JP4428103B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a rotating brush and a developing device for removing deposits attached to an image carrier in an image forming apparatus such as an electrophotographic copying machine or a laser printer.

  Conventionally, in electrophotography, an electrostatic latent image created by charging and exposing the outer peripheral surface of an image carrier such as a photosensitive drum is developed with toner, thereby visualizing the electrostatic latent image on the image carrier. A toner image is formed on the recording medium, and the toner image is transferred to a recording medium such as paper and fixed to form an image on the recording medium.

  In such an image forming apparatus, a charging device that charges the image carrier by uniformly applying an electric charge to the outer peripheral surface of the image carrier that carries the toner image is used. As these charging devices, those of a contact charging type using a charging roller utilizing discharge in a minute gap are known.

  However, when such a contact-type charging device is used, the discharge product easily adheres to the outer peripheral surface of the image carrier, and in a high humidity environment, the discharge product absorbs moisture and the charge escapes. There is a problem that image flow occurs.

  Therefore, in addition to solving the above-mentioned problems, image formation that performs stable image formation by preventing the image defect due to deterioration of the photosensitive layer of the image carrier by controlling the amount of wear of the image carrier while removing discharge products. An apparatus is disclosed (see Patent Document 1). In this image forming apparatus, the discharge product adhering to the outer peripheral surface of the image carrier is removed by rubbing the web with a sponge roller.

However, in the above case, since the discharge product is removed by bringing the web into contact with the image carrier, the outer peripheral surface of the image carrier is damaged. Further, there is a problem that toner filming on the surface of the image carrier occurs, in which the web presses and fixes the toner to the outer peripheral surface of the image carrier. When image formation is performed in a state where toner filming has occurred on the image carrier, afterimages and streaks occur in the obtained image, leading to a reduction in image quality.
JP-A-8-123195

  In consideration of the above facts, the present invention reliably removes discharge products adhering to the outer peripheral surface of the image carrier, so that the outer peripheral surface of the image carrier is not excessively worn or damaged. An object of the present invention is to prevent occurrence of ming and obtain stable image quality over a long period of time.

According to the first aspect of the present invention, there is provided an image carrier that forms a latent image when irradiated with a light beam, a charging device that contacts the image carrier and charges the image carrier, a carrier, and toner. a developing roller the developer carrying for developing a latent image of said image bearing member including, a toner image is formed and developed on the image bearing member and the transfer member for transferring the recording medium, the outer circumferential surface of the image bearing member An image forming apparatus of a bladeless system that does not use a blade as a cleaning unit for the image carrier, and the charging roller charges the image carrier with the developing roller and the rotary brush. when, to remove discharge products adhering to the image carrier, the developing roller and the rotary brush is rotated in the reverse direction in the image bearing member and the counter unit, the rotary brush is a rotary shaft, said A brush member provided around the rotating shaft, in the configuration, the peripheral speed difference between the outer peripheral surface of the image bearing member and the tip portion of the brush member is 1.0 or more, the brush of the brush member When the denier is between 6.5d and 4.2d and the amount of biting is 2.0 mm or less, the tip force per brush of the brush member is 7.0E-05g or more, and 1.7E- It is characterized by being set to be 04 g or less .

  According to the first aspect of the present invention, the image carrier and the developing roll rotate in opposite directions at the opposing portion, that is, the developing roll rotates in the same direction as the rotation direction of the image carrier, and the carrier, the toner, The latent image on the image carrier is developed by carrying a developer containing The rotating brush contacts the outer peripheral surface of the image carrier while rotating in the opposite direction to the rotation direction of the image carrier at the portion facing the image carrier.

  In this configuration, by rotating the developing roll, the magnetic brush scrapes off the discharge product adhering to the outer peripheral surface of the image carrier. At this time, by rotating the developing roll in the opposite direction to the rotation direction of the image carrier at the opposing portion, the relative peripheral speed of the developing roll with respect to the image carrier increases, and the magnetic brush adheres to the outer peripheral surface of the image carrier. Efficiently scrapes the discharged product.

  Further, by rotating the rotating brush in contact with the outer peripheral surface of the image carrier in the same direction as the image carrier, that is, by rotating the rotating brush opposite to the rotation direction of the image carrier at a portion facing the image carrier, The scraping force of the rotating brush with respect to the outer peripheral surface of the image carrier is increased. For these reasons, it is possible to reliably remove the discharge products adhering to the outer peripheral surface of the image carrier.

Further, when the ratio to the peripheral speed of the outer peripheral surface of the peripheral speed image bearing member at the tip portion of the brush member is smaller than 1.0, the scraping force can not be obtained sufficiently with respect to the outer peripheral surface of the image bearing member of the brush member, The discharge product remains on the outer peripheral surface of the image carrier.

  Furthermore, when the denier of the brush of the brush member is between 6.5d and 4.2d and the biting amount is in the range of 2.0 mm or less, the tip force per brush of the brush member is 7.0E-05 g or more, In addition, by setting the pressure to be 1.7E-04 g or less, the discharge product adhering to the outer peripheral surface of the image carrier can be removed without causing filming.

Therefore, the difference between the circumferential speed of the outer peripheral surface of the peripheral speed and the image bearing member at the tip portion of the brush member is 1.0 or more, among 4.2d denier brush of the brush member from 6.5D, the amount of bite is In the range of 2.0 mm or less, by setting the tip force per brush of the brush member to be 7.0E-05 g or more and 1.7E-04 g or less, the outer periphery of the image carrier The discharge product adhering to the outer peripheral surface can be removed without causing filming on the surface.

The invention according to claim 2 is characterized in that the difference between the peripheral speed of the developing roll and the peripheral speed of the image carrier is 150 to 250 mm / sec.

According to the second aspect of the present invention, when the difference between the peripheral speed of the developing roll and the peripheral speed of the image carrier is smaller than 150 mm / sec, the discharge product attached to the outer peripheral surface of the image carrier is formed on the developing roll. It cannot be removed with a magnetic brush. On the other hand, if the difference in peripheral speed is larger than 250 mm / sec, the outer peripheral surface of the image carrier is worn more than necessary. Therefore, when the difference between the peripheral speed of the developing roll and the peripheral speed of the image carrier is set to 150 to 250 mm / sec, the discharge products attached to the outer peripheral surface of the image carrier are efficiently removed.

The invention described in claim 3 is characterized in that a ferrite carrier is used as the carrier.

According to the invention of claim 3, by using an iron-based ferrite carrier as the carrier, the scraping force of the outer peripheral surface of the image carrier by the magnetic brush formed on the outer peripheral surface of the developing roll is resin-based. Larger than when using a carrier. Therefore, by using the ferrite carrier, it is possible to remove the discharge product adhering to the outer peripheral surface of the image carrier. The invention according to claim 4 is characterized in that the denier of the brush member is 6 or less.
According to the invention described in claim 4, since the denier of the brush member is 6 or less, the latitude of the amount of biting is large.

  Since the present invention is configured as described above, the discharge product adhering to the outer peripheral surface of the image carrier is reliably removed, the outer peripheral surface of the image carrier is not excessively worn or damaged, and the toner film is not damaged. The occurrence of ming is prevented and stable image quality can be obtained over a long period of time.

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, a color laser printer (hereinafter referred to as a printer) 10 as an image forming apparatus includes yellow, magenta, cyan, and black developing units 12Y, 12M, 12C, and 12K and photoreceptors 13Y, 13M, This is a so-called tandem type full-color laser printer in which 13C and 13K are arranged in parallel facing the intermediate transfer belt 14 and the toner images of four colors are superposed while the intermediate transfer belt 14 makes one round.

  The printer 10 includes a paper feed tray 16 at the bottom. A paper feed roller 18 is in contact with the leading end of the paper P set in the paper feed tray 16 in the transport direction, and the paper P is fed one sheet at a time by the paper feed roller 18 and a paper handling means (not shown). Paper is fed from the tray 16 to the downstream side in the transport direction. Two sets of transport rollers 20 are arranged on the downstream side in the transport direction of the paper feed roller 18, and the paper P is transported to the upper transfer unit 22 by the transport force from the transport rollers 20.

  The transfer unit 22 is provided with a belt conveyance roller 24A around which the intermediate transfer belt 14 is wound, and a transfer roller 26 pressed against the belt conveyance roller 24A. The intermediate transfer belt 14 is sandwiched between the opposed portions of the belt conveyance roller 24A and the transfer roller 26, and the toner image is transferred from the intermediate transfer belt 14 when the paper P passes through the opposed portions.

  A fixing unit 28 is disposed above the transfer unit 22 and downstream in the transport direction. The fixing unit 28 is provided with a heat roller 28A that becomes high temperature and a backup roller 28B that is in pressure contact with the heat roller 28A, and the sheet P passes through a facing portion between the heat roller 28A and the backup roller 28B. At this time, the toner is melted and solidified to be fixed on the paper P. Then, the paper P is discharged by a paper discharge roller 29 disposed on the downstream side in the transport direction of the fixing unit 28.

  Here, the printing unit 30 in which the photoreceptors 13Y, 13M, 13C, and 13K superimpose the toner image on the intermediate transfer belt 14 will be described. Note that when distinguishing each color of yellow, magenta, cyan, and black, Y, M, C, and K are added after the code. However, if there is no need to distinguish each color, Y, M, C, and K are omitted.

  As shown in FIG. 2, the intermediate transfer belt 14 includes the above-described belt conveyance roller 24A, a belt conveyance roller 24B disposed below the belt conveyance roller 24A, and an obliquely upper side of the belt conveyance roller 24B and in the sheet conveyance path. It is wound around a belt conveying roller 24C disposed on the opposite side.

  A surface of the intermediate transfer belt 14 between the belt conveyance roller 24B and the belt conveyance roller 24C facing obliquely downward is a transfer surface 14A on which a toner image is transferred from the photoreceptors 13Y, M, C, and K. The developing units 12Y, M, C, and K and the photoconductors 13Y, M, C, and K are arranged in parallel so as to face the transfer surface 14A, and the photoconductors 13Y, M, C, and K are transferred to the transfer surface. 14A. Further, the transfer rollers 32Y, 32M, 32C, and 32K are pressed against the photoreceptors 13Y, 13M, 13C, and 13K via the transfer surface 14A.

  A sensor 15 for detecting the density of the toner transferred to the intermediate transfer belt 14 is disposed on the transfer surface 14A downstream of the photoreceptor 13K.

  As shown in FIG. 3, the intermediate transfer belt 14, the brush roller 34, the charging roller 36, and the developing roll 38 installed in the developing unit 12 are in contact with the outer peripheral surface of the photoconductor 13 in order in the rotation direction. Details of the developing unit 12 and the brush roller 34 will be described later.

  Further, between the charging roller 36 and the developing roller 38, an LED array head 40 that performs line exposure on the outer peripheral surface of the photoreceptor 13 is disposed.

  Next, the developing unit 12 including the developing roll 38 that is in contact with the photosensitive surface of the photoreceptor 13 will be described.

  As shown in FIGS. 3 and 4, the developing unit 12 includes a housing 50. An opening 52 is formed at a position facing the photoconductor 13 of the housing 50, and a part of the developing roll 38 is exposed from the opening 52. The developing roll 38 includes a magnet roll 38B and a developing sleeve 38A that rotates around the magnet roll 38B. The developing unit 12 is arranged such that a predetermined gap is formed between the photoconductor 13 and the developing roll 38.

  Screw augers 58 and 60 are disposed in the housing 50. The developer contained in the housing 50 is stirred by the screw augers 58 and 60 and conveyed to the developing roll 38.

  Further, a trimmer bar 62 is disposed on the upstream side of the opening 52 of the developing roll 38 in the housing 50 in the rotation direction, and the thickness of the developer attached to the surface of the developing sleeve is regulated by the trimmer bar 62. The position of the trimmer bar 62 is arranged in the direction away from the developing roll 38 (arrow H direction). As a result, a thick layer is formed on the surface of the developing roll 38 by the developer. That is, the amount of developer per unit area increases and the density of the magnetic brush described later increases, so that the surface scraping force of the photoreceptor 13 by the magnetic brush is increased.

  As the developer, a two-component developer in which a nonmagnetic toner 67 and a magnetic carrier 68 are mixed is used. As a result, the developer supplied to the developing roll 38 forms a magnetic brush composed of the carrier 68 and the toner 67 on the surface of the developing sleeve 38A by the magnetic force of the magnet roll 38B of the developing roll 38. This magnetic brush Comes into contact with the photosensitive member 13, so that the toner 67 adsorbed on the carrier 68 is supplied to the photosensitive member 13. As a result, the electrostatic latent image is visualized on the photosensitive member 13.

  An iron-based ferrite carrier is used as the magnetic carrier of the developer. Thereby, compared with the case where a resin-type carrier is used, the scraping power of the discharge product adhering to the outer peripheral surface of the photoreceptor 13 by a magnetic brush becomes strong.

  Next, the brush roller 34 in contact with the photosensitive surface of the photoreceptor 13 will be described.

  As shown in FIGS. 3 and 5, the brush roller 34 includes a sleeve 64, and a brush 66 in which brush fibers 66 </ b> A are planted around a base material 66 </ b> B is wound around the sleeve 64. In the experiment, a brush made of conductive nylon fiber having an outer diameter of Φ10 or Φ12 was used.

  Hereinafter, a flow until the toner image is transferred to the intermediate transfer belt 14 will be described.

  As shown in FIG. 3, when the photosensitive member 13 rotates counterclockwise in the drawing, first, the outer peripheral surface of the photosensitive member 13 is uniformly AC charged to a predetermined polarity potential by the charging roller 36. When the photoconductor 13 further rotates, the charged surface on the outer periphery of the photoconductor 13 is exposed by the LED array head 40, and the potential of the exposed portion of the charged surface is lowered to form an electrostatic latent image. Thereafter, the electrostatic latent image is developed by electrically adhering the toner 67 in the developer charged to the same polarity as the charged polarity of the photosensitive member 13 to the potential lowering portion of the charged surface by the developing roll 38. To do. The toner 67 is electrically attracted to the transfer roller 32 to which a transfer voltage having a polarity opposite to that of the toner 67 is applied. As a result, the toner image is transferred from the photoreceptor 13 to the intermediate transfer belt 14.

  In this step, when the outer peripheral surface of the photoconductor 13 is charged by the charging roller 36, the charging roller 36 is brought into contact with the photoconductor 13, so that the discharge product adheres to the outer peripheral surface of the photoconductor 13 of the photoconductor 13. .

  As shown in FIG. 4, the magnetic brush formed on the developing sleeve 38 </ b> A of the developing roll 38 forms a toner image with the toner 67 as described above on the downstream side, and forms the toner image with the toner 67. The discharge product adhering to the outer peripheral surface of the photosensitive member 13 is collected into the developing unit 12 by rubbing with the magnetic brush on the upstream side.

  At this time, the developing roll 38 is rotated in the same direction as the rotation direction of the photoreceptor 13. That is, the developing roller 38 is rotated in the reverse direction with respect to the photosensitive member 13 at the portion facing the photosensitive member 13. As a result, the relative peripheral speed of the developing roll 38 with respect to the photoconductor 13 can be increased, so that the scraping force of the discharge products adhering to the outer peripheral surface of the photoconductor 13 is increased.

  In order to increase the relative peripheral speed of the developing roller 38 with respect to the photosensitive member 13, it may be rotated faster than the photosensitive member 13 in the opposite direction to the photosensitive member 13, but the developing roller 38 is rotated at a high speed. May cause toner cloud. Further, rotating the developing roll 38 at a peripheral speed more than necessary does not have a good influence on the image quality.

  FIG. 6 is a graph showing the relationship between the peripheral speed difference between the developing roller 38 and the photosensitive member 13 and the amount of wear on the outer peripheral surface of the photosensitive member 13 by the developing roller 38 when the photosensitive member 13 rotates 1000 times.

  From this graph, it can be seen that the larger the peripheral speed difference between the photosensitive member 13 and the developing roll 38, the greater the amount of wear on the outer peripheral surface of the photosensitive member 13. That is, when the developing roller 38 is rotated in the same direction as the rotation direction of the photoconductor 13 (the opposite direction to the photoconductor 13), the amount of wear on the outer peripheral surface of the photoconductor 13 increases.

  By the way, in order to remove discharge products adhering to the outer peripheral surface of the photoconductor 13, it is necessary to wear the outer peripheral surface of the photoconductor 13 by 10 nm when the photoconductor 13 is rotated 1000 times. When the amount of wear is 10 nm or less, the discharge product adhering to the outer peripheral surface of the photoreceptor 13 cannot be removed. Further, the amount of wear on the outer peripheral surface of the photoconductor 13 when the photoconductor 13 is rotated 1000 times needs to be 25 nm or less. When this amount of wear is 25 nm or more, the outer peripheral surface of the photoreceptor 13 is worn more than necessary.

  Therefore, from the graph shown in FIG. 6, when the difference between the peripheral speed of the photosensitive member 13 and the peripheral speed of the developing roll 38 when the amount of wear on the outer peripheral surface of the photosensitive member 13 is 10 to 25 nm is read, this peripheral speed difference is 150 to 250 mm / sec. Therefore, if the circumferential speed of the developing roll 38 is set in the direction opposite to the photosensitive body 13 and the difference from the circumferential speed of the photosensitive body 13 is set in a range of 150 to 250 mm / sec, the developing roll 38 is formed on the developing sleeve 38A. It can be seen that the discharge product adhering to the outer peripheral surface of the photoreceptor 13 can be efficiently removed by the magnetic brush.

  Next, a method for removing the discharge products attached to the outer peripheral surface of the photoreceptor 13 by the brush roller 34 will be described.

  Here, the graph of FIG. 7 shows which factor has the most influence in order to remove the discharge product adhering to the outer peripheral surface of the photoreceptor 13. As can be judged from the sensitivity (db) in the table, it can be seen that the diameter of the brush 66 and the amount of biting of the brush 66 into the photosensitive member 13 are affected.

  The amount of biting of the brush 66 with respect to the photosensitive member 13 refers to the amount of deformation of the tip portion of the brush 66 caused by pressing the tip portion of the brush 66 of the brush roller 34 against the outer peripheral surface of the photosensitive member 13. For example, as shown in FIG. 8, when the amount of biting is 0, the tip of the brush 66 is brought into contact with the surface of the photosensitive member 13, and the distance between the center of the brush roller 34 and the center of the photosensitive member 13 at this time is L. To do. When the biting amount is α, the distance connecting the brush roller 34 and the center of the photosensitive member 13 is L−α. The amount of α is defined as the amount of biting.

  As shown in FIG. 5, the brush roller 34 is rotated in the same direction as the rotation direction of the photosensitive member 13. That is, the brush roller 34 is rotated reversely with respect to the photoconductor 13 at a portion facing the photoconductor 13. As a result, the brush tip of the brush roller 34 strikes the outer peripheral surface of the photoconductor 13 with a stronger force than when the opposite portion is rotated in the same direction with respect to the photoconductor 13.

  Further, the difference between the peripheral speed of the brush roller 34 and the peripheral speed of the photosensitive member 13 is set to be 1.0 or more. If the difference in peripheral speed is smaller than 1.0, the scraping force of the outer peripheral surface of the photoconductor 13 of the brush roller 34 becomes weak, and the discharge products attached to the outer peripheral surface of the photoconductor 13 cannot be removed.

  Therefore, a predetermined voltage (-1 kV in this embodiment) is applied to the brush roller 34 to rotate it in the same direction as the rotation direction of the photoconductor 13, and the peripheral speed difference between the brush roller 34 and the photoconductor 13 is 1.5 or more. By doing so, the discharge product adhering to the outer peripheral surface of the photosensitive member 13 is efficiently removed by the brush roller 34.

  Next, the brush diameter of the brush roller 34 will be described. FIG. 9 is a graph showing the relationship between the amount of biting of the brush tip of the brush roller 34 into the outer peripheral surface of the photosensitive member 13 and the tip force per brush for each brush diameter. From this graph, it can be seen that when the brush diameter is larger than 6 denier, the tip force on the outer peripheral surface of the photoreceptor 13 per brush becomes too large. As a result, if the brush diameter is larger than 6 deniers, the latitude of the biting amount cannot be obtained, and scratches are generated on the outer peripheral surface of the photosensitive member 13, or the toner on the outer peripheral surface of the photosensitive member 13 is removed at the tip of the brush 66. It will be crushed and cause toner filming.

  Therefore, when the brush diameter is 6 denier or less, the outer peripheral surface of the photoreceptor 13 is not damaged and the toner is not crushed.

  Next, the discharge product removal level on the outer peripheral surface of the photosensitive member 13 when one or both of the developing roller 38 and the brush roller 34 were used was examined. Here, a predetermined amount of pure water is dropped on the outer peripheral surface of the photoconductor 13 to create water droplets on the outer peripheral surface of the photoconductor 13. Then, a change in the contact angle of water droplets on the outer peripheral surface of the photoconductor 13 when a voltage of 1.2 mA was applied to the photoconductor 13 for discharge was observed.

  In FIG. 10, when the outer peripheral surface of the photosensitive member 13 is scraped only by the brush roller 34, when the outer peripheral surface of the photosensitive member 13 is scraped only by the magnetic brush of the developing roll 38, the outer peripheral surface of the photosensitive member 13 is brushed. In each case of scraping with both the roller 34 and the magnetic brush of the developing roll 38, the value of the contact angle of water droplets on the outer peripheral surface of the photoconductor 13 when a voltage of 1.2 mA is applied to the photoconductor 13 is measured. Shown in the graph. Note that the contact angle of water droplets on the outer peripheral surface of the photosensitive member 13 in the initial state (state where no voltage is applied to the photosensitive member 13) is 90 degrees.

  From this graph, when neither the brush roller 34 nor the magnetic brush of the developing roll 38 is used, the contact angle is 40 degrees, and a considerable amount of discharge product is adhered to the outer peripheral surface of the photoreceptor 13. I understand. Further, when the outer peripheral surface of the photosensitive member 13 is scraped with only the developing roll 38 using only the magnetic brush, the contact angle becomes 70 degrees, and in this case, the discharge product is not sufficiently removed. I understand that. Further, even when only the magnetic brush is used, the contact angle is 75 degrees, and it is understood that the discharge product cannot be completely removed in this case. Therefore, in these cases, the discharge product is not completely removed, and it is considered that the image flow is caused.

  On the other hand, when both the developing roller 38 and the brush roller 34 are used, the contact angle is 80 degrees or more, so that the discharge products can be almost completely removed to the extent that no image flow occurs. I understand that Therefore, in order to almost completely remove the discharge products adhering to the outer peripheral surface of the photoconductor 13, it is necessary to scrape the outer peripheral surface of the photoconductor 13 using both the developing roll 38 and the brush roller 34. .

1 is a schematic configuration diagram of an image forming apparatus according to an exemplary embodiment. 1 is a schematic configuration diagram of a printing unit of an image forming apparatus according to an embodiment. FIG. 3 is an enlarged cross-sectional view illustrating a configuration of a printing unit of the image forming apparatus according to the present exemplary embodiment. It is explanatory drawing of the method of removing the discharge product adhering to the photosensitive surface of the photoreceptor of the image forming apparatus of this embodiment with a developing roll. It is explanatory drawing of the method of removing the discharge product adhering to the photosensitive surface of the photoreceptor of the image forming apparatus of this embodiment with a brush roller. 5 is a graph showing the relationship between the difference between the peripheral speed of the developing roll and the peripheral speed of the photosensitive member and the amount of wear on the photosensitive surface in the image forming apparatus of the present embodiment. In the image forming apparatus according to this embodiment, which factor has the most influence when the discharge product attached to the outer peripheral surface of the photosensitive member is removed is shown. In the image forming apparatus of this embodiment, it is explanatory drawing about the definition of the amount of biting of the brush tip part of a brush roller with respect to the outer peripheral surface of a photoconductor. In the image forming apparatus of this embodiment, the graph shows the relationship between the amount of biting into the photosensitive surface of the brush tip of the brush roller and the tip force per brush for each brush diameter. 6 is a graph showing a combination when a developing roll and a brush roller are used when removing a discharge product adhering to the photosensitive surface of the photosensitive member of the image forming apparatus according to the exemplary embodiment.

Explanation of symbols

10 Printer (image forming device)
13 Photoconductor (image carrier)
22 Transfer section (transfer member)
34 Brush roller (Rotating brush)
38 Developing roll 64 Sleeve (rotating shaft)
66 Brush (Brush member)
67 Toner 68 Carrier

Claims (4)

An image bearing member for forming a latent image by the light beam is irradiated, a charging device for charging the image bearing member in contact with the image bearing member, carries a developer containing a carrier and a toner The image bearing A developing roll that develops a latent image on the body, a transfer member that transfers the toner image formed and developed on the image carrier to a recording medium, and a rotating brush that contacts the outer peripheral surface of the image carrier, In an image forming apparatus of a bladeless system that does not use a blade as a cleaning unit of the image carrier,
The developing roll and the rotating brush remove discharge products adhering to the image carrier when the charging device charges the image carrier,
The developing roll and the rotating brush rotate in a reverse direction at a portion facing the image carrier,
The rotating brush includes a rotating shaft and a brush member provided around the rotating shaft,
The peripheral speed difference between the outer peripheral surface of the image bearing member and the tip portion of the brush member is 1.0 or more,
In the range where the denier of the brush of the brush member is between 6.5d and 4.2d and the biting amount is 2.0 mm or less,
An image forming apparatus, wherein the tip force per brush of the brush member is set to be 7.0E-05 g or more and 1.7E-04 g or less .   The image forming apparatus according to claim 1, wherein a difference between a peripheral speed of the developing roll and a peripheral speed of the image carrier is 150 to 250 mm / sec.   The image forming apparatus according to claim 1, wherein a ferrite carrier is used as the carrier.   The image forming apparatus according to claim 1, wherein the brush member has a denier of 6 or less.

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