JP2018054655A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can stabilize a stretched state of an intermediate transfer belt on immediate upstream of a secondary transfer counter roller, while reducing the influence of a stretch condition on portions other than the vicinity of a secondary transfer nip, so as to prevent image defects due to waviness of the belt or shock.SOLUTION: A pressing member and a pressing auxiliary member arranged in the downstream vicinity of a secondary transfer counter roller back up conveyance of an intermediate transfer belt to stabilize a stretched state of the intermediate transfer belt immediately before a secondary transfer nip.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a printing machine.

  In recent years, with the increase in the speed of image forming apparatuses, a configuration in which a plurality of image forming units are arranged side by side corresponding to a belt member and an image forming process of each color is processed in parallel has become mainstream. For example, a typical example is an intermediate transfer belt in an electrophotographic full-color image forming apparatus. In the intermediate transfer belt, toner images of respective colors are sequentially superimposed on the belt surface and transferred (primary transfer), and the color toner images are collectively transferred (secondary transfer) to the recording material.

  The image forming apparatus includes a stretching roller that is a plurality of stretching members including a driving roller that drives the intermediate transfer belt, and a secondary transfer roller that performs secondary transfer. It is known that stretching conditions such as the arrangement, tension, and outer diameter of these rollers affect image quality in secondary transfer.

  To deal with such problems, Patent Document 1 proposes a means for reducing image density unevenness by applying a tensile force to the belt at both ends by forming the secondary transfer counter roller in an inverted crown shape.

  Patent Document 2 proposes a means for reducing image waviness by pressing a backup member that has been subjected to fluorine processing from the inside of the intermediate transfer belt in front of the secondary transfer counter roller.

Japanese Patent Laid-Open No. 2001-22466 JP 2000-172084 A

  However, changing the outer diameter in the longitudinal direction of the roller as in Patent Document 1 includes tradeoffs such as non-uniform secondary transfer pressure and belt meandering, and conditions such as belt tension and offset amount. Depending on the situation, there is a problem that the roller must be made more accurate. In addition, when a backup member is provided inside the intermediate transfer belt as in Patent Document 2, in a configuration in which the sheet material is conveyed in close contact with the intermediate transfer belt before the secondary transfer nip, a shock is applied to the sheet at the backup unit. Image shock.

In order to solve the above problems, an image forming apparatus according to the present invention includes:
An intermediate transfer belt (1) that is stretched around a plurality of rollers and carries a toner image, a drive roller (2) that conveys the belt, and two for transferring an image on the belt to a recording material S. In an image forming apparatus comprising a secondary transfer roller (156) and a secondary transfer counter roller (2) disposed to face the secondary transfer roller (156),
A pressing member (20) arranged and driven to press from the inner peripheral side to the outer peripheral side of the intermediate transfer belt (1) at a position close to the downstream of the secondary transfer counter roller (2); It has a pressing auxiliary member (21) rotatably held at a position facing the pressing member (20).

  According to the image forming apparatus of the present invention, in the intermediate transfer belt unit that rotates the intermediate transfer belt that is rotated by the driving roller, the intermediate transfer belt is located downstream and in the vicinity of the secondary transfer counter roller in the intermediate transfer belt rotation direction. By arranging a pair of rollers to back up the conveyance, the tension of the intermediate transfer belt just upstream of the secondary transfer counter roller is stabilized while suppressing the influence of the tension condition outside the vicinity of the secondary transfer nip. Thus, it is possible to prevent image defects due to belt waviness or shock.

1 is a cross-sectional view of an intermediate transfer type image forming apparatus. FIG. 3 is a cross-sectional view around the intermediate transfer belt unit in a state where the intermediate transfer belt is in contact with the drum in the embodiment of the present invention. 1 is a cross-sectional view of an intermediate transfer belt and its vicinity in Embodiment 1 of the present invention. FIG. 3 is a perspective view of an intermediate transfer belt unit in Embodiment 1 of the present invention. FIG. 3 is a perspective view of an intermediate transfer belt unit in Embodiment 1 of the present invention. FIG. 6 is a cross-sectional view of an intermediate transfer belt and its vicinity in Embodiment 2 of the present invention. FIG. 6 is a perspective view of an intermediate transfer belt unit in Embodiment 2 of the present invention. FIG. 6 is a perspective view of an intermediate transfer belt unit in Embodiment 2 of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Example 1]
First, the operation of the electrophotographic image forming apparatus will be described with reference to FIG. The image forming apparatus 101 is a cross-sectional view of a so-called intermediate transfer tandem type image forming apparatus in which four color image forming units are arranged side by side on an intermediate transfer belt. It has become.

<Image creation process>
An image forming process up to the secondary transfer portion will be described. In this embodiment, an image forming unit 110Y that forms an image with yellow (Y) toner, an image forming unit 110M that forms an image with magenta (M) toner, and an image formation that forms an image with cyan (C) toner. 110C and an image forming unit 110BK that forms an image with black (BK) toner. Since the image forming unit 110Y, the image forming unit 110M, the image forming unit 110C, and the image forming unit 110BK have the same configuration except for the color of the toner, the image forming unit 110Y will be described as a representative.

  The image forming unit 110Y as a toner image forming unit includes a photoconductor 111 as an image carrier, a charger 112 for charging the photoconductor 111, an exposure unit 113, a developing device 114, a primary transfer member 115, and a photoconductor cleaner 116. Composed. The surface of the photoconductor 111 rotating in the direction of the arrow m in the figure is uniformly charged by the charger 112. Laser light modulated in accordance with an image signal is output from a scanner unit 117 including a laser and a polygon mirror correction system lens, and this laser light is reflected by a folding mirror, and the photosensitive member 111 charged by the exposure unit 113 is exposed. As a result, an electrostatic latent image is formed.

  The electrostatic latent image formed on the photoconductor 111 is developed by the developing device 114, and a toner image is formed on the photoconductor. Thereafter, a yellow toner image is transferred onto the intermediate transfer belt 1 as a belt member by the primary transfer member 115 with a predetermined pressure and primary transfer bias. Thereafter, the untransferred toner remaining on the photoconductor 111 is collected by the photoconductor cleaner 116 and prepared for the next image formation again.

  In the case of FIG. 1, the image forming unit 110 described above has four sets of yellow (Y), magenta (M), cyan (C), and black (Bk). Therefore, the magenta toner image formed by the image forming unit M is transferred to the intermediate transfer belt 1 with respect to the yellow toner image formed on the intermediate transfer belt 1. Further, the cyan toner image formed in the image forming portion C is transferred to the intermediate transfer belt 1 with respect to the formed magenta toner image. Further, the black toner image formed by the image forming unit BK is transferred to the intermediate transfer belt 1 with respect to the cyan toner image.

  As described above, the toner images of different colors are formed on the intermediate transfer belt 1 so as to overlap each other, so that a full color image is formed on the intermediate transfer belt 1. Although the number of colors in this embodiment is four, the number of colors is not limited to four, and the order of colors is not limited to this.

  Next, the intermediate transfer belt unit 102 including the intermediate transfer belt 1 will be described. The intermediate transfer belt 1 is stretched by a secondary transfer driving roller 2 serving as a driving member and a secondary transfer inner member, a steering roller 3 as a steering member, a pre-secondary transfer roller 4 as a stretching member, and a post-steer roller 5. It is built. The intermediate transfer belt 1 is a belt member that is conveyed and driven in the direction of arrow V in the figure.

  The secondary pre-transfer roller 4 is disposed upstream of the secondary transfer drive roller 2 with respect to the conveyance direction V of the intermediate transfer belt 1, the steering roller 3 is disposed downstream of the secondary transfer drive roller 2, and A rear steering roller 5 is disposed downstream thereof. A primary transfer roller 115 for bringing the intermediate transfer belt 1 into contact with the photoreceptor 111 is disposed between the post-steering roller 5 and the pre-secondary transfer roller 4. The distance between the secondary transfer driving roller 2 and the steering roller 3 is shorter than that between the pre-next transfer roller 4 and the secondary transfer driving roller 2.

  The steering roller 3, the pre-secondary transfer roller 4, and the post-steer roller 5 are not driven, and rotate following the conveyance of the intermediate transfer belt 1. Further, it is assumed that the steering roller 3 also has the function of a tension roller that applies a predetermined tension to the intermediate transfer belt 1 by the tension spring 11. The outer peripheral portion of the secondary transfer inner drive roller 2 is such that the secondary transfer inner drive roller 2 can convey the intermediate transfer belt 1 by frictional force while the intermediate transfer belt 1 is tensioned by the tension roller. It is made of conductive EPDM. The initial frictional resistance μ of the outer peripheral surface of the secondary transfer inner drive roller is set to about 1.0 to 1.5.

  The image forming process of each color processed in parallel by each of the image forming units 110Y, 110M, 110C, and 110BK described above is performed at a timing of superimposing on the upstream color toner image that is primarily transferred onto the intermediate transfer belt 1. As a result, a full-color toner image is finally formed on the intermediate transfer belt 1 and conveyed to the secondary transfer unit. The number of rollers for stretching the intermediate transfer belt 1 is not limited to the configuration shown in FIG. Further, the material of the secondary transfer inner drive roller 2 and the initial frictional resistance of the outer peripheral surface are not limited to the above-described configuration. Although the driving member also serves as the secondary transfer inner member, the driving member and the secondary transfer inner member may be configured by separate rollers.

<Transfer material transfer process>
The recording material S is stored so as to be stacked on the lift-up device 152 in the recording material storage unit 151, and is fed by the paper feed roller 153 at the timing of image formation. Of course, other paper feeding methods may be used. The recording material S delivered by the paper feed roller 153 passes through the paper feed conveyance path 154 and is conveyed to the registration roller 155. After the skew correction and timing correction are performed in the registration roller 155, the recording material S is sent to the secondary transfer portion. The secondary transfer portion is a transfer nip portion formed by the opposing secondary transfer driving roller 2 that is the first secondary transfer member and the secondary transfer outer roller 156 that is the second secondary transfer member.

  The toner image on the intermediate transfer belt is transferred onto the recording material S by applying a predetermined pressure and a secondary transfer bias. If a gap is generated between the secondary transfer outer roller 156, the recording material S, and the intermediate transfer belt 1 in the upstream portion of the transfer nip, the secondary transfer bias may be abnormally discharged in the gap portion. The material S is sent to the transfer nip portion in close contact with the intermediate transfer belt.

<Process after secondary transfer>
As described above, the full-color toner image formed on the intermediate transfer belt 1 in the secondary transfer portion is secondarily transferred onto the recording material S by the conveyance process and the image forming process of the recording material S described above. Thereafter, the recording material S is transported to the fixing device 158 by the pre-fixing transport unit 157. The fixing device 158 has various configurations and methods. In FIG. 1, a toner image is formed on the recording material S by applying a predetermined pressure and heat in a fixing nip formed by the opposing fixing roller 159 and pressure roller 160. Is melt-fixed.

  Here, the fixing roller 159 includes a heater serving as a heat source, and the pressure roller is urged toward the fixing roller 159. The recording material S that has passed through the fixing device 158 and is conveyed to the paper discharge reversing roller 161 is discharged as it is onto the paper discharge tray 162, or when double-sided image formation is required, the recording material S is guided to the branching device 163 and double-sided conveyance device. A route is selected to be conveyed to 164. When double-sided image formation is required, the recording material S is conveyed to the double-sided conveyance device 164 by switching the leading and trailing ends by performing a switchback operation by the paper discharge reverse roller 161.

  Thereafter, the recording paper of the subsequent job conveyed from the paper feed roller 153 is synchronized with the recording material of the subsequent job, and the paper is fed from the refeed path 165 to the paper feed conveyance path 154 and similarly sent to the secondary transfer unit. The image forming process on the back surface (second surface) is the same as that of the above-described front surface (first surface), and thus description thereof is omitted. Further, the toner remaining on the intermediate transfer belt 1 without being secondarily transferred to the recording material S is removed by the intermediate transfer cleaner 50 in contact with the intermediate transfer belt 1.

  The intermediate transfer belt 1 is conveyed in the direction of arrow V by the conveying force of the secondary transfer driving roller 2 that is a driving member that is driven and inputted from a driving coupling that is a driving transmission member. In this embodiment, the steering roller 3 as a steering member is provided with a belt automatic centering mechanism using a balance of frictional forces.

<Tension stability assist configuration>
Next, means for stabilizing the tension state of the intermediate transfer belt 1 before the secondary transfer nip, which is a feature of the present invention, will be described in detail. 2 to 5 show a sectional view and a perspective view of an embodiment of the present invention. FIG. 5 shows a state where the intermediate transfer belt 1 is removed from FIG.

  A pressing roller 20 is disposed inside the intermediate transfer belt 1 in the vicinity of the downstream of the secondary transfer driving inner roller 2, and a pressing auxiliary roller 21 is disposed outside the intermediate transfer belt 1 in a nipped state. The pressure roller 20 is disposed so as to enter the stretched line of the intermediate transfer belt 1, and the rotation shaft is fixed while the pressure roller 20 and the pressure auxiliary roller 21 are rotatable. The pressure roller 20 is rotated by driving transmitted from the secondary transfer inner drive roller 2, and the pressure assist roller 21 is rotated by the rotation of the intermediate transfer belt 1.

The pressing roller 20 and the pressing auxiliary roller 21 are each provided with a plurality of pressing portions 20A, 21A in a direction perpendicular to the conveying direction of the intermediate transfer belt 1, and the pressing portion 20A of the pressing roller 20 and the pressing auxiliary roller 21 are pressed. The parts 21A are arranged alternately. By arranging the nips alternately, the conveying force F _B applied to the intermediate transfer belt 1 is set to be smaller than the conveying force F _A by the secondary transfer driving roller 2.

As a result, the conveyance speed of the secondary transfer driving roller 2 becomes dominant with respect to the conveyance speed of the intermediate transfer belt 1, and the conveyance force is assisted by the pressing roller 20, so that the intermediate transfer belt 1 is stretched and conveyed. Speed stabilizes. Further, a pre-secondary transfer resistance member (not shown) serving as a rotational resistance of the pre-secondary transfer roller 4 is provided on the shaft of the pre-secondary transfer roller 4. By pre-secondary transfer roller 4 is subjected to rotational resistance, conveyance reaction force F _C of the intermediate transfer belt 1 is caused by the pre-secondary transfer roller 4, before secondary transfer roller 4 and between the inner secondary transfer driving roller 2 The tension force of the intermediate transfer belt 1 is increased, and the tension state is further stabilized. Here, the transport reaction force F _C is a sufficiently small force to the conveying force F _A of the secondary transfer inner drive roller 2.

Here, the rotation shafts of the pressing roller 20 and the pressing auxiliary roller 21 are fixed, but the present invention is not limited thereto, and for example, a configuration in which the pressing auxiliary roller 21 is pressed may be used. Moreover, no is employed an intermediate transfer belt 1 of the conveying force F _B staggered the roller pairs so as not to exceed the conveying force F _A is due to the secondary transfer in the drive roller 2 change the relationship of the conveying force by the pressing roller 20 For example, it is not limited to this.

[Example 2]
6 to 8 show a tension stabilization auxiliary configuration in the form of the second embodiment. The configuration of the image forming apparatus is the same as that in the above-described embodiment, and the description is omitted.

<Tension stability assist configuration>
Next, the pressing structure disposed downstream of the secondary transfer counter roller 2 which is a feature of the present invention will be described in detail.

  FIG. 8 shows a state where the intermediate transfer belt 1 is removed from FIG. A pressing roller 30 is arranged inside the intermediate transfer belt 1 near the downstream side of the secondary transfer driving roller 2 and a pressing auxiliary roller 31 is arranged outside the intermediate transfer belt 1 in a nipped state. The pressing roller 30 and the pressing auxiliary roller 31 each have a rotating shaft fixed in a rotatable state. The pressure roller 30 is rotated by driving transmitted from the secondary transfer driving roller 2, and the pressure assist roller 31 is driven to rotate with respect to the rotation of the intermediate transfer belt 1. The peripheral speed of the pressing roller 30 is set to be approximately the same as the peripheral speed of the secondary transfer inner drive roller 2.

  The drive train to the pressing roller 2 is provided with a one-way clutch (not shown). In the steady state, the one-way clutch rotates idly in the pressing roller and does not apply a conveying force to the intermediate transfer belt 1. When the peripheral speed of the intermediate transfer belt 1 becomes slower than the peripheral speed of the drive roller 2 in the secondary transfer due to an operational disturbance such as the entry of the recording material S into the secondary transfer nip, the pressing roller 30 moves to the intermediate transfer belt 1. Maintains a stable state with no change in the stretched state by applying a conveying force.

  Here, the rotation shafts of the pressing roller 30 and the pressing auxiliary roller 31 are fixed, but the present invention is not limited thereto, and for example, a configuration in which the pressing auxiliary roller 31 is pressurized may be used.

DESCRIPTION OF SYMBOLS 1 Intermediate transfer belt, 2 Secondary transfer inner drive roller, 3 Steering roller, 4 Secondary transfer roller, 20 (30) Press roller, 21 (31) Press auxiliary roller, 156 Secondary transfer outer roller

Claims (6)

An intermediate transfer belt (1) stretched around a plurality of rollers and carrying a toner image, a secondary transfer roller (156) for transferring an image on the belt to the recording material S, and the secondary transfer roller In the image forming apparatus including the secondary transfer counter roller (2) disposed to face the (156),
A pressing member (20) arranged and driven to press from the inner peripheral side to the outer peripheral side of the intermediate transfer belt (1) at a position close to the downstream of the secondary transfer counter roller (2); An image forming apparatus comprising: a pressing auxiliary member (21) rotatably held at a position facing the pressing member (20). The image forming apparatus according to claim 1, wherein the secondary transfer counter roller (2) conveys the belt. An idler roller resistance that generates a force that acts as a conveyance resistance in the conveyance direction of the intermediate transfer belt on a rotatable idler roller (4) disposed upstream of the secondary transfer counter roller (2) and downstream of the primary transfer portion. The image forming apparatus according to claim 2, further comprising a member. The conveying force (F _B ) to the intermediate transfer belt (1) due to the rotation of the pressing member (20) and the pressing auxiliary member (21) is sufficiently smaller than the conveying force (F _A ) of the driving roller 2, and the pressing member The peripheral speed of (20) is greater than the peripheral speed of the drive roller (21), and the peripheral speed of the intermediate transfer belt (1) is the same as the peripheral speed of the drive roller (2). The image forming apparatus according to claim 3. A plurality of pressing portions (20A) of the pressing member (20) and pressing portions (21A) of the pressing assisting member (21) are provided with an interval with respect to a direction perpendicular to the conveying direction of the intermediate transfer belt (1). The image forming apparatus according to claim 4, wherein the pressing portions (20 </ b> A) of the pressing member (20) and the pressing portions (21 </ b> A) of the pressing auxiliary member (21) are alternately arranged. The image forming apparatus according to any one of claims 1 to 3, wherein a one-way clutch is provided on a drive train for driving the pressing member (30) or an axis of the pressing member (30). .