage unit in this order at the end of image formation. In this way, it is possible to prevent color abnormalities caused by the mixing of transfer residual toner of other colors in the developing means. In addition, in this embodiment, the transfer residual toner can be moved to the transfer belt and collected by the belt cleaning mechanism, and even if the transfer residual toner moves to the transfer belt, it can be collected by the belt cleaning mechanism.

[0168] (Sixth embodiment) Next, another embodiment of the present invention will be described, and a description of the same matters as those in the above embodiment will be omitted. This embodiment is a configuration of a direct transfer color machine, and is an example in which a transfer belt is used to transport a transfer target. Like the fourth and fifth embodiments, this embodiment has a temporary collection unit. In this embodiment, residual toner discharged from the temporary collection unit in the yellow (Y), magenta (M), and cyan (C) photosensitive units moves to the transfer belt and is collected by the developing roller of the black (K) photosensitive unit. The difference from the fifth embodiment is that the image forming apparatus of this embodiment does not have a belt cleaning mechanism or a waste toner storage unit.

[0169] When yellow (Y), magenta (M), and cyan (C) color toners are collected by the developing means, they become mixed, making it difficult to collect toners of other colors in the developing means. On the other hand, because they are the three primary colors, when they mix together they become black, so even if toners of other colors are collected by the developing means that supplies black (K) toner, there is less change in color than with other colors.

[0170] For this reason, in this embodiment, toner of other colors is collected by the black (K) developing means. As a result, in this embodiment, the belt cleaning mechanism and waste toner storage unit can be omitted, thereby reducing costs. Also, in this embodiment, toner collection is not required in the developing means that supply yellow (Y), magenta (M), and cyan (C) color toner, so color abnormalities can be reduced.

[0171] Fig. 15 is a schematic diagram for explaining an example of an image forming apparatus of this embodiment, and is a diagram similar to Fig. 14. As shown in Fig. 15, the image forming apparatus of this example has photosensitive units 172Y, 172M, 172C, and 172K, and does not have the belt cleaning mechanism and waste toner storage unit shown in Fig. 14. The photosensitive unit 172 and the like common to Fig. 14 can be similar to those described above, and therefore description thereof will be omitted here.

[0172] An example of the operation in this embodiment will be described. At the end of the job, a positive voltage is applied to the temporary cleaning roller 166. Due to the potential difference between the temporary cleaning roller 166 and the photosensitive drum 10, the positive residual toner temporarily stored on the temporary cleaning roller 166 moves to the photosensitive drum 10. At this time, the yellow (Y), magenta (M), and cyan (C) color developing rollers 72Y, 72M, and 72C are separated from the photosensitive drums 10Y, 10M, and 10C. As a result, the color toner ejected from the temporary cleaning rollers 166Y, 166M, and 166C onto the photosensitive drums 10Y, 10M, and 10C passes through the developing rollers 72Y, 72M, and 72C (development area) and moves to the transfer area. At this time, the toner on the photosensitive drum 10 moves to the transfer belt 180 by controlling the voltage of the color transfer rollers 62Y, 62M, and 62C.

[0173] The color toner that has moved to the transfer belt 180 is then transported by the transfer belt 180. At this time, the voltage of the black transfer roller 62K is controlled to move the color toner on the transfer belt 180 to the photosensitive drum 10K. Then, the charger 163K performs pre-charge discharge on the transfer residual toner that has moved to the photosensitive drum 10K, injecting a negative charge into the toner. The toner that has been injected with the negative charge is then collected by the developing roller 72K.

[0174] In the figure, it is shown that the color transfer residual toner moves from the yellow, magenta, and cyan photosensitive drums 10 to the transfer belt 180 and is transported by the transfer belt 180. The transfer residual toner that has moved to the transfer belt 180 is given, for example, the reference numeral 203. The transfer residual toner of the color that has moved to the transfer belt 180 then moves to the black photosensitive drum 10 and is collected by the developing roller 72K in the black photosensitive unit 172K.

[0175] In this embodiment, the black photosensitive unit 172K performs the predetermined pre-charge discharge and recovery process described in the above embodiment. As described above, in the present invention, the adhesive force of the transfer residual toner to the image carrier can be reduced by appropriately controlling the voltage applied to the charging member during pre-charge discharge. Therefore, even if color transfer residual toner from other photosensitive units moves to the black image carrier via the transfer belt, as in this embodiment, the adhesive force between the transfer residual toner and the image carrier can be reduced, allowing it to be efficiently recovered by the black developing roller.

[0176] As shown in the figure, in this embodiment, it is preferable that the black photosensitive unit 172K is located downstream of the other photosensitive units in the direction of rotation of the transfer belt (indicated by the arrow in the figure). In this case, the residual toner that has moved from the other photosensitive units to the transfer belt quickly reaches the downstream black photosensitive unit, thereby shortening the distance that it is transported by the transfer belt.

[0177] This embodiment will be described again. The image forming apparatus of this embodiment includes a plurality of photosensitive units, each having the image carrier, the charging member, the developing means, and the temporary collection means. The transfer means includes a transfer roller facing the image carrier and a transfer belt sandwiched between the transfer roller and the image carrier. The photosensitive units include color photosensitive units having the developing means that supply color toner to the image carrier, and a black photosensitive unit having the developing means that supply black toner to the image carrier. The black photosensitive unit is disposed downstream of the color photosensitive units in the rotation direction of the transfer belt. Of the color transfer residual toner temporarily collected by the temporary collection means in the color photosensitive units, the transfer residual toner that has moved to the transfer belt is collected by the developing means of the black photosensitive unit via the image carrier of the black photosensitive unit. According to this embodiment, even when color toners are used and a cleanerless system in which toner is collected by a developing roller is adopted, color abnormalities can be reduced by collecting toners of other colors using the developing means that supplies black (K) toner. In addition, a belt cleaning mechanism and a waste toner storage unit can be omitted, which allows for cost reduction and a more compact device.

[0178] For example, aspects of the present invention are as follows. <1> an image carrier; a charging member for charging the image bearing member; a charging voltage applying means for applying a voltage to the charging member; an exposure unit that exposes the charged image carrier to light to form a latent image on the surface of the image carrier; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer means for transferring the toner image onto a transfer target; a control unit that controls a recovery operation for recovering residual toner remaining on the image carrier after transfer into the developing unit, The recovery operation is an operation performed during non-image formation, i.e., a period when the exposure unit is not performing exposure, and includes a discharge process for charging the transfer residual toner by discharging between the charging member and the image carrier, and a recovery process for recovering the charged transfer residual toner by the developing unit, The control unit controls the charging voltage application unit so that the absolute value of the voltage applied to the charging member in the discharge process is greater than the absolute value of the surface potential of the image carrier before the charging member passes through a charging position where the charging member and the image carrier face each other, is equal to or greater than the absolute value of a discharge start voltage, and is smaller than the absolute value of the voltage applied to the charging member during image formation, which is a period during which the exposure unit is performing exposure. An image forming apparatus characterized by: <2> The control unit controls the charging voltage application means so that the difference between the absolute value of the voltage applied to the charging member during the image formation and the absolute value of the voltage applied to the charging member during the non-image formation is 150 V or more. Characterized by <1> 2. The image forming apparatus according to claim 1 . <3> the transfer means has a transfer member disposed in contact with the image carrier and transferring the toner image to a transfer-receiving body passing through a contact portion with the image carrier; A voltage is applied to the transfer member to perform the transfer; The absolute value of the current flowing through the transfer member when a voltage is applied to the transfer member is 10 μA or more. Characterized by <1> or <2> 2. The image forming apparatus according to claim 1 . <4> the charging member is a charging roller that contacts the surface of the image carrier, a cleaning mode in which the toner adhering to the charging roller is transferred to the surface of the image carrier; The cleaning mode is performed during the non-image formation period. Characterized by <1> from <3> 10. The image forming apparatus according to claim 9, wherein: <5> the charging member is a charging roller that contacts the surface of the image carrier, a cleaning member that contacts the surface of the charging member; a cleaning mode in which the toner adhering to the cleaning member is transferred to the charging member, and the toner transferred to the charging roller is transferred to the surface of the image carrier; The cleaning mode is performed during the non-image formation period. Characterized by <1> from <3> 10. The image forming apparatus according to claim 9, wherein: <6> The control unit controls the voltage applied to the charging member based on the absolute humidity inside or outside the image forming apparatus. Characterized by <1> from <5> 10. The image forming apparatus according to claim 9, wherein: <7> The charging member is provided so as to be in contact with the image bearing member. Characterized by <1> from <6> 10. The image forming apparatus according to claim 9, wherein: <8> a peeling roller is provided downstream of a position where the transfer means performs transfer in the rotation direction of the image carrier and upstream of the charging position; The peeling roller rotates in contact with the image carrier, and peels off the transfer residual toner adhering to the surface of the image carrier by the difference in peripheral speed between the peeling roller and the image carrier. Characterized by <1> from <7> 10. The image forming apparatus according to claim 9, wherein: <9> A voltage smaller in absolute value than the voltage applied to the charging member in the discharge treatment is applied to the peeling roller. Characterized by <8> 2. The image forming apparatus according to claim 1 . <10> the charging member is a non-contact charging member that does not come into contact with the image bearing member, a temporary collection means located downstream of a position where the transfer means performs transfer in the rotation direction of the image carrier and upstream of the charging position; The temporary collecting means temporarily collects the transfer residual toner that is charged with a polarity opposite to the normal charge on the surface of the image carrier. Characterized by <1> from <9> 10. The image forming apparatus according to claim 9, wherein: <11> a cleaning voltage applying means for applying a voltage to the temporary collecting means; The control unit controls the cleaning voltage application unit to move the transfer residual toner collected by the temporary collection unit to the image carrier at the end of image formation. Characterized by <10> 2. The image forming apparatus according to claim 1 . <12> the transfer unit includes a transfer roller facing the image carrier and a transfer belt sandwiched between the transfer roller and the image carrier; a belt cleaning mechanism that collects toner adhering to the transfer belt from the transfer belt; and a waste toner storage unit that stores the toner collected by the belt cleaning mechanism, The control unit moves the transfer residual toner collected by the temporary collection unit to the image carrier, the transfer belt, the belt cleaning mechanism, and the waste toner storage unit in this order when image formation is completed. Characterized by <10> or <11> 2. The image forming apparatus according to claim 1 . <13> a plurality of photosensitive units each having the image carrier, the charging member, the developing means, and the temporary collection means; the transfer unit includes a transfer roller facing the image carrier and a transfer belt sandwiched between the transfer roller and the image carrier; the photosensitive unit includes a color photosensitive unit having the developing means for supplying color toner to the image carrier, and a black photosensitive unit having the developing means for supplying black toner to the image carrier, the black photosensitive unit is disposed downstream of the color photosensitive units in the rotation direction of the transfer belt, Of the color transfer residual toners temporarily collected by the temporary collection means in the color photosensitive units, the transfer residual toners that have moved to the transfer belt are collected by the developing means of the black photosensitive unit via the image carrier of the black photosensitive unit. Characterized by <1> from <12> 10. The image forming apparatus according to claim 9, wherein: <14> an image carrier; a charging member for charging the image bearing member; an exposure unit that exposes the charged image carrier to light to form a latent image on the surface of the image carrier; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer unit that transfers the toner image onto a transfer receiving member, and a method for recovering transfer residual toner by the developing unit, the method being performed by an image forming apparatus having the transfer unit and recovering transfer residual toner remaining on the image carrier after transfer, the method comprising: During a non-image formation period in which the exposure means is not performing exposure, a discharging step is performed in which discharge is caused between the charging member and the image carrier to charge the transfer residual toner, and a recovery step is performed in which the charged transfer residual toner is recovered by the developing means, In the discharging step, the absolute value of the voltage applied to the charging member is greater than the absolute value of the surface potential of the image carrier before the charging member passes through a charging position where the charging member and the image carrier face each other, and is equal to or greater than the absolute value of a discharge start voltage, and is smaller than the absolute value of the voltage applied to the charging member during image formation, which is a period during which the exposure means is performing exposure. A method for recovering residual toner after transfer. [Explanation of symbols]

[0179] 10 Electrostatic latent image carrier (photosensitive drum) 28 Fixing device 61 Developing device 62 Transfer roller 64 Static elimination lamp 72 Developing roller 73 Agitating roller 105 Recording paper 121 Exposure equipment 160 charging roller 161 Collection Brush 165 Peeling roller 166 Temporary cleaning roller 172 Photoconductor unit 180 Transfer belt 181 Conveyor roller 182 Cleaning roller 183 Recovery Roller 184 Cleaning Blade 185 Belt cleaning mechanism 186 Waste toner container [Prior art documents] [Patent documents]

[0180] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-071296 [Patent Document 2] Japanese Patent Application Publication No. 2023-137933

Claims

1. an image carrier; a charging member for charging the image bearing member; a charging voltage applying means for applying a voltage to the charging member; an exposure unit that exposes the charged image carrier to light to form a latent image on the surface of the image carrier; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer means for transferring the toner image onto a transfer target; a control unit that controls a recovery operation for recovering residual toner remaining on the image carrier after transfer into the developing unit, The recovery operation is an operation performed during non-image formation, i.e., a period when the exposure unit is not performing exposure, and includes a discharge process for charging the transfer residual toner by discharging between the charging member and the image carrier, and a recovery process for recovering the charged transfer residual toner by the developing unit, The control unit controls the charging voltage application unit so that the absolute value of the voltage applied to the charging member in the discharge process is greater than the absolute value of the surface potential of the image carrier before the charging member passes through a charging position where the charging member and the image carrier face each other, is equal to or greater than the absolute value of a discharge start voltage, and is smaller than the absolute value of the voltage applied to the charging member during image formation, which is a period during which the exposure unit is performing exposure. An image forming apparatus characterized by:

2. The control unit controls the charging voltage application means so that the difference between the absolute value of the voltage applied to the charging member during the image formation and the absolute value of the voltage applied to the charging member during the non-image formation is 150 V or more.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. the transfer means has a transfer member disposed in contact with the image carrier and transferring the toner image to a transfer-receiving body passing through a contact portion with the image carrier; A voltage is applied to the transfer member to perform the transfer; The absolute value of the current flowing through the transfer member when a voltage is applied to the transfer member is 10 μA or more.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. The charging member is a charging roller that contacts the surface of the image carrier, a cleaning mode in which the toner adhering to the charging roller is transferred to the surface of the image carrier; The cleaning mode is performed during the non-image formation period.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. The charging member is a charging roller that contacts the surface of the image carrier, a cleaning member that contacts the surface of the charging member; a cleaning mode in which the toner adhering to the cleaning member is transferred to the charging member, and the toner transferred to the charging roller is transferred to the surface of the image carrier; The cleaning mode is performed during the non-image formation period.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. The control unit controls the voltage applied to the charging member based on the absolute humidity inside or outside the image forming apparatus.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

7. The charging member is provided so as to be in contact with the image bearing member.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

8. a peeling roller is provided downstream of a position where the transfer means performs transfer in the rotation direction of the image carrier and upstream of the charging position; The peeling roller rotates in contact with the image carrier, and peels off the transfer residual toner adhering to the surface of the image carrier by the difference in peripheral speed between the peeling roller and the image carrier.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

9. A voltage smaller in absolute value than the voltage applied to the charging member in the discharge treatment is applied to the peeling roller.

9. The image forming apparatus according to claim 8,

10. the charging member is a non-contact charging member that does not come into contact with the image bearing member, a temporary collection means located downstream of a position where the transfer means performs transfer in the rotation direction of the image carrier and upstream of the charging position; The temporary collecting means temporarily collects the transfer residual toner that is charged with a polarity opposite to the normal charge on the surface of the image carrier.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

11. a cleaning voltage applying means for applying a voltage to the temporary collecting means; The control unit controls the cleaning voltage application unit to move the transfer residual toner collected by the temporary collection unit to the image carrier at the end of image formation.

11. The image forming apparatus according to claim 10.

12. the transfer unit includes a transfer roller facing the image carrier and a transfer belt sandwiched between the transfer roller and the image carrier; a belt cleaning mechanism that collects toner adhering to the transfer belt from the transfer belt; and a waste toner storage unit that stores the toner collected by the belt cleaning mechanism, The control unit moves the transfer residual toner collected by the temporary collection unit to the image carrier, the transfer belt, the belt cleaning mechanism, and the waste toner storage unit in this order when image formation is completed.

11. The image forming apparatus according to claim 10.

13. a plurality of photosensitive units each having the image carrier, the charging member, the developing means, and the temporary collection means; the transfer unit includes a transfer roller facing the image carrier and a transfer belt sandwiched between the transfer roller and the image carrier; the photosensitive unit includes a color photosensitive unit having the developing means for supplying color toner to the image carrier, and a black photosensitive unit having the developing means for supplying black toner to the image carrier, the black photosensitive unit is disposed downstream of the color photosensitive units in the rotation direction of the transfer belt, Of the color transfer residual toners temporarily collected by the temporary collection means in the color photosensitive units, the transfer residual toners that have moved to the transfer belt are collected by the developing means of the black photosensitive unit via the image carrier of the black photosensitive unit.

11. The image forming apparatus according to claim 10.

14. an image carrier; a charging member for charging the image bearing member; an exposure unit that exposes the charged image carrier to light to form a latent image on the surface of the image carrier; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer unit that transfers the toner image onto a transfer receiving member, and a method for recovering transfer residual toner by the developing unit, the method being performed by an image forming apparatus having the transfer unit and recovering transfer residual toner remaining on the image carrier after transfer, the method comprising: During a non-image formation period in which the exposure means is not performing exposure, a discharging step is performed in which the transfer residual toner is charged by discharging between the charging member and the image carrier, and a recovery step is performed in which the charged transfer residual toner is recovered by the developing means, In the discharging step, the absolute value of the voltage applied to the charging member is greater than the absolute value of the surface potential of the image carrier before the charging member passes through a charging position where the charging member and the image carrier face each other, and is equal to or greater than the absolute value of a discharge start voltage, and is smaller than the absolute value of the voltage applied to the charging member during image formation, which is a period during which the exposure means is performing exposure. A method for recovering residual toner after transfer.

Images