JP2008268610A - Transfer unit and image forming apparatus with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer unit capable of stably obtaining a high quality image without changing transfer conditions in a monochrome mode and in a color mode. <P>SOLUTION: The transfer unit includes: an intermediate transfer belt 1; a plurality of photoreceptor drums (image carriers) 2a to 2d; and a plurality of transfer rollers 3a to 3d disposed in contact with the corresponding photoreceptor drums 2a to 2d via a transfer belt 4. The transfer unit can select the color mode in which toner images in their respective colors are transferred to the transfer belt 4 or the monochrome mode in which a monochrome toner image is transferred to the transfer belt 4. In the monochrome mode, the transfer unit separates the transfer belt 4 and transfer rollers 3a to 3c from the color photoreceptor drums 2a to 2c. In the transfer unit, a movable roller 10 is disposed on the internal circumference of the transfer belt 4. In monochrome mode, the movable roller 10 is moved and pressed against the transfer belt 4, so that the angle of a transfer nip between the intermediate transfer belt 4 and monochrome photoreceptor 2d in the monochrome mode is equal to that in the color mode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a transfer unit for transferring toner images of respective colors formed on a plurality of image carriers onto a transfer belt, and an image forming apparatus including the transfer unit.

  In recent years, there has been a strong demand for colorization of image forming apparatuses such as copiers and printers that form images by electrophotography, and color image forming apparatuses have been developed in response to this demand and are already in practical use. Since this type of color image forming apparatus requires an output speed comparable to that of a monochrome image, a tandem type color image forming apparatus has attracted attention.

  In a tandem type color image forming apparatus, at least an endless intermediate transfer belt stretched between a driving roller, a tension roller, and a driven roller, a monochrome black image carrier, and three types of yellow, magenta, and cyan A system is provided in which a color image carrier is provided and toner images of each color formed on each image carrier are transferred to the intermediate transfer belt.

  By the way, in the color image forming apparatus, a color mode for outputting a color image and a monochrome mode for outputting a monochrome image of a single black color can be selected. When operating yellow, magenta, and cyan color image carriers that are not used for formation, these color image carriers come into contact with the intermediate transfer belt, and the color image carrier and the intermediate transfer belt are worn to reduce their lifespan. Problem occurs.

  Therefore, in Patent Document 1, in an image forming apparatus provided with at least two image carriers, a paper conveyance unit, and a transfer unit, the conveyance unit and the transfer unit are rotationally moved about a rotation axis of one image carrier. In addition, a technique has been proposed in which the contact between one image carrier and the transport unit is shifted to separate the other image carrier and the transport unit, thereby preventing meandering of the intermediate transfer belt and wear of the image carrier.

  Further, Patent Document 2 discloses a belt-like member (intermediate transfer member, latent image carrier or transfer material conveying member) and a plurality of opposing members arranged in parallel so as to face or approach the belt-like member. In an image forming apparatus provided with (a latent image carrier or a developer carrier), by providing a separating unit that separates the belt-like member and a part of the opposing member, the opposing member and the belt-like member are unnecessary. Techniques have been proposed to prevent the occurrence of problems such as a decrease in life due to contact.

  However, the techniques proposed in Patent Documents 1 and 2 have a problem that the structure is complicated and the transfer unit is enlarged.

Therefore, Patent Document 3 proposes a reduction in the size of the entire apparatus by adding a retract roll that moves between a position in contact with the belt and a position away from the belt to change the circulation movement path of the belt. ing.
JP 2000-181184 A JP 2001-242680 A JP 2003-337454 A

  However, in the configuration proposed in Patent Document 3, the transfer condition also changes because the angle of the transfer nip between the black image carrier and the belt in the monochrome mode changes with respect to that in the color mode. May not be obtained stably.

  In addition, the inclusion of the retract roll increases the inclusions on the back side of the belt, and the inclusions cause wear on the back side of the belt to reduce the life of the belt, and wear powder generated by scraping the belt is caught in the transfer roller. There is a possibility that transfer defects occur and image distortion occurs.

  The present invention has been made in view of the above problems, and the object of the present invention is that a high-quality image can be stably obtained without changing the transfer conditions in the monochrome mode and the color mode, and the transfer belt An object of the present invention is to provide a transfer unit capable of suppressing wear and an image forming apparatus including the transfer unit.

  In order to achieve the above object, an invention according to claim 1 is characterized in that at least an endless transfer belt stretched between a driving roller, a tension roller, and a fixed roller, a plurality of image carriers including monochrome, and A plurality of transfer rollers that come into contact with the respective image carriers through a transfer belt, and a color mode for transferring the toner images of the respective colors formed on the plurality of image carriers to the transfer belt, and a monochrome image carrier A monochrome mode for transferring the formed monochrome toner image to the transfer belt can be selected. In the monochrome mode, the transfer belt and the transfer roller are separated from a plurality of color image carriers other than monochrome. In the transfer unit, a movable roller is provided in the circumference of the transfer belt, and the movable roller is moved and pressed against the transfer belt in the monochrome mode. Wherein the angle of the transfer nip between the transfer belt and the monochrome image bearing member, characterized in that set to be the same as that of the color mode at the time Nokuromodo.

  According to a second aspect of the present invention, the image forming apparatus includes the transfer unit according to the first aspect.

  According to the present invention, the movable roller is moved in the monochrome mode so that the angle of the transfer nip between the transfer belt in the monochrome mode and the monochrome image carrier is the same as that in the color mode. The transfer conditions in the color mode are the same, and a high-quality monochrome image can be stably obtained.

  Further, according to the present invention, since the movable roller contacts the transfer belt only in the monochrome mode and is separated from the transfer belt in the color mode, wear of the transfer belt is suppressed and its durability is enhanced.

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

  1 and 2 are cross-sectional views of a main part of an image forming apparatus provided with a transfer unit according to the present invention. FIG. 1 shows a state in a color mode, and FIG. 2 shows a state in a monochrome mode.

  The image forming apparatus according to the present embodiment can output a color image and a monochrome image, and a yellow image forming unit 1Y, a magenta image forming unit 1M, a cyan image forming unit 1C, and a black image forming unit are provided inside the main body. Units 1Bk are arranged in tandem at regular intervals.

  Each of the image forming units 1Y, 1M, 1C, and 1Bk includes photosensitive drums 2a, 2b, 2c, and 2d as image carriers, and transfer rollers 3a, 3b, 3c, and 3d as primary charging means, and is not shown. A primary charger, a developing device, and a drum cleaning device are provided.

  Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are rotationally driven at a predetermined process speed in a direction indicated by an arrow (clockwise) by a driving device (not shown). The developing device (not shown) accommodates yellow (Y) toner, magenta (M) toner, cyan (C) toner, and black (Bk) toner, and is formed on each of the photosensitive drums 2a to 2d. Each electrostatic latent image is made to adhere to each color toner, and each electrostatic latent image is developed to make each color toner image visible.

  The transfer rollers 3a to 3d as the primary charging means are disposed so as to be able to contact the photosensitive drums 2a to 2d via the endless intermediate transfer belt 4 at each primary transfer portion. Here, the transfer rollers 3a to 3d and the intermediate transfer belt 4 constitute a transfer unit according to the present invention. The intermediate transfer belt 4 includes a drive roller 5, a tension roller 6, and a fixed roller (secondary transfer counter roller) 7. The transfer rollers 3a to 3d are arranged in the circumference of the intermediate transfer belt 4 so that the intermediate transfer belt 4 is moved around the intermediate transfer belt 4. The photosensitive drums 2a to 2d are pressed with a predetermined pressure. The fixed roller 7 is in contact with the secondary transfer roller 8 via the intermediate transfer belt 4 in the secondary transfer portion. As a material for the intermediate transfer belt 4, a derivative resin such as polycarbonate, polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), or the like is selected.

  Thus, in the present embodiment, a retract roll 9 that is movable up and down is provided within the circumference of the intermediate transfer belt 4 and between the magenta transfer roller 3b and the cyan transfer roller 3c. A movable roller 10 is also provided between the transfer roller 3c and the black transfer roller 3d. The transfer rollers 3a to 3d are urged toward the photosensitive drums 2a to 2d by an urging means (not shown) such as a spring. In the color mode shown in FIG. 1, all the transfer rollers 3a to 3d are intermediate transfer. The photosensitive drums 2 a to 2 d are pressed with a predetermined pressure via the belt 4. The tension roller 6 is pressed against the intermediate transfer belt 4 by a biasing means such as a spring (not shown) to apply a predetermined tension to the intermediate transfer belt 4. Further, although not shown, a belt cleaning device is provided on the downstream side of the secondary transfer portion of the transfer unit.

  On the other hand, a registration roller 11 is disposed in the middle of the conveyance path L below the transfer unit in the main body of the image forming apparatus and upstream of the secondary transfer unit (left side in FIG. 1). A conveying belt 12 is disposed on the downstream side (right side in FIG. 1), and a fixing device 13 is further provided on the downstream side. Here, the fixing device 13 includes a fixing roller 14 and a pressure roller 15 that rotate while being pressed against each other. Although not shown, a paper feed cassette containing a plurality of sheets stacked therein is detachably installed at the bottom of the image forming apparatus main body.

  Next, an image forming operation by the image forming apparatus having the above configuration will be described.

  The image forming apparatus according to the present embodiment can select a color mode for outputting a color image and a monochrome mode for outputting a monochrome image. When the color mode is selected, as shown in FIG. All the transfer rollers 3 a to 3 d are pressed against the photosensitive drums 2 a to 2 d via the intermediate transfer belt 4, the retract roll 9 is brought into contact with the intermediate transfer belt 4, and the movable roller 10 is separated from the intermediate transfer belt 4. is doing.

When an image start signal is issued in the above state,
In each of the image forming units 1Y, 1M, 1C, and 1Bk, the photosensitive drums 2a to 2d are rotationally driven at a predetermined process speed in the arrow direction (clockwise) in FIG. 1, and these photosensitive drums 2a to 2d are not shown. It is uniformly charged by the primary charger. When the laser light modulated by the color image signal for each color is irradiated to each of the photosensitive drums 2a to 2d from, for example, a laser scanner unit (not shown), the color image signals corresponding to the respective color image signals on the photosensitive drums 2a to 2d. An electrostatic latent image is formed.

  Then, first, the electrostatic latent image formed on the photosensitive drum 2a of the yellow image forming unit 1Y is developed by a developing device (not shown) and visualized as a yellow toner image. The yellow toner image is rotated in the direction indicated by the arrow (counterclockwise) in FIG. 1 by the action of the transfer roller 3a at the primary transfer portion between the photosensitive drum 2a and the transfer roller 3a. Primary transferred onto.

  The intermediate transfer belt 4 on which the yellow toner image is primarily transferred as described above moves to the next magenta image forming unit 1M. In the magenta image forming unit 1M, similarly to the above, the magenta toner image formed on the photosensitive drum 2b is transferred onto the intermediate transfer belt 4 so as to be superimposed on the yellow toner image in the primary transfer portion.

  Similarly, cyan and black toners respectively formed on the photosensitive drums 2c and 2d of the cyan and black image forming units 1C and 1Bk on the yellow and magenta toner images superimposed and transferred on the intermediate transfer belt 4, respectively. The images are sequentially superimposed at each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 4. The transfer residual toner that is not transferred onto the intermediate transfer belt 4 but remains on the photosensitive drums 2a to 2d is removed by drum cleaning devices (not shown), and the photosensitive drums 2a to 2d are prepared for the next image formation. It is done.

  Then, in accordance with the timing at which the front end of the full-color toner image on the intermediate transfer belt 4 reaches the secondary transfer portion between the fixed roller (secondary transfer counter roller) 7 and the secondary transfer roller 8, the paper cassette is not shown. The sheet sent to the conveyance path L is conveyed to the secondary transfer unit by the registration roller 11. Then, in the secondary transfer portion, the full color toner image on the intermediate transfer belt 4 is secondarily transferred collectively onto the paper by the action of the secondary transfer roller 8. Incidentally, the untransferred toner remaining on the intermediate transfer belt 4 without being transferred onto the sheet is removed by a belt cleaning device (not shown), and the intermediate transfer belt 4 is prepared for the next image formation.

  The sheet on which the full color toner image has been transferred as described above is conveyed to the fixing device 13, and the full color toner image is heated in the process of being conveyed while being sandwiched between the fixing roller 14 and the pressure roller 15 in the fixing device 13. Then, it is pressurized and thermally fixed on the surface of the paper. The sheet on which the toner image is fixed is discharged to a discharge tray (not shown) outside the apparatus main body.

  On the other hand, when the monochrome mode is selected, as shown in FIG. 2, the movable roller 10 moves up to push up the intermediate transfer belt 4, and the color transfer rollers 3a to 3c and the retract roll 9 move down. The color transfer rollers 3a to 3c and the intermediate transfer belt 4 are separated from the color photosensitive drums 2a to 2c. At this time, the moving amount of the movable roller 10 is set so that the angle of the transfer nip between the intermediate transfer belt 4 and the monochrome photosensitive drum 2d is the same as that in the color mode. Accordingly, in this monochrome mode, the transfer roller 5d and the intermediate transfer belt 4 are in contact with the photosensitive drum 2d only in the black image forming unit 1Bk.

  Thus, in the monochrome mode, only the black image forming unit 1Bk operates and the other yellow, magenta, and cyan image forming units 1Y, 1M, and 1C are paused. The black toner image formed on 2d is primarily transferred onto the intermediate transfer belt 4 at the primary transfer portion, and the black toner image transferred onto the intermediate transfer belt 4 is supplied to the secondary transfer portion at an appropriate timing. Secondary transferred onto paper. Then, the paper on which the black toner image is transferred is conveyed to the fixing device 13, where the black toner image is heated and pressurized and thermally fixed on the surface of the paper, and the black toner image is fixed. The paper is discharged to a paper discharge tray (not shown) outside the apparatus main body.

  As described above, in this embodiment, the movable roller 10 is moved in the monochrome mode, and the angle of the transfer nip between the intermediate transfer belt 4 and the black photosensitive drum 3d in the monochrome mode becomes the same as that in the color mode. Therefore, the transfer conditions in the monochrome mode and the color mode are the same, and a high-quality monochrome image can be stably obtained.

  Further, according to the present embodiment, the movable roller 10 abuts on the intermediate transfer belt 4 only in the monochrome mode and is separated from the intermediate transfer belt 4 in the color mode. Sexuality is enhanced.

FIG. 3 is a cross-sectional view (color mode) of a main part of an image forming apparatus including a transfer unit according to the present invention. 1 is a cross-sectional view (monochrome mode) of a main part of an image forming apparatus including a transfer unit according to the present invention.

Explanation of symbols

1Y Yellow image forming unit 1M Magenta image forming unit 1C Cyan image forming unit 1Bk Black image forming unit 2a to 2d Photosensitive drum (image carrier)
3a to 3d Transfer roller 4 Intermediate transfer belt (transfer belt)
5 Driving roller 6 Tension roller 7 Fixed roller (secondary transfer counter roller)
8 Secondary transfer roller 9 Retract roll 10 Movable roller 11 Registration roller 12 Conveying belt 13 Fixing device 14 Fixing roller 15 Pressure roller L Conveyance path

Claims (2)

An endless transfer belt stretched between at least a driving roller, a tension roller, and a fixed roller; a plurality of monochrome image-bearing bodies; and a plurality of image carriers that are in contact with the image-bearing bodies via the transfer belt. A color mode that includes a transfer roller and transfers toner images of each color formed on a plurality of image carriers to the transfer belt; and a monochrome mode that transfers a monochrome toner image formed on a monochrome image carrier to the transfer belt In the transfer unit in which the transfer belt and the transfer roller are separated from a plurality of color image carriers other than those for monochrome in the monochrome mode,
A movable roller is provided in the periphery of the transfer belt, and the movable roller is moved and pressed against the transfer belt in the monochrome mode, and the angle of the transfer nip between the transfer belt and the monochrome image carrier in the monochrome mode is a color mode. A transfer unit characterized by being the same as that of time. An image forming apparatus comprising the transfer unit according to claim 1.

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