JP2009063681A - Image forming apparatus - Google Patents

Abstract

To improve the cleaning performance of an image carrier in a configuration including a toner collecting and holding unit for collecting and holding a transfer residual toner from an image carrier and a toner charging unit for charging a transfer residual toner on the image carrier. An image forming apparatus is provided.
An image forming apparatus 10, the moving speed of the surface of the image carrier 2 and PS, the image carrier 2 in the operating position to Q ₁ on the surface of the image carrier 2 of the toner recovery holding means 31 of the surface The distance between the upstream end portion in the moving direction and the downstream end portion in the moving direction of the surface of the image carrier ₂ at the operating position Q ₂ of the toner charging means 32 on the surface of the image carrier 2 is L _1. In the process, when the time interval from the switching of the voltage output by the first voltage output unit 41 to the toner collection holding unit 31 to the next switching is defined as t ₁ , the following equation, t ₁ ≧ L ₁ / PS It is assumed that the relationship is established.
[Selection] Figure 3

Description

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

  In recent years, colorization has progressed in image forming apparatuses such as printers, copiers, and facsimiles. For example, an intermediate transfer type image forming apparatus is well known as an image forming apparatus capable of forming a full-color image using an electrophotographic system. In an intermediate transfer type image forming apparatus, typically, a plurality of electrophotographic photosensitive members (photosensitive members) provided in accordance with each of a plurality of colors are arranged in a line (in-line type, tandem type). Then, after the toner images of the respective colors formed on the respective photoconductors are sequentially superimposed and transferred (primary transfer) onto the intermediate transfer body, the multiple toner images are collectively transferred from the intermediate transfer body to the recording material. (Secondary transfer) and fixed.

  In the intermediate transfer type image forming apparatus, after the toner image is transferred from the intermediate transfer member to the recording material, the toner remains on the intermediate transfer member. The toner remaining on the intermediate transfer member (secondary transfer residual toner) is removed and recovered from the intermediate transfer member by the intermediate transfer member cleaning means.

  As the intermediate transfer member cleaning means, one that scrapes off the toner on the intermediate transfer member with an elastic blade as a cleaning member is well known.

  Further, as the intermediate transfer member cleaning means, there are also the following. That is, a fur brush as a cleaning member is provided, and a bias having a polarity opposite to that of the secondary transfer residual toner on the intermediate transfer member is applied to the fur brush, and the secondary transfer residual toner is collected in the fur brush. The secondary transfer residual toner collected by the fur brush is once attached to a bias roller such as a metal roller and then scraped off by a blade.

  In the configuration of the intermediate transfer member cleaning unit as described above, a mechanism for storing the collected toner is required as the intermediate transfer member cleaning unit.

  Patent Document 1 proposes to provide a toner charging unit that charges the secondary transfer residual toner on the intermediate transfer member with a polarity opposite to the normal charging polarity of the toner as another intermediate transfer member cleaning unit. . In this case, the secondary transfer residual toner is charged to a polarity opposite to the normal charging polarity of the toner, and is transferred from the intermediate transfer member to the photosensitive member at the primary transfer nip portion of the image forming unit immediately after that. . The toner transferred to the photoconductor is removed and collected from the photoconductor by the photoconductor cleaning means. According to such an intermediate transfer member cleaning means, the intermediate transfer member can be cleaned simultaneously with the primary transfer.

  Patent Document 2 proposes the following intermediate transfer member cleaning means. That is, a recovery member that temporarily recovers the secondary transfer residual toner is provided, and the secondary transfer residual toner recovered on the recovery member is discharged again to the intermediate transfer member. Then, the discharged toner is removed and collected by the photosensitive member cleaning means of the image forming unit immediately after that.

  In any of the configurations of Patent Documents 1 and 2, it is possible to omit providing a mechanism for storing the collected toner as an intermediate transfer member cleaning unit. Therefore, usability can be improved by reducing the number of replacement units.

  In Patent Document 3, the following proposal is made in an inline type image forming apparatus having a toner charging unit for applying a predetermined charge to secondary transfer residual toner on an intermediate transfer member. That is, in the inline type image forming apparatus, a large amount of secondary transfer residual toner is collected in the collected toner container of a specific image forming unit, so that the replacement frequency of only the cartridge of the image forming unit is increased, which is uneconomical. Sometimes. For this reason, the capacity of the collected toner container is increased only in the cartridge of the image forming unit where a large amount of secondary transfer residual toner is collected.

  In the configuration of Patent Document 3, there is a problem that a cartridge with a large capacity of the collected toner container becomes large or the cartridge configuration cannot be made common.

  In addition, the configuration shown in Patent Document 2 that collects and holds the secondary transfer residual toner on the intermediate transfer member and the secondary transfer residual toner on the intermediate transfer member are charged with a polarity opposite to the normal charging polarity of the toner. An in-line image forming apparatus combining the configuration disclosed in Patent Document 1 is conceivable. In the image forming apparatus having such a configuration, it is possible to suppress a large amount of secondary transfer residual toner from entering the collected toner container of the specific image forming unit.

  FIG. 9 shows a configuration in which an intermediate transfer belt 120 is provided as an intermediate transfer body, and secondary transfer residual toner is collected and held in a belt cleaning device 130 as an intermediate transfer body cleaning unit, and secondary transfer residual toner is charged. 1 shows a schematic cross section of a main part of an image forming apparatus provided with a configuration. The illustrated image forming apparatus includes first, second, third, and fourth image forming units 101 a, 101 b, 101 c, and 101 d along the moving direction of the surface of the intermediate transfer belt 120.

  That is, the belt cleaning device 130 includes a conductive brush 131 as a toner collecting and holding unit that collects and holds the secondary transfer residual toner, and a toner charging roller 132 as a toner charging unit that charges the secondary transfer residual toner. Have.

  The conductive brush 131 collects and holds a part of the secondary transfer residual toner. The toner collected and held by the conductive brush 13 is discharged to the intermediate transfer belt 120 at a predetermined timing such as during a post-rotation operation which is a preparatory operation performed after the image forming operation. Then, the toner discharged onto the intermediate transfer belt 120 is selectively collected, for example, in the collected toner container 162 of the second image forming unit 101b or the third image forming unit 101c. As a method for selectively collecting the toner, for example, the first image forming unit 101a or the like, such as 1 in the primary transfer nip N of the image forming unit where the toner discharged on the intermediate transfer belt 120 is not desired to be collected. There is a method of separating the next transfer roller 105 from the photosensitive member 102. Alternatively, in the image forming unit where it is not desired to collect the toner discharged on the intermediate transfer belt 120, the primary transfer roller 105 applies a voltage having a polarity such that the discharged toner is not transferred from the intermediate transfer belt 120 to the photosensitive member 102. There is a method to apply to. The voltage having such a polarity that the toner discharged on the intermediate transfer belt 120 is not transferred to the photosensitive member 102 is opposite in polarity to the toner discharged on the intermediate transfer belt 120 (for example, opposite to the normal charging polarity of the toner). Is the voltage.

  By collecting and holding a part of the secondary transfer residual toner with the conductive brush 131, the amount of toner passing through the toner charging roller 132 during the image forming operation can be reduced. The amount of toner adhesion can be greatly reduced. As a result, since the toner can be stably charged by the toner charging roller 132, better cleaning performance can be ensured.

  The toner charging roller 132 charges the secondary transfer residual toner that has not been collected by the conductive brush 131, for example, to a polarity opposite to the normal charging polarity of the toner. That is, the secondary transfer residual toner after passing through the toner charging roller 132 is charged to a polarity opposite to the normal charging polarity of the toner. Accordingly, the toner is transferred from the intermediate transfer belt 120 to the photosensitive member 102 at the primary transfer nip N of the first image forming unit 101a immediately after that, and is transferred to the collected toner container 162 of the first image forming unit 101a. To be recovered.

That is, one of the advantages of providing a configuration for collecting and holding the secondary transfer residual toner and a configuration for charging the secondary transfer residual toner to a polarity opposite to the normal charging polarity of the toner is specified. It is possible to prevent a large amount of secondary transfer residual toner from entering the collected toner container of the image forming unit.
Japanese Patent No. 3267507 JP 09-197750 A Japanese Patent Laid-Open No. 2004-21134

  However, an image forming apparatus provided with a configuration for collecting and holding the secondary transfer residual toner as described above and a configuration for charging the secondary transfer residual toner with a polarity opposite to the normal charging polarity of the toner. Then, it turned out that there were the following problems.

  In other words, the toner discharged from the conductive brush 131 onto the intermediate transfer belt 120 may adhere to the toner charging roller 132 and the charging performance of the toner charging roller 132 may deteriorate. As a result, the charge amount of the toner after passing through the toner charging roller 132 may not be a desired charge amount. As a result, the secondary transfer residual toner cannot be transferred from the intermediate transfer belt 120 to the photosensitive member 102, and a previous toner image may remain on the image being formed, and an image defect due to a cleaning defect may occur.

  In addition, the toner discharged from the conductive brush 131 onto the intermediate transfer belt 120 may be electrostatically attracted to the conductive brush 131 and the toner charging roller 132 and scattered. When a large amount of toner is scattered, the inside of the belt cleaning device 130 and the image forming apparatus is stained with toner. As a result, a part of the dirt of the belt cleaning device 130 may adhere to the toner charging roller 132 and a cleaning failure may occur due to the deterioration of the charging performance of the toner charging roller 132. In addition, toner contamination may adhere to the recording material, and more specifically, toner contamination on the recording material may occur due to toner drop on the recording material or contamination on the recording material conveyance path.

  In the above, the problems related to the intermediate transfer member cleaning means for cleaning the intermediate transfer member as the image carrier in the intermediate transfer type image forming apparatus have been described. However, the same problem may occur when a toner collecting and holding unit and a toner charging unit are used as a photosensitive member cleaning unit for cleaning a photosensitive member as an image carrier.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image carrier having a configuration including a toner collecting and holding unit for collecting and holding a transfer residual toner from an image carrier and a toner charging unit for charging the transfer residual toner on the image carrier. An object of the present invention is to provide an image forming apparatus with improved cleaning performance.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image carrier that carries a toner image, a toner collection and holding unit that collects and holds toner from the image carrier, and collects and holds the toner with respect to the toner collection and holding unit. A first voltage output means for outputting a voltage for charging, and a toner charging means arranged on the downstream side of the toner collecting and holding means in the moving direction of the surface of the image carrier to charge the toner on the image carrier. And a second voltage output means for outputting a voltage for charging the toner to the toner charging means, and a voltage output from the first voltage output means to the toner collection and holding means Is an image forming apparatus that performs a discharge process of transferring the toner collected and held by the toner collecting and holding means to the image carrier, and the surface of the image carrier. On the surface of the image carrier of the toner charging unit from the upstream end in the moving direction of the surface of the image carrier at the position where the toner collecting and holding unit is operated on the surface of the image carrier, with the moving speed being PS. The distance from the downstream end portion in the moving direction of the surface of the image carrier at the operation position is L _1, and the first voltage output means outputs the toner collection and holding means to the toner collecting and holding means in the discharging step. The image forming apparatus is characterized in that a relationship of t ₁ ≧ L ₁ / PS is established, where t ₁ is a time interval from the voltage switching to the next switching.

  According to the present invention, the cleaning performance of the image carrier in a configuration including the toner collection and holding unit that collects and holds the transfer residual toner from the image carrier and the toner charging unit that charges the transfer residual toner on the image carrier. Can be improved.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. The dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions. The present invention is not intended to be limited to the following examples.

Example 1
(1) Image Forming Apparatus First, the overall configuration of an embodiment of an image forming apparatus according to the present invention will be described with reference to FIG.

  FIG. 1 shows a schematic cross section of an image forming apparatus 10 of this embodiment. The image forming apparatus 10 according to the present exemplary embodiment is an inline type and intermediate transfer type full color printer using an electrophotographic method.

  The image forming apparatus 10 includes first, second, third, and fourth image forming units (image forming units) 1a, 1b, 1c, and 1d as a plurality of image forming units. The first, second, third, and fourth image forming units 1a, 1b, 1c, and 1d are for forming yellow, magenta, cyan, and black color images, respectively. These four image forming units 1a to 1d are arranged in a line at a constant interval.

  In this embodiment, the configurations of the first to fourth image forming units 1a to 1d are substantially the same except that the color of the toner used is different. Therefore, in the following, unless there is a particular distinction, the subscripts a, b, c, and d given to the reference numerals in the drawings are omitted to indicate that they are elements provided for any color, I will explain it.

  The image forming unit 1 is provided with a drum-type electrophotographic photosensitive member (photosensitive member) as a first image carrier, that is, a photosensitive drum 2. Around the photosensitive drum 2, a charging roller 3 as a charging unit, a developing device 4 as a developing unit, a primary transfer roller 5 as a primary transfer unit, and a drum cleaning device 6 as a photosensitive unit cleaning unit are installed. ing. An exposure device (laser scanner device) 7 as an exposure means (image writing means) is installed above the charging roller 3 and the developing device 4 in the drawing.

  Further, an intermediate transfer belt 20 that is an endless belt-like intermediate transfer member as a second image carrier is disposed so as to face all of the photosensitive drums 2a to 2d of the image forming units 1a to 1d. . The intermediate transfer belt 20 is wound around a driving roller 21 and a secondary transfer counter roller 23 as a plurality of support members. On the inner peripheral surface side of the intermediate transfer belt 20, primary transfer rollers 5a to 5d are arranged corresponding to the photosensitive drums 2a to 2d of the image forming units 1a to 1d. A secondary transfer roller 24 as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 23 on the outer peripheral surface side of the intermediate transfer belt 20.

  In this embodiment, the photosensitive drum 2 is a negatively chargeable OPC (organic photoconductor) photosensitive member, and has a photosensitive layer on an aluminum drum base. The photosensitive drum 2 is rotationally driven at a predetermined peripheral speed (surface movement speed) in a direction indicated by an arrow R1 (clockwise) by a driving device (not shown). In this embodiment, the peripheral speed of the photosensitive drum 2 corresponds to the process speed (PS) of the image forming apparatus 10.

  The charging roller 3 is in contact with the photosensitive drum 2 with a predetermined pressing force, and a predetermined charging bias is applied from a charging bias power source (not shown) as a charging voltage output means, and the surface of the photosensitive drum 2 is applied. Charge uniformly to a predetermined potential. In this embodiment, the photosensitive drum 2 is charged negatively by the charging roller 3.

  The exposure device 7 forms an electrostatic latent image (electrostatic image) corresponding to image information on the surface of the photosensitive drum 2 charged by the charging roller 3 by exposing the surface of the photosensitive drum 2. That is, in the exposure apparatus 7, a laser beam modulated in response to a time-series electric digital pixel signal of image information input from a host computer (not shown) is output from the laser output unit, and this laser beam is reflected by the reflection mirror. The surface of the photosensitive drum 2 is irradiated through

  In this embodiment, the developing device 4 uses a contact developing method as a developing method. The developing device 4 has a developing roller as a developer carrier. The toner carried in a thin layer on the developing roller is conveyed to a portion facing the photosensitive drum 2 (developing portion) by rotating the developing roller by a driving unit (not shown). Then, a developing bias is applied to the developing roller from a developing bias power source as a developing voltage output means to the developing roller, whereby the electrostatic latent image formed on the photosensitive drum 2 is developed as a toner image in the developing unit. Is done. In this embodiment, the electrostatic latent image is developed by a reversal development method. That is, the toner charged to the same polarity as the charging polarity of the photosensitive drum 2 is attached to a portion (exposed portion) on the photosensitive drum 2 after being uniformly charged, where the charge is attenuated by exposure. Then, the electrostatic latent image on the photosensitive drum 2 is developed as a toner image. In this embodiment, the normal charging polarity of the toner is negative, and the toner forming the toner image has mainly negative charge.

  Each of the developing devices 4a, 4b, 4c, and 4d stores toner of each color of yellow, magenta, cyan, and black. In the full-color image forming mode, all the developing rollers of the four developing devices 4 are in contact with the photosensitive drum 2, and in the mono-color (single color) image forming mode, the developing devices 4 other than the image forming unit for forming an image are developed. The roller is configured to be separated from the photosensitive drum 2. This is to prevent deterioration and consumption of the developing roller and toner.

  As the intermediate transfer belt 20, an endless belt-shaped resin made of PVdF (vinylidene fluoride resin), ETFE (tetrafluoroethylene-ethylene copolymer resin), polyimide, PET (polyethylene terephthalate), polycarbonate, or the like is used. be able to. Alternatively, the intermediate transfer belt 20 may be an endless belt formed by coating, for example, a rubber base layer such as EPDM with a fluorine resin such as PTFE dispersed in urethane rubber. The intermediate transfer belt 20 is driven substantially in the direction indicated by the arrow R3 (counterclockwise) in the direction indicated by the arrow R2 (counterclockwise). That is, it moves around (rotates) at a predetermined process speed (PS).

  The primary transfer roller 5 is made of an elastic member such as sponge rubber. The primary transfer roller 5 contacts the photosensitive drum 2 via the intermediate transfer belt 20, and a primary transfer nip portion (primary transfer portion) N is formed at a contact portion between the intermediate transfer belt 20 and the photosensitive drum 2. Form. The primary transfer roller 5 rotates following the movement of the intermediate transfer belt 20.

  A primary transfer bias power source 40 as a primary transfer voltage output unit is connected to the primary transfer roller 5, and a primary transfer bias is applied from the primary transfer bias power source 40 to the primary transfer roller 5. . The toner image formed on the photosensitive drum 2 is transferred onto the rotating intermediate transfer belt 20 by the primary transfer roller 5 to which a primary transfer bias having a polarity opposite to the normal charging polarity of the toner is applied. (Primary transfer).

  The secondary transfer roller 24 is in contact with the secondary transfer counter roller 23 via the intermediate transfer belt 20, and a secondary transfer nip portion (secondary transfer portion) is brought into contact with the secondary transfer roller 24 and the intermediate transfer belt 20. ) M is formed. The toner image formed on the intermediate transfer belt 20 has been conveyed to the secondary transfer nip portion M by the secondary transfer roller 5 to which a secondary transfer bias having a polarity opposite to the normal charging polarity of the toner is applied. Transfer (secondary transfer) is performed on the recording material P.

  In the vicinity of the secondary transfer counter roller 23 outside the intermediate transfer belt 20, a belt cleaning device 30 as an intermediate transfer member cleaning unit is installed. Details of the configuration and operation of the belt cleaning device 30 will be described later.

  A registration roller 13 that constitutes a recording material supply unit is installed upstream of the secondary transfer nip M in the conveyance direction of the recording material P.

  Further, a fixing device 12 as a fixing unit is installed downstream of the secondary transfer nip portion M in the conveyance direction of the recording material P. The fixing device 12 includes a fixing roller 12A provided with a heat source, and a pressure roller 12B in pressure contact with the fixing roller 12A.

  Next, an image forming operation performed by the image forming apparatus 10 according to the present exemplary embodiment will be described using the full-color image forming mode as an example.

  First, toner images of respective colors are formed on the photosensitive drums 2a to 2d of the image forming units 1a to 1d, respectively, by an electrophotographic process.

  That is, when an image forming operation start signal is issued, the photosensitive drums 2a to 2d that are rotationally driven at a predetermined process speed (PS) are uniformly charged by the charging rollers 3a to 3d, respectively.

  Then, each of the exposure devices 7a to 7d converts the input color-separated color image signal into an optical signal at the laser output unit. Each of the exposure devices 7a to 7d scans and exposes the uniformly charged photosensitive drums 2a to 2d with the laser beam that is the converted optical signal, and then onto each of the photosensitive drums 2a to 2d. An electrostatic latent image is formed.

  In the first image forming unit 1a, the electrostatic latent image formed on the photosensitive drum 2a is obtained by electrostatically adsorbing yellow toner in accordance with the surface potential of the photosensitive drum 2a. Developed as an image. At this time, a developing bias having the same polarity as the charging polarity (negative polarity in this embodiment) of the photosensitive drum 2a is applied to the developing roller of the developing device 4a.

  The yellow toner image on the photosensitive drum 2a is subjected to primary transfer to which a primary transfer bias having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied at the primary transfer nip Na. The image is primarily transferred onto the rotating intermediate transfer belt 20 by the roller 5a. The intermediate transfer belt 20 to which the yellow toner image is transferred moves to the image forming unit 1b side.

  In the second image forming unit 1b, similarly to the first image forming unit 1a, a magenta toner image is formed on the photosensitive drum 2b. Then, the magenta toner image is primary-transferred superimposed on the yellow toner image on the intermediate transfer belt 20 at the primary transfer nip portion Nb.

  Similarly, in the third and fourth image forming portions 1c and 1d, the primary transfer nip portion Nc is formed on the yellow and magenta toner images that are primarily transferred and superimposed on the intermediate transfer belt 20. , Nd, cyan and black toner images are sequentially superposed and primarily transferred.

  In this way, a multi-toner image composed of a plurality of color toner images is formed on the intermediate transfer belt 20 in which the toner images of the respective colors are primary-transferred in the primary transfer nip portions Na to Nd.

  The recording material P is conveyed to the secondary transfer nip M by the registration roller 13 in accordance with the timing at which the leading edge of the toner image on the intermediate transfer belt 20 moves to the secondary transfer nip M. In the secondary transfer nip portion M, the secondary transfer roller 24 to which a secondary transfer bias having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied is applied to the intermediate transfer belt 20. The multiple toner images are secondarily transferred onto the recording material P all at once.

  Thereafter, the recording material P onto which the toner image has been transferred is conveyed to the fixing device 12. The recording material P carrying the toner image is heated and pressed at a fixing nip portion between the fixing roller 12A and the pressure roller 12B installed in the fixing device 12. As a result, the toner image is thermally fixed (melted and fixed) on the surface of the recording material P, and a full-color image (or multicolor image) is formed on the recording material P. Thereafter, the recording material P is discharged to the outside of the image forming apparatus 10 and a series of image forming operations is completed.

  The toner remaining on the photosensitive drum 2 after the primary transfer step (primary transfer residual toner) is removed from the photosensitive drum 2 by the drum cleaning device 6 and collected. The drum cleaning device 6 includes a cleaning blade 61 that is a plate-like member formed of an elastic body as a cleaning member, a collected toner container 62 that stores toner scraped from the photosensitive drum 2 by the cleaning blade 61, and Have

  The toner remaining on the intermediate transfer belt 20 after the secondary transfer process (secondary transfer residual toner) is removed from the intermediate transfer belt 20 and collected by the belt cleaning device 30 as described in detail below.

(2) Belt Cleaning Mechanism The belt cleaning device 30 includes a conductive brush 31 as a toner collection and holding unit that collects and holds the secondary transfer residual toner, and a toner charging roller as a toner charging unit that charges the secondary transfer residual toner. 32.

  The conductive brush 31, which is a brush-like member, is located downstream of the secondary transfer nip portion M in the movement direction (rotation direction) of the surface of the intermediate transfer belt 20 and collects a part of the secondary transfer residual toner. Hold.

In this embodiment, the conductive brush 31 is made of nylon, the fineness is 7 dtex, the pile length is 5 mm, the brush width is 5 mm, and the electric resistance value is 1.0 × 10 ⁶ Ω. The conductive brush 31 is connected to a recovery holding power source 41 as first cleaning voltage output means (first voltage output means). A predetermined DC voltage is applied to the conductive brush 31 from the power supply 41 for recovery and holding. The applied voltage varies depending on the material of the conductive brush 31 and the environment (temperature, humidity) in which the image forming apparatus 10 is used.

  The toner on the intermediate transfer belt 20 before the secondary transfer process is charged with a negative polarity having the same polarity as the charged charge on the surface of the photosensitive drum 2 and with a small variation in charge distribution. On the other hand, the secondary transfer residual toner on the intermediate transfer belt 20 after the secondary transfer process has a broad charge distribution and a peak on the positive polarity side opposite to the normal charging polarity of the toner. Form a shifted distribution. As a result, the secondary transfer residual toner is in a state where a negatively charged toner, a hardly charged toner, and a positively charged toner are mixed.

  Here, by applying a positive voltage to the conductive brush 31 during the cleaning operation of the intermediate transfer belt 20 during the image forming operation, the negatively charged secondary transfer residual toner as described above is made negative. The charged toner can be collected in the conductive brush 31. Thereby, the amount of toner passing through the toner charging roller 32 during the image forming operation can be reduced. Further, by applying a positive voltage to the conductive brush 31, in addition to collecting negative toner, a discharge occurs between the conductive brush 31 and the secondary transfer residual toner, so that the toner becomes positive. There is an action to charge to the side. Therefore, the negative transfer toner hardly exists in the secondary transfer residual toner that is not collected by the conductive brush 31.

  The toner on the surface of the toner charging roller 32 to which a positive voltage is applied to charge the toner as will be described later by suppressing the amount of toner passing through the toner charging roller 32 and removing the negative toner. Adhesion can be greatly reduced. As a result, since the toner can be stably charged by the toner charging roller 32, better cleaning performance can be ensured.

  As the toner collecting and holding means, in addition to the fixedly arranged brush-like member as in the present embodiment, a fixedly arranged foamed sponge-like member, a rotatable fur brush roller, a rotatable foamed sponge roller, etc. May be used. As the foamed sponge, for example, those formed of urethane rubber or NBR + hydrin rubber can be suitably used.

  The toner charging roller 32, which is a roller-like member, is located downstream of the conductive brush 31 in the movement direction (rotation direction) of the surface of the intermediate transfer belt 20, and the secondary transfer that has not been collected by the conductive brush 31. The remaining toner is charged to a desired positive charge amount.

In this embodiment, the toner charging roller 32 is a nickel-plated steel rod having a diameter of 6 mm and a solid elastic body in which carbon is dispersed in EPDM rubber and is coated with a thickness of 5 mm. The electric resistance value of the toner charging roller 32 is 5.0 × 10 ⁷ Ω when 500 V is applied. The toner charging roller 32 is connected to a toner charging power source 42 as second cleaning voltage output means (second voltage output means). Then, a predetermined DC voltage is applied to the toner charging roller 32 from the toner charging power source 42. The applied voltage varies depending on the material of the toner charging roller 32 and the environment (temperature, humidity) in which the image forming apparatus 10 is used.

  By applying a positive voltage to the toner charging roller 32 during the cleaning operation of the intermediate transfer belt 20 during image formation, the toner on the intermediate transfer belt 20 can be uniformly charged to the positive polarity. The toner charged to the positive polarity by the toner charging roller 32 proceeds to the primary transfer nip Na of the first image forming unit 1a. The positive transfer bias applied to the primary transfer roller 5a of the first image forming unit 1a is applied to the photosensitive drum 2a of the first image forming unit 1a from the intermediate transfer belt 20. Transcribed. The toner transferred to the photosensitive drum 2a is then collected by the drum cleaning device 6a of the first image forming unit 1a.

  In this embodiment, both the conductive brush 31 and the toner charging roller 32 are disposed to face the secondary transfer counter roller 23 with the intermediate transfer belt 20 interposed therebetween. In this embodiment, the conductive brush 31 and the toner charging roller 32 are in contact with the intermediate transfer belt 20 and pressed against the secondary transfer counter roller 23 with a predetermined pressure. By using the secondary transfer facing roller 23 without newly providing a facing roller (facing member) with respect to the conductive brush 31 and the toner charging roller 32, it is possible to avoid an increase in cost and an increase in the size of the apparatus. Further, if an opposing roller is provided separately for each of the conductive brush 31 and the toner charging roller 32, the toner is likely to be scattered at the separation portion between the opposing roller and the intermediate transfer belt 20. On the other hand, there is an advantage that the scattering of the toner can be reduced by using a common roller for the conductive brush 31 and the toner charging roller 32 as in the present embodiment.

  When a large amount of toner is scattered, the inside of the belt cleaning device 30 and the image forming apparatus 10 is stained with toner. As a result, dirt inside the belt cleaning device 30 may adhere to the toner charging roller 32, and cleaning failure may occur due to the charging performance of the toner charging roller 32 being impaired. In addition, toner stains may adhere to the recording material P. More specifically, there may be toner stains on the recording material due to toner drop on the recording material or contamination on the recording material conveyance path. Therefore, it is desirable to minimize toner scattering.

(3) Discharging Process Next, a process of transferring the secondary transfer residual toner collected and held by the conductive brush 31 to the intermediate transfer belt 20, that is, a discharging process will be described.

  The toner collected by the conductive brush 31 accumulates, and when it reaches a predetermined amount, it becomes impossible to collect and hold any more toner, and the cleaning performance deteriorates. Therefore, a step of transferring the toner held on the conductive brush 31 to the intermediate transfer belt 20 again, that is, a discharging step is performed at a predetermined timing. As a result, the amount of toner accumulated in the conductive brush 31 is reduced, and the deterioration of the cleaning performance is suppressed.

In this embodiment, in the discharge process, a negative direct current voltage V _1m and a positive direct current voltage V _1p are alternately applied from the recovery holding power supply 41 to the conductive brush 31. When a negative DC voltage V _1m is applied to the conductive brush 31, the negative toner held on the conductive brush 31 is discharged to the intermediate transfer belt 20. Most of the toner held on the conductive brush 31 is negatively charged, but a small amount of toner that has become positive due to discharge is also held. Therefore, by applying a positive DC voltage V _1p to the conductive brush 31, the positively charged toner is discharged to the intermediate transfer belt 20.

In this embodiment, V _1m = −800V and V _1p = + 800V.

  As the image forming apparatus 10 is used, a part of the secondary transfer residual toner adheres to the toner charging roller 32 and the surface of the toner charging roller 32 becomes dirty with toner. If the surface of the toner charging roller 32 is contaminated with toner, the charging of the secondary transfer residual toner by the toner charging roller 32 becomes unstable, and the charge amount of the secondary transfer residual toner becomes unstable. To do. Therefore, in this embodiment, the same operation as that for transferring the toner from the conductive brush 31 to the intermediate transfer belt 20 is also performed on the toner charging roller 32 in the discharging step in this embodiment.

That is, in this embodiment, in the discharging step, the negative DC voltage V _2m and the positive DC voltage V _2p are alternately applied from the toner charging power source 42 to the toner charging roller 32. As a result, the toner adhering to the surface of the toner charging roller 32 is removed.

In this embodiment, V _2m = −800V and V _2p = + 800V.

  In this embodiment, each of the recovery holding power supply 41 and the toner charging power supply 42 has a first voltage output unit (high voltage circuit) that outputs a voltage having a first polarity, and has a polarity opposite to the first polarity. And a second voltage output unit (high voltage circuit) that outputs a voltage of the second polarity. The recovery holding power supply 41 and the toner charging power supply 42 each output a voltage from the first voltage output unit, output a voltage from the second voltage output unit, or turn off (stop) the voltage output. ) Has a switching means for selectively switching whether to do. The switching means may further be capable of changing the output voltage value. In this embodiment, control such as switching of the output voltage value and the polarity of the output voltage in the recovery holding power supply 41 and the toner charging power supply 42 is provided by a control unit that comprehensively controls the operation of the image forming apparatus 10. This is performed by the CPU 50 (FIG. 1) as control means. The CPU 50 performs sequence control of the operation of the image forming apparatus 10 according to the program and data stored in the storage means built in or connected to the CPU 50. In particular, the collection holding power source 41, the toner are related to this embodiment. The voltage output from the charging power source 42 is controlled.

  The discharging process is performed at a timing when image formation is not performed (during non-image formation), such as during post-rotation or processing operation after occurrence of a jam (recording material P is jammed in the conveyance path). In the present embodiment, the toner discharged to the intermediate transfer belt 20 in the discharging step is selectively collected in the collected toner containers 62b and 62c of the second image forming unit 1b and the third image forming unit 1c. As a method of selectively collecting in this way, in the present embodiment, the primary transfer nip portion N of the image forming portion where it is not desired to collect the toner discharged onto the intermediate transfer belt 20, such as the first image forming portion 1a. A method of separating the primary transfer roller 5 from the photosensitive drum 2 was used. By selecting the recovery toner container 62 that recovers the toner discharged to the intermediate transfer belt 20 in the discharge process, secondary transfer to the specific recovery toner container 62 of the specific image forming unit 1 is performed in the inline type image forming apparatus. A large amount of residual toner can be suppressed.

  Incidentally, as described above, the following problems may occur in an image forming apparatus having a toner collecting and holding unit and a toner charging unit. That is, the toner discharged from the toner collecting and holding unit may adhere to the toner, and the charging performance of the toner charging unit may be deteriorated, resulting in an image defect due to a cleaning failure. In addition, the toner discharged from the toner collecting and holding unit is electrostatically attracted to and scattered by the toner collecting and holding unit and the toner charging unit. May adhere.

  The main object of the present embodiment is to provide an image carrier having a configuration including a toner collection and holding unit that collects and holds the transfer residual toner from the image carrier, and a toner charging unit that charges the transfer residual toner on the image carrier. It is to improve the cleaning performance. One of the more detailed purposes of this embodiment is to suppress the occurrence of image defects due to poor cleaning of the intermediate transfer belt 20 and the adhesion of toner stains to the recording material P.

  Therefore, in this embodiment, in the step of discharging toner from the conductive brush 31 to the intermediate transfer belt 20 in the intermediate transfer type image forming apparatus 10 having the conductive brush 31 and the toner charging roller 32, the following is performed. Use settings. That is, the time interval until the voltage to be applied to the conductive brush 31 is switched until the toner discharged from the conductive brush 31 to the intermediate transfer belt 20 exceeds the toner charging roller 32 on the downstream side in the moving direction. The time is longer than this time.

  With reference to FIG.2 and FIG.3, the timing which switches the voltage applied to the conductive brush 31 and the toner charging roller 32 in a discharge process is demonstrated. For simplification, the toner discharged from the toner charging roller 32 is omitted in FIG.

In the figure, Q ₁ indicates an operation position of the conductive brush 31 on the surface of the intermediate transfer belt 20 (hereinafter referred to as “collection operation position”), and Q ₂ indicates the surface of the intermediate transfer belt 20 of the toner charging roller 32. The above operating position (hereinafter referred to as “charging operating position”) is shown. In the drawing, W ₁ indicates the width in the moving direction of the surface of the intermediate transfer belt 20 at the recovery operation position Q ₁ , and W ₂ indicates the width in the moving direction of the surface of the intermediate transfer belt 20 at the charging operation position Q _2. PS represents the process speed (moving speed of the surface of the intermediate transfer belt 20). Further, in the drawing, L ₁ is the rear end of the charging operation position Q ₂ from the front end of the recovery operation position Q ₁ (the upstream end in the movement direction of the surface of the intermediate transfer belt 20) along the surface of the intermediate transfer belt 20. The distance to the end of the surface of the intermediate transfer belt 20 on the downstream side in the movement direction is shown. Further, in the drawing, L ₂ is the leading end of the charging operation position Q ₂ from the rear end of the recovery operation position Q ₁ (the downstream end in the movement direction of the surface of the intermediate transfer belt 20) along the surface of the intermediate transfer belt 20. The distance to (the upstream end of the intermediate transfer belt 20 in the moving direction) is shown. L ₁ and L ₂ include the following equations:
L ₁ = L ₂ + W ₁ + W ₂
The relationship is established.

  At this time, in this embodiment, the voltage applied to the conductive brush 31 and the toner charging roller 32 in the discharging process is switched as follows. In particular, in this embodiment, the voltage polarity is switched as follows.

First, the timing for switching the polarity between the voltage applied to the conductive brush 31 and the voltage applied to the toner charging roller 32 is made uniform (that is, substantially the same timing) and switched so as to have the same polarity. Then, the time interval t ₁ until the polarity of the voltage applied to the conductive brush 31 and the toner charging roller 32 is switched is expressed by the following equation:
t ₁ ≧ L ₁ / PS (Formula 1)
Is set so that the relationship is established.

  As a result, the toner discharged from the conductive brush 31 to the intermediate transfer belt 20 is scattered between the conductive brush 31 and the toner charging roller 32, and the discharged toner adheres to the surface of the toner charging roller 32. Can be suppressed.

  More specifically, FIGS. 3A to 3D schematically show a state in the vicinity of the belt cleaning device 30 in the discharging process.

FIG. 3A is a schematic diagram at time t ₀ when the discharge process is started. A transient current flows through the conductive brush 31 by applying a negative DC voltage to the conductive brush 31 to which a positive DC voltage is applied during the image forming operation, that is, by switching the applied voltage. As a result, the negative-polarity toner held on the conductive brush 31 is discharged to the intermediate transfer belt 20 with a width of W ₁ in the range of the recovery operation position Q ₁ .

Thereafter, as shown in FIG. 3B, the toner discharged to the intermediate transfer belt 20 advances toward the toner charging roller 32 as the intermediate transfer belt 20 moves. If a positive voltage is applied to the conductive brush 31 or the toner charging roller 32 at this time, the negative toner discharged to the intermediate transfer belt 20 is applied to the conductive brush 31 or the toner charging roller 32. Are attracted electrostatically, and toner scattering is likely to occur. Therefore, while the toner discharged to the intermediate transfer belt 20 exists between the recovery operation position Q ₁ and the charging operation position Q ₂ (t ₀ <t <t ₀ + L ₂ / PS), the conductive brush 31 and The voltage applied to the toner charging roller 32 needs to be as follows. That is, the voltage applied to the conductive brush 31 and the toner charging roller 32 has the same polarity (negative polarity in this embodiment), and the polarity is not switched.

FIG. 3C is a schematic diagram during the time when the toner discharged to the intermediate transfer belt 20 at the time t ₀ exists in the charging operation position Q ₂ (t ₀ + L ₂ / PS <t <t ₀ + L ₁ / PS). FIG. If the polarity of the voltage applied to the toner charging roller 32 is switched at this time, the negative toner discharged to the intermediate transfer belt 20 adheres to the toner charging roller 32 to which the positive voltage is applied. Accordingly, the polarity of the voltage applied to the conductive brush 31 and the toner charging roller 32 is not switched even at this time.

FIG. 3D is a schematic diagram after the toner discharged at t ₀ passes through the charging operation position Q ₂ (t> t ₀ + L ₁ / PS). At this point, the voltage applied to the conductive brush 31 and the toner charging roller 32 is switched from negative polarity to positive polarity. As a result, negative toner discharged from the conductive brush 31 to the intermediate transfer belt 20 is prevented from scattering between the conductive brush 31 and the toner charging roller 32, and the toner charging roller 32 has a surface thereof. It can suppress adhering. This time is assumed to be t = t ₀ + t ₁ .

When the voltage applied to the conductive brush 31 and the toner charging roller 32 is switched to the positive polarity (t = t ₀ + t ₁ ), the toner having the positive polarity held in the conductive brush 31 becomes a transient current. Is discharged to the intermediate transfer belt 20. Thereafter, the voltage applied to the conductive brush 31 and the toner charging roller 32 at a time point t = t ₀ + 2 × t ₁ is obtained after the polarity is reversed from that shown in FIGS. Switch to negative polarity again. As a result, as in the case of the negative toner, the positive toner discharged to the intermediate transfer belt 20 is prevented from being scattered between the conductive brush 31 and the toner charging roller 32, and the toner Adhesion to the surface of the charging roller 32 can be suppressed.

  Here, in the above description, the toner discharged from the conductive brush 31 is described as toner discharged at the width of the conductive brush 31 due to a transient current at the timing when the voltage applied to the conductive brush 31 is switched. . Actually, after the voltage applied to the conductive brush 31 is switched to the negative DC voltage, the negative DC voltage is continuously applied as it is. Therefore, strictly speaking, negative-polarity toner is discharged from the conductive brush 31 at this time as well. However, since the amount of toner is sufficiently smaller than the amount of toner discharged due to a transient current, the influence of toner scattering and adhesion to the toner charging roller 32 is sufficiently small. Therefore, it is important to suppress the scattering of the toner discharged by the transient current and the adhesion to the surface of the toner charging roller 32.

As shown in FIG. 4, the above process is repeated to obtain the following formula:
t = t ₀ + n × t ₁ (Formula 2)
At each time point, the polarity of the voltage applied to the conductive brush 31 and the toner charging roller 32 is switched. Thus, the toner discharging process from the conductive brush 31 to the intermediate transfer belt 20 is completed.

  In Equation 2, n is a natural number from 1 to m. In this embodiment, m is a natural number from 2 to 19, and the voltage is switched differently depending on the image forming mode, the image ratio (printing rate), the occurrence of a jam, and the calibration.

  Here, in the discharging process, the number of times of switching the polarity of the voltage applied to the conductive brush 31 and the toner charging roller 32 is preferably set to the minimum necessary number of times so as not to reduce the image forming productivity as much as possible. .

In the discharging process, it is desirable that the time interval t ₁ for switching the polarity of the voltage applied to the conductive brush 31 and the toner charging roller 32 is as short as possible within the range satisfying Equation 1. This is because, as the time interval t ₁ is shorter, the number of discharges within a certain time increases, so that highly efficient discharge can be realized. Preferably, t ₁ = L ₁ / PS. However, this time interval t ₁ can be set as appropriate within the following range.

That is, along the surface of the intermediate transfer belt 20, from the tip of the recovery operating position to Q ₁ conductive brush 31, the image forming unit 1a for collecting toner discharging, 1b, 1c or transfer operative position Na in 1d, Nb, Let the distance to the rear end of Nc or Nd be L ₃ . In this embodiment, the discharged toner is selected so as to be collected using the collected toner container 62 of the specific image forming unit as a collection destination. Further, the front end of the recovery operating position Q _1, is a moving direction upstream side end portion of the surface of the intermediate transfer belt 20 of the recovery operating position Q _1. Further, the rear end of the transfer action position Na, Nb, Nc or Nd is a transfer action position (that is, a discharge toner removal action position from the intermediate transfer belt 20) N of the image forming unit 1 that collects the discharged toner. This is the downstream end of the surface of the intermediate transfer belt 20 in the moving direction. At this time, t ₁ is usually L ₃ / PS or less. This is because if the toner discharged from the conductive brush 31 onto the intermediate transfer belt 20 is collected (removed), the scattering does not occur.

  In this embodiment, the absolute value of the voltage applied to the conductive brush 31 and the absolute value of the voltage applied to the toner charging roller 32 during the discharging process are set to be equal. In this case, because of the relationship between the electric resistance values of the conductive brush 31 and the toner charging roller 32 (the electric resistance of the toner charging roller 32 is higher than that of the conductive brush 31), the current flowing through the conductive brush 31 is charged by the toner. It becomes larger than the current flowing through the roller 32. In such a system, when the conductive brush 31 and the toner charging roller 32 are close to each other as in this embodiment, a current flows from the conductive brush 31 to the toner charging roller 32 side through the intermediate transfer belt 20 ( Interference). When this current flow occurs, more toner can be discharged from the conductive brush 31, and more efficient discharge can be realized. Further, since the toner is discharged from the conductive brush 31 with high efficiency, the time required for the discharge can be shortened. Therefore, the productivity of image formation can be improved and the usability is excellent.

In this embodiment, the time interval t ₁ is shorter than the time for which the toner charging roller 32 rotates once. That is, in this embodiment, when the radius of the toner charging roller 32 is r,
t ₁ <2πr / PS (Formula 3)
The relationship is established.

  Therefore, in this embodiment, a toner charging means cleaning process for removing the toner adhering to the surface of the toner charging roller 32 is performed separately from the discharge process described above. This is because when the polarity of the voltage applied to the conductive brush 31 and the toner charging roller 32 is switched earlier than the time during which the toner charging roller 32 makes one rotation in the discharging step, the toner is applied to the surface of the toner charging roller 32. This is because there are parts that cannot be removed.

The operation in the toner charging unit cleaning process is basically the same as the operation in the discharge process described above. However, in the toner charging means cleaning step, the time interval t ₂ for switching the polarity of the voltage applied to the conductive brush 31 and the toner charging roller 32 is expressed by the following equation:
t ₂ ≧ 2πr / PS (Formula 4)
Is set so that the relationship is established. Usually, t ₂ is L ₃ / PS or less, similarly to t ₁ . This is because if the toner discharged from the conductive brush 31 onto the intermediate transfer belt 20 is collected (removed), the scattering does not occur.

In this embodiment, as shown in FIG. 5, after performing the discharging step with the time interval for switching the polarity of the voltage applied to the conductive brush 31 and the toner charging roller 32 as t ₁ , the time interval is set to t ₂ . The toner charging means cleaning step is performed for a time of t ₂ × 6.

  In both the discharging step and the toner charging unit cleaning step, the toner is normally discharged from the conductive brush 31 and the toner charging roller 32 to the intermediate transfer belt 20. Therefore, the discharging process can be considered to be a mode mainly for discharging toner from the conductive brush 31 in the refresh operation of the belt cleaning device 30. The toner charging means cleaning process can be considered to be a mode mainly for discharging toner from the toner charging roller 32 in the refresh operation of the belt cleaning device 30.

(4) Image Output Experiment Result of the Present Example Next, the result of the image output experiment when the image forming apparatus 10 of the present example is used will be described.

As a durability experiment, CLC color laser copier paper (Canon sales, product name) was used as the recording material P, and the image ratio of each color of C (cyan), M (magenta), Y (yellow), and K (black) was 25%. 100,000 images were formed by repeating continuous image formation of two images. The plain paper mode was used as the image forming mode, the process speed (PS) was 100 mm / sec, and the throughput was 18 sheets per minute. During the durability experiment, the discharge process was performed every time two continuous image formations were completed with the time interval t _{1 set} to L ₁ / PS.

  In addition, the evaluation images were sampled at the start of the durability experiment and every 10,000 images formed during the durability experiment. As evaluation images to be sampled, CLC color laser copier paper (Canon sales, trade name) was used as the recording material P, and the following was output. That is, a solid image (maximum density level image), a halftone image, and a character thin line image are respectively converted into C (cyan), M (magenta), Y (yellow), K (black), R (red), and B (blue). , G (green) were output in duplicate for each color.

  The sampled evaluation images were ranked and evaluated in terms of two image defects: (1) defective cleaning and (2) toner contamination on the recording material P. Specifically, the cleaning failure was evaluated by observing whether or not an image of one rotation before the intermediate transfer belt 20 occurred in a ghost shape in the sampled evaluation image. Further, the toner contamination on the recording material P was evaluated by observing whether the sampled evaluation image is contaminated with the toner around the belt cleaning device 30. As the criteria for ranking, ○ when the image defect does not occur at all, ○ △ when it can be confirmed slightly (within practically acceptable range), △ when it can be confirmed, △ × when the level is slightly bad, Bad cases were marked with x.

  The atmosphere environment in which the experiment was performed is an NN environment with a temperature of 23 ° C. and a humidity of 50%.

  The evaluation results are shown in Table 1.

  In this example, the defective cleaning did not occur up to 80,000 sheets, but occurred to the extent that it could be confirmed slightly from 90,000 sheets, but this was within a practically acceptable range. On the other hand, toner contamination on the recording material P did not occur throughout the durability test of 100,000 sheets.

(5) Image Output Experiment Result of Comparative Example Next, the result of the image output experiment of Comparative Examples 1 and 2 as a control of the image forming apparatus 10 of the present embodiment will be described.

The image forming apparatus of Comparative Example 1 has the same basic configuration as that used in the experiment of the present embodiment, but the time interval t ₁ in the discharge process is set to W ₁ / PS.

The image forming apparatus of Comparative Example 2 has the same basic configuration as that used in the experiment of the present embodiment, but in the discharge process, only the polarity of the voltage applied to the conductive brush 31 is set to the time interval t ₁ by L ₁ / Switching to PS, a positive voltage was continuously applied to the toner charging roller 32.

  The evaluation results are shown in Table 2.

  In Comparative Example 1, it was confirmed that the cleaning failure did not occur up to 40,000 sheets, but occurred to the extent that it could be confirmed slightly after 50,000 sheets, and deteriorated as the durability experiment progressed. On the other hand, it was confirmed that adhesion of toner to the recording material P caused an image defect that could be confirmed from 60,000 sheets and worsened as the durability experiment progressed.

  Further, in Comparative Example 2, it was confirmed that cleaning failure did not occur up to 50,000 sheets, but occurred to the extent that it could be confirmed slightly from 60,000 sheets, and deteriorated as the durability experiment progressed. On the other hand, it was confirmed that adhesion of toner to the recording material P occurred to a level that could be confirmed slightly on 90,000 sheets, and the level deteriorated on 100,000 sheets.

(6) Summary As described above, in this embodiment, in the step of discharging toner from the conductive brush 31 to the intermediate transfer belt 20 in the intermediate transfer type image forming apparatus 10 having the conductive brush 31 and the toner charging roller 32, Use the following settings: That is, the toner discharged from the conductive brush 31 to the intermediate transfer belt 20 exceeds the toner charging roller 32 on the downstream side in the moving direction at a time interval t ₁ until the voltage applied to the conductive brush 31 is switched. It takes longer than the time it takes to complete. As a result, it is possible to suppress the occurrence of image defects due to poor cleaning of the intermediate transfer belt 20 and the adhesion of toner stains to the recording material P. As described above, according to the present invention, the image carrier in the configuration having the toner collecting and holding unit for collecting and holding the transfer residual toner from the image carrier and the toner charging unit for charging the transfer residual toner on the image carrier. The body cleaning performance can be improved.

Example 2
Next, another embodiment according to the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, elements having the same functions or configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 6 schematically shows the vicinity of the belt cleaning device 30 in the image forming apparatus 10 of the present embodiment.

  In this embodiment, a conductive brush (hereinafter referred to as “toner charging brush”) 33 is used as a toner charging unit in the belt cleaning device 30 instead of the toner charging roller 32 of the first embodiment.

  As with the toner charging roller 32 in the first exemplary embodiment, the toner charging brush 33 is located downstream of the conductive brush 31 in the moving direction (rotating direction) of the surface of the intermediate transfer belt 20. Further, like the toner charging roller 32 in the first exemplary embodiment, the toner charging brush 33 has a role of positively charging the secondary transfer residual toner that has not been collected by the conductive brush 31.

In this embodiment, the toner charging brush 33 is made of nylon, the fineness is 7 dtex, the pile length is 5 mm, the brush width is 5 mm, and the electric resistance value is 1.0 × 10 ⁸ Ω. The toner charging brush 33 has an electric resistance higher than that of the conductive brush 31 as a toner collecting and holding unit. This increases the ability of the toner charging brush 33 to charge the toner.

  A toner charging power source 42 is connected to the toner charging brush 33. A predetermined DC voltage is applied to the toner charging brush 33 from the toner charging power source 42. The applied voltage varies depending on the material of the toner charging brush 33 and the environment (temperature, humidity) in which the image forming apparatus 10 is used.

  During the cleaning operation of the intermediate transfer belt 20, by applying a positive voltage to the toner charging brush 33, the secondary transfer residual toner that has not been collected by the conductive brush 31 can be uniformly charged to the positive polarity. . The toner charged to the positive polarity by the toner charging brush 33 proceeds to the primary transfer nip Na of the first image forming unit 1a. The positive transfer bias applied to the primary transfer roller 5a of the first image forming unit 1a is applied to the photosensitive drum 2a of the first image forming unit 1a from the intermediate transfer belt 20. Transcribed. The toner transferred to the photosensitive drum 2a is then collected by the drum cleaning device 6a of the first image forming unit 1a.

  When the cleaning operation is repeated as the image forming apparatus 10 is used, a part of the secondary transfer residual toner is captured by the toner charging brush 33 and the toner charging brush 33 becomes dirty with the toner. If the toner charging brush 33 is contaminated with toner, the charging of the secondary transfer residual toner by the toner charging brush 33 becomes unstable, and as a result, the charge amount of the secondary transfer residual toner becomes unstable, so that the cleaning performance is deteriorated. To do. Therefore, in this embodiment, the same operation as that for transferring the toner from the conductive brush 31 to the intermediate transfer belt 20 is also performed on the toner charging brush 33 in the discharging step in this embodiment.

That is, in this embodiment, in the discharging process, the negative DC voltage V _2m and the positive DC voltage V _2p are alternately applied from the toner charging power source 42 to the toner charging brush 33. As a result, the toner adhering to the inside of the toner charging brush 33 is removed.

In this embodiment, V _2m = −800V and V _2p = + 800V.

  The timing for switching the polarity of the voltage applied to the conductive brush 31 and the toner charging brush 33 in the discharging process is the same as in the first embodiment.

  With the configuration as described above, in this embodiment as well as in Embodiment 1, the toner discharged to the intermediate transfer belt 20 is prevented from scattering and the toner is prevented from adhering to the toner charging brush 33. Can be obtained.

In the first embodiment, the toner charging means cleaning step with the time interval t ₂ after the discharge step with the time interval t ₁ for switching the polarity of the voltage applied to the conductive brush 31 and the toner charging roller 32 is performed. went. However, in this embodiment, the toner charging unit cleaning step as in the first embodiment is not necessary. In this embodiment, the discharge of the toner in the toner charging brush 33 is completed by performing the discharging step with the time interval for switching the polarity of the voltage applied to the conductive brush 31 and the toner charging brush 33 as t _1. Because. Thus, according to the configuration of the present embodiment, there is an advantage that the time required for the refresh operation of the belt cleaning device 30 can be made shorter than that of the first embodiment. Therefore, the productivity of image formation can be improved and the usability is excellent.

As described above, in the present exemplary embodiment, in the toner discharging process from the conductive brush 31 to the intermediate transfer belt 20 in the intermediate transfer type image forming apparatus 10 including the conductive brush 31 and the toner charging brush 33, the following is performed. Use settings. That is, the toner discharged from the conductive brush 31 to the intermediate transfer belt 20 exceeds the toner charging brush 33 on the downstream side in the moving direction at a time interval t ₁ until the voltage applied to the conductive brush 31 is switched. It takes longer than the time it takes to complete. As a result, it is possible to suppress the occurrence of image defects due to poor cleaning of the intermediate transfer belt 20 and the adhesion of toner stains to the recording material P.

Example 3
Next, another embodiment according to the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are substantially the same as those of the first embodiment. Accordingly, elements having the same functions or configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, a needle charger is used as a toner charging unit in the belt cleaning device 30 instead of the toner charging roller 32 of the first embodiment.

  FIG. 7 shows a schematic configuration of the needle charger 34 in the present embodiment.

  Needle-shaped charger 34 is located downstream of conductive brush 31 in the moving direction (rotating direction) of surface of intermediate transfer belt 20, similar to toner charging roller 32 in the first embodiment. The needle charger 34 has the role of charging the secondary transfer residual toner not collected by the conductive brush 31 to the positive polarity, like the toner charging roller 32 in the first embodiment.

  The needle charger 34 is disposed near the needle tip 34A1 of the needle electrode 34A and the needle electrode 34A formed with a plurality of needle tips 34A1 arranged in a straight line at predetermined intervals, and serves as a discharge assisting member. A discharge auxiliary plate 34B that fulfills the above and an insulating spacer 34C. The acicular electrode 34A and the auxiliary discharge plate 34B are made of metal. The insulating spacer 34C is made of an electrically insulating material.

  The acicular electrode 34A and the auxiliary discharge plate 34B are electrically insulated with the insulating spacer 34C interposed therebetween and maintaining a distance d. The auxiliary discharge plate 34B is electrically grounded (grounded), and a toner charging power source 44 is connected to the needle electrode 34A. In this embodiment, d = 5.0 mm.

  In this embodiment, a predetermined DC voltage is applied from the toner charging power supply 44 to the needle electrode 34A, thereby generating a corona discharge between the needle electrode 34A and the auxiliary discharge plate 34B, thereby generating the needle electrode 34A. Can be charged positively. The voltage to be applied differs depending on the configuration of the needle charger 34 and the environment (temperature, humidity) in which the image forming apparatus 10 is used.

  When the needle charger 34 is used as the toner charging means as in the present embodiment, there is an advantage that the negative high voltage circuit in the toner charging power supply 44 can be omitted. This is because the needle-shaped charger 34 is not in contact with the intermediate transfer belt 20, so that it is not necessary to discharge toner from the needle-shaped charger 34 to the intermediate transfer belt 20 by applying a negative voltage. Because. That is, in this embodiment, unlike the first or second embodiment, it is not necessary to apply a negative voltage to the needle charger 34 for the purpose of cleaning the toner charging means.

In the present embodiment, the voltage applied to the conductive brush 31 and the needle charger 34 in the discharging process is changed as follows. That is, first, the timing for switching the voltage between the conductive brush 31 and the needle charger 34 is made uniform. Then, during the time interval t _{1 at} which the voltage is switched, the toner discharged from the conductive brush 31 to the intermediate transfer belt 20 is needle-like charged downstream of the conductive brush 31 in the moving direction of the surface of the intermediate transfer belt 20. It is assumed that the time is longer than the time required to exceed the vessel 34. When a positive voltage is applied to the conductive brush 31, a voltage having the same polarity (ie, positive polarity) is applied to the needle charger 34, and when a negative voltage is applied to the conductive brush 31, The voltage application to the needle charger 34 is turned off.

  With the configuration as described above, in this example as well as in the first embodiment, the toner discharged to the intermediate transfer belt 20 is suppressed from being scattered, and further, the toner adheres to the acicular charger 34. The effect of suppressing can be acquired.

  Similar to the second embodiment, the present embodiment also has an advantage that the toner charging means cleaning process is not required and the time required for the refresh operation of the belt cleaning device 30 can be made shorter than that of the first embodiment. Therefore, the productivity of image formation can be improved and the usability is excellent.

As described above, in the present exemplary embodiment, in the step of discharging toner from the conductive brush 31 to the intermediate transfer belt 20 in the intermediate transfer type image forming apparatus 10 having the conductive brush 31 and the needle charger 34, the following is performed. Use the correct setting. That is, the toner discharged from the conductive brush 31 to the intermediate transfer belt 20 at the time interval t ₁ until the voltage to be applied to the conductive brush 31 is changed over the needle-shaped charger 34 on the downstream side in the moving direction. It takes longer than the time it takes to exceed. As a result, it is possible to suppress the occurrence of image defects due to poor cleaning of the intermediate transfer belt 20 and the adhesion of toner stains to the recording material P.

Example 4
Next, another embodiment according to the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are substantially the same as those of the third embodiment. Accordingly, elements having the same or equivalent functions and configurations as those of the third embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this example, in the same configuration as that of Example 3, instead of alternately applying a positive voltage and a negative voltage to the conductive brush 31 in the discharging step, a state and a voltage in which a positive voltage is applied are set. The state of not applying is alternately repeated.

  When the needle charger 34 is used as the toner charging means and the voltage applied to the conductive brush 31 is only positive in the discharging process as in the present embodiment, the toner charging power supply 44 and the holding and recovery power supply are used. There is an advantage that the negative high voltage circuit in 41 can be omitted.

In the present embodiment, the voltage applied to the conductive brush 31 and the needle charger 34 in the discharging process is changed as follows. That is, first, the timing for switching the voltage between the conductive brush 31 and the needle charger 34 is made uniform. Then, during the time interval t _{1 at} which the voltage is switched, the toner discharged from the conductive brush 31 to the intermediate transfer belt 20 is needle-like charged downstream of the conductive brush 31 in the moving direction of the surface of the intermediate transfer belt 20. It is assumed that the time is longer than the time required to exceed the vessel 34. When a positive voltage is applied to the conductive brush 31, a voltage of the same polarity (that is, positive polarity) is applied to the needle charger 34, and when the voltage application to the conductive brush 31 is turned off, the needle is charged. The voltage application to the charger 34 is turned off.

  With the configuration as described above, in this embodiment as well, as in the first and third embodiments, the toner discharged to the intermediate transfer belt 20 is suppressed from being scattered, and further, the toner adheres to the acicular charger 34. It is possible to obtain an effect of suppressing the operation.

Example 5
Next, another embodiment of the present invention will be described. In this embodiment, the present invention is applied to a photosensitive member cleaning unit in a monocolor image forming apparatus. In this embodiment, elements having the same or equivalent functions and configurations as those in the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 8 shows a schematic cross section of the image forming apparatus 11 of this embodiment.

  The image forming apparatus 11 includes an image forming unit 1 that forms a black image. The image forming unit 1 is provided with a photosensitive drum 2 as an image carrier. Around the photosensitive drum 2, a conductive brush 31 as a toner collecting and holding unit, a charging roller 32 as a charging unit, a developing device 4 as a developing unit, and a transfer roller 5 as a transferring unit are installed. An exposure device (laser scanner device) 7 as an exposure unit is installed above the charging roller 32 and the developing device 4 in the drawing. The developing device 4 stores black toner. In this embodiment, toner having negative charge is used.

  In this embodiment, the charging roller 32 serves as both a photosensitive member charging unit that charges the photosensitive drum 2 and a toner charging unit that charges the transfer residual toner on the photosensitive drum 2. In this embodiment, the drum cleaning device 30 as the photosensitive member cleaning unit is configured by including the conductive brush 31 and the charging roller 32.

  The photosensitive drum 2 is rotationally driven at a predetermined peripheral speed (surface movement speed) in a direction indicated by an arrow R1 (clockwise) by a driving device (not shown). In this embodiment, the peripheral speed of the photosensitive drum 2 corresponds to the process speed (PS) of the image forming apparatus 11.

  The charging roller 32 is in contact with the photosensitive drum 2 with a predetermined pressure contact force, and rotates following the rotation of the photosensitive drum 2. A predetermined charging bias voltage is applied to the charging roller 32 from the power source 42 to uniformly charge the surface of the photosensitive drum 2 to a predetermined potential. In this embodiment, the photosensitive drum 2 is charged negatively by the charging roller 32. In this embodiment, the power source 42 functions as a second cleaning voltage output unit and a photosensitive member charging voltage output unit.

  The exposure device (laser scanner device) 7 exposes the surface of the photosensitive drum 2 to expose the surface of the photosensitive drum 2 charged by the charging roller 32 to an electrostatic latent image (electrostatic image) corresponding to image information. Form. That is, in the exposure apparatus 7, a laser beam modulated in accordance with a time-series electric digital pixel signal of image information input from a host computer (not shown) is output from the laser output unit, and this laser beam is reflected by each reflection. The surface of the photosensitive drum 2 is irradiated through a mirror.

  The developing device 4 supplies developer toner onto the photosensitive drum 2 to visualize the electrostatic latent image on the photosensitive drum 2. In this embodiment, the developing device 4 uses a two-component magnetic brush developing method as a developing method, and develops the electrostatic latent image by reversal development.

  More specifically, the developing device 4 includes a developing container (developing device main body) 4A containing a two-component developer 4E as a developer, and a nonmagnetic developing sleeve 4B as a developer carrying member. The developing sleeve 4B is rotatably disposed in the developing container 4A with a part of the outer peripheral surface thereof exposed to the outside of the developing container 4A. Further, the developing device 4 includes a magnet roller 4C as a magnetic field generating means provided in a non-rotating manner in the developing sleeve 4B, and a coating blade 4D as a developer regulating member.

The two-component developer 4E in the developing container 4A is mainly a mixture of nonmagnetic resin toner particles (toner) and magnetic carrier particles (carrier), and a stirring member (not shown) provided in the developing container 4A. Is stirred. In this embodiment, the carrier has an electric resistance of about 10 ¹³ Ωcm and a particle size of about 40 μm. The toner is triboelectrically charged to a negative polarity by rubbing with the carrier.

The developing sleeve 4 </ b> B is disposed to face the photosensitive drum 2 while keeping the closest distance (S-Dgap) to the photosensitive drum 2 at 350 μm. The developing sleeve 4B is rotationally driven so that the moving direction of the surface thereof is opposite to the moving direction of the surface of the photosensitive drum 2 at a portion (developing portion) G facing the photosensitive drum 2. Part of the two-component developer 4E in the developing container 4A is attracted and held as a magnetic brush layer on the outer peripheral surface of the developing sleeve 4B by the magnetic force generated by the magnet roller 4C. Then, as the developing sleeve 4B rotates, the two-component developer 2E on the developing sleeve 4B is transported and formed into a thin layer with a predetermined thickness by the coating blade 4D, and then the portion facing the photosensitive drum 2 (Development unit) G is supplied. The magnetic brush layer of the two-component developer 4E on the developing sleeve 4B comes into contact with the surface of the photosensitive drum 2 in the developing portion G and rubs the surface of the photosensitive drum 2 appropriately. A predetermined developing bias is applied to the developing sleeve 4B from a developing bias power source (not shown) as a developing voltage output means. In this embodiment, the developing bias voltage applied to the developing sleeve 4B is an oscillating voltage in which a DC voltage (Vdc) and an AC voltage (Vac) are superimposed. More specifically, in this embodiment, the setting of the DC voltage (Vdc) and the AC voltage (Vac) is as follows.
DC voltage Vdc; -350V
AC voltage Vac; 1600V

  In this way, the toner in the two-component developer carried on the surface of the developing sleeve 4B is applied to the surface of the photosensitive drum 2 corresponding to the electrostatic latent image on the photosensitive drum 2 by the electric field due to the developing bias. Selectively adheres. As a result, the electrostatic latent image formed on the photosensitive drum 2 is developed as a toner image. In this embodiment, toner adheres to the exposed bright portion of the surface of the photosensitive drum 2 and the electrostatic latent image is reversely developed.

  The transfer roller 5 abuts on the photosensitive drum 2 and forms a transfer nip portion (transfer portion) N at a contact portion with the photosensitive drum 2. Then, the transfer roller 5 rotates following the rotation of the photosensitive drum 2.

  A transfer bias power source 40 as a transfer voltage output unit is connected to the transfer roller 5, and a transfer bias is applied from the transfer bias power source 40 to the transfer roller 5. The toner image formed on the photosensitive drum 2 is moved through the transfer nip N by a transfer roller 5 to which a transfer bias having a polarity opposite to the normal charging polarity of the toner is applied. Transcribed above.

  On the downstream side of the transfer nip portion N in the movement direction (rotation direction) of the surface of the photosensitive drum 2, toner (transfer residual toner) remaining on the surface of the photosensitive drum 2 after the transfer of the toner image to the recording material P is transferred. A drum cleaning device 30 is installed for removal and collection.

  The image forming apparatus 11 of this embodiment is of a so-called cleanerless system (cleanerless system) and does not include a special mechanism for collecting and storing the transfer residual toner. In this embodiment, the transfer residual toner is collected by the developing device 4 by simultaneous development cleaning. The configuration and operation of the cleanerless system by the drum cleaning device 30 will be described later.

  On the upstream side of the primary transfer nip portion N in the conveyance direction of the recording material P, a registration roller 13 constituting a recording material supply unit is installed. The registration roller 13 feeds the recording material P to the transfer nip portion N at a predetermined timing.

  Further, a fixing device 12 as a fixing unit is installed downstream of the transfer nip portion N in the conveyance direction of the recording material P. The fixing unit 12 fixes the toner image transferred onto the recording material P to the recording material P.

  Next, a cleaning mechanism for residual toner in this embodiment will be described.

  In the present embodiment, the transfer nip N is downstream in the movement direction (rotation direction) of the surface of the photosensitive drum 2 and the upstream side of the charging roller 32 in the movement direction (rotation direction) of the surface of the photosensitive drum 2. The conductive brush 31 is provided at the position.

  During the image forming operation, a DC voltage of −600 V is applied to the conductive brush 31 by the recovery holding power source 41. By applying this voltage, the conductive brush 31 collects and retains the transfer residual toner charged to the positive polarity, which is opposite to the normal charging polarity, in the conductive brush 31, while maintaining the normal charging polarity. Transfer residual toner charged to a certain negative polarity can be passed.

  On the other hand, a DC voltage of −900 V is applied to the charging roller 32 in order to charge the peripheral surface of the photosensitive drum 2. The untransferred toner that has passed through the conductive brush 31 is further given a negative charge when passing through the charging roller 32, and has a desired charge amount. At this time, the charge amount of the toner is preferably close to the charge amount of the toner after the reverse development.

  The untransferred toner that has passed through the charging roller 32 is carried to the developing portion G with the subsequent rotation of the photosensitive drum 2 and is collected by the developing device 4 by simultaneous development cleaning.

  More specifically, a part of the untransferred toner that has passed through the charging roller 32 is returned from the surface of the photosensitive drum 2 to the magnetic brush layer on the developing sleeve 4B by the electric field due to the developing bias, and the other remaining toner. The portion selectively adheres to the surface of the photosensitive drum 2 corresponding to the electrostatic latent image. That is, the transfer residual toner adhering to the exposure dark part is collected by the developing device 4 by the simultaneous development cleaning.

  Next, the discharge process in a present Example is demonstrated.

  Also in this embodiment, the toner held by the conductive brush 31 is discharged to the photosensitive drum 2 at a predetermined timing, and the amount of accumulated toner is reduced, thereby suppressing the deterioration of the cleaning performance.

  In this embodiment, in the discharge process, a negative direct current voltage and a positive direct current voltage are alternately applied from the collection holding power supply 41 to the conductive brush 31. This is because, in this embodiment, the polarity of most of the toner accumulated in the conductive brush 31 is negative, but the positive toner is also slightly accumulated in the conductive brush 31.

  As the image forming apparatus 11 is used, a part of the transfer residual toner adheres to the charging roller 32 and the surface of the charging roller 32 becomes dirty. If the surface of the charging roller 32 is contaminated with toner, the charging of the transfer residual toner by the charging roller 32 and the charging of the photosensitive drum 2 become unstable, and the cleaning performance and the image deteriorate. Therefore, in this embodiment, the same operation as that for transferring the toner from the conductive brush 31 to the photosensitive drum 2 is also performed on the charging roller 32 in the discharging step.

  That is, in this embodiment, in the discharging process, a negative DC voltage and a positive DC voltage are alternately applied from the power source 42 to the charging roller 32. As a result, the toner adhering to the surface of the charging roller 32 is removed.

  The discharge process is performed at a timing when image formation is not performed, such as during post-rotation or processing operation after occurrence of a jam. In this embodiment, the toner discharged to the photosensitive drum 2 in the discharging process is collected by the developing device 4.

  More specifically, when the negative polarity toner discharged to the photosensitive drum 2 is collected, when the position on the photosensitive drum 2 where the toner is discharged passes through the exposure position by the exposure device 7, the photosensitive toner is discharged. The position on the body drum 2 is not exposed by the exposure device 7. The same developing bias as that during the image forming operation is applied to the developing sleeve 4B of the developing device 4. As a result, the negative toner discharged to the photosensitive drum 2 can be collected in the developing device 4.

  Further, when the positive toner discharged to the photosensitive drum 2 is collected, when the position on the photosensitive drum 2 where the toner is discharged passes the exposure position by the exposure device 7, the photosensitive drum is recovered. 2 is exposed by the exposure device 7. The same developing bias as that during the image forming operation is applied to the developing sleeve 4B of the developing device 4. Thereby, the positive toner discharged to the photosensitive drum 2 can be collected in the developing device 4.

  The timing for switching the polarity of the voltage applied to the conductive brush 31 and the charging roller 33 in the discharging process is the same as in the first embodiment.

  With the configuration as described above, in this embodiment as well, the toner discharged to the photosensitive drum 2 is prevented from scattering and the toner is prevented from adhering to the charging roller 32 as in the first embodiment. The effects such as can be obtained.

  Also in the photosensitive member cleaning means, the toner charging means having other forms as described in the second to fourth embodiments can be used.

As described above, in this embodiment, the toner discharging process from the conductive brush 31 to the photosensitive drum 2 in the monocolor image forming apparatus 11 including the drum cleaning device 30 including the conductive brush 31 and the charging roller 32. The following settings are used. That is, the time interval t ₁ until the voltage applied to the conductive brush 31 is switched until the toner discharged from the conductive brush 31 to the photosensitive drum 2 exceeds the charging roller 32 on the downstream side in the moving direction. It takes longer than the time it takes. As a result, it is possible to suppress the occurrence of image defects due to poor cleaning of the photosensitive drum 2 and the adhesion of toner stains to the recording material P.

(Other examples)
Although the present invention has been described with reference to specific embodiments, it should be understood that the present invention is not limited to the embodiments described above.

  For example, in the above-described embodiments, the embodiments in which the present invention is applied to a tandem intermediate transfer type color image forming apparatus or a monocolor image forming apparatus have been described. However, the present invention can also be applied to an image forming apparatus having other basic configurations well known to those skilled in the art, and can achieve the same effects as the above-described embodiments. Other basic configurations of the image forming apparatus include the following. That is, recording material conveyance in a tandem type direct transfer type color image forming apparatus, a four-cycle type intermediate transfer type or direct transfer type color image forming apparatus, or a monocolor image forming apparatus or an intermediate transfer type color image forming apparatus. For example, a belt is used. The direct transfer type image forming apparatus directly transfers a toner image formed on a plurality or a single image carrier onto a recording material carried on an endless belt-like conveyance belt as a recording material carrier, and thereafter A recorded image is obtained by fixing. A four-cycle type image forming apparatus has a plurality of (typically four) developing units for one image carrier, and a toner image formed by the plurality of developing units on the image carrier. It is transferred to a transfer target (intermediate transfer member or recording material on a recording material carrier).

  In the above-described first to fourth embodiments, the toner discharged to the intermediate transfer belt is selectively collected in a collection toner container of a specific image forming unit. The primary transfer roller was separated from the photosensitive drum in the section. However, selectively collecting the toner in the collected toner container of the specific image forming unit selects the bias to be applied to the primary transfer roller of the image forming unit that is not desired to be collected or selects the potential of the photosensitive drum. The same effect can be obtained by the method. That is, in the image forming unit that is not desired to be collected, a bias is applied to the primary transfer roller so that the toner is not transferred from the intermediate transfer belt to the photosensitive drum in the primary transfer nip portion. Further, in the image forming unit that is not desired to be collected, the potential of the photosensitive drum is set so that the toner is not transferred from the intermediate transfer belt to the photosensitive drum depending on the setting of the charging bias and the presence or absence of exposure.

  In the fifth embodiment described above, there is a method in which the negative polarity toner and the positive polarity toner discharged to the photosensitive drum are collected in the developing device with the same developing bias setting depending on whether or not the photosensitive drum is exposed. Using. However, for the collection of both negative and positive toner discharged to the photosensitive drum by the developing device, the setting of the developing bias is selected so that the negative and positive toners are collected by the developing device. It can also be achieved by the method, and the same effect can be obtained.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic view of the vicinity of a belt cleaning device used in the image forming apparatus of FIG. 1. It is a schematic diagram of the vicinity of the belt cleaning device at each time during the discharge process according to the present invention. It is a chart figure which shows an example of the voltage application sequence in the discharge process according to this invention. It is a chart which shows an example of the voltage application sequence in the discharge process and toner charging means cleaning process according to this invention. FIG. 6 is a schematic view of the vicinity of a belt cleaning device used in another embodiment of the image forming apparatus according to the present invention. It is a schematic perspective view of an example of a needle charger in a belt cleaning device used in another embodiment of the image forming apparatus according to the present invention. It is a schematic sectional drawing of other Example of the image forming apparatus which concerns on this invention. It is a principal part schematic sectional drawing of the image forming apparatus for demonstrating an example of a belt cleaning mechanism.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image formation part 2 Photosensitive drum 6 Drum cleaning apparatus 20 Intermediate transfer belt 30 Belt cleaning apparatus 31 Conductive brush 32 Toner charging roller 33 Toner charging brush 34 Needle-shaped charger 41 Power supply for collection and retention 42 Power supply for toner charging

Claims (8)

An image carrier that carries a toner image, a toner collection and holding unit that collects and holds toner from the image carrier, and a first voltage that outputs a voltage for collecting and holding the toner to the toner collection and holding unit A voltage output unit, a toner charging unit disposed downstream of the toner collection and holding unit in the moving direction of the surface of the image carrier and charging the toner on the image carrier, and the toner charging unit Second voltage output means for outputting a voltage for charging the toner, and switching the voltage output from the first voltage output means to the toner collection and holding means, thereby collecting and holding the toner. An image forming apparatus that performs a discharge step of transferring toner collected and held by a means to the image carrier,
The moving speed of the surface of the image carrier is PS, and the toner charging means is connected to the toner charging means from the upstream end in the moving direction of the surface of the image carrier at the operation position of the toner collection and holding means on the surface of the image carrier. The distance from the downstream end of the image carrier surface in the moving direction at the working position on the surface of the image carrier is L _1, and the _first step with respect to the toner collecting and holding means in the discharging step. When the time interval from switching the voltage output by the voltage output means to the next switching is t ₁ ,
t ₁ ≧ L ₁ / PS
An image forming apparatus characterized in that the relationship is established.   The voltage output by the first voltage output means in the discharging step is switched between a voltage having a first polarity and a voltage having a second polarity that is opposite to the first polarity. The image forming apparatus according to claim 1.   The voltage output from the first voltage output means in the discharging step is switched between a state of outputting a voltage having a specific polarity and a state of stopping the output of the voltage. Image forming apparatus. The following formula,
t ₁ = L ₁ / PS
The image forming apparatus according to claim 1, wherein the relationship is established.   The image forming apparatus according to claim 1, wherein the toner collecting and holding unit is a brush-like member.   During the discharging step, the second voltage output means outputs to the toner charging means a voltage having the same polarity as the voltage output from the first voltage output means to the toner collection and holding means. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   During the discharging step, the voltage output from the second voltage output unit to the toner charging unit is a timing at which the voltage output from the first voltage output unit to the toner collection holding unit is switched. The image forming apparatus according to claim 1, wherein the image forming apparatus is switched at substantially the same timing. The toner charging means is a roller-shaped member having a radius r, and the time interval t ₁ in the discharging step is expressed by the following equation:
t ₁ <2πr / PS
Satisfy the relationship
After the discharging step, the toner charging means for transferring the toner attached to the toner charging means to the image carrier by switching the voltage output from the second voltage output means to the toner charging means. When the time interval between the switching of the voltage output from the second voltage output unit to the toner charging unit and the subsequent switching is set to t ₂ in the toner charging unit cleaning step, the time The interval t ₂ is given by
t ₂ ≧ 2πr / PS
The image forming apparatus according to claim 1, wherein the relationship is satisfied.

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