JP2008089785A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent ghost on images due to remaining toner for cleaning. <P>SOLUTION: An image forming device has: an image carrier 2 for carrying toner images; an intermediate transfer body 6 on which the toner images is transferred from the image carrier; a primary transfer means 7 for primarily transferring the toner images carried on the image carrier on the intermediate transfer body; a secondary transfer means 8 for secondarily transferring the toner images transferred to the intermediate transfer body to a transfer material; and a cleaning charging means 27 for cleaning the image carrier by charging secondarily transferred remaining toner remaining on the intermediate transfer body and reversely transferring it to the image carrier by the primary transfer means. The length of the axial direction of the primary transfer means 7 is set longer than the length of the axial direction of the cleaning charging means 27. The cleaning charging means is arranged inside the axial direction of the primary transfer means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer or a copier that employs an electrophotographic method, and in particular, cleans the surface of the intermediate transfer member by returning toner remaining on the intermediate transfer member onto the image carrier. The present invention relates to an image forming apparatus configured as described above.

Japanese Patent No. 3604087 Japanese Patent Laid-Open No. 11-52665

  Conventionally, among image forming apparatuses such as printers and copiers adopting this type of electrophotographic system, color image forming apparatuses capable of forming color images include, for example, yellow (Y), magenta (M), cyan (C), toner images of multiple colors such as black (K), etc. are transferred onto the intermediate transfer belt in a multiplex fashion, and then transferred onto the intermediate transfer belt as a primary transfer to yellow (Y), magenta (M), There is a configuration in which a color image is formed by secondarily transferring and fixing a plurality of color toner images such as cyan (C) and black (K) onto a transfer sheet.

  In such an image forming apparatus, a plurality of color toner images such as yellow (Y), magenta (M), cyan (C), and black (K) are once transferred onto the intermediate transfer belt in a multiple manner, and then the intermediate transfer belt. Since a color image is formed by performing a secondary transfer on the transfer paper at once, the surface condition of the intermediate transfer belt and the presence of residual toner directly affect the image quality of the color image formed on the transfer paper. To do.

  Therefore, as a technique for preventing the image quality from being deteriorated due to the surface state of the intermediate transfer belt and the presence of the transfer residual toner, those disclosed in, for example, Japanese Patent No. 36060476 and Japanese Patent Laid-Open No. 11-52665 have already been proposed. Has been.

An image forming apparatus according to Japanese Patent No. 3604871 includes an image carrier that carries a toner image, and an intermediate transfer belt that receives primary transfer of the toner image formed on the image carrier at a first transfer site. A transfer means for secondary transfer of the toner image on the intermediate transfer belt onto a transfer material at a second transfer site to form a toner image on the transfer material; and on the intermediate transfer belt after the secondary transfer. Charging means for applying a charge to the remaining secondary transfer residual toner, and the intermediate transfer belt has a layer having a thickness of 2 to 100 μm and a volume resistivity of 10 ⁸ to 10 ¹⁸ Ω · cm, The transfer unit has a function of charging the intermediate transfer belt within a range of a transfer width Wt, and the secondary transfer residual toner to which the charge is applied by the charging unit is transferred to the first transfer portion as a primary transfer. In parallel, reverse transfer onto the image carrier In the color image forming apparatus,
An AC bias is applied to the charging unit, and the AC bias has a voltage amplitude center value of 0 V, and the surface of the intermediate transfer belt is applied to the secondary transfer residual toner while applying the charge required for the reverse transfer. The transfer width Wt in the direction perpendicular to the moving direction of the intermediate transfer belt of the transfer unit has a function of discharging to approximately 0 V, and the charging width Wc in the direction perpendicular to the moving direction of the intermediate transfer belt of the charging unit It is comprised so that it may exist in the range corresponded inside.

  Further, the image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 11-52665 exposes the surface of the first image carrier charged by the first charging unit to form an electrostatic latent image, and develops the developing unit. A step of attaching a toner to the electrostatic latent image by the agent carrier and developing the toner image, and a step of electrostatically transferring the toner image on the second image carrier at the first transfer site. Are repeated for a plurality of color toners to superimpose a plurality of color toner images on the second image carrier, and these toner images are secondarily transferred onto a transfer material at a second transfer site. A color image is formed and transferred to the transfer material at the time of the secondary transfer on the downstream side of the second transfer site and the upstream side of the first transfer site in the moving direction of the second image carrier. Secondary transfer residual toner remaining on the second image carrier Forming a second charging means for applying an electric charge to the toner, and reversely transferring the secondary transfer residual toner from the second image carrier onto the first image carrier at the first transfer site In the apparatus, the region charged by the second charging unit on the surface of the second image carrier is more than the region charged by the first charging unit on the surface of the first image carrier. And the developer thin layer forming region on the surface of the developer carrying member is located inside the region charged by the second charging unit on the surface of the second image carrier. It is composed.

  However, the conventional technique has the following problems. That is, in the case of the image forming apparatus according to Japanese Patent No. 3604876, the transfer width Wt in the direction orthogonal to the moving direction of the intermediate transfer belt of the transfer unit is the direction orthogonal to the moving direction of the intermediate transfer belt of the charging unit. The transfer width of the primary transfer means for transferring the toner image formed on the image carrier to the intermediate transfer belt is defined in any way. It has not been.

  Therefore, in the case of the image forming apparatus according to the above-mentioned Japanese Patent No. 3604876, the primary transfer unit has a width larger than the width of the charging unit that applies charge to the secondary transfer residual toner remaining on the intermediate transfer belt after the secondary transfer. If the width is small, the toner scattered on the intermediate transfer belt remains on the intermediate transfer belt without being reversely transferred onto the image carrier due to the charging of the primary transfer means, and remains on the image as a ghost due to residual cleaning toner. Had problems.

  In the case of the image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 11-52665, the region charged by the second charging means on the surface of the second image carrier is the surface of the first image carrier. The developer thin layer forming region on the surface of the developer carrying member that is inside the region charged by the first charging unit is charged by the second charging unit on the surface of the second image carrier. The transfer width of the primary transfer means for transferring the toner image formed on the image carrier onto the intermediate transfer belt is not defined at all.

  Therefore, in the case of the image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 11-52665, the primary transfer is larger than the width of the charging unit that applies charge to the secondary transfer residual toner remaining on the intermediate transfer belt after the secondary transfer. When the width of the means is small, the toner scattered on the intermediate transfer belt remains on the intermediate transfer belt without being reversely transferred onto the image carrier due to the charge of the primary transfer means, and remains on the image as a ghost due to residual cleaning toner. It had the problem that it ended up.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to reliably reverse transfer the toner remaining on the intermediate transfer member onto the image carrier. An object of the present invention is to provide an image forming apparatus that can be cleaned and can prevent a ghost from being generated due to residual toner in the image.

That is, the invention described in claim 1 includes an image carrier that carries a toner image, an intermediate transfer member onto which the toner image is transferred from the image carrier, and a toner image carried on the image carrier. Primary transfer means for primary transfer onto the intermediate transfer body, secondary transfer means for secondary transfer of the toner image transferred onto the intermediate transfer body onto the transfer material, and secondary remaining on the intermediate transfer body An image having a cleaning charging unit to which a residual toner is charged, reversely transferred to the image carrier by the primary transfer unit, and applied with a cleaning bias to be removed by a cleaning unit for cleaning the image carrier; In the forming device,
The primary transfer unit is set such that its axial length is longer than the axial length of the cleaning charging unit, and the cleaning charging unit is disposed inside the primary transfer unit in the axial direction. An image forming apparatus.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the intermediate transfer member is formed of an endless elastic belt and is wound around the surface of the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed and rotates following the rotation of the image carrier.

  Further, the invention described in claim 3 is the image forming apparatus according to claim 1 or 2, wherein the cleaning charging means is composed of a conductive brush roll.

  According to a fourth aspect of the invention, there is provided the image forming apparatus according to the first or second aspect, wherein the cleaning charging means comprises a conductive roll.

  Further, the invention described in claim 5 is the image forming apparatus according to claim 1 or 2, wherein the cleaning charging means is made of a conductive film.

  According to a sixth aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, wherein the conductive film is made of a material having a charge series having the same polarity as the toner. Device.

  Furthermore, the invention described in claim 7 is the image forming apparatus according to any one of claims 1 to 6, wherein the cleaning charging unit is arranged in a non-contact state with respect to the intermediate transfer member. An image forming apparatus.

  According to an eighth aspect of the present invention, there is provided the image forming apparatus according to the seventh aspect, wherein the cleaning charging means arranged in the non-contact state comprises a corotron. is there.

  Furthermore, the invention described in claim 9 is the image forming apparatus according to any one of claims 1 to 4, wherein the rotational speed of the cleaning charging unit can be switched to a plurality of speeds. The image forming apparatus is characterized.

  The invention described in claim 10 is the image forming apparatus according to any one of claims 1 to 6, wherein the cleaning charging unit removes and collects the toner attached to the cleaning charging unit. An image forming apparatus including a collecting unit.

  According to the first aspect of the present invention, even when there is secondary transfer residual toner scattered outward from the axial end of the cleaning charging unit, the secondary transfer residual toner is The image is reliably reversely transferred onto the image carrier by the primary transfer means.

  According to the second aspect of the present invention, a driving mechanism for the intermediate transfer member is not required, and the apparatus can be reduced in size and cost.

  Further, according to the invention described in claim 3, the cleaning charging means can be constituted by an inexpensive member, and the mechanical load on the intermediate transfer member can be reduced as compared with the rubber roll. . Further, the transfer residual toner can be charged satisfactorily.

  According to the fourth aspect of the present invention, the cleaning charging means can be configured at low cost.

  Furthermore, according to the invention described in claim 5, the cleaning charging means can be configured at low cost.

  Further, according to the invention described in claim 6, an effect by frictional charging can be added.

  According to the seventh aspect of the present invention, the toner image forming position can be maintained with high accuracy without applying a mechanical load to the intermediate transfer member.

  According to the eighth aspect of the invention, the secondary transfer residual toner can be reliably charged.

  Furthermore, according to the ninth aspect of the invention, the cleaning performance and the positional accuracy of the toner image can be favorably maintained in accordance with an image forming mode such as a color image or monochrome.

  In addition, according to the invention described in claim 10, it is possible to suppress the deterioration of the charging performance for cleaning.

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

  Embodiment 1

  FIG. 2 shows a four-cycle full-color printer as an image forming apparatus according to Embodiment 1 of the present invention. Note that the image forming apparatus is not limited to a printer, and may be a copying machine or a facsimile provided with an image reading device, or a multifunction machine having these functions.

  In FIG. 2, reference numeral 1 denotes a main body of a full-color printer. Inside the full-color printer main body 1, a photosensitive drum 2 as an image carrier is disposed substantially above the center. As this photosensitive drum 2, for example, a drum made of a conductive cylinder having a diameter of about 47 mm whose surface is coated with a photosensitive layer made of OPC or the like is used. For example, it is configured to be rotationally driven at a process speed of about 160 mm / sec. This full-color printer has a process speed of about 160 mm / sec, which is set relatively fast for similar models, and has high productivity. Of course, the process speed of the full-color printer may be set to be faster than 160 mm / sec in the monochrome mode, for example.

  The surface of the photosensitive drum 2 is uniformly charged to a predetermined potential by a charging roll 3 serving as a charging means disposed immediately below the photosensitive drum 2, and then separated from the photosensitive drum 2. A laser beam (LB) is irradiated by a ROS (Raster Output Scanner) 4 serving as an image exposure unit disposed at a predetermined position, and each color of yellow (Y), magenta (M), cyan (C), and black (K) is irradiated. Electrostatic latent images corresponding to the image information are sequentially formed. The electrostatic latent image formed on the photosensitive drum 2 passes through the developing devices 5Y, 5M, 5C, and 5K of yellow (Y), magenta (M), cyan (C), and black (K) in the circumferential direction. The toner is developed by a rotary developing device 5 disposed along the toner image to form a toner image of a predetermined color. In each of the developing devices 5Y, 5M, 5C, and 5K for each color, for example, a two-component developing system is used and toner charged to a negative polarity is used, but a one-component developing system is used. Of course, it's okay.

  As shown in FIG. 3, the rotary developing device 5 includes four developing devices 5Y, 5M, 5C, and 5K of yellow (Y), magenta (M), cyan (C), and black (K) that rotate. The rotating frames 52 that rotate about the shaft 51 are mounted so as to form an angle of 90 degrees along the circumferential direction. Further, the four developing devices 5Y, 5M, 5C, and 5K of yellow (Y), magenta (M), cyan (C), and black (K) have the rotational position of the rotating frame 52 set to the rotating frame 52. By detecting and controlling according to the position of the slit (not shown) provided, the developing roller 53 provided in the opening of each developing device 5Y, 5M, 5C, 5K is stopped at the developing position facing the photosensitive drum 2. The electrostatic latent image formed on the photosensitive drum 2 is developed with toner of a desired color.

  Further, the developing devices 5Y, 5M, 5C, and 5K adopting the two-component developing system of yellow (Y), magenta (M), cyan (C), and black (K) include the developing devices 5Y, 5M. The toner cartridges 50Y, 50M, 50C, and 50K are mounted so as to be adjacent to 5C and 5K. From the toner cartridges 50Y, 50M, 50C, and 50K, toner and The toner density in each of the developing devices 5Y, 5M, 5C, and 5K can be adjusted by appropriately supplying a developer including a carrier at a predetermined timing as necessary.

  As shown in FIG. 2, charging, exposure, and development processes are repeated on the surface of the photosensitive drum 2 a predetermined number of times according to the color of the image to be formed. In the rotary developing device 5, the developing rollers 53 of the corresponding color developing devices 5Y, 5M, 5C, and 5K move to the developing position facing the photosensitive drum 2. For example, when a full-color image is formed, the charging, exposure, and development processes are performed on the surface of the photosensitive drum 2 in yellow (Y), magenta (M), cyan (C), and black (K) colors. The toner image corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) is sequentially formed on the surface of the photosensitive drum 2. . The number of rotations of the photosensitive drum 2 when the toner image is formed varies depending on the size of the image. For example, in the case of the A3 size, one image can be obtained by rotating the photosensitive drum 2 four times. It is formed. That is, a toner image corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) is sequentially formed on the surface of the photosensitive drum 2 every time the photosensitive drum 2 rotates four times. It is formed.

  As shown in FIG. 4, toner images of yellow (Y), magenta (M), cyan (C), and black (K) that are sequentially formed on the photosensitive drum 2 are formed on the outer periphery of the photosensitive drum 2. A primary transfer roll 7 to which a predetermined transfer bias is applied in a state of being superimposed on the intermediate transfer belt 6 in a primary transfer nip portion N1 around which a part of the intermediate transfer belt 6 as an intermediate transfer member is wound. The primary transfer is performed. The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred onto the intermediate transfer belt 6 in a multiple manner are transferred to a predetermined level by a secondary transfer roll 8 to which a plus bias is applied. The secondary transfer is performed collectively at the secondary transfer position N2 on the transfer paper 9 as the transfer material fed at the timing of. As shown in FIG. 2, the transfer paper 9 is fed by a feed roll 11 from a paper feed cassette 10 disposed at the lower part of the full-color printer main body 1, and is also rolled one by one by the feed roll 11 and the retard roll 12. The secondary transfer of the intermediate transfer belt 6 is carried out in synchronization with the toner image transferred onto the intermediate transfer belt 6 by the registration roll 15 via the paper conveyance path 14 provided with the conveyance roll 13. It is conveyed to position N2.

  The secondary transfer roll 8 is configured to be able to come into contact with and separate from the surface of the intermediate transfer belt 6 and is in a state of being separated from the intermediate transfer belt 6 until the primary transfer of the final color toner image is completed. ing.

  In addition, the surface of the photosensitive drum 2 after the toner image transfer process is completed, the cleaning device 16 serving as a cleaning unit disposed obliquely below the photosensitive drum 2 every time the photosensitive drum 2 rotates once. Residual toner is removed by the cleaning blade 17 to prepare for the next image forming step.

  By the way, the transfer residual toner removed by the cleaning blade 17 of the cleaning device 16 is collected in a state of being accommodated in a collection container 35 configured integrally with the cleaning device 16. As shown in FIGS. 2 and 3, the collection container 35 has a large volume and is set to have a replacement time substantially equal to or sufficiently long with respect to the life of the photosensitive drum 2. When the photoconductor drum 2 reaches the end of its service life, the photoconductor drum 2 is replaced integrally with an exchange unit including the photoconductor drum 2.

  The intermediate transfer belt 6 is stretched by a plurality of rolls and is driven along with the rotation of the photosensitive drum 2 so as to circulate and move at a predetermined process speed (about 160 mm / sec). The intermediate transfer belt 6 is formed in an endless belt shape that can be expanded and contracted by an elastic body made of a rubber material such as chloroprene rubber or EPDM. The intermediate transfer belt 6 intermediately transfers a wrap-in roll 18 that specifies the wrap position of the intermediate transfer belt 6 on the upstream side in the rotational direction of the photosensitive drum 2 and a toner image formed on the photosensitive drum 2. The primary transfer roll 7 to be transferred onto the belt 6, the wrap-out roll 19 for specifying the wrap position of the intermediate transfer belt 6 on the downstream side of the wrap position, the idler roll 20, and the intermediate transfer belt 6 to the secondary transfer roll 8. A backup roll 21 that is in contact with the intermediate transfer belt 6, a first cleaning backup roll 23 that faces the cleaning device 22 of the intermediate transfer belt 6, and a second cleaning backup roll 24 are stretched with a predetermined tension.

  The intermediate transfer belt 6 may be formed of a synthetic resin film such as polyimide, not an elastic body, and may be configured to contact the surface of the photosensitive drum 2 only by the primary transfer roll 7.

  Further, as described above, the intermediate transfer belt 6 is stretched by a plurality of rolls 7, 18 to 21, 23, 24. In this embodiment, the shape drawn by the outer periphery is a substantially right triangle. The primary transfer nip portion N1 of the photosensitive drum 2 is a portion corresponding to the hypotenuse of the intermediate transfer belt 6 disposed so as to have a substantially right-angled triangle shape. It is set near one apex along the moving direction of the belt 6.

  More specifically, as shown in FIGS. 2 and 3, the intermediate transfer belt 6 has the backup roll 21 such that the portion stretched around the backup roll 21 forms a substantially right angle (about 90 to 100 degrees). The idler roll 20 and the idler roll 23 are arranged so that the shape drawn by the outer periphery thereof is a substantially right triangle. The intermediate transfer belt 6 is driven by the photosensitive drum 2 so as to circulate counterclockwise. The intermediate transfer belt 6 is a portion corresponding to the hypotenuse of the intermediate transfer belt 6 in which the primary transfer nip portion N1 of the photosensitive drum 2 is disposed so as to have a substantially right triangle shape. It is set closer to the cleaning backup roll 24 along the moving direction of the belt 6.

  Furthermore, in this embodiment, as shown in FIG. 2, the entire full-color printer is miniaturized as much as possible, but the rotary developing device 5 occupies a large space of the full-color printer main body 1. Therefore, the full-color printer main body 1 is designed to improve the maintainability of the intermediate transfer belt 6 and the rotary developing device 5 while achieving downsizing of the device. Specifically, the intermediate transfer belt 6 includes the photosensitive drum 2, the charging roll 3, the collection container 35, and the like, and integrally constitutes a process cartridge 25. 2 The entire process cartridge 25 is configured to be detachable from the full-color printer body 1 by opening the cover located on the right side.

  Further, as shown in FIG. 1, the cleaning device 22 for the intermediate transfer belt 6 is a conductive member as a cleaning charging member disposed so as to be in contact with the surface of the intermediate transfer belt 6 stretched by a cleaning backup roll 24. A conductive brush roll 27 and a housing 28 surrounding the conductive brush roll 27.

  The conductive brush roll 27 does not scrape the secondary transfer residual toner remaining on the intermediate transfer belt 6 but is a brush in which conductive fibers to which a positive bias is applied are densely planted. This is for charging the transfer residual toner remaining on the toner to a positive polarity opposite to the negative polarity which is the original charging polarity. The conductive brush roll 27 is placed on the photosensitive drum 2 from the intermediate transfer belt 6 when the transfer residual toner remaining on the intermediate transfer belt 6 moves to the primary transfer nip portion N1 of the photosensitive drum 2. The transfer residual toner is moved electrostatically, and the transfer residual toner moved onto the photosensitive drum 2 is removed by a cleaning blade 17 of a cleaning device 16 for the photosensitive drum 2 as shown in FIG. The intermediate transfer belt 6 is cleaned.

  The conductive brush roll 27 is configured to be applied with a positive bias voltage by a bias power source (not shown), and the conductive brush roll 27 is driven in the same direction or in the opposite direction to the intermediate transfer belt 6. It is configured to be.

  In the cleaning device 22, a conductive brush roll 27 is disposed so as to be capable of swinging counterclockwise in the drawing around a swing shaft (not shown). Until the image exposure is completed, the conductive brush roll 27 is retracted to a position separated from the surface of the intermediate transfer belt 6, and when the exposure of the final color toner image is completed, the secondary transfer residual toner is removed. It is configured to abut on the surface of the intermediate transfer belt 6 at a predetermined timing before passing.

  Further, as shown in FIG. 2, the transfer sheet 9 onto which the toner image is transferred from the intermediate transfer belt 6 is conveyed to a fixing device 30 disposed at the upper right end of the printer body 1. The toner image is fixed on the transfer paper 9 by heat and pressure, and is discharged as it is onto a discharge tray 32 provided on the upper portion of the printer body 1 by a discharge roll 31.

  Further, when images are formed on both sides of the transfer sheet 9, the transfer sheet 9 with the toner image fixed on one side is not discharged as it is by the discharge roll 31 as shown in FIG. While the rear end of the sheet 9 is held by the discharge roll 31, the transfer roll 9 having the image formed on one side is conveyed to the double-sided sheet conveyance path 33 by reversing the discharge roll 31. An image is formed again on the back surface of the image.

  By the way, in this embodiment, an image carrier that carries a toner image, an intermediate transfer member to which a toner image is transferred from the image carrier, and a toner image carried on the image carrier is an intermediate transfer member. Primary transfer means for primary transfer, secondary transfer means for secondary transfer of a toner image transferred onto the intermediate transfer body onto a transfer material, and secondary transfer residual toner remaining on the intermediate transfer body. An image forming apparatus comprising: a cleaning charging unit that is charged, reversely transferred to the image carrier by the primary transfer unit, and applied with a cleaning bias to be removed by a cleaning unit that cleans the image carrier. The primary transfer means is set such that its axial length is longer than the axial length of the cleaning charging means, and the cleaning charging means It is configured to be disposed inside the axial direction of the shooting means.

That is, in this embodiment, as shown in FIGS. 1 and 7, the transfer sheet 9 is fed (so-called center registration) with reference to the central portion C along the direction orthogonal to the feeding direction. The width W _T2 of the secondary transfer roll 8 is set to be larger than the width W _p along the direction perpendicular to the feeding direction of the transfer paper 9 of the maximum size. As shown in FIG. 2, the secondary transfer roll 8 also has a function of conveying the transfer paper 9. The secondary transfer roll 8 has a transfer paper 9 of the secondary transfer roll 8 rather than the transfer paper 9 of the maximum size. The contact width W _T2 is set to be large. The secondary transfer roll 8 can stably transfer the transfer paper 9 and can reliably secondary-transfer the toner image formed on the intermediate transfer belt 6 onto the transfer paper 9. as such, than the width W _p of the transfer paper 9 of maximum size, for example, it is set to be longer respectively about 1mm on both sides.

The effective developing width W _D of the developing roller 53 of the developing device 5, as shown in FIGS. 1 and 7, the width (length along the axial direction) of the secondary transfer roll 8 is set larger than the W _T2 together we are a width W _CLN conductive brush roller 27 for cleaning is set larger than the effective developing width W _D of the developing roller 53.

Further, as shown in FIG. 1, the width W _T1 of the primary transfer roll 7 is set larger than the width W _{CLN of} the cleaning conductive brush roll 27, and the cleaning conductive brush roll 27 is It is arranged inside the primary transfer roll 7 in the axial direction. At that time, the width W _T1 of the primary transfer roll 7 is set to be, for example, about 3 mm longer than the width W _CLN of the conductive brush roll 27 for cleaning.

Further, as shown in FIG. 1, the effective image formation width W _PR of the photosensitive drum 2 is set to be larger than the width W _T1 of the primary transfer roll 7 and smaller than the width W _IT of the intermediate transfer belt 6. It is set.

Thus, the width W _p along the direction perpendicular to the sheet feeding direction of the transfer paper 9 of maximum size, the width W _T2 of the secondary transfer roll 8, and the effective developing width W _D of the developing roller 53, cleaning As shown in FIG. 1, there is a relationship of W _p <W _T2 <W _D <W _CLN <W _T1 between the width W _CLN of the conductive brush roll 27 and the width W _T1 of the primary transfer roll 7. It is configured to hold.

  Furthermore, in this embodiment, as shown in FIG. 7, the width of the cleaning blade 17 is set slightly larger than the width of the charging roll 3, and one end of the cleaning blade 17 is connected to the intermediate transfer belt 6. It is set so as to coincide with one end portion.

  Further, the tracking rolls disposed at both ends in the axial direction of the developing roll 53 are disposed so as to contact the flange portion of the photosensitive drum 2.

  In the above configuration, the four-cycle full-color printer as the image forming apparatus according to this embodiment reliably reverse-transfers the toner remaining on the intermediate transfer member onto the image carrier as follows. It is possible to perform cleaning, and it is possible to prevent ghosts from being generated due to residual toner in the image.

  That is, in the full-color printer, as shown in FIG. 2, toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are sequentially formed on the photosensitive drum 2. The yellow (Y), magenta (M), cyan (C), and black (K) toner images sequentially formed on the photosensitive drum 2 are transferred to the positive transfer nip N1 at the positive polarity. After primary transfer onto the intermediate transfer belt 6 by the primary transfer roll 7 to which a bias is applied, the secondary transfer roll 8 collectively moves from the intermediate transfer belt 6 to the transfer paper 9 at the secondary transfer nip portion N2. Second transfer is performed.

  At that time, the yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred onto the intermediate transfer belt 6 in a multiple primary transfer are, as shown in FIG. In the next transfer nip portion N2, the secondary transfer roll 8 to which a positive transfer bias is applied is transferred from the intermediate transfer belt 6 to the transfer paper 9, and all the toner images are transferred to the transfer paper 9. As shown in FIG. 5, a part of the toner remains on the intermediate transfer belt 6 as a transfer residual toner. At this time, a part of the residual toner remaining on the intermediate transfer belt 6 is charged with a reverse polarity plus polarity by a transfer electric field. The transfer residual toner remaining on the intermediate transfer belt 6 moves to the position of the cleaning device 22 as the intermediate transfer belt 6 moves, and a conductive brush roll for cleaning disposed inside the cleaning device 22. 27 is charged with a positive polarity and charged to a positive polarity opposite to the original charged polarity.

  As described above, the transfer residual toner remaining on the intermediate transfer belt 6 charged to a positive polarity moves to a wrap position where the intermediate transfer belt 6 is wound around the outer peripheral surface of the photosensitive drum 2. At this time, the photosensitive drum 2 is normally charged with a negative polarity and is maintained at about −700 V. Therefore, the transfer residual toner charged with a positive polarity attached on the intermediate transfer belt 6 is electrostatically charged. After being attracted and transferred to the surface of the photosensitive drum 2, it is removed by the cleaning blade 17 of the cleaning device 16 that cleans the surface of the photosensitive drum 2.

  By the way, in the above embodiment, as shown in FIG. 1, the width of the cleaning conductive brush roll 27 that imparts electric charge to the secondary transfer residual toner remaining on the intermediate transfer belt 6 after the secondary transfer, Since the width of the primary transfer roll 7 is set larger, there is toner scattered to the outside in the width direction of the intermediate transfer belt 6 due to homopolar repulsion when the conductive brush roll 27 is charged with a positive polarity. Even so, the scattered toner can be reliably reverse-transferred onto the photosensitive drum 2 by a positive charging electric field applied to the primary transfer roll 7 and does not remain on the intermediate transfer belt 6. Therefore, it is possible to reliably prevent the image from remaining as a ghost due to the cleaning residual toner during the next image formation.

FIG. 1 is a schematic diagram showing the main part of a four-cycle full-color printer as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a configuration diagram showing a four-cycle full-color printer as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a block diagram showing the main part of a 4-cycle full-color printer as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 4 is an explanatory view showing the operation of the 4-cycle full-color printer as the image forming apparatus according to Embodiment 1 of the present invention. FIG. 5 is an explanatory view showing the operation of the four-cycle full-color printer as the image forming apparatus according to Embodiment 1 of the present invention. FIG. 6 is an explanatory diagram showing the operation of the four-cycle full-color printer as the image forming apparatus according to Embodiment 1 of the present invention. FIG. 7 is a block diagram showing a main part of a four-cycle full-color printer as an image forming apparatus according to Embodiment 1 of the present invention.

Explanation of symbols

  2: photosensitive drum, 6: intermediate transfer belt, 9: transfer paper, 7: secondary transfer roll, 8: secondary transfer roll, 27: conductive brush roll for cleaning, C: central portion.

Claims (10)

An image carrier that carries a toner image, an intermediate transfer member on which the toner image is transferred from the image carrier, and a primary transfer unit that primarily transfers the toner image carried on the image carrier onto the intermediate transfer member A secondary transfer means for secondary transfer of the toner image transferred onto the intermediate transfer body onto a transfer material; and a secondary transfer residual toner remaining on the intermediate transfer body is charged by the primary transfer means. In an image forming apparatus having a cleaning charging unit to which a cleaning bias is applied to reversely transfer to the image carrier and to be removed by a cleaning unit that cleans the image carrier.
The primary transfer unit is set such that its axial length is longer than the axial length of the cleaning charging unit, and the cleaning charging unit is disposed inside the primary transfer unit in the axial direction. An image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the intermediate transfer member is formed of an endless elastic belt and is disposed in a state of being wound around the surface of the image carrier, and is driven by the rotation of the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus rotates. 3. The image forming apparatus according to claim 1, wherein the cleaning charging unit includes a conductive brush roll. 3. The image forming apparatus according to claim 1, wherein the cleaning charging unit includes a conductive roll. 3. The image forming apparatus according to claim 1, wherein the cleaning charging unit is made of a conductive film. 3. The image forming apparatus according to claim 1, wherein the conductive film is made of a material having a charging series having the same polarity as the toner. 7. The image forming apparatus according to claim 1, wherein the cleaning charging unit is disposed in a non-contact state with respect to the intermediate transfer member. 8. The image forming apparatus according to claim 7, wherein the cleaning charging unit arranged in the non-contact state is made of corotron. 5. The image forming apparatus according to claim 1, wherein a rotational speed of the cleaning charging unit is switchable between a plurality of speeds. 7. The image forming apparatus according to claim 1, wherein the cleaning charging unit includes a removing and collecting unit that removes and collects toner attached to the cleaning charging unit. Forming equipment.

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