JP2014119542A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing stains of toner from being transferred to a marginal part outside an image forming area of a recording material.SOLUTION: An image forming apparatus applies a transfer voltage to a primary transfer member to primarily transfer toner images from image carriers 2a to 2d to an intermediate transfer belt 8, and secondarily transfer the toner images from the intermediate transfer belt 8 to paper P to form images on the paper P. The primary transfer member is a rotating member that has a rotation shaft extending in a width direction orthogonal to a direction of rotation of the intermediate transfer belt 8, and includes a conductive part 30 provided in a range corresponding to an area in which the toner images are primarily transferred on the intermediate transfer belt 8, and insulation parts 31 provided on both sides of the conductive part 30 to be brought into contact with the intermediate transfer belt 8.

Description

  The present invention relates to an image forming apparatus that forms an image by electrophotography.

Conventionally, an image forming apparatus having a configuration using an intermediate transfer member is known as an image forming apparatus such as a copying machine, a laser beam printer, and a facsimile. In this image forming apparatus, as a primary transfer process, a toner image formed on the surface of a photosensitive drum as an image carrier is transferred onto an intermediate transfer member at a primary transfer portion formed by the photosensitive drum and the intermediate transfer member. Perform primary transfer. This primary transfer process is performed for each of a plurality of colors to superimpose toner images of the respective colors, thereby forming a toner image having a plurality of colors on the surface of the intermediate transfer member. Subsequently, as a secondary transfer step, a plurality of color toner images formed on the surface of the intermediate transfer member are collectively transferred onto the surface of a recording material such as paper by applying a voltage to the secondary transfer member. The batch-transferred toner images are then permanently fixed on the recording material by a fixing unit, thereby forming a color image on the recording material.
Patent Document 1 discloses a configuration in which a primary transfer roller to which a voltage is applied from a power source is arranged corresponding to each photosensitive drum. Specifically, an endless belt-like member is used as an intermediate transfer member (hereinafter referred to as an intermediate transfer belt), and a primary transfer roller is disposed at a position corresponding to each photosensitive drum on the inner peripheral surface side of the intermediate transfer belt. . Then, rollers are arranged at both ends of the primary transfer roller in the rotation axis direction, and the primary transfer roller is brought into contact with the intermediate transfer belt without bringing the primary transfer roller into contact with the intermediate transfer belt. Form.

JP 2005-134735 A

  Japanese Patent Application Laid-Open No. H10-228688 discloses that the positions where the rollers are arranged are the positions corresponding to the non-image forming area of the photosensitive drum at both ends of the primary transfer roller. However, Patent Document 1 does not describe the positional relationship between the end portion of the primary transfer roller and the non-image forming area of the photosensitive drum. For this reason, if the primary transfer roller is configured to extend outside the image forming area, the toner stains outside the image forming area on the surface of the photosensitive drum may be transferred to the margin of the recording material. was there.

  An object of the present invention is to provide an image forming apparatus capable of suppressing transfer of dirt due to toner to a blank portion outside an image forming area of a recording material.

In order to achieve the above object, an image forming apparatus of the present invention includes:
An image carrier for carrying a toner image;
An intermediate transfer belt that is rotatably stretched by a plurality of stretching members and is in contact with the image carrier;
In the transfer belt, the toner image is disposed on the peripheral surface opposite to the side on which the image carrier is in contact with the position corresponding to the image carrier, and a voltage is applied so that the toner image is transferred to the image carrier. A primary transfer member for primary transfer from the intermediate transfer belt to the intermediate transfer belt;
With
In an image forming apparatus for forming an image on a recording material by secondarily transferring a toner image from the intermediate transfer belt to the recording material,
The primary transfer member is a rotation member whose rotation axis is a width direction orthogonal to the rotation direction of the intermediate transfer belt, and corresponds to a region where a toner image is primarily transferred on the intermediate transfer belt in the width direction. And a conductive portion provided in a range to be provided, and an insulating portion in contact with the intermediate transfer belt on both sides of the conductive portion.

  According to the present invention, it is possible to suppress the transfer of dirt due to toner to a blank portion outside the image forming area of the recording material.

1 is a perspective view of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. Sectional drawing which shows the relationship between the photoconductive drum and primary transfer roller in the Example of this invention. The figure explaining the structure of the width direction of the primary transfer roller in the Example of this invention. The figure explaining the structure of the edge part of the primary transfer roller in the Example of this invention

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

(Example)
A schematic configuration of an image forming apparatus according to an embodiment of the present invention (in this embodiment, a full color image forming apparatus such as an electrophotographic tandem type laser printer) will be described with reference to FIGS. FIG. 1 is a perspective view of the image forming apparatus according to the present embodiment. FIG. 2 is a schematic cross-sectional view of the image forming apparatus according to the present embodiment. FIG. 3 is a schematic cross-sectional view of the image forming apparatus according to the present embodiment, and shows only the configuration inside the apparatus.

  In the image forming apparatus main body 100, the laser scanner 7, the photosensitive drums 2a, 2b, 2c, and 2d, the developing devices 4a, 4b, 4c, and 4d, the intermediate transfer belt 8, the fixing device 17, the feeding tray 20, A feeding roller 21 and the like are installed. A sheet P as a recording material stacked and stored in the feeding tray 20 is fed by a feeding roller 21 that rotates in the clockwise direction in the drawing, and a nip portion (2) between the belt driving roller 11 and the secondary transfer roller 12. To the next transfer section). The photosensitive drums 2a to 2d as image bearing members rotate counterclockwise in the drawing, and the surfaces thereof are uniformly charged by charging rollers 3a, 3b, 3c, and 3d as charging means. Then, electrostatic latent images are sequentially formed on the outer peripheral surfaces of the photosensitive drums 2a to 2d by the laser light L from the laser scanner 7 as an exposure unit. Subsequently, the electrostatic latent images described above are developed by the developing devices 4a to 4d on the outer peripheral surfaces of the photosensitive drums 2a to 2d to form toner images.

  The toner images formed on the photosensitive drums 2 a to 2 d are transferred to the intermediate transfer belt 8. In the case of forming a color image, yellow, magenta, cyan, and black colors are developed on the photoconductive drums 2 a to 2 d, and the toner images formed on the respective colors are sequentially transferred to the intermediate transfer belt 8. That is, the toner images formed on the photosensitive drums 2a to 2d are superimposed and transferred to the intermediate transfer belt 8 at each primary transfer portion.

Next, the toner image formed on the intermediate transfer belt 8 is transferred to the paper P sent to the nip portion between the belt driving roller 11 and the secondary transfer roller 12. The toner image on the intermediate transfer belt 8 is transferred onto the paper P by applying a voltage to the secondary transfer roller 12 from the transfer power source 25 connected to the secondary transfer roller 12. Here, as described above, in the case of a color image, the toner images superimposed and transferred onto the intermediate transfer belt 8 are collectively transferred onto the paper P at the secondary transfer portion. Further, the paper P onto which the toner image has been transferred is sent to the nip portion between the fixing film 18 and the pressure roller 19 in the fixing device 17 where it is heated and pressed to fix the toner image on the paper P. The paper P on which the toner image is fixed is discharged to the paper discharge tray 23 by the paper discharge roller pair 22.

  In the image forming apparatus according to this embodiment, the photosensitive drums 2a to 2d can be attached to and detached from the image forming apparatus main body 100 as process cartridges 1Y, 1M, 1C, and 1K integrated with process means acting thereon. It is configured. The process means includes charging rollers 3a to 3d, developing devices 4a to 4d, and the like.

  The intermediate transfer belt 8 is a belt-like intermediate transfer body that is stretched so as to be movable (rotatable) by rollers 11, 14, and 15 that are a plurality of stretching members. The intermediate transfer belt 8 is in contact with the photosensitive drums 2a to 2d at each primary transfer portion N. The four photosensitive drums 2 a to 2 d are arranged in a line at regular intervals with a constant interval in the moving direction of the intermediate transfer belt 8.

<Configuration of primary transfer unit>.
The image forming apparatus according to the present embodiment is configured to perform transfer in each primary transfer unit by passing a current in the circumferential direction of the intermediate transfer belt 8. As shown in FIG. 3, the contact surface between the intermediate transfer belt 8 and the photosensitive drums 2 a to 2 d is formed by a belt driving roller 11 and a tension roller 14. Each of the primary transfer rollers 30 serving as a conductive portion of the primary transfer member that is a rotating member disposed between the rollers 11 and 14 and the stretching roller 15 includes one (common ) Connected to the voltage stabilizing element 24.

  The intermediate transfer belt 8 is an endless belt obtained by adding a conductive agent to a resin material to provide conductivity. The intermediate transfer belt 8 is composed of a plurality of stretching members, that is, a belt driving roller 11, a tension roller 14, and a stretching roller 15. It is stretched and tensioned by a tension roller 14 with a predetermined tension. The intermediate transfer belt 8 is rotationally driven at substantially the same peripheral speed as the photosensitive drums 2a to 2d in a direction (forward direction) in which the intermediate transfer belt 8 moves in the same direction as the photosensitive drums 2a to 2d rotating in the primary transfer portion. .

  FIG. 4A is a schematic cross-sectional view showing each image forming station (image forming unit) and the intermediate transfer belt 8. As shown in FIG. 4A, in each image forming station, the photosensitive drums 2a to 2d are disposed on the surface of the intermediate transfer belt 8 opposite to the surface where the photosensitive drums 2a to 2d are in contact. The primary transfer rollers 30 are arranged so as to face each other. With such a configuration, each primary transfer roller 30 forms a primary transfer portion N with each of the photosensitive drums 2 a to 2 d and the intermediate transfer belt 8.

FIG. 4B is a schematic cross-sectional view illustrating another example of the contact arrangement configuration of the photosensitive drums 2 a to 2 d and the primary transfer roller 30 with respect to the intermediate transfer belt 8. As shown in FIG. 4B, each primary transfer roller 30 is intermediate on the downstream side in the moving direction of the intermediate transfer belt 8 by a predetermined amount from the contact portion of the intermediate transfer belt 8 with the photosensitive drums 2a to 2d. It can also be arranged so as to contact the transfer belt 8. Each primary transfer roller 30 is arranged at a position lifted by a distance h with respect to a horizontal plane formed by the photosensitive drums 2a to 2d and the intermediate transfer belt 8 (a position where the photosensitive drum has entered the photosensitive drum side). The intermediate transfer belt 8 is brought into contact with (wound around) each of the photosensitive drums 2a to 2d. Thereby, a nip portion between each of the photosensitive drums 2a to 2d and the intermediate transfer belt 8 is formed. By adopting such a configuration, the primary transfer portion N can be formed, and the intermediate transfer belt 8 can be wound around each of the photoconductive drums 2a to 2d, and the photoconductive drums 2a to 2d can be more reliably wound. And the intermediate transfer belt 8 can be brought into contact with each other. Further, the photosensitive drum 2a
The surface ˜2d is not damaged even when the primary transfer roller 30 is a hard object such as a metal roller.

  Further, the three stretching rollers 11, 14, 15 for stretching the intermediate transfer belt 8 and the primary transfer roller 30 are grounded via the voltage stabilizing element 24 as described above. The intermediate transfer belt 8 is integrated with the driving roller 11, the tension roller 14, the stretching roller 15 and the primary transfer roller 30 as an intermediate transfer belt unit 10. The intermediate transfer belt unit 10 is configured to be detachable from the image forming apparatus main body 100.

  The configuration of the primary transfer roller 30 will be further described with reference to FIGS. FIG. 5 schematically shows the arrangement of the paper P, the photosensitive drum 2, the intermediate transfer belt 8, and the primary transfer roller 30 in the configuration in the width direction orthogonal to the moving direction (rotation direction) of the intermediate transfer belt 8. It is a figure explaining. End reinforcing tapes 9 are attached to both ends of the intermediate transfer belt 8 over the entire circumference in the circumferential direction in order to prevent the belt from being bent at the ends or broken due to cracks. At this time, in order to prevent the end portion reinforcing tape 9 from rubbing with the paper P and a gap between the intermediate transfer belt 8 and the paper P, the outer side of the paper P is outside the width of the paper P (outside the passage region of the paper P). Be placed.

  At both ends of the primary transfer roller 30, primary transfer rollers 31 formed of an insulator are inserted as insulating portions of the primary transfer member. The primary transfer roller 31 is pivotally supported on the rotation shaft of the primary transfer roller 30 so as to be rotatable with respect to the primary transfer roller 30. The position of the outer end portion of the primary transfer roller 31 is within the pasting range of the end reinforcing tape 9 in order to prevent the intermediate transfer belt 8 from being folded or broken at the outer end portion of the primary transfer roller 31.

  The primary transfer roller 30 is electrically connected to the voltage stabilizing element 24 and is electrically connected for primary transfer. Therefore, in this embodiment, at least the range of the image forming area A of the primary transfer roller 30 is configured by a rigid conductive member. More preferably, the primary transfer roller 30 and the image forming area A have the same dimensions in the width direction (axial direction). As shown in FIG. 5, the both ends of the primary transfer roller 30 may be configured to slightly protrude from the range of the image forming area A. In this case, the extent of the protrusion is appropriately determined in consideration of a shift in the width direction during the conveyance of the paper P and the like within a range in which toner transfer to the marginal portion of the paper P can be suppressed. That is, it is only necessary that the dimensions of the primary transfer roller 30 and the image forming area A in the width direction substantially coincide with each other in a range where toner transfer to the blank portion of the paper P does not occur. As a result, toner outside the image forming area attached to the photosensitive drum 2 can be suppressed from being transferred to the paper P, and the cost can be reduced compared to the case where the entire width of the primary transfer roller 30 is made of a conductive member. Is possible.

  FIG. 6 is an enlarged view of one end of the primary transfer roller 30 in the axial direction. 6A is a diagram when the outer diameter of the primary transfer roller 31 is made larger than the outer diameter of the primary transfer roller 30, and FIG. 6B is a diagram illustrating the outer diameter of the primary transfer roller 31. FIG. FIG. 6 is a view when the outer diameter of the primary transfer roller 30 is made smaller. In addition, about the other edge part, since it is the same structure as left-right symmetry with one edge part, description is abbreviate | omitted. In this embodiment, any of the configurations shown in FIGS. 6A and 6B may be adopted, but the configuration shown in FIG. 6B is preferably adopted. That is, as shown in FIG. 6A, when the diameter of the primary transfer roller 31 is larger than the primary transfer roller 30, the primary transfer roller 31 is stretched with a gap g between the primary transfer roller 30. At this time, since the voltage from the potential stabilizing element 24 is not supplied and an image defect may occur, the diameter of the primary transfer roller 31 is made smaller than that of the primary transfer roller 30 as shown in FIG. It is desirable.

In this manner, the insulating primary transfer rollers 31 are arranged on both sides of the primary transfer roller 30 in the axial direction. Thereby, damage to the end portion in the width direction of the intermediate transfer belt 8 can be prevented. In addition, since the outside of the image forming area of the intermediate transfer belt 8 is an insulated primary transfer roller 31, toner transfer outside the image forming area can be suppressed. As a result, it is possible to prevent the belt body from being damaged, and to suppress the transfer of dirt to the blank portion outside the image forming area of the recording material.

  In order to improve the followability of the primary transfer roller 30 accompanying the rotation of the intermediate transfer belt 8, the outer peripheral surface of the primary transfer roller 31 or the entire surface is made of a high friction material such as rubber (a material having a higher friction coefficient than that of the conductive portion). It is also possible to configure.

  N: primary transfer portion, P: paper, 2a, 2b, 2c, 2d ... photosensitive drum (image carrier), 8 ... intermediate transfer belt, 100 ... image forming apparatus main body, 30 ... primary transfer roller (primary) Conductive portion of transfer member), 31... Primary transfer roller (insulating portion of primary transfer member)

Claims (6)

An image carrier for carrying a toner image;
An intermediate transfer belt that is rotatably stretched by a plurality of stretching members and is in contact with the image carrier;
In the transfer belt, the toner image is disposed on the peripheral surface opposite to the side on which the image carrier is in contact with the position corresponding to the image carrier, and a voltage is applied so that the toner image is transferred to the image carrier. A primary transfer member for primary transfer from the intermediate transfer belt to the intermediate transfer belt;
With
In an image forming apparatus for forming an image on a recording material by secondarily transferring a toner image from the intermediate transfer belt to the recording material,
The primary transfer member is a rotation member whose rotation axis is a width direction orthogonal to the rotation direction of the intermediate transfer belt, and corresponds to a region where a toner image is primarily transferred on the intermediate transfer belt in the width direction. An image forming apparatus comprising: a conductive portion provided in a range to be covered; and an insulating portion that contacts the intermediate transfer belt on both sides of the conductive portion.   The image forming apparatus according to claim 1, wherein the primary transfer member has an outer diameter of the insulating portion smaller than an outer diameter of the conductive portion.   The image forming apparatus according to claim 1, wherein the primary transfer member has an outer diameter of the insulating portion larger than an outer diameter of the conductive portion.   The image forming apparatus according to claim 1, wherein the primary transfer member is configured such that the insulating portion is rotatable with respect to the conductive portion.   5. The intermediate transfer belt according to any one of claims 1 to 4, wherein a reinforcing tape is attached to both end portions outside the region where the toner image is primarily transferred in the width direction. The image forming apparatus described.   6. The primary transfer member according to claim 5, wherein an outer end portion of the insulating portion in the width direction contacts the intermediate transfer belt within a range where the reinforcing tape is attached. Image forming apparatus.

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