Image forming apparatus

Abstract

To provide an image forming apparatus that can suppress the occurrence of secondary transfer defects. [Solution] The image forming apparatus further comprises a support member. The support member is positioned downstream of the second belt support roller and upstream of the first belt support roller with respect to the rotational direction of the intermediate transfer belt, and faces the inner circumferential surface of the intermediate transfer belt with a gap between them. The support member supports the intermediate transfer belt when the intermediate transfer belt bends inward due to contact with the sheet.

Description

Technical Field

[0006] , ,

[0005] , ,

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] Conventional image forming apparatuses include an image carrier, an endless intermediate transfer belt, a primary transfer roller, a driving roller (first belt support roller), and a secondary transfer roller. The image carrier carries a toner image on its surface. The intermediate transfer belt is disposed adjacent to the image carrier and is rotatably supported. The primary transfer roller is disposed opposite to the image carrier across the intermediate transfer belt, and transfers the toner image carried on the image carrier to the intermediate transfer belt by primary transfer.

[0003] The driving roller is rotatably supported with respect to the rotation direction of the intermediate transfer belt and stretches the intermediate transfer belt. The secondary transfer roller faces the driving roller across the intermediate transfer belt, and transfers the toner image to a sheet passing between the secondary transfer roller and the intermediate transfer belt by secondary transfer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the configuration of Patent Document 1, the sheet heading toward the secondary transfer roller contacts the intermediate transfer belt on the upstream side of the secondary transfer roller. At this time, due to the contact of the sheet, the intermediate transfer belt may be deflected. In particular, when thick paper is used for the sheet, the intermediate transfer belt is likely to be deflected. As a result, the rotation speed of the intermediate transfer belt 8 may fluctuate, and secondary transfer failure may occur.

[0006] The present invention has been made in view of the above points, and aims to provide an image forming apparatus that can suppress the occurrence of secondary transfer defects. [Means for solving the problem]

[0007] To solve the above problems, the image forming apparatus of the present invention comprises an image carrier, an endless intermediate transfer belt, a primary transfer roller, a first belt support roller, a secondary transfer roller, and a second belt support roller. The image carrier carries a toner image on its surface. The intermediate transfer belt is positioned adjacent to the image carrier and is rotatably supported. The primary transfer roller is positioned opposite the image carrier with the intermediate transfer belt in between, and primarily transfers the toner image carried on the image carrier to the intermediate transfer belt. The first belt support roller is rotatably supported at a position downstream of the primary transfer roller with respect to the rotation direction of the intermediate transfer belt, and tensions the intermediate transfer belt. The secondary transfer roller faces the first belt support roller with respect to the intermediate transfer belt, and secondary transfers the toner image to a sheet passing between the intermediate transfer belt and the secondary transfer roller. The second belt support roller is rotatably supported at a position downstream of the primary transfer roller and upstream of the first belt support roller with respect to the rotation direction of the intermediate transfer belt, and contacts the inner circumferential surface of the intermediate transfer belt. The image forming apparatus further includes a support member. The support member is positioned downstream of the second belt support roller and upstream of the first belt support roller with respect to the rotational direction of the intermediate transfer belt, and faces the inner circumferential surface of the intermediate transfer belt with a gap between them. The support member supports the intermediate transfer belt when the intermediate transfer belt bends inward due to contact with the sheet. [Effects of the Invention]

[0008] According to the configuration of the present invention, it is possible to provide an image forming apparatus that can suppress the occurrence of secondary transfer defects. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view showing the internal structure of an image forming apparatus 100 according to one embodiment of the present invention. [Figure 2]This is a schematic, magnified cross-sectional view showing the area around the secondary transfer nip N of an image forming apparatus 100 according to one embodiment of the present invention. [Figure 3] This is a schematic, magnified cross-sectional view showing the area around the secondary transfer nip N of an image forming apparatus 100 according to one embodiment of the present invention. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following. Figure 1 is a schematic cross-sectional view of the image forming apparatus 100, which shows a tandem-type color printer. Four image forming units Pa, Pb, Pc and Pd are arranged inside the main body of the image forming apparatus 100 in order from the upstream side in the transport direction (left side in Figure 1). These image forming units Pa to Pd are provided to correspond to images of four different colors (cyan, magenta, yellow and black), and sequentially form cyan, magenta, yellow and black images through the processes of charging, exposure, development and transfer, respectively.

[0011] The image forming sections Pa to Pd are rotatably supported by photoreceptor drums 1a to 1d (image carriers). The photoreceptor drums 1a to 1d carry visible images (toner images) of each color. The photoreceptor drums 1a to 1d are connected to a main motor (not shown). The photoreceptor drums 1a to 1d rotate in the clockwise direction shown in Figure 1 by the rotational driving force of the main motor.

[0012] Around and below the photoreceptor drums 1a to 1d, charging devices 2a to 2d, an exposure device 5, developing devices 3a to 3d, and cleaning devices 7a to 7d are provided.

[0013] The charging devices 2a to 2d charge the photoreceptor drums 1a to 1d. The exposure device 5 exposes each photoreceptor drum 1a to 1d with image information. The developing devices 3a to 3d are each filled with a predetermined amount of two-component developer containing cyan, magenta, yellow, and black toners, respectively.

[0014] The developing units 3a to 3d form a toner image on the photoreceptor drums 1a to 1d. The polarity of this toner image is positive. If the proportion of toner in the two-component developer filled in the developing units 3a to 3d falls below a specified value, toner is replenished from the toner containers 4a to 4d to each developing unit 3a to 3d. The cleaning units 7a to 7d remove any remaining developer (toner) from the photoreceptor drums 1a to 1d.

[0015] An intermediate transfer belt 8 is provided adjacent to each image forming section Pa to Pd. The intermediate transfer belt 8 is made of a dielectric resin sheet (a resin material containing conductive carbon) and is a seamless belt.

[0016] Inside the intermediate transfer belt 8 are the driven roller 10, the drive roller 11 (first belt support roller), the primary transfer rollers 6a to 6d, and the backup roller 26 (second belt support roller).

[0017] The driven roller 10 and the drive roller 11 are arranged horizontally. The driven roller 10 and the drive roller 11 are rotatably supported. The drive roller 11 is connected to a belt-driven motor (not shown) that outputs rotational driving force.

[0018] The intermediate transfer belt 8 is stretched between the upstream driven roller 10 and the downstream drive roller 11. The rotational force of the drive motor causes the drive roller 11 to rotate, which in turn causes the intermediate transfer belt 8 to rotate along the circumferential direction of the drive roller 11. The driven roller 10 rotates in accordance with the intermediate transfer belt 8.

[0019] The intermediate transfer belt 8 is in contact with each of the photoreceptor drums 1a to 1d. The primary transfer rollers 6a to 6d face the photoreceptor drums 1a to 1d with the intermediate transfer belt 8 in between. The primary transfer rollers 6a to 6d apply an electric field to the intermediate transfer belt 8 at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photoreceptor drums 1a to 1d.

[0020] The backup roller 26 is located on the downstream side of the primary transfer roller 6d with respect to the rotation direction of the intermediate transfer belt 8 and on the upstream side of the drive roller 11. The backup roller 26 is rotatably supported. The backup roller 26 is pressed against the inner peripheral surface of the intermediate transfer belt 8 to stretch the intermediate transfer belt 8.

[0021] The drive roller 11 faces the secondary transfer roller 9 with the intermediate transfer belt 8 interposed therebetween. A secondary transfer nip is formed between the secondary transfer roller 9 and the intermediate transfer belt 8.

[0022] A sheet cassette 16 for accommodating a sheet S (a recording medium such as printing paper or an OHP sheet) is provided at the lower part of the main body of the image forming apparatus 100. Further, a paper feed roller 12, a main conveyance path 31, a pair of discharge rollers 15, a secondary transfer roller 9, a fixing device 13, and a pair of registration rollers 19 are provided on the side part of the main body of the image forming apparatus 100.

[0023] The paper feed roller 12 is provided above the sheet cassette 16 and abuts against the uppermost sheet S in the sheet cassette 16. The main conveyance path 31 is a path through which the sheet S is conveyed, extending from the paper feed roller 12 toward a pair of discharge rollers 15 provided at the upper part of the image forming apparatus 100. The paper feed roller 12 feeds the sheets S in the sheet cassette 16 one by one to the main conveyance path 31.

[0024] The main conveyance path 31 branches into a duplex conveyance path 18 at an intermediate position. The duplex conveyance path 18 extends downward from the branching point between the main conveyance path 31 and the duplex conveyance path 18 and rejoins the main conveyance path 31. A branching portion 14 is provided at this branching point. The branching portion 14 distributes the sheet S in the main conveyance path 31 to the pair of discharge rollers 15 or the duplex conveyance path 18. The pair of discharge rollers 15 discharges the distributed sheet S onto a discharge tray 17 formed on the upper surface of the image forming apparatus 100.

[0025] The secondary transfer roller 9 is located upstream of the branching point 14 of the main transport path 31 with respect to the sheet transport direction, and downstream of the point where the double-sided transport path 18 and the main transport path 31 rejoin. The secondary transfer roller 9 faces the drive roller 11 with the intermediate transfer belt 8 in between. The secondary transfer roller 9 forms a secondary transfer nip N between itself and the intermediate transfer belt 8.

[0026] The secondary transfer roller 9 comprises a core metal 32 and a laminated portion 33 (see Figure 2). The core metal 32 is a cylindrical body made of metal. The laminated portion 33 is laminated on the outer surface of the core metal 32. The laminated portion 33 is formed of a foamed resin member made by foaming an ion-conductive resin material, or a resin member containing conductive carbon.

[0027] The resist roller pair 19 is located downstream of the point where the main transport path 31 and the double-sided transport path 18 rejoin the main transport path 31. The resist roller pair 19 corrects the skew of the sheet S fed into the main transport path 31 and transports the sheet S to the secondary transfer nip N described above at a predetermined timing.

[0028] Next, the image formation on sheet S will be explained in detail. When image data is input from a higher-level device such as a personal computer, first, the surfaces of the photoreceptor drums 1a to 1d are uniformly charged by the charging devices 2a to 2d. Then, the exposure device 5 irradiates light according to the image data, forming an electrostatic latent image on each photoreceptor drum 1a to 1d. Next, toner is supplied onto the photoreceptor drums 1a to 1d by the developing devices 3a to 3d. As the toner adheres electrostatically, a toner image corresponding to the electrostatic latent image is formed.

[0029] When the drive roller 11 is rotated by the belt-driven motor, the intermediate transfer belt 8 begins to rotate in the counterclockwise direction shown in Figure 1 as the drive roller 11 rotates. As the intermediate transfer belt 8 rotates, the cyan, magenta, yellow, and black toner images formed on the photoreceptor drums 1a to 1d are sequentially transferred onto the intermediate transfer belt 8.

[0030] Toner and other materials remaining on the surface of the photoreceptor drums 1a to 1d after the primary transfer are removed by cleaning devices 7a to 7d in preparation for the subsequent formation of a new electrostatic latent image.

[0031] Subsequently, the sheet S is conveyed from the resist roller pair 19 toward the secondary transfer nip N at a predetermined timing. The sheet S, conveyed downstream by the resist roller pair 19, comes into contact with the intermediate transfer belt 8 upstream of the secondary transfer nip N. More specifically, the sheet S comes into contact with the intermediate transfer belt 8 at a position between the drive roller 11 and the backup roller 26 with respect to the rotational direction of the intermediate transfer belt 8. The sheet S is conveyed toward the secondary transfer nip N while remaining in contact with the intermediate transfer belt 8.

[0032] Here, when secondary transfer is performed, a voltage is applied to the drive roller 11, and a secondary transfer current flows from the drive roller 11 to the secondary transfer roller 9. As the sheet S is transported to the secondary transfer nip N while in contact with the intermediate transfer belt 8, the full-color image on the intermediate transfer belt 8 is transferred to the sheet S by the secondary transfer current.

[0033] The sheet S on which the toner image has been secondarily transferred is transported to the fuser unit 13. The sheet S transported to the fuser unit 13 is heated and pressurized by the fuser roller 132 and the pressure roller 131. The toner image is then fixed to the surface of the sheet S, forming a predetermined full-color image. The sheet S on which the full-color image has been formed is then transported in a direction determined by a branching section 14 that branches in multiple directions, and is then discharged into the discharge tray 17 by the discharge roller pair 15 (or after being sent to the double-sided transport path 18 where images are formed on both sides).

[0034] Figures 2 and 3 are schematic cross-sectional views showing an enlarged view of the area around the secondary transfer nip N, with the sheet S indicated by a dashed line. Figure 2 shows the state of the sheet S before contact with the intermediate transfer belt 8, and Figure 3 shows the state of the sheet S after contact with the intermediate transfer belt 8.

[0035] In this embodiment, the image forming apparatus 100 further includes a support member 20. The support member 20 is positioned downstream of the backup roller 26 (second belt support roller) and upstream of the drive roller 11 (first belt support roller) with respect to the rotation direction X of the intermediate transfer belt 8, and faces the inner circumferential surface of the intermediate transfer belt 8 with a gap between them.

[0036] The support member 20 supports the intermediate transfer belt 8 when it bends inward due to contact with the sheet S. This suppresses the bending of the intermediate transfer belt 8. Therefore, it is possible to suppress fluctuations in the rotational speed of the intermediate transfer belt 8 due to the bending of the intermediate transfer belt 8. This prevents secondary transfer defects such as the appearance of dark horizontal lines in the printed image. In addition, under normal conditions, the support member 20 faces the inner circumferential surface of the intermediate transfer belt 8 with a gap in between and does not come into contact with the intermediate transfer belt 8. This prevents the intermediate transfer belt 8 from being damaged by rubbing against the support member 20. Furthermore, under normal conditions, it is possible to prevent the intermediate transfer belt 8 from meandering due to contact with the support member 20.

[0037] Furthermore, it is preferable that the support member 20 is longer than the intermediate transfer belt 8 in the axial direction of the drive roller 11 (first belt support roller). This allows the support member 20 to stably support the intermediate transfer belt 8 when it bends. Therefore, the occurrence of secondary transfer defects can be further prevented.

[0038] The support member 20 is preferably made of, for example, a molded resin product, and a synthetic resin film 20a with low frictional resistance is arranged on the surface facing the intermediate transfer belt 8. A polyethylene terephthalate film (e.g., Lumirror Sheet®), which has low frictional resistance, is preferably used as the synthetic resin film 20a. By using a synthetic resin film 20a with low frictional resistance, damage to the intermediate transfer belt 8 when it comes into contact with the support member 20 can be further reduced. Using a polyethylene terephthalate film can reduce costs and improve the durability of the support member 20.

[0039] In addition to polyethylene terephthalate film, which has low frictional resistance, other synthetic resin films such as Teflon® sheets and Kapton® may also be used. By using a synthetic resin film with low frictional resistance, damage to the intermediate transfer belt 8 when it comes into contact with the support member 20 can be further reduced.

[0040] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, the driven roller 10 and the secondary transfer roller 9 may be connected to a belt-driven motor (not shown), and the drive roller 11 may be used as the driven roller. [Industrial applicability]

[0041] The present invention is applicable to an image forming apparatus equipped with an endless intermediate transfer belt. [Explanation of Symbols]

[0042] 1a~1d Photoreceptor drum (image carrier) 2a~2d Charging device 3a~3d developing device 4a~4d Toner container 5. Exposure apparatus 6a~6d Primary transfer roller 7a~7d Cleaning equipment 8. Intermediate transfer belt 8 sheets 9. Secondary transfer roller 10 Driven rollers 11. Drive roller (first belt support roller) 12 Paper feed rollers 13 Fixing device 14 Branching point 15 Discharge roller pair 16-sheet cassette 17. Discharge tray 18-sided transport path 19 Resist Roller vs 20 Support members 20a Synthetic resin film 26 Backup roller (second belt support roller) 31 Main transport path 32 Mandrel 33 Laminated section 100 Image forming apparatus 131 Pressure Roller 132 Fixing Roller N Secondary Transfer Nip Pa~Pd Image Forming Unit S Seat X rotation direction

Claims

1. An image carrier that holds a toner image on its surface, An endless intermediate transfer belt, positioned adjacent to the image carrier and rotatably supported, A primary transfer roller is positioned opposite the image carrier with the intermediate transfer belt in between, and transfers the toner image supported on the image carrier to the intermediate transfer belt. A first belt support roller is rotatably supported at a position downstream of the primary transfer roller with respect to the rotational direction of the intermediate transfer belt, and tensions the intermediate transfer belt. A secondary transfer roller, which is positioned opposite the first belt support roller with the intermediate transfer belt in between, and which secondarily transfers the toner image onto a sheet passing between the intermediate transfer belt and the first belt support roller, A second belt support roller is rotatably supported at a position downstream of the primary transfer roller and upstream of the first belt support roller with respect to the rotation direction of the intermediate transfer belt, and contacts the inner circumferential surface of the intermediate transfer belt. Equipped with, The intermediate transfer belt is further provided with a support member positioned downstream of the second belt support roller and upstream of the first belt support roller with respect to the rotational direction of the intermediate transfer belt, and facing the inner circumferential surface of the intermediate transfer belt with a gap between them. The support member supports the intermediate transfer belt when the intermediate transfer belt bends inward due to contact with the sheet, in an image forming apparatus.

2. The image forming apparatus according to claim 1, wherein the support member is longer than the intermediate transfer belt in the axial direction of the first belt support roller.

3. The image forming apparatus according to claim 1 or claim 2, wherein the support member has a synthetic resin film disposed on the surface facing the intermediate transfer belt.

4. The image forming apparatus according to claim 3, wherein the synthetic resin film is a polyethylene terephthalate film.

Images